Influence of Gas Components on the Formation of Carbonyl Sulfide over Water-Gas Shift Catalyst B303Q

Availableonlineatwww.sciencedirect.com° ScienceDirectJournal of Natural Gas Chemistry 16(2007)53-SCIENCE PRESSArticleInfluence of Gas Components on the Formation of CarbonylSulfide over Water-Gas Shift Catalyst B303QJu Shangguan*, Litong Liang, Huiling Fan, Fang ShenKey Laboratory of Coal Science and Technology, Taiyuan University of Technology, Ministry ofEducation and Shanzi Province, Taiyuan 030024, Shanri, China[ Manuscript received August 29, 2006; revised October 26, 2006 1Abstract: Water-gas shift reaction catalyst at lower temperature(200-400'C)may improve the con-version of carbon monoxide. But carbonyl sulfide was found to be present over the sulfided cobaltmolybdenum/alumina catalyst for water-gas shift reaction. The influences of temperature, space velocity,and gas components on the formation of carbonyl sulfide over sulfided cobalt-molybdenum/alumina cat-alyst B303Q at 200-400'C were studied in a tubular fixed-bed quartz-glass reactor under simulatedwater-gas shift conditions. The experimental results showed that the yield of carbonyl sulfide over B303Qcatalyst reached a maximum at 220C with the increase in temperature, sharply decreased with the in-crease in space velocity and the content of water vapor, increased with the increase in the content ofcarbon monoxide and carbon dioxide, and its yield increased and then reached a stable value with theincrease in the content of hydrogen and hydrogen sulfide. The formation mechanism of carbonyl sulfideover B303Q catalyst at 200-400oC was discussed on the basis of how these factors influence the formationof COS. The yield of carbonyl sulfide over B303Q catalyst at 200-400"C was the combined result of tworeactions, that is, CoS was first produced by the reaction of carbon monoxide with hydrogen sulfide,and then the as-produced COS was converted to hydrogen sulfide and carbon dioxide by hydrolysis. Themechanism of COS formation is assumed as follows: sulfur atoms in the Cog Ss-MoS2/ Al2 O3 crystal latticewere easily removed and formed carbonyl sulfide with CO, and then hydrogen sulfide in the water-gasshift gas reacted with the crystal lattice oxygen atoms in CoO-MoO3/Al2O to form Cog Sg-MoS2/Al2O3This mechanism for the formation of COS over water-gas shift catalyst B303Q is in accordance with theMars- van Krevelen's redox mechanism over metal sulfideKey words: formation; carbonyl sulfide; sulfided cobalt-molybdenum/ alumina catalyst; water-gas shift1. Introductioncenters in water-gas shift reaction, CoO-MoO3/Al2 O3catalyst should be presulfided by carbon disulfideWater-gas shift reaction is used for the produc- hydrogen sulfide before application, and it should btion of chemicals or fuels from synthesis gas derived operated in water-gas shift gas containing the properfrom natural gas, coal, and petroleum. Because of content of hydrogen sulfide to maintain a viable com-high conversion efficiency and low reaction temper- mercial activity. To remove sulfide for synthetic gas, aature, the CoO-MoO3/Al203 catalyst is widely ap- fine desulfurization process is followed after the water-plied for water-gas shift reaction at low temperatures gasThe formatinn of carbonyl sulfide(200-400C)in fertilizer plants and methanol syn- over中国煤化工aystwas observedthesis plants. Because Cog Sg and MoS2 are the activeCNMHG among the sulfurCorrespondingauthor.Tel:+86-351-6010530;Fax:+86-351-6010530;E-mail:shanggj@public.tysx.cnFoundation items: the National Basic Research Program of China(No. 2005CB221203)Ju Shangguan et al. Journal of Natural Gas Chemistry Vol. 16 No. 1 2007containing impurities because it is odorless, taste- formation of COS over sulfided CoO-MoO3/Al2O3less, and colorless. COS is a polar molecule, and catalyst at lower temperatures in the water-gas shiftit is very difficult to be directly removed from the process have not been carried out. In this article, thegas by simple absorption method. Therefore, a two- influence of temperature, space velocity, and gas com-step method involving COS hydrolysis and H2S ab- ponents on the formation of carbonyl sulfide over thesorption reaction was applied for the subsequent fine