Photodegradation of low molecular weight organic compounds by 185-nm UV light in ultrapure water production system

The photodegradation of low molecular weight organic compounds by 185-nm UV light was studied using a continuously operated column reactor which can be simulated the TOC reduction UV unit in ultrapure water production (UPW) process. Six chemicals (methanol, ethanol, acetaldehyde, isopropyl alcohol (IPA), acetone, and methyl ethyl ketone (MEK)) were chosen as target compounds, because they are frequently observed in influent of a total organic carbon (TOC) reduction UV unit in UPW production process. The degradation efficiency of each chemical and the proportions of intermediate byproducts and the final product (CO2) were measured by TOC and gas chromatography mass spectrometry (GC–MS). The degradation efficiency by 185-nm UV based on GC–MS analysis was as follows, from highest to lowest: acetaldehyde, IPA, ethanol, MEK, methanol, and acetone. The fastest oxidation to CO2 was observed in methanol degradation in which 13 % of methanol was transformed to CO2 which was 6 times higher than that of ethanol, the slowest one. In the analysis of the intermediate byproducts of chemical degradation, except for IPA, the percentage of charged byproduct was higher than that of uncharged byproduct. These findings constitute a theoretical basis for placement of ion exchange (IX) resin behind a TOC reduction UV unit to increase the TOC removal efficiency because charged organic materials are removed by IX resin.