Catalytic Fast Pyrolysis of Poly (Ethylene Terephthalate) (PET) with Zeolite and Nickel Chloride

Polyethylene terephthalate conversion into liquid fuel by its co-pyrolysis with low- and high-density polyethylene employing scrape aluminium as catalyst

The co-pyrolysis of polyethylene terephthalate (PET) with low-density polyethylene (LDPE) and high-density polyethylene (HDPE) was carried out in a batch steel pyrolyzer in order to convert the PET into pyrolysis oil as its pyrolysis alone resulted in wax and gases. The study also aimed to increase the aromatic content of pyrolysis oil by the interaction of degradation fragments of linear chains of LDPE and HDPE with the benzene ring of PET during the pyrolysis. The reaction conditions were optimized for a higher yield of pyrolysis oil which were found to be 500 °C pyrolysis temperature with a heating rate of 0.5 °Cs-1, 1 h reaction time and 20 g of the initial mass of polymer mixture having 20% PET, 40% LDPE and 40% HDPE. Waste aluminium particles were applied as an economical catalyst in the process. The thermal co-pyrolysis yielded 8% pyrolysis oil, 32.3 wax, 39.7 wt% gases and 20% coke while the catalytic co-pyrolysis produced 30.2% pyrolysis oil, 4.2% wax, 53.6 wt% gases and 12% coke. The fractional distillation of catalytic oil resulted in 46% gasoline range oil, 31% kerosene range oil and 23% diesel range oil. These fractions resembled the standard fuels in terms of their fuel properties as well as FT-IR spectra. The GC-MS analysis revealed that the catalytic co-pyrolysis favoured the formation of relatively short-chain hydrocarbons with olefins and isoparaffins as major components while the thermal co-pyrolysis formed long-chain paraffins. The naphthenes and aromatics were also found in higher amounts in the catalytic oil compared with the thermal oil.

A review on value-addition to plastic waste towards achieving a circular economy

Plastic and mixed plastic waste (PW) has received increased worldwide attention owing to its huge rate of production, high persistency in the environment, and unsustainable waste management practices. Therefore, sustainable PW management and upcycling approaches are imperative to achieve the objectives of the United Nations Sustainable Development Goals. Numerous recent studies have shown the application and feasibility of various PW conversion techniques to produce materials with better economic value. Within this framework, the current review provides an in-depth analysis of cutting-edge thermochemical technologies such as pyrolysis, gasification, carbonization, and photocatalysis that can be used to value plastic and mixed PW in order to produce energy and industrial chemicals. Additionally, a thorough examination of the environmental impacts of contemporary PW upcycling techniques and their commercial feasibility through life cycle assessment (LCA) and techno-economical assessment are provided in this review. Finally, this review emphasizes the opportunities and challenges accompanying with existing PW upcycling techniques and deliver recommendations for future research works.

Application of Infrared Pyrolysis and Chemical Post-Activation in the Conversion of Polyethylene Terephthalate Waste into Porous Carbons for Water Purification

In this study, we compared the conversion of polyethylene terephthalate (PET) into porous carbons for water purification using pyrolysis and post-activation with KOH. Pyrolysis was conducted at 400-850 °C, followed by KOH activation at 850 °C for samples pyrolyzed at 400, 650, and 850 °C. Both pyrolyzed and post-activated carbons showed high specific surface areas, up to 504.2 and 617.7 m2 g-1, respectively. As the pyrolysis temperature increases, the crystallite size of the graphite phase rises simultaneously with a decrease in specific surface area. This phenomenon significantly influences the final specific surface area values of the activated samples. Despite their relatively high specific surface areas, pyrolyzed PET-derived carbons prove unsuitable as adsorbents for purifying aqueous media from methylene blue dye. A sample pyrolyzed at 650 °C, with a surface area of 504.2 m2 g-1, exhibited a maximum adsorption value of only 20.4 mg g-1. We propose that the pyrolyzed samples have a surface coating of amorphous carbon poor in oxygen groups, impeding the diffusion of dye molecules. Conversely, post-activated samples emerge as promising adsorbents, exhibiting a maximum adsorption capacity of up to 127.7 mg g-1. This suggests their potential for efficient dye removal in water purification applications.

