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Some aspects of biodiesel oxidative stability
Abstract
Biodiesel, an “alternative” diesel fuel derived from vegetable oils, animals fats or used frying oils, largely consists of the mono-alkyl esters of the fatty acids comprising these feedstocks. One of the major technical issue facing biodiesel is its susceptibility to oxidation upon exposure to oxygen in ambient air. This susceptibility is due to its content of unsaturated fatty acid chains, especially those with bis-allylic methylene moieties. Oxidation of fatty acid chains is a complex process that proceeds by a variety of mechanisms. Besides the presence of air, various other factors influence the oxidation process of biodiesel including presence of light, elevated temperature, extraneous materials such as metals which may be even present in the container material, peroxides, and antioxidants, as well as the size of the surface area between biodiesel and air. Approaches to improving biodiesel oxidative stability include the deliberate addition of antioxidants or modification of the fatty ester profile. This article discusses some factors influencing biodiesel oxidative stability and their interaction. Resulting approaches to improving this property of biodiesel are related to these factors and the corresponding mechanisms.
... This phenomenon is as a result of presence of large amount of natural antioxidant in their oil structure as shown in Table 11 and thus exhibit a significant stability to oxidation at higher temperatures. The stability of fatty acid esters to oxidation are usually influenced by the type and composition of saturated and unsaturated fatty acid ester, light, temperature, nature of storage containers, metallic contaminants and the presence of natural antioxidants (Knothe 2007;McCormick et al., 2007;Chhetri et al., 2008). ...
... The presence of unsaturation in the fatty acid or ester molecules activates high levels of oxygen reactivity (Knothe and Dunn 2003) and the oxidation products will adversely interfere with the original properties of the fluid such as density, kinematic viscosity. Total acid number, peroxide value and most importantly oxidative stability among others (Fox and Stachowiak 2007;Knothe 2007). Observations from Tables 5 and 6 showed that the parent oil has higher stability to oxidation than the fatty acid ester. ...
... Here, the unsaturated FAMEs display a negative correlation, and thus, show a decrease in the oxidation stability when the concentration increases. The saturated FAMEs show a positive correlation, and thus, show an increase in the oxidation stability when the concentration increases, which is in agreement with most authors [8,[10][11][12][13]. The figures, however, clearly indicate that the relationships among the mass percentages of the saturated and unsaturated FAs deviate from linearity. ...
... For one-way interactions, the unsaturation of the fatty acid methyl ester plays a major role, and they are more vulnerable to oxidation. In [10], the number of double bonds is once again mentioned as a major effect on the oxidation stability. The oxidation rate depends on the presence of air and light, which have the most important effects, but also on the presence of metals, which act as a catalyst, peroxides, elevated temperatures, and the size of the surface in contact with air. ...
Air quality currently poses a major risk for human health. Currently, diesel is widely used as fuel and is a significant source of nitrogen oxides (NOx) and particulate matter (PM), both hazardous to human health. A good alternative for mineral diesel is biodiesel, not only for the improvement of hazardous components in the exhaust gases but also because it can be produced in view of a circular economy. Biodiesel consists of a mix of different fatty acid methyl esters, which can react with oxygen. As a consequence, the oxidation stability of biodiesel has to be studied, because the oxidation of biodiesel could affect the performance of the engine due to the wear of injectors and fuel pumps. The oxidation stability could also affect the quality of the exhaust gases due to increases in NOx and PM. The basic question we try to answer in this communication is: ‘Can we find an optimal fatty acid composition in order to have a maximal oxidation stability?’ In this article, we try to find the optimal fatty acid composition according to the five most common fatty acid methyl esters present in biodiesel in order to reach a maximal oxidation stability. The measurements and statistical analysis show, however, that there is no useful regression model because there are statistically significant two- and three-way interactions among the different fatty acids.
... According to the European EN 15,751 standards and the ASTM D6751 biodiesel fuel standard, the induction period can be used to deduce oxidation stability (Knothe 2007). Therefore, the oxidation stability of the biofuel was measured using an induction period at a minimum of 6 h using Rancimat or PetroOXY oxidation stability measurements. ...
... Interestingly, the oxygen was in radical form, which significantly accelerated oxidation (Christensen and McCormick 2014). The radical oxygen was formed via photo-reaction, which is 30,000 times faster than autoxidation in oleic acid and 1500 faster than linoleic acid methyl ester (Knothe 2007). ...
Fewer
fossil fuel deposits, price volatility, and environmental concerns have intensified biofuel-based studies. Saccharification, gasification, and pyrolysis are some of the potential methods of producing carbohydrate-based fuels, while lipid extraction is the preferred method of producing biodiesel and green diesel. Over the years, multiple studies have attempted to identify an ideal catalyst as well as optimize the abovementioned methods to produce higher yields at a lower cost. Therefore, this present study comprehensively examined the factors affecting biodiesel stability. Firstly, isomerization, which is typically used to reduce unsaturated fatty acid content, was found to improve oxidative stability as well as maintain and improve cold flow properties. Meanwhile, polymers, surfactants, or small molecules with low melting points were found to improve the cold flow properties of biodiesel. Meanwhile, transesterification with an enzyme could be used to remove monoacylglycerols from oil feedstock. Furthermore, combining two natural antioxidants could potentially slow lipid oxidation if stainless steel, carbon steel, or aluminum are used as biodiesel storage materials. This present review also recommends combining green diesel and biodiesel to improve stability. Furthermore, green diesel can be co-produced at oil refineries that are more selective and have a limited supply of hydrogen. Lastly, next-generation farming should be examined to avoid competing interests in food and energy as well as to improve agricultural efficiency.
... Thus, there is every possibility that these fuels will be hydrolysed to produce acids and alcohol in the presence of air (Staat and Vallet 1994). These factors reduce the stability of biodiesels when stored for a certain period and henceforth, remnant products of biodiesel, such as acids, aldehydes and insoluble gums formed during deterioration which may trigger problems in an engine such as filter clogging, injector coking and corrosion of metal parts (Knothe 2007;Moser 2011). Thus, biodiesels are characterised by various physicochemical parameters which the pure biodiesel must exhibit in the recommended limits to be utilised in neat form or being blended with petrodiesel. ...
... The characteristics of the biodiesels are evaluated according to ASTM D-6751 and EN 14214 standard methods (ASTM 2008; ASTM 2011). The oxidation stability, viscosity, calorific value, flash point and cetane number are prominent parameters, which establish the candidature of material as biodiesel and have been extensively reported (Knothe 2007;Sarin 2012). Although, some variation exists in the literature regarding the values of these parameters due to the non-consistency in the measurement environment and temperature, yet a broader agreement about the values can be seen. ...
Biodiesel is chemically an ester molecule; there is every possibility that in the presence of air or oxygen, it will be hydrolysed to alcohol and acid. The oxidation of the biodiesels in an ambient air environment leads to deterioration, which diminishes their prospects as mainstream fuel due to their lesser strength against oxidation. The present work reports the oxidation stability of Jatropha biodiesel and Pongamia biodiesel when exposed to sunlight and ultraviolet (UV) irradiation for up to 10 h and 30 days, respectively. The experimentation was further extended with novel biodiesel, Tectona Grandis biodiesel. The different synthetic antioxidants: Butylated hydroxyanisole, Butylated hydroxytoluene, and Tert-butyl hydroquinone (TBHQ) were added to the biodiesel to observe their impact along with varying storage ambiance. The experimental results reveal that exposure to UV and sunlight prompted the oxidation process and the addition of antioxidants is functional to beat the negative influence of irradiation.
... Specifications related to oxidative stability are included in the European biodiesel standard EN 14214 and the D6751-07 ASTM biodiesel standard. Both biodiesel standards call for determining oxidative stability at 110 °C with a minimum induction time of 6 h for EN 14214 and 3 h D6751-07 using the Rancimat method (Knothe, 2007). ...
... The obtained oxidative stabilities from both pretreatment methods did not meet the required induction time by the EN14214 of 6h. The Biodiesel from neutralized feedstock meets the requirement of the ASTM D6751-07 of 3h induction time (Knothe, 2007). It seems that, during the acid pretreatment step, a modification of the composition of the minor components in the oil particularly the antioxidants, was higher in acid pretreated oil. ...
Biodiesel is an alternative fuel for engine and other appliances that is obtained by transesterifying vegetable oils or other materials largely comprised of triacylglycerols with monohydric alcohols to give the corresponding mono-alkyl esters. The quality of feedstocks for the biodiesel production dictates the method of its production and quality. Based on the initial amount of minor components in f eedstocks, a process comparison of acid pre-treatment and caustic pretreatment of feedstock for alkali transesterification was done. Acid pre-treatment was carried out with 0.60 w/w methanol-to-oil ratios in the presence of 2% w/w H 2 SO 4 as an acid catalyst in 2 h reaction at 60 °C. In caustic pretreatment process, the same amount of oil was neutralized with the required amount of sodium hydroxide based on the initial amount of free fatty acid and gums in the oil. The acid pretreatment process gives a 4% loss in feedstock compared to 20% from the neutralization process. The yields 96% and 94% of biodiesel from acid pretreated and caustic pretreatment feedstock were obtained respectively. The oxidation stabilities of biodiesel from acid pretreatment and neutralized feedstock were 1.12h and 3h respectively. The biodiesel from acid pretreatment oil could not pass the ASTM standard.
... Biotechnology for Biofuels and Bioproducts 15:33 oil can be divided into two classes in accordance with fatty acids types, that is, saturated fatty acids (SFAs) and polyunsaturated fatty acids (PUFAs). SFAs such as palmitic acid (C16:0) and stearic acid (C18:0), have [14][15][16][17][18][19][20] carbons and are valuable for biodiesel production due to their high oxygen stability and energy density [5,6]. PUFAs such as eicosapentaenoic acid (EPA, C20:5) and docosahexaenoic acid (DHA, C22: 6), have more than 20 carbons and are mainly used as supplements in food and medicine that are considered as essential for human health [7]. ...
... SFAs such as palmitic acid (C16:0) and stearic acid (C18:0), have [14][15][16][17][18][19][20] carbons and are valuable for biodiesel production due to their high oxygen stability and energy density [5,6]. PUFAs such as eicosapentaenoic acid (EPA, C20:5) and docosahexaenoic acid (DHA, C22: 6), have more than 20 carbons and are mainly used as supplements in food and medicine that are considered as essential for human health [7]. In recent years, DHA has attracted extensive attention for its crucial roles in promoting brain development; protecting the retinal; and reducing the risk of some diseases, such as Alzheimer's disease, schizophrenia, and mood disorders [8]. ...
Background
Schizochytrium sp. is a marine heterotrophic protist and an important sustainable resource for high value-added docosahexaenoic acid in the future. The production of different phenotypes during the continuous subculture of Schizochytrium sp. results in a serious reduction in lipid yield and complicates the used of this strain in scientific research and industrial production. Hence, obtaining an improved understanding of the phenotypic differences and molecular mechanisms underlying the cell-to-cell heterogeneity of Schizochytrium sp. is necessary.
Results
After continuous culture passage, Schizochytrium sp. H016 differentiated into two subpopulations with different morphologies and showed decreased capacity for lipid production. The presence of cell subpopulations with degraded lipid droplets led to a substantial decrease in overall lipid yield. Here, a rapid screening strategy based on fluorescence-activated cell sorting was proposed to classify and isolate subpopulations quickly in accordance with their lipid-producing capability. The final biomass and lipid yield of the subpopulation with high cell lipid content (i.e., H016-H) were 38.83 and 17.22 g/L, respectively, which were 2.07- and 5.38-fold higher than those of the subpopulation with low lipid content (i.e., H016-L), respectively. Subsequently, time‑resolved transcriptome analysis was performed to elucidate the mechanism of phenotypic heterogeneity in different subpopulations. Results showed that the expression of genes related to the cell cycle and lipid degradation was significantly upregulated in H016-L, whereas the metabolic pathways related to fatty acid synthesis and glyceride accumulation were remarkably upregulated in H016-H.