sulfided CoO-MoO3Al2 O3 catalyst B303Q atdesulfurization process. Thus, the formation of Cos temperatures in the water-gas shift reaction isincreases the cost of the subsequent fine desulfur- ied to prevent the formation of COS in water-gas shiftization process. Therefore, study on the formation processof carbonyl sulfide over sulfided CoO-MoO3/Al2O3catalyst at lower temperature is very significant as 2. Experimentalit decreases the cost of subsequent fine desulfurize-tion process. As far as we know, previous studies 2.1 Water-gas shift catalyst samplewere mainly focused on the formation of cos dur-ing the catalytic reduction of SO2 by co over theB303Q, manufactured by Hubei Chemistry Insti-supported sulfide catalyst 2 and in the direct syn- tute of Hubei Province of China, was used as the exthesis of methanethiol and the formation of Ch3SH perimental water- gas shift catalyst in this study. Thebased on TiO2 and Al2O3 [3 ]. However, studies on the lyst are shown in Table erties of the B303Q cata-from CO and H2S using sulfide vanadium catalysts physical and chemical projTable 1. Physical and chemical properties of catalyst B303QSizeSurface areaAl2O3 Alkali metalTypeCoo(w%)M03A0Imn)(kg/)(wt%) oxide(wt%)sphere beige 4-6 0.8-0.9 150-30015-2250-72.2 Apparatus and procedureThe experimental installation consisted of a fixedbed, device for the preparation of the gas mixtureThe COS formation reaction over water-gas shift temperature controller, and GC9A and WLSP for thecatalyst B303Q were carried out using a tubular fixed- on-line analyses of gas concentrations. The gases werebed quartz-glass reactor system under atmospheric dosed by rotor flow meters. Water vapor was intro-pressure. The experimental diagram used in this duced by gas mixture flow saturated at a desired tem-study is shown in Figure 1perature. The inlet temperature of the gas mixturein the reactor was controlled. The reactor consistedof a quartz tube with an inner diameter of 25The maximum length of the reactor is 0.8 m. Thetemperature within the reactor was measured by athermocouple. The temperature in the reactor waskept constant by a furnace in contact with the out-side wall of the reactor. The reactor was providedcowith a bypass, and it is used for measuring the gasconcentration before starting an experiment.2. 3 Reaction conditions回82‖2Water-gas shift catalyst B303Q was presulfided中国煤化工 experiment consistedFigure 1. Experimental diagram of COS formationCNMHdation and water-gasI-Reducing valve, 2-Flowmeter, 3-Thermostat water bath4-Inlet sample point, 5-Shift catalyst, 6-Oven, 7-Thermo-junction, 8-Temperature controller, 9-ChromatographB303Q catalyst was sulfided under a system10-Absorption vessel, 11-Drainmade up of 20-30 g/mCS2, 25%CO, 15%CO2Journal of Natural Gas Chemistry Vol. 16 No. 1 200750%H2, and the balance N2, atmospheric pressure, obtained at 220C under the experimental condition180-350°℃, space velocity700hAs the COS formation reaction is controlled by ki-COS formation reaction over B303Q catalyst was netics, the yield of COS increases with the increasemeasured in a system made up of 50-500 mg/m in temperature. However, the result of this studyH2S, 20%-30%CO, 10%-20% CO2, 40%-60% H2, suggested that COS formation reaction over sulfided4%-10% H2O, and the balance N2, atmospheric pres- B303Q catalyst was not a simple kinetically controlledsure, 190-310C, space velocity 500-1500h-1reaction. it was also affected by the themIcequilibrium of the above two reactions2.4 AnalysisH2, co, CO2, and N2 concentrations of inletand outlet gases were measured using GC9A madein Japan equipped with a thermal conductivity detector. The lowest detected concentration for TCD is0.01%CoS and H?S concentration of inlet and out-let gases were measured using WiSP made inChina equipped with a flame photometric detec- 5tor. The lowest detected concentration for FPD is0.01 mgS/m3.180200220240260280300320The yield of COS at the reactor outlet was theratio of outlet COS concentration to inlet H2s con- Figure 2. The yield of Cos as a function of tempera-centration and defined as followsture over sulfided water-gas shift catalystReaction conditions: 150 mg/m2 H2S, 25% CO, 15% CO2, 50%YH2SH2, 6% H2O, and balance N2, atmosphericlocity 