H e L. BEOHSER AND A, The P e r m u t i t Company, New Y o r k , N e Y e
%onexchange processes are being increasingly utilized in many varied chemical processes. One of the most useful and promising fields of application i s the treatment of wastes. Some of the general principles of ion exchange and the application of ion exchange to waste treatment are discussed briefly, Unique examples of ion exchange grocesses are described. A m o n g these are metal recovery- bj both cation and anion exchange, recovery of organic cations, recovery of organic anions by several methods. manufacture of pectin, and purification of diaute fruit sugar wastes.
URlKO recent years ion exchange has captured the interest of many chemists and chemical engineers as a method ofsolving a wide variety of their problems. While ion exchange itself i s an old process, only during the last 10 or 1% years has extensive work been conducted on the use of the process outside the field of mater treatment for accomplishing the following ( 1 1 ) : Removal of undesirable ionic impurities from solution Addition of specific ions t,o solutions Recovery of valuable substances from soIutions Separation or fractionation of electrolytes Use as solid contact agent,s or catalysts ION EXCHANGE, MATEXXALS
The early t,ypes of inorganic ion exchangers such as processed glauconites or greensands and synthetic sodium aluminosilicates are widely used commercially for water softening. However, since the organic exchangers are m r e stable to extremes in pH they therefore are more versatile for use in other applications. Consequently, these materials have received the bulk of the attention and study of chemists in recent years. The organic cation exchangers contain the following active groups: sulfonic, carboxylic, and phenolic. All t,hree of these groups may be present in one material--for example, as in sulfonated coal or modified phenol-formaldehyde resins. Monofunctional exchange materials also have been developed in which the active groups are primarily sulfonic acid groups or carboxylic groups. Anion exchange resins may be either aliphat'ic or aromatic amine resins or the more strongly basic resins. The characteristics of all these materials vary great,lg from one type to another and even within each type. Therefore familiarity must be had with all materials to select the proper one for a particular application.
removing harmful impurities. Such treated solutions may then be concentrated or further processed for sa10 or i-e-use, An example would be the ~ ~ r n ~ n e r ofa pineapple ~ ~ z ~ tinill ~ ~juice ~ for the production of sugar sirup. The treatment of waste sohtions b y ion exchange should be practiced at the point where interfering electrolytes arc at, a minimum in order to obtain most effective treatmcnt a,t lowcse cost for regenerants. Generally, the waste solution 1-0 be taeal;ed should be relatively clear and free of t'urbidity so that deterioration of the ion exchange matcrials is rnininiized. In treating wastes by ion exchange, it i s important t o beax in m i i d t h a t the regenerant solution produced must be of such a character t h a t i t can be disposed of readily. Certain t,yyes of wastes undoubtedly can be purified by ion exchange, producing a valuable effluent for re-use, but thc regenerant effluent would bo just as harmful for discharging into streams as the original wastcs. I n such, cases further concentration of the regenerant effluent may be feasible. METhE ~~~~~~~~,~~~
Cation Exchange. The recovery of eopper by ion cxchange has received wide attention. Beaton and Furnas used. a c o d derivetive, %eo-Karb €I>for the concentration and i ~ e r eable to effect a, 221-fold concentration from the dilute influent t o the relatively concentrated regenerani, effluent using 4 N sulfuric acid as %he regenerant (2'). If hydrochloric acid is used for removing tho copper from the exhausted hydrogen exchanger, the excess acid ma.y be distilled for re-use (13). Copper and chromium in copper alloy pickle wash waters can be concentrated more than 25-fold by taking u p these mgtal cations on a carbonaceous hydrogen exchanger and subsequently regenerating with normal sulfuric acid. These data (10) are 3
GEXERAL PRINGXPLES OF' W A S T E TREATMEKT
En the treatment of n-astes by ion exchange a few important generalizations are as Sollows (7): Unless some relatively valuable material can be recovered for sale or re-use, ion exchange generally is not an economicd method of treating wastes. The recovery of such valuable materials may be accomplished by either of two methods: by removing electrolytes present in extremely Iow concentrri.tions by ion exchange, and subsequently recovering the concentrated electrolytes from the exchange material as the recovery of metals or organic acids: and the recovery of valuable products in waste materials by
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INDUSTRIAL AND ENGINEERlNG CHEMISTRY
shown in Figures 1, 2, and 3. By proper selection of the concentration of regenerant, flow rate, and by fractionation and reuse of the regenerant effluent it should be possible to effect even greater concentration. Work is continuing on this project to study the effect of temperature in an effort to improve chromium take-up. I t is believed that advantage may be taken of the formation of chromium complexes present a t different temperatures, thus reducing the amount of leakage of chromium and perhaps improving the amount recovered from the bed.
