Phase equilibria of semi-clathrate hydrates of tetra-n-butyl phosphonium bromide at atmospheric pressure and in presence of CH₄ and CO₂ + CH₄

Gas separation and gas storage involving semi-clathrate formation are promising processes that can be used in many industrial fields. Among them, there is the possibility to purify the biogas, which is a gas mixture composed essentially of carbon dioxide (CO₂) and methane (CH₄). The investigations of the feasibility of these processes require knowledge about the phase diagram of the involved system. This work presents the phase diagrams of the systems of tetra-n-butyl phosphonium bromide (TBPB) + H₂O, CH₄ + TBPB + H₂O and CO₂ + CH₄ + TBPB + H₂O. The dissociation temperatures of the semi-clathrate phase were determined at a mass fraction of TBPB varying from 0.05 to 0.35 and at a 1-MPa pressure range. For CH₄ + TBPB + H₂O systems the measured temperatures varied from 280.8 to 293.1 K. The dissociation temperature of the semi-clathrate formed with TBPB has also been obtained in the case of CH₄ + CO₂ mixtures, the proportion of the gases being close to what is observed in typical biogases.