| Methyl ethyl ketone(MEK),which is an important petrochemicals in the chemical industry,it is also an important organic solvent with excellent property,which has adequate boiling point,good solubility,quick volatile rate,good stability.Currently,the most common route for the production of MEK directly or indirectly depends on petroleum feedstock Compared to the conventional route,catalytic dehydration of 2,3-butanediol to methyl ethyl ketone can reduce the reliance on fossil fuels and operate at lower temperature.Moreover,methyl ethyl ketone is easier to be separated and purified.In this paper,Zn-Mn-Co/HZSM-5 catalysts were prepared by HZSM-5 impregnated with Zn2+,Mn2+,Co2+ mixture solution under the hydrothermal condition;The catalytic activity of compound modification catalysts prepared at different conditions were investigated.The crystal form,microtopography,elemental composition,pore structures and superacid center of the prepared catalyst were characterized by SEM,XRD,BET,XRF,FT-IR and XPS.The effects of reaction conditions on the 2,3-butanediol dehydration to methyl ethyl ketone were studied and the production conditions were optimized by response surface methodology(RSM).The results show that the catalysts have high activity at a temperature as low as 250?surface.The optimal load of ZnO,MnO,CoO were 8%,6%,8%by mass percent respectively,and the synergistic effect between Zn2+,Mn2+ and Co2+;Different hydrothermal modification temperature and time will affect the surface area?pore structure and the distribution of activity center;The optimal hydrothermal modification temperature and time were 180? and 4h respectively;The optimal calcination temperature was 600? in the preparation of catalysts,the calcination temperature too low,acid center structure is formed not easily,however,high roasting temperature can destroy acid structure center and molecular sieve skeleton,which causes the Zn-Mn-Co/ZSM-5 catalyst activity decline;Calcination time has little effect on the catalytic performance,so we can improve the stability of the catalyst by means of extension of the Calcination time appropriately.The results of catalyst characterization prove that the preparation of the catalyst can damage the structure of molecular sieve;Zn,Mn,Co species can be highly decentralized to the surface or channel of ZSM-5 by impregnation method,which don't change the crystalline of zeolite and the pore structure,but the crystallinity,surface area and pore volume decreased because of the increase of metal species;Fourier infrared spectrum and XPS characterization results show molecular sieves are kept on ZSM-5 the basic characteristics of skeleton absorption peaks in before and after the modification,This suggests that its functional group structure is not altered after the modification,and metal ion exist in metal oxide forms in catalyst;Carbon deposit can be removed or reduced by means of calcination.The Zn-Mn-Co/ZSM-5 catalyst showed high activity and selectivity and was applicable to different concentrations of 2,3-butanediol,Continuous reaction still can maintain a higher conversion and selectivity after the 100h.The optimal conditions for maximum 2,3-butanediol yield by RSM were as follows:2,3-butanediol concentration was 17.14%,reaction temperature was 254.30?,WHSV was 2.27h-1 and the corresponding 2,3-butanediol yield achieved 69.6695%.The order of the significant effects between factors was reaction temperature=WHSV>2,3-butanediol concentration,and these factors have interaction. |
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