A Novel Sulfided Mo/C Catalyst for Direct Vapor Phase Carbonylation of Methanol at Atmospheric Press

Journul of Natural Gas Chemistry 120203)31-36SCIENCE PRESSA Novel Sulfided Mo/C Catalyst for Direct Vapor PhaseCarbonylation of Methanol at Atmospheric PressureFeng Peng”Department of Chemucal Engineering, South Chira UInuerasty of T'echmnoloyy, Guangzhou 510640, China[Manuscript receivcu December 9. 202; revised February 19, 2003Abstract: The diree. carbonylation of methanol, without any halide in t.he fee 8s a pronoter. ispresented. A series of No catalysts supporteri on nctivated carbon, ~-Al2O3 and SIO2 were prepared.The results show that the siuport greatly affects the Mo catalyst in the direct vapor phase carbony lalionof methanol. and activated carbon is the best supports of the investignted supports. In addition, therelationships between adsorptions of NHs and CO and carbonylation of tet hanol were investigated. A tnovelsulided Mo/C catalyst had high activity and selectivity for the vapor plhase carbonylation of methano! 1omethyl acetate without the addition of a CH3I promoter to the feed. The rcactiun conditions worc optirmizedat a renction ternperature of 573 K: a mnethanol concentration of 23 1o% and a carbon monoxide spacevelocity of 3,000 L/(kgh). Under these optimal conditions a nethanol conversion uf 50%, carbonylationselectivity of 80 mol%. and space-time yield of 8.0 nol/(kg-h) were obtained. Tle active phase of thisnovel sulfded Mo/C cratalyst is the non- crystalline pbase. and the active counponent is present a MuS2 5on the surfacc of the activated carbon.Key words: methanol, carbonylation, sulfided catalyst, molybdenun. catalyst support, activated carbon.het erogeneous catalysis1. Introductionhas been very little Ssucccss in finding hetcrogeneousor homogeneous catalysts that can fectively uper-Aithough idide promotcd Rh-catalyzed carbony-ate without a halide pronoter |6.7]. According tolation of muetlhanol is onc of the most successful Cx-the klown carbonylation lechanism; methvi iodideamples of homogeneous catalysis eunployed in indus-(CH3I) first directly carbonylatcs with carbon monox-try today, it is afccted by the disadvantagcs associ-ide to form CH3COI, which further interacts withated with a vcry noble rhodium and a highly corlo-methanol (MeOH) to form mcthyl acetate (AcOMe)sive reaction mediun due to the use of methyl iodideand HI, and ther MeOH reacts with HI to forn CH3I.as a promoter. Mauy research cfforts have been in-Thus it seens likely that nuethanol docs not directlydulged in the search for an appropriate calalyst (e.g.carbonylate with CO during the catalytic cycle, andsiupportcd rhodium complexes [1], Ni/C and Ni-Sn/Cthus this carbonylation reaction is indirect catalyticcatalysts [2- 5]) to carry onut vapor phase carbonylt-carbonylation. Peng preseuted this as dircct carbony-tion under atospheric pressure. A nickel-based cat-lation of methanol without any balide in the feed aalyst was found to exhibit satisfactory activity anda promnoter (8. A mnovel sulfided Mo/C catalyst hasselectivity for the carbonylation of metharol, andbeen found to have a high activity and selectivity formethyl iodide was essential in these cases. The ratc-the vapor phase carbonylation of mcthanol to methyldetermining step of the reaction was discovered to beacetAte without the addition of a CH3I promotcr tothe clecavage of the C-I bond of melhy! iodide. Therethe feed |9.10]." Corresponding author. Tel: (020)87111884; E-inail: vefpengascint.ec中国煤化工YHCNMHG32Feng Peng/ .Journal of Nuturul Gius Clrcnuisry Vol. 12 No, 1 20032. Experimentalplaced in a Pyrex tube and treated at 673 K underflowing helium for 1 h. The tempcrature was then de-2.1. Catalyst preparationcrcascd to 323 K under the same helium flow. Carbonmonoxide was introduced into the samnple cell by pulseThe catalyst was prepared by ineipient inpregla-methou at this Lemperature. and the adsurption quatl+tion. Predctermined quantities of anniun hepta-tilty was determiued. After 15 minutes, the samplemoly' bdatc were dissolved in deionized water. A co1n-was heated at a rate of 10, 20 and 30 K/min, respec-mereially available gramlar activated carbon (olivetively. A thermal conductivity detector was utilizedbased. 