Progress in catalytic membrane reactors for removing sulfur from natural gas

June 2007Journal of Chongqing University- English EditionVol 6 No. 2Article D:1671-8224(2007)02008805To clte this article: TAO Chang-yuan, LIU Zuo hua, DU Jun, LIU Ren-long. Progress in catalytic membrane reactors for removing sulfur from natural gas [J].JChongqing Univ: Eng Ed(ISSN 1671-8224), 2007, 6(2): 88-92Progress in catalytic membrane reactors for removingsulfur from natural gasTAO Chang-yuan", LlU Zuo hua, DU Jun, LIU Ren-longCollege of Chemistry Chemical Engineering, Chongqing University, Chongqing 400044, P. R. ChinaReceived 15 September 2006: revised 1 November 2006Abstract: Increasingly high requirement driven by environmental concern leads to more rigorous standards for sulfur dosagein fuel. Natural gas desulfurization is an important unit for industrial natural gas process. Catalytic membrane reactor for sulfurcompounds removal is a newly emerged and integrated membrane technology. We reviewed the current progress fordesulfurization of natural gas with membrane process, and predicted that the process combined with catalytic membranereactor and microwave irradiation for desulfurization of natural gas might be an integrated and promising unit for large scaledesulfurization with high efficiencyKeywords: natural gas; catalytic membrane reactor; microwave; desulfurizationCLC number: E 868Document code: AIntroduction2 Membrane for natural gas separationRecently, energy security has aroused heightenedFrom the literature, desulfurization techniquespriority again owing to the growth of both population include mainly the following: absorbing H2s withand economy. Continued natural gas demand will reagents and scrubbing solutions such asplay a bigger role in energy consumption. But natural ethanolamines and mixed organic solvents; hotgas processing in the future will encounter a more aqueous potassium carbonate processes; hot metalsignificantly sour raw gas, i.e., gas containing H2s metal oxide-molten carbonate schemes; physicalfrom 15%to 20% or even higher [1], and there are separation plants; selective membrane permeationother kinds of ingredients in natural gas that need processes; Claus Process; air-chemical oxidationpurifying, too. Natural gas purification processnd the Stretfordially desulfurization unit, affects the design and Process. There are another three methods still in pilotdownstream stepsstage which split His into H2 and s by thermalmicrowave decomposition, respective( posdecomposition, electrochemical decomposition, andIn traditional processes, all unitsTAO Chang-yuan(P KTc): Male; PhD: Prof. Research sulfur from natural gas include some modification ofinterest:petrochemical engineering, membrane separation the Claus process patented in 1883. With thetechniques;E-mail:taocy@cqu.edu.cn;Tel:+86-23-65111231.developmentofmembraneseparationtechnology,Funded by the Natural Science Fundation of China forese中国煤化工 on natural gasCreative Research Groups(No. 50621403)and the Visiting puriCN MH Ganes and inorganicScholar Foundation of Key Lab. of University Projects membranes. Frantz [2]developed a two-stage(KLVF20065membrane separation process for sweetening naturalVol 6 No. 2Tao Chang-yuan, et al Catalytic membrane reactors to remove sulfur from natural gasgas(e.g, with separation of CO2 and H2S), which formulations, including perovskite structured oxidesuses a gas turbine powered with an impure fuel gas and ceria-supported precious metals, have beenstream derived from a permeate stream from the identified to be of high reforming activity, stablesecond or later stage membrane separation processes. performance in the presence of hydrogen sulfide, andAl-Juaied M et al [3] studied intrinsically defect-free high regeneration capability [7-9]. Chan et al [10]asymmetric hollow fiber polyimide membrane reported the performance of a catalytic membranemodules in respectively the presence and the absence reactor containing a packed bed of Ru-Mo sulfideof saturated and aromatic components. Smith C H et catalyst with an aim to improve H2 yield beyond theal [4] installed a membrane separation unit, utilizing equilibrium ceiling. Blach [11] developed a catalyticcellulose acetate spiral wound membrane elements for ceramic membrane reactor for the decomposition ofDuke Energy Field Services, Inc., Weld County, hydrogen sulfide into hydrogen and sulfur, and itColorado. Membrane technology has the merits of showed good separation performance for decompo-low capital and operating costs, schedule compliansition products. The ceramic catalyst layer wasand flexibility in controlling CO2 removal rate. deposited directly on the tubular ceramic porousHowever for desulfurization of natural gas, much membrane element. Eow [12] reviewed the recoveryeffort has been invested in catalytic decomposition of of sulfur from sour acid gas and compared differentsulfur compounds and separation with membrane. So, processes in terms of the sulfur recovery efficiency,catalytically composite membranes have greater hazards and disadvantages, reliability and advantages,potential for natural gas desulfurization [5-61plant capacity and ecological impacts. He alsodescribed changes and new trends, such as the3 Catalytic membranes for natural gasintroduction of non-permselective catalytic membranepurification- desulfurizationreactors for the Claus reaction, and the in situadsorption of water inside the Claus catalytic reactor.The successful utilization of Hs by converting it toA method for >99.9% removal of toxic sulfur(s) sulfur and H2 realizes waste minimization, resourcecompounds from natural and petroleum gases utilization, and environmental pollution reduction atcombines nontraditional technology with well-known the same time. There are photochemical andprocesses. The novel solutions in the method are: 1) plasmochemical methods still in the developmentmembrane separation of petroleum gas to concentrate stage. It is expected that the ongoing research on theH2s in one of streams; 2) selective oxidation of H2s relationship of micropores and macropores to obtainto form elemental S in hydrocarbon-gas phase in the an optimum porous catalyst structure will result