November, 1924
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1173
Manufacture and Uses of Refined Dextrose' By W. B. Newkirk CORNPRODUCTS REFINING Co.,ARGO,ILL.
T T H E Rochester Meeting of the AMERICAN CHEMICAL SOCIETY, April, 1921, Dr. Porst gave a historical article describing the advancement of the dextrose industry.2 At that meeting a paper giving the technical data was promised. These data have been withheld until it seemed more certain that the industry was on a sound basis commercially and scientifically. It is believed that some of the problems which have now been met and overcome will be of interest to all sugar men.
A
PREPARATION OF LIQUORS FOR CRYSTALLIZATION The preparation of the liquors for crystallization will be briefly roviewed as it might be called standard practice in all plants making corn sugars. The starch is introduced into e bronze vessel called a converter. The starch charged varies from 4000 to 9500 pounds, depending upon the qualities desired in the finished sugar. From 0.25 to 0.5 per I c e n t hydrochloric acid on I starch basis is added. The I I converter is placed under about m/ --, I 40 pounds pressure by the inI troduction of live steam. When (1 io) I the conversion has proceeded I I until as high a purity as is posI sible (generally 88 to 90 per I cent) is obtained, the liquor is I I discharged into a neutralizer. I The acidity is reduced practiI cally to neutrality with sodium I carbonate. This neutralizaI I tion flocculates the insoluble impurities and increases the ash content by the formation of sodium chloride from the acid. After neutralization the liquor is passed through a Jeffery c e n t r i f u g a l separator to remove fats liberated from the starch granules. It is then passed to the Sweetland filters to remove insoluble materials such as solid proteins, fiber, etc. It is then given a treatment of bone black called light bone filtration. After passing through triple-effect evaporators it returns to the filter house for heavy bone-black filtration. This filtration is conducted at as heavy a density as possible (usually 30" Be.), so that upon further concentration no insoluble material will be thrown out. After this it is concentrated in a single-effect evaporator to 3So-45O BB. for crystallization. Thus far no radical changes have been made that would differ from the so-called standard practice in any refinery, either cane or corn. DIFFICULTIES IN CRYSTALLIZATION From the finishing pans the liquor is sent to the crystallizing house, and it is here that the trouble begins. I n the first place, there are two kinds of dextrose crystals, hydrous and anhydrous, and in order to make the centrifugal process 1 Presenred before the Division of Sugar Chemistry a t the 67th Meeting of the American Chemical Society, Washington, D. C., April 21 to 26, 1924. f Chem. A g e ( N . Y.), 29, 213 (1921).
commercial all the crystals must be of one kind. The anhydrous fillmass containing hydrate will not cure in a manner which will permit of its being centrifuged. Secondly, there are different types of crystals in each of these two main groups. For example, three distinct types of hydrate crystals are present. There is a congregation of crystals twinning and retwinning as elongated needles starting from a common crystal nucleus forming a wartlike or cauliflower-like mass. This form of crystallization is impossible to cent'rifuge, as when these crystal masses encounter the centrifugal force they break up and form an impervious mass through which the greens cannot pass, and which is impossible to wash. Again there is an elongated, needlelike crystal. Such crystals cause trouble in two places: First, as the fillmass is brought together these fragile needles break into small pieces; second, when discharged into the centrifugals an impervious mass is formed through which it is difficult to pass the greens. The third type of crystal is that desired. It is normally somewhat broader than it is thick and of approximately the same length as breadth.3 Detailed information on the crystal forms of dextrose is found ~ measured both the anhydrous only in an article of B e ~ k e . He dextrose and the hydrate, and the following data are quoted from this article: Anhydrous Dexlrose. The anhydrous crystals belong to the rhombic system and appear as elongated prisms with hemihedrsl end surfaces (Fig. 1). The characteristic surfaces are those of the vertical prism, m (1101, and the right sphenoid, 9 , the hemihedral form of the octaheder (111). The relation between the axes is a:b:c = 0.704: 1:0.336. Cross twins are common, the prisms growing through each other a t an angle of about 60 degrees. Dextrose Hydrate. The hydrate crystallizes in the monoclinic system and forms thin plates of hemimorph development (Fig. 2 ) . The relation between the axes is a: b: c = 1.735:1:1.908,6 = 97 degrees 59 minutes. The main surfaces are the vertical prism, m (110), the horizontal prism, 2, d (101). the pinacoid, p (001). Hemimorph forms are common, with the pinacoid (010) appearing instead of the two (110) surfaces on the right side. The smaller crystals show frequently hemimorph development with pentagonal outlines, but the larger crystals are as a rule hexagonal in outline. However, these crystals seem to be made up of hemimorph individuals grown together in twin formation, the line of the pinacoid (010) often showing across the pinacoid (001) straight or in a series of jogs.
