- Email: [email protected]
Cellulose acetate benzoate membranes developed
News and Views The r e m a i n d e r c o n t a i n e d the c o n c e n t r a t e , which c a n be t r e a t e d for p o s s i b l e c o n t a i n m e n t . In t h e p r e s e n c e of h i g h l y inactive a m m o n i u m n i t r a t e c o n c e n t r a t i o n s , it m a y be p r e f e r a b l e to u s e a m o d e r a t e l y rejecting m e m b r a n e which h a s a d e c o n t a m i n a t i o n factor of a r o u n d I 0 0 a n d o p t i m u m p e r m e a t e flux rates. Better p e r f o r m a n c e m i g h t b e a c h i e v e d b y u s i n g n a n o f i l t r a t i o n m e m b r a n e s in the p r e s e n c e of polyelectrolytes, a n d t h i s is a c o n t i n u i n g a r e a of study.
Further Informatlon from: S. Prabhakar, Desalination Division, Bhabha Atomic Research Centre, Bombay 400085, India.
New t y p e o f h o l l o w fibre pertractor The p e r f o r m a n c e of a new h o l l o w - f i b r e s - l n - t u b e type p e r t r a c t o r h a s b e e n s t u d i e d b y r e s e a r c h e r s in Slovakia, a n d r e s u l t s a r e p r e s e n t e d in Separation Science and Technology, (29, p p 765-780). This p e r t r a c t o r c o n s i s t s of a h y d r o p h i l i c t u b e in which a b u n d l e of h y d r o p h o b i c hollow fibres is inserted. A p e r t r a c t o r is f o r m e d b y two types of p o r o u s wails, h y d r o p h i l i c a n d h y d r o p h o b i c a s s h o w n in the figure. In a u s u a l system, two b u n d l e s of hollow fibres with m i c r o p o r o u s walls a r e p l a c e d in a cylinder with solvent b e t w e e n t h e fibres. M a s s t r a n s f e r from one b u n d l e to a n o t h e r occurs. A large interfacial a r e a c a n be formed w i t h o u t the n e e d for m e c h a n l c a l d i s p e r s i o n , which is u s e f u l for s y s t e m s with an e m u l s i o n - f o r m i n g tendency. An n - a l k a n e fraction w a s u s e d a s t h e m e m b r a n e p h a s e in t h e s e e x p e r i m e n t s . The a q u e o u s feed c o n t a i n e d I g.L "| p h e n o l a n d O. 1 M Na2SO4 with a pH of a b o u t 3.5. In t h i s p e r t r a c t o r a b u n d l e of eight hollow fibres w a s i n s e r t e d into a polysulfone t u b u l e t a n d g l u e d into a 4 m m d i a m e t e r g l a s s tube. It o p e r a t e d in two m o d e s . In t h e first m o d e the feed flowed t h r o u g h t h e p e r t r a c t o r shell a n d the s t r i p p i n g s o l u t i o n flowed t h r o u g h t h e hollow fibres. In one of these m o d e s t h e feed w a s fed g r a v i t a t i o n a l l y to avoid p u l s a t i o n s , In t h e s e c o n d m o d e the feed flowed t h r o u g h t h e hollow fibres a n d t h e s t r i p p i n g s o l u t i o n flowed t h r o u g h the s h e d - - in t h i s c a s e t h e feed w a s in c o n t a c t with the h y d r o p h i l i c wa11. P u l s a t i o n of the m e m b r a n e p h a s e w a s s h o w n to i n c r e a s e t h e m a s s flux b y m o r e t h a n 40% at a relatively low p u l s e velocity a n d r e a c h e d a m a x i m u m value at a b o u t 10 m m s" I. A s u b s t a n t i a l l y h i g h e r m a s s flux, by a b o u t 60%, c a n be r e a c h e d w h e n the
Membrane Technology No. 50
2
1 F
I
s
#
~
R
F Feed
/~ Z . J i
Liqui¢ memb
Stripping sotution
= i
hydrophobic watt
hydrophitic watt
Schematic of the three.phase system in a pertractor with two immobilized interfaces using mlcroporous walls of different wettablllties. s t r i p p i n g solution is in c o n t a c t with the h y d r o p h i l i c wall. A n a l y s i s of m a s s - t r a n s f e r r e s i s t a n c e s in i n d i v i d u a l p h a s e s a n d l a y e r s revealed t h a t the m a i n r e s i s t a n c e w a s in the liquid m e m b r a n e . This w a s especially n o t i c e a b l e in the h y d r o p h o b i c wall pores. The m a s s flux per u n i t v o l u m e of t h e c o n t a c t o r hollow-fibre-type w a s f o u n d to be higher t h a n in c l a s s i c a l b u l k liquid m e m b r a n e c o n t a c t o r s , a n d c o m p a r a b l e with s u p p o r t e d a n d e m u l s l o n - t y p e liquid m e m b r a n e contactors.