Conclusion
This study innovatively used flow cytometry combined with transcriptome technology to provide new insights into the phenotypic heterogeneity of different cell subpopulations of Schizochytrium sp. Furthermore, these results lay a strong foundation for guiding the breeding of oleaginous microorganisms with high lipid contents.
... 90 89 From Figure 10 it can also be seen that there is a negligible change in density of R100 than in B100 and diesel. Turn et al. 90 and Knothe 93 in their work have shown that with increase in temperature adherent insolubles are formed and with increase in pressure more filterable insolubles are formed over a long time-period (37 weeks). 90,93 However, in the present work no such insolubles were observed over 24 weeks, but, the density of R30D70 was more by 2.02% than R100 and less by 1.64% than diesel. ...
... Turn et al. 90 and Knothe 93 in their work have shown that with increase in temperature adherent insolubles are formed and with increase in pressure more filterable insolubles are formed over a long time-period (37 weeks). 90,93 However, in the present work no such insolubles were observed over 24 weeks, but, the density of R30D70 was more by 2.02% than R100 and less by 1.64% than diesel. This also leads to the conclusion that R100 and its 30% blend with diesel on combustion can produce less emissions due to less density 63 and negligible change in its density over a period of 6 months is an added advantage due to its molecular structure and molecular weight which is in agreement with Stella, Knothe and Subramaniam et al. 4,5,94,95 One of the major factors in an engine's performance is the CV of the fuel used. ...
The quest of moving from conventional diesel fuels to alternate fuels is never‐ending. Renewable diesel stands out as it has a similar molecular structure to that of diesel. Renewable diesel from hydroprocessing of Jatropha oil in presence of ruthenium catalyst is not much researched and the same has been worked upon in this paper. The objective of this paper is to analyze physiochemical properties of renewable diesel (R100), biodiesel (B100), and blends of diesel (D100) and renewable diesel and to check the operational feasibility. Renewable diesel was mixed in 10%, 20%, 30%, 40%, and 50%, by volume in diesel. It was observed that renewable diesel had better cold flow properties than diesel. Calorific value (CV) of renewable diesel and biodiesel was 1.84% and 3.92% less than diesel respectively. Present study shows up to 30% renewable diesel in diesel is a substitute fuel, as their viscosities (2.55, 2.60, 2.64cSt), densities (834.4 kg/m³, 831.87 kg/m³, 830.6 kg/m³) and CVs (42.42 MJ/kg, 42.30 MJ/kg, 42.09 MJ/kg) are close to diesel (2.42cSt, 837 kg/m³ and 42.57 MJ/kg). This is also confirmed by a storage stability test conducted for 24 weeks. Cetane number of blends of R100 greater than 30% are found to be high; this can interfere with engine power output hence requiring amendments in current engines, which is not possible, therefore it is feasible to use blends only up to 30% of R100. GC–MS and Fourier transform infrared radiation showed a higher number of hydrocarbon atoms with diminutive oxygen percentage in R100, vis‐a‐vis, higher levels of unsaturation with more oxygen in B100.
... 9) (Nascimento et al. 2013), oxidative stability (OS) (Eq. 10) (Knothe 2007), cold-flow properties like cloud point (CP) (Eq. 11), pour point (PP) (Eq. ...
The green microalga Chlorella vulgaris was used as a test organism during this study for evaluation of the impact of different heavy metal stress, Mn²⁺, Co²⁺, and Zn²⁺, on enhancing the biodiesel production. The algal cultures were grown for 13 days under heavy metal stress after which were subjected to estimation of growth, some primary metabolites, lipid, and fatty acid profiles. The maximum lipid accumulation (283.30 mg/g CDW) was recorded in the algal culture treated with 3 µM cobalt nitrate. Application of 2 mM manganese chloride; 1, 2, and 3 μM cobalt nitrate; and 0.2, 0.4, and 0.6 mM zinc sulfate caused highly significant increases in the lipid contents amounting to 183.8, 191.4, 230.6, 283.3, 176.3, 226.0, and 212.1 mg/g CDW, respectively, in comparison to control (153.4 mg/g CDW). The maximum proportion of saturated fatty acids (SFA) (64.44%) was noted in the culture treated with 6 mM MnCl2 due to the existence of palmitic acid (C16:0), stearic acid (C18:0), and pentadecylic acid (C15:0) which are represented by 53.59%, 5.96%, and 1.37%, respectively, of the total FAs. Relative increase in energy compound (REEC) showed that 1, 2, and 3 µM Co²⁺ lead to the highest stimulation in lipid and carbohydrate contents to 0.207, 0.352, and 0.329 × 10³%, respectively. Empirical formulas were used for the assessment of biodiesel fuel properties based on FAME composition. The estimated properties met the prescribed international standard criteria.
... The antioxidant (AH) acts by impeding the progression of the peroxide radical (ROO . ) by preventing the production of radicals in the autoxidation pathway [37]. Multiple studies have indicated that Schiff bases exhibit advantageous antioxidant characteristics as a result of the inclusion of a nitrogen atom in the azomethine group, which is located in the sp 2 hybrid orbit. ...
Ten new Schiff bases, including thiocarbohydrazone derivatives (1–10), were synthesized using an efficient, uncomplicated, and environmentally friendly approach using the reaction of alkyl-substituted aldehydes. The thiocarbohydrazones that were obtained were derived from o-phthalaldehyde. The chemical structures of the compounds were identified by the utilization of UV-Vis spectroscopy, Fourier transform infrared (FT-IR), 1H nuclear magnetic resonance (1H NMR), 13C nuclear magnetic resonance (13C NMR), and elemental analysis methods. The thermal stability of thiocarbohydrazones was examined using thermogravimetric analysis (TGA-DSC). Investigations were conducted on urease inhibition tests, pharmacokinetic property research, and molecular docking. The collection of samples with the urease enzyme revealed significant molecular docking findings, with MolDock scores ranging from -153 to -189. The compounds have the potential to be effective drug candidates for treating certain diseases, as indicated by the consistent results of molecular docking, urease inhibition tests, and pharmacokinetic characteristics investigations.
... The in situ production may induce the degradation of the C16:1 compound; this fact could be associated with the reduced oxidative stability of unsaturated compounds (Knothe, 2007), justifying the low yield obtained in the reaction. In contrast, the oil from the macrophyte Azolla filiculoides does not present high contents of C16:1 (Brouwer, van der Werf, Schluepmann, Reichart, & Nierop, 2016), while Miranda, Liu, Rochfort, and Mouradov (2018) did not report this fatty acid ester in biodiesel from A. filiculoides. ...
Macrophytes are aquatic plants that can cause environmental and economic damage due to their rapid growth in eutrophicated environments; however, this characteristic makes these biomasses promising alternatives for biodiesel production. Thus, this study aims to characterize and evaluate the chemical composition of the biodiesel produced from the macrophyte Salvinia molesta DC Mitchell (Salviniaceae). The biodiesel production was carried out in situ through the ethyl and methyl process. Attenuated total reflectance-Fourier transform infrared spectroscopy (FTIR-ATR) and gas chromatography with a flame ionization detector (GC-FID) were used to characterize the product. A commercial sample was also analyzed for comparison purposes. The biofuel produced with ethanol and methanol showed characteristic peaks between 900 to 1300 cm-1 and 1750 to 1735 cm-1 in the FTIR-ATR. Both samples showed less unsaturation degree compared to the commercial sample, with 34.44% of monounsaturated compounds (MUFA) and 36.73% of polyunsaturated compounds (PUFA) for methylic biodiesel, 34.79% of MUFA and 36.89% of PUFA for ethylic biodiesel, and 55.34% of MUFA and 24.14% of PUFA for commercial biodiesel. Samples produced by both routes showed similar chemical composition, with higher contents of saturated compounds than the commercial sample. The average chain size and the number of double bonds are smaller for S. molesta samples, 17.38 and 1.15 for S. molesta biodiesels and 17.65 and 1.41 for commercial biodiesel, respectively. The chemical composition of S. molesta biodiesel demonstrates the potential to be an alternative to commercial biodiesel.
... ,56 A oxidação do biodiesel se caracteriza por uma reação de transferência de elétrons ou hidrogênio de um composto para um agente oxidante e afeta o combustível em estágios iniciais de uso, durante o transporte e o armazenamento, quando entra em contato com ar, e quando expostos a altas temperaturas.57 A oxidação do biodiesel influencia significativamente na sua qualidade, com o aumento da oxidação, o biodiesel se torna mais denso devido a hidrogenação das ligações insaturadas, tornando-o impróprio ao uso. ...
As mudanças climáticas e a escassez de recursos naturais representam ameaças globais que afetam a sustentabilidade dos sistemas econômicos. Para enfrentar esses desafios, soluções estão sendo desenvolvidas, como a redução das emissões de poluentes e a busca por fontes de energia sustentáveis. Embora o sistema econômico dependa principalmente de combustíveis fósseis, que causam poluição e são limitados, as energias sustentáveis, como os biocombustíveis, estão ganhando importância como alternativas renováveis. No entanto, a estabilidade dos biocombustíveis é um obstáculo a ser superado, e soluções, como aditivos, estão sendo pesquisadas. Este artigo aborda as implicações dos biocombustíveis, os desafios que enfrentam e como a pesquisa estrutural e teórica pode contribuir para o desenvolvimento de aditivos para melhorar sua estabilidade.
... The quality of biodiesel mostly relies on the length of the carbon chain, position, and number of double bonds in 408 the unsaturated fatty acids[79]. The long-chain saturated factor (LCSF) and cold filter plugging point (CFPP)409 depend on the concentration of saturated fatty acids that are indicative of diesel flow efficiency at low 410 temperatures [80]. ...
Algal bioprospecting in ecosystems leads to exploring native microalgae and the competency evaluation of economically producing lipids as biofuel or nutritional applications. In this study, ten microalgae species were screened from the saltwater lake. Chlorella vulgaris , Chlorella sorokiniana , Chlamydomonas raudensis , Chlamydomonas hedleyi , Dunaliella salina , Picochlorum bazangan sp. nov . , Tetraselmis bazangan sp. nov., Haematococcus lacustris , Nannochloropsis oceanic , and Scenedesmu rubescens were isolated and identified using 18SrDNA and tuf A markers. Biodiesel potentials were assayed by the determination of biomass productivity, biochemical components, fatty acid profile, and biodiesel properties. The results showed that the maximum biomass yield (1.22 gL ⁻¹ ) belonged to C. vulgaris . The highest protein, carbohydrate, chlorophyll, and carotenoid content were recorded in C. vulgaris , C. raudensis , C. sorokiniana , and D. salina , respectively. N. oceanica accumulated high lipid content and omega-3 fractions (31.09%). However, C. hedleyi had the highest lipid productivity (11.64 gL ⁻¹ d ⁻¹ ) compared to other microalgae. The best species for biodiesel production was C. vulgaris , with a specific growth rate of 0.36d ⁻¹ , lipid productivity of 7.45 gL ⁻¹ d ⁻¹ , and C16-C18 fatty acid profile of 78.3%. The microalgae C. vulgaris had appropriate biodiesel properties of low viscosity (4.49), high cetane number (55.38), and relatively low cloud point (4.98). Another choice was N. oceanic , with high lipid productivity, cetane number (59.79), oxidative stability (56.43), and low iodine value (47.11). Microalgae T. bazangan sp. nov. had a cetane number (55.24), low cloud point (4.71), and C16-C18 fatty acid profile of 82.34%. Accordingly, C. vulgaris , T. bazangan sp. nov., and N. oceanic can be considered potential species for biodiesel.
