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The escalating volume of sewage sludge (SS) generated poses challenges in disposal, given its potential harm to the environment and human health. This study explored sustainable solutions for SS management with a focus on energy recovery. Employing CO 2 -assisted pyrolysis, we converted SS into flammable gases (H 2 and CO; syngas). Single-stage pyrolysis of SS in a CO 2 conditions demonstrated that CO 2 enhances flammable gas production (especially CO) through gas phase reactions (GPRs) with volatile matter (VM) at temperatures ≥520 °C. Specifically, the CO 2 partially oxidized the VM released from SS and concurrently underwent reduction into CO. To enhance the syngas production at temperatures ≤520 °C, multi-stage pyrolysis setup with additional heat energy and a Ni/Al 2 O 3 catalyst were utilized. These configurations significantly increased flammable gas production, particularly CO, at temperatures ≤520 °C. Indeed, the flammable gas yield in the catalytic pyrolysis of SS increased from 200.3 mmol under N 2 conditions to 219.2 mmol under CO 2 conditions, representing a 4.4-fold increase compared to single-stage pyrolysis under CO 2 conditions (50.0 mmol). By integrating a water-gas-shift reaction, the flammable gases produced from CO 2 -assisted catalytic pyrolysis were expected to have the potential to generate revenue of US$4.04 billion. These findings highlight the effectiveness of employing CO 2 in SS pyrolysis as a sustainable and effective approach for treating and valorising SS into valuable energy resources., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

To address the challenges associated with medical plastic waste and to characterize its heterogeneity, non-recyclability, and potential biohazard risks, this study explored a carbon dioxide (CO 2 )-assisted pyrolysis process as a sustainable disposal method. Medical plastic waste typically includes polypropylene, polystyrene, and polyvinyl chloride. To experimentally evaluate the functional reactivity of CO 2 , we employed three pyrolysis setups (one-stage, two-stage, and catalytic processes). The technical advantages of using CO 2 over inert gases such as nitrogen (N 2 ) were demonstrated through pyrolysis tests. The results showed that energy production was enhanced under CO 2 conditions, with catalytic pyrolysis generating 146% more flammable gases compared to pyrolysis in an N 2 environment. The use of CO 2 also led to a reduction in the formation of toxic chemicals due to improved thermal cracking. The CO 2 -assisted pyrolysis process exhibited net negative CO 2 emissions when a catalyst was present, as a substantial amount of CO 2 was consumed during the process. In conclusion, CO 2 -assisted pyrolysis of medical plastic waste offers a sustainable management solution that maximizes the utilization of carbon resources., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Thermosetting polymers are used in a wide range of applications due to their robust mechanical strength and superior flame retardancy. Despite these technical benefits, recycling of thermosetting polymers has been challenging because of their crosslinking nature. Moreover, their disposal through conventional methods (landfill and combustion) poses environmental concerns, such as microplastics and air pollutants. To address these issues, this study introduces a thermo-chemical disposal platform for thermosetting polymer wastes that employs carbon dioxide (CO 2 ) as a reactive medium. In this work, melamine-formaldehyde was used as model compound of thermosetting polymers. In single-stage pyrolysis, it was revealed that CO 2 plays a crucial role in controlling in the compositional matrices of pyrolytic gases, liquid products, and wax. These compositional changes were attributed to the homogeneous reactions between CO 2 and the volatile compounds released from the thermolysis of MF. To enhance the thermal cracking of the MF, a double-stage pyrolysis process was tested, which increased the production of pyrolytic gases and eliminated wax formation. However, the slow kinetics governing the reactivity of CO 2 limits the occurrence of homogeneous reactions. A nickel-based catalyst was used to accelerate reaction kinetics. The catalytic pyrolysis under CO 2 conditions led to substantial increases in syngas (H 2 and CO) production of 880% and 460%, respectively, compared with double-stage pyrolysis. These findings demonstrate that thermosetting polymer wastes can be valorized into gaseous fuels through thermo-chemical process, and CO 2 enhances the recovery of energy and chemicals. Therefore, this study presents an innovative technical platform to convert thermosetting polymer wastes and CO 2 into syngas., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This study explored the valorisation of silkworm by-product, a major by-product of the silk industry (sericulture), which amounts to 16 million tonnes annually. The focus was on transforming waste into energy resources through pyrolysis under CO 2 conditions. In one-stage pyrolysis, the evolution of syngas under N 2 was found to be comparable to that under CO 2 . A notable allocation of carbon to biocrude rather than syngas was observed. The two-stage pyrolysis resulted in increased syngas production. However, achieving a homogeneous reaction between CO 2 and the volatiles liberated from silkworm byproduct proved challenging. Indeed, the reaction kinetics governing CO 2 reactivity was not fast although the temperature windows of the reaction were aligned in the two-stage pyrolysis. To address this issue, pyrolysis was performed using a Ni-based catalyst to expedite the reaction kinetics. Consequently, syngas formation, particularly CO formation, was significantly enhanced under CO 2 conditions compared to that under N 2 conditions. The syngas yield under CO 2 was 36.42 wt% which was 2-fold higher than that of N 2 . This suggested the potential of CO 2 altering the carbon distribution from biocrude to syngas. This strategy would contribute to the establishment of sustainable production of silk by converting sericulture by-product into energy/chemical resources., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

This study investigated the conversion of agricultural biomass waste (specifically, spent mushroom substrate) into syngas via pyrolysis. Carbon dioxide was used to provide a green/sustainable feature in the pyrolysis process. All the experimental data highlight the mechanistic role of carbon dioxide (CO 2 ) in the process, demonstrated by the enhanced carbon monoxide (CO) yield from pyrolysis under CO 2 . Carbon dioxide was indeed reactive at ≥ 500 ˚C. Carbon dioxide was reduced and subsequently oxidized volatiles stemming from the thermolysis of spent mushroom substrate via the gas-phase reaction, thereby resulting in the enhanced formation of CO. Carbon dioxide radically diverted the carbon distribution patterns of the pyrogenic products, as more carbon in the oil was allocated to syngas by the gas-phase reaction of volatiles and CO 2 . To enhance the mechanistic role of CO 2 , a Ni-based catalyst was added to the pyrolysis process, which greatly accelerated the gas-phase reaction of volatiles and CO 2 ., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

This study proposes a sustainable hydrogen production platform using a fast-growing and inedible biomass waste, silver grass (Miscanthus sinensis). Pyrolysis of silver grass waste (SGW) was investigated using CO 2 as a co-feedstock, focusing on the distribution of hydrogen in different products. When the catalyst was absent, hydrogen element distribution to H 2 gas during pyrolysis of SGW at 800 °C reached 10 wt%. During pyrolysis with the Ni/SiO 2 catalyst, 60.3 wt% of hydrogen was converted into H 2 gas, and 7.3 wt% of hydrogen was distributed in gaseous hydrocarbons at 600 °C. Owing to the addition of CO 2 , CO production was promoted by the catalytic conversion of CO 2 and volatile matter. Notably, CO 2 has been proven to be a useful reactant for producing value-added CO. Thus, catalytic pyrolysis in the presence of CO 2 can be considered as a renewable approach to produce flammable gases with the mitigation of CO 2 emissions., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier Ltd.)

