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Experimental determination and theoretical correlation for the solubilities of dicarboxylic acid esters in supercritical carbon dioxide
Abstract
The synthesis of high molecular weight esters such as bis (2-ethylhexyl) sebacate is of significance for its use as a lubricant. This ester is synthesized by the transesterification of dimethyl sebacate with 2-ethylhexanol. Therefore, the solubilities of bis (2-ethylhexyl) sebacate and dimethyl sebacate were determined at 308–328 K at pressures of 10–18 MPa in supercritical carbon dioxide. The solubility of dimethyl sebacate was always higher than bis (2-ethylhexyl) sebacate at a given temperature and pressure. The Mendez-Teja model was used to verify the self-consistency of data. Further, a new semi-empirical model with three parameters was developed using the solution theory coupled with Wilson activity coefficient. This model was used to correlate the experimental data of this work and solubilities of many high molecular weight esters reported in the literature.
... Several pronounced concentrations of DEHS were observed in the D1 district (an old city center), with an average level sevenfold higher than other sites. This result implied that there were emissions of DEHS at this site, which is commonly applied in products such as cable, leather, and aviation engine oil (Narayan et al. 2015). Concentrations of DMT and DET were relatively lower with median values under 16.6 pg/m 3 and 5.01 pg/m 3 , respectively. ...
... Factor 3 is featured by the high loading of most LMW PAEs, DEHA, and DEHS. These plasticizers are widely used as functional accessory ingredients in solvents applied in dye, paint, ink, adhesives, and insecticide materials (Benjamin et al. 2017;Narayan et al. 2015;Santangeli et al., 2017. These products are used extensively in interior/ commercial decoration and household/public sanitation at these residential sites with high population density. ...
... Considering the intensive industrial activities in these districts, the application of the commercial DEHP in the industry may emit and contribute most of DEHP and DNOP in the air at the same time. The significant loading of DEHS and DEHA indicates these chemicals are also heavily applied in the industry of Guangzhou since they were commonly PAE substitutes (Narayan et al. 2015;Nehring et al. 2019). Moreover, compared to the less industrialized districts, fewer species of plasticizer congeners were loaded in factor 1 for the industrialized districts. ...
Plasticizers are ubiquitous pollutants in the environment, whereas few efforts have been made to elucidate their emission sources in the atmosphere. In this research, the spatioseasonal variations and sources of particle-bound (PM 2.5) phthalates (PAEs) and their substitutes (APs) at residential sites in seven districts and at four potential point-source sites across a megac-ity in South China were revealed. The total concentrations of PAEs ranging from 10.7 to 528 ng/m 3 were substantially higher than those of APs (1.45.58.5 ng/m 3). Significant spatial variations in the concentrations of the pollutants were observed, which were generally higher at the sites with intensive industrial activities and the point-source sites. Most atmospheric plasticizer levels peaked in summer, probably due to the temperature-promoted volatilization. Seven sources of plasticizers were identified by the positive matrix factorization (PMF) model. The sources in less industrialized districts are mainly associated with domestic and commercial emissions and with industry in the industrialized districts. Specifically, plastics and personal care products together contributed 60% of the plasticizers in the atmosphere of this city, followed by solvents and polyester industry sources. The incremental lifetime cancer risk of inhalation exposure to bis(2-ethylhexyl) phthalate in the study city is below the acceptable level. Relatively higher risks were found for residents living around sites with intensive industrial activities and around wastewater treatment plant.
... In this study, some recent models such as Andonova-Garlapati model based on degree of freedom [49], Narayan model [50]and Rathnam model [51] both based on solution theory combined to Wilson's activity coefficient which include the ratio of molar densities ...
... Model formulation Andonova-Garlapati [49] y 2 = a 0 (ρ r ) a1 (T r ) a2 Narayan [50] ; ln ; ...
... The three first models in Table 1 don't use directly the density of SC-CO 2 , Andonova-Garlapati model [49] uses ρ r which is the reduced density given by ρ ρ c 1 where ρ c 1 ¼ 468 kg m 3 is the critical density of CO 2 and the model led to the highest AARD with a value of 15%. While Narayan et al. [50] and Rathnam et al. [51] models uses ρ′ which is also molar volumes ratio ...
Developing environmentally friendly processes as supercritical technologies for the pharmaceutical industry producing micro-sized drug particles is crucially important. For achieving such a purpose, the solid drug's solubility in supercritical fluids (SCFs) should be accurately measured and correlated. In this work, the equilibrium solubility of the losartan potassium (L-K), an antihypertensive drug, in supercritical carbon dioxide (SC-CO2) has been determined for the first time. Measurements were carried out at pressures ranging from (120 to 270) bar, and temperatures from (308 to 338) K. Obtained solubilities (presented in mole fraction) are in the range of 2.03 × 10⁻⁶ - 1.88 × 10⁻⁵and their behavior was examined with respect to the pressure and density of the SC-CO2. The crossover region was observed at about 190 barin all isotherms in term of mole fraction-pressure plots. Some semi-empirical models based on different approaches as activity coefficient and fugacity coefficient were used for correlating solubilities data. The dilute solution -based MST model (Mendez-Santiago-Teja) led to the best AARD with a value of 2.8%, and correlated results with this model endorsed internal consistency of experimental solubility data. Moreover, endothermic process was corroborated with both experimental results and estimated enthalpies.
... Most of the existing models correlate the solubilities of solid solutes in SCCO 2 . However, the models correlating the solubility of liquid solutes are scarce [56][57][58]. The few existing correlations for liquid solutes have utilized association and solution theories coupled with the Wilson, van Laar, and Margules activity coefficient models. ...
... However, only two possible models were derived using the solution theory in the existing exhaustive study [58]. In these models, Wilson activity coefficient model was always used to account the non-ideality of SCF phase and, the van Laar activity coefficient was used to account the liquid phase non-ideality of the solute, respectively [56,58]. In addition, it was observed that, when the nonideality in the SCF phase was accounted using the van Laar activity coefficient model, the correlation results to a simple trivial equation (solubility was only a function of temperature) [58]. ...
... The detailed description of the flow saturation technique used to measure solubility in SCCO 2 has been reported in our earlier studies [56][57][58][59]. The gaseous CO 2 cylinder at 6 MPa was passed through the silica gel bed to increase the purity by 0.999 mass fraction. ...
... Despite the availability of several models for correlating solubilities of solids, models correlating solubility of liquid solutes in SCCO 2 are scarce. A solution model combined with Wilson activity coefficient model was developed by Narayan and Madras [40] for the solubilities of liquids in SCCO 2 . ...
... In this study, the flow saturation technique, i.e., dynamic method was used for the measurement of solubilities. The equipment and details of operation is provided in our previous study [40]. The gas from the CO 2 cylinder was passed via chiller at −10 • C where it was liquefied. ...
... In Eq. (3), y m is the solubility of solute in kg m −3 , k is association number, is density of the solvent in kg m −3 , T is temperature in K and A 3 and B 3 are the regression coefficients. Another correlation for the liquid solutes based on solution model [40] is given by the following expression, ...
... 8 As an example, di-2-ethylhexyl sebacate (DEHS), a dicarboxylic acid ester of sebacic acid with 2-ethyl hexanol, has been in use as a lubricating oil in aircraft engines since the 1940s. 4 It has also been reported that DEHS as a fuel additive can significantly improve the lubricity, ignition quality, cold flow performance, and cetane quality of diesel fuels. 9,10 The above high-value synthetic esters, including biodiesels and biolubricants, are usually synthesized using fatty acids, methyl esters, or triglycerides as precursors by a chemical process known as transesterification. ...
... 11 For example, the dicarboxylic acid esters of DEHS are mainly synthesized by using base/acid catalysts, 12,13 enzyme catalysts, 14,15 as well as noncatalytic reactions in supercritical fluids. 4,16 The conventional synthesis procedures for such high-value esters usually suffer from high cost and reduced purity, which are associated with the consumption of petroleum sources, wastewater, and deactivated catalysts. ...
Dicarboxylic acid esters possessing the consistency with conventional hydrocarbon oils have been utilized as biolubricants and additives. In general, dicarboxylic acid esters biolubricants are obtained by catalytic transesterification between fatty acids, methyl esters or triglycerides as precursors. Here, we develop a new strategy to produce dicarboxylic acid esters through chemically recycling of thermosetting polymer waste. Thermosets with tunable mechanical properties derived from epoxy oligomer and dicarboxyl acid can be decomposed in Zinc acetylacetonate/2-ethyl-hexanol solution at relatively mild temperatures (<170oC) and ordinary pressure. The epoxy dissolution rate can be enhanced by increasing temperature and catalyst loading. The depolymerized epoxy oligomer of dicarboxylic acid ester was obtained as a biolubricant. In addition, the catalyst can be facilely reclaimed and reused. This work presents a new approach for engineering polymer waste to generate eco-friendly high-value oil, such as biolubricant, which is beneficial to reduce environmental pollution and alleviate petrochemical sources consumption.
... Most of the organic compounds, with the exception of strongly polar substances, have appreciable solubility in SCCO2 and can be extracted using neat SCCO2. The solubility of polar compounds in SCCO2 can be enhanced by using a co-solvent or an entrainer [25][26][27] using the solution and association theories coupled with the different activity coefficient models [36][37][38]. Along with these models, different semi-empirical models have also been reported in ...
