Preparation Of Catalysts For The Mannich Condensation Of Formaldehyde And Propionaldehyde

Methacrolein（MAL）is an important chemical intermediate,mainly used for the production of methyl methacrylate（MMA）.Propionaldehyde is produced by hydroformylation of ethylene and syngas,and ethylene,syngas,formaldehyde and methanol can be produced with coal as raw materials.Study on the preparation of MAL by liquid-phase condensation of formaldehyde and propionaldehyde,and to develop the production technology of MMA with coal not only meets the energy situation of"rich coal and poor oil"in China,but also meets the relevant requirements of green chemistry,and has broad application prospect.Firstly,the catalytic performance of homogeneous catalysts including ionic liquids and amino acids was studied in the liquid-phase condensation of formaldehyde and propionaldehyde.Using L-proline as the catalyst,when the reaction time was 25min and the reaction temperature was 43℃,the propionaldehyde（PA）conversion was 83.58%and the MAL selectivity was 94.62%.However,the homogeneous catalytic system has the problems of large catalyst consumption and difficult product separation.In this paper,L-proline and its derivatives were immobilized to prepare heterogeneous catalysts for liquid-phase condensation of formaldehyde and propionaldehyde.（1）The heterogeneous catalyst MCM-41-Pro was prepared by grafting L-hydroxyproline onto the surface of MCM-41 with silylation reagent containing chloropropyl group.The successful grafting of L-hydroxyproline was confirmed by XRD,FT-IR and other characterization methods,and the effect of reaction conditions on its catalytic performance was investigated.By optimizing the reaction conditions,the PA conversion was 50.71%,the MAL selectivity was 75.89%,and the TOF value was 36.67 h^-1.The results of EA analysis and reuse experiment showed that there was a loss of active components during the reaction.（2）Based on the structural memory effect of layered double hydroxides（LDHs）,the solid base catalysts Re-M_xAl-LDHs（M=Mg,Ca;X=2-4）with different metal elements as well as ratios were prepared by precursor roasting treatment and hydration recovery process.The highest MAL selectivity was 36.01%due to the limitation of base catalysis.On this basis,the hydrotalcite-based catalysts（Mg₃Al-Pro-LDHs and Re-Mg₃Al-Pro-LDHs）with L-proline intercalation were prepared by introducing L-proline as the guest anion into the interlayer of LDHs through co-precipitation and rehydration routes,taking advantage of the exchangeability of interlayer anions and the amphotericity of amino acids.The successful intercalation of L-proline was confirmed by characterization methods,and the arrangement of L-proline between the laminate was speculated.By optimizing the reaction conditions,the PA conversion was91.39%,and the MAL selectivity was 51.48%.Compared with above LDHs solid base catalysts,MAL selectivity was significantly improved.After four cycles,the PA conversion decreased and the MAL selectivity remained unchanged.