Enhanced Selectivity of the Separation of CO2 from N2 during Crystallization of Semi-Clathrates from Quaternary Ammonium Solutions

CO2 mitigation is crucial environmental problem and a societal challenge for this century. CO2 capture and sequestration is a route to solve a part of the problem, especially for the industries in which the gases to be treated are well localized. CO2 capture by using hydrate is a process in which the cost of the separation is due to compression of gases to reach the gas hydrate formation conditions. Under pressure, the water and gas forms a solid that encapsulates preferentially CO2. The gas hydrate formation requires high pressures and low temperatures, which explains the use of thermodynamic promoters to decrease the operative pressure. Quaternary ammonium salts represent an interesting family of components because of their thermodynamic effect, but also because they can generate crystals that are easily handled. In this work, we have made experiments concerning the equilibrium of (CO2, N2) in presence of Tetra-n-Butyl Ammonium Bromide (TBAB) which form a semi-clathrate hydrate. We propose equilibrium data (pressure, temperature) in presence of TBAB at different concentrations and we compare them to the literature. We have also measured the composition of the hydrate phase in equilibrium with the gas phase at different CO2 concentrations. We observe that the selectivity of the separation is dramatically increased in comparison to the selectivity of the pure water gas clathrate hydrate. We observe also a benefice on the operative pressure which can be dropped down to the atmospheric pressure. (authors)