Hydrate phase equilibrium measurement of 50 mol.% carbon dioxide / 33 mol.% dimethyl ether / 17 mol.% propane in the presence of tetrahydrofuran, cyclopentane, tetra‑n‑butylammonium bromide, and tetra‑n‑butylammonium chloride

Abstract

Hydrate-based cold storage and refrigeration offer notable efficiency and safety advantages. By leveraging the high cold storage density of CO₂ hydrate and the low phase equilibrium pressure and GWP of DME and C₃H₈ hydrates, a gas mixture hydrate (50 mol.% CO₂, 33 mol.% DME, 17 mol.% C₃H₈) was used as a refrigerant for phase equilibrium assessment. Results showed phase equilibrium temperatures of 274.5 to 278.9 K at pressures from 0.4 to 0.86 MPa, aligning with conventional air conditioning pressures. Additives like THF, CP, TBAB, and TBAC improved conditions. Liquid promoters (THF, CP) increased temperatures by 4.5 to 7.9 K, while solid promoters (TBAB, TBAC) raised them by 5.3 to 11.1 K. Liquid promoters shifted the phase equilibrium curve for CO₂-DME-C₃H₈ hydrate almost parallel to the right, while solid promoters steepened the curve slope. A predictive model was developed, showing good molar phase change enthalpy.