... The solubility of TOMAC in neat SCCO2 was also correlated using two activity coefficient based models, solution theory based Wilson activity coefficient model [36] and association theory based van Laar activity coefficient model [59]. The details of the models and the obtained results are described in the supporting information (see electronic supplementary information Section 2, Table S1, Figure S3). ...
Solubility of trioctylmethylammonium chloride (TOMAC) in supercritical carbon dioxide (SCCO2) was measured at 313, 323 and 333 K with pressure ranging from 10 to 30 MPa. Solubilities (in mole fraction) ranged from 0.5 × 10⁻⁵ to 12.7 × 10⁻⁵ in the investigated region. Influence of co-solvents on the solubility of TOMAC was studied at 313 and 323 K. Among the four models employed for correlating solubility of TOMAC in neat SCCO2, association theory based on van Laar activity coefficient model resulted in average deviation of 2%, while use of other models resulted within 10%. Solubility data were found to be self-consistent based on the Mendez-Teja model. Two new models were developed for the ternary system (SCCO2 + co-solvent + liquid solute) based upon association theory along with the Wilson and van Laar activity coefficient models. These models successfully correlated solubility of TOMAC in SCCO2 + co-solvent with an average deviation of <8%.
... Correlating the solubility of different materials in sc-CO 2 through the Wilson's model has been previously performed by several researchers such as, Nasri (2018) Narayan et al. (2015), and Reddy and Madras (2013), Reddy and Madras (2012). Wilson's equation includes a combinatorial contribution part based on Flory's theory, and another part based on the Gibbs excess energyðG E Þ, as follows (Nasri, 2018): ...
The design and development of supercritical carbon dioxide (sc-CO2) based processes for production of pharmaceutical micro/nanoparticles is one of the interesting research topics of pharmaceutical industries owing to its attractive advantages. The solubility of drugs in sc-CO2 at different temperatures and pressures is an essential parameter which should be determined for this purpose. Chloroquine as a traditional antirheumatic and antimalarial agent is approved as an effective drug for the treatment of Covid-19. Pishnamazi et al. (Pishnamazi et al., 2021) measured the solubility of this drug in sc-CO2 at the pressure range of 120-400 bar and temperature range of 308-338 K, and correlated the obtained data using some empirical models. In this work, a comprehensive computational approach was developed to more accurately study the supercritical solubility of Chloroquine. The thermodynamic models include two equations-of-state based models (Peng-Robinson and Soave-Redlich-Kowang) and two activity coefficient-based models (modified Wilson's and UNIQUAC)), as well as, a multi-layer perceptron neural network (MLPNN)) were used for this purpose. Also, molecular modeling was performed to study the electronic structure of Chloroquine and identify the potential centers of intermolecular interactions during the dissolution process. According to the obtained results, all of the theoretical models can predict Chloroquine solubility in sc-CO2 with acceptable accuracy. Among these models, the MLPNN model possesses the highest precision with the lowest average absolute relative deviation (AARD%) of 1.76% and the highest Radj value of 0.999.
... Modified Wilson's model has been satisfactory applied to correlate the solubility of different compounds in scCO 2 , like N,N-dialkylamides [44], trioctylmethylammonium chloride [45], dicarboxylic acid esters [46], aromatic solid pollutants [47], and some others [18,31,48]. As the same way, the UNIQUAC model has been utilized to correlate the solubility of some materials in scCO 2 , such as methylbenzoic acid isomers and dihydroxybenzoic acid [49], and some others [31,32,50]. ...
Alendronic acid, with the commercial name of Alendronate, is a bisphosphonate medicine which is generally used orally to treat the osteoporosis and Paget's disease of bones. However, its absorption is poor, and its oral bioavailability is less than 1%. So, development of novel delivery systems to enhance its bioavailability and reduce its side effects is essential.
The design and development of modern drug delivery systems, based on supercritical carbon dioxide (scCO2) as a green solvent, can be an efficient solution to increase the therapeutic efficacy and bioavailability, as well as reduce the toxicity and side effects of various medicines. The solubility of pharmaceutical substances in scCO2 is an essential parameter that must be determined for this purpose.
In this research, solubility of Alendronate in scCO2 was experimentally determined in the span of 0.01×10⁻⁴ - 1.5×10⁻⁴ (equilibrium mole fraction), at 308 to 338 K and 120 to 300 bar. Also, obtained experimental values were correlated by two fugacity coefficient models (PR-EoS and SRK-EoS), and two activity coefficient models (modified Wilson and UNIQUAC). All these models could successfully correlate the Alderonate solubility values. Meanwhile, the solubility data obtained from the SRK-EoS (AARD% = 10.11) and modified Wilson’s model (AARD%= 11.52) are more accurately fitted to the experimental data.
... The liquid phase is considered as an expanded liquid phase of ScCO 2 . At equilibrium, the solubility may be expressed as [53][54][55][56][57] where γ ∞ 2 is drug activity coefficient at infinitesimal dilution in ScCO 2 and f S 2 and f L 2 are fugacities of drug in the solid and ScCO 2 phases, respectively. The f S 2 /f L 2 ratio may be expressed as follows: www.nature.com/scientificreports/ ...
The solubility of empagliflozin in supercritical carbon dioxide was measured at temperatures (308 to 338 K) and pressures (12 to 27 MPa), for the first time. The measured solubility in terms of mole faction ranged from 5.14 × 10–6 to 25.9 × 10–6. The cross over region was observed at 16.5 MPa. A new solubility model was derived to correlate the solubility data using solid–liquid equilibrium criteria combined with Wilson activity coefficient model at infinite dilution for the activity coefficient. The proposed model correlated the data with average absolute relative deviation (AARD) and Akaike’s information criterion (AICc), 7.22% and − 637.24, respectively. Further, the measured data was also correlated with 11 existing (three, five and six parameters empirical and semi-empirical) models and also with Redlich-Kwong equation of state (RKEoS) along with Kwak-Mansoori mixing rules (KMmr) model. Among density-based models, Bian et al., model was the best and corresponding AARD% was calculated 5.1. The RKEoS + KMmr was observed to correlate the data with 8.07% (correspond AICc is − 635.79). Finally, total, sublimation and solvation enthalpies of empagliflozin were calculated.
... The individual AARDs for each amide have been presented in Table 2. A solution theory coupled with Wilson activity coefficient model [54] was also examined for correlation of solubilities of N,N-dialkylamides and the results are discussed in Supporting Information (Section 1). ...
N,N-Dialkylamides are the potential ligands for the extraction of actinides in nuclear-fuel cycle operations. Supercritical carbon dioxide (SCCO2) containing N,N-dialkylamides is a green solvent for the extraction of actinides with minimum liquid waste generation. In this connection, the solubilities of six N,N-dialkylamides in SCCO2 (313–333 K and 10–20 MPa) were measured to evaluate their utility as extractants for actinide separations. The solubilities are ranging from 0.005 × 10⁻³ to 102 × 10⁻³ mol mol⁻¹. The solubility of amides can be improved by increasing pressure and reducing temperature in the investigated region. The internal-consistency of solubility data was tested with Mendez-Teja equation. The solubility data was correlated with Chrastil, Mendez-Teja, solution theory with Wilson activity coefficient model and association theory with van Laar activity coefficient model. The correlation results demonstrated that, association theory with van Laar activity coefficient model predicts the solubilities with an average deviation of <8% and is best among the models studied.
... The equilibrium solubilities of a liquid mixture in SCCO 2 were determined by flow saturation technique (Jasco International Company, Japan). The detailed procedure about the experimental setup has been reported earlier [19]. Carbon dioxide was sent to a chiller and this was pumped into the 50 ml column having an optimized amount of 30 ml of the solute mixture. ...
The mixture solubilities of methyl 10-undecenoate (M10U) + methyl ricinoleate (MR) in supercritical carbon dioxide (SCCO2) were determined at temperatures from 313 to 333 K, and pressures from 10 to 18 MPa. At constant pressure, the solubilities decreased with an increase with temperature for the investigated range of operating conditions. The maximum solubility enhancement for the current mixture was observed to be 32% for the MR in a mixture of M10U + MR. The maximum selectivity of SCCO2 was 12 towards M10U in a mixture of M10U + MR. The experimental data obtained was internally consistent, as verified by Mendez-Teja model. A new association theory based model was derived and used to model the solubilities of the investigated mixture in SCCO2 along with the literature data.
... A dynamic flow saturation technique was used to determine the equilibrium solubilities in SCCO 2 at various operating conditions. The detailed procedure of the equipment was reported in the earlier works [16,21]. The solubility of 1-octanol was obtained from this equipment and verified with the literature reported values [22]. ...
The solubilities of liquid mixtures of 10-undecenoic acid + methyl 10-undecenoate, and 10-undecenoic acid + methyl ricinoleate in SCCO2 were determined at T = 313–333 K and P = 10–18 MPa. The selectivity is higher towards methyl 10-undecenoate in a mixture of 10-undecenoic acid + methyl 10-undecenoate, whereas the selectivity is higher towards 10-undecenoic acid in a mixture of 10-undecenoic acid + methyl ricinoleate. A new model was developed based on the solution theory coupled with regular solution theory. The absolute average relative deviation (AARD%) obtained using the new model for the system of 10-undecenoic acid + methyl 10-undecenoate was 10.5 and 9.10 for the 10-undecenoic acid and methyl 10-undecenoate, respectively, whereas for the system of 10-undecenoic acid + methyl ricinoleate, the AARD% was 4.71 and 4.91 for the 10-undecenoic acid and methyl ricinoleate, respectively. These AARDs were significantly lower than the existing models indicating utility of the new model.
