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THE JOURNAL OF INDUSTRIAL A N D ENGINEEBING CHEMIjSTBY
FILTRATION-use an asbestos mat Gooch crucible. The mat should contain at lesst.0.20 g. of dry asbestos for a precipitate weighing from 0.2 to 0.5 g. It is unnecessary to wash the mat free from h e fibers or to weigh the crucible before filtering the gums. The flask containing the precipitate should be drained before rinsing, and the rinsings of wash alcohol should not be added until the last dropof the original liquor has passed through the mat. The filtration and washing of precipitates weighing about 0.01 g. ordinarily need not require more than 5 min., and precipitates of about 0.05 g. can be handled in 15 min. Alundum crucibles if used need not be weighed before filtration of the gums. WASH ALCOHOL-The requirement for the wash alcohol is that it shall be of higher alcohol concentration and of less acidity than the alcohol in the mixture of sirup, alcohol, and acid. This avoids any solvent effect on the precipitate. It is advisable to use the same strength alcohol for washing as was used in precipitating the gums. Occasionally alittle acid in the wash alcohol will speed up the filtration. DRYING-Dry at 100" to 105" c. for 1 hr. For verylarge precipitates it is well to see whether this is sufficient to give constant weight.
Vol. 14, No. 12
WEIGHING-After drying and ignition the crucible should be cooled in a desiccator and weighed. These weighings should be on a balance accurate to 0.0001 g. IGNITION-The ignition of the organic matter may be accomplished in a mufle or by a Bunsen flame, and must be continued until all the carbon is consumed. This usually requires 10 to 15 min. The difference between the weight after drying and after ignit,ion represents the dried gums. For very accurate work or where the precipitate weighed is very small, (t correction must be applied for the loss in weight of the dried crucible and mat during ignition. For a 14- to 18-g. Gooch crucible with a 0.20 to 0.25 g. asbestos mat, this correction amounts to 0.0010 g. This correction may be determined once for all for any, crucible and mat. The mats nearly constant in weight are prepared by using the same volume of a thoroughly shaken stock suspension of asbestos and water. ACKNOWLEDGMENT The authors are indebted to the Engineering Experiment Station of the Ohio State University for support in a portion of this work, as well as to certain sugar men, refineries, and plantations, for laboratory courtesies.
Color and Ash Absorption by Boneblack and Decolorizing Carbons' By W. D. Home N A T I O N A L SUGAR REFINIUG COMPANY OF NEW JERSEY, YONKERS, N.
HE WIDE interest in decolorizing carbons and the fact that they are frequently offered as substitutes for boneblack in certain lines of work give importance to the comparison of their relative advantages in various technical applications. Some of the carbons produced in recent years possess a remarkable color-absorbing capacity when applied to sugar solutions, and this has in some cases proved all that was needed to make them of value in some industries, and at the same time has rather diverted attention from their frequent inability to absorb much, if any, ash, which is such an important feature in sugar refining. ORDINARY PRACTICE
T
I n sugar refining, from 75 to 100 lbs. of boneblack are ordinarily used for the filtration of each 100 Ibs. of raw sugar. This boneblack is applied in the filtration of washed sugar and washings, and to sirups from centrifugals at various stages in the process. In this way one-third to one-half of the organic impurities may be removed and one-quarter to one-third of the ash, while about three-quarters of the total color is taken out. On the other hand, the decolorizing carbons are used in much smaller proportion to sugar, and usually vary from 3 to 10 per cent of the weight of solids in the sugar solution. They remove commonly from about two-thirds to nearIy all of the color present without absorbing any notable amount of ash. For example, in a comparative study of four commercial decolorizing carbons, 250 cc. of bag-filtered, washed sugar solution a t 80" C. were added in each case to 25 cc. of the car1 Presented before the Division of Sugar Chemistry at the 63rd Meeting of the American Chemical Society, Birmingham, Ala., April 3 t o 7,1922.