5.0
RECOVERY OF ORGANIC COMPOUNDS
Organic Cations. A considerable amount of work has been done on the recovery of organic acids and bases by ion exchange. Most of the work has involved acid recovery by anion exchangers but some information has been published on recovering alkaloids by cation exchange. Nicotine has been recovered from the exhaust gases of cigarette tobacco dryers by scrubbing the gases with water or dilute acid and passing this nicotine solution through Zeo-Karb H, a cation exchanger of the sulfonated coal type operating on the hydrogen cycle. The nicotine v a s then removed by treating the exhausted exchanger with ammoniacal alcohol (4). This process is illustrated in Figure 4. Organic Acids. Western Regional Research Laboratories reported the results of their pilot plant work on the recovery of tartrates from winery wastes by anion exchange. The tartratecontaining waste liquors were passed through a bed of anion exchange material exhausted to the hydrochloride salt. The tartrate anions were exchanged for chlorlde ions and after exhaustion the tartrates were recovered from the anion exchanger as the sodium salt by passing relatively concentrated sodium chloride brine through the bed. The salt solution was then limed to form crude calcium tartrate (5, 6).
'0° 10
20 30 40 SO EFFLUENT VOLUMEPER VOLUME ZEO-KARB
449
60
r
250 C R + CU RECOVERED
Figure 2. Effluent Analysis in Chromium and Copper Waste Recovery with Zeo-Karb (Bed volume, flow rate, and analyais of influent, same as shown for Figure 1)
The recovery of copper from cuprammonium wastes has been accomplished on a large commercial scale a t the Dormogen and Eberfeld plants of I. G. Farbenindustrie ( 1 ) . It is reported that the amount of copper recovered by these plants was over 17 tons per day. In these plants the cation exchange resin, Wofatit D, was used. The copper was removed from the cuprammonium waste as the diamine complex and, after exhaustion, the recovery was carried out by means of sulfuric acid. It is reported that the copper sulfate recovered was extremely pure and better for dissolving cellulose than the copper oxychloride in ammonia previously used. Anion Exchange. Processes for the recovery of metals by anion exchange also have been developed and reported in the literature. Nachod disclosed a p r o r ~ s sfor recovering gold and metals of the platinum group present in the form of anions of a complex acid by contacting the solution with an anion exchange material containing basic nitrogen groups ( 9 ) . Recovery of the precious metal values may then be carried out either by chemical means or by igniting the exhausted resin. . The recovery of other metals by anion exchange has been Ieported by Sussman, Sachod, and Wood ( l a ) . Among these metals were chromium, molybdenum, vanadium, iron, and the precious metals, gold, palladium, and platinum. In contrast to the process disclosed in the patent mentioned above, however, this metal recovery process utilizes an anion exchanger exhausted with hydrochloric acid rather than regenerated to the free base Kith an alkali. Other acids may be used, but the best results on metal recovery were obtained when the anion exchanger was exhausted with hydrochloric acid so that chloride ions are exchanged for the metal anion complexes. After exhaustion of the anion exchanger bed, it was treated with an allrali such as ammonium hydroxide, sodium carbonate, or sodium hydroxide, for the recovery of the metal salt. In preliminary laboratory work concentrations of about 2.5 to 3% have been made representing approximately %-fold concentration. I n some cases recoveries as high as 97% were realized.
