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Energy recovery from sewage sludge waste blends: Detailed characteristics of pyrolytic oil and gas
Abstract
Using waste as an alternative energy source may partially replace fossil fuels. In this paper, energy recovery from waste blends (sewage sludge (SS), polyethylene (LDPE) and polypropylene (PP), paper rejects (PR), and waste tyres) was tested through laboratory-scale co-pyrolysis. For each copyrolysis test, 7 l of waste blend in different ratios were used. The results of pyrolytic oil and gas analyses show valuable compounds and chemical materials recovered. The detailed analyses show the effects of co-pyrolysis parameters, especially the ratios of waste blends with respect to the process temperature of 600◦C, on the pyrolytic gas and oil. The highest volumes of gas (0.66 m3) and oil (699 ml) were obtained from sample 5_8 (PES:SS:PR). Waste blend 15_1 (LDPE:SS) had the highest gross calorific value (GCV) of 43.82 MJ/m3 in gas, and had the highest proportion of flammable components (46.31% of methane). Sample 5_8 had the highest calorific value in pyrolytic oil (45 MJ/kg) and sample 5_3 had the lowest (28.113 MJ/kg), which is comparable to coal. High-quality pyrolytic gas and oil were obtained with average GCV of 44 MJ/m3 and 40 MJ/kg respectively, where the average GCV of the most calorific fossil fuels is 43.6 MJ/kg in crude oil and 34 MJ/m3 in natural gas. We conclude that co-pyrolysis of sewage sludge and waste is a convenient and simple method of waste disposal under a synergetic effect of efficient waste management, energy production, and reduction of dependence on fossil fuels,
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Sewage sludge (biosolids) management represents a worldwide issue. Due to its valuable properties, approximately one half of the EU production is recovered in agriculture. Nevertheless, growing attention is given to potential negative effects deriving from the presence of harmful pollutants. It is recognized that a (even very detailed) chemical characterization is not able to predict ecotoxicity of a mixture. However, this can be directly measured by bioassays. Actually, the choice of the most suitable tests is still under debate. This paper presents a multilevel characterization protocol of sewage sludge and other organic residues, based on bioassays and chemical-physical-microbiological analyses. The detailed description of the experimental procedure includes all the involved steps: the criteria for selecting the organic matrices to be tested and compared; the sample pre-treatment required before the analyses execution; the chemical, physical and microbiological characterisation; the bioassays, grouped in three classes (baseline toxicity; specific mode of action; reactive mode of action); data processing. The novelty of this paper lies in the integrated use of advanced tools, and is based on three pillars:
•the direct ecosafety assessment of the matrices to be reused
•the adoption of innovative bioassays and analytical procedures
•the original criteria for data normalization and processing.
The worldwide enhancement in the accumulation of waste tires and associated upcoming environmental and social concerns are becoming the primary intimidations. Waste tires are considered an undervalued resource globally, and their sheer volume is used to be disposed of in landfills, a primary concern. Instead of disposing of waste materials after recycling, the utilization can have a considerable impact. The trend of extracting steel fibers from waste tires is emerging nowadays. Incorporating waste recycled tire steel (WRTS) fibers, obtained from waste tires in concrete is a potential profit-gaining engineering application. But there are still some challenges, like WRTS fibers' suitable volumetric content and length selection, which need to be addressed by having in-depth exploration. Research has been conducted on incorporating reused waste materials in cementitious composites. Concrete ingredients are meant to provide strength, but adding reused waste materials to concrete helps reduce environmental pollution and make it sustainable and economical. In previous literature, the impact of such waste fibers on the key properties of concrete, such as ultrasonic pulse velocity, compressive, splitting-tensile and flexural strengths, energy absorption, modulus of elasticity, toughness, and ductility, were investigated. Adding WRTS fibers to concrete can enhance its compressive strength by more than 10% and flexural strength by more than 50%. This paper aims to review the application of WRTS fiber-reinforced concrete to identify the research gap for researchers in this direction. The available research outcomes and the recycling process of WRTS fibers are summarized and discussed. It is concluded that incorporating WRTS fibers in concrete would result in sustainable development by providing economical and environment-friendly construction materials with improved mechanical properties.
Waste from the Miscanthus production cycle may be a promising source of material for the pyrolysis and biochar production. The biochar can be used to enrich the soil on which the crop grows, thus increasing productivity. A sample of Miscanthus rhizomes was used as a raw material in a series of experiments in order to find the most suitable conditions for the preparation of biochar. Miscanthus biochar was prepared in a laboratory unit using four different temperatures (i.e., 400, 500, 600 and 700 °C). All pyrolysis products were subsequently evaluated in terms of their quality and product yields were determined. For a temperature of 600 °C and a residence time of 2 h, the appropriate properties of biochar were achieved and the process was still economical. The biochar contained a minimal number of polycyclic aromatic hydrocarbons and a high percentage of carbon. Surface area was measured to be 217 m2/g. The aqueous extract of biochar was alkaline.
Plastic particles smaller than 5 mm, i.e., microplastics, have been detected in a number of environments. The number of studies on microplastics in marine environments, fresh water, wastewater, the atmosphere, and the human body are increasing along with a rise in the amounts of plastic materials introduced into the environment every year, all contributing to a range of health and environmental issues. Although the use of primary microplastics has been gradually reduced by recent legislation in many countries, new knowledge and data on these problems are needed to understand the overall lifecycle of secondary microplastics in particular. The aim of this review is to provide unified information on the pathways of microplastics into the environment, their degradation, and related legislation, with a special focus on the methods of their sampling, determination, and instrumental analysis. To deal with the health and environmental issues associated with the abundance of microplastics in the environment, researchers should focus on agreeing on a uniform methodology to determine the gravity of the problem through obtaining comparable data, thus leading to new and stricter legislation enforcing more sustainable plastic production and recycling, and hopefully contributing to reversing the trend of high amounts of microplastics worldwide.
Waste paper, an essential substitute for wood and other plant-based fibers in paper making, is an indispensable part of the circular economy; yet, the impacts of China’s ban on global waste paper cycles have not been well understood. We modeled the evolution of the global waste paper trade network during 1995–2019. We found that the cumulative trade volume of global waste paper reached 1010 million tons in the last 25 years and showed a downward trend since 2015. The global import center of waste paper experienced a transfer from Europe to East Asia and then to Southeast Asia. The ban has stimulated some developed countries to reduce the exports of unsorted waste paper since 2017, but for many major importers their changes in waste paper trade patterns were related to waste paperboard, which was not banned by China, suggesting that this import change trend may be inevitable and irrespective of China’s ban. Besides, India has replaced China to become a new import hub of unsorted waste paper. Our results lay a foundation for exploring the evolution of the future global solid waste cycle under the background of zero import of solid waste increasingly implemented by China and many other developing countries.
