32
INDUSTRIAL A X D EAVGINEERISG CHELIIISTRY
1-01. 18, S o . 1
Decolorizing Carbons' By A. A. Blowski & J. H. Bon CALIFORNIA A N D HAWAIIAN SUGARREFININGCORP.,CROCKBTT, CALIF.
N RECEKT years we have witnessed a rapidly develop- as a standard carbon, and used in all tests described in this ing interest in the subject of activated carbons, par- section. It was assumed that the other carbons examined ticularly with regard to their application as decolorants in the course of the investigation would exhibit the same genin the sugar industry. During this period a vast number era1 properties as the standard carbon. of articles on the subject have been published. Many of Eflect of Time of Contact of Liquor and Carbon these articles, originating with the manufacturers of some PLANOF TESTS-one hundred cubic centimeters of 47.5' particular carbon, assume an attitude of unwarranted optimism with regard to the results which this carbon will ac- Brix crystallizer remelt sugar liauor, color 520' Stammer per 100' Brix, were mixed complish; others are based in an Erlenmeyer flask with upon insufficient data, mak4 per cent of carbon on ing it exceedingly difficult Of a n u m b e r of well-known decolorizing carbons solids, and heated in a water to form an opinion of the examined, all showed fair o r h i g h decolorizing power bath a t 80' C. Several real merit of decolorizing a n d a s h adsorptive properties in some degree. Howsimilar samples were placed carbons, and their benefits ever, all b u t two of t h e s e carbons were poor filtering in the bath a t the start of and disadvantages as comm e d i u m s , m a k i n g t h e m unsatisfactory for practical the test, being withdrawn pared with bone char. use. singly a t the termination of I n view of the stress that Laboratory-scale tests indicate t h a t w i t h t h e dedifferent periods of time. has been laid upon the value colorizing carbon process it would be possible t o proT h e l i q u o r was filtered of decolorizing carbons, and duce a g r a n u l a t e d s u g a r which compares favorably rapidly through paper and t h e very limited real inw i t h t h e s u g a r produced w i t h t h e bone-char process. Filter-Cel, the color removal formation available on the However, a s t h e n e t cost of t h e two processes would be from the resulting filtrate subject, an i n v e s t i g a t i o n a b o u t equal, a n d difficult practical problems would being determined with the w a s c a r r i e d out in this require solution before decolorizing carbons could aid of a Stammer colorimlaboratory with the pricompletely t a k e t h e place of bone c h a r , a refiner would eter. mary object of determining have n o t h i n g t o gain a n d possibly a g r e a t deal t o lose RESULTS-AS would be whethpr decolorizing carby s u b s t i t u t i n g t h e carbon process for t h e bone-char expected from the observabons offer any practical process. A combined bone-char a n d decolorizing c a r tions of many investigators, advantage over bone char bon process is also f o u n d t o be a n undesirable s u b s t i the adsorption of color was for the refining of sugar. t u t e for t h e simple bone-char process. found to be extremely rapid. The data were assembled The results (Plate I) show with a threefold purpose: that approximate equilib1-To obtain an understanding with regard to the mechanics rium is attained after 15 minutes' contact between carbon and of the action of decolorizing carbons on sugar liquors-i. e., the liquor, and after 1 hour no further color adsorption is observed. effect of such variable factors as time, temperature, concenIt is evident that even with the brief period of contact tration, reaction, quality of test liquor, and amount of carbon between carbon and liquors which would be the rule if a used. 2-To compare a number of the standard decolorizing carbons refinery were using the carbon process, approximate color with each other and with bone char, on the basis of decolorizing adsorption equilibrium would be reached.
I
power, ash-adsorptive properties, and filtration efficiency. 3-To form an idea of the advantages which might be anticipated from the employment of decolorizing carbon as a substitute for, or as an auxiliary to the bone-char process in the refining of sugar.
As the investigation progressed, its scope broadened considerably. There follows a brief outline of the points which it has attempted to cover in this paper: I-Factors influencing the action of decolorizing carbons on a sugar liquor 11-Development of an efficiency test for evaluating carbons 111-Comparison of the properties of representative carbons and bone char. IV-Desirability of the use of carbons in the refining of sugar.
I-Factors
Influencing Action of Decolorizing Carbon on a Sugar Liquor
The following experiments were carried out for the purpose of obtaining a general insight into the mechanics involved in the decolorization of sugar liquors by activated carbon. A commercial carbon of American manufacture was chosen 1 Presented before the Division of Sugar Chemistry at the 70th Meeting of the American Chemical Society, Los Angel-, Calif., August 3 to 8, 1925.
Effect of T e m p e r a t u r e of T e s t Liquor
PLANOF TESTS-one hundred cubic centimeter portions of 47.5' Brix crystallizer remelt sugar liquor, color 530" Stammer per 100" Brix, were mixed in Erlenmeyer flasks with 4 per cent of carbon on solids, individual tests being held a t temperatures ranging from room temperature to 100' C. (The 100' C. digestion was made under a reflux condenser.) Three series of tests were made, the times of contact being 15 minutes, 30 minutes, and 1 hour, respectively. The liquors were filtered rapidly through paper and Filter-Cel, and the color removal from the resulting filtrates was determined with the aid of a Stammer colorimeter. RESULTS-Plate I1 shows that for temperatures between 40' and 100" C. the color removal is apparently proportional to the temperature; below 40" C., however, the color removal deviates somewhat from the linear function, falling off as the temperature decreases. When applying carbons to sugar liquors, it is evident that in order to obtain the maximum decolorizing effect the temperature of the liquor should be maintained as high as is possible without causing excessive losses through decomposition of sugar by heat.
January, 1926
I.VD USTRIAL AND ENGINEERI-VG CHEMISTRY
Effect of Concentration of Test Liquor ( " Brix)
PLAYOF TESTS-TWOseries of tests were run, one with 2 per cent of carbon on dry substance, and the other with 4 per cent of carbon on dry substance. The density of the test liquor, crystallizer remelt sugar liquor, was varied from 10" to 60" Brix. One hundred cubic centimeters of test liquor mixed with the weighed amount of carbon (2 or 4 per cent) were heated for 1 hour at 80" C., and filtered and tested for color as before. REsULTs-Results of these tests are shown graphically on Plate 111. The curves make it evident that a higher degree of decolorization is obtained in dilute solution than in concentrated solution, the per cent of carbon on dry substance in test liquor being maintained constant. The rate of decrease in color removal becomes more pronounced above 35" Brix. This decrease in color removal may be the result of the increased viscosity of the high-density liquors.