20-40 mesh particle size, 1.000 mn2 /g) was thenfur detecting the desorption. Acetic acid and methylimpregnated with the solution for 4 6 h. The slurryacetate were introduced into the sample cell by pulsewas pulidized in an (NH)2S aqueous solutionn (S28%at 343 K. The desorption procedure was similar tonass)for4handthendriedinaairovenat393Kthat of CO.for 12 h. Prior to the catalytic tests, the dried cat-An X-ray difractometer (D/max-IIA. Japan)alyst; were treated in situ with II2 at 673 K for 2was used for XRD (X-ray difraction) analysis. Theh. The Mo content in the catalysts was 10% (mass).radiatiou source was Cu Ko. and the applied cur-Mo catalysts supported on ~-Al2O; and SiO2 wererent and voltage were 30 mA and 40 kV; respectively.prepared using the same procedure.During the analysis, the sample was scanned fromA scrics of non-supportcd Mo catalysts were pre-4° to 70". The surface morplology and compositionparcd. Activating MoS2 with a flow of H2 at 673 Kwere charactcrized using SEM (Scanning electron mi-created the MS1 catalyst. MS2 arose froun sulfidizingcrosCopy, XL-30FED, Philips Company) and EMPAMoO3 with a flow of 5%H2S-H2 at 673 K. MS3 and(elcctron probe unicroanalysis, DX-4i, EDAX Com-MS4 were fabricated from an anmnoniun heptamolyb-pany) instrunents.date solution by sulfdizing in all H2S and (NH4 )2Saqueous solution, respectively and subsequently acti-3. Results and discussionvated with a flow of H2 at 673 K. MS5 was preparedfrom an ammonium heptamolybdatc solution by sul-3.1. Efect of supportsfidizing in an (NH4)2S aqueous solution aund subse-quently treated with a flow of N2 al 673 K.Table 1 shows the efect.s of supports on catalyticactivity for vapor phase carbonylation of methanol.2.2. Catalyst testThe table reveals that Mo catalysts are very sensi-tive to the effects of their supports. Activated car-Methanol carbonylation was carried ont in a fixed-bon is the best supports.Mo catalysts supportedbed reactor with a continlous flow systcm at atmo-on个Al2O3 have a high methanol conversion but luwspheric prossure. The catalyst bed contained a nix-carbonylation sIcctivity. Mo/SiO2 catalysts have ature of catalyst (2.0 g) and powdered quartz (2.0 g). .lower methanol conversion, and the carbonylation se-The latter was employed to decrease the gas chan-lectivity is nearly zeru.neling and teluperature gradient in the bed. FachThe rlatiouships betwecn NH3 and CO adsorp-carbouylation experinent started with a catalyst re-tions and carboylation of methanol were also il-ductiou perforned in situ at 673 K under fowing H2vestigated. The results show a higher anount olfor 2 l. The temuperature of the catalyst bed wasabsorbed NH3 on the Mo/C and Mo/~Al2O3 thanthen dereased to the desired reaction tempcraturc,Mo/SiO2. The acidity of a catal!yst is nessaryand the reactants were contimnously fed at that ten-in order to activate methanol, and the coversionperature into the bed. The efucnt gas was sampled of methanol is determined by the numnber of acidicby a sampling valve and immcdiately analyzed by a sites. The amount of co chenisorption fllowsgas chromatograph. Methanol conversion and yieldthis order: Mo/C(1,190 urmol/g)>Mo/r- Al2O3( 198for the reaction are defined as in refercnccs 9 and 11.