ENGINEERING AND PROCESS DEVELOPMENT the production cost of levo-butanediol would be 34.1 cents per pound corrected to June 1952. The selling price for a return of 20% on the investment would be 47.7 cents per pound. If the Name materials of construction were used for the two plants, the selling price of diol from molasses would be considerably lower than the selling price of diol from wheat. Commercial Production May Lead to Expanded Industrial Use of Butanediol
Until recently, 2,3-butanediol has not been available in commercial quantities, so industrial uses for i t have not been developed. However, in 1951 following completion of the work described in this paper, Celanese Corp. of America announced production of synthetic 2,3-butanediol in tank car quantities ( 4 ) at a price of 14 cents per pound (6). The hygroscopic and solubility properties of 2,3-butanediol suggest its use in printing inks and pastes, dyes, soaps, ointments, and wood and leather stains. With polybasic acids, it condenses to form polyesters of the alkyd type ($39). In these more general uses, 2,3-butanediol would have t o be compared with competitive pioducts such 8 6 ethylene glycol, glycerol, and other glycols. Prices reported ( I ; ) for tank car quantities of four such products are as follows: Cents per Pound 16 17 18.5 39.5
1,3-Butanediol Ethylene glycol Cellosolve Synthetic glycerol
Because of its longer chain length, 2,3-butanediol might have greater compatibility or, because of specific properties, result in a better product in some preparations. h more specific use of 2,a-butanediol would be its use as a chemical intermediate. Diacetyl, a food and butter flavoring, could be readily prepared by oxidation. Cyclic acetals and ketals (1 7 ) ,which might have interesting chemical and solubility properties. are another possibility. Acknowledgment
Vapor-liquid equilibria data were determined by V. P. Milo, whose assistance in other phases of the work is acknowledged.
Literature Cited
(1) Bliss, H., Chena. Eng., 54, No. 5, 126-38 (1947); 54, No. 6, 100-2 (1947). (2) Blom, R. H., et al., IND. ENG.CHEM.,37, 870-2 (1945). (3) Blom, R. H., et al., Ibid., 37, 865-70 (1945). (4) Chem. Eng., 58, No. 3, 164 (1951). (5) Chem. Eng. News, 30, 5110, 5210, 5323 (1952). (6) Chilton, C. H., Chem. Eng., 56, No. 6 , 97-106 (1949). (7) Ibid., 57, No. 4, 112-14 (1950). (8) Considine, D. M., Ibid., 56, No. 3, 124-6 (1949). (9) FOX,L. E., Ibid., 54, KO.8, 100-1 (1947). (10) Preeman, G. G., and Morrison, R. I., J . SOC. Chem. Ind. (London), 66,216-21 (1947). (11) Happel, J., Aries, R. S., and Borns, W. J., Chem. Eng., 53, No. 10, 99-102 (1946); 53, NO,12, 97-100 (1946). (12) Jackson, D . H., Ibid., 54, No. 5, 123 (1947). (13) Lang, H. J., Ibid., 54, No 9, 130-3 (1947). (14) Ibid., 54, NO. 10, 117-21 (1947). (15) Ibid., 56, NO. 6 , 112-13 (1948). (16) Neish, A . C., Natl. Research Council Can., Div. dppl. Biology, Rept. 46-8-3 (June 1946). (17) Neish, A. C., and MacDonald, F J . , Can. J . Research, B25, 709 (1947). (18) Othmer, D . F., et al., IND.E m . CHEM.,37, 890-4 (1945). (19) Owen, W. L., Facts About Sugar, 33, No. 6 , 45-8 (1938). (20) Perry, J. H., ed., “Chemical Engineers’ Handbook,” 3rd ed., New York, McGraw-Hill Book Co., 1950. (21) Reich, G. T., Trans. A m . I n s t . Chem. Engrs., 38,1049-66 (1942). (22) Sieder, 0. E., Chem. Eng., 54, KO. 5, 117 (1947). (23) Stevens, R. W., Ibid., 54, No. 11, 124-6 (1947). (24) Tollefson, E. L., Wheat, J. A , , and Leslie, J. D., Can. J . Research, F24, 300-10 (1946). (25) Tomkins, R. V., Scott, D. S . , and Simpson, F. J., Ibid., F26, 497-502 (1948). (26) Tomkins, R. V., Wheat, J. A,, and Stranks, D. W., Ibid., F26, 168-74 (1948). (27) Vilbrandt, F. C., “Chemical Engineering Plant