100
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I
4
I 6
EFFLUENT VOLUME PER VOLUME
I
B
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ZED-KARB
Figure 3. Regeneration in Chromium arid Copper Waste Recovery with Zeo-Karb Bed volume 55-ml. Zeo-ICarb i n 16-mm. diameter tube; regenerant, i 1 9 m l . 1 N HgSOa a t 15.8 cc./minute; rinse, 300 ml. a t 15.8 cc./minute
The recovery of organic acids taken up by anion cxchangers may be accomplished by three different methods: Displacement of the organic anion by an inorganic anion present in relatively high concentrations-for example, the displacement of the tartrate anion with chloride from sodium chloride brine. The displacement of the organic anion with an inorganic anion supplied by an acid-for example, the displacement of tartaric acid from an anion exchanger with sulfuric acid. Regeneration of the exhausted anion exchanger with an alkali to form a salt of the organic acid. The last two methods of anion recovery were investigated in this laboratory in the recovery of tartrates by a unique process, shown in Figure 5 . The tartrate raw material was obtained by extracting pomace, the skins, stems, and seeds of grapes, thus forming a potassium acid tartrate solution of approximately 0.5% concentration. This solution then was passed through a bed of an anion exchanger, where the free acid in the potassium acid tartrate solution was removed leaving potassium tartrate. The potassium tartrate solution remaining was pbssed through a hydrogen
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
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Vol. 41, No. 3
water followed by a small amount of fresh brine. Regeiieration entirely with brine may make the process uneconomical. R C W A Hydrogen Exchange. ,5,unique RCCOVCRY process for utilizing waste grapefruit peel inwlving ion exchange has bccn in factory scale commercial use for the last 7 years by Universal Colloids Company, Inc., LIcAllen, Tes. (8). ThiR process is the manufacture of high t grade pect,in from albedo; the rag arid peel of grapefruit remain after extrscting the grapefruit juice or grapefruit sections. A flow diagram of this process is shown in Figure 6. The grapefruit peel used in this process is obtained from local canneries. The peel is received by truck and is unloaded into a hopper which empties on a conveyer belt discharging to R E inclined belt,. Here t,he peel is sprnyc~i with water to remove adhering mat+ rial from the peel. The inclined coliveyer discharges to a cylindrical rotary washer with numerous holes where the peel is depulped and deseerled. The cleaned peel then goes to a storage bin and from there by elevator to another storage bin above a large grinder. Here the peel is ground and st,ored ill bins. Thc pcel then is dropped into a wash tank equipped with a flat) ayitaior and false bottom. The peel is washed three t,imes;first, with nearly boiling water to inactivate the enzymes in the peel, then with two washes at 140" F. The washed peel is pressed in a hydraulic press and either dried and stored for post) season processing or used in the pressed condition for immediate extraction.
exchanger bed where the potassium tartrate was converted to tartaric acid, The tartaric acid v,-as removed by a third step in the process, again using an anion exchanger. The first anion exchanger bed was treated with 15% sulfuric acid resulting in 8 to 10% tartaric acid rccovcry cffluent. The ot,her anion exchanger bed xas regenerated with 10% potassium hydroxide solution resulting in the formation of approximately 10% potassium tartrate. These two tartrate solutions were decolorized, mixed, and cooled overnight resulting in the crystallizat,ion of pure potassium acid tartrate. To complete the cycle, the first De-Acidite unit was regenerated o ~ 5 z ~ o ~ ~ s sA C /~ / Dx c71 1 with alkali.
