Synthetic Membranes: Volume I - American Chemical Society

1 The Loeb-Sourirajan Membrane: How It Came About SIDNEY

LOEB

Downloaded by BOSTON UNIV on October 9, 2013 | http://pubs.acs.org Publication Date: May 21, 1981 | doi: 10.1021/bk-1981-0153.ch001

Chemical Engineering Department, Ben-Gurion University of the Negev, Beersheva, Israel

In the early 1950's Professor Samuel Yuster at the Univer s i t y of California, Los Angeles (UCLA) conceived the idea of using the Gibbs adsorption equation as a guideline to find tech niques for producing fresh water from brines (1,2). The Gibbs equation i s given by: U =

-(1/νRT)(əσ/ə1na)T,Ar

(1)

where U is the adsorption of solute per unit area of surface, ν is the number of ions into which the electrolyte can dissociate, R is the gas constant, Τ is the absolute temperature, σ is the surface tension of the solution, a is the activity of the solute, and Ar is the area of the surface of the solution. According to this equation, brines in contact with air or other hydrophobic surfaces, will have a layer of relatively pure water, 3 or 4 Ang stroms thick, adjacent to the interface. Therefore i t should be possible to 'skim off' this fresh water, and in fact the project was called "Sea Water Demineralization by the 'Surface-Skimming' Process" until 1960. After funding by the State of California began in the mid50s, efforts were made to skim fresh water, first with fine capil lary tubes and second with bubble generation to transport the (hopefully) water-enriched solution surrounding the bubbles.Both efforts failed. I. S h i f t t o Reverse Osmosis - Discovery o f the Semipermeability of Cellulose Acetate. The f i r s t success at UCLA was r e p o r t e d i n 1958 (1^,2). A f l a t p l a s t i c f i l m , supported by a porous p l a t e , was use3". The f i l m was p r e s s u r i z e d by a s a l t s o l u t i o n such that water permea t i o n could occur by v i r t u e o f the pressure drop across the f i l m and a more concentrated b r i n e c o u l d be l e f t behind. T h i s was

0097-615 6 / 8 1 / 0 1 5 3-0001$05.00/ 0 © 1981 American Chemical Society

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

2

SYNTHETIC

MEMBRANES:

DESALINATION

reverse osmosis to a l l i n t e n t s and purposes. Pressure was o b t a i n e d by a hand-operated h y d r a u l i c pump, and t h i s was adequate c o n s i d e r i n g the permeation r a t e s that were o b t a i n e d . A commercially a v a i l a b l e c e l l u l o s e acetate f i l m which we would now d e s c r i b e as homogeneous or i s o t r o p i c , gave the r e s u l t s shown i n Row 2 o f Table I . The v o l u m e t r i c permeation r a t e o f water p e r u n i t membrane a r e a , c a l l e d the water permeation f l u x J 3 / 2 d a y , and the water permeation c o n s t a n t , A , m / m day atm were both very low, but a s a l t r e j e c t i o n o f 94 percent was o b tained. We d e f i n e : 3

1 > m


J

x

2

m

= A(AP - An)

(2)

but say that f o r our purposes: j

i

= ( P - n)

(3)

A

where AP and All are the h y d r a u l i c and osmotic pressure d i f f e r e n ces across the w a l l o f the membrane, P and It are the h y d r a u l i c and osmotic pressures on the feed b r i n e . Also:

Sa«

re]

ec io„. * - UOO, (. t

SEffiTSj

»>

S o u r i r a j a n took a few m i l l i l i t e r s o f d e s a l i n i z e d water ( c o l l e c t e d over a p e r i o d o f a few days i n the 15.5 cm c e l l ) , to the home o f Professor Y u s t e r , by then t e r m i n a l l y i l l . Neverthel e s s he e x c i t e d l y got out o f bed and p r e d i c t e d ( c o r r e c t l y ) that i f i t c o u l d be done with a few m i l l i l i t e r s i t could be done with a million gallons. (This anecdote was t o l d to me by someone who was p r e s e n t , a r e l a t i v e o f S h u s t e r ' s ) . Unbeknownst to S o u r i r a j a n , Breton and Reid working at the U n i v e r s i t y o f F l o r i d a under O f f i c e o f S a l i n e Water sponsorship, a l s o found that c e l l u l o s e acetate i s semipermeable to sea water e l e c t r o l y t e s (3, 4 ) . Comparative r e s u l t s o f Breton and Reid are shown i n Row 1 o f Table I . I t can be seen that the water permeat i o n constant i s c o n s i d e r a b l y h i g h e r than that o f S o u r i r a j a n . T h i s d i f f e r e n c e i s l a r g e l y accounted f o r by the d i f f e r e n c e i n thickness o f the homogeneous membranes i n v o l v e d , such that the product o f water permeation constant and membrane thickness i s about the same f o r both membranes. The constant a r i s e s from the d i f f u s i o n model o f permeation i n which: 2

