Equilibrium conditions of hydrate dissociation of CO2 + bromocyclohexane or tetrahydrothiophene + H2O

Abstract

Hydrate can be used as an effective way to separate CO2. However, the formation of CO2 hydrate requires high pressure and low temperature conditions in pure water, it limits the hydrate method application for the separation of CO2. Thermodynamic prompters can be used to reduce the pressure of CO2 hydrate formation. In this work, the effect of tetrahydrothiophene and bromocyclohexane on CO2 hydrate dissociation conditions is first studied. The addition of tetrahydrothiophene can greatly reduce the equilibrium pressure of CO2 hydrate dissociation. Structure II hydrate forms in the system of CO2 + tetrahydrothiophene + H2O, while structure I hydrate forms in the system of CO2 + H2O. Hydrate equilibrium pressure increases with the increase of temperature. At any temperature, the hydrate equilibrium pressure of CO2 + tetrahydrothiophene + H2O reduces more than 2 MPa, compared the hydrate equilibrium pressure of CO2 in pure water in this work. Bromocyclohexane has almost no effect on the phase equilibrium conditions of CO2 hydrate. The experimental results also show that tetrahydrothiophene can be as a promoter for CO2 hydrate formation.