Design,” 2nd ed., New York, McGraw-Hill Book Co., 1942. (28) Walmesley, R. A., and Davis, W. R . , U. S . Patent 2,397,065 (March 18, 1946). (29) Watson, R. W., Grace, iK. H., and Barnwell, 3. L., Can. J. Research, B28, 652-9 (1950). (30) Wheat, J. A., Can. J. Technol., 31, 42-56 (1953). (31) Ibid., pp. 73-84. (32) Wheat, J. A., Natl. Research Council Can., Div. Appl. Biology, Rept. 51/1/1, December 1950. (33) Wheat, J. 24~, Leslie, J, D., Tomkins, R. V., hlitton, H. E., Scott, D. S.,and Ledingham, G. A . , Can. J . Research, F26, 469-96 (1948). (34) Whitney, R.P., and Vivian, J. E., Chern. E.ng. P w g r . , 45,323-37 (1949). for review M a y 22, 1953. ACCEPTEDAugust 31, 1953. RECEIVED Issued as Paper 162 on the “Uses of Plant Products,” and as N.R.C. 3099.
Demineralization of Water Electrol and Ion Exchange Processes I.STREICHER
A. E. B O W E R S
AND
Metropolitan W a f e r Districf of Soufhern California, l a Verne, Calif.
R. E. BRIGGS, P . 0 .
BOX
247, San Dimas, Calif.
SCREASIKG demands foi augmented Tater supplies to meet the needs of a growing population and expanding industry and recurrent droughts within recent years in important metropolitan areas have accented the need for efficient methods for producing potable and industrially usable waters from presently unsuitable sources. Among the methods which have aroused considerable interest and discussion in recent months is the electrolytic process for demineralization of water. The publicity accorded to the development of ion evchange membranes (4,5, 8) 23’34
and Langelier’s discussion of electrocheniical processes for desalting sea water (6, 7 ) have done much to renew general interest in this field of investigation. Demineralization of water by the application of direct current in specially designed cells with diaphragms of canvas or similar materials is not new. Bartow and associates (1, 2 ) described an electrolytic apparatus for removing positive and negative ions from mater and listed references t o earlier experiments of this nature performed in this country and in Europe in the middle
I N D U S T R I A L A N D E N G I N E E R I N,G C H E M I S T R Y
Vol. 45, No. 11
ENGINEERING AND PROCESS DEVELOPMENT 1920's. More recently, Briggs (3) and Streicher (11 ) discussed softening and partial demineralization of water by electrochemical means in a two-compartment cell. In all but the last two papers, data relating t o electrical energy requirements were either hypothetical or derived from tests on laboratory scale units; Briggs and Streicher presented data derived from the operation of small pilot units.
(b)
BASIC 2-COMPARTMENT CELL
Figure 1,
Basic Electrolytic Cells
More recent investigations by the Metropolitan Water District of Southern California with a relatively large pilot unit of the two-compartment type and with an electrolytic demineralizing cell developed by Briggs, the latter operated in conjunction with ion exchange beds, have produced new data which shed additional light upon the ultimate potentialities and the limitations of electrolytic processes for demineralization of water. Inasmuch as earlier tests with the smaller water softening units had proved that this type of treatment could improve very measurably the quality of the raw waters so treated, the primary objectives of the tests proposed with the larger unit were t o obtain as much information as possible relative t o the following: Power and chemical costs to produce a finished water of the desired quality Effect of operation variables on finished water quality Design and construction features which might influence the practicibility and cost of large units of this type Maintenance requirements for and life expectancy of the various materials in the units.