... These recombination reactions create monomers, which turn them into stable and nonradical products, as seen in Figure 4. Transesterifying an oil or fat with an alcohol, usually methanol, leads to the corresponding alkyl esters, which are defined as biodiesel, as represented in Figure 5. Biodiesel has the same fatty acid profile as the parent oil or fat. Due to the fact that many vegetable oils, including nonedible and edible ones such as jatropha, rapeseed, and soybean, possess a significant amount of fatty acids with double bonds, oxidative stability is of concern, especially when storing biodiesel over an extended period of time [52]. The presence of double bonds that are highly chemically reactive in the fatty acid chain is the source of the primary oxidation products, allylic hydroperoxides [53]. ...
Growing concerns about energy security and environmental sustainability have fueled demand for sustainable and renewable energy sources in recent years. Biodiesel, a renewable alternative to conventional fuels, has gained significant attention as a potential source of energy. However, the stability of biodiesel during storage and its susceptibility to oxidation remain major challenges. To address these issues, researchers have turned their focus to the utilization of natural antioxidants. Studies on sources of natural antioxidants, particularly those made from waste, such as food, have been extensively conducted. However, there are still some restrictions, such as inconsistency in quality, the development of microbes, and difficulties with regulations, all of which have an impact on sustainability and the phenolic contents. Phenolic compounds are known for their excellent antioxidant properties and ability to inhibit the oxidation process. The review provides an overview of various underutilized plant resources and agricultural wastes that are rich in phenolic contents and demonstrate higher antioxidant activities, such as Vitex doniana, Uapaca kirkiana, Parinari curatellifolia, Tamarindus indica L, fruit peels, and crop residues. It discusses the extraction methods employed to obtain phenolic antioxidants from these sources and highlights their antioxidant activities. Additionally, the review examines the effects of phenolic antioxidants on key parameters, including induction period, peroxide value, acid value, and viscosity. The review concluded by highlighting the potential of underutilized plant resources and agricultural wastes as sustainable sources of phenolic-rich natural antioxidants for enhancing biodiesel stability. According to the literatures, phenolic antioxidants present in underutilized plant resources and agricultural wastes can chelate metal ions, scavenge free radicals, and break oxidation chain reactions, thereby preventing the degradation of biodiesel. Moreover, the limitation of the use of natural antioxidants in the stabilization of biodiesel like instability at high temperatures has been highlighted.
... The combustion of biodiesel produces insignificant amount of waste gases in comparison to those of conventional fuel [5]. Nevertheless, the complications like augmented NOx release [6] and reduced oxidative stability [7] is a major concern for scientists. The biofuel produced from plant sources like grape seeds [8] and sunflower seeds [9] is referred to as the first generation biofuel. ...
The current study is focused on the lipid extract of microalgae; Pectinodesmus strain PHM3 and its general analysis in terms of chemical contents. Combinations of both chemical and mechanistic approaches were applied to obtain the maximum yield of lipids which was recorded to be 23% per gram through continuous agitation using Folch solution. The extraction methods used in this study included: Bligh and Dyers method, Continuous agitation method, Extraction using Soxhlet and Acid base extraction method. Lipid quantification of ethanol and Folch solution lipid extract was performed through gravimetric methods and qualification was done through Fourier Transmission Infrared Spectroscopy (FTIR) and Gas Chromatographymass spectrometry (GC-MS). Phytochemical analysis identified other compounds in ethanol extract and the results confirmed the presence of steroids, coumarins, tannins, phenols and carbohydrates. Transesterification of lipids showed 7% per gram dry weight yield of Pectinodesmus PHM3. GC-MS studies of extracted biodiesel suggested that 72% of biofuels was in the form of dipropyl ether, ethyl butyl ethers, methyl butyl ether and propyl butyl ether. Lipid processing of acid-base extract showed that oily nature of lipid shifted to a more precipitated form which is a common observation when mixture of lipids is converted to phosphatides.
... [24] The combustion runs cleaner and decrease soot emissions. [25] In terms of fuel aging, the thermo-oxidative environment can induce the oxidation of primary alcohols to carboxylic acid functionalities. Therefore, alcohols can possibly interact or catalyze oxidation reactions at double bonds. ...
The energy crisis and dependence on fossil fuels forces societies to develop alternative pathways to secure energy supplies. Therefore, non‐fossil fuels such as biofuels and e‐fuels can help counteract the resulting demand for existing combustion engines. However, biofuels, like biodiesel, have disadvantages in terms of oxidation stability. In general, aging of biodiesel is a complex mechanism due to interaction of various components. In order to develop an ideal fuel, the mechanism must be understood in full detail. In this work, an attempt is made to simplify the system by using methyl oleate as a biodiesel model component. In addition, other fuel components of interest such as alcohols and their respective acids help to clarify the aging mechanism. This work used isopropylidene glycerol (solketal) as the main alcohol, 1‐octanol and octanoic acid. A holistic biodiesel aging scheme was developed by using generated data and evaluating the role of acids. They epoxidize unsaturated fatty acid via Prileschajev reactions. In addition, the role of epoxides in oligomerization reactions is confirmed. Moreover, the alcohols show that the suppression of oligomerization can be achieved by the reaction with methyl oleate. The alcohol‐dependent aging products were determined by quadrupole time‐of‐flight (Q‐TOF) mass spectrometry.
... With regard to oxygen, a distinction can be made between pero using triplet and singlet oxygen [11]. Classical peroxidation with oxygen is car using triplet oxygen, which reacts with a radical of the biodiesel [12]. Neverthe vegetable oil literature shows that singlet oxygen and the associated Schenck-Ene can occur during oil rancidity [13]. ...
The complexity of biodiesel aging has shown that the mechanism needs further research. The rate of aging product formation and associated interactions can help improve fuel quality. Since biodiesel is a multicomponent system and constant changes occur in the chemical environment, which interactions yield which products must be shown in more detail. Particularly under observation was the correlation between peroxides and epoxides. In addition, it is critical that the influence and interactions of new drop-in fuel candidates be investigated. In this work, the kinetics of the formation of aging products of methyl oleate (C18:1) are studied. The aim was to reduce the complexity in order to be able to make more precise and detailed statements about the mechanism. Ketones, acids, peroxide, and epoxide values were recorded. A distinction is made between pure methyl oleate and mixtures with 3 wt% isopropylidene glycerine (solketal). After solketal decomposed in the blends, the aging process showed changes. The influence of solketal resulted in a higher number of acids and epoxides over time. It implied that peroxides are not necessarily the precursor of epoxides. In summary, correlation and solketal’s influence showed that a sequence of aging products could be detected.
... Despite the widespread use of the fuel, negative consequences of the switch to biodiesel have been observed [7]. The hygroscopic biodiesel absorbs water in environments with high humidity or when water is introduced by leakage or as ballast [8][9][10][11][12]. The interface that develops when water and biodiesel separate can also host extensive growth of microorganisms that use FAMEs as an electron donor and carbon source [7,8,[13][14][15][16][17][18][19]. ...
Split-chamber zero resistance ammetry (SC-ZRA) was used to study microbiologically influenced corrosion by aerobic chemoorganotrophic microeukaryotes isolated from biodiesel storage tanks. The magnitude and direction of electric current were measured between two shorted carbon steel electrodes, which were deployed in separate chambers connected by a salt bridge (via a SC-ZRA assembly). This approach permitted rapid screening for the corrosive activity of these previously understudied microeukaryotes. During this study, two previously understudied microeukaryotes (Byssochlamys sp. SW2 and Yarrowia lipolytica) showed increased biomass, an increase in electrochemical signal (current), and a corresponding increase in corrosion rate (weight loss). However, other previously understudied microeukaryote (Wickerhammomyces sp. SE3) showed an increase in biomass without an increase in electrochemical signal and minimal corrosion rate, indicating that the SC-ZRA technique can screen for the corrosive activity of a microorganism, regardless of overall microbial activity. This technique could be used to quickly assess the corrosive potential for a range of previously understudied microorganisms.
Graphical Abstract
... Yüksek kalitede biyodizel yakıtı elde etmek için oksidasyon kararlılığının arttırılması oldukça önemlidir (Uğuz, 2021). Biyodizelin oksidasyon kararlılığını yükseltmek amacı ile biyodizelde meydana gelen oksidasyon reaksiyonunu antioksidanın ihtiva ettiği radikaller ile engellemek için, biyodizele belirli oranlarda antioksidan ilavesi yapılır (Knothe, 2007;Romagnoli et al., 2018). Bu şekilde elde edilen biyodizelin kalitesi, depolanma süresi ve dayanıklılığı artmaktadır (Cuenca et al., 2018). ...
... Under standard conditions, they are easily oxidised in the presence of light, metal ions, etc., to produce unstable primary oxidation products. These unstable primary oxidation products produce water, acids, aldehydes, alcohols, and insoluble gelatinous materials that acidify, thicken, and delaminate the blended fuel (Knothe, 2007;Serrano et al., 2013). This fuel in the engine causes fuel blockage, engine power loss, and engine corrosion (Ashok and Nanthagopal, 2019;Gülüm and Bilgin, 2015). ...
This article investigates the volatilization characteristics of binary and ternary fuel blends of cottonseed partially hydrogenated biodiesel, ethanol, and conventional diesel. The vapor pressure, enthalpy of evaporation, and activation energy of the fuel blends were obtained by thermogravimetric analysis and kinetic calculation. The physicochemical properties of the fuel blends showed that the ternary fuel blend of suitable mixing ratio had satisfactory cetane number, improved oxidation stability, and oxygen content with a significant decrease in the kinematic viscosity. In addition, the vapor pressure of the PHCME ternary fuel blends was increased by 18.4%, 17.2%, and 20.4% compared with PHCME binary fuel blends, and the enthalpies of evaporation of the ternary fuel blends increased slightly with different mixing ratios. The activation energy of PHCME ternary fuel blends was decreased by 3.5%, 6.8%, and 16.3% respectively, compared to the PHCME binary fuel blends. In conclusion, ethanol addition in the PHCME fuel blend improved the volatilization characteristics and the kinematic viscosity of the fuel blend without a significant adverse effect on the fuel properties of hydrogenated biodiesel.
... Indian approach to biofuels is based solely on non-food feedstocks to be raised on degraded or wastelands, thus avoiding a possible conflict of fuel vs food security 5 . One of the major technical issues facing biodiesel is its susceptibility to oxidation upon exposure to oxygen in ambient air 6 . Stability of karanja oil methyl ester (KOME) has been improved by adding different antioxidants [7][8][9] [tert-butylated hydroxy toluene (BHT), tert-butylated hydroxyanisole (BHA), pyrogallol (PY), propyl galate (PrG) and tert-butyl hydroxyl quinone (TBHQ)]. ...
This study presents extraction of oil by mechanical expeller and solvent extraction technique from jatropha and karanja seeds. Physico-chemical properties of extracted oil, jatropha oil methyl ester (JOME) and karanja oil methyl ester (KOME) were tested for their suitability in diesel engine. Mechanical extraction efficiency with expeller developed by IIT Delhi was found to be better (jatropha, 87%; karanja, 86%) as compared to traditional expeller (67-69%). Induction periods (oxidation stability) at 110°C were found to be: JOME, 1.76; and KOME, 2.24 h. Calorific value of JOME (38.65 MJ/kg) and KOME (40.75 MJ/kg) was comparatively lower to base diesel (44.50 MJ/kg). Comparative performance (brake thermal efficiency, brake specific fuel consumption) and emission (CO, THC, NO x and smoke opacity) characteristics were tested in 4.4 kW, single cylinder, compression ignition engine with constant speed (1500 rpm).
... Despite the widespread use of the fuel, negative consequences of the switch to biodiesel have been observed [7] . The hygroscopic biodiesel absorbs water in environments with high humidity or when water is introduced by leakage or as ballast [8][9][10][11][12] . The interface that develops when water and biodiesel separate can also host extensive growth of microorganisms that use FAMEs as an electron donor and carbon source [7,8,13−19] . ...