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 CO 2 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/SiO 2 ). The yield of H 2 from the catalytic pyrolysis process of WB was more than one magnitude higher comparing to that from the non-catalytic one. H 2 formation also increased as catalyst loading increased. When flow gas was switched from inert gas to CO 2 , CO gas formation was enhanced due to the chemical reactions between CO 2 and styrene derivatives over Ni catalysts. Syngas (H 2 /CO) formation under the CO 2 condition was 5 times higher in comparison to the N 2 condition in catalytic pyrolyses of WB with 10 wt% Ni/SiO 2 . CO 2 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 (CO 2 ), converting them into value-added fuel., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

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 CO 2 as a co-reactant. AHH was chosen as it discharges bisphenol A (BPA) and aromatic compounds. Under CO 2 condition, emissions of BPA and its derivatives were suppressed by 14.5% due to gas phase reactions (GPRs) with CO 2 . 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 CO 2 -assisted catalytic pyrolysis of AHH decreased by 86.1% and 66.7% over Ni and Co catalysts, comparing to those from N 2 environment., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Global warming increases a chance of eutrophication, and such fact offers that unhygienic organic waste materials (OWMs) in water must be treated. Hence, this study laid emphasis on the thermal-chemical (pyrolysis) process to establish a rapid valorization platform for OWMs. Indeed, OWMs were collected from the eutrophication site, and OWMs were mainly comprised of lignocellulosic biomass, microalgae (cyanobacteria) and the diverse types of bacteria (commonly observed from livestock waste). In an attempt to offer more sustainable valorization route for OWMs, CO 2 was used as a raw material in pyrolysis process. From the CO 2 -assisted pyrolysis, the conversion of CO 2 and OWMs into gaseous fuel (CO) was observed. A cheap Ni-based catalyst was used in pyrolysis of OWMs as a strategic practice to promote conversion of CO 2 into CO. Indeed, syngas production (38 %) was enhanced from catalytic pyrolysis over Ni/SiO 2 under CO 2 condition as compared to inert condition (N 2 )., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Cellulose acetate (CA) is one of widely used polymers for chemical and medical applications due to its versatile physico-chemical functionalities. Although its recycle is available after a deacetylation process, the recycle process releases a huge amount of wastewater. Thus, this study investigated a direct disposal process of CA with its valorization to syngas (H 2 and CO) through pyrolysis. To construct more environmentally benign process, CO 2 was used as a co-feedstock with CA to simultaneously convert them into syngas. Pyrolysis of CA in N 2 was performed as a reference study to examine the effectiveness of CO 2 on valorization of CA. Acetic acid and methyl acetate were main volatile pyrolysates (VPs) from CA pyrolysis, and the further thermal cracking of VPs resulted in syngas and CH 4 formations under both N 2 and CO 2 conditions. To expedite syngas formations, multi-stage pyrolysis (two-stage pyrolysis) and catalytic pyrolysis were employed. With the increased thermal energy through two-stage pyrolysis, four times more production of syngas was shown, comparing to the result of a single-stage pyrolysis. With Ni catalysts, the syngas formation was the two orders of magnitude higher than the single-stage pyrolysis, and the significant enhancement of CO formation was shown in the presence of CO 2 due to combined effects of CO 2 and the Ni-based catalysts. This CO enhancement resulted from catalytically expedited gas phase reactions between CO 2 and VPs evolved from CA. In addition, the CO 2 contributed to the suppression of coke deposition on the catalyst, thereby suggesting more technical and environmental benefits of CO 2 as a reactive co-feedstock of pyrolysis in reference to N 2 . Therefore, this study proved the direct and versatile technical platform to convert CA and CO 2 into syngas., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

This study investigated the mechanistic functions of CO 2 on the pyrolysis of two different biomasses to elucidate the effect of CO 2 on syngas formations during pyrolysis. To this end, CO 2 -assisted pyrolysis of cellulosic biomass (barnyard grass, Echinochloa) and lignin-rich woody biomass (retinispora, Chamaecyparis obtusa) were compared. The confirmed mechanistic effectiveness of CO 2 on pyrolysis of biomass was gas phase reactions between CO 2 and volatile matters from biomass pyrolysis. Lignin-rich biomass had more CO 2 susceptibility, resulting in more enhanced CO formation via the gas phase reactions. To expedite the slow reaction rate of the gas phase reactions during biomass pyrolysis, earth-abundant catalysts (Co/SiO 2 and Ni/SiO 2 ) were employed for pyrolysis of two biomass substrates. With Co and Ni catalysts, the syngas formations were 2 and 3 times higher comparing to the pyrolysis of without catalyst. The cumulative formations of syngas from lignin-rich biomass was nearly doubled than that from cellulosic biomass., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

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, CO 2 was used as a raw material for WT pyrolysis. Thermal cracking of WT led to the production of syngas and CH 4 under the CO 2 environment. CO 2 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, CO 2 -assisted catalytic pyrolysis had 3- and 8-times higher production of H 2 and CO, respectively. This process also suppressed catalyst deactivation, converting more than 80 wt% of WT into syngas and CH 4 . The more generation of CO from the use of CO 2 as a raw material offers an effective means to minimize the formations of harmful chemical species, such as benzene derivatives and polycyclic aromatic hydrocarbons., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

