Pyrolysis Of Mixed Plastic Waste Research Articles

Catalytic pyrolysis of plastic waste using metal-incorporated activated carbons for monomer recovery and carbon nanotube synthesis

As the global plastic waste crisis intensifies, innovative and sustainable solutions are urgently needed. This study evaluated waste-derived metal-incorporated activated carbon (AC) catalysts for the pyrolysis of mixed plastic waste to generate value-added products, focusing on product yield distribution, composition, hydrogen, and carbon nanotube (CNT) formation. Pyrolysis-catalysis experiments were conducted using a two-stage fixed-bed reactor, wherein the temperature was maintained at 500 °C in first stage (pyrolysis) and varied (500, 600, and 700 °C) in the second stage (catalysis). The tested ACs were incorporated with nickel (Ni-AC), iron (Fe-AC), and zinc (Zn-AC) to assess the impact of metal particles distributed on the carbonaceous support in the second stage. The results from the ACs were compared to those obtained using zeolite (H-ZSM-5), Raw-AC, and non-catalytic runs. The Ni-AC and Fe-AC demonstrated superior catalytic activity, with Ni-AC being more efficient in producing hydrogen (4.24 wt%) and CNTs (34.5 wt%) with diameters of approximately 30 nm, and Fe-AC leading to higher gas yields (68.8 wt%) and CNTs (12.4 wt%) of around 60 nm. In contrast, Zn-AC and Raw-AC presented limited effectiveness, although Raw-AC moderately outperformed Zn-AC with enhanced gas yields and reduced oil/wax yields. The zeolite H-ZSM-5 exhibited the highest gas yields (78 wt%), converting heavy fractions into lighter molecules, notably the monomers ethylene and propylene. These findings provide valuable insights into catalyst selection and optimization for plastic waste pyrolysis processes, with H-ZSM-5 being the most effective catalyst for monomer recovery, and Ni-AC and Fe-AC demonstrating promising results.

Exploring the potential of clay catalysts in catalytic pyrolysis of mixed plastic waste for fuel and energy recovery

Developing low-cost and high-activity catalysts is one of the keys to promoting the catalytic pyrolysis of waste plastics to fuels for plastic recycling. This work studied the effect of clay as the catalyst on mixed plastic pyrolysis for fuel and energy recovery. Four kinds of clay, including nanoclay, montmorillonite, kaolin, and hydrotalcite, were used as catalysts for the pyrolysis of mixed plastic consisted of polyethylene terephthalate, polystyrene, polypropylene, low-density polyethylene, and high-density polyethylene. The product yield and distribution varied with different clay in pyrolysis. The highest yield of oil was 71.0 % when using montmorillonite as the catalyst. While the highest contents of gasoline range hydrocarbons and diesel range hydrocarbons in the oil were achieved when using kaolin and nanoclay, respectively as catalysts. For the gas products, the CO, C2H4, C2H6, C3H6, and C4H10 increased with decreased CO2 in the gaseous products when using clay as catalysts. In general, the mild acidity of clay catalyst was essential to improve the oil yields and the proportion of the gasoline or diesel range fuels in the catalytic pyrolysis of mixed plastic waste.

Integrating PET chemical recycling with pyrolysis of mixed plastic waste via pressureless alkaline depolymerization in a hydrocarbon solvent

This study presents a proof of concept for a technology train that integrates polyethylene terephthalate (PET) recovery from mixed plastic waste and plastic pyrolysis. PET is depolymerized into terephthalic acid (TPA) by hydrolysis using a low volatility oil as medium, which enables (i) low-pressure operation, and (ii) a selective separation and recovery of TPA from the product mix by a simple process of filtration, washing, and precipitation. Full PET conversion and high TPA recovery (>98 %) were achieved at 260 °C.This technology train is demonstrated to be effective for processing mixed waste streams, leading to higher yield and quality of liquid product from thermal pyrolysis when compared with feedstock that has not been pre-treated. Further, the technology could be readily integrated with a plastics pyrolysis process, whereby a by-product from the pyrolysis could be used as the low-volatility oil.