Natural asphalt cannot be used directly because of hardness and low penetration, so it needs to be softened with a solvent. A solvent that can be used is from oil plastic pyrolysis as an alternative additive. Plastics are now an inseparable item from daily necessities and are the largest pollutant on the environment. Plastic is a polymer that is difficult to be decomposed, and one way to decompose it is through pyrolysis or thermal cracking. This research studies the quality effect of low-density polyethylene (LDPE) plastics waste on the quantity and quality of oil yield produced through the pyrolysis process in the three reactor outlets. LDPE plastics waste used was distinguished: LDPE-White, LDPE Mixed-plastic, and LDPE Blend-plastic. The results showed that, in the process of plastic pyrolysis LDPE, in addition to affecting the yield of produced oil, the quality of plastic is also influenced by the length of time of pyrolysis. The better the quality of the plastic is, the higher the oil yield and the shorter the pyrolysis times are. LDPE plastic pyrolysis at 250 °C produces the maximum yield. Most oil yields, namely 99.78%, 75.60%, and 50.29% were produced by LDPE white plastics, mixed plastics, and blend plastics, respectively, when pyrolyzed for 110, 180, and 270 minutes. The economic yields of each plastic of 88.78%, 60.68%, and 40.35% were generated if each was hydrolyzed for 60, and 80 minutes.
In line with the requirements of the circular economy, the European Union’s waste management legislative changes also concern the treatment of sewage sludge. Although sewage sludge production cannot be prevented, its quantities may be reduced by the synergetic effect of energy recovery via choosing a proper technology. Sewage sludge is difficult to apply as fuel alone, because of its high moisture and ash content. However, its energy use will be increased by adding suitable waste materials (different types of plastics, waste tires and paper rejects). Most recently, the thermal utilization of sewage sludge via incineration or pyrolysis has grown in importance. This article describes the fuel parameters of particular waste materials and of their blends with sewage sludge in connection with laboratory-scale thermal decomposition in an inert atmosphere, for their potential use in a semi-pilot plant pyrolysis unit. For pyrolytic application, the results of thermogravimetric analysis are needed in order to know the maximal temperature of thermal decomposition in an inert atmosphere, maximal mass losses, and weight loss rates. The samples of different thermoplastics mixed with sewage sludge, and low-density polyethylene blends with sewage sludge, had the lowest residual masses (70–74%) and the highest weight loss rates (11–19%/min). On the other hand, the blend of polyester rejects from tire processing, paper rejects and sewage sludge had the second highest residual mass (60%) and the lowest weight loss rate (3%/min).
Fast pyrolysis of sawdust (SD) and upgrading of the derived bio-oil* (water-free basis) over Shenmu bituminous coal char (SMC) were conducted in an integrated free fall pyrolyzer and moving bed upgrading reactor. The water soluble and heavy bio-oil* (THF soluble) yields decrease and the content of light bio-oil* (CH2Cl2 soluble) increases significantly compared that without SMC despite the decrease of light bio-oil* yield. Chemical analyses of the light bio-oil* were performed using GC–MS and ¹H NMR techniques. The results show that during volatiles-char interaction, the SMC plays important roles in deoxygenation and denitrogenation. The role of SMC in the upgrading process was explored by BET, FT-IR and XRD characterization. The porous structure provides reaction active sites for the bio-oil upgrading. After volatiles-char interaction, the specific surface area of SMC decreases significantly and the carbon crystallite size increases. With increasing the char updating rate from 1 g/min to 4 g/min, the relatively fresh SMC surface leads to the increased active sites, the conversion of heavy bio-oil* is slightly promoted and the removal effects of heteroatoms (O, N) compounds in the light bio-oil* are enhanced. The changes in SMC specific surface area and microcrystalline size are weakened accordingly.
Despite the ubiquitous and persistent presence of microplastic (MP) in marine ecosystems, knowledge of its potential harmful ecological effects is low. In this work, we assessed the risk of floating MP (1 μm – 5 mm) to marine ecosystems by comparing ambient concentrations in the global ocean with available ecotoxicity data. The integration of twenty-three species-specific effect threshold concentration data in a species sensitivity distribution yielded a median unacceptable level of 1.21 * 10⁵ MP m⁻³ (95% CI: 7.99 * 10³ – 1.49 * 10⁶ MP m⁻³). We found that in 2010 for 0.17% of the surface layer (0 – 5 m) of the global ocean a threatening risk would occur. By 2050 and 2100, this fraction increases to 0.52% and 1.62%, respectively, according to the worst-case predicted future plastic discharge into the ocean. Our results reveal a spatial and multidecadal variability of MP-related risk at the global ocean surface. For example, we have identified the Mediterranean Sea and the Yellow Sea as hotspots of marine microplastic risks already now and even more pronounced in future decades.
Thermochemical conversion of wheat husk biomass, LDPE and its blends was performed in a fixed bed reactor at 500 °C. The fixed bed reactor was designed and developed for pyrolysis reaction that can withstand up to 1000 °C. Based on thermogravimetric analysis (TGA) profile, the experiment was carried out at different temperature ranges from 350 to 550 °C to optimize the temperature for higher oil production. The study was conducted to investigate the co-pyrolysis effect on oil yield by adding LDPE as a blend with wheat husk at 1:0, 1:1, 2:1, 1:2 and 0:1 at 500 °C. It is noted that the blend of 1:2 found to produce more liquid component compared with other blends. Addition of LDPE drastically increases the calorific value in the oil component; meanwhile, it also decreases the oxygenated group present in the oil sample. Co-pyrolysis obtained is then analysed with GC-MS and FTIR to elucidate the functional group present in the oil sample. Calorific value of wheat husk and LDPE was found around 22.91 MJ kg−1 and 18.43 MJ kg−1, where the calorific value of the oil for the blends of 0:1, 1:1, 2:1, 1:2 and 1:0 were found to be 27.99 MJ kg−1, 28.09 MJ kg−1, 28.38 MJ kg−1, 29.45 MJ kg−1, 30.64 MJ kg−1, respectively. This attributes that co-pyrolytic oil tends to produce fuel with higher energy content.
