Synthetic Membranes: Volume II - American Chemical Society

12 Externally Wound Tubular Membrane Elements in Modular Assemblies: Production and Application S. M A N J I K I A N

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A R A M C O , Dhahran, Saudi Arabia C. K . W O J C I K University of Petroleum & Minerals, Dhahran, Saudi Arabia

Tubular R.O. systems have been slow t o develop e s p e c i a l l y when compared w i t h the s u c c e s s f u l mass marketing of spiral and hollow f i n e f i b e r type R.O. systems. I n the water d e s a l i n a t i o n field, the h i g h membrane packing d e n s i t y of spiral and hollow f i n e fiber systems has given them an overwhelming economic advantage over t u b u l a r systems. However, the advantageous design f e a t u r e of spiral and hollow f i n e fiber u n i t s a l s o serves t o limit t h e i r a p p l i c a t i o n t o relatively c l e a r fluids f r e e of colloidal and particulate matter. This effectively curtails their practical a p p l i c a t i o n in areas such as the s e p a r a t i o n and c o n c e n t r a t i o n of fluid foods, pharmaceutical mixtures and the treatment of industrial wastes. Tubular system can and should effectively fill this gap. The e x t e r n a l l y wound t u b u l a r membrane system and c o n v e n t i o n a l t u b u l a r designs have the necessary d e s i g n , p r o d u c t i o n and functional f e a t u r e s t o meet more demanding task of p r o c e s s i n g fluids of h i g h p a r t i c u l a t e content and, in r o t a r y assemblies, treatment of d e l i c a t e and structurally s e n s i t i v e fluids and chemical mixtures. System D e s c r i p t i o n The e x t e r n a l l y wound membranes were developed by U n i v e r s a l Water Corp., San Diego, C a l i f o r n i a . I n t h i s d e s i g n , the membrane element c o n s i s t s of a porous supporting tube on which are s i m u l taneously wound, i n h e l i c a l f a s h i o n , a s t r i p of permeable f a b r i c o v e r l a i d w i t h a h e l i c a l wound s t r i p of semipermeable membrane f i l m . Adjacent turns of the membrane overlap i n winding, and these overlaps a r e sealed by a bonding solvent so t h a t , the membrane i t s e l f

0097-6156/81/0154-0193$05.00/0 © 1981 American Chemical Society

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


194

SYNTHETIC

MEMBRANES:

HF AND U F

USES

forms a u n i t a r y tube e n c l o s i n g the f a b r i c and the porous supporting tube. A diagram of such h e l i c a l l y wound membrane element i s shown i n F i g . 1. Modular assemblies designed t o house a number of h e l i c a l e l e ments a r e constructed by arranging i n d i v i d u a l membrane elements, i n spaced r e l a t i o n s h i p s , w i t h i n f l o w guide tubes i n s i d e a s u i t a b l e pressure v e s s e l . V a r i o u s diameter flow tubes are used t o p r o v i d e the d e s i r e d annular spacing between membrane surfaces and b r i n e flow channel w a l l s . By t h i s means the cross s e c t i o n a l area of b r i n e flow channels around each element can be s e l e c t e d t o p r o v i d e best c o n d i t i o n s f o r s p e c i f i c processing a p p l i c a t i o n s . For example, a r e l a t i v e l y wide spacing may be r e q u i r e d f o r f l u i d s that are v i s cous or have a h i g h content of p a r t i c u l a t e or c o l l o i d a l matter as i n food p r o c e s s i n g a p p l i c a t i o n s . On the other hand, c l o s e spacing may be r e q u i r e d i n water d e s a l i n a t i o n a p p l i c a t i o n s t o prevent conc e n t r a t i o n p o l a r i z a t i o n by producing a t u r b u l e n t f l o w and t o reduce pumping r a t e s . The diagram of a t y p i c a l module i s shown i n F i g . 2. A module j u s t described i s a f i x e d module i n which the membrane elements a r e s t a t i o n a r y . A r a d i c a l departure from the conv e n t i o n a l mode of R.O. systems o p e r a t i o n s i s the r o t a r y system wherein e x t e r n a l l y wound membrane elements c l u s t e r e d around a c e n t r a l s h a f t a r e r o t a t e d i n a s t a t i o n a r y pressure v e s s e l f i l l e d w i t h p r e s s u r i z e d feed stock. Here the separated permeate i s replaced by an equivalent volume of f r e s h feed stock under a constant head. The b a s i c r o t a r y concept i s depicted i n F i g . 3. The most important f e a t u r e s of the e x t e r n a l l y wound membranes are: • Low c o s t . No advanced technology o r s o p h i s t i c a t e d equipment i s i n v o l v e d i n making of such membrane elements. They can be manufactured on s i t e . • S e r v i c e a b i l i t y and maintenance. Being on the outer surface of t u b u l a r elements, the membranes a r e r e a d i l y a c c e s s i b l e to i n s p e c t i o n and c l e a n i n g . Assembly and disassembly of modules can be accomplished e a s i l y and q u i c k l y i n the f l u i d . • Good mechanical r e l i a b i l i t y of the system. The membrane elements a r e subjected t o compressive s t r e s s e s o n l y , t h e r e f o r e , n o n - c o r r o s i v e m a t e r i a l s of lower t e n s i l e s t r e n g t h may be used. Membranes Membranes f o r e x t e r n a l l y wound elements were e i t h e r obtained as f i n i s h e d product from commercial sources, or produced in-house from raw m a t e r i a l s . Purchased membranes were i n i t i a l l y t e s t e d f o r compliance w i t h the s p e c i f i c a t i o n s designed t o assure t h e i r s u i t a b i l i t y f o r winding o p e r a t i o n s ( t h i c k n e s s , t e n s i l e s t r e n g t h and e l o n g a t i o n ) and for t h e i r performance c h a r a c t e r i s t i c s ( f l u x and s a l t r e j e c t i o n )