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amount o' f carbon to use to effect the desired degree of decolorization. Effect of Reaction (pH) of Liquor
PWNOF TEsTs-Three portions of 98.8" purity washed raw sugar liquor were adjusted with dilute acetic acid and ammonia to pH 5.0, 7.0, and 9.0, respectively. One hundred cubic centimeter portions of each were treated with 1 per cent carbon on dry substance. To aid in maintaining a constant reaction, portions of carbon were previously adjusted to the same pH values as the test liquors. The liquor-carbon mixtures were digested for 1 hour a t 80" C., then filtered through paper and Filter-Cel. Portions of washed raw
Effect of Variation in A m o u n t of Carbon
P L . ~ NOF TESTS-seven 1oo-cc. portions of 47.5" Brix standard test liquor (and a blank) were treated with carbon in the same manner as in the previous tests, except that the percentage of carbon used was varied from 0.5 per cent to 10 per cent on dry substance. REsuLTs-From the data represented graphically on Plate I V it will be observed that the adsorption of color from solution by activated carbons is not a linear function of the amount of carbon used. Rather, it appears in general to follow the Freundlich adsorption equation: X / M = KC'/"
which states that the adsorption of color per unit weight of adsorbing agent is proportional to a definite power of the coloring matter in solution a t equilibrium. I n this equation X represents the color adsorbed from solution by the adsorbing agent, -If the weight of adsorbing agent, and C the color remaining in solution when equilibrium between carbon and liquor is attained. K and n are constants, characteristic of the system to which the equation is being applied, n never being less than unity.
I ?a
30
40
Or@no/ Co/w 5ZO*2ammer M 60 Pmpn-dum &@PS
-
z
80
n
roD
Centgnwb
sugar liquor a t the same hydrogen-ion concentrations, but without carbon, were run in parallel with the above tests. Color and p H determinations were made on the filtrates. The color removal for each pH was calculated, and the results mere used for the preparation of the curve in Plate V. RESULTS-It is a generally accepted fact that increasing the acidity of a sugar liquor results in a higher degree of decolorization by carbon, and it is often assumed that a highly acid melt liquor is a prerequisite for satisfactory decolorization. Tanner2 states that the increased decoloriaation in acid liquors is due to one or more of these factors: 1-A portion of the coloring matter acts as a n indicator, becoming lighter as the acidity increases. 2-The solubility of color-forming bodies is lowered in acid solutions, making it easier for the carbon to adsorb them. 3-The increased acidity furnishes more H + ions for the carbon t o adsorb, causing it to become positively charged, and giving it more power to adsorb the negatively charged color radical of polyphenol coloring bodies.
The curve of Plate IV is termed an "adsorption isotherm." From a comparison of such decolorizing isotherms an estimate of the relative decolorizing efficiency of a series of carbons may be obtained. I n a control of large-scale operations the decolorizing isotherm for the particular carbon and liquor being treated would be very useful in estimating the proper
.
In this series of tests the "indicator effect" was very striking. A change in acidity from pH 5.0 to pH 9.0 caused a n increase in color from 11.4" to 26.3" Stammer per 100" Brix. This effect was eliminated, however, in figuring the percentage of color removed by calculating this on the colors of the original and carbon-treated liquors when both were a t the same acidity. The curve on Plate V shows that this activated carbon is undoubtedly a more effective decolorizing agent in acid solution, but the difference is not sufficient to be of great importance. Satisfactory decolorization can be obtained in neutral or even slightly alkaline solutions, within the accepted safe alkalinity limits of refinery practice (pH 6.5 to pH 7.5). Further work, as indicated later, shows that in general this is true of all the carbons examined. Effect of "Quality of Color" in Liquor
On Plate VI are plotted decolorizing isotherms obtained with four test liquors, each containing a different type of coloring matter: 2
THISJOURNAL, 14, 441 (1922).
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
34
( a ) Washed raw sugar liquor, of course, contains the*coloring matter of the cane, much of which is of very complex structure, probably colloidal, and hence is very readily adsorbed by the carbon. The decolorizing isotherm for this liquor shows a very ready decolorization, with a sharp break a t approximately 2 per cent carbon and 90 per cent color removal, manifesting practical exhaustion of the coloring matter. The remaining color is much more difficult t o remove, as shown by the small increase in decolorization caused by the use of successively larger amounts of carbon (above 2 per cent).
Vol. 18, No. 1
N o t c T h e standard sugar, prepared by drying crystallizer remelt sugar, is of the following composition: Per cent Per cent Sucrose (Clerget) 83.17 Direct polarization 82.80 Moisture 1.16 Apparent purity 83.77 Ash 3.96 True Clerget purity 84.15 Invert sugar 5.59 Color, 520' Stammer per 100" Brix Organic nonsugar 6.12 at 47.5' Brix. Total 100.00
The mixture is then cooled rapidly and the liquor is decanted into paper filters and allowed t o filter overnight. A blank and a standard sample of bone char, arbitrarily rated at 100 per cent efficiency, are run in parallel with t h e bone chars being tested. The color removed from each filtered solution is determined, and efficiencies are calculated on the basis of 100 per cent for the standard bone char. The residues of the filtrates are used for ash removal tests, sulfated ash being determined. The ash removal efficiency is calculated on the basis of 100 per cent for the standard bone char.
This char efficiency test is admittedly empirical, and does not duplicate conditions as they exist in the refinery. However, it is believed that the test reveals variations in the efficiency of the bone char occurring from month to month. The test is on a volumetric basis, since bone char is employed on this basis. I U
I 20
Cwce&wtk
I
a
I 40
I
so
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60
Efficiency Test f o r Decolorizing Carbons
M 7 2Lquor / v r r e s Brix).
(b) No. 3 granulated sirup is a light-colored sirup, part of -the color of which is due t o the residuum from a highly charfiltered liquor, and the remainder of which is color developed in boiling. Decolorization of this liquor is considerably more difficult than decolorization of washed raw sugar liquor, owing t o the different character of t h e coloring matter. (c) Crystallizer remelt sugar liquor is a very highly colored product, the major part of its color being developed as a result of heating. The crystallizer remelt isotherm is of an entirely different nature from any of t h e others considered, as it shows no sudden break. Because of the large amount of coloring matter in this liquor, there is no exhaustion of color as with the light liquors considered. ( d ) With No. 555 liquor, a very highly char-filtered liquor with a color approximating t h a t of washed raw sugar liquor, a curve exhibiting a sharp break is obtained, this break, however, occurring between 50 and 60 per cent decolorization, instead of at 90 per cent decolorization, as with washed raw sugar liquor. This is an indication t h a t this liquor contains two types of coloring matter in approximately equal quantities, one of which is comparatively readily removed by carbon, and the other of which is removed with difficulty.
A consideration of these curves warrants the following conclusions : 1-The major part of the coloring matter of washed raw sugar liquor, probably t h a t part bordering on the colloidal state, is very readily removable by a small percentage of decolorizing carbon. The removal of the residual color is a much more difficult problem, requiring increased amounts of carbon. 2-The color of a highly char-filtered liquor is removed with great difficulty by decolorizing carbon. I n a liquor of this nature the char has presumably adsorbed most of the readily removable color constituents, leaving those less readily removable t o be adsorbed by the carbon.
11-Development of an Efficiency Test for Evaluating Carbons Bone-Char Efficiency Test
At this refinery the efficiencies of the different grades of bone char in process are determined periodically by means of the arbitrary test outlined below: Exactly 170 cc. of properly sampled bone char t o be tested are introduced into a 500-cc. Erlenmeyer flask containing 10 cc. of dry Filter-Cel used for obtaining a clear filtrate. Two hundred cubic centimeters of a 47.5' Brix standard crystallizer remelt sugar solution are added t o the bone char, the mixture shaken for 30 seconds, and then digested a t 80' C. in the water bath for 3 hours, shaking for 30 seconds every half hour.
