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An external thermal high-temperature continuous feed moving bed tubular reactor was used for the gasification of high moisture content lignite (30.41 wt.%) under CO2 and an auto-generated steam atmosphere. The objectives of this study are to illustrate the synergistic gasification characteristics of high moisture content lignite and CO2 in the tubular reactor; CO2 and auto-generated steam (steam released from the lignite) were used as gasification agents for lignite gasification. The effects of temperature and CO2 flow rate were also investigated. Experimental results showed that when the gasification temperature increased from 800 °C to 1000 °C, the H2 yield also increased from 8.45 mol kg−1 to 17.86 mol kg−1. This may indicate that the H2O-CO2 gasification of semi-coke was enhanced with the rise in temperature. At 900 °C, the gas yield increased with the increase in CO2 flow rate, while the yield of char and liquid product showed an opposite trend. The lower heating value of the H2-rich syngas varied from 11.73 MJ m−3 to 12.77 MJ Nm−3. The experimental results proved that the high moisture content lignite in-situ CO2 gasification process is an effective methodology for the clean and efficient utilization of lignite. [ABSTRACT FROM AUTHOR]

Pyrolysis-coupled gasification-melting is a promising technology as it can dispose of the petrochemical sludge (PS) and recover the leftover energy. Unfortunately, there has been little research investigating the effects of pyrolysis degree on melting characteristics of the pyrolysis residue (PR) and the transformation properties of the heavy metal (HM). In this study, the function of inherent components and disposal temperature were elucidated. The results show that the moisture and light volatile could disperse the melting residue (MR) during gasification-melting treatment, causing different morphology and color of the MR. In addition, as pyrolysis temperature increased, the HMs speciation (e.g. Zn, Cu, and Cr) in the PR was transformed from bioavailable to a stable state, and the yield of PR decreased from 66.8% to 36.5%. The PR produced at 800 °C could decrease about 0.9 ∼ 1.9 potential ecological risk of releasing substances during the subsequent high-temperature gasification-melting owing to its stable HMs state and less char composition. Moreover, the gasification at 1250 °C could realize the safe disposal of the PR. Further increasing the gasification temperature to 1450 °C could not improve the acid-leaching resistance of the HMs, although the apparent concentration of C and the acid dissolution proportion of slag decreased by 6.3% and 1.7%, respectively. [Display omitted] • The melting behavior of PR produced at different pyrolysis temperature was studied. • Dispersion effects of moisture and light volatile on melting residue were observed. • Pyrolysis affected HM immobilization of MR by altering HM state and char matrix. • 800-PR possessed the lowest potential ecological risk of RP during disposal. • Reduction of PR component complexity impaired the surface morphology of slag. [ABSTRACT FROM AUTHOR]

Oxidative dehydrogenation of ethane with CO 2 (ODEC) is an attractive reaction for reduction of carbon footprints and ethene production. In this work, we present photothermal catalysis on confined bimetal catalysts for ODEC. Carbon nanotubes confined non-noble bimetal alloy (i.e., CoNi@CNTs and FeNi@CNTs) catalysts were prepared and FeNi@CNTs showed effective performance in photothermal catalytic ODEC to ethene. Experiments and simulations reveal that UV and visible lights (420 – 490 nm) are responsible for ODEC and non-oxidative dehydrogenation of ethane, respectively, to ethene. Additionally, ODEC to ethene is preferred to C-C cracking to methane on FeNi@CNTs in light (> 490 nm)-induced thermocatalysis. The photothermal effect turns more significant when introduced into thermocatalytic ODEC (500 °C), with ethene generation at one order of magnitude. This work advances new mechanism of photo-mediated catalysis and sheds light on utilization of full-spectrum solar energy and non-noble metallic catalysts for ethene production and CO 2 recycling at moderate conditions. [Display omitted] • Carbon nanotubes confined non-noble bimetal alloy catalysts were prepared. • The catalysts are effective in photothermal dehydrogenation of ethane with CO 2 (ODEC). • UV and visible lights induce ODEC and non-oxidative dehydrogenation, respectively. • C-C cracking to methane occurs in light (> 490 nm)-induced thermocatalysis. • The photothermal effect improves ethene generation with one order of magnitude. [ABSTRACT FROM AUTHOR]

