August. 1926
INDUSTRIAL A N D ENGINEERING CHEMISTRY
847
Influence of Absorption Spectra of Technical Sugar Products on the Decolorizing Efficiency of Bone Char' 1
By T. B. Wayne IMPERIAL SUGARCo.,SUGAR LAND,TEXAS
The most useful feature of this new method of color deHE decolorizing efficiency of bone char and the vegetable carbons, and various methods of evaluation and termination is the absorption ratios, which Peters and Phelps comparison, have been favorite subjects of many designate as the ratio, Q, between unit absorption a t 560 investigators during recent years, but owing to the confusion m p and absorption at other wave lengths a t definite intervals of methods used, the lack of a satisfactory method of color throughout the spectrum. A study of decolorization by determination, and, in many instances, the impracticable chars when using this method reveals certain facts concernviewpoint of the investigator, much confusion still exists. ing the kind of coloring matter adsorbed by char under defiA recent article by Blowski and Ban,* however. has very nite conditions of comparison as regards density, purity, capably presented comparisons between bone char and time of contact, reaction, etc.; that is, if solutions are precertain vegetable carbons in a manner which will enable the pared which are nearly identical in all of these particulars and are treated under identechnologist to grasp some tical conditions, one can of the underlying principles then determine what regions of decolorization by actiSTUDY of the decolorizing action of bone char on of the spectrum yield most v a t e d carbons. As ihese high-purity sugar liquors and sirups, using the specreadily to adsorption by the authors have shown, when trophotometric method of Peters and Phelps, reveals char. The types of coloring all of the facts connected that no definite assertions can be made to the effect matter in the sugar product with the industrial use of that, in general, bone char shows selectivity for any to be decolorized may be activated carbons in sugar particular coloring matter. Frequent statements in grouped according to their r e f i n i n g are consideredthe literature indicate that bone char has difficulty in absorption ratios, Q, which namely, other factors beremoving the red coloring matter resulting from dePeters and Phelps use to insides decolorization-there struction of sucrose and invert sugar by lime and heat, dicate the relative absorpstill remains a considerable but data presented in this paper show that even in the tion a t other wave lengths balance in favor of bone char case of these caramel-like substances the decolorizing than 560 mp throughout over other activated caraction and selectivity for any particular type of coloring the visible spectrum. This bons in their present state matter varies with the degree of caramelization. Bone has been possible to some of development. This dischar evidently has a selective action in the removal of e x t e n t in the past when cussion, therefore, will congreen coloring matter derived from the cane because of u s i n g t h e arbitrary color sider only bone char. the limited solubility of this class of impurities. HowPeters and Phelps,3 of the standards and color units, ever, evidence shows that the final residual coloring but usually such standards National Bureau of Standmatter present in highly char-filtered liquors of high and methods covered wide a r d s , h a v e s t u d i e d the purity is of a type giving high absorption for light in and overlapping s p e c t r a 1 problems in connection with the red end of the spectrum. b a n d s which, even when the development of a satisf a c t o r y m e t h o d of color they did give results satisdetermination, and in factory for c o m D a r a t i v e various papers presented before the Sugar Division of the purposes, failed to give a clear Understanding of ^the types AMERICAN CHEMICAL SOCIETY have outlined a method which and properties of the various kinds of coloring matter usually is based on rational principles. By a study of :ibsorption found in sugar products. The lack of an understanding of the quality of the coloring spectra and luminosity integrals of many sugar products they have formulated a simple method wherein the intensity matter in a sugar product has led to many erroneous compariof absorption at 560 n i p may be converted into a correct sons between various activated carbons. Some investigators colorimetric determination. Although the accuracy of the have selected a dilute solution of blackstrap molasses as a method is influenced largely by certain colloid-chemical standard solution for testing the decolorizing efficiencies of phenomena which are not readily controlled and the equip- various carbons and, after treating portions of this solution ment is somewhat expensive, i t is undoubtedly the most with equal or varying proportions of the carbons under exsatisfactory method of color determination available. I n amination, have attempted to arrive a t a figure representing control work, if standard color solutions are prepared and the relative efficiencies of the carbons. They have really standardized in terms of absorption a t 560 mp, and then obtained adsorption curves for these carbons on that parviewed in comparison with the unknown sample through a ticular solution containing its particular types of coloring light filter transmitting light of a n effective wave length of matter a t that one concentration. Other factors which 560 mp, a satisfactory and simple colorimetric method automatically entered into the conditions of these tests were results. I n this manner the original sirups or liquors are (1) time of contact, ( 2 ) concentration of the test liquor, directly compared, and the troublesome difficulties arising (3) composition of the test liquor, (4)temperature, ( 5 ) refrom certain colloidal and chemical phenomena attending action of both the test liquor and carbon, and (6) other miscellaneous factors such as viscosity, clarity of the test liquor, the dissolving and purifying of the products are avoided. and the fineness of the carbon. All of these must be dupli1 Received April 2, 1926. cated in order to secure identical results, and the same car*THISJOURNAL, 18, 32 (1826). 8 Sugar, 27, 223 (1925:. bons subjected to different conditions may show entirely
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A
848
INDUSTRIAL A N D ENGINEERING CHEMISTRY
different efficiencies. The only method of comparison that is approximately correct is one in which all of these factors are similar to those encountered in the industrial conditions under which the carbon must be used. The carbon which attains the results expected of it a t the lowest net cost per unit of refined product is selected, and in making this selection there are many factors other than the decolorizing efficiency to be considered. Blowski and BonZhave made comparisons between various activated chars taking into consideration the factors influencing the decolorizing action on sugar liquors. One of these factors, the effect of the “quality of color” in the liquor, has been discussed briefly by making adsorption curves for carbons on four test liquors each containing a different type of coloring matter. No attempt is made to examine these test liquors spectrophotometrically to determine, if possible, just what types of coloring matter were present in these liquors, and how each affects the decolorizing efficiency of the carbon. The data presented below are the result of a n attempt to identify the different types of coloring matter found in raw sugar and in refinery products and, if possible, to account for their origin. Of course, in doing this it will also be possible to locate those parts of the spectrum in which bone char shows the greatest adsorption. The Coloring Matter in Cane Juice
Something of the nature and properties of the coloring matters found in raw cane juices as they come from the mill may be found by reference to standard handbooks and reference books on cane-sugar manufacture by Spencer,‘ Geerligs,s and Harloff and SchmidtS6 Chlorophyl, antho-
Figure 1-Absorption Ratios (a) Grayish raw sugar before washing ( b ) After washing
cyan, saccharetin, and certain polyphenols of iron have been located in varying amounts in the raw juice. Some of these are readily eliminated by clarification with lime and heat, while others are more troublesome and may pass into the clarified juices and sirups from which the raw sugar is boiled. Most of them impart a grayish color to the products in which they appear, and raw sugar boiled from improperly clarified juices is usually characterized by a grayish or greenish color. 4 Handbook for Cane Sugar Manufacturers, 6th ed., 1917, p. 6. John Wiley & Sons, Inc. 1 “Practical White Sugar Manufacture,” 1918, p. 8. Norman Rodger, London. 6 “Plantation White Sugar Manufacture,” 1915, p. 11. Norman Rodger, London.