Plastic waste as pyrolysis feedstock for plastic oil production: A review

Turning plastic waste into plastic oil by pyrolysis is one of the promising techniques to eradicate plastic waste pollution and accelerate the circular economy of plastic materials. Plastic waste is an attractive pyrolysis feedstock for plastic oil production owing to its favorable chemical properties of proximate analysis, ultimate analysis, and heating value other than its abundant availability. Despite the exponential growth of scientific output from 2015 to 2022, a vast majority of the current review articles cover the pyrolysis of plastic waste into a series of fuels and value-added products, and up-to-date reviews exclusively on plastic oil production from pyrolysis are relatively scarce. In light of this void in the current review articles, this review attempts to provide an up-to-date overview of plastic waste as pyrolysis feedstock for plastic oil production. A particular emphasis is placed on the common types of plastic as primary sources of plastic pollution, the characteristics (proximate analysis, ultimate analysis, hydrogen/carbon ratio, heating value, and degradation temperature) of various plastic wastes and their potential as pyrolysis feedstock, and the pyrolysis systems (reactor type and heating method) and conditions (temperature, heating rate, residence time, pressure, particle size, reaction atmosphere, catalyst and its operation modes, and single and mixed plastic wastes) used in plastic waste pyrolysis for plastic oil production. The characteristics of plastic oil from pyrolysis in terms of physical properties and chemical composition are also outlined and discussed. The major challenges and future prospects for the large-scale production of plastic oil from pyrolysis are also addressed.

Depolymerization of plastics by means of electrified spatiotemporal heating

Depolymerization is a promising strategy for recycling waste plastic into constituent monomers for subsequent repolymerization1. However, many commodity plastics cannot be selectively depolymerized using conventional thermochemical approaches, as it is difficult to control the reaction progress and pathway. Although catalysts can improve the selectivity, they are susceptible to performance degradation2. Here we present a catalyst-free, far-from-equilibrium thermochemical depolymerization method that can generate monomers from commodity plastics (polypropylene (PP) and poly(ethylene terephthalate) (PET)) by means of pyrolysis. This selective depolymerization process is realized by two features: (1) a spatial temperature gradient and (2) a temporal heating profile. The spatial temperature gradient is achieved using a bilayer structure of porous carbon felt, in which the top electrically heated layer generates and conducts heat down to the underlying reactor layer and plastic. The resulting temperature gradient promotes continuous melting, wicking, vaporization and reaction of the plastic as it encounters the increasing temperature traversing the bilayer, enabling a high degree of depolymerization. Meanwhile, pulsing the electrical current through the top heater layer generates a temporal heating profile that features periodic high peak temperatures (for example, about 600 °C) to enable depolymerization, yet the transient heating duration (for example, 0.11 s) can suppress unwanted side reactions. Using this approach, we depolymerized PP and PET to their monomers with yields of about 36% and about 43%, respectively. Overall, this electrified spatiotemporal heating (STH) approach potentially offers a solution to the global plastic waste problem.

Catalytic Steam-Assisted Pyrolysis of PET for the Upgrading of TPA

Compared with conventional pyrolysis, steam-assisted pyrolysis of polyethylene terephthalate (PET) can effectively eliminate char and upgrade terephthalic acid (TPA). However, during steam-assisted pyrolysis of PET, the degree of cracking still varies greatly, and while some of the product is excessively cracked to gas, the other part is still insufficiently cracked. In addition, these two types of products seriously affect the yield and purity of TPA. To further enhance the TPA, an attempt was made to reduce these impurities simultaneously by synergistic catalysis among the different components of the metal-acid catalyst. Through a series of experiments, Pt@Hzsm-5 was screened as the optimal catalyst. In the catalytic steam-assisted pyrolysis of PET, the optimum reaction temperature decreased to 400 °C, the calculated yield of TPA increased to 98.23 wt%, and the purity increased to 92.2%. The Pt@Hzsm-5 could be recycled three times with no significant decrease in the obtained yield of TPA. The catalytic mechanism of the Pt@Hzsm-5 was investigated through the analysis of the products and isotope tracing experiments. The Pt catalyzed the hydrogen transfer reaction between the water molecules and PET molecules, which inhibited the excessive cracking of TPA by improving the hydrogen transfer efficiency, reduced the generation of gaseous products, and improved the calculated yield of TPA. In contrast, the Hzsm-5 catalyzed the reaction of monovinyl ester cracking to TPA, effectively reducing the impurities in the solid product, increasing the olefin yield, and improving the purity of TPA. This discovery not only clarifies the synergistic catalytic effect of the Pt@Hzsm-5 in the steam-assisted pyrolysis of the PET reaction but also lays the foundation for further screening of other inexpensive metal-acid catalysts. This is of great significance to realize the industrial application of TPA preparation by PET pyrolysis.

