Separation of CO2/CH4 and O-2/N-2 by polysulfone hollow fiber membranes: effects of membrane support properties and surface coating materials

Abstract

n this study, six different types of polysulfone hollow fiber membranes were fabricated from the same polymeric dope solution by manipulating several important parameters during the spinning process, aiming to find the best membrane supports for the coating layer in the gas separation process. The experimental results showed that upon the polydimethylsiloxane (PDMS) coating process, the gas pair selectivities of all six types of membranes were significantly increased with respect to carbon dioxide (CO2)/methane (CH4) and oxygen (O2)/nitrogen (N2) separation. However, the membrane support spun at higher air gap and lower dope extrusion rate was found to be the best support for PDMS coating owing to its good structural integrity that led to a good balance between gas permeance and gas pair selectivity. Further investigation showed that the use of poly(ether block amide) (Pebax) as coating material did not certainly improve both gas permeance and the selectivity of hollow fiber membranes, although Pebax was previously reported to exhibit better performance than PDMS in flat sheet membranes. One of the main reasons is the difficulty of forming a defect-free Pebax coating layer on the outer surface of hollow fibers owing to the stickiness issue among fibers upon coating. More research is still needed to optimize the Pebax coating solution and its drying process in order to achieve the full potential of such coating material for hollow fiber membranes.