I N D U S T R I A L A N D ENGIXEERING CHEMISTRY
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Vol. 23, No. 11
Commercial Production of Levulose I-General Considerations' J . H. McGlumphy and J. W. Eichinger, Jr., with R. M. Hixonand J. H. Buchanan DEPARTMENT OF CHEMISTRY, IOWA STATECOLLEGE, AXES,IOWA
EVCLOSE occupies the
A semi-commercial plant capable of producing 50 pounds (22.7 kg.) of levulose per day has been in operation during the past year, using t h e Jerusalem artichoke as t h e raw material because of its many good features from a n agricultural viewpoint. By drying t h e artichokes, many advantages are obtained, including t h e operation of the plant throughout the year. A continuous-precipitation process has been developed, yielding very granular lime levulate, which may be easily filtered and washed. The preparation of' crystalline levulose in good yields has been accomplished at ordinary temperatures (15' C . ) without t h e use of refrigeration.
m a n d developed far in advance of its successful commercial p r o d u c t i o n . The possible uses have been widely discussed in many scientific and popular articles. From a s t r i c t 1y h u m a n i t a r i a n standpoint the r e m a r k a b l e levulose tolerance (12) exhibited by diabetic patients should warrant the greatest efforts to make this valuable sugar quickly available in order that further tests may be carried out. As a result of several years' study of this problem, a semicommercial plant capable of producing 50 pounds (22.7 kg.) of levulose per day has been in operation a t Iowa State College during the past year. The object of this series of papers is to present details of the process developed and the experimental data obtained. Hlstorical Harding (8) has summarized the history of levulose up to the year 1923. Since that time important work has been done by Hoche (9), who used chicory as the raw material, and by Jackson, Silsbee, and Proffitt (11), who worked with the Jerusalem artichoke and the dahlia. The latter workers revived the old Dubrunfaut (6) method of separating levulose by precipitation with lime, making improvements in the technic used in order to produce a more easily filterable precipitate. Both Hoche (9) and Jackson (11) were able to crystallize levulose from aqueous solution without the use of organic solvents. It is difficult to give proper credit for the first successful crystallization of levulose from water. Browne (3) in 1912 published a method for preparing levulose on a laboratory scale, in which crystallization from water was accomplished. Thorp's chemical dictionary (21) states that levulose crystallizes from alcohol and even from aqueous solution, but no authority is quoted. Schering (17) obtained a patent on the treatment of an aqueous pulp of inulin with a volatile organic acid and subsequent concentration to obtain the fructose direct. When carbon dioxide is used, the treatment is carried out in autoclaves. Arsem ( 1 ) secured a number of patents in 1927 covering the purification and hydrolysis of inulin under various conditions. I n 1929 Waterman, Rooseboom, and Oberg (24) reported that calcium fructosate, which is easily prepared by adding calcium hydroxide to a 5 per cent solution of fructose and allowing to crystallize, is partially decomposed on drying. They stated that, if fructose is to be prepared, the fructosate must be worked up while wet and suggested that fructose could be prepared from invert sugar and beet molasses. The same year Arsem (2) secured two additional patents, the first covering the clarification of inulin-bearing juice, 1
Received August 11, 1931.
and the second covering the hydrolysis of the polysaccharides contained in the residue a f t e r inulin had been recovered from the juice. Golovin, B r y u k h anov a , and Fridman (6) reported a l a b o r a t o r y preparation of crystalline levulose in 1929. The method used was very similar to that of Dubrunfaut (t5). , \-
Kleiderer and Englis (IS) made a study of the hydrolysis of inulin under pressure, using carbon dioxide, sulfur dioxide, and nitrogen. All of the attempts to prepare levulose may be classified under three general types: The Crookewitt method (e), consisting of the isolation and purification of inulin, and the subsequent hydrolysis of the inulin to produce levulose. The Dubrunfaut method ( 5 ) ,in which levulose is isolated as the insoluble lime salt. The Harding method (7), in which levulose is separated from glucose with glacial acetic acid. Selection of Method
Because of the expense involved in working with organic solvents, Harding's method is of doubtful commercial interest. The use of Crookewitt's method requires a raw material, such as dahlia or chicory, which is high in inulin and low in the other levulose-yielding polysaccharides. Unfortunately these plants are somewhat difficult to propagate and do not lend themselves to large-scale mechanized agriculture. By the use of Dubrunfaut's lime precipitation, the easily cultivated Jerusalem artichoke or girasole may be selected as a raw material. Shoemaker (IO),Schoth (It?), and Traub and his co-workers (23) have published much valuable information regarding the Jerusalem artichoke. This plant offers sufficient agricultural advantages to more than off set any possible manufacturing advantages of Crookewitt's method. The Dubrunfaut method yields sirups of a higher purity