To valorize tea waste (TW), catalytic pyrolysis was done as a practical measure for recovering energy as a form of syngas. Considering CO 2 as a reactive gas medium in place of conventional pyrolysis gas, a sustainable pyrolysis platform was established. In addition, mechanistic effectiveness of CO 2 on TW pyrolysis was examined. In the presence of CO 2 , homogeneous reaction with volatile organic compounds (VOCs) derived from TW pyrolysis contributed to CO formation. To enhance the formation of syngas at low pyrolysis temperature, catalytic pyrolysis over a Ni/SiO 2 was investigated. The synergistic effects of Ni/SiO 2 catalyst and CO 2 promoted thermal cracking of VOCs and further homogeneous reaction with CO 2 , thereby resulting in the substantial enhancement (28 times more) of H 2 and CO production than non-catalytic pyrolysis. It was also confirmed that CO 2 could be considered a reactive gas medium to produce biochar (34-35 wt.% yield), having competitive porosity and surface area, in comparison to that from pyrolysis in N 2 . Therefore, CO 2 can be employed to build a sustainable waste conversion platform for energy and biochar production through pyrolysis instead of using N 2 ., Competing Interests: Declaration of Competing Interest None., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Pyrolysis of swine manure (SM) was conducted as a case study to establish an environmentally sound management of livestock manure. To build a more renewable pyrolysis platform for SM, this study selected carbon dioxide (CO 2 ) as the reaction medium. In addition, CO 2 was used in pyrolysis of SM to restrict the formation of toxic compounds, such as benzene derivatives and polycyclic aromatic hydrocarbons (PAHs). A series of thermo-gravimetric analysis (TGA) tests was done to understand the thermolysis of SM in the CO 2 environment. The TGA tests elucidated no occurrence of heterogeneous reactions between the SM sample and the CO 2 . Moreover, the TGA tests of SM suggested that SM contains more volatile matter (VM) than lignocellulosic biomass. Non-catalytic transesterification of SM lipids confirmed that the dried SM sample contained 8.85 ± 0.05 wt% of lipids. This study also confirmed that the mechanistic role of CO 2 was realized through the gas phase reactions between volatile pyrolysates evolved from the thermolysis of SM and CO 2 . In summary, CO 2 donates O, enhancing the generation of CO through homogeneous reactions. In parallel, this study confirmed that CO 2 suppress dehydrogenation. Therefore, the identified gas phase reactions between volatile pyrolysates and CO 2 led to the compositional modifications in the condensable pyrolysates. However, such mechanistic features arising from CO 2 only initiated at ≥520 °C. To expedite the reaction kinetics of the homogeneous reaction triggered by CO 2 , steel slag (SS) was used as a catalyst. Hence, the reaction kinetics associated with the mechanistic role of CO 2 were substantially enhanced (up to 80%) when SS was used as a catalyst. Therefore, all experimental findings strongly suggest that CO 2 can be utilized as a raw material in a thermo-chemical process. More importantly, all observations suggest that CO 2 lopping can also be achieved in a thermo-chemical process. Lastly, this study shows that the high Cu content in SM was effectively immobilized through pyrolysis. Conclusively, this study experimentally proved that CO 2 could be promising for restricting the formation of toxic pollutant in the thermo-chemical treatment in that CO 2 offers an innovative and strategic means for controlling the ratio of C to H. Note that aromaticity and toxicity of chemical compounds are highly contingent on the ratio of C to H., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)

In an effort to seek a new technical platform for disposal of drinking water treatment sludge (DWTS: alum sludge), pyrolysis of DWTS was mainly investigated in this study. To establish a more sustainable thermolytic platform for DWTS, this study particularly employed CO 2 as reactive gas medium. Thus, this study laid great emphasis on elucidating the mechanistic roles of CO 2 during the thermolysis of DWTS. A series of the TGA tests of DWTS in CO 2 in reference to N 2 revealed no occurrence of the heterogeneous reaction between CO 2 and the sample surface of DWTS. As such, at the temperature regime before initiating the Boudouard reaction (i.e., ≥700 °C), the mass decay patterns of DWTS in N 2 and CO 2 were nearly identical. However, the gaseous effluents from lab-scale pyrolysis of DWTS in CO 2 in reference to N 2 were different. In sum, the homogeneous reactions between CO 2 and volatile matters (VMs) evolved from the thermolysis of DWTS led to the enhanced generation of CO. Also, CO 2 suppressed dehydrogenation of VMs. Such the genuine mechanistic roles of CO 2 in the thermolysis of DWTS subsequently led to the compositional modifications of the chemical species in pyrolytic oil. Furthermore, the biochar composite was obtained as byproduct of pyrolysis of DWTS. Considering that the high content of Al 2 O 3 and Fe-species in the biochar composite imparts a strong affinity for As(V), the practical use of the biochar composite as a sorptive material for arsenic (V) was evaluated at the fundamental levels. This work reported that adsorption of As(V) onto the biochar composite followed the pseudo-second order model and the Freundlich isotherm model., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)

To valorize biomass waste, pyrolysis of orange peel was mainly investigated as a case study. In an effort to establish a more sustainable thermolytic platform for orange peel, this study particularly employed CO 2 as reactive gas medium. Accordingly, this study laid great emphasis on elucidating the mechanistic role of CO 2 in pyrolysis of orange peel. The thermo-gravimetric analysis (TGA) confirmed that no occurrence of the heterogeneous reactions between the solid sample and CO 2 . However, the gaseous effluents from pyrolysis of orange peel experimentally proved that CO 2 effectively suppressed dehydrogenation of volatile matters (VMs) evolved from the thermolysis of orange peel by random bond scissions. Moreover, CO 2 reacted VMs, thereby resulting in the formation of CO. Note that the formation of CO was being initiated at temperatures ≥550 °C. The two identified roles of CO 2 led to the compositional modification of pyrolytic oil by means of lowering aromaticity., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

This study employs chicken manure as a feedstock to produce different forms of energy to abate environmental burdens. To achieve ultimate carbon management, the possible utilization of CO 2 during pyrolysis of chicken manure was fundamentally investigated. The roles of CO 2 in pyrolysis of chicken manure include enhanced thermal cracking and shifting of the carbon distribution via reaction between volatile organic compounds and CO 2 . The identified roles induced by CO 2 were catalytically enhanced because of the inorganic content in the feedstock. The morphology of biochar created from the chicken manure pyrolysis was significantly affected by CO 2 . For example, a well-developed pore structure was observed in the biochar developed under a CO 2 environment; this biochar was used as an effective porous material for biodiesel synthesis., (Copyright © 2019 Elsevier Inc. All rights reserved.)

