Influence of metal-oxide-supported bentonites on the pyrolysis behavior of polypropylene and high-density polyethylene

Comparison of the Effect of Kaolin and Bentonite Clay (Raw, Acid-Treated, and Metal-Impregnated) on the Pyrolysis of Waste Tire

This study investigates the effectiveness of kaolin and bentonite catalysts in improving liquid hydrocarbon yields during the pyrolysis of waste tires. Raw clay, nitric acid-treated clay, and mono- or bimetal-impregnated clay were used as catalysts in the pyrolysis of waste tire. Acid-treated kaolin produced a higher yield of liquid hydrocarbons (43.24-47%) compared to acid-treated bentonite (35.34-41.85%). This improvement in the liquid yield can be attributed to the higher specific surface area and pore diameter of the acid-treated clay in comparison to raw kaolin (39.48%) and raw bentonite (31.62%). Moreover, the use of metal-impregnated catalysts, such as Fe/kaolin and Ni/Fe/kaolin, resulted in higher liquid yields (47%) compared to the 3 M HNO3-treated kaolin catalyst (43.24%). Gas chromatography-mass spectrometry (GC-MS) analysis confirmed the presence of limonene, a crucial ingredient for commercial perfume production, in the liquid products. The calorific values of oil obtained through kaolin and bentonite catalysis were measured at 13,922 and 10,174 kcal/kg, respectively, further highlighting the potential of these catalysts in waste tire valorization.

Production of diesel-range oil through pyrolysis of polyolefins recovered from municipal solid waste

Pyrolysis is an effective method to valorize plastic waste and obtain value-added fuels. This study adopted the ANN-GA (artificial neural network-genetic algorithm) coupled with a central composition factorial design to optimize the oil production from the pyrolysis of waste polyolefins (WP). The interactive effects of PE mass fraction (20-80 wt%), residence time (20-60 min), and carrier gas flow rate (0-100 mL/min) on the yields of WP pyrolysis products were investigated extensively by ANN. Moreover, the highest WP pyrolysis oil production of 78.87 wt%, optimized by GA, was obtained under 80 wt% PE, 60 min, and 0 mL/min. It was found that the different conditions of PE mass fraction, residence time, and carrier gas flow rate did not change the types of oil's main functional groups (-CH2-, -C=C-, -C=CH2, -CH3, and =C-H). The conditions affected the WP pyrolysis oil fractions significantly. The highest diesel selectivity of 91.42% was obtained under 20 wt% PE, 20 min, and 0 mL/min. Additionally, according to the interactive effects of different conditions on the productions of WP pyrolysis products, the pyrolysis pathways were proposed to understand the pyrolysis mechanism of WP better.

Thermocatalytic Conversion of Plastics into Liquid Fuels over Clays

Recycling polymer waste is a great challenge in the context of the growing use of plastics. Given the non-renewability of fossil fuels, the task of processing plastic waste into liquid fuels seems to be a promising one. Thermocatalytic conversion is one of the methods that allows obtaining liquid products of the required hydrocarbon range. Clays and clay minerals can be distinguished among possible environmentally friendly, cheap, and common catalysts. The moderate acidity and the presence of both Lewis and Brønsted acid sites on the surface of clays favor heavier hydrocarbons in liquid products of reactions occurring in their pores. Liquids produced with the use of clays are often reported as being in the gasoline and diesel range. In this review, the comprehensive information on the thermocatalytic conversion of plastics over clays obtained during the last two decades was summarized. The main experimental parameters for catalytic conversion of plastics according to the articles’ analysis, were the reaction temperature, the acidity of modified catalysts, and the catalyst-to-plastic ratio. The best clay catalysts observed were the following: bentonite/spent fluid cracking catalyst for high-density polyethylene (HDPE); acid-restructured montmorillonite for medium-density polyethylene (MDPE); neat kaolin powder for low-density polyethylene (LDPE); Ni/acid-washed bentonite clay for polypropylene (PP); neat kaolin for polystyrene (PS); Fe-restructured natural clay for a mixture of polyethylene, PP, PS, polyvinyl chloride (PVC), and polyethylene terephthalate (PET). The main problem in using natural clays and clay minerals as catalysts is their heterogeneous composition, which can vary even within the same deposit. The serpentine group is of interest in studying its catalytic properties as fairly common clay minerals.

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.

Recent Progress in Low-Cost Catalysts for Pyrolysis of Plastic Waste to Fuels

The catalytic and thermal decomposition of plastic waste to fuels over low-cost catalysts like zeolite, clay, and bimetallic material is highlighted. In this paper, several relevant studies are examined, specifically the effects of each type of catalyst used on the characteristics and product distribution of the produced products. The type of catalyst plays an important role in the decomposition of plastic waste and the characteristics of the oil yields and quality. In addition, the quality and yield of the oil products depend on several factors such as (i) the operating temperature, (ii) the ratio of plastic waste and catalyst, and (iii) the type of reactor. The development of low-cost catalysts is revisited for designing better and effective materials for plastic solid waste (PSW) conversion to oil/bio-oil products.

