Reverse Osmosis Performance of Sulfonated Poly(2,6

process was about 60% in the mild and 65% in the severe conditions. From the yield of benzene produced in the mild and severe conditions, the ratio of reformillg pactiolis could have beell as shown in Table IV. From the yield of aromatics produced in the mild and severe conditions, the reactions as shown in Table V probably took place.

Drehman, L. E., Hepp, H. J. (to Phillips Petroleum Co.), u. s. Patent 3,258,503 (June 28, 1966). Engel, J. H., Waldly, R. W. (to Phillips Petroleum Co.), U. S. Patent 3,280,022 (Oct. 28, 1966). Haensel, V. (to Univ. oil Prod. C0.h u. S.Patent 2,911,451 (Nov. 3, 1959). Haensel, V., Addison, G. E., “Seventh World Petroleum Congress,” Vol. 4, pp. 113-23, Elsevier, New York, N. Y., 1967. Honeycutt, E. 111. (to Sun Oil Co.), U. S. Patent 3,070,637 (Dec. 25, 1962). Rlaslyanskii, G. Tu’., Barkan, S. A,, Int. Chem. Eng.,8 (Z), 218-20 (1969) \ - - - - I

literature Cited

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 9, 2015 | http://pubs.acs.org Publication Date: September 1, 1971 | doi: 10.1021/i360039a015

Ciapetta, F. G., Petro./Chenz. Eng., C19-C31, Rlay 1961. Coley, J. It., Evering, B. L., 111cCollum J. D. (to Standard Oil Co.), U. S. Patent 2,861,944 (Nov. 26, 1958). Connor, Jr., J. E., Ciapetta, F. G., Leum, L. N., Fowle, 111. J., Ind. Eng. Chem., 47 ( l ) , 152-6 (1955).

Nelson, W. L., Oil Gas J.,67 (5), 104-5 (1969). “Reforming,” Hydrocarbon Process., 47 (9), 155-62 (1968). Skraba, F. W. (to Phillips Petroleum Co.), U. S. Patent 3,121,676 (Feb. 1964). Smol’nik, Y. E., Bryanskaya, X. G., Vampol’skii, K . G., Shurba, A. S., Cherednichenko, G . I., Sobol, E. P., Khznz. Tckhnol. Topl. lVfaseZ, 13 (6), 10-12 (1968). 1~ECcIvi.ofor review September 9, 1970 ACCEPTEDMay 12, 1971

Reverse Osmosis Performance of Sulfonated Poly(2,6=dimethylphenylene Ether) Ion Exchange Membranes Shiro G. Kimura General Electric Corporate Research and Development, Schenectady, S.Y . 12301

Sulfonated poly(2,6-dimethylphenglene ether] cation exchange membranes show promise as reverse osmosis membranes, having from 8 to 10 times CIS high water permeability as homogeneous cellulose acetate at the same salt rejection levels for 1 % NaCl feeds. Membrane morphologies can b e varied to give u wide range of salt rejections and water permeabilities. Since the principal mechanism of salt rejection is Donnan exclusion, membrane performance is highly dependent on feed composition.

T h e r e exist, basically, two types of reverse osmosis membranes -solutioii-diff usion mcmbraiies with or Ivithout coupled flows and ion exchange membranes. 111 a solution-diffusion membrane, solvelit a i d solute pass through the membrane by first being dissolved in the membrane polymer aiid then diffusing across. Salt rejectioii occurs because solvent and solute solubilities and diffusion coefficients differ. Flow coupling exists when there are membrane imperfections of sufficient size to permit viscous flow and allow solute to be transported by drag fbrces. Cellulose acetate membranes are examples of solution-diff usion membranes. Ion exchange membranes are viscous flow xiiembranes which exclude salt by electrical forces. When ai1 ion eschaiige membrane is immersed in an electrolyte solution, there is a tendency for counterions to diffuse out into the solution and coions to diffuse from the solution into the memhraiie because of concentration differences betweeii the meinbralie aiid the surrouiiding solution. Thus a charge imbalaiice is created, and the membrane takes 011 n potential, the Doimaii poteiitial, which inhibik further coion upt,ake. -1 cation exchange membrane takes 011 a negative charge mid, thus, excludes anions. Since electroiieutrality must be maiiitniiied, coion rejection is equivalent to salt rejection. Sulfonated

poly(2,6-dimcthyl~)liciiylciic cthei,) mein1)raiies are of tliis type. 11IcKelvey et al. (1057, 1964) first iiitroduced the idea of usiiig Doiinnii rcjcctioii as a Iiasis for reverse omobi.;. Experimental Procedure