7 ~ 4 ~
RECYCLIIVG OF RECOVERY EFFLUEIVTS
In recovery methods such as those described, it is necessary that some recycling of the recovery effluent be practiced, no matter which method of recovery is used. Buck and Mottern described such a method of recycling in t'he recovery of malic acid ( 3 ) . They segregated the recovery ef'duent into several fract,ions and fortified these fractions with fresh regenerant. In this manner they wcre able to obtain approxiniately 5% malic acid concentrations in small scale tube work. RE.1IOVAL OF IMPIJRITIES
70 WAST F
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Base Exchange. Processes based on thc Fig ure 5 . Three- Step Demineralizing-Tartrate Kecovery treatment of wastes by ion exchange for the production of a usable by-product by the reThe washed peel from storage is transferred to a scale where moval of undesirable impurities include processes of base exabout 5 pounds of peel are weighed out to 1 pound of wet Zeochange, hydrogen exchange, and demineralizing. An example Karb (39.5'% moisture). Water is added to this mixture and of the purification of wastes by base exchange is a process for the extraction of the pectin is accomplished with agitation for 1 hour softening of sulfite waste liquors (14). The calcium in the waste near boiling. The Zeo-Karb H converts residual salts present liquor is exchanged for sodium from the zeolite at 180" F. The in the peel t o the corresponding acids, lowering the pR t,o about, softened liquor then is evaporated to 45 to 65% solids content 2.7 and taking up metal cations from solution. Thus, the pectin and this liquor is burned. I t is claimed that the heat obtained is freed to solution without breakdown of the pectin due to esfrom burning the concentrated liquor is greater than that required cessively low pH conditions. for evaporation of the dilute softened waste liquor and that The extraction mixture t,hen is centrifuged; during this operation valuable sodium salts may be recovered from the ash. Regenthe Zeo-Karb collects mostly on the outside wall of the basket and eration of the exhausted zeolite may be accomplished with sea
45 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1949
the extracted pulp nearer the center of the basket. The pectin solution, which contains about 0.6% pectin, goes t o a tank where filter aid and activated carbon are added. The solution is filtered and evaporated in two stages producing a pectin solution containing approximately 5% pectin. The jelly strength of the pectin solution then is adjusted to the desired strength; after this it is dried by means of a drum dryer, producing granular pectin.
pineapple slices in place of sucrose solutions made from refined cane sugar. At the same time the citric acid, one of the impurities taken out by ion exchange, is recovered as a valuable byproduct. The citrus industry is confronted with a similar waste problem in the peel remaining after removing the citrus juice or fruit sections. In the past this problem has been met either by dumping
PEEL PR o-
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REGENERATED
50
Figure 6.
SCALES
Pectin Manufacture by Zeo-Karb Process
The grade of pectin before blending is approximately 260 although grades higher than 300 have been obtained by means of this process, (Pectin grade equals the pounds of sugar gelled by 1 pound of pectin.) The Zeo-Karb and spent peel mixture from the centrifuge are transferred into an agitation tank from which they overflow to a reel sprayed with water. The Zeo-Karb washes out through the screen and the peel is retained inside and discharged to waste. The Zeo-Karb passing through the screen is caught in a tank and that which settles out is taken to a storage tank located above the regeneration tank. After 90 cubic feet of exhausted Zeo-Karb have been accumulated, it is dropped into the regeneration tank, backwashed thoroughly with water to loosen and remove adhering particles of peel and then regenerated with 2% sulfuric acid. The excess sulfuric acid is rinsed out and the regenerated ZeoKarb is discharged to a storage tank from which it is withdrawn for use in the extraction process, as required. Approximately 6 pounds of 100 grade pectin are produced per 100 pounds of washed peel. In spite of all the handling of Zeo-Karb in this process, the loss amounts to only 0.15 to 0.2 pound of Zeo-Karb per pound of 100 grade pectin produced. Demineralizing. The demineralization of a number of waste sugar solutions has been studied. Among such sugar solutions are whey, which contains about 5% lactose, and the wastes from fruit canneries such as citrus fruit canneries and pineapple canneries which contain 6 to 8% sugar. A large demineralizing plant for removing both organic and inorganic impurities from pineapple mill juice has been installed in Hawaii, The effluent, purified by ion exchange, is concentrated to a sirup for canning
