Selective occupancy of methane by cage symmetry in TBAB ionic clathrate hydrate.

Methane trapped in the two distinct dodecahedral cages of the ionic clathrate hydrate of TBAB was studied by single crystal XRD and MD simulation

Structure-driven CO2 selectivity and gas capacity of ionic clathrate hydrates

Abstract Ionic clathrate hydrates can selectively capture small gas molecules such as CO2, N2, CH4 and H2. We investigated CO2 + N2 mixed gas separation properties of ionic clathrate hydrates formed with tetra-n-butylammonium bromide (TBAB), tetra-n-butylammonium chloride (TBAC), tetra-n-butylphosphonium bromide (TBPB) and tetra-n-butylphosphonium chloride (TBPC). The results showed that CO2 selectivity of TBAC hydrates was remarkably higher than those of the other hydrates despite less gas capacity of TBAC hydrates. The TBAB hydrates also showed irregularly high CO2 selectivity at a low pressure. X-ray diffraction and Raman spectroscopic analyses clarified that TBAC stably formed the tetragonal hydrate structure, and TBPB and TBPC formed the orthorhombic hydrate structure. The TBAB hydrates showed polymorphic phases which may consist of the both orthorhombic and tetragonal hydrate structures. These results showed that the tetragonal hydrate captured CO2 more efficiently than the orthorhombic hydrate, while the orthorhombic hydrate has the largest gas capacity among the basic four structures of ionic clathrate hydrates. The present study suggests new potential for improving gas capacity and selectivity of ionic clathrate hydrates by choosing suitable ionic guest substances for guest gas components

Guest-induced symmetry lowering of an ionic clathrate material for carbon capture

We report a new lattice structure of the ionic clathrate hydrate of tetra-n-butylammonium bromide induced by guest CO<inf>2</inf> molecules, which is found to provide high CO<inf>2</inf> storage capacity. The structure was characterized by a set of methods, including single crystal X-ray diffraction, NMR, and MD simulations.Peer reviewed: YesNRC publication: Ye

Phase Behavior and Structural Characterization of Ionic Clathrate Hydrate Formed with Tetra‑<i>n</i>‑butylphosphonium Hydroxide: Discovery of Primitive Crystal Structure

This paper reports phase equilibrium measurements and crystal structure analysis on the ionic clathrate hydrate formed from tetra-<i>n</i>-butylphosphonium hydroxide (TBPOH). Phase equilibrium temperatures were measured in the mole fraction range of TBPOH in aqueous solution from 0.0072 to 0.0416. The highest ionic clathrate hydrate–solution equilibrium temperature was determined to be 290.2 K at a TBPOH mole fraction of 0.0340, which corresponds to the congruent composition. Single-crystal X-ray diffraction measurements were performed on the crystal formed at 288.7 K, and the chemical composition of the TBPOH hydrate crystal was determined to be TBPOH·29.6H₂O, which is consistent with the congruent composition obtained by the phase equilibrium measurement. The crystal structure of the TBPOH hydrate has a superstructure identical with Jeffrey’s type I cubic structure, with an <i>I</i>4̅3<i>d</i> space group with a lattice constant of 24.5191(13) Å. The TBPOH hydrate structure is compared with the same hydrate structure formed by the tetra-<i>n</i>-butylammonium fluoride. We provide a comprehensive overview of the dissociation temperature, the counteranion, and the hydrate structure regarding TBP and TBA salt hydrates. The dissociation temperatures decrease linearly with the increase in the partial molal volume of anions for TBA and TBP salt hydrates, changing the hydrate structures from the primitive cubic one that has the minimum hydration number

Design of Ecological CO2 Enrichment System for Greenhouse Production using TBAB + CO2 Semi-Clathrate Hydrate

This paper proposes an innovative CO2 enrichment system for crop production under a controlled greenhouse environment by means of tetra-n-butylammonium bromide (TBAB) + CO2 semi-clathrate hydrate (SC). In this system, CO2 is captured directly from exhaust gas from a combustion heater at night, which can be used for stimulating photosynthesis of crops in greenhouses during daytime. Although the gas capacity of TBAB + CO2 SC is less than that of CO2 gas hydrate, it is shown that TBAB + CO2 SC can store CO2 for CO2 enrichment in crop production even under moderate pressure conditions (&lt;1.0 MPa) at 283 K