Sulfonated Poly(2,6-dimethylphenylene ether) Freparation. Poly(2,6-diniethylpheiiyleiic ether) wnb aulfoiiatrd using the procedure of Fox aiid Sheiiian (1966). U l ~ o i iwctioii i with chlorosulfonic acid ~ ~ o l \ ( 2 , 6 - d i m e t h ~ l ~ ) l i c i i yether) l~iic becomes:

r

1

wheie I may vary fiom 0 to 1. Complete sulfoiintioii, .r = 1, correspoiids to aii 1011 e\cliaiige capacity (IEC’) of 5.0 mcy “/gram of dry pols mer. Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 3, 1971

335

I

I

1

I

1

I

I

I

I

I

I

I

I

IEC

0

2.8-3.0

&

26-2.7 2.0-2.2

H

1

0

1

-

I

I

I

1

1

I

I

I

I

006

008

OD

012

014

016

018

020

022

1

002 004

I

i

L l

024

WATER PERMEABILITY,

Figure 1.

Stirred reverse osmosis cell

Figure 4. Sulfonated PPO membrane reverse osmosis performance

SINTERED METAL PaEssuRE PAD


PZRYEATE GUT PORT

UPPER

BLocy

/

Water content,

%

MEMBRANE

FEED FLU10 OU1

Porosity, or

yo of

=

wt water

wt water wt dry polymer

+

x

100

pore vol =

\ . , I

G ’ RING SEAL

LOWER BLOCK-’

vol water vol water vol polymer

+

Figure 2. Reverse osmosis cell-Gulf General Atomic Inc., as reproduced from advertising brochure

100

wt water

wt water Membrane Casting. Sfembralies were prepared by doctor blade casting from metliaiiol, methaiiol-chloroform, or metliaiiol-isol)rol)aiiol-chloroform solutioiis. These casting solutioiis were filtered through Flotroiiics porous silver filters and all mcmbraiie castiiig doiie in a laminar flow clean bench. Dilute casting solutiolis (2-1070 solids) were spread on a glass plate using a Gardiier film casting knife. The membranes were either air dried or dried under a pyres dish t o slow down the desolvatioii rate to preveirt orange peeling. The resultaiit membranes were generally clear, slightly yellowish films 0.1 to 1.0 mil i i i tliickiiess. Reverse Osmosis Test Apparatus. T w o different reverse osmosis system5 were used, with coiiceiitratioii boundary layer beiiig controlled i n the first system by the use of a s t i i x d cell and in the other by uaiiig a high flow velocity over the membrane. Figures 1 and 2 are drawings of these two cells, respectively. I3ot,li reverse osmosis systems were opeii-loop systems-Le., the feed lvas kept a t atmospheric pressure and the pump used to rreatc both pressure and flow (Figure 3). Water Content Measurements. Water content measurerneiits were performed by soaking a membrane in distilled water, blotting the surfaces to remove surface water, weighing the wet membrane, aud then drying the membrane aiid reweighiiig.

x

=

+ wt polymer/l.06

x

100

Results and Discussion

13ecaiise sulfoiia,ted ~~oly(2,6-dimetliylplienyleiieether) polymer is solvent castable, it caii be cast into membranes of any thickness aiid differciit polymer morphologies, yielding a wide range of water permeabilities and salt rejections. Figure 4 is a compilation of much of the reverse osmosis data availalile taken a t 800 psi for 1% NaC1. Pressure. Typical reverse osmosis performance as a fuiictioii of pressure is seen iii Figure 5. Both water and salt flux are h e a r with pressure to a t least 1200 psi, indicating 110 collapse in pore structure a t these pressures. M e m b r a n e Ion Exchange Capacity (IEC). T h e effects of I E C 011 membrane characteristics are two-fold. I E C , to a large esteiit, determines the percent pore volume, or porosity, of the membranes as well as the charge deiisity. For membraiies cast under identical conditions, the water content increases sharply with I E C as seen iii Figure 6. It should be not,ed, too, that percent pore volume caii vary widely for ail individual polymer depending 011 the castiiig solvent, with porosities iiicreasiiig with the percentage of

pi

400 S, 30-

- 50 MILROYAL SIMPLEX 164 m h

1300’iii

OR

PRESSURE, psi

MILROYAL MODEL A SIMPLEX 3 4 9Ph 2000 psi

Figure 3.

