Superhydrophilic and underwater superoleophobic nano zeolite membranes for efficient oil-in-water nanoemulsion separation

Nano zeolite-Y ultrafiltration (UF) membrane, with mean pore diameter of 28 nm was fabricated using a simple isostatic pressing technique. Zeolite-Y has preferential water pathways and a unique 3-D microporous structure. The zeolite-Y used in this study has an Al to Si (Al/Si) ratio of 0.07 which renders the membrane superhydrophilic with complete wetting of water in air. Whereas, when it is underwater, the membrane is superoleophobic with a contact angle of 156 degrees. This study compared membranes with two different zeolite particle sizes, above and below 100 nm for their membrane morphology, and wetting properties, directly affecting the separation of oil-in-water separation. The membrane separation capabilities were tested for 600 mg/L of xylene, motor oil and crude oil mixture in water. There are limited studies on treating oil/water mixtures having nanoemulsions with stand-alone zeolite membranes, and thus this study provides a deeper insight on utilizing such a ceramic material for improved separation processes. A flux of 45-70 L/m(2).h was obtained for the nano-zeolite membrane, depending upon the type of oil, with the motor oil giving the lowest flux due to its heavy components. The nano-zeolite membranes produced similar to 20 % higher flux than the micro-zeolite membrane at a membrane pressure of 70 kPa. A higher flux was attributed to the higher membrane porosity and favored nano-channel pathways along the zeolite pores for the water molecules. In addition, oil rejections as high as 99.8 % with oil content as low as 1.57 +/- 0.2 mg/L were obtained. Thus, the membrane was found to be very effective in nanoemulsion oil-water separation owing to its exceptional structural properties and superoleophobicity of oil under water.