As a way of improving process efficiency of pyrolysis of waste biomass, the effect of carbon dioxide (CO 2 ) on pyrolysis of spent coffee grounds (SCGs) was examined using a two-stage pyrolysis reactor consisting of a region with increasing temperature and an isothermal region. It was experimentally validated that CO 2 accelerates thermal cracking of organic compounds formed during the pyrolysis of SCGs. The expedited thermal cracking attributed to employing CO 2 in pyrolysis of SCGs led to changing pyrolytic products in gas, liquid, and solid phases. The production of gaseous carbon monoxide was increased when using CO 2 as the pyrolysis medium. In liquid pyrolytic products, the formation of phenolic compounds was hindered in the CO 2 -assited pyrolysis. Biochar morphology (solid pyrolytic product) was also changed with different pyrolysis environments. This study shows that CO 2 can help improve applicability of pyrolysis of waste biomass by modifying three phase pyrolytic products in a two-stage pyrolyzer., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

This study proposes a strategic principle to enhance the thermal efficiency of pyrolysis of municipal solid waste (MSW). An environmentally sound energy recovery platform was established by suppressing the formation of harmful organic compounds evolved from pyrolysis of MSW. Using CO 2 as reaction medium/feedstock, CO generation was enhanced through the following: 1) expediting the thermal cracking of volatile organic carbons (VOCs) evolved from the thermal degradation of the MSWs and 2) directly reacting VOCs with CO 2 . This particular influence of CO 2 on pyrolysis of the MSWs also led to the in-situ mitigation of harmful organic compounds (e.g., benzene derivatives and polycyclic aromatic hydrocarbons (PAHs)) considering that CO 2 acted as a carbon scavenger to block reaction pathways toward benzenes and PAHs in pyrolysis. To understand the fundamental influence of CO 2 , simulated MSWs (i.e., various ratios of biomass to polymer) were used to avoid any complexities arising from the heterogeneous matrix of MSW. All experimental findings in this study suggested the foreseeable environmental application of CO 2 to energy recovery from MSW together with disposal of MSW., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

This work confirmed that dominant microalgal strain in the eutrophic site (the Han River in Korea) was Microcystis aeruginosa (M. aeruginosa) secreting toxins. Collected and dried microalgal biomass had an offensive odor due to microalgal lipid, of which the content reached up to 2±0.2wt.% of microalgal biomass (dry basis). This study has validated that the offensive odor is attributed to the C3-6 range of volatile fatty acids (VFAs), which was experimentally identified by the non-catalytic transformation of triglycerides (TGs) and free fatty acids (FFAs) in microalgal biomass into fatty acid methyl esters (FAMEs). In particular, this study mechanistically investigated the influence of CO2 in the thermal destruction (i.e., pyrolysis) of hazardous microalgal biomass in order to achieve dual purposes (i.e., thermal disposal of hazardous microalgal biomass and energy recovery). The influence of CO2 in pyrolysis of microalgal biomass was identified as 1) the enhanced thermal cracking behaviors of volatile organic compounds (VOCs) from the thermal degradation of microalgal biomass and 2) the direct gas phase reaction between CO2 and VOCs. These identified influences of CO2 in pyrolysis of microalgal biomass significantly enhanced the generation of CO: the enhanced generation of CO in the presence of CO2 was 590% at 660°C, 1260% at 690°C, and 3200% at 720°C. In addition, two identified influences of CO2 (i.e., enhanced thermal cracking and direct gas phase reaction) occurred simultaneously and independently. The identified gas phase reaction in the presence of CO2 was only initiated at temperatures higher than 500°C, which was different from the Boudouard reaction. Lastly, the experimental work justified that exploiting CO2 as a reaction medium and/or chemical feedstock will provide new technical approaches for controlling syngas ratio and in-situ air pollutant control without using catalysts., (Copyright © 2016 Elsevier B.V. All rights reserved.)

This work mechanistically investigated the influence of CO2 in the thermo-chemical process of microalgal biomass (Chlorella vulgaris and Microcystis aeruginosa) to achieve a fast virtuous cycle of carbon via recovering energy. This work experimentally justified that the influence of CO2 in pyrolysis of microalgal biomass could be initiated at temperatures higher than 530 °C, which directly led to the enhanced generation of syngas. For example, the concentration of CO from pyrolysis of M. aeruginosa increased up to ∼ 3000% at 670 °C in the presence of CO2. The identified universal influence of CO2 could be summarized by the expedited thermal cracking of VOCs evolved from microalgal biomass and by the unknown reaction between VOCs and CO2. This identified effectiveness of CO2 was different from the Boudouard reaction, which was independently occurred with dehydrogenation. Thus, microalgal biomass could be a candidate for the thermo-chemical process (pyrolysis and gasification)., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Our work reported the CO2-assisted mitigation of PAHs and VOCs in the thermo-chemical process (i.e., pyrolysis). To investigate the pyrolysis of used tires to recover energy and chemical products, the experiments were conducted using a laboratory-scale batch-type reactor. In particular, to examine the influence of the CO2 in pyrolysis of a tire, the pyrolytic products including C1-5-hydrocarbons (HCs), volatile organic carbons (VOCs), and polycyclic aromatic hydrocarbons (PAHs) were evaluated qualitatively by gas chromatography (GC) with mass spectroscopy (MS) as well as with a thermal conductivity detector (TCD). The mass balance of the pyrolytic products under various pyrolytic conditions was established on the basis of their weight fractions of the pyrolytic products. Our experimental work experimentally validated that the amount of gaseous pyrolytic products increased when using CO2 as a pyrolysis medium, while substantially altering the production of pyrolytic oil in absolute content (7.3-17.2%) and in relative composition (including PAHs and VOCs). Thus, the co-feeding of CO2 in the pyrolysis process can be considered an environmentally benign and energy efficient process., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

This study investigated the utilization of CO2 as carbon neutral chemical feedstock in the thermo-chemical processing (i.e., pyrolysis and gasification) of biomass to enhance sustainability via modification of the composition of end products. To justify the universal function of CO2 in the thermo-chemical process, the biomass experimented on in this work was not limited to ligno-cellulosic biomass; seaweed (i.e., red macroalgae) was used to expand biofuel feedstock beyond terrestrial biomass. Our experimental results validated the achieved enhanced generation of ∼200% for H2 and ∼1000% for CO by means of adopting CO2 in the thermo-chemical process, as compared to the case in N2. This can be explained by the enhanced thermal cracking of volatile organic carbons (VOCs) evolved from the thermal degradation of biomass and the reaction between CO2 and VOCs. Considering mass balance under our experimental conditions, we confirmed reaction between CO2 and VOCs, which was universally observed in pyrolysis of all biomass samples used in this work. Thus, the identified influence of CO2 in the thermo-chemical process can be directly applied in a variety of research and industrial fields, which would be environmentally desirable.

