the critical diameter in any given membrane remain fixed for all the related solution systems. This explains the basis for the existence of the unique relationships for the separation and flow characteristics of the membrane for such systems. It also explains why the characteristics of a membrane for the systems [MgC12-H20] and [Na2S04-H20] may not be uniquely fixed by the corresponding data for the system [NaCl-H20]. Acknowledgment
T h e author is grateful to I. E. Puddington and G. L. Osberg for their encouragement of this project; to W. S. Peterson, A. E. McIlhinney, and Neil H. Scheel for their help in building the equipment; and to Lucien Pageau and A. G. Baxter for their valuable assistance in the progress of these investigations. Literature Cited (1) Ambard, L., Trautmann, S., “Ultrafiltration,” pp. 3-1 4,
Charles C Thomas, Springfield, Ill., 1960. (2) Breton, E. J., Jr., “Water and Ion Flow through Imperfect Osmotic Membranes,” U. S. Dept. Interior, Office of Saline Water Research and Development, Progress Rept. 16, 1-66 (1 0 5 7I) .
(8) Lane, J. A , , Riggle, J. W., Ibid., 5 5 , No. 24, 127 (1959). (9) Loeb, S., Sourirajan, S., Advan. Chem. Ser., No. 38, 117 (1963). (10) Lorirner, J. W., Boterenbrood, E. I., Hermans, J. J., Discussions Faraday SOC.21, 141 (1956). (11) McKelvey, J. G., Spiegler, K. S., Wyllie, M. R. J., Chem. Eng. Progr. Symp. Ser. 5 5 , No. 24, 199 (1959 (12) Malherbe, P. L. R., Mandersloot, W. B., “Demineralization by Electrodialysis,” J. R. Wilson, ed., pp. 48-131, Butterworths, London, 1960. (13) Mazur, P., Overbeek, J. Th. G., Rec. Trav. Chim. 70, 83 (1951). (14) Reid, C. E., Breton, E. J., J . Appl. Polymer Sci. 1, 133 (1959). (15) Reid, C. E., Spencer, H. G., Ibid., 4, 354 (1960); J . Phys. Chem. 64, 1587 (1960). (16) Sollner, K., Svensk Kem. Tidskr. 6-7, 267 (1958). (17) Sollner, K., Dray, S., Grim, E., Neihof, R., “Ion Transport across Membranes,“ H. T. Clarke, and David Nachmanson, eds., pp. 144-88, Academic Press, New York, 1954. (18) Sourirajan, S., IND. ENG. CHEM. FUNDAMENTALS 2, 51 (1963). (19 Sourirajan, S., Nature 199, No. 4893, 590 (1963). ( 2 4 SP’iegler, K. S., Trans. Faraday Soc. 54, 1408 (1958). (21) Staverman, A. J., Ibid., 48, 176 (1952). (22) Tuwiner, S. B., “Diffusion and Membrane Technology,” DD. 170-9., Rpinhold. New York..1962. ~ ~ ~ ~ ~ (25F-Van Oss, C. J., Science 139, l i 2 3 (1963). (24 Yuster, S. T., Sourirajan, S., Bernstein, K., “Sea Water demineralization by the Surface Skimming Process.” Department of Engineering. Universitv of CalifGrnia. LOS Anieles. Rept. 58-26 11958).
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(3) Breton, E. J., Jr., Reid, C. E., Chem. Eng. Progr. Symp. Ser. 5 5 , No. 24. 171 (1959). (4) Chem: Eng. ‘70, No. 9, 49 (1963). (5) Clark, W. E., Science 138, 148 (1962); 139, 1125 (1963). (6) Glasstone, S., “Text Book of Physical Chemistry,” 2nd ed., p. 1254, Van Nostrand, New York, 1946. (7) Henderson, W. E., Yliepcevich, C. M., Chem. Eng. Progr. Symp. Ser. 5 5 , No. 24, 145 (1959).
RECEIVED for review July 29, 1963 ACCEPTED February 24, 1964 Annual Chemical Engineering Symposium, Division of Industrial and Engineering Chemistry, ACS, University of Maryland, College Park, Md., November 1963. Issued as N.R.C. No. 7915.
BOUNDARY-LAYER EFFECTS IN REVERSE OSMOSIS U L R I C H M E R T E N , H . K. LONSDALE, A N D
R . L . R I L E Y
John Jay Hopkins Laboratory for Pure and Applied Science, General Atomic Division, General Dynamics Gorp., San Diego, Calif.
Boundary-layer effects on membrane permeation in a reverse osmosis system have been studied experimentally. Two distinct effects of boundary-layer conditions on permeation rate were observed. The first occurred with a highly soluble salt (NaCI) in the system, and was attributed to changes in interface salt concentration and hence in effective osmotic pressure as the boundary-layer conditions were varied. The second occurred with a relatively insoluble salt (CaS04)in the system, and was attributed to precipitation at the interface under certain flow conditions.
recently been suggested (6) that boundary-layer phenomena in apparatus for water desalination by reverse osmosis will impose restrictions on throughput in two somewhat different ways. First, the accumulation of dissolved salts at the solution-membrane interface will raise the osmotic pressure of the brine locally and hence decrease the driving force for diffusion through the membrane. Second, when the interface concentration exceeds saturation for any constituent of the brine, the constituent may precipitate and effectively limit flow through the membrane to some value just high enough to maintain saturation a t the interface. T h e experiments reported here were designed to test these suggestions. T
I
HAS
Experimental Procedure
T h e membranes used in this work were prepared from Eastman E-398-3 cellulose acetate following essentially the procedures recommended by Loeb and Sourirajan (4). The 210
I&EC FUNDAMENTALS
salt solutions were prepared from reagent grade chemicals and distilled water. T h e osmosis experiments were carried out in a desalination cell in which the circulating brine flowed lengthwise along a rectangular membrane 1 by 3 inches in area. with the inlet and outlet arranged to make the flow across the membrane uniform and to minimize boundary-layel effects a t high circulation rates. The membrane chamber was 0.1 inch high. The membrane was supported on a piece of filter paper placed on a porous stainless steel backing plate. T h e salt content of the desalinized water was determined periodically to ascertain that the membranes had not ruptured. All the data reported here are for membranes and flow conditions that reduced the salt content in the desalinized water to
