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[Display omitted] • Development of NH 3 -fuel demands catalytic de-N 2 O unit for stack gas treatment. • Zn x Co 1− x Co 2 O 4 spinel catalysts were evaluated for low-temperature de-N 2 O. • T 50 of 203.3 °C and X N2O of 94.2 % at 250 °C were achieved when x = 0.73. • Zn induced the formation of oxygen vacancies, enhancing the resistance to O 2. • Zn strengthen the bond between Co and –NO species. The recent advancement of NH 3 -based fuel demands the development of catalysts that can decompose N 2 O at low temperatures and are stable against various inhibitors. Zn-doped cobalt spinel (Zn x Co 1− x Co 2 O 4) catalysts have demonstrated superior activity for N 2 O decomposition at low temperatures. However, their optimization and deactivation mechanisms with respect to Zn loading when inhibitors are present require further investigation. Herein, we reviewed the effects of Zn loading on catalysts at low temperatures without or with the presence of inhibitors (3 vol% O 2 , 6 vol% H 2 O, 200 ppm NO). The results showed that adding an appropriate amount of Zn into Co 3 O 4 spinel catalysts improves their N 2 O decomposition activity. The Zn-induced enhancement of the catalysts' redox properties, and reducibility was the underlying mechanism behind the activity promotion. The presence of structural defects created through the addition of Zn enhanced the catalyst's resistance to O 2. The deactivation by H 2 O and NO upon the addition of Zn could be correlated with the reduced availability of surface Co species and Co2+ as adsorption-active sites and the stronger bond of Co with –NO, respectively. This study underscores the importance of controlling the Zn loading as a bulk redox promoter in Zn x Co 1− x Co 2 O 4 spinel catalysts for practical applications. [ABSTRACT FROM AUTHOR]

• Bio-heavy-oil (BHO) was produced by supercritical (SC) reaction of sewage sludge (SS). • Process flow diagram for 100 t/d SS plants is proposed using SC ethanol and methanol. • The BHO plant with SC methanol was more profitable than that with SC ethanol. • The full-scale BHO plant with scMeOH showed economic feasibility with a 21% ROI. The solvothermal liquefaction of sewage sludge (SS) has received much attention as an ecofriendly method of liquid fuel production. In this study, we evaluated the economic feasibility of bio-heavy-oil (BHO) production from 100 t/d SS using supercritical ethanol (scEtOH) and methanol (scMeOH). The process included a dryer, supercritical reactor, BHO separator, steam boiler, wastewater treatment unit and storages. Two cases for the techno-economic analysis (TEA) were considered: BHO production with scEtOH (Case 1) and with scMeOH (Case 2). The four-level economic potential approach (4-level EP) was used for the TEA. The total capital investments of Cases 1 and 2 were 19.6 and 19.5 million dollars, respectively. Case 2 showed higher economic potential than Case 1 because of the low price of methanol. The BHO plant using scMeOH was economically feasible with a return on investment of 21%/a. [ABSTRACT FROM AUTHOR]

In this study, the effects of product separation on the distribution of liquid products and the energy efficiency of sewage sludge liquefaction in supercritical alcohol and supercritical alcohol–water mixtures were investigated. While considering alcohol participation in the liquefaction reaction (6–47 wt%), the effects of process parameters such as temperature (300–400 °C), residence time (10–120 min), concentration (9.1–25.0 wt%), and type of supercritical fluid (water, methanol, ethanol, water–alcohol mixture) on the yield and properties of bio-oils were examined. Accounting for alcohol participation and product separation allowed the bio-oil yield, energy recovery, and energy efficiency to be newly defined. Application of the new separation protocol developed in this study realized a 10–25 wt% increase in bio-oil yield because light fractions were efficiently captured. When supercritical methanol was used, the light fractions consisted primarily of methylated short-chain esters, whereas ketones and alcohols were the major species when supercritical ethanol was used. Liquefaction at 400 °C and 20 wt% sewage sludge in a mixture of water–methanol (80:20, v/v) resulted in a bio-oil with a high calorific value (35.8 MJ kg −1 ), achieving 155% energy recovery and 106% energy efficiency. Computational fluid dynamics (CFD) analysis of bio-oil combustion conducted in a commercial boiler demonstrated that cofiring with a mixture of petroleum heavy oil and bio-oil resulted in a high firing temperature of 1570 °C and a heat transfer rate, which were comparable to that obtained from conventional heavy oil firing. [ABSTRACT FROM AUTHOR]

Herein, a supercritical methanol (scMeOH) route for efficient upgrading of the low-boiling fraction of fast pyrolysis bio-oil containing a large amount of low-molecular-weight acids and water was investigated. The effects of various reaction parameters, including the temperature, concentration, and time, were explored. The yield of bio-oil and the energy efficiency of the scMeOH upgrading process were determined based on the amount of methanol that participated in the reaction during upgrading and fractionation of the upgraded heavy-fraction bio-oils (UHBOs) and upgraded light-fraction bio-oils (ULBOs). Upgrading at 400 °C with 9.1 wt% bio-oil for 30 min generated a high bio-oil yield of 78.4 wt% with a low total acid number (TAN) of 4.0 mg-KOH/g-oil and a higher heating value of 29.9 MJ kg −1 . The energy recovery (ER) was 94–131% and the energy efficiency (EE) was in the range of 79–109% depending on the calorific values of the ULBOs. Compared with upgrading in supercritical ethanol and supercritical isopropanol, less alcohol participation, a lower TAN, and higher ER and EE were achieved with scMeOH upgrading. Plausible pathways for bio-oil upgrading in supercritical alcohols based on detailed compositional analysis of the UHBO, ULBO, and gaseous products were discussed. [ABSTRACT FROM AUTHOR]

