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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 16, No. 12
A Method for the Manufacture of Levulose' By R. F. Jackson, C. G. Sibbee, and M.J. Profitt POLARIMETRY SECTION.
EVULOSE is t h e
BUREAU O F STANDARDS, WASHINOTON, D. C.
The artichoke is a plant The Jerusalem artichoke oflers an inexpensive and prolific source that has fought for its exissweetest and one of from which levulose may be extracted. The process of manufacfure tence through the extremes the most nutritious consists of juice extraction, a combined conversion and defecation, of climate, against insect members of the sugar group. pests in North and South lime precipitation, and crystallization in which the most expensive America, and as far as we Its sweetness is estimated reagent required is the ordinary grade of sugar house lime. have been able to learn, has by various authorities to be I t has been found feasible to crystallize levulose from its aqueous mastered all its enemies. We about 50 per cent greater solutions with a facility approaching that of sucrose or dextrose. know no other crop that can than that of cane sugar. be produced at so small an New data on the solubility of levulose are given. expenditure of time, labor, or Inasmuch as cane sugar is It is probable that 80 to 85 per cent of the levulose in the extracted cash. hydrolyzed to dextrose and juice can be recovered as crystalline sugar. levulose during the initial Under favorable oondiprocesses of digestion, it is tions existing at Mr. Sibley's apparent that indirectly in the form of sucrose and directly farm the crop yields about 15 tons per acre. The tubers are in the form of sirups, honey, and sweet fruits the nation con- uninjured by frost and may be harvested either in autumn sumes about 6 billion pounds of levulose annually. There or early spring. is consequently no doubt of its nutritive value. It has, The levulose occurs in the tuber in polymerized forms which therefore, all the intrinsic qualifications of a staple commodity are mainly inulin, inulenin, and synanthrin, the latter prefor ordinary commercial purposes. Of the pure crystalline dominating. In addition, there are varying amounts of sulevulose, however, there are to be found but a few scattered crose and reducing sugar. All of these complex compounds ounces, which may be purchased at costs varying from $30 may be converted by dilute acids to levulose. The converted to $110 a pound, The reason for these prohibitive prices is liquors produced from the samples obtained from Mr. Sibley to be found in the apparent difficulties of preparation of the contained in the months of November and December an avercrystalline sugar. I n the present paper it will be demon- age of 12.1 per cent levulose on tubers; in January, February, strated that levulose can be manufactured by methods capable and March, 10.7 per cent; and in April, May, and June, of large-scale operation a t costs which bring it within the 10.7 per cent. The tubers that have remained in the ground range of possible commercial development. during the winter, however, are of somewhat larger size than those harvested in autumn, so that the yield of sugar per acre SOURCESOF LEVULOSE may not have suffered so much as the percentages indicate. There are a number of abundant or potentially abundant Here is a most prolific, hardy, and inexpensive crop which sources of crude material from which levulose may be ex- thus far has never been selected for its levulose content. tracted. Among the cheap sources may be mentioned beet What selective agriculture may accomplish in further imand cane molasses, which, however, from the standpoint of provement it would be hazardous to conjecture. economy are only practicable if combined with a fermentation process for the recovery of valuable by-products. PRELIMINARY PROCEDURE Among the many farm crops that are capable of development for this purpose are the dahlia, chicory, and Jerusalem The juice purities with respect to levulose are very low, artichoke. This discussion, however, will be confined to the amounting to an average of about 60 per cent. Although Jerusalem artichoke as a source of levulose. ultimately it will probably prove possible to crystallize The artichoke is the subterranean stem tuber of a native sugar even from so low a purity juice, the present process sunflower. In France it was early recognized as a possible depends upon the separation of levulose by the lime precipisource of alcohol and by artificial selection was greatly tation process originally discovered by Dubrunfaut in 1869. improved. As a result of this selection a strain was developed Since this process accomplishes the purification of the juices, which is known as t,he Mammoth White French Jerusalem it is evident that no very elaborate defecation is required. Artichoke. It has been the writers' privilege to have enlisted Defecation proved at first a baffling step. An attempt was the interest of Hon. Joseph C. Sibley, of River Ridge Farm, made to apply the lime and carbonation process, which is so Franklin, Pa., who has been kind enough to supply abundant successful in beet sugar manufacture. The result was satisquantities of tubers for experiment and analysis. Mr. Sib- factory