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J. G. MCKELVEY, JR.,K. S. SPIEGLERAND M. R. J. WYLLIE
tive aspects of the problem, especially since the latter may vary with the fine detail of membrane structure. Although this report is restricted to the behavior of a single membrane, it is possible to multiply the sing1e membrane effect by inserting additional membranes loosely between the two active surfaces in the basic cell. The multimembrane electrogravitational cell so formed may be operated continuously by feeding an influent solution a t an intermediate height in the cell and withdrawing two product streams, one from the
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uppermost level and the other from the bottom of the cell. Such cells have been constructed and operated successfully in our laboratories. The results of these studies will be reported elsewhere. Acknowledgment.-The author expresses his apPreciation to Dr. C* Cdmon and Mr* M. E. Gilwood Of the permutit for encouraging the above investigation, and to Dr. Dwight D. Prater of Socony Mobil Laboratories for comments on the manuscript.
SALT FILTERING BY ION-EXCHANGE GRAINS AND MEMBRANES BY J. G. MCKELVEY, JR.,I(.S. SPIEGLER AND M. R. J. WYLLIE Gulf Research & Development Co., Pittsburgh, Pennsylvania Received J u l y 90,1958
A 0.1 solution of sodium chloride was forced through a “Permaplex (2-10” cation-exchange resin membrane in the sodium form. It was found that the exuding solution was depleted in salt. This salt filtering action probably is due to ion exclusion and not to ion exchange. Various types of ion-exchange resin granules were equilibrated with sodium chloride solution and synthetic sea water. The resin granules were then separated from the solution and subjected to pressure. It was found that the concentration of salt in the solution expressed from the resin decreased gradually. The ratio of the concentrations of the various dissolved salts also changes as the compression proceeds.
It is well known that an ion-exchange resin when water from the Gulf of Mexico (chlorinity 17.90j0~) in equilibrium with an aqueous electrolyte solution, and magnesium chloride (0.204 normal). The ion-exchange resin granules were equilibrated contains less of the soluble electrolyte per unit weight of water than the solution.2 This electro- with the respective salt solution, filtered on a lyte exclusion phenomenon, which is essentially a ‘‘Buechner” filter and the moist resin granules were “Donnan” effect, may be utilized in various ways to then loaded into a steel cylinder. They were subseparate an electrolyte solution into a more con- jected to pressure by means of a steel piston with centrated and a more dilute portion. This note “0”ring seals and a hand operated hydraulic press. deals with two methods by which this may be A “341-20” press (Loomis Engineering & Mfg. Co., achieved : namely, (a) equilibration of resin grains Newark, N. J.) was used for the cation-exchange with a salt solution; separation of the grains; appli- resin while a “1315” press (Buehler Co., Chicago, cation of pressure to the grains and collection of the Ill.) was used for the experiments with the aniondilute solution squeezed from them, and (b) com- exchange resin. The resin bed was supported by a pression of a salt solution through an ion-exchange micro-metallic porous disc (Micro Metallic Corp., Glen Cove, N. Y.) which allowed the exuded solumembrane and collection of the dilute filtrate. It is important that these separation processes tion to pass through and be collected. The apparaare probably caused primarily by the electrical tus is shown schematically in Fig. 1. The volume properties of the ion-exchange resins; the filtering of the resin bed was decreased stepwise and the action is probably not due to the relative size of the liquid exuding after each step collected as a sepaions and resin “pores”. These processes are quite rate sample. At first, the application of pressure different from regular ion-exchange demineraliza- did not cause any liquid to emerge at the top, since tion since chemical regeneration of the resins is not the solution squeezed from the resin merely filled required. They are related to the new process of the interstitial space of the bed. Later, solution “Ion Excl~sion’’~ in which separation between emerged and the volume exuding after each preselectrolytes and non-electrolytes is effected by a sure increase was collected as a separate sample. The position of the piston and hence the depth column technique but without application of presof the resin bed were measured before the initial sure. 1. Squeezing of Solutions from Ion-exchange application of pressure, when the particles were Resins.-The resins used in these experiments were loosely packed, and after each subsequent pressure After application of pressure in each ‘‘ Dowex 50,” a sulfonated polystyrene cation ex- increase. changer (Dow Chemical Co., Midland, Mich.) and step the pressure gage rose sharply and then dropped “Amberlite IRA 411” a quaternary amine anion rapidly, leveling off to a time-independent value. This latter pressure was recorded and served as refexchanger (Rohm & Haas Co., Philadelphia, Pa.). erence to the particular stage of the experiment. The resin grain size was 20-50 mesh (wet U. S. in the effluent was deterChloride Standard Screen). The solutions used were sea mined by concentration titration with standard mercuric nitrate (1) The results of these experiments have been reported in part a t magnesium and calcium concentration the AAAS Gordon Conference on “Ion Exchange,” 1054. (2) J. Schubert, Ann. Rev. PRys. Chem., 6, 413 (1954). (3) R. M. Wheaton and W. C. Baurnan, Ind. Eng. Chem., 4 5 , 228 (1958.)
