共查询到20条相似文献,搜索用时 15 毫秒
1.
Shi-run Yan Ki-won Jun Ji-sook Hong Sang-bong Lee Myoung-jae Choi Kyu-wan Lee 《Korean Journal of Chemical Engineering》1999,16(3):357-361
The hydrogenation of CO2 to hydrocarbons over a precipitated Fe-Cu-Al/K catalyst was studied in a slurry reactor for the first time. Reducibility
of the catalyst and effect of reaction variables (temperature, pressure and H2/CO2 ratio of the feed gas) on the catalytic reaction performance were investigated. The reaction results indicated that the Fe-Cu-Al/K
catalyst showed a good CO2 hydrogenation performance at a relatively low temperature (533 K). With the increase of reaction temperature CO2 conversion and olefin to paraffin (O/P) ratio in C2-C4 hydrocarbons as well as the selectivity to C2-C4 fraction increased, while CO and CH4 selectivity showed a reverse trend. With the increase in reaction pressure, CO2 conversion and the selectivity to hydrocarbons increased, while the CO selectivity and O/P ratio of C2-C4 hydrocarbons decreased. The investigation of H2/CO2 ratio revealed that CO2 conversion and CH4 selectivity increased while CO selectivity and O/P ratio of C2-C4 decreased with increasing H2/CO2 ratio. 相似文献
2.
CO2 reaction and formation pathways during Fischer–Tropsch synthesis (FTS) on a co-precipitated Fe–Zn catalyst promoted with Cu and K were studied using a kinetic analysis of reversible reactions and with the addition of 13C-labeled and unlabeled CO2 to synthesis gas. Primary pathways for the removal of adsorbed oxygen formed in CO dissociation steps include reactions with adsorbed hydrogen to form H2O and with adsorbed CO to form CO2. The H2O selectivity for these pathways is much higher than that predicted from WGS reaction equilibrium; therefore readsorption of H2O followed by its subsequent reaction with CO-derived intermediates leads to the net formation of CO2 with increasing reactor residence time. The forward rate of CO2 formation increases with increasing residence time as H2O concentration increases, but the net CO2 formation rate decreases because of the gradual approach to WGS reaction equilibrium. CO2 addition to synthesis gas does not influence CO2 forward rates, but increases the rate of their reverse steps in the manner predicted by kinetic analyses of reversible reactions using non-equilibrium thermodynamic treatments. Thus the addition of CO2 could lead to the minimization of CO2 formation during FTS and to the preferential removal of oxygen as H2O. This, in turn, leads to lower average H2/CO ratios throughout the catalyst bed and to higher olefin content and C5+ selectivity among reaction products. The addition of 13CO2 to H2/12CO reactants did not lead to significant isotopic enrichment in hydrocarbon products, indicating that CO2 is much less reactive than CO in chain initiation and growth. We find no evidence of competitive reactions of CO2 to form hydrocarbons during reactions of H2/CO/CO2 mixtures, except via gas phase and adsorbed CO intermediates, which become kinetically indistinguishable from CO2 as the chemical interconversion of CO and CO2 becomes rapid at WGS reaction equilibrium. 相似文献
3.
Gökhan Uysal A. Nilgün Akın Z. İlsen Önsan Ramazan Yıldırım 《Catalysis Letters》2006,111(3-4):173-176
The effects of reaction gases including CO2 and H2O and temperature on the selective low-temperature oxidation of CO were studied in hydrogen rich streams using a flow micro-reactor
packed with a Pt–SnO2/Al2O3 sol–gel catalyst that was initially designed and optimized for operation in the absence of CO2 and H2O. 100% CO conversion was achieved over the 1 wt% Pt–3 wt% SnO2/Al2O3 catalyst at 110 °C using a feed composition of 1.0% CO, 1.5% O2, 25% CO2, 10% H2O, 58% H2 and He as balance at a space velocity of 24,000 cm3/(g h). CO2 in the feed was found to decrease CO conversion significantly while the presence of H2O in the feed increased CO conversion, balancing the effect of CO2. 相似文献
4.