From a consideration of the data presented in Part I of this paper, it is possible to devise a very satisfactory test for rating carbons with regard to their decolorizing powers, analogous to the bone-char efficiency test. The important features of such a test are outlined below: Method of Measuring Carbon. In contrast t o the bone-char efficiency test, which is on a volumetric basis, a test for t h e evaluation of a decolorizing carbon should be on a gravimetric basis, since i t is on this basis t h a t carbon is employed. The gravimetric basis has therefore been adopted, the amount of carbon used being expressed as percentage by weight on dry substance in liquor. Percentage of Carbon Used in Test. We have noted that a single test does not-yield sufficient information on which to base a n estimate of the decolorizing power of a carbon. A series of tests, with the percentage of carbon ranging from 0.5 t o 10 per cent must be made, the per cent decolorization determined in each case and plotted in the form of a curve (per cent decolorization against per cent carbon) which is known as a decolorizing isotherm. From a comparison of decolorizing isotherms for a number of carbons, obtained under identical conditions, an idea of the relative efficiencies of these carbons may be obtained. I n obtaining the relative decolorizing power of all carbons investigated in subsequent tests, decolorizing isotherms were emplGyed. T i m e of Contact. Equilibrium between carbon and liquor is Dracticallv effected a t the end of 15 minutes. However, i n order t o -insure equilibrium, 1 hour has been adopted as t h e standard time of contact for these tests. Temperature. A temperature of 80' C. was chosen as standard for the efficiency test. This is the standard temperature for t h e C. & H. bone-char efficiency test, and incidentally is the highest temperature a t which it is considered safe t o carry refinery liquors without excessive decomposition. Density of Test Liquor. Inasmuch as 47.5" Brix is the specified density for test liquor in the bone-char efficiency test, this density was used in carbon efficiency tests. Test Liquor. In comparing the decolorizing powers of the carbons, two sets of isotherms were prepared, one with washed raw sugar liquor, and the second with standard crystallizer remelt sugar liquor. The two sets of isotherms were found t o range the carbons in a slightly different order of decolorizing power. However, as carbon would probably be employed on the lightcolored washed raw sugar liquor, more importance should be placed in the results obtained with this liquor. The volume of test liquor used in individual tests was fixed a t 100 cc. Method of Calculating Eficiency. A number of methods for calculating the relative decolorizing efficiencies of carbons have been proposed by different investigators, the two most commonly used being: ( a ) efficiency calculation based on the relative amounts of carbon necessary t o remove a given percentage of the total color of a liquor, and (b) efficiency calculation based
January, 1926
INDUSTRIAL AND ENGINEERING CHEMISTRY
on the relative amounts of color removed by a given percentage of carbon. The first of these methods seems t h e most logical and most desirable, since in comparing carbons we are primarily interested in the relative amounts of different carbons required t o effect a given decolorization. This is, therefore, the method employed in determining decolorizing efficiencies.
The efficiency test which was used in comparing the color adsorptive powers of the carbons considered in this investigation may be summarized as follows : One hundred cubic centimeter portions of 47.5” Brix test liquor (washed raw sugar liquor or standard crystallizer remelt sugar liquor) are heated for 1 hour at 80’ C. with amounts of carbon ranging from 0.5 t o 10 per cent by weight on dry substance in liquor. The flasks containing carbon and liquor are shaken for 30 seconds a t 15-minute intervals during the test t o keep the carbon in suspension. At the conclusion of the digestion, the flasks are cooled rapidly and the contents are filtered through paper and Filter-Cel, the color of filtrate being determined with a Stammer colorimeter or by comparison with standards when too light t o be read on the colorimeter. Per cent decolorization is plotted against per cent carbon, t o obtain the decolorizing isotherm for the carbon under investigation. I
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tion. Second in importance to the decolorizing properties of the carbon are its filtering qualities. The separation of carbon from decolorized liquor is effected in some type of filter press. I n order to permit of handling the treated liquors with a reasonable filter press installation, an ideal carbon should be highly efficient as a filter aid. The filtration of carbon-liquor mixtures can, of course, be improved by addition of kieselguhr or other filter aid, but this is not a desirable’expedient, as the addition of foreign matter complicates the regeneration of the carbon. The ideal carbon should have a high capacity for adsorbing nonsugars. Each pound of ash eliminated from sugar liquors means an increase of approximately 2.5 pounds of sugar recovered through crystallization. The ideal carbon should be low in first cost, and should be economical to regenerate. In order to make it possible to draw comparisons of their relative value from the above standpoints, the carbons listed below were examined from all angles that might have a bearing on their value. (Because of the critical comparison made in this paper, the names of the carbons are withheld, each carbon being designated by a letter.) Carbon “ A ,” a widely advertised commercial carbon of European manufacture. Carbons “B,” “C,” and “D,”well-known commercial carbons manufactured,fn the United States. Carbon “ E , a carbon developed in the Hawaiian Islands, and not yet manufactured on a commercial scale. New bone char, 8/24 mesh, of the quality ordinarily used in this refinery, was used for comparison with the above carbons.
The following modifications of new bone char were also prepared and tested with the carbons: ( a ) Powdered new bone char. (b) Char carbon, the residue after repeated extractions of bone char with concentrated hydrochloric acid.
Prior to testing, all the carbons and the bone char were very thoroughly washed first with pure hot tap water and finally with hot distilled water, then dried a t 110’ C. Those carbons which still showed an acid reaction after washing were treated with dilute ammonia until approximately neutral, rewashed, and redried. It was iater found necessary, in order to obtain satisfactory ash removal tests, to digest samples of carbons “A,” “C,” “D,” and “E” with 1 per cent hydrochloric acid in order to remove mineral matter soluble in the slightly acid crystallizer remelt sugar liquor. After digestion, these carbons were thoroughly washed, neutralized, and dried. These carbons were examined as shown in the next section. z
c
6
6
P e e d Corbon on Dry 5u&stonce.
Efficiencies are calculated from the relative amounts of carbon necessary t o effect a n equal decolorization (80 per cent on raw liquor and 50 per cent on crystallizer remelt sugar liquor). These percentages were arbitrarily selected as being high and reasonable decolorizations, attainable in practice, yet low enough o n the curves to allow proper comparison.
111-Comparison of Properties of Representative Carbons and Bone Char Let us first consider briefly the properties which should be possessed by a carbon suitable for use in the refining of sugar. Of primary importance, of course, is the decolorizing power of the carbon. The greater its capacity for adsorbing coior, the smaller the amount of carbon which must be used for the decolorization of a given quantity of sugar liquor. The decolorizing efficiency should be high in neutral or alkaline liquors, in order to avoid inversion losses that would occur i f it were necessary to maintain the liquors in an acid condi-
Chemical and Physical Properties
CHEMICAL ANALYSIS-The are given in Table I.
