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National Renewable Energy Laboratory (NREL) and Pacific Northwest National Laboratory (PNNL) are conducting research to investigate the feasibility of producing mixed alcohols from biomass-derived synthesis gas (syngas). PNNL is tasked with obtaining commercially available or preparing promising mixed-alcohol catalysts and screening them in a labor...
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... The final yield and the selectivity of the reaction is governed by the ratio of H 2 to CO + CO 2 and CO 2 /CO ratio, respectively [73]. Thus, CO 2 is required to be removed to increase the selectivity as well as the yield of methanol [41]. ...
Use of abundantly available virgin and waste biomasses as feed-stock for producing gaseous (bio-gas) and liquid fuels (bio-methanol, bio-ethanol and bio-butanol) is being considered as the sustainable and viable alternative to fossil fuels (coal, natural gas and petro-fuels like gasoline and diesel). Out of these bio-methanol is being considered as an attractive liquid fuel as well as feed-stock for the synthesis of enumerable valuable organic compounds currently being produced from coal, natural gas, and petroleum feed stocks. This review presents an overview of various thermo-chemical and biochemical routes that are being explored for the sustainable production of bio-methanol from waste biomass. The advantages and limitations of both the routes are discussed to provide a brief account of their basic principles and also indicate the issues to be addressed through further technological up-gradations for satiating the future energy demand. It focuses specially on the biochemical conversion route which utilizes microbes as biocatalysts for methanol production under normal temperature and pressure conditions. Available information on various process parameters affecting microbial production of bio-methanol have been critically reviewed. To make the process cost effective certain improvements like utilization of raw biogas instead of natural gas for methanol production and development of methane-utilizing microbes through genetic engineering as the subject for future research are discussed. The gap existing in the current knowledge that needs to be bridged to facilitate development of technology for large scale production of bio-methanol at an economical rate to meet the future demands are also pointed out.
... However, these figures are decreasing if a cobalt content in catalyst more than 10%. At the same time, catalytic systems with a capacity of at least 150-200 g/kg Kt·h are considered to be economically promising for the synthesis of alcohols from CO and H 2 [11]. ...
... Syngas conversion to higher oxygenates provides a promising pathway to transform coal, natural gas, and biomass into high value chemicals and transportation fuels [1][2][3] . However, development of catalysts with satisfactory activity and well-defined selectivity towards C 2+ oxygenates remains challenging [3][4][5] and hampers commercialization of this process. Rhodium (Rh) is often cited as the only elemental metal exhibiting some selectivity towards C 2+ oxygenates. ...
Synthesis gas (CO + H2) conversion is a promising route to converting coal, natural gas, or biomass into synthetic liquid fuels. Rhodium has long been studied as it is the only elemental catalyst that has demonstrated selectivity to ethanol and other C2+ oxygenates. However, the fundamentals of syngas conversion over rhodium are still debated. In this work a microkinetic model is developed for conversion of CO and H2 into methane, ethanol, and acetaldehyde on the Rh (211) and (111) surfaces, chosen to describe steps and close-packed facets on catalyst par-ticles. The model is based on DFT calculations using the BEEF-vdW functional. The mean-field kinetic model includes lateral adsorbate-adsorbate interactions, and the BEEF-vdW error estimation ensemble is used to propagate error from the DFT calculations to the predicted rates. The model shows the Rh(211) surface to be ~6 orders of magni-tude more active than (111) surface, but highly selectivity towards methane, while the Rh(111) surface is intrinsically selective toward acetaldehyde. A variety of Rh/SiO2 catalysts are synthesized, tested for catalytic oxygenate produc-tion, and characterized using TEM and DRIFTS. The experimental results indicate that the Rh(111) surface is intrinsi-cally selective towards acetaldehyde, and a strong inverse correlation between catalytic activity and oxygenate selec-tivity is observed. Furthermore, iron impurities are shown to play a key role in modulating the selectivity of Rh/SiO2 catalysts toward ethanol. The experimental observations are consistent with the structure-sensitivity predicted from theory. This work provides an improved atomic-scale understanding and new insight into the mechanism, active site, and intrinsic selectivity of syngas conversion over rhodium catalysts and may also guide rational design of alloy cata-lysts made from more abundant elements.
... To achieve high catalytic performance for producing ethanol and higher alcohols, noble Rh-based catalysts, modified methanol synthesis based catalysts, modified F-T synthesis Fe based catalysts, and modified Mo-based catalysts have been investigated. [199,200] Table 7 lists the operating conditions and advantages/disadvantages associated with these four types of catalysts. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Catalytic system: Although Rh-based catalysts are the most promising candidates, the associated prohibitive cost and limited supply prevent their practical implementation on a large scale. ...
