An Evaluation of the Ideality of Benzene, Toluene, Ethylbenzene, and Xylene on Activity Coefficients in Gas Condensate and the Implications for Dissolution in Groundwater

Abstract

Studies were conducted to measure aqueous concentrations of benzene and xylene in BTEX (benzene, ethylbenzene, toluene, xylene) mixtures and in groundwater contaminated with gas-condensates, to support the remediation of contaminated subsurface environments at gas plants in western Canada. Volume ratios investigated were 20:5:2:2:2:2 and 40:5:2:2:2:2 for B:T:E:o-X:p-X:m-X. and 1:1 for sour-gas condensate and benzene mixtures. As expected, the equilibrium concentrations of benzene partitioning in the water for hydrocarbon mixtures could be estimated using Raoult’s Law. However, this was not the case for T, E, X where there was poor agreement with Raoult’s Law. In particular, the measured concentration for xylene was 2 to 10 times higher than that expected for ideal behaviour and was in the range 30–45 mg/L for aqueous BTEX mixtures and 8–30 mg/L for gas condensate contaminated groundwater. It is shown that this non-ideal behaviour was due to the high activity coefficients (γ > 1) of TEX in the gas condensate. In general, values of γ for BTEX in petroleum mixtures could be estimated to within an error of 25% of measured values using the empirical equation γ = 0.224 S−0.402, where S is the aqueous solubility (mg/L) of the pure component.