< < &
Becke remarks that the values of the angles are only approximations, as the surfaces were too irregular to give good reflexes in the goniometer. In the growth of the hydrate crystals there
m fi/%>
___--- ----------- ---
ni (1 io)
(o/o) +/) FIG. 2-DEXTROSEHYDRATE (BECKB)
is a great tendency towards the formation of vicinal surfaces which result in a scratched or rounded appearance of the main surfaces. It would be of 'interest to have a series made of more accurate angle measurements, but for this purpose it would be necessary to carry out the crystallization under very closely controlled conditions, on a laboratory scale.
Another natural difficulty had to be overcome-the tendency to produce grains of extremely fine microscopical size. a Sjostrum, unpublished manuscript. 4
Tschermak's Min. Mitteilungen, 10, 464 (1889).
1174
INDUSTRIAL A N D ENGINEERING CHEMISTRY
I n the crystallization of dextrose considerable heat is produced. As the crystallization is exothermic this condition of heat added to the crystallizing mass a t its critical period of crystallization presents a difficulty that must be handled with precision. Again, unknown impurities arb found which have a very marked influence upon the crystallization, as they not only apparently control the rate of crystal growth but also influence the kind of crystals that will be formed. After an enormous amount of research work, the control of crystallization has only partially been learned. SOLUTION OF DIFFICULTIES The solution of the joint presence of hydrate and anhydrous sugar together lay not alone in the temperatures consistent with their stability. Other conditions being right, the anhydrous sugar can be crystallized in conditions unstable to it and stable to the hydrate. The same conditions which give us this ability also in a measure answer for overcoming other difficulties. ' I n order to maintain the acceptable form of crystals two things have to be controlled-the initial crystal present and the proper mode of its formation. Along these lines all common methods of crystal induction were tried, such as induction by shock, rapid cooling, dry seeding, conditions of supersaturation, cut strikes, wet seeding, seeding by use of fondant, etc. I n all these methods certain troubles arise -the inability to control the number of crystal nuclei to be built into finished crystals at the end of the cure, the inability to control the relative uniformity of the size of the crystal in the finished batch, or inability to control the desired form of crystal or the size of the crystal in the finished batch. By the common-sense use of the phase rule governing the existence of dextrose as a solid and a solute in the same liquid suspension with its nonsugar impurities it was possible to put the crystallization on a fairly consistent basis. These interesting scientific phenomena are not yet in a sufficiently presentable state to give any definite theories or proofs but they can be used as a commercial tool. If a definite amount (which will vary from time to time) of wet seed from a preceding batch is allowed to remain in the crystallizer, and introduced upon this wet seed is a liquor having a supersaturated condition restricted to a fairly narrow range, the kind of crystal existing in the preceding batch can be reproduced in such numbers that when the batch is finished the crystals will be of approximately the desired size and uniformity. The number of crystal nuclei formed must be sufficient so that their spheres of influence will cover the entire liquid mass a t all times during the curing process. Otherwise, as advantage is taken of the temperature drop, which has been shown to be difficult, to maintain the supersaturation, false crystals will be formed consisting of any of the three natural crystal forms previously mentioned. This introduces not only troubles in the centrifugal operation but a more serious difficulty in succeeding batches, as this false crystal will also tend to reproduce itself in the crystal nuclei thrown off in the liquor surrounding it. Therefore, the solid phase which is introduced into the batch must consist of a pedigree crystal of known workable qualities. The tendency to produce a grain of microscopically small size is retarded by controlling the temperature and degree of supersaturation. This particular control is not a t present on scientific basis, but is simply an art judged by the educated finger tips of the crystallizer operator, who can be likened to the pan man in the refinery. The education of this man's finger tips has been the most expensive part in the development of this process, and it is hoped that relief from the pressure of production will soon make it possible to put this on a scientific basis.