VOl. 18, No. 8
This color is largely in the molasses film on the crystals and is separated into the affination sirups when the sugar enters the refinery wash plant, but may also occur in the crystals themselves. I n the latter case the sugars cannot be washed white, and the washed sugar liquors therefrom have a greenish or grayish cast which is easily identified and recorded by means of spectrophotometric analysis. Table I1 shows a spectrophotometric analysis of a typical gray sugar of Philippine origin having the chemical analysis shown in Table I. After the washing process and filtration through Sweetland filters using Filter Cel, the spectrophotometric analysis of the washed sugar assumes a different color distribution curve, as is shown in Figure 1. These data illustrate the statements in the preceding paragraph. The trend of the curve made by plotting absorption ratios against wave lengths shows something of the origin of the coloring matter present in sugar products. Raw cane juice would have a curve different from the sugar just mentioned, and different from the improperly clarified juice from which this sugar was boiled, because the red color developed during the manufacturing process will increase toward the last stages of the process and produce a sugar showing more absorption in the blue end of the spectrum. I n order to make a bright raw sugar, the juice clarification must be complete enough to remove most of these grayish or greenish bodies, although the juice acquires more color of a red or yellow character. That is, upon spectrophotometric analysis the absorption curve will be higher in the blue end of the spectrum, denoting a reddish color in the product. Table I-Analysis Constituent Sucrose Invert sugar Ash (direct) Nonsugars
of Philippine Raw Sugar Per cent 96.28 1.13 0.50 (sulfated, 0.78) 1.49
The absorption ratios given in Table I1 as compared with absorption ratios of the washed sugar are plotted in Figure 1. It is evident that in sugars of this type the gray coloring matter may be boiled into the crystals. Whether this coloring matter is due to ferric compounds or to anthocyan which has not been completely precipitated from juices expressed from dark colored canes, is problematical. Regardless of all theoretical considerations concerning the probable composition of the gray coloring matter found associated with certain raw sugars, in refining raw sugars we have to contend with (1) the gray coloring matter which may have been derived from the cane or through the presence of iron polyphenol compounds developed during the manufacturing process, (2) the red coloring matter formed by the action of heat and alkalies on the reducing sugars during process, and (3) any coloring matter which may have developed from miscellaneous sources, which for practical purposes may be disregarded. Red Coloring Matter Developed during Process
Carameliration When sucrose and invert sugar are heated in neutral solutions for any length of time, incipient caramelization occurs with the formation of compounds which impart to the solutions what is commonly designated as a red color. I n the presence of alkali, even in small quantities, the formation of this color ia greatly accelerated. Spectrophotometric analyses of color formed during the various stages between incipient and nearly complete caramelization-in fact, caramelization far enough advanced to cause the formation of considerable carbon-show a progressive decrease in the absorption ratios in the blue end of the spectrum accompanied by some increase in those for the opposite end of the spectrum. These facts are demonstrated by the following experiments.
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
August, 1926
Table 11-Spectrophotometric 440 3.392 2.94
QLon
480 2.766 240
480 2.185 1.89
500 1.764 1.53
Table 111-Spectrophotometric Caramel 440
450
460
480
Table IV-Effect
-
Caramel 2 4 0 (a)
(d)
6:i6 4.37 3.70
450 9.42 5.46 3.93 3.31
460 7.86 4.80 3.48 2.99
500
520 1.509 1.31
540 1.306 1.13
Analysis of Philippine Raw Sugar Wave Length, mp 560 580 600 620 1.153 1.034 0.902 0.808 1.00 0.90 0.78 0.70
849
_640 0,722 0.63
660 0.634 0.55
Analysis of Sucrose Caramels Expressed a s Absorption Ratios, Q Wave Length, mp 520 540 560 580 600 620 640 660
-
680 0.551 0.48
700 0.475 0.41
680
700
680 0.14 0.21 0.29 0.31
70; 0.11 0.18 0.24 0.26
-
of L i m e on Caramelization of Sucrose Solutions, Expressed a s Absorption Ratios
480 4.85 3.45 2.61 2.35
500 3.16 2.47 2.00 1.89
520 2.15 1.85 1.82 1.50
Wave Length, 540 560 1.48 1.00 1.32 1.00 1.28 1.00 1.24 1.00
m
bo
0.70
0.77 0.81 0.82
600 0.51 0.59 0.64 0.67
620 0.38 0.46 0.52 0.55
640 0.27 0.33 0.43 0.43
680 0.20 0.26 0.35 0.37
I n presenting these data the words "color" and 'Lcoloring length selected for 1.0 gram saccharine dry substance in 1 matter" have been used freely to designate what the prac- cc. and 1 cm. cell thickness. I n calculating absorption ratios, tical observer visualizes. Technical sugar products are Q, absorption a t 560 mp is 1.00 and absorptions a t the various usually classified as red, yellow, grayish, or greenish, accord- other wave lengths selected are ratioed accordingly. This ing to the physical sensation registered by the observer's procedure allows direct comparisons to be made between the eye. However, in order to record these sensations and yet trends of the absorption curves of different products n-ithout avoid the highly technical nomenclature and descriptions regard to their respective colorimetric equivalents. Since, used by the physicist in classifying colors, the writer has used in the case of the caramels, the objects are to treat them the absorption ratios of Peters and Phelps3 as a means of as though they had been formed in process by the action of tracing the absorption trends of the different products a t heat and alkalies on the sugars and to establish the fact different wave lengths throughout the visible spectrum. that caramels possessing different trends to their absorption Since in this discussion we are