Thermogravimetric Analysis and Stability Test of Fluoroalkylsilanes Grafted on Alumina Hollow Fibre Membranes

Abstract

Alumina hollow fibre membrane surface were modified from hydrophilic to hydrophobic using fluoroalkylsilane (FAS) grafting technique which was found to be effective as shown by the increased contact angle (CA) from less than 90° to more than 100°. The CA increased with respect to the grafting time and leveled off after 24 hours of grafting. The thermogravimetric analysis (TGA) showed that the FAS attached to the membranes were approximately 0.05–0.6% of the original membrane weight depending on the grafting time and the amount of hydroxyl groups present on the membrane substrates. According to the TGA result, the grafted membranes were thermally stable up to 250°C where FAS began to decompose. Then the grafted membranes were used as a contacting media for stripping CO₂ off 2.5 M monoethanolamine (MEA) solution at 80–100°C. The membranes were in contact with hot and corrosive MEA solution for approximately 100 hours without any operational problem. The scanning electron microscopy of the membrane surface showed no difference between the membrane before and after the operation. Also, the CAs of the grafted membranes remained unchanged. These findings suggest that FAS grafted membranes are chemically and thermally stable and can be used in membrane contactors at high temperatures and in chemically harsh conditions.