Catalytic pyrolysis of mechanically non-recyclable waste plastics mixture: Kinetics and pyrolysis in laboratory-scale reactor

A solvent-targeted recovery and precipitation scheme for the recycling of up to ten polymers from post-industrial mixed plastic waste

Solvent-Targeted Recovery and Precipitation (STRAPTM) separates polymers within a plastic waste stream by selective dissolution. In this work, the STRAP framework, which combines computational modeling and experiments, was applied to develop a series of steps to separate up to 10 polymers from post-industrial mixed plastic waste (MPW) and the main components recovered were LDPE, HDPE, and PET. The STRAP steps were initially demonstrated with a physical polymer mixture containing LDPE, HDPE, PS, PVC, EVOH, PET, PP, PA6, PA66, and PA66/6, in which recoveries of 89% or higher were achieved for each polymer. This paper demonstrates a solvent selection approach that can be applied to separate unknown plastics materials into purer components.

Optimization of process parameters of catalytic pyrolysis using natural zeolite and synthetic zeolites on yield of plastic oil through response surface methodology

This study aims to reach a sustainable solution for waste management of medical plastics through value-added product extraction. It uses the DOE technique to examine the effect of natural zeolite and synthetic Al2O3 and SiO2 as catalysts. A small lab-scale pyrolysis setup was used for medical plastic waste management treatment. Pyrolysis of medical plastics with temperature range (350-450 °C), three catalysts, and wt.% are examined. This process is designed for 3 factors and 3 levels, such as type of catalyst, catalyst wt.%, and temperature, to create an L9 orthogonal array. At the same time, the heating rate and residence time are maintained constant at 5 °C/min and 75 minutes, respectively. Furthermore, this study analyzed the input variables in catalytic pyrolysis using response surface methodology. As a result of the study, generating the regression equation for oil yield, F and P values assure the model is significant. Optimization result shows the type of catalyst, temperature, and catalyst concentration values are found as aluminum oxide, 376 °C, and 6.6 wt.%, respectively. HDPE and LDPE oil yield a value of 58.3648 and 61.2051 wt%, respectively, under the optimum variables condition. For oil yield prediction, HDPE and LDPE's correlation coefficient (R2) were 0.9949 and 0.9943, respectively. Authentication of the model response using a regression equation validated with the experimental result shows good agreement. The produced medical plastic oil has a density, viscosity, flash & fire point, carbon residue, and cetane number 904 kg/m3, 2.3 cSt, 42 & 45 °C, 7.1 wt.% and 51 respectively. Finally, this study concludes that plastic oil extraction from medical waste through catalytic pyrolysis can be a potential source of alternative fuels in IC engines. Priority to optimization and low-cost catalysts highlights medical plastics waste management under the socio-economic model.

Steam gasification of char derived from refuse-derived fuel pyrolysis: adsorption behaviour in phenol solutions

The increasing waste generation trends resulted in growing attention to the technologies that aim to reduce or prevent landfilling. The pyrolysis and gasification of refuse-derived fuel (RDF) allow waste to be turned into new raw materials, like pyrolysis gas and syngas. However, the wet gas cleaning processes result in the production of highly contaminated liquid waste. Phenolic compounds are common constituents of this wastewater and often appear in the wastewater of other industries as well. In this research, the laboratory-scale steam gasification of an RDF char was performed to produce syngas and adsorbent simultaneously. The RDF was previously pyrolyzed at 700 °C maximum temperature in a Hungarian pyrolysis pilot plant with approximately 120 kg h-1 capacity. In this thermal waste processing plant, the pyrolysis gas is already utilised by burning, but currently, the char ends up in landfills. The gasification of char samples was examined with different steam-to-carbon ratios (0.56, 0.84, and 1.12) and duration (30, 60, and 120 min) at 900 °C. Following gasification, the phenol removal capability of the solid by-products was investigated. The results show that its composition and energetic properties make the produced syngas more suitable to use as a raw material in the chemical industry rather than a fuel. At lower concentrations, the effectiveness of the solid by-product for phenol removal was comparable to commercial activated carbon. These are promising results about producing activated carbon from waste without any chemical treatment.

