Air–water partitioning of greenhouse gases and volatile organic compounds

Abstract

Henry's constants of volatile organic compounds (VOCs) in 58 systems containing water and one or more salts have been correlated using a thermodynamic model based on dilute solution theory. Several classes of VOCs were studied, including the 2-ketones, 1-alkanols, tert-butyl ethers, organic sulfides, aromatic hydrocarbons, and chlorinated organics. Henry's constants in 39 of these systems were measured in our laboratory using a single experimental technique that provided internally consistent data for the development of models. Both salting-out and salting-in behavior were observed in the systems studied, and we were able to correlate all data within experimental error using the dilute solution model and one ternary salt-effect parameter. This parameter was found to increase linearly with the size of the VOC within a homologous series when the VOC was salted-out by the addition of salt, and to decrease linearly with size when the VOC was salted-in. Henry's constants of light gases (methane and nitrogen) were also correlated over a wide range of temperatures, pressures, and salt concentrations using a Krichevsky–Kasarnovsky type extension of the dilute solution theory. When the extended model was used to estimate methane losses from produced water tanks, our estimates were significantly different from published calculations, emphasizing the need for experimental data when salts are present.