INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1951
1065
ACKNOWLEDGMENT
lateral placed 4 inches above the resin bed. To obtain proper contact time, the rate Of brine introduction and subsequent rinsing with fresh water must not exceed 20 gallons per minute for this particular bed having 33 square feet of area.
The authors are grateful for the cooperation of J. s. D'Amico and John Kay in carrying out laboratory experimental work reported in this paper.
SUMMARY
LITERATURE CITED
Research in cooperation with plant operation has established the fact that Nalcite HCR is physically and chemically stable t o . accumulation conditions of high temperatureand high p ~ The of information on expansion characteristics, capacity and water quality, effects of turbidity, thermal stability, operating rates of flow, resin bed depths, and regeneration techniques, all for application a t 230' F., has resulted in early acceptance by the power industry of the two-stage hot lime-resinous zeolite system of water treatment.
(1) Bauman, W. C., Skidmore, J. R., and Osmun, R. H., IND.ENG. CHEM.,4 0 , 1 3 5 (1948). C O . ) , u- s. Patent 2,386,007 (Deo. 26,1944). (3) Kahler, F. H., proc.Ninth ~~~~~l waterconf, ~ ~sot, Western Penn., 40 (1948). (4) Lindsay, F. K., J . Am. Water Works Assoc., 42, 75-80 (January 1950). (5) National Aluminate Corp., Tech. Bull. 4 8 (January 1950).
(2) D'Alelio, G. F. (to General Electric
RECEIVED October 3, 1950.
h
C.P. Glycerol by Ion Exchange D. M. STROMQUIST A N D A. C. REENTS Illinoia Water Treatment Co., Rockford, Ill.
A
S THE ion exchange operation was first conceived and de-
veloped, it was primarily used for the removal of ionized solids from water, but the ramifications of the process soon became evident from the intensive study and development t h a t pointed the way toward removal of impurities and ionized solids from aqueous solutions of valuable nonionized constituents. This paper deals with work done in the research laboratories of the Illinois Water Treatment Co. over a period of years on the deionization of glycerol sweet water and crude glycerols, in laboratory, pilot plant, and full scale operations in various glycerol plants. Glycerol may be produced by several methods; the following are the most important: 1. Saponification of oils and fats for soap production with glycerol as the by-product 2. The splitting of fats and oils by the Twitchell process for soap production 3. The so-called synthetic production of glycerol from propylene by chlorination and hydrolysis
T h e work that is described in this paper was undertaken to determine if the ion exchange process could be adapted successfully to the purification of all types of glycerol solutions. The goal was the production of a pure glycerol which would meet U.S.P. specifications. The results indicate that by the use of the proper ion exchange resins and techniques the color, odor, and dissolved salts can be removed from various impure glycerols as produced by the soap and fatty acids industries. The degree of removal is sufficient that U.S.P. specifications are met by the finished product. Glycerol solutions purified by ion exchange are concentrated by vacuum evaporation to a 95% glycerol. Thus the process is directly applicable to glycerol sweet waters produced by the Twitchell and Emery-Colgate processes. The present method of C.P. glycerol manufacture consists of concentrating to a crude which is distilled to yield the pure product. In the ion exchange process distillation is eliminated.
~
-
A number of impurities are inherent to the production of glycerol and it is of course desirable that they be held to a minimum. Generally speaking, the impurities are present as fatty acids, metallic soaps, salts, and as other organic impurities. The glycerol produced by these processes is evaporated to a crude glycerol. When evaporating spent soap lyes, the concentration of the glycerol increases, and the solubility of the salt decreases. As a result, the salt crystallizes out and is separated from the glycerol, forming one of the first steps in the glycerol purification. The resulting crude glycerol is purified further, if desired, by steam distillation under vacuum. Redistillation of this product produces a chemically pure glycerol, and this is generally the extent of purification by distillation. Treatment by ion exchange involves passage of the material t o be purified through successive beds of regenerated cation and anion exchange resins. X o heat is required for the reaction, as is true with distillation, nor does the material go through any change of state. No excessive amounts of caustic need be added to the glycerol to be deionized to prevent fatty acid carry-over as is the case with distillation. Instead,' these fatty acids and other ionized solids are remove'd in the various ion exchange steps leaving a pure glycerol and water solution that may be evaporated t o a chemically pure product, provided that there is
no excess of nonionised material (such as polyglycerides) in the original. There are several requirements t h a t must be adhered to for the raw glycerol solution t h a t is fed t o the ion exchange units: 1. The solution must be dilute enough and low enough in viscosity so that there is no excessive pressure drop across the exchanger beds-that is, generally 35% solids or below. 2. The solution must be relatively free from free fats and oils as these tend to foul the exchanger beds. 3. Turbidity in the solution must be kept t o a minimum as suspended solids also hinder and retard the exchange process as well as the incidental color removal. 4. The temperature of the solution t o be treated must definitely be 95 "F. or lower, preferably in the 70 O to 80 O F. range.