Recycling of waste plastics is essential for reducing environmental degradation and ensuring future resource security. The quantity of domestic plastic waste recycled is increasing yearly, reaching 83 % in 2014. However, only 26 % and 4 % of the recycled waste plastic is treated by mechanical and feedstock recycling, respectively, whereas 70 % is treated by energy recovery (incineration). Therefore, the mechanical and feedstock recycling rates must be improved. This review examines the pyrolysis of waste plastics, which is a treatment method classed as feedstock recycling. Pyrolysis can convert waste plastics, which cannot be treated by mechanical recycling, into oils and gases. However, polyvinylchloride (PVC) and poly(ethylene terephthalate) (PET) produce corrosive gases and sublimating substances during pyrolysis, resulting in reduced quality of pyrolysis products, and damage to the treatment plant. Dehydrochlorination and dechlorination of PVC, in addition to catalytic pyrolysis of PET using Ca-based catalysts, have been developed. Recent studies into the pyrolysis of major plastics such as polyethylene (PE), polypropylene (PP), and polystyrene (PS) are summarized here, together with research on the dry and wet treatment of PVC and the catalytic pyrolysis of PET.
Pyrolysis of polypropylene (PP) and high density polyethylene (HDPE) into fuel like products was investigated over temperature range of 250 to 400 °C. The product yields as a function of temperature were studied. Total conversion as high as 98.66 % (liquid; 69.82%, gas; 28.84%, and residue; 1.34 %) was achieved at 300 °C in case of PP and 98.12 % (liquid; 80.88 %, gas; 17.24 %, and residue; 1.88 %) in case of HDPE at 350 °C. The liquid fractions were analyzed by FTIR and GC-MS. The results showed that the liquid fractions consisted of a wide range of hydrocarbons mainly distributed within the C6–C16. The liquid product obtained in case of PP is enriched in the naphtha range hydrocarbons. Similarly, the liquid product obtained in case of HDPE is also enriched in naphtha range hydrocarbons with preponderance in gasoline and diesel range hydrocarbons. The % distribution of paraffinic, olefinic, and naphthenic hydrocarbons in liquid product derived from PP is 66.55, 25.7, and 7.58 %, respectively, whereas in case HDPE, the % distribution is 59.70, 31.90, and 8.40 %, respectively. Upon comparing the hydrocarbon group type yields, PP gave high yield of paraffinic hydrocarbons while HDPE gave high yields of olefins and naphthenes. The whole liquid fractions and their corresponding distillates fractions were also analyzed for fuel properties. The results indicated that the derived liquid fractions were fuel-like meeting the fuel grade criteria.
The yield as well as molecular weight and composition of the condensed product generated from the HDPE was studied to gain insight into the role of temperature, equilibrium FCC catalyst, agitator speed and carrier gas on the pyrolysis products. Pyrolysis was done in a suite stirred bucchi stainless-steel autoclave reactor. The effect of process parameters such as degradation temperature, catalyst/polymer ratio (%), carrier gas type and stirrer rate on the condensed product yield and composition was determined. Reaction products were determined by GC analysis and shown to contain naphthenes (cycloalkanes), paraffins (alkanes), olefins (alkenes) and aromatics.The maximum “fuel like” condensed product yields were at 450 °C and 10% catalyst, respectively.The influence of different types of carrier gasses with varied molecular weights and reactivity was studied. Hydrogen as a reactive carrier gas increased the condensed and paraffinic product yield. Appropriate heat transfer – by stirring – can increase the catalyst efficiency in a stirred reactor. It is demonstrated that the use of equilibrium FCC commercial catalyst under appropriate reaction conditions can have the ability to control both the condensed yield and carbon number distribution from HDPE degradation, and thus potentially decrease the process cost with more valuable hydrocarbons.
In recent years, about 370 million tonnes of waste plastic are generated annually with about 9 % recycled, 80 % landfilled and 11 % converted to energy. As recycling of waste plastics are quite expensive and labour-intensive, the focus has now been shifted towards converting waste plastics into energy products. Pyrolysis of waste plastic generates liquid oil (crude), gas, char and wax among which liquid oil is the most valuable product. In this review, emphasis has been given on the pyrolysis products yield from both thermal and catalytic pyrolysis and the factors that affect pyrolysis products yield. The use of homogenous catalysts, for example AlCl3, can significantly improve the quality of waste plastic pyrolytic oil (WPPO), reduce time and energy consumption of the process, and help remove the contaminants of waste plastic. This study also thoroughly reviewed physico-chemical properties of WPPO to understand their thermal stability, elemental composition, and functional groups. Although liquid oil exhibits comparable heating value with commercial fuel (diesel/petrol), for example higher heating value of Polypropylene (PP) and Polyethylene (PE) are 50 and 42 MJ/kg which is between 42 and 46 MJ/kg for commercial diesel the other properties depend on several parameters such as plastic and pyrolysis reactor types, temperature, feed size, reaction time, heating rate and catalysts. A techno-economic analysis indicate that the liquid oil production cost could be about 0.6 USD/l if plant capacity is ≥175,000 million litres/year with a breakeven of 1 year. After-treatment of WPPO through distillation and hydrotreatment is recommended for improving the physio-chemical properties comparable to commercial fuel to use in automobile applications. This paper will be a valuable guide for stakeholders, and decision and policy makers for proper utilization of waste plastics.
Currently, 60–80 % of litter is plastic, and almost 10 % ends up in the ocean directly or indirectly. Plastics often suffer from photooxidation producing microplastics and these microplastics derived from the breakdown of larger plastics are called secondary microplastics. These compounds simply cannot be extracted from the oceans, and once mixed, they enter the food chain and may have toxic effects.
This work reviews the current existing information on the topic in the scientific literature. Then, the current plastic management strategies in the marine environment are analysed, with the objective of identifying possible needs and improvements from a sustainable point of view, and to define new approaches. Simultaneously, a material flows analysis in different media of the marine environment is carried out using system dynamics. A preliminary model of plastics mobilization into the ocean to other media of the marine environment (like sediments and biota) is developed and validated with the existing data from the previous steps of the work.
This work expands the current knowledge on the plastics management, their transformations and accumulation in the marine environment and the harmful effects on it. Likewise, preliminary dynamic model of mobilization of plastics in the ocean is implemented, run, and validated. The developed model can be used to predict trends in the distribution of the plastics in the ocean with time. In addition, the most important reservoirs of plastics in the ocean can be observed. Although plastics undergo transformations in the marine environment, it is not a means of disposal since most of them are non-biodegradable. Most plastics accumulate on the seabed. The proportion of microplastics found in sediments is higher than that of macroplastics.