This work mainly presents the influence of CO2 as a reaction medium in the thermo-chemical process (pyrolysis) of waste biomass. Our experimental work mechanistically validated two key roles of CO2 in pyrolysis of biomass. For example, CO2 expedited the thermal cracking of volatile organic compounds (VOCs) evolved from the thermal degradation of spent coffee ground (SCG) and reacted with VOCs. This enhanced thermal cracking behavior and reaction triggered by CO2 directly led to the enhanced generation of CO (∼ 3000%) in the presence of CO2. As a result, this identified influence of CO2 also directly led to the substantial decrease (∼ 40-60%) of the condensable hydrocarbons (tar). Finally, the morphologic change of biochar was distinctive in the presence of CO2. Therefore, a series of the adsorption experiments with dye were conducted to preliminary explore the physico-chemical properties of biochar induced by CO2., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

This work proposed a novel methodology for energy recovery from sewage sludge via the thermo-chemical process. The impact of CO2 co-feed on the thermo-chemical process (pyrolysis and gasification) of sewage sludge was mainly investigated to enhance thermal efficiency and to modify the end products from the pyrolysis and gasification process. The CO2 injected into the pyrolysis and gasification process enhance the generation of CO. As compared to the thermo-chemical process in an inert atmosphere (i.e., N2), the generation of CO in the presence of CO2 was enhanced approximately 200% at the temperature regime from 600 to 900 °C. The introduction of CO2 into the pyrolysis and gasification process enabled the condensable hydrocarbons (tar) to be reduced considerably by expediting thermal cracking (i.e., approximately 30-40%); thus, exploiting CO2 as chemical feedstock and/or reaction medium for the pyrolysis and gasification process leads to higher thermal efficiency, which leads to environmental benefits. This work also showed that sewage sludge could be a very strong candidate for energy recovery and a raw material for chemical feedstock., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Using biomass as a renewable energy source via currently available thermochemical processes (i.e., pyrolysis and gasification) is environmentally advantageous owing to its intrinsic carbon neutrality. Developing methodologies to enhance the thermal efficiency of these proven technologies is therefore imperative. This study aimed to investigate the use of CO2 as a reaction medium to increase not only thermal efficiency but also environmental benefit. The influence of CO2 on thermochemical processes at a fundamental level was experimentally validated with the main constituents of biomass (i.e., cellulose and xylan) to avoid complexities arising from the heterogeneous matrix of biomass. For instance, gaseous products including H2, CH4, and CO were substantially enhanced in the presence of CO2 because CO2 expedited thermal cracking behavior (i.e., 200-1000%). This behavior was then universally observed in our case study with real biomass (i.e., corn stover) during pyrolysis and steam gasification. However, further study is urgently needed to optimize these experimental findings.

The enhanced gasification of municipal solid waste (MSW) using carbon dioxide (CO(2)) as the gasification medium was investigated to achieve environmentally benign and energy efficient ways for the disposal of MSW. Two main steps of thermal decomposition of MSW were observed. The first thermal degradation step occurs at temperature between 280 and 350°C and consists of the decomposition of the biomass component into light C(1-3)-hydrocarbons. The second thermal degradation step occurs between 380 and 450°C and is mainly attributed to polymer components, such as plastics and rubber, in MSW. To extend this understanding to a more practical level, MSW samples were tested in a drop tube reactor (DTR) at a temperature range from 500 to 1000°C under various atmospheres with CO(2) concentrations of 0-30%. The release of major chemical species from the DTR has been determined using a micro-GC. For example, CO (≈ 30%), H(2) (≈ 25%) and CH(4) (≈ 10%) were generated., (Copyright © 2012. Published by Elsevier Ltd.)

The enhanced thermo-chemical process (i.e., pyrolysis/gasification) of various macroalgae using carbon dioxide (CO(2)) as a reaction medium was mainly investigated. The enhanced thermo-chemical process was achieved by expediting the thermal cracking of volatile chemical species derived from the thermal degradation of the macroalgae. This process enables the modification of the end products from the thermo-chemical process and significant reduction of the amount of condensable hydrocarbons (i.e., tar, ∼50%), thereby directly increasing the efficiency of the gasification process., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The CO(2) cofeed impact on the pyrolysis of styrene butadiene rubber (SBR) was investigated using thermogravimetric analysis (TGA) coupled to online gas chromatography/mass spectroscopy (GC/MS). The direct comparison of the chemical species evolved from the thermal degradation of SBR in N(2) and CO(2) led to a preliminary mechanistic understanding of the formation and relationship of light hydrocarbons (C(1-4)), aromatic derivatives, and polycyclic aromatic hydrocarbons (PAHs), clarifying the role of CO(2) in the thermal degradation of SBR. The identification and quantification of over 50 major and minor chemical species from hydrogen and benzo[ghi]perylene were carried out experimentally in the temperature regime between 300 and 500 °C in N(2) and CO(2). The significant amounts of benzene derivatives from the direct bond dissociation of the backbone of SBR, induced by thermal degradation, provided favorable conditions for PAHs by the gas-phase addition reaction at a relatively low temperature compared to that with conventional fuels such as coal and petroleum-derived fuels. However, the formation of PAHs in a CO(2) atmosphere was decreased considerably (i.e., ∼50%) by the enhanced thermal cracking behavior, and the ultimate fates of these species were determined by different pathways in CO(2) and N(2) atmospheres. Consequently, this work has provided a new approach to mitigate PAHs by utilizing CO(2) as a reaction medium in thermochemical processes.

Composite materials have been widely used because of their superior properties compared to those of the original material. Separation of the constituent materials is not easy in the recycling process, and such an effort lowers economic viability. As such, this study employed a pyrolysis as a valorizing method for the composite material. Disposable paper cup waste (DPCW) was chosen as the model compound for paper-plastic composites. To offer green/sustainable features, CO2 was employed as a raw and reactive material in the pyrolysis process. It was proved that DPCW primarily composed of cellulose (outer layer) and polyethylene (inner layer). In the single-stage and multistage pyrolysis of DPCW, the CO2 reactivity in the homogeneous reaction of CO2 and DPCW-derived volatiles was not rapid. To accelerate the reaction kinetics governing the reactivity of CO2, the catalytic pyrolysis of DPCW over Ni/SiO2 was performed. The formation of syngas increases significantly, suggesting that CO2 reactivity was catalytically enhanced. The generation of syngas (enhanced by CO2) was inversely related to the DPCW oil generation, indicating that more carbon was assigned from the oil to the gaseous pyrogenic products. The study results would offer a strategic means to valorize paper-plastic composites and CO2 into energy through pyrolysis. [ABSTRACT FROM AUTHOR]

Summary: To valorize disposed animal manure into flammable gases, pyrolysis of cattle manure (CM) was investigated in this study. To make this process more efficient and environmentally benign, CO2, a greenhouse gas, was harnessed as a reactive gas. In CO2‐assisted pyrolysis of CM, enhanced CO production was observed, compared to pyrolysis from inert condition (N2). The gas‐phase reactions between CO2 and gaseous biocrude produced from CM thermolysis led to improved CO formation. In reference to the case of lignocellulosic biomass (rice straw), 5 times more CO production was observed from CM pyrolysis under CO2. For an in‐depth study of CO2 functionality as an oxidant, the effects of operational parameters on syngas formation were considered. The key parameter to activate the functionality of CO2 was temperature. These results offer that CO2 and CM could be considered promising reactants to produce value‐added syngas in line with mitigation of pollutant emissions through a pyrolysis platform. [ABSTRACT FROM AUTHOR]