Attempts have been made prior to this date to incorporate ion exchange in various glycerol and polyhydric alcohol purification processes, but these have been incomplete and have not covered the scope of the present work. Schwarz (6) incorporated a zeolite in his process to exchange excess calcium for sodium after a lime treatment and precipitation. Hoyt (5)suggested the use of an acid adsorbing synthetic resin for removing any free acid present in a glycerol solution after saponification and treatment with sulfuric acid to precipitate calcium sulfate.
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
1066
Metzger ( 5 ) performed work dealing with the removal of acid from glycols by a simple anion exchange reaction. Rrandner ( 1 ) used ion exchange for the purification of polyhydric alcohols by the use of cation and anion exchangers for removing reducing sugars. This was accomplished by digestion of the reducing sugars prior to ion exchange. CR. I W E M - 1 , 0 3 5 CoLoR-71%T AT 410 MU PH-6.10
SP CR. EFFUIEM-1.033 COLOR-81%7: AT 410 MU PH-1.50
y!
[0.6 gram of Ca(OH), per liter] a t a temperature of 160" F. to flocculate suspended solids. The sweet water, after filtration, had the following analysis:
PH
I I
0
20
40
60
80
100
120
j40
160
14.3 0.074 0.9
This sweet water was passed through those ion exchange resins. The analysis a t the various stages is given in Table I.
Sweet Water Analysis Ilk0 '2-231
I
9.75 28
pH Color (transmittance a t 41Ofi), Glycerol, % ' Total alkalinity (as Ka2C03),% Turbidity, p.p.m.
Table I.
20
Vol. 43. No. 5
Ib
Acidity, % Mineral Total Color (transmittance a t 4 1 0 ~ compared to water blank), % Resistivity, ohms/ml. Glycerol, '%
Effluent from Illco Illco -1-364 CA
Illco mixed bed
3.08
6.50
6.35
6.9;
0.043 0.10
0
0 0.006
0
0.005
78 55,000
62
...
14.2
0
99
101 1,400,000 13.8
50,000
14.0
13.9
GAL. SWEET WATERKU. FT. CATION EXCHANGER
Figure 1.
Acidity and pH of Glycerol Sweet WaterCation Exchanger
ii British patent ( 2 ) discloses that work was done in glycerol purification by passing a glycerol solution successively through a plurality of pairs of ion exchangers but that distillation was still required t o produce an acceptable glycerol. Preliminary work on the purification of glycerol bv ion exchange has also been reported by Kahler ( 4 ) . I O N EXCHANGE TREATMENT OF GLYCERINE SWEET WATERS
Sweet Waters Produced by Emery-Colgate Process. K h e n fats and oils are treated with water at high temperature and pressure, hydrolysis occurs, yielding fatty acids and a glycerol sweet water having a glycerol concentration of 8 t o 15%. T o produce saponification crude glycerol, the fatty acids arc separated from the glycerol sweet water. Alum and caustic are normally added t o this sweet water to free the solution of fatty acids and unreacted fat. Following filtration, the sweet water is concentrated by evaporation under vacuum to yield saponification crude glycerol. The glycerol sweet water produced by this method contains a n average of 0.2% ionized solids. These ionized solids consist largely of sodium sulfate plus the sodium salts of organic acids such as acetic, butyric, and stearic. In addition, color is present in varying amounts. The sweet water generally has an offensive odor. The following experimental results were obtained by ion exchanging a typical sweet water of this type: The laboratory ion exchange apparatus used in this work consisted of 2-inch diameter by 48-inch glass tubes, supplied with quartz supporting media for the ion exchange resins. Resin bed depths were 28 inches. Softened water mas used for anion exchanger regeneration. Sulfuric acid, 570 by weight, was used for cation exchanger regeneration, and sodium hydroxide, 4Y0, was employed for anion exchanger regeneration. Regenerant flow rates were 2.0 gallons per square foot per minute. Rinsing was carried out a t a flow rate of 3.0 gallons per square foot per minute. The following ion exchange resins were used in the deionization study: 1.
2. 3. 4.