not primarily conctmed with curves are formed under different conditions, no colorimetric the quantitative determination of color, the -log t values equivalents are necessary. at 560 mp and a t the other wave lengths selected arc' not given (a) Ten grams of C. P. sucrose were dissolved in 20 cc. of in all cases, and the reader is expected to follow the trend neutral distilled water. The solution was poured into a porceof the absorption ratios given, as these are indicative of the lain casserole and heated cautiously with constant stirring quality of the light-absorbing bodies present. All measure- until a yellow color began to form. It was then cooled and, ments were made with the Keuffel & Esser color analyzer, after diluting with water-white sucrose sirup, was prepared for analysis by repeated filtrations through an and the -log t values from which the & ratios were calculated spectrophotometric especially prepared asbestos mat in a Gooch crucible until no are on the basis of 1 gram solids per cubic centimeter and turbidity could be detected when viewed before a powerful slanting beam of light. 1 em. cell thickness. PREPARATION OF CARAMELS FOR SPECTROPHOTOMETRIC( b ) A similar solution of sucrose was heated in the same except t h a t the caramelization was carried to the point AmLYsIs-The object was to obtain caramels prepared manner where the solution was distinctly red. It was then diluted with by carrying the caramelization to several stages and then water-white sucrose solution and analyzed as described above. analyze them spectrophotometrically. I n order to analyze (c) The experiment was repeated in the same manner, except them by the same methods which were used later in estab- that caramelization was continued until the entire contents of lishing absorption curves for sugar products, two solutions the dish became black and brittle after cooling. ( d ) I n this instance the caramelization was carried t o the of pure sucrose were prepared and decolorized completely point where considerable amount of carbon had formed. by treating with a n iron-free decolorizing carhon. The The absorption ratios of these solutions are shown in Table first of these solutions was adjusted to 57.5" Brix a t 17.5" C. and the second to 50.0" Brix a t 17.5" C., and both were then 111. As an additional check, a solution of pure invert sugar adjusted to exactly pH 7.0. The water-white sucrose solution was then colored with the various caramel solutions was prepared and, after adjusting to pH 7.0, a parallel series in the form of filtered water extracts. The caramel sirups of experiments was made under conditions resembling those thus prepared were finally adjusted with the two sucrose just described. It was found that the absorption ratios of solutions until they were a t a density of 55.0" Brix at, 17.5" C., the four caramels so prepared were approximately the same and after being filtered optically void they gave transmission as those shown in Table 111, any differences being traceable readings of between 18.0and 20.0 in a 10-em. tube when read to differences in the degree to which the caramelization was at 560 m,u in the Keuffel & Esser spectrophotometer. It made. However, as would be expected, the caramelization was considered desirable to read all of the caramels so pre- occurred somewhat more rapidly in the inrert sugar solutions. pared at the same value for c (grams saccharine solids per Eflect of Lime and Heat cubic centimeter) and so that they all had practically the same -log t value a t 560 m,u. Then, since the same optically Under the usual manufacturing conditions in a raw sugar void solution was read throughout the spectrum a t certain factory, the red coloring first forms during the heating of the wave lengths selected to yield sufficient data for tracing the limed raw juice. For best results in clarification, the raw absorption trend of each caramel, by using cells of different juice is usually limed to about pH 8.4, and, after coming out thicknesses (values for b ) -log t values were established and of the heaters and settling, the clarified juice from a good from these the absorption ratios, &, were calculatc,d. clarification has a reaction of about pH 7.6. Under these Briefly summarized, in order that these caramels might be conditions, and to a lesser extent when the clarification is directly compared with technical sugar products, the ab- more acid, the juice acquires a red color from the action of sorption ratios, Q, were obtained in exactly the same manner lime and heat on the invert sugars present. After this as is recommended by Peters and Phelps.3 The calculation clarified juice is concentrated in the multiple effects, the reselected in each case is based on light absorption a t each wave action has dropped to pH 7.0 or lower, depending on t h e
INDUSTRIAL AND ENGINEERING CHEMISTRY
850
Vol. 18, No. 8
original reaction of the clarified juice, and whatever color is acquired after that may be regarded as the result of heat alone, if we disregard the possibility of iron compounds. I n order to study the effect of lime on the quality of coloring matter formed by heat in the presence of free alkali, the experiments described under sections (a) to (d) were repeated with the variation that in each case the sugar solutions were adjusted to pH 8.6 before applying the heat. The results are shown in Table IV. Although lime greatly accelerates the rate of color formation, it is doubtful whether the quality of the color thus formed will be any different from that formed by heat alone, if the latter could be determined at the same degree of caramelization. I n each instance, whether the caramelization is accomplished by the action of lime and heat or by heat alone, the first incipient action produced a coloring matter with a very high absorption ratio in the blue end of the spectrum, and as the action proceeds the absorption curve tends to straighten out by a decrease in the blue end and some increase in the red end of the absorption spectrum.
