Search

• Use of CO 2 in pyrolysis to develop an environmentally benign food waste treatment method. • More non-condensable gases are generated under CO 2 atmosphere. • Less condensable compounds are generated under CO 2 atmosphere. • CO 2 may inhibit free radical addition and/or dehydrogenation of linear compounds. Herein, carbon dioxide (CO 2) was applied to thermal treatment of real food waste to develop an environmentally benign way to dispose food waste. The food waste used in this study was collected from a food waste treatment plant. The application of CO 2 to the thermal treatment of food waste affected the amount of non-condensable gases and condensable compounds produced from the thermal process, while it did not affect the amount of solid residue. When CO 2 was supplied during the thermal treatment of food waste, less condensable compounds but more non-condensable gases such as H 2 , CO, and CH 4 were generated during the thermal treatment of food waste at a range of temperatures from 400 to 700 °C. In addition to the change in product distribution, the generation of cyclic compounds was inhibited by applying CO 2 to the thermal treatment. For example, approximately 30% less ring-structured compounds (e.g., benzene derivatives) were produced from the thermal treatment at 700 °C in CO 2 condition than from the thermal treatment in inert condition. This was likely because CO 2 inhibits gas phase free radical addition and/or dehydrogenation of linear compounds. This study suggests that the application of CO 2 to thermally treating food waste would help develop a more environmentally friendly food waste treatment method. [ABSTRACT FROM AUTHOR]

Highlights • CO 2 plays a critical role in characteristics of pyrolytic products. • The use of CO 2 improves thermal efficiency of pyrolysis of waste feedstocks. • CO 2 -assisted pyrolysis suppresses harmful chemical formation. Abstract Pyrolysis is a thermochemical conversion method for the production of energy and chemicals from carbonaceous substances. In this review, we emphasize the recent progress in the pyrolysis of waste feedstocks in the presence of carbon dioxide (CO 2). CO 2 -assisted pyrolysis is compared to typical pyrolysis (i.e., pyrolysis under inert environment, such as nitrogen). It has been shown that CO 2 plays a crucial role in increasing the yield of combustible permanent gas (e.g., carbon monoxide) while decreasing tar yield. CO 2 -assisted pyrolysis is also an attractive technique to treat waste (municipal solid waste, plastic waste, etc.) because CO 2 enhances the thermal cracking of volatile species, thereby suppressing the formation of harmful chemical compounds, such as benzene derivatives and polycyclic aromatic hydrocarbons. In addition to highlighting the recent achievements in the CO 2 -assisted pyrolysis processes, we discuss the points that should be considered for future research. [ABSTRACT FROM AUTHOR]

Anthropogenic activities and advancements in industries boost global energy demand and increase fossil fuel consumption, causing several global environmental problems, such as climate change. As a climate change mitigation strategy, the use of renewable energy technologies has gained unprecedented interest. In particular, the thermochemical processing of lignocellulosic biomass integrated with other renewable energy technologies has emerged rapidly. It is critical to select appropriate integrated renewable energy system configurations for sustainable and feasible power generation towards higher environmental benefits. Understanding the possible configurations of thermochemical lignocellulosic biomass processing technologies (gasification, pyrolysis, hydrothermal gasification, or hydrothermal carbonization) integrated with renewable energy technologies (solar thermal, fuel cell, fusion power, or energy storage) is crucial for the further development and propagation of the integrated renewable energy system. Hence, we provide a systematic review of the thermochemical conversion of lignocellulosic biomass integrated with the other renewable energy technologies. Finally, the challenges associated with the implementation of these systems and suggestions for future research on the systems are discussed. • Renewable energy technology is integrated with thermochemical biomass conversion process. • The integrated bioenergy systems help overcome limitations of single-source energy systems. • Challenges and prospects for the integrated systems are highlighted. [ABSTRACT FROM AUTHOR]

