Thermodynamic analysis of hydrate-based pre-combustion capture of CO₂

This paper presents the phase equilibria of quaternary CO₂ + H₂ + cyclopentane (CP) + water systems containing gas hydrates and proposes a staged-separation scheme based on the thermodynamic data. The phase equilibria of HLLV of quaternary CO₂ + H₂ + CP + water systems are determined by using a high-pressure differential scanning calorimeter (DSC). The equilibrium dissociation pressures are dependent on the vapor composition and they shift to lower values with the increase in the CO₂ mole fraction. The difference in the dissociation pressures between various CO₂ fractions vanishes as the temperature approaches the melting point of CP hydrates at 0.1 MPa. The hydrate dissociation enthalpy is independent of vapor compositions and it is 144 kJ mol (gas)^{- 1} over the temperature range. Experimental data are compared to the calculated ones from John-Holder's three-shell model. The prediction matches well with experimental data. The presence of CP reduces the operation pressure of a hydrate-based CO₂ capturing process from the pre-combustion stream. Two equilibrium stages of hydrate crystallization and dissociation can enrich CO₂ in the vapor-phase significantly from 0.4 of CO₂ mole fraction to 0.98 at 282 K. This thermodynamic analysis provides a conceptual design for developing a new process of pre-combustion CO₂ capture in IGCC plants.