CO 2 -to-DME (CTD) technology has been considered as a worthy solution for waste CO 2 upcycling and green DME production. Faced with various emerging CTD routes with pros and cons, it is important to systematically assess and compare their attractiveness and difference, and identify the most sustainable technologies for further development and improvement. Thus, the present study proposed four promising CTD routes (i.e., two-step routes using high- and medium-concentration methanol as intermediates, and one-step routes with and without RWGS reactions) and developed a multi-criteria sustainability assessment and decision-making framework for alternative routes comparison and prioritization. Eleven KPIs were considered from technical, economic, and environmental perspectives to evaluate system sustainability. Exergoeconomic and exergoenvironmental analysis were conducted to pinpoint the location, magnitude, and sources of system inefficiencies from the component level. A TOPSIS method was employed to integrate multidimensional performances and present an informed decision-making process. As a result, all the alternative routes are sustainable for DME synthesis, and therein the one-step route without RWGS reaction always ranks as the most competitive choice through rigorous sensitivity analysis. Moreover, this work provides a strategic decision support for assessing the trade-offs involved in existing and emerging sustainable CO 2 upcycling technologies towards carbon neutrality. [Display omitted] • Four promising DME synthesis routes via CO 2 hydrogenation were proposed and modeled. • A multi-criteria sustainability assessment and decision-making framework for CTD technology prioritization was set up. • Exergoeconomic and exergoenvironmental analysis were implemented to evaluate the CTD system from the component-level. • The one-step CTD route without RWGS reaction was identified as the most sustainable strategy. [ABSTRACT FROM AUTHOR]

• Two PtL/PtG hybrid processes are proposed for upcycling CO 2 into green fuels. • CO 2 is converted through RWGS, Fe-based FTS and/or CO 2 methanation. • A comparative analysis of the present & previous PtL/PtG processes is conducted. • The syncrude production of the present PtL/PtG process has been increased by 30.95%. • The total product revenue of the present PtL/PtG process has been increased by 12.73%. Power-to-X (PtX) technologies, especially for the Power-to-Liquids (PtL) and Power-to-Gas (PtG) have attracted extensive attention recently, as promising pathways for carbon upcycling via converting CO 2 into high-value products including liquid fuels and substitute natural gas (SNG). Herein, aiming at further improving the PtX process efficiency, we proposed two novel PtL/PtG hybrid processes, namely an indirect process (with RWGS unit) and a direct process (without RWGS unit) by integrating Fe-based Fischer-Tropsch synthesis (FTS) and olefin oligomerization technologies, which co-produce syncrude and SNG. Both process simulation and techno-economic analysis were implemented to evaluate the overall process performances, through various indicators involving technical indicators (e.g., syncrude production, energy efficiency, and net CO 2 reduction), and economic indicators such as total capital investment, net CO 2 reduction costs together with total product costs. Both proposed PtL/PtG processes are efficient in converting CO 2 into valuable hydrocarbon fuels, and the syncrude production and total product revenues of indirect process are 2.35–14.58% and 7.55–8.51% higher than those of the direct process, respectively. Whereas, the direct process has lower net CO 2 reduction cost of 206.09 $/tonne CO 2. Moreover, the present PtL/PtG processes have higher syncrude production and total product revenues than those of our previous studies including a direct PtL/PtG process coupled with Fe-based FTS and two indirect PTL/PTG processes combined with RWGS and Fe/Co-based FTS reaction, with rates of 30.95 and 12.73% at most. [ABSTRACT FROM AUTHOR]

• Relation between pyrolysis degree and microstructure property of PRPS was studied. • 800-PRPS presents the best CO 2 -gasification reactivity in the microstructure level. • The function of calcium evolution during PRPS-CO 2 reaction was found. • PRPS-CO 2 reaction consists of carbonation, gasification, and CaCO 3 decomposition. Pyrolysis-gasification coupling process is an effective technology that can realize the thorough reutilization and clean disposal of petrochemical sludge. However, pyrolysis residue of petrochemical sludge (PRPS) produced at different temperatures possesses obviously different structure properties, which profoundly impacts the subsequent gasification. This study reveals the effect of pyrolysis degree of PRPS on the CO 2 gasification reactivity by evaluating the micromorphology, pore property, existed form of calcium mineral and carbon structural characteristics. Results demonstrate that micromorphology development of the PRPSs with diverse pyrolysis degree (PRPS prepared at 500–900 °C) has three main stages, namely, the emergence of macropores and fissures (500–600 °C), the pore development (700–800 °C), and the pore jam (900 °C). The optimal PRPS was obtained at 800 °C-pyrolysis (800-PRPS) as the maximal specific surface area and desorption pores volume were observed. In addition, Raman analysis indicated that the 800-PRPS has the best carbon activity as well. By further increasing pyrolysis temperature to 900 °C, the carbon disordering, defect, and active sites of the PRPS decreased. Moreover, results of non-isothermal PRPS-CO 2 reaction indicated that the basic calcium compound carbonation, gasification, calcium carbonate decomposition regimes were involved. Compared with 800–900 PRPSs, 500–700 PRPSs were more vulnerable in the lower gasification temperature owing to the more char matrix remain. In addition, owing to the occurrence of the carbonation reaction, the calcium carbonate product layer was formed and might affect the early-age gasification. [ABSTRACT FROM AUTHOR]