111~0C-231 111~0A-364 Illco CA Illco mixed bed
Cation exchanger Anion exchanger Color adsorbent Mixed cation and anion exchange resins
Five gallons of the glycerol sweet water were treated with lime
Figures 1 and 2 illustrate the chemical and physical changes that occur during the passage of this type glycerol sweet water through the primary cation and anion exchange resins of the ion exchange system. Figure 1, illustrating the cation exchange cycle, gives the acidities and p H values of the glycerol solution at various points throughout the cycle. The cation exchange resin was considered to be exhausted when the total acidity dropped 20% from the maximum. The primary cation exchanger removes about 90% of the cations (sodium, calcium, magnesium, and iron) present in the raw sweet water. The analyses shown in Figure 1 indicate some color removal a t this point. This color reduction is not due to actual adsorption by the resin but is caused by the lowering of the pH. Color is subsequently completely removed by further exchange steps. I
I
I
I
1
GAL, SWEET WATER/CU. FT. ANION EXCHANGER
Figure 2.
Conductivity, Color, and pH of Glycerol Sweet Water--Anion Exchanger
Figure 2 gives the pH, color, and conductivity values of the glycerol during the primary anion exchange cycle. A considerable amount of the color present is removed at this point. This resin was considered exhausted when the total acidity of t h e effluent reached 20% of the influent. Following ion exchange, a portion of the glycerol sweet water was concentrated in a bliter spherical flask equipped with a GlasCol heater. The vacuum was maintained a t 25 inches of mercury, Whcn the temperature of the glycerol solution reached 80" C., evaporation was stopped. The analysis of this concen-
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1951 Table
XI. Analysis of Concentrated Glycerol Solution 7.05 1.2487 95.2 Conforms to test Conforms to test 2.0 (conforms to test, 0.004%) Conforms to test Conforms to test (2) British P a t e n t 633,343 (Dec. 12, 1949). (3) Hoyt, Howard E., U. S.P a t e n t 2,381,055 (.lug. 7, 1943). (4) Kahler, F., Chem. Eng., 57, S o . 7 , 109 (1950). (5) Metzger, F.J., U. S.P a t e n t 2,409,441 (Oc,t. 15, 1946). (6) Schwarz, T h e o . , Ibid., 1,824,507 ( S e p t . 22, 1931). RECEIVED Serjtember 9, 1950.
Glycerol S. E. ZACER' AND T. C. DOODY Purdue University, L a f a y e t t e , Ind.
HE physical separation of glycerol from water has long been accomplished by evaporation or more recently by solvent extraction (6-8, 12-14), However, with the advent of new anion exchange resins, having properties comparable to those of strong bases, a chemical method has been developed for this separation. It is well known that boric acid cannot be titrated satisfactorily with strong base, using phenolphthalein as an indicator, unless a suitable material such as glycerol or mannitol is added (10). Boeseken and coworkers (2-5) postulated that such behavior was caused by a complex formed b e b e e n boric acid and glycerol nimilar to the type
T h e removal of glycerol from an aqueous solution by a continuous adsorption process promised to be more economical than the distillation of large volumes of dilute solutions. Exploratory tests show-ed possibilities for the removal of glycerol on an anion exchange resin as a glycerol borate complex anion. Boric acid and sodium tetraborate both gave complex anions which were firm13 attached to anion exchange resins. The best runs showed 93 to 9Sqo removal of glycerol from the solutions up to the breakthrough point of the resins. Desorptions by aqueous solutions and organic solvents have not yet given practical methods for recovery of the glycerol. Analysis of aqueous glj cero1 solutions by refractive index gave excellent agreement with chemical methods of analysis. The refractive index, y , is related to the percentage of glycerol by weight, 2, by the equation y = 0.001247~3- 1.33321
where glycerol and certain other polyhydric alcohols may be irpresented by R. Schafer (9) reported that this type structure predominates Kith mannitol, fructose, erythritol, and glycerol. Tuzuki (11) confirmed the existence of such a complex by polarimetric methods. Hc also reported that a complex can be formed hetween glycerol and sodium tetraborate under conditions which 1
Present address, Johns-Manville, Ino. hlanville, N. J.
render complex formation between glycerol and boric acid impossible. As glycerol forms a complex anion n i t h borate compounds, strongly basic anion exchange resins ought to remove the complex from solution. The resuking investigation was directed toward the removal of the glycerol by this technique. Preliminary investigation showed that more glycerol could be removed if boric acid or sodium t,etraborate were held on the
