A novel ethanol dehydration process by forward osmosis

• The feasibility of FO for ethanol dehydration was systemically verified.
• Ethanol concentration and membrane orientation had significant impact.
• Reverse salt flux was negligible while forward ethanol flux was significant.
• Long time contact with ethanol caused deterioration in membrane performance.

Bioethanol, one of the alternative energy sources, has drawn increasing attention as a potential solution of energy crisis and global warming. However, the current ethanol dehydration processes are still energy intensive. In this study, the feasibility of ethanol dehydration by forward osmosis (FO) was systematically investigated using a commercial cellulose triacetate membrane containing a dense film (active layer) and a porous substrate. The results showed that water can be removed from ethanol solutions to potentially produce an ethanol solution of 90 wt%. The ethanol concentration and membrane orientation have significant impact on the membrane performance in term of membrane flux, reverse salt flux and forward ethanol flux. For instance, higher total fluxes and lower reverse salt flux when the active layer faces the draw (salt) solution instead of the porous substrate. However, the forward ethanol flux is significantly high in both of the orientations, being 1420–2249 g h−1 m−2 at the 75% ethanol feed concentration. The membrane durability study over the 30 days of exposure in 30% and absolute ethanol solutions indicates that the membrane performance deteriorates which is caused by the membrane active layer undergoing chemical modification. The results provide a general proof of concept and scientific understanding into the FO dehydration process and FO membrane development.