(4) (a) F. E. Clarke, Anal. Chem.,22, 553 (1950); (b) M. Calvin and A. E. Martell, “Chemistry of the Metal Chelate Cornpbunds,” Prentice-Hall, Inc., Now York, N. Y., 1052.
SALTFILTERING BY JON-EXCHANGE GRAINSAND MEMBRANES
Feb., 1957
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.50 .45
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I
Ea
t
Fig. 1.-Steel apparatus for squeezing of solutions from ion-exchange resin grains through a steel assembly, effluent is collected a t top: a, Saran tube; b, top section of hydraulic press; c, “0” ring; d, microporous disc; e, steel body; f , resin grains; g, piston.
either by titration with ethylenediaminetetraacetic acid,(b or with the flame photometer. Sodium and potassium concentrations were determined only with the flame photometer. Figure 2 shows typical results for a squeezing experiment with ((Dowex50” initially equilibrated with sea water. The figure shows the amount of solution exuding from the resin bed as a function of the applied pressure, and also the C1-, Ca++ and Mg++ concentrations in this solution. The points of curve 1 relate to the pressure necessary to remove a certain volume of solution from the resin bed; the points on curve 2 refer to the average effluent concentration in the sample collected between two necessary pressures; they are, therefore, plotted midway between these pressures. The results of a similar experiment with an anion-exchange resin originally in equilibrium with a magnesium chloride solution (0.204 N ) are shown in Fig. 3. It is seen that on application of pressure, the solution is first squeezed out rather easily, but a stage is reached at which large additional pressure causes only a minor increase in the volume of solution collected. At this stage, about 45 and 62% of the total water content of the cation- and anionexchange resin, respectively (as determined by drying at 110’) has been squeezed out. It is well to remember that not all the water determined by this drying procedure is free to migrate, since some
2
.40
35
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.30
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5
a
.25
I
K
p .20 b
.05 0 0
5
IO
I5 20 25 30 EFFLUENT VOLUME (ML).
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Fig. 2.-Squeezing of solution from cation-exchange resin grains: 150 g. (moist weight) “Dowex 50” (20-50 mesh) previously equilibrated with sea water. Initial and final volumes of resin bed-160 and 74 ml., respectively. Total volume of solution exuded-32.2 ml. (1) applied pressure us. effluent volume; (2) normality of C1-, Mg++ and C a + + in effluent us. effluent volume.
must be considered tightly b ~ u n d . ~It, ~is seen that the total chloride concentration in the first few samples was about the same as in the original equilibrium solution while the concentration in the later samples was much lower. The first samples represent surface adsorbed fluid not removed by filtration. The slight initial increase in chloride concentration, as compared to the equilibrium solution was also observed in several other experiments. It may be due to some evaporation. Later samples are more representative of the solution held in (5) H. P. Gregor, J. Am. Chem. Soc., 73,642 (1951). (6) I