Further Informatlon from: ~tefan Schlosser and Iveta Rothovd, Department of Chemlcal and Biochemical Engineering, Slovak Technlcal University, Radllnsk~ho 9, 812 37 Bratlslava, Slovak~a.
Cellulose acetate benzoate membranes developed The d e v e l o p m e n t a n d c h a r a c t e r i z a t i o n of cellulose a c e t a t e b e n z o a t e (CABz) fiat o s m o t i c m e m b r a n e s h a s b e e n s t u d i e d b y r e s e a r c h e r s in India, a n d their results a r e p r e s e n t e d in Journal of Applied Polymer Science, (52, pp 1031-1035). The a i m of the r e s e a r c h w a s to optimize t h e d e v e l o p m e n t of CABz fiat o s m o t i c m e m b r a n e s of a degree of s u b s t i t u t i o n for t h e b e n z o y l r a d i c a l b e t w e e n 2.6 a n d 2.7. I n c r e a s i n g the s u b s t i t u t i o n with t h e
5
News and Views benzoyl radical should increase the intrinsic salt rejection of a dense film of CABz. Different p a r a m e t e r s of casting solutions a n d casting conditions were studied for the development of the m e m b r a n e s . The m e m b r a n e s were given different evaporation periods a n d annealing t e m p e r a t u r e s u n d e r different RH. Different annealing b a t h s were also used. The m e m b r a n e s were characterized with respect to b o u n d water content, specific water content, transport properties b y direct osmosis, salt intake by direct immersion, water permeability coefficient of the dense m e m b r a n e , diffusion coefficient, salt permeability, a n d salt distribution by electrical conductivity. A concentration of 23% of the polymer CABz in the casting solution was observed to be optimum to obtain a casting solution viscosity of 42 200 cps, m e m b r a n e strength of 1700 psi, a n d salt rejection of 94.4% with a flux of 14.5 gallons per square foot per day. The CABz m e m b r a n e with a total cast thickness of 0.20 m m gave a very good performance. On comparison with CA m e m b r a n e s , the CABz m e m b r a n e s showed better salt diffusion, distribution coefficient, a n d salt permeability.
Further Informatton from: I.C. Mody, Central Salt and Marine Chemicals Research Institute, Bhavnagar-364 002, India.