With this article we extend our review series on high-pressure (above 1 MPa) phase equilibrium data to articles published between 2013 and 2016, including a compilation of systems investigated, recent developments, and trends. We considered phase equilibria of vapor, liquid, and solid phases, hydrates, critical points, solubility of high-boiling substances in supercritical fluids, solubility of gases in liquids, and solubility (sorption) of volatile components in ionic liquids and in polymers. In total, we found 1400 relevant articles in the four-year period 2013–2016 which means a 40 % increase as compared to the previous review period 2009–2012. This can be explained by a more elaborated search strategy, new publication strategies of the authors, and by the ongoing scientific interest in high-pressure phase equilibria. We summarize scientific areas that drive the measurement of high-pressure phase equilibria, and we give examples of review articles, which focus on a specific topic related to experimental high-pressure phase equilibrium data.
Apart from 14 systematically searched journals, we observed a tremendous increase in the number of articles found in other journals, rising from 59 articles (2009–2012) to 473 articles (2013–2016). Until the late 1990s, the average number of authors per article was approximately 3. From then on, it has been increasing almost linearly and has reached a value of 4.7 in 2016. More than one third of the articles contain data on only one system. While the average number of systems per article is close to 3, the median value is 2.
For more than 4000 systems, the reference, the temperature and pressure range of the data, and the experimental method used for the measurements is given in 41 tables. Information on hydrate systems and systems containing ionic liquids are given in 6 additional tables. 47.1 % of all systems of the review period 2013–2016 contain CO2 as one of the components. Other frequently measured components are water (32 %), methane (12.3 %), nitrogen (5.1 %), propane (3.7 %), ethane (3 %), hydrogen (2.7 %), and ethanol (2.2 %). In the period 2013–2016, 18 % of the data sets involve hydrate equilibria, 15.4 % of the systems include an ionic liquid, and 7.7 % contain a refrigerant. In the period from 1988 to 2016, we observed a clear shift in the investigated systems from chlorofluorocarbon to hydrofluorocarbon and then to hydrofluoroolefin refrigerants.
The number of investigations at very high temperatures and pressures has increased, since a higher number of data sets from the Earth and planetary sciences have been found and included in the period of this review. The average internal volume of all cells used for measurements in the review period is 141 mL. Many different methods for the measurements of high-pressure phase equilibrium data exist. We discuss the main advantages and challenges of the methods and give examples of their use in the period 2013–2016. The percentage of the use of synthetic methods constantly rose from 29 % in the first period (1988–1993) to 62 % in the fourth period (2005–2008). Since then, it has stayed almost constant. Analytical–isobaric–isothermal (flow) methods have been used less and less, from 22 % (1988–1993) to 5 % (2013–2016). Synthetic-nonvisual methods are used more and more often, rising from 3 % (1988–1993) to 23 % (2013–2016).
Ibrutinib (PCI-32765), marketed under the trade name IMBRUVICA, is a first-in-class irreversible inhibitor drug of Bruton tyrosine kinase (BTK). In the current research, its solubility was measuredat operational conditions 120-270 bar and 308-338 K, for the first time.The drug solubilityhas been reported between 3.90×〖10〗^(-6)to 1.30×〖10〗^(-5)based on mole fraction. Analysis of the curves confirms strong dependency of ibrutinib solubility to operational conditions due to their direct effect on solvating power of solvent. Also, pressure effect was more pronounced at the higher temperatures and the cross-over point was located around 170 bar. Besides, theoretical investigation and computational approach were carried out to correlate and extrapolate the experimental solubility of this medicine using thermodynamic models based on different approaches;semi-empirical models, activity coefficient (modified model of Margules), fugacity coefficient (mPR and mRK cEoSs) and dilute solution theory by the model of Wang-Tavlarides. Best correlation results were obtained by the modified model of Margules (AARD=6.68%) and the empirical model of Jouybanet al., (9.62%).Additionally, different enthalpies of ibrutinib-Sc-CO2 system were estimated.
Supercritical carbon dioxide (SC‐CO2) is CO2 that is stored beyond its critical point of 7.4 MPa and 31.1 °C. Given the request for consumption of a green solvent for the environment, SC‐CO2 is widely utilized in chemical, food, and pharmaceutical industries. To design material and drug production processes using supercritical fluid (SCF) technology, knowledge of their solubility is important. Temperature and pressure are the main factors in the study of solubility. Solubility data are then evaluated using equation of state, semi‐empirical, and intelligence models to establish suitable correlations. SC‐CO2 is one of the most important materials used in SCFs to study solubility. Another application of SC‐CO2 is in the field of material extraction to reduce the consumption of organic solvents. Nanoparticles production in drug industry is another advantage of SC‐CO2. Micro and nanoparticles can be produced using SCF techniques. In this review, the applications of SC‐CO2 in drug solubility, extraction of valuable materials, and nanoparticles production for pharmaceutical processes are reported and discussed. Finally, the main challenges are explained.
We are very hopeful and confident that epoxy vitrimers could replace traditional epoxy resins to be used in various fields, because epoxy vitrimers have excellent physical and chemical properties at service temperatures theoretically, just like traditional epoxy resins.
Chrastil’s semi-empirical model has been widely used, since its introduction in 1982, to fit solubility in supercritical carbon dioxide. However, it has been used with different sources for carbon dioxide’s density, with different objective functions and different numerical algorithms to determine the three Chrastil coefficients. These differences lead to an unnecessary variance in fitting performance and Chrastil coefficient values. The result is a reduction in the perceived quality of Chrastil’s model. Also, calculated solubilities based on published Chrastil coefficients but with a different source for carbon dioxide’s density risks introducing considerable incremental error. This work uses Span and Wagner’s Fundamental Equation of State and a two-pass Nelder Mead algorithm to minimize the absolute average relative deviation (AARD) for 701 binary data sets. The median AARD is just 8.8% while just 5.2% of the 701 systems have an AARD greater than 30%.
From cars to airplanes, from household appliances to indoor ornaments, from biomedical devices to factory equipment, epoxy resins have been deeply rooted in modern society. But at the same time, they also bring about a lot of wastes after use due to their insoluble and infusible nature. Vitrimer opens up great opportunities towards a sustainable society by producing reprocessable epoxies and even thermosets. Epoxy vitrimers are not only the first reported vitrimers, but also the most studied vitrimers. Epoxy vitrimers are reversible covalently crosslinked networks with dynamic covalent bonds, combining excellent mechanic properties of thermosets with reprocessability of thermoplastics. Moreover, the exchangeable network endows vitrimers with excellent reprocessing, self-healing, welding, reshaping and recycling properties. So vitrimers are hopeful to replace traditional thermosets for a wide range of applications in aerospace materials, electronic devices, consumer products of daily life and so on. This review summarizes recent advances in epoxy vitrimer research. The classification and fabrication of epoxy vitrimers and their composites are thoroughly discussed. New properties of epoxy vitrimers brought by the dynamic covalent bonds are also reviewed in-depth. Their potential applications are subsequently explored and summarized.
The solubilities of dibutylhydrogen phosphonate (DBHP) and dihexylhydrogen phosphonate (DHHP) in supercritical carbon dioxide were determined at 313–333 K and 10–20 MPa. The mole fraction solubility of DBHP and DHHP are in the range of 3.4 × 10⁻⁴ to 66.4 × 10⁻⁴ and 4.5 × 10⁻⁴ to 806.6 × 10−4, respectively. The solubility data are self-consistent with Mendez–Teja model. The experimental solubilities were correlated using Chrastil, Hezave–Lashkarbolooki and three models based on activity coefficient models. Hezave–Lashkarbolooki model resulted in better solubility predictions for DBHP with an AARD of 5%. Chrastil and van Laar activity coefficient based model correlated the solubility of DHHP with a lowest AARD of 11%.
A systematic study on the phase behavior of saturated ethyl esters with supercritical CO2 is presented. High pressure phase behavior measurements for the systems CO2/ethyl decanoate, CO2/ethyl dodecanoate, CO2/ethyl tetradecanoate, and CO2/ethyl hexadecanoate were conducted in a static synthetic view cell in the temperature range 308–358 K. Phase transition pressures were measured in the range 5.86–23.01 MPa for ethyl ester mass fractions in the range 0.0174–0.657 and complement existing literature data. Throughout the temperature and compositional range measured, which encompassed the liquid phase, mixture critical region, and vapor phase, an increase in temperature leads to an increase in phase transition pressure with no temperature inversions or three phase regions observed. Additionally, an increase in hydrocarbon backbone length leads to an ever-increasing phase-transition pressure, suggesting fractionation of ethyl esters according to molecular mass with supercritical CO2 is possible. Finally, the measured and previously published CO2/ethyl ester data were successfully correlated with a modified Chrastil models and the MT model. While these models cannot easily be used predictively and depend on the data sets used for correlation, these are simple and easy methods that can be used to interpolate data.
A review of the solubility data for solids in sub- and supercritical fluids published in the literature between 2010 and 2017 is presented, including the pressure and temperature ranges and correlation methods. Compounds are categorized into the following groups: pharmaceutical, biological, aromatic, nonaromatic, organometallic, and polymer. The most commonly used solvent is supercritical CO2; some data have also been published for other solvents, such as argon, propane, and fluorinated hydrocarbons.