the mills, tanks, and other equipment in the sugar factory. The amount of iron used in these experiments is more than will be likely to occur in the primary juices, liquors, and sirups of the sugar factory, and the formation of polyphenols or related compounds by the destruction of sugar has been greater, possibly, because of the more complete caramelization. However, the absorption curves of these iron-treated caramels show that the coloring matter formed in this manner cannot account for the gray or greenish color of certain raw sugars, as the latter often exhibit much less absorption in the blue end of the spectrum, and with a higher absorption in the red end, than do the caramels presented above. The physical equivalent of such absorption curves is-a grayish sugar. A study of the absorption ratios of typical raw sugars of colors ranging from bright red to a dull gray will reveal that the coloring matter is composed, first, of the grayish or greenish bodies derived mainly from the raw juice because of failure to eliminate them by proper clarification, and second, bodies produced by the action of heat and alkalies on the sugars, both with and without the presence of ferric Effect of Ferric Iron iron. The quality of the coloring matter is determined largely Ferric iron, as a producer of a grayish cast in certain sugars by the proportion of these two opposite types of colored and sugar products, has been studied by Schneller,' Zerban,& bodies present. and G e e r l i g ~ . ~Polyphenols ~~ and related compounds, which Selective Decolorization by Bone Char are present originally in the raw juice or formed later in The concensus of opinion regarding selective decolorization process, react with ferric iron to produce ferric polyphenol by char is that the gray coloring matter is more easily recompounds. Anyone who has had experience in raw sugar manufacture moved than the red. This assertion is made in many of the is familiar with the darkening of juices when allowed to stand. older treatises on the subject, and recently Bardorff and Balllo This is more noticeable when there is a temporary pause have stated that "it has come to be generally admitted that in the manufacturing process; the mill juice will darken gray raws are preferable over the red kind for all purposes of while standing in the juice tanks, and the clarified juice refining; the grays part more readily with their coloring will do likewise, especially if allowed to cool somewhat. matter than do the red sugars, and therefore require less As this darkening occurs both before and after the juice has char for attaining a certain percentage of decolorization or been limed and heated, it is evident that natural polyphenol will yield clearer and more cheerful liquors from equivalent compounds have been active. There is also a possibility char filtration." I n recognition of the possibility that bone char may not that polyphenols or related compounds have been formed always exhibit the same kind of selective adsorption on later in process. To investigate this point further, 33 grams of 50" Brix coloring matters found in different kinds of sugar products, invert sugar sirup were treated with a solution of ferric am- the question has been investigated by using a variety of monium sulfate in such a manner as to bring the ferric iron liquors having different types of absorption curves. content of the sirup up to 100 p. p. m. iron. This sirup and Washed Sugar Liquors a similar portion without the iron treatment were placed on Washed sugar liquors from four general types of 96 test centrifa wide hot plate and boiled down until the caramelization was ugal raws were prepared by washing the raws up to approxifairly complete. Both caramels were taken up with water- mately 99 purity, melting to 60" Brix a t 17.5' C., liming to p H white sucrose sirup and prepared for spectrophotometric 6.8, and then filtering through a small filter operating on the principle of the Sweetland press with the aid of Filter Cel after analysis in the usual manner. The caramel-colored sirup from the check sample was heating to 83" C. (180: F.). Two hundred and sixty cubic centimeters of washed sugar then treated with ferric iron in the same proportion, and liquor prepared in this manner were heated in a constant-temafter refiltration was analyzed. perature water bath to 80' C. and bone char (new char of 12 X 28 mesh, washed and burned) was added in the proportions of 20, The results of both treatments are shown in Table V. Table V-Effect Caramel +IO0 p. p. m. Fe Check Check 100 p. p. m. Fe
+
'440 3.50 3.92 3.65
of Ferric Iron on Absorption by Caramels as S h o w n by Absorption Ratios
460 2.81 3.07 2.91
480 2.26 2.45 2.33
500 1.79 2.00 1.85
520 1.45 1.59 1.50
These experiments indicate that compounds of ferric iron and po~ypheno~ compounds formed by the destruction of sugar do exist, and will cause the formation of a grayish color, but that color from this source is very likely to be of secondary importance to that formed as the result of interaction of natural po~ypheno~sof the cane with iron acquired from La. Agr. Expt. Sta., Bull. 167 (1916). I b i d . , 166 (1919). 9 "Cane Sugar and Its Manufacture," 1909, p. 8. London. 9
640 1.15 1.26 1.24
Wave Length mp 560 58)O 600 0.83 0.70 1.00 0.82 0.67 1.00 0.84 0.71 1.00
620 0.59 0.63 0.60
640 0.50 0.42 0.50
660
0.43 0.33 0.43
680 0.37 0.28 0.37
700' 0.31 0.24 0.31
30, 40, and 60 per cent of the weight of solids present. Reflux condensers were connected to each flask to prevent evaporation. The liquor was heated at 80" C. in contact with the char for 3 hours, the contents of the flasks being thoroughly shaken for 16 seconds every 30 minutes. The liquor was then drained off the char and, after cooling, asbestos fiber was added and filtration effected through small Biichner funnels until the filtrate was free from visible suspended matter. The liquors were then prepared for spectrophotometric analysis by repeated filtration
8
Norman Rodger,
1o"The Elements of Sugar Refining? 1926, p. 33. Publishing Company.
The Chemical
through specially prepared asbestos mats in Gooch crucibles. The absorption spectrum was determined a t intervals of 10 mp from 440 t o 500 mp, and at 20 mp intervals t o 700 mp. Absorption ratios were then calculated using the -log t value a t 560 mH as 1.00. From Tables VI t o IX, the trend of the absorption ratios after treatment with different proportions of char may be compared with t h a t of the original liquor. ( a ) Green Louisiana R a w Sugar. This sugar represents a n extreme seldom found in raw sugars. The absorption ratios are very low in the blue end of the spectrum, and examination shows t h a t much of the original greenish bodies present in the raw cane juice has been boiled directly into the crystals. The affination sirup is green instead of red and, after purging the sugar free from adhering molasses film by repeated washing in the centrifugals, the washed sugar liquor prepared therefrom is green instead of reddish. The washed sugar liquor had very much the appearance of cane juice, and it was filtered with great difficulty. A slight change in temperature caused the liquor t o become turbid again owing t o the precipitation of slightly soluble matter which is ordinarily removed by lime and heat i n the raw sugar factory. The results obtained by treating this liquor with varying amounts of bone char are shown in Table VI. T a b l e VI--Green L o u i s i a n a R a w Suclar Washed sugar liquor: 5 9 . F Brix, 99.0 purity, p H 7.0 Char used Color Decolorization Per cent solids logt Per cent 0.2527 Original sirup 0.0994 20 0.0619 30 40 0.0265 60 0.0152
