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Asymmetric polyimide membrane for pervaporation
News and Views s e p a r a t i o n (C2042-/C1 ") on the b a s i s of a kinetic-based theoretical a p p r o a c h . In both eases, the p r o p o s e d model fitted d a t a satisfactortly, in c o n t r a s t to the classical solution-diffusion model, which w a s u n a b l e to a c c o u n t for the strong d e p e n d e n c y of the m e a s u r e d s e p a r a t i o n factors on the electric c u r r e n t density applied. This model w a s s u g g e s t e d to be a potentially attractive tool for engineering design p u r p o s e s . In fact, p l a n t s for edible salt p r o d u c t i o n are generally designed in multiple-stage systems. The stages are fed consecutively with the diluate, whose monovalent-ion c o n c e n t r a t i o n s are progressively depleted while t h o s e of divalent ions increase. The separability of the ions b e c o m e s m o r e critical at e a c h stage, which is a s s i s t e d b y lower operating c u r r e n t densities. It w a s suggested b y the a u t h o r s of the p a p e r t h a t the developed model m i g h t be particularly helpful for p l a n t design p u r p o s e s whenever n e w s e p a r a t i o n s are studied u s i n g monovalent-lon-permselective m e m b r a n e s , for example in the recovery t r e a t m e n t of industrial wastewater. Further information from: Guido Saracco, Dtpartlmento dl Sclenzta dei Matertal! e lngengnerla Chimtca, Polttecnlco dt Torlno, C.so Duca degll Abruzzl, 24, 10129 Torlno, Italy.
New s t a i n l e s s s t e e l RO h o u s i n g s O s m o n l c s h a s i n t r o d u c e d n e w stainless steel RO h o u s i n g s for 2-inch spiral-wound s e p r a l a t o r s ( m e m b r a n e elements), which, it claims, offer superior durability at a price competitive to plastics housings. The OSMO 2-inch RO h o u s i n g s a r e m a d e of c o r r o s i o n - r e s i s t a n t stainless steel. Precise dimensional uniformity of the stainless steel h o u s i n g s a s s u r e s a secure m e m b r a n e fit a n d p r e v e n t s rotation of s e p r a l a t o r s a n d leakage a r o u n d seals.
Stainless steel RO houslng f r o m Osmonlcs.
M e m b r a n e T e c h n o l o g y No. 4 5
These h o u s i n g s feature a simplified design which incorporates a c l a m p - t y p e e n d c a p closure allowing e a s y a s s e m b l y a n d quick s e p r a l a t o r replacement. They are c a p a b l e of operating at p r e s s u r e s u p to 300 psig (20.7 bar). They are available in 26 a n d 39-inch lengths a n d c a n b e u s e d with all b r a n d s of m e m b r a n e e l e m e n t s a s well a s O s m o n i c s OSMO 112 a n d OSMO 192 s e p r a l a t o r s a n d FASTEK $ 2 0 2 6 a n d $ 2 0 4 0 m e m b r a n e elements. Further information from: Osmonics Inc, 5951 Clearwater Drive, MlnneWnka, MN 55343-8990, USA. Tel: +1 612 933 2277. Fax: +1 612 933 0141.
Mini-cartridge filters available The HiFLO Sol-Vent MC Series of mlnl-cartridge filters h a s b e e n introduced to m e e t the rigorous r e q u i r e m e n t s of the p h a r m a c e u t i c a l i n d u s t r y for purity, safety a n d p e r f o r m a n c e , s a y s its m a n u f a c t u r e r G e l m a n Sciences. This series of cartridge filters c o n t a i n s 0.2 ~m hydrophobic PTFE m e m b r a n e a n d polypropylene s u p p o r t layers. They are available in two styles to retrofit m o s t competitive minl-cartridge h o u s i n g assemblies. Further Informatlon from: Gelman Sciences Inc, 600 South Wagner Road, A n n Arbor, M148106, USA. Tel: +1 313 665 0651.
