Thermodynamic and Spectroscopic Identification of Guest Gas Enclathration in the Double Tetra-n-butylammonium Fluoride Semiclathrates

Abstract

The precise nature and unique pattern of the double tetra-n-butylammonium fluoride (TBAF) semiclathrates with a guest gas (CH(4) or CO(2)) was closely investigated through thermodynamic and spectroscopic analyses. The three-phase equilibria of semiclathrate (H), liquid water (L(W)), and vapor (V) for the ternary CH(4) + TBAF + water and CO(2) + TBAF + water mixtures with various TBAF concentrations were experimentally measured in order to determine the stability conditions of the double TBAF semiclathrates. The double CH(4) (or CO(2)) + TBAF semiclathrates showed remarkably enhanced thermal stability when compared with pure CH(4) (or CO(2)) hydrate. The highest stabilization effect was observed at the stoichiometric concentration of pure TBAF semiclathrate, which is 3.3 mol %. Gas uptake measurements were undertaken in order to estimate the amount of gas consumed during double semiclathrate formation. CH(4) was found to be a relatively more favorable guest for the 5(12) cages of the double TBAF semiclathrate than CO(2). From the results of the NMR and Raman spectroscopic analyses it was identified that the guest gas molecules (CH(4) or CO(2)) were enclathrated in the 5(12) cages of the double TBAF semiclathrates. The overall results given in this study are useful for understanding the fundamental guest gas enclathration behavior in the double semiclathrates.

Accurate measurement of phase equilibria and dissociation enthalpies of HFC-134a hydrates in the presence of NaCl for potential application in desalination

“…The Chekcell program was used for the refinement of the obtained PXRD patterns. A more detailed description of the experimental methods and procedures has been provided in previous papers [23][24][25][26][27].…”

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

“…A fiber optic Raman probe that was installed in the high pressure reactor provided time dependent Raman spectra as semiclathrate formation proceeded. A more detailed description of the experimental methods and procedure are given in our previous papers [11,30,41].…”

“…In QAS semiclathrates, anions such as Br À , Cl À , and F À are involved in forming cage structures with the host water molecules, and tetra-n-butyl ammonium (TBA) cations are incorporated into the large cages. In addition, the QAS semiclathrates have small 5 12 cages which are left vacant and thus, can be used for capturing small-sized gas molecules [19,22,23,[25][26][27][28][31][32][33][34][35][36][37][38][39][40][41]. Due to their significant thermodynamic stability and guest gas enclathrating ability, QAS semiclathrates have been investigated as an alternative to gas hydrates for gas storage and separation [23,27,31,[42][43][44][45][46][47][48].…”

Hydrate-based CO2 capture and CH4 purification from simulated biogas with synergic additives based on gas solvent

“…For instance, when the simulated landfill gas hydrate formed with 0.0234 mol fraction tetra-n-butyl ammonium bromide (TBAB), the equilibrium hydrate formation pressure could reduce by approximately 90% [17], it is very close to the realistic temperature and pressure condition for separation operating. However, it has been reported that even though the quaternary ammonium salts hydrate could offer greatly enhanced thermal stability, the hydrate formation rate and gas storage capability were very low [21]. Hence, the last three essentials have been the major bottlenecks for the gas hydrate application technologies.…”