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