336

Reverse osmosis test systems

Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 3, 1971

Figure 5. pressure

Typical membrane performance as a function of

Table 1.

Effect of Solvent Composition on Pore Volume

I E C = 2.25 meq/g dry polymer

CHC13,

ION EXCHANGE CAPACITY,

pm

me9 H* POCrMER

Figure 6. Effect of IEC on water content for similarly cast membranes

,


0.28,

I

I

1

1

%

CHIOH,

%

Porosity, vol pore liquid vol wet membrane

0 10 30 50

100 90 70 50

57 56 54 50

33 33 0 0

I E C = 2.40 meq/g dry polymer 67 67 100 100

52 55 58 69

1

Table II. Dependence of Reverse Osmosis Performance on Solute Type

0.241

I E C = 2.04 meq/g dry polymer. Thickness g 0.2 mil (wet) Pressure = 800 psi

Membrane

MF-1 &IF-2 I

05 PoRoSITY,

Figure 7. meability

I

1

I

0.6 VOL PORE LIO. VOL. WET MEMBRANE

1

08

07

30r *

80

IEC -

I

I

I

1

300

60

3OL---L

Figure 8.

o

1

0 70

0 80

- - - A p l

0 40

I

I

0 50

0 60 VOL PORE LlOUlO PoRoSITY* VOL WET MEMBRANE

Effect of membrane porosity on salt rejection Feed is 1% N a C l a t 800 psi

gOl 80

60 w

YI

" S A L T REJECTION ESTIMATED FROM 1100 PSI DATA I

15 20 CHARGE DENSITY, me9 H'/cc

Figure 9.

NaCl h4gS04 LIgC12 XaC1 Na2S04

10,000 10,300 8,130 10 , 000 12 , 130

Water flux, gsfd

8 4 4 7 6

4 6 3 5 7

Rejection,

% 91 7 98 1 81 3 92 1 99 7

Effect of membrane porosity on water perFeed is 1 % N a C l a t 800 psi

Ow)

Feed

Concn., PPm

25 PORE VOLUME

30

Salt rejection as a function of charge density Feed is 1 % N a C l a t 800 psi

alcohol iri a dual solvent, tem. Ail iiidicatioll of this is seeii in Table I, which shows the effect of casting solution compositioii on 1)orosity for otherwise identically cast membraues. Porosity, in turn, has a strong effect oii hoth the w t c r permeability and the salt rejection as seeii in Figures 7 and 8, respectively. Water 1)ermeability jiicreascs r n pidly with i i i creasing porosity. The effect of porosity 011 salt rejection is less distinct. LIerteri et al. (1967) using the methods of Ilressiier (1965) aiid Dresstier aiid Kraus (1963) have tletcrmiiicti the effect of various membrane 1)arametcrsoii salt rejection. AIerteii coilcludes that, in the brackish water range for mcml)ralics with charge deiisit,ies of alq)rosimately 5 meq/cc, distribution coefficiciits are stroiigly depeiident on porosity a~itlrelatively indepeiident of charge density. Figure 8 shows the dependence of salt rcjectioii 011 porosity, and in Figure 9 the salt rejectioli dependence oii cliargc tleiisit'y is shown. If Nerteii is correct, t,heii Figure 8 nould consist of a single line as sliown. If there is R charge deiisity delielidelice, then there should be a family of parallel curves with one curve for each IEC. Although Figure 9 indicates a charge density dependence, the scatter in the data preclude more detailed analysis. Feed Composition. Eflect of Salt Type. Donnaii theory Iiredicts that for ion exchange membranes, salt rejection increases with decreasiiig couuterioii valence and increasing coioii valence. Thus, for a cation eschaiige membrane such as sulfonated ~)oly(2,6-dimetliyl~~he1iyle1~c Ether) membrane, one would expect t h a t salt rejection would increase in t,he following order: RIgCl? < SaC1, AIgS04 < Na2S04. Table I1 shows that this rule is inderd followed. ConcentraInd. Eng. Chem. Prod. Res. Develop., Vol. 10,

No. 3, 1971

337

Table 111.

Comparison of Membrane Performance with 1 % N a C l Feed a n d Webster Water Feed 1% N a C l


Rejection,

Webrter.__ water

Membrane

%

Flux, gal/ft2 d a y

R D C-I-A RDC-111-K RDC-111-AI JE-112-SA JE-104-S3

81 76 71 79

20.2 23.5 86.8 21.3

.