Effects of melt-state shear homogenization on catalytic pyrolysis of mixed plastic waste for feedstock recycling

Although significant effort has been made to develop separation and sorting strategies for recycling mixed plastic waste in recent decades, these processes are often complex, time-consuming, and labor-intensive, and may not be efficient when scaled up. This research aims to evaluate the potential of a homogenization and dechlorination algorithm based on a remelting-restabilization technique to improve the homogeneity of heterogeneous mixed plastic waste through high-shear pulverization. The effectiveness of this method for chemical recycling in the presence of a synthesized clay catalyst was evaluated and modeled using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and kinetic studies. The results showed a significant increase in the homogeneity level of mixed plastic in terms of physical, thermal, and rheological behavior after two runs of extrusions. Additionally, the amount of chlorine in the mixed waste samples was reduced from 18.3 mg/kg to 1.45 mg/kg after thermal treatment at 300 °C for 2 hours. The inclusion of a modified clay catalyst resulted in a reduction in activation energy and initial degradation temperature by approximately 13% and 31%, respectively. The modeled kinetics results showed that the reaction rate in the presence of the catalyst increased at both low and high conversions over a wide range of temperatures. However, an increase in the number of extrusions only increased the degradation rate at high temperatures due to induced thermal history. Py-GC-MS test results revealed that the use of clay catalyst in homogenized samples enhanced the amount of low carbon atom products (C5 to C12) by 7.5% and 27% at 450 °C and 550 °C, respectively. Furthermore, the amount of aromatic product increased after the inclusion of the clay catalyst for both pyrolysis temperatures, including 450 °C and 550 °C.

Techno-economic analysis and life cycle assessment for catalytic fast pyrolysis of mixed plastic waste

This study analyzes catalytic fast pyrolysis as a conversion technology for mixed plastic waste, highlighting key economic and environmental drivers and potential opportunities for process improvements.

Pyrolysis of mixed plastic waste: Predicting the product yields

The predictability of pyrolysis yields and product composition of mixed plastics has been studied. To do so, pyrolysis of virgin polymers (HDPE, LDPE, PP, PS and PET) and eight individual sorting categories from a real waste DKR-350 stream (PE rigid/film, PP rigid/film, PET, PS, multilayer flexibles, and clogged materials) was performed in a batch reactor at 500 °C at laboratory scale. The obtained oil/wax, gas, and solid yields and the composition of oil/wax of those individual feedstocks were used as input of a superposition model to predict the corresponding pyrolysis yields and oil/wax composition of mixed feeds, which were later compared with the experimentally measured product yields from the pyrolysis of those mixed streams. This linear model predicts the oil/wax yield of the mixed streams to a reasonable extent, with a maximum yield deviation (overestimation) of 8 percentage points. However, the presence of significant amounts of PET (above 33 wt%) in the mixed plastic streams negatively impacts the production of the condensable product and promotes the formation of solid products beyond the expected predicted values. Quantification of the type of carbon (aliphatic, aromatic and carbonyl) present in all the oil/wax products was done using 13C NMR spectroscopy. A linear model could also predict the aliphatic carbon yield in the condensable product from plastic waste streams with high accuracy (maximum yield difference of 6 percentage points). However, the aromatic carbon yield could not be predicted, probably due to the observed behavior of PET, which interacts with other polymers to promote solid product formation.

