Evaluation of PFAS Solubility in Supercritical Carbon Dioxide — 89a — Joseph T. Hilsendeger¹, Dakota A. Remington¹, Dylan L. Tipton², Emma V. Kinyon², Kenneth M. Benjamin¹, Lori J. Groven¹, Travis W. Walker¹ 

¹ Karen M. Swindler Chemical and Biological Engineering Department, South Dakota School of Mines & Technology, Rapid City, SD, USA 

² Stevens High School, Rapid City, SD, USA 

PFAS (per- and polyfluoroalkyl substances) compounds have contaminated many different solid and aqueous matrices in the United States and are present above allowable limits. Exposure to PFAS has been linked to various forms of cancer and birth defects. A common method for remediation of PFAS compounds from aqueous matrices is through filtration with granular activated carbon (GAC). From available published work, GAC has an adsorption capacity for perfluorooctanoic acid (PFOA) of about 0.05 mL of PFOA per 1 mL of GAC. For context, this means about 1 liter of PFOA removed from water via GAC filtration creates about 20 liters of solid GAC waste. A fluid is described as supercritical when the fluid is raised to a temperature and pressure that are respectively above its critical temperature and pressure. When a fluid is under supercritical conditions, its diffusivity will be similar to a gas even though its density will be similar to a liquid. Carbon dioxide is an abundant, low-cost, and non-toxic fluid that has been used in supercritical fluid extraction (SFE) for decades. SFE with carbon dioxide has been shown to be effective in extracting nonpolar solids. Since many PFAS compounds fit this profile, SFE with carbon dioxide has been shown to be effective at removing PFAS from solid matrices. In this work, we experimentally evaluate the solubility and solubility kinetics of perfluoropentanoic acid (PFPeA) mixed with GAC in supercritical carbon dioxide at 150 bar and varying temperatures using a static supercritical fluid extraction. We confirm these results via gravimetric analysis and ATR-FTIR. With this data, we can use thermodynamic equations of state to model the solubility of PFPeA in supercritical carbon dioxide. The modeling of solubility will allow for simulation of a large range of process parameters that can optimize SFE of PFPeA and other PFAS compounds from solid matrices.

South Dakota School of Mines & Technology
Dr. Travis Walker