Selection of elastomeric membranes for the separation of organic compounds in acidic media

A series of elastomers were investigated, by measuring their toluene permeability and acid resistance, for their potential for use in the extraction of organics from hydrochloric acid and other membrane processes utilising acidic aqueous phases. In this study, toluene was used as a solute in aqueous solution to measure permeabilities of the elastomers, and their acid resistance was assessed after immersion in 37 wt.% hydrochloric acid by tensile-strain tests. Silicone rubber has the highest permeability among the elastomers investigated in this study, but it has poor resistance to concentrated HCl. Polyoctenamer is the best membrane material in terms of permeability and acid resistance. Other olefin based materials such as poly(ethylene-co-propylene) and poly(ethylene-co-propylene-co-diene) (EPDM) are also good candidates. The permeability generally decreases with an increase in T-g for the elastomers investigated. However, for the EPDM materials with T-g values grouped around -60 degreesC, the relationship between T-g and permeabilities is not clear. A model derived from Flory-Huggins Theory and the Hildebrand and Scatchard equation was used to predict the partition coefficients of toluene between the elastomers and aqueous solution, and the predictive power found to depend critically on the value employed for the water solubility parameter. The diffusion coefficients of toluene in the elastomers can be explained by considering the polymer structure. (C) 2002 Elsevier Science B.V. All rights reserved.