NAMS 2002 Workshop - ICOM 2008

Pervaporation and Vapor Permeation I – 5
Tuesday July 15, 11:00 AM-11:30 AM, Honolulu/Kahuku
Investigation of the Fundamental Differences between Polyamide-imide
(PAI) and Polyetherimide (PEI) Membranes for Isopropanol Dehydration via
Pervaporation
Y. Wang (Speaker), National University of Singapore, Singapore
L. Jiang, National University of Singapore, Singapore
T. Chung, National University of Singapore, Singapore
T. Matsuura, University of Ottawa, Ottawa, Ontario, Canada
S. Goh, National University of Singapore, Singapore
Polyimides (PI) are recently emerging as a promising material for pervaporation
dehydration of alcohols because of their excellent thermal, chemical and
mechanical stabilities. In this study, two kinds of polyimides, Torlon 4000TF
polyamide- imide (PAI) and Ultem 1010 polyetherimide (PEI) membranes are
investigated as membrane materials for the pervaporation dehydration of
isopropanol. Generally, PAI membranes are found to have higher separation
performance than PEI membranes. The physicochemical properties of these two
materials and the as-fabricated membranes are investigated and correlated to
the pervaporation performance through different characterizations (DSC, TGA,
Goniometery, X-ray diffraction, gas permeation, and water sorption). PAI
membranes exhibited better pervaporation performance which is attributed to the
greater hydrophilicity, higher glass transition temperature, narrower d-space,
higher density and higher water uptake. Compared with PEI dense membranes,
PAI dense membranes show a much higher separation factor (up to 3000 at 60
°C) and comparable flux. PAI membranes also showed higher O2/N2 selectivity
than PEI with comparable gas permeability. The results showed that, for the
fabrication of the asymmetric membranes, the dope concentration is a very
important factor on its pervaporation performance. For both PAI and PEI
membranes, dope concentrations equal to or higher than their critical
concentrations are essential to produce useful pervaporation membranes. In
addition, heat treatment is an effective way to reduce defects and enhance
separation performance. This is because the molecular chain packing of the top
dense layer becomes denser with increasing dope concentration or thermal
treatment temperature of the membrane. Further increase of the dope
concentration or thermal treatment temperature may cause an increased
substrate resistance, which leads to the decrease of the selectivity.
Pervaporation process using different operation modes is also studied. The
separation using a membrane with porous structure facing against the feed
solution shows a much higher separation factor with only a slight decrease of
flux. This important phenomenon can be explained in terms of the balance