Multilayer composite polysulfone hollow fiber membrane modified by graphene oxide for gas separation

Abstract

One of the most critical issues encountered by polymeric membranes for gas separation process is the trade-off effect between gas permeability and selectivity. The aim of this work is to develop a simple yet effective coating technique to modify the surface properties of commonly used polysulfone (PSF) hollow fiber membranes to address the trade-off challenge on CO2/CH4 and O2/N2 separation issue. More specifically, the first objective of this work is to study the effects of different types of PSF hollow fiber support on the gas separation performance of surface-coated membranes by varying significant imperative parameters, i.e., air gap (1–4 cm), dope extrusion rate (1–2 mL/min), bore fluid rate (0.33–0.67 mL/min) and polymer concentration (15–35 wt.%). Results showed that the support membrane spun at highest air gap of 4 cm and lowest dope extrusion rate at 1 mL/min were ideal for the coated membrane preparation owing to its good structural integrity that could produce a membrane with optimum balance composition for gas permeance and selectivity. The findings also revealed that the support membrane made of 25 wt.% PSF was the best for single layer coating and the membrane coated with polyether block amide (Pebax) performed better in terms of selectivity than the membrane coated with polydimethylsiloxane (PDMS) because Pebax solution tended to form denser layer as a result of its higher solution viscosity. However, the Pebax solution is prone to penetrate into the pores of support membrane, and thus lowering its permeability. Due to this, the second objective of this work is to investigate the efficiency of multilayer coating technique by forming Pebax (1–9 wt%) as selective outer layer and PDMS (3 wt%) as gutter layer on the PSF membrane surface. Results indicated that the optimized multilayer coated membrane at 3 wt% Pebax could achieve CO2/CH4 and O2/N2 selectivity of 35.19 and 6.56, respectively. As a comparison, the membrane coated with 1 wt% Pebax only showed 29.47 and 6.07, respectively. To further enhance the performance of multilayer coated membrane, the third objective of this work is to evaluate the impacts of graphene oxide (GO) loading from 0–1.0 wt% on the Pebax selective layer on the membrane performance. Experimental findings revealed that incorporating 0.8 wt% GO into the composites could further improve membrane performance, achieving selectivity as high as 52.57 and 8.05 for CO2/CH4 and O2/N2, respectively. This is due to formation of improved tortuous structure that created higher resistance to larger gas molecules (CH4 and N2) compared to smaller gas molecules (CO2 and O2). In conclusion, it can be said that the newly developed multilayer coating technique that combines polymeric materials and nanofillers could overcome the drawbacks of typical PSF membranes, producing a multilayer composite hollow fiber membrane with improved surface properties for gas separation.