Study On The Potassium Based Catalysts For The Synthesis Of Methylacrylate With Methyl Acetate

Methyl acetate is produced as a by-product in the industrial production process of polyvinyl alcohol. It has large yield and low added value. In the research, the industrial by-product methyl acetate was used as raw material, and it achieved the green synthesis of methyl acrylate. The factors such as active component, preparation conditions and catalyst additives were studied in order to reduce the manufacture costs with potassium replacement of cesium as the catalyst active center. Different kinds of treatments such as X-ray diffraction（XRD）, thermal weight, scanning electron microscopy（SEM） and chemical adsorption were used to study the performance of carrier and catalysts, such as specific surface area, pore volume, pore size, crystal structure, surface morphology and the alkali center strength. The details of the research and the research findings are shown as follows.（1）The pore structure parameters were characterized by way of N2 adsorption/desorption methods. The information about pore size distribution was obtained. The pore size of micropore structure was concentrated between 0.8nm and 1.2nm. In addition, the pore size of mesoporous structure was concentrated between 5nm and 15 nm. The minimum effective aperture of the carrier is estimated theoretically, and its value was 1.4nm. It provided the theoretical basis for the selection of the carrier.（2）In the research, the close-packed model was improved, and the dispersion threshold was calculated with the close-packed mode. The value was 8.21%. The effect of the loading capacity of the active component on the experiment was studied. The results showed that when the loading was 15%, the catalyst exhibited higher activity. The yield of methyl acrylate reached 6.8%.（3）The effect of catalyst preparation conditions on the catalytic performance was studied such as impregnation method and calcination process. The catalyst performance was characterized by way of SEM and CO₂-TPD. The results showed that the dispersion degree of the active component on the surface of the carrier can be increased by ultrasonic impregnation. Increasing the calcination temperature can increase the probability of potassium nitrate decomposition into potassium nitrite, and the basicity of catalyst was enhanced.（4）The effect of different additives on the performance of catalyst was studied. The factors, such as the loading additive elements and impregnation sequence were discussed in detail. The preparation conditions of catalyst were optimized: potassium nitrate as a source of potassium, potassium loading capacity of 15%, ultrasonic impregnation time of 1.5h, calcinations time of 8h under 550 ℃, magnesium load of 1g/100molSiO₂, sodium load of 0.5g/100molSiO₂, impregnated first with sodium, magnesium and last with potassium elements. Under these conditions, the prepared catalyst was proved to possess preferable catalytic performance, with the active site loaded uniformly on the surface of the carrier, and the yield of methyl acrylate was up to 10.65%.（5）The optimal process conditions for synthesizing methyl acrylate were determined, namely, reaction temperature at 340℃, feed space velocity at 3.2 h-1, methylal/methyl acetatemolar ratio at 1:3, methanol content in the feed liquid at 30%.（6）The reasons for deactivation of catalyst were studied. The results of catalyst stability evaluation experiment showed that the catalyst activity decreased faster with the increase of reaction time. The deactivated catalyst was characterized by ICP, and BET and SEM. The results showed that the loss of active components and the pore structure blockage caused by carbon deposition on the catalyst were the main reason for the deactivation of the catalyst.