July 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
1211
LITERATURE CITED
(13)
Kienle, R. H., and Race, H. H., Trans. Electrochem. SOC.,65,
(1) Bozza, G., Giorn. chim. ind. applicata, 14,294-6,400-7 (1932). (2) Bradlev. T. F.. IND. ENQ.CHEM.,30, 1087 (1938). (35 Bradley; T. F.; and Johnston, W. B., Ibid., 32,802-9 (1940). (4) Ibid., 33, 86-9 (1941). (5) Brasseur, F.,and Champetier, G., Bull. soc. chim., 1946,265-71. ( 6 ) Clarke, T. H., and Stegemann, G., J . Am. Chem. Soc., 62, 181517 (1940). (7) Daubert, B: F., and King, C. G., Zbid., 60,3003-5 (1938). ( 8 ) Zbid., 61, 3328 (1939). (9) Fairbourne, A . , and Cowdrey, G. W., J . Chem. SOC.,1929, 12935. (IO) Hanel, H., Kunststoffe,21, 76-9, 105-9, 132-6 (1931)t (11) Houwink, R., and Klaassen, K. H., Kolloid Z., 70,329-36 (1935). (12) Kienle, R. H.. and Hovey, A. G., J . Am. Chem. Soc., 51, 509-19 (1929).
(14)
Kogan, A. I., J . Applied Chem. (U.S.S.R.) Series B, 9, 1070
(15) (16) (17) (18) (19) (20)
Marcusson, J., Z . angew. Chem., 39,476-9 (1926). Ruemele, Th., Kunststofe, 23, 132-4 (1933). Savard, J., and Diner, 8.. Bull. SOC. chim., [4 I 51,597-615 (1932). Scheiber, J., Fette u. Seifen, 50, 12-18 (1943). Schlenker, E., Allgem. Oel-u. Fett-Ztg., 29,658-63 (1932). Warren, H., and Bevan, E. A., Brit.Plastics, 2, 387-8, 390, 394,
(21)
Winning, C. H., and Williams, J. W., J . Phgs. Chem., 36, 2915-
(22) (23)
Wornum, W. E., Chem. Age, 3 0 , 2 4 5 (1934). Wornum, W. E., J . Oil & Colour Chemists’ Assoc., 16, 231-48
231 ~-~
(1934). .----,
(1936); 10, 900 (1937).
4 4 3 - 4 , 4 4 6 , 6 2 4 4 , 5 4 8 , 5 5 0 (1931). 35 (1932). (1933); 17, 119-45 (1934).
RECEIVED Maroh 17,1947.
Demineralization of Sugar Cane Juice A PILOT PLANT STUDY A. B . MINDLER The Permutit Company, New York IS, N . Y . T h e demineralization of Cuban and Louisiana sugar cane juices has been investigated on a pilot plant scale. Removal of 90 to 95% of the ash and 70 to 75% of the nonsugar solids was realized by the two-step demineralizing process. The purity rise for Cuban juice averages 4.7% and for Louisiana juice 6.5%. However, the calculated increase in sugar yield to be expected from juice of higher
T
H E treatment of sugar solutions by ion exchange has recently been the subject of intense publicity in popular and technical journals and in the patent literature. Actually, it was over fifty years ago that Harm (3) in 1896 suggested the use of a zeolite for replacing the melassigenic or molasses-forming alkali metal cations, sodium and potassium, with the less melassigenic calcium cation, in order to imprave sugar yield. However, Harm’s process proved unsuccessful, mainly because it increased evaporator scale. I n 1936 Liebknecht (4) suggested for the first time the demineralization of sugar solutions by passage successively through a n acid-regenerated cation exchanger and a n alkali-regenerated anion exchanger. This process has aroused increased interest during the past twelve years with the development of more rugged ion exchangers of higher capacity. The first laboratory and pilot plant tests on demineralizing beet sugar solutions in the United States were initiated by The Permutit Company at the Mount Pleasant, Mich., factory of the Isabella Sugar Company from 1932 t o 1939. The interesting results obtained in these tests led to the installation at that plant of large factory demineralizing units in 1940. The operation of this installation was described by Weitz (8) and Gutleben and Harvey (1). Some pilot plant data on beet sugar demineralization were reported by Haagensen (Z), but very little has been published on the demineralization of sugar cane juice, from which a major portion of our sugar supply is derived. This report presents the results obtained in the course of pilot plant investigations on the demineralization of Louisiana and Cuban sugar cane juices.
