Removal of isopropyl alcohol (IPA) in UPW by synergistic photocatalytic oxidation and adsorption

Abstract

Earlier work showed that the commercial granular activated carbon (GAC) could effectively remove large non‐polar molecules, but showed poor removal efficiency for small polar compounds such as isopropyl alcohol (IPA) [Schmotzer et al. Clean Technol. Environ. Policy 2002;4:125; Cong et al. J. Phys. Chem. C 2007;111:6976]. To achieve the goal of increasing the lifetime and removal efficiency of GAC bed for small polar organic compounds in ultrapure water (UPW), the synergistic partial photocatalytic oxidation and adsorption system using commercial GAC coated with nitrogen doped titanium dioxide as an adsorbate was proposed in this work. The influence of operating factors such as UV intensity, flow rate, feed concentration, and the sudden injection of air or inorganic acid on IPA removal efficiency was systematically investigated. Compared to the traditional GAC adsorption bed, at feed total organic carbon (TOC) concentration of 800 ppb, the lifetime of GAC bed in this synergistic photocatalytic oxidation and adsorption system was extended from 348 to 600 min and the outlet TOC concentration was decreased from 793 to 499 ppb. The difference of the TOC outlet concentration in those two configurations was attributed to the photocatalytic effect by GAC coated with nitrogen doped titanium dioxide. The reactions between oxidation radicals and organic contaminants caused the majority of IPA to be decomposed into secondary organic compounds such as acetone and acetone had already been shown a higher affinity to GAC than that of IPA. Experiments also demonstrated the injection of air or inorganic acid in the stream would facilitate the removal of IPA in UPW.