Split chamber zero resistance ammetry (SC-ZRA) was used to study microbiologically influenced corrosion by aerobic chemoorganotrophic microeukaryotes isolated from biodiesel storage tanks. The magnitude and direction of electric current were measured between two shorted carbon steel electrodes, which were deployed in separate chambers connected by a salt bridge (via a SC-ZRA assembly). This approach permitted rapid screening for the corrosive activity of these previously understudied microeukaryotes. During this study, two previously understudied microeukaryotes ( Byssochlamys sp. SW2 and Yarrowia lipolytica ) showed increased biomass, an increase in electrochemical signal (current), and a corresponding increase in corrosion rate (weight loss). However, other previously understudied microeukaryote ( Wickerhammomyces sp. SE3) showed an increase in biomass without an increase in electrochemical signal and minimal corrosion rate. Indicating, that the SC-ZRA technique can screen for the corrosive activity of a microorganism, regardless of overall microbial activity. This technique could be used to quickly assess the corrosive potential for a range of previously understudied microorganisms.
... It is well reported in the literature that interactions of atmospheric agents such as oxygen and air temperature, and others, like humidity tend to introduce problems in the quality of stored biodiesel (KNOTHE, 2007). This is particularly notable in countries like Brazil, where limited shelf-life of stored biodiesel have been reported (CAVALCANTI et al, 2018). ...
... The various plant extracts also have been used as an antioxidant in biodiesel (Lau et al. 2022). However, biodiesel produced from plant oil contains more natural antioxidants and better stability, but they do not meet other fuel specifications as per standard ASTM methods (Knothe 2007;Sharma, Singh, and Upadhyay 2008). Nanoparticle chemistry is an emerging addition to the biodiesel field. ...
Biodiesel is an emerging solution to petrodiesel owing to its high flash point, low toxicity, biodegradability, and less greenhouse gas (GHG) emissions. It is still a problem for end-users due to poor oxidation stability and cold flow properties. However, biodiesel can be used as a lubricity improver in petrodiesel, but high dosages of biodiesel may be cost-intensive. Multifunctional additives can provide a robust solution to the said challenge. We report herein the Schiff base ethyl levulinate coupled with N-phenyl-p-phenylenediamine (EL-NPPD) as multifunctional additive, viz. antioxidant and lubricity enhancer for the biodiesel. The additive was synthesized in two steps: ethyl levulinate (EL) production followed by imine formation. The final product was characterized using thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), and nuclear magnetic resonance (NMR) spectroscopy. The antioxidant properties of the synthesized additive were checked in terms of induction time using Rancimat as per EN14112 methods. At the 1000 ppm concentration, the induction period value of 7.94 ± 0.6 was observed. Further, as the concentration increased, induction time got increased. Furthermore, the antioxidant potential was checked with 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical inhibition-based method in which different concentrations of additive ranging from 1000 to 5000 ppm were used against commercial antioxidants. As concentration increased to 4000 ppm, % inhibition values got increased by 15%, which showed better antioxidant activity of EL-NPPD. Similarly, the lubricity tests were performed using the HFRR test in which additive ranging from 1000 to 2000 ppm was used, and the average wear scar diameter (AWSD) was significantly reduced from 258 ± 11 to 248 ± 10, i.e. around 5% reduction than neat biodiesel sample.
... Biodiesel can be used directly in engines as well as in blended form without any engine modification. With increased lubricity and high cetane number, running diesel engines on biodiesel could be advantageous in terms of energy security and environmental safety (Canakci 2007, Knothe 2007). On the other hand, biodiesel fuels have poor low-temperature properties and are more susceptible to auto-oxidation during storage (Mohamed et al. 2017). ...
Biodiesel generated from a variety of non-edible feedstocks has gained widespread acceptance as a limited diesel fuel alternative in compression ignition engines. For the reliable implementation of biodiesel in commercial sectors, its effect on engine combustion, emission, and performance needs to be examined experimentally. In this study, 10% (N10) and 20 % (N20) Neem oil methyl ester (NME) blends were tested in a direct injection 4-stroke single-cylinder diesel engine incorporated with 5% and 10% exhaust gas recirculation (EGR). At maximum load conditions, Brake thermal efficiency (BTE) was found highest for N20 by 7.2%, and also Brake specific energy consumption (BSEC) was reduced by 11.4% for N20 as compared to diesel. Meanwhile, the incorporation of EGR deteriorates the performance parameters for the N20 blend. The results of emission analysis showed that oxides of nitrogen (NOx) increased with the addition of biodiesel whereas the addition of EGR diminished the NOx value for both biodiesel blends at all loading conditions. Unburnt hydrocarbon (UHC), Carbon monoxide (CO), and smoke emissions decreased by 40.6%, 31.2%, and 29.6% for the N20 blend respectively at full load when compared to diesel. Interestingly, when EGR was provided, CO, UHC, and smoke density values are increased for both N10 and N20 blends at all loading conditions, however lower than diesel operation.
... The higher mono-unsaturated fatty acid (MUFA) percentage in both the media leads to improved oxidative stability (OS) and cetane number (CN) of the biodiesel produced. The Iodine value (IV), density, OS, CN and kinematic viscosity (kV) determined in this study are under the limit specified by ASTM and EU standards (Knothe, 2009(Knothe, , 2007. Hence, the lipid composition of R. pacifica cultivated in MSCBH was concluded to be more appropriate for the production of biodiesel. ...
Dependency on fossil fuels raises an economic and ecological concern that has urged to look for alternative sources of energy. Bio-refinery concept is one of the alternate frameworks for the biomass conversion into biofuel and other value-added by-products. The present work illustrates importance of an oleaginous yeast Rhodotorula pacifica INDKK in an integrated bio-refinery field by utilizing renewable sugars generated from lignocellulosic biomass. The maximum 11.8 g/L lipid titer, 210.4 mg/L β-carotene and 7.1 g animal feed were produced by R. pacifica INDKK in bioreactor containing 5 % (v/v) molasses supplemented with enzymatically hydrolyzed and alkali-pretreated sugarcane bagasse hydrolysate (35 % v/v). Furthermore, xylooligosaccharides (20.6 g/L), a beneficial prebiotics were also produced from the hemicellulosic fraction separated after alkali pretreatment of bagasse. This novel concept of integrated yeast bio-refinery for concomitant production of biodiesel and multiple value-added products with minimum waste generation is proposed as a sustainable and profitable process.
... The greatest influence is exerted by esters of oleic, linoleic, and linolenic acids, whose relative oxidation rates are 1, 41, and 98, respectively. This is a major problem in [63,70,71]. However, in our case FAME obtained after cultivation of microalgae on glucose and acetate did not contain a high amount of long-chain PUFA, improving the oxidative stability of biodiesel. ...
To address the issue of high organic carbon costs in heterotrophic cultivation of microalgae, we evaluated the hypotheses by employing microalgae as a biorefinery for proteins and advanced biofuels after heterotrophic cultivation on volatile fatty acids (VFAs) instead of pure glucose. To prevent the inhibitory effect of VFAs on lipid synthesis, strains capable of tolerating high levels of VFAs were selected. Growth and lipid synthesis by two freshwater microalgae, Auxenochlorella protothecoides and Chlorella sorokiniana, was optimized at different VFA concentrations. Maximum biomass and lipid content in A. protothecoides (10.66 g/L, 33.93%) and C. sorokiniana (7.98 g/L, 39.80%) were obtained by replacing glucose with 30 g/L acetate at C/N 60. The generated lipids were compliant with existing standards for biodiesel. Moreover, when grown on acetate, both microalgae contained the complete range of essential and non-essential amino acids. Finally, single-source commercial VFAs were replaced with VFAs mixture after acidogenic fermentation of waste lignocellulosic biomass from brewers’ spent grain. The mixture allowed successful mixotrophic and heterotrophic cultivation of both microalgae, demonstrating feasibility of this low-cost carbon source in fuel-grade biodiesel production.
... A qualidade de ignição é em geral expressa em termos do Número de Cetano (NC), aspecto relacionado ao intervalo de autoignição que o combustível apresenta em um motor de testes (KNOTHE, 2006;KNOTHE, 2007). Monoésteres de cadeias mais longas apresentam intervalos de autoignição mais curtos (KNOTHE, 2005), i.e., NC mais elevado, enquanto insaturações na cadeia tendem a diminuir esse número: quanto maior o número de grupos CH 2 (metileno) em sequência na cadeia, mais elevado é o valor dessa propriedade. ...
p>Dentre as diversas matérias-primas viáveis para a produção de biodiesel, a pupunheira ( Bactris gasipaes ) apresenta-se como uma promissora fonte de óleo, a partir do mesocarpo e amêndoa. Essa palmeira natural da América Central e do Noroeste da América do Sul apresenta também um grande potencial agroindustrial e biotecnológico, devido às características do palmito e composição dos seus resíduos: bainha, folhas e frutos. Os resíduos da agroindústria podem ser utilizados como suplementos alimentares para ruminantes, devido ao alto teor de proteínas, na fabricação ou elaboração de biofertilizantes e na produção de etanol, bebidas alcoólicas e outros produtos. Esse aproveitamento dos resíduos consiste de grande importância, tendo em vista o aumento recente da área cultivada no país. A viabilidade técnica da produção de biodiesel da pupunha depende, entre outros aspectos, da qualidade dos lipídios obtidos para produção de combustíveis líquidos. Assim sendo, este trabalho apresenta a relação entre a composição do óleo do mesocarpo da pupunha e a qualidade do biodiesel, com foco na estimação do Número de Cetano e do Ponto de Entupimento a Frio. Aspectos biotecnológicos e agroindustriais são discutidos, e processos integrados são sugeridos com objetivo de viabilizar a produção de biocombustível com maximização dos ganhos e diminuição dos impactos ambientais. </p
There is an urgent need to convert Composite waste oils (CWOs) from domestic and industrial sources using circular system thinking approach due to the growing concern of their socio-economic, environmental and governance effects and impacts of increased human anthropogenic activities. CWO was first pre-treated by sieving, heated to reduce moisture/water concentration and the acid value lowered with the addition of sufficient KOH, then base transesterification reaction with ethanol (1:1), 1% KOH at 700C for 2 h. The physio-chemical and fuel properties of the CWO100 was analyzed using standard analytical methods, and the data statistically using SPSS version 20.0. CWO100 (FAEE) has lowest value of water and sediment, acid value, free fatty acid, carbon residue and sulphur, and the highest values for viscosity, specific gravity, density, colour, flash point, iodine. Most of its parameters are within the ASTM/EN standards except in CWOs that requires pre-treatment. CWO100 is better than petroleum diesel and can be applied in diesel engines, plants with little or no modification as a major alternative now and thereafter.
Biodiesel tends to oxidation during the time of storage due to chemical structure, makes deterioration of fuel quality. Hence, the presence in feed stock required to gain standard quality for biodiesel commercialization. Natural antioxidant, mainly oryzanol found in rice bran feed stock, have been worked in biodiesel oxidation synergistic without any additional of synthetic antioxidant. In this work, the potential natural antioxidant has been evaluated by the oxidation stability. The biodiesel exhibited oxidation stability gained the induction period at 3 h by Rancimat method. It was found that the concentration of oryzanol above 300 ppm keep the biodiesel from oxidation. Even though very small amount 3 ppm oryzanol was obtained but contribute as cost implication due to antioxidants are costly chemicals. Otherwise adding synthetic antioxidant making high cost on biodiesel storage and utilization.
Material compatibility is one of the significant issues concerning the application of biodiesel in IC engines. In this paper, the corrosive nature of acid oil biodiesel has been investigated as per ASTM G31 standard procedure. Three base materials, stainless steel, aluminum and copper, which were used to make different components of the fuel system, are selected for the investigation. The corrosion rates of these materials in acid oil biodiesel were determined and compared with petroleum-based diesel. From the static immersion test conducted, the corrosion rate of stainless steel, aluminium and copper was found to be 0.0018, 0.0104 and 0.1407 (mpy), respectively.KeywordsAcid oil biodieselBiodiesel material compatibilityBiodiesel
Biodiesel is a promising fuel with the potential to reduce some negative aspects of fossil fuels, such as the emission of pollutants and greenhouse gases (GHG), scarcity of natural resources...
