Experimental and Modeling Study on Phase Equilibria of Semiclathrate Hydrates of Tetra-n-butyl Ammonium Bromide + CH4, CO2, N2, or Gas Mixtures

Abstract

Tetra-n-butyl ammonium bromide (TBAB) is most-widely used as a hydrate promoter in the separation of flue gases and CO2 sequestration. Because of the complicacy of semiclathrate hydrate formed by TBAB aqueous solution and gases, few researchers have investigated the thermodynamic modeling of phase equilibria of semiclathrate hydrates. In this work, the CH4–N2 hydrate dissociation conditions were determined in TBAB solution first, and then a thermodynamic model for gas hydrate proposed by Chen and Guo was extended for semiclathrate hydrates of gas mixtures in TBAB aqueous solution. The Patel-Teja equation of state (PT EoS) was used for calculation of the fugacity of the gas phase. To evaluate the activity of water and activity coefficients of TBAB in TBAB aqueous solution, a correlation on the basis of existing osmotic coefficient and activity coefficient values is employed. For modeling the hydrate phase, parameters for sII hydrates proposed in the Chen–Guo hydrate model were used to calculate the fugacit...