Thermodynamic Equilibrium Conditions for Simulated Landfill Gas Hydrate Formation in Aqueous Solutions of Additives

Abstract

This work presents the thermodynamic study of separating CH4 and CO2 from the simulated landfill gas (LFG) [CO2 (0.45) + CH4 (0.55)] based on hydrate crystallization in the presence of tetra-n-butyl ammonium bromide (TBAB), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), and their mixtures. The mole fractions of TBAB, THF, and DMSO aqueous solutions were fixed at 0.0234, 0.0556, and 0.0165, respectively. The equilibrium hydrate formation conditions were measured by T-cycle method in the temperature range of (274.15 to 294.95) K and the pressure ranges up to 6.72 MPa. The gas phase in the crystallizer at the equilibrium points was also sampled and analyzed. For the additives with the fixed concentrations studied in this work, it was found that both TBAB and THF can remarkably reduce the equilibrium hydrate formation pressure of LFG mixture gas, but the effect of THF is better than that of TBAB in the high temperature region, while DMSO have no obvious pressure drop effect on the equilibrium hydrate formation conditions but can promote the solubility of CO2 in the solution. However, the mixture additives of TBAB + DMSO and THF + DMSO can not only remarkably promote the solubility of CO2 but also remarkably reduce the equilibrium hydrate formation pressure of CO2 + CH4 + H2O hydrate. Moreover, the pressure drop effect of THF + DMSO is better than that of TBAB + DMSO on the CO2 + CH4 + H2O equilibrium hydrate formation in the high temperature region.