Development of Novel Synthetic Amine Absorbents for CO2 Capture

AbstractIn the present paper, we investigated five synthetic amine based absorbents, including three formulated solvents. Aqueous solutions of the amines (mass fraction; 30% for single amine and >30% for blended solvents) were used to evaluate the performance for CO2 capture. Gas scrubbing, vapor-liquid equilibrium (VLE), and reaction calorimetry experiments were conducted in the laboratory to obtain the absorption rate, the amount of CO2 absorbed, cyclic CO2 capacity, and heat of reaction for each absorbent. The results of these absorbents were compared with the conventional absorbent monoethanolamine (MEA). Three high performing synthetic absorbents (IPAE, IPAP and IBAE) were found, and these had lower heats of reaction, higher cyclic capacities, and comparable absorption rates compared with MEA. All formulated absorbents showed excellent cyclic CO2 capacity and keeping moderately good absorption rate and lower heats of absorption. Some blended solvents were already demonstrated with real blast furnace gas at pilot test plants with capacities of 1 ton-CO2/day and 30 ton-CO2/day and showed promising results in terms of reducing absorbent regeneration energy

Ab Initio Study of CO2 Capture Mechanisms in Monoethanolamine Aqueous Solution: Reaction Pathways from Carbamate to Bicarbonate

AbstractAb initio calculations combined with the continuum solvation model have been conducted to obtain complete reaction pathways involved in the CO2 capture into monoethanol (MEA) aqueous solution. We have investigated the reaction pathways for the decomposition of MEA carbamate into bicarbonate. Although the already known pathways invoke a generation of free CO2(aq), we are concerned with another mechanism which does not involve such an intermediate. The neutral hydrolysis of the MEA carbamate was found to be a slow reaction that has an essentially two-step nature. We propose an alternative pathway that involves the carbamic acid as an intermediate that undergoes an alkaline hydrolysis leading to the formation of bicarbonate. Taking account of the novel reaction pathways elucidated here as well as the established routes for the formation of carbamate and bicarbonate may lead to a comprehensive understanding and a better prediction of the chemical CO2 capture process under specific conditions including pH (concentration of amine) and partial pressure of CO2

Ab Initio Study of CO₂ Capture Mechanisms in Aqueous Monoethanolamine: Reaction Pathways for the Direct Interconversion of Carbamate and Bicarbonate

Ab initio molecular orbital calculations combined with the polarizable continuum model (PCM) formalism have been carried out for a comprehensive understanding of the mechanism of carbon dioxide (CO₂) absorption by aqueous amine solutions. CO₂ is captured by amines to generate carbamates and bicarbonate. We have examined the direct interconversion pathways of these two species (collectively represented by a reversible hydrolysis of carbamate) with the prototypical amine, monoethanolamine (MEA). We evaluate both a concerted and a stepwise mechanism for the neutral hydrolysis of MEA carbamate. Large activation energies (ca. 36 kcal/mol) and lack of increase in catalytic efficiency with the inclusion of additional water molecules are predicted in both the mechanisms. We also examined the mechanism of alkaline hydrolysis of MEA carbamate at high concentrations of amine (high pH). The addition of OH^– ion to carbamate anion was theoretically not allowed due to the reduction in the nucleophilicity of the former as a result of microsolvation. We propose an alternative pathway for hydrolysis: a proton transfer from protonated MEA to carbamate to generate the carbamic acid that initially undergoes a nucleophilic addition of OH^– and subsequent low-barrier reactions leading to the formation of bicarbonate and free MEA. On the basis of the calculated activation energies, this pathway would be the most efficient route for the direct interconversion of carbamate and bicarbonate without the intermediacy of the free CO₂, while the actual contributions will be dependent on the concentrations of protonated MEA and OH^– ions