Preparation Of MgO-SiO₂ And Its Catalytic Performance For The Synthesis Of 1,3-Butadiene From Ethanol

1,3-butadiene is widely used in the production of synthetic rubber,synthetic resin and fine chemical products as an important basic raw material in chemical industry.Currently,global butadiene is mainly obtained from the extraction process of C₄ steam cracker fractions.Due to the excessive dependence on oil resources and the resulting serious environmental problems,it is urgent to develop a green,sustainable butadiene production process.On the other hand,as the production technology of bioethanol gradually matures and the scale of production continues to expand,the production of butadiene from ethanol has received extensive attention.In this paper,the influences of preparation process of MgO-SiO₂ catalyst?including different SiO₂ supports,preparation methods,MgO contents,calcination temperatures and modification of metal promoters?and reaction conditions on the catalytic activity are systematically studied.It was found that in the MgO-SiO₂ catalyst,the certain Mg-O-Si structure could be formed between active component MgO and support SiO₂.There existed the synergistic effect between the new acidic structure and the basic sites of MgO,which was contributed to improve the butadiene selectivity.Compared with the impregnation method,in the catalyst prepared by wet-kneading method most of the active component MgO existed in the form of crystals,which could effectively inhibit the generation of some by-products,such as butanol,p-xylene,so that the butadiene selectivity could be significantly increased.When the commercial Nano-SiO₂-80 was used as support and MgO content was 20 wt%,the MgO-SiO₂ catalyst obtained after calcination in air at 500°C showed higher catalytic activity.The total conversion of ethanol and acetaldehyde was 25.8%and the butadiene selectivity was 50.4%.The comparative studies on various metal promoters?Cu,Y,Zr and Nb?were carried out,and the results showed that MgO-SiO₂ catalysts modified by ZrO₂ showed excellent catalytic activity.It was found that the addition of ZrO₂ could effectively promote the MPV reaction step,reduce the amount of heavy by-products such as p-xylene,and thus increase the selectivity of butadiene.In this work,the influence of different promoter doping methods on the catalytic performance was investigated.The MgO in the 2%Zr/MgO-SiO₂ catalyst prepared by wet-kneading after impregnation showed higher crystallinity,which could effectively inhibit the formation of butanol and other heavier by-products,therefore the selectivity of butadiene was higher than that of the catalyst prepared by wet-kneading before impregination.Under the optimal reaction conditions of ethanol acetaldehyde volumetric ratio of 3.5:1,WHSV of 0.4h^-1 and reaction temperature of 320°C,the total conversion of ethanol and acetaldehyde was 32.8%,the selectivity of butadiene was 68.7%and the catalytic activity could be maintained within 12 h.