Chemical recycling of mixed plastic waste via catalytic pyrolysis

The recovery rate of plastic waste has increased over recent years, however, there are still a large amounts of waste disposed in landfills or littered in the environment. As a result, advanced thermochemical technologies, such as catalytic pyrolysis, have become a promising approach to solve plastic waste management issues. This work aims to assess inexpensive catalysts derived from waste biomass for pyrolysis of mixed plastic waste for high-value products. Conventional thermal pyrolysis at high temperatures, i.e. 800 °C only increased the gas yield (up to 52 wt% from the 32 wt% obtained at 500 °C) but had no significant effect on the proportion of individual compounds in the gas fraction. A two-stage catalytic pyrolysis of mixed plastic waste at 600 °C (first stage) combined with biochar catalyst held isothermally at 800 °C (second stage) significantly enhanced the cracking process compared to thermal pyrolysis. In presence of the biochar catalyst, the gas yield increased up to 85 wt% mainly by an increase in the yield of hydrogen (from 0.2 wt% to 3.3 wt%) and methane (from 1.4 wt% to 55 wt%). Biochar also removed all the benzoic acid in the wax fraction. Therefore, the use of biochar derived from biomass waste as a catalyst opens-up an opportunity to develop a sustainable and efficient process to valorise waste.

Effect of aluminum leaching pretreatment on catalytic pyrolysis of metallised food packaging plastics and its linear and nonlinear kinetic behaviour

This research aims to study the effect of aluminum (Al) leaching pre-treatment on the catalytic pyrolysis of metallised food packaging plastics waste (MFPW). The experiments started with removal of Al from MFPW using leaching process to prepare Al-free mixed plastic waste (MPW). The catalytic pyrolysis of MPW over ZSM-5 zeolite catalyst was carried out using thermogravimetric (TG) analysis coupled with FTIR, while GC–MS was used to observe the compounds of the volatile products. The catalytic pyrolysis kinetic behaviour of MPW was studied using the linear and nonlinear isoconversional approaches. The elemental and proximate results showed that MPW is very rich in carbon elements (79 %) and volatile content (99 %). The TG results showed that MPW and ZSM/MPW were fully decomposed in the range of 376–496 °C without any presence of char. Based on TG-FTIR analysis, methane and carboxylic acid residue were the main groups of the synthesized volatile products, whereas nitrous oxide, 1-Butanol, 1-Propene, acetic acid, and formic acid were the major GC compounds. In case of ZSM/MPW, carbon dioxide and acetic acid were the major GC compounds at 5–25 °C/min, triphenylphosphine oxide and Phosphine oxide at 30 °C/min. The kinetic analysis showed that when the activation energies are located in the range 287–297 kJ/mol (MPW) and 153–187 kJ/mol (ZSM/MPW) and KAS, Vyazovkin, and Cai methods are the most suitable models to study pyrolysis kinetic of MPW with R2 > 89. Based on that, leaching and catalytic pyrolysis processes are a highly suggested technology that can be used to convert MFPW into high-added energy and chemical products.

Pyrolysis of mixed plastic waste (DKR-350): Effect of washing pre-treatment and fate of chlorine

Pyrolysis of a post-consumer plastic waste stream (DKR-350) has been performed at a laboratory scale in a fixed-bed reactor at 500 °C. DKR-350 is a complex mixture of post-consumer plastics comprising polyethylene, polypropylene, polystyrene, polyethylene terephthalate, clogged materials, multilayer flexibles, together with considerable amounts of biogenic and inorganic residues and halogens. The influence of different washing procedures on feedstock composition and pyrolysis product yields was investigated. Washing effectively lowers the biogenic, inorganic and halogen contents in DKR-350, though does not affect the yield of the desired oil/wax (66 to 69 wt%). 27% of the oil/wax lies in the boiling point range of naphtha and gasoline (< 200 °C). During pyrolysis, the oxygen content of the oil/wax is reduced to 8–14 wt%, compared to 10–16 wt% in the feed. Chlorine analysis revealed that most of the chlorine present in the feed is removed by washing. Nevertheless, the concentration of chlorine in the oil/wax is still high (>150 ppm), showing the presence of recalcitrant organochlorides in the feed. Thus, post-treatment is still required to upgrade it to feedstock for the production of fuels and/or chemicals.

Conversion of plastic waste into fuel oil using zeolite catalysts in a bench-scale pyrolysis reactor.

