Isomerization of methylenedianilines using shape-selective zeolites

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.