Transesterification of expired vegetable oils is possible by heating them with a significant amount of methanol and an acidic or basic catalyst to improve the reaction rate and yield. In this study 4 samples have been selected, including 4 types of vegetable oils, namely: soybean, sunflower, rapeseed, pumpkin seed. The operative conditions of the reaction were reaction time (4 h), catalyst concentration (1 w/wt %), and oil-to-methanol molar ratio (6:1). The parameters studied to compare the quality of biodiesel obtained by each type of compound are: yield, pH, density, acid value. The results shows that The pumpkin seed have a positive effect on increasing the yield of Soybean biodiesels as well as biodiesel blends based on Soybean, Sunflower and rapeseed. This paper examines also the degradation of several biofuels in comparison with fossil fuels (Diesel and gasoline) with different storage conditions over 9 Weeks period. The Results indicated that: High temperature combined with the lighting strongly enhances the degradation phenomenon. The acid value of biodiesel (HM) is rapidly increasing at a rate of 0.91 mg KOH/g /Week. The pH of diesel has experienced a strong decrease of 66%. In comparison with Diesel, Diesel degrades strongly and rapidly from a biodiesel in terms of Acid Value, pH and Density.
Biodiesel has a significant added value compared to petrodiesel regarding a series of improved properties such as biodegradability and reduction of most regulated exhaust emissions. However, some challenges associated with biodiesel include physicochemical improvements in oxidative stability, which can be addressed by antioxidants. In this aspect, chalcone derivatives are simple chemical scaffolds with industrial applications that can be boosted by the insertion of a sulfonamide group. An extensive structure characterization was carried out for arylsulfonamide chalcone N-(2-(3–4-methoxyphenyl-propanoyl)-phenyl)-benzenesulfonamide and its isomer, to describe their supramolecular arrangements and conformational changes. Solid state arrangements were described by XRD and stabilized by C–H⋯O and π⋯π stacking interactions. Theoretical calculations were carried out by DFT using the M06-2X/6-311++G(d,p) level of theory to identify the reactive sites of arylsulfonamide chalcones and their molecular electrostatic potential maps. The fundamental factors were correlated to antioxidant molecules and commercial additives found in the literature. The analysis carried out in this work will be a gateway to confirm the relationship between the structure of arylsulfonamide chalcones and their additive properties as biofuels.
The current study is focused on the lipid extract of microalgae; Pectinodesmus strain HM3 (PHM3) and its general analysis in terms of chemical contents. Combinations of both chemical and mechanistic approaches were applied to obtain the maximum yield of lipids which was recorded to be 23% per gram through continuous agitation using Folch solution. The extraction methods used in this study included: Bligh and Dyers method, Continuous agitation method, Extraction using Soxhlet and Acid base extraction method. Lipid quantification of ethanol and Folch solution lipid extract was performed through gravimetric methods and qualification was done through Fourier Transmission Infrared Spectroscopy (FTIR) and Gas Chromatography-mass spectrometry (GC-MS). Phytochemical analysis identified other compounds in ethanol extract and the results confirmed the presence of steroids, coumarins, tannins, phenols and carbohydrates. Transesterification of lipids showed 7% per gram dry weight yield of Pectinodesmus PHM3. GC-MS studies of extracted biodiesel suggested that 72% of biofuels was in the form of dipropyl ether, ethyl butyl ethers, methyl butyl ether and propyl butyl ether. Lipid processing of acid-base extract showed that oily nature of lipid shifted to a more precipitated form which is a common observation when mixture of lipids is converted to phosphatides.
The biodiesel susceptibility to oxidation causes its qualitative deterioration and affects both its handling and long-term storage. This study aims to evaluate biodiesel (commercial-grade and fresh samples) oxidative degradation via combined extended storage studies and under dynamic laboratory-scale accelerated conditions. Biodiesel samples from various feedstocks (waste cooking oils, tallow oil, vegetable oils) with and without addition of a synthetic commercial antioxidant (Chimec HR 876 HFP, 500 mg/kg) were stored at ambient conditions for long-time periods (6 and 14 months), and/or submitted to accelerated aging. During the accelerated oxidation tests, the samples were exposed to an air flow rate of 100, 200 and 300 mL/min for 2, 4 and 6 h at 120 °C. The storage stability of biodiesels depended on the utilized feedstock, while the antioxidant addition rendered the storage of the samples from waste cooking oil and tallow oil for ~ 12 months. The biodiesels were intensively deteriorated when submitted to dynamic oxidation (at 120 °C with air flow rate of 300 mL/min for 6 h), as confirmed by the acidity and induction period. After 2 h of intense oxidation, the IP of the biodiesels decreased below EN 14214 limit, while after ~ 2–4 h, the TAN values exceeded the respective limit (with the exception of PME samples). These conditions could correspond to the biodiesel’s quality deterioration after ~ 1–3 months of storage under the examined conditions, accounting the biodiesel type. Based on these results, the stability of biodiesel is associated with the aging conditions, its type and the antioxidant, as well.
Graphical abstract
Fossil fuel depletion in the recent decade poses a greater threat to the energy security of the global community. This forces the scientific community to move on to a renewable fuel for transportation purposes. Biodiesel is the methyl ester of fatty acids which proves to be a ray of hope to satisfy the energy demand of diesel fleets in transportation. Storage stability is one of the major problems of biodiesel fuels in the view of commercialization. In this present research work, biodiesel derived from date seed oil is taken for stability enhancement by doping coffee leaf pigment in various concentrations. The produced antioxidant showed smooth and irregular morphological structure on examination using Scanning Electron Microscope. In addition, the thermogravimetric analysis showed a clear weight loss in the temperature range of 250–450 °C. The rancimat experiments showed that adding antioxidants enhanced the stability of the biodiesel sample and the highest induction period has been recorded as 8.94 hr for the DSC1500 blend.
Biodiesel is a renewable and non-toxic fuel used in compression ignition engines as a blend with diesel without modifying the engine. It has a drawback of poor oxidation, thermal stability and long-term storage stability, preventing widespread use as a commercial fuel. The leaf extract with antioxidant properties will improve biofuel's stability by inhibiting the free radical formation or absorbing the free radicals. Natural antioxidants derived from natural products are the recent innovation in antioxidants. The present work analyses leaf extract's effect as additive with Calophyllum inophyllum methyl ester on thermal stability, storage stability, and oxidation stability. The addition of leaf extract has shown a significant improvement in thermal stability and reduced residual formation. 20 ml of the additive with biodiesel has improved the induction period of the B20 up to 9.2 h. On storage, the peroxide value, acid number, and viscosity have increased significantly due to oxidation, acid formation, and long-chain organic compounds, respectively. The additive addition has reduced the peroxide value, acid number, and viscosity by quenching the free radicals formed during biodiesel's oxidation.
Biodiesel biodegradation has been a limiting factor for its use as an alternative for petrol diesel. Thanks to low structural complexity, a group of enzymes such as alkane monooxygenase ( ladA ) can readily degrade several fatty acids, but the understanding of the mechanism of degradation is unclear yet. Then, we combined molecular docking and hybrid molecular dynamics (QM/MM) approaches for the study of ladA . The results showed that the bending of the isoalloxazine ring to the original plan enhanced its electrical coupling with a substrate. The flavin mononucleotide-FMN oxidation yields an activation energy of 74.29 kJ.mol ⁻¹ , which is necessary to make an oxygen molecule reactive. In addition, the initial activation energy determined for palmitic acid was 59.82 kJ.mol ⁻¹ and 64.64 kJ.mol ⁻¹ for linoleic acid. The diffusion of oxygen molecules into the active site is controlled by the movement of some residues that compose the tunnel access or by a water bridge.
The Federal Institute of Agricultural Engineering in Austria has been gaining more experience about the technical performance of biodiesel with a high iodine number. Long term tests were carried out on the test bench with rape seed oil methyl ester, sunflower oil methyl ester and camelina oil methyl ester with an iodine number of 107 to 150. The oil viscosity was observed and the engine parts were inspected after each run. To demonstrate the suitability of a methyl ester with a high iodine number a fleet test with 9 vehicles and 1 stationary engine was carried out over a period of 1 to 3 engine oil drain intervals. Camelina oil methyl ester was used with a content of 37% linolenic acid (C18:3). No unusual deposits could be observed after dismantling the engines.
During storage and use, vegetable oil-derived industrial products such as biodiesel and biodegradable lubricants can be subjected
to conditions that promote oxidation of their unsaturated components. The materials arising during oxidation and subsequent
degradation can seriously impair the quality and performance of such products. Therefore, oxidative stability is a significant
issue facing these vegetable oil-derived products, and enhanced understanding of the influence of various components of vegetable
oils and storage parameters is necessary. In this work, the oil stability index (OSI) was used for assessing oxidation of
monoalkyl esters of FA by varying several parameters. Neat fatty compounds and prepared mixtures thereof were studied for
assessing the influence of compound structure and concentration. Small amounts of more highly unsaturated compounds had a
disproportionately strong effect on oxidative stability. The recently developed concept of bis-allylic equivalents correlated
more closely than the iodine value with the OSI times of mixtures of fatty esters. The OSI times of free acids were shorter
than those of the corresponding alkyl esters. The presence of copper, iron, and nickel also reduced oxidative stability, but
their effect was less than the presence of more highly unsaturated fatty compounds. Of these metals, copper had the strongest
catalytic effect on OSI time. OSI may be an alternative to long-term storage tests for determining the influence of extraneous
materials such as metals on oxidative stability.
Biodiesel, an alternative diesel fuel derived from transesterification of vegetable oils or animal fats, is composed of saturated
and unsaturated long-chain FA alkyl esters. During long-term storage, oxidation caused by contact with air (autoxidation)
presents a legitimate concern with respect to monitoring and maintaining fuel quality. Extensive oxidative degradation may
compromise quality by adversely affecting kinematic viscosity, acid value, or PV. This work examines the oil stability index
(OSI) as a parameter for monitoring the oxidative stability of soybean oil FAME (SME). SME samples from five separate sources
and with varying storage and handling histories were analyzed for OSI at 60°C using an oxidative stability instrument. Results
showed that OSI may be used to measure relative oxidative stability of SME samples as well as to differentiate between samples
from different producers. Although addition of α-tocopherol or TBHQ increased OSI, responses to these antioxidants varied
with respect to SME sample. Variations in response to added antioxidant were attributed to aging and other effects that may
have caused oxidative degradation in samples prior to acquisition for this study. Results showed that OSI was more sensitive
than iodine value in detecting the effects of oxidative degradation in its early stages when monitoring SME during storage.
Renewable vegetable fuels are spreading rapidly throughout Europe and North America. Because biodiesel fuel has now acquired
an important market share, it is necessary to thoroughly examine aspects of its use not previously considered either at the
research stage or when overhauling the production technology. One of these aspects is its medium-term storage. The object
of the present work is to study the behavior of biodiesel under controlled storage conditions that simulate those found in
reality. Samples of biodiesel were kept in the dark, at two different temperatures (20°C and 40°C), in both glass and iron
containers. They were controlled by the parameters that indicate their state of oxidation. Another group of samples was stored
in glass and kept under the conditions described above in the presence of increasing quantities of water to determine its
influence on the formation of acidity.
Biodiesel derived from transesterification of soybean oil and methanol is an attractive alternative fuel for combustion in
direct-injection compression ignition (diesel) engines. During long-term storage, oxidation due to contact with air (autoxidation)
presents a legitimate concern with respect to maintaining fuel quality of biodiesel. This work examines the effects of oxidation
under controlled accelerated conditions on fuel properties of methyl soyate (SME). SME samples from four separate sources
with varying storage histories were oxidized at elevated temperature under a 0.5 standard cm3/min air purge and with continuous stirring. Results showed that reaction time significantly affects kinematic viscosity (ν).