the cathode compartment, the remainder flowing through the anode compartment, As in the three-compartment cell, the anolyte becomes acid and the catholyte caustic. Because of the high p H values developed in the cathode compartment, magnesium is precipitated as the hydroxide and calcium as the carbonate. These are permitted t o settle out in a clarifier, leaving a softened and partially demineralized water as the final product. Of course, no reduction of sodium is effected in this process (actually, the sodium content is somewhat increased because of the migration of sodium ions from the anode compartment) but anion concentration is appreciably reduced and the over-all quality of the water is much improved. A battery of two-compartment cells, Figure 2, can be made simply by alternating anode and cathode compartments to p r e duce a compact unit of the capacity desired, Pilot Plant Assembly. I n the spring of 1950, the MetropoBitan Water Distript of Southern California constructed and put under test at its softening and filtration plant a t La Verne, Calif., a 125-gallon-per-minute pilot unit of the two-compartment cell type. A flow diagram of the entire pilot plant assembly is sh0T-n in Figure 3. Tests with the smaller experimental units had indicated that, under the operating procedures described above, the waste of acid anolyte usually amounted t o 15 to 30% of the total influent water. These tests further indicated that anolyte neutralization (with lime) and recirculation would appreciably reduce this waste and provide more economical operation. With this in mind, tests were run first with lime addition t o and recirculation of the anolyte, and then with no lime addition or recirculation but with a higher percentage waste. Under the first procedure, the loss was set initially at 5% and reduced in succeeding tests until it was down to 2%. The quality
Performance and Economics of TwoCompartment Cell Are Tested by Pilot Size Unit *
e
Design and Operation. A diagram of a simple three-compartment cell, similar t o t h a t used by the early European investigators who studied this process, is shown in Figure 1, a. It was reported t h a t about 50% of the raw water was passed through the center compartment during operation, the remainder being divided between the outer, electrode compartments. Under the influence of a direct current applied to this system, the cations migrated into the cathode compartment while the anions moved into the anode compartment. The caustic catholyte and acid anolyte were discharged t o waste. The effluent from the center compartment was recovered a s partly demineralized water or passed through the center compartments of several such units in series t o achieve any degree of demineralization desired. Figure 1, b, is a diagram of a simple two-compartment cell. I n this type of unit the center compartment, without electrodes, is omitted. About 70 t o 85% of the raw water, depending upon its chemical character, is pmsed through November 1953
u u Figure 3. 1.
Flow Diagram of Electrolytic Water Softening Pilot Plans
Direct current generator Anode bus Cathode bus 4. Raw water inlet 5. Anolyte make-up water 6. Recirculated anolyte 7. Catholyte drain 8. Anolyte drain 9. Anode 10. Cathode 1 1 . Canvas dia phrag rn 2. 3.
12. 13. 14. 15.
Treated water Anolyte discharge Anolyte neutralizing tank Anolyte reaction tank 16. Anolyte return pump 17. Anolyte waste pump 18. Sludge pump 19. Treated, clarified water 20. Clarifier 2 1, lime feeder 22. Waste
INDUSTRIAL AND ENGINEERING CHEMISTRY
8
2395
ENGINEERING AND PROCESS DEVELOPMENT of the finished water appeared to change little with this variation. Enough lime was used t o raise the p H of the anolyte from about 2.0 to 2.5 t o approximately 7. One difficulty was encountered, however, when the waste was limited to 3.5% or less with a water high in sulfate content. This difficulty was precipitation of calcium sulfate along the anode compartment and inside the pipes carrying the anolyte from the unit. T h e result was serious loss of carrying capacity. The calcium sulfate was redissolved when the waste was increased beyond 4%.
