Reaction kinetics of carbon dioxide absorption into aqueous potassium salt of histidine

Abstract

Aqueous amino acid salts are attractive absorbents for carbon dioxide (CO2) capture due to low volatility and resistance to oxidative degradation. The kinetics of CO2 absorption into aqueous solutions of potassium histidinate (HisK) was investigated using a wetted wall column at concentrations ranging from 0.26 to 2.07M and temperatures from 298 to 333K. Density, viscosity of aqueous HisK and physical solubility of N2O in these solutions were measured. A temperature dependant ion parameter hHis− was correlated to estimate Henry׳s constants of CO2. The zwitterion and termolecular mechanisms as well as ionic strength effect on reaction rate were applied to interpret the absorption rate of CO2 in non-ideal systems. Under the pseudo-first-order regime, the overall reaction rate constants increase strongly with the increasing HisK concentration and temperature. HisK shows comparable chemical reactivity toward CO2 with the industrial standard monoethanolamine (MEA). The partial reaction order with respect to HisK was found to be an average value of 1.26. Zwitterion deprotonation by water and HisK should be the rate-determining step. Two proposed models from zwitterion and termolecular mechanisms could successfully predict the experimental data within 12% AAD. The activation energy was calculated to be approximately 25.0kJmol−1.