OS6A-7:THERMODYNAMIC MODELING OF PHASE EQUILIBRIA OF TETRABUTYL AMMONIUM HALIDE (BROMIDE, CHLORIDE, OR FLUORIDE) PLUS METHANE OR CARBON DIOXIDE SEMICLATHRATE HYDRATES

Lingli SHI1, 2, Deqing LIANG1
1. Guangzhou Centre for Gas Hydrate Research, Guangzhou Institute of Energy Conversion, CHINA; 2. Graduate University of Chinese Academy of Sciences, CHINA,

    Semiclathrate hydrates of tetrabutyl ammonium halide provide potential use for gas storage and transportation, and the phase equilibrium conditions are vital to their industrial applications. Unfortunately, models for prediction of phase equilibria of these systems are rather scarce in open literatures. In this work, based on the van der Waals-Platteeuw (vdW-P) theory, a thermodynamic approach is proposed to determine the phase equilibria of tetrabutyl ammonium halide (bromide, chloride, or fluoride) + CH4, + CO2 semiclathrate hydrates which belong to three different structures of hexagonal structure-Ⅰ (HS-Ⅰ), tetragonal structure-Ⅰ (TS-Ⅰ), and cubic superstructure-Ⅰ (CSS-Ⅰ), respectively. Two modifications for evaluations of vapor pressure of water in the empty hydrate lattice and Langmuir constants relating to the salt concentration in aqueous solution and temperature are applied. The Peng-Robinson (PR-EoS) equation is used to calculate the fugacity of gaseous hydrate former, and the electrolyte-Non-Random Two-Liquid (e-NRTL) activity model is employed to obtain the activity coefficients of species in the aqueous phase. It is shown that the presented model results are in acceptable agreement with the experimental phase equilibrium data for the systems studied over wide temperature, pressure, and salt concentration ranges from (280.5 to 305.0) K, from (0.40 to 10.41) MPa, and from (0.040 to 0.045), respectively.