Miriam StiefelRuaa Ahmad Ulrich ArnoldManfred Döring 《Fuel Processing Technology》2011,92(8):1466-1474
Various dehydration catalysts were studied in the synthesis of dimethyl ether (DME) directly from carbon-monoxide-rich synthesis gas under a series of different reaction conditions. The investigated catalyst systems consisted of combinations of a methanol catalyst (CuO/ZnO system) with catalysts for methanol dehydration based on γ-Al2O3 or zeolites and γ-Al2O3 was identified as the most favorable dehydration catalyst. Various reaction parameters such as temperature, H2/CO ratio and space velocity were studied. The impact of water on Cu/ZnO/Al2O3-γ-Al2O3 catalysts was investigated and no deactivation could be observed at water contents below 10% during running times of several hours. A running time of several days and a water content of 10% led to a significant increase of CO conversion but the water gas shift reaction became dominating and CO2 was the main product. After termination of water feeding significant deactivation of the catalyst system was observed but the system returned to high DME selectivity. Catalyst stability and the influence of CO2 in the gas feed were studied in experiments lasting for about three weeks. The presence of 8% of CO2 caused an approximately 10% lower CO conversion and an about 5% lower DME selectivity compared to the reaction system without CO2. 相似文献
5.
A new process is proposed which converts CO2 and CH4 containing gas streams to synthesis gas, a mixture of CO and H2 via the catalytic reaction scheme of steam-carbon dioxide reforming of methane or the respective one of only carbon dioxide reforming of methane, in permeable (membrane) reactors. The membrane reformer (permreactor) can be made by reactive or inert materials such as metal alloys, microporous ceramics, glasses and composites which all are hydrogen permselective. The rejected CO reacts with steam and converted catalytically to CO2 and H2 via the water gas shift in a consecutive permreactor made by similar to the reformer materials and alternatively by high glass transition temperature polymers. Both permreactors can recover H2 in permeate by using metal membranes, and H2 rich mixtures by using ceramic, glass and composite type permselective membranes. H2 and CO2 can be recovered simultaneously in water gas shift step after steam condensation by using organic polymer membranes. Product yields are increased through permreactor equilibrium shift and reaction separation process integration. CO and H2 can be combined in first step to be used for chemical synthesis or as fuel in power generation cycles. Mixtures of CO2 and H2 in second step can be used for synthesis as well (e.g., alternative methanol synthesis) and as direct feed in molten carbonate fuel cells. Pure H2 from the above processes can be used also for synthesis or as fuel in power systems and fuel cells. The overall process can be considered environmentally benign because it offers an in-situ abatement of the greenhouse CO2 and CH4 gases and related hydrocarbon-CO2 feedstocks (e.g., coal, landfill, natural, flue gases), through chemical reactions, to the upgraded calorific value synthesis gas and H2, H2 mixture products. 相似文献
6.
Mechanistic Study of Selective Oxidation of Dimethyl Ether to Formaldehyde over Alumina-supported Molybdenum Oxide Catalyst 总被引:1,自引:0,他引:1
XPS and IR spectroscopies were used to investigate the surface intermediates of dimethyl ether (DME) oxidation to formaldehyde
over MoOx/Al2O3 catalyst. The reaction performances were tested by employing three typical reaction conditions, depending on the O2/DME ratio and the reaction temperature. When there was sufficient oxygen present in the reaction media, a terminal or bridged
CH3O* species formed by DME dissociation was highly active and rapidly reacted with lattice oxygen to produce formaldehyde, leading
to higher selectivity of HCHO. When oxygen was consumed completely or only DME was present in the reaction media, CH3O species bonded to more than two Mo atoms (μ-OCH3) and CHx (x=1–3) species attached to the Mo atoms were observed and the relative ratio of (μ-OCH3) /Mo–CHx was significantly dependent on the reduction degree of MoOx domains. The (μCH3O) species was related to the formation of CH3OH or COx, and the Mo–CHx species led to the formation of CH4. 相似文献
7.