The solubility of tri-iso-amyl phosphate (TiAP) in supercritical carbon dioxide (SCCO2) was determined at 313–333 K with pressure ranging from 10 to 25 MPa. The solubility data of TiAP in SCCO2 medium were correlated using four semi-empirical models. Selective extraction of uranium from simulated dissolver solution was demonstrated using SCCO2 modified with TiAP. The extraction efficiency of uranium was found to be 95 ± 5%. The influence of temperature, pressure and acidity on the extraction of uranium was studied. An attempt was made to explain the plausible extraction mechanism.
The bis(2-ethylhexyl)ester of sebacic acid is a widely used synthetic lubricant having various applications in the aerospace, automobile and manufacturing industries. This ester was synthesized directly from sebacic acid under subcritical and near critical conditions of 2-ethylhexanol without the addition of external catalysts for the first time. Reversible reaction kinetics was used to fit the experimental data considering the effect of acid catalysis across different initial molar ratios and temperatures. Equilibrium conversion was achieved within an hour of reaction even under subcritical conditions and at a lower temperature of 523 K. The synthesis route undertaken is proposed to have an economic as well as an environmental edge, due to lower molar excess of alcohol and shorter reaction time even without the addition of external catalysts.
Dialkylalkyl phosphonates have found renewed interest in the selective extraction of actinides from different matrices. In this context, two dialkylalkyl phosphonates, dibutylbutyl phosphonate (DBBP) and diamylamyl phosphonate (DAAP) were synthesised and their solubilities in supercritical carbon dioxide (SCCO2) medium were determined in the pressure range of 10–25 MPa at 313–333 K. Solubility studies were carried out to examine their utility as ligands during supercritical fluid extraction of actinides. Solubilities of dialkylalkyl phosphonates ranged from 0.06 to 0.12 mole fraction. Experimental solubilities were correlated using Mendez-Santiago, Chrastil, solution theory with Wilson activity coefficient model and association model based on van Laar activity coefficient model. Comparison among these models revealed that the association model with van Laar activity coefficient model provides better solubility predictions. SCCO2 containing DAAP was employed for the (i) selective extraction of uranium in the presence of simulated fission products and (ii) extraction of uranyl nitrate from acidic medium.
Two new semi-empirical models were proposed to calculate and predict the solubility data of some compounds in supercritical carbon dioxide (SCCO2). The new model I was constructed based on the models of Chrastil. Its ability of calculating solubility data was evaluated and compared with the models of Chrastil, Adachi-Lu and de Valle using solubility data of 40 compounds collected from literature published in recent years, and results showed that the new model I is better than other models. However, the new model I as well as other models mentioned above can only be fitted for each solute without the ability of prediction for the unknown solubility data. Meanwhile, the molecular connectivity indices (MCIs) have been widely used as the structure descriptors encoding a large amount of structure information on an entire molecule. Therefore, the new model II was developed by combining the modified MCIs with the new model I to calculate the solubility data of fatty acids, fatty alcohols, fatty acid esters and aromatic compounds in SCCO2. The relation between the solutes' solubility data and their molecular structures was developed by a one-off correlation of experimental data and then the inductive relation was used in the new model II to predict the solubility data of homogeneous solutes successfully.
The solubilities of a series of trialkyl phosphates in supercritical carbon dioxide have been investigated. The solubility measurement was carried out using a dynamic flow method. The measurements were performed at 313, 323 and 333 K and in the pressure range of 10 to 25 MPa. The trialkyl phosphates were found to be highly soluble in supercritical carbon dioxide and the solubilities were in the range of 0.01 to 0.1 mol fraction. The solubility of trialkyl phosphates increases with an increase in pressure at constant temperature. A reverse behavior was observed, wherein the solubilities decreased with increase in temperature in the investigated pressure region. At constant temperature and pressure, the solubilities of the trialkyl phosphates decrease with the alkyl chain length. The solubility data was found to be consistent with the Mendez-Teja model. The solubilities were correlated by the Chrastil model and an association model based on the van Laar activity coefficient model with absolute deviations of less than 10%. A key result is that the model parameters based on the association model varied linearly with the carbon number.
The solubilities of two lipid derivatives, geranyl butyrate and 10-undecen-1-ol, in SCCO2 (supercritical carbon dioxide) were measured at different operating conditions of temperature (308.15 to 333.15 K) and pressure (10 to18 MPa). The solubilities (in mole fraction) ranged from 2.1x10-3 to 23.2x10-3 for geranyl butyrate and 2.2x10-3 to 25.0x10-3 for 10-undecen-1-ol, respectively. The solubility data showed a retrograde behavior in the pressure and temperature range investigated. Various combinations of association and solution theory along with the different activity coefficient models were developed. The experimental data for the solubilities of 21 liquid solutes along with geranyl butyrate and 10-undecen-1-ol were correlated using both the newly derived models and the existing models. The average deviation of the correlation of the new models was below 15%.
The current study aimed to evaluate the effect of long-chain and branch alcohol on lubricity of sebacic acid based ester. Since currently synthesis of a new lubricant to improve the lubricity properties and quality of lubricant is increasing, in this study, sebacic acid esters were synthesized by the conventional esterification method with some modification using sulfuric acid (SA) as catalyst. Twelve samples of sebacic acid esters with different chemical structures were synthesized including di-2-octyl sebacate, didecyl sebacate, di-2 ethylhexanol sebacate, di-2-ethylbutyl sebacate and dioleyl sebacate. These diesters were tested in terms of their suitability as lubricant. The results showed that the pour point, flash point and oxidation stability were affected by liner and branch of the alcohol used. Di-2-ethylbutyl sebacate (D2EBS) and di-2-ethylhexanol sebacate (D2EHS) showed very low pour point at -44°C and -60°C respectively, while the same carbon number of dihexyl sebacate (DHS) and dioctyl sebacate (DOS) recorded high pour point at 8°C and 15 °C respectively. These differences were due to the presence of the branching. DOS recorded the highest oxidative stability at 290°C. However, there was a slight negative effect of the branching on the flash point.
The solubilities of butyl stearate and butyl laurate were determined in the temperature range of 308 K to 323 K and 313 K to 328 K, respectively, at pressures of 10 MPa to 16 MPa. The solubility of butyl laurate was higher than that of butyl stearate by almost an order in magnitude. Retrograde behavior was observed throughout the investigated pressure range. Semiempirical models such as Mendez-Teja, Chrastil, and other density-based models were used to correlate the experimental data of our work as well as several other liquid solutes.
Two Chrastil type expressions have been developed to model the solubility of supercritical fluids/gases in liquids. The three parameter expressions proposed correlates the solubility as a function of temperature, pressure and density. The equation can also be used to check the self-consistency of the experimental data of liquid phase compositions for supercritical fluid-liquid equilibria. Fifty three different binary systems (carbon-dioxide + liquid) with around 2700 data points encompassing a wide range of compounds like esters, alcohols, carboxylic acids and ionic liquids were successfully modeled for a wide range of temperatures and pressures. Besides the test for self-consistency, based on the data at one temperature, the model can be used to predict the solubility of supercritical fluids in liquids at different temperatures.
Five samples of dibasic acid esters with varied chemical structures were synthesized. These included didecyl carbonate, didecyl adipate and didecyl sebacate as well as modern oligomeric esters of adipic acid and sebacic acid. These esters were tested in terms of their suitability as additives of fully synthetic engine oils. It was noted that an addition of 10% of the respective esters to oils based on polyalphaolefins led to an improvement of their properties. The pour point of the oils as well as their low temperature viscosity were reduced. The viscosity index rose and oil lubricity improved. Esters of oligomeric structures synthesized by the transesterification of dimethyl adipate or dimethyl sebacate with a mixture of neopentyl glycol and decanol showed particularly suitable properties. The tested esters were compatible with the other oil components, forming a stable solution in a wide temperature range.
A high pressure, variable-volume visual cell was used to perform static measurements of phase equilibria involving carbon dioxide and two different fatty acid ethyl esters: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) ethyl esters. Six temperatures ranging from 303.15 to 353.15 K were selected. In a second step, our data were compared with predictions obtained by two group contribution based models previously published. Both models are able to predict with quite high accuracy our data whatever the temperature.
The requirement for environmentally adapted lubricants has begun to play an increasingly important role in many industrial applications, particularly in the last two decades. The present-day requirements for biodegrable and eco-friendly lubricants imply that lubricants have properties that can minimise, if not eliminate, negative environmental impact, such as contamination of soil and water, caused by lost lubrication, leakage and accidents. The dominant factors that have a direct impact on the environment and which characterise the lubricant and its chemical composition, are toxicity, bio-accumulation and biodegradability. Biodegradability is perhaps the most important factor which determines the fate of lubricant in the environment. Various commercial, governmental, and regulatory initiatives exist that protect the interests of the consumer. Life cycle analysis can help in assessing the total environmental impact of lubricants. This paper reviews the essential requirements of environmentally adapted lubricants, i.e., chemical composition, eco-toxicity, biodegradability, bio-accumulation, and eco-labelling schemes, and life cycle analysis.
The oxidative degradation test of di-2-ethylhexyl sebacate (DEHS) was carried out by a sealed stainless steel reactor. Fourier transform infrared spectroscopy and gas chromatography–mass spectrometry (GC–MS) were utilised to characterise the chemical composition and molecular structure of the oxidation products. The results revealed that 2-ethyl-1-hexanol and mono(2-ethylhexyl)sebacate were major degradation products in the liquid phase. Tribological behaviour was measured using a four-ball tester. Scanning electron microscopy was employed to investigate the morphologies of the worn surface. Tribological results showed that anti-wear and friction-reducing performances of DEHS were highly dependent on the chemical composition of the oxidation products generated during the test. The hydroperoxides formed during the initial oxidation process could deteriorate lubrication properties of DEHS. However, certain amount of highly polar degradation products (acids and alcohols) generated could significantly improve the friction-reducing performance of DEHS by the formation of boundary adsorption films on the rubbing surfaces. Copyright © 2013 John Wiley & Sons, Ltd.
