It is promising to convert waste oil and plastics to renewable fuels and chemicals by microwave catalytic co-pyrolysis, enabling pollution reduction and resource recovery. The purpose of this study ...was to evaluate the effect of catalysts on the product selectivity of microwave-assisted co-pyrolysis of waste cooking oil and low-density polyethylene and optimize the pyrolysis process, including pyrolysis temperature, catalytic temperature, waste cooking oil to low-density polyethylene ratio, and catalyst to feedstocks ratio. The results indicated that catalysts had a great influence on the product distribution, and the yield of BTX (benzene, toluene, and xylenes), which increased in the following order: SAPO-34 < Hβ < HY < HZSM-5. HZSM-5 was more active for the formation of light aromatic hydrocarbons as compared to others, where the concentrations of toluene, benzene and xylenes reached 252.59 mg/mL, 114.7 mg/mL and 132.91 mg/mL, respectively. The optimum pyrolysis temperature, catalytic temperature, waste cooking oil to low-density polyethylene ratio and catalyst to feedstocks ratio could be 550 °C, 450 °C, 1:1 and 1:2, respectively, to maximize the formation of BTX and inhibit the formation of polycyclic aromatic hydrocarbons.
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•Microwave co-pyrolysis of waste cooking oil and LDPE comprehensively investigated.•HZSM-5 was the most effective aromatization catalyst for light aromatics.•This co-pyrolysis increased the content of monocyclic aromatic hydrocarbons.•Benzene, toluene, xylenes, ethylbenzene, and styrene were quantified.
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•Composite catalysts (ZSM-5/MCM-41) were synthesized and its optimum catalytic conditions were studied.•Microwave-assisted catalytic fast co-pyrolysis (co-MACFP) was adopted in this ...experiment.•The synergistic effect of lignin and catalyst promotes the formation of aromatic compounds.
Microwave-assisted catalytic fast co-pyrolysis (MACFP) of lignin and waste oil with SiC as microwave absorbent and hierarchical ZSM-5/MCM-41 as catalyst were implemented in a microwave-induced reactor. ZSM-5/MCM-41 is a kind of composite catalyst with MCM-41 as shell and ZSM as core. The effects of catalyst temperature, the ratio of feedstock-to-catalyst and the ratio of two reactants (lignin and waste oil) on product distribution and yield were studied. The study shows that catalytic co-pyrolysis is a complex reaction process, and many reaction conditions could affect the final reaction results. The optimum reaction conditions are as follows: catalytic temperature 400 °C, the feedstock-to-catalyst ratio of 10:1 and the ratio of lignin to waste oil of 2:1. Under this reaction condition, the conversion of feedstocks reached 76.00%, the proportion of aromatics was 50.31% and the selectivity of monocyclic aromatic hydrocarbons (MAHs) was 42.83%.
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•Catalytic conversion of soapstock over HZSM-5 was conducted to produce aromatics.•Effect of unsaturation degree on product distribution and composition was studied.•The pyrolysis ...mechanism of soapstock and fatty acid salt over HZSM-5 was proposed.
Hydrocarbon-rich fuel from vegetable oil soapstock is potentially a good alternative to conventional fossil-derived fuels. This paper reported on pyrolysis experiments with compounds including vegetable oil soapstock, sodium stearate(C18), sodium palmitate(C16), sodium oleate(C18:1), and sodium linoleate(C18:2). The effects of pyrolysis temperature, HZSM-5 catalyst, unsaturation degree and carbon chain length on the formation of aromatic hydrocarbons were explored. Experimental results indicated that the relative content of oxygenated compounds significantly decreased in the condensable organic compounds of soapstock pyrolysis, and aromatic hydrocarbons increased when the HZSM-5 catalyst was used, in which toluene and xylene had the highest relative selectivity. High catalytic pyrolysis temperature was beneficial to the relative selectivity of benzene and toluene, but inhibited the relative selectivity of xylene and ethylbenzene. The increase in saturation of fatty acid salts promoted the reaction toward the production of polycyclic aromatic hydrocarbons, which were a kind of typical precursor of catalyst coking deactivation and carcinogenic pollutants.
Abstract The quest for low-carbon alternatives to fossil fuels and the carbon emissions associated with the natural degradation of biomass have accelerated the development of biomass processing ...technologies. Microwave catalytic pyrolysis is emerging as a technology for efficient conversion of biomass into energy, fuels and chemicals. However, due to the inherent poor dielectric properties and complex composition of biomass, two main technical challenges faced by microwave catalytic pyrolysis of biomass are efficient heating of biomass and improving the selectivity of target products. Potential solutions involve the use of microwave absorbents and catalysts, respectively. This review begins by addressing the difficulty in balancing energy efficiency and conversion efficiency by introducing microwave absorbents that play a positive role in improving heating efficiency. The principle of microwave absorbents in assisting biomass heating is revealed, and the impacts of the microwave absorbent type (related to microwave properties and physical properties) and the additive amount on the heating effect and biomass pyrolysis product distribution are discussed. Subsequently, the search for catalysts applied in biomass microwave pyrolysis for modulation of product distribution is explored. Special attention has been paid to the catalysts with microwave absorption properties, including activated carbon, zeolites, some metal oxides and metal salts. In addition, the energy efficiency, economic feasibility, and environmental impacts of this processing technology utilizing microwave absorbents and catalysts are examined based on energy analysis, techno-economic assessment, and life cycle assessment. The current scale-up challenges of microwave catalytic pyrolysis of biomass and some potential solutions to enhance the commercial feasibility of this technology are also discussed. Finally, the review provides some future development directions of this technology.
