Clathrate phase equilibria of the ternary systmes containing mixed guest molecules

Abstract

Clathrate hydrates (or gas hydrates) are crystalline compounds which are formed by physically stable interaction between water and relatively small guest molecules occupied in the cavities built by water molecules. There are small and large cavities capable of entrapping guest molecules in an open network of host molecules composed of unit crystalline structures. Temperature-pressure phase equilibrium of structure H hydrate for the methane+water+2-methylbutane, methane+water+2,2-dimethybutane and methane+water+methylcyclohexane systems containing $MgCl_2$ were determined experimentally in the four-phase locus of hydrate, water-rich liquid, liquid hydrocarbon and vapor. The concentration in aqueous solution was 10 mole %. The experiments were conducted at temperature from 276.25 to 281.65 K and pressure from 30.6 to 35.4 bar. The $MgCl_2$ showed the largest inhibition effect on the hydrate formation conditions. The thermodynamic model of the hydrate inhibition could predict experimental data for each four-phase hydrate equilibrium conditions. Experimental data on the phase equilibrium of carbon dioxide and R22 mixture were obtained at temperature from 288.06 to 291.96K and pressure from 13.45 to 38.0 bar. To determine the phase behavior, the $L_w$-$L_{R22}$-$L_{co2}$-V equilibrium line and the $L_w$-$L_{R22}$-H-V equilibrium line were measured. In addition, the quintuple point where the coexisting phases are hydrate, water-rich liquid, liquid carbon dioxide, liquid R22 and vapor appeared at 287.06 K and 34.50 bar. The phase equilibrium condition for carbon dioxide and methane mixture were measured experimentally at constant pressure. The experiments were conducted at temperature from 272.36 to 283.56 K and pressure 15, 20.26, 35 and 50 bar. The composition of hydrate and vapor was analyzed at the pressure 20, 26 and 35 bar. The composition of carbon dioxide in hydrate phase decrease with increasing pressure. The thermodynamic model for the three-phase equilibriu...