Robust design of durable PTFE/graphene hollow fiber composite membrane for high-temperature lubricant recycling

Abstract

Nowadays, the lubricant recycling becomes difficult due to its complex composition and high viscosity. Reinforced hollow fiber membranes (HFM) have been widely used in various separation fields due to their controllable separation accuracy, large specific area, backwashability, as well as low operation and maintenance requirements. Herein, a durable polytetrafluoroethylene (PTFE)/graphene (GE) hollow fiber composite membrane (HFCM) with high temperature resistance was designed through the laminated-sintering process to solve the lubricant issue. The membrane featured a solid three-layer reinforced structure and compared with the pure GE membrane, the adverse effects from GE brittleness are efficiently avoided, which ultimately improved the membrane flexibility and morphological stability. Moreover, this PTFE/GE HFCMs showed superior high-temperature resistance and lipophilicity with an oil contact angle of 0°. With a reasonable regulation of lubricant temperature and GE content, the membrane flux exceeded 917 L·m−2·h−1·bar−1 and stabilized at 458 L·m−2·h−1·bar−1 after 12 h of membrane operation at 150 °C. The membrane flux remained at a relatively high level of 103 L·m−2·h−1·bar−1 after four cycles, with a flux recovery over 83 %. In addition, the membrane separation-efficiency up to 99.02 % for activated carbon in lubricants. Overall, the PTFE/GE HFCMs presented great potential for recycling lubricants or other heavy crude oils at high temperatures.