Table 1.
Two-Compartment Electrolytic Tests with Anolyte Neutralization and Recirculation Raw Water
Catholyte
AZALYSIS
S O , , p.p.m. Ca, p.p.m. lfg, p . p . m . S a , p.p.m. Cos, p.p.m. HCOa, p.p.m. SOa, p.p.m. c1. u.u.111. OH- p.p.m. T o t h hardness (as CaCOs), p.p.m. Total dissolved solids, p.p.m. -4lkalinity (phenolphthalein), p.p.m. Alkalinity (total), p.p.m. Hydrogen ion concn., p H Electrical conductivity ( X 106) Anolyte C1, p.p.m. Hydrogen ion concn., pH
8 8 78 28.5 92 2 137 29 1 80 0 312 649 2 116 8 3 1030
'
2 45 3 99 12 0 200 54 12 125 427 48 58 10 8 830 515 2 5
Recirculated Anolyte after Keutralization Hydrogen ion concn., pH
5 8 OPER4TISG
I15
110 0 9
IO LIME D O S l G E -
Figure 4.
12
1 1 pound,
coo
34
2
30
0
14
13
p e r 1000 ~ m l i o n rf r n , r h e d
DATA
Catholyte flow rate, gal./min. Anolyte recirculation rate, gal./min. Anolyte make-up, gal./min. Anolyte waste, % of influent water Current input, amp. Applied e.m.f., v. Am~.-hr./gal.~ Electrical energy, kw.-hr./1000 gal.& Lime dosage, lb./1000 gaL5 Electrode area, sq. ft. Based on finished water.
103 4 50 4 8 4.4 74 2 6 4 0.698 3 82 1 25 2350
Effect of Lime Dosage in Recirculated Anolyte on Finished Water Hardness
nomical and certainly simpler to operate without this step and permit a greater anolyte loss. Comparative costs of the two I n Table I, data are presented showing the operating conditions methods of operation are given in Tables I11 and I V and in Figmaintained during a series of tests and giving the analysis of the ure 6, for operation at 6 volts and a t 4 volts. Where power raw water and treated water produced under those conditions. costs are sufficiently low, maximum economy can be achieved As a finished water hardness of 125 p.p.m. is now maintained in when lime neutralization is not used. normal operation of the district's 200,000,000-gallon-per-day One important item of cost which is not included in the foresoftening plant, the same hardness was set as the goal for the going data is the charge for anode replacement. The loss of carelectrolytic pilot plant tests. I n addition t o the softening which bon from the anodes during these tests was so severe that it was has taken place, an appreciable reduction in the sulfate and chloestimated t h a t the cost of anode replacement alone would exceed ride content has been achieved, with a net reduction of about 34% all other treatment costs combined. H a d an electromotive force in the dissolved solids content of the water. Figure 4 shows the of approximately 4 volts been maintained throughout the tests, variation in finished water hardness which occurred as the lime this loss would undoubtedly have been markedly reduced. Since dosage t o the anolyte was varied. D a t a showing operating conditions and quality of treated water when anolyte neutralizaTable II. Two-Compartment Electrolytic Tests without Anolyte Recirculation tion with lime was not pracRaw ticed are given in Table I1 and Water Catholyte Figure 5 . Under these conAnalysis ditions, the anolyte waste var2 5 2 3 8.8 &On, p.p.m. 22 17 20 19 78 Ca, p.p.m. ied from about 12 t o 20%. De22 20.5 28.5 7.5 18 3Ig. p.p.m. 108 107 116 113 92 spite a slightly higher current 43 28 2 30 35 n requirement, the total solids 10 0 0 137 227 222 178 291 197 reduction was lower than when 48 61 62 80 54 2 2 9 0 0 lime was used for anolyte pH 74 143 7 85 123 312 correction; but the cost of lime 4 80 406 477 443 649 25 34 49 43 2 and the additional operating 58 63 72 79 116 difficulties resulting from the 10.2 10.4 9.8 10.7 8.3 Hydrogen ion concn., p H 840 800 825 800 1030 Electrical conductivity ( X 109 iise of a small lime feeder, ..~. equipment for agitating the Anolyte ~
anolyte-lime mixture, recirculating pumps, etc., were eliminated. With this larger pilot unit i t was established that,, because of the present high cost of lime and the expense of additional e q u i p m e n t n e e d e d when anolyte n e u t r a l i z a t i o n was used, it was almost as eco-
2396
E$$;&:
ion concn., pH
catholyte
AOW
iiz$k:
rate, gal./min.