Asymmetric polyimide m e m b r a n e for pervaporation The p r e p a r a t i o n of polyimide p e r v a p o r a t i o n m e m b r a n e s for the s e p a r a t i o n of a q u e o u s ethanol solutions h a s b e e n investigated b y r e s e a r c h e r s in J a p a n (J. Membrane Scl., 848, p p 231-240, 1994). T h e pervaporation p r o c e s s is i m p o r t a n t for the s e p a r a t i o n of azeotropic m i x t u r e s s u c h a s a n a q u e o u s 95 vol% ethanol solution, b u t few r e p o r t s exist for the p r e p a r a t i o n of a s y m m e t r i c m e m b r a n e s for pervaporation, b e c a u s e of the difficulties in finding the proper conditions for their p r e p a r a t i o n . In this research, a s y m m e t r i c m e m b r a n e s w e r e p r e p a r e d b y the p h a s e inversion process from casting solutions c o m p o s e d of a r o m a t i c polymllde (PI-2080), N,N'-dimethyiformamide (DMF) a n d 1,4-dioxane. The m e m b r a n e s were a n n e a l e d at 300°C in a v a c u u m oven.
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News and Views The pervaporation performance of a n a q u e o u s ethanol solution was measured. Cross sections of the m e m b r a n e s were observed b y s c a n n i n g electron microscopy. Results showed that the best m e m b r a n e was m a d e from a casting solution c o m p o s e d of 25 wt% polylmide, 37.5% wt% DMF a n d 37.5 wt% dloxane. The o p t i m u m annealing condition of the polytmide m e m b r a n e was found to be 300°C for 3 hours. These m e m b r a n e s exhibited a separation factor (H20/EtOH) = 900 with a flux of 1.0 k g / m 2 h for a n a q u e o u s 95 vol% ethanol solution at 60°C. The researchers concluded that the pervaporatlon performance of this asymmetric polyiinide m e m b r a n e is not only governed by the molecular s t r u c t u r e of the membrane, b u t also the fine structure of the membrane, in the same way a s the reverse osmosis membrane.
In the m e t h o d proposed here, one-way valves are inserted in the recirculation circuit, which eliminates the need for the recirculation p u m p . Equipment cost is therefore reduced, a n d less hydraulic energy is required due to a decrease in time-mean velocity. The technique was tested on red wine clarification u s i n g zironimn oxide m e m b r a n e s on c a r b o n support. Observations of pressure a n d flow recordings showed that the permeate flux time variation followed closely that of the t r a n s m e m b r a n e pressure, confirming that the m e m b r a n e flux time was able to r e s p o n d to transient p r e s s u r e c h a n g e s without being pevallzed by concentration polarization build-up. The researchers concluded that the results of their experiments were promising with regard to energy efficiency, b u t the technique m u s t still be evaluated in long term experiments corresponding to industrial applications.
Further information from: H. Yanagtshita, National Institute of Materials and Chemical Research 1-1, Hlgashi, Tsukuba, Ibaraki, 305, Japan.
Further Informatlon.from: M.Y. Jaffrin, URA CNRS 858, University of Technology of Complegne, BP 649, 60206 Compelgne Cedex, France.
Energy saving
crossfl.ow
filtration
Investigations into a new mode of crossflow filtration in which the steady flow p u m p is replaced b y a piston-in-cylinder which p r o d u c e s periodic b u r s t s of velocity a n d pressure along the m e m b r a n e at frequencies between 0.5 a n d 1.5 Hz, have been carried out by researchers in France (J. Membrane ScL, 86, pp 281-290, 1994), In processes s u c h as the clarification of wine a n d beer, the use of m e m b r a n e s is still costly in terms of energy c o n s u m p t i o n a n d equipment cost when c o m p a r e d to traditional adsorption processes s u c h as Kieselguhr. This is due to a high energy requirement for the large circulation velocities of u p to 6 m / s which are needed to limit cake formation a n d to retain sufficient permeability. Various a p p r o a c h e s have been u s e d to increase permeate fluxes, a n d one of these is the superposition of p r e s s u r e a n d flow pulsations created by a piston to perturb concentration polarization a n d cake layer formation. However, a pulsation generator is required, along with a recirculation p u m p to avoid back filtration.