Yongwon Seo Sung-Ho Jo Ho-Jung Ryu Hee Dal Bae Chong Kul Ryu Chang-Keun Yi 《Korean Journal of Chemical Engineering》2007,24(3):457-460
A bubbling fluidized bed reactor was used to study CO2 capture from flue gas by using a potassium-based solid sorbent, sorbKX35 which was manufactured by the Korea Electric Power
Research Institute. A dry sorbent, sorbKX35, consists of K2CO3 for absorption and supporters for mechanical strength. To increase initial CO2 removal, some amount of H2O was absorbed in the sorbent before injecting simulated flue gas. It was possible to achieve 100% CO2 removal for more than 10 minutes at 60°C and a residence time of 2 s with H2O pretreatment. When H2O pretreatment time was long enough to convert K2CO3 of sorbKX35 into K2CO3 · 1.5H2O, CO2 removal was excellent. The results obtained in this study can be used as basic data for designing and operating a large scale
CO2 capture process with two fluidized bed reactors.
This work was presented at the 6
th
Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006. 相似文献
8.
15N solid state NMR study of the reactions of propane or propene, 15NO and oxygen on Na‐, H‐, and CuZSM‐5 总被引:1,自引:0,他引:1
Ni- and Co-based catalysts derived from NiAl- and CoAl-layered double hydroxides were tested in four kinds of reactions of
methanol, namely decomposition of methanol (DCM), partial oxidation of methanol (POM), steam reforming of methanol (SRM),
and oxidative steam reforming of methanol (OSRM), for the purpose of H2 production for fuel cells. H2, CO and/or CO2 were the predominant products with minor amounts of dimethyl ether (DME) and CH4 depending on the reaction temperature. Among the four kinds of reactions tested, the OSRM reaction was found to be more effective
in terms of MeOH conversion and H2 selectivity over these catalysts. Higher selectivity of H2 and CO2 with only traces of CO could be obtained at about 100% methanol conversion around 300 °C in the OSRM reaction over the catalyst
derived from CoAl-LDH. Substitution of a part of Al by Sn in the NiAl- and CoAl-LDH systems was found to be inhibiting the
methanol conversion. On the other hand, the selectivities to DME and CH4 were declined with a consequent increase in the selectivity to H2. In addition, considerable amount of formaldehyde was also noticed, especially over the catalyst derived from CoAlSn-LDH
at lower reaction temperatures. The observed difference in the catalytic performance upon Sn incorporation was attributed
to an improved redox capability of the Ni- and Co-based oxide catalysts, as determined by temperature-programmed reduction
(TPR) experiments.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
Sungyong Park Hwanam Kim Byungchul Choi 《Journal of Industrial and Engineering Chemistry》2010,16(5):734-740
Recently, DME has received attention as a clean fuel and is now considered an alternative fuel for diesel engines. DME diesels need de-NOx catalysts such as LNT (Lean NOx Trap) and SCR (Selective Catalytic Reduction) systems. DME is an attractive source of hydrogen because it can be stored easily and is a good transportation fuel. Hydrogen and CO enriched gas as a reductant was used with the LNT catalyst in order to reduce NOx emissions. The steam reforming catalyst of DME was used to formation of hydrogen. It has been reported that Cu-based catalysts have high selectivity and activity in the steam reforming of DME. This research used 600 cPsi cordierite as a catalyst, which was coated with copper. The catalysts were made via a sol–gel and impregnation methods. The formation of H2 and CO under the prepared catalysts was tested by a model gas. Experimental parameters were considered; the space velocity (SV) and concentrations of H2O, O2, and CO2 were evaluated. The Cu 30%/γ-Al2O3 catalyst from the sol–gel method exhibited high and stable activity in the production of hydrogen from the steam reforming of DME. Both DME conversion and the selectivity of hydrogen were affected by SV and the concentrations of H2O, O2, and CO2. 相似文献
10.
The oxy-CO2 methane reforming reaction (OCRM) has been investigated over CoOx supported on a MgO precoated highly macroporous silica–alumina catalyst carrier (SA-5205) at different reaction temperatures (700–900 °C), O2/CH4 ratios (0.3–0.45) and space velocites (20,000–100,000 cc/g/h). The reaction temperature had a profound influence on the OCRM performance over the CoO/MgO/SA-5205 catalyst; the methane conversion, CO2 conversion and H2 selectivity increased while the H2/CO ratio decreased markedly with increasing reaction temperature. While the O2/CH4 ratio did not strongly affect the CH4 and CO2 conversion and H2 selectivity, it had an intense influence on the H2/CO ratio. The CH4 and CO2 conversion and the H2 selectivity decreased while the H2/CO increased with increasing space velocity. The O2/CH4 ratio and the reaction temperature could be used to manipulate the heat of the reaction for the OCRM process. Depending on the O2/CH4 ratio and temperature the OCRM process could be operated in a mildly exothermic, thermal neutral or mildly endothermic mode. The OCRM reaction became almost thermoneutral at an OCRM reaction temperature of 850 °C, O2/CH4 ratio of 0.45 and space velocity of 46,000 cc/g/h. The CH4 conversion and H2 selectivity over the CoO/MgO/SA-5205 catalyst corresponding to thermoneutral conditions were excellent: 95% and 97%, respectively with a H2/CO ratio of 1.8. 相似文献
11.