750 h3. Results and discussion3.2 Influence of space velocity on the forma-3.1 Influence of temperature on the formatiotion of COSof COSThe influence of space velocity on the formationThe influence of temperature on the formation of of COS over water-gas shift catalyst was measured inCOS over water-gas shift catalyst was measured in a a range of 500-1500 h-. The results are shown inrange of190-320℃.Theresults are showwn in Fig- Figure 3Figure 2 shows that the sulfided B303Q cata-lyst exhibited an activity of COs formation undersimulated water-gas shift reaction condition. CO30was adsorbed on the metal phase and easily reactedwith the crystal lattice sulfur atoms of sulfided CoO-MoO3/Al2O3 catalyst to form COS, and theformed CoS was converted into hydrogen sulfide andcarbon dioxide by hydrolysis, and these proceduresare described in the subsequent sections. The car-bonyl sulfide was formed as a result of the above tworeactions. The yield of COS over sulfided B303Q4006001000120014001600catalyst increased with the increase in temperaturefrom 190-220oc and it was raised 3.66 times, but Figur中国煤化function of spacedecreased with the increase in temperature fromCNMHG water-gas shift220-310C and was reduced 1.53 times. The maxi- Reaction conditions: 150 mg/m H2S, 25% CO, 15%CO2, 50%mum yield of COS over sulfided B303Q catalyst was H2, 6% H2O, and balance N2, atmospheric pressure, 250oCJu Shangguan et al. Journal of Natural Gas Chemistry Vol. 16 No. 1 2007As shown in Figure 3, the yield of COS over 3.4 Influence of the content of cO2 on the for-sulfided B303Q catalyst rapidly decreased with the mation of COSincrease in space velocity from 500-1500 h-I and itwas reduced 7.89 times under the experimental conThe influence of the content of CO2 on the fordition. The increase of space velocity decreased the mation of COS over water-gas shift catalyst was mea-reaction time of the formation of cOS over sulfided sured in a range of 10%-20% cO2. The results areB303Q catalyst. This result indicated that the for- shown in Figure 5mation of COS during the water-gas shift process canbe accomplished by reducing the reaction time in thecatalyst bed3.3 Influence of content of water vapor on theformation of COSThe influence of content of water vapor on theformation of COS over water-gas shift catalyst wasmeasured in a range of the content of water vapor of4%-10%. The results are shown in Figure 4Figure 5. The yield of COS as a function of the con-sent of CO2 over sulfided water-gas shiftReaction conditions: 150 mg/m3 H2S, 25% CO, 50% H29 H2O, and the balance N2, atmospheric pressure, 250C750hFigure 5 shows that the yield of COS over sulfidedB303Q catalyst rapidly increased with the increase ofthe content of cO2 from 10%-20%, and it was raised2 times under the experimental condition. The as-formed COS was catalytically converted into H2S andCO2 by hydrolysis reaction over the sulfided watergas shift catalyst CoO-MoO3/Al2O3. The increase ofcarbon dioxide content destroyed the thermodynamicWater vapor content(%)bility of the conversion of CoS to H2S, thereforeFigure 4. The yield of COS as a function of contentthe yield of COS increasedof water vapor over the sulfided water-gasshift catalyst B303QReaction conditions: 150 mg/m H2S, 25%CO, 15%CO2, 50% 3.5 Influence of the content of Co on the for-H2, and balance N2, atmospheric pressure, 250.C, 750 h-Imation of cOsSimilar to the influence of space velocity on theThe influence of the content of CO on the forma-yield of COS, the yield of COS over sulfided B303Q tion of COS over water-gas shift catalyst was mea-atalyst rapidly dropped with the increase of the con- sured in a range of 20%0-30%CO. The results aretent of water vapor from 4.42%-9.98% and it was shown in Figure 6reduced 12 times under the experimental condition.Figure 6 shows that the yield of COS over theThe formed COS was catalytically converted into H2s sulfided B303Q catalyst was rapidly increased withby hydrolysis reaction over sulfided water-gas shift thecatalyst CoO-MoO3/Al2 O3. The increase of the con- it watent of water vapor improved the thermodynamic via- wasH中国煤化工tom20%-30%,andntal conditiCNMHGand easily reactedbility of the conversion of Cos to H2S, therefore, the with the