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(si °a,so, 7 Schematic diagram offl/tration unit: (1)feed reservoir; (2)feed pump; (3) recirculaUng pump; (4)flltratlon modules; (5) pulsating generator; (6) electronic scale; (7) microcomputer; (8) electromagnetic f l o w meter; pl,p2,p3, pressure transducers; Tur, turbldlmeter; Q, flow rate; JF, permeate flux.
M e m b r a n e Technology No. 45
New s t a i n l e s s s t e e l RO h o u s i n g s O s m o n l c s h a s i n t r o d u c e d n e w stainless steel RO h o u s i n g s for 2-inch spiral-wound s e p r a l a t o r s ( m e m b r a n e elements), which, it claims, offer superior durability at a price competitive to plastics housings. The OSMO 2-inch RO h o u s i n g s a r e m a d e of c o r r o s i o n - r e s i s t a n t stainless steel. Precise dimensional uniformity of the stainless steel h o u s i n g s a s s u r e s a secure m e m b r a n e fit a n d p r e v e n t s rotation of s e p r a l a t o r s a n d leakage a r o u n d seals.
Stainless steel RO houslng f r o m Osmonlcs.
M e m b r a n e T e c h n o l o g y No. 4 5
These h o u s i n g s feature a simplified design which incorporates a c l a m p - t y p e e n d c a p closure allowing e a s y a s s e m b l y a n d quick s e p r a l a t o r replacement. They are c a p a b l e of operating at p r e s s u r e s u p to 300 psig (20.7 bar). They are available in 26 a n d 39-inch lengths a n d c a n b e u s e d with all b r a n d s of m e m b r a n e e l e m e n t s a s well a s O s m o n i c s OSMO 112 a n d OSMO 192 s e p r a l a t o r s a n d FASTEK $ 2 0 2 6 a n d $ 2 0 4 0 m e m b r a n e elements. Further information from: Osmonics Inc, 5951 Clearwater Drive, MlnneWnka, MN 55343-8990, USA. Tel: +1 612 933 2277. Fax: +1 612 933 0141.
Mini-cartridge filters available The HiFLO Sol-Vent MC Series of mlnl-cartridge filters h a s b e e n introduced to m e e t the rigorous r e q u i r e m e n t s of the p h a r m a c e u t i c a l i n d u s t r y for purity, safety a n d p e r f o r m a n c e , s a y s its m a n u f a c t u r e r G e l m a n Sciences. This series of cartridge filters c o n t a i n s 0.2 ~m hydrophobic PTFE m e m b r a n e a n d polypropylene s u p p o r t layers. They are available in two styles to retrofit m o s t competitive minl-cartridge h o u s i n g assemblies. Further Informatlon from: Gelman Sciences Inc, 600 South Wagner Road, A n n Arbor, M148106, USA. Tel: +1 313 665 0651.
Asymmetric polyimide m e m b r a n e for pervaporation The p r e p a r a t i o n of polyimide p e r v a p o r a t i o n m e m b r a n e s for the s e p a r a t i o n of a q u e o u s ethanol solutions h a s b e e n investigated b y r e s e a r c h e r s in J a p a n (J. Membrane Scl., 848, p p 231-240, 1994). T h e pervaporation p r o c e s s is i m p o r t a n t for the s e p a r a t i o n of azeotropic m i x t u r e s s u c h a s a n a q u e o u s 95 vol% ethanol solution, b u t few r e p o r t s exist for the p r e p a r a t i o n of a s y m m e t r i c m e m b r a n e s for pervaporation, b e c a u s e of the difficulties in finding the proper conditions for their p r e p a r a t i o n . In this research, a s y m m e t r i c m e m b r a n e s w e r e p r e p a r e d b y the p h a s e inversion process from casting solutions c o m p o s e d of a r o m a t i c polymllde (PI-2080), N,N'-dimethyiformamide (DMF) a n d 1,4-dioxane. The m e m b r a n e s were a n n e a l e d at 300°C in a v a c u u m oven.