Ying Liu Cheng-Hua Zhang Yu Wang Ying Li Xu Hao Liang Bai Hong-Wei Xiang Yuan-Yuan Xu Bing Zhong Yong-Wang Li 《Fuel Processing Technology》2008
The effect of co-feeding CO2 on the catalytic properties of an Fe–Mn catalyst during Fischer–Tropsch synthesis (FTS) was investigated in a spinning basket reactor by varying added CO2 partial pressure in the feed gas. It was found that co-feeding CO2 to syngas did not decrease the activity of the catalyst, on the contrary, a dramatic increase of the activity and an increase of methane selectivity were observed over the catalyst after removal of CO2 from the feed gas. The addition of CO2 led to an increase in olefin/paraffin ratios of low carbon hydrocarbons and a slight decrease in C19+ selectivity. It also slightly decreased CO2 formation rate on the catalyst by increasing the rate of reverse step of the water–gas shift (WGS) reaction and pushing the reaction towards equilibrium, and did not remarkably influence the hydrocarbon formation rate. However, the co-feeding CO2 can significantly increase the water formation rate and the overall oxygenate formation rate under these reaction conditions. 相似文献
12.
利用介质阻挡放电(DBD)产生低温等离子体进行烟气的脱硝实验,研究了在乙烯存在的条件下,温度和其他烟气成分对NOx脱除率的影响。结果表明:随着温度的升高,NO脱除速率增快;模拟烟气中加入CO2,在能量密度较低时,CO2作为电负性分子会降低自由基的生成,导致NO的脱除率降低,随着能量密度的升高,CO2对NO脱除的影响减小;模拟烟气中加入水后可以产生更多的OH、HO2等自由基,促进NO的氧化;SO2的加入会与自由基O反应,使初始反应中O与C2H4的反应速率减弱,从而影响了NO的氧化速率,但O3、HO2等强氧化自由基会优先与NO反应,因此SO2的加入不会影响NO最终的脱除率。 相似文献
13.
Shin-ichiro Fujita Masahito Usui Etsuko Ohara Nobutsune Takezawa 《Catalysis Letters》1992,13(4):349-358
Methanol synthesis from CO2 and H2 was carried out over a Cu/ZnO catalyst (Cu/Zn = 3/7) at atmospheric pressure, and the surface species formed were analyzed by diffuse reflectance FT-IR spectroscopy and temperature programmed desorption method. Two types of formate species and zinc methoxide were formed in the course of the reaction. Zinc methoxide was readily hydrolyzed to methanol. H2O formed through the reverse water gas shift reaction was suggested to be involved in the hydrolysis of zinc methoxide. 相似文献
14.
Regeneration behaviors of Fe/Si‐2 and Fe–Mn/Si‐2 catalysts for C2H6 dehydrogenation with CO2 to C2H4
Longya Xu Jinxiang Liu Hong Yang Yide Xu Qingxia Wang Liwu Lin 《Catalysis Letters》1999,62(2-4):185-189
The catalytic performance of Fe/Si‐2 and Fe–Mn/Si‐2 catalysts for conversion of C2H6 with CO2 to C2H4 was examined in a continuous‐flow and fixed‐bed reactor. The results show that the Fe–Mn/Si‐2 catalyst exhibits much better
reaction activity and selectivity to C2H4 than those of the Fe/Si‐2 catalyst. Furthermore, the coking–decoking behaviors of these catalysts were studied through TG.
