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

Abstract

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°. 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/m2.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 ∼ 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.