Kinetic and thermodynamic studies on direct synthesis of methyl methacrylate from methyl propionate and methanol catalyzed by highly efficient cobalt complex at mild conditions

Abstract

Methyl methacrylate (MMA) typically produced from the petroleum-based ethylene or isobutene selective oxidation route is a significantly important chemical widely used in industrial manufacture. Herein, an innovative and highly efficient liquid-phase catalytic system, cobalt complex catalyzed O2-interrupted hydrogen borrowing pathways, was developed for direct synthesis of MMA from methyl propionate and methanol at mild conditions, considering the problems of poor selectivity, rapid catalyst deactivation, and formaldehyde polymerization existed in one-step aldol reaction of methyl propionate with formaldehyde at 350–380 °C. The yield and selectivity of MMA could reach up to 50.2% and 81.8% at 60 °C and 1 atm. Thermodynamic calculations and analysis for this novel transformative process were conducted to confirm the feasibility and reasonability for MMA production at low temperature (below 100 °C). On the basis of the reaction networks proposed according to the experimentally detected products, studies on the kinetic informatics of this new process were conducted. The formaldehyde oxidation, aldol condensation of methyl/t-butyl propionate with formaldehyde and transesterification of t-butyl propionate/methacrylate with methanol are first-order dependent on their reactant concentrations. While the methanol dehydrogenation and transesterification of methyl propionate/methacrylate with t-BuOK are first-order dependent on the concentration of only methanol and t-BuOK. With the understanding of kinetic behavior of these reaction steps composed, the global kinetic model was established to describe this catalytic system and the corresponding parameters including pre-exponential factor and activation energy were calculated. The oxidative dehydrogenation of methanol to formaldehyde, with the highest activation energy of 84 kJ/mol, was the kinetic-relevant step, while the aldol condensation of methyl propionate with formaldehyde showed the lowest energy of 36 kJ/mol.