analyses of the carbons tested
Table I-Analyses
Char carbon Carbon “D” Carbon “A” Carbon “E” Carbon ‘“2” Carbon “B” New char
Carbon Per cent 98.69 98.55 97.09 96.34 93.60 69.32 9.43
of Carbons Insoluble ash Per cent 1.31 0.78 1.81 0.77 6.00 30.31 0.04
“21-soluble ash Per cent Trace 0.67 1.10 2.89 0.40 0.37 90.53
It will be noted that all the carbons, with one exception, are very rich in carbon and low in ash content. Bone char, as we know, has a very low carbon content and contains q large percentage of acid-soluble ash, mainly calcium phosphate. REACTIONOF CARBONS-The pH of each carbon, after washing, was determined by boiling 20 cc. of carbon with
INDUSTRIAL AND ENGINEHUNG CHEMISTRY
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40
CC. of distilled water for 1 minute, filtering, and testing the filtrate. The pH values so determined are given in Table 11. Table 11-Reaction Carbon “A” New char Carbon “C” Carbon “D” Char carbon Carbon “ E ’ Carbon “B”
of Washed Carbon PH 8.25 8.05 6.75 6.25 ’ 6.25 5.50 4.50
,
It was found impossible to neutralize the acid reaction of the last five carbons by washing alone. a weak alkaline digestion, followed by a thorough washing, being necessary. The low pH of carbon “B” is presumably residual acidity from treatment with an acid solvent after carbonizing. Carbon “E” owes its acidity to the presence of traces of phosphoric acid used in its manufacture. New bone char is always alkaline, owing to the high calcium carbonate content and to the presence of traces of calcium oxide produced in the kilning process. Carbon “A” is stated by its manufacturers to contain a small percentage of slightly soluble ash, which imparts an alkaline reaction to the carbon and is best removed by digestion with 1 per cent hydrochloric acid prior to use. When using carbon on a large scale, in order to prevent serious inversion losses and a t the same time obtain a high decolorizing effect, the carbon, as well as the liquor, should have a pH of from 6.5 to 7.5. An acid carbon, like “B,” or an alkaline carbon, like “A,” would require neutralization prior to use. These preliminary treatments would involve considerable extra handling and expense. WEIGHTPER CUBICFoe-Table I11 is a tabulation of the weight per cubic foot of the carbons, loose pack and solid pack. Table 111-Weight Carbon ‘OD” Carbon “A” Carbon “E’ Carbon “C” Carbon “B” Powdered bone char
-
per Cubic Foot of Carbons Loose pack Solid pack Lbs./cu. ft. Lbs./cu. ft. 10.5 13.5 14.5 18.4 14.4 26.9 16.0 19.2 17.9 22.5 38.3
...
The carbons with the highest ash content-i. e., powdered bone char, r‘B,rland “C”-have the highest unit %.eight, and, as will be observed later, the lowest efficiency as filter aids. SCREEN ANALYSES-sCreen analyses of the carbons tested are tabulated in Table IV (50-gram samples screened for 10 minutes in a Tyler Ro-Tap machine): Table IV-Screen Screen “E” mesh 0.8 On 50 On 70 3.8 5.3 On 100 11.2 On 150 13.7 On 200 6.5 On 250 6.5 On 300 10.3 On 350 41.9 Through 350
Analyses of Carbons, Per c e n t
“A”
“B”
“D”
0.2 7.2 11.1 14.5 12.7 4.8 8.2 10.2 31.1
1.6 7.9 13.2 16.5 20.3 3.7 6.6 6.6 23.6
7.1 20.5 11.7 13.8 14.2 5.4 8.0
5.5 13.8
Powdered ”C” bone char 0.4 0.0 1.3 0.1 8.4 1.4 20.5 10.0 38.9 24.3 12.5 9.2 7.9 22.3 2.1 11.6 8.0 21.1
The wide variation in the percentage of fines contained
in the different carbons should be noted. MICROSCOPIC EXAMINATION-When viewed under the microscope, Carbon “A” is seen to consist of innumerable needle-like carbonized vegetable fibers. Carbon “B” and powdered bone char have a somewhat granular structure, while “C,” “D,” and “E” are very flocculent powders. Filtration Efficiency
A consideration of prime importance in forming an estimate of the desirability of any carbon is its efficiency as a filter
Vol. 18, No. 1
medium. The use of a decolorizing carbon on a large scale in the sugar house would be quite out of the question if the carbon-treated liquors could not be handled with a reasonable filter press installation. As mentioned earlier in this section, the addition of kieselguhr or other filter aid to carbon-treated liquors is an undesirable expedient for improving filtration, as it would complicate the regeneration of the carbon. In order to rate the carbons under examination with regard to their efficiency as filter aids, they are compared with standard Filter-Cel by means of the Elliott filtration test for raw sugars, the Filter-Cel being arbitrarily rated as 100 per cent efficient. Two sets of filtration tests were run. In the first, the filter aid and liquor were allowed 5 minutes’ time of contact in the cold (this being the standard method of conducting the test), and in the second, the filter aid and liquor were heated just to boiling, then cooled to room temperature, in order to allow the adsorptive properties of the carbons to assert themselves. Table V gives the results of these filtration tests. Table V-Filtration Efficiencies of Decolorizing Carbons (Compared with standard Filter-Cel as standard. 2% decolorizing carbon on solids) Carbon and liquor Carbon and liquor mixed in cold mired heated to boiling, ’then cooled 5 minutes’ contact FILTSR MGDIUM Per cent Per cent 100.0 Standard Filter-Cel 150.0 Carbon “A“ 59.7 127.5 Carbon “D” 33.0 82.2 Carbon “C” 30.0 58.8 36.0 Carbon “E” 15.4 62.5 11.6 Carbon “B” Powdered bone char 9.2 34.8
The results of the first set of tests, in which the time of contact of liquor and carbon was limited to 5 minutes in the cold, may be assumed to indicate the relative value of the carbons as filter aids due to their actual physical structure. It will be noted that under these conditions Carbon “A” is approximately 60 per cent as efficient a filter medium as the standard Filter-Cel while the other carbons are relatively much lower in filtration efficiency. Structurally, therefore, none of the carbon examined compares at all favorably with Filter-Cel as a filter aid. Date Z
P
P 4%
i3
Rrn
1,
‘\
/ifhence of Reactioo o f Te5t LJOUOTM Deco/orzot/on b y Car& Test L i ~ u o rWa5hed Raw -Suer L/quor Pur,t y 98d 9 B r i x 4Z5 Co/or /54xammer
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IAYDL7STRISLA S D E-VGINEERISG CHE.IIISTRI;
January, 1926
factory filtration rates without prefiltration through or mixture with some filter aid. The results of these tests are striking evidence of the poor filtering qualities of the average carbon and indicate the need for development along these lines. Decolorizing Efficiency
On the basis of the decolorizing test developed in Part 11, two sets of decolorizing isotherms were prepared for each carbon under consideration. In one set of curves the test liquor was wished raw sugar liquor of 98.8” purity, and 15” to 20” Stammer per 100” Brix, and in the other the test liquor was crystallizer remelt sugar liquor of 88.5” purity, and 520” Stammer per 100’ Brix. WASHED RAWSUGAR LIQUORISOTHERhfR, PLATES VI11 AND IX-It will be noted that all the washed raw sugar liquor isotherms exhibit the characteristic form discussed in Section 11. The relatively low decolorizing power of granular bone char, due to its limited adsorptive surface, is very striking. Powdered bone char is much higher in decolorizing efficiency, and the carbon extracted from bone char by acid digestion is still better. All these substances, however, are decidedly inferior to the carbons tested. CRYSTALLIZER REMELTSUGAR LIQUOR IBOTHERMS-PlateS X and X I show a series of decolorizing isotherms obtained with crystallizer remelt sugar liquor (standard sugar) as a test liquor. CALCULATION OF DECOLORIZING EmIcImcY-The efficiency figures in Table VI were calculated from the foregoing decolorizing isotherms. The figures in ( a ) were calculated on the basis of the relative weights of carbon necessary to remove 80 per cent of the color from washed raw sugar liquor, 47.5” Brix. The figures in ( b ) were calculated on the basis of the relative weights of carbon required to remove 50 per cent of the color from crystallizer remelt sugar liquor, 47.5” Brix. Table VI-Decolorizing
Efficiency in Terms of Bone-Char Efficiency ( b ) Based on crystallizer raw sugar liquor remelt sugar liquor 86.4 33.7 54 3 14.4 43.5 15.9 34 4 14.6 32.8 16.9 19.3 6.9 12 4 4.2 1.0 1 .o
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There seems to be a great lack of agreement concerning the comparative ash-removal powers of decolorizing carbons and char. These tests, however, clearly indicate that all of the carbons examined exhibit ash-removal powers in some degree. Weight for weight, Carbons “,4,”“B,” and “C” are inferior to bone char, whereas “D” and “E” have decidedly higher ash-removal powers than bone char. This is a surprising result, since the statement is generally made that decolorizing carbons do not compare with char in regard to their ash-removal powers. One possible explanation for
