Permeation characteristics of 4-substituted phenols and anilines in aqueous solution during removal by a silicone rubber membrane

The objective of this study is to determine the correlation of permeability of phenols and anilines through the silicone rubber membrane (SRM) with hydrophobicity and acid–base properties and to gain insight into the permeation characteristics of phenols and anilines through the SRM. The permeation characteristics of 4-substituted phenols and anilines for a SRM in the permeation and chemical desorption (PCD) method were investigated. The phenols or anilines in aqueous solution were successfully recovered to aqueous NaOH or HCl solutions, respectively. Although permeation rates increased with alkyl chain length for both phenols and anilines, a marked difference was found in permeation characteristics based on molar volume. An increase in permeability of anilines through the SRM with increasing molar volume was significantly greater than that of the phenols. This was due to a greater membrane distribution coefficient (mc) and a smaller reduction of diffusivity (D) in the SRM with increasing molar volume of the anilines, as compared with the phenols. During permeation of the phenols and anilines through the SRM, their distribution process through the membrane had a significant influence. Hydrophobicity (log POW: 1-octanol/water partition coefficient) and acid dissociation constant (pKa) values of the compounds played an important role in the distribution process. A regression equation was derived that related log mc of the compounds through the SRM, including log POW and pKa values. The strong correlation indicates that the permeation rate of a target compound through the SRM using the PCD method may be predicted from known physical properties, such as POW and pKa.