With worldwide concern about climate change, waste-to-fuel technologies have been revived in the argument over whether waste-to-energy is still the best choice. A process-oriented life cycle assessment for municipal solid waste (MSW) was performed on the basis of full-scale operational data to compare the carbon footprints of the pyrolysis technology enhanced by mechanical and biological treatment (MBT) and incineration technology. Material and carbon flow analyses reveal that MBT produces refuse-derived fuels (RDFs) of 330 kg/ton MSW for pyrolysis, in which 67% of the carbon ends up in tar and char. Based on the Chinese energy structure in 2020 and MSW composition with 13% plastics, incineration and MBT–pyrolysis provide similar net carbon savings around 200 kg CO2-eq/ton. As the MSW contains more plastic fraction and the energy system becomes greener, the carbon savings from MBT–pyrolysis are less affected compared with those from incineration. The full-scale MBT–pyrolysis was verily optimised to maximise the RDF production and yield more tar and less syngas by identifying the important parameters, resulting in 30% higher savings in carbon footprint. With the energy structure at year 2050, the carbon footprints from MBT–pyrolysis are completely superior to that from incineration, regardless of the waste composition and heat recovery. From the low carbon perspective, fuel recovery with MBT − pyrolysis deserves priority over electricity recovery with incineration. This potential difference between waste-to-fuel and waste-to-energy technologies is for the first time quantitatively identified, and thus calls for a reconsideration on the long-term waste management and technological improvements.
Pyrolysis is a thermo-chemical decomposition process that converts organic or inorganic materials into solid, liquid and gaseous products. The pyrolysis process involves multiple complex chemical reactions, and the derived products are highly dependent on the pyrolysis operating parameters and type of feedstock. In the present review, progress on the state-of-the-art pyrolysis technology, feedstock and properties of the end products are thoroughly reviewed. The potential application of the pyrolysis products in the industries is discussed: solid leftover can be upgraded and used as a bio-adsorbant, soil amendment, fertilizer or solid fuel; pyrolysis liquid can be used as a bio-chemical source or upgraded into liquid fuel; gaseous products can be used as recirculating gas for the pyrolysis environment or burnt as fuel for heat and power generation. Despite the potential of pyrolysis in processing agricultural or industrial wastes, studies regarding the economic feasibility and environment sustainability of scaled-up pyrolysis plant are scarce. A comprehensive overview on the type of pyrolysis reactor technology, potential feedstock and the properties of the derived products is presented. Further, the sustainability of the technology is assessed from the aspects of energy balance, environment and economics. In spite of the potential benefits to the environment and recovery of valuable products, there are several challenges that need to be addressed to ensure the sustainability and commercialibility of the pyrolysis technologies.
The transformation of plastic waste into valuable fuel products via catalytic pyrolysis is a promising and eco-friendly strategy. Herein, a series of Co/Ni pillared montmorillonites were developed as low-cost and effective catalysts for the pyrolysis of post-consumer film waste, which is one of the representative plastic wastes in nature. The best-performing catalyst produced 80.2% of liquid product, with a high selectivity of 43.5% of hydrocarbons at C10–C13 range, and 42.0 vol% of H2 which is nearly increased by 40-fold as compared to that in non-catalytic run. The improved results were ascribed to the pillared structure, the oxidation state of Co/Ni, and the distribution of acid sites. Particularly, the Lewis acidity (which governs the cyclization and alkanisation) coupled with high surface area and uniform dispersion of transition metallic sites, were found to promote the selectivity of condensable product. The pyrolytic mechanism towards H2 production was explored by theoretical calculations. The lattice oxygen bonded to both Ni and Co in an octahedral environment was found to promote the adsorption of the fragment of polymer in dehydrogenation. Additionally, the solid residues are potentially applied for the production of valuable carbonaceous materials since they displayed high heating value. This work is expected to provide a direction for the development of pyrolysis technology for fuel production with sustainability and economic viability.
Plastics, papers, and textiles are the main dry waste components of municipal solid waste (MSW). Product-oriented pyrolysis of these wastes under proper blend ratio could be important not only for improving the quality of char, oil, or gas from MSW pyrolysis, but also for enhancing the recycle of plastics from MSW. In this study, the pyrolysis characteristics of papers (ivory board, coated duplex board with grey back, kraft paper and offset printing paper), plastics (polypropylene and polyethylene), and textiles (cotton and polyester) were studied using thermogravimetric-Fourier transform infrared (TG-FTIR) analysis, gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) to obtain the optimum blend ratios for the desired products (gas, oil, volatile and char). The synergistic effects amongst different components during pyrolysis were investigated. Results showed that the co-pyrolysis of papers, plastics, and textiles under equal blend ratio promoted the production of aromatics, alkenes, water, alcohol, and phenol in volatile, but inhibited the production of CO2, CO, alkanes, and carbonyls. The optimum mass blend ratios were found to be paper: plastic: textile = 25 wt%: 50 wt%: 25 wt% and 12 wt%: 50 wt%: 38 wt%, respectively for obtaining the highest energy share in volatile and gas. While for producing char with higher surface area, higher paper ratio and lower plastics ratio is preferred. When the plastics percentage in mixture was increased from 12.5 wt% to 25 wt%, the oxygenates percentage in pyrolysis oil was reduced from 82 area% to 19 area%, further increase in plastics percentage, or, alterations of papers and textiles percentages did not show significant influence on oil composition, indicating that plastics can be recycled, without lowering the calorific values of pyrolysis oil or MSW for incineration, when their blend ratio in MSW exceeds 25 wt%.
Pyrolysis oils with different effective hydrogen (H/Ceff) ratios are mixed with tetralin at a mass ratio of 1:1 and treated at 400 °C for 2 h under 6 MPa H2 over Pt/C and Ru/C, respectively, to examine the effect of H/Ceff ratio on the yield and quality of the upgraded oil. Pyrolysis oil with higher H/Ceff ratios results in an upgraded oil with higher yield and H/Ceff ratios. The highest S and O reduction ratios of 96.11% and 56.26% are achieved with added Pt/C at an H/Ceff ratio of 1.39 of the feedstock. In comparison, the highest N reduction ratios of 34.50% is achieved with added Ru/C at an H/Ceff ratio of 1.38 of the feedstock. The N and S poison the catalyst's active sites and reduce the deoxygenation efficiency. Thus, we view that the H/Ceff plays a vital role in improving the properties of the bio-oil.
As a solid waste rich in organic matter, pharmaceutical sludge can be effectively treated by pyrolysis and converted into energy. In this study, biochar prepared from pharmaceutical sludge was used for autocatalytic pyrolysis so as to improve the yield and quality of biogas while reducing the production of bio-oil. The results showed that biochar produced by pyrolysis from pharmaceutical sludge has high specific surface area and abundant functional groups. The addition of catalyst reduced the yield of bio-oil and increased the content of aromatics in bio-oil. At the same time, the yield of biogas was improved. When the catalyst was added to 60% at 800 °C, the combustible component in biogas reached 72.93% and the HHV reached 13.23 MJ/m³. Through calcination and deashing treatment of pharmaceutical sludge biochar, the roles of ash and deashing biochar in the autocatalytic process were analyzed. The results showed that ash was the active component of autocatalysis, and carbon was involved in the reaction as a reactant. Meanwhile, the porous structure of biochar increased the active sites. The experiment results showed that autocatalysis process can produce clean energy while treating pharmaceutical sludge, which has guiding significance for the industrial application of treating sludge produced by pharmaceutical enterprises.