Vol. 16, No. 11
The different concentrations and temperatures required for this control would be given with precision if it were not for the effect of the converter impurities upon crystallization. As before stated, these impurities affect the rate and crystallization of the kind of crystals formed. Several research men are working on the physical chemistry of these substances, but at present no worth-while information has been obtained. The control of the liquors to offset the effect of these impurities is still a matter of guesswork in which trouble is corrected as the curing of the batch proceeds.
OTHER STEPSIN PROCESS The crystallizers used in the foregoing process are of the common type used throughout the sugar world. They are water-jacketed steel cylinders lying on their side with a slowmoving agitator inside. When the mass has finished curing it is dropped into a battery of standard centrifugals fed from a mixer of sufficient size to contain the entire batch. The process from this point on is common in all sugarhouses. The machine is charged while in motion. When sufficient sugar has been introduced the charge gate is closed. The green liquors are purged off. Mechanical washers apply the wash water. When the sugar has been washed so that its purity and color are within the allowed limits, the washing is stopped. The machines are allowed to continue spinning for a short time to reduce the moisture content as low as is economically possible. Because of the finer grain than is common in cane or beet, the wall of sugar offers an excellent filter medium. This requires that the wash water be absolutely free from any suspended material. The wash water is treated with aluminium and allowed to settle. It is then passed through two sand filters into the small storage tank. From the small storage tank it is fed to the centrifugal machines through a charcoal filter. The finished sugar is sent through a double-pass drier until it is free from any free moistures-i. e., if anhydrous it is dried until there is no moisture present; if it is the hydrate it is dried until the moisture content is less than 8 per cent. After leaving the driers, the sugar is passed over Hummer screens and discharged into the packing hopper. The liquids leaving the centrifugals return to the refinery in the manner standard to all sugarhouses-i. e., the first greens to make seconds, second greens to make thirds, etc. The wash waters return to the refinery and are introduced into pans of a similar purity. The remelts are remelted with wash water and also are boiled in pans of similar nature. The low fillmasses-i. e., seconds and thirds-are handled the same as firsts except that they are slower curing and more troublesome owing to their greater content of impurities. It will be seen by the samples that sugar of almost any grade desired can be produced. All these samples of refined dextrose were produced without milling even in the finest stages. It is thus apparent that one can control, within reasonable limits, the size of grain, and irregularities of the size of the grain in the centrifuging process. It will be noted that throughout this entire process the sugar has been handled in the same hygienic manner as is refined sugar; that it is handled by mechanical means; that it does not come into contact with any contaminating influence (the bacteriological laboratories found no difference in the bacteria contained in cane sugar and refined dextrose taken from the warehouse, the average bacterial count in both cases being less than 20 per gram dry substance sugar, and the contaminating bacteria identified as molds which could come from the storage conditions); that it has been freed from ash and nonsugars, and is placed on the market, practically speaking, chemically pure.
INDUSTRIAL A N D ENGINEERING CHEMISTR Y
November, 1924
USESOF DEXTROSE Dextrose is not intended to be used as a substitute for cane sugar, but owing to certain peculiarities which it possesses it is in certain respects superior to cane sugar for manufacturing purposes. One of these is its tendency to form microscopically small crystals. Thus, fondants, creams, etc., can be produced which have that velvety feel and appearance so desired in these products. It also seems to affect the crystallization of cane sugar in the same way, and has thus become a necessity to the manufacturers producing the more fancy types of candies, cakes, cold icings, milk chocolate, chewing gum, etc. It does not possess the sweetness of cane sugar and, according to some of the larger fruit packers, it is the ideal sugar for preserving fruits of mild or delicate flavors which are masked by the extreme sweetness of cane sugar when used in the amounts necessary. I n the baking trade it is preferred as the yeast nutrient in a bread sponge. For medicinal purposes, especially in cases of acidosis, anemia, and the earlier stages of Bright’s disease, it is the only sugar now commercially available which does not aggravate these conditions. The ice cream trade desires the sugar on account of its
1175
lack of sweetness, because the average ice cream user demands a certain body which is produced only by the use of sugar, and by using refined dextrose this body can be more successfully produced without making the ice cream too sweet. The cruller and doughnut manufacturers and pancake flour manufacturers prefer the use of refined dextrose due to its low caramelization temperatures and the fact that it gives doughnuts and pancakes that delightful brown without any burnt taste. The cracker and biscuit manufacturers are using it for purposes best known to themselves. The manufacturers of commercial pectin are quite large users of this product. The wine and vinegar manufacturers use it in the natural fermentation processes, as it carries with it a maximum fermentability with no troublesome secondary flavors which later have to be removed in vinegars and which would spoil wine as it is consumed direct. Dye manufacturers are becoming large users of the product. The condensed milk manufacturers are very desirous of using it. I t s preserving qualities are equal to those of cane sugar, and in this particular case its lack of sweetness is the desirable feature.