( a ) Based on washed
Carbon “E” Carbon “D,’,’ Carbon “B Carbon “C” Carbon “A” Char carbon Powdered char Granular char
The efficiency figures for these carbons cover a wide range of values. A comparison of the two sets of figures indicates that as the character and intensity of the coloring matter in the test liquor is varied the relative order of decolorizing power of the carbons changes. This is due to differences in the selective adsorptive properties of the carbons. As carbons would presumably be used on the high-purity washed raw sugar liquor, more significance should be attached to the efficiency figures calculated from the washed raw sugar liquor isotherms. Ash Adsorption
Sulfated-ash determinations on the filtrates from the crystallizer remelt sugar liquor decolorizing tests were made to determine the ash adsorption by the various carbons under consideration. Table VI1 contains results of these tests. Table VII-Ash Adsorption Carbon ondry , GRAMS ASH REMOVED BY^--substance Powdered Unground “A” Char .CB” Per cent “D” char “E” char carbon “C” 2 0.0012 0.0030 0.0013 0.0012 0.0010 0.0009 0.0005 0.0007 4 0.0046 0.0033 0.0042 0.0033 0.0019 0,0009 6 0.0064 0.0051 0.0048 0.0036 0.0027 0.0015 o.OOi4 8 0.0089 0.0070 0.0066 0.0041 0.0034 0.0026 O.OOi7 0.0014 10 0.0105 0.0091 0.0074 0.0056 0.0027 0.0031 0.0032 0.0027 a Ash removal from 10 grams solution, containing 0.1940 gram ash.
...
I
I
2
I
I 4
6
Ar Ced Co~bun clr)Dry
0
I
-5ubstoeco
this belief is that, prior to testing carbons, they may not always be freed from ash soluble in slightly acid test liquors, whereas in these tests the carbons were digested with dilute acid and then thoroughly washed. It will be noted that grinding increases the ash-adsorptive power of char, a result of increasing the adsorptive surface. However, the char carbon, from which practically all of the mineral matter has been removed, is a less efficient ash adsorbent than the powdered char. This lends evidence to the theory that the mineral skeleton of the char is mainly responsible for the ash-adsorptive properties of this substance. The ash adsorbed by decolorizing carbons, in actual practice, would be almost negligible, even in the case of those carbons which exhibit a higher ash-adsorptive power than char, weight for weight. This is due to the small percentages of carbon used and to the fact that only high-purity liquors would be treated, as will be explained in a later section. Effect of Change in Reaction of Liquor on Color Removal
On Plate VI1 will be found curves for each of the carbons, showing the effect of pH of test liquor on color removal. The curves were prepared in the same manner as that discussed in Section 11. All curves, except those for Carbon “E” and char carbon, show the same general form, a considerably greater color
INDUSTRIAL AND ENGINEERING CHEMISTRY
38
removal in acid liquors than in neutral liquors, and a slightly lower color removal on the alkaline side. It will be observed that change in acidity of the test liquor apparently does not affect the decolorizing power of Carbon “E.” The color removal efficiency of char carbon apparently is not greatly improved in acid solution, but in an alkaline solution it decreases rapidly. The important information contained on Plate VI1 is this: Between pH 6.5 and pH 7.5, the range of alkalinity maintained in refinery liquors, any one of the carbons under consideration shows a very satisfactory color removal. The decolorization would be increased by lowering the pH of liquors, it is true, but only at the expense of a certain amount of inversion. Owing to the carbonate content of bone char and its consequent buffer action in acid liquors, no attempt was made to prepare a pH color removal curve for powdered char.
Vol. 18, No. 1
carbons. They both have reasonably high decolorizing efficiencies, good qualities as filter aids, and presumably ean be as economically regenerated as the other carbons. Of these two carbons, Carbon “A,” in spite of its lower decolorizing efficiency, could probably be employed with the least expense because of its superior filtering qualities.
IV-Desirability
of Use of Carbons for Refining Sugar
In the refining of raw sugar, there are three types of impurities to be eliminated: (1) solid suspended matter, (2) gums, ash, and other nonsugars in solution, and (3) soluble coloring matter. The first step in the refining process is the washing of the raw sugar, which separates it into a washed sugar of over 99” purity, subsequently melted to a liquor of 60” to 65” Brix, and a low-grade sirup of about 80’ purity, which conS u m m a r y of Comparisons, a n d Selection of Most Detains most of the nonsugars of the original raw sugar. sirable Carbon a m o n g Those Examined In the bone-char process of refining, these liquors are clariIf the decolorizing power alone were sufficient t80determine fied by a cloth filtration and then filtered over bone char. the suitability of a carbon for use in the refining of sugars, The char filtration serves a dual purpose-it decolorizes the Carbon “E” would unquestionably be chosen as the most high-purity liquors, and removes a large part of the color and soluble nonsugars from the low-grade products. This suitable of the carbons tested. However, we have seen that elimination of nonsugars, which commonly amounts to apthe following factors are also to be considered: (1) efficiency proximately 1 per cent on the melt, results in a reduced as a filter aid, (2) capacity for eliminating nonsugars, (3) unit molasses production and a consequent increased sucrose cost, and (4) ease and economy of regeneration. recovery, and is one of the outstanding advantages of the We have concluded that the capacity for eliminating nonbone-char refining process. In a refinery melting 500,000 sugars is of relatively small importance owing to the conditions under which carbons are used-i. e., very small amounts tons of raws per year, the value of the sucrose recovered as a result of char filtration is approximately $450,000, based of carbon applied to liquors. on a value of 6 cents per pound. The use of decolorizing carbons as a substitute for bone char in the refining of sugar has in recent years been strongly advocated by producers of carbon and by others interested in the sugar industry. This movement has not, however, been reoeived with much enthusiasm by bone-char refiners. The following study was made in an effort to determine whether or not this attitude is justified. To summarize the main points involved, the outstanding advantages and disadvantages of the bone-char and decolorizing-carbon processes are enumerated as follows : The bone-char process, which is established as the standard process for the refining of sugar, possesses the following important advantages:
~ m p ~ r o t uBO’C, r . Tme ofCmtuct. /flour o.Carb6o -8 .b.Carbon A
L Carbon ”C
e=- Carbon ‘f* c- Carbon ‘0‘ f- Char Ccvbon /%Carbon w ) Dry Subsronce usedma//tes&
AC/lty
Of
Test Liquor /n p H u n h
90
As regards cost, there is little choice between carbons examined. The prices of decolorizing carbons range from $300 to $350 a ton, approximately three and one-half to four times the unit cost of first-grade bone char. The high price, coupled with the large losses in regeneration, is a serious deterrent to the use of carbons on a large scale. This limits the factors upon which the selection is made to three-decolorizing power, filtration efficiency, and ease and economy of regeneration. On the basis of these factors, it appears that Carbons “A” and “D” are the most suitable
I-Elimination of Nonsugars. In the bone-char filtration process approximately 1 per cent of nonsugars on melt is eliminated, resulting in a decteased molasses production and a n increased sucrose recovery amounting to about 1 per cent in melt. 2-Ease of Regeneration. Spent bone char may be readily restored t o practically its original efficiency by a process of washing and kilning, which involves small losses and is easily controlled. 3-Small Replacements. The replacement of char due t o shrinkage and dust removal is small-in a carefully managed plant amounting to between 13 and 15 per cent per annum of ihe char in process. 4-Highly Developed Technology. As the process is already highly developed, there is no difficult and expensive period of pioneer work to he gone through before it can be considered successful.