μmol/g)> Mo/SiO2( 100 pumnol/g). The adsorbed COmmolecules might migratc from metal sites tu activated2.3. Catalyst characterizationcarbon (spillover), thus enlaucing the amount of ab-sorbed CO, This result denoustrates that the cffect ofFor the temperature prograrned desorptionchemisorbed CO on t.he selectivity" for carbonylat ion(TPD) experiment, 140 mg of activated sarnple was中国煤化工TYHCNMHGJournal of Natural Gas Chemistry Vol. 12 No.1 200333Table 1. Effect of supports on catalytic ativity for direct vapor phase carbonylation of methanolBFT areaMothanolSelectivity (mol%)CH3C0OCH3Catalyst(m2 /g)conversion (别) Ci-C2CH3OCH3CHIyCOOCHyyield (mol%)Mo/C(a)96865.410.22.087.8574Mo/Cib)102068.210.9(.888.260.1Mo/Cl2)150067.311.0.487.0 .58.6Mo/~-Al2O3 .17094.886.312.311.7Mo/SiO21003.18.551.01.50.0258.7C!b)10505.Reaction conditions: T=553 K, p=100 kPa, GHSV=3.300 L/(kgh). n(CHzOH)/n(CO)=1/9(u)- coul-beased activutcd caurbon, (b)- oliv-buseud activuted earbon. (c)- trcated olive-based activnted rarbonTable 2. Relationships between NHz and CO chemisorptions and methanol vapor phase carbonylationMethanolCHgCOOCH3Uplake (umnol/g)n(CO)/n(Mo)conversiun (%)yield (nol%)CONHgMo/C4601.Mo/-Al2Oz1985250.193.2001:0.14Reuction conditions are the same as Table 1.The probable reaction mechanism of the directdecrcasc in the carbouylation selectivity and to an in-vapor-phase carbonylation of methanol is prescntedcrease in inethane selectivity.below. The initial stcp of this reaction is the cleav-age of methanol to form CH，flloweldl by adsorbed0ls-CO insertion into the metal-mnethyl bond, forning。 (3)CH3C(O)+ , which further interacts with nethanol toform methyl acetate.80IyCHsOH+ H+→CHOHI→CH +H2O (1)i0 tCH +CO→CHgC(O)+(2)CH3C(O)+ + CHzOH→CH;COOCH3+H+ (3)CHg0H + CH3OH→CH3OCH3+ H2O+ H+ (4)CH3OH +C0→CH4+H+ +CO2 (5)20 t(4)3.2. Effect of reaction conditions(2Figurc 1 shows tbe efect of reaction tempera-53373593ture on the activity and selectivity. Data for tem-perature exaninations were collected with the novelMo/C catalyst on stream for at least 4 h (consideredFigure 1. Effect of temperature on the carbonyla-tion of methanolas steady state), The mnethyl acetate selcctivity de-Reaction conditious: p=0.1 MPa. t=4 b, GHSV-3.000creases with the temperature, and the methanol con-L/(kg-h), n(CH3OH)/n(CO)=1/11version increases with the tcmperature. The maxi-(1) x, (2) S(DME). (3) S(AcOMe), (4) S(CHa)mun carbonylation activity is rcached at 573 K. Fig-ure 1 shows that methane is formed as the mainFigurc 2 shows the effect of methanol concen-byproduct, while dimethyl ether (DME) is formued to tration on the carbouylation. The reaction coludi-a lesser extent. Met hanol carbonylation is a very se-tions are optinized as follows: reaction terlperaturelective reaction to mcthyl acetate at lower tenpera- of 57323 mol% andtures (T < 553K). Higher temperatures lead a sharpcarbon中国煤化工.000 L/kgh).YHCNMHG34Fung Peng/ Journal of Natural Gias Chemisry Vol. 12 No.I 2003Under thesc optimal conditions, a methanol conver-50 mol% carbonylation selectivity, 0.15 mo/(kgHl)sion of 50%，carbonylatiou seletivity of 80 mol%,space-tine yield) and RhW l2PO4n/SiO2 catalystsand spac-time yield of 8.0 mnol/(kgh) are obtained.(40% Imethaol conversion. 50 nol% carbonylation se-Thesc data are surprisingly higher than those of sul-lectivity) reported in different literature [6.7]. Thesefided CoMo/C catalysts (20% methanol conversion,results sggest that this Mo/C catalyst Inay bepronising for methyl acetate production from the car-bonylation of methanol at atmnospleric pressure with-out requiring nethyl iodide as a promoter.3.3. Relationship between adsorption and00-methanol vapor phase carbonylation2)80 t.A series of non-supported Mo-catalysts were pre-pared. and their catalytic performanccs for Inethanol(3)direct vapor-phase (arbonylation and the relationshipbetween adsorption and catalytic activity are shownin Table 3. The results suggest the signilicant in-fucnce of the preparation method. MS1 and MS2n0jcatalysts havc a lower conversion of mcthanol and sc-Iectivity to methyl acetate, while MS3 and MS4 cat-50 talysts have a higher activity and selectivity. Mostsignifcantly, the carbonylation activity over MS4 isforty timcs higher than over MS1. MS3 and MS4 have10high methanol conversion and metlhyI acctate selectiv-ity bcause MS3 and MS4 have a better adsorption30 L.ability of CO, CH3OH and AcOMc than MS1 and0MS2. MS5 (treated with a fAow of N2) has a lowerCH,OH concentration (mo1%)carbonylation activity than NS4 (treated with a flowFigure 