Vapour permeation applied for the separation of water from organic compounds and gases using asymmetric polyetherimide/polyvinylpyrrolidone capillary tubes

Abstract

Asymmetric integrally skinned capillary tubes were produced from the polymers PEI (polyetherimide) and PVP (polyvinylpyrrolidone) for vapour permeation modules which were applied for the separation of water from organic compounds and gases. Water treatment and recovery of desirable organic compounds was achieved. The capillary tubes had intrinsic permeability coefficients of 7.5 x I@' mol/m2+Pa for water and 1.6 x IC9 mol/rn'.s.Pa for 1 -propano1 for a 1 : 1 mass ratio vapour feed mixture under pyrolysis conditions. The vapour was fed at the interior of the capillary tubes with total pressure of 30 kPa; the permeate total pressure was 14 kPa, and the temperature was 86°C. Modules, with surface areas up to 1.0 m2, were constructed and tested with feed flow rates as high as 4 kg/h with a process development unit. Tests were performed with the vapours from wood chips and contaminated soils subjected to vacuum pyrolysis. he application of vapour permeation membranes to T industry is very recent. However, it is rapidly growing, aided by previous experience with reverse osmosis and pervaporation technology. The first industrial vapour permeation application was in 1989 (Sander and Janssen, 1991; Sander, 199 1) using flat sheet composite membranes originally designed for pervaporation for the dehydration of ethanol from 94% to 99.9%. Will and Lichtenthaler (1 992a,b) showed that polyvinyl alcohol/polyacrylonitrile composite membranes can be used for the separation of water/alcohol mixtures by pervaporation and vapour permeation. Deng et al. (1995) prepared flat sheet asymmetric polyetherimide (PEI) membranes and studied the recovery of solvents from air exhaust streams. Tanihara et al. (1992) prepared polyimide hollow fibers to study the separation of alcohol/water mixtures by vapour permeation.Regarding the effect of polyvinylpyrrolidone (PVP) additive to the casting solution, Cabasso et al. (1 976) made an intensive study. Miyano et al. (1990) showed that residual PVP remained in the membrane even after extraction of PVP in the gelation bath.

Water vapor sorption and transport in dense polyimide membranes

“…The permeation tests of water vapor in the dense polyimide membranes were carried out with a laboratory test cell,3, 8 in which the water vapor was generated by the pumping of pure water through a preheating tubing that was heated to 140–160°C for the evaporation of water. Water vapor was introduced to the membrane test unit at a given temperature and feed pressure through long, circular tubing placed in a constant‐temperature oven.…”

“…Water vapor separation membranes have attracted great interest because of their applications for the dehumidification of gases, air, and organic vapors 1, 2. In the development of membranes for the separation of water vapor from organic compounds, especially for the treatment of byproduct streams in wood drying or pyrolysis processes, the thermal and chemical resistance of membranes is of primary importance 3, 4. Polyimides, with their excellent thermal, mechanical, and chemical properties, have been widely used in the microelectronics and aerospace industries, and they have also attracted much attention as gas separation membranes since the early 1970s because of their high separation factors 5–8.…”

Development of polyimide membranes for the separation of water vapor from organic compounds

“…The separation performance of the membranes was tested by using a laboratory‐ scale separation unit, 3, 12 whereby the separation of model vaporous mixtures of 1‐propanol (1‐PrOH)/ H 2 O and acetic acid (AA)/H 2 O was attempted. Mixtures with 10–90 wt % of organic components were used as vaporous feeds.…”

“…The separation performance of the membranes was tested by using a laboratory-scale separation unit, 3,12 whereby the separation of model vaporous mixtures of 1-propanol (1-PrOH)/H 2 O and 2 . Membrane bundles were tested at 85-135°C with feed vapor supplied to the bore side of the capillary fibers.…”

“…Hence, their treatment is required. Similarly in the vacuum pyrolysis process, when water‐containing feedstocks, such as urban wastes and biomass are treated, 2, 3 a large quantity of water is produced and released, requiring treatment before discharge. On the other hand, some organic compounds released during wood drying and pyrolysis processes are valuable and may be recovered.…”