The utilisation of renewable sources of energy has become an integral part of sustainable development. Municipal solid waste (MSW) has great potential to be used as a renewable source of energy if it can be combined with modern technologies such as pyrolysis. Pyrolysis technology is regarded as a revolutionary and easy energy production process for converting MSW into biofuel. Thus, the aim of this review is to present the state-of-the-art data on energy recovery from MSW. The review also includes information on its environmental impacts, challenges associated with the use of pyrolysis and a set of potential guidelines to overcome the challenges. The rotary pyrolysis technique is found to be the most used process for pyrolysis of MSW, as it provides ample heat transfer with comparatively low energy consumption. Temperature is the dominant parameter which is widely studied in MSW pyrolysis. Intermediate temperatures during pyrolysis normally provide maximum yields of bio-oil. Furthermore, the interactions of various parameters can affect the pyrolysis process. Pyrolysis facilities should be equipped with emission control systems to make the MSW pyrolysis operation environmentally friendly. Overall, pyrolysis of MSW yields around 43% bio-oil, 27% biochar and 25% syngas. It can be concluded that pyrolysis has the potential to be used as an effective and eco-friendly technology to generate biofuel and other value-added products from MSW.
Microplastic is an emerging contaminant of concern in soil globally due to its widespread and potential risks on the ecological system. Some basic issues such as the occurrence, source, potential risks, and quantification and estimation of regional emissions of microplastics in the soil are still open questions. These problems arise due to the lack of systematic and comprehensive analysis of microplastic in soils. Therefore, we comprehensively reviewed the current status of knowledge on microplastics in soil on detection, occurrence, characterization, source, and potential risk. Our review suggests that microplastics are ubiquitous in soil matrices globally. However, the research progress of microplastics in the soil is restricted by inherent technological inconsistencies and difficulties in analyzing particles in complex matrices, and studies on the occurrence and distribution of microplastics in soil environments remain very scarce, especially in Africa, South America, and Oceania. The consistency of the characteristics and composition of the microplastics in the aquatic environment and soil demonstrate they share sources and exchange microplastics. Wide and varied sources of microplastic are constantly filling the soil, which causes the accumulation of microplastics in the soil. Studies on the effects and potential risks of microplastics in soil ecosystems are also reviewed. Limited research has shown that the combination and interaction of microplastics with contaminants they absorbed may affect soil health and function, and even migration along the food chain. The occurrence and impact of microplastic on the soil depend on the morphology, chemical components, and natural factors. We conclude that large research gaps exist in the quantification and estimation of regional emissions of microplastics in soil, factors affecting the concentration of microplastics, and microplastic disguising as soil carbon storage, which need more effort.
This study performed TGA coupled with FTIR to evaluate the evolved gas and kinetic parameters of sewage and textile sludge thermal decomposition. Temperature-based FTIR spectrum presented common organics and also some nitrogen and sulfur-containing compounds in the produced gas. A multi-step determination of the kinetic analysis with TGA data could provide a more reasonable interpretation of kinetic triplets, including the activation energy and reaction mechanism. Hence, using the multi-step method would avoid overestimation for further calculation. The multi-step-based method yielded kinetic parameters for three pseudo reactions during the decomposition of sewage sludge (SS), textile sludge (TS), and their blends. Compared to sewage sludge, the activation energy of textile sludge for three consecutive stages varied more widely in the 90-160, 100-190, and 230-320 kJ/mol range, respectively. Aside from the activation energy, the reaction mechanism and pre-exponential factor would enrich sludge decomposition kinetic insight.
A range of energy fuels (ethanol, char, oil/wax and gas) was produced from fibre waste contaminated with plastic through the application of a fermentation-pyrolysis route. The fibre component was first converted to ethanol by simultaneous saccharification and fermentation (SSF), achieving an ethanol concentration of 39.8 g/L. The residue, enriched in lignin and plastics, was subjected to fast pyrolysis at temperatures between 350 and 550 °C. A wax product with a higher heating value (HHV) higher than 28 MJ/kg was obtained for temperatures higher than 450 °C, while values lower than 15 MJ/kg were observed for the oils produced from the untreated waste stream. Pyrolysis at 550 °C produced a wax with an HHV as high as 32.1 MJ/kg, where 51.8% of the energy content of the fermentation residue was transferred. The attractive energy contents of the pyrolysis products were enabled by oxygen removal from the feedstock during fermentation to ethanol.
This paper aims to evaluate the effect of low-cost clays (kaolin with different particle size and montmorillonite (MTT) modified with ZnCl2 and HCl) as catalysts on the pyrolysis products from waste tire. The results show that clays can improve the quality and yield of pyrolysis products. Different particle size and modification conditions have significant influence on the distribution and component of pyrolysis products. Compared with blank group, the content of combustible gas (including CH4 of 56.35%, H2 of 35.67% and CO of 7.98%) in ZnCl2 group is increased. Moreover, the hydrocarbon content of pyrolysis oil in each group exceed 90%. The N-containing compounds can be removed by hydrodenitrogenation (HDN) reaction and convert into aromatics through ring-opening reaction. Meanwhile, the yield of the O-containing compounds in each group is less than 3%, and the lowest content is ZnCl2 group. ZnCl2-modified MTT have high specific surface area and rich mesoporous structure, which can promote deoxidation and aromatization to reach the highest aromatics content (90.23%). In addition, the content of C11–C20 in addition groups can be increased by small molecule polymerization. The catalysts promote the formation of diesel fraction through alkylation of benzene and naphthalene.
The fluidized bed fast pyrolysis of two different kinds of fuels, namely, wood pellets (WP) and solid recovered fuel (SRF) pellets made up of a municipal solid waste by ECONWARD TECH, S.L. (EP) has been carried out. Thus, the analysis of the influence of pyrolysis reactor temperature (600–800 °C) and fuel type in terms of product distribution, e.g. gases, char and tar has been performed. The conditions used in this work are of special interest for the gasification in fluidized beds, in which fast pyrolysis plays a relevant role as it is the first step of fuel conversion. The gas composition was continuously recorded and the tar samples collected during the experiments were analyzed by GC technique. The higher ash content in the EP enhanced charring and decarboxylation reactions, which greatly influenced the distribution of the gaseous products leading to a high CO2 yield. Tar composition was also affected by the constituents of the fuels used, with the content of phenolic compounds in the EP tar obtained at 650 °C being particularly low at the expense of a higher light aromatic content. The rise in temperature decreased the fraction of phenolic compounds and led to a gradual formation of light and heavy polycyclic aromatic hydrocarbons (PAHs), with naphthalene being the major compound in tars of both fuels, WP and EP, at high temperature. The results can be used to derive pyrolysis sub-models for fluidized bed gasification modeling.
