Isomer separation by a hollow fiber contained liquid membrane permeator

Continuous separation of different isomeric mixtures of organic compounds has been studied in laboratory scale by means of a hollow fiber contained liquid membrane permeator (HFCLMP). An aqueous liquid membrane based on cyclodextrin (CD) was successfully employed to separate two different typical equimolar isomeric mixtures present in an organic feed solution; the permeate phase employed the same organic solvent without any of the isomers. The first mixture was that of the structural isomers p-nitroaniline (p-NA) and o-nitroaniline (o-NA) in 80% n-octanol - 20% n-heptane used as the organic solvent. For a once-through operation, the selectivity for p-NA over o-NA was found to be almost 5 (~ 4.6) at a concentration of 0.7 M β-CD; a 50-50 feed mixture was treated to yield a permeate stream mixture of 82-18 in favor of p-NA. The performance was stable. The second mixture employed stereoisomers, cis-stilbene and trans-stilbene, using liquid membranes having 0.02-0.2 M β-CD concentration. The maximum selectivity of cis-stilbene over trans-stilbene achieved in this separation was always less than 2, whereas pure water was selective for trans-stilbene over cis-stilbene.