The high pressure phase equilibria of ethyl esters (ethyl decanoate/caprate, ethyl dodecanoate/laurate, ethyl tetradecanoate/myristate and ethyl hexadecanoate/palmitate) in supercritical ethane and propane have been measured in the temperature ranges 311–358 K (TR = 1.02–1.17) and 376–409 K (TR = 1.02–1.11), respectively. The measurements were conducted in a high pressure view cell for ethyl ester mass fractions between 0.015 and 0.65. The results show a generally linear relationship between the phase transition temperature and pressure. No temperature inversions or three phase regions were observed. An increase in hydrocarbon backbone length leads to an increase in phase transition pressure. For ethane as supercritical solvent, this increase is linear. For propane as supercritical solvent, the nature of the increase was not quantified as the magnitude of the increase would be significantly influenced by the experimental measurement error as the observed increase is not very large. Comparison of the phase behaviour of ethyl esters with methyl esters shows very little difference, yet the phase transition pressure of ethyl esters in supercritical ethane and propane is significantly lower than those of the corresponding acids. The phase transition pressure of ethyl esters in ethane and propane is also lower than those in carbon dioxide.
Data on the phase behaviour of long chain fatty acids (octanoic, decanoic, undecanoic, dodecanoic, tetradecanoic, hexadecanoic and octadecanoic) in supercritical carbon dioxide is presented at temperatures between 308 and 358 K and pressures up to 27 MPa. No three-phase regions were observed and at constant composition, an increase in temperature leads to an increase in phase transition pressure. An increase in hydrocarbon backbone length also leads to an increase in phase transition pressure. Comparison of the measured data with literature data of n-alkanes, 1-alcohols, methyl esters and ethyl esters of the same hydrocarbon backbone length shows that carbon dioxide is able to easily distinguish between acids and n-alkanes, methyl esters or ethyl ester and, with selection of the correct conditions, carbon dioxide is also able to distinguish between acids and 1-alcohols. However, unlike for propane, the phase behaviour of an acid in carbon dioxide does not mimic that of an alkane with double the number of carbon atoms, most probably due to the effect of the quadrupole moment of carbon dioxide.
The experimental solubilities of the mixture of nitrophenol (m- and p-) isomers were determined at 308, 318 and 328 K over a pressure range of 10–17.55 MPa. Compared to the binary solubilities, the ternary solubilities of m-nitrophenol increased at 308, 318 and 328 K. The ternary solubilities of p-nitrophenol increased at 308 K, while the ternary solubilities decreased at lower pressures and increased at higher pressure at 318 and 328 K. The solubilities of the solid mixtures in supercritical carbon dioxide (SCCO2) were correlated with solution models by incorporating the non-idealities using activity coefficient based models. The Wilson and NRTL activity coefficient models were applied to determine the nature of the interactions between the molecules. The equation developed by using the NRTL model has three parameters and correlates mixture solubilities of solid solutes in terms of temperature and cosolute composition. The equation derived from the Wilson model contains five parameters and correlates solubilities in terms of temperature, density and cosolute composition. These two new equations developed in this work were used to correlate the solubilities of 25 binary solid mixtures including the current data. The average AARDs of the model equations derived using the NRTL and Wilson models for the solid mixtures were found to be 7% and 4%, respectively.
The ability to model and predict the behaviour of high-pressure alcohol and carbon dioxide mixtures is important for industrial purposes. The phase equilibria behaviour of four 8-carbon alcohols in supercritical carbon dioxide are measured to determine the effect of the hydroxyl group position on alcohol solubility. Experimental bubble- and dew point data are generated on a high pressure phase equilibrium cell for the systems 1-octanol, 2-octanol, 3-octanol and 4-octanol in supercritical carbon dioxide between 35 °C and 75 °C. 1-Octanol is shown to be the least soluble and, at 35 °C, exhibits a phase transition pressure 85 bar higher than that of 2-octanol. 1-Octanol also exhibits a temperature inversion near the critical temperature of carbon dioxide in the mixture critical region. 2-Octanol possesses marginally higher phase transition pressures than 3-octanol which, in turn, possesses marginally higher phase transition pressures than 4-octanol. This difference in phase equilibria is believed to result from a difference in polarity. Shifting the hydroxyl group from the first to the second carbon atom causes a large decrease in polarity and increase in solubility. Further movements toward the molecule centre result in progressively smaller polarity reductions and solubility increases, producing phase boundaries that coincide or differ minimally.
In order to study the possibility of using supercritical CO2 to concentrate tocopherols from soybean oil de-odorizer distillate (DOD), the binary phase equilibrium data for methyl oleate–CO2 and α-tocopherol–CO2 were measured at 313.15–353.15 K in the pressure ranges of 5–23 MPa for methyl oleate and 5–30 MPa for α-tocopherol, respectively. The measured data were well correlated using the Soave–Redlich–Kwong (SRK) equation of state (EOS) with the Adachi–Sugie (AS) mixing rule. The solubilities and distribution coefficients of methyl oleate and α-tocopherol in CO2 were investigated. Finally, on the basis of these results, a conclusion was preliminarily drawn, supercritical CO2 can be used to concentrate natural tocopherols from the esterified DOD in the experimental range investigated. In addition, the critical points of methyl oleate–CO2 at three temperatures were estimated.
The ability to correlate and predict the solubility of solids in supercritical fluids is important in many applications, including solid deposition in natural gases and the supercritical extraction of natural products. We show below that a simple linear expression, based on the theory of dilute solutions, can be used to correlate solid solubility data. The linear relationship may also be used to check the consistency of experimental data. The proposed equation for solid solubility requires a knowledge of the sublimation pressure of the solid of interest. Since sublimation pressures of `nonvolatile' solids are often not available, we have developed another relationship for the solid solubility that incorporates a Clausius–Clapeyron equation for the sublimation pressure. Although the resulting expression contains three parameters, we have found that these parameters are independent of temperature and pressure. The proposed expression may therefore be used to extrapolate data to temperatures where experimental information may not be available.
The phase equilibria of high molecular mass 1-alcohols in supercritical propane is measured to investigate the relationship between the phase equilibrium pressure and the number of carbon atoms and by comparison with n-alkanes, to show the effect of the hydroxyl group. Binary phase equilibrium measurements of high molecular mass 1-alcohols (with 10, 12, 16, 18 and 22 carbon atoms) in supercritical propane are measured between 378 and 408 K for 1-alcohol mass fractions of 0.0175–0.600. Complete solubility below 100 bar, with no region of liquid–liquid immiscibility, is observed and the phase transition pressure increases with increasing number of carbon atoms. By plotting the number of carbon atoms as a function of the phase transition pressure at constant temperature and mass fraction 1-alcohol, a linear relationship is realized. This linear relationship can be used to estimate the phase equilibrium of 1-alcohols with 10–22 carbon atoms in propane. When the measured 1-alcohol–propane data is compared to published n-alkane–propane data it can be seen that the hydroxyl group has the effect of increasing the phase equilibrium pressure of the 1-alcohol in comparison to the n-alkane.
The oxidative degradation process and oxidation mechanism of di-2-ethylhexyl sebacate (DEHS) were studied in present work. GC–MS results revealed that 2-ethyl-1-hexanol and mono (2-ethylhexyl) sebacate were major degradation products in the liquid phase. Further investigation of degradation mechanism of DEHS showed that oxidation reactions and hydrolysis were main factors degradation of DEHS. The four-ball test results showed that chemical composition changes of DEHS during oxidation could significantly influence its tribological behavior. The formation of hydroperoxides in the initial oxidation period could seriously deteriorate lubrication properties of DEHS. However, as the oxidation proceeded, high polar products (acids, alcohols and monoesters) formed could significantly improve the anti-wear and friction-reducing properties of DEHS.
Vapour—liquid equilibrium data are reported for four binary systems, carbon dioxide—methyl stearate, carbon dioxide-methyl palmitate, carbon dioxide—methyl myristate and carbon dioxide—methyl oleate, at 313.15, 323.15, 333.15 and 343.15 K. A new recirculating static-type apparatus was developed for these measurements. Fairly good correlation of the data could be obtained except in the critical region by using the Peng—Robinson equation of state and the modified van der Waals mixing rules which required two adjustable binary parameters.
Vapor-liquid equilibria were measured and correlated using the Peng-Robinson equation of state for five binary systems of carbon dioxide and fatty acid ethyl esters (ethyl stearate, ethyl oleate, ethyl linoleate, ethyl eicosapentanoate, ethyl docosahexanoate) at 313.15 K, 323.15 K and 333.15 K. Solubility in CO2 of fatty acid ethyl esters of equal chain length but of various degrees of unsaturation was compared. Although there was no distinct difference in solubility at lower pressures, at higher pressures (more than 15 MPa), those with a higher degree of unsaturation showed a slightly higher solubility. When the solubility in CO2 of methyl esters and the corresponding ethyl esters were compared, it was noted that the former showed a slightly higher solubility at all system pressures measured in this work.