Micellar-enhanced UF to r e m o v e divalent metal cations Micellar-enhanced ultraflltration (MEUF) is a novel m e m b r a n e - b a s e d separation technique that can be used to remove multivalent metal cations from a q u e o u s streams. Researchers in the USA a n d Egypt looked at the use of this technique for the removal of cadmium, zinc, copper (II) a n d calcium ions and their results are given in Separatlon Science and Technology, (29, pp 809-830). In this technique, a n anionic s u r f a c t a n t is injected into the a q u e o u s stream coming from an industrial process. The final s u r f a c t a n t concentration in the stream should be well above the critical micelle concentration {CMC) of the surfactant, so that micelles form in solutions. In the miceUe the hydrophobic tail groups are in the central core, with the hydrophilic anionic h e a d groups towards the outer surface. This surface h a s a high charge density a n d attracts the multivalent metal cations. When p a s s e d t h r o u g h a UF m e m b r a n e the micelies are rejected from the stream, a n d the resultant permeate stream contains only very low concentrations of the metal cations a n d surfactant. In these studies the anionic s u r f a c t a n t was sodium dodecyl sulfate (SDS). Metal chlorlde salts were u s e d as a source of the metal ions in order to have the same co-ion in the systems studied. As well
6
as single c o m p o n e n t systems, mixtures of metals were also investigated. Rejections of 96.28-98.08% at 20 mM metal ion concentration were obtained. The results were consistent with a previously developed equilibrium binding model. Under reasonable conditions, the flux rates are not substantially below that of pure water, which indicated the feasibility of u s i n g MEUF in industrial applications.
Further Information from: John F. Scamehorn, Instltute for Applied Surfactant Research, University of Oklahoma, Norman, OK 73019, USA.
N e w ca filters
ridge
Gelman Sciences h a s introduced its Suporflow I 0 0 cartridge filter, specifically designed for ultrapure water applications a n d other a q u e o u s solutions requiring 0,1 ~m filtration. Suporflow 100 contains patented, Supor m e m b r a n e (hydrophflic polyethersulfone), that improves deionized water quality b y particle retention u s i n g sieve retention, while maintaining flow rates. The cartridge filters resist the strong oxidizing agents used in system sanitizing, says the company. They are available in nominal lengths of I0, 20, 30 a n d 40 inches and are 100% integrity tested during manufacture. In addition, the c o m p a n y h a s introduced its Suporflow 200 sterilizing-grade cartridge flter, which incorporates its 0.2 tan Supor membrane. It is constructed from polyethersuifone and polypropylene, a n d is sterilizable by autoclave, in-line steam and chemical methods.
Further Informatton from: Gelman Sciences, Inc, 600 South Wagner Road, Ann Arbor, M148106, USA. Tel: +1 313 665 0651; or: Gelman Sciences Ltd, Brackmllls Business Park, Caswell Road, Northampton NN4 7EZ, UK. Tel: 0604 765141. Fax: 0604 761383.
Suporflow 200from Gelman Sciences.
M e m b r a n e Technology No. 5 0
Further Informatlon from: S. Prabhakar, Desalination Division, Bhabha Atomic Research Centre, Bombay 400085, India.
New t y p e o f h o l l o w fibre pertractor The p e r f o r m a n c e of a new h o l l o w - f i b r e s - l n - t u b e type p e r t r a c t o r h a s b e e n s t u d i e d b y r e s e a r c h e r s in Slovakia, a n d r e s u l t s a r e p r e s e n t e d in Separation Science and Technology, (29, p p 765-780). This p e r t r a c t o r c o n s i s t s of a h y d r o p h i l i c t u b e in which a b u n d l e of h y d r o p h o b i c hollow fibres is inserted. A p e r t r a c t o r is f o r m e d b y two types of p o r o u s wails, h y d r o p h i l i c a n d h y d r o p h o b i c a s s h o w n in the figure. In a u s u a l system, two b u n d l e s of hollow fibres with m i c r o p o r o u s walls a r e p l a c e d in a cylinder with solvent b e t w e e n t h e fibres. M a s s t r a n s f e r from one b u n d l e to a n o t h e r occurs. A large interfacial a r e a c a n be formed w i t h o u t the n e e d for m e c h a n l c a l d i s p e r s i o n , which is u s e f u l for s y s t e m s with an e m u l s i o n - f o r m i n g tendency. An n - a