• Energy Research

Abstract This study aimed to determine the synergistic effects of CO2 on the catalytic pyrolysis of pine sawdust over a Ni-based catalyst (Ni/SiO2) to establish a sustainable platform for H2 production. To elucidate the reaction mechanism, the CO2-cofeeding pyrolysis of pine sawdust was performed. The CO2-cofeeding pyrolysis of pine sawdust proved that the gas-phase reaction between CO2 and pyrolysates led to the increase in the amount of generated CO. The CO2 enhanced thermal cracking and dehydrogenation. These mechanistic features of CO2 were catalytically enhanced when Ni/SiO2 was employed as heterogeneous catalyst, which led to an increase in the amounts of generated H2 and CO. Hence, the CO that was additionally generated during the gas-phase reaction of CO2 and pyrolysates could be further converted into H2. In addition, CO2 could be looped in the CO2-cofeeding pyrolysis of pine sawdust. Furthermore, exploiting CO2 as raw material or reactive gas medium in the catalytic pyrolysis process also offered a strategic means for preventing coke formation.

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 Pyrolysis of spent coffee grounds (SCG) was performed to achieve the multiple purposes of waste disposal and energy recovery. This study placed great emphasis on pretreatment of SCG with FeCl 3 (Fe-SCG) and utilizing carbon dioxide (CO 2 ) as a reaction medium to enhance the generation of syngas while reducing condensable hydrocarbons (e.g., tar). For example, the principal effect of CO 2 was the enhanced generation of syngas via the CO 2 -induced thermal cracking of volatile organic compounds (VOCs) and the reaction between CO 2 and VOCs, which resulted in subsequent reduction of tar. These identified effects on pyrolysis of SCG were more pronounced in pyrolysis of Fe-SCG, which could be attributable to the catalytic effect of the Fe mineral formed from phase transition of FeCl 3 during pyrolysis. The generation of CO in pyrolysis of Fe-SCG in the presence of CO 2 increased up to 8000% as compared to pyrolysis of SCG in N 2 .

This study experimentally evidenced that bovine fat could be directly converted into fatty acid methyl esters (FAMEs) without lipid extraction step via thermally assisted in-situ transesterification on a porous material such as SiO2 since providing thermal energy from an external heating source drove pseudocatalytic mechanisms caused by mobility difference between lipid in bovine fat and acyl acceptor. In particular, this study employed dimethyl carbonate (DMC) as an acyl acceptor due to its nontoxicity and economic viability. In order to validate thermal assisted in-situ transesterification, thermal degradation of bovine fat was characterized, which revealed that thermal behavior of lipid in bovine fat was nearly identical to refined lipid. The results also evidenced that bovine fat contains 12.51 wt % impurities. Fatty acid profiles were identical under different transesterification conditions, which provide evidence that the thermal assisted in-situ transesterification should be technically feasible. I...

Abstract Pyrolysis of defatted Euglena gracilis was investigated in this study to maximize energy recovery from algal biomass after lipid extraction. Prior to pyrolysis of defatted E. gracilis, the growth rate of E. gracilis was monitored to determine its potential as an initial carbonaceous feedstock for pyrolysis. This study revealed that the cell density of E. gracilis linearly increased for the first 5 days, during which the cell density reached 6.06 ± 0.82 g L−1, demonstrating that defatted E. gracilis is a promising feedstock for pyrolysis. To increase the thermal efficiency of defatted E. gracilis pyrolysis, CO2 was employed as a reactive gas medium. CO levels were increased by 45% following pyrolysis of defatted E. gracilis in a CO2 environment compared to in an N2 environment. Considering that CO is a highly combustible permanent gas, the use of CO2 in pyrolysis may result in the production of more fuel-range gaseous chemicals. Additionally, CO2 utilization increased the gaseous product yield compared to N2-pyrolysis for treating the defatted algal biomass while decreasing tar yield.

Green hydrogen has been proposed as a clean and sustainable source of energy with unrivaled potential to play a pivotal role in every country's transition toward a low-carbon economy while striving to achieve Sustainable Development Goals. Herein, we provide perspective of using green hydrogen to enhance the sustainability in Pakistan. As renewable energy resources (e.g. solar and wind power) are abundantly available in Pakistan, the production of green hydrogen linked to renewable energy resources is conscious. As a representative case, the green hydrogen project in Sindh, Pakistan was announced—hydrogen is produced by water electrolysis powered by renewable electricity generated from solar or wind power. The potential of a circular economic approach to green hydrogen production in Pakistan is discussed in terms of policy development, public and private participation, public demand, and public awareness. Green hydrogen is indeed the green light of the future for Pakistan, as it can potentially help boost its economy while mitigating climate change. The insights given by this study can be useful to further develop any future green hydrogen roadmap for Pakistan.

Catalytic fast pyrolysis of low sulfonated Kraft lignin was performed under different atmospheric environments such as N2, CH4, and the gas derived from CH4 decomposition (CH4-D). The use of Zn- or Mo-loaded HZSM-5 as catalyst led to a higher pyrolytic oil yield compared to parent HZSM-5 in CH4 and CH4-D atmospheres. The yields of benzene, toluene, and xylenes were increased by the synergistic effects from metal loading, higher H/Ceff ratio, higher acidity, and CH4 activation. The enhanced CH4 activation via metal loading resulted in higher methylation of alkyl moieties and 33% increase in the total yield of benzene, toluene, and xylenes in comparison to parent HZSM-5. A higher H/Ceff ratio of 6 via CH4 decomposition led to the formation of a hydro-pyrolysis environment. Moreover, the CH4-D environment showed H2/CH4 ratio of 0.36 in the product gas which warranted the presence of more H2 under the CH4-D pyrolysis environment.

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.

Abstract This work mechanistically investigated the influence of CO 2 in co-pyrolysis of sub-bituminous coal and main constituents of ligno-cellulosic biomass (cellulose and hemicellulose). Our experimental work identified the crucial role of CO 2 in co-pyrolysis of coal and biomass. For example, CO 2 not only enhanced the thermal cracking behavior of VOCs evolved from the thermal degradation of a carbonaceous solid sample ( i . e ., sub-bituminous coal, cellulose, and xylan) via blocking the addition reaction, but also directly reacted with VOCs and CO 2 . The genuine effects induced by CO 2 led to a significant reduction of condensable hydrocarbons ( i . e ., tar), which directly lead to a significant enhancement of syngas production and modification of ratio of CO to H 2 : the ratio of CO to H 2 was increased approximately ∼1200% at 680 °C in pyrolysis of coal in the CO 2 environment and the ratio of CO to H 2 was adjustable by means of using a different amount of CO 2 during the pyrolysis process of carbonaceous samples. Furthermore, the identified role of CO 2 would be applicable to the in-situ air pollution control in various industrial applications, such as steelworks. Lastly, the identified role of CO 2 in pyrolysis will be applied in the gasification process since pyrolysis is the intermediate step for the gasification process.