t;\/gl;twater
Current e.m.f., Applied i n w t , amp. v. .4mp.-hr./gal.a Electrical gal." Electrode energy, area, sq.kw.-hr./1000 it.
180 2.0 Operating Data 81.3 11 12.1 1117 9.8 1.145 11.22 2350
135 2.2 81.2 11 12.0 6 07 7.0 0.625 4.38 2350
165 2.1
127 2.1
80.9 20 19.8 1122 10.0 1.156 11.56 2350
81.9' 20 19.6 609 7.4 0.620 4.59 2350
Based on finished water.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 45, No. 11
ENGINEERING AND PROCESS DEVELOPMENT IS0
I
I
I
I
I
I
A M P E R E HOURS P E R GALLON FINISHED W A T E R
Figure 5.
Effect
of Current Density on Finished Water Hardness
10
Figure
d
L
20
IO
6.
30
40
SO
60
70
80
90
100
Comparative Costs of Two-Compartment Electrolytic Treatment
these tests, however, Briggs has effected changes in design and operation which, i t appears, may reduce anode replacement costs t o a relatively insignificant figure. The first experimental work with the electrolytic process was started by the district in 1943 when the raw water contained a p proximately 800 p.p.m. of dissolved solids and had a hardness of 380 p.p.m. (as calcium carbonate). By the time the 125-gallonper-minute unit was built in 1950, the raw water quality had improved t o the point where the dissolved solids content was about 660 p.p.m. and the hardness 315 p.p.m. With the higher electrical resistance of the less saline water, the unit cost per part per million for hardness removal had increased and, as a result, this process could not complete economically with the zeolite softening used in the plant. At the same time, the need for pronounced dissolved solids reduction had decreased. I n view of the above, i t was cbncluded that the use of this process by the district for treatmegt of Golorado River water could not be justified a t the present time. Muhicompartment Cell-Ion Exchanger Assembly I s Economical Over-all Treatment
It was pointed out earlier that although hardness and anion reduction can be achieved in a two-compartment cell, the sodium content of the water is actually increased slightly in this type of unit. A three-compartment cell, on the other hand, does reduoe sodium as well as the other cations and is, therefore, better suited for the treatment of saline but not necessarily hard waters. November 1953
To explore the possibilities of demineralizing highly saline natural waters, industrial wastes, and sewage plant effluent waters by means of the electrolytic process, a limited investigation waa conducted by the district with a small unit about 0.5 to 1 gallon per hour in capacity. This unit was designed and built by Briggs specifically for improved efficiency in demineralization. Although it embodied the principle of the basic three-compartment cell, i t differed from the latter in both design and operating features. As shown in Figure 7, between the center compartment and each of the electrode compartments were two so-called buffer zones, formed by installing two additional dyne1 diaphragms parallel to and slightly removed from each of the original diaphragms of the simple three-compartment cell. I n effect this unit became a seven-compartment cell, but no water was intentionally introduced into or withdrawn from the buffer zones. These zones permitted better hydraulic separation between the demineralized water in the center compartment and the anolyte and catholyte in the outer compartments, with the result that the solutions in the electrode compartments could be permitted t o attain higher concentrations without impairing the quality of the treated water, At the same time, the yield of finished water from the unit was increased. Furthermore, whereas the anolyte and catholyte from the conventional three-compartment unit had always been discarded as wastes, the corresponding solutions from the multicompartment unit described above can, because of their higher concentrations, be successfully utilized as regenerants for certain ion exchange resins. Thus, the multicompartment cell could partially demineralize the input water, and the anolyte and catholyte produced in the process would, in turn, act as agents for the ultimate further reduction of the mineral content of the water. T o evaluate the efficiency of such an assembly, two la/&ch tubes, one containing a 27-inch depth of carboxylic acid type cation exchanger and the other an equivalent amount of strongly
Table 111.