However, a number of equally evident disadvantages may be enumerated: 1-Large Investment in Plant. The expensive char equipment and the large amount of char in process necessitate a large investment of capital in a bone-char refinery. 2-Large Amount of Material to Be Handled. In the bone-char filtration process there is a great bulk of hone char and liquor in process a t all times. 3-Large Wash-Water Consumption. For the washing of the exhausted bone char a large quantity of hot water is necessary..
January, 1926
INDUSTRIAL A N D ENGINEERING CHEMISTRY
The following arguments in favor of the decolorizing carbon process are advanced : I-Simplicity of Process. Owing to the high decolorizing power of carbon, and to its rapid action, the amount of carbon required t o decolorize a given quantity of liquor is small, and the time in process is short. Hence it follows that labor and handling charges in the carbon process are low. 2-Reduced Inversion Losses. Owing to the shorter time that sugar liquors are in process, there should be smaller inversion losses than exist with the bone-char process. 3-Smaller Investment Necessary. Because there is no large quantity of char in process and because the necessary equipment is simpler, the capital invested in a carbon refinery is considerably less than in a bone-char refinery of the same capacity. 4-Small Wash-Water Requirements. The washing of carbon requires no such volume of hot water as does the washing of bone char.
39
Possibility of Use of Carbon Process to Produce Rejined Sugars. It is assumed that in the carbon process the raw sugar would be washed to 99" purity or higher, and melted to 60" Brix, as in the bone-char process. The clarification and decolorization of the resulting melt liquor would be combined in the carbon treatment, producing a granulated liquor by multiple carbon filtration. (Multiple filtration would be used to reduce the amount of carbon required to effect decolorization.) The affination sirup (a dark sirup of about 80" apparent purity secured from the washing of raw sugar
Against these advantages must be balanced the following disadvantages : 1-Low Nonsugar Elimination. The nonsugar elimination obtained with the carbon process is for all practical purposes negligible, because the amount of carbon used to effect decolorization is very small and only high-purity liquors are treated. 2-High Losses in Regeneration. It is stated by producers of carbon that the losses in the regeneration process amount t o not more than 5 per cent per cycle. This can probably be safely interpreted as meaning that the losses will amount to a t least 5 per cent per cycle. It can readily be seen t h a t with the price of carbon over $300 per ton the replacement cost is no small item in the cost of manufacture. 3-Increased Remeli Boiling. Because there is a negligible elimination of nonsugars in the carbon process, calculations show that the burden on the remelt pans would be increased by at least 140 per cent, necessitating a proportional increase in operating expenses on the remelt station. Also, the additional equipment required to handle these remelts would offset a considerable portion of the saving in investment secured by the elimination of the char equipment. d
In order to obtain an intelligent idea of the relative merits of the bone-char and the decolorizing-carbon processes, all the foregoing points must be considered. Most of the sugar consumed in this country is refined by the bone-char process and is supplied to a trade which demands the very highest quality of granulated sugar and, in addition, an assortment of specialty sugars and soft yellow sugars. On the other hand, the application of the carbon process has been confined to restricted localities and to only a small portion of the sugar trade. It therefore has not seriously entered into the real competitive market and has not been so much concerned with high quality and with the production of special grades of sugar. Any proposal to use carbons in a large way, therefore, must give consideration to many points that can be overlooked by present users. Two applications of decolorizing carbon in the refining of raw sugar will be discussed-carbon as a substitute for bone char, and carbon as an adjunct to the bone-char process. The use of carbon for the production of plantation white sugars has not been considered, as this is a field entirely apart from the refining of raw sugar, which involves not only different technical problems but an entirely different set of economic problems. Use of Carbon as a Substitute for Bone Char
The substitution of the carbon process for the bone-char process in the refining of raw sugar must be considered from two angles-41) the feasibility of the carbon process, and (2) the economic comparison of the carbon and bone-char processes. FEASIBILITY OF CARBON PRocEss-The feasibility of the carbon process is discussed from two standpoints-a consideration of the possibility of the use of the carbon process, and a consideration of the problems to be overcome before its success is assured.
and containing the bulk of its impurities) and concentrated sweetwater would presumably be disposed of by boiling directly to remelts, the remelt sugar liquors then to be decolorized with carbon and sent to the granulating pans. Direct treatment of affination sirup and concentrated sweetwater with carbon would be unwise for the following reasons: 1-The value of sucrose recovered as a result of elimination of nonsugars would not cover the cost of the carbon treatment. 2-The resulting liquors, even if sufficiently decolorized, would not be of high enough purity to produce a good quality of granulated sugar-as purity is as important as color in a white refined sugar. 3-The filtration of unclarified low-grade liquors through carbon would undoubtedly seriously impair the carbon efficiency.
In order to determine whether a satisfactory granulated liquor can be produced by multiple filtration of raw liquor with carbon, the following decolorizing tests were made: Five hundred cubic centimeter portions of washed raw sugar liquor, of 60" Brix and 16.67' Stammer, were treated with carbon for half an hour a t 80" C., and filtered on a Biichner funnel. Fresh carbon was used to effect the final decolorization, this carbon being re-used on partially decolorized liquor and used a third time on unfiltered melt liquor. This laboratory test approximates the three-stage decolorization process to which the melt liquor would be subjected in actual operation. Color determinations were made at each stage of the decolorizing process (Table VIII).
INDUSTRIAL AND ENGINEERING CHEMISTRY
40 Table VIII-Color
Per
Determinations
FIRST FILTRATION SECONDFILTRATION THIRDFILTRATION
(with twice-used cent carbon) carPercent bon Stammer Cube color used color color removal 1 5.66 , 66.1 2 2.23 86.7 3 1.39 91.2 a Satisfactory granulated
.. ... ...
(with once-used (with fresh carbon) carbon) Per cent StamPercent Stammer Cube color mer Cube color color color removal color color removal 1.59 90.5 0.66 1600 96.0 0 72 95.6 0.25 600” 98.5 0:30 ?io5 98.2 liquor.
