Effect of operating variables on the flux and selectivity in sweep gas membrane distillation for dilute aqueous isopropanol

Sweep gas membrane distillation was examined as a possible technique for isopropanol (IPA)–water separation using PTFE hollow fiber membrane module. The composition and flux of the permeate were monitored when feed concentration, operating temperature and flow rate were varied. The upper feed concentration tested was 10 wt.% IPA. Within the feed temperature range of about 20–50°C, IPA selectivity of 10–25 was achieved. Since the concentration near the surface on the membrane increased by the selective adsorption of IPA on the hydrophobic membrane, the selectivity increases. The permeate flux and IPA selectivity increase as feed temperature increase. The flux and selectivity increase at higher flow rates is mainly due to the reduced effects of concentration and temperature polarization. The effect of salt addition to the feed mixture was also examined.