12.

MANJIKIAN

A N D WOJCIK

Tubular

Membrane

Elements

195

I I ε

I S .00


SYNTHETIC

MEMBRANES:

HF

AND


196

UF

3 PS

I s


USES


12.

MANJIKIAN AND wojciK

Tubular

Membrane

Elements

κ.


197


198

SYNTHETIC MEMBRANES:

HF

AND

UF

USES

w i t h i n the p r e s c r i b e d range of o p e r a t i o n . A f t e r meeting successf u l l y these s p e c i f i c a t i o n s , they were evaluated i n teridb of t h e i r a p p l i c a b i l i t y to h e l i c a l winding and c o m p a t i b i l i t y w i t h overlap s e a l a n t s . Most of the commercial membranes were found to be s u i t able f o r h e l i c a l winding a p p l i c a t i o n . The in-house membranes were f a b r i c a t e d , w i t h minor m o d i f i c a t i o n s , along w e l l e s t a b l i s h e d procedures which i n c l u d e d : formulat i o n , c a s t i n g or forming, g e l l a t i o n and c u r i n g a t elevated tempera t u r e s . Various c a s t i n g s o l u t i o n s were t r i e d f i r s t f o r t h e i r performance as f l a t t e s t membranes before t h e i r s u i t a b i l i t y f o r winding operations was considered. The p r e f e r r e d c a s t i n g f o r m u l a t i o n f o r membranes used i n the h e l i c a l l y wound elements comprises: 24% C e l l u l o s e acetate E-398-6 or -10 29% Formamide 35% Acetone 12% P y r i d i n e A d d i t i o n of p y r i d i n e t o the c e l l u l o s i c c a s t i n g formulations r e s u l t s i n membranes having s u p e r i o r mechanical p r o p e r t i e s i n terms of t h e i r s t r e n g t h and d u c t i l i t y . P r i o r t o c a s t i n g , the mixed formulations were f i l t e r e d f o r removal of p a r t i c u l a t e and i n s o l u a b l e matter and t r a n s f e r r e d to s p e c i a l c a n i s t e r s . Casting was done a t ambient temperatures and water c u r i n g a t 1°C f o r a p e r i o d of 45 minutes. P r i o r t o use, the membranes were f i r s t annealed and then s l i t i n t o s t r i p s , say 1.065 ± 0.005 i n c h wide f o r a 7/16 i n c h diameter element, and r o l l e d on s p e c i a l capsules f o r i n s e r t i o n i n t o winding feeders. The c u r i n g temperatures r e q u i r e d f o r given performance s p e c i f i c a t i o n s f o r the e x t e r n a l l y would membranes were found t o be 2 t o 5 C higher than those f o r f l a t membranes. For b r a c k i s h water a p p l i c a t i o n s , the membrane elements were cured a t 84 C ± 0.2 C f o r the p e r i o d of 10 ± 0.5 minutes. Support S t r u c t u r e s In the c o n s t r u c t i o n and assembly of e x t e r n a l l y wound t u b u l a r membrane systems, the support s t r u c t u r e i s g e n e r a l l y a r i g i d noncompressible t u b u l a r body of s u f f i c i e n t mechanical s t r e n g t h t o withstand r e q u i r e d operating pressures and of adequate p o r o s i t y t o f r e e l y transmit the separated permeate. M a t e r i a l s having uniform p o r o s i t y would be the most d e s i r a b l e , however, c e l l u l a r p o r o s i t y i s o f t e n (at l e a s t i n the cases tested) a s s o c i a t e d w i t h low mechanical s t r e n g t h , l a c k of u n i f j r m i t y and long term r e l i a b i l i t y and a r e l a t i v e l y high cost of production. I n absence of such m a t e r i a l s , p o r o s i t y i n supporting tubes was achieved by d r i l l i n g holes a t spaced i n t e r v a l s u s i n g a s p e c i a l l y designed m u l t i - s p i n d l e d r i l l i n g f i x t u r e . I t was e s t a b l i s h e d experimentally that the most s a t i s f a c t o r y passage of water was achieved through 0.028 i n c h diameter p e r f o r a t i o n s spaced at three i n c h i n t e r v a l s along two s t r a i g h t l i n e s 180 degrees apart.


