Enantioseparation of trans-stilbene oxide using a cellulose acetate membrane

An enantioselective membrane was prepared using cellulose acetate as the membrane material. Cellulose acetate was chosen as it is in widespread use already for separations and cellulose triacetate is the first practical chiral stationary phase of polysaccharide due to the multichiral carbons in its molecular structure unit. The flux and permselective properties of a membrane was studied using a 33.3% ethanol solution of (R, S)-trans-stilbene oxide as the feed solution. The top surface and cross-section morphology of the resulting membrane were examined using scanning electron microscopy. An optical resolution of over 85% enantiomeric excess was achieved when the enantioselective membrane was prepared with 30 wt.% cellulose acetate and 25 wt.% N,N-dimethylformamide in the casting solution of acetone; 5 min was the time for evaporation of the liquid membrane, and a 10 °C water bath was used for the gelation of the membrane; the operating pressure and the feed concentration of the trans-stilbene oxide were 2 kgf/cm2 and 0.5 mg/L, respectively. This is the first report that cellulose acetate can be used as a membrane material for isolating optical isomers. This work indicates that the large-scale purification of chiral molecules from racemic mixtures will be realized by the enantioselective membrane technique in the near future and that the enantioselective cellulose acetate membrane could soon become very attractive for industrial uses.