In light of the depletion of fossil fuels and the increased daily requirements for liquid fuels and chemicals, CO2 should indeed be regarded as a valuable C1 additional feedstock for sustainable manufacturing of liquid fuels and chemicals. Development and deployment of CO2 capture and chemical conversion processes are among the grand challenges faced by today's scientists and engineers. Very few of the reported CO2 capture and conversion technologies have been employed for industrial installations on a large scale, where high-efficiency, cost/energy-effectiveness, and environmental friendliness are three keys factors. The CO2 capture technologies from stationary sources and ambient air based on solvents, solid sorbents, and membranes are discussed first. Transforming CO2 to liquid fuels and chemicals, which are presently produced from petroleum, through thermochemical, electrochemical, photochemical, and biochemical routes are discussed next. The relevant state-of-the-art computational methods and tools as a complement to experiments are also briefly discussed. Finally, after pointing out the advantages and disadvantages of the currently available technologies for CO2 capture and conversion, ideas and perspectives for the development of new techniques, opportunities, and challenges are highlighted.
... The most abundant products are low carbon chain alcohols (C 2 AC 4 ), methanol, hydrocarbons and CO 2 . There are several types of mixed alcohol catalysts with a great variety on alloy composition and the promoters [57] which are classified into two main categories, modified Fischer-Tropsch synthesis (Fe, Ni, Co, Mo, Rh based) and modified Methanol synthesis (K, Zn, Cr, Cu based) catalysts [58]. In the framework of this study, two catalysts from each group are selected from the literature and are investigated. ...
... Ethanol formation from syngas is a highly exothermic reaction (Eq. (1)), and heat dissipation may be a problem for scale-up [36]. Alkali promoted molybdenum sulphide catalysts produce linear alcohols and ethanol and higher alcohols are formed via a classical insertion of CO into the corresponding precursor alcohol [21]. ...
... The low conversions and ethanol selectivity obtained in this phase were probably due to the absence of transition metals in the catalysts' compositions and were in accordance with literature [36], as can be seen in Table 2. ...
72 MoS2 catalysts were tested in the conversion of syngas to alcohols, using a high-throughput catalyst evaluation unit, to identify the best catalyst, based on CO conversion, both ethanol and higher alcohols and total alcohols selectivity. Catalysts prepared by thermal decomposition of (NH4)2MoS4 at low temperature showed a higher selectivity to total alcohols. The highest selectivity to ethanol and higher alcohols was obtained at 300 °C by a catalyst prepared by reacting Mo(CO)6 with sulphur. Catalysts prepared by thermal decomposition of (NH4)2MoS4 at high temperature showed very low activity. Catalysts prepared by thermal decomposition of (NH4)2MoS4 in tridecane/water with hydrogen atmosphere showed low activity and selectivity. There was no significant difference among the alkaline metal promoters K, Cs and Rb regarding total alcohols selectivities. Incorporation of Co and Ni led to catalysts with activity levels equivalent to catalysts that contain Rh.
... This observation is consistent with those previously reported in the literature. 20,56,57 Conducting the reaction under supercritical hexanes phase conditions again yielded linear alcohols, although the enhancement in productivity of higher alcohols was quite significant. For example, the productivity of 1-butanol increased from 0.5 to 1.4 g/kg cat. ...
Higher alcohol synthesis (HAS) from syngas over a Cu-Co based catalyst was investigated under supercritical hexanes conditions. The effects of hexanes/syngas molar ratio, H2/CO molar ratio and GHSV on gas phase HAS (GP-HAS) and supercritical hexanes phase HAS (SC-HAS) was investigated. The CO conversion remained relatively constant with increases in the hexanes/syngas molar ratio, while the CH4 selectivity decreased. Higher alcohol productivity was found to increase monotonically with an increase in the hexanes/syngas molar ratio. Productivity of higher alcohols increased with an increase in the H2/CO ratio under the gas phase conditions. An opposite trend in higher alcohol productivity with H2/CO was observed in SC-HAS. Further experiments were performed using argon as the reaction medium for comparison with the supercritical hexanes medium results. The enhanced higher alcohol productivity observed in this system can be attributed to improved extraction of alcohol products from the catalyst pores under the supercritical conditions. © 2013 American Institute of Chemical Engineers AIChE J, 2013
... However, in this study, the hydrocarbons formation is not taken into account, even though it is expected, according to similar studies [31,44,45]. The methane selectivity is assumed to an average value of 5% obtained from Refs. ...
... The methane selectivity is assumed to an average value of 5% obtained from Refs. [31,44,45]. The expressions of the kinetic rates of the reactions that take place in the MAR and the parameters values are presented in Table 5 and 6a and b respectively. ...
