A Calorimetric Study on the Phase Behavior of Tetra-n-butyl Phosphonium Bromide + CO2 Semiclathrate Hydrate and Evaluation of CO2 Consumption─Impact of a Surfactant

This work presents data on the phase behavior of tetra-n-butyl phosphonium bromide (TBPB) semiclathrate hydrate formed in the presence of CO2 at a stoichiometric concentration (2.57 mol % TBPB). A high pressure microdifferential scanning calorimeter (HP μ-DSC) was employed to measure the phase equilibrium data and identify the dissociation behaviors of TBPB + CO2 semiclathrate hydrate. It was found that the phase equilibrium conditions for TBPB + CO2 semiclathrate hydrate formed at 2.57 mol % TBPB were lower than CO2 hydrate formed in pure water and TBPB + CO2 semiclathrate hydrate formed at 0.5 mol % TBPB. The coexistence of CO2 hydrate (sI) and TBPB + CO2 semiclathrate were identified in the 2.57 mol % TBPB solution. When adding 500 ppm sodium dodecyl sulfate (SDS) into the 2.57 mol % TBPB solution, CO2 hydrate disappeared and more TBPB + CO2 semiclathrate hydrate was formed. However, under the same temperature and pressure conditions, CO2 consumption during the formation of TBPB + CO2 semiclathrate hydrate was reduced when 500 ppm of SDS was added to the 2.57 mol % TBPB solution. Therefore, future work should aim to increase the CO2 storage capacity of TBPB semiclathrate hydrate.