Mole fraction measurement of methane and ethane in aqueous solutions of NaCl and MgCl2 during hydrate growth

Abstract

In this paper, the mole fraction of methane and ethane in aqueous solutions of NaCl and MgCl2 during hydrate growth in a semi-batch stirred tank reactor is reported. Methane mole fraction measurements in aqueous solutions of NaCl were conducted at molalities of 0.529 and 1.092, temperatures of 275.15–290.15 K, and pressures of 40–68 bar. The same conditions were provided to measure the mole fraction in the aqueous solution of MgCl2 at molalities of 0.325 and 0.670 mol kg−1. We also report the mole fraction of ethane in aqueous solution of NaCl at molalities of 1.901 and 3.020 mol kg−1, temperatures of 273.15–278.15 K, and pressures of 11–24 bar; however, molalities of 0.325 and 0.791 mol kg−1, temperatures of 279.15–283.15 K, and pressures of 14–29 bar were investigated for the C2H6-MgCl2 system. Furthermore, the effects of pressure and salt concentrations on the mole fraction of these gases in aqueous phase in the presence of hydrate were investigated. It was observed the mole fraction of hydrate formers in the aqueous phase are close to solubility of this gases at experimental temperature and corresponding equilibrium pressure. In addition, it was found the mole fraction of methane and ethane in bulk liquid phase remain constant during the hydrate growth period, whereby the fugacity of the aqueous phase was constant throughout this period.