l k a n e fraction w a s u s e d a s t h e m e m b r a n e p h a s e in t h e s e e x p e r i m e n t s . The a q u e o u s feed c o n t a i n e d I g.L "| p h e n o l a n d O. 1 M Na2SO4 with a pH of a b o u t 3.5. In t h i s p e r t r a c t o r a b u n d l e of eight hollow fibres w a s i n s e r t e d into a polysulfone t u b u l e t a n d g l u e d into a 4 m m d i a m e t e r g l a s s tube. It o p e r a t e d in two m o d e s . In t h e first m o d e the feed flowed t h r o u g h t h e p e r t r a c t o r shell a n d the s t r i p p i n g s o l u t i o n flowed t h r o u g h t h e hollow fibres. In one of these m o d e s t h e feed w a s fed g r a v i t a t i o n a l l y to avoid p u l s a t i o n s , In t h e s e c o n d m o d e the feed flowed t h r o u g h t h e hollow fibres a n d t h e s t r i p p i n g s o l u t i o n flowed t h r o u g h the s h e d - - in t h i s c a s e t h e feed w a s in c o n t a c t with the h y d r o p h i l i c wa11. P u l s a t i o n of the m e m b r a n e p h a s e w a s s h o w n to i n c r e a s e t h e m a s s flux b y m o r e t h a n 40% at a relatively low p u l s e velocity a n d r e a c h e d a m a x i m u m value at a b o u t 10 m m s" I. A s u b s t a n t i a l l y h i g h e r m a s s flux, by a b o u t 60%, c a n be r e a c h e d w h e n the
Membrane Technology No. 50
2
1 F
I
s
#
~
R
F Feed
/~ Z . J i
Liqui¢ memb
Stripping sotution
= i
hydrophobic watt
hydrophitic watt
Schematic of the three.phase system in a pertractor with two immobilized interfaces using mlcroporous walls of different wettablllties. s t r i p p i n g solution is in c o n t a c t with the h y d r o p h i l i c wall. A n a l y s i s of m a s s - t r a n s f e r r e s i s t a n c e s in i n d i v i d u a l p h a s e s a n d l a y e r s revealed t h a t the m a i n r e s i s t a n c e w a s in the liquid m e m b r a n e . This w a s especially n o t i c e a b l e in the h y d r o p h o b i c wall pores. The m a s s flux per u n i t v o l u m e of t h e c o n t a c t o r hollow-fibre-type w a s f o u n d to be higher t h a n in c l a s s i c a l b u l k liquid m e m b r a n e c o n t a c t o r s , a n d c o m p a r a b l e with s u p p o r t e d a n d e m u l s l o n - t y p e liquid m e m b r a n e contactors.
Further Informatlon from: ~tefan Schlosser and Iveta Rothovd, Department of Chemlcal and Biochemical Engineering, Slovak Technlcal University, Radllnsk~ho 9, 812 37 Bratlslava, Slovak~a.
Cellulose acetate benzoate membranes developed The d e v e l o p m e n t a n d c h a r a c t e r i z a t i o n of cellulose a c e t a t e b e n z o a t e (CABz) fiat o s m o t i c m e m b r a n e s h a s b e e n s t u d i e d b y r e s e a r c h e r s in India, a n d their results a r e p r e s e n t e d in Journal of Applied Polymer Science, (52, pp 1031-1035). The a i m of the r e s e a r c h w a s to optimize t h e d e v e l o p m e n t of CABz fiat o s m o t i c m e m b r a n e s of a degree of s u b s t i t u t i o n for t h e b e n z o y l r a d i c a l b e t w e e n 2.6 a n d 2.7. I n c r e a s i n g the s u b s t i t u t i o n with t h e
5
News and Views benzoyl radical should increase the intrinsic salt rejection of a dense film of CABz. Different p a r a m e t e r s of casting solutions a n d casting conditions were studied for the development of the m e m b r a n e s . The m e m b r a n e s were given different evaporation periods a n d annealing t e m p e r a t u r e s u n d e r different RH. Different annealing b a t h s were also used. The m e m b r a n e s were characterized with respect to b o u n d water content, specific water content, transport properties b y direct osmosis, salt intake by direct immersion, water permeability coefficient of the dense m e m b r a n e , diffusion coefficient, salt permeability, a n d salt distribution by electrical conductivity. A concentration of 23% of the polymer CABz in the casting solution was observed to be optimum to obtain a casting solution viscosity of 42 200 cps, m e m b r a n e strength of 1700 psi, a n d salt rejection of 94.4% with a flux of 14.5 gallons per square foot per day. The CABz m e m b r a n e with a total cast thickness of 0.20 m m gave a very good performance. On comparison with CA m e m b r a n e s , the CABz m e m b r a n e s showed better salt diffusion, distribution coefficient, a n d salt permeability.