Cost
of Two-Compartment Electrolytic Treatment operating Data With Anolyte Neutralization
4.3%" molyte waste Amp .-hr./gal. finished water v. . Appl ied-e.m.f.. Electrical ene; kw.-hr./ I 000 000 g a l Y Lide d&age, lb./1,000,000 ga1.b Anolyte waste, gal. Electrical energy, lime, and anolyte waste0 Cost/l 000 000 gal. cost/abre-it. I
0.59 511
3,480 960 44,900
Electrical Energy, Cost/Kw.-Hr. $0.005 $0.01
.. ..
.. ..
$17.40 10.43 1.38
$34.80 10.43 1.38
29.21 9 52
46.41 15.19
Without Anolyte Neutralization 12%" anolyte waste Amp.-hr./gal. finished water 1.00 Applied e.m.f v. 9.5 Electrical en$g kw.-hr./ I,OOO,OOO gal.? 9,500 47.50 3.79 Anolyte waste, gal. 123,600 Electrical energy and anolyte wastee Cost /1 000 000 gal. 51.29 Cost/a&e-it, 16.71 20'7 a anolyte waste A&.-hr./gal. fihished water 0.72 7.8 ADDlied e.m.f.. v. ..Eiictrical energy, kw.-hr./ 1 000 000 gal. b 5,610 28.05 Andlyte) waste, gal. 250,000 7.68
.. ..
.. ..
35.73 11.64
.. .. 95.00 3 :79 98.79 32.19
.. .. 56.10 7.88 63.78 20.78
Baaed on total influent raw water. Based on finished water. Excludes operation, maintenance, replacement, interest, and amortization of capital investment. Baaed on lime, .$21.73/ton; water, $30.70/1,000,000gal.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
2397
ENGINEERING AND PROCESS DEVELOPMENT Three different waters were treated in the district laboratories in a pilot plant demineralE.M.F. 6 Volts E.M.F. 4 T'olts Electrical Electrical izing unit of the type described. Energy. Cost/ Energy, Cost/ first, was Colorado River The Operating Kw.-H~. Operating Kw.-Hr. data S0.006 $0.01 data (0.005 $0.01 water which had p w e d through the main plant softener units With Anolyte Neutralization and was, therefore, very soft 4.355' anolyte waate Amp.-hr./gal. finished water 0.69 0.59 but still fairly high in total disElectrical energy, iiw.-hr.,'1,000,000 gal. 3,450 $17:25 ~34.'50 2,360 cii:so t23.'60 Lime dosage, lb./1,000,000 gal. b 906 10.43 10.43 960 10.43 10.43 solved solids, particularly sodium hnolyte waste, gal. 44,BO0 1.38 1.38 44,900 1.38 1.38 and sulfate ions. I n Table V are Electrical energy, lime, and anolgtc waste 20.08 46.31 23.61 35.41 data showing the quality of the Cost/l,000,000gal. 9.47 1 8 . 0 0 7.69 11.54 Cost/acre-ft. effluent from the ion exchange Vitliout hiiolyte Nc:itralization units. Also shown are some 1 2 7 e anolyte waste chemical characteristics o f the .A:ip.-hr./gal, finished water 1,oo 1.00 Electrical energy, kw.-hr./1,0O0,000 pal. 6,000 30:OO 60:00 4,000 20:00 4h:OO anolyte and catholyte solutions hnolyte waste, gal. 123,600 3.70 3.79 123,600 3.79 3.79 used for regeneration of the Electrical energy and aiiolyte wastec 33.70 63.70 stand-by exchanger units and 23.70 43.79 Cost/1,000,000 gal 11.01 20.79 7.78 14.27 Cost/acre-ft. the current and voltage require2 0 % a anolyte waste ments for the entire operation. Amp.-hr. /gal. finished water 0.72 0.72 Electrical energy, kw.-hr./1,000,000 m1.b 4,320 2i.'60 43.'20 2,880 i$.'40 28:so Dissolved solids were reduced by Anolyte waste. gal. 250,000 7.88 7 . 6 8 260.000 1.68 7.68 31% in the electrolytic unit, and Electrical energy and anolyte wastec 29.28 30.88 22.08 36.48 only about 6% of the original Cost/l 000 000 gal, 9.84 16.58 i.19 11.89 cost/abre-it. mineral constituents remained in a Baaed on total influent raw water. the treated water after passage b Based on finished water. 