Catalytic pyrolysis of mixed plastic waste to fuel oil experiment was tested with ZSM-5 zeolite (commercial and synthesized) catalysts along with other catalysts. The ZSM-5 zeolite catalyst was effectively produced using a hydrothermal technique via metakaolin as an alumina source. The catalytic pyrolysis of different types of plastic (single and multilayer) wastes in the presence of various catalysts was tested with a bench-scale pyrolysis setup with 2 kg per batch capacity. Polyolefin based plastics (low-density polyethylene, high-density polyethylene, and polypropylene), multilayer plastics such as biaxial oriented polypropylene (BOPP), metalized biaxial oriented polypropylene layers (MET BOPP), polyethylene terephthalate (PET), metalized polyethylene terephthalate (MET/PET), polyethylene terephthalate combined polyethylene (PET/PE), and mixed plastic waste collected from the corporation sorting center were pyrolyzed in a batch pyrolysis system with 1 kg feed to determine the oil, gas and char distributions. The performances of commercial ZSM-5 and lab synthesized ZSM-5 catalysts were compared for the pyrolysis of non-recyclable plastic wastes. Other commercial catalysts including mordenite and gamma alumina were also tested for pyrolysis experiments. The gross calorific value of oil obtained from different combinations of multilayer packaging waste varied between 10 789–7156 kcal kg−1. BOPP-based plastic waste gave higher oil yield and calorific value than PET-based plastic waste. Sulfur content present in the oil from different plastic wastes was measured below the detection limit. The synthesized ZSM-5 zeolite catalyst produced a maximum oil output of 70% and corresponding gas and char of 16% and 14% for LDPE plastic. The strong acidic properties and microporous crystalline structure of the synthesized ZSM-5 catalyst enables increased cracking and isomerization, leading to an increased breakup of larger molecules to smaller molecules forming more oil yield in the pyrolysis experiments. Residual char analysis showed the maximum percentage of carbon with heavy metal concentrations (mg kg−1) in the range of viz., chromium (15.36–97.48), aluminium (1.03–2.54), cobalt (1.0–5.85), copper (115.37–213.59), lead (89.12–217.3), and nickel (21.05–175.41), respectively.

Understanding the Dechlorination of Chlorinated Hydrocarbons in the Pyrolysis of Mixed Plastics

The dechlorination of chlorine containing hydrocarbons in pyrolysis vapor is poorly understood. In order to shed new light on the dechlorination mechanism, a model mixture composed of iso-octane doped with 2-chlorobutane, 2-chloroethylbenzene, and chlorobenzene was used to study the dechlorination of chlorinated hydrocarbons by alkali adsorption. These three chlorinated hydrocarbons were selected as they can be typically produced from the pyrolysis of mixed plastic waste containing polyvinyl chloride (PVC). The mixture is pumped continuously through a Na₂CO₃ or CaCO₃/alumina bed, and GC-MS is used to identify the dechlorination products and to follow the dechlorination reactions. When chlorine is bonded to an aliphatic carbon with an adjacent aliphatic hydrogen, the chlorinated compound first undergoes a dehydrochlorination reaction to form HCl and olefins, and subsequently the HCl is reacted with the alkali in the absorbents. In our experiments, 2-chlorobutane is converted to 2-butene, and 2-chloroethylbenzene is converted to styrene. The formation of HCl and subsequent reaction with alkali components in the absorbent is verified by IR spectroscopy and XRD. In the presence of an alkali, the aliphatic chlorinated hydrocarbons underwent dechlorination at a temperature of 180 °C. The removal of chlorine from aromatic chlorinated compounds operates in a different mechanism, in which the C–Cl bond scission is promoted significantly by the presence of an alumina and hydrocarbon medium. It was found that chlorobenzene undergoes dechlorination forming phenol and benzene.

