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 CO 2 absorptions with primary/secondary amines involving ‘catalytic carbamate formation’. Compared with the non-catalytic ‘Zwitterion mechanism’, this Eley–Rideal model was proposed for CO 2 + RR′NH with MCO 3 (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 CO 2 –MEA absorptions with the existence of 0–25 g CaCO 3 , MgCO 3 and BaCO 3 . 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 CO 2 + primary/secondary amines over alkaline earth metal carbonate (MCO 3 ).

Evaluating Energy-Efficient Solutions of CO2 Capture within Tri-solvent MEA+BEA+AMP within 0.1+2+2–0.5+2+2 mol/L Combining Heterogeneous Acid–Base Catalysts

“…The mechanism of solid base catalysts of CaCO 3 was published via the Eley–Rideal model . The elementary steps and energy diagram were published.…”

“…The mechanism of solid base catalysts of CaCO 3 was published via the Eley–Rideal model . The elementary steps and energy diagram were published. Briefly, the amine molecule (MEA/BEA) was adsorbed onto the active sites of the catalyst surface first, and then the CO 2 molecule was connected to the N atom of amine molecules .…”

“…The elementary steps and energy diagram were published. Briefly, the amine molecule (MEA/BEA) was adsorbed onto the active sites of the catalyst surface first, and then the CO 2 molecule was connected to the N atom of amine molecules . In catalytic absorption, there were several different mechanisms based on different catalysts, which had not reached an agreement yet …”

“…This pipette process was independent from the CO 2 absorption process, where the introduction of CO 2 gas was stopped temporarily. The solvent loss was about 20–30 mL out of 300 mL, but the solution maintained a constant amine concentration [C], which had little effect on the reaction rate r = k [C] a . The CO 2 loadings of samples were tested at least twice to ensure the accuracy of AAD = 5% …”

“…For catalytic absorption, Idem’s group has selected seven solid alkaline catalysts and focused on K/MgO since 2018. − They completed catalytic CO 2 absorption with CaCO 3 , MgCO 3 , BaCO 3 with MEA, , DEA, and MEA+DEA , and R 3 N . For catalytic CO 2 desorption, many researchers adopted various solid acid catakysts ,,,,− ,,− for MEA, MEA+R 3 N, and BEA+AMP, etc.…”