Catalytic Approaches to Tackle Mixed Plastic Waste Challenges: A Review

Plastics are widely used materials in our daily lives and various industries due to their affordability and versatility. The massive production of plastic waste, however, has recently emerged as a pressing environmental concern across all media. To address this, emerging technologies are being explored for the sustainable valorization of postconsumer plastic wastes including thermochemical, physical, and catalytic processes aimed at transforming them into higher value-added products. However, the chemical recycling of mixed plastic wastes poses a formidable challenge due to the diverse array of monomers and catalyst systems involved, each employing distinct mechanisms. Complicating matters further is that contaminants reduce catalytic efficacy, requiring rigorous and labor-intensive separation and purification processes to extract individual plastic streams from practical plastic waste mixtures. Consequently, the majority of such mixtures often end up in incineration and landfills, perpetuating environmental and societal challenges, such as leachate, carbon dioxide emissions, and other air pollutants. This review will introduce current technical developments available for recycling practical plastic waste mixtures through catalytic processes. The current challenges in process performance, low selectivity of the desired products, and catalyst deactivation from the catalysis of plastic waste mixtures are also discussed. Promising approaches to overcome the problems are suggested in future research directions.

Combustion characteristics and gasification kinetics of Brazilian municipal solid waste subjected to different atmospheres by thermogravimetric analysis

This study examines the gasification kinetics of Brazilian municipal solid waste (MSW) and its components under air, CO2, and air/CO2 (70/30 vol%) atmospheres. The ignition indices of paper and plastic are 6 and 3 times that of food waste, which are 38.6 × 10-3 %/min3 and 19.6 × 10-3 %/min3, respectively, implying a faster separation of volatile compounds from the paper and plastic. The minimum Eα values of 132 kJ/mol and 140 kJ/mol have been obtained for paper waste under air and air/CO2, respectively. On CO2 condition, MSW has an average Ea value of 96 kJ/mol. Under an air/CO2 atmosphere, a high synergistic ΔW of -4.7 wt% has been identified between individual components. The presence of air and CO2 improves the oxidation and char gasification process, thus resulting in better combustion. Hence, the gasification of MSW under an air/CO2 atmosphere would improve the waste-to-energy plant's performance and minimize the CO2 emission.

Effect of Feed Mass, Reactor Temperature, and Time on the Yield of Waste Polypropylene Pyrolysis Oil Produced via a Fixed-Bed Reactor

This paper presents the results of investigations into the pyrolysis of waste polypropylene in a laboratory fixed-bed batch reactor. The experiments were designed and verified in such a way as to allow the application of the response surface methodology (RSM) in the development of an empirical mathematical model that quantifies the impacts mentioned above. The influence of the mass of the raw material (50, 100, and 150 g) together with the reactor temperature (450, 475, and 500 °C) and the reaction time (45, 50 and 75 min) was examined. It has been shown that the mass of the raw material, i.e., the filling volume of the reactor, has a significant influence on the pyrolysis oil yield. This influence exceeds the influence of reactor temperature and reaction time. This was explained by observing the temperature change inside the reactor at three different spots at the bottom, middle, and top of the reactor. The recorded temperature diagrams show that, with greater masses of feedstock, local overheating occurs in the middle part of the reactor, which leads to the overcracking of volatile products and, from there, to an increased formation of non-condensable gases, i.e., a reduced yield of pyrolytic oil.

Production of hydrogen-rich fuel gas from waste plastics using continuous plasma pyrolysis reactor