purity could not be confirmed in the pilot plant operation. Consideration is given to other advantages of the process, including elimination ef evaporator scaling and improvement in sugar and molasses quality. A discussion of the disadvantages deriving from the process includes inversion losses, capacity losses, water requirements, and dilution of the juice during processing. THE DEMINERALIZING PROCESS
The-demineralizing process is a two-step process for the removal of electrolytes from solution. First, the solution is passed through an acid-regenerated cation exchanger bed where hydrogen ions are exchanged for metal cations in solution : reaction
HzZ
+ 2K+ 7 KzZ + 2 H +
(1)
regeneration
where HzZ represents the acid-regenerated cation exchanger and potassium a typical metal cation. RAW I N FLUENT
REGENERATING
* EFFLUENT
Figure 1. Flow Diagram of Demineralizing Process
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- __ _ _I _
--I
-1-
18"? 7'-O"STR
24"t 7'6"STR,
rlOT RAW CLARIFIED JUICE
RUBBER LINED
RUBBER LINED
2 EO-KARB "
~
DE-ACIDITE UNIT
EVAPORATOR a VACUUM PAN 7CU.FT. VOLUME
CONTAINING 5 CUFT DE-ACIDITE
WATER INLET
EXCHANGER
r-
ZEO-KARB CENTRIFUGAL-40%
Figure 2.
Flow Diagram of Process for Demineralizing Sugar Cane Juice
Acids are formed corresponding to the organic and inorganic salts originally present. In the second step these acids are removed by passing the acid solution through an anion exchanger or acid-removal bed:
R3N
12"
1
+ HCl
reaction ___f
(R8NH)Cl
where R3N represents the free anion exchange material in the base condition and hydrochloric acid typifies the acids removed. Thus, it is possible to remove substantially all the electrolytes from solution. Nonelectrolytes pass on through both exchange materials. A flow diagram of the process is shown in Figure 1. After the cation exchanger has been exhausted to its capacity for exchanging hydrogen ions for metal cations, it is backwashed with water and regenerated with an acid, usually dilute sulfuric acid. The anion exchanger is likewise backwashed and then regenerated with an alkali, usually dilute sodium carbonate solution, although sodium or ammonium hydroxide may be used. After the excem regenerants have been rinsed out, the ion exchanger beds are ready for the next demineralizing cycle.
in solution. The flow rate used was 6 gallons per minute per square foot of bed area, the same as that generally employed in demineralizing water. A photograph of the demineralizing plant is included in Figure 3. The demineralized juice was collected in a treated juice tank, sampled, and boiled to a sirup having a solids content of about 58" Brix. The sirup was then boiled to a strike of sugar which was purged in a centrifugal. The molasses from these strikes were set aside and boiled back three times to obtain a "D" sugar. OPERATISG DATA
During the course of the work regenerant dosages investigated varied from 2 to 6 pounds of sulfuric acid of Zeo-Karb and from 2.6 to 7.6 pounds of sodiuni carbonate per cubic foot of DeAcidite. The dosages used in most of the work were 3 pounds of sulfuric acid per cubic foot of Zeo-Karb and 3.9 pounds of sodium carbonate per cubic foot of De-Acidite, both introduced as 2% solutions. Regeneration was carried out in a manner similar to
PILOT PLANT EQUIPnlENT 4 h D OPERATING PROCEDURES
A flow diagiam of the equipment used in the pilot plant work in Cuba is shown in Figure 2. The lime-defecated juice, usually 295 gallons, was taken from the clarifier and cooled to about 30" to 35' C. by passage through a heat exchanger to the feed tank, I t xas then introduced into a rubber-lined steel hydrogen exchange unit 24 inches in diameter by 7 foot 6 inches in straight height, containing 10 cubic feet of Zeo-Karb H (a cation exchanger of the sulfonated coal type) through a low-level distributor located about 3 inches above the bed. The acid effluent from the Zeo-Iiarb H bed, having a pH of about 1.8, was then introduced through a lowlevel distributor into a rubberlined steel acid removal unlt 18 inches in diameter by 7 feet in straight height, containing 5 cubic feet of De-Acidite. The De-Acidite removed the acids, leaving substantially only the sugars
Figure 3.
