Catalytic Pyrolysis of Polystyrene over Steel Slag under CO2 Environment

Enhancing styrene monomer recovery from polystyrene pyrolysis: insights from density functional theory

CONTEXT

Plastic waste pyrolysis offers a potential solution to reduce plastic accumulation, but prioritizing monomer recovery from the process is crucial to effectively address the environmental consequences of plastic accumulation. This study focuses on enhancing the yield of styrene during the pyrolysis of polystyrene by investigating thermal and kinetic data. A comprehensive investigation into the thermal degradation pathways of polystyrene is imperative to overcome the challenges associated with its waste management. The calculated bond dissociation energies reveal that the cleavage of non-terminal carbon-carbon bonds is energetically favorable, resulting in the formation of high molecular weight benzylic radicals. Based on these findings, four pyrolysis pathways are proposed, and the associated thermodynamic and kinetic parameters are determined using the DFT method. The major products identified in this study include styrene, α-methylstyrene, isopropylbenzene, methylbenzene, ethylbenzene, and methane. Furthermore, optimizing the temperature profile of the reactor is shown to enhance the recovery of styrene, thereby contributing to the reduction of plastic waste. This study provides valuable insights into the effective resource recovery from polystyrene waste pyrolysis, emphasizing the significance of managing pyrolysis conditions to achieve maximum yield. By controlling the temperature profile during the pyrolysis process, it is possible to obtain a high yield of styrene, facilitating the efficient recovery of the monomer from waste polystyrene and addressing the environmental concerns associated with plastic accumulation.

METHODS

In this study, all calculations were performed using the B3LYP/6-31G(d) level of theory with the Gaussian 16 program package. The proposed model underwent geometry optimization and frequency calculations. Transition states were optimized using the TS Berny method, and energy profiles along reaction pathways were refined using the QST3 method. The IRC method validated proposed mechanisms and investigated energy profiles. Structural models were visualized using GaussView 6.0.

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.

Environmental benefits from the use of CO2 in the thermal disposal of cigarette butts

As the global consumption of cigarettes has increased, the massive generation of cigarette butts (CBs) has led to critical environmental and health problems. Landfilling or incineration of CBs has been conventionally carried out, but such disposal protocols have suffered from the potential risks of the unwanted/uncontrolled release of leachates, carcinogens, and toxic chemicals into all environmental media. Thus, this study focuses on developing an environmentally dependable method for CB disposal. Littered CBs from filtered/electronic cigarettes were valorized into syngas (H₂/CO). To seek a greener approach for the valorization of CBs, CO₂ was intentionally considered as a reaction intermediate. Prior to multiple pyrolysis studies, the toxic chemicals in the CBs were qualitatively determined. This study experimentally proved that the toxic chemicals in CBs were detoxified/valorized into syngas. Furthermore, this work demonstrated that CO₂ was effective in thermally destroying toxic chemicals in CBs via a gas-phase reaction. The reaction features and CO₂ synergistically enhance syngas production. With the use of a supported Ni catalyst and CO₂, syngas production from the catalytic pyrolysis of CBs was greatly enhanced (approximately 4 times). Finally, the gas-phase reaction by CO₂ was reliably maintained owing to the synergistic mechanistic/reaction feature of CO₂ for coke formation prevention on the catalyst surface.

Adsorption removal of styrene on C-Cl grafted silica gel adsorbents

The heat desorption of styrene from adsorbents is impracticable owing to its spontaneous polymerization under heating conditions. However, the feature also brings a potential promoting effect on styrene adsorption. Therefore, it is expected to develop the non-regenerative adsorbents with large adsorption capacity by strengthening the polymerization effect. In this work, C-Cl grafted silica gel adsorbents were prepared by introducing (Chloromethyl)dimethylchlorosilane (CMDMCS) and FeCl₂ into silica gel. The C-Cl grafted silica gel exhibited excellent styrene adsorption performance, its adsorption amounts for styrene were 4.67 times and 9 times of unmodified silica gel under dry air condition and high humidity condition (RH = 80%), respectively. In addition, the adsorption of styrene on C-Cl grafted silica gel was almost unaffected by the presence of toluene. The characterization of adsorbents after styrene adsorption indicated that the improvement of adsorption capacity of C-Cl grafted silica gel for styrene can be attributed to atom transfer radical polymerization (ATRP) of styrene molecules on modified silica gel during adsorption process.