Catalytic methods for chemical recycling or upcycling of commercial polymers

Polymers (plastics) have transformed our lives by providing access to inexpensive and versatile materials with a variety of useful properties. While polymers have improved our lives in many ways, their longevity has created some unintended consequences. The extreme stability and durability of most commercial polymers, combined with the lack of equivalent degradable alternatives and ineffective collection and recycling policies, have led to an accumulation of polymers in landfills and oceans. This problem is reaching a critical threat to the environment, creating a demand for immediate action. Chemical recycling and upcycling involve the conversion of polymer materials into their original monomers, fuels or chemical precursors for value-added products. These approaches are the most promising for value-recovery of post-consumer polymer products; however, they are often cost-prohibitive in comparison to current recycling and disposal methods. Catalysts can be used to accelerate and improve product selectivity for chemical recycling and upcycling of polymers. This review aims to not only highlight and describe the tremendous efforts towards the development of improved catalysts for well-known chemical recycling processes, but also identify new promising methods for catalytic recycling or upcycling of the most abundant commercial polymers.

Sludge char-to-fuel approaches based on the catalytic pyrolysis II: heat release

The pyrolyzed sludge is concerned currently, while the produced higher heating value (HHV) is unclear yet. In this work, the effects of moisture content (MC), catalysts amount, and catalytic types on the HHV production were investigated. Based on the known fatty acids (FAs) and alcohol content, the heat release by catalytic and non-catalytic pyrolysis product was examined. A good correlation between the measured and calculated HHV in non-catalytic pyrolysis indicates that the method can effectively evaluate the pyrolysis effect. The results show that a higher HHV can be obtained by adding a catalyst when the MC was between 20 and 40% compared to the non-catalytic pyrolysis. In the catalytic pyrolysis, the maximum HHV produced by bentonite is 50.61 MJ kg^-1. Bentonite can rapidly initiate the decarboxylation but sand was a potential efficient catalyst because of the enrichment of large amounts of FAs C_16:0. If sand is used in combination with bentonite, C_16:0 may be enriched and further decarboxylated, eventually releasing more heat. Since sand is composed of SiO₂ and Al₂O₃, in the production of HHV, the addition of Al₂O₃ has a better catalytic effect than adding SiO₂. For the evaluation of catalytic pyrolysis products and HHV, it is proposed that the possibility of adding two types of catalysts for pyrolysis is of great significance for realizing sludge to the fuel.

Theoretical studies on thermal degradation reaction mechanism of model compound of bisphenol A polycarbonate

Density functional theory methods (DFT) M062X have been used to investigate the thermal degradation processes of model compound of bisphenol A polycarbonate (MPC) and to identify the optimal reaction paths in the thermal decomposition of bisphenol A polycarbonate (PC). The bond dissociation energies of main bonds in MPC were calculated, and it is found that the weakest bond in MPC is the single bond between the methylic carbon and carbon atom and the second weakest bond in MPC is the single bond between oxygen atom and the carbonyl carbon. On the basis of computational results of kinetic parameters, a mechanism is proposed where the hydrolysis (or alcoholysis) reaction is the main degradation pathways for the formation of the evolved products, and the homolytic cleavage and rearrangement reactions are the competitive reaction pathways in the thermal degradation of PC. The proposed mechanism is consistent with experimental observations of CO₂, bisphenol A and 1,1-bis(4-hydroxyphenyl)-ethane as the main degradation products, together with a small amount of CO, alkyl phenol and diphenyl carbonate.

Plant-derived cis-β-ocimene as a precursor for biocompatible, transparent, thermally-stable dielectric and encapsulating layers for organic electronics

This article presents low-temperature, one-step dry synthesis of optically transparent thermally-stable, biocompatible cis-β-ocimene-based thin films for applications as interlayer dielectric and encapsulating layer for flexible electronic devices, e.g. OLEDs. Morphological analysis of thin films shows uniform, very smooth (R_q < 1 nm) and defect-free moderately hydrophilic surfaces. The films are optically transparent, with a refractive index of ~1.58 at 600 nm, an optical band gap of ~2.85 eV, and dielectric constant of 3.5-3.6 at 1 kHz. Upon heating, thin films are chemically and optically stable up to at least 200 °C, where thermal stability increases for films manufactured at higher RF power as well as for films deposited away from the plasma glow. Heating of the sample increases the dielectric constant, from 3.7 (25 °C) to 4.7 (120 °C) at 1 kHz for polymer fabricated at 25 W. Polymers are biocompatible with non-adherent THP-1 cells and adherent mouse macrophage cells, including LPS-stimulated macrophages, and maintain their material properties after 48 h of immersion into simulated body fluid. The versatile nature of the films fabricated in this study may be exploited in next-generation consumer electronics and energy technologies.