I N D U S T R I A L A N D ENGINEERING CHEMISTRY
-784
or carbon tetracliloride.
Here, too, there is a possibility
of obtainine an advantage by making a preliminary extrac-
tion of the beans with ether or carbon tetrachloride, and a subsequent extraction with a weak alcoholic solution. The analytical characters of the final extracts are now being
VOl. 15, No. 8
determined and it is proposed also to determine the relative flavoring quality of the extracts made with the different solvents by comparing the taste of custards, junket, cakes, beverages, and other edible material to which the extracts have been added.
Adsorption of Color from Sugar Solutions by Chars’ By Marshall T. Sanders ATLASPOWDER Co., WILMINGTON, DEL.
T THE fall meeting of this SOCIETY in 1921, F. W. Zerban presented a paper in which he showed conclusively that the action of decolorizing carbons in removing color from sugar and molasses solutions can be expressed by Freundlich’s adsorption equation X / M = KC1/n, where X = the amount of solute adsorbed by M grams of carbon, C is the concentration of the solute at equilibrium, and K and n are constants. He further showed that the “color units” proposed by Meade and Harris2 could be used in place of the concentration terms X and C. Unfortunately, Dr. Zerban has not as yet published this paper. At this laboratory it has also been found that the color removal by vegetable carbons follows the Freundlich equation in the cases of sugar and molasses solutions. Plate I shows the relation between the percentage of color removed from a certain molasses solution and the weight of the carbon used. Since 2 grams of carbon do not remove twice as much color as 1 gram, it is obvious that the carbon did not do as much work per gram when the larger quantity was used as it did with the smaller quantity. The term X / M in the Freundlich equation is really the work done by a unit weight of carbon. This equation states that the work done by a unit weight of carbon ( X / M ) is proportional to some power of the concentration of the solute at equilibrium.
A
7oc
/‘
,
preparing Plate I, with the exception that in Plate I1 color units are used instead of percentage of color. Curve C, Plate IV,is for the data in Plate I, with the color expressed as per cent. Any errors in determining the color of the solutions a t the left-hand end of the curve cause approximately a horizon/DO0
,-
I
PLATE L?’ /U
I
I
,,,I
,
I
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I
psper is given in Plate 11 for the same data as were used in Prevented before the Division of Sugar Chemistry at t h e 65th Meeting of t h e American Chemical Society, New Haven, Conn., April 2 t o 7,
PLATE LT
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
August, 1923
with the undecolorized solution, it is obvious that it has removed more color per unit weight than if the treatment were given in one stage and the carbon were separated from a highly decolorized solution. Suppose the action of two carbons on a solution is as represented in Plate 111. For high degrees of decolorization in a single application, A would be superior to B, weight for weight, a t the point of intersection they would be equally efficient, and for low degrees of decolorization or counterflow work B would be superior to A. All other things being equal, A would be chosen if a high degree of decolorization were desired in one application of the carbon, B would be superior for countercurrent decolorization. The values for two carbons of the function X / M at‘ any final concentration, C, represent the relative work done by the carbons to obtain that degree of decolorization. It follows that if one carbon adsorbs more color per gram than another, less of it than of the poorer carbon will be required ’ in any given case. A consideration of these logarithmic plots shows the fallacies of certain methods of testing carbons. These methods are used by some companies or are given in the various johrnals, and have come to the attention of this laboratory from time to time. One of these is to weigh out 1 gram of carbon, suspend it in 100 cc. of water, and add a dye solution until the color is just perceptible in the supernatant liquor after the carbon has settled, or until the color appears when a drop is “spotted” on filter paper. This is equivalent to measuring the value of X / M for some final , color, C, which is b a r e 1y perceptible. This method is faulty %$ for two reasons-fist, El$ the method deter4mines only one point 85 1 06/ on the curve; second, fixed. the final The color ciso lnot or
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should be determined by matching w i t h some standard. The use of the term
785
A certain weight of the unknown carbon is used to treat the standard molasse!$ solution and the decolorized solution is matched with the samples prepared by use of the standard carbon. The relative weights of the standard and unknown carbons used to obtain the same degree of decolorization are taken as a measure of the efficiency of the unknown carbon. This method assumes that the adsorption curves of the two carbons are parallel, which may not be the case, and has the objection that only one point on the curve is determined. The use of the Freundlich equation will enable one to determine the relative decolorizing capacity of the various carbons with the minimum number of tests. It would seem needless to state that the samples of carbon should be taken on a dry basis; yet two or three cases have come to our attention where the carbons were weighed out as received. Carbons can readily absorb up to 10 or 15 per cent moisture. It is obvious that the results of such tests are misleading. In the present state of our knowledge concerning the action of decolorizing carbons, there should be no attempt to arbitrarily rate one carbon in terms of another. The user should test out the carbons on the solution he intends to decolorize. I n choosing a carbon, other factors than its decolorizing ability must be taken into consideration. The apparent density of the carbon, its filterability, and its staying or lasting qualities must also be considered. The user is interested, not in any one of these properties alone, but in decolorizing his solution a t the minimum cost and, consequently, greatest profit.
Calculations for Decolorizing Carbons’ [STJPPEMENTARYT O
PRECEDING
ARTICLE.]
By M.T. Sanders ATLASPOWDER Co., WILMINGTON, DEL.
1N working with decolorizing carbons, it is very desirable
to be able to calculate the mass of carbon necessary for a given degree of decolorization. It has been s h o ~ n ~ ~in3 the ~ 4 case of sugar solutions, that Freundlich’s adsorption equation is applicable to color removal by vegetable chars. This equation as used is: X / M = KCVn Units of color removed by M grams of Fraction of carbon color remaining in decolorized C = Units of solution Fraction of K and l / n are constants depending on the amount and kind of solution treated with the carbon. where
X
=
1.
5
To determine the constants K and l/n, several equal volumes or masses of the solution in question are treated with various quantities of carbon. These quantities of carbon are so chosen as to give a series of values of log C with approximately equal increments, these values being taken over a range corresponding to from 20 t o 95 per cent decolorization. The values of X / M and C are computed and these values plotted on the so-called double logarithmic paper. The author prefers to use the fraction of decolorization instead of units of color, because by so doing a piece of logarithmic paper 10 inches square, with two 5-inch scales on each axis, is sufficient to take care of all data from 0 to 99 per cent decolorization. Received June 19, 1923. Zerban a n d Byall, “Adsorption Isotherms of Some Decolorizing Carbons.” Presented before the Section of Sugar Chemistry a t the 62nd September Meeting of t h e American Chemical Soclety, New York, N. Y., 6 t o 9, 1921. a Sanders, Chem. Met. Eng., 28, 541 (1923). 4 Sanders, “Adsorption of Color from Sugar Solutions by Chars,” preceding artiCle. 1 2