Y.
bon, and the whole kept at 80" on the water bath, with frequent stirring, for 40 rnin., and then filtered. The original liquor had a color of 8, according to an arbitrary scale in which water reads 0 and a rich brown caramel solution reads 100. The four filtrates a, b, c, and d read, respectively, 1.5, 0, 3, and 1, showing removal of 81.75, 100, 62.5, and 87.5 per cent. The carbons were then washed and boiled with 30 cc. saturated solution of caustic soda diluted to 75 cc., filtered, and washed free from alkali. Then 80.5 per cent of the original weight of each of these carbons was taken, and to this were added 250 cc. of this liquor darkened with raw sugar washings, the whole heated a t 80" C. on the water bath, with frequent stirring, for 40 min., and filtered. The color of this composite liquor was 55, and the filtrates were 10, 8, 32, and 14, respectively. The percentages of color removed were 81 81, 85.50, 41.81, and 74.54. The ash removal was not determined for the first filtration, but by the second filtration practically no ash was absorbed, for, while the original solution contained 0.35 per cent of ash on a dry basis, the amounts found in the filtrates, respectively, were 0.36, 0.37, 0.34, and 0.39 per cent.
EXPERIMENTS TO DETERMINESEAT OF ASH-ABSORBINQ POWER
A set of filtrations was conducted, using the main constituents of boneblack separately, and, for comparison, some of the original material at the same time. The original boneblack contained 8.26 per cent carbon, 0.50 per cent insoluble ash, 1.64 per cent calcium sulfate, 0.09 per cent calcium sulfide, 0.17 per cent iron, and 3.89 per cent calcium carbonate. The rest was mainly calcium phosphate. To prepare the samples, 250 g. of high-grade boneblack were digested, heated with about 2 liters of 25 per cent commercial
THE JOURNAL OF INDUXTRIAL AND ENGINEERING CHEMIXTRY
Dee., 1922
hydrochloric acid, and the residue washed until it was neutral to litmus paper. The wet carbon and undissolved mineral matter weighed 167 g., and contained 87.95 per cent water, and 12.05 per cent carbon and mineral matter. Another weight of 250 g. of the same boneblack was carefully and thoroughly burned off in the muffle furnace, at a low reddish heat, until all combustible matter was removed. This left 227 g., or 90.80 per cent of the original weight of the char. For the filtration test, three burets were placed in a doublewalled glass box heated by an electric lamp, and 25 g. of the boneblack, for a standard of comparison, were placed in one of the burets above a cotton plug. In the second buret was put burned char weighing 22.9 g., calculated to represent the same original amount of boneblack as in the first buret. For the third tube were set aside 18.1 g. of the wet carbonaceous residue, calculated to contain as much carbon and insoluble ash as 25 g. of the original boneblack. A raw sugar solution at 40' Brix was prepared, and clarified by defecation with infusorial earth and filtering over paper. The original and the burned boneblack were covered with this liquor and allowed to stand 1 hr. a t about 75' C., after which the liquor was allowed to percolate slowly through at tho rate of 25 cc. per hr. As the wet carbon would have diluted the filtrate unevenly, it was mixed with 100 cc. of the sugar solution and heated near the boiling point for about 10 min., to obtain an even distribution of the 15.9 cc. of contained water with the 100 cc. of liquor. This mixture was poured into the third buret tube, and after standing an hour was drawn off in the same manner as the others. The readings were corrected for the dilution. By this procedure the following results were obtained: WHOLEBONE- BURNEDBONE- CARBON' FROM BLACK BLACK BONEBLACK 1st 2nd 1st 2nd 1st 2nd SOLUTION 2 5 C c . 25 Cc. 25 Cc. 2 5 C c . 25 Cc. 25 Cc. 103 4 20 27 60 8 16' ORIGINAL
Color Color absorbed, 96.10 80.58 73.80 per cent Ash (on dry substance) per cent 2.914 1.535 2 . 1 3 3 2.235 Ash absorbed, 4 7 . 3 2 2 6 . 8 0 23.30 per cent 2 Color of liquor supernatant to the carbon. It late through.
...
...
41.78
92.30 84.50
2.378
...
2.678
...