Further Informatton from: I.C. Mody, Central Salt and Marine Chemicals Research Institute, Bhavnagar-364 002, India.
Micellar-enhanced UF to r e m o v e divalent metal cations Micellar-enhanced ultraflltration (MEUF) is a novel m e m b r a n e - b a s e d separation technique that can be used to remove multivalent metal cations from a q u e o u s streams. Researchers in the USA a n d Egypt looked at the use of this technique for the removal of cadmium, zinc, copper (II) a n d calcium ions and their results are given in Separatlon Science and Technology, (29, pp 809-830). In this technique, a n anionic s u r f a c t a n t is injected into the a q u e o u s stream coming from an industrial process. The final s u r f a c t a n t concentration in the stream should be well above the critical micelle concentration {CMC) of the surfactant, so that micelles form in solutions. In the miceUe the hydrophobic tail groups are in the central core, with the hydrophilic anionic h e a d groups towards the outer surface. This surface h a s a high charge density a n d attracts the multivalent metal cations. When p a s s e d t h r o u g h a UF m e m b r a n e the micelies are rejected from the stream, a n d the resultant permeate stream contains only very low concentrations of the metal cations a n d surfactant. In these studies the anionic s u r f a c t a n t was sodium dodecyl sulfate (SDS). Metal chlorlde salts were u s e d as a source of the metal ions in order to have the same co-ion in the systems studied. As well
6
as single c o m p o n e n t systems, mixtures of metals were also investigated. Rejections of 96.28-98.08% at 20 mM metal ion concentration were obtained. The results were consistent with a previously developed equilibrium binding model. Under reasonable conditions, the flux rates are not substantially below that of pure water, which indicated the feasibility of u s i n g MEUF in industrial applications.
Further Information from: John F. Scamehorn, Instltute for Applied Surfactant Research, University of Oklahoma, Norman, OK 73019, USA.
N e w ca filters
ridge
Gelman Sciences h a s introduced its Suporflow I 0 0 cartridge filter, specifically designed for ultrapure water applications a n d other a q u e o u s solutions requiring 0,1 ~m filtration. Suporflow 100 contains patented, Supor m e m b r a n e (hydrophflic polyethersulfone), that improves deionized water quality b y particle retention u s i n g sieve retention, while maintaining flow rates. The cartridge filters resist the strong oxidizing agents used in system sanitizing, says the company. They are available in nominal lengths of I0, 20, 30 a n d 40 inches and are 100% integrity tested during manufacture. In addition, the c o m p a n y h a s introduced its Suporflow 200 sterilizing-grade cartridge flter, which incorporates its 0.2 tan Supor membrane. It is constructed from polyethersuifone and polypropylene, a n d is sterilizable by autoclave, in-line steam and chemical methods.
Further Informatton from: Gelman Sciences, Inc, 600 South Wagner Road, Ann Arbor, M148106, USA. Tel: +1 313 665 0651; or: Gelman Sciences Ltd, Brackmllls Business Park, Caswell Road, Northampton NN4 7EZ, UK. Tel: 0604 765141. Fax: 0604 761383.
Suporflow 200from Gelman Sciences.
M e m b r a n e Technology No. 5 0