Co-pyrolysis is a promising approach to recover energy from sewage sludge (SS) and municipal solid waste (MSW). Hg emission during this process has serious environmental risks. To reduce the environmental impact, orthogonal experiments on the blending ratio, heating rate, pyrolysis temperature, and residence time were conducted during SS and MSW co-pyrolysis. Variance analysis was used to determine the influence and synergetic effects of these factors. Multivariate nonlinear, neural network, random forest, and support vector machine models were used to simulate the Hg distribution based on four parameters, which were later optimized to optimize the Hg fixing ratio in pyrolysis char. The Hg was mainly distributed in the pyrolysis gas and char. The variance analysis results indicate that the blending ratio is the key factor influencing Hg distribution, and there is little synergetic effect among the four factors. Further experiments showed that a blending ratio of 87.5 SS wt% could enhance Hg fixation in char. The neural network model shows the best simulation performance with a mean relative error of 8.92%. The optimal parameters are a heating rate of 7 °C/min, pyrolysis temperature of 300 °C, and residence time of 10 min, resulting in a Hg fixing ratio of 25.68 wt% in pyrolysis char. The simulated Hg fixation characteristics correlate with the experimental results. This study provides insights into Hg distribution under various conditions during co-pyrolysis of SS and MSW. It is hoped that this work can contribute to the control of Hg during the waste treatment and utilization process.
The thermal and catalytic decomposition of waste plastics through pyrolysis is one of the best approaches of handling plastics waste and most prospective alternative of converting waste to wealth by transforming the waste plastics into lighter fuel oils which has potential to at least replenish petroleum resources if not replace the fossil fuels through this process of recycling. Further advancement in this area of research was to co-process waste plastics along with petroleum residues and other used oil with a similar intention, opening up a new prospect of reclaiming and upgrading altogether, two relatively low graded materials to a superior quality product which may be further refined for reprocessing in the petroleum refinery. In this paper, an attempt has been made to review the literature on cracking of plastics waste and it's co-processing with petroleum residues and other heavy oil, the types of reactors and the catalyst employed in the process. The resulting product especially the liquid product from the co-processing of waste oil with polyolefin waste material has been found to possess good calorific values in the range of 44–47 MJ kg⁻¹ while the heating value of the gaseous product was found to be in the range of 27–32 MJ Nm⁻³ and other characteristics similar to those of conventional fuel like diesel and thereby have a very good potential to be used as transportation fuel and other chemical feedstocks on further refining, while co-processing with other heavy oils residues have been found to have similar potential and prospect as an alternative to the conventional fuels and energy.
Pyrolysis is currently an effective way to recycle plastics. High-pressure conditions can change the pyrolysis product component distribution, but the microscopic mechanism has not been well elucidated. To explore the relationship of product distribution versus pressure and explain the microscopic mechanism of polyethylene high-pressure pyrolysis, experiments under a large initial pressure range from 1 bar to 51 bar at initial temperatures of 330–380 °C were carried out in an autoclave. In the process of polyethylene high-pressure pyrolysis, the temperature within the reactor exceeded the set temperature by 100 °C at a rate of 150 °C/min. The thermal runaway phenomenon was caused by the polymerization of concentrated olefins in liquid form, which was initiated by hydrocarbon radicals. As the pressure increased, the reaction peak temperature was risen and more small molecules were produced. Under an initial temperature of 340 °C and high-pressure conditions, polyethylene was completely converted into liquid and gas products. The experimental results also revealed that high-pressure conditions led to the production of aromatic compounds and isoparaffins, as well as more cycloalkanes and fewer olefins in the liquid product, making the product characteristics closer to the fuel standard. Finally, this paper proposes the radical microscopic mechanisms of polyethylene thermal degradation under atmospheric-pressure and high-pressure conditions.
The catalytic upgrading of beech wood pyrolysis oil has been carried out over microporous and hierarchical MFI zeolites to produce a blendable stream with FCC unit feedstock. Mesoporosity was introduced within the zeolite structure through the desilication process by alkaline NaOH solution with various concentrations aiming at investigating the effect of porosity improvement on catalytic upgrading parameters. The zeolite catalysts were characterized using XRD, SEM, EDS, BET and NH3-TPD analyses and the results showed that the desilication improved textural properties of the zeolites preserving crystallinity. In addition, the effect of mesoporosity, catalyst to biomass ratio, and their interactions on the bio-oil upgrading parameters such as upgrading factor, degree of deoxygenation, effective hydrogen index, relative content of various compounds and coke yield have also been analyzed. The results revealed a significant effect of the parameters on the deoxygenation activity, coke formation potential, and selectivity towards desired products. Indeed, the improved accessibility of weak and strong acid sites, as well as controlled acidity caused to the enhanced conversion of large, oxygenates to smaller ones. The larger coke yield for the optimum hierarchical catalyst (synthesized by 0.5 M solution) was associated with a lower oxidation temperature, which is suited for cost-effective catalyst regeneration.
In this study, we assessed plastic accumulation in marine sediments due to finfish aquaculture using floating net-pens. We studied plastic concentrations around three fish farms located at the Mediterranean coastline of Spain. The macroplastic categories and abundances were determined by video monitoring, detecting the majority of elements (78%), including ropes, nets and fibres, a basket trap and a cable tie, close to the facilities, which were not exclusively linked to fish farming but also to fishing activities. Concentrations of microplastics (<5 mm) ranged from 0 to 213 particles/kg dry weight sediment with higher values in sites directly under the influence of the fish farms. Most particles (27.8%) were within the size fraction from 1.1 to 2.0 mm and fibre was the most common shape with 62.2%. The Infrared spectroscopy analysis showed that PE and PP were the predominant types of polymers analysed. In addition, changes in the enthalpy of melting (ΔHm (J/g)) and the degree of crystallinity indicate degradation of the microplastics analysed. This study shows that, in the studied fish farms, levels of microplastic pollution can be one order of magnitude lower compared to other areas suffering other anthropogenic pressures from the same or similar regions. Nevertheless, more research effort is needed to get concluding results.