-
Wave length mu 440 450 460 470 480 490 500 520 540 .ifin 580 600 620 640 660 680 700 _ I _
Absorption Ralios No char 2.37 “10 1.86 1.67 1.53 1 42 1 33 i 19 1 10 1
nn
0 95
0 0 0 0 0 0
83 75 67 58 50 43
20% char 3:66 3.00 2.50 2.16 1.89 1.68 1.52 1.30 1.14
40% char 3:s7 3.27 2.75 2.30 2.00 1.77 1.60 1.34 1.15
0.86 0.75 0.65 0.54 0.44 0.36 0.28
0.89 0.77 0.67 0.56 0.47 0.39 0.32
1 -
__
nn
1
nn
Bone char shows a selective adsorptivity in the red end of the spectrum on sugar liquors of this type. The fact that most of the light-absorbing bodies in this sugar were probably derived from the natural coloring matter of the cane, probably present in a state bordering on the colloidal, explains the ease with which bone char removes them. ( b ) Philippine R a w Sugar. This sugar resembles the previous one in that some of the natural greenish colored cane products are present. However, its appearance is grayish owing to the presence of a larger proportion of the other types of coloring matter usually found associated with raw sugars. T a b l e VII-Philippine R a w S u g a r Washed sugar liquor: 59.1° Brix, 98.8 purity, pH 7.0 Char used Color Decolorization Per cent solids - log t Per cent Original sirup 0.2795 52.7 0.1322 20 iO.0 30 0.0839 33.5 40 0,0461 60 93.4 0.0184 Wave length mp
440 450 460 470 450 490 500 520 540 560 580 600 620 640 660 680 700
851
INDUSTRIA L S X D EA’GINEERING CHEMISTRY
August, 1926
Absorption Ralios Xvo char
2.95 2.64 2.36 2.12 1.90 1.71 1.56 1.33 1.14 1.00 0.88 0.78 0.69 0.60 0 54 0.47 0.42
2070 char 3.37 2.99 2.61 2.28 2.00 1.80 1.64 1.39 1.16 1.00 0.84 0.74 0.64 0.54 0.45 0.36 0.28
lo%
char 3.10 2.80 2.50 2.23 1.96 1.77 1.62 1.37 1.15 1.00 0.85 0.75 0.65 0.55 0.47 0.40 0.34
I n its action on this liquor the bone char appears first to adsorb the readily available coloring matter in the red end of the ab-
sorption spectrum, and then as the proportion of char t o solids is increased its selectivity for the coloring matters responsible for light absorption in the blue end is more pronounced. We have here the first indication t h a t other light-absorbing bodies possessing maximum absorption in the red end of the spectrum may be present, and t h a t these may be even more resistant t o adsorption by char than the decomposition products of the sugars which show maximum light absorption in the blue end of the spectrum. The fact that this liquor first shows an increase in the blue end, accompanied by a decrease in the red end, of the absorption spectrum, then a reverse to the opposite condition as the proportion of char t o solids is increased, bears out this conclusion. (c) Average Cuban R a w Sugar. This sugar has a n absorption spectrum of average trend, and the washed sugar liquor obtained from it shows a n average trend of absorption ratios from the blue to red ends of the spectrum. T a b l e VIII-Averale- C u b a n R a w S u aar Washed sugar liquor: 59.3O Brix, 99.0 purity, p H 6.9 Char used Color Decolorization Per cent solids log t Per cent 0.2942 58.4 0.1225 69.5 0,0897 76.8 0.0683 82.9 0.0504
-
Wave length mu 440 450 460 470 480 490 500 520 540 560 580 600 620 640 660 680 700
Absorption Ratios 20% .- char 3.62 3.22 2.85 2.52 2.21 1.92 1.68 1.35 1.15 1.00 0.88 0.76 0.65 0.55 0.46 0.40 0.34
No char 3.13 2.77 2.48 2.20 1.92 1.70 1.55 1.30 1.14 1.00 0.89 0.80 0.71 0.64 0.57 0.50 0.44
40% . _char 2.97 2.65 2.35 2.08 1.81 1.62 1.49 1.30 1.14 1.00 0.90 0.81 0.73 0.65 0.58 0.52 0.47
Treatment with 20 per cent bone char likewise removes first the easily adsorbed coloring matter from the red end of the spectrum, yielding a partially decolorized !iquor whose absorption sDectrum is higher in the blue end and lower in the red end. However, if 40 peqcent char is used, the ratios decrease in the blue end and rise in the red end t o the extent that the resulting liquor shows less absorption in the blue and more in the red ends than was the case with the original liquor before char treatment. This same tendency was noted in decolorizing the liquor described under ( b ) , but to a smaller extent. ( d ) Reddish Cuban R a w Sugar. This sugar has a bright reddish appearance. The grain is large and clear, and purges very cleanly in the centrifugals. .The washed sugar liquor prepared from it is bright, and redder than the usual run of raw sugars produced. T a b l e IX-Reddish Cuban Raw Sugar Washed sugar liquor: 59.0’ Brix 99.0 purity, p H 6.9 Char used Color Decolorization Per cent solids loa t Per cent Original sirup 0.2305
-
20 3U
Wave length
m/r 440 450 460 470 480 490 500 520 540 560 580 600 620 640 660 680 700
44.3 51.4
0. u . OEW3832
40 60
0.0732 0.0388
68.2 83.3
Absouption Ratios No char 3.30 3.00 2.69 2.39 2.08 1.8: 1.67 1.40 1,18 1.00 0.84 0.74 0.64 0.56 0.47 0.40 0.35
20% char 3.15 2.77 2.49 2.20 1.95 1.74 1.56 1.30 1.14 1.00 0.87 0.78 0.70 0.62 0.56 0.50 0.45
40% char 2.43 2.22 2.03 1.85 1.70 1.56 1.45 1.27 1.12 1.00 0.90 0.83 0.77 0.71 0.66 0.61 0.57
Examination of the data presented in Table IX shows that there is a progressive increase in the absorption ratios in the red end accompanied by a decrease in the opposite end of the spectrum. This liquor was prepared from a raw sugar which
INDUSTRIAL A N D ENGINEERING CHEMISTRY
852
had evidently been manufactured from a heavily clarified juice. T h a t is, the precipitation of impurities from the raw juice had been very complete because an excess of lime and heat had been used during the clarification, and the resulting sugar had acquired a reddish appearance. When decolorized by bone char, the coloring matter causing absorption in the blue end of the spectrum was removed, leaving the light-absorbing bodies showing greater absorption in the opposite end of the spectrum. Since the characteristics of the decomposition products of sugar are not well enough defined and understood to warrant any definite conclusions, it is unknown whether these char-resistant bodies are residual green or gray materials from the raw cane juice which were not removed by the clarification process in the raw sugar factory, or formed from sugar by the action of lime and heat.