sulfur atoms of sulfided CoO-MoO3/Al2OCOS yield decreasedat the crystal lattice to form COS. The increase ofJournal of Natural Gas Chemistry VoL. 16 No. 1 2007the content of carbon monoxide improved the ther- but slightly increased from 50% to 60% under the ex-modynamic viability of the conversion of H2S to COs, perimental condition. The as-formed Cos was cat-therefore the COs yield increasedalytically converted into H2S and CO by hydrogena-tion reaction over the sulfided waCoO-MoO3/Al2O3. The increase of the content of H2improved the thermodynamic viability of the conversion of COS to H2S and CO, therefore, increase of thecontent of H2 can result in the decrease of the yieldof cos3.7 Influence of the content of H2S on COsformationThe influence of H2S content on the formation ofcoS over water-gas shift catalyst was studied in arange of 70-680 mgS/m. The results are shown inCO content(%)Figure 6. The yield of COS as a function of the con-tent of cothe sulfided water-gasReaction conditions: 150 mg/m H2S, 15% CO2, 50% H2, 6%H20, and balance N2, atmospheric pressure, 250C, 750h-I8643.6 Influence of the content of H on the for-mation of COSThe influence of the content of H, on the forma-tion of Cos over water-gas shift catalyst B303Q wasmeasured in a range of 40%-60%H2. The results areshown in Figure 7.0030040050060070035Figure 8. The yield of COS as a function of the con-tent of H2S over sulfided water-gas shiftReaction conditions: 25% CO, 15% CO 2, 50%H2, 6% H2O, andbalance N2, atmospheric pressure, 250"C, 750 h-IFigure 8 shows that the yield of COS over sulfidedB303Q catalyst slightly decreased with the increase ofthe content of H2S from 70 to 340 mg/m, but rapidlyincreased from 340 to 680 mgS/m3H2s in the water-gas shift gas was necessary tomaintain the viable commercial activity of the waterFigure 7. The yield of CoS as a function of the con-gas reaction catalyst, and it is also involved in thetent of H2 over sulfided water-gas shiftformation of COS. When H2S concentration was lowcatalyst B303Qit was used to meet the need of thermodynamic equiReaction conditions: 150 mg/m3 H2S, 25% CO, 15% CO2, librium for metal sulfide formation. Therefore, the6% H2O, and the balance N2, atmospheric pressure, 250C,750h-1中国煤化 Tle crystal lattice su-F/Al2O3 was very low,Figure 7 shows that the yield of COS over the andCNMHGtration on the yieldsulfided B303Q catalyst rapidly decreased by half of COS was negligible. When H2s concentration waswith the increase of the content of H2 from 40%-50%, higher than that desired for thermodynamic equilib-Ju Shangguan et al. Journal of Natural Gas Chemistry Vol 16 No. 1 2007rium for metal sulfide formation, then H2S acceler- experimental yield of COS exceeded the equilibriumated the formation of COSyield of COS formed by the reactions given in equa-tion 2 and was below the equilibrium yield of COS3.8 COS formation mechanismformed by the reaction given in Equation 1. It wassuggested that H2S was converted to COs by the re-The formation of COS in the simulated water-gas action given in Equation 1, and the as-formed COSshift gas may be resulted from the conversion of H2s was converted to H2S by H20 according to the reverseto COs according to the reactions given belowreaction of Equation 2. It was concluded that COS isH2S+Co- COS+H2 +3.49kJ/mol(1) formed via the reaction given in Equation 1 and COSH,S+C02-COS+H20-3553kJ/mol (2) given in Equations 1 and on of the two reactionsis yielded via the combinatThe reaction of hydrogen sulfide and carbonmonoxide has occurred in a temperature range of170-380C over several sulfided metal catalysts 5which is the reverse reaction of COS hydrogenationCOS hydrogenation is a reversible and weak endother- 6mic reaction, and its equilibrium constant rises withthe increase in reaction temperature. Therefore, theincrease ofreactIontemperature results in the de-50crease in the yield of COs in water-carbon monoxideshift gasThe reaction of hydrogen sulfide and carbon dioxide has been considered as the reverse reaction of car-bonyl sulfide hydrolysis [ 6. COS hydrolysis is a re-emperature(C)versible and weak exothermic reaction, and its equi-Figure 9. The calculated equilibrium and the exper-imental yield of COS formed in