Catalytic Pyrolysis of Polystyrene Waste in Hydrocarbon Medium

The fast catalytic pyrolysis of polystyrene in the hydrocarbon medium (light and heavy cycle oil) over zeolite catalysts at 450-550 °C was investigated. The influence of reaction conditions (medium, temperature, vapor residence time, polystyrene concentration) on polymer conversion and product distribution was studied. It was found that the polymer conversion is close to 100%, while ethylbenzene, benzene, and toluene are the main products of its transformation. The maximum yield of ethylbenzene (80%) was achieved at 550 °C, vapor residence time 1-2 s, polystyrene concentration 10%, and heavy cycle oil as the medium. The influence of zeolite topology on product distribution was explored. The possible mechanism of polystyrene pyrolysis was proposed.

Preparation and Characterization of Biochars Obtained from Biomasses for Combustible Briquette Applications

Renewable energies have been considered as alternative, clean, available, and ecological sources of energy. The production of biochar from biomass by thermochemical means is considered an efficient method of converting biomass for energy production. In this study, the biochars were produced from the biomasses of peanut shells and sugar cane bagasse at different pyrolysis temperatures (400°C, 450°C, and 500°C). The biomass samples and their produced biochars were characterized using calorific value, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy and energy dispersive X-ray spectrometry (SEM and EDX), compressibility index, and combustion behavior in order to analyze their potential. Experimental results showed that biochar has better fuel qualities compared to raw biomass. We also found that increasing the pyrolysis temperature clearly improved the calorific value, the morphology, the porosity of the biochars as well as the compressibility index of the biochars. The interest of this study was to produce renewable biochar from peanut shell waste and sugar cane bagasse for use as solid fuel.

Sustainable valorization of styrofoam and CO2 into syngas

Plastic is a versatile material broadly used in a variety of industries. However, the current disposal practices for plastic wastes (incineration/landfilling) add the hazardous materials into the environment. To offer a sustainable valorization platform for plastic waste, this study adopted the catalytic pyrolysis process using CO₂ as a co-feedstock. A model plastic waste collected from a seaport was waste buoy (WB), which has been widely used in fishing industry. Prior to the pyrolysis tests, the exact type of plastic in WB and the thermolytic characteristics of WB were examined. Since the WB was made of polystyrene, it was mainly converted into styrene monomer (styrene), dimer (diphenyl-1-butene), and trimer (2,4,6-triphenyl-1-hexene) from pyrolysis of WB. To further valorize/detoxify styrene derivatives into value-added syngas, catalytic pyrolysis of WB was practiced using the Ni-based catalysts (2/5/10 wt% Ni/SiO₂). The yield of H₂ from the catalytic pyrolysis process of WB was more than one magnitude higher comparing to that from the non-catalytic one. H₂ formation also increased as catalyst loading increased. When flow gas was switched from inert gas to CO₂, CO gas formation was enhanced due to the chemical reactions between CO₂ and styrene derivatives over Ni catalysts. Syngas (H₂/CO) formation under the CO₂ condition was 5 times higher in comparison to the N₂ condition in catalytic pyrolyses of WB with 10 wt% Ni/SiO₂. CO₂ also effectively suppressed coke deposition on a Ni catalyst. This study proposes a sustainable valorization and disposal platform for used plastic waste and greenhouse gas (CO₂), converting them into value-added fuel.

Valorizing plastic toy wastes to flammable gases through CO2-mediated pyrolysis with a Co-based catalyst

Toys are discarded due to their short life cycle. Unfortunately, development of sustainable disposal platform for toy has not gained particular concern. To establish a reliable disposal platform, this study employed a pyrolysis platform to valorize plastics into value-added fuels. To confer more environmentally resilient process, CO₂ was used as a feedstock to enhance the process efficiency from a perspective of the yield of flammable gases. To this end, waste toy brick (WTB) was used as a model compound. The exact types of plastics (polyacrylonitrile, polybutadiene, polystyrene, and polymethyl methacrylate) in WTB were experimentally determined. In pyrolysis of WTB, the complicated mixture of benzene derivatives was inevitably generated. To detoxify them by means of syngas (H₂/CO) production, catalytic pyrolysis was performed. Co catalyst effectively induced chemical bond scissions, leading to substantially enhanced H₂ formation. Also, the gas phase reactions (GPRs) between CO₂ and volatile compounds over Co catalyst expedited the production rate of CO, and such CO enhancement effectively offered a chance to mitigate toxic chemical generations. The synergistic contribution of CO₂ and Co catalyst enhanced syngas formation more than 25 times in reference to pyrolysis of WTB without Co catalyst. The GPRs also greatly prevented catalyst deactivation.