Caramel Sirups I n the preceding studies of the decolorization of four general classes of centrifugal washed raw sugars, it was indicated t h a t bone char has a very great selectivity for the greenish bodies sometimes found in raw sugars as the result of imperfect clarification in the raw sugar factory. These materials, possibly entirely organic, are likely to be present in a semicolloidal state, and hence yield readily t o the action of bone char. Next in ease of removal are the bodies causing maximum absorption in the blue end of the spectrum, the physical equivalent of which t o the eye is a red color. Finally, as complete decolorization is approached, the cume of the absorption spectrum again tends to straighten out by a n increase in the red end and a decrease i n the blue end. ( a ) Since this phenomenon was noted even in the case of red liquors, a caramel sirup was prepared by caramelizing pure refined sugar t o the point where it showed an absorption in the extreme ends of the visible spectrum similar t o a red sugar liquor. It has previously been shown t h a t the degree of caramelization determined the trend of t h e absorption curve. This caramel was dissolved in water-white sucrose sirup and adjusted t o 59.8' Brix a t 17.5" C., and 260-cc. portions were treated with 20,30,40, and 60 per cent char for 3 hours a t 80" C., j u s t as were the raw sugar liquors. The per cent decolorization was determined by the same methods employed for the sugars, and the absorption ratios for the 20, 40, and 60 per cent bonechar treatments are tabulated in the usual manner. Char used Per cent solids Original sirup 20 30 40 60
Wave length mN 440 450 460 470 480 490 500 520 540 560 580 600 620 640 660 680 700
Table X-Caramel Sirup (a) Color log t 0.4946 0.3091 0.2443 0.1885 0.1047 A bsorotion Ratios
No char 3.55 3.14 2.75 2.43 2.14 1.90 1.70 1.43 1.19 1.00 0.85 0.75 0.65 0.56 0.50 0.43 0.36
-
20% char 3.31 2.97 2.61 2.31 2: 05 1.83 1.65 1.39 1.16 1.00 0.86 0.75 0.66 0.58 0.52 0.45 0.38
4 0 % char 3.03 2.73 2.43 2.19 1.95 1.75 1.60 1.37 1.15 1 .oo 0.86 0.77 0.68 0.61 0.54 0.48 0.42
Decolorization Per cent
...
38.0 51.0 62.2 76.1
60% char 2.77 2.53 2.29 2.08 1.80 1.70 1.55 1.32 1.13 1.00 0.87 0.78 0.70 0.63 0.57 0.52 0.49
The caramel sirup used was sufficiently high-colored t o yield a decolorized liquor from the 60 per cent char treatment with enough color t o permit readings throughout the visible spectrum. The absorption ratios steadily decline in the blue end and rise in the red end as the proportion of char is increased, resembling the absorption ratios for the reddish Cuban sugar. Since this sirup was prepared from pure sucrose in the absence of iron and the organic nonsugars which may have been present t o some extent in the raw sugar liquors, it is concluded t h a t the reddish decomposition products of the sugars contain certain bodies of unknown composition which absorb light strongly from the red end of the spectrum and which are strongly resistant t o adsorption by bone char. The products of caramelization which absorb light strongly from the blue end of the spectrum (the physical equivalent of which t o the eye is the characteristic deep red) yield most readily to adsorption by the char: It is doubtful whether any caramel of this type is ever found associated with technical sugar products unless incrustations from heater tubes, coils, etc., are formed and dissolved in the juices or sirups. The caramel products likely t o be found are
Vol. 18, S o . 8
formed by more incipient caramelization, and have a higher trend in the blue end and lower trend in the red end of the spectrum. ( b ) Another caramel sirup was prepared by overheating a quantity of sucrose sirup until some caramel had formed. The sirup so prepared was adjusted to 60O Brix at 17.5' C. and after analyzing spectrophotometrically, 260-cc. portions were treated in the usual manner with 20, 30, 40, and 60 per cent char on the solids content. Char used Per cent solids Original sirup 20 30 40 60
Table XI-Caramel Color
...
0.3449 0.1296 0.0962 0.0742 0.0437 A bsovption Ratios
mP
SOchar
440 450 460 470 480 490 500 520 540 560 580 600 620
4.94 4.30 3.65 3.10 2.67 2.34 2.01 1.57 1.22 1.00 0.83 0.70 0.59 0.50 0.42 0.36 0.30
%
Decolorization Per cent
- log t
Wave length
680 700
Sirup (b)
20% char 7.60 6.32 5.30 4.41 3.62 3.00 2.51 1.90 1.39 1.00 0.76 0.57 0.42 0.32 0.25 0.18 0.11
62.4 72.1 78.5 87.3 407" . _ char 8.18 7.11 6.17 5.20 4.46 3.70 3.05 2.05 1.43 1.00 0.75 0.56 0.41 0.31 0.23 0.16 0.10
607" char 8.74 7.75 6.70 5.69 4.80 3.87 3.20 2.10 1.45 1.00 0.72 0.53 0.40 0.29 0.21 0.14 0.09
The selective action of bone char reverses from the blue t o the red end of the spectrum in caramel solutions of this type. I t appears t h a t the degree t o which the caramelization is carried determines its resistance t o decolorization. I n one instance where the cararnelization was fairly complete, resulting in a caramel which showed less absorption in the blue end of the spectrum than in the present instance, bone char selectively removed coloring matter from the blue end, while the caramel showing the highest absorption in the blue end is selectively decolorized in the red end of its absorption spectrum,
Granulated Sirups Granulated sirups are the sirups obtained from strikes of granulated sugar massecuite after drying in the factory centrifugals. Under the usual system of boiling, the highly filtered liquors of 99.5 purity are boiled t o strikes of granulated sugar and the wash therefrom is taken back into the pans and used in boiling other strikes of granulated sugar. After a time the sirups have dropped in purity and their color has risen t o the point where further char filtration is required. Sirups of this type are relatively hard to decolorize, as their color is made up of concentrated coloring matter from that originally present in the high-grade liquors, together with some caramel formed by heat. Table XII-Granulated Sirups Granulated sirup: 60.0° Brix, 96.9 purity, pH 6.4 Char used Color Decolorization Per cent solids log t Per cent 0.0571 Original sirup 0.0263 53.9 20 0.0376 65.8 30 0.0145 74.6 40 0.0097 83.7 60 A b s o r p t i o n Ratio S Wave length Before filtration Once char-fill.ered mfi 4.53 3.90 440 4 . 0 0 3.50 450 3.58 3.15 460 3 . 1 5 2.76 470 2.70 2.40 480 2.07 2.35 490 2.00 1.83 500 1.55 1.45 520 1.19 1.23 540 1.00 1.00 560 0.82 0.80 580 0.71 0.64 600 0.62 0.54 620 0.54 0.46 640 0 .46 0 . 3 9 660 0.40 0.33 680 0 .35 0 . 2 8 700
-
...