6 Escludes operation, maintenance, replacement, interest, and amortization of capital investment. through the ion exchange columns. Almost 65% of the input water was recovered as a finished product, the remainder passing through the anode and cathode compartments and forming the regenerants for the ion exchange step. The quantity of elcctricity required, as sliown in Table V, was only 1.31 niiiperehours per gallon of finished xater. Even at the high electromotive force of 15.5 volts used in this test this would represent an energy coiisuiiiption of only 20.3 km.-hr. per 1000 gallons. If the unit were designed t o permit operation at the flow rates desirccl with a n electromotive force of 4 to 6 volts, the cost of operation could be proportionately reduced. The two other n-aters tested in the electrolytic-ion exchange pilot plant Trere both synthetic waters having chemical qualities similar to those of two selvage effluents discharged in the Los Angelcs nirt'ropolitan area (10). As both were fairly hard, it was dccidetl t o use the more economical two-compartment electrolytic unit for the initial step in the process, followed by the multicompartment unit and the ion exchanger columns in turn. The data derived from these test,s are shown in Tables VI and 1'11. The rater described in Table VI was reduced in mineral content from 1063 to 30 p.p.m. in the threestcp process wit,h an electricity consumption of 4.77 ampere-hours per gallon of finished water. About 44% of the total input was recovereci as fullyprocbasic polymerized amine anion exchanger, were operated in esseci water. The second syntl~et,icwater with an initial minelectrolytic series with and following this multicoii~partnie~~t eral content of 1412 p.p.ni. was reduced to 49 p.p.ni. dissolved soldemineralization unit, as shown in Figures 7 and 8. Two sets of ion exchange units m r e available so tliiit one might be ids h y this saine process. The quant,ity of electricity consumed regenerated while the orher as in service. During operation, for this treatment v-as 5 . 3 2 ampere-hours per gallon of finished the raw water was divided among the center anti the electrode water, and the recovery vas about 43% of the input water. compartments of the electrolytic unit, the rata of flow through -in npprecialble increase in the percentage recovery of processed each being dependent upon the quality of the influent water and mater could undout)t.edly have been effected if the process had the degree of demineralization desired. The partiall). demineralhcen coiitrolicd to yield a, higher mineral content in the finished ized effluent from the center coxnpartnient was pnssed first water. With this type of operation the current requirement, too, through the anion cxchanger and then t,hrough the cation exwould have been inore favoraiile. Unfortunat~ly,time did not changer: cmergingfrom t,helatter as a x-ater suit,ablefor almost all permit the further investigation of these factors before t'he p r e p industrial applications. While further demineralizat,ion of the aration oE this article. water is taking place in one set of ion exchange units, the acid The assenihly consisting of the multicompartment electrolytic anolyte from the electyolytic unit is flowing into and through the unit and the ion erchange colunins was taken to Tesas by Briggs second cation exchanger, regenerating the resin contained therein. for field tests on a yell water in the vicinity of Garland. AS The caustic catholyte is similarly regenerating the anion exchange shown in Table VIII, the initial dissolved solids content of the material in the stand-by unit. Thus, the anolyte and catholyte water was 1162 p.p.ni. This was reduced to 424 p.p.m. in the are no longer mated, but are utilized t o increase further the deelect,rolytic cell and iurtlier reduced t o 38 p.p.m. in the ion exmineralizing capncity of the system. Table IV.