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MANJIKIAN

AND WOJCIK

Tubular Membrane Elements

199

D e s i r a b l e p r o p e r t i e s f o r supporting tubes are: c o r r o s i o n r e s i s t a n c e , thermal s t a b i l i t y , dimensional s t a b i l i t y under wet c o n d i t i o n s , c o m p a t i b i l i t y w i t h other components of the module, mechanical s t r e n g t h , and good m a c h i n e a b i l i t y . A h i g h l y p r a c t i c a l m a t e r i a l i s ABS ( a c r y l o n i t r i t e - b u t a d i e n e s t y r e n e ) . Membrane elements, f a b r i c a t e d w i t h 7/16 nominal diameters extruded ABS tubing as support s t r u c t u r e s , were successf u l l y operated a t pressure up t o 1500 p s i g .


Backing M a t e r i a l s Backing m a t e r i a l s are used i n the c o n s t r u c t i o n and assembly of e x t e r n a l l y wound t u b u l a r membrane elements t o provide f o r l a t e r a l t r a n s f e r of permeate t o spaced p e r f o r a t i o n s i t e s i n the support s t r u c t u r e . P r i n c i p a l c h a r a c t e r i s t i c s d e s i r a b l e i n membrane backing m a t e r i a l s i n c l u d e h i g h p o r o s i t y f o r adequate l i q u i d permeation a t minimum p r e s s u r e s , h i g h d e n s i t y combined w i t h a smooth surface t e x t u r e t o minimize embossing or otherwise deforming of membrane s u r f a c e s and mechanical s t r e n g t h t o b r i d g e over p e r f o r a t i o n s i n the support tube. Dacron pressed paper was found t o be h i g h l y adequate f o r permeate t r a n s p o r t w h i l e possessing the wet s t r e n g t h p l a s t i c propert i e s needed i n winding o p e r a t i o n s . Dacron paper was a l s o used i n c a s t i n g membranes d i r e c t l y on support s t r u c t u r e s . Sealants In the f a b r i c a t i o n of e x t e r n a l l y wound t u b u l a r membrane elements and modular assemblies s o l v e n t bonding f l u i d s and 0-rings are commonly used as s e a l a n t s . I n winding o p e r a t i o n s , s t r i p s o f membranes a r e wound i n an overlapping manner t o form a u n i t a r y tube where h e l i c a l winding overlaps a r e s o l v e n t bonded d u r i n g winding w h i l e the ends of the windings are sealed t o the support tube. Commercially a v a i l a b l e glues and bonding mixtures were found t o be i m p r a c t i c a l i n the continuous and immediate s e a l i n g requirements of the winding process. Most of the epoxy formulat i o n s were r e j e c t e d because of t h e i r s e t t i n g and c u r i n g time requirements. Commonly known c e l l u l o s e acetate s o l v e n t s were t e s t e d i n d i v i d u a l l y and i n combination. I n g e n e r a l , pure s o l v e n t s were found t o be too strong f o r t h a t purpose, as they tended t o penetrate membrane surfaces r a t h e r than spread over the overlap i n t e r f a c e , thus, r e s u l t i n g i n an i m p e r f e c t l y bonded seams, w i t h p h y s i c a l l y weak and b r i t t l e areas at the j o i n t . E x p e r i m e n t a l l y , weak s o l v e n t s i n combination w i t h d i l u e n t s and p l a s t i c i z e r s were found t o be h i g h l y acceptable. A composition, found t o be the most e f f e c t i v e , c o n s i s t e d of a mixture of t r i a c e t i n and a l c o h o l . C e l l u l o s e a c e t a t e was added t o the mixture to i n c r e a s e i t s v i s c o s i t y and a dye t o c o l o r i t f o r the q u a l i t y c o n t r o l purposes. This mixture, a weak s o l v e n t by i t s e l f , produced an extremely strong and r e l i a b l e bond of the membrane o v e r l a p s . The composition of t h i s sealant mixture was:


200

SYNTHETIC


Triacetin 94 1-Propanol 6* C e l l u l o s e acetate (E 398 - 10) 3 Red commercial dye 1

MEMBRANES:

HF

AND

UF

USES

p a r t s by volume p a r t s by volume g per 100 ml of t r i a c e t i n g per l i t e r of mix.

The bond obtained u s i n g t h i s sealant was found t o be e f f e c t i v e w i t h both wet and d r y membranes. F u r t h e r , t e n s i l e t e s t s showed that the bond was a t l e a s t as strong as the membrane i t s e l f . Most important, the bonding took p l a c e i n s t a n t a n e o u s l y a t ambient temperatures. No c u r i n g or s e t t i n g time i s r e q u i r e d . Hence, t h i s bonding method was found t o be i d e a l l y s u i t e d f o r the automatic and continuous winding of membrane elements. Pressure adhesive tape was used f o r s e a l i n g membrane winding edges and a f f i x i n g same to the supporting tube. Structural Materials As noted above, e x t e r n a l l y wound t u b u l a r membrane elements are f a b r i c a t e d p r i m a r i l y of extruded ABS tubing ( n a t u r a l ) , c e l l u l o s i c or blend membranes and dacron paper. The c a r t r i d g e assembly designed t o house the membrane elements and provide f o r the u n i form d i s t r i b u t i o n / f l o w of feed stock i s f a b r i c a t e d of extruded t h i n w a l l e d p o l y s t y r e n e headers. Pressure v e s s e l s were f a b r i c a t e d e i t h e r by u s i n g epoxy coated s t e e l pipe or f i b e r g l a s s v e s s e l s . H e l i c a l Winding Process Fabrication/assembly of e x t e r n a l l y wound t u b u l a r membrane elements i s accomplished by s p e c i a l l y designed equipment that simultaneously and c o n t i n u o u s l y winds, i n h e l i c a l f a s h i o n , i n f i n i t e lengths of membrane and backing m a t e r i a l s t r i p s onto p r e f a b r i c a t e d t u b u l a r support s t r u c t u r e s . Membrane s t r i p winding overlaps are solvent bonded during the winding process. A s u c c e s s f u l method f o r a c h i e v i n g t h i s motion i s based on the use of three d r i v i n g r o l l e r s e q u a l l y spaced on the circumference of the support tube. In o p e r a t i o n such r o l l e r s are i n compressive contact w i t h the surface of the supporting tube and p o s i t i o n e d a t an angle t o i t s a x i s . The r o l l e r s are d r i v e n by a s i n g l e motor and thus r o t a t e a t i d e n t i c a l speeds. This arrangement imparts a p r e c i s e h e l i c a l motion t o the element support tubing w i t h respect to the s t a t i o n a r y feeding spools. To maintain a constant h e l i x angle, s y n c h r o n i z a t i o n of r o t a r y and l i n e a r motions i s e s s e n t i a l . A l s o , the determination and use of backing m a t e r i a l s and membrane s t r i p s of proper width i s important i n o p t i m i z i n g the e f f e c t i v e membrane surface area f o r a given support tubing nominal diameter. The geometrical r e l a t i o n ships between these widths and the h e l i x angle are given i n F i g . 4. Here, the h e l i x angle i s denoted by a, d i s the diameter of the



(a)

Backing m a t e r i a l

Figure 4. Winding geometry



202

SYNTHETIC

MEMBRANES:

H F AND U F

USES

supporting tube ( i t i s a l s o the nominal diameter of the element), and c i s the amount of membrane overlap ( u s u a l l y 0.062 t o 0.125 in.). I n p r a c t i c e , the h e l i x angle was s e t i n the range of 35 45°. Another important f a c t o r i n the winding o p e r a t i o n i s t e n s i o n a p p l i e d t o the backing m a t e r i a l and t o the membrane s t r i p . Tension i s needed t o i n s u r e smooth w r i n k l e - f r e e wound surfaces and t o prov i d e the necessary pressure between membrane overlaps t o o b t a i n proper ponding. A minimum t e n s i o n of about 3 l b / i n i s r e q u i r e d f o r winding the backing m a t e r i a l , w h i l e the optimal t e n s i o n f o r membrane s t r i p s amounted t o 1 l b / i n . Winding machinery comprises: (1) a d r i v e mechanism t o provide means f o r imparting simultaneous r o t a r y and l i n e a r motion t o support s t r u c t u r e s i n a continuous manner, (2) membrane and backing m a t e r i a l feeder c a r t r i d g e s , (3) a sealant a p p l i c a t o r assembly, (4) electromechanical c o n t r o l s , (5) cut o f f / s e p a r a t i o n t o o l i n g , and (6) completed element handling equipment. Modular

Assemblies

A modular assembly housing e x t e r n a l l y wound t u b u l a r membrane elements may be d e f i n e d as a pressure v e s s e l w i t h i n which a r e assembled a m u l t i p l i c i t y of i n d i v i d u a l elements, means f o r connect i n g and s e a l i n g s a i d elements t o common headers and a feed stock d i s t r i b u t i o n system that provides f o r adequate feed f l o w across membrane s u r f a c e s . In the development and design of modular assemblies^ housing a m u l t i p l i c i t y of e x t e r n a l l y wound t u b u l a r membrane elements, the f o l l o w i n g f a c t o r s were considered: e f f e c t i v e n e s s of element packing arrangements and d e n s i t y , feed stock d i s t r i b u t i o n p a t t e r n s f o r c o n t r o l l e d and uniform feed f l o w across membrane s u r f a c e s , s e a l i n g r e l i a b i l i t y of modular sub-assemblies, o v e r a l l system r e l i a b i l i t y , module s e r v i c e a b i l i t y and ease of maintenance, system p r o d u c t i b i l i t y , and economic v i a b i l i t y . In u t i l i z a t i o n of e x t e r n a l l y wound t u b u l a r membrane elements i n modular assemblies f o r conventional systems o p e r a t i o n s , that i s , s e l e c t i v e s e p a r a t i o n v i a the c i r c u l a t i o n of p r e s s u r i z e d feed across membrane s u r f a c e s , flow guide tubes were found t o be e s s e n t i a l f o r the proper d i s t r i b u t i o n and c o n t r o l of feed flow. This was achieved s i n g u l a r l y by the use of i n d i v i d u a l element shrouds or flow tubes c r e a t i n g an annular gap through which feed stock was c i r c u l a t e d across membrane s u r f a c e s . A r e p r e s e n t a t i v e multi-element modular assembly i s depicted i n F i g . 2. I n t h i s design the module comprises three major components: • 36 membrane element assemblies • flow guide tube c a r t r i d g e assembly • 5 i n . diameter 12 f t . long pressure v e s s e l .