... Because of the sulphide form, it is reported that this catalyst is highly stable in the presence of sulphur components. Thus, the H 2 S concentration should actually be above 100 ppm to keep the catalyst active and stable15161718. The synthesis is assumed to take place in a fixed bed reactor. To simulate the product distribution from the mixed alcohol synthesis, a kinetic model [12, 19] is used. ...
Bioethanol as a transportation fuel offers various advantages. It can directly be used in existing transportation options and it can be produced by different conversion routes (i.e. thermochemical or biochemical processes) as well as from various types of feedstock (i.e. biomass containing sugar or starch, lignocellulosic biomass). Especially, the conversion of lignocellulosic biomass promises to improve the environmental performance, e.g. in terms of greenhouse gas emissions, and seems to have a better acceptance compared to sugar- or starch-based processes (i.e. food vs. fuel discussion). However, the process technology for the production of bioethanol from lignocellulosic biomass is still under development. Thus, within this paper, three basic process routes for ethanol from lignocelluloses are analysed from a systems point of view to allow for statements how the further technological development should be directed. For this reason, thermochemical gasification based on wood followed by alcohol synthesis and thermochemical gasification followed by syngas fermentation is compared to a process based on saccharification and subsequent fermentation. This analysis shows that ethanol yields exceeding the theoretical potential based on glucose cannot be reached with the analysed processes. Nevertheless, gasification with syngas fermentation and mixed alcohol synthesis is promising regarding alcohol yields as well as overall energy efficiencies, also compared to other options for liquid biofuels like Fischer–Tropsch diesel or methanol.
... All rights reserved. doi:10.1016/j.jcat.2010.02.020 second metals such as Mn on the supported Rh catalysts, in order to improve activity and selectivity [5,6,11,12]. For example, Ellgen et al. studied CO hydrogenation over Rh/SiO 2 and Rh/Mn/SiO 2 at high pressures (30-200 atm) and temperatures between 250 and 300°C in a back-mixed reactor with unity H 2 /CO ratio [13]. ...
... The KMC-simulated reaction kinetics are then compared directly to our experimental results, as well as those from the literatures. Except for Mn, the effects of other promoters on the catalytic activity and selectivity of ethanol formation over SiO 2 supported Rh catalysts were also investigated [6,12,[26][27][28][29]. The enhanced activity was found using Ti and V promoters, while Li would improve the selectivity toward C þ 2 oxygenates [6]. ...
... As we mentioned earlier, first-principles DFT calculations performed in this work focused on the reaction energetics of the most important steps in the catalytic CO hydrogenation mechanism and their dependence upon the promoter identity. Previous experiments suggested that methane is a major side product (over 50% of all products) in CO hydrogenation over Rh-based catalysts [7][8][9][10][11][12][13]. To improve the selectivity to ethanol, different promoters were added to Rh catalysts to control the reaction routes to either methanation or CO insertion to CH x leading to ethanol and other C 2 oxygenates [5,6]. ...
Catalytic conversion of biomass-derived synthesis gas to ethanol and other C2+ oxygenates has received considerable attention recently due to the strong demands for alternative, renewable energy sources. Combining experimental measurements with first-principles-based kinetic modeling, we investigated the reaction kinetics of ethanol synthesis from CO hydrogenation over SiO2 -supported Rh/Mn alloy catalysts. We find that an Mn promoter can exist in a binary alloy with Rh and play a critical role in lowering the CO insertion reaction (CO+CHx (x=1–3)) barriers thus improving the selectivity toward ethanol and other C2+ oxygenates, although the barrier toward methane formation is unaffected. The postulation of supported Rh/Mn alloy nanoparticle being the active phase is supported by our experimental characterization using X-ray photoelectron spectroscopy, transmission electron microscopy, and X-ray diffraction of practically used Rh/Mn/SiO2 catalysts. First-principles density functional theory (DFT) calculations further confirmed that the binary Rh/Mn alloy is thermodynamically more stable than the mixed metal/metal oxides under the reducing reaction condition. The reaction kinetics of CO hydrogenation to ethanol on the three-dimensional Rh/Mn nanoparticle under experimental operating conditions was studied using kinetic Monte Carlo (KMC) simulations. The simulated reaction kinetics is qualitatively consistent with experimental observations. Finally, the effects of various promoters (M=Ir, Ga, V, Ti, Sc, Ca, and Li) on the CO insertion reaction over Rh/M alloy nanoparticles were investigated using DFT calculations. We found alloying the promoters with the electronegativity difference, Δχ, between the promoter (M) and Rh being 0.7 is the most effective in lowering the barriers of CO insertion reaction, which leads to higher selectivity to ethanol. This conclusion is in excellent accord with the reported catalytic performance of CO hydrogenation over Rh-based catalysts with different promoters. We believe that the electronegativity difference criterion is very useful in improving the catalytic performance using transition metal-based catalysts for ethanol synthesis from CO hydrogenation.
