A New Method for Separating HFC-134a from Gas Mixtures Using Clathrate Hydrate Formation

Abstract

A new separation method using gas hydrate formation is proposed for separating HFC-134a from gas mixtures containing N2 and HFC-134a. The feasibility of this separation method was investigated from various points of view. First, to determine the mixed hydrate stability region, three-phase equilibria of hydrate (H), liquid water (Lw), and vapor (V) for HFC-134a + N2 + water mixtures with various HFC-134a vapor compositions were closely examined in the temperature and pressure ranges of 275-285 K and 0.1-2.7 MPa, respectively. Second, the compositions of the hydrate and vapor phases at a three-phase equilibrium state were analyzed for identical mixtures at 278.15 and 282.15 K to confirm the actual separation efficiency. Third, kinetic experiments were performed to monitor the composition change behavior of the vapor phase and to determine the time required for an equilibrium state to be reached. Furthermore, X-ray diffraction confirmed that the mixed HFC-134a + N2 hydrates were structure II. Through an overall investigation of the experimental results, it was verified that more than 99 mol % HFC-134a could be obtained from gas mixtures after hydrate formation and subsequent dissociation processes. Separation of HFC-134a using hydrate formation can be carried out at mild temperature and low-pressure ranges. No additive is needed to lower the hydrate formation pressure.

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

“…In desalination via gas hydrate formation, appropriate hydrateforming substances should be determined in order to operate the process in milder pressure and temperature conditions for economic competitiveness. Thermodynamic and kinetic studies have been conducted on possible guests such as SF 6 , hydrofluorocarbons, CO 2 , cyclopentane, and cyclohexane for hydrate-based desalination [5,8,[12][13][14][15].…”

“…Although the phase equilibria of HFC hydrates including 1,1,1,2-tetrafluoroethane (HFC-134a), pentafluoroethane (HFC-125), and 1,1,1-trifluoroethane (HFC-143a) have already been examined, more attention should be given to the thermodynamic behavior, structural identification, and dissociation enthalpies of HFC hydrates in the presence of salts [13,[16][17][18].…”

Inter-cage dynamics in structure I, II, and H fluoromethane hydrates as studied by NMR and molecular dynamics simulations

“…4 Clathrate hydrates of each type occur naturally with different hydrocarbon guests; sI with methane (CH 4 ) as main guest, the other two structures with the small cages filled mostly with CH 4 and the larger cages with propane, isobutane, methyl butanes, and methyl substituted cycloalkanes. 5,6 Prospective industrial application of clathrate hydrates as materials for gas separation [7][8][9][10] and as storage and transport medium of energy carrying gases have been considered. 11 However, high pressure and low temperature conditions are required for hydrate formation, 1 clathrate hydrates contain relatively low mass percent gas content, 12 and the kinetics of hydrate formation is nonuniform 13 increasing the difficulties to achieve complete hydrate formation in a) Present address: Max Planck Institute for Solid State Research, Stuttgart 70569, Germany.…”

An analysis of gas separation processes of HFC-134a from gaseous mixtures with nitrogen—Comparison of two types of gas separation methods, liquefaction and hydrate-based methods, in terms of the equilibrium recovery ratio

“…Recently, a new type of gas separation method using gas hydrates was proposed by several authors [1][2][3][4][5][6][7][8]13] (Seo and Lee, 2001). Gas hydrate is a kind of inclusion compound of which the * Corresponding author.…”