Eley–Rideal model of heterogeneous catalytic carbamate formation based on CO ₂ –MEA absorptions with CaCO ₃ , MgCO ₃ and BaCO ₃

Abstract

The mechanism was proposed of heterogeneous catalytic CO₂ absorptions with primary/secondary amines involving 'catalytic carbamate formation'. Compared with the non-catalytic 'Zwitterion mechanism', this Eley-Rideal model was proposed for CO₂ + RR'NH with MCO₃ (M = Ca, Mg, and Ba) with four elementary reaction steps: (B1) amine adsorption, (B2) Zwitterion formation, (B3) carbamate formation, and (B4) carbamate desorption. The rate law if determining step of each elementary step was generated based on 'steady-state approximation'. Furthermore, the solid chemicals were characterized by SEM and BET, and this rate model was verified with 39 sets of experimental datasets of catalytic CO₂-MEA absorptions with the existence of 0-25 g CaCO₃, MgCO₃ and BaCO₃. The results indicated that the rate-determining step was B1 as amine adsorption onto solid surface, which was pseudo-first-order for MEA. This was the first time that the Eley-Rideal model had been adopted onto the reactions of CO₂ + primary/secondary amines over alkaline earth metal carbonate (MCO₃).