Microwave-assisted pyrolysis is considered a promising technique for the thermochemical conversion of solid waste such as sewage sludge to useful energy products, including bio-char, bio-oil and bio-gas. However, a limited number of reports are found on the fundamentals and application of this process to extend the high potential of microwave-assisted pyrolysis of sewage sludge. This article presents up-to-date knowledge regarding important aspects of sewage sludge microwave pyrolysis, starting with the pretreatment of sewage sludge and the latest studies of conventional and microwave pyrolysis heating. This article further explores the products generated by microwave-assisted pyrolysis for sewage sludge including composition and yield. For instance, recent progress in experimental studies of both the catalytic and non-catalytic microwave-assisted pyrolysis of sewage sludge are reviewed and their results are analyzed in comparison to the product distributions resulting from non-microwave heating methods. Finally, this review discusses both the advantages and challenges of sewage sludge pyrolysis using microwave heating and the milestones that are necessary to be obtained in the future.
The simplex plays an important role as sample space in many practical situations where compositional data, in the form of proportions of some whole, require interpretation. It is argued that the statistical analysis of such data has proved difficult because of a lack both of concepts of independence and of rich enough parametric classes of distributions in the simplex. A variety of independence hypotheses are introduced and interrelated, and new classes of transformed‐normal distributions in the simplex are provided as models within which the independence hypotheses can be tested through standard theory of parametric hypothesis testing. The new concepts and statistical methodology are illustrated by a number of applications.
Continuous growth of human population and industrialization has increased the energy demands all over the world and this has resulted in a number of energy related challenges including depletion of fossil fuels, environmental pollution, and shortage of electricity supply. These challenges made it imperative to develop and maximize the abundant renewable energy resources, particularly the biomass via upgrading thermochemical conversion routes such as co-pyrolysis. This review paper presents an overview of previous studies, recent advances, and future directions on co-pyrolysis of biomass and waste plastics for high-grade biofuel production particularly in China and elsewhere worldwide. This paper also discussed the advantages of the co-pyrolysis process, co-pyrolysis product yields, co-pyrolysis mechanisms of biomass with plastics, and synergistic effects between them during co-pyrolysis, as well as the effects of some operating parameters especially the biomass mixing ratio and pyrolysis temperature on co-pyrolysis yields. The result of this critical review showed that co-pyrolysis of biomass with waste plastics is more beneficial than the normal biomass pyrolysis alone, and that it is also a simple, effective, and optional solution to increase the energy security of a nation, achieve effective waste management, and reduce dependency on fossil fuels.
This article describes the production and properties of gases produced by the pyrolyses of poly(ethylene terephthalate) (PET), polypropylene (PP), polyethylene (PE), poly(vinyl chloride) (PVC), and polystyrene (PS), and three of their mixtures at process temperatures of 500, 700, and 900 °C. The overall aim was to characterize all 24 gases in terms of their production and physical properties, and compare the data obtained to those of traditional fuels, namely natural gas (NG) and propane. In addition to experimental and analytical approaches for determining quantities and compositions of the pyrolysis products, various mathematical methods and their combinations were also used to determine product properties. The highest conversion of material into gas occurred during the pyrolysis of PP at 900 °C (66.88 wt% conversion into gaseous products). The pyrolyses of PE and PP at 500 °C were found to generate pyrolysis gases with the highest energy, with gross calorific values of 86.58 and 81.09 MJ m⁻³N, respectively. The highest chemical energy yield was obtained by the pyrolysis of PP at 900 °C. Gases produced from PVC had a high thermal conductivity of about 104.83 mW m⁻¹ K⁻¹. The gas generated from PP at 500 °C exhibited a high specific heat of 2.94 kJ m⁻³N K⁻¹, and that obtained from PS at 500 °C had a very low kinematic viscosity (5.28 10⁻⁶ m² s⁻¹) and thermal diffusivity (7.90 10⁻⁶ m² s⁻¹).
Even though numerous reports have dealt with pyrolysis gases, there is still not sufficient information about the specific physical properties of these gases. This article attempts to fill this gap and induce scientific interest in this field.
The usefulness of any material, including polymer blends, depends on its degradability and durability. The blend composition can significantly affect the degradative behavior of a polymer blend and can differ from the degradation routes of the pure components since the interactions among different species in the blends during degradation, and among the degradation products, can occur. These reactions can lead either to an acceleration of the degradation rate or to a stabilizing effect in comparison with the pure components. Thus, the additive rule cannot be often applied in case of degradation of polymer blends and, therefore, it is difficult to predict the degradative behavior of a polymer blend on the base of the properties of pure components.
The continuous increase in the generation of waste plastics together with the need for developing more sustainable waste management policies have promoted a great research effort dealing with their valorization routes. In this review, the main thermochemical routes are analyzed for the valorization of waste polyolefins to produce chemicals and fuels. Amongst the different strategies, pyrolysis has received greater attention, but most studies are of preliminary character. Likewise, the studies pursuing the incorporation of waste plastics into refinery units (mainly fluid catalytic cracking and hydrocracking) have been carried out in batch laboratory-scale units. Other promising alternative to which great attention is being paid is the process based on two steps: pyrolysis and in-line intensification for olefin production by means of catalytic cracking or thermal cracking at high temperatures.
The three primary lignocellulosic biomass components (cellulose, xylan and lignin), synthetic biomass samples (prepared by mixing the three primary components) and lignocellulosic biomass (oak, spruce and pine) were pyrolysed in a thermogravimetric analyser and a wire mesh reactor. Different reactivities were observed between the three biomass components. Cellulose mainly produced condensables and was less dependent on heating rate, while xylan and lignin contributed most char yields and were significantly affected by heating rate. While xylan and lignin pyrolysed over a large temperature range and showed the behaviour characteristic of solid fuels, cellulose decomposition is sharp in a narrow temperature range, a behaviour typical of linear polymers. Comparison of the pyrolysis behaviour of individual components with that of their synthetic mixtures showed that interactions between cellulose and the other two components take place, but no interaction was found between xylan and lignin. No obvious interaction occurred for synthetic mixtures and lignocellulosic biomass at 325 °C, before the beginning of cellulose pyrolysis, in slow and high heating rate. At higher pyrolysis temperatures, more char was obtained for synthetic mixtures containing cellulose compared to the estimated value based on the individual components and their proportions in the mixture. For lignocellulosic biomass, less char and more tar were obtained than predicted from the components, which may be associated with the morphology of samples. The porous structure of lignocellulosic biomass provided a release route for pyrolysis vapours.
