Februarv. 1924
INDUSTRIAL A N D ENGINEERING CHEMISTRY
165
Comparative Ash Adsorption of Vegetable and Bone Chars' By Paul M. Horton and P. T. Sengson LOUISIANA STATEUNIVERSITY, BATONROUGE, LA.
D
In the majority of the URING the last few Comparison of the ash adsorbed by bone char and vegetable char foregoing references only Years the adsorptive under comparable conditions shows that, volume for volume, bone the conclusions are pubProperty of various char remooes much more ash. When equal weights of the chars lished, without supporting vegetable chars has been are compared, it is found that as the amount of char is increased, experimental data. It is made ~e of in the refining of keeping the volume of the testing solution constant. the relative the purpose of this work to raw W%a'r and cane juices. eficiency of the vegetable char seems to approach that of bone char. show how the various conThis has naturally evolved flicting opinions may, in a some controversy and conway, be reconciled. flict with the proponents of the old and established bone char process. Chemists are apparently united in the belief that EXPERIMENTAL the vegetable carbons are much superior in decolorizing power, In determining the ash adsorbed by norit, Sauer proceeded but there is considerable discussion concerning cost, reliability, as follows: Impure sugar was melted to a sirup having a and, in particular, the ash-adsorbing power. Many claim Brix of 50." To any quantity of this sirup was added that bone char adsorbs a very considerable portion of the ash from a raw sugar melt, while vegetable chars do so only to 5 per cent of the char based on the total solids, and the mixa slight extent, if at all. This one item seems to be of suffi- ture was heated to 90" C . for about 2 minutes. .After cient importance to merit an investigation. It is generally filtration the amount of mineral matter removed was figured believed that small-scale laboratory tests of decolorizing (1) from the analysis and purity of the sirup before and after carbons are of little worth. Certainly, the data are gen- treatment with the char, and (2) by determining the ash erally inconclusive, but it is felt that the work as described content of the char before and after its use in the impure below will have a certain value, and is for this reason given sugar solution. I n the experiments carried out by Horne the chars were heated with a raw sugar melt at 80" C. for in some detail. 40 minutes. The ash content of the sirups was found by PREVIOUS WORK direct incineration. Equal volumes of the various chars I n 1916, Wijnbergz found that after norit had been in use were used. Method 2 of Sauer seems to be the most rapid for some length of time a quantity of inorganic salts ac- and logical. It was found to be accurate and the ash adcumulated in the char, a finding in agreement with the results sorbed is not washed out by the wash solution when removing of othcr investigators. In 1918, Zerban and Taggarts investithe adhering sirup. gated ihe ash adsorption from cane juice using rice-hull carbon. In the present work it was decided to use a final molasses As an average of four experiments it was found that 4.8 per cent of the total ash in the juice was removed. When the char solution as the standard. It was found by experiment that was introduced into the sirup, the ash adsorption was much a solution of 15" Brix gave maximum adsorption and was greater. At about this time Weinrich4 printed his version of the subject, in which he denied that any vegetable carbon is not too viscous to filter. In all the following work the capable of removing ash from solution. This conclusion seems ash was determined directly by incineration of the char, to be based on results obtained with vegetable carbons known previously washed free of adhering molasses by hot water. thirty years ago. On the other hand, Sauer6 shows that norit The adsorbed ash was not removed in this manner. The will adsorb many other substances in addition to the usual coloring matters, among which are colloidal gums, silica, and temperature of ignition was held a t 650" to 700" C. The soluble salts such as the calcium and potassium salts of the ignition was carried out in platinum in an electrically heated various organic acids. The analytical methods used by Sauer muffle furnace. will be discussed later. Furthermore, Home6 in a study of The bone char used was a commercial sample of granular, four difyerent chars proceeds to the same conclusion as Weinrich. His method of testing was slightly different from Sauer's, but acid-washed material. The sample was ground and sized it is difficult to assign a reason for his experimental figures. to through 60 mesh and on 80 mesh. It was then air-dried From a raw sugar melt showing 0.35 per cent ash he obtained a and bottled. The norit used was a commercial sample of filtrate after the treatment with char containing 0.36, 0.87, the powdered, acid-washed material, and was simply sized as 0.34, arid 0.39 per cent, respectively. Lastly, and most recently, Avot7 has made a comparative study of bone and vegetable char, above and bottled. By a series of preliminary experiments it was found that in which he comes to the conclusion that vegetable chars do remove ash almost to the same extent as does bone char. adsorption of ash in any given case was practically complete Sugars refined by vegetable char were shown to contain on after 40 minutes' boiling. Therefore, the procedure adopted an average of 0.05 per cent more ash than those refined by bone char. This is to be expected, however, when the relative was to reflux for 1 hour and allow the char to subside for amounis of the carbons used per pound of sugar are taken into 30 minutes and then filter. The filtration was effected on consideration. an ashless filter held in a Buchner funnel. EFPSCTOP CONCENTRATION UPON ADSORPTION OF ASR Any attempt to compare the various statements and claims Ash after Per cent Ash published is rendered difficult by the lack of numerical data. Weight of Char 'Brix of Ash in Adsorption Adsorbed 1 Risceived June 28, 1923. Presented before the Division of Sugar Chemistry at the 66th Meeting of the American Chemical Society, Milwaukee Wis., September 10 to 14, 1923. Abstracted from thesis presented by M i . Sengson in partial requirement for the degree of M.Sc. in chemistry. * I n t e r n .Sugar J . , 18, 194 (1916). 8 Louisiana State Expt. Sta., Bull. 161. 4 Intern. Sugar J . , 20, 424 (1918). 6 Ibid., 20, 24 (1918). 8 TEISJOURNAL, 14, 1134 (1922). 7 Iniern. Sugar J., 26, 196 (1923).
Grams 1.5784 1.6362 1.6502
Solution 10 16 20
Orininal Char 89.12 . 89.12 89.12
Per cent 90.12 92.69 92.91
Per cent Char 1.00
3.47 3.79
The foregoing experiment was made with bone