A ^ D j / ( E f f e c t i v e membrane thickness)

(5)

where i s d i f f u s i v i t y o f the permeate i n the membrane. We see then t h a t with homogeneous membranes, f o r which the e f f e c t i v e membrane thickness i s a l s o X, the t o t a l t h i c k n e s s , AX i s p r o p o r tional to ^nbrane d i f f u s i v i t y .



2

L-S h e a t e d t o 80 ° C

Asymmetric

S & S heated to? ° C

Asymmetric

DP

Homogeneous

Morphology Fabricator B - Breton DP - Du P o n t S and S S c h l e i c h e r and Schuell L-S Loeb and Sourirajan Homogeneous B 43% - 6

=100

100

39. 8%

X

% not known

% not known 30

>

microns

a

given

(2) To c o n v e r t t o g a l / f t ^ d a y p s i m u l t i p l y by 5/3

4%

Sea water

3.5%

Sea water

3.7%

NaCl

not

%

Type o f % feed b r i n e acetylation s o l u t e concentration Total thickness

(1) To c o n v e r t t o g a l / f t d a y m u l t i p l y b y 24.5

L & S-Ref.ll p.127

L & S - Ref.ll p. 125

Y, S & B Ref.l,p.45

B - Ref.3,p.21

B - Breton R - Reid Y - Yuster S - Sourirajan Be - B e r n s t e i n L - Loeb

Investigator

I

-ft ),

given

= 29 P-V=73

tr

P = 102

P =» 102 = 25

P-tT= 55

P = 85 ^ - 30

not

atmospheres

(P

Pressures, Hydraulic, P Osmotic, Net d r i v i n g

2

given

0.35

0.073

0.0013

not

l ( N o t e 1) m3 m day

J

Water p e r meation flux,

(48)(10)"4

(9.5)(10)-4

(0.24)(10)~

(1.2)(10)-4

3

4

m m2 day atm

Water permeation constant, A (Note 2)

PERFORMANCE OF HOMOGENEOUS AND ASYMMETRIC CELLULOSE ACETATE MEMBRANES

T A B L E


(4800)(10)-4

(950X10)-*

(7.2)(10)-4

(7.2)(10)~4

3

ra m i c r o n m2 day atm

Constant times t o t a l thickness A

99

92

94

99+

%

Solute rejection

4

SYNTHETIC

MEMBRANES:

DESALINATION

I t was recognized by both .the F l o r i d a and UCLA groups that economic u t i l i z a t i o n o f reverse osmosis depended on o b t a i n i n g a great increase i n flux(and water permeation constant) without s e r i o u s l o s s i n e l e c t r o l y t e r e j e c t i o n p r o p e r t i e s . I t was also recognized t h a t one path to i n c r e a s e d f l u x l a y i n decreased membrane t h i c k n e s s .