Summary: As the global vehicle demand increases, the significance of waste materials generated from end‐of‐life‐vehicles (ELVs) becomes more severe. However, the heterogeneity of most components of vehicles made them difficult to be recycled. In this study, a sustainable valorization platform for the vehicle wastes was suggested via pyrolysis process. As a case study, bumper waste was used as a feedstock material. Prior to the thermo‐chemical process of bumper waste, multiple analytical tools were employed to identify and quantify the chemical constituents of the bumper waste. Because the bumper consists of mainly polypropylene (PP), pyrolysis of bumper produced hydrogen and different types of hydrocarbons (HCs), and the product distribution was highly contingent on pyrolysis setups and operating conditions. One‐step pyrolysis of PP at 600°C resulted in C8‐46 aliphatic HCs, while two‐step pyrolysis converted the long‐chain HCs into C7‐8 aromatic compounds in line with H2 production. During catalytic pyrolysis over Co and Ni catalysts, the dehydrogenation of HCs led to rapid H2 generation with coke formation on the catalysts. When CO2 was used as a reactive gas medium, additional CO production and suppression of coke formation were shown through gas‐phase reactions between CO2 and volatile HCs evolved from thermolysis of PP. The alteration of H2/CO ratios (>15 to 0.7) of output gas also was achieved, controlling the N2/CO purge gas ratios during catalytic pyrolysis. Therefore, CO2‐assisted pyrolysis can be a considerable valorization platform of vehicle waste materials and CO2 by converting them into energy‐intensive products. [ABSTRACT FROM AUTHOR]

• Constructing waste to energy platform was achieved by macadamia nutshell pyrolysis. • For a sustainable energy production, CO 2 was utilized as a reactive gas medium. • Two stage CO 2 -cofeeding pyrolysis expedited syngas (H 2 and CO) formation. • Thermal cracking of VOCs via catalytic pyrolysis enhanced syngas formation. Here in this study, we laid great stress on a development of sustainable waste-to-energy (WtE) platform via CO 2 -cofeeding catalytic pyrolysis of macadamia nutshell (MNS) at mild temperature region. To this end, one-stage and two-stage (non-catalytic/catalytic) pyrolysis of MNS was performed to establish the fundamental relationship of temperature effect on syngas formation. The formation of gaseous pyrolysates was substantially enhanced when two-stage pyrolysis of MNS was applied, and second heating zone isothermally ran at 700 °C. Such the enhanced generation of gaseous pyrolysates from two-stage MNS pyrolysis of MNS was likely due to temperature-driven cracking of volatile organic compounds (VOCs). Also, catalytic two-stage pyrolysis of MNS was performed at lower isothermal running temperature (500 °C) over Ni/SiO 2 and Co/SiO 2. The enhanced formation of syngas (H 2 and CO) was observed from catalytic pyrolysis of MNS. Therefore, pyrolysis of MNS over Ni/SiO 2 or Co/SiO 2 could be a reliable platform for enhancing syngas formation at mild temperature (≤ 500 °C) under CO 2 environment. In addition, all experimental findings suggested that the use of CO 2 is beneficial in the WtE platform, and the use of CO 2 could be a practical climate change mitigation measure. [ABSTRACT FROM AUTHOR]

• 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]

• Using CO 2 in pyrolysis of brown algae enhanced the production of gaseous products by 610%. • Pyrolysis of brown algae in two-stage pyrolysis setup yielded a negligible amount of pyrolytic oil. • Oyster shell effectively provided CO 2 in in situ pyrolysis of brown algae in N 2 and enhanced CO production by 185%. • Ex situ brown algae pyrolysis in CO 2 with oyster shell at ≥315 °C produced 670% more CO and 3120% more H 2 than in situ pyrolysis. In this work, the pyrolysis of brown algae (Saccharina japonica (S. japonica)) was investigated to recover energy as a form of syngas (H 2 and CO). For this, this work emphasizes the use of CO 2 as a pyrolysis medium and oyster shell as a catalytic material in the pyrolysis of S. japonica. Pyrogenic products generated from the catalytic pyrolysis of S. japonica in N 2 and CO 2 were characterized. In particular, the enhanced generation of CO was substantial at 720 °C. This enhanced generation of CO was most likely because of the enhanced thermal cracking of volatile matter that evolved during the catalytic pyrolysis of S. japonica. The enhanced CO generation was likely catalytically expedited by biogenic salts such as calcite (CaCO 3) in the oyster shell. The introduced approach for exploiting CO 2 in the catalytic pyrolysis could be a more sustainable option to treat algal biomass such as brown algae and develop an effective waste-to-energy strategy. [ABSTRACT FROM AUTHOR]

• The conversion of carbon dioxide (CO 2) into fuels using solar energy. • Various materials improved the solar to energy conversion efficiencies for photocatalysts. • III-V semiconductors, oxide semiconductors and perovskites materials were highlighted. The conversion of carbon dioxide (CO 2) into fuels using solar energy have been studied extensively since it is very attractive in that this can provide a solution to both problems of the increasing carbon dioxide concentration in the atmosphere and the finding new energy sources. Various materials have been explored to improve the solar to energy conversion efficiencies for photocatalysts or photoelectrodes in light-assisted photoelectrochemical (PEC) systems. Although lots of progress have been, the efficiencies still need to be increased for future commercial applications. This review is focused on the recent works related to III-V semiconductors, oxide semiconductors and perovskites materials and the achievement by modifying the physical and chemical properties of these materials. Photovoltaic cell biased PEC system in which the absorption subsystem and the reduction subsystem can be optimized independently is described and a prospect in the CO 2 photoconversion systems is discussed. [ABSTRACT FROM AUTHOR]

• Strategic use of biochar for CO2 capture and storage (CCS). • Porosity of biochar proves a significant determinant for CCS. • Economic viability of biochar is superior in reference to other CCS materials. • Carbon negativity of biochar maximizes the effect of CCS. Dramatic increase of CO 2 emissions to sate the global carbon demand for chemicals, goods, and fuels has been regarded as one of the main contributors triggering global warming. Note that CO 2 emissions are over the Earth's full capacity to assimilate carbons via the natural carbon cycle. In these respects, CO 2 capture and sequestration have been considered as one of the strategic principles to cancel out CO 2 release from the anthropogenic activities in line with the use of fossil fuels. Thus, it is desirable to develop the efficient CO 2 sorptive materials that are economically viable. Among CO 2 sorptive materials, biochar (i.e., porous carbon-based materials) has been considered as one of the promising candidates. Indeed, a great deal of researches on biomass has been performed. Based on these rationales, this review laid great emphasis on informing the recent studies of activated biochars for CO 2 adsorption, which were fabricated from various biomasses. Also, this review offered the up-to-date knowledge on the physicochemical properties of activated biochars in line with their synthesis procedures. Lastly, the effects of biochar properties on CO 2 capture and separation was summarized with in-depth assessment of the activated biochars. [ABSTRACT FROM AUTHOR]