5
News and Views The pervaporation performance of a n a q u e o u s ethanol solution was measured. Cross sections of the m e m b r a n e s were observed b y s c a n n i n g electron microscopy. Results showed that the best m e m b r a n e was m a d e from a casting solution c o m p o s e d of 25 wt% polylmide, 37.5% wt% DMF a n d 37.5 wt% dloxane. The o p t i m u m annealing condition of the polytmide m e m b r a n e was found to be 300°C for 3 hours. These m e m b r a n e s exhibited a separation factor (H20/EtOH) = 900 with a flux of 1.0 k g / m 2 h for a n a q u e o u s 95 vol% ethanol solution at 60°C. The researchers concluded that the pervaporatlon performance of this asymmetric polyiinide m e m b r a n e is not only governed by the molecular s t r u c t u r e of the membrane, b u t also the fine structure of the membrane, in the same way a s the reverse osmosis membrane.
In the m e t h o d proposed here, one-way valves are inserted in the recirculation circuit, which eliminates the need for the recirculation p u m p . Equipment cost is therefore reduced, a n d less hydraulic energy is required due to a decrease in time-mean velocity. The technique was tested on red wine clarification u s i n g zironimn oxide m e m b r a n e s on c a r b o n support. Observations of pressure a n d flow recordings showed that the permeate flux time variation followed closely that of the t r a n s m e m b r a n e pressure, confirming that the m e m b r a n e flux time was able to r e s p o n d to transient p r e s s u r e c h a n g e s without being pevallzed by concentration polarization build-up. The researchers concluded that the results of their experiments were promising with regard to energy efficiency, b u t the technique m u s t still be evaluated in long term experiments corresponding to industrial applications.
Further information from: H. Yanagtshita, National Institute of Materials and Chemical Research 1-1, Hlgashi, Tsukuba, Ibaraki, 305, Japan.
Further Informatlon.from: M.Y. Jaffrin, URA CNRS 858, University of Technology of Complegne, BP 649, 60206 Compelgne Cedex, France.
Energy saving
crossfl.ow
filtration
Investigations into a new mode of crossflow filtration in which the steady flow p u m p is replaced b y a piston-in-cylinder which p r o d u c e s periodic b u r s t s of velocity a n d pressure along the m e m b r a n e at frequencies between 0.5 a n d 1.5 Hz, have been carried out by researchers in France (J. Membrane ScL, 86, pp 281-290, 1994), In processes s u c h as the clarification of wine a n d beer, the use of m e m b r a n e s is still costly in terms of energy c o n s u m p t i o n a n d equipment cost when c o m p a r e d to traditional adsorption processes s u c h as Kieselguhr. This is due to a high energy requirement for the large circulation velocities of u p to 6 m / s which are needed to limit cake formation a n d to retain sufficient permeability. Various a p p r o a c h e s have been u s e d to increase permeate fluxes, a n d one of these is the superposition of p r e s s u r e a n d flow pulsations created by a piston to perturb concentration polarization a n d cake layer formation. However, a pulsation generator is required, along with a recirculation p u m p to avoid back filtration.
6
4
°
°I
(si °a,so, 7 Schematic diagram offl/tration unit: (1)feed reservoir; (2)feed pump; (3) recirculaUng pump; (4)flltratlon modules; (5) pulsating generator; (6) electronic scale; (7) microcomputer; (8) electromagnetic f l o w meter; pl,p2,p3, pressure transducers; Tur, turbldlmeter; Q, flow rate; JF, permeate flux.
M e m b r a n e Technology No. 45