Promoted CO2 Desorption in N-(2-Hydroxyethyl)ethylenediamine Solutions Catalyzed by Histidine

Abstract

This study systematically investigates the catalytic effect of histidine (HIS) on CO2 desorption in amine-based solvents, with a primary focus on 30 wt% N-(2-aminoethylamino)ethanol (AEEA) and its blends with N-methyldiethanolamine (MDEA). Experimental results show that the addition of 0.22 wt% HIS significantly enhances both the equilibrium desorption amount and the maximum desorption rate of CO2, particularly at elevated temperatures (e.g., 100 °C). Under optimal conditions, HIS increased the maximum desorption rate by 22.1% and reduced the heat duty to 71.7% compared to the non-catalytic benchmark. The catalytic performance was further confirmed in AEEA-MDEA mixed solvents, with the most pronounced effect observed in the 3:2 molar ratio system, where HIS enhanced both the equilibrium desorption amount and the maximum desorption rate by 15.3% and 20.8%, respectively. Through 13C NMR analysis and pH-dependent speciation monitoring, we revealed that HIS alters the reaction pathway by suppressing the formation of stable carbamate species (AEEA(a)COO−). The protonated (HIS+) and neutral (HIS±) forms were identified as the active species that promote more direct CO2 release from carbamate, while the deprotonated (HIS−) form facilitates proton transfer and amine regeneration. HIS also exhibited excellent catalytic stability over 10 absorption–desorption cycles. These findings highlight HIS as an efficient and stable organocatalyst for energy-efficient CO2 desorption processes.