Analysis of Fuel Alternative Products Obtained by the Pyrolysis of Diverse Types of Plastic Materials Isolated from a Dumpsite Origin in Pakistan

The current energy crisis and waste management problems have compelled people to find alternatives to conventional non-renewable fuels and utilize waste to recover energy. Pyrolysis of plastics, which make up a considerable portion of municipal and industrial waste, has emerged as a feasible resolution to both satisfy our energy needs and mitigate the issue of plastic waste. This study was therefore conducted to find a solution for plastic waste management problems, as well as to find an alternative to mitigate the current energy crisis. Pyrolysis of five of the most commonly used plastics, polyethylene terephthalate (PET), high- and low-density polyethylene (HDPE, LDPE), polypropylene (PP), and polystyrene (PS), was executed in a pyrolytic reactor designed utilizing a cylindrical shaped stainless steel container with pressure and temperature gauges and a condenser to cool down the hydrocarbons produced. The liquid products collected were highly flammable and their chemical properties revealed them as fuel alternatives. Among them, the highest yield of fuel conversion (82%) was observed for HDPE followed by PP, PS, LDPE, PS, and PET (61.8%, 58.0%, 50.0%, and 11.0%, respectively). The calorific values of the products, 46.2, 46.2, 45.9, 42.8 and 42.4 MJ/kg for LPDE, PP, HPDE, PS, and PET, respectively, were comparable to those of diesel and gasoline. Spectroscopic and chromatographic analysis proved the presence of alkanes and alkenes with carbon number ranges of C₉-C₁₅, C₉-C₂₄, C₁₀-C₂₁, C₁₀-C₂₈, and C₉-C₁₇ for PP, PET, HDPE, LDPE, and PS, respectively. If implemented, the study will prove to be beneficial and contribute to mitigating the major energy and environmental issues of developing countries, as well as enhance entrepreneurship opportunities by replicating the process at small-scale and industrial levels.

An Overview on Co-Pyrolysis of Biodegradable and Non-Biodegradable Wastes

Continuous urbanization and modernization have increased the burning of fossil fuels to meet energy needs across the globe, emanating environmental pollution and depleting fossil fuels. Therefore, a shift towards sustainable and renewable energy is necessary. Several techniques to exploit biomass to yield energy are trending, with pyrolysis one of them. Usually, a single feedstock is employed in pyrolysis for anoxygenic generation of biochar together with bio-oil at elevated temperatures (350–600 °C). Bio-oil produced through pyrolysis can be upgraded to crude oil after some modification. However, these modifications of bio-oil are one of the major drawbacks for its large-scale adoption, as upgradation increases the overall cost. Therefore, in recent years the scientific community has been researching co-pyrolysis technology that involves the pyrolysis of lignocellulosic biomass waste with non-biodegradable waste. Co-pyrolysis reduces the need for post-modification of bio-oil, unlike pyrolysis of a single feedstock. This review article discusses the recent advancements and technological challenges in waste biomass co-pyrolysis, the mechanism of co-pyrolysis, and factors that affect co-pyrolysis. The current study critically analyzes different recent research articles presented in databases such as PubMed, MDPI, ScienceDirect, Springer, etc. Hence, this review is one-of-a-kind in that it attempts to explain each and every aspect of the co-pyrolysis process and its current progress in the scientific field. Consequently, this review also compiles the remarkable achievements in co-pyrolysis and recommendations for the future.

Pyrolysis Combined with the Dry Reforming of Waste Plastics as a Potential Method for Resource Recovery—A Review of Process Parameters and Catalysts

Emissions of greenhouse gases and growing amounts of waste plastic are serious environmental threats that need urgent attention. The current methods dedicated to waste plastic recycling are still insufficient and it is necessary to search for new technologies for waste plastic management. The pyrolysis-catalytic dry reforming (PCDR) of waste plastic is a promising pro-environmental way employed for the reduction of both CO2 and waste plastic remains. PCDR allows for resource recovery, converting carbon dioxide and waste plastics into synthetic gas. The development and optimization of this technology for the high yield of high-quality synthesis gas generation requires the full understanding of the complex influence of the process parameters on efficiency and selectivity. In this regard, this review summarizes the recent findings in the field. The effect of process parameters as well as the type of catalyst and feedstock are reviewed and discussed.

Catalytic co-pyrolysis of LDPE and PET with HZSM-5, H-beta, and HY: experiments and kinetic modelling

This study determines interaction effects and conducts kinetic modeling for catalytic co-pyrolysis of LDPE and PET with multiple zeolite frameworks.