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•White pollution and energy crisis can be alleviated via fuels conversion from plastic wastes.•The application of efficient catalysts enables directional selection of targeted ...products.•The downstream upgrading towards high-value products creates added value to a plastic-to-fuel process.•Techno-economic assessment of catalytic pyrolysis systems for plastic wastes shows attractive industrialization prospects.
With the continuous increase of plastic wastes and the decrease of fossil energy, pyrolysis has emerged as a promising technology for the valorization of plastic wastes to produce fuels and chemicals. Properties of common plastics, mainly polyethylene terephthalate (PET), polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), polystyrene (PS) and their mixtures are discussed with a focus on the pyrolysis mechanism and product distribution. The application of the most common catalysts (microporous/mesoporous zeolites, base catalysts, and clays) shows overwhelming advantages over thermal cracking, and an in-depth understanding of catalysts in several catalytic processes (ex-situ catalysts, tandem catalysts, bi-functional catalysts, multi-modal pore catalysts, and regenerated catalysts) is critical for efficient fuel production. Despite high-quality liquid fuels obtained, further upgrading (filtration, hydrogenation, distillation, liquid–liquid extraction or blending with conventional fuels) is required before their commercial application. Non-condensable gas is another co-product that can be upgraded for heat generation or as the precursor of high-value products (ethylene, propylene, carbon nanotubes (CNTs), etc.). Finally, a more integrated techno-economic assessment process is conducted based on feedstock logistics, utilization of liquid fuels, full use of co-products, capital and operating costs. This review aims to inspire both fundamental and applied research efforts for the production of high-value products from the catalytic pyrolysis of plastic wastes and their full utilization to create the necessary technological and economic push for a circular economy.
•Catalytic pyrolysis of waste oil for the hydrocarbon fuels production was reviewed.•Comparison of electric and microwave heating pyrolysis of waste oil was outlined.•Catalysts used in waste oil ...pyrolysis have been extensively introduced.•In-situ catalytic and ex-situ catalytic reactors were introduced and compared.
The deterioration of environment and the depletion of fossil fuels have inspired the exploration for alternative fuels based on renewable raw materials. This review presented the catalytic pyrolysis of waste oil for producing renewable hydrocarbon fuels. After the discussion of various process parameters, including waste oil characteristics, microwave absorbents, co-pyrolysis technology, catalysts, and reactor types, the best conditions for improving the yield and quality of hydrocarbon fuels were obtained. The advantages and limitations of microwave-assisted pyrolysis and conventional electric heating were discussed. Microwave-assisted pyrolysis is a relatively new technology compared with traditional electric heating pyrolysis, which has great development potential. In the future, the catalysts with low pressure drop and coking rate need to be developed and their microwave absorption characteristics in microwave-assisted pyrolysis must be fully investigated. Simultaneously, a continuous microwave-assisted pyrolysis system needs to be constructed to achieve the large-scale production of renewable hydrocarbon fuels from waste oil.
Rapid consumption of petroleum and concerns about carbon emissions have promoted utilization of renewable energy such as biomass. Pyrolysis of biomass is one of effective sustainable routes for ...aromatic hydrocarbons production. However, it has not been applied commercially on a large scale. One of the biggest challenges is inferior characteristics of biomass, including complex crosslinking structure, high content of alkali and alkaline earth metals (AAEMs), and low hydrogen to carbon effective ratio (H/Ceff). Main objective of this review is to investigate main methods that enhance aromatic hydrocarbons production, while screening out option to maximize aromatic hydrocarbons production, taking economic analysis and technical application progress as a reference. Results show that pre enhancement methods including physical, thermal, chemical and biological biomass pretreatments are mainly used to break crosslinking structure and remove AAEMs. The most significantly influential factor limiting biomass conversion is low H/Ceff, and thus in-process enhancement methods including deoxidation via catalysis, and hydrogenation via co-pyrolysis and atmosphere regulation are more effective for improving aromatic hydrocarbons. Industrial problems, existed in co-pyrolysis (great characteristics differences, etc.) and atmosphere regulation (high investment cost, etc.), have not been solved yet. By comparison, development of catalysts is relatively mature, and there are successful commercial cases. Total production cost of catalytic pyrolysis of biomass is only 67% of petroleum refining route, showing best economic potential. Accurate design and construction of catalysts with high activity and long life based on biomass characteristics is the most feasible and promising development direction.