Owing to the small amount of coloring matter present in granulated sirups, i t was not possible to make complete spectrophotometric analyses of the decolorized liquors from the 20, 40, and 60 per cent char treatments. Therefore, arrangements
August, 1926
INDUSTRIAL A S D E-VGINEERI-VG CHEMISTRY
were made t o secure samples of unfiltered and once-filtered granulated sirups from the refinery. These analyses, representing results obtained under factory practice, are shown in Table X I I . A portion of this same granulated sirup was used i n the decolorization studies described in the preceding paragraph. Bone char selectively removes the coloring matter from granulated sirups which show maximum absorption in the blue end of the spectrum. This has been proved by previous work by the laboratory of the Imperial Sugar Company. The residual color in double-filtered granulated sirups is characterized by high absorption in the red end of the spectrum; those colored bodies which excite the physical sensations of red and yellow are selectively removed by char because of the higher resistance of t h e greenish substances. Since the greenish or grayish substances present in these sirups are mainly residues from the coloring matter remaining after repeated char filtration of highpurity liquors, they are naturally more resistant t o adsorption by char than the caramel formed by heat in neutral solutions of sugar. I n the decolorization of various types of centrifugal raw sugars, i t has been shown t h a t the gray or green coloring matter derived from the cane is most easily removed by char; so the residual color of this type remaining after the many char filtrations that these high-purity liquors receive is either derived from the action of heat or may be a n extremely charresistant substance present in small quantities in the original raw sugar. Low-Purity Wash Sirups Under this heading come the affination sirup removed from the crystals of raw sugar by the affining process and the wash sirups from the various high and low remelt and soft sugar strikes. T h e lower purity wash sirups are char-filtered for use as barrel sirups, while affination sirups are usually char-filtered over two or more grades of char in order t h a t a certain amount of off-grade granulated sugar may be obtained before boiling them t o remelt. Decolorization of low-purity sirups is more difficult than in the case of high-purity washed sugar liquors. Since in refinery practice these sirups are filtered after the char has been used for filtration of higher purity liquors, they seldom come into contact with highly active fresh char. Decolorization studies on this class of sirups will not be presented in detail, but in general char will first remove coloring matter showing highest light absorption in the red end of the spectrum and cause the absorption ratios t o increase in the blue end. In the case of affination sirups, however, if the filtration is carried t o the point where additional char does not effect a marked reduction in color, spectrophotometric analysis reveals t h a t this residual color is quite sjmilar t o t h a t found after extensive filtration of granulated sirups. Barrel sirups, however, invariably show a n increase in absorption ratios at the blue end as the decolorization proceeds. Owing t o the high original color in this class of sirup, and the relatively inactive grade of char used in filtering them, decolorization never reaches the point where the trend of absorption ratios reverses.
Decolorizing Studies
Per cent decolorization on each type of liquor and sirup with 20, 30, 40, and 60 per cent char on solids content at 60' Brix was determined in the course of the experiments used in establishing the absorption ratios. While the presentation of adsorption curves is not the primary object of this paper, fairly accurate curves may be plotted from the values determined at these four points, as shown in Figure 2. These curves reveal some interesting facts. The greenish appearing Louisiana raw sugar (a) shows a steep curve up to 86 per cent decolorization by 40 per cent char, but the curve straightens out considerably between 40 and 60 per cent char. The easily rernoved organic nonsugars derived from the cane are probably exhausted near this point, and the char meets more highly resistant coloring matter. Since it is this residual coloring matter which appears in the highpurity liquors from which granulated sugar is boiled, if decolorization cannot be increased much above 94 per cent, this sugar may not be so desirable from the refiners' standpoint as might be inferred by comparison with the decolorizing curves of some of the other sugars. The color value of 0.015 attained with 60 per cent char is far from satisfactory for the manufacture of high-grade granulated sugar, and should the decolorization curve straighten out from this
853
point on, the apparently high decolorization at this point may be misleading. The same may apply to the gray-green Philippine raw sugar ( b ) . The Cuban raw sugar (c) of average trend, or possibly somewhat grayer than the average raw sugar, falls off considerably as decolorization becomes more complete. The reddish Cuban raw sugar (d) shows less decolorization a t all points than the other raw sugars, but there is no sharp decline in the curve. Had decolorization been carried to the point necessary for the production of high-grade granulated sugar, the color of this liquor might have been less than the other sugars, when larger percentages of char were used. u Good refinery practice c a l l s f o r nearlv 100 pounds of char per 100 pounds of sugar melted, 90 so had the decolorizat i o n c u r v e f o r this sugar been extended to SO this point it might perhaps have crossed some of those for other sugars 70 which showed higher i n i t i a l decolorization with smaller percent60 ages of char. All of this merely emphasizes the complexity of the $ 50 mechanics and r e a c - *U tions of decolorization, B and illustrates how far 40 from correct empirical GI d e c o l o r i z a t i o n tests may be if the condi30 tions under which they are made vary from the industrial c o n d i t i o n s 20 under which the carbon will be used. 10 The caramel-sucrose solution ( e ) has a decolorizing curve very similar to that of the I I r e d d i s h C u b a n raw Figure 2-Decolorizing Curves sugar (d) in that there a ) Green Louisiana raw sugar liquor is ';lo sudden break in ((b) Gray-green Philippine raw sugar liquor per cent decolorization ~ ~ ~ ~ ~ ~ ~ ~ , u " , ~ ~ ~ a s as the amount of char ( c , n Caramel sirups ( 8 ) Granulated sirup is increased. There is similarity between the curves for the caramelsucrose solution (f) and the granulated sirup (g). No doubt the red coloring matter present in the granulated sirup is caramel having a similar curve of absorption ratios, since any caramelization in such a sirup must be of very incipient nature. However, on the other hand, the fact that the total color present in the caramel sirup is nearly seven times as great as that present in the granulated sirup renders it difficult to explain why the curve for the granulated sirup is lower a t all points. This may mean that coloring matter in the granulated sirup is made up of the residual green or gray matter left after extensive char filtration plus a small quantity of caramel having a very high light absorption in the blue end of the spectrum. The mixture of these opposite types of coloring matter, when read at the different points in the visible spectrum, gives a curve of absorption ratios similar to that which may be plotted from the values determined for the granulated sirup.