Despite the widespread use of biodegradable mulch films, they are often unsuitable for disposal in open environments and cannot be recycled in the same manner as conventional plastics; hence, an effective disposal method needs to be suggested. Herein, pyrolysis of biodegradable mulch film made of polybutylene adipate terephthalate (PBAT) and polylactic acid (PLA) was considered. The pyrolysis of the PBAT/PLA mulch film in CO 2 yielded more non-condensable gases than the pyrolysis in N 2 due to an enhanced thermal cracking of volatiles at 800 °C. At higher than 600 °C in CO 2 , reverse water-gas shift reaction considerably increased CO selectivity. Using CO 2 in the pyrolysis suppressed the generation of wax and char, attributed to CO 2 enhancing not only thermal cleavage of pyrolytic volatiles released from the PBAT/PLA mulch film but also O–H and C–H bonds existing on the substance. The CO 2 pyrolysis agent forwarded the cleavage of the polymeric bond of PBAT to produce more monomeric compounds (e.g., adipates and phthalates), while it suppressed radical reactions to produce less polycyclic compounds and phenyls. Rising temperature raised the gaseous pyrolyzate yield and lowered the char and wax yields. The use of CO 2 agents in pyrolysis has a significant feature of upcycling biodegradable plastic wastes. [Display omitted] • Pyrolysis was suggested as a method to dispose of biodegradable mulch film (BMF). • CO 2 medium enhanced the yield of combustible gas compounds from BMF via pyrolysis. • CO 2 medium suppressed the production of polycyclic and phenolic compounds for BMF pyrolysis. [ABSTRACT FROM AUTHOR]

Although biodegradable straws are widely used, they are often unsuitable for disposal in open environments and cannot be recycled in the same manner as conventional plastic straws. Hence, an effective disposal method needs to be developed. Herein, the thermochemical conversion of biodegradable straws made mostly of polylactic acid (PLA) was considered, and the effects of CO 2 on the characteristics of thermochemical products produced from biodegradable straws were explored. The thermochemical conversion of the biodegradable straw in CO 2 atmosphere yielded more non-condensable gases than the thermochemical conversion in N 2 owing to an enhanced thermal cracking of volatiles at 800 °C. At temperatures > 600 °C in CO 2 , the reverse water-gas shift reaction considerably increased the CO selectivity. Using CO 2 in the thermochemical conversion decreased yields of char and wax, which was attributed to CO 2 enhancing thermal cracking of volatiles evolved during the thermochemical conversion and C–H and O–H bonds present in the feedstock. The CO 2 thermal agent promoted the cleavage of the polymeric bond of PLA to produce up to 14-fold more lactic acid (the monomer of PLA) than that produced with N 2 agent, while it suppressed radical reactions to produce fewer phenyls and polycyclic aromatic hydrocarbons. Thermochemical treatment in a CO 2 environment has a significant feature of upcycling biodegradable plastic waste, such as biodegradable straws. • Biodegradable straw (BS) was thermochemically converted in N 2 and CO 2. • CO 2 promoted dehydrogenation, reverse water–gas shift reactions in the BS conversion. • CO 2 promoted polylactic acid bond cleavage, enhancing lactic acid recovery. • CO 2 decreased the production of polycyclic aromatic hydrocarbons and phenyls. [ABSTRACT FROM AUTHOR]

Everyday waste is a serious matter of concern because of its disruptive impact on the environment. Although disposal and reclaim of such material represent the first lines of intervention to solve this problem, upcycling strategies should eventually be necessary to reconvert huge amounts of the waste. In addition to waste, climate change caused by greenhouse gas emissions (e.g., carbon dioxide (CO 2)) is other global environmental problem. Here, we employed a thermal treatment process conducted in CO 2 environment to upcycle waste tea bag (a surrogate feedstock for everyday waste) and utilize CO 2 simultaneously. Through lab-scale experiments, 6 wt% caprolactam (a value-added nylon monomer), 12.7 wt% combustible gases (higher heating value (HHV): 24.8 MJ kg−1), and 13.8 wt% char (HHV: 28.1 MJ kg−1) were obtained at 500 °C. Based on the experimental results, a large-scale energy analysis of the process was conducted by developing a simulation model of an integrated process to produce caprolactam-rich liquid product. For the integrated process, CO 2 in gaseous product mixture is separated, and the separated CO 2 is recirculated to the thermal treatment step. The combustible gases and char are used to supply energy to thermal treatment and separation steps. The proposed process has a significant feature that there is no need for external energy with no CO 2 emission (i.e., CO 2 is fully recirculated in the waste treatment process). • Tea waste treatment process was proposed via experiment and large-scale simulation. • Through the process, fuels and monomer could be produced from waste tea bag. • The proposed process requires no external energy with no CO 2 emission. [ABSTRACT FROM AUTHOR]

