Physicochemical effects of hydrolyzed asymmetric polyacrylonitrile membrane microstructure on dehydrating butanol.

Traditionally, polyacrylonitrile (PAN) is coated with a selective layer to tailor it for dehydrating butanol 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 CONH 2 , which was further converted to COOH. As a result, the hydrolyzed PAN (HPAN) was made more hydrophilic, as evidenced from water contact angle data. CONH 2 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). [ABSTRACT FROM AUTHOR]