Hierarchical LTL zeolite as an efficient solid acid catalyst for replacing HCl in the production of polyurethane intermediates

Abstract

Caustic mineral acid catalysts have been gradually replaced with green solid acids such as zeolites in many industrially important reactions. Enormous efforts have been devoted to replacing HCl to produce methylenedianiline (MDA), an essential intermediate in polyurethane production. Unfortunately, limited success has been achieved thus far due to low catalytic activity, selectivity towards the desired 4,4'-MDA, and rapid catalyst deactivation. We currently report that meso-/microporous hierarchical LTL zeolite exhibits high catalytic activity, selectivity, and stability. The one-dimenosional cage-like microporous structure of LTL zeolite can promote the bimolecular reaction between two para-aminobenzylaniline intermediates to selectively produce 4,4'-MDA and inhibit the formation of undesired isomers and heavy oligomers. Meanwhile, the secondary mesopores facilitate mass transfer, resulting in a 7.8-fold higher MDA formation rate compared to solely microporous LTL zeolite. Due to suppressed oligomer formation and fast mass transfer, the catalyst exhibits unprecedented deactivation behavior in an industrially relevant continuous flow reactor.