18.39 8.10 would no longer perco-
Here we see that while the color removal is more vigorous by the carbon than it is by the mineral framework of the boneblack, the burned boneblack far more strikingly absorbs the ash constituents of the sugar solution. This is so very evident that we cannot wonder at the relatively insignificant ash removal by carbons. The assumption, on the other hand, that the mineral portion exercises the predominating influence in ash absorption, is borne out by the behavior of an artificial boneblack formed by the fixation of carbon on a more or less porous earthy substratum. ARTIFICIAL CHARvs. BONEBLACK
I n a filtration test arranged much as was the one just described, the artificial char was compared with high-grade boneblack, with the following results: ORIGINAL LIQUOR
Calor Color absorbed., Der cent Ash (an dry substance), per cent Ash absorbed, per cent
100
.. ..
2.81
BONEBLACK SUBSTITUTE 1st 2nd 1st 2nd 30 Cc. 30 Cc. 30 Cc. 30 Cc. 2 6 10 24 98 1.84 34.52
94
.. ..
90
76
2.12 24.60
..
..
If this hint is followed, we may eventually expect to be able to develop a decolorizing carbonaceous compound, which will not only take up color, but will also absorb ash. When viewed from the financial standpoint of the refiner,
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this is an important matter. To demonstrate the point more specifically, reference is made to a certain carbon, prepared from a by-product in manufacture, having good color-absorbing power, but which had no ashabsorbing power. When 4 g. of this carbon were treated 7 times successively with 100 cc. of washed sugar solution without intermediate washing or revivifying, it was found to be 12 times as effective in color removal as the same weight of boneblack, the boneblack being used but once. The boneblack must be washed and revivified by heat after each use. A refinery working 225 days a year can count on its boneblack wearing out in about 3 years. As the boneblack makes the cycle of its operations about once in 3 days, in the first year the full char will be used 75 times, in the second year two-thirds of the char will be used 75 times, in the third year one-third of the char will be used 75 times-making 150 times in all, calculated for the full char. If boneblack can be used 150 times, it will be necessary to use this carbon through 12.5 cycles of 7 mixings with liquor in each cycle to get the same decolorizing effect. As the vegetable carbons are rather soft, they have been found to wear down under the attrition of use, and, as the grains grow smaller, gradually to choke the cloths of the filter press. It seems a fair assumption, from experience in this field, that 18 cycles of this kind would nearly exhaust the utility of most vegetable carbons. In other words, by the time this carbon has done 150 per cent as much decolorizing as an equal weight of boneblack can do in its whole life, the carbon will have been exhausted. COMPARATIVE COSTS
On a color basis alone, then, it appears that such a carbon must not cost more than 150 per cent as much as char does per pound. The cost of boneblack can be taken at about 5 cents a pound net, as an allowance can be made for old boneblack sold on its phosphoric oxide content. This carbon, then, should not cost over 7 . 5 cents per Ib., on a color absorption basis. With regard to ash absorption, however, the average raw sugar contains about 0.6 per cent ash, of which the boneblack treatment removes from 0 . 2 to 0 . 3 per cent. The carbon failing to do this, the above-mentioned 0 . 2 per cent of ash holds back about 5 times its weight of sugar from crystallizing, or 1.0 per cent on the weight of raw sugar melted. The 0.4 per cent of ash left after char filtration is ordinarily accompanied by the production of about 4 . 5 per cent of final molasses. If none of the ash is removed, we might expect to have half again as much molasses; but the carbon removes organic impurities which also have a melassagenic influence, and so it is probably more nearly correct to assume that there will be about one-quarter more molasses with carbon than with boneblack. Thus, 100 Ibs. of raw sugar treated with 80 Ibs. of boneblack should produce 93 Ibs. of refined sugar a t 5.1 cents per lb., or $4.743, and 4 . 5 lbs. of molasses at 1 cent, or $4.788 altogether. The same amount of raw sugar refined with carbon would give about 92 Ibs. of sugar ($4,692) and 5.625 Ibs. of molasses at 0.8 cent per lb. (cheaper because of its higher ash content), worth 4 . 5 cents or $4.737 altogether, which is 5 . 1 cents less than when boneblack is used. The cost of the 80 lbs. of char needed for handling 100 Ibs. of raw sugar a t 5 cents net is $4.00, and if this can be used in all 150 times, the cost for a single use will be 2.66 cents. Since the boneblack thus effects a saving, compared with carbon, in refining, of nearly twice as much as the boneblack costs, it is evident that such a carbon cannot compete with it at any price. To offset this, in erecting a plant to use carbon instead of
