Heat and mass transfer correlations and fouling in air gap membrane distillation of benzene–water

This study focused on the separation of a benzene-water mixture using the air gap membrane distillation. The hydrophobic microporous membrane made up of poly-tetrafluoroethylene of 0.22 micron average pore size was used in the membrane module of the air gap membrane distillation experimental setup. The heat transfer and mass transfer correlations have been developed. It was found that the heat transfer and mass transfer coefficient increases from 523.27 to 1786.36 W/m2K, and 1.08 × 10-1 to 1.99 × 10-1 cm/s, respectively, on increasing the feed bulk inlet temperature from 40 to 60°C at a feed flow rate of 5 lpm under a 3 mm air gap in the membrane module. The effect of fouling phenomena on permeate flux and membrane characteristics was also investigated, and it was found that the permeate flux decreased from 6.50 kg/m2h to 6.38 kg/m2h under 420 hr. This clearly shows that negligible fouling was encountered on the membrane surface during continuous usage of the air gap membrane distillation setup. The membrane before and after 420 hr was characterized quantitatively and qualitatively using atomic force microscopy and field emission scanning electron microscope. The average pore size for the new membrane, used membrane after 420 hr and water wash membrane was analyzed using Image J software. Pore Size Distribution is plotted which confirms that the membrane characteristics were not affected to an extent. This clearly shows the stand alone capability of air gap membrane distillation process for separation of organic compounds from aqueous solution.