Semipilot Production of Sucrose from Sorghum T h e beet sugar industry needs a crop it can process during the intercampaign period, when beets are not available for processing. Semipilot operations were conducted in the Carlton plant in the Imperial Valley of California in order to evaluate the possibility of processing sorghum, variety Rex, for sucrose. The cane has starch as well as sucrose in the stalk. Compared to beets, the purity is low and thus the yield of crystalline sugar per ton of cane is below that of beets, but i t exceeds that of Louisiana sugar cane. Results of study over two seasons on production of sucrose from sorghum in the Imperial Valley indicate a good possibility that sorghum will one day be an added commercial source of refined white sugar.
ROBERT H. COTTON, LLOYD W. NORMAN, GUY RORABAUGH, AND H. F. HANEY Holly Sugar Corp., Colorado Springs, Colo.
E
ARLY in the development of the sugar industry in the United States the sorgo cane (Sorghum vulgare Pers.) was recognized
as a potential raw material for commercial production of sucrose. T h e favorable agronomic characteristics of the plant, combined with a fair sucrose content, provided impetus for much study of t h e possibility of obtaining crystalline sucrose from the juice of the stalk (15). These efforts were eventually abandoned, however, because of failure t o devise a satisfactory method of crystalIizing sucrose from the sorgo juices. This was primarily attributed t o the presence of “gums.” which caused excessive viscosity of the concentrated sirups and when present in large enough quantities caused actual jellying. Sherwood (10) indicated in 1923 that starch was the cause of jellying or clabbering of sorgo sirups, and Willaman and Davison (20) found 0.32 t o 1,15y0 in normal sirups and 1.17 to 3.36% in sirups that jelly. Walton and Ventre (18) devised in 1937 a farm scale method for preventing slow boiling and scorching of sorgo juices caused by the presence of starch. Then in 1940 Ventre reported on two years of pilot scale work wherein he was able to obtain successfully a crystalline raw sugar ( 1 5 ) . The process which Ventre found t o be most satisfactory parallels that commonly used in sugar cane production, except for the treatment of the juice and sirup for starch removal by centrifugation and enzyme treatment>,and the removal and recovery of salts of aconitic acid, which he also found to inhibit sucrose crystallization. The essential steps were:
Pressing the juice from the sorgo with rollers Centrifuging the raw juice to remove starch Clarification of the raw juice by lime defecation Treatment by enzyme to convert final traces of starch to glucose Removal and recovery of aconitic acid by precipitation as the calcium salt Crystallization of sucrose from the purified sirups by usual sugar house techniques In addition to the recent technological advancements in processing Rorgo, tests by the United States Department of Agriculture have indirated t h a t the Imperial Valley in California is one of the most promising areas in the United States for producing sugar-yielding sorgo (9). The crop is relatively easy t o grow, and i t would fit well into the prevailing crop rotation. The sucrose content of the cane and purity of the extracted juice are relatively high. The sorgo g r o w during the summer season when but few other crops are gronn in this area. Thus, a crop would be avail-
able for processing by the Imperial Valley factory a t a time when it mould otherwise be idle. The investigations reported here were conducted in the Carlton (Imperial Valley) factory on sorgo grown in that area. The sorgo used in this work was of the variety Rex, thought to be one of the most promising for Imperial S’alley conditions. Table I shows average analyses of the cane grown during the 1949 season and of the juice extracted therefrom.
Table I.
Average Analyses of Sorgo Cane and Juice Sorgo Juice, ’%
Sucrose in Cane,
%
12.7
Invert sugar on solids 4.01
Aconitic acid on solids
1.67
Purity 77.1
Laboratory scale studies were started in the fall of 1948 and intensified in the 1949 season, Tvhen semipilot investigations were also conducted. Two distinctly different methods of juice treatment were established and carried out in the pilot operations as outlined by simplified, parallel flow diagrams shown in Table 11. The primary difference beh-een the two lies in clarification of the raw juice.
