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"Synthesis gas."
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Bioenergetic constraints for conversion of syngas to biofuels in acetogenic bacteria
Synthesis gas (syngas) is a gas mixture consisting mainly of H2, CO, and CO2 and can be derived from different sources, including renewable materials like lignocellulose. The fermentation of syngas to certain biofuels, using acetogenic bacteria, has attracted more and more interest over the last years. However, this technology is limited by two things: (1) the lack of complete knowledge of the energy metabolism of acetogenic bacteria, and (2) the lack of sophisticated genetic tools for the modification of acetogens. In this review, we discuss the bioenergetic constraints for the conversion of syngas to different biofuels. We will mainly focus on Acetobacterium woodii, which is the best understood acetogen in terms of energy conservation. Syngas fermentation with Clostridium autoethanogenum will also be discussed, since this organism is well suited to convert syngas to certain products and already used in large-scale industrial processes.
Journal Article
Activity and Selectivity Trends in Synthesis Gas Conversion to Higher Alcohols
Production of higher alcohols directly from synthesis gas is an attractive chemical process due to the high value of alcohols as fuel blends and the numerous possibilities for production of synthesis gas. Despite years of research the industrial viability of such a process is severely limited due to lack of suitable catalysts. In this work we contribute to an understanding why it has been difficult to find transition-metal higher alcohol catalysts, and point to possible strategies for discovering new active and selective catalysts. Our analysis is based on extensive density functional theory calculations to determine the energetics of ethanol formation on a series of metal (211) surfaces. The energetic information is used to construct a mean-field micro-kinetic model for the formation of ethanol via CHx–CO coupling. The kinetic model is used along with a descriptor-based analysis to gain insight into the fundamental factors determining activity and selectivity on transition-metal surfaces.
Journal Article
A Modified Two-Step Coprecipitation Method Provides Better CuZnO/Al2O3 Methanol Synthesis Catalyst with More Uniform Distribution of Alumina
A modified two-step coprecipitation method has been formulated to prepare a series of model CuZnO/Al
2
O
3
catalysts for methanol synthesis from syngas. Evaluation at industrially relevant condition showed slightly higher activity and much higher stability for model catalysts than for a commercial catalyst. Due to the same CuZn-binary precursor, the model catalysts had similar structural properties with large specific surface area and pore volume, small CuO crystallites and good reducibility, resembling that of the commercial catalyst. However, the model catalysts showed much better uniformity of alumina distribution, which accounted for their better performance. Strong positive correlation between the deactivation rate and the coefficient of variation of Al/Zn indicates the uniformity of alumina distribution plays an important role in determining stability. Specifically, CuZnO/Al
2
O
3
catalysts with alumina distributed more uniformly had higher stability. This work demonstrated that the formulated modified two-step coprecipitation could provide excellent CuZnO/Al
2
O
3
catalysts for industrial applications. Additionally, it also affords new clues for the development of even better industrial catalysts.
Graphical Abstract
Journal Article
Study on the minimum extinguishing concentration of C6F12O for extinguishing synthesis gas flame of lithium-ion battery
Accidents involving lithium-ion batteries in electric vehicles frequently occur, which limits the industry's growth and makes it more challenging to build the energy supply sustainably. In this study, we add a liquid-phase input end to make cup burner suitable for the fire-extinguishing test of liquid-phase fire-extinguishing agent and test the minimum extinguishing concentration (MEC) of C
6
F
12
O on the synthesis gas of lithium-ion battery. Furthermore, the physical effects and chemical effects of C
6
F
12
O on lithium-ion battery syngas fire are quantified by the perfect stirred reactor (PSR) model. The result shows that the fire-extinguishing effect of C
6
F
12
O on lithium-ion battery fire mainly depends on the physical effect of cooling.