Adsorption Effects of Filtering Materials on Sugar Solutions’ By G . H.Hardin and F. W. Zerban NEWYORKSUGAR TRADE LABORATORY, NEW YORK,N. Y.
wholly reversed to negative N THE course of the Dry filter paper takes u p water from sugar solutions, while filter a d s o r p t i o n . Freundlich4 routine work performed paper with high moisture content tends to dilute the sugar solution; states that negative adsorpin this laboratory, it there is an intermediate point where equilibrium obtains. The tion is more often observed was ‘frequently observed effect of these phenomena on saccharimetric analysis has been in the case of gels than with that when a raw sugar solustudied quantitatioely, and it is concluded that in practical sugar other a d s o r b e n t s . T h e tion prepared for polarianalysis, using dry filter paper, it is not suficient to discard only a well-known occurrence of metric analysis was, for small part of the fiItrate, as practiced by some analysts, but that at “adsorption water” in beet some reason or other, passed least 25 of the 100 cc. should be rejected to attain the closest possible and cane fiber should also through a second filter, unapproximation to the correct polarization. Absorbent cotton acts be mentioned in this connecder the usual . . precautions of 1ih.efilter paper, while dry asbestos or Filter-Cel did not measurably tion. covering with a watch glass, affect the polarization. In view of these cmsiderthe polarization of the final ations a study was made of filtrate was always slightly but distinctly higher than when the analysis was repeated ac- the effect of the commonly used filtering materials, such as cording to the regular procedure with one filtration. This in- paper, cotton, asbestos, and kieselguhr, on the concentration of crease in polarization may, a priori, be ascribed either to evap- sugar solutions. Most of the tests were made with ordinary oration, or to a concentration change brought about by the filter paper, as this is the medium used in regular sugar analyfilter paper itself. The first of these causes did not seem prob- sis. It was, of course, necessary either to avoid evaporation able, since Rates and PhelpsZ have shown that “practically all altogether or to be able to correct for it. increase in polarization, regardless of atmospheric conditions, In some experiments made for the purpose of orientation may be prevented by covering the funnel with a watch glass,” an attempt was first made to attain this end by centrifuging even if the solution is filtered twice through the same filter. the mixture of paper and sugar solution in a conical glass According to previous literature, cellulose is, from the tube, filling the other tube with the sugar solution itself. colloid-chemical standpoint, a gel, and as such sorbs water Both tub& were covered with rubber caps. It was found quite strongly. References cited by Bancroft3 show that impossible to obtain a clear enough liquid from the mixture absorbent cotton takes up 21 per cent of water in the presence to be able to make accurate readings in the saccharimeter. of saturated water vapor, and that it will hold 400 per cent Filtering the mixture of paper and sugar solution through a of liquid water when centrifuged wet a t 4000 r. p. m. It is small piece of filter paper or a little asbestos placed over the therefore not surprising that, although filter paper in many end of a pipet with broken-off point was also tried. But here cases exhibits positive adsorption, this is often reduced in there is the objection that the solution is under a partial degree by the simultaneous sorption of water, and may be vacuum while being filtered. The average results by both of these methods gave an’in1 Presented before the Division of Sugar Chemistry at the 67th Meeting of the American Chemical Society, Washington, D. C., April 21 to 26, 1924. crease of 0.4’ V. when 100 cc. of a normal solution of refined
I
2
Intern Sugar J . , 16, 266 (1914).
3
“Applied Colloid Chemistry,” p. 76.
4
“Kapillarchemie.” 3rd ed., p. 046.