STORAGE OF CANE The sucrose content of all sugar-bearing crops decreases once the plant is harvested. Preliminary studies of sorgo stored in the dry, hot air of the Imperial Valley indicated large losses. In 1948 cane stored in the shade for 24 hours experienced a rise in invert sugar from 3.5 t o 11.8%. When the canes were covered by burlap saturated with water, invert sugar increased from 3.98 to only 4.07y0 in 24 hours and rose to ll.2Y0 only after 48 hours. These changes were similar t o but of much greater magnitude than those reported for sugar cane by Lauritzen, Balch, and Fort ( 5 ) and for sugar beets by Orleans and Cotton (’7). The work on storage of the harvested sorgo canes was continued and expanded during the 1949 season. I n order more nearly t o approximate practical large scale storage facilities, an open rack was built, such t h a t the sorgo canes could be placed upon it and humidified air could be blown through the stored canes. The changes in the components of the cane could then be
628
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1951
Table 11. Simple Flow Diagram of Processing Methods Studied Defecation Process Carbpnation Process Cane ,storage Can? storage
G
Diffusion battery
I
Lime +
Defecation
Mud
Filtration
so2
4
+
I
1+
Sulfitption
+
Concytration
G
+
Diffusion battery
3. .1 First carbonation 3. Filtration
G
Filtration
4 Su1fi:ation
.1
+-
Crystallization
4 Molasses
+ Mud + COS
4 0 h
-PURITY
(HUMID)
+
I
2
so2
4
Conyentration
G
.1
Crystallization
4 Molasses
+
Aconitate
+ Sugar
EXTRACTION OF SUCROSE FROM CANE
x
, , $05
* Mud
closely followed and compared with corresponding results obtained with cane stored in dry, sheltered conditions. The data are shown in Figure 1. Humidification of storage facilities for sorgo cane markedly reduces sugar losses, but even this treatment does not prevent serious loss of sugar within a few days. This would indicate the need for a well coordinated system of harvest and delivery of canes t o the factory, such that processing of the cane could be started within 24 hours of the time it is cut. I n addition to the sugar loss and the purity drop as shown in Figure 1, invert sugar content and aconitic acid content of the canes were also followed during the storage period. The invert sugar content increased during storage, as would be expected in view of the drop in purity and sucrose loss. Only the aconitic acid content failed to show significant change during the storage period, and no difference in this component could be noted between the two methods of storage.
&
demonstrate the superiority of the diffusion technique, as pressed juice upon standing a few minutes yielded a large amount of white settlings in the bottom of the container, whereas diffusion juice produced very little. Pressed juice was cloudy in appearance, but diffusion juice was only slightly murky. Filtration of the diffusion juice proceeded rapidly in the laboratory and a clear filtrate was obtainable; however, filtration of pressed juice was slow and a cloudy filtrate came through the filter paper.
:E+:
4 Secopd carbonation
Aconitate + Aconitate removal Aeonitate removal (pH 6.5 t o 6.8) (pH 6.5 to 6.8) Sugar
+ Lime
Preliming
629
A countercurrent extraction with water in a diffusion “battery” is employed in the beet sugar industry for extraction of sucrose. The cane sugar industry, on the other hand, employs huge rollers or presses which squeeze the sugar-bearing juices from the cane. Again a countercurrent scheme is followed, in which several passes through the press are made and water is utilized to help remove the greatest possible amount of sucrose. Both of these common methods were studied in connection with the extraction of sorgo sugar. Laboratory work indicated early t h a t the diffusion method held several important advantages over extraction by pressing, and these advantages were repeatedly demonstrated throughout the work. I n the first place, nearly all of the starch, the most troublesome offender in inhibiting crystallization of sucrose from sorgo sirups, was eliminated frbm the “raw” (untreated) sorgo juices by the diffusion technique, as indicated by the iodine color test for the presence of starch. Although this color test is not quantitative, it can be considered semiquantitative in low starch concentration because of the changes from light green through deeper green to blue and blueblack with increase in starch concentration. Sorgo juice obtained by diffusion usually produced a light green color, while expressed juices always showed deep blue to blue-black. Qualitative comparison of the two juiceR by visual observation also served to
I
DAYS
1
I
3
4
IN STORAGE
I
5
60
Figure 1. Loss of Purity and Total Sucrose from Harvested Sorgo Cane in Storage The second great advantage of diffusion is evidenced by the percentage extraction of sucrose realized by this method (see Table 111). Over 98% of the sucrose present in the cane could be extracted by diffusion, but only 85% could be recovered with four passes through a small cane press with the use of 35% imbibition water. A fairer basis for comparison, however, might be the average extraction obtained in commercial sugar cane mills. The average obtained by Louisiana mills is given by Spencer and Meade ( 1 1 ) as about 93%; Cuba and Java average about the same, though Hawaii extracts about 95.5%. Extraction obtained in the authors’ beet sugar diffusion operations was consistently over 98%.