.

I

...

Na

Mg

Ca

72 57 48 61 74

92 82 64 79 93

95 89 65 82 96

tions of solute were chosen so that anion normalities were similar for each salt. There is a large water flus decrease for the N g 2 + salts indicating a decrease in pore volume due to partial association of the Mg2+ioiis and the membrane and a resultant decrease in swelling pressure. On the other hand, it has been found that for cellulose acetate, a solution-diffusion membrane, that, generally speaking, divalent ions are more strongly rejected than univalent ions-e.g., AIgC12 is more strongly rejected than NaCl (Reid and Breton, 1959). Mixed Feeds. T h e effect of anion composition on reverse osmosis performance was determined by measuring performance for NaCl-SaZSOd mixtures. As seeii in Figure 10 rejection increased linearly with increasing amounts of Na2S01. The effect of cation composition is less easily predicted since feed composition determines $e membrane counterion form. To determine this effect, reverse osmosis performance was noted as a function of XIgC12 conceiitration in NaCl solutions. Figure 11 shows these results. For the pure salt's, SaCl rejection is considerably higher

100

-7-J --- so; - -r T

T--

TDS No+

Total

Flux, gal/ft2 d a y

Dry thickness, mil

19.1 34.3 65.7 16.9 10.8

0.15 0.15 0.15 0.30 0.20

87

80 57 75 88

thaii that for MgC12. As small amounts of LlgCl2 are added to a NaCl solution, perfarmance changes abruptly. This is due to the conversion of membrane from the S a + form to the Mg2+ form since cation eschange membraiies arc much more selective to ,\Ig2+thaii N a + (Helfferich, 1962). As noted earlier, the Mg2+form is p a h l l y associated, and thus there is pore shrinkage accompaiiied hy lowered Doiinan potential. The dominant mode of salt rejectioii becomes solution-diff usion rather thaii Doniiaii esclusion as seen by the reversal of order--i.e., 1Ig2+ is more ntroiiglg rejected thaii Na+. There is also an accompanying water flus decrease, and this result is extremely important nheii consitleriiig the potential of the membrane with natiiral waters. Consider the following: a brackish water containing 10,000 ppm S a C l and 1000 ppm hIgC12 is treated with a membrane which had a measured salt rejection for pure 10,000 ppm of 80%. For the nlisture, however, thc S a C l rejection is 60% and the hlgCl2 rejection is 8501,. Thuq, the overall rejection is approximately 63%. Consider a second case iii which the feed is a high hardiiess, high sulfate brackish water. Such a water is Rebster water, which has the followiiig composition: S a + 130 ppm, 1\Ig2+80, Ca2+ 180, 8042-800, HCQ3- 300, and C1- 20. Table I11 shorn reverse osmosis with Kcbiiter water and pure 10,000 ppm NaCl as a coml)arisoii. In each case there is a substantial Ka+ rejection decrcase as coml)ared to 10,000 ppm NaCl; however, okviiig to thc increased divalent ion rejectioii aiid the large amount of divalent ioiis, the overall rejection remains high. Effect of Salt Concentration. T h e Donnan p o t e n t i d , aiid hence the ioii esclusion, is highly depciident on the relatioiiship bet,weeii the membrane charge density and the solutioil ioii coiiceiitratioii. I t increases with increasing meml)raiie counterioii and decreasing solution couiitcrioii coiicentratioiis. Figure 12 shows a slight change of salt rejection with concentration until concentrations of the same order of magrii-

100,

0

~

_

_

I

-

I

~

T__-

i?: Y Y

I

e

1 -

K

10-3

L

10-2 10-1 FEED CONCENTRATION. MOLARITY

Figure 12. Effect of feed composition on salt rejection for NaCl feeds a t 800 psi

338

Ind. Eng. Chem. Prod. Res. Develop., Vol. 10,

No. 3, 1971

tude as t h a t of the membrane counterion concentration are approached. Then there is a rapid decrease in salt rejection. Conclusions


Sulfonated poly(2,6-dimethylpheiiylene ether) polymer has been shown to have excellent potential as a reverse osmosis membrane material. Under conditions of moderate salt rejection it has extremely high water l)ermeabilities-e.g., 15 X [gal/ft2 dag][mil/atm] as compared to 1.8 X [gal/ft2 d a y ] [mil/atm] for dense cellulose acetate wheii both are evaluated at 800 psi and 957, salt rejection for 1 yoKaC1. Since its reverse osmosis performance is highly depeiident on feed composition, sulfonated 1,oly(2,6-dimeth?-l1,hen?-leiie ether) nieml)rane ran be compared to other membranes only under conditions of identical solute composition. Sulfonated 1)0ly(2,6-diinet~hyll)heiiyleiieether) niembraiie can be espected to have good performance for high hardness, high sulfate feeds, and poorer performalice for feeds with predominantly uiiiunivaleiit salts and some hardness.