More and more enzymes are being explored as alternatives to conventional catalysts in chemical reactions. To utilize these biocatalysts to their fullest, it is incumbent on researchers to gain a complete understanding of the reaction conditions that particular enzymes will tolerate. To this end siloxane-containing polyesters and polyamides have been produced via N435-mediated catalysis at temperatures well above the normal denaturation temperature for free CalB. Low molecular weight disiloxane-based acceptors release the enzyme from its acylated state with equal proficiency while longer chain siloxanes favours polyester synthesis. The thermal tolerance of the enzyme catalyst is increased using longer chain diesters and generally more hydrophobic substrates.
Hyperbranched polymers (HBPs) have attracted more and more attention because of their specially branched architecture and interesting properties. A series of novel poly(amine-ester)-type HBPs were synthesized through CALB-catalyzed polycondensation between triethanolamine (TEOA) and diesters after the optimization of reaction conditions. The precise structure including degree of branching, components percentage, and the controllable terminal structures at the outer surface were determined by FTIR, 1H NMR, 13C NMR, 2D NMR and GPC. The interesting multifunctionality displayed by the poly(amine-ester)-type HBPs was investigated. These HBPs could be degraded efficiently under the catalysis of lipase in weak acid buffer. The amphiphilic HBPs with hydroxyl terminals were able to form multimolecular micelles with 250–400 nm diameter, and 0.042 g L−1 CMC. They were nontoxic to COS-7 cells, while they could effectively inhibit the growth of cancer cells HepG2 with IC50 of 130 μg mL−1 after an anticancer drug was encapsulated within the micelles. All these results indicated the prepared poly(amine-ester)-type HBPs can serve as multifunctional biomaterials for biomedical applications.
This work reviews the available data on thermodynamic properties of carbon dioxide and presents a new equation of state in the form of a fundamental equation explicit in the Helmholtz free energy. The function for the residual part of the Helmholtz free energy was fitted to selected data of the following properties: (a) thermal properties of the single-phase region (p&rgr;T) and (b) of the liquid-vapor saturation curve (ps, &rgr;′, &rgr;″) including the Maxwell criterion, (c) speed of sound w and (d) specific isobaric heat capacity cp of the single phase region and of the saturation curve, (e) specific isochoric heat capacity cv, (f) specific enthalpy h, (g) specific internal energy u, and (h) Joule–Thomson coefficient μ. By applying modern strategies for the optimization of the mathematical form of the equation of state and for the simultaneous nonlinear fit to the data of all these properties, the resulting formulation is able to represent even the most accurate data to within their experimental uncertainty. In the technically most important region up to pressures of 30 MPa and up to temperatures of 523 K, the estimated uncertainty of the equation ranges from ±0.03% to ±0.05% in the density, ±0.03% to ±1% in the speed of sound, and ±0.15% to ±1.5% in the isobaric heat capacity. Special interest has been focused on the description of the critical region and the extrapolation behavior of the formulation. Without a complex coupling to a scaled equation of state, the new formulation yields a reasonable description even of the caloric properties in the immediate vicinity of the critical point. At least for the basic properties such as pressure, fugacity, and enthalpy, the equation can be extrapolated up to the limits of the chemical stability of carbon dioxide. Independent equations for the vapor pressure and for the pressure on the sublimation and melting curve, for the saturated liquid and vapor densities, and for the isobaric ideal gas heat capacity are also included. Property tables calculated from the equation of state are given in the appendix.
Synthetic and vegetable oil based esters offer the best choice in formulating environment friendly lubricants. In the present review an attempt has been made to highlight some recent developments in the area of biodegradable synthetic ester base stocks for formulation of new generation lubricants including the efforts made so far at the author's laboratory in this direction. The developed products find applications in automotive transmission fluids, metal working fluids, cold rolling oils, fire resistant hydraulic fluids, industrial gear oils, neat cutting oils and automotive gear lubricants either alone or in formulations.
High pressure phase equilibria measurements of long chain saturated methyl esters (methyl decanoate, methyl dodecanoate, methyl tetradecanoate, methyl hexadecanoate, methyl octadecanoate and methyl docosanoate) in supercritical ethane have been measured for temperatures between 312K and 355K and for methyl ester mass fractions from 0.65 to 0.018. The results show a generally linear relationship between the phase equilibria pressure and the temperature with complete mutual solubility above 17MPa. No three-phase regions or temperature inversions (change in sign of gradient of temperature–pressure relationship at constant composition) were observed while maxima in the phase transition pressures were found for methyl ester mass fractions usually between 0.2 and 0.3. When the phase transition pressure is plotted as a function of carbon number at constant temperature and mass fraction methyl ester, a linear relationship is realised. This linear relationship can be used to determine the solubility of any saturated methyl ester with between 10 and 22 carbon atoms, with limited extrapolation being possible. Thermodynamic modelling of the measured phase equilibria with the sPC-SAFT and Peng Robinson equations of state showed that, even with the use of an interaction parameter, these equations of state are not able to model the phase behaviour and the linear pressure–carbon numbers provide more accurate predictions.
Although it has been known that many of the enzymes may be instable in harsh conditions of supercritical CO2, recent experimental studies argued that the enzymes are active and stable in near-critical propane with same pressure and temperature condition. But there are no clear reasons at the molecular level for the activity and stability of the enzymes in such condition. Moreover, it is difficult to experimentally monitor the microstructure and dynamics of the enzyme in a supercritical fluid in situ. In this study the enzyme microenvironment in near-critical propane is investigated using molecular dynamic simulation. For comparison with other solvent models the enzyme was also simulated in water, hexane and supercritical CO2. We examined the overall structural properties of Candida antarctica lipase B in these four solvents and found that in supercritical CO2 there are high structural deviations from native form while in near-critical propane deviations are low and very close to those of in the mild aqueous solution and even are lower than those of in hexane. α-Helix and β-sheet contents of the enzyme remain intact in near-critical propane. These theoretical results are in agreement with experimental evidences of the stability and activity of the enzyme in near-critical propane. Moreover, it was found that the activity of the enzyme in near-critical propane can be related to the water partitioning on the surface of the enzyme. The results of this study not only confirm the reported experimental findings about enzyme stability and activity in near-critical propane, but also shed light on the structural situation of the enzyme in this condition. To the best of our knowledge, this is the first molecular dynamic simulation of a protein in a non-CO2-based compressed gas.
Essential oil of Zataria multiflora Boiss, cultivated in Iran, was isolated by steam distillation and compared with supercritical fluid CO2 extracts. The oils and extracts were analyzed by capillary gas chromatography, using flame ionization and mass spectrometric detection. Different parameters, such as temperature, pressure, extraction period (dynamic) and modifier (methanol) concentration were employed to maximize the SFE efficiency. The results showed that, under optimum conditions (P=30.4 MPa, T=55 °C, tdynamic=20 min and Vmodifier=0 μl) extraction of Z. multiflora Boiss was more efficient. Chemical analysis revealed that components extracted under different SFE conditions possessed widely different percentages of constituents [thymol (14.2–67.6%), λ-terpinene (0.1–19.5%) and ρ-cymene (3.6–12.0%)]. The amounts, of co-extracted cuticular waxes varied too. Oil obtained by steam distillation was also compared to the SFE extracts. The results showed that the major components of Z. multiflora Boiss were thymol (44.6%), λ-terpinene (21.5%) and ρ-cymene (13.7%), based on steam distillation.
Solubilities of 2-ethyl-1-hexanol (1), 2-ethyl hexanoic acid (2), and their mixtures in supercritical carbon dioxide (SC-CO2) (3) were reported. Solubilities were measured at a constant temperature of 313 K and 323 K, at pressures varying from (68 to 180) bar for the binary systems and at a constant pressure of 138 bar at temperatures varying from (313 to 373) K for the ternary system. Temperature dependences of the solubilities for a x1 = 0.5 mixture were determined. The effect of the mixture composition of the acid + alcohol mixture in SC-CO2 was studied. The total solubility of the mixtures in SC-CO2 is independent of the x1 of the liquid mixture in the equilibrium cell. The Chrastil model for solubilities at 313 K and 323 K was evaluated.
Vapour and liquid equilibrium phase compositions were determined at the temperatures (323.2, 352.6, 394.2, and 477.6) K for (carbon dioxide + methanol). Measurements were made at pressures from the vapor pressure of the methanol to the critical region. Equilibrium ratios for each component were calculated at each temperature from the phase compositions. The critical temperatures and corresponding critical pressures were determined graphically and the critical locus was constructed for the binary mixture.
The density of marine lipids in equilibrium with carbon dioxide (CO2) was determined using a view cell equipped with a novel spring balance based on Archimedes’ principle. The densities of fish oil triglycerides (TG) and fish oil fatty acid ethyl esters (FAEE) were measured at pressures ranging from 0.1 to about 25MPa and temperatures of 40, 55 and 70°C. In the pressure and temperature ranges investigated, the density increased with pressure and decreased with temperature. The density increase from atmospheric pressure to about 25MPa at temperatures of 40, 55 and 70°C was 4.1, 3.2, 2.7% and 5.3, 4.0, 3.6% for TG and FAEE, respectively. Volumetric expansion of fish oil TG and FAEE saturated with CO2 was determined at 40°C and pressures ranging from 0.1 to 22MPa. With increasing pressure a relative volume change of up to 38 and 67% was observed for TG and FAEE, respectively. The density and volumetric expansion of lipids in equilibrium with CO2 are important for optimal design of high pressure processes involving mass and momentum transfer.