I I . T e s t i n g o f M a t e r i a l s Other than C e l l u l o s e Acetate. In the summer o f 1958 S o u r i r a j a n accepted me as a p a r t n e r . In the next s i x months a nuiriber o f p l a s t i c fiims were tested(5^,6) but none were equal to c e l l u l o s e a c e t a t e . Among other negative r e s u l t s was an attempt to increase f l u x by h e a t i n g o f the membrane.The hope was that some permanent expansion could be induced and that such expansion would enlarge pores thus i n c r e a s i n g f l u x . U n f o r t u n a t e l y i t was found t h a t h e a t i n g c o n t r a c t e d the membrane. A number o f t e s t s were made with porous T e f l o n sheet. T e f l o n was chosen f o r i t s hydrophobic nature as r e q u i r e d by the Gibbs equation. A s e r i e s o f s i n t e r i n g experiments were made to f i n d just the r i g h t coirbination o f heat and pressure which would reduce the pores to the proper dimension as r e q u i r e d by the Gibbs equati o n . No such combination was found except two which gave a low l e v e l d e s a l i n a t i o n f o r a short p e r i o d . As a r e s u l t o f these t e s t s my own enthusiasm waned f o r f u r t h e r use o f the Gibbs adsorption equation as a primary g u i d e l i n e to membrane development. I I I . Tests With S c h l e i c h e r and S c h u e l l C e l l u l o s e Acetate Membranes. C e l l u l o s e acetate membranes were then reconsidered with emphasis on p o r o s i t y to increase f l u x . In 1959 we t e s t e d such porous membranes e x t e n s i v e l y ( 7 , 8 , 9 , 1 0 ) . These membranes , made i n Germany and marketed by the S c h l e i c h e r and S c h u e l l ( S § S) Co. o f Keene,N.H. ,were a c t u a l l y u l t r a f i l t r a t i o n membranes and only the " U l t r a f i n e , Superdense" grade was u s e f u l f o r u s . T h i s grade a l l e g e d l y contains pores o f 50 Angstroms o r l e s s . Nevertheless, as r e c e i v e d , the S § S membrane gave a very high f l u x and no desal i n a t i o n , as expected from an u l t r a f i l t r a t i o n membrane. The S § S membranes were immersed i n d i l u t e alcohol s o l u t i o n s during shipment and storage. The a l c o h o l could be replaced by water, but the menforane c o u l d not be allowed t o - d r y o r i t would shrink i n an i r r e v e r s i b l e manner to become a u s e l e s s membrane. R e c a l l i n g the unsuccessful t e s t s o f S e c t i o n II we heated the S § S membranes under water to temperatures i n the order o f 80 9 0 ° C . By t h i s means the d e s a l i n i z i n g c a p a b i l i t y o f the membrane could be i n c r e a s e d p r o p o r t i o n a t e l y to the increase i n h e a t i n g temperatures, i . e . , the membrane c o u l d be t a i l o r e d to the desal i n i z i n g job at hand. The water permeation flux was an inverse function o f the heating temperature. A curious problem arose i n the t e s t i n g o f the S § S membrane. Tf

!T



1.

LOEB

Loeb-Sourirajan

Membrane

5

The r e s u l t s with the same membrane were sometimes good and sometimes very b a d , i . e . , r e j e c t i o n might be q u i t e good the f i r s t time a membrane would be mounted i n the t e s t c e l l , bad the next t i m e , good the next two times, e t c . N a t u r a l l y a leak was suspected and n a t u r a l l y i t was attempted to f i x the blame on Ed S e l o v e r , who made the c e l l . However, i t was f i n a l l y r e a l i z e d t h a t the incidence o f f a i l u r e s about e q u a l l e d the incidence o f successes with the randomness o f r e s u l t s obtained when a coin i s f l i p n e d , and from there i t was c o r r e c t l y p o s t u l a t e d t h a t when one s i d e o f the membrane faced the b r i n e , r e s u l t s would be d i f f e r e n t from those when the o t h e r s i d e was against the b r i n e . The membrane d i d indeed have a "rough" s i d e and a "smooth" s i d e and i t was the rough s i d e which had t o face the b r i n e . This was our f i r s t encounter with membrane asymmetry o r a n i s o t r o p y . Comparative r e s u l t s with the S c h l e i c h e r and S c h u e l l membrane are shown i n the t h i r d row o f Table 1(11). The flux and the water permeation constant i n c r e a s e d by a f a c t o r o f 40 over the previous r e s u l t s . Furthermore AA, the product o f water permeation constant and t o t a l membrane thickness i n c r e a s e d by a f a c t o r o f 130. The most obvious explanation f o r these r e s u l t s i s t h a t the e f f e c t i v e membrane thickness was much l e s s than the t o t a l membrane t h i c k n e s s . Thus the concept o f membrane asymmetry was also supported by a comparison o f S c h l e i c h e r and Schuell membrane performance with that o f homogeneous membranes. The study o f the S § S membrane p r o v i d e d s e v e r a l important steps i n the development o f the technique f o r f a b r i c a t i o n o f the Loebv- S o u r i r a j a n membrane, v i z . , s t o r a g e under water, h e a t i n g under water t o an appropriate temperature to t a i l o r membrane performance p r o p e r t i e s , and f i n a l l y r e c o g n i t i o n that membrane asymmetry may p l a y an important r o l e i n the obtainment o f a s u f f i c i e n t l y l a r g e flux f o r economic o p e r a t i o n s . Such r e c o g n i t i o n was t h r u s t upon us by the experimental r e s u l t s . It would be n i c e to say that we made a n a l y t i c a l c a l c u l a t i o n s which i n d i c a t e d a p r i o r i the n e c e s s i t y f o r a very t h i n s k i n surmounting a porous s u b s t r u c t u r e , but that i s n ' t the way i t happened. IV. The Work o f Dobry. The S § S f i l m represented a quantum jump i n membrane p e r f o r mance. However,it s t i l l wasn't good enough to meet our g o a l . Spec i f i c a l l y we c o u l d not produce potable water, l e s s than 500 ppm s a l t , from sea water i n one pass through the S § S f i l m , n o matter how high we heated the f i l m . Therefore we undertook to make our own membranes, with the f o l l o w i n g g u i d e l i n e s ( 1 1 ) : 1) c e l l u l o s e acetate would be used as the f i l m m a t r i x ; 2) acetone or o t h e r solvent would be used i n the c a s t i n g s o l u t i o n ; 3) some means f o r making the f i l m nermeable to water would be employed. As a r e s u l t o f a l i t e r a t u r e search i t appeared t h a t a t e c h nique described i n 1936 by Dobry(12) , a French i n v e s t i g a t o r , m i g h t


