Semiclathrate-based CO2 capture from flue gas mixtures: An experimental approach with thermodynamic and Raman spectroscopic analyses

Semiclathrate-based CO2 capture from flue gas in the presence of various quaternary ammonium salts (QASs) such as tetra-n-butyl ammonium bromide (TBAB), tetra-n-butyl ammonium chloride (TBAC), and tetra-n-butyl ammonium fluoride (TBAF) was investigated with a primary focus on the thermodynamic, kinetic, and spectroscopic aspects. The thermodynamic stability of the CO2 (20%) + N-2 (80%) + QAS semiclathrates was examined with an isochoric method using a high pressure reactor as well as with dissociation enthalpy measurement using a high pressure micro-differential scanning calorimeter (HP mu-DSC). The TBAF semiclathrate with CO2 (20%) + N-2 (80%) showed the most significant equilibrium pressure reduction at a specified temperature. However, the TBAC semiclathrate had the highest gas uptake and steepest CO2 concentration change in the vapor phase, which indicates the largest gas storage capacity for CO2 capture. CO2 was observed to be preferentially captured and enriched to approximately 60% in the semiclathrate phase. The CO2 selectivity was independent of the type of QASs used. The Raman spectroscopic results revealed that both CO2 and N-2 are enclathrated in the small cages of the QAS semiclathrates and that the enclathration of guest gas molecules does not change the structure of the semiclathrates. (C) 2015 Elsevier Ltd. All rights reserved.