@ I.
\;I
, , a 4 : ~ ~
INDliXTRIAL A N D ENGINEERING CHEMISTRY
854
Conclusion
Spectrophotometric analysis of sugar products reveals certain facts regarding decolorization by char which ordinary colorimetric methods have never explained. The method of Peters and Phelps is based on rational principles, and allows colorimetric comparisons between different types of sugar products having different optical centers of gravity. This is especially advantageous when comparing original with decolorized sugar products, as it is possible to follow the selective properties of the char a t the same time. It cannot be stated definitely that bone char always has more difficulty in removing what appears to the eye as the red coloring matter, or that the gray or green matter is always selectively
Vol. 18, Xo. 8
removed. The selectivity may be in either the blue or red end of the product’s absorption spectrum, depending upon the nature of the coloring matter present and the relative proportions of the different general types of coloring matter present. I n refinery practice intelligent use of spectrophotometric color determinations is a n invaluable aid to the technologist in his efforts to locate and eliminate the imperfectly understood and empirical factors in refinery operation. As he proceeds further in his investigations and approaches the ultimate solution of the majority of his problems, he finds that the chief cause of operating difficulties is unsatisfactory raw sugars.
Action of Sodium and Magnesium Sulfates on Portland Cement’’z By G. R. Shelton UNIVERSITY OF SASKATCHEWAN, SASKATOON, CANADA
HE analysis of the coml i m e w e r e present. These After having determined the action of sulfate solumercial cement is given results are in agreement with tions on the separate compounds found in Portland in the first paper of the work done at the Geocement clinker and also on calcium aluminates,* exphysical Laboratory6 and a t this ~ e r i e s . ~The white Portperiments were made using the same sulfate solutions t h e B u r e a u of Standards,6 land cement was made in this with a commercial and a white Portland cement. which is being questioned a t l a b o r a t o r y from alumina, The object of the present investigation was to deterpresent in studies made by white marble, and flint, mixed mine the difference in sulfate action on Portland ceDyckerhoff and Nacken.’ so that the resulting clinker ment clinker and on its compounds taken separately. The tests with solutions of would have the same percentsodium and magnesium sulage of CaO, A1203, and Si02 as the mean percentages of these oxides in analyses of a number of fates were made in small stoppered tubes, as described in commercial cements. Three heat treatments with intermedi- similar tests on the constituents of Portland cement and ate grinding and sieving were necessary to give a homogeneous also on calcium aluminate.3 The sulfate solutions were in the following molar concentraproduct. To prevent contamination of the mixture it was molded in the form of a hollow cylinder 15 em. high and 12 cm. tions: 0.05, 0.1, 0.2, 0.4, 0.8. The mixtures contained 0.08 in diameter, which was placed on a magnesite disk in the fur- gram of clinker and 5 cc. of the sulfate solution. Before presenting the data obtained in the present investiganace, the bottom of the cylinder being chipped off after each firing. The temperature of the furnace was read by means of tion, a brief summary will be given of the results obtained a Thwing optical pyrometer sighted on the bottom of an alun- with mixtures of sulfate solutions and each of the respective dum tube which projected into the furnace for about 5 em. pure constituents. and almost touched the cylinder. The maximum temperaCrystalline Cements and Sodium Sulfate ture attained was 1500’ C. No gypsum was added.
T
Analysis of Clinker
Loss on ignition Silica (SiOz) Alumina (A120a) Ferric oxide (FezOa) Lime (CaO) Magnesia (MgO)
Per cent 0.30 24.01 9.05 0.29 66.14 0.36
Microscopic examination showed irregular-shaped grains, which between crossed nicols revealed the presence of bright crystalline fragments, surrounded and held together by an isotropic substance, The largest grains gave a positive interference figure, and had refractive indices of 1.735 and 1.715, proving them to be p-dicalcium silicate. Other grains, showing a gray interference color, negative optical figure with refractive index 1.715, were tricalcium silicate. The isotropic substance had a refractive index of 1.710 and was tricalcium aluminate. KO 5:3 calcium aluminate or free Received February 23, 1926. This work was done under the auspices of a research committee of the Engineering Institute of Canada with the financial support of the Research Council of Canada, the Canada Cement Co., the Canadian Pacific Railway, and the three Prairie Provinces of Canada. 8 THISJOURNAL, 17, 589, 1267 (1925). 4 I b i d . , 17, 467 (1925). I
2
SUMMARY OF PREVIOUS RESULTS WITH PURECONSTITCENTS Pure constituents Reaction products 3 CaO Ah03 Gel, sulfoaluminate crystals, and in 0.035 M solution, hydrated 3CaO.Alz03 crystals 3 CaO.Si0a Gypsum and gel surrounding original grains, which remained unchanged in the 0.035 and 0.14 M solutions for about 2 months 8-2 CaO.SiOz Gypsum and original crystalline grains covered with gel in all the solutions; no change after 2 months
WHITEPORTLAND CEMENT-The results were very similar to those obtained by the action of these solutions of the pure crystalline tricalcium aluminate, the only crystalline products being the needles of tricalcium sulfoaluminate. No hydrated tricalcium aluminate crystals were noted in the 0.5 -Wsolution, nor was gypsum found in any of the mixtures. Original crystalline silicate grains were covered with layers of gel, but the centers could be detected between crossed nicols. These centers disappeared after 5 weeks. COMMERCIAL PORTLAKD CEMEN?LCIYSta1S Of SUlfOalUminate were found in all the mixtures, and gypsum in all except the 0.05 and 0.1 M solutions. The crystalline centers, con6
6
7
Shepherd and Rankin, THISJOURNAL, 3, 211 (1911). Concrete-Cement i l g e , 2, 3 (1913). Zenzent, 14, 174, 419 (1925).