Conversion of sewage sludge into fuel was investigated using a catalyst- and external hydrogen-free supercritical fluid route. When dried sewage sludge was treated in supercritical ethanol, an extremely high bio-oil yield of 87.8 wt% and a remarkable higher heating value (HHV) of 34.6 MJ kg −1 were obtained. The possibility of using non-dried sewage sludge as a fuel source was tested using various alcohol–water mixtures; the presence of water resulted in an almost complete (96%) conversion and high HHVs of 36.8 and 37.3 MJ kg −1 for methanol–water (3:7, v/v) and ethanol–water (3:7, v/v) mixtures, respectively. The main chemical compounds in the bio-oils were found to be esters and nitrogenated species. Plausible reaction mechanisms for sewage sludge conversion in each supercritical fluid are discussed. [ABSTRACT FROM AUTHOR]

Fast pyrolysis bio-oil derived from empty palm fruit bunch was upgraded in supercritical ethanol (scEtOH) without using external catalysts and molecular hydrogen. The effects of the reaction temperature and time on the product yield and the quality of the upgraded oil based on parameters like the elemental content, total acid number (TAN), water content, high heating value (HHV), and viscosity were examined. At 400 °C, almost all of the organic species in the fast pyrolysis bio-oil were converted to the liquid and gas phase in 30 min, resulting in a high yield of the upgraded oil (83.0 wt%) with an enhanced HHV of 34.1 MJ kg −1 and very low values of TAN (4.8 mg KOH g −1 ) and water (1.6 wt%) when compared to the fast pyrolysis bio-oil (HHV, 24.3 MJ kg −1 ; TAN, 69.4 mg KOH g −1 ; water, 14.0 wt%). The major chemical species in the upgraded oil were alcohols, esters, phenols, hydrocarbons, and aromatics. After aging at 80 °C for one week, a marginal increase in the viscosity of the upgraded bio-oil was observed, indicating a significant improvement in the stability of the bio-oil. Computational fluid dynamics (CFD) analysis of the process performed in a commercial boiler demonstrated that the upgraded oil firing exhibited high gas temperature profiles, a high firing peak of 1599 °C, and a high total heat transfer rate of 121.81 MW th . These results are comparable to the performance parameters of conventional heavy oil-firing processes. [ABSTRACT FROM AUTHOR]

• Gasification behavior of solvent-extracted ash-free coal (AF) chars was evaluated. • Reactivity of AFs was affected by the polarity of extraction solvent. • Ash-free AF chars can be a proper feedstock for the catalytic coal gasification. • AF chars with tailorable composition are applicable as functional carbons. Coal that contains >70 wt% carbon is possibly an economical option as fuel for highly efficient power generation system such as catalytic coal gasification and direct carbon fuel cell, when mineral ashes in coal are removed. In this work, ash-free coals (AFs) are prepared via thermal extraction of carbonaceous components in parent raw coal (PA) and chars of AFs are made by pyrolysis at 300–900 °C. Then, those are characterized concerning the compositional change associated with the extraction and carbonization condition, based on the steam gasification behavior. The composition of AF chars changes depending on the polarity of the extraction solvent. Chars of AF extracted using a polar solvent (N-Methyl-2-Pyrrolidone) show much higher gasification rate than that using a non-polar solvent (1-methylnaphthalene). The addition of K 2 CO 3 catalyst to the AF chars improves the conversion rate significantly, showing that AFs can be a feedstock of the catalytic coal gasification. The effect of the pyrolysis temperature on the reactivity varies between the AFs, implying the difference in the aromaticity and the chemical composition. The property of the AF chars that can be somewhat adjusted by the extraction and pyrolysis condition possibly provides a custom-made product for a particular application including a precursor of the functional carbon materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • First comprehensive overview on low temperature CO 2 methanation. • Overview on CO 2 methanation fundamentals, catalysts and reactor technologies. • Identified challenges and opportunities in each of the areas reviewed. • A critical process simulation result for low temperature CO 2 methanation. CO 2 utilization technologies can not only provide a pathway to reduce greenhouse gas emissions but may also enable renewable energy to be incorporated into important materials used in the society such as fuel and chemicals. Power to gas (PtG) technologies, especially Power to methane has been deemed as one of the promising pathways for the conversion of CO 2 into valuable gaseous fuel. Many reports have reviewed the academic literature related to CO 2 methanation. While the benefits of high temperature methanation for overall process efficiency are well understood, the potential for low-temperature methanation is less understood. In particular the opportunities that arise from coupling a low-temperature methanation process with low temperature hydrogen production technologies, such as PEM electrolysis, have received little attention. It is therefore considered valuable to provide a critical review of the state of the art of this technology at low temperature conditions for the interests of broader research community. In this paper we focus on the recent work around low temperature CO 2 methanation including reaction thermodynamics and kinetics, catalyst materials including supports and promoters, and suitable reactor technologies. We discuss each of these critical aspects of the technology and identify key challenges and opportunities for low temperature CO 2 methanation (methanation conducted at temperatures less than 300 °C). As part of this paper, we also present the results of an ASPEN Plus simulation study based on data available from the literature to highlight the potential energy efficiency gains of a low temperature methanation process. [ABSTRACT FROM AUTHOR]