Hydrate phase equilibria of carbon dioxide/propane gas mixture in concentrated aqueous sodium chloride solutions: Experimental data and prediction

Abstract

The information on hydrate equilibrium conditions of gas hydrate formers in concentrated NaCl solutions are the prerequisites for hydrate-based desalination methods. Hydrate dissociation conditions for CO2-C3H8 mixture, as a good candidate for this application, were measured for the temperature and pressure ranges of 269–283 K and 0.3–3.4 MPa, respectively using an isochoric pressure-search method. The used gas mixture was a solution of 10 mol% C3H8 + 90 mol% CO2 and NaCl concentrations varied between 8 and 12 wt%. The promoting effect of propane was obviously observed from the experimental data. This promoting effect nearly balanced the inhibitory effect of 12 wt% NaCl. A thermodynamic model was applied to predict the experimental data using SRK, PR, and VPT EOSs. All EOSs had accurate results for prediction of CO2 hydrate equilibrium pressures, with the best result by PR EOS. The overall average absolute percent deviation (AAPD) of PR EOS in pure water and 8 wt% NaCl solution were 5.29 and 3.8 %, respectively. For gas mixture (CO2-C3H8) in pure water, the best accuracy was obtained by using SRK EOS with AAPD of 4.44 %. However, the results of VPT and PR for gas mixture in NaCl solutions, were more accurate than SRK with AAPDs equal to 7.47 and 7.75 %, respectively.