as far as clarification was concerned, but the juices ley's pioneer work has established the fact that the artichoke invariably suffered losses of levulose amounting to from 5 to is invaluable for stock-feeding purposes. The tuber is con- 12 per cent. The final procedure adopted was one in which sumed eagerly by cattle and swine and the stalks may be made conversion and defecation were combined in a single series of into hay, which the animals apparently prefer to green corn steps. fodder. The crop is, moreover, extremely prolific and hardy The extracted juices were immediately acidified with and its agricultural requirements are simple. Planting, sufficient sulfuric acid to supply about one-fifth normality. cultivating, and harvesting are accomplished mechanically, They were then converted a t 70" C . for about 30 minutes. no hand labor being required. To quote from one of Mr. During the conversion an abundant coagulation of albumiSibley's numerous pamphlets: noids occurred, which were subsequently removed by filtration. The converted juices were neutralized by lime to give 1 Presented before the Division of Sugar Chemistry at the 68th Meeting of the American Chemical Society, Ithaca, N. Y., September 8 to 13, 1924. a very slight alkalinity, pH 7.5 to 8.0. The filtrate from the This necessarily abridged description will be supplemented by a paper to be calcium sulfate and defecation mud was perfectly clear, published at a later date, Printed by permission of the Director, U. S. but somewhat darker than a beet juice. Bureau of Standards.
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
December, 1924
The juice was then ready for the separation of calcium levulate. LIMEPRECIPITATION The lime precipitation of levulose as ordinarily carried out leaves much to be desired. But little improvement in detail has been effected since the time of Dubrunfaut. The method in vogue is to cool the sirups to about freezing temperature and throw in slaked lime with vigorous stirring. Under these conditions the precipitation occurs with vast numbers of minute particles which resist the flow of the waste water to such a degree as to preclude the use of ordinary filtration methods. Harding2 advocates the use of a centrifugal machine for this purpose, but this procedure would hardly serve industrial requirements. Consequently the preparation and properties of the calcium levulate have been studied in detail. The results of this study will be briefly summarized. It is thus Calcium levulate has the formula C6H&.Ca0. a monocalcium levulate which is probably hydrated. Its solubility is low in pure water, 100 cc. containing about 0.07 gram of levulose. Its solubility increases to a marked degree in the presence of dissolved sugar, either dextrose or levulose. Thus the presence of 6 grams of dextrose per 100 cc. increases the solubility about nine times. It is for this reason that the preparation of levulose from invert sugar gives a yield of but 70 per cent of the theory. The levulate has a strong tendency to form supersaturated solutions. In an effort to improve the physical condition of the precipitate an attempt was made to precipitate slowly by adding lime to the sugar solution in small batches. The lime dissolved completely until an extremely high supersaturation resulted, when suddenly the entire mass crystallized to a creamy paste. The knowledge of the properties of the compound gained by preliminary experiments led to the following satisfactory procedure: The precipitations were carried out in an 8-quart ice cream freezer. The lime milk was added in small successive fractions through a hole in the cover, while the sugar solution dripped continually through a hole drilled in the shaft of the dasher. By this procedure the equivalent quantities of lime and levulose entered the reaction vessel continually, each entering portion being diluted to the whole volume of the mixture before undergoing reaction. It was found preferable to maintain the lime in slight excess a t all times and thus limit the supersaturation caused by an excess of sugar. The soluble alkalinity was in this way kept at its minimum. The effect of this method was to build up the levulate crystals to such size as to be frequently visible and granular. The remlting levulate milk filtered freely and was washed readily. It was found possible to filter a 1-inch cake on a 7-inch Biichner funnel in less than 7 minutes. Artichoke juices contain reducing sugars other than levulose in the proportion of 3 parts levulose to 1part nonlevulose. These iionlevulose sugars probably consist mainly of dextrose, which, as we have seen, increases the solubility of calcium Ievulate. The precipitation of levulose is then less than quantitative. An average of sixteen precipitations show that 85 per cent of the levulose was recovered in the levulate cake. After carbonation of the cake in the usual manner, the levulose sirups possessed a purity of about 94 per cent and were, when dilute, nearly water-white. It is probable that with more suitable equipment and further experience, both the purity and yield can be improved. CRYSTALLIZATION All methods hitherto practiced for the crystallization of levulose have required the use of nonaqueous solvents. Sugar, 26, 406 (1923).