With respect to increasing reaction temperature, ν, acid value (AV), PV, and specific gravity (SG) increased significantly,
whereas cold flow properties were minimally affected for temperatures up to 150°C. Antioxidants TBHQ and α-tocopherol showed
beneficial effects on retarding oxidative degradation of SME under conditions of this study. Results indicated that ν and
AV have the best potential as parameters for timely and easy monitoring of biodiesel fuel quality during storage.
Fatty acid alkyl esters, especially FAME, are the most commonly used liquid biofuel. Because biofuels are expected to be important
alternative renewable energy sources in the near future, more studies on their stability against oxidation need to be addressed.
Biofuel derived from vegetable oils is well researched, currently with more attention focused on the reuse of waste oil sources
than on pure vegetable oil for such production. A method to convert used palm oil, i.e., used frying oil, and residual oil
of spent bleaching earths (SPE) to their respective methyl esters has been established by the Malaysian Palm Oil Board. These
methyl esters can be used as diesel substitute. However, the methyl esters obtained from used frying oil have a low induction
period (3.42 h). In Europe, any methyl esters must have an induction period of at least 6 h in Rancimat stability to be usable
as biodiesel, as required by European Biodiesel Standard (EN 14214). To meet this requirement, the used frying oil methyl
esters (UFOME) obtained can be treated with different types of antioxidants, either synthetic or natural, at different treatment
levels, such as vitamin E, 3-ert-butyl-4-hydroxyanisole (BHA), 2,6-di-tert-butyl-4-methyl-phenol (BHT), 2,5-di-tert-butyl hydroquinone (TBHQ), and n-propyl gallate (PG), to investigate their oxidative stability and storage behavior. The order of increasing antioxidant effectiveness
with respect to the oxidative stability of UFOME is: vitamin E<BHT<TBHQ<BHA<PG. Because methyl esters derived from residual
oil of SBE have an induction period of 14.6 h, their treatment with antioxidants is unnecessary.
Crude and distilled palm oil methyl esters conveniently known as palm diesel have been successfully evaluated as diesel substitute. Crude palm oil methyl esters are produced from transesterification of crude palm oil with minor components such as carotenes and vitamin E still intact and they are reddish in colour. The distilled palm oil methyl esters are obtained after the recovery of minor components (e.g. Carotenes and vitamin E) From the crude palm oil methyl esters. These valuable minor components are preferably to be recovered as they can be sold as value-added products before they are burnt together with the methyl esters as fuel. Although both possesses fuel characteristics which are comparable to those of petroleum diesel, crude palm oil methyl esters are found to exhibit better oxidative stability (rancimat induction period >25 h) than distilled palm oil methyl esters (about 3.5 h). It is attributed to the presence of vitamin E (about 600 ppm), a natural antioxidant in the former. While the distilled palm oil methyl esters contain practically no vitamin E (<50 ppm) and as a result, they exhibit poor oxidative stability. Thus, the crude palm oil methyl esters meet the european standard for biodiesel (EN 14214) which has set a minimum rancimat induction period of 6 h. In the present study, research was conducted to enhance the oxidative stability of distilled palm oil methyl esters in order to meet the aforementioned standard. Natural and synthetic antioxidants were used in the present study to investigate their effect on the oxidative stability of distilled palm oil methyl esters. It was found that both types of antioxidant showed beneficial effects in inhibiting the oxidation of distilled palm oil methyl esters. Comparatively, the synthetic antioxidants were found to be more effective than the natural antioxidants as lower dosage (17 times less) was needed to achieve the minimum rancimat induction period of 6 h.
Biodiesel, an alternative diesel fuel that may be derived from soybean oil, is composed of long-chain saturated and unsaturated fatty acid alkyl esters. Extensive oxidative degradation can compromise viscosity, acid value, peroxide value, and other parameters in the current ASTM biodiesel fuel guideline. This work examines pressurized-differential scanning calorimetry (P-DSC) for analysis of oxidative stability of biodiesel. Heating scans were conducted under static air-atmosphere with 5°C/min ramping. Increasing pressure from 1000 to 5000 kPa did not significantly affect results and 2000 kPa was selected for the remainder of this study. Curves were analyzed for oxidation temperature (OT) of methyl soyate samples from four separate sources. With respect to unmodified methyl soyate, addition of antioxidants increased OT from 108.4-127.2°C to 137.2-163.4°C. Mixtures with added tert.-butylhydroquinone consistently gave higher OT values than those with ±α-tocopherol; therefore, P-DSC may be useful for screening antioxidants. Although P-DSC results were consistent with corresponding oil stability index (OSI) data measured at 50°C, no correlation for predicting OSI directly from OT results was evident, with the possible exception of unmodified methyl soyate. This work establishes P-DSC as an analytical tool in evaluating the oxidative stability of biodiesel with and without antioxidants.
Biodiesel, an alternative diesel fuel made from transesterification of vegetable oils or animal fats, is composed of saturated and unsaturated long−chain fatty acid alkyl esters. During long−term storage, oxidation caused by contact with ambient air presents legitimate concerns for monitoring fuel quality. Extended oxidative degradation can affect kinematic viscosity, cetane number, and acid value of the fuel. This work investigates the suitability of dynamic mode (positive air purge) pressurized−differential scanning calorimetry (P−DSC) as a means for evaluating the oxidation reaction during non−isothermal heating scans. Methyl oleate, methyl linoleate, and soybean oil fatty acid methyl esters (FAME) were analyzed by P−DSC and the results compared with those from thermogravimetric analyses (TGA), conventional DSC, and static mode (zero purge gas flow) P−DSC scans. Results from TGA showed that ambient air pressure was too low to allow measurable oxidation during analyses. Although some degree of oxidation was detected for DSC and static mode P−DSC heating scans, results demonstrated that the highest degree of oxidation occurred during dynamic mode P−DSC scans. For DSC and P−DSC analyses, oxidation onset temperature (OT) increased with relative oxidative stability, with the highest values being observed for methyl oleate. Treating soybean oil FAME with antioxidants increased their relative oxidative stability, resulting in an increase in OT. Statistical comparison of response factors (RF) relative to methyl oleate obtained from non−isothermal heating scans with those obtained from OSI analyses showed the highest degree of correlation (P = 0.79) with respect to dynamic mode P−DSC.
In this investigation the identity characteristics of the pure plant oils were compiled from literature sources and our own experimental results. The quality characteristics were determined and the results compared to those given in the literature data. Lastly, an attempt was made to evaluate the oils according to their oxidative stability. Accelerated storage tests were done on the pure oils and the plant oil-diesel mixtures. Literature sources contained information on the stability and composition of pure refined oils but very little on degummed and crude oils and none on the characteristics of plant oil-diesel mixtures.
The oxidative stability of two samples of rapeseed oil methyl esters from different production sites was determined. The effect of various antioxidants on the induction period at 120°C was studied. As the additives did not show a positive effect on the stability of the rapeseed oil methyl ester under the test conditions, the temperature was varied and the effect of a random antioxidant in comparison to the pure ester was determined. The antioxidant HITEC did show a negative effect at 120°C and positive effects both at 100°C and 90°C. However, the difference in induction period was very low. The test method used was an automated version of the active oxygen method (AOM) at ambient temperature.
The oxidative stability of different plant oil based fatty acid methyl esters can be estimated by determining the induction period with the active oxygen method. Measuring the volatile and oil soluble acids for a long period preceding the induction period shows that the alues are approaching a certain limit. Even if the esters do not differ dramatically in the composition of fatty acids it is a fact that the different production processes influence the amount of tocopherols significantly. The exclusion of light is more crucial than the exclusion of air when storing plant oil based fatty acid esters.
Methyl and ethyl esters, prepared from various vegetable oils by the process of transesterification, have shown much promise as fuels for all types of diesel engines. Very limited information is available on possible deterioration of biodiesel in storage. This project was designed to determine the extent of deterioration of Rape Methyl Ester (RME) and Rape Ethyl Ester (REE) in storage. The study involved triplicate samples of RME and REE stored in glass and steel containers at room temperature (inside) and at the local ambient outdoor temperatures (outside). The study was conducted for 24 months. At the beginning of the study and at three-month intervals, samples were taken for measurement of peroxide value, acid value, density, viscosity, and heat of combustion. At the conclusion of the study, engine performance tests were conducted with the two year stored REE and RME, new REE and RME, and low sulfur diesel reference fuel. On the average, the esters increased over time in all of the previously mentioned properties with the exception of heat of combustion, which decreased. Regression models are presented to predict the deterioration with time. Engine power varied less than 2% for both Biodiesel fuels compared to the stored counterparts while smoke density decreased 3.2% for the stored RME and increased 17.5% for stored REE.
Biodiesel is an alternative diesel fuel produced by transesterification of vegetable oils or animal fats. While biodiesel provides numerous environmental benefits such as reduced exhaust emissions, it is more prone to oxidation than petroleum-based diesel fuel and this can alter its properties. When oxidation occurs at ordinary temperatures, the initial products are hydroperoxides. As the oxidation continues, the peroxides may split and form aldehydes, ketones, and short chain acids that produce unpleasant odors. Sediment and gums are formed through polymerization of the peroxides and can cause fuel filter plugging. The objective of this study was to relate the chemical and physical processes associated with biodiesel oxidation to the conditions that affect diesel fuel system performance. A relationship was sought between the test that is used by the engine industry to define engine fuel stability requirements (ASTM D2274) and the tests used by the fats and oils industry to characterize oxidation (Peroxide Value and Acid Value). It was found during the course of this study that the ASTM fuel stability method is not suitable for biodiesel. While oxidation causes the fuel viscosity to increase, fuel filter plugging was not necessarily a natural consequence of biodiesel oxidation even when the fuel was oxidized to a level beyond what would be observed in practice. The effect of fuel temperature and blending with diesel fuel on the oxidation was investigated and the interrelationship between the fuel's acid value and viscosity is shown.
In order to assure customer acceptance standardization and quality assurance is the key factor to the market introduction of biodiesel as a transport and heating fuel. In 1997 the European Commission mandated CEN to develop standards concerning minimum requirements and test methods of biodiesel. Working groups have achieved substantial progress. It was turned out, however, that in one complex key parameter, fuel stability, detailed research is absolutely needed. It is proposed to investigate all relevant topics to overcome this gap of knowledge. Suitable determination methods for the oxidation, thermal and storage stability will be worked out. The influence of storage conditions on the fuel quality properties and the effects of natural and synthetic antioxidants will be investigated. A comprehensive test program including bench and field tests will be carried out in order to find a relationship between the stability and special effects during use. The project "Stability of Biodiesel" (BIOSTAB) is supported by the European Commission in the frame of the 'Quality-of-Life-Program'. (Project number: QLK5-2000-00533). The project's duration is March 2001 until August 2003. Biodiesel can reduce the European dependence on oil imports and contribute to the security of energy supply. Liquid biofuels are the only alternative fuels for transportation which can be realised in short term and in considerable amounts. Renewable raw materials from the agriculture for the biodiesel production play an important role in the integrated rural policy. Biodiesel has been produced on an industrial level in the past decade, largely in response to positive signals from the EU institutions. The production of biodiesel in Europe will receive 1 mill. t, produced mainly in Austria, France, Germany and Italy. It absorbs the production of nearly 1 mill. ha of arable land. And it shows tremendous absorbing potential for additional acreage coming into the enlarged European Union from new East European member countries. The European Commission has set itself the ambitious aim to increase the market share of renewable energy to 12% until 2010. The ways and means used for accomplishing this aim, i.e. establishing regulations concerning the creation of favourable conditions for renewable sources of energy, are summarised in the "White Paper on Renewable Sources of Energy" [1]. The "campaign for take-off" 1999-2003 determines to support different key sectors, like e.g. "5 million tons of liquid biofuels", by means of specific programmes and actions of the Community. Within the internal market European standards for technical equipment using renewable sources of energy will be developed in CEN. The creation of standards shall help to expand the industry for renewable sources of energy on a EU level [2]. In 1997 the European Commission mandated CEN to develop standards for high-quality biodiesel used as a fuel for diesel engines and as heating fuel as well as the necessary standards concerning the analytical methods applied [3]. The proposed standards support Community objectives of free trade of biodiesel and of high-quality guarantees for the use of biodiesel. In 2001 two drafts (prEN14213 – FAME as heating fuel and prEN14214 – FAME as automotive diesel fuel) were subject of the public inquiry. In the drafting process a lack of knowledge about the stability of biodiesel was established. However the stability was considered as an important issue. It turned out that fuel stability has been overlooked and detailed research is needed in this area.