There is a serious concern about the large amount of accumulated plastic waste all around the world. Synthetic polymers such as polyethylene terephthalate (PET), polypropylene (PP), and polyethylene (HDPE, LDPE) are substantially present in the plastic waste generated. There are various methods reported to minimise such plastics waste with certain limitations. To overcome such limitations the present study have been carried out in which thermal decomposition of plastic waste of PET, PP, HDPE, and LDPE studied using a novel plasma pyrolysis reactor. The major objective of this work is to investigate the viability of the continuous plasma pyrolysis process for the treatment of various plastic wastes with respect to waste volume reduction and production of combustible hydrogen-rich fuel gas. The effect of temperature and feed flow rate on product gas yield, product gas efficiency, solid residue yield, and H2/CO ratio has been evaluated. The experiments have been carried out at different temperatures within the range of 700-1000 °C. Plasma pyrolysis system exhibited combustible hydrogen-rich gas as a product and solid residue. Liquid products have not been observed during plasma pyrolysis, unlike conventional pyrolysis. The reaction mechanism of plastic cracking has been discussed based on literature and products obtained in the present work. The effects of feed flow rate and temperature on exergy efficiency were studied using the response surface method. The mass, energy, and exergy analyses have also been carried out for all the experiments, which are in the range of 0.95-0.99, 0.48 to 0.77, and 0.30 to 0.69, respectively.

Investigating the Phase Transition Kinetics of 1-Octadecanol/Sorbitol Derivative/Expanded Graphite Composite Phase Change Material with Isoconversional and Multivariate Non-Linear Regression Methods

Organic composite phase change materials (PCMs) have been extensively studied, and it is important to investigate the effect of added components on the phase change process of the organic matrix. Herein, the phase transition process of the composite PCM with 1-octadecanol (OD) as the matrix adsorbed by a network framework composed of 1,3:2,4-di-(3,4-dimethyl) benzylidene sorbitol (DMDBS) and expanded graphite (EG) was measured using differential scanning calorimetry (DSC) at several linear heating rates. Using isoconversional and multivariate non-linear regression methods, a two-step consecutive reaction model for the composite PCM was established, while the apparent activation energies and pre-exponential factors were determined. The reaction mechanism of the first step was altered compared to pure OD, while the activation energies significantly decreased at the initial stage of the phase transition process and increased at the later stage. Combined with microscopic morphology analysis, the main reasons were the size and nanoconfinement effect. The predictions of the composite PCM under various conditions suggested that the composite PCM had a wider available temperature range compared to pure OD. This research provided a new idea for the in-depth study of the phase transition process of organic composite PCMs, which was helpful for the evaluation of organic composite PCMs.

Chemical Upcycling of Waste Plastics to High Value-Added Products via Pyrolysis: Current Trends, Future Perspectives, and Techno-Feasibility Analysis

Chemical upcycling of waste plastics into high-value-added products is one of the most effective, cost-efficient, and environmentally beneficial solutions. Many studies have been published over the past few years on the topic of recycling plastics into usable materials through a process called catalytic pyrolysis. There is a significant research gap that must be bridged in order to use catalytic pyrolysis of waste plastics to produce high-value products. This review focuses on the enhanced catalytic pyrolysis of waste plastics to produce jet fuel, diesel oil, lubricants, aromatic compounds, syngas, and other gases. Moreover, the reaction mechanism, a brief and critical comparison of different catalytic pyrolysis studies, as well as the techno-feasibility analysis of waste plastic pyrolysis and the proposed catalytic plastic pyrolysis setup for commercialization is also covered.

Progress and perspective for conversion of plastic wastes into valuable chemicals

Today, discarded plastics in nature have caused serious "white pollution", however these plastic wastes contain abundant carbon resources that could serve as the feedstock to produce commodities. Because of this, it is requisite to convert these plastic wastes into valuable chemicals. Herein, the state-of-the-art techniques for plastic conversion are divided into two categories, those performed under violent conditions and mild conditions, in which the conversion mechanisms are discussed. The strategies under violent conditions are closer to practical application thanks to their excellent conversion efficiencies, while the strategies under mild conditions are more environmentally friendly, showing enormous development potential in the future. We summarize in detail the pyrolysis, hydropyrolysis, solvolysis and microwave-initiated catalysis for bond cleavage in plastic wastes at temperatures ranging from 448 to 973 K. Also, we overview the photocatalysis, electrocatalysis and biocatalysis for bond cleavage in plastic wastes at near and even normal temperature and pressure. Finally, we present some suggestions and outlooks concerning the improvement of current techniques and in-depth mechanisms of investigation for conversion of plastics into valuable chemicals.