The catalytic performances of the catalysts after regeneration for conversion of C2H6 or dilute C2H6 in FCC off‐gas with CO2 to C2H4 were also examined. The results show that both activity and selectivity of the Fe–Mn/Si‐2 catalyst after regeneration reached
the same level as those of the fresh catalyst, whereas it is difficult for the Fe/Si‐2 catalyst to refresh its reaction behavior
after regeneration.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
《分离科学与技术》2012,47(13):2079-2084
Solubility and selective absorption of hydrogen sulfide (H2S) over carbon dioxide (CO2) in a room temperature ionic liquid, 1-butyl-3-methylimidazolium bromide ([BMIM][Br]) has been evaluated under ambient temperature and pressure. [BMIM][Br] demonstrated its potential as a solvent for selective removal of H2S from CO2/H2S mixture. Our investigation indicated that H2S solubility in [BMIM][Br] is comparable to or better than that in commercially available MDEA-based solvents. Meanwhile, CO2 solubility in [BMIM][Br] is lower than that in the same amine resulting in H2S/CO2 absorption selectivity of within 3.5 to 3.75. The solubility behavior is relatively maintained after 4 times absorption-desorption cycles. A computational molecular study suggested that intramolecular hydrogen bonding interaction between anion Br and hydrogen atom of H2S could stabilize the complex and resulted lower complexation energy than CO2 interaction with [BMIM][Br]. Based on the experiment results, a separation process employing [BMIM][Br] is proposed to control the CO2/H2S ratio existing in a natural gas feed. 相似文献
16.
Carbonation of fly ash in oxy-fuel CFB combustion 总被引:1,自引:0,他引:1
Oxy-fuel combustion of fossil fuel is one of the most promising methods to produce a stream of concentrated CO2 ready for sequestration. Oxy-fuel FBC (fluidized bed combustion) can use limestone as a sorbent for in situ capture of sulphur dioxide. Limestone will not calcine to CaO under typical oxy-fuel circulating FBC (CFBC) operating temperatures because of the high CO2 partial pressures. However, for some fuels, such as anthracites and petroleum cokes, the typical combustion temperature is above 900 °C. At CO2 concentrations of 80-85% (typical of oxy-fuel CFBC conditions with flue gas recycle) limestone still calcines, but when the ash cools to the calcination temperature, carbonation of fly ash deposited on cool surfaces may occur. This phenomenon has the potential to cause fouling of the heat transfer surfaces in the back end of the boiler, and to create serious operational difficulties. In this study, fly ash generated in a utility CFBC boiler was carbonated in a thermogravimetric analyzer (TGA) under conditions expected in an oxy-fuel CFBC. The temperature range investigated was from 250 to 800 °C with CO2 concentration set at 80% and H2O concentrations at 0%, 8% and 15%, and the rate and the extent of the carbonation reaction were determined. Both temperature and H2O concentrations played important roles in determining the reaction rate and extent of carbonation. The results also showed that, in different temperature ranges, the carbonation of fly ash displayed different characteristics: in the range 400 °C < T ? 800 °C, the higher the temperature the higher the CaO-to-carbonate conversion ratio. The presence of H2O in the gas phase always resulted in higher CaO conversion ratio than that obtainable without H2O. For T ? 400 °C, no fly ash carbonation occurred without the presence of H2O in the gas phase. However, on water vapour addition, carbonation was observed, even at 250 °C. For T ? 300 °C, small amounts of Ca(OH)2 were found in the final product alongside CaCO3. Here, the carbonation mechanism is discussed and the apparent activation energy for the overall reaction determined. 相似文献
17.
Petar Djinovi?Ilja Gasan Osojnik ?rnivec Jurka BatistaJanez Levec Albin Pintar 《Chemical Engineering and Processing: Process Intensification》2011,50(10):1054-1062
In this work, 3% Ru-Al2O3 and 2% Rh-CeO2 catalysts were synthesized and tested for CH4-CO2 reforming activity using either CO2-rich or CO2-lean model biogas feed. Low carbon deposition was observed on both catalysts, which negligibly influenced catalytic activity. Catalyst deactivation during temperature programmed reaction was observed only with Ru-Al2O3, which was caused by metallic cluster sintering. Both catalysts exhibited good stability during the 70 h exposure to undiluted equimolar CH4/CO2 gas stream at 750 °C. By varying residence time in the reactor during CH4-CO2 reforming, very similar quantities of H2 were consumed for water formation. Reverse water-gas shift (RWGS) reaction occurred to a very similar extent either with low or high WHSV values over both catalysts, revealing that product gas mixture contained near RWGS equilibrium composition, confirming the dominance of WGS reaction and showing that shortening the contact time would actually decrease the H2/CO ratio in the syngas produced by CH4-CO2 reforming, as long as RWGS is quasi equilibrated. H2/CO molar ratio in the produced syngas can be increased either by operating at higher temperatures, or by using a feed stream with CH4/CO2 ratio well above 1. 相似文献
18.