Disposal of plastic mulching film through CO2-assisted catalytic pyrolysis as a strategic means for microplastic mitigation

Conventional disposal processes (incineration and landfilling) of agricultural plastic wastes release harmful chemicals and microplastics into our ecosystems. To provide a disposal platform not releasing harmful chemicals, pyrolysis of a representative agricultural plastic waste was proposed in this study. Spent plastic mulching film (SMF) was used as a model waste compound. To make pyrolysis process more environmentally benign, CO₂ was used as a raw material in pyrolysis of SMF. H₂ and hydrocarbons were produced from pyrolysis of SMF under the inert (N₂) and CO₂ conditions, because SMF is composed of polyethylene. To enhance conversion of hydrocarbons into H₂, catalytic pyrolysis of SMF was conducted over Ni/SiO₂. Compared to non-catalytic pyrolysis, total concentration of pyrolytic gases was enhanced up to 3.1 and 11.3 times under N₂ and CO₂ conditions, respectively. The gas phase reactions between CO₂ and hydrocarbons led to formation of CO, which enhanced production of pyrolytic gases under the CO₂ condition. Moreover, gas phase reactions resulted in less production of pyrolytic oil from CO₂ condition (15.9 wt%) in reference to the N₂ condition (22.6 wt%). All experimental results confirmed that CO₂ and SMF can be used as useful feedstocks to produce value-added products. ENVIRONMENTAL IMPLICATION: Plastic waste used from a sector of agriculture is incinerated or/and landfilled, generating hazardous microplastic and volatile compounds into the environment. Thus, an environmentally friendly process for plastic waste materials in the agricultural industry is required. This study converted a spent plastic mulching film (SMF), broadly used for plastic greenhouse, into value-added syngas through catalytic pyrolysis. CO₂ was used as a reactant. We found that concentration of CO₂ was key to improve syngas formation from pyrolysis of SMF. Thus, this study suggested that CO₂/SMF are used as useful feedstocks through catalytic pyrolysis, while they were previously discarded as waste materials.

Removal of Inorganic Salts in Municipal Solid Waste Incineration Fly Ash Using a Washing Ejector and Its Application for CO2 Capture

This study investigated the effects of washing equipment for inorganic salts, such as NaCl, KCl, and CaClOH, to decontaminate municipal solid waste incineration fly ash (MSW-IFA). Based on the feature of hydrodynamic cavitation, the device developed in this study (referred to as a ‘washing ejector’) utilizes the cavitation bubbles. A washing ejector was analyzed under a range of conditions, employing as little water as possible. In hydrodynamic cavitation, the increase in fluid pressure with increasing static pressure is mainly attributed to the increase in particle–bubble collisions via the cavitation flow. The results revealed that the fluid pressure influenced the removal of inorganic salts during cavitation in water. This is because during the washing process from the collapse of cavitation bubbles, the release is achieved through the dissolution of inorganic salts weakly bound to the surface. After treatment by a washing ejector, the removal of soluble salts elements such as Cl, Na, and K was reduced by approximately 90%. Removing the inorganic salts in the IFA altered the characteristics of the Ca-related phase, and amorphous CaCO₃ was formed as the cavitation flow reacted with CO₂ in the ambient air. Furthermore, the washing effluent produced by washing IFA was found to be beneficial for CO₂ capture. The washing effluent was enriched with dissolved Ca from the IFA, and the initial pH was the most favorable condition for the formation of CaCO₃; thus, the effluent was sufficient for use as a CO₂ sequestration medium and substitute for the reuse of water. Overall, the process presented herein could be effective for removing soluble salts from IFA, and this process is conducive to utilizing IFA as a resource.