Over the past two decades, fats and oils processing using supercritical carbon dioxide (SC-CO2) has developed from focusing only on extraction to fractionation of complex lipid mixtures, conducting reactions in supercritical fluid media and particle formation techniques for the delivery of bioactive lipid components. Extraction of specialty oils and column fractionation of deodorizer distillates to concentrate tocopherols have reached commercial scale. Even though significant progress has been made in fundamental aspects, many challenges lie ahead to better understand the phase behavior and solubility of multicomponent lipid mixtures in SC-CO2 and to generate the much needed fundamental data, including transport properties, density and interfacial tension. Considering the increasing consumer demand for “natural” products and stricter government regulations on the use of organic solvents like hexane, the future of SC-CO2 processing of lipids is bright. Based on the know-how accumulated, integrated processes can be developed, targeting ingredients for both food and non-food industrial applications, which would fit well into a larger biorefinery approach.
Solubility data of drugs in supercritical fluids (SCF) are crucial for designing pharmaceutical processes, such as micronization of drug powders or extraction using SCF. A new empirical equation is proposed to correlate solute solubility in supercritical carbon dioxide (SC CO2) with temperature, pressure and density of pure SC CO2. The proposed equation is lny2=M0+M1P+M2P2+M3PT+(M4T)/P+M5lnρ, where y2 is the mole fraction solubility of the solute in the supercritical phase, M0–M5 are the model constants calculated by least squares method, P (bar) is the applied pressure, T is temperature (K) and ρ is the density of pure SC CO2. The accuracy of the proposed model and four other empirical equations employing P, T and ρ variables, was evaluated using 106 published solubility data sets by calculating the average of absolute relative deviation (AARD). The mean AARD for the proposed model is 21.4 (±15.9)%, which is an acceptable error when compared with the experimental uncertainty. The AARD values for other equations were 33.7 (±24.5), 36.2 (±27.2), 48.3 (±77.2) and 27.1 (±21.2). The mean AARD of the new equation is significantly lower than those obtained from previous empirical models (paired t-test, P
The equilibrium compositions and densities in the gaseous and liquid phases of the binary system carbon dioxide/methyl laurate (dodecanoic acid methyl ester) have been measured at 40 °C, 50 °C and 60 °C, and at pressures up to 120 bar. Equilibrium was attained by recirculating both phases through a high-pressure view cell. A vibrating sensor tube was used to determine densities. Compositions were measured by taking samples from both phases by means of six-way valves.
Lubricants based on renewable raw materials and their derivatives are drawing increased attraction in various applications. Here, the environmental awareness is the key factor of success. The use of such rapidly biodegradable materials is especially favourable in loss-lubrication and hydraulic systems with increased risk of damage. Environmentally friendly, biodegradable alternatives are available for a large variety of mineral oil based lubricants. The substitution of mineral oil with biodegradable base oils is a primary objective. Vegetable oils are the major source of these base fluids. Compared to conventional mineral oil based fluids most of such substances exhibit lower thermal and oxidation stability and even worse low-temperature behaviour. These physical and chemical properties can be improved by chemical modification. This review covers chemical reactions performed on fatty compounds on both laboratory and industrial scale. Economic processes are presented as well as new reactions with potential market value. Alternative routes to improved rapidly biodegradable base fluids are mentioned too, e.g. breeding successes with high oleic sunflower oil.
Sebacic acid esters are a promising class of low toxicity plasticizers for PVC. They are lipophylic substances and thus, their interaction with biomembranes must be considered.DPPC liposomes in the presence of increasing amounts of dimethylsebacate (DMS), diethylsebacate (DES), dibutylsebacate (DBS) and di-(2-ethylhexyl)sebacate (DEHS) have been studied by DSC, both on heating and cooling.As a general feature, the melting point decreases and the enthalpy ΔH increases along with the half-width and asymmetry of the transition in most of the systems. The observed effects are strongly dependent on the length and the shape of the ester-chains suggesting that both polar interactions between carboxylic groups of sebacates and the polar heads of the lipids as well the hydrophobic interactions involving penetration into the bilayer are important. The effects are noticeable also in the presence of small amounts of plasticizers.In the presence of large amounts of DES and DBS, a complex structure of the transition arising from the coexistence of aggregates of different types and also the appearance of new phases were observed.The behaviour of sebacates to model biomembranes is quite different for other classes of lipophylic PVC plasticizers, such as phthalates and we explain the differences on the basis of the greater flexibility of the sebacic acid chain.
A semi-flow type apparatus was used to measure the vapor–liquid equilibria (VLE) of CO2 with diethyl oxalate, ethyl laurate, and dibutyl phthalate binary mixtures at 308.15, 318.15, and 328.15K over the pressure range from 1.4 to 13MPa. New VLE data for CO2 with esters are presented and the Henry’s constants were determined from these results. These VLE data were also correlated using the Soave–Redlich–Kwong and the Peng–Robinson equations of state with various types of the van der Waals, composition-dependent and Huron–Vidal mixing rules. It is shown that both equations of state with the van der Waals mixing rules and two adjustable parameters gave satisfactory correlation results.
Lipases from Candida antarctica (Novozym 435) and Rhizomucor miehei (Lipozyme IM) showed good reactivity in the alcoholysis of dimethyl adipate by racemic 2-ethylhexanol as well as neopentyl glycol. Novozym 435 was found to be the more reactive biocatalyst but less enantioselective compared with Lipozyme IM in the synthesis of methyl-2-ethylhexyl adipate. Di-2-ethylhexyl adipate obtained was optically inactive. Using dimethyl adipate and neopentyl glycol as starting material, oligomer esters with different range of molecular mass were synthesised (Novozym 435). An attempted of alcoholysis of dimethyl adipate by non-linear trihydric trimethylolpropane was unsuccessful.
The Journal of Supercritical Fluids j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s u p f l u a b s t r a c t The equilibrium quaternary solubilities of dihydroxybenzene (resorcinol + pyrocatechol + hydroquinone + SCCO 2) isomers were experimentally determined at 308, 318 and 328 K over a pressure range of 9.8–15.7 MPa by using a saturation method. The effects of temperature, pressure and the components on each other have been thoroughly investigated. The selectivity of SCCO 2 for ternary (resorcinol + pyrocatechol + SCCO 2) and quaternary systems was discussed. A new model equation for quaternary solubilities of solids has been developed by accounting for non-idealities by combining the solution model with Wilson activity coefficient model. The model equation has five adjustable parameters and correlates the quaternary solubilities of current data along with two other quaternary data reported in the literature.
The Journal of Supercritical Fluids j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s u p f l u a b s t r a c t The ternary solubilities of solid isomers of nitrobenzoic acid (NBA) were experimentally determined at 308, 318 and 328 K over a pressure range of 12–18 MPa in supercritical carbon dioxide (SCCO 2). Com-pared to its binary solubility, the ternary solubilities of m-NBA increased at 308 K while it decreased at 328 K. However, the ternary solubilities of p-NBA increased at all temperatures and pressures except at 13 MPa and 328 K. A new model was developed by applying solution model and activity coefficient model for the ternary solubilities of pharmaceutical and non-pharmaceutical solid mixtures in terms of temperature, density and cosolute composition. The model equation involves four temperature inde-pendent constraint-free parameters. The model equation correlates the ternary solubilities of seven pharmaceutical solid mixtures along with current data with an average AARD around 9.5% and sixteen non-pharmaceutical solid mixtures with 9% AARD.
a b s t r a c t The solubilities of various solid pollutants in supercritical carbon dioxide were investigated. The inter-molecular interactions play a significant role in determining the solubilities of solids in supercritical carbon dioxide. A new model equation was derived by using the concepts of association and activity coefficient model to correlate the solubilities of solids. The model equation combines the association and Wilson activity coefficient models and includes the interaction potentials between the molecules, which are useful in understanding the behavior of the solid solutes in SCCO 2 . The new model equation involves five adjustable parameters to correlate the solubilities of solids by incorporating the interactions between the molecules. The equation correlated 75 solid systems with an average AARD of around 9%, which was better than the correlations obtained from standard models such as Méndez Santiago–Teja (MT) model and association model.
An apparatus for the determination of the solubilities of solids and liquids in dense gases is described. The solubilities of stearic acid, oleic acid, behenic acid, tributyrin, tripalmitin, triolein, trilinolein, palmityl behenate, behenyl behenate, α-tocopherol, cholesterol, water, and cafestol in supercritical carbon dioxide at different temperatures and pressures were determined. An equation was derived from the association laws and/or from the entropies of the components and was compared with these experimental results. The equation agreed with experimental results over a wide range of pressures and temperatures. Some experimental results from the literature (naphthalene, anthraquinone, p-chloroiodobenzene) were also reproduced by means of this equation. Very good agreement with these experimental results was found, as in previous examples. The association number, heats of solution, and other thermodynamical characteristics of compounds dissolved in dense gases are discussed. The separation of α-tocopherol and tripalmitin by the supercritical carbon dioxide extraction was measured experimentally at different pressures and temperatures. The equation describing the ideal separation of two independent components by means of a dense gas extraction is described.
