Low-viscosity and efficient regeneration of carbon dioxide capture using a biphasic solvent regulated by 2-amino-2-methyl-1-propanol

Abstract

Biphasic solvents have attracted increasing attention in recent years due to their great potential to reduce the energy consumption of carbon dioxide (CO2) capture. In the present work, 2-amino-2-methyl-1-propanol (AMP) was used as a regulator to overcome the defects of a diethylenetriamine and pentamethyldiethylenetriamine (DETA-PMDETA) biphasic solvent—particularly, its high viscosity and inferior regenerability. The viscosity of the CO2-saturated biphasic solvent significantly decreased from 541.0 to 152.0 mPa·s and the CO2 cyclic capacity increased from 1.85 to 4.28 mol·L−1 (M) when the formula of the biphasic solvent was changed from 2 M DETA + 3 M PMDETA (2D3P) to 0.5 M DETA + 1.5 M AMP + 3 M PMDETA (0.5D1.5A3P). The sensible heat requirement for the regeneration of the solvent 0.5D1.5A3P could be reduced by 58.9% compared with that of 2D3P. The results indicated the positive regulatory effects of AMP on the biphasic solvent. Based on the characterizations and quantum chemical calculation, the regulatory mechanism of AMP in the biphasic system was elucidated. In the DETA-PMDETA system, CO2 was absorbed to mainly form DETA-carbamate. In the DETA-AMP-PMDETA system, CO2 was first absorbed to form DETA-carbamate and AMP-carbamate, while AMP-carbamate was rapidly hydrolyzed to HCO3−/CO32−, resulting in fewer carbamate products in the saturated solvent. Since HCO3−/CO32− did not tend to form hydrogen bonds and decomposed more easily than DETA-carbamate, the DETA-AMP-PMDETA system presented a lower viscosity and better regeneration performance. Moreover, in the presence of AMP, free protons were easily generated by multiple pathways to facilitate the dissociation of DETA-carbamate, which resulted in a deep CO2 stripping. Therefore, an AMP-regulated DETA-PMDETA biphasic solvent for low-viscosity and efficient regeneration of CO2 capture would further reduce the associated energy consumption.