Table 111.
Comparison of Sucrose Extraction by Diffusion and Pressing
Method, of Extraction Cane press
Diffusion battery Diffusion battery
No. of
Sucrose Extracted,
4
..
83.5-86
Remarks imhjhition 35?ater equiv. to No water 135 draft. on 1st pass
.. ..
14 14
98-98.5 92-98
150 draft 100 draft
No. of Passes
Cells
%
Higher extraction of sucrose also means further extraction of soluble impurities present in the cane. A comparison of the purity of the juices obtained by the two different methods of extraction gave no noticeable consistent difference in purity on a starch-free basis, indicating no greater percentage loss of sucrose t o molasses incurred by the additional sucrose recovery realizable by diffusion. Therefore, the method of sucrose extraction employed in the semipilot operations was exclusively that of diffusion. T h e diffusion battery used in the semipilot operations was of the batch or cell type, very similar in operation t o the familiar cell-type battery long in service in the beet sugar industry (6). It consisted of 14 cells constructed of 8-inch pipe, each cell about 14 inches in height. The cells were filled and emptied manually inch thick. with cane “chips,” diagonal slices of cane about Piping of the cells was so arranged that the juice passed upward
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
630
s1 Figure 3.
Vol. 43, No. 3
supply of diffusion juice, the draft was reduced to 100 and o p o a tion of the battery was speeded up. Table I11 indicates estratctiori of 92 to 989&with this lon. draft. The raw juice Brix (per cent solids) obtained with the sorgo cane ranged from about 12.0 to about 14.5. This was cvithin the range of commercial beet and cane juices. Tests were carried out to cletcrmine the effect of temperature and time upon the removal of starch from chipped sorgo cane by diffusion. Temperature was a critical factor for two reasons: ,4 high temperature is essential in order to minimize bacterial acBtion in the battery ( l 4 ) , and a temperature in excess of about 70 ' C. will cause solubilization of starch ( 8 )which would seriously intcrfere with recovery of sucrose.
Diagram of Sorgo Semipilot Plant
through the cells, and provision R as made for countercurrent flow of the juice through the battery-that is, fresh water came into contact with the cane that was most nearly exhausted and fiesh cane was first extracted by the most concentrated juice. I n early operation of the battery a "draft" (weight of ram juice X 100 divided by weight of cane) of 1.50 was used in order t o determine whether or not high extraction of sucrose could be obtained. Losses of sucrose in the exhausted cane pulp (the waste called bagasse in the cane sugar industry) and in the accompanying pulp water were 0.13 and 0.050/,, respectively, corresponding to an extraction of 98.6% of the sucrose in the cane. Figures 2 and 3 show semipilot equipment I n the semipilot operations it was found that the battery was dow rrlative t o the rest of the equipment. In order to speed the
Table IV. Effect of Time and Temperature upon Elimination of Starch by Diffusion as Measured by Iodine Color Test Time, IIours 0.5 2 3
60' C.
(33' C .
++ (faint) (faint) ++ (faint) ++ (faint) +$- (faint) (faint) (faint) (faint)
70' C .
+ ++ (faint) (faint) + (faint) (faint)
750
c.
++ + ( v e r y strong) +++ f + (very strong) + + + strong) + + + ++ (very (aery ntvong)
As shown in Table IT', very little starch was found in t h e diffusion juice a t temperatures of 70" C: and less. A t these lovier temperatures a light green color vc-as obtained with iodine, while a t 7.5" C. the typical dark blue color appeared after only 0.5-hour diffusion time.
Table V.
Clarification by Carbonation
Purity Risea 1
10.45 10.0 10.0
55 55 55 55
10.7 10.0 10.0
9.55 9.7 9.65
5 6
10.0
55
10.0
9.45
10.0
55
10.0
7
10.6
55
10.6
8
10.6
55
9
10.6
55
10
10.6
55
10.7
2 3
4
a
b
10.3
9.6
9.65
55 55 55 65
Poor Poor
55 55
Poor 150 ml.,10 min. 150mL6.5 min. 150m1.,9.8 min. 150ml.,9.5 min. 150ml.,9,5 min.
10.3
55
10.6
10.3
55
10.6
10.3
55
10.6
10.3
55
Poor Good
...
0'85b
0.5 2.0
1 09 0 73
2.0 2.0
0'82
0.92
2 0 2.0
2.4
0.40
0.78
2.0
4.6
0.42
.. ,.
..
3.2 3.2