Highlights • Valorization of livestock manure to chemicals and energy. • Use of livestock manure as an initial feedstock for the biorefinery. • Furfural production via the acid-catalyzed dehydration of livestock manure. • Sustainable pyrolytic platform using CO 2 as reactive gas medium. Abstract Furfural has been considered a potential feedstock of biofuels and biopolymers. As a waste-to-resource opportunity, this study focused on the valorization of goat excreta to obtain furfural and recover energy in the form of pyrolytic gas that helps increase thermochemical process efficiency. Three feedstocks (goat excreta, rice straw, and corncob) were compared to verify whether goat excreta is a promising feedstock of furfural. The furfural concentration from goat excreta (3.2 g L−1) via acid-catalyzed dehydration was comparable to that from rice straw or corncob. To maximize energy recovery from goat excreta via pyrolysis, CO 2 was employed as a reactive medium (compared with typical pyrolysis with N 2). This study experimentally proved that CO 2 plays a pivotal role in shifting carbon distribution from pyrolytic oil to pyrolytic gas, thereby enhancing the generation of CO (the main component of pyrolytic gas). Based on the experimental results, it is suggested that goat excreta can be a promising initial feedstock for the production of furfural and energy recovery. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Effective energy recovery from a low-rank coal. • Thermolysis of brown coal in CO 2 produced more CO than that in N 2. • Reduction of benzene derivatives in pyrolytic oil of brown coal using CO 2. Abstract This work investigates the effect of CO 2 in pyrolysis of brown coal (also referred to as lignite). CO 2 changes the distribution of pyrolytic products of brown coal. More CO is generated for the pyrolysis of brown coal in CO 2 than that in N 2. Differential scanning calorimeter (DSC) experiments show that the pyrolysis of brown coal in CO 2 is more exothermic than that in N 2. This may indicate that the enhanced generation of CO is attributed to an enhanced thermal cracking induced by CO 2. The more generation of CO for the reaction in CO 2 (4.2 mol.% at 700 °C) than in N 2 (0.5 mol.% at 700 °C) is a result of shifting carbon distribution from condensable hydrocarbons (e.g. , tar) to CO. In addition, more CO is generated from the pyrolysis of brown coal in CO 2 than pyrolysis of sub-bituminous coal. This study signifies that low-rank coal can be effectively used as an energy source when CO 2 is employed during pyrolysis process. [ABSTRACT FROM AUTHOR]

Co-impregnated biochars were fabricated by pyrolysis of spent coffee grounds (SCG) or glucose as carbon (C) sources under N 2 and CO 2 . The formed biochar samples were characterized with FE-SEM, TEM/EDS, XRD, TGA, Raman, XPS, and BET, and further used as catalytic medium for the reduction of p -nitrophenol in the presence of NaBH 4 . The physicochemical characteristics of biochar significantly changed with the types of C precursor and flow gas stream. The biochar from pyrolysis of SCG under N 2 gas stream showed good dispersion of Co nanoparticles (10–20 nm) in carbon matrix as compared to that produced under CO 2 stream, but BET surface area was very small (4.5 m 2 g −1 ) due to pore blockage by thermal degradation products. SCG-derived biochar formed in the presence of CO 2 possessed highly porous structure due to CO 2 -assisted C volatilization. In contrast, for glucose-derived biochar, significant reduction in porosity of biochar occurred with excess devolatilization of C under CO 2 conditions, while the pyrolysis under N 2 flow produced porous biochar. These contrasting results demonstrated the significance of structure crystallinity and thermal degradability of C precursors. The catalytic performance of biochar was better correlated with the external surface area rather than microporosity. [ABSTRACT FROM AUTHOR]

Here in this study, the genuine role of CO 2 in co-pyrolysis of swine manure and coal was mainly investigated to increase the thermal efficiency of the thermo-chemical process. The TGA test of swine manure and coal revealed that the CO 2 co-feeding impact on any reactions (≤740 °C) between CO 2 and the sample surface ( i.e., heterogeneous reaction) should be excluded. A batch-type co-pyrolysis revealed two genuine CO 2 co-feeding impacts on co-pyrolysis of swine manure and coal. First, CO 2 can be an additional source for C and O through a plausible reaction between pyrolytic oil and CO 2 , which led to the enhanced generation of CO by the conversion of volatile organic carbons (VOCs) evolved from thermal deconstruction of pyrolytic substrate. Second, CO 2 expedite the thermal cracking of VOCs, which also resulted in the more generation of H 2 and CH 4 . Two genuine roles of CO 2 in co-pyrolysis of swine manure and coal occurred independently. All experimental findings will be directly applicable to the gasification process since pyrolysis is an intermediate step for the gasification. [ABSTRACT FROM AUTHOR]

This study investigated the preparation of magnetic biochar from N 2 - and CO 2 -assisted pyrolysis of spent coffee ground (SCG) for use as an adsorption medium for As(V), and the effects of FeCl 3 pretreatment of SCG on the material properties and adsorption capability of the produced biochar. Pyrolysis of FeCl 3 -pretreated SCG in CO 2 atmosphere produced highly porous biochar with its surface area ∼70 times greater than that produced in N 2 condition. However, despite the small surface area, biochar produced in N 2 showed greater As(V) adsorption capability. X-ray diffraction and X-ray photoelectron spectrometer analyses identified Fe 3 C and Fe 3 O 4 as dominant mineral phases in N 2 and CO 2 conditions, with the former being much more adsorptive toward As(V). The overall results suggest functional biochar can be facilely fabricated by necessary pretreatment to expand the applicability of biochar for specific purposes. [ABSTRACT FROM AUTHOR]

In this study, CO 2 was used as a reaction medium in the pyrolysis of printed circuit boards (PCBs), thus providing a novel route to mitigate the evolution of harmful chemical species during the thermal degradation of PCBs. For example, this study showed that CO 2 acts as an effective carbon scavenger during the pyrolysis of PCBs. CO 2 facilitated the thermal cracking of volatile organic compounds (VOCs) that evolved from the thermal degradation of PCBs. As a result, CO 2 mitigated the evolution of various harmful pollutants such as phenol and benzene derivatives, PAHs and brominated pollutants, which resulted in the increased generation of syngas (H 2 and CO). This study indicates that using CO 2 as a reaction medium could lead to the development of a more environmentally benign process for the thermal treatment of PCBs and other harmful and/or refractory wastes. [ABSTRACT FROM AUTHOR]

