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

Abstract

This work presents data on the phase behavior of tetra-n-butyl phosphonium bromide (TBPB) semiclathrate hydrate formed in the presence of CO 2 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 + CO 2 semiclathrate hydrate. It was found that the phase equilibrium conditions for TBPB + CO 2 semiclathrate hydrate formed at 2.57 mol % TBPB were lower than CO 2 hydrate formed in pure water and TBPB + CO 2 semiclathrate hydrate formed at 0.5 mol % TBPB. The coexistence of CO 2 hydrate (sI) and TBPB + CO 2 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, CO 2 hydrate disappeared and more TBPB + CO 2 semiclathrate hydrate was formed. However, under the same temperature and pressure conditions, CO 2 consumption during the formation of TBPB + CO 2 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 CO 2 storage capacity of TBPB semiclathrate hydrate.

Minireview of Hydrate-Based CO2 Separation from a CO2/CH4 Gas Mixture: Progress and Outlook

“…Further work should be carried out to reduce toxicity and prolong the THF life cycle. In addition, quaternary ammonium/phosphonium salts (QAS/QPS) like tetra- n -butyl ammonium bromide (TBAB), , tetra- n -butyl ammonium chloride (TBAC), , and tetra- n -butyl phosphonium bromide (TBPB) − have been used to form semiclathrate hydrate for CO 2 capture. TBAB semiclathrate has a strong preference for the incorporation of CO 2 molecules, but there remains a large margin for the increase of gas consumption before it is used on the industrial scale .…”