One-step Synthesis of n-Butanol from Ethanol Condensation over Alumina-supported Metal Catalysts

Chinese Chemical Letters vol. 15, No 12, pp 1497-1500, 20041497http://www.immac.cn/journal/ccl.htmlOne-step Synthesis of n-Butanol from Ethanol Condensationover Alumina-supported Metal CatalystsKe Wu Yang, Xuan Zhen JIANG", Wei Chao ZHANGartment of Chemistry, Zhejiang University, Hangzhou 31002Abstract: One-step synthesis of n-butanol from bimolecular condensation of ethanol was firstlyachieved over nickel supported gamma alumina catalyst. A mechanism of dehydration path for thegrowth of carbon chain by eliminating a hydroxy group from one ethanol molecule with a a-H ofother ethanol molecule rather than aldol condensation was verifiedKeywords: Ethanol condensation, n-butanol, nickel supported on gamma alumina, dehydrationAn important commercial chemical, n-butanol, was widely used as an organic solvent andn additive to gasoline as well. The traditional synthetic method of n-butanol was aldolondensation of acetaldehyde, followed by catalytic hydrogenation of the condensedintermediates over basic zeolites. It was reported that n-butanol was produced with theselectivity of 43 at optimum reaction temperature of 420C via bimolecularcondensation of ethanol on alkali cation zeolites such as rb-LiX zeolite. An alternativemechanism was proposed, in which one molecule of ethanol its C-H bond in B-positionwas activated on the basic zeolite and condensed with another ethanol molecule bydehydrationIn the present study the gamma alumina-supported nickel catalyst was the first timebe utilized as a catalyst to achieve bimolecular condensation of ethanol to give n-butanolwith the selectivity of 64% at relatively low reaction temperature of 200'C. The possiblereaction mechanism examined in this study supported the mechanism reported inAlumina-supported metal catalysts were prepared by adding 20 to 40 mesh y-Al2Opurchased from Shanghai Chemical Reagent Company)to a solution containing therequired amount of Ni(NO3 )2 6H2O (or other nitrates needed). The mixture was kept atroom temperature for two days and then was dried at 150 C. Before catalytic testing 1.0 gcatalyst was loaded in a ceramic tube reactor and pretreated under hydrogen flow at 500Cfor 4 hE-mail:chejiang@zju.edu.cn中国煤化工CNMHG1498Ke Wu yang et alThe ethanol condensation reactions were carried out at 200"C and l atm in a fixed bedceramic tube reactor with the inner diameter of 8 mm. Ethanol was introduced by a pumpwith LHSV of 0.67 h. The products were analyzed by GC-FID(HP-1102G)equippedwith ov-101 column and identified by GC/MS(HP5970)The X-ray diffraction of the catalyst was performed with Ni-filtered Cu-Ka radiationfrom a 12-kw Rigaku rotating anode X-ray source operated at 45 kV and 50 mA after thecatalyst was reduced by hydrogen at 500C for 4 h and cooled to room temperature underhydrogen flow in a specially designed cellTemperature-programmed reduction (TPR)of the catalysts was performed in amicro-reactor(ca 80 mg sample loading )at a heating rate of 10C min" using a mixtureof 5 vol H2/N2 as reducing gas after passing through a 4A molecular sieve trap toremove water. A gas chromatography with TCD was used for monitoring the hydrogenconsumption and recorded the tpr profilesResults and discussionThe catalytic performances over 8%Fe/y-AlO3, 8%Co/y-Al2O3 and 8%Ni/y-AlO3atalysts were given in Table 1. It can be seen from Table 1 that among them the8%Ni/y-Al2O3 catalyst exhibited the highest catalytic activity with 19. 1% conversion ofethanol and 64.3% selectivity of n-butanol, respectively. However no n-butanol wasobtained over 8%Fe/y-Al2O, mainly producing acetaldehyde. Over 8%Co/y-AL2Ocatalyst the considerable amounts of n-butanol was obtained with selectivity of 22%To optimize nickel loading for alumina-supported nickel catalysts, three differentloading catalysts, 4%Ni/Y-Al2O3, 8%Ni/y-Al2O3 and 15%Ni/y-Al2O3 were prepared andtheir catalytic performances at the same reaction conditions were listed in Table 2Table 1 The catalytic performances of different catalysts over ethanol condensation reactionsBDCatalystConv (Sel (8%Co/y-AlO17,214.115,929,222.718.43.164.323.0a)Reaction conditions: temp: 200 C, LHSV: 0.67hb)AD: Acetaldehyde; BD: Butaldehyde, EA: Ethanyl acetate: BO: n-butanolc)Others: 2-Ethylbutanol, n-hexanol, ethyl ether, n-butyl ether etc.Table 2 Catalytic performances over different nickel loading catalystscatalystEthanol Conv (%)n-Butanol yield(%)8%Ni/Y-Al2O319.115%Ni/Y-Al2012.0中国煤化工CNMHGOne-step Synthesis of n-Butanol from Ethanol1499Figure 1 XRD patterns of y-Al2O3 and 8%Ni/y-Al2O326(°)A: Blank y-Al2O3 B: 8%Ni/y-Al2O3 after H2 reductionFigure 2 Profiles of temperature-programmed reduction over4%Ni/y-Al2O3 8%Ni/y-Al2O3 and 15%Ni/y-Al2O330060090Temperature CFrom therein one can see that 8%Ni/y-Al2O3 catalyst demonstrated relatively highcatalytic activity and selectivity of n-butanol. To explore the active site of the catalyst,semi-in-situ XRD was performed and the results was shown in Figure 1. From the XRDprofiles Ni(o) was confirmed in the catalyst and it may act as the active sitesThis will be further confirmed by TPR profiles as shown in Figure 2. In the TPrprofiles the first peak maximum(Tm)in the lower temperature region due to the reductionof Ni(NO3)2 to NiO were observed on three catalysts. The corresponding Tm value510C(on 15%Ni/y-Al2O3), 560C(on 8%Ni/Y-Al2O3) and 590'C(on 4%Ni/y-Al2O3)wereshifted to higher temperatures as decreasing nickel loading. The second peakmaximum(TM)in the higher temperature region mainly ascribed to the reduction of nio toNi(0) were observed on both 8%Ni/y-Al2O3 and 4%Ni/y-Al2O3 samples; while only tinypeak on 15%Ni/y-Al2O3 sample indicating the formation of less Ni(O) species over highloading sample. Analogously the Tm values of second reduction peaks: 705C(on8%Ni/y-Al2O3)and 745 C(on 4%Ni/y-Al2O3) showed the same tendency. Reduction ofNio to Ni(O) required increasing temperature as nickel loading decreased. The reasonprobably was attributed to that low nickel loading catalyst had a relatively large proportionof unreduced nickel which was stabilized at the vacancies of y-Al2O3 with defective spinelstructure. Therefore 8%Ni supported on y-Al2O3 may be a suitable catalyst whichexhibited relatively high catalytic activity as given in Table 3. It implied that metallicnickel was most likely to be the active sites for ethanol condensation to n-butanolV凵中国煤化工CNMHG1500Ke Wu yang et alTo explore the reaction mechanism of bimolecular condensation of ethanol ton-butanol by separately adding acetaldehyde and crotonaldehyde into the reactant feed, thevariation in reactivities was observed as listed in Table 32-Ethylbutanol and n-hexanol were detected in the products. They the products ofwere consideredas the products of the condensation of ethanol and n-butanol. Howeverhigher molecular weight alcohols such as 2-ethylbutanol and n-hexanol were remarkablydecreased compared with the case of absence of so called intermediates. After theddition of crotonaldehyde to the reactant feed the yield of n-butanol obviously decreasedas given in Table 3, it revealed that crotonaldehyde was not able to be a intermediate ofthis ethanol condensation reaction. This point was consistent with the reportedmechanism in literature". It indicated that the growth of carbon chain in this ethanolcondensation reaction was not taken place via aldol condensation pathway. Thefollowing alternative dehydration path(Scheme 1) for extending the carbon chain byeliminating a hydroxyl group from one ethanol molecule with a a-H of other ethanolmolecule was verifiedTable 3 The effect of addtion of different"intermediates"on reactivity ofthanol condensation reactions"Intermediate"added n-butanol yield (% 2-ethylbutanol yield(%)n-hexanol yield(%)10% AcetaldehydeNo intermediate12.3Scheme 1 Dehydration pathwayCH 3CH2 +CH 2 2CH2OH-C4H9OH+H2OReererencesL.R. Martens, w.J. Vermeiren, D.R. Huybrechts, P J Grobet, P. A Jacobs, in"Proceeding, gInternational Congress on Catalysis, Calgary, 1988", VoLI, p 420. Chem. Institute of CanadaOttawa. 19882. C. Yang, Z.Y. Meng, J Catal, 1993, 142, 37.3. C. Yang, Z.Y. Meng, Acta Chemica Sinica, 1993, 51, 794. B. Xu, C. Yang, Z.Y. Meng, Chinese Journal of Catalysis, 1994, 15(6), 482.5. Z.H. Li, X. Y, Zhang, B W. Wang, H. Y Chang, Journal of Sichuan University(EngineeringScience Edition), 2002, 34(5), 246. R. Molina. G. Poncelet. Catal. 1998./73. 257Received 20 October 2003中国煤化工CNMHG