Heat-Treated Polyacrylonitrile (PAN) Hollow Fiber Structured Packings in Isopropanol (IPA)/Water Distillation with Improved Thermal and Chemical Stability

Abstract

In this study, polyacrylonitrile (PAN) hollow fiber membrane (HFM) was heat-treated by muffle furnace to strengthen the thermal and chemical stability. Membrane morphology with different materials was characterized by scanning electron microscopy (SEM). It has shown that both porosity and pore size decreased with increasing heat treatment time (<i>t</i> = 0.5, 6, 12 h) and temperature (<i>T</i> = 200, 250, 300, and 350 °C). FTIR was used to explore the change of chemical bonds and found that dehydrogenation, cyclization, and cross-linking reactions occurred in thermal treatment. Compared with original PAN membrane, the hydrophobicity of heat-treated membranes was obviously improved. The heat-treated membrane PAN-250-6 (PAN–temperature–duration) was selected and immersed in various boiling solvents for 24 h to test material stability. PAN-250-6 membrane presented excellent thermal and chemical stability especially in strong solvent, <i>N</i>,<i>N</i>-dimethylacetamide (166.1 °C), whereas original PAN membrane was dissolved completely. For comparison, PAN and PAN-250-6 HFMs were further chosen for packing modules, which were used for the distillation of isopropanol–water solution. During 10 days of operation, module PAN-250-6 showed high separation efficiency with comparatively low height of mass transfer unit (HTU) and larger overall mass transfer coefficients in the ranges of 0.1–0.18 m and 2.5–3.2 cm/s respectively. By analyzing the impact of wetting condition on mass transfer, it was found that membrane resistance should be sensitive and attributed more to the change of the overall resistance. The membrane with better hydrophobicity after heat treatment was more conducive to distillation with HFMs. With superior thermal and chemical stability in distillation, this kind of heat-treated hollow fiber structured packing will be promising in future distillation applictions