Biodiesel is an alternative fuel for diesel engines that can be produced from renewable feedstocks such as vegetable oil and animal fats. These feedstocks are reacted with an alcohol to produce alkyl monoesters that can be used in conventional diesel engines with little or no modification. Biodiesel, especially if produced from highly unsaturated oils, oxidizes more rapidly than diesel fuel. This article reports the results of experiments to track the chemical and physical changes that occur in biodiesel as it oxidizes. These results show the impact of time, oxygen flow rate, temperature, metals, and feedstock type on the rate of oxidation. Blending with diesel fuel and the addition of antioxidants are explored also. The data indicate that without antioxidants, biodiesel will oxidize very quickly at temperatures typical of diesel engines. This oxidation results in increases in peroxide value, acid value, and viscosity. While the peroxide value generally reaches a plateau of about 350 meq/kg ester, the acid value and viscosity increase monotonically as oxidation proceeds.
As part of a survey of biodiesel quality and stability in the United States, 27 biodiesel (B100) samples were collected from blenders and distributor nationwide. For this sample set, 85% met all of the requirements of the industry standard for biodiesel, ASTM D6751.
A study was carried out in order to evaluate the evolution of peroxide value, anisidine value, kinematic viscosity at 40 °C, ester and linolenic acid content, UV absorbency, acid value, polymer and tocopherol content during the oxidation of fatty acid methyl ester (FAME) using the Rancimat test chosen by CEN for measuring oxidation stability of FAME (pr EN 14112). The oxidation curves obtained during Rancimat test were compared with those obtained by the variation of oxidation parameters mentioned above, against the time. All quality parameters studied present visible variation along Rancimat test except UV 270 nm. At the end of Rancimat induction period, the seven samples tested do not meet FAME or oils and fats specifications such as kinematic viscosity, acid value, ester content or peroxide value. Rancimat induction period is well correlated to induction period given by quality parameters (0.963<R2<0.999), but Rancimat induction period is almost 10% higher than induction period given by quality parameters. Main conclusion is that induction period determined by conductivity is well correlated to degradation of quality parameters along Rancimat test.
Results obtained from a long-term storage study using eleven different biodiesel samples are presented. Samples prepared from several feedstocks using different manufacturing technologies (with or without biodiesel distillation), some containing an antioxidant additive, were stored in 200 l drums. These were periodically monitored during the complete storage period by analysis of fifteen different properties.
Several properties do not show any significant change during storage, while others such as viscosity, peroxide value and more dramatically, Rancimat Induction Period demonstrated changes related to the nature of the starting product.
A parallel test, carried out in simulated wrong storage conditions (occasional shaking promoting intimate contact between biodiesel and air oxygen) lead to some strong changes in biodiesel composition and can be used as a guide for devising biodiesel production set-up, storage and distribution chain.
The recorded changes in 8 different samples of biodiesel (from 4 different feedstocks, both undistilled and distilled) during accelerated ageing are shown in this paper. ASTM D 4625 method for quick ageing of common diesel fuels, carried out at 43 °C, allows to simulate the changes taking place in fuel during a long-term storage. All quality parameters of biodiesel are changing during time, according to the storage stability of different samples. The changes in other parameters not included in CEN tentative specification such as polymer content and peroxide value were recorded and plotted against storage time. Samples were also evaluated in terms of insoluble formation (filterable + adherent) but in any case significant insoluble formation was observed. The conclusion was that polymers formed during storage of biodiesel in controlled conditions are soluble in oxidised biodiesel, thanks to its high polarity and become insoluble only when oxidised biodiesel is mixed with diesel fuel.
Concerning their environmental impact, native based fuels and lubricants show immense potential. In fact, these products are highly exposed to oxidative processes during storage or application [1, 2]. One way to raise oxidative stabilities is the addition of synthetic antioxidants. Another way may be the modification of the fatty acid composition, since polyunsaturated fatty acids show a much higher proneness to autoxidation. In order to decrease the content of polyunsaturated and to raise the content of saturated components, experiments for fractional distillation and crystallisation as well as for hydrogenation of fatty acid methyl esters have been carried out.
In distillation experiments with separation columns the methyl esters performed good separation of the lower-boiling esters with a chain-length up to 16C-atoms, from the C-18 fraction, causing a degree of saturation up to 75 wt-% in the distillate. In tests with fractional crystallisation, the rate of saturation could be raised up to 92.8 wt-%. Using the process of catalytic hydrogenation, a rate of saturation up to 100 wt-% could be achieved, depending on the duration of the hydrogenation process. By partial hydrogenation of the polyunsaturated components, products with high oxidation stability and low pour point could be produced within relatively short hydrogenation time.
The results obtained during the set-up of a method for the prediction of biodiesel storage stability are shown. In order to speed up the rate of ageing processes, the test temperature was set to 80 °C, and tests were carried out within 24 h in a Rancimat modified cell apparatus. The effect of the quick ageing process can be monitored by means of the evaluation of changes in ester content, polymer content and peroxide value. By comparing the results obtained during a 1-year experiment, carried out under real storage conditions, and during a second test, carried out at 43 °C for 24 wk according to ASTM D 4625 method, with the ones reported in this paper, several discrepancies regarding the different degradation reactions as well as the rate at which these reactions take place were evidenced. Finally, a tentative relationship between the results obtained with the proposed quick test and the real Rancimat induction period, shown by different samples after 12 months of real storage, are shown. From the results obtained during this work, the Oxidation Stability test carried out according to EN 14112:2003 and the Storage Stability test reported herein may provide different information for the evaluation of the overall stability of a biodiesel sample.
The potential of 11 different synthetic phenolic antioxidants to improve the oxidation stability of biodiesel prepared from different feedstocks was investigated. Measurements of oxidation stability were carried out according to the European biodiesel specifications with a Rancimat instrument at 110 °C. At antioxidant concentrations of 1000 mg/kg, an improvement in oxidation stability could be achieved with all antioxidants tested. Especially the antioxidants DTBHQ, IONOX 220, Vulkanox ZKF, Vulkanox BKF, and Baynox were able to significantly improve the oxidation stability, leading to stabilization factors between 1.89 and 13.07. Variation of antioxidant concentrations between 100 and 1000 mg/kg showed that the efficiency of the antioxidants varied depending on the different types of biodiesel. When used as additives, Baynox showed good effects on rapeseed oil methyl ester (RME) stability, DBHQ on recycled cooking oil methyl ester (RCOME) stability, Vulkanox BKF on distilled RCOME (DRCOME) stability, and IONOX 220 on tallow methyl ester (TME) stability. Evaluation of the influence of the antioxidants on critical biodiesel fuel parameters showed no negative impacts on viscosities, densities, carbon residues, CFPP, and sulphated ash contents of the different biodiesel samples. However, in terms of acid values, a noticeable increase could be observed at antioxidant levels of 1000 mg/kg. At lower antioxidant concentrations, this increase was much lower and the values remained within the required limits.
The influence of the diesel particulate filter additives (DPA) SATACEN and EOLYS on biodiesel fuel quality has been evaluated. Both additives significantly affected the oxidation stability of neat biodiesel. The influence on acid values and CFPP was found to be only small. Combination of diesel additives with biodiesel additives like oxidation stability and CFPP improvers led to similar results. Results indicated that DPA also lowered the efficiency of the oxidation stability improver Baynox. Furthermore, the CFPP additives Chimec and Infineum were also prone to have a small influence on biodiesel oxidation stability.
The common unsaturated fatty acids present in many vegetable oils (oleic, linoleic and linolenic acids) can be quantitated by 1H-nuclear magnetic resonance spectroscopy (1H-NMR). A key feature is that the signals of the terminal methyl group of linolenic acid are shifted downfield from the corresponding signals in the other fatty acids, permitting their separate integration and quantitation of linolenic acid. Then, using the integration values of the signals of the allylic and bis-allylic protons, oleic and linoleic acids can be quantitated. The procedure was verified for mixtures of triacylglycerols (vegetable oils) and methyl esters of oleic, linoleic and linolenic acids as well as palmitic and stearic acids. Generally, the NMR (400 MHz) results were in good agreement with gas chromatographic (GC) analyses. As the present 1H-NMR-based procedure can be applied to neat vegetable oils, the preparation of derivatives for GC would be unnecessary. The present method is extended to quantitating saturated (palmitic and stearic) acids, although in this case the results deviate more strongly from actual values and GC analyses. Alternatives to the iodine value (allylic position equivalents and bis-allylic position equivalents) can be derived directly from the integration values of the allylic and bis-allylic protons.
High-resolution nuclear magnetic resonance (NMR) spectroscopy provides useful data for analyzing fatty acid compositions of
edible vegetable oils. Quantitation of each fatty acid was carried out by evaluation of particular peaks. According to the
1H NMR method, terminal methyl protons, divinyl protons, and allyl protons are useful to calculate linolenic acid, linoleic
acid, and oleic acid, respectively. The ω-2 carbon, divinyl carbon, and allylic carbons were used for calculation of these
acids by the 13C NMR method. Compositional results obtained by NMR coincided well with those of the conventional gas chromatography (GC)
method. Results from 13C NMR were in better agreement with those from GC than were the results obtained by the 1H NMR method.
The degree of physical and chemical deterioration of biodiesel produced from rapeseed and used frying oil was studied under
different storage conditions. These produced drastic effects when the fuel was exposed to daylight and air. However, there
were no significant differences between undistilled biodiesel made from fresh rapeseed oil and used frying oil. The viscosity
and neutralization numbers rose during storage owing to the formation of dimers and polymers and to hydrolytic cleavage of
methyl esters into fatty acids. However, even for samples studied under different storage conditions for over 150 d the specified
limits for viscosity and neutralization numbers had not been reached. In European biodiesel specifications there will be a
mandatory limit for oxidative stability, because it may be a crucial parameter for injection pump performance. The value for
the induction period of the distilled product was very low. The induction period values for the undistilled samples decreased
very rapidly during storage, especially with exposure to light and air.
The oxidation stability of methyl esters derived from fresh rapeseed oil and waste frying oil, used as alternative biodiesel
fuels, both distilled and undistilled, unstabilized and stabilized by pyrogallol and BHT, was studied by differential thermal
analysis (DTA) under nonisothermal conditions at various heating rates and by the Rancimat test under isothermal conditions
at 110°C. The results obtained by both techniques are compared. Both techniques show that oxidation stability increases considerably
with the addition of antioxidants and that pyrogallol is very efficient. Distillation of the methyl esters prepared from rapeseed
oil decreases their oxidation stability, obviously owing to the removal of natural antioxidants. The stability of methyl esters
prepared from the waste frying oil is determined mainly by the history of the oil. From the DTA measurements, the kinetic
parameters of an Arrhenius-like equation describing the temperature dependence of the oxidation induction period were obtained.
The parameters enable one to assess the protective factor of antioxidants for temperatures outside the measuring region, estimate
the residual stability, and model the process of biodiesel oxidation under nonisothermal conditions.
