预吸附及择形脱附对甲醇胺化产物分布的影响(英文)

Effect of Preadsorption and Shape Selective Desorption on Methanol Amination Product Distribution

低分子量的胺是合成含氮有机化合物的重要原料 .以NaM、HM、NaHM和NaKHM为催化剂 ,采用CH3 OH/NH3 _TPD、XPS、比表面积和孔容分布测量等手段研究了甲醇胺化反应 .结果表明 :胺化产物分布受氨NH3 的预吸附和甲胺 (MMA)、二甲胺 (DMA)及三甲胺 (TMA)的择形脱附控制 .由于沸石孔道中部分孔穴被氨填充和堵塞 ,导致孔体积变小、空间位阻增大 ,难以生成分子较大的三甲胺 (TMA) .NH3 预吸附造成的另一个结果是预吸附过程中Na+ 和K+ 由分子筛体相向孔口迁移 .这些位于孔口的金属阳离子有利于甲胺和二甲胺的选择脱附 ,而不利于三甲胺分子从孔口的有效脱附 ,因而强化了三甲胺到二甲胺的歧化反应 ,其结果是增大了二甲胺的选择性 ,使产物分布符合预先设想 .

Low molecular weight amines are important raw materials for synthesis of nitrogen_containing organic compounds. In the present paper, the methanol amination with the catalysts of NaM, HM, NaHM and NaKHM was investigated by CH 3OH/NH 3_TPD, XPS, specific surface area and pore volume distribution measurements. It can be found from the results that the amine product distribution was controlled by the NH 3 preadsorption and by the shape selective desorption of MMA,DMA and TMA. The zeolite cavities were partially blocked by NH 3 filling, so the pore volume became smaller which introduced steric constraints for larger trimethylamine (TMA) molecule formation. Another consequence of the NH 3 preadsorption was that the Na + and K + ions migrated from the bulk phase to the pore mouth during the process of preadsorption. These cations which located at the pore mouth benefited the selective desorption of different amines, and prevented TMA molecule from getting away from pore mouth effectively and thus improved the disproportionation reaction of TMA to DMA. Therefore, it enhanced the selectivity of DMA and caused a desired distribution of product.