Pilot Plant for Demineralizing Sugar Juices
July 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
that used in demineralizing water, except that the regeneration dosage was somewhat higher than that generally used in water work. Five and sometimes six runs were made per day, averaging about 4.5 hours for a complete cycle. Similar operating conditions were used in both the Cuban and Louisiana pilot plant tests.
would give a maximum retention of 94.8%. This should increase the yield of 97” purity sugar by 3.5% or 112 pounds. Obviously, 37.95 purity final molasses is very high for a normal’raw sugar house operation, but this value was used in these calculations because it is the value of the most exhausted molasses produced from demineralized juice during this work. However, a more exhausted molasses would have resulted had the “D” massecuite been allowed t o crystallize longer than 21 days and if agitation had been used on the crystallizer.
EFFLUENT VOLUME
Figure 4. Solids Content and Conductivity of Effluents Operating data for Louisiana cane juice Flow rate, 10 gallons per minute Temperature, 15’ F. Conductivity, 130 grains per gallon Brix, 13.94
Samples of both the Zeo-Karb and De-Acidite effluents were taken a t regular intervals during the run and analyzed for solids content, conductivity, pH, and titration value in order t o obtain breakthrough points and capacities of both ion exchange materials. These data for a typical run on Louisiana cane juice are shown in Figures 4 and 5. PURITY RISE
The demineralization of Cuban sugar cane juice by the twostep process resulted in the removal of 90 to 95% of the ash and 70 to 75% of the nonsugar solids, and gave a n apparent puflty rise of 4.7%, the average for 150 rqns during the 1946 crop on Cuban cane juice at Central Espafia. For Louisiana juice at Godchaux Sugars, Raceland, La., during the 1943 crop the purity rise was somewhat higher because of less mature cane. The removal of ash and nonsugar solids was of the same order as for Cuban juice, but the apparent purity rise averaged 6.5% for 50 runs. The degree of color removal from the sugar juice was somewhat disappointing in this work, in t h a t the treated juice after”the first few runs was not water white. Only a rough quantitative test was available for determining the color of the juice. Color removal from the juice amounted to roughly 50 t o 75%. Figures 6 and 7 illustrate the degree of color removal during the first few runs and after 30 runs on Louisiana juice. Figure 8 illustrates the quality of a typical “A” sugar obtained directly from demineralized juice during this work, the sugar was not washed and there was no carbon or other treatment whatever.
1213
Figure 5.
- BILLONS ,
Normality and pH of Effluents
Operating data for Louiuiana cane juice O Brix 13.94 pH 6.2 Noxkality, 0.0024
The eight batches of juice mentioned above were boiled t o strikes, the resulting molasses were boiled back three times, and a careful account of the sugar balance was kept. Because of the difficulties in operating this small scale vacuum pan and centrifugal equipment it was not possible t o determine quantitatively the amount of extra sugar obtainable. Furthermore, high boiling efficiencies, usually made possible by mixing richer sirups with I1 11 A and “B” molasses in the vacuum pan, could not be practiced in this small scale operation. ’ For Louisiana juice the purity rise averaged 6.5%; thus the purity of the juice was increased from about 78 t o about 84.5.
INCREASED SUGAR YIELD
Eight batches of clarified juice having a n apparent purity of 85.54% were demineralized, resulting in a purity rise t o 89.83%. The raw juice of these eight batches contained a total of 3205 pounds of sucrose. According to the SJM formula of Noel Deerr, if apparent purities were used instead of true purities which is standard practice for comparative purposes (6), the maximum retention when boiling t o a 37.95 purity molasses is 11.3%. Boiling to the same molasses, the demineralized juice
Figure 6 . Juice Samples of R u n 2 Left to right. Before deniineralizing, after hydrogen exchange, and after demineralizing
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 40, No. 7
tance. The final molasses obtained after four strikes has the following analysis: Brix Polarization. Purity, Yo Reducing sugars (as glucose), Ash (dry basis)
80.02 80.02 30.38 37.95 34.57 3.08 3.08
DILL TION
Figure 7 .
Juice Samples of Run 30
Left to right.