Catalytic Pyrolysis of Plastic Waste and Molecular Symmetry Effects: A Review

The present review addresses the latest findings and limitations in catalytic pyrolysis for the processing of plastic waste into valuable fuels. Compared to thermal degradation of plastics, catalytic pyrolysis provides better results in regards to the quality of the obtained liquid hydrocarbon fuel. Different types of catalysts can be used in order to improve the thermal degradation of plastics. Some of the most used catalysts are different types of zeolites (HUSY, HZSM-5, Hβ), Fluid Catalytic Cracking (FCC), silica-alumina catalysts, or natural clays. There is a need to find affordable and effective catalysts in the aim of achieving commercialization of catalytic pyrolysis of plastic waste. Therefore, this study summarizes and presents the most significant results found in the literature in regards to catalytic pyrolysis. This paper also investigates the symmetry effects of molecules on the pyrolysis process.

Efficiency of municipal packaging waste recovery chain and suitability of separated residual waste fractions for use in alternative fuels production

Due to the sheer quantity and quality of material, packaging waste is separately collected by municipal waste management systems, with a primary goal of its use in material recovery. The residual waste, i.e. rejected waste in the separation process can be energy recovered. Both recovery options have specific input material quality requirements. Therefore, it is important to know the characteristics of individual waste streams. This research analysed the composition and morphological characteristics of separately collected packaging waste from municipal waste management system, residual (rejected) waste fractions after separation steps and produced refuse-derived fuel (RDF). The efficiency of primary and secondary (manual) waste separation, as well as of the RDF production step, are tracked. Results show that primary waste separation produces material with under 7% of contaminants and secondary manual waste separation efficiency ranges between 45% and 55%. Physico-chemical comparison of simulated RDF strongly coincides with analysed properties of RDF as a final product which indicates very high separation efficiency in the RDF production. From the energy recovery/conversion standpoint, this can be quantified through deviations in the lower heating value (LHV) and the effective H/C molar ratio between simulated and real RDF samples, which are on the level of 1.8% and 1.1% respectively. The following conclusion can be made from the estimated relation between changes in separation efficiency and RDF energy-related characteristics; the separation efficiency of individual components plays important role in alternative fuel production as chemical compositions directly influence suitability for high-quality liquid fuel production. Results of this analysis shed a light on the connection between aspirations to increase material recovery share and the suitability of produced residual waste for further recovery and valorisation. The material and energetic valorisation are competitors, and further evaluation should be done to understand the investments needed to increase valuable fractions of wastes separation that, in turn, could diminish the energetic value of residual fractions and, therefore, the economic viability of energy recovery facilities.

Preparation of adsorptive polyethyleneimine/polyvinyl chloride electrospun nanofiber membrane: Characterization and application

Landfilling and burning plastic waste, especially waste polyvinyl chloride (PVC), can produce highly toxic and carcinogenic by-products that threaten the ecosystem and human health. However, there is still a lack of proper methods for waste PVC recycling. Therefore, developing feasible ways for waste PVC recovery is urgently needed. The purpose of this study is to analyze the characteristics of PVC-based adsorptive nanofiber membranes and test their ability for the treatment of wastewater containing Cibacron Brilliant Yellow 3G-P, a widely used reactive dye. The polyethylenimine/polyvinyl chloride membrane (PEI/PVCM) was characterized by FTIR, FE-SEM, TGA, tensile analysis, water contact angle measurement, and zeta-potential analysis. The FTIR analysis confirmed that the PEI has successfully crosslinked with PVC. The FE-SEM images showed that the nanofibers constituting PEI/PVCM are compact with an average fiber diameter of 181 nm. The TGA results showed that the membrane was able to remain stable in wastewater below 150 °C. The average stress and strain of the PEI/PVCM were 7.64 ± 0.32 MPa and 934.14 ± 48.12%, respectively. The water contact angle and zeta potential analysis showed that after the introduction of PEI, the membrane converted from hydrophobic to hydrophilic, and the pH_pzc was increased from 3.1 to 1.08. The pure water flux of the membrane was measured at 0.1 MPa and the result was 3013 ± 60 L/m²‧h. The wastewater purification capability of PEI/PVCM was measured at an initial dye concentration of 10 ppm and pH 4-9 at 0.1 MPa. The reusability of PEI/PVCM was verified through three adsorption-desorption cycles. The results demonstrated that the PEI/PVCM is a reusable membrane for efficient purification of wastewater containing reactive dyes over a wide pH range (pH 4-8).

