Fabrication of mullite ceramic-supported carbon nanotube composite membranes with enhanced performance in direct separation of high-temperature emulsified oil droplets

Abstract

The direct treatment of high-temperature oil-in-water (O/W) emulsions is a challenging energy-saving water treatment issue for membrane technology, where thermally resistant separation membranes are required. This work proposes the rational design and facile fabrication of a thermally resistant mullite-CNT (carbon nanotube) composite membrane with a hierarchical structure for the high-temperature direct removal of tiny oil droplets from O/W emulsions. CNTs were grown in situ on/inside robust mullite ceramic hollow fibers by chemical vapor deposition (CVD), where hydrogen gas was produced as by-product with a concentration as high as 5.5% at 600 °C. After structural characterization, the high-temperature separation capability of mullite-CNT composite ultrafiltration membranes was assessed. The membranes exhibited excellent performance with high oil rejection of 100%, 99.99%, 99.99% and 99.99% and increased initial permeate fluxes from 6.5, 9.7, 12.8–15.7 L m−2 h−1 at the investigated temperatures of 25, 50, 80 and 100 °C. A simple cleaning method using dilute aqueous NaOH without energy consumption was used to effectively accomplish membrane regeneration. Our results indicate that ceramic-CNT membrane is promising for highly efficient direct separation of high-temperature O/W emulsions without the necessity of including a cooling process, thus providing recovered hot water with intensive energy saving in practical industrial applications.