Lubricants based on vegetable oils are growing in popularity in various applications. Environmentally friendly, vegetable oils and their derivatives constitute alternatives to mineral-based lubricants. Soybean oil, sunflower oil and rapeseed oil have better viscosity indices than mineral oils and even some synthetic oils, are biodegradable and have low production costs. However, vegetable oils have disadvantages, such as poor thermo-oxidative stability due to the carbon–carbon double bonds and poor low-temperature properties, which limit their use as lubricant base stocks. This study describes new base-stock oils obtained from mixture of vegetable oils and di-2-ethylhexyl-sebacate synthetic oil, which become lubricants when additives are introduced. These mixtures offer a large range of kinematic viscosities, while their pour points are under −33°C and their flash points over 240°C. The copper strip corrosion test result is 1a. The diameters of wear scars measured under four-ball testing (40dyn) are less than 1mm. A differential scanning calorimetry study and a thermo-gravimetric study under a nitrogen atmosphere for the mixed oils are reported. In the former study two-endothermic processes were observed between −15°C and −50°C. In the thermo-gravimetric analysis curve the weight loss is specific for each vegetable and synthetic oil component. From these studies a higher thermal stability was observed for vegetable oils than for ester oils, and it was concluded that the mixtures of vegetable and synthetic oils of diester type are physically homogeneous mixtures. The low production cost of lubricants based on vegetable oils makes them attractive alternatives for mineral oil based lubricants. Overall the mixtures of vegetable and ester oils can be competitive base oils for environmentally friendly lubricants. Copyright © 2006 John Wiley & Sons, Ltd.
The requirement for environmentally adapted lubricants has begun to play an increasingly important role in many industrial applications, particularly in the last two decades. The present-day requirements for biodegradable and eco-friendly lubricants imply that lubricants have properties that can minimise, if not eliminate, negative environmental impact, such as contamination of soil and water, caused by lost lubrication, leakage and accidents. The dominant factors that have a direct impact on the environment and which characterise the lubricant and its chemical composition, are toxicity, bio-accumulation and biodegradability. Biodegradability is perhaps the most important factor which determines the fate of lubricant in the environment.
Various commercial, governmental, and regulatory initiatives exist that protect the interests of the consumer. Life cycle analysis can help in assessing the total environmental impact of lubricants. This paper reviews the essential requirements of environmentally adapted lubricants, i.e., chemical composition, eco-toxicity, biodegradability, bio-accumulation, and eco-labelling schemes, and life cycle analysis.
Environmentally friendly vegetable oils and their derivatives represent alternatives to mineral-based lubricants. Vegetable
oils have high biodegradability and low production costs. Their poor thermo-oxidative stability and poor low temperature properties
are disadvantages in their use as lubricant basestocks. In our study we used corn oil and diester mixtures, which become lubricants
when additives are introduced. These mixtures of corn oil and di-2-ethylhexyl-adipate (DOA) and di-2-ethylhexyl-sebacate (DOS)
offer a wide range of kinematic viscosities, pour points lower than −39°C and flash points over 218°C. The diameters of
wear scars measured under four-ball testing (40daN) are less than 0.90mm and the copper strip corrosion test result is 1a.
The differential scanning calorimetry study and thermogravimetric study under nitrogen atmosphere and in synthetic air are
reported. From these studies a higher thermal stability was observed for corn oil than for diester oils. The thermo-oxidative
instability occurred at temperatures higher than 350°C. The low production cost of corn oil and its mixtures with diesters
makes them an attractive alternative to mineral oil lubricants.
Alkali pyrolysis of castor oil was carried out in the presence of white mineral oil. The operating parameters were optimized
to obtain high yields of 2-octanol and sebacic acid. Alkali pyrolysis at 280±2°C in the presence of 1% red lead catalyst yielded
70.1% 2-octanol and 72.5% sebacic acid on the basis of their respective theoretical yields.
Off-flavors and unfavorable odors in tuna fish oil were successfully removed and identified using supercritical carbon dioxide
extraction, while retaining variable compounds, polyunsaturated fatty acids such as EPA (eicosapentaenoic acid) and DHA (docosahexaenoic
acid). Samples of oil were extracted in a 100 mL semi-batch stainless steel vessel under conditions which ranged from 8 to
20 MPa and 20 to 60°C with solvent (CO2) flows from 10 g/min. GC-MS was used to identify the main volatile components contributing to the off-flavors and odors which
included 2-methyl-1-propanol, 2,4-hexadienal, cyclopropane, and octadiene. Analyses of oil extracted at 40°C, 20 MPa showed
a 99.8% reduction in dimethyl disulfide. Other significant off-flavors identified were 2-methyl-butene, 3-hydroxy butanal
and ethylbenzene.
High pressure phase equilibria of supercritical carbon dioxide with n-alkanes, n-C12, n-C16, n-C20, n-C24, n-C28 and n-C36, have been measured over the temperature range of 313–367 K, and are reported in this work. Of the various equations of state investigated, it was found that the Patel Teja equation of state provided the best fit of the CO2–n-alkane systems.
Using supercritical carbon dioxide (SC-CO2) as the solvent, the solubility of methyl esters, ethyl esters, fatty acids, triglycerides, and fats and oils were studied over a range of temperature and pressures. Equilibrium data from the literature were correlated using the Peng-Robinson equation of state. With the van der Waals (VDW) and Panagiotopoulos and Reid (PR) mixing rules. The data were also correlated using statistical methods and the solubilities predicted by various models were compared with experimental solubilities at the temperature and pressure conditions studied. The equation of state method provided good agreement of theory with experiment for the solubilities of fatty acids and their esters, but less so for the triglycerides, fats and oils. The statistical methods on the other hand, not only predicted the solubilities of fatty acids and fatty acid esters well, but also gave good agreement with the solubilities of triglycerides, fats and oils. Chain length, degree of unsaturation, and functional groups in compounds are known to affect the vapor pressures of these compounds which in turn influence their solubilities in SCCO2. As expected solubilities decreased in going from fatty acid esters, to fatty acids, to triglycerides.
High-pressure vapor–liquid equilibrium (VLE) data were measured for binary CO2–alcohol systems (e.g. methanol, ethanol, 2-methoxyethanol, and 2-ethoxyethanol) at various isotherms (313.15–345.15 K). The quantitative VLE data and mixture critical conditions were measured using a new design for a circulation VLE system. The measure data were correlated by the classical Peng–Robinson and the multi-fluid nonrandom lattice fluid hydrogen-bonding (MF-NLF-HB) equation of state. The MF-NLF-HB model was formulated previously by the present authors based on the proton donor–acceptor principle to the hydrogen-bonding interaction in CO2–alcohol systems. For the measured and calculated data of CO2–alcohol systems, the relative accuracy of the data was discussed.
Starting from a screw-type manual pump, a high-pressure variable-volume view cell was designed to perform static measurements of equilibria involving CO2 and fatty acid esters. Though the design of the cell allows both the upper and the lower phases to be sampled, the synthetic method was chosen for this study. The efficiencies of both the apparatus and the method were first checked through preliminary experiments related to a compound already studied, namely methyl oleate. The good agreement between our measurements and those published in the literature allowed us to study other compounds, more precisely the ethyl esters of myristic, palmitic and stearic acids. These measurements were obtained at three different temperatures, 313.15, 323.15 and 333.15 K, and at pressures ranging from 1 to 18 MPa. The data were correlated using the modified Peng–Robinson equation of state with the classical quadratic mixing rules. An interesting feature of the apparatus is its low consumption of substance for a rather large amount of acquired data.
Carbon dioxide is often promoted as a sustainable solvent, as CO2 is non-flammable, exhibits a relatively low toxicity and is naturally abundant. However, injudicious use of carbon dioxide in a process or product can reduce rather than enhance overall sustainability. This review specifically examines the use of CO2 to create greener processes and products, with a focus on research and commercialization efforts performed since 1995. The literature reveals that use of CO2 has permeated almost all facets of the chemical industry and that careful application of CO2 technology can result in products (and processes) that are cleaner, less expensive and of higher quality.
The solubility of the antibiotic Penicillin G in supercritical carbon dioxide was measured at pressures from 100 to 350 bar and temperatures from 313.15 to 333.15 K using a dynamic flow apparatus. Physical properties and critical parameters of Penicillin G were estimated using Fedor's and Ambrose's group contribution methods. The experimental data were correlated using the Redlich–Kwong and Soave–Redlich–Kwong equations of state, with Lorent–Berthelot mixing rules. A second order empirical model to correlate solubility directly with temperature and pressure was used.
In this study experimental P–T–x–y equilibrium data for four binary mixtures over a wide range of pressure (10.44–23.54 MPa) were determined at 313 K and 333 K. Liquid and vapor densities of carbon dioxide + four fatty acid ester systems, including oleic acid methyl ester, linoleic acid methyl ester, eicosapentaenoic acid ethyl ester, and docosahexaenoic acid ethyl ester were measured by using two circulating systems consisting of two vibrating tube densitometers. The vapor-phase density was observed to increase more significantly with pressure than the liquid-phase density at constant temperature. Experimental equilibrium constants of oleic acid methyl ester and linoleic acid methyl ester were found to be larger than those of eicosapentaenoic acid ethyl ester, docosahaxaenoic acid ethyl ester, linoleic acid, triolein, and tocopherol. This indicates that the two methylated fatty acids would be extracted easier than the other compounds in a separation process using supercritical CO2 extraction. The equilibrium data were successfully correlated using the Peng–Robinson and modified Soave–Redlich–Kwong equations of state with quadratic (two parameters), Panagiotopoulos–Reid (three parameters), and Adachi–Sugie (three parameters) mixing rules. In general, the Soave–Redlich–Kwong equation of state with the Panagiotopoulos–Reid mixing rules and the quadratic mixing rules give the best correlation for methylated fatty acids and ethylated fatty acids, respectively.