Cost of Two-Compartment Electrolytic Treatment for Different Cell Voltages
C
'
2398
I N D U S T R I,A L A N D E N G I N E E R I N G C H E M I S T R Y
Vol. 45, No. 11
ENGINEERING AND PROCESS DEVELOPMENT change units. The electricity required for this process was 2.62 ampere-hours per gallon. If a unit were designed for a comparable treatment at an electromotive force of 4 volts, only 10.5 kw.-hr. would be consumed per 1000 gallons of treated water. For the improvement in water quality achieved, this figure is quite attractive, The recovery of finished water, too, was very encouraging in the Garland test, since it was slightly more than 70% of the input water. Power Cost and Availability Determine Competitive Position of Precess 4
Among the data presented in each table are figures relating t o t h e electrode area of the pilot unit used in the test described. Only in the 125-gallon-per-minute unit of the two-compartment type was the electrode area sufficient to permit efficient operation at low voltages. I n the later tests with the small multicompartment unit, the voltages were necessarily higher t o permit effective treatment, at relatively higher rates of flow. T o reduce the electrical resistance of the system and thereby keep operating costs at a minimum, the electrode area for a given rate of flow can be increased (with a higher initial investment). This will permit a certain flexibility in operation, however, as at low and moderate flows the plant can be operated a t minimum voltages and costs, while during periods of peak flow the voltage could be increased t o maintain uniform treated water quality without the need for immediate plant enlargement. Accurate estimates of cost of construction and installation of an electrolytic unit cannot be given unless the quality of the raw water, quality of treated water desired, and proposed throughput rate are known. Briggs has prepared the following estimate of size and approximate cost of an electrolytic cell assembly alone for a treatment, of a water similar to the Garland, Tex., supply (for 75% dissolved solids reduction): Capacity Number of units in electrical series Conductance area, sq. it. per gal./hr. Voltage drop (d.c.) over each unit Capacity per unit, gal./hr. Total capacity of assembly, gal./hr. Floor space, sq. ft. per 1000 gal./hr.
-
4
Investment (estimated) Equipment (base cost, without power supply and supplemental ion $8000 exchange units) Installation $8000 This estimate indicates that the cost of such an installation would not be unreasonable when compared with the reported costs (9) of $35,000 and $200,000 for ion exchange demineralizer and vapor compression distillation units, respectively, each approximately 1600 gallons per hour in capacity. The improved fabrics developed with the advent of synthetic fibers have solved the diaphragm problem in the electrolytic units of the type tested by the authors of this paper. The cathodes were not subject to corrosion (except by stray current leakage in case of improper design) and would be expected t o last almost indefinitely. November 1953
4 4 4 250 1000 750
Figure 8.
Electrolytic and Ion Exchange Demineralizing Unit
Electrolytic unit at top ion exchange columns at right of power supply
Table V.
Electrolytic-Ion Exchange Treatment of Softened Colorado River Water Softened Colorado River Water
Miilticompartment Electrolytic Unit Partially demineraliaed Anolyte Catholyte water
~ f f l ~ ~ ~ t from Ion Exchange Units
Analysis SiOz, p.p.m. Ca, p.p.m. Mg, p.p.m. N a , p.p.m. I