Life cycle environmental impacts of chemical recycling via pyrolysis of mixed plastic waste in comparison with mechanical recycling and energy recovery

A large portion of plastic produced each year is used to make single-use packaging and other short-lived consumer products that are discarded quickly, creating significant amounts of waste. It is important that such waste be managed appropriately in line with circular-economy principles. One option for managing plastic waste is chemical recycling via pyrolysis, which can convert it back into chemical feedstock that can then be used to manufacture virgin-quality polymers. However, given that this is an emerging technology not yet used widely in practice, it is not clear if pyrolysis of waste plastics is sustainable on a life cycle basis and how it compares to other plastics waste management options as well as to the production of virgin plastics. Therefore, this study uses life cycle assessment (LCA) to compare the environmental impacts of chemical recycling of mixed plastic waste (MPW) via pyrolysis with the established waste management alternatives: mechanical recycling and energy recovery. Three LCA studies have been carried out under three perspectives: waste, product and a combination of the two. To ensure robust comparisons, the impacts have been estimated using two impact assessment methods: Environmental footprint and ReCiPe. The results suggest that chemical recycling via pyrolysis has a 50% lower climate change impact and life cycle energy use than the energy recovery option. The climate change impact and energy use of pyrolysis and mechanical recycling of MPW are similar if the quality of the recyclate is taken into account. Furthermore, MPW recycled by pyrolysis has a significantly lower climate change impact (−0.45 vs 1.89 t CO2 eq./t plastic) than the equivalent made from virgin fossil resources. However, pyrolysis has significantly higher other impacts than mechanical recycling, energy recovery and production of virgin plastics. Sensitivity analyses show that some assumptions have notable effects on the results, including the assumed geographical region and its energy mix, carbon conversion efficiency of pyrolysis and recyclate quality. These results will be of interest to the chemical, plastics and waste industries, as well as to policy makers.

Economic assessment of a 40,000 t/y mixed plastic waste pyrolysis plant using direct heat treatment with molten metal: A case study of a plant located in Belgium

Pyrolysis has been identified as an ideal process to recycle mixed plastic waste (MPW). This study investigates the economics of a 40,000 t/y MPW pyrolysis process, called PlastPyro, located in Belgium, to an accuracy of ±15% i.e. “Definite Estimate”. The process uses molten metal in a direct heat treatment process to pyrolyse the waste. An internal rate of return (IRR) of 20% strongly indicates that a 40,000 t/y PlastPyro plant is financially attractive for private investors. The capital expenditure (CAPEX) is estimated to be €20.1 m or €26.1 m if the cost of capital is included. The operating expenditures (OPEX) of the plant are estimated €3.4 m per year. The sensitivity analysis shows six main variables having major impacts on the financial returns of a PlastPyro plant: (1) the addressable volume and quality of plastic waste, (2) the feedstock costs, (3) the capital and operating expenditures, (4) the revenues from the sale of the produced pyrolysis oil (P-oil), (5) the tipping fees and (6) the potential to co-locate a PlastPyro plant with a waste plastic sorting facility. For example, the 15-year low P-oil revenue price of €210/t results in an IRR of 20%; but on the 6th of March 2020 the P-oil price may have achieved €227/t, resulting in an IRR of 37%. The paper also shows that a reliable supply of MPW is available, and that reliable, accessible markets for the P-oil are available. Finally, cost estimates should state their accuracy and usually factorial cost estimates are not accurate enough to state the IRR.

Economic performance of pyrolysis of mixed plastic waste: Open-loop versus closed-loop recycling