6

SYNTHETIC

MEMBRANES:

DESALINATION

meet a l l three o f the above g u i d e l i n e s . She d i s s o l v e d incompletely a c e t y l a t e d c e l l u l o s e acetate ( i . e . , not a l l hydroxyl groups had been r e p l a c e d by a c e t y l groups) i n an aqueous s o l u t i o n o f a p e r chlorate such as magnesium p e r c h l o r a t e , M g ( C 1 0 . ) 2 « S h e then spread the s o l u t i o n i n a t h i n f i l m on a glass p l a t e and plunged i t under water. The Mg(C10 ) d i f f u s e d i n t o the water l e a v i n g a porous f i l m o f c e l l u l o s e a c e t a t e . (Mme Ducleaux, nee Dobry,has been informed o f t h i s symposium. She conveys f e l i c i t a t i o n s and also h e r best wishes to a i l the p a r t i c i p a n t s i n the symposium(13)) : 4

2


V . F a b r i c a t i o n Technique f o r the L o e b - S o u r i r a j a n Membrane. We followed the i n s t r u c t i o n s o f Dobry, making up s o l u t i o n s c o n t a i n i n g 4 , 8 , and 10 percent o f c e l l u l o s e acetate(Eastman) i n saturated aqueous magnesium p e r c h l o r a t e s o l u t i o n s ( 1 4 ) . Membranes made by immersion o f such s o l u t i o n s i n water were f a r too porous for our purposes; i . e . no d e s a l i n a t i o n was obtained. It was bel i e v e d that the r a t i o o f c e l l u l o s e acetate to M g ( C 1 0 ) had to be i n c r e a s e d , but above 10% o f c e l l u l o s e acetate i n the s a t u r a t e d s o l u t i o n the c a s t i n g s o l u t i o n v i s c o s i t y was too h i g h . As an a l t e r native the M g ( C 1 0 ) c o u l d be reduced by using an undersaturated perchlorate s o l u t i o n , but then the c e l l u l o s e acetate was not s o l u b l e . The s o l u t i o n to t h i s problem, suggested by L l o y d Graham, a graduate student on the p r o j e c t , was p a r t i a l l y to replace the Mg(C10^) s o l u t i o n with acetone, a s o l v e n t f o r c e l l u l o s e a c e t a t e . 4

4

2

2

?