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•Biomass inferior properties affecting aromatics conversion by pyrolysis are given.•Physical, thermal, chemical and biological pretreatment enhancement is introduced.•Deoxidation enhancement via zeolites and modified zeolites catalysis is described.•Hydrogenation enhancement via co-pyrolysis and atmosphere regulation is described.•Optimization of key operational parameters during biomass pyrolysis is summarized.
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•The synergism on co-pyrolysis of polyethylene and lignin is promoted by pressure.•Radical mass transfer efficiency is regulated by pressure and raw material ratio.•Pressure helps to ...inhibit coke by promoting radical transfer and water release.•Aromatics with smaller steric hindrance are easier to alkylate and polycondensate.
Ex-situ catalytic co-pyrolysis of plastic and biomass to aromatics has been extensively investigated, simultaneously, aromatization have been reported to be promoted under pressure, but available research did not discuss the combined effect of catalytic co-pyrolysis and pressure on aromatics production. In this work, ex-situ catalytic co-pyrolysis of polyethylene and lignin over HZSM-5 under a series of pressure (0.1–0.8 MPa) in a Py-GC/MS system was investigated. We show that pressurized operation during co-pyrolysis of polyethylene and lignin leads to a large increase in BTEX relative yield while maintaining catalyst stability. A very high BTEX relative yield of 70.94% can be achieved at temperature of 650 °C, pressure of 0.5 MPa, polyethylene to lignin ratio of 1:1, and catalyst to raw material ratio of 4:1. Ratio of two raw materials significantly affects efficiency of hydrogen radicals-mass transfer by regulation of hydrogen radical emission and reception. A peak value of BTEX relative yield of 70.27% was obtained at a polyethylene to lignin ratio of 4:3. Among BTEX, benzene and toluene are more prone to alkylate and polycondensate into highly branched and polycyclic aromatics, due to a lower steric hindrance. Hydrogen radicals-mass transfer has a significant effect on BTEX production, and mass transfer efficiency can be regulated by appropriate pressure and raw materials ratios. Meanwhile, pressurized operation has a dual positive effect on coke inhibition via promoting hydrogen radicals-mass transfer and water release, such that catalyst stability and BTEX production are promoted. This study offers new insight into efficient production of BTEX.
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•The addition of MCM-41 was beneficial in prolonging the life of HZSM-5.•The optimal operating conditions were determined.•Co-pyrolysis of soapstock with straw advanced the ...deoxygenation especially phenol.•Co-pyrolysis with a dual-catalyst system is a promising technology.
Microwave-assisted co-pyrolysis of low hydrogen-to-carbon and high hydrogen-to-carbon effective ratio materials with the aid of HZSM-5 and MCM-41 is a promising technique to improve the bio-oil quality. The low content of hydrocarbons and short life cycle of catalyst limit the application of pyrolysis technology in biomass energy conversion. The effects of catalytic temperature, and HZSM-5-to-MCM-41, feedstock-to-catalyst, and straw-to-soapstock ratios on the yield and composition of bio-oil were studied in this work. The quality of bio-oil during biomass pyrolysis can be improved by adjusting the operating conditions. The optimal catalytic temperature, and ratios of HZSM-5-to-MCM-41, feedstock-to-catalyst, and straw-to-soapstock were 400 °C, 1:1, 2:1, and 1:2, respectively. The addition of MCM-41 was beneficial in prolonging the life of HZSM-5 since the macromolecular compounds cracked when MCM-41 was added which restrain the generation of coke. The co-pyrolysis of soapstock with straw advanced the deoxygenation of oxygen-containing compounds especially phenol from straw during pyrolysis.
Pyrolysis of nitrogen-containing biomass holds tremendous potential for producing varieties of high value-added products, alleviating energy depletion. Based on the research status about ...nitrogen-containing biomass pyrolysis, the effect of biomass feedstock composition on pyrolysis products is first introduced from the aspects of elemental analysis, proximate analysis, and biochemical composition. The properties of biomass with high and low nitrogen used in pyrolysis are briefly summarized. Then, with the pyrolysis of nitrogen-containing biomass as the core, biofuel characteristics, nitrogen migration during pyrolysis, the application prospects, unique advantages of nitrogen-doped carbon materials for catalysis, adsorption and energy storage are introduced, as well as their feasibility in producing nitrogen-containing chemicals (acetonitrile and nitrogen heterocyclic) are reviewed. The future outlook for the application of the pyrolysis of nitrogen-containing biomass, specifically, how to realize the denitrification and upgrading of bio-oil, performance improvement of nitrogen-doped carbon materials, as well as separation and purification of nitrogen-containing chemicals, are addressed.
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•The research status of biomass pyrolysis containing nitrogen is reviewed.•Transformation of N is associated with the formation of N containing components.•Solid products have obvious advantages in catalysis, adsorption and energy storage.•Acetonitrile and N-heterocyclic chemicals can be prepared from nitrogenous biomass.
