The CO 2 desorption tests were conducted at 363-378 K for 5.0 mol/L blended monoethanolamine (MEA)-diethanolamine (DEA) solutions to develop the energy efficient solvents with high CO 2 production and low energy consumptions. These desorption tests were performed with a recirculation process for various preloaded, 5 mol/L (4.5 + 0.5 to 0.5 + 4.5) MEA-DEA solutions to find out the optimized solvents with minimum heat duty. Therefore, 1-4 mol/L and 0.5-0.45 mol/L MEA-DEA solvents have larger CO 2 production (nCO 2 ) and lower heat duties (H CO 2 ) than 5 mol/L DEA under similar operation conditions. They have lower heat duty (510 and 538 kJ/mol) than DEA (572 kJ/mol) due to increased CO 2 desorption rates, despite 10% higher heat input (Q Total ) than DEA. Moreover, the critical points were studied as research focus of amine regeneration curves, along with reaction energy calculation. Finally, secondary amines blending minor MEA (<20%) as promotor turned out to be an alternative approach of solvents improvement with low energy requirement.

Heat-duty reduction is the major challenge in CO 2 desorption and amine regeneration. The use of a combination of heterogeneous catalytic desorption with improved amine solvents is a novel approach to address this issue. We studied CO 2 -desorption tests of noncatalytic diethylamine (DEA) solvents as a benchmark and focused on five blended amines (DEA−monoethanolamine, MEA; 4.5:0.5 to 2.5:2.5 M) with three types of catalysts (γ-Al 2 O 3 , H-ZSM-5, and 2:1 blended γ-Al 2 O 3 −H-ZSM-5) to explore the synergy effects of DEA-based amine blends with solid catalysts. The heat duty and CO 2 production of each case scenario were tested for six sets of solutions with initial loading of 0.5 mol of CO 2 per mole of amine at 363−378 K and were compared with those of 5 M DEA solvents. The results showed that the three catalyst conditions (blended catalyst, H-ZSM-5, and γ-Al 2 O 3 ) followed different trends at rich and lean loadings. Finally, both 5 M DEA and 4.5:0.5 M DEA−MEA with blended catalysts exhibited very low heat duties of 151.2 and 168.0 kJ per mole of CO 2 at loadings of 0.50− 0.20 mol per mole of amine at 378 K among the six solutions. Both approaches proved to be the most-energy-efficient amine solutions whereas the blended amine with blended catalysts was the best strategy that was applicable in the CO 2 desorber.

Studies of catalytic CO2 absorption and desorption were completed in two well-performed tertiary amines: diethylmonoethanolamine (DEEA) and 1-dimethylamino-2-propanol (1DMA-2P), with the aid of CaCO3 and MgCO3 in the absorption process, and with the aid of γ-Al2O3 and H-ZSM-5 in the desorption process. The batch process was used for CO2 absorption with solid alkalis, and the recirculation process was used for CO2 desorption with solid acid catalysts. The CO2 equilibrium solubility and pKa were also measured at 293 K with results comparable to the literature. The catalytic tests discovered that the heterogeneous catalysis of tertiary amines on both absorption and desorption sides were quite different from monoethanolamine (MEA) and diethanolamine (DEA). These results were illustrative as a start-up to further study of the kinetics of heterogeneous catalysis of CO2 to tertiary amines based on their special reaction schemes and base-catalyzed hydration mechanism.

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 ).

Abstract. The CO 2 desorption analyses of amines were performed to reveal the behaviour of amine regeneration process. A typical primary amine (MEA) and two other secondary amines (MMEA and DEA) were selected in preparation for amine solutions under different concentrations, from 1-7 mol/L. The regeneration curves were plotted to describe the process. It was discovered that the specific CO 2 loading (mol/mol) that distinguish the amine regeneration curves into different regions were the same for the specific amine, despite different concentrations. These points were defined as "turning points" on regeneration curves. The turning points of MEA, MMEA and DEA are located at CO 2 loading of 0.40 mol/mol, 0.38 mol/mol and 0.28 mol/mol, respectively. The regeneration tests compared the relative heat duty at the first 2 hours: MMEA > MEA > > DEA.