Removal of isopropyl alcohol and methanol in ultrapure water production system using a 185 nm ultraviolet and ion exchange system

• Low-molecular-weight (LMW) compounds was seldom removed in the production of UPW.
• Oxidative characteristics of LMW compounds in UV oxidation and ion exchange system.
• UV irradiation was effective to transform LMW compounds to more oxidative products.
• Ion exchange system removed organic acids as by-products of LMW from UV irradiation.
• Baffle in UV reactor enhanced solution turbidity and oxidation efficiency.

The oxidation of low-molecular-weight (LMW) compounds, including isopropyl alcohol (IPA) and methanol in ultrapure water (UPW) production system was evaluated using the continuously operating 185 nm total organic carbon (TOC) reduction UV and ion exchange system. The initial concentration of compounds was in the range of tens of ppb which was the general feed condition of UV system located after 2 pass reverse osmosis (RO) in the UPW production system. UV irradiation transformed the compounds to less oxidative products that were ultimately converted to CO2. The ion exchange system then removed carboxyl-containing organic acids generated by UV oxidation. It means that the oxidation efficiency of organic compounds by UV irradiation can be accurately measured by the summation of the final product (CO2) and the by-product containing carboxyl functional group. The removal efficiency of LMW compounds decreased when either the initial TOC concentration increased or the UV intensity was reduced. Finally, the insertion of a baffle into the UV oxidation system was found to enhance solution turbulence and improve the oxidation efficiency.