or by liming the peel, then pressing i t t o remove moisture. The pressed peel has been dried for use as cattle feed and the juice evaporated t o citrus molasses for use either in cattle feed or in alcohol manufacture. Alternatively, the citrus peel press juice has been lagooned or disposed of in sewage plants, but since the B.O.D. is high i t has created serious problems no matter how i t has been treated heretofore. Both orange and grapefruit peel contain glucosides. The glucoside in orange peel and in the extracted juice is hesperidin and in grapefruit, naringin. These materials have no properties which would lead one to expect removal by ion exchange, but they are removed t o a certain extent, presumably by adsorption on ion exchange materials. The sirup produced by demineralizing may be utilized either directly by commercial users such as bakers, bottlers, candy manufacturers, as a-flavored sirup, or as a sweetening agent in the canning industry. A large demineralizing plant has been installed for demineralizing citrus peel press by Juice Industries, Dunedin, Fla. These few examples illustrate some of the methods by which ion exchange can be used in the treatment of wastes. With federal, state, and municipal governments and numerous other organizations becoming increasingly concerned over pollution of streams, rivers, and other waters, industry undoubtedly will be forced t o pay more attention to the treatment of harmful wastes than has been paid in the past. Such treatments can be expensive to carry out unless by-products are recovered. Ion exchange offers a means for such recovery which in many cases may pay the major portion of the cost of treatment and sometimes a handsome return besides.
INDUSTRIAL AND ENGINEERING CHEMISTRY LITERATURE CITED
Vol. 41, No. 3
(8) Myers, P. B., and Rouse, A H. (to Sardik Inc.), U. S. I'rit(xrlt
Anon., Chem. & M e t . Eng., 52, 214 (1945). Beaton, R. H., and Furnas, C. C., IND. ENG.CHEW,33, 150013 (1941).
Buck, R. E., and hlottern, H. H., Ibid., 39, 1087-90 (1947). Kingsbury, A. W., Gilwood, M. E., and Mindler, A. B., Chem. Eng. Prog., 44, 497-500 (1948). Matchett, J. R., Fruit Products J . , 107-12 (December 1943) Matchett, J. R., Legault, A. A., Ninimo, C . C., and Notter, G . K., IND.XNG. CHEM.,36, 851-7 (1944). Mindler, A. B., and Gilwood, M. E., Proc. Ann. Water Conf. Engrs. 8 0 c . west. f e n n . , 181-2 (1947). ~
2,323,483 (July 6 , 1943). (9) Nachod, F. C. (to Permutit Company), Ibid., 2,371,119 ( 5 I a I c h 6 , 1945). (10) Permutit Company, New York, N. Y., unpublished data. (11) Sussman, S., and Mindler, A . B., Chem. Inds., 56,989-95 (1Y45, (12) Sussman, S., Nachod, F. C., and Wood, W., I K DENC. ~ CHEM., 37, 618-24 (1945). (13) Tiger, H.L., and Goeta, P. C . (to Permutit Company), U . S, Patent 2,397,575 (April 2, 1946). (14) Tyler, R. G., Zbid., 2,392,43,5 (Jan. 8, 1946). RECEIVED August 9, 1948.
A TRIPLE-PASS C O U ION E X C H A N G E S Y S T E M 'I'* George iM. Moflett Research Laboratories, Corn Products Rejking Company, Argo, I l l . triple-pass, countercurrent ion exchange station was operated on a continunus basis in a pilot plant refinery producing dextrose by the hydrolSsis of starch. Ion exchange refining was evaluated by the extent of removal of ash, acid, color, copper, iron, nitrogen, turbidity, and 5-hydrox~methylfurfural from liquors passing through each of the columns in service. Although specifications as to the temperature of liquids undergoing ion exchange treatment usually limit operations to 100' F., resins in the pilot plant hapebeen in use for over 200 cq cIes at 140" FHot water has been inrorporated into the regeneration
A
procedure during this period. Loss in cation resin cupacity for ash was overcome i n laboratory studies by treatment with a 470 sodium hydroxide solution a t 1.55' F . This restored capacity was approximately 35 less than the original capacity of the resin, but was a constant valuw obtained on restoring resins with varying numbers of cycles. In a n effort to restore the capacity of the anion resin for acid removal, a 10% sulfuric acid treatment at 140" F. was applied. No increase in acid removal capacitj was obtained; b u t color and nitrogen removal properlie. of the resin were improved.