The styrene conversion and product (viz. styrene oxide, phenyl acetaldehyde, benzaldehyde) selectivity in the liquid-phase epoxidation of styrene by H2O2 (H2O2/styrene = 2) over TS-1 (Si/Ti = 80) and -Al2O3 are strongly influenced by the presence of water and/or base (viz. urea and pyridine) in the reaction mixture. The TS-1 showed high styrene conversion activity but no epoxide selectivity in the absence of any base. When anhydrous H2O2 (24% H2O2 in ethyl acetate), with the continuous removal of the reaction water (using the DeanStark trap), was used instead of 50% aqueous H2O2, both the conversion and epoxide yield are increased drastically for the -Al2O3, whereas for the TS-1, the increase in the conversion was quite small and there was also no improvement in the epoxide selectivity and/or yield. However, when urea or pyridine was added in the reaction mixture, the epoxide selectivity for both the catalysts was increased depending on the concentration of the base added; the increase in the selectivity was very large for the TS-1 but small for the -Al2O3. Poisoning of the acid sites of the -Al2O3 by the chemisorbed ammonia or pyridine (at 100 °C) caused a small decrease in the conversion, but it also caused a large decrease in the epoxide selectivity. However, the pyridine poisoning of the TS-1 caused a little beneficial effect, a small increase in the epoxide selectivity. The ammonia poisoning of the TS-1, however, resulted in a small decrease in the conversion with no improvement in the epoxide selectivity. As compared to the TS-1, the -Al2O3 catalyst showed a much better performance in the epoxidation by anhydrous H2O2 with the continuous removal of the reaction water. However, the reaction water, if not removed continuously, is detrimental to the -Al2O3, causing a large decrease in the catalytic activity and selectivity for styrene oxide but an increase in the selectivity for benzaldehyde. 相似文献
19.
Yingying Zhu Xiaolan Ge Qian Liu Zhongyang Luo Kefa Cen 《Fuel Processing Technology》2010,91(4):424-429
Dimethyl ether (DME) has received growing attention due to its potential use as a multi-purpose fuel. A new technical route of improved two step synthesis is proposed for DME production, which is composed of methanol synthesis and methanol dehydration in a fixed-bed reactor. The influences of the operating conditions including reaction pressure, temperature, H2/CO mole ratio in the syngas and space velocity on CO conversion, selectivity and yield of DME are investigated. CO conversion and DME yield both increase monotonically with the pressure increase. The optimal reaction temperatures for the synthesis and dehydration of methanol are different. CO conversion increases at first and keeps constant when the H2/CO mole ratio is above 2. DME yield increases obviously and then decreases gradually with the space velocity increase. The optimal conditions are obtained to maximize the CO conversion and DME selectivity. The reaction temperatures of the top and bottom stage are in the range of 270-280 °C and 235-245 °C, respectively. The optimal ratio of H2/CO is above 2, and the space velocity is in the range of 1000-1300 h− 1. 相似文献
20.
The effects of CO2 and H2O on the NO
x
storage and reduction characteristics of a Pt/Ba/Al2O3 catalyst were investigated. The presence of CO2 and H2O, individually or together, affect the performance and therefore the chemistry that occurs at the catalyst surface. The effects of CO2 were observed in both the trapping and reduction phases of the experiments, whereas the effect of H2O seems limited to the trapping phase. The data also indicate that multiple types of sorption sites (or mechanisms for sorption) exist on the catalyst. One mechanism is characterized by a rapid and complete uptake of NO
x
. A second mechanism is characterized by a slower rate of NO
x
uptake, but this mechanism is active for a longer time period. As the temperature is increased, the effect of H2O decreases compared to that of CO2. At the highest temperatures examined, the elimination of H2O when CO2 is present did not affect the performance. 相似文献