. ..
... ...
...
The color of very light granulated and specialty liquors is determined by comparison with a dilute potassium dichromatecobalt chloride solution, termed C. & H. cube color standard, which has a color corresponding to a very good quality of specialty liquor, from which cube sugars and confectioner’s suggr (large crystals) are produced, and is arbitrarily rated a t 100 on the cube color scale.
Vol. 18, No. 1
in carbon-filtered liquors is of this nature would have to be determined by large-scale tests. The foregoing laboratory tests indicate that by using the carbon process it would apparently be possible to produce a granulated sugar which compares favorably with standard bone char granulated, but that the production of satisfactory specialty sugars is somewhat problematical.
Problems to Be Overcome in Substituting the Carbon Process for the Bone-Char Process. As is the case with any new process, the adoption of the carbon process would undoubtedly be attended with a host of difficulties, many of which would be serious enough to completely demoralize an enterprise until they could be solved. Let us consider the most serious of these problems: Production of Satisfactory Specialty Sugars. Specialty sugarsi. e., cube sugar and confectioner’s sugar (large crystals)-make up a small but very important part of the output of every refinery. It has already been noted that the production of good specialty sugars by the carbon process is more or less problematical. Production of Good Soft Yellow Sugars. Soft sugars also form a very necessary part of the refined output, and, in addition, are very profitable. It has never been demonstrated, t o the writers’ knowledge, that good soft sugars-i. e., sugars possessing satisfactory flavor, color, bloom, keeping qualities, and the required polarizations-can be produced from carbon-treated liquors. Probably very extensive investigation would be necess&y t o solve this problem. Maintaining the Filtration Eficiency of the Carbon. Carbon used on unfiltired liquors suffers’a graduai reduction in filtration efficiency, owing to the formation of very fine secondary carbon in the regeneration process. The maintenance of the filtration efficiency of carbon in process is a problem which would have to be solved t o insure uniform operation of the plant. Chemical Regeneration. It is stated by the manufacturers that carbon in process requires a periodic acid regeneration t o reduce its ash content and restore its decolorizing efficiency. The effectiveness of this treatment, and the frequency with which it is necessary, would develop only in the operation of the carbon process. The chemical treatment of carbon would therefore be a n uncertain item in the expense of the process. Removal of Last Traces of Carbon f r o m Liquors. It is known that failure t o remove the last traces of carbon from decolorized liquors results in the production of specky sugars or sugars with a grayish cast. It would probably develop that in order to insure absolute clarity a final filtration of decolorized liquors with a standard filter aid would be necessary. This would necessitate additional filter press capacity and considerable added expense.
These tests indicate that a satisfactory granulated liquor can be produced from washed raw sugar liquor by applying 2 per cent of carbon on melt in a three-stage decolorization process. Although various carbon manufacturers state that washed raw sugar liquor is almost completely decolorized when treated with 1 to 2 per cent carbon in a one-stage process, the writers have never been able to produce anything approaching a refinery granulated liquor with less than a three-stage process. It will be seen from the results that the liquor produced by a three-stage process contained six times as much color as a good quality specialty liquor. Further tests indicated that it is possible to produce a liquor approximating but not equal to the quality of this company’s specialty liquor, from which cube sugar and confectioner’s sugar (large crystals) are produced, by an additional treatment of granulated liquor with 2 per cent of carbon. However, little is known of the quality of the residual color in liquor decolorized by carbon. Liquors containing very minute quantities of certain types of coloring matter are known to produce specialty sugars of a very undesirable color. Whether or not the residual color
These problems, upon the outcome of which the succem of the carbon process depends, could be solved only after very exhaustive experimental work, carried out on a factory scale. On the basis of experimental data, the production of B standard granulated sugar by the carbon process appears possible. The production of specialty sugars-i.. e., cube sugar and confectioner’s sugar (large crystals)-and soft sugars is; however, problematical, and there are other problems involved in the operation of the process which are of sufficient importance to jeopardize its success when applied on a refinery scale. It is evident, therefore, that it would be most inadvisable for an established char refinery to scrap its equipment and substitute the carbon process, or even for a new refinery to install the carbon process, unless it showed the prospect of a very substantial financial advantage and until material progress is made toward the solution of the above problems. ECONOMIC COMPARISON OF CARBONAND BONE-CHILR PROCESSES-changes Necessary to Convert a Bone-Char Re$wry to a Carbon Refinery. In order to convert an existing bone-char refinery into a carbon refinery the following modifications in equipment would be necessary:
(1),The char-handling equipment would have to be scrapped, resulting in almost a total loss of the capital invested in this equipment.
I N D LTST RIAL A IVD ENGI AiEERISG CHE JfIS TR Y
January, 1926
(2) Equipment for regenerating carbon would have t o be installed. (3) The facilities for handling remelts-i. e.. low-grade pans, mixers, centrifugals, and sirup tanks-would have t o be increased t o provide for a t least a 140 per cent increase in remelt massecuites t o be boiled. It should be remarked that with the use of char approximately 50 per cent of the entering nonsugars is eliminated, a further 15 per cent diverted t o the soft system, and the remaining 35 per cent is handled as remelts. With the carbon process 15 per cent would be diverted to the soft system and the remaining 85 per cent of nonsugars would have to be handled at the remelt station. This amounts t o a 140 per cent increase in nonsugars t o the remelt station. Probably discontinuance of cloth filtration of low-grade products would make available sufficient filter press capacity for the two refiltrations of the carbon-treated melt liquor.