The * r e s u l t i n g 4-component s o l u t i o n was j u s t what was needed. Since the Mg(ClC> J need no longer p l a y a s o l v e n t r o l e , i t s conc e n t r a t i o n c o u l d be optimized f o r i t s r o l e as "pore-producing agent" o r "flux-enhancer" depending uoon whether one thought o f i t from the standpoint o f cause o r e f f e c t . A t y p i c a l l y good c a s t ing s o l u t i o n contained c e l l u l o s e a c e t a t e , acetone,water, and magnesium p e r c h l o r a t e i n the weight percentages 2 2 . 2 , 6 6 . 7 , 1 0 . 0 and 1-1 (15). Thus f i n a l l y the magnesium p e r c h l o r a t e was only a small p a r t o f the t o t a l c a s t i n g mix, but n e i t h e r i t nor water c o u l d be e l i m i n a t e d without a d i s a s t r o u s reduction i n membrane performance. Membranes could now be cast with appropriate porous propert i e s such t h a t the p r e v i o u s l y mentioned " t a i l o r i n g " o p e r a t i o n c o u l d be c a r r i e d o u t , i . e . , the underwater h e a t i n g o f the membrane t o a temperature which would provide adequate d e s a l i n a t i o n . For best r e s u l t s two other features were found to be u s e f u l , a s discussed i n the d e t a i l e d f a b r i c a t i o n i n s t r u c t i o n s o f Reference 15. F i r s t , t h e c a s t i n g was c a r r i e d out with a l l components, chemical and mechanical,at a low temperature, 0 ° to - 1 0 ° C ; Second, the as-cast f i l m had to be immersed i n i c e water w i t h i n a short time a f t e r c a s t i n g . As with the modified S § S membrane, the L-S membrane was found to be asymmetric. The s i d e o f the membrane away from the c a s t i n g surface had to be i n contact with the feed b r i n e during service. The performance o f an L - S membrane heated to 80°C i s shown 4

2


1.

LOEB

Loeb-Sourirajan

Membrane

7


i n the l a s t row o f Table I . The improvement i n water permeation constant over the modified S and S membrane i s by a f a c t o r o f f i v e and would be c o n s i d e r a b l y more i f the L - S membrane were f a b r i c a t e d t o give the same r e j e c t i o n , 92%, as s t a t e d f o r the S and S membrane. For the s t a t e d r e j e c t i o n o f 99 percent i t i s also i n s t r u c t i v e to compare the L - S membrane with the p r e v i o u s l y discussed membranes by examining the l a s t column o f Table I . The f u r t h e r dramatic increase o f AX, the product o f water permeation constant and t o t a l membrane t h i c k n e s s , again supports the asymmet r y p o s t u l a t e (See Section I I I ) , and can be e x p l a i n e d by a r a t i o o f e f f e c t i v e to t o t a l membrane thickness c o n s i d e r a b l y lower even than t h a t with the S and S membrane. V I . Summary. In r e t r o s p e c t ; ( a vantage p o i n t from which accomplished research f r e q u e n t l y appears as a marvel o f l o g i c a l l y s e q u e n t i a l steps) the development o f the L o e b - S o u r i r a j a n membrane can be a t t r i b u t e d t o : a determination to apply the Gibbs adsorption equation to d e s a l i n a t i o n ; the d i s c o v e r y o f the semipermeability o f c e l l u l o s e a c e t a t e ; the p r i o r existence o f a. c e l l u l o s e acetate u l t r a f i l t e r which, by a novel heat treatment c o u l d be made i n t o an asymmetric reverse osmosis membrane; the r e c o g n i t i o n o f t h i s asymmetry and i t s importance i n o b t a i n i n g a f l u x g r e a t l y i n creased over that o f p r e v i o u s l y - t e s t e d membranes, which were homogeneous; the d i s c o v e r y by an e a r l i e r i n v e s t i g a t o r o f the s p e c i a l p r o p e r t i e s o f aqueous p e r c h l o r a t e s o l u t i o n s v i s - a - v i s incompletely a c e t y l a t e d c e l l u l o s e a c e t a t e ; and f i n a l l y u t i l i z a t i o n of a l l t h i s hard-won m a t e r i a l , t o g e t h e r with f u r t h e r novel modif i c a t i o n s , to produce a working reverse osmosis membrane. VII.

