利用择形分子筛异构化亚甲基二苯胺

Isomerization of methylenedianilines using shape-selective zeolites

亚甲基二苯胺(MDA)被广泛用作生产聚氨酯和聚异氰脲酸酯的中间体.然而,当前MDA的生产工艺在控制(4,4’/(2,4’+2,2’))异构体比例方面还存在局限.其中,4,4’-MDA被认为是最有价值的异构体.尽管2,4'-MDA在市场上也有一定的需求,但如果能将其有效地转化为4,4'-MDA,将能显著提升其附加值.本文在使用苯胺的条件下,利用β分子筛等催化剂,通过双分子机制,可以选择性地将2,4'-MDA异构化为4,4'-MDA.尽管实验显示,多种酸性沸石具有较高的异构化活性,但MCM-68(具有MSE拓扑结构)的催化性能尤为出色,它不仅展现出高异构化活性,而且具有很好的选择性.MCM-68主要催化2,4'-MDA异构化为4,4'-MDA,而2,2'-MDA和低聚物的形成则可以忽略不计.本文还深入探讨了该择形作用的原因,并详细研究了酸位置在MSE分子筛孔道限制中的关键作用.

Methylenedianilines(MDA)are widely used as intermediates in the production of polyurethanes and polyisocyanurates.The current routes for the production of MDA offer only limited control of the isomer ratio(4,4’/(2,4’+2,2’)),with 4,4’-MDA being the most valuable isomer.While 2,4’-MDA is also marketed,significant added value could be unlocked upon further steering the production towards 4,4’-MDA.We here show that zeolites such as Beta can selectively isomerize 2,4’-MDA towards the desired 4,4’-MDA via a bimolecular mechanism,in an aniline background.While several acid zeolites were found to be active isomerization catalysts,MCM-68(MSE topology)in particular combines high isomerization activity with efficient shape-selective suppression of the formation of unwanted 2,2’-MDA and oligomers.The origin of this shape-selectivity was studied,highlighting the crucial role of the acid site location in the pore confinement of MSE zeolites.