To better understand pyrolysis mechanism and further develop selective pyrolysis technology, characteristics of volatile products in the pyrolysis of three main components (cellulose, hemicellulose and lignin) were investigated and compared by amplifying experiments in a tube furnace at 300–700 °C. Distribution of volatile products (including bio-oil and bio-gas), the influence of temperature and contributions of each single component were discussed in depth. It was found that, for each sample pyrolysis, pyrolysis temperature and their own chemical structures played an important role in the yields, composition of bio-oil and bio-gas. The optimal temperatures for production of bio-oil from cellulose, hemicellulose and lignin focused at 500 °C, 450 °C and 600 °C, respectively, and cellulose made greater contribution to bio-oil formation, and hemiellulose was the major contributor for bio-gas. Moreover, the more bio-gases from the three components generated at the higher temperature, but compositions of volatile products were different depending on their unique chemical structures. In the three components, cellulose produced the highest CO, hemicellulose owned the highest CO2, and lignin generated the highest CH4 characterized by the largest HHV. As for bio-oil, cellulose bio-oil displayed unique saccharides and higher furans, hemicellulose bio-oil contained higher acids and ketones, while phenols were the dominant composition of lignin bio-oil.
This paper reviews the progress and challenges of the catalytic pyrolysis of plastic waste
along with future perspectives in comparison to thermal pyrolysis. The factors affecting the
catalytic pyrolysis process such as the temperature, retention time, feedstock composition
and the use of catalyst were evaluated in detail to improve the process of catalytic pyrolysis.
Pyrolysis can be carried out via thermal or catalytic routes. Thermal pyrolysis produces
low quality liquid oil and requires both a high temperature and retention time. In order
to overcome these issues, catalytic pyrolysis of plastic waste has emerged with the use of
a catalyst. It has the potential to convert 70–80% of plastic waste into liquid oil that has
similar characteristics to conventional diesel fuel; such as the high heating value (HHV) of
38–45.86 MJ/kg, a density of 0.77–0.84 g/cm3, a viscosity of 1.74–2.5 mm2/s, a kinematic viscosity
of 1.1–2.27 cSt, a pour point of (−9) to (−67) ◦C, a boiling point of 68–352 ◦C, and a flash
point of 26.1–48 ◦C. Thus the liquid oil from catalytic pyrolysis is of higher quality and can be
used in several energy-related applications such as electricity generation, transport fuel and
heating source. Moreover, process by-products such as char has the potential to be used as
an adsorbent material for the removal of heavy metals, pollutants and odor from wastewater
and polluted air, while the produced gases have the potential to be used as energy carriers.
Despite all the potential advantages of the catalytic pyrolysis, some limitations such as
high parasitic energy demand, catalyst costs and less reuse of catalyst are still remaining.
The recommended solutions for these challenges include exploration of cheaper catalysts,
catalyst regeneration and overall process optimization.
This chapter provides a review of catalytic fast pyrolysis of biomass and its potential for improving fast pyrolysis oil quality. Catalytic pyrolysis focuses on the use of catalysts in a fast pyrolysis system processing biomass and/or waste materials for the production of bio-oil, liquid, and secondary products. As the development of sustainable energy and fuel sources is of growing concern, different approaches to pyrolysis are being considered to alleviate fears of climate change and fuel shortages. These are discussed in other chapters. This review describes the current catalytic fast pyrolysis field with particular focus on the effect of fast pyrolysis conditions on catalyst reactivity and life time. The different active solid materials that can be used within a pyrolysis system to improve pyrolysis oil are described and compared. Current reactor design and technology is also summarized.
Biomass is the most widely used non-fossil fuel in the world. Biomass resources show a considerable potential in the long-term given the increasing proliferation of dedicated energy crops for biofuels. The second edition of Biomass Gasification and Pyrolysis is enhanced with new topics, such as torrefaction and cofiring, making it a versatile resource that not only explains the basic principles of energy conversion systems, but also provides valuable insight into the design of biomass conversion systems. This book will allow professionals, such as engineers, scientists, and operating personnel of biomass gasification, pyrolysis or torrefaction plants, to gain a better comprehension of the basics of biomass conversion. The author provides many worked out design problems, step-by-step design procedures and real data on commercially operating systems. With a dedicated focus on the design, analysis, and operational aspects of biomass gasification, pyrolysis, and torrefaction, Biomass Gasification, Pyrolysis and Torrefaction, Second Edition offers comprehensive coverage of biomass in its gas, liquid, and solid states in a single easy-to-access source. Contains new and updated step-by-step process flow diagrams, design data and conversion charts, and numerical examples with solutions. Includes chapters dedicated to evolving torrefaction technologies, practicing option of biomass cofiring, and biomass conversion economics. Expanded coverage of syngas and other Fischer-Tropsch alternatives. Spotlights advanced processes such as supercritical water gasification and torrefaction of biomass. Provides available research results in an easy-to-use design methodology.
A mixture of hospital post-commercial polymer waste (LDPE/HDPE/PP/PS) was pyrolyzed over various catalysts using a fluidized-bed reactor operating isothermally at ambient pressure. The yield of volatile hydrocarbons with zeolitic catalysts (ZSM-5>MOR>USY) were higher than with non-zeolitic catalysts (MCM-41>ASA). MCM-41 with large mesopores and ASA with weaker acid sites resulted in a highly olefinic product mixture with a wide carbon number distribution, whereas USY yielded a saturate–rich product mixture with a wide carbon number distribution and substantial coke levels. The systematic experiments discussed in this paper show that the use of various catalysts improves the yield of hydrocarbon products and provide better selectivity in the product distributions. A novel developed model based on kinetic and mechanistic considerations which take into account chemical reactions and catalyst deactivation for the catalytic degradation of commingled polymer waste has been investigated. This model represents the benefits of product selectivity for the chemical composition such as alkanes, alkenes, aromatics and coke in relation to the performance and the particle size selection of the catalyst used as well as the effect of the fluidizing gas and reaction temperature.
Catalytic degradation of waste high-density polyethylene (HDPE) to hydrocarbons by ZSM-5, zeolite-Y, mordenite and amorphous silica–alumina were carried out in a batch reactor to investigate the cracking efficiency of catalysts by analyzing the oily products including paraffins, olefins, naphthenes and aromatics with gas chromatography/mass spectrometry (GC/MS). Catalytic degradation of HDPE with zeolite-Y, mordenite and amorphous silica–alumina yielded 71–82 wt.% oil fraction, which mostly consisted of C6–C12 hydrocarbons, whereas ZSM-5 yielded much lower 35% oil fraction, which mostly consisted of C6–C12 hydrocarbons. Both all zeolites and silica–alumina increased olefin content in oil products, and ZSM-5 and zeolite-Y particularly enhanced the formation of aromatics and branched hydrocarbons. ZSM-5 among zeolites showed the greatest catalytic activity on cracking waste HDPE to light hydrocarbons, whereas mordenite produced the greatest amount of coke. Amorphous silica–alumina also showed a great activity on cracking HDPE to lighter olefins in high yield, but no activity on aromatic formation.