than the Crookewitt method, and therefore crystallization is more easily accomplished. This is because of the fact that levulose is not the sole product of the hydrolysis of inulin (10, 20). Traub, Thor, Willaman, and Oliver (22) have made a study of the storage of Jerusalem artichokes and concluded that, for the manufacture of levulose, harvesting and use should take place near the time of maturity. When allowed to remain in the ground and even when stored under carefully regulated conditions, there is a consistent decrease in the levulose-glucose ratio and in the levulose-total sugar ratio. The most satisfactory storage conditions were found to be a temperature of 32-35' F. (0-1.7" C.) and a relative humidity of 82-92 per cent. Their results in regard to the loss of levulose during storage are confirmed by observations of the present authors. Schering (16) secured a patent on the preservation of the inulin content of sliced chicory roots or carbohydrates of
November, 1931
INDUSTRIAL An’D ENGIXEERIA’G CHElVISTRY
other plant materials by treatment with chloroform vapor or other narcotic gases, such as ethylene bromide, toluene, acetic ester, carbon dioxide, carbon monoxide, water gas, or hydrogen cyanide. Since the storage of artichokes is more difficult and less satisfactory than the storage of sugar beets, it would seem highly probable that the annual campaign would be shorter for a levulose factory than for a beet-sugar factory. For this reason and for others to be pointed out later, it was considered advisable to investigate the desiccation of Jerusalem artichokes. Desiccation
Very little work has been reported on the desiccation of Jerusalem artichokes. Xichols (14) described conditions for the drying of artichokes, evidently for the purpose of using them as food. No analytical data were given to show the effect of the drying on tpe constituents present. A study has been made of the drying of artichokes, the effect of the drying process on the sugar content, and the utilization of the dried tubers for the preparation of levulose. The optimum conditions for the desiccation of artichokes have been determined. When the process is properly carried out, no loss of levulose occurs and the product keeps indefinitely. Samples kept for over three years have shown no change in levulose content. A complete report of the desiccation study will be presented in a later paper. I n addition to the preservation of the plant tissues, other important advantages of the desiccation process have become apparent. According to the experience of Owen (15) with sugar beets, the saving on freight alone more than pays for the cost of drying, when local drying stations are used. Smaller factories could be built and operated throughout the year with many resulting economies. The storage space required for dried tubers is decreased from one-half to twothirds that required for the fresh tubers. Drying coagulates the albuminous matter and causes an increase of about 5 per cent of the total albuminoids to be retained by the pulp upon extraction. The drying also renders the soluble albuminous matter more easily coagulable, and thus simplifies the clarification of the extract. By the use of dried tubers, extracts containing over 50 per cent total solids have been obtained. The higher concentration of the juice permits a saving in the quantity of acid required for hydrolysis, a saving of neutralizing reagents, a saving in quantity of clarifying agents, and a saving in time required for filtering and other handling.
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of conversion of artichoke juices for different strengths of hydrochloric and sulfuric acids. The concentration of the juices employed was not given. An exhaustive study of the conversion reaction has been made in this laboratory. It was found that concentration of juice is one of the important factors affecting the velocity constant. For commercial operation it is necessary to know the conditions for complete conversion of a juice of any concentration or composition in a reasonable time and without the destruction of levulose. This information has been collected in the form of tables and charts and will be presented in a later paper. I n general the levulosans in the extract can be hydrolyzed to the free sugar by acidifying to a pH of 1.5 with sulfuric acid, or 1.75 with hydrochloric acid, and heating to 80’ C . for 1 hour. Under these conditions no appreciable destruction of levulose occurred.
Lime L e v u h k 5 h ~
Figure 1-Continuous-Precipitation Unit
Neutralization
Following the conversion of the levulosans to levulose, it is necessary to neutralize the acid by the addition of hydrated lime until a p H of 7.0-7.5 is reached. The juice is filtered and is then ready for precipitation of the lime levulate.
Diffusion
Precipitation
The diffusion of the desiccated tubers presents no problems. The types of diffusion batteries used in the beet-sugar industry are well adapted to the handling of the dried material. The diffusion is carried out in a miniature diffusion battery operating on the same principle as the larger units. The battery has a capacity of 12 pounds of dried tubers per hour. This is equivalent to about 7 pounds (3.2 kg.) of levulose per hour or 56 pounds (25.6 kg.) per 8-hour day. This unit contains only eight cells, and the extracts obtained average 40 per cent total solids.
