Effects of PES support layer structure on pervaporation performances of PDMS/PES hollow fiber composite membranes

Abstract

Polyethersulfone (PES) hollow fiber ultrafiltration (UF) membranes were fabricated by the dry/wet-spinning method; hydrophobic PDMS/PES composite membranes which were supported by self-prepared PES hollow fiber UF membranes were prepared for the pervaporation (PV) separation of ethanol from water. Impacts of PES support layer on the PV performances of PDMS/PES composite membranes were studied. Experimental results showed that, while working as a support to PDMS active layer, PES hollow fiber membrane could affect the PV performance of PDMS/PES membranes greatly. Pervaporation performance of the membrane which its PES support layer had bigger porosity and bigger mean pore size was apparently superior to that of the membrane which its PES support layer had smaller porosity and smaller mean pore size. After being treated with ethanol and hexane, PES membrane was dried in air for 20 min before being immersed in PDMS coating solution; the prepared PDMS/PES membrane had the best PV performance with a permeate flux of 330 g/(m2 h) and a separation factor of 5.8. Effects of process parameters, such as feed temperature, permeate pressure, and feed flow rate, on membrane properties were investigated. For the separation of a 5 wt.% ethanol–water mixture, with an increase in feed temperature from 30 to 60°C, water flux and ethanol flux increased from 51 to 328 g/(m2 h) and from 14 to 88 g/(m2 h), respectively; the variation of permeation flux followed the Arrhenius relationship and the activation energy values for water and ethanol were 54.54 and 53.44 kJ/mol, respectively; separation factor varied from 5.1 to 6.0. When the feed temperature was 50°C and feed concentration was 5 wt.%, with an increase in permeate-side pressure from 1 to 40 mm Hg, water flux dropped sharply from 334 to 14 g/(m2 h) and ethanol flux dropped moderately from 82 to 22 g/(m2 h), and as a result, separation factor increased. With the increase in feed flow rate from 0.1 to 10 L/min, both flux and separation factor increased rapidly at first and then leveled off at 2 L/min for the reason of concentration polarization.