Studies Of Catalysts For Synthesising Methyl Mathacrylate From Methyl Propionate And Formaldehyde

As an unsaturated organic monomer,methyl methacrylate（MMA）is commonly used in the production of high-value-added chemicals,such as poly（methyl methacrylate）.Catalytic condensation between HCHO and methyl propionate derived from ethylene carbonyl esterification offers an environmental-friendly process for the production of MMA.However,the development of industrial catalysts for the above Aldol reaction remains to be solved.In this thesis,a series of Si O₂ andγ-Al₂O₃ catalysts modified by alkaline were prepared and tested in the condensation of methyl propionate with formaldehyde,with attention focused mainly on the acid-base properties of catalysts.The main results and conclusions are listed as follows:（1）The MMA selectivity is closely related to the weak basic sites instead of the moderately strong basic sites of catalysts in the Aldol reaction between methyl propionate and HCHO.This is supported by the observed results obtained on theγ-Al₂O₃ and Si O₂ oxides modified by Na⁺,K⁺and Cs⁺.The selectivity of MMA was roughly linear to the ratio of weak basic sites presenting on the catalyst surface;while the presence of acidic and moderately strong basic sites facilitated the formation of dimethyl ether and methyl isobutyrate,respectively.As a result,catalytic activity and selectivity declined.（2）Al₂O₃ acts as an excellent binder to extrude Cs/Si O₂ catalyst and enhance its mechanical strength.Considering the by-products caused by the acidity of Al₂O₃,30 wt%Al₂O₃ is suitable for extrusion,and the conversion of methyl propionate reached 35.55%in the presence of such a catalyst.Introducing 15%Cs₂CO₃ onto the Si O₂-Al₂O₃ mixed oxide,the methyl propionate conversion and MMA selectivity were as high as 39.3%and 98.74%,respectively,in the optimized conditions.Nevertheless,the active Cs/Si O₂-Al₂O₃ catalyst tended to be deactivated by the organic deposits formed in the condensation reaction.