CO2 Heat of Absorption in Aqueous Solutions of MDEA and MDEA/Piperazine

In the present study, calorimetric measurements were conducted to determine CO2 behavior in aqueous solutions of 30 and 50 wt % N-methyl diethanolamine (MDEA) and 40 + 10 wt % MDEA–piperazine (PZ) at 323.15 and 353.15 K at pressures from 0.5 to 4 MPa. The effects of temperature, pressure, MDEA concentration, and addition of PZ on the heat of absorption and CO2 solubility were investigated based on the calorimetric results, which were verified to be consistent with the vapor–liquid equilibrium data. No apparent effect of MDEA concentration was observed, while the heat of absorption was influenced by the temperature and pressure. The heat of absorption of the solution with PZ was enhanced, but the enhancement decreased with the increase of CO2 loading. The CO2 solubilities in aqueous solutions of 50 wt % MDEA and 40 + 10 wt % MDEA–PZ were compared in the experimental range, and the results showed no effect of PZ on the CO2 capture capacity. In addition, the absorption processes with and without PZ were simulated using Aspen Plus on the basis of the electrolyte non-random two-liquid model and a further study on the effect of the composition of MDEA and PZ in the solution was also conducted. The reaction mechanism was derived to give insights into the contribution of all reactions to the integral heat of absorption.