Acknowledgements

To the people and l e g i s l a t o r s o f the State o f C a l i f o r n i a who have had the patience and f o r e s i g h t to support t h i s and o t h e r d e s a l i n a t i o n p r o j e c t s at the U n i v e r s i t y from the middle 1950*s u n t i l now. To Emeritus P r o f e s s o r E v e r e t t Howe o f the Berkeley Campus. P r o f e s s o r Howe was a very e f f e c t i v e statewide c o o r d i n a t o r o f U n i v e r s i t y D e s a l i n a t i o n Research, a job which r e q u i r e d s k i l l f u l l i a i s o n between the l e g i s l a t u r e and the research workers, i n a d d i t i o n t o a t e c h n o l o g i c a l purview o f the various p r o j e c t s . To P r o f e s s o r L l e w e l l y n B o e l t e r , deceased, who had o v e r a l l cognizance o f the UCLA e f f o r t , as Dean o f E n g i n e e r i n g , and who also c o n t r i b u t e d , i n my o p i n i o n , by v i r t u e o f h i s q u a l i t i e s as a r e a l human b e i n g . To Edward S e l o v e r who has been i n v o l v e d with mechanical component design and f a b r i c a t i o n at UCLA s i n c e the beginning o f the p r o j e c t . I t i s only a f t e r I have been deprived o f h i s work that I have r e a l i z e d how much he c o n t r i b u t e d to the p r o j e c t . He s t i l l does.


8

SYNTHETIC

MEMBRANES:

DESALINATION

The above acknowledgements cover the p e r i o d from the i n c e p t i o n o f the p r o j e c t u n t i l 1960. Thus subsequent important c o n t r i butions from UCLA such as that o f M a n j i k i a n , and the leadership o f McCutchan a f t e r 1966,are not discussed nor the tremendous body o f knowledge l a t e r c o n t r i b u t e d by the ever-widening reverse osmosis community, the United States p a r t o f which was l a r g e l y e s t a b l i s h e d by the O f f i c e of S a l i n e Water, U . S , Dept. o f the I n terior.


VIII.

2.

Literature Cited

1. Yuster,S.T., Sourirajan,S., Bernstein,K., "Sea Water Demineralization by the 'Surface Skimming' Process" University of California (UCLA), Dept. of Engineering, March, 1958,Rept.58-26. Sourirajan, S . , "Sea Water Demineralization by the'Surface Skimming'Process",UCLA Dept. of Engineering, May,1958, Sea Water Research Quarterly Progress Repts. 58-46, 48, 50, 51 (Collected in one report). 3. B r e t o n , E . J . J r . , "Water and Ion Flow Through Imperfect Osmotic Membranes", Office of Saline Water,U.S.Dept. of the Interior, April,1957,Res.&Dev.Prog.Rept.16. 4. Reid,C.E.,Breton.E.J.,"Water and Ion Flow Across Cellulosic Membranes", J . Appl.Polymer S c i . , 1959, I (Issue No.2),133-143. 5. Sourirajan,S., "Sea Water Demineralization by the 'Surface Skimming' Process", UCLA Dept. of Engineering,June-Aug,1958, Sea Water Research Quarterly Progress Rept. 58-65. 6. Loeb,S., Sourirajan,S., "Sea Water Demineralization by the 'Surface Skimming'Process", UCLA,Dept.of Engineering,Nov,1958, Sea Water Research Quarterly Progress Rept. 59-3. Loeb,S.,"Sea Water Demineralization by the 'Surface Skimming' Process, UCLA Dept. of Engineering, Sea Water Research, Quarterly Progress Repts. (OPR): 7. Dec, 1958 - Feb,1959 OPR 59-28. 8. March-May,1959, QPR 59-46 . 9. July-Sept, 1959, QPR 60-5. 10. Loeb,S., "Characteristics of Porous Acetyl Cellulose Membranes for Pressure Desalination of Dilute Sodium Chloride Solution", Master of Science Thesis,UCLA Dept. of Engineering,May, 1959. 11. Loeb,S., Sourirajan,S., "Sea Water Demineralization by Means of an Osmotic Membrane", American Chemical Society,Advances in Chemistry Series, ACS 38, 1963, 117-132 . 12. Dobry, A . , "Les Perchlorates Comme Solvants de l a Cellulose et de ses Derives",Bull. de l a Societe Chim. de France, 1936, 5 Serie,t.3,312-318. 13. Private Communication from Mme Ducleaux, 27 June, 1980. 14. Loeb,S., Graham,L., "Sea Water Demineralization by Means of a Semipermeable Membrane", UCLA Dept. of Engineering,Oct-Dec , 1959, Sea Water Research Quarterly Progress Report 60-26. e


1.

LOEB

Loeb-Sourirajan

Membrane

15. Loeb,S., Sourirajan,S., "Sea Water Demineralization by Means of a Semipermeable Membrane", UCLA Dept. of Engineering, July, 1960, Sea Water Research Rept. 60-60. December 4,

1980.


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Synthetic Membranes: Volume I - American Chemical Society

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