Ionic Clathrate Hydrates of Tetraalkylammonium/phosphonium Salts: Structures, Properties, Some Applications, and Perspectives

Abstract

Ionic clathrate hydrates (ICHs) belong to one of the groups of a wide class of clathrate hydrates. In the crystal structures of ICHs, cation–anion pairs of guest molecules, typically tetraalkylammonium/phosphonium salts, are included into the host framework of hydrogen-bonded water molecules. Because of their suitable phase change temperature and latent heat, ICHs are considered as promising phase change materials for application in cold energy storage and transportation. The presence of vacant cavities in ICHs structures, which can incorporate small gas molecules such as, for example, H2, CH4, CO2, N2, H2S, determines the possibility of their use for the separation and storage of gases. The formation of these double ICHs occurs under much milder pressure and temperature conditions compared to the pure gas hydrates of the same gases. Studying of the structural characteristics and thermophysical properties of ICHs and double ICHs with gases is the necessary basis for their effective applications in different practical ends. This work reviews information related to the new details and features of the structures of ICHs and double ICHs with gases revealed over the last decade or a little more as well as some thermophysical data such as hydrate numbers, temperatures and enthalpies of dissociation. This review focuses only on ICHs of tetrabutyl-, tetraisoamylammonium (TBA, TiAA), and tetrabutylphosphonium (TBP) salts, which are the most common representatives of this class of compounds. One of the sections is devoted to ICHs of TBA and TiAA with polymeric anions such as cross-linked polyacrylates. The purpose of the present paper is to review the studies that have been relatively little addressed in previous works.

2022 Pioneers in Energy Research: John Ripmeester

“…Piezoelasticity properties of methane hydrates were calculated using density functional theory (DFT) at 0 K and high pressure to study the strength and nature of small and large cages of structure I (sI) hydrates. 39 ■ APPLICATIONS A review by Rodionova et al 40 discussed structures of single and double ionic clathrate hydrates (semi-clathrates) in the presence of different gases and possibilities of structural transition as a result of the presence of these gases. Gas hydrates could be used as a molecular sieve, whereby depending upon the shape and size of the hydrate-forming guests, one of the gases from a gas mixture may preferentially occupy the solid hydrate cages and become separated from its mixture.…”

“…A review by Rodionova et al discussed structures of single and double ionic clathrate hydrates (semi-clathrates) in the presence of different gases and possibilities of structural transition as a result of the presence of these gases. Gas hydrates could be used as a molecular sieve, whereby depending upon the shape and size of the hydrate-forming guests, one of the gases from a gas mixture may preferentially occupy the solid hydrate cages and become separated from its mixture .…”

Effect of introducing a cyclobutylmethyl group into an onium cation on the thermodynamic properties of ionic clathrate hydrates

“…[1][2][3] For the latent heat storage materials, water, 1-3 paraffin, 3,4 and molten salt 4,5 have been well known. Ionic clathrate hydrate (ICH) is also one of the promising thermal storage materials, especially, suitable for being utilized as a source of thermal energy in a temperature range of 273-300 K. [6][7][8][9] ICHs are crystalline inclusion compounds composed of hydrogen-bonded water molecules and quaternary alkylammonium or alkylphosphonium salts. [8][9][10][11][12] ICHs have equilibrium temperatures around 270-300 K, with the dissociation enthalpies around 200 J g À1 .…”

Abnormal structural transformation of tetra-n-butyl ammonium chloride + Xe clathrates and its significance for clathrate-based Xe capture and storage

“…25,[34][35][36] The semi-clathrates have vacant small (5 12 ) cages that can be used for capturing and storing small gas molecules, even though they have several different structure types (cubic, tetragonal, and orthorhombic). [35][36][37][38] The incorporation of small gas molecules such as CH 4 , CO 2 , N 2 , H 2 , and Xe in the small (5 12 ) cages of semi-clathrates might result in structural transformations. 21,39,40 Among TBAX semi-clathrates, TBAF semi-clathrate has the highest dissociation temperature (300.75 K) at its stoichiometric concentration, 41 whereas TBAC and TBAB semiclathrates can store a larger amount of gas than the TBAF semi-clathrate.…”

“…25,34–36 The semi-clathrates have vacant small (5 12 ) cages that can be used for capturing and storing small gas molecules, even though they have several different structure types (cubic, tetragonal, and orthorhombic). 35–38 The incorporation of small gas molecules such as CH 4 , CO 2 , N 2 , H 2 , and Xe in the small (5 12 ) cages of semi-clathrates might result in structural transformations. 21,39,40…”