• Everyday waste such as waste tea bag was valorized via CO 2 -assisted pyrolysis. • High temperature led to yielding more gas and less solid products. • CO 2 pyrolysis medium yielded more hydrogen and less phenolic compounds. • Char obtained under CO 2 atmosphere had higher heating value that is comparable to coal. Pyrolysis is an effective method for both waste valorization and treatment. Herein, carbon dioxide-assisted pyrolysis was conducted for the valorization and treatment of everyday waste, namely used tea bags. The effects of pyrolysis temperature and medium (N 2 and CO 2) on the composition and yield of the pyrolytic products were explored. The changes in the pyrolysis temperature and pyrolysis medium affected the compositions and yields of pyrolytic products. More non-condensable gases and less char were produced as the temperature increased. CO 2 increased the yield of pyrolytic gases, particularly hydrogen and also prevented the formation of environmental pollutants such as phenolic compounds, benzene derivatives, and polycyclic aromatic hydrocarbons. The char produced from waste tea bags via CO 2 -assisted pyrolysis had a higher heating value (26.8 MJ kg−1) comparable to that of coal. This study demonstrates the effectiveness of CO 2 utilization in pyrolysis for valorization of everyday waste. [ABSTRACT FROM AUTHOR]

Food waste is one of the world's most serious environmental issues, with waste and losses generated at every stage of the food supply chain. There are various waste management methods for the disposal of food waste, but these have several problems such as high costs, the generation of toxic by-products, and environmental pollution. Pyrolysis has recently attracted increased interest as a potentially sustainable and environmentally friendly solution for the valorization of food waste via the development of novel products. This review focuses on state-of-the-art non-catalytic and catalytic pyrolysis processes for a wide range of food waste types that can generate high-quality liquid, solid, and gas phase products. The aim of this study is to review the effect of the reaction parameters and catalyst selection on pyrolysis performance and the distribution of pyrolytic products. This is because the production of desired compounds such as bio-oil, syngas, and biochar primarily depends on these factors. Here, we highlight the results for several methods of food waste pyrolysis that utilize different materials, catalysts, and microwave irradiation settings. This review also discusses the drawbacks of current pyrolysis technology and suggests further research that needs to be conducted on the transformation of food waste into value-added products. [ABSTRACT FROM AUTHOR]

A Pt catalyst supported on activated carbon (Pt/AC) was used for an environmentally friendly thermal treatment of food waste under an inert atmosphere (i.e., pyrolysis). This catalyst influenced the amounts of condensable hydrocarbons and noncondensable gases but not that of the solid remaining after the pyrolysis; in particular, it contributed to shifting the carbon distribution from the condensable hydrocarbons to the noncondensable gases for the food waste pyrolysis. Moreover, its use suppressed the generation of harmful chemical compounds, especially at high temperatures. For example, a Pt/AC-catalyzed pyrolysis at 700 °C produced about 4 times fewer benzene derivatives than the same treatment without a catalyst; this probably occurred because the Pt sites catalyzed the decyclization reaction and/or the free radical mechanism, which is dominant in the thermal cracking of carbon-containing feedstock. This study suggests that a Pt/AC-catalyzed pyrolysis would be a more environmentally benign food waste treatment method. • The Pt catalyst influenced the amounts of the products of food waste pyrolysis. • The Pt catalyst reduced the generated condensable hydrocarbon content. • The Pt catalyst increased the generated noncondensable gas content. • The Pt catalyst reduced the generated benzene derivative content. [ABSTRACT FROM AUTHOR]