This study laid great emphasis on strategic use of CO 2 as reaction medium and raw material for energy recovery from food waste via shifting carbon distribution from pyrolytic oil to syngas. Thus, the mechanistic understanding of CO 2 in pyrolysis of food waste was investigated systematically in this study. To this end, the thermo-gravimetric analysis (TGA) of food waste in N 2 and CO 2 was carried out. The TGA test evidenced that any physical aspects describing the thermal degradation such as onset and end temperature were not influenced by CO 2 . A scale-up experimental work was also conducted with a batch-type tubular reactor to figure out any chemical influences induced by CO 2 in pyrolysis of food waste. CO 2 in pyrolysis of food waste imparted the genuine capability for shifting carbon distribution from pyrolytic oil to syngas. CO 2 led to carbon distribution shift from pyrolytic oil to syngas ( i.e. , enhanced generation of H 2 and CO). Particularly, the generation of CO evolved from pyrolysis of food waste in CO 2 was substantially enhanced by a factor of 100 at 800 °C. Thus, all experimental findings in this study significantly introduced an innovative way to use CO 2 as energy resources, thereby substantially boosting the sustainability in the thermo-chemical process. [ABSTRACT FROM AUTHOR]

This study proposes a strategic principle to enhance the thermal efficiency of pyrolysis of municipal solid waste (MSW). An environmentally sound energy recovery platform was established by suppressing the formation of harmful organic compounds evolved from pyrolysis of MSW. Using CO2 as reaction medium/feedstock, CO generation was enhanced through the following: 1) expediting the thermal cracking of volatile organic carbons (VOCs) evolved from the thermal degradation of the MSWs and 2) directly reacting VOCs with CO2. This particular influence of CO2 on pyrolysis of the MSWs also led to the in-situ mitigation of harmful organic compounds (e.g., benzene derivatives and polycyclic aromatic hydrocarbons (PAHs)) considering that CO2 acted as a carbon scavenger to block reaction pathways toward benzenes and PAHs in pyrolysis. To understand the fundamental influence of CO2, simulated MSWs (i.e., various ratios of biomass to polymer) were used to avoid any complexities arising from the heterogeneous matrix of MSW. All experimental findings in this study suggested the foreseeable environmental application of CO2 to energy recovery from MSW together with disposal of MSW. [ABSTRACT FROM AUTHOR]

This study mechanistically investigated the influences of CO 2 on syngas (H 2 and CO) production during thermo-chemical conversion of red seaweed, and further explored the possible utility of the produced biochar as a medium for adsorption of inorganic/organic contaminants in aqueous phase. In order to elucidate the key roles of CO 2 in the thermo-chemical process, the composition analysis of syngas and the qualitative analysis of pyrolytic oil were conducted and compared with those in pyrolysis in N 2 condition. Pyrolysis of red seaweed in the presence of CO 2 led to the enhanced generation of syngas at the entire experimental temperatures. For example, the ratio of CO to H 2 in the presence of CO 2 at 620 °C was enhanced by ∼400%, as compared to the case in N 2 . This enhanced generation of syngas resulted in significant pyrolytic oil reduction by ∼70% at 620 °C via the unknown reactions between VOCs and CO 2 . In addition, biochar generated in the CO 2 environment exhibited comparatively higher surface area (61 m 2 g −1 ) and more porous structure. The morphological modification induced by CO 2 provided the favorable condition for removal of methylene blue from the aqueous phase. Thus, this study experimentally demonstrated that exploiting CO 2 as a reaction medium would provide an attractive option for the enhanced generation of syngas and the tuned adsorption capability of biochar. [ABSTRACT FROM AUTHOR]

Highlights: [•] Non-catalytic transforming triglyceride into biodiesel. [•] Non-catalytic esterification of free fatty acids (FFAs). [•] Enhanced biodiesel conversion under the presence of CO2. [•] Non-catalytic biodiesel conversion via the continuous flow system. [•] High tolerance of the amount of free fatty acids. [ABSTRACT FROM AUTHOR]

This work proposed a novel methodology for energy recovery from sewage sludge via the thermo-chemical process. The impact of CO2 co-feed on the thermo-chemical process (pyrolysis and gasification) of sewage sludge was mainly investigated to enhance thermal efficiency and to modify the end products from the pyrolysis and gasification process. The CO2 injected into the pyrolysis and gasification process enhance the generation of CO. As compared to the thermo-chemical process in an inert atmosphere (i.e., N2), the generation of CO in the presence of CO2 was enhanced approximately 200% at the temperature regime from 600 to 900 °C. The introduction of CO2 into the pyrolysis and gasification process enabled the condensable hydrocarbons (tar) to be reduced considerably by expediting thermal cracking (i.e., approximately 30–40%); thus, exploiting CO2 as chemical feedstock and/or reaction medium for the pyrolysis and gasification process leads to higher thermal efficiency, which leads to environmental benefits. This work also showed that sewage sludge could be a very strong candidate for energy recovery and a raw material for chemical feedstock. [Copyright &y& Elsevier]

Abstract: The enhanced gasification of municipal solid waste (MSW) using carbon dioxide (CO2) as the gasification medium was investigated to achieve environmentally benign and energy efficient ways for the disposal of MSW. Two main steps of thermal decomposition of MSW were observed. The first thermal degradation step occurs at temperature between 280 and 350°C and consists of the decomposition of the biomass component into light C1–3-hydrocarbons. The second thermal degradation step occurs between 380 and 450°C and is mainly attributed to polymer components, such as plastics and rubber, in MSW. To extend this understanding to a more practical level, MSW samples were tested in a drop tube reactor (DTR) at a temperature range from 500 to 1000°C under various atmospheres with CO2 concentrations of 0–30%. The release of major chemical species from the DTR has been determined using a micro-GC. For example, CO (∼30%), H2 (∼25%) and CH4 (∼10%) were generated. [Copyright &y& Elsevier]

Abstract: The enhanced thermo-chemical process (i.e., pyrolysis/gasification) of various macroalgae using carbon dioxide (CO2) as a reaction medium was mainly investigated. The enhanced thermo-chemical process was achieved by expediting the thermal cracking of volatile chemical species derived from the thermal degradation of the macroalgae. This process enables the modification of the end products from the thermo-chemical process and significant reduction of the amount of condensable hydrocarbons (i.e., tar, ∼50%), thereby directly increasing the efficiency of the gasification process. [Copyright &y& Elsevier]