simulatedlibrium constant drops with the increase in reactiontemperature. Therefore, the increase of reaction tem- Reaction conditions: 25%CO, 15%CO2,50%H2,6%H2O,andperature results in the increase in the yield of COs inbalance N2water-carbon monoxide shift gasCombining Equations 1 and 2, the following equThe catalytic mechanism of COS formationtion is obtainedvolves the following steps: catalyst presulfidation re-action, reaction of Co with the crystal sulfur atoms of2H2S+Co+CO2++2COS+H2+H20(3) metal sulfide and reaction of H2S with crystal oxygenatoms in metal oxideThe above reaction is the combined result of the re-Presulfided reactions for water-gas shift catalyactions given in Equations 1 and 2. The yield of CoO-MoO3/Al2O3 involve the sulfidation of metal oxCOS over sulfided water-carbon monoxide shift cat- ide by carbon disulfide or hydrogen sulfide to foralyst CoO-MoO3/ Al2O3 was experimentally calcu- metal sulfide. The reactions are shown as followslated. The equilibrium concentrations of Cos ob-tained from the reactions given in Equations 1 and9Co0+8H2S+H2CogS+9H2O2 under the experimental condition were calculatedMoO3+2H2S+H2 MoS2+3H2Oby considering the thermodynamic properties of the 9Co0+4CS2+17H2 - CogSs+4CH4+9H206composition gases1003+CS2+5H2MoS2+CH4+3H20(7)According to the data from literature 7], the cal-culated and experimental equilibrium yield of Cos CO was adsorbed on the metal phase and easilyformed in simulated water-carbon monoxide shift gas acted with the lattice sulfur atoms of metal sulfiare shown in Figure 9.H中国煤化工As shown in Figure 9, the experimenof COS over sulfided water-gas shift catalyst B303QCNMHG12H20were in between the equilibrium yield of COS formed03/Al2U3+Ms+24H2by the reactions given in Equations 1 and 2. The Metal oxide reacted with H2S in water-gas shift gas toJournal of Natural Gas Chemistry VoL. 16 No. 1 2007form metal sulfide. The reaction is shown as follows: COS was converted to hydrogen sulfide and carbondioxide by hydrolysis9Co0-MoO3/Al2O3+10H2S +2H23 Co was adsorbed on the metal phase and eas-CogSg-MoS2/Al2O3+ 12H2Oily reacted with the lattice sulfur atoms of sulfidedshown in the above reactions, sulfur atoms in COs CoO-MoO3/Al2O3 to form COS H2S in the waterwere not directly formed from H2S in the water-gasmonoxide shift gas was used as an alternative forshift gas, but from the metal sulfide catalyst. H2s the lattice sulfur atoms of sulfide CoO-MoO3/Al2O3in water-carbon monoxide shift gas was usedwhich was replaced by oxygen atom during the formation of COSalternative for the sulfur atom consumed during theformation of COS over the catalyst. This mechanism(4) To decrease the rate of formation of COS overfor the formation of COs over water-gas shift catalystthe water-gas shift catalyst, the following operationis in accordance with the mars- Van Krevelen, s redoxconditions are suggested high ratio of water vapor toshift gas, short residence time and suitable tempera-mechanism for metal sulfide4. ConclusionsReferencesThe main results obtained under the experimental [1] Chen L, Zhuo Z J. Dadanfei(Large Scale Nitroogenousonditions of this study can be summarized as followsFertilizer Industry), 2001, 24(3 ): 201(1)The yield of COS increased with the increase (2) Zhuang S X, Magara H,Yamazaki M,Takahashiin temperature and reached the maximum at 220C,Y, Yamada M. Applied Catalysis B: Environmentaldecreased with space velocity and water vapor con-2000,24:89tent as well as hydrogen content, and increased with 3] Mul G, Wachs I E, Hirschon A S. Catalysis Today,Co content and CO2 content as well as HaS concen-2003,78:32714 Mellor J R, Copperthwaite R G, Coville N J. Applied2)There was COS formation reaction from COCatalysis A: General, 1997, 164: 69and H2S over sulfided water-gas shift catalyst B303Q5 Fukuda K, Dokiya M, Kameyama T, Kotera Y. Journal of catalysis, 1977, 49: 379in the lower temperature range. The yield of COS was (6 Rhodes C, Riddel S A, West J, Williams B P, Hutchthe combined results of two reactions, that is, cosings G J. Catalysis Today, 2000, 59: 443was first produced by the reaction of carbon monox- [7] Guo H X. Huafei Cuihua(Fertilizer and Catalysis)ide with hydrogen sulfide, and then the as-produced中国煤化工CNMHG