PILOT plant with a capacity of over 5000 pounds of dextiose sugar per dav and employing a triple-pass countercurrent ion exchange station for refining was operated during the last 2 years ( 2 ) . It is the purpose of this paper t o point out some refining characteristics of the multipass ion exchange system and to show the effect of continued use and special restorative treatments on resin capacity. I n the preparation of commercial dextrose, TT ashed corn starch is converted to dextiose in the presence of acid at elevated temperatures. ApprovimatPly 85 yo of the resultant hydrolyzate dry substance is dextrose. After conversion, the acid is neutralized n i t h soda ash, and the impurities and degradation products in the hydrolyzate are removed to a sufficient degree t o permit the dextrose to be crystallized from solution ( 3 ) . Generally, bone char and activated vegptable carbon are employed for the refining operation. In this 13-ork, the ion exchange materials were used in place of the soda ash neutralization and bone char refining ( I ) , -4 simplified flow sheet of the ion exchange process for dextrose manufacturing is shown in Figuie 1.
carried on through six alteriiately placed anion and uat,iori units one pair of columns was off-stream for regeneration. At eyuililirium in continuous operat,ions, raw liquor entered the niw1 exhausted pair of colunins and refined liquor left the most rrccntly rcgencrated pair. Periodically, a freshly rcggneratcd pair of columns was added to the end of the stream and two exhausted columns removed from the first and second positions. Regeneration of the exhausted columns was accomplished in n manner similar to that employed in the demineralization of water. .Is a preliminary step, the residual sirup in the columns \vas rinsed out and collected for reprocessing. The resin bed5 thcn were backivashed with water a t 140' I?. and the respective regenerants introduced. Anion tcgenerant was introduced upflow and consisted of 50 gallo'ris of 4% aqueous ammonia, or 0 2 gallon of 26" E&. ammonia per cubic foot of resin. Cation regeneration was done in the standard dawnflow manner and rcquircd 150 gallons of 2% sulfuric acid (0.4 gallon of 66' B6. acid per cubic foot of resin). Excess regenerant was rinsed from t h r columns with condensate a t 140 F. t o complete the regeneration cycle. Since the fresh columns were inserted at the end of thr triple-pass system, a cycle for any pair of columns consisted oi regeneration followed by service in the last, middle, and firs1 positions on stream.
TRIPLE-PASS COUNTERC URREBT IOU EXCHANGE SYSTEM
Pilot Plant Equipment. The ion exchange station in the pilot plant consisted of eight rubberlined and pressure-tight columns, each 18 inches in diameter and 7 feet high. The anion and cation exchange materials, respectively, were a polyamine phenolic resin and a sulfonated phenolic resin. Each anion column contained 5 cubic feet of resin to a bed depth of 3 feet, whereas each cation column held 4.25 cubic fcet, equivalent to a 2.5-foot bed depth. A view of the pilot plant columns is shown in Figure 2. Operation. Operation of the triple-pass countercurrent ion exchange system is illustrated in Figure 3. Sirup refining was
REFINING CHARACTERISTICS O F THE SYSTEM
The refining contributions of each of the six columns comprisirig the multipass system were evaluated. Although a satisfactory effluent liquor was obtained from the station as a unit, several refining characteristics of a continuously operated countercurrwt multipass ion exchange system were observed in the colunin to column surveys. A qualification to be noted, however, is the1 thc