Microwave co-pyrolysis for simultaneous disposal of environmentally hazardous hospital plastic waste, lignocellulosic, and triglyceride biowaste

Microwave co-pyrolysis was examined as an approach for simultaneous reduction and treatment of environmentally hazardous hospital plastic waste (HPW), lignocellulosic (palm kernel shell, PKS) and triglycerides (waste vegetable oil, WVO) biowaste as co-feedstock. The co-pyrolysis demonstrated faster heating rate (16-43 °C/min) compared to microwave pyrolysis of single feedstock (9-17 °C/min). Microwave co-pyrolysis of HPW/WVO performed at 1:1 ratio produced a higher yield (80.5 wt%) of hydrocarbon liquid fuel compared to HPW/PKS (78.2 wt%). The liquid oil possessed a low nitrogen content (< 4 wt%) and free of sulfur that could reduce the release of hazardous pollutants during its use as fuel in combustion. In particular, the liquid oil obtained from co-pyrolysis of HPW/WVO has low oxygenated compounds (< 16%) leading to reduction in generation of potentially hazardous sludge or problematic acidic tar during oil storage. Insignificant amount of benzene derivatives (< 1%) was also found in the liquid oil, indicating the desirable feature of this pyrolysis approach to suppress the formation of toxic polycyclic aromatic hydrocarbons (PAHs). Microwave co-pyrolysis of HPW/WVO improved the yield and properties of liquid oil for potential use as a cleaner fuel, whereas the liquid oil from co-pyrolysis of HPW/PKS is applicable in the synthesis of phenolic resin.

Functional use of CO2 to mitigate the formation of bisphenol A in catalytic pyrolysis of polycarbonate

The growing consumption of plastic materials has increased hazardous threats to all environmental media, since current plastic waste management methods release microplastics and toxic chemicals. As such, massive generation of plastic derived pollutants leads to significant public health and environmental problems. In this work, an environmentally sound method for valorization of plastic waste is suggested. In detail, pyrolysis of polycarbonate-containing plastic waste such as automotive headlight housing (AHH) was carried out using CO₂ as a co-reactant. AHH was chosen as it discharges bisphenol A (BPA) and aromatic compounds. Under CO₂ condition, emissions of BPA and its derivatives were suppressed by 14.5% due to gas phase reactions (GPRs) with CO₂. Nevertheless, reaction kinetics for GPRs was not significant. To impart the GPRs, catalytic pyrolysis was done using Ni and Co-based catalysts. During catalytic pyrolysis, syngas production was more than tenfold up comparing to pyrolysis without catalyst. The expedited GPRs over catalysts resulted in the enhanced syngas formation. Total concentration of the toxic chemicals from CO₂-assisted catalytic pyrolysis of AHH decreased by 86.1% and 66.7% over Ni and Co catalysts, comparing to those from N₂ environment.

Study on the polystyrene plastic degradation in supercritical water/CO2 mixed environment and carbon fixation of polystyrene plastic in CO2 environment

Through the degradation of organic waste, the carbon can be extracted and converted into syngas with calorific value, and the CO₂ generated can also be used after fixed. In this work, the gasification of polystyrene (PS) in supercritical water with CO₂ was studied in the temperature range of 400 °C-700 °C and time range of 0-30 min. In addition, PS containing only carbon and hydrogen can react with CO₂ to generate CO in CO₂ atmosphere. Therefore, the degradation of PS plastics in CO₂ atmosphere was also studied. The results showed that PS plastic was hardly gasified at 400 °C, and as the temperature rose, the liquid composition changed. In supercritical water, under certain feedstock conditions, reacting for 20 min, the carbon conversion efficiency of PS plastic reached 47.6% at 700 °C. Under all CO₂ atmosphere conditions in this experiment, the highest proportion of CO₂ consumed by PS degradation was 12.5%. Moreover, the higher the temperature, the smaller the average diameter of carbon microspheres in the solid product. The morphology of carbon microsphere was also related to the reaction time, and the main change came from the gasification of carbon microspheres and the precipitation and adhesion of carbon element in liquid product.