Plummer of the General Electric Direct Conversion Business Section, who supplied many of the membranes and provided much of the water content data. He also wishes to thank W. J. Ward for many helpful discussions. literature Cited

Ilressner, L., J . Ph!/s. Chcni., 69, 2Z30 (106.5). Ihesener, L., Kraus, K. A4., J . P h p . Chcm., 67, 990 (1963). Fox, 11. W., Shenian, P., U.S. Patent 3,2.59,.?92(Jlily 3, 1966). Helfferich, F., “Ion Exchange,” pp ‘35-200, SlcGraw-Hill, New York, S . Y . , 1962. XlcKelvey, J. G,, Spiegler, K. S., FVyllie, Sl. It., J . Phys. Chenz., 61, 174 (1937). McKelvey, J . G., Spiegler, K. S., Wyllie, AI. 11. (to Gulf Research and 1)evelopment Co.), U.S. Patetit 3,132,094 (1Iay -5, 1964). SIerten, U.,Lowdale, IT. K., IIiley, II. L., \‘os, K., Office of Saline Water (U.S. Ilept. of Interior), Res. and ])evelop. Progr. Ilept. No. 263 (1067). lteid, C . E,, Breton, 15. J., J . A p p l . I’oL/jnir>rSci.,1, 133 (19-39). 1t~:ci~;tvI;i) for review September 21, 1970 ACCLPTI..DJune 4, 1971

Acknowledgment

The author wishes to acknodcdge the coiitributioiis of W. I. Foss, who was of invaluable assistance, atid C,‘. W.

1Iuch of the work deycribed was wppoited by The Office of Saline Water, 1)epartment of the Interior, wider contract No. 14-01-0001, 2114.

Production of Aluminum Chloride from AI-Zn Alloy’ Frank R. Jorgensen and Robert Dorin Division of Jlineral Chemistru, CSIRO, Port .lfelbourne, 3207, .lustralia

Aluminum chloride was produced in a gas-sparged reactor by the reaction between chlorine and a molten aluminum-zinc alloy. The impurity content of the product was dependent on the depth of sparging, flow rate, and temperature of the alloy. Analysis of the results, using impurity content as an indicator of sparger performance, showed them to b e generally in accord with the behavior exhibited by submerged orifices in aqueous systems. Typical product compositions ranged from 200-600 pprn Zn and from 25-1 50 pprn Fe. Production rates up to 25 Ib/hr were achieved. Subsequent purification of the product by passage through heated aluminum turnings produced a purified product containing less than 30 pprn of Fe and Zn.

A source of aii~iyirou*alumilium chloride valior was required for cxpei.iinenta1 This niaterial is usually purposes.

produced (Kirk atid Othmer, 1966) by the reaction of gasecus chlcrine witli niolten aluiiiiiiurii. 1)isadvalitages attriidant with this nictliotl of maiiufacture are the comparatively high operatiiig temperat’urea i d the use of refractory as n matcrial of constiwtioii. d ~)rocesshas been develolled (I)erh:im, 1966) for the recovery of zitic from tiiecast scrap in w h i c h the aluriiiiiurn is pi,efercntially chloriiiated froin the niolteir alloy. The same Iwiiiciples caii be applied to the 1)roduction of aluniiiiurn chloritle with the appueiit advantages over t,he more ~ O I I V C I I tioiial prorrss using molten alumilium of: a lower operatiiig trnil)craturc (420°C vs. 700”C), and the use of mild htrcl ratlier t h a i i refractory as a material of coiistructioii. ‘I’hcse Address correspondence to I). F. A. Koch, I)ivision of SIiireral Chemistry, CSIIIO, P . 0 . Box 124, Port llelbourtie, Vic.., :3207, Australia. Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 3, 1971

339

Reverse Osmosis Performance of Sulfonated Poly(2,6

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