Nafion membranes for conversion of sodium phenoxides into undissociated phenols

Abstract

Nafion membranes are used for conversion of sodium phenoxides into undissociated phenols, conventionally performed through direct acidification by strong acids. The acidification through electro-membranes combines the possibility to achieve high conversion values with the advantage of keeping the process stream, containing sodium phenoxides, separated from the acid stream (HCl solution). Cationic membranes are assembled to perform ionic substitution by electrodialysis; two stack arrangements are considered in which N450 or N350+N966 are used. High conversions are obtained in electrodialysis operation mode, although slightly lower efficiencies were achieved also in the absence of electric current (diffusion dialysis operation mode). Process feasibility as well as membrane resistance is tested; maximum conversion and process rate are greatly affected by the ratio between protons in the acid solution and sodium ions in the process salt solution. For both the arrangements, phenols losses into the acid stream and chloride contamination of the process stream can be reduced by working with diluted solutions. With respect to the N450 arrangement, the separation efficiency is higher in the N350+N966 arrangement, in which phenols losses into the acid stream are remarkably negligible. A continuous steady-state system is designed. The process analysis is performed and the membrane area required is calculated in correspondence with various process specifications.