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A N D WOJCIK


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Rotary Modules Conventional reverse osmosis systems are g e n e r a l l y designed to operate by p r e s s u r i z i n g raw feed f l u i d s to r e q u i r e d operating pressures and c i r c u l a t i n g s a i d f l u i d s across membrane s u r f a c e s . To meet the operating requirements of the reverse osmosis process, a pumping system i s commonly used t o p r e s s u r i z e and c i r c u l a t e feed f l u i d s a t s u f f i c i e n t v e l o c i t i e s to maintain the d e s i r e d turbulence and t o provide p r e s s u r i z e d make-up f l u i d t o r e p l a c e withdrawn permeate and concentrate f l u i d s . The above approach i s o f t e n uneconomical and energy consuming s i n c e i n most cases s u b s t a n t i a l amounts of p r e s s u r i z e d f l u i d are r e q u i r e d t o maintain the d e s i r e d t u r b u l e n t flow. A d d i t i o n a l l y , i n treatment of c e r t a i n f l u i d s c o n t a i n i n g c o l l o i d a l and p a r t i c u l a t e matter, t u r b u l e n t flow of the raw f l u i d does not always accomplish the c l e a n i n g a c t i o n necessary to keep the membrane a c t i v e surface f r e e of f o u l i n g d e p o s i t s . A unique and improved method which s u b s t a n t i a l l y reduces the r e q u i r e d amount of p r e s s u r i z e d f l u i d flow has been developed by U n i v e r s a l Water Corporation. I n t h i s approach the pumping system i s p r i m a r i l y employed t o p r e s s u r i z e the raw f l u i d and a r o t a b l e assembly c a r r y i n g membrane elements i s used t o provide turbulence over the membrane s u r f a c e s . This approach separates the f u n c t i o n s of p r e s s u r i z a t i o n and feed f l u i d r e c i r c u l a t i o n . Thus, the pumping system needs t o p r e s s u r i z e and pump only the volume of feed stock necessary t o make up f o r the separated permeate w h i l e r o t a t i o n of the membrane element assembly provides the d e s i r e d turbulence. A d d i t i o n a l l y , and more s p e c i f i c a l l y i n batch processing systems, p r e s s u r i z a t i o n can be achieved by means other than a pump. In essence,a r o t a r y system comprises a pressure v e s s e l cont a i n i n g a r o t a b l e assembly c a r r y i n g membrane elements, means f o r p r e s s u r i z i n g the f l u i d feed, and means f o r r o t a t i n g the membraneelement assembly. A conceptual r e n d i t i o n of a r o t a r y module i s shown i n F i g . 3, and a flow schematic of a r o t a r y system i s shown i n F i g . 5. Main advantages of the r o t a r y approach i n c l u d e : • reduced energy consumption • continuous by-batch operation convenient f o r food processing • minimal exposure of t r e a t e d f l u i d s to pumping system, pressure f l u c t u a t i o n s and contamination • reduced c l e a n i n g and maintenance costs • high s u i t a b i l i t y f o r maximum r e c o v e r i e s and e f f i c i e n t c o n c e n t r a t i o n of t r e a t e d f l u i d r e l a t i v e l y uniform c o n c e n t r a t i o n of feed f l u i d s w i t h i n modules • s u i t a b i l i t y f o r use w i t h f l u i d s c o n t a i n i n g p a r t i c u l a t e and c o l l o i d a l matter. • l i m i t e d exposure of t r e a t e d f l u i d s t o contamination.



Control Box

Electric Motor

Figure 5.

Shutoff Valve

Pump

Pressure Regulator

Flow diagram for rotary module

Accumulator

7N

P r e s s u r e Gage

Module

Dump valve

V V

Tank

EH


> d

w

w >

3 w

H w H

4^

to o

12.

MANJIKIAN

AND WOJCIK


205

The r o t a r y concept makes p o s s i b l e the design of modular assemblies which would t r u l y permit the i n s i t u c l e a n i n g of membranes during operation by simply changing the d i r e c t i o n and r a t e of r o t a t i o n s .


Areas of A p p l i c a t i o n R.O. systems u t i l i z i n g e x t e r n a l l y wound t u b u l a r membrane e l e ment i n modular assemblies have been used i n the d e s a l i n a t i o n of b r a c k i s h and sea waters, the treatment and/or concentration of i n d u s t r i a l waste waters, the separation/concentration of f l u i d food, pharmaceuticals and chemical s o l u t i o n s , and the manufacture of water p u r i f i e r s f o r domestic use. G e n e r a l l y , e x t e r n a l l y wound t u b u l a r membrane systems have been found t o be h i g h l y s u i t a b l e f o r u l t r a f i l t r a t i o n a p p l i c a t i o n s i n the processing i n d u s t r y and i n water p o l l u t i o n c o n t r o l a p p l i c a t i o n s . More s p e c i f i c a l l y , these systems, whether operated i n the conventional mode o r as r o t a r y u n i t s have been s u c c e s s f u l l y u t i l i z e d i n a p p l i c a t i o n s such as the recovery of p r o t e i n and l a c tose from cheese whey^ separation of fermentation products, conc e n t r a t i o n of f l u i d s foods and j u i c e s , manually operable sea water d e s a l i n a t o r s , recovery of s t a r c h from potato processing f l u i d s , and processing/separation of pharmaceutical and chemical mixtures. RECEIVED

December 4, 1980.


Synthetic Membranes: Volume II - American Chemical Society

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