In recent decades new recycling technologies for mixed plastic waste have emerged. In pyrolysis, the polymer chains are thermally broken (pyrolyzed) to obtain hydrocarbon materials of different molecular weights such as naphtha, oil or waxes, whose yields can be controlled by varying the reaction parameters. Naphtha represents a closed-loop recycling process as it is a feedstock for (poly)olefins; while the co-production of waxes, having several applications in e.g. the construction industry, exemplifies an open-loop recycling process. This paper compares the economic performance of the pyrolysis of mixed polyolefin waste in a closed-loop and open-loop scheme, including a probabilistic approach to the most important variables. From an economic perspective, open-loop pyrolysis as presented outperforms closed-loop recycling, due to the high prices of wax. However, the results present a high dispersion caused by the volatility of the prices of crude oil and its derivates. Considering the current oil price projections, our case study analysis showed that for open-loop recycling there is a future probability of almost a 98% of observing positive results and around 57% of probability in the case of closed-loop recycling, under the assumptions made. Yet, in a future scenario where decarbonized electricity would decrease oil prices, the probability of a positive outcome reduces to 57% for the open-loop case and to less than 8% in the case of closed-loop recycling. To make these pathways attractive to investors, the nameplate capacity should be at least 70 kt/year for open-loop recycling and 115 kt/year for closed-loop recycling. A 120 kt/year plant should operate minimally at 80% of its capacity for open-loop recycling, while closed-loop recycling would demand running close to maximum capacity. Security of feedstock supply therefore is required.

Molten Solar Salt Pyrolysis of Mixed Plastic Waste: Process Simulation and Technoeconomic Evaluation

A process simulation and techno-economic evaluation of using molten solar salt as the heating medium for pyrolysis of mixed plastic waste (MPW) containing poly(vinyl chloride) (PVC) was performed. ...

Waste plastic to pyrolytic oil and its utilization in CI engine: Performance analysis and combustion characteristics

For application of pure plastic pyrolytic oil (PPO) several modifications in the engine is required which rejects the utilization of the existing engines while a blend of conventional fuel and PPO can be used with a slight change in engine without having a high impact on engine performance and hence the blends are preferred over the utilization of PPO as crude oil for diesel engines. In this study, the non-catalytic pyrolysis of mixed plastic waste at a temperature of 450 °C is done to obtain high-grade pyrolytic oil having a composition similar to petroleum fuels such as gasoline and diesel. Physical properties of the PPO were analysed, and the compound analysis was done with GC–MS. Further FTIR of PPO and diesel were analysed and compared. Five different ratios of 10, 20, 30, 40 and 50% PPO with diesel in blends were utilized as a fuel in a diesel engine to determine the engine performance and characteristics. The higher presence of PPO in blend increases the brake thermal efficiency (BTE) and reduces specific fuel consumption (SFC) with an increase in load as reported. The presence of PPO results in high heat release and delayed ignition resulting in high in-cylinder pressure. Further high amount of oxygenated compounds in PPO helps in reducing the emission from the combustion. The utilization of PPO with diesel upto 50% in the blend can be used in diesel engines with a slight increase in emission of CO at higher loads.

Plastic waste to fuel via pyrolysis: A key way to solving the severe plastic waste problem in Ghana

The accumulation of plastic waste on the globe, with its harmful environmental impact is on the rise. Development of an efficient conversional method for heterogeneous plastic waste streams would not only provide a solution to this problem, but also, provide a boost to local economies. This study, seeks to exploit the possibility of employing pyrolysis as a means of converting a mixture of plastic waste materials into a resource; to recover crude fuel oil from the waste and also reduce the environmental impacts. Pyrolysis was conducted in a fixed bed reactor at 350 °C with nitrogen gas flow of 200 ml/min for 2 h, 40 min cracking time. The resulted crude product was analyzed by various analytical methods such as FT-IR, GC-MS, and Kinematic Viscosity. The results from the Fourier transform infrared spectroscopy (FT-IR) analysis shows that the fuel oil produced is made up of 21 functional groups which is a blend of aliphatic and aromatic groups of compounds; aliphatic compounds are the most abundant. Also according to the GC-MS results obtained, the fuel oil contains substances that are within the diesel fuel range (C12-C24), with behenic alcohol as the highest peaked compound. The crude fuel oil has a kinematic viscosity of 1.036 mm2 s−1, which decreases with increasing temperature. The results show that the crude fuel oil obtained has the possibility to be used as an alternative fuel for wide range of purposes in the future. In this regard, pyrolysis of mixed plastic waste studied here presents an efficient, clean and effective means of removing plastic debris from the environment. Plastic waste isn’t the whole problem, how we handle it also count. Thus the responsibility is on us to be smart on how we handle plastic; as pollution, or as an economical resource.

