Solubility of chemical warfare agent simulants in supercritical carbon dioxide: experiments and modeling

Solubility data are reported for ethyl phenyl sulfide (EPS) and 2-chloroethyl ethyl sulfide (CEES) in CO2 at temperatures from 25 to 100 °C. These two sulfide-based compounds are homomorphs for chemical warfare agents (CWAs). Both sulfide–CO2 mixtures exhibit type-I phase behavior. The maximum in the 100 °C isotherm is approximately 2600 psia for the CEES–CO2 system and approximately 3400 psia for the EPS–CO2 system. The Peng–Robinson equation of state (PREOS) is used to model both sulfide–CO2 mixtures as well as the phase behavior of the 2-chloroethyl methyl sulfide (CEMS)–CO2 system previously reported in the literature. The Joback–Lydersen group contribution method is used to estimate the critical temperature, critical pressure, and acentric factor for the sulfides. Semi-quantitative estimates of the phase behavior are obtained for the CEES–CO2 and EPS–CO2 systems with a constant value of kij, the binary interaction parameter, fit to the 75 °C isotherms. However, very poor fits are obtained for the 2-chloroethyl methyl sulfide–CO2 system regardless of the value of kij. On the basis of the high solubility of EPS and CEES in CO2, supercritical fluid (SCF)-based technology could be used to recycle or recover chemical warfare materials.