41
Table IX-Difference in Costs of Bone-Char a n d Carbon Processes (Based on a melt of 500,000 tons per year) -Carbon ProcessDr. Cr. (1) Saving in operating expenses in carbon process, hlowuDs to Dan tanks $314,000 180,000 (2) Saving i; wasL-wateFckts in carbon process Savings in fixed charges, due to smaller capital (3) investment, carbon process 100,000 (4) Valuebf increased molasses production, carbon process 70,000 ( 5 ) Value of sucrose lost as molasses, due to lack of elimination in carbon process (based on 1 per cent nonsugar elimination, with sugar at 5 cents per pound) $440,000 (6) Cost of increased remelt boiling in carbon process 200,000 (7) Balance in favor of carbon process
$640,000
24,000 -
$664,000
$664,000
It is evident that the conversion of an existing bone-char Tefinery into a carbon refinery would involve the loss of the greater part of the capital invested in bone-char equipment, and would require the investment of additional capital to provide carbon regenerating equipment and increased lowgrade boiling equipment. The erection of a new carbon refbery, however, would require a smaller investment of capital than a bone-char refinery of the same capacity, since in the carbon refinery the cost of carbon-regenerating equipment, increased remelt sugar-handling facilities, and buildings would be decidedly less than the cost of char equipment and buildings in the bone-char refinery. Comparison of Costs-Bone-Char and Carbon Processes. The accompanying tabulation (Table IX) is a very approximate comparison showing the difference in costs of refining by the bone-char process and by the carbon process. The I
I
I
I
available cost data for the bone-char process are quite exact, but the figures for the carbon process are a t best only estimates, hence liable to considerable error. For obvious reasons, the detailed statement of operating costs is not included in this report, merely the differences in costs of the two processes being shown:
No allowance is made for saving due to a possible reduced inversion of sugar with the carbon process, because this cannot be estimated. In fact, such figures as have been published indicate that the losses are much larger with the use of decolorizing carbons than with bone char, though it is possible that this is due to poor plant control. However, if such saving exists it is not believed to be very large for the following reason: The tobZ undetermined loss in a sugar refinery is much less, for example, than the recovery of sugar due t o elimination of nonsugar noted above. Furthermore, i t is not conceivable that all of the present undetermined loss can be due to inversion in the char filters, so it is felt that any reduction in inversion, by use of the carbon process, would represent only a portion of the loss now obtained with the use of bone char. In addition, it must be remembered that with the carbon process there will be a decided increase in the amount of remelts handled, and it is believed that a considerable portion of the inversion losses takes place in t h a t station. This, therefore, would tend to offset any reduction of inversion due to the elimination of char filters,
The actual operating cost of the carbon process, from blowups to pan tanks, is seen to be far below the corresponding cost for the bone-char process. The first item in the tabulation represents this difference in operating costs, in favor of the carbon process. I n assembling this figure, the cost of decolorization in the carbon process-i. e., three filtrations of melt liquor with 2 per cent carbon-was assumed to be equal to the cost of clarification in the bone-char process, less cost of filter aid used. The two refiltrations of melt liquor are estimated to equal the cost of the low-grade clarification practiced in the bone-char process, and eliminated in the carbon process. The cost of regenerating carbon is estimated from cost figures included in a report by tiller^,^ and from the cost of parallel operations in the char-kilning process. It is to be noted that the largest single item in the cost of the carbon process appears to be the expense for replacement of carbon. The third entry in the tabulation of comparative costs is the net saving in fixed charges to be credited to the carbon process, as a result of the smaller capital investment required. On balancing the cost of the char equipment and the additional buildings required in the bone-char refinery against the cost of carbon-regenerating equipment and the additional low-grade boiling and handling equipment required in the carbon refinery, there appears to be a saving of approximately $l,OOO,OOO in capital invested, in the case of a carbon refinery melting 500,000 tons per year. Interest and depreciation on this sum is figured a t 10 per cent. In the carbon process there is no appreciable elimination of nonsugars, as in the bone-char process. Consequently, there is a considerable loss of crystallized sucrose, and an increased production of molasses. Item 4 represents the value of the increased molasses production, credited to the carbon process, and Item 5 represents the loss of recoverable :Louisiana Planter, 67, 9 (1921).
*
42
INDUSTRIAL A N D ENGINEERING CHEMISTRY
sucrose as molasses, debited to the carbon process. These figures are based on a nonsugar eIimination of 1 per cent on melt (in the bone-char process), with crystallizable sugar valued a t 5 cents per pound and sugar in molasses valued a t 0.8 cent per pound. Item 6 represents the cost of' the increased remel! boiling necessary in the carbon process. Because there is no a p p r e ciable elimination, the quantity of nonsugars to be handled a t the remelt station is increased by 140 per cent, and the operating costs are increased proportionately.
Vol. 18, No. 1
In the combined carbon and bone-char process, the production of soft sugars and specialty liquors would present no serious problem. Soft sugars would be produced from char filtered liquors and, if necessary, a portion of the char could be reserved for specialty liquors. CONSIDERATION OF CosTs-The cost of refining by this process would be equal to the ,sum of the operating costs in the decolorizing carbon process and the eosts in the bone-char process, less the cost of clarifying melt liquor included in the char process. This would result in a refining cost for the combined bone char-carbon process of about $464oo,OOO per year more than for the bone-char process alone, on the basis of the 500,000-ton annual melt considered above. The sole advantage of the combined bone char-carbon process over the bone-char process alone would therefore be the increased nonsugar elimination and consequent increased sucrose recovery, due to more intensive char filtration of lowgrade liquors. To offset the increased cost of the combined process, it is evident that this increased sucrose recovery would have to amount to $4400,000 per year. This would necessitate a 90 per cent increase in nonsugar elimination, which experienced refiners will recognize as an impossibility. It must therefore be concluded that the combined bone char-carbon process presents no prospect of saving over the simple bone-char process. Conclusion
It will be seen that the decolorizing carbon process appears to offer a slight saving-so small, however, that, in view of possible errors and oversights, it must be considered a balance. On the other hand, unforeseen developments might increase the cost of the carbon process and the special problems arising might take years for solution, making it difficult or impossible for the refiner to compete in all markets. It is evident, therefore, that if a refiner were to adopt such a process he would be assuming a great risk with his investment and yet would have practically nothing to gain, if successful.
It is possible that the carbon process can be profitably used for a restricted trade that does not demand the highest quality of refined output or does not require the miscellaneous special grades, and where the market is not competitive. It is evident, however, that neither of the applications of the carbon process which have been considered-i. e., carbon as a substitute for bone char, and carbon as an adjunct to the bone-char process-offers sufficient advantage over the bone-char process at the present time to justify its adoption in the refining of sugar on a large scale. This is especially true in markets where quality of output is a vital consideration, and where keen competition prevails. The carbon process is a comparatively recent development, and it is reasonable to suppose that in future years improvements will be introduced which will make possible a more favorable comparison with the bonechar process. However, it is apparent that in order to make the improvement that is necessary a large amount of study and exhaustive investigation will be necessary.
Use of Carbons as an Adjunct to the Char Process In such a scheme it is assumed that the melt liquors would be decolorized with carbon, the clarification and decolorization being combined in the carbon treatment. Satisfactory decolorization would be obtained by using 2 per cent carbon on melt, with three f2trations. Sirups and low-grade liquors, after cloth atration, would be filtered over bone char. The decolorization of melt liquors by carbon would release approximately 12 per cent of the char which is normally tied up with raw liquor filtration. This would permit the revivification of a larger quantity of char per unit of melt, more intensive char atration of low grades, and consequent increased nonsugar elimination. To adapt an existing refinery to the combined process a complete carbon-handling equipment would have to be installed to provide for the decolorization of the melt liquor, and the filter press capacity would have to be increased t o provide for the two refiltrations of melt liquor necessary to produce satisfactory granulated liquor.
Bureau of Chemistry Tests Paper for Wrapping Fruit Practical tests t o determine suitable papers for wrapping fruits and vegetables conducted by the Bureau of Chemistry show that paper for wrapping apples, oranges, lemons, pears, and tomatoes should weigh 10 or 12 pounds per ream of 500 sheets 24 by 76 inches in size, and have a bursting strength of not less than 6 points. It should have sufficient flexibility and strength to withstand the vigorous rapid twist given it in wrapping and t o give a smooth, attractive appearance t o the wrapped fruit. Proper wrapping papers will retard evaporation and tend to keep fruits and vegetables in a fresh condition. They will reduce damage in shipment from rubbing or jarring. retard final ripening until removed by the retailer, and give protection from dust, frost, or the sun. The Bureau of Chemistry will examine samples of paper that have proved unsatisfactory. The sample submitted should consist of a t least 20 wrappers, 10 new and 10 that show the paper torn or damaged in wrapping fruit. A full statement as t o the points in which the paper is unsatisfactory, name of maker, brand name of paper, and approximate percentage of the paper failing during wrapping, should accompany the sample.
