Modification of polyacrylonitrile membranes via plasma treatment followed by polydimethylsiloxane coating for recovery of ethyl acetate from aqueous solution through vacuum membrane distillation

For the recovery of ethyl acetate (EtAc) from aqueous solution via vacuum membrane distillation (VMD), hydrophobic porous membranes with high and stable separation performance were prepared by carbon tetra fluoride (CF4) plasma treatment on polyacrylonitrile (PAN) membrane followed by polydimethylsiloxane (PDMS) coating. The effects of plasma treatment conditions and PDMS contents on the morphology, surface porosity and separation performance of modified membranes were investigated. It was found that both the two modification operations increased the hydrophobicity of the PAN membrane. CF4 plasma treatment increased the hydrophobicity (the contact angle increased from 42 to 124 measured by 2.5 wt% EtAc solution), surface mean pore size (from 24.6 nm to 150.5 nm) and porosity (from 7% to 32.3%) of hydrophilic PAN membrane, suggesting that the CF4-modified membranes (PAN-C membranes) with high hydrophobicity could be used in VMD. Optimized PDMS coating on the PAN-C membranes (PAN-C-P membranes) further narrowed the pore size distribution but retained porous and hydrophobic surface. The PAN-C membranes were much less efficient and stable in separating EtAc from water comparing with the PAN-C-P ones. For instance, for the separation of 1 wt% EtAc/water mixture, the best VMD performance in this work was achieved by the PAN-C3-P3 membrane with a separation factor of 70 and a total flux of 7.85 kg/m(2) h (PSI = 542). Moreover, the PAN-C3-P3 membrane showed a very stable separation performance than that of the PAN-C3 membrane during a 90 h intermittent VMD operation, indicating a very promising application prospect for EtAc recycling.