Oxidation stability of bodiesel is an important issue because FA derivatives are more sensitive to oxidative degradation than
mineral fuel. Therefore, in the most recent European Specifications for biodiesel, a minimum value of 6 h for the induction
period at 110°C, measured with a Rancimat instrument, is specified. To guarantee this value at the filling station, the use
of additional antioxidants will be necessary. In this paper we show the influence of different synthetic and natural antioxidants
on the oxidation stability, using the specified test method. Biodiesel produced from rapeseed oil, sunflower oil, used frying
oil, and beef tallow, both undistilled and distilled, was investigated. The four synthetic antioxidants pyrogallol (PY), propylgallate
(PG), TBHQ, and BHA produced the greatest enhancement of the induction period. These four compounds and the widely used BHT
were selected for further studies at concentrations from 100 to 1000 mg/kg. The induction periods of methyl esters from rapeseed,
oil, used frying oil, and tallow could be improved significantly with PY, PG, and TBHQ, whereas BHT was not very effective.
A good correlation was found between the improvement of the oxidation stability and the FA composition.
Fatty acid esters, high in linoleic acid, were prepared and stored for long-term engine tests. Storage tests with these esters were undertaken to obtain more information on optimal storage requirements and general stability characteristics.
Samples were kept at three temperature levels (20 C, 30 C and fluctuating around 50 C) for a 90-day period and were removed at regular intervals for chemical and physical analysis. The influence of air, temperature, light, TBHQ and contact with mild steel was evaluated by comparing the free fatty acid, peroxide, anisidine, ultraviolet absorption, viscosity and induction periods. A statistical model was used to evaluate the data and to reduce the large number of data points to comparable curves.
Storage of esters in contact with air, especially at a temperature above 30 C, resulted in significant increases in peroxide, ultraviolet absorption, free fatty acid, viscosity and anisidine values. Exclusion of air retarded oxidation at all temperature levels.
A direct relationship between viscosity increases and oxidation parameters was evident. Exposure to light caused a small increase in the oxidation parameters of esters stored at the highest temperature level. Addition of TBHQ prevented oxidation of samples stored under moderate conditions. Under unfavorable storage conditions the anti-oxidant was no longer effective. Mild steel had very little effect on the oxidation parameters. Only the anisidine values of samples stored at the highest temperature level were slightly increased. Methyl esters performed slightly better than ethyl esters during the storage test.
The following practical guidelines for storage of fatty acid ester fuels are: (i) airtight containers should be used; (ii) the storage temperature should be <30 C; (iii) mild steel (rust free) containers may be used, and (iv) TBHQ has a beneficial effect on oxidation stability.
Most common analytical methods in FA chemistry can be categorized as yielding either structure or quality indices. Quality
indices often describe components in fats and oils arising from processing, storage, and naturally occurring, nonfatty materials.
Common structure indices are the iodine value (IV), the saponification value, and the hydroxyl value. Although modern analytical
methods yield more detailed and reliable information, structure indices are still widely used. The IV, which indicates total
unsaturation, has even been included in some standards for industrial products such as biodiesel. However, the IV index is
too general to allow the correlation of physical and chemical properties with FA composition. The IV is treated in a theoretical
fashion regarding biodiesel- and oxidative stability-related issues. That the concept of IV as a structure index is unsatisfactory
is shown by the development of a quaternary composition diagram (QCD). The QCD demonstrates the derivation of a specific IV
from varying FA compositions. Improved correlations are possible among the structure indices. Alternative indices for the
IV are developed. Possible alternatives are the allylic position equivalent (APE) and the bisallylic position equivalent (BAPE)
which better relate structure and amount of common component FA in vegetable oils to observed properties. The APE and BAPE
indices are based on the number of reactive positions in oxidation.
Biodiesel, defined as the mono-alkyl esters of vegetable oils and animal fats is an alternative diesel fuel that is steadily gaining attention and significance. One of the most important fuel properties of biodiesel and conventional diesel fuel derived from petroleum is viscosity, which is also an important property of lubricants. Ranges of acceptable kinematic viscosity are specified in various biodiesel and petrodiesel standards. In this work, the kinematic viscosity of numerous fatty compounds as well as components of petrodiesel were determined at 40 °C (ASTM D445) as this is the temperature prescribed in biodiesel and petrodiesel standards. The objective is to obtain a database on kinematic viscosity under identical conditions that can be used to define the influence of compound structure on kinematic viscosity. Kinematic viscosity increases with chain length of either the fatty acid or alcohol moiety in a fatty ester or in an aliphatic hydrocarbon. The increase in kinematic viscosity over a certain number of carbons is smaller in aliphatic hydrocarbons than in fatty compounds. The kinematic viscosity of unsaturated fatty compounds strongly depends on the nature and number of double bonds with double bond position affecting viscosity less. Terminal double bonds in aliphatic hydrocarbons have a comparatively small viscosity-reducing effect. Branching in the alcohol moiety does not significantly affect viscosity compared to straight-chain analogues. Free fatty acids or compounds with hydroxy groups possess significantly higher viscosity. The viscosity range of fatty compounds is greater than that of various hydrocarbons comprising petrodiesel. The effect of dibenzothiophene, a sulfur-containing compound found in petrodiesel fuel, on viscosity of toluene is less than that of fatty esters or long-chain aliphatic hydrocarbons. To further assess the influence of the nature of oxygenated moieties on kinematic viscosity, compounds with 10 carbons and varying oxygenated moieties were investigated. A reversal in the effect on viscosity of the carboxylic acid moiety vs. the alcohol moiety is noted for the C10 compounds compared to unsaturated C18 compounds. Overall, the sequence of influence on kinematic viscosity of oxygenated moieties is COOH≈C–OH>COOCH3≈CO>C–O–C> no oxygen.
Biodiesel is continuously gaining attention and significance as an alternative diesel fuel. An important issue facing biodiesel is fuel stability upon exposure to air due to its content of unsaturated fatty acids. Numerous factors influence the oxidative stability of biodiesel, and several methods for its assessment have been developed. In the present work, a defined amount of biodiesel (methyl soyate) was heated in open beakers, with the only difference being the size of the beaker, i.e. the surface area of the biodiesel exposed to air. Biodiesel oxidized in this fashion was analyzed by 1H-NMR, kinematic viscosity and acid value. Acid values and kinematic viscosity increased with time and surface area. A previously developed 1H-NMR procedure was used to evaluate the unsaturation and residual fatty acid composition. The amounts of saturated fatty acids determined by this method increased, with monounsaturated and diunsaturated species increasing and then decreasing with time. After "flash" (3 h, 165 °C) oxidation, NMR shows the greatest effect on saturates and compounds with two double bonds, the former increasing and the latter decreasing. The double bond originally located at delta 15 in 18:3 is largely retained, showing that other double bond positions in 18:3 are initially affected by oxidation. The methyl ester signal decreases, coinciding with the increase in acid value. An increasingly strong absorption was observed in the UV-VIS spectra. Increasing surface area accelerated oxidation and affected fatty acid composition.
Biodiesel, an alternative diesel fuel derived from transesterification of vegetable oils or animal fats, is composed of saturated and unsaturated long-chain fatty acid alkyl esters. When exposed to air during storage, autoxidation of biodiesel can cause degradation of fuel quality by adversely affecting properties such as kinematic viscosity, acid value and peroxide value. One approach for increasing resistance of fatty derivatives against autoxidation is to treat them with oxidation inhibitors (antioxidants). This study examines the effectiveness of five such antioxidants, tert-butylhydroquinone (TBHQ), butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PrG) and α-Tocopherol in mixtures with soybean oil fatty acid methyl esters (SME). Antioxidant activity in terms of increasing oxidation onset temperature (OT) was determined by non-isothermal pressurized-differential scanning calorimetry (P-DSC). Analyses were conducted in static (zero gas flow) and dynamic (positive gas flow) mode under 2000 kPa (290 psig) pressure and 5 °C/min heating scan rate. Results showed that PrG, BHT and BHA were most effective and α-Tocopherol least effective in increasing OT. Increasing antioxidant loading (concentration) showed sharp increases in activity for loadings up to 1000 ppm followed by smaller increases in activity at higher loadings. Phase equilibrium studies were also conducted to test physical compatibility of antioxidants in SME-No. 2 diesel fuel (D2) blends. Overall, this study recommends BHA or TBHQ (loadings up to 3000 ppm) for safeguarding biodiesel from effects of autoxidation during storage. BHT is also suitable at relatively low loadings (210 ppm after blending). PrG showed some compatibility problems and may not be readily soluble in blends with larger SME ratios. Although α-Tocopherol showed very good compatibility in blends, it was significantly less effective than the synthetic antioxidants screened in this work.
The primary products formed from the autoxidation of lipids can be understood based upon a mechanism that involves five different reaction types. These reactions are: reaction of a carbon radical and molecular oxygen, atom transfer of a hydrogen from substrate to the chain carrying peroxyl, fragmentation of the chain carrying peroxyl to give oxygen and a carbon radical, rearrangement of the peroxyl, and cyclization of the peroxyl. The mechanism of these primary reaction steps has been the focus of extensive research over the past fifty years, and the current level of understanding of these transformations is the subject of this review.
The synthesis and study of a series of 6-substituted-2,4-dimethyl-3-pyridinols having interesting antioxidant properties is reported. The general synthetic strategy leading to the compounds involved a low-temperature aryl bromide-to-alcohol conversion as the last step. 2,4-dimethyl-3-pyridinol (1a), 2,4,6-trimethyl-3-pyridinol (1b), and 2,4-dimethyl-6-(dimethylamino)-3-pyridinol (1d) were thus prepared from the corresponding 3-bromopyridine precursor. The methoxy derivative 2,4-dimethyl-6-(methoxy)-3-pyridinol (1c) was also prepared by an alternate route via a Baeyer-Villiger reaction on the substituted benzaldehyde precursor. Novel bicyclic pyridinols 2 and 3 required prior construction of the ring structure. Thus, 2 was prepared by the use of a 6-step intramolecular Friedel-Crafts strategy, and 3 required an 11-step sequence with a thermolytic intramolecular inverse-demand Diels-Alder reaction between a pyrimidine ring and an alkyne as the key step. Basicities of the pyridinols approached physiological pH with increasing electron density in the ring. Pyridinols 1a-d were found to be indefinitely stable to air oxidation while 2 and 3 decomposed upon extended exposure to the atmosphere. The reactivities of the pyridinols toward chain-carrying peroxyl radicals in homogeneous organic solution were examined by studying the kinetics of radical-initiated styrene autoxidations under controlled conditions. These experiments revealed that some of the newly synthesized pyridinols are the most effective phenolic chain-breaking antioxidants reported to date.
This paper aimed to investigate the biodiesel degradation characteristics under different storage conditions. The qualities of twelve biodiesel samples, which were divided into 3 groups and stored at different temperatures and environments, were monitored at regular interval over a period of 52 weeks. Experimental results demonstrated that the biodiesel under test degraded less than 10% within 52 weeks for those samples stored at 4 and 20 degrees C while nearly 40% degradation was found for those samples stored at a higher temperature, i.e. 40 degrees C. The results suggested that high temperature, together with air exposure, greatly increase the biodiesel degradation rate. The temperature or air exposure alone, however, had little effect on biodiesel degradation. Water content in biodiesel will enhance biodiesel degradation due to hydrolysis but its effect is much less than the above two factors.
The theory of initiation in lipid autoxidation, which deals with the supply of radicals to the chain reaction, has not been substantively advanced for several decades. Most researchers have long assumed a mechanism of initiation in which main-product hydroperoxide is centrally responsible for autocatalytic radical generation. However, this paper, in which we investigate autoxidizing methyl linoleate, presents decisive evidence against such an assumption: Autoxidation-accelerating activity under mild conditions was not found in the chromatographically separated main-product hydroperoxide fraction but was found in other fractions; and highly active substances with structures containing a peroxide-linked dimer with two hydroperoxy groups were actually obtained.