A novel and green synthesis of methylcyclohexane diisocyanate: Reaction properties, deactivation and regeneration of Rh/γ-Al2O3 catalyst in benzene ring selective hydrogenation

Abstract

Methylcyclohexane diisocyanate (HTDI) is the core raw material for the synthesis of high-grade polyurethane. Aiming at the problems existing environmental pollution and safety risks in the phosgene process, a novel and green synthesis route of HTDI was proposed. We studied the catalytic hydrogenation of dimethyl toluene dicarbamate (TDC) benzene ring to methyl cyclohexyldicarbamate (HTDC) in this novel route. The effects of metal active components, supports and metal Rh loadings on the catalytic performance were investigated. It was found that the supported Rh/γ-Al2O3 catalyst had excellent catalytic activity and selectivity. The yield of HTDC was close to 100 % at 100 °C under 3 MPa hydrogen pressure. However, the catalyst was deactivated seriously after the reaction. The organic matter adsorbed on the catalyst surface and covered the active metal was the main reason for the catalyst deactivation. Fortunately, the deactivated catalyst could be regenerated by solvent washing and high temperature calcination.