Upgrading of chlorinated oils coming from pyrolysis of plastic waste

The objective of this paper is the upgrading of chlorinated oils coming from the pyrolysis of mixed plastic waste, in order to use them as fuel or feedstock for refineries. Two different samples of pyrolysis oils have been thermally and catalytically cracked in a 300mL autoclave at 325°C and the auto-generated pressure. Thermal cracking converts the plastic pyrolysis heavy oils into light liquid fractions which are only composed of alkanes and aromatics. These light fractions present a very low quantity of chlorine compared to the initial oils and resemble gasoline and diesel-like products. Besides, a gaseous fraction rich in methane and with very high heating value is also produced, together with a fuel-like viscous product which remains in the autoclave. The relative proportions of each of these three fractions depend on the nature of the initial oils. Red Mud has proved to be a dehydrochlorination and cracking catalyst, since it gives rise to higher quantity of gases and light liquid fractions with a very low chlorine content (<0.1wt.%). Therefore, dechlorinated light oils can be obtained by Red Mud low temperature catalytic cracking of plastic derived chlorinated pyrolysis oils.

Pyrolysis of Polyvinyl Chloride (PVC)-Containing Mixed Plastic Wastes for Recovery of Hydrocarbons

The pyrolysis of mixed plastic waste (high-density polyethylene, polypropylene, polystyrene, and polyvinyl chloride) using a long residence time (25 min) in a horizontal tube reactor at 530 °C has been investigated. The reactor was fitted with atmospheric and vacuum distillation columns, so that the pyrolysis products could be separated into heavy oil, light oil, gasoline, and gases. The effect of the polyvinyl chloride (PVC) concentration on the properties of products was investigated. Products were characterized using gas chromatography, infrared spectroscopy, and energy-dispersive X-ray spectroscopy, whereas some other standardized methods were used to determine the main properties of hydrocarbons. Results show that the mixed plastic waste samples could be converted into gases, gasoline, and light oil with yields of 36.9−59.6% depending upon the composition of feed polymers, and the conversion of decomposition is significantly increased with an increasing concentration of PVC. It was found that product...

Interaction of Plastics in Mixed-Plastics Pyrolysis

The pyrolysis of mixed-plastic waste has been proposed as a means of recycling to produce petrochemical feedstock. The interaction of the main plastic types in plastic mixtures is significant in predicting the likely yield and composition of products from different plastic mixtures. The six main plastics in municipal solid waste are high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), poly(vinyl chloride) (PVC), and poly(ethylene terephthalate) (PET). Each of the plastics was pyrolyzed individually in a fixed-bed reactor heated at 25 °C min-1 to a final temperature of 700 °C. Polystyrene was then mixed with each of the other five plastics in a ratio of 1:1 and pyrolyzed in the fixed-bed reactor under the same pyrolysis conditions. The yield and composition of the derived oil/wax and gases was determined. The main gases produced from the individual plastics were hydrogen, methane, ethane, ethene, propane, propene, butane, and butene and for the PET plastic carbon dioxide and carbon monoxide. Hydrogen chloride was also produced with PVC. Analysis of the oil/wax showed that the polyalkene plastics, HDPE, LDPE, and PP, gave a mainly aliphatic composition consisting of a series of alkanes, alkenes, and alkadienes. PVC gave a mainly aromatic oil, and PS and PET, which have aromatic groups in their structures, also showed a more aromatic composition. There was a higher gas yield from the mixtures of the plastics with PS than would be expected from the pyrolysis of the individual plastics, coupled with a reduction in the oil/wax phase. The average molecular weight of the oil/wax from the mixed plastics was less than expected from the individual molecular weights. Compositional analysis of the oil/wax showed that changes in the concentration of aromatic hydrocarbons and polycyclic aromatic hydrocarbons were produced with the mixture compared to that expected from the individual plastics.