The technic of the lime precipitation is of the greatest importance in the successful preparation of levulose. The lime levulate must be sufficiently granular to filter readily and to be washed thoroughly and quickly. The conditions prevailing during the precipitation of lime levulate are extremely deleterious to levulose. If the destruction of appreciable amounts of levulose is to be avoided, the processing must progress rapidly through the carbonation stage. In order to meet these conditions, a continuous-precipitation process has been developed. A diagrammatic sketch of the apparatus used for this purpose is shown in Figure 1.
Conversion
Although considerable information is available concerning the hydrolysis of pure inulin, very little has been reported regarding the conversion of the levulose-yielding polysaccharides of the Jerusalem artichoke. Jackson (11) and his associates u-ere apparently the first to really study the conversion of artichoke juices. They concluded that the resultant of the various reactions occurring during the conversion process follonx substantially the course of a unimolecular reaction, and they reported velocity constants for the rate
I n the drawing, 1 indicates a container for the levulose solution. A float, 2, a t the surface of the solution adjusts, by means of ropes and pulleys, a curved overflow pipe, 5, attached to tank 4 in such a manner that the upper end may be raised or lowered. The mechanism, 3, consisting of pulleys of varying size, makes it possible to vary the relative rate a t which the overflow pipe, 5. is lowered in comparison with the change in level of the float, 2. The valve, 7, is adjusted to give any desired rate of flow for the sugar solution, the lime being added in the required ratio by the mechanical arrangement, 3, for lowering the overflow pipe, 5. Both the sugar solution and the lime suspension enter the reaction chamber, 6, where they react to form lime levulate in the presence
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I,VDUSZ’RIAL A N D ENGINEERING CHEMISTRY
of a predominating quantity of seed which offers an enormous area for crystal growth with resulting granular precipitate and ease of filtration. As the reactants are added, the suspension of lime levulate overflows from the reaction chamber, 6, through the overflow pipe, 8, to a storage tank or to a continuous filter. Chambers 6 and 8 are jacketed for temperature control.
Previous workers have always precipitated lime levulate a t comparatively low temperatures. On large-scale operation this would necessitate considerable expense for refrigeration. I n this laboratory the precipitation is carried out successfully a t 15’ C. This temperature is easily maintained by water circulation. At present a loss of about 10 per cent in yield is experienced when operating a t this temperature. There are two causes for this loss-the increased solubility of lime levulate and the greater destruction of levulose as the temperature is increased. The distribution of the loss between these two factors is now being studied. The loss due to solubility can be decreased by increasing the concentrations of the lime suspension and levulose-containing solution, while the decomposition can be retarded by more rapid manipulation. The desiccation process, which enables any desired concentration of extract to be obtained, together with the continuous precipitation provide excellent control over these conditions. It will probably be more economical to operate a t the higher temperature, even though a loss is experienced. Any levulose not precipitated may be utilized, together with the glucose, for fermentation processes. When concentrated solutions are fed to the continuous-precipitation unit, the filtrate is an ideal material for fermentation purposes, no evaporation being necessary. The recovery of this valuable by-product is another factor which must be listed in favor of the desiccation process. Filtration a n d Washing
Lime levulate prepared by the continuous-precipitation method is of a very granular nature and is easily filtered and washed free from impurities. The precipitate may be handled either on a continuous filter or on a standard filter press equipped for washing. Thorough washing is of the utmost importance if crystalline levulose is to be produced. Since a quantity of free lime is present with the lime levulate, it is unnecessary to use lime in the wash water. Washing is accomplished with ordinary tap water. The filter cake is suspended in distilled water and is then ready for carbonation. Carbonation a n d Evaporation
The carbonation is carried out in a rotating drum under a pressure of 15 pounds per square inch (0.91 kg. per sq. cm.). The mixture is kept a t 15” C. during the process. Any of the commercial carbonators designed to operate upon saccharates could be utilized for this purpose. The calcium carbonate is filtered out and the sirup containing 20 to 25 per cent levulose is evaporated in vacuo to a concentration of 40 per cent. It is sometimes desirable during this evaporation to decolorize with chars, such as norite. The sirup is filtered and evaporation continued until a concentration of 88 to 90 per cent is reached. Crystallization