Synergistic effects of CO2 on complete thermal degradation of plastic waste mixture through a catalytic pyrolysis platform: A case study of disposable diaper

Consumption of diverse plastics has posed an environmental threat because their disposal practices, landfilling and incineration, release toxic chemicals and microplastics into all environmental media. Indeed, heterogeneous matrix of plastic wastes makes them hard to be disposed. As such, this study aimed to introduce an environmentally benign/reliable disposal platform for complete decomposition of plastic wastes. Pyrolysis process was adapted to convert plastics into syngas, and a disposable diaper (DD) was used as model plastic waste, because it is composed of a variety of polymeric materials. Pyrolysis of DD resulted in the formation of gaseous products and pyrogenic oils, composed of (oxygenated) hydrocarbons. Nonetheless, reactivity of CO₂ as an oxidant in pyrolysis of DD was negligible. To impart the strong/desired reactivity of CO₂, Ni-based catalyst was adopted. Ni catalyst enhanced H₂ and CO formations 4 and 15 times more than pyrolysis without catalyst at 700 °C under CO₂. The value-added syngas production was originated from the reduction of polymeric waste, and its derivatives including aromatic compounds. Thus, CO₂ offered a strategic means to produce value-added chemicals and reduce aromaticity of pyrogenic products. The observations could offer an innovative way to control the fate of toxic chemicals derived from plastic pyrolysis.

Heterogeneous Diels-Alder tandem catalysis for converting cellulose and polyethylene into BTX

Producing biomass-derived aromatic hydrocarbons via controllable Diels-Alder reactions is a promising approach to recover energy and chemicals from waste streams. A tandem Diels-Alder catalysis consisting of SAPO-34 and Fe/HZSM-5 (stacked catalysis or mixed catalysis) was evaluated for thermochemical conversion of cellulose and polyethylene blends into benzene, toluene, and xylenes (BTX). Aromatization catalyst type significantly affected the activity of tandem catalysis, and the BTX obtained from the HZSM-5 stacked catalysis was ~2.3 times higher than that of the USY stacked one. An introduction of Fe active promoters into HZSM-5 increased the Lewis to Brønsted acid sites molar ratio (L/B) from 0.4 to 4.1. The comparison between Fe/HZSM-5 stacked catalysis and parent HZSM-5 single catalysis indicated that the former was more effective for BTX production, obtaining a nearly two-fold increase in yield with a high selectivity of 82.8%. A close proximity between Fe/HZSM-5 and SAPO-34 in the mixed catalysis increased the BTX enhancement to 1.8. A synergistic effect was provided by the coordination of Lewis and Brønsted acid sites in the Fe/HZSM-5 mixed catalysts for facilitating BTX generation, achieving a maximum of 25.9% at a Fe/HZSM-5 to SAPO-34 mass ratio of 1:1 with a theoretical L/B of 7.2. This work provides a sustainable strategy to produce biomass-derived aromatic hydrocarbons.

Strategic disposal of flood debris via CO2-assisted catalytic pyrolysis

Recent abnormal climate changes resulted in the dramatic alternation of rainfall and flood patterns in many countries. The massive generation of flood debris, a mixture of soil (sediment), biomass, plastic, metal, and various hazardous materials, poses various environmental and public health problems. This study suggests a sustainable technical platform to convert the hazardous materials into value-added products. CO₂-assisted pyrolysis was used to thermally convert flood debris into syngas (H₂ and CO). CO₂ enhanced the syngas production due to gas phase homogeneous reactions (HRs) between CO₂ and volatile hydrocarbons evolved from pyrolysis of flood debris. For improvement of HRs in line with enhancement of syngas production, additional thermal energy and earth abundant catalyst were used. In particular, Ni/SiO₂ catalyst increased more than one order of magnitude higher syngas production, comparing to non-catalytic pyrolysis. Synergistic effect of CO₂ and Ni catalyst showed nearly 50% more production of syngas in reference to catalytic pyrolysis under N₂. During flood debris pyrolysis, compositional matrix of flood debris was also determined by detecting index chemicals of waste materials that cannot be identified by naked eyes. Thus, this study confirmed that CO₂-assisted pyrolysis is a useful tool for conversion of flood debris into value-added chemicals.

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.

