부산대학교 도서관

Hydrate-containing phase equilibria of CO2 mixture are important for flow assurance in transportation of captured CO2. Consistent experimental data and reliable thermodynamic model containing hydrate phase are necessary for accurate design of the process. The maximum allowable water content in CO2-rich mixture to prevent hydrate formation is key information but the recent experimental data are significantly inconsistent. Common impurities in flue gases (N2 and SO2) and inhibitors of hydrate formation (methanol and electrolytes) influence the hydrate formation condition of CO2 causing complex phase behaviors. The effects of SO2 have been rarely reported in literatures.Several literature data on ternary systems are available, which were reported with loading ratio of two-component, but such data sets do not include the effect of the amount of remaining one component. According to Duhem’s theorem, accurate measurements are possible with overall loading compositions for completely determined system. In this work, the effects of overall composition on three-phase equilibria were examined. The incipient hydrate formation conditions were sensitive to relative amounts of water at fixed loading ratio of binary guests, resulting from the solubility difference of the binary guest in water. Similarly, the isobaric dissociation temperatures were found to increase as CO2 contents increases at same methanol fraction in aqueous solution, indicating a decreased inhibition effect.An electrolyte hydrogen-bonding nonrandom lattice fluid equation of state for fluid phases was used to include contributions of hydrogen-bonding and long-range interactions. CO2 and SO2 as hydrogen acceptors were considered to solvate with water for improving the mutual solubility. Hydrate phases were modeled by van der Waals and Platteeuw theory. Guest-independent empty hydrate vapor pressure equations with Kihara potential parameters were determined from hydrate phase equilibrium data of single and binary guests including CH4, C2H6, C3H8, i-C4H10, CO2, N2 and H2S. Results of three-phase calculations for CO2 + N2 + water mixtures were comparable to those of CSMGem but for CO2 + water + methanol showed better agreements. Present model significantly improved the description of water solubility in CO2-rich liquid phase for hydrate formation region with and without methanol. As the first modeling attempt of SO2 hydrate, prediction results were found in general agreement with present data for CO2 + SO2 + water system. Complex phase behaviors composed of two-, three- and four-phase for the mixtures were analyzed by comparing the experimental data with model calculations. Three-phase locus of binary guest is located between the loci of two single guests if they present same three-phase equilibria of Lw-H-V or Lw-H-Lg at given temperatures or pressures, but shows three- or four-phase behaviors between or beyond the loci depending on loading compositions if not. Single four-phase locus is generated connecting two three-phase equilibria. Thy hydrogen-bonding interaction of inhibitors with water in aqueous phase plays a key role for determination of the inhibition effects.