Recent Trends in the Pyrolysis of Non-Degradable Waste Plastics

Waste plastics are non-degradable constituents that can stay in the environment for centuries. Their large land space consumption is unsafe to humans and animals. Concomitantly, the continuous engineering of plastics, which causes depletion of petroleum, poses another problem since they are petroleum-based materials. Therefore, energy recovering trough pyrolysis is an innovative and sustainable solution since it can be practiced without liberating toxic gases into the atmosphere. The most commonly used plastics, such as HDPE, LDPE (high- and low-density polyethylene), PP (polypropylene), PS (polystyrene), and, to some extent, PC (polycarbonate), PVC (polyvinyl chloride), and PET (polyethylene terephthalate), are used for fuel oil recovery through this process. The oils which are generated from the wastes showed caloric values almost comparable with conventional fuels. The main aim of the present review is to highlight and summarize the trends of thermal and catalytic pyrolysis of waste plastic into valuable fuel products through manipulating the operational parameters that influence the quality or quantity of the recovered results. The properties and product distribution of the pyrolytic fuels and the depolymerization reaction mechanisms of each plastic and their byproduct composition are also discussed.

Utilization of liquid product through pyrolysis of LDPE and C/LDPE as commercial wax

In this study, pyrolysis of low-density polyethylene (LDPE) and LDPE with aluminum (C/LDPE) wastes was carried out with different heating rates (5, 10, 20 °C/min) at different temperatures (400, 600, 800 °C). Product yields of LDPE and C/LDPE wastes were compared, and optimum liquid products were analyzed to utilize as commercial waxes for future use. The properties of pyrolyzed wastes was investigated with proximate, elemental analysis, and TGA. The as-produced liquid from pyrolysis of wastes was characterized by different characteristic tools, such as elemental analyses, GC-MS analyses, 1H-NMR tests, FT-IR spectra, the density, melting point, and carbon residue to compare commercial waxes. As a result of pyrolysis, the highest liquid product yield was achieved at 800 °C with 5 °C/min heating rate (85.87%) and at 600 °C with 5 °C/min heating rate (71.3%) for LDPE and C/LDPE, respectively. The results indicated that the derived liquid products are similar to commercial heavy wax.

Upcycling of PET waste into methane-rich gas and hierarchical porous carbon for high-performance supercapacitor by autogenic pressure pyrolysis and activation

The explosive growth of polyethylene terephthalate (PET) wastes has brought serious pollution to the environment. Here, PET waste was upcycled into methane-rich pyrolysis gas and carbon material for energy storage through autogenic pressure pyrolysis and post-activation. The pyrolysis gas contained 34.58 ± 0.23 vol% CH₄. After CO₂ removal, the high caloric value of the pyrolysis gas could reach 29.2 MJ m^-3, which could be used as a substitute natural gas. Pyrolytic carbon was further activated by KOH and ZnCl₂. KOH-activated carbon (AC-K) obtained a hierarchical porous structure, a high specific surface area of 2683 m² g^-1 and abundant surface functional groups. Working as supercapacitor electrodes, AC-K exhibited an outstanding specific capacitance of 325 F g^-1 at a current density of 0.5 A g^-1. After 5000 charge-discharge cycles, AC-K still retained 91.86% of the initial specific capacitance. This study provides a sustainable way to control plastic-derived pollution and alleviate the energy crisis.

Potential Chemicals from Plastic Wastes

Plastic is referred to as a “material of every application”. From the packaging and automotive industries to the medical apparatus and computer electronics sectors, plastic materials are fulfilling demands efficiently. These plastics usually end up in landfills and incinerators, creating plastic waste pollution. According to the Environmental Protection Agency (EPA), in 2015, 9.1% of the plastic materials generated in the U.S. municipal solid waste stream was recycled, 15.5% was combusted for energy, and 75.4% was sent to landfills. If we can produce high-value chemicals from plastic wastes, a range of various product portfolios can be created. This will help to transform chemical industries, especially the petrochemical and plastic sectors. In turn, we can manage plastic waste pollution, reduce the consumption of virgin petroleum, and protect human health and the environment. This review provides a description of chemicals that can be produced from different plastic wastes and the research challenges involved in plastic waste to chemical production. This review also provides a brief overview of the state-of-the-art processes to help future system designers in the plastic waste to chemicals area.

Strategic Possibility Routes of Recycled PET

The polyethylene terephthalate (PET) application has many challenges and potential due to its sustainability. The conventional PET degradation was developed for several technologies to get higher yield products of ethylene glycol, bis(2-hydroxyethyl terephthalate) and terephthalic acid. The chemical recycling of PET is reviewed, such as pyrolysis, hydrolysis, methanolysis, glycolysis, ionic-liquid, phase-transfer catalysis and combination of glycolysis-hydrolysis, glycolysis-methanolysis and methanolysis-hydrolysis. Furthermore, the reaction kinetics and reaction conditions were investigated both theoretically and experimentally. The recycling of PET is to solve environmental problems and find another source of raw material for petrochemical products and energy.