By seeding in the evaporator, crystals approaching commercial sucrose crystals in size have been obtained. This problem is being studied, and it seems probable that, when the proper technic is developed, crystal size may be controlled a t will. No difficulty whatever is experienced in crystallizing levulose with mechanical stirring and gradual lowering of temperature. However, the crystals obtained are less desirable from the standpoint of uniformity and size. Two
Vol. 23, No. 11
and three crops of crystals have been obtained. The molasses may be returned to the lime precipitation or used as sirup. The molasses is light in color and very sweet, and no bitter taste is present. Experimental D a t a
The following data are typical of the semi-commercial operation: Fresh Jerusalem artichoke tubers, dug November 1, 1930, were immediately washed and sliced in a vegetable slicer to a thickness of 5 / 6 1 inch (0.03 cm.). The slices were dried while being carried through a series of three chambers by means of a screw conveyor. Preheated air was forced through the screen bottoms of the three chambers a t temperatures of llOo, 99”, and 77“ C., respectively. The slices were fed onto the conveyor a t the rate of 1 bushel per hour (0.352 hectoliters per hour). The average moisture content of the desiccated tubers was 5-6 per cent. Complete drying data will be presented in the later paper. Forty-one kilograms of these dried tubers were extracted, yielding 63.2 liters of extract contaiqing 40 per cent total solids. An analysis of this extract was made, and it was found to contain 16.8 kg. of levulose and 6.8 kg. of glucose. The extract was acidified to a pH of 1.5 by the addition of 934 cc. OF concentrated sulfuric acid (1.73 grams sulfuric acid per cubic centimeter) and heated to 80’ C. for 1 hour. After cooling to40’ C., the juice was limed to slight alkalinity (pH = 7.5) by the addition of approximately 1.5 kg. of finely powdered hydrated lime and was filtered. Twenty-one kilograms of hydrated lime were suspended in 100 liters of water. The filtered extract and the lime suspension were fed to the continuous-precipitation unit, which was maintained a t 15’ C. The resulting l i w levulate was filtered and washed four times, using 50 liters of water for each washing. The levulate cake was suspended in distilled water and carbonated a t 15” C. under 15 pounds per square inch (0.91 kg. per sq. cm.) carbon dioxide pressure. After filtration, the sirup was concentrated in a vacuum kettle a t 60” C. until a concentration of approximately 40 per cent was reached. It was then filtered, and the evaporation continued until the sirup had a concentration of 90 per cent total solids. Thirteen and four-tenths kilograms of sirup (apparent purity = 95.32 per cent) were obtained. This represented a yield of 6.09 per cent of the weight of the original fresh artichokes. The sirup was crystallized in motion with gradual lowering of temperature. The massecuite, when centrifuged, yielded 3.2 kg. of white levulose crystals. After concentration of the molasses, a second crop of 2.3 kg. of white crystals was obtained. These crystals analyzed 98.55 per cent levulose. Similar runs in which the levulate was precipitated a t 0’ C. resulted in a 10-11 per cent increase in yield. Literature Cited Arsem, U. S. Patents 1,616,164; 1,616,165; 1,616,166; 1,616,167; 1,616,169; 1,616,170; 1,616,171; 1,616,172 (1927). Arsem, U. S. Patents 1,663,233; 1,663,234 (1928). Browne, “Handbook of Sugar Analysis,” pp. 617-1 8, U’iley, 1912. Crookewitt, Ann., 45, 184 (1843). Dubrunfaut, A n n . chim. phys., 21, 169 (1847). Golovin, Bryukhanova, and Fridman, Zhurnal Sakharnoi Prom., 3, 140-2 (1929). Harding, J . d m . Chem. Soc., 44, 1765 (1922). Harding, Sugar, 25, 406, 636 (1923). Hoche, Z . Ver. deul. Zucberind., 76, 821 (1926); Sugar, 29, 181 (1927). Jackson and Goergen, Bur. Standards, Research PaDer 79, 27-38 (1929). Jackson, Silsbee, and Proffitt, IND. E N G . CHEM.,16, 1250 (1924); Bur. Standards, Sci. Paper 619, 614 (1926). J o s h , “Diabetic Metabolism with High and Low Diets,” Carnegie Inst. Wash., Pub. 313, 211 (1923). Kleiderer and Englis, IXD. ENC.CHEM.,23, 332-4 (1931). Nichols, Fruit Producls J . A m . l’inegar Ind., 9, 71 (1929). Owen, “Desiccation of Sugar Beet,” His Majesty’s Stationery Office, London, 1927; Food Ind.. 1, 699-702 (1929). Schering, British Patent 266,695 (Feb. 26, 192’5). Schering, French Patent 634,363 (1927). Schoth, Oregon Agr. Expt. Sta., Circ. 89 (1929). Shoemaker, U. S. Dept. Agr., Tech. Bull. 33 (1927). Tanret, Bull. soc. chim., 111, 9, 227 (1893). Thorp, “Dictionary of Applied Chemistry,” Vol. 1, p , 641, Longmans, 1912. Traub, Thor, Willaman, and Oliver, Plant P h y s i o l o g i , 4, 123 (1929). Traub, Thor, Zeleny, and Willaman, J . .Igr. Research, 39, 551-6 (1929). Waterman, Rooseboom, and Oberg, Chem. Weekblad, 26, 50 (1928).
