Traditionally, polyacrylonitrile (PAN) is coated with a selective layer to tailor it for dehydrating butanel by pervaporation. But we hydrolyzed PAN with sodium hydroxide for such a purpose. Fourier transform infrared and X-ray photoelectron spectroscopy indicated that PAN's CN group was hydrolyzed to CONH2, which was further converted to COOH. As a result, the hydrolyzed PAN (HPAN) was made more hydrophilic, as evidenced from water contact angle data. CONH2 and COOH formed hydrogen bonds between them, causing molecular chains to rearrange (according to X-ray diffraction) and pores to shrink (shown by scanning electron microscopy). Positron annihilation lifetime spectroscopy revealed that hydrolysis led to free volume radius decrease; however, prolonged hydrolysis caused breakage of molecular chains. The HPAN produced after 4 h hydrolysis exhibited narrow free volume distribution and delivered exceptional performance (water concentration in permeate = 99.1 wt%; permeation flux = 2.03 kg/m(2)h). (C) 2015 Elsevier B.V. All rights reserved.