in apresence of a fluidized-bed catalyst; 3) thermo- way for effective conversion of H2S and SO2.catalytic decomposition of H2s to form H and S; andUp to now, to prepare the membrane with sulfur4)treatment of solid and liquid wastes with a tolerant catalysts is a hot research field for theaccelerated electron beam. It also inherits from conversion of sulfur compounds to elemental sulfurtraditional technologies the following arts: 1) [13-16]. Obuchi et al [17] desighed a device andalkanolamine purification of petroleum gas; 2) method for desulfurization and steam reforming ofadsorption, drying, and removal of S compounds; 3) hydrocarbon raw materials to produce synthesis gashydrogenation of s compounds to H2S; 4)s and high-concentration hydrogen gas. The applicationproduction by Claus process; and 5)purification of included a desulfurization section to remove sulfurwaste gases with shell Claus Off-gas treating(SCOT) from the hydrocarbon raw materials(e.g, natural gasprocessandforming section forAlthough sulfur can be toxic to some catalysts, refor.中国煤化工bon at500°Ctosome researchers found the way to produce stable 600HHCNMHGSt to obtain a highcatalysts tolerant"to high levels of H2s up to(10- concentration hydrogen gas, with a partition wall100)mg L. A number of promising catalyst having H-permeable hydrogen separation membraneJ Chongqing Univ. Eng. EdVol 6 Nbetween 2 sections to concentrate hydrogen gas which preparation, especially in catalytic membrane reactor.fed back to the desulfurization section via the microwave heating has become a more and morenembrane for hydrodesulfurization. Nevertheless, the popular approach to make composite membrane. Liconversion temperature for desulfurization is YS et al [21] developed a new method called"in-siturelatively high and the efficiency of removal sulfur by aging-microwave synthesis" for zeolite membranecatalytic membrane reactor needs improvingsynthesis. High quality LTA zeolite membranes weresuccessfully microwave-synthesized without seeding4 Microwave assisted desulfurization It was found that the formed zeolite layer wasprocesscomposed of sphere grains with undefined crystalfacets and that in-situ aging temperature andMicrowave has been applied in many fuel process microwave heating time had the most significantfields for its high efficiency. Ma [18] reviewed the influences on the synthesis LTA zeolite membranesprinciple of microwave action and its applicationsynthesized by "in-situ aging-microwave heatingthe exploitation of oil and gas Microwave increases method showed superior gas permeation propertiesthe yield of heavy crude oil by 1 to 4 times with no and it paved a promising way toward mass productionthe depth of oil bearing reservoir, of LTA zeolite membranes. Chen X B et al [22]shortens the dewaxing period from 45 min to 7 min, reported the Naa zeolite membranes with highand turns out an relative increase of 16.7% to 45.7% permeance synthesized by microwave heating methodin dewatering efficiency with an obvious effect in Zhang et al [23] prepared Pt/C catalysts for protondewatering crude oil emulsion flooded by polymer. In exchange membrane fuel cell(PEMFC) bynatural gas, 91.2% of the H2s can be decomposed into microwave-sol process. Catalysts prepared bH2 and s by microwave [19]. Cha et al [20] studied microwave-sol process have larger BET surface areamicrowave induced conversion of hydrogen sulfide, (herein BET stands for Brunauer, Emmett, and Teller,and found the reaction of hydrogen sulfide with trona the three scientists who optimized the theory forand calcium oxide in the presence of char startedmeasuring surface area [24])and total pore volumesoon as microwave energy was applied; whereas with The smaller the particle size, the larger the BETconventional heating, the reaction started only when surface area of the catalyst is and the higher thethe bed temperature reached around 540C. Char activity of the catalyst in oxidation-reduction reactionabsorbing microwave energy was rapidly heatedcan be obtained. The crystals prepared by microwave-very high temperatures, enhancing the H2s reaction sol process have higher activity compared with thosewith oxides contained in or added into the char in the prepared by conventional immersion process. Kang etreaction. A 100% conversion of trona was achieved al [25] prepared ceramic composite membranes by aaximal mass fraction of char required to microwave-heating method similar to that used ininduce the reaction of His and trona with microwave making mesoporous powders. By a modified Yoldasenergy was 20% in the char-trona mixture. When the method, a sol-gel technique and microwave heating,atrona content in the mixture of char-trona mixture was ceramic composite membrane was preparedover 50%0, an additional conversion of H2s occurred successfully and the preparation time was greatlyto produce some amount of elemental s that was reduced. Chen et al [26] developed an effectivedeposited in the bed. This clearly demonstrates that strategy by using microwave heating in reversechar combined with microwave induces H2S reaction microemulsion (water in oil) to produce uniformwith mineral oxidestemplate-free zeolite nanoparticles. Reverse中国煤化工 fining nanoreactors5 Microwave assisted membrane preparation andneous and preferen-and membrane separation processCNM HGe (not the oil phase)where zeolite particles are produced. It provides aMicrowave is also applied to inorganic membrane general route for producing template-free zeoliteVol. 6 No. 2 Tao Chang-yuan, et aL. /Catalytic membrane reactors to remove sulfur from natural gasnanocrystals that can be widely used in gas separation natural gas process unit.membrane, catalyst and nanocomposite membranesIn the meanwhile, microwave can supply a special Referencesmpetus for membrane separation process. Nakai et al[27] measured the permeability coefficients of various [1] Goar BG, Nasato E. Largegases for a cellulose acetate(CA)and polystyrene(PS)processes stress efficiency []membrane under microwave irradiation by using ahandmade apparatus which gave off microwave of [2] Frantz SR. High-effionatural gas sweetening2 450 MHz. 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