Heat Capacity of CO₂-Loaded Aqueous Methyldiethanolamine + Piperazine + Sulfolane Solutions

Heat capacities of CO2-loaded aqueous N-methyldiethanolamine (MDEA) and piperazine (PZ) and sulfolane (SFL) solutions were experimentally measured. MDEA, PZ, and SFL concentrations in aqueous solutions were selected in the ranges (0.192–0.360), (0–0.113), and (0–0.156) on the mass fraction scale, respectively. Solubility and heat capacity were measured simultaneously at temperatures from 303.15 to 363.15 K, at 20 K steps, and at pressures up to about 1000 kPa using the previously developed experimental setup. The results show that the mixture heat capacities decrease with increasing CO2 loading at each constant temperature and increase with increasing temperature in all loading values. A modified Setchenow equation was employed to correlate the solutions' heat capacities. The average and maximum percent relative deviation, ARD and MRD%, of the correlated heat capacities from the experimental data were 0.52 and 1.65%, respectively, indicating quite good correlative accuracy of the model used. The Setchenow model developed was employed to predict the heat capacities of fresh/unloaded and CO2-loaded, aqueous MDEA and MDEA + PZ solutions reported in the literature. The average percent deviation of Setchenow-predicted heat capacities from reported data was 1.5%, further indicating quite good consistency of our data with the reliable experimental data previously reported.