Journal Article
Highly Stable Photocatalytic Dry and Bi-Reforming of Methane with the Role of a Hole Scavenger for Syngas Production over a Defective Co-Doped g-C3N4 Nanotexture
Photocatalytic reduction of CO2 with CH4 through the dry reforming of methane (DRM) is an attractive approach to recycling greenhouse gases into valuable chemicals and fuels; however, this process is quite challenging. Although there is growing interest in designing efficient photocatalysts, they are less stable, and have lower photoactivity when employed for DRM reactions. Herein, we developed a noble metal-free hierarchical graphitic carbon nitride (HC3N4) loaded with cobalt (Co) for highly efficient and stable photocatalytic dry reforming of methane to produce synthesis gases (CO and H2). The performance of the newly designed Co/HC3N4 composite was tested for different reforming systems such as the dry reforming of methane, bi-reforming of methane (BRM) and reforming of CO2 with methanol–water. The performance of HC3N4 was much higher compared to bulk g-C3N4, whereas Co/HC3N4 was found to be promising for higher charge carrier separation and visible light absorption. The yield of CO and H2 with HC3N4 was 1.85- and 1.81-fold higher than when using g-C3N4 due to higher charge carrier separation. The optimized 2% Co/HC3N4 produces CO and H2 at an evolution rate of 555 and 41.2 µmol g−1 h−1, which was 18.28- and 1.74-fold more than using HC3N4 during photocatalytic dry reforming of methane (DRM), with a CH4/CO2 feed ratio of 1.0. This significantly enhanced photocatalytic CO and H2 evolution during DRM was due to efficient charge carrier separation in the presence of Co. The CH4/CO2 feed ratio was further investigated, and a 2:1 ratio was best for CO production. In contrast, the highest H2 was produced with a 1:1 feed ratio due to the competitive adsorption of the reactants over the catalyst surface. The performance of the composite was further investigated for bi-reforming methane and methanol. Using photocatalytic CO2 reduction with CH4/H2O, the production of CO and H2 was reduced, whereas significantly higher CO and H2 evolved using the BRM process involving methanol. Using methanol with CO2 and H2O, 10.77- and 1.39-fold more H2 and CO efficiency was achieved than when using dry reforming of methane. The composite was also very stable for continuous synthesis gas production during DRM in consecutive cycles. Thus, a co-assisted g-C3N4 nanotexture is promising for promoting photocatalytic activity and can be further explored in other solar energy applications.
Journal Article
Small-Scaled Production of Blue Hydrogen with Reduced Carbon Footprint
This article reviews a method of hydrogen production based on partial non-catalytic oxidation of natural gas in an original synthesis gas generator. The working principles of the unit are similar to those of liquid-propellant rocket engines. This paper presents a description of the operation and technical characteristics of the synthesis gas generator. Its application in the creation of small-scaled plants with a capacity of up to 5–7 thousand m3/h of hydrogen is justified. Hydrogen production in the developed installation requires a two-stage method and includes a technological unit for producing a hydrogen-containing gas. Typical balance compositions of hydrogen-containing gas at the synthesis gas generator’s outlet are given. To increase the hydrogen concentration, it is proposed to carry out a two-stage steam catalytic conversion of carbon monoxide contained in the hydrogen-containing gas at the synthesis gas generator’s outlet using a single Cu–Zn–cement-containing composition. Based on thermodynamic calculations, quasi-optimal modes of natural gas partial oxidation with oxygen are formulated and the results of material balance calculation for the installation are presented. In order to produce “blue” hydrogen, the scheme of carbon dioxide separation and liquefaction is developed. The conclusion section of the paper contains the test results of a pilot demonstration unit and the recommendations for improving the technology and preventing soot formation.
Journal Article
The Effect of Composition of Synthesis Gas on the Parameters of Supercharged Combustion Engine
Synthesis gases produced from municipal waste or plastic waste pose a great alternative source of energy, as they are not only reducing dependency on the fossil fuels, but also diversify energy sector and reduce the amount of a landfilled waste. This is directly related to the recent initiatives and legislation related to the greening of transport. The presented contribution focuses on the influence of six selected synthesis gases on the internal parameters of an internal combustion engine intended for cogeneration. The investigated gases fall into the category of medium-energy gases (8 – 14 MJ.kg−1). The experimental measurements have shown that mainly the proportion of hydrogen in the mixture has an effect on shortening the burning time and also on the maximum rate of pressure increase. A higher proportion of CO and H2 increased the maximum combustion pressure with slightly reduced power. The concentration of CH4 directly affected the volumetric value of the heating value of the mixture with a subsequent direct effect on the IMEP or engine torque. The engine operating at full load at speed of 1500 min−1, when running on the selected mixtures in comparison with the operation on natural gas, decreased its engine torque in the range between 13 and 20% and increased its hourly fuel consumption from 2.31 kg.h−1 for natural gas to the span of 7.90 - 12.30 kg.h−1 for measured gases. During the measurement of the control characteristic all investigated synthesis gases have developed an abnormal (detonation) combustion near the optimum pre-ignition angle.
Journal Article
Analysis of the Influence of Gas Composition from Renewable Energy Sources on the Integral Parameters of a Turbocharged Internal Combustion Engine
This study explores municipal waste-derived synthesis gas as a sustainable alternative fuel for internal combustion engines. Syngas properties, including lower heating value and combustion behavior, were linked to the feedstock characteristics and production method. Experimental investigations conducted on a turbocharged Lombardini LGW 702 spark-ignition engine showed that syngas mixtures with higher lower heating values (approximately 11–12 MJ/kg) achieved torque and mean effective pressure values close to those obtained with natural gas. In contrast, low-calorific syngases (approximately 8–9 MJ/kg) resulted in a torque reduction of about 6–15% and a significant increase in specific fuel consumption. The calculated specific energy of the stoichiometric fuel–air mixture ranged from approximately 2.3 to 2.8 MJ/kg under full-load conditions. The results confirm the technical feasibility of municipal waste-derived syngas for engine applications and its potential contribution to greenhouse gas reduction and the development of renewable energy systems.
Journal Article