2. Effect of methanol concentration on theof H2). The lowest activated energies of desorptioncarbonylation of methanolReuction conditions: T=573 K, p=0.1 MPa, GHSV=3.000and snaller quantities of adsorption are observed onL/(kgh)MS5. All the result indicates that the catalyst activ-(1) x, (2) S(AcOMe). (3) STY(AcOMe)ity is grcatly afferted by the pretreatment conditions.Table 3. Relationship between adsorption and mothanol vapor phase carbonylationSelectivity (%)Uptake (unoi/g)E (kJ/mo)CatalystsX/%CAF (b-1)C-C2 MeOMe AcOMeco CH3OH ArOMeCO CH:OH AcOMeMSI6.76.514.59.00.00573.66.14.348.1 24.139.1MfS211.5 61.520.518.00.018012.021.116.4 43.771.2MS354.2 37.530.232.30.170055.670.220.616.0 14.917.5MS462.30.220067.975.426.815.8 15.016.6MS515.2 45.843.310.90.016015.38.67.18.9.76.9Reaction conditions: T=573 K, p= 100 kPa, GISV= 3.0 L/(gb), n(CHgOH)/n(C0)=1/9X-conversion of methanol; CAF- carbonylation activity factor. AcOMe mol/(nol-h); E- activation energy ofdesorption; MeOMe- -dincthyl ether; AcOMc- methyI acetate3.4. Structure characterization of catalystscatalysts have a different microscopic structure ducto the different preparation method. Figure 4 showsScanning-electron microscopy photographs of thethat the crystalline structure MoS2 catalyst has lit-catalysts are show1 in Figure 3. Comnparing Figurestle carbonylation activily (MS1 and MS2): the 1011-3(a) and 3(b), the surface morplology of the sul-erystalline structure MoS2 catalyst has a higher acfided Mu/C catalyst does not show ay conspicuoustivity, and the novcl sulfided Mo/C cataulyst shouldchauges. However, the non- supported sulfided Mo-中国煤化工YHCNMHGJournal of Natural Gas Chenisury Vol. 12 No, 1 200335Ta)Figure 3. SEM of catalysts (x 1,000)(a) Mo/C, (0) Mo/C afcr reaction, (e) MSI, {d) MS2, (e) MIS3, () MSATable 4. Surface elerent analysis of catalysts withEMPA (atomic%)MoO,Catalyst C ，MoSS/Mo●B-MoS,Mo/C86.34.82.25.2.5Mo/C"2.35.12.4MS1033.564.31.M山MS233.055.711.30.MS35.963.52.1MS46.129.365.62.* Mo/C calalyst alfter carbonylation reaction for 6 h. .(3The surface compositions of the catalysts werealalyzed by clectron probe microanalysis (EPMA).From Table 4, the molar ratio of S to Mo is 2.2sus070(MoS2.2) for MS4 and 2.1 (MoS2.1) for MS3. The sig-29/“)nificantly higher carbonylation activity on .MIS4 conI-Figure 4. XRD spectra of catalystspared tcomparatively(1) MSI, (2) MS2, (3) MS3. (4) MS4, (5) Mo/Clarger S中国煤化工Mo/C catalyst,YHCNMHG36Feng Peng/ Journal of Natural Gas Chenistry Vol. 12 No.1 2103which has a high activity and selectivity for methanolScience Foundation of China (No.29903003).vapor-phase carbonylation, whose active phasc is then-rystalline phase, the active componcnt is presentReferencesa MoS2.5 on the surface of activated carbon.川JiangH, LiuZ Y, PanP L. Yuan G Q. J Mol Cattal.4. Conclusions1999, 148(1/2): 215[2; Fjinoto K, Bischoff s. Omata K. Yagita H. J Catal,A nove!l sulfided Mo/C catalyst with a high activ-1992, 133(2): 370ity andl sclectivity for the vapor phase carbonylation(3) Merenov A S. Abrahaum M A. Catal Today. 1998.of nethanol to methyl acctate without the addition of40(4): 397a CH;I promoter to the feed has been discovered. Un-[川Merenov A s, Nelson A, Abralar M A. Catal Torlay.2000. 55(2): 91der optimal conditions, this catalyst caul attain 50%(5] Liu T C, ChiuS J. Appl Catal A.1994. 117(1): 17met hanol conversion, 80 mol% carbonylation selectiv-[6] Calafat A, Laine J. Catal Lett, 1994, 28(1): 69ity. and a spacc time yield of 8.0 mol/(kgh) AcOMe.[7] Wcgman R W. J Cher Soc: Cheru Comunun, 1991The active phase of the novel slfidcd Mo/C catalyst(8): 947is tle non crystalline phase, and thc active component[8] Peng F. Cuihua Xuebao (Chin J Catal), 1998, 19(3):is present 出MoS2.5 on the surface of the activated387carbon.[9] Peng F. Chem J Internet, 2000, 2(7): 32[10| Peng F, Zheng G s. Ranliao Huaxue Xuebao (Cbin JAcknowledgementsFuel Chem Tchno), 2000, 28(4): 340[1] Peng F, lluang Z T. Chin J Chem Eng, 1997, 5(3):This work was supported by the National Nature261中国煤化工MYHCNMHG