Evaluating ionic behavior of bicarbonate and carbamate species in blended Diisopropanolamine/2-amino-2-methyl propanol aqueous solutions using CO2 solubility experimental data and electrolyte activity coefficient models

Abstract

The role of bicarbonate and carbamate species is very important in chemical absorption of CO2 using aqueous amine solutions. Through rigorous activity coefficient thermodynamic models validated by experimental data, this study pinpoints the impact of bicarbonate and carbamate species on CO2 solubility in the blend of aqueous diisopropanolamine (DIPA)/2-amino-2-methyl propanol (AMP). In this study, experiments were conducted for CO2 solubility in the blended DIPA/ AMP aqueous solutions at different mixing ratios of DIPA/AMP/H2O (9:21:70, 15:15:70, and 21:9:70 wt%) and temperatures (323.15 and 383.15 K). The successive substitution (iterative) approach was introduced to calculate the concentration of all chemical species, including bicarbonate and carbamate ions, by solving one charge balance, four mass balance and six equilibrium equations simultaneously. Two activity coefficient models such as the electrolyte nonrandom two-liquid (electrolyte NRTL) and the electrolyte universal quasi-chemical (electrolyte UNIQUAC), were used to reduce the discrepancies between experimental data and predicted values. Compared to the electrolyte UNIQUAC model, the electrolyte NRTL model is more appropriate for simulating the CO2 solubility of the DIPA-AMP-H2O-CO2 system. Ultimately, CO2 partial pressure in the gas phase, concentration of all the species in the liquid phase, pH changes, heat of absorption, and cyclic CO2 loading capacities were estimated at the absorption/desorption temperatures according to DIPA/AMP blending ratios. Model was further extended to elucidate the behavior of pH and heat of CO2 absorption in DIPA/AMP blend.