Mitigation of harmful chemical formation from pyrolysis of tobacco waste using CO2

Global consumption of tobacco has been continuously increasing. This results in the considerable generation of toxic waste materials from the tobacco industry and daily life. Conventional disposal methods for them (incineration and landfilling) could be a potential hazard for releasing carcinogens and toxins into our eco-system. Accordingly, an eco-friendly disposal platform for converting tobacco waste (TW) into syngas was mainly studied in this present work. To realize this, pyrolysis of two commercial cigarette products (Marlboro and HEETS (electronic cigarette)) was done under the CO2/N2 conditions. One of the main findings from the present study was that CO2 reacted with volatile matters (VMs) obtained from the thermolysis of TW through the gas phase reactions (GPRs), which provided a strategic measure to manipulate carbon rearrangement of all pyrolysates. In particular, the GPRs expedited the carbon rearrangement of harmful chemical species, converting toxic chemicals into syngas. When the fraction of VMs in TWs increased, the GPR were more effective. Therefore, the introduced eco-friendly method using CO2-mediated thermochemical process could be beneficial for energy recovery from TWs while mitigating the formations of harmful chemical species.

Valorization of synthetic textile waste using CO2 as a raw material in the catalytic pyrolysis process

Since an invention of synthetic fibers (textiles), our life quality has been improved. However, the cumulative production and disposal of them have perceived as significant since they are not biodegradable and hard to be upcycled/recycled. From washing textiles, microplastics are released into the environment, which are regarded as emerging contaminants. As a means for source reduction of microplastics, this study proposed a rapid disposal platform for waste textiles (WTs), converting them into value-added products. To this end, catalytic pyrolysis of WT was studied. To offer more environmentally sound process, CO₂ was used as a raw material for WT pyrolysis. Thermal cracking of WT led to the production of syngas and CH₄ under the CO₂ environment. CO₂ resulted in additional CO production via gas phase reaction with volatile compounds evolved from pyrolysis of WT. To expedite the reaction kinetics for syngas formation, catalytic pyrolysis was done over Co-based catalyst. Comparing to non-catalytic pyrolysis, CO₂-assisted catalytic pyrolysis had 3- and 8-times higher production of H₂ and CO, respectively. This process also suppressed catalyst deactivation, converting more than 80 wt% of WT into syngas and CH₄. The more generation of CO from the use of CO₂ as a raw material offers an effective means to minimize the formations of harmful chemical species, such as benzene derivatives and polycyclic aromatic hydrocarbons.

Chemical recycling of plastic waste: Bitumen, solvents, and polystyrene from pyrolysis oil

As an alternative to conventional plastic-waste treatments, herein, we report a pyrolytic plastic-recovery process in which diverse compounds and materials are recovered from the pyrolysis oil obtained from the plastic waste. Distillation of the pyrolysis oil led to a bitumen and a distilled fraction. The composition of the bitumen, as determined by saturate, aromatic, resin, and asphaltene (S.A.R.A.) analysis and corroborated by Fourier-transform infrared (FTIR) spectroscopy, was found to principally contain aromatics (55.05 wt%) and saturates (33.41 wt%), and has great potential as a modifier for bitumen mixtures by decreasing the viscosities or softening points of final products. The distilled fraction was characterised and compared to pyrolysis oil in terms of its physicochemical properties and composition. Analysis by gas-chromatography/mass-spectrometry (GC-MS) revealed high levels of aromatics, namely styrene, benzene, toluene, ethylbenzene, and α-methylstyrene, which are potentially recoverable base compounds for industrial use. With this in mind, the distillate was subjected to various processes, including aromatic extraction with sulfolane and subsequent fractional distillation to recover the principal compounds in the various GC-MS fractions. Fraction 1 was found to be rich in ethylbenzene and toluene, while fraction 2 contained 73.26 wt% styrene and was used to synthesise recycled polystyrene (PS), whose yield and molecular weight (M_w) were optimised by adjusting the initiator concentration, temperature, and time. The optimised recycled PS was characterised to provide a yield of 77.64% and a M_w higher than 53,000 g/mol; this recycled PS exhibited similar thermal properties to those of conventional PS prepared using petrochemical sources.

Sustainable Utilization of Steel Slag from Traditional Industry and Agriculture to Catalysis

Steel slag is a large amount of residual material produced in the process of steel manufacturing. With the requirements of sustainable development in China, the utilization of steel slag has become a hot issue. Through an in-depth study on steel slag, it is apparent that it has been widely used in various fields in recent years. The resource utilization of steel slag is not only conducive to resource conservation, but also conducive to sustainable production and environmental protection. In this paper, the common ways of resource utilization of steel slag in construction, agriculture, industry, and catalysis are reviewed. Steel slag as a solid waste with great development potential and large output is expected to be widely developed into high value-added products such as catalytic material in the future.