Many authors have advocated the complete dehydration of the sirups with absolute alcohol; others have succeeded in inducing crystallization from aqueous alcohol. Harding suggests the use of glacial acetic acid for this purpose. Obviously, these methods preclude any large scale of commercial development. I n the present investigation it has been found that not only will levulose crystallize from water solution, but the crystal growth is capable of control to very nearly the same degree as sucrose or dextrose. The first step was to determine whether the solubility of levulose was low enough to warrant an attempt at crystallization. No measurements of its solubility in water have hitherto been published. The writers' determinations were made in the usual manner by agitating at constant temperature the solution in contact with a large excess of the solid phase until equilibrium had been effected. The solution was then filtered and analyzed. The saturated solutions contained 78.94 per cent at 20" C., 81.6 per cent a t 30" C., 84.34 per cent a t 40" C., and 88.1 per cent a t 55" C. The t,emperature coefficient of solubility is relatively large. If the solubilities are expressed as parts of levulose dissolved by 100 parts of water, a drop of 10" C . diminishes the solubility by 20 per cent. Similar calculations for sucrose show a diminution for 10" C. of but 8 per cent. It is therefore evident that crystallization in a crystallizer by the method of temperature drop should be efficient. In fact, after numerous trials to gain the necessary experience, it has been found possible to obtain perfectly acceptable massecuites containing a fairly uniform, relatively large grain, which purges on a centrifugal machine with a facility but little less than a sucrose massecuite. The crystallization experiments were performed in a small ice cream freezer operating as a crystallizer. The crank was replaced by a large pulley which was driven by a motor through a system of reducing gears a t a speed of one revolution in 2 to 3 minutes. The freezer was placed in an air bath the temperature of which could be regulated, The levulose sirup was concentrated in a vacuum to about 91 per cent solids, transferred to the crystallizer, and heated to about 55" C. Crystallization, which was started from seed, continued for 24 to 36 hours, during which time the temperature was gradually dropped to that of the roomabout 25" C. The massecuite was then spun on a centrifugal machine. On account of the very high solubility of levulose, washing is best accomplished by means of a white sirup. A typical crystallization sheet follows: Massecuite
Brix Apparent purity Final temperature
Run-off sirup Wash
84.0 82.0 81.4 90.5
Brix
Purity Brix Purity Weight dry crystals Weight massecuite = 51 '
90.6 94.4
26.OoC.
per cent
The run-off sirups vary in purity from 80 to 85. From sirups of this purity there is but slightly greater difficulty in securing a massecuite from which a white sugar may be obtained. The molasses from the second lot of crystals has a purity of about 69. These molasses if concentrated and allowed to stand deposit crystals of sugar very slowly, but after a lapse of several weeks permit of a fairly satisfactory yield of raw sugar. The final molasses may again be submitted to the lime precipitation process for the recovery of the remaining levulose. Thus far no tendency for any foreign substance to accumulate in the reworked molasses has been discovered. The recovery of levulose in crystal form is apparently from 80 to 85 per cent of that in the extracted juice.