Characterization of the Different Oils Obtained through the Catalytic In Situ Pyrolysis of Polyethylene Film from Municipal Solid Waste

Nowadays, the thermal and catalytic decomposition of plastic wastes by pyrolysis is one of the best alternatives to convert these wastes into quality fuel oils, thus replenishing some petroleum resources. This work studied the catalytic pyrolysis of polyethylene film waste from the remaining organic fraction on different catalysts under dynamic operating conditions in a batch reactor. These catalysts have been characterized through isotherms of adsorption-desorption with N2 and X-ray powder diffraction for structural characterization to see the differences in their use. The results obtained have been compared with the pyrolysis of the same material without a catalyst. Special attention has been paid to the similarities and differences with thermal pyrolysis. The characterization of the liquid fraction, including physical and chemical properties, has been carried out. The liquid yield varies from 37 to 43%; it has good calorific values of 46–48 MJ/kg, an average density of 0.82 g/cm3, and a fairly low viscosity compared to the product without the catalyst. Other properties like the American Petroleum Institute (API) gravity or pH were also determined and found to be similar to conventional fuels. Oils are mainly composed of paraffins, naphthenes, and aromatic hydrocarbons. The general distribution of carbons is C7 to C31. Finally, a detailed analysis of the composition of liquid products shows they present heavy naphtha, kerosene, and diesel fractions in different proportions in the function of the catalyst used.

Sustainable development in period of climate crisis

The ongoing process of climate change has shown that sustainable development of humankind is a necessity. Existing resources need to be used in a form of a circular economy, and no more in a linear economy as has been the case until now. Resources need to be better managed to meet the needs of future generations. Therefore, energy, water and environment systems need to be integrated in order to slow down their overexploitation. This paper discusses some of the latest developments in three main areas of sustainability, i.e., energy, water and environment, that emerged from the four "Sustainable Development of Energy, Water and Environment Systems" (SDEWES) Conferences that took place in 2020. The purpose of this review introduction article is to provide a brief introduction to the field and the articles included in this Virtual Special Issue. As such, it acts as an editorial paper for the virtual special issue of the Journal of Environmental Management, dedicated to the SDEWES 2020 conferences.

Catalytic Pyrolysis of High-Density Polyethylene: Decomposition Efficiency and Kinetics

Organic waste is generally characterized by high volume-to-weight ratios, requiring implementation of waste minimization processes. In the present study, the decomposition of high-density polyethylene (HDPE), was studied under thermal and catalytic pyrolysis conditions on two experimental systems. Firstly, pyrolytic conditions for HDPE decomposition were optimized in a laboratory-scale batch reactor. In order to maximize gas yields and minimize secondary waste, the effects of aluminosilicate catalysts, catalyst loading, and reaction temperature on decomposition efficiency were examined. Secondly, kinetics and reaction temperatures were studied on a large capacity thermobalance, especially adjusted to perform experiments under pyrolytic conditions at a larger scale (up to 20 g). The addition of catalysts was shown to enhance polymer decomposition, demonstrated by higher gas conversions. Condensable yields could be further minimized by increasing the catalyst to polymer ratio from 0.1 to 0.2. The most prominent reduction in pyrolysis temperature was obtained over ZSM-5 catalysts with low Si/Al ratios; however, this impact was accompanied by a slower reaction rate. Of the zeolites tested, the ZSM-5 catalyst with a Si/Al of 25 was found to be the most efficient catalyst for waste minimization and organic destruction, leading to high gas conversions (~90 wt%.) and a 30-fold reduction in solid waste mass.