Pervaporation of hypochlorous acid using a hollow fiber membrane made from silicone rubber and its application for indoor disinfection

The high permeability of silicone rubber is beneficial for use in membranes for pervaporation. In this study, pervaporation of hypochlorous acid (HOCl) was studied using a separation module containing a 6,000 silicone rubber (SR) hollow fiber membrane. Pervaporation experiments were conducted in a 1 m³ chamber. The membrane module was operated without using a vacuum pump, and the permeation of HOCl proceeded according to the solution-diffusion process. When weakly acidic (pH 5.0) hypochlorite solutions with concentrations of 100-1,000 mg/L were fed through the lumen of the SR hollow fiber membrane, the permeation of HOCl proceeded spontaneously under atmospheric pressure. During the operation of the membrane module, the concentration of gaseous hypochlorous acid (HOCl_(g)) in the chamber gradually increased and reached a steady state. The steady-state HOCl_(g) concentration increased as the concentration of undissociated hypochlorous acids (HOCl_(aq)) in the feed hypochlorite solutions increased. An exponential dependence of the steady-state HOCl_(g) concentration on the steady-state HOCl_(aq) concentration was observed. Operation of the SR hollow fiber membrane fed with weakly acidic hypochlorite solutions (i.e., 500 mg/L) in a 75 m³ room resulted in a uniform distribution of 7-10 ppb HOCl_(g), thereby exerting a moderate bactericidal effect against Staphylococcus aureus cells.