Before demineralizing, after hydrogen exchange, after demineralizing (beginning of run), after demineralizing (composite sample), and water
According to the SJRI formula the increased sugar yield would be 6.2%. INVERSION
During the hydrogen exchange step the pH of the sugar juice drops to about 1.8 and the p H remains a t this low level while the juice is passed down through the lower layers of the hydrogen zeolite bed, the gravel supporting bed, and the interconnecting piping, until the acid is removed from the HzZ effluent by the anion exchanger. The period of time a t the low p H is approximately 3 minutes. Obviously some inversion will take place during this time. Theoretically, a t the operating temperature of 30" C., about 0.1% of the sucrose introduced will be inverted in 3 minutes at pH 1.8 (6). I n this work, however, the actual amount of inversion encountered was closer to 0.570 of the sucrose introduced and the only explanation of the variation between the low theoretical inversion expected and the relatively high amount realized lies in fermentation or catalytic inversion by the hydrogen exchange material. No evidence of fermentation in the beds v a s found and therefore attention was shifted to catalytic inversion. The increase in "glucose ratio" (ratio of sucrose to reducing sugar as glucose), from 8.35 a t 15.12" Brix Cor Louisiana juice to 124 for 1.63" Brix sweetening off water, indicates that a considerable portion of the inversion encountered arises from this catalytic reaction. Here sucrose is maintained in intimate contact with the solid acid, the hydrogen exchanger, For approximately 45 minutes. These data confirm qualitative eests previously reported on the inversion of sucrose by hydrogen exchangers ( 7 ) . The sucrose converted to reducing sugars (calculated as glucose) will, of course, appear in the final molasses, which is suitable for many edible purposes where color is not of impor-
Figure 8.
Unwashed Sugar Produced from Demineralized Juice
Obviously, the normal water-treating practice of introducing the solution to be treated into the exchanger shell through a high-level distributor located just below the top head of the shell, cannot be used in treating sugar solutions which are heavier than water, since these solutions would be diluted by the water above the bed and a heavy load would be placed on the evaporators. Some provision must be made for minimizing this dilution. In conventional work of this type it has been the custom to drain the water above the bed to just above bed level and introduce the sugar liquor through the low-level distributor, maintaining an air cushion above the liquid level throughout the treatment, or alternatively allowing the liquid to fill the entire shell. I n this work, however, the sugar juice was introduced into the ion exchanger shell through the low-level distributor underneath the superimposed column of water above the bed. Surprisingly enough, the water stays in place during the entire run and the amount of diffusion of sugar into the water column is very small, The simplicity of operating by this method can readily be realized, since it eliminates all complicated level control apparatus. Table I indicates the magnitude of the diffusion layer during a run of 2 hours 32 minutes a t 3 gallons per minute per square foot, using a feed material of 13.5" Brix.
TABLE I.
MAGXITUDE OF DIFFUSIOX LAYER
Time, Min. n
Height of Diffusion Layer above Distributor, Inches 0
2 4 5 5.5 6 6.25 6.76
7 7.5 7.75
The analyses of the diffusion layer a t 2-inch intervals confirm the small amount of sugar in the diffusion layer, since a t the end of the run the solids content was as shown in Table 11.
TABLE IT, SOLIDS CONTENT Inches above Distributor
Brix at 200 c. 13.2 12.8 10.0 4.9 0.2
At a flow rate of 6 gallons per minute per square foot of bed area, the diffusion layer reaches to 10 inches above the distributor in 45 minutes, the length of a normal run, because of increased eddy currents through the particular distributor used in this work, which was a perforated cap type. A redesigned distributor would undoubtedly decrease this diffusion laycr greatly. A comparison of a typical hydraulic head run with a typical air dome run is shown in Figure 9. Calculations indicate that the extra evaporation required to overcome dilution during demineralizing, when srveet waters above 1.5"Brix (corrected to
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1948
'
SWEETENINO ON AN0 OFF CURVES
eo
I
FEED,MATERlAL- AIR O W E - 249 O I L - 1818.iBRlX FEED MATERIAL- HYDRAULIC HEAD 250 QAL- IB.I(L*BRIX
-
1215
25 runs. More effective restoration treatments have been devised more recently. With these the quality of the demineralized effluent is improved in lower ash content and color a n d the capacity is maintained even more effectively. WATER REQUIREMENTS
I
o,'
A
Id0
I
I-
Id0 EFFLUENT
,do
VOLUME
I
-
\
,do
zdo GALLONS
,do
3do
Figure 9. Efauent Solids Content in Air Dome and Hydraulic Head Methods of Operation
20" C.) are included, is about 10% for either type of operation. For example, in these two runs the per cent evaporation t o obtain a 58" Brix sirup is 72.8% with the air dome method with straight juice and 83.0% with demineralized juice. With hydraulic head operation the evaporation is 73.6% using straight juice and 83.6% using demineralized juice. This extra evaporator load can be reduced by about 30% by re-using sweet water for the first portion of sweetening off instead of water, as shown in Figure 10. While this work was carried out with a juice having a solids content of only 12.6' Brix, the magnitude of savings in evaporation would be about the same for a n 18.5O Brix juice. The seriousness of the dilution problem is somewhat decreased by the fact t h a t the demineralizing process removes all scaleforming salts from the juice and permits continuous operation throughout the crop with the evaporators operating at top efficiency, and thus avoids the customary weekly shutdown for washout of evaporators. During the work in Louisiana, a n evaporator of forced convection type was operated for the equivalent of 28 days of continuous operation of a natural convection evaporator. No loss in pounds of evaporation per square foot per hour was experienced. Inspection of the tubes at the end of the crop indicated only a paper-thin black scale of an undetermined but probably organic nature.
One of the most serious problems in the installation of this type of equipment for demineralization of sugar cane juice is the large quantity of water required for washing and regenerating the ion exchange beds and for cooling the juice. This pilot plant work indicated that when waste water is not re-used 1800 gallons of water are required per ton of cane ground merely for operating the exchanger beds. The water requirement per ton of cane ground in a commercial ion exchange installation would be somewhat less. Furthermore, re-use of waste water in a commercial installation would reduce the water requirement per ton considerably. I t is desirable to provide for re-use of some of this water either in the ion exchange plant itself or at some other point in the process. For heat economy the demineralized juice can be used for countercurrently cooling the hot clarified juice going t o the demineralizing equipment. However, some water is necessary to provide supplementary cooling of the hot juice. SUMMARY
These pilot plant tests on ion exchange purification of cane sugar juice indicate that the ion exchange treatment resulted in:
A purity rise of 4.7% with Cuban cane; 6.501, with Louisiana cane. An estimated increased sugar yield of 3.8y0with Cuban cane; 6.2y0 with Louisiana cane. Approyimately o.5y0 inversion. However, the glucose thus produced can be recovered as an improved final molasses. The small amount of deterioration of the ion exchangers was unimportant in the economics of the process. Hydraulic head and air dome head operation were equally suitable. Water requirements for the ion exchange process were found to be 1800 gallons per ton of cane ground, but by proper re-use of water in the plant, they can be reduced considerably. CONCLUSION
CAPACITY LOSS
During the 150 runs carried out with the Zeo-Karb and DeAcidite beds originally installed, the Zeo-Karb capacity dropped 3% and the De-Acidite capacity 8.870. These capacities are based on titration of the effluents of each unit t o determine the amount of acid added by the hydrogen exchanger or removed by the anion exchanger. They include both attrition and chemical losses. The quality of efffuent remained approximately the same throughout these 150 runs in that, as indicated by conductivity ash determinations, 90% of the electrolytes were removed. Restoration treatments of both the exchanger beds were carried out intermittently. These consisted of contacting the Zeo-Karb with 0.5% sodium hydroxide at 50" C. every 50 runs; the De-Acidite with 10% sulfuric acid at 50" C. every I
I
I
RE-WE OF SWEET WITER HIDRUJLIO H E 4 0 OPERAllON
c
'
b
FEED MATERIAL 254 GAL.- IP.(L*,BRIX
I
Figure 10. Evaporation on *Re-use of Sweet Water
This pilot plant work has provided some indication of the benefits obtained in demineralizing sugar cane juice, but has also revealed some of the drawbacks of the process. Further work is progressing on eliminating these drawbacks, in order t h a t the ion exchange process may offer a n improved means for purifying sugar cane juice. ACKNOWLEDGMENT
The author wishes t o express his appreciation t o Godchaux Sugar, Raceland, La., t o the Pepsi Cola Company's sugar plant at Central Espafia, Cuba, and t o their staffs for the cooperation and assistance given in this work. LITERATURE CITED
(1) Gutleben, D.,and Harvey, F., International Sugar J., 47, 11-13 (1945). (2) Haagensen, E.,Sugar, 41,4,36-41(April 1946). (3) Harm, F.,German Patent 95,447(June 2,1896). (4) Liebknecht, O.,French Patent 808,612 (Nov. 14, 1936); U. 5. Patent 2,155,318(April 18, L939,assigned to Permutit Co.). (5) Spencer, G.L., and Mead, G. P., "Cane Sugar Handbook," 8th ed., p. 613,New York, John Wiley & Sons, 1945. (6) Spengler, O.,and Todt, F., 2. Ver. deut. Zuckerind., 78, 393-405 (1928). (7) Sussman, S.,IND. ENQ.CREM.,38,1228-30 (1946). (8) Weitz, F. W., Sugar, 38,26-31 (January 1943). RECEIVED May 29, 1947. Presented before the Division of Sugar Chemistry and Technology a t the 111th Meeting of the AMERICAN CHEMICAL SOCIETY, Atlantic City, N. J.
