Filtration of per- and poly-fluoroalkyl from water and recycling of fluorine: a thermochemical equilibrium analysis

Abstract

In the present work, a process concept is proposed and assessed for the separation of per- and poly-fluoroalkyl components referred to as “PFAS” from the activated carbon used in the process of water filtration and further utilization of fluorine as sodium fluoride. PFAS components are highly toxic materials, which have been spread in soil and water over past decades due to the use of fire-fighting foams and via different industrial processes. The current commercially available technology to separate PFAS from water is to use activated carbon to adsorb the chemical compounds, while transferring the pollution from water or soil into activated carbon and combust the activated carbon using an air-blown combustor which transfers the PFAS components to environment in form of chlorofluorocarbon materials. So, the current technology only transfers the pollution from soil or water into atmosphere. However, the proposed process consists of drying process, combustion and chemical reaction, which ultimately converts PFAS into a product with hygienic applications. The drying process removes a large portion of water from the activated carbon proving a better condition for the combustion of remaining carbon. The combustor breaks the long chain of fluorocarbons into smaller molecules of CF₄ using oxy-blown combustion. The exhaust gases from the combustor react with sodium in a sodium reactor to produce high-purity NaF compound which has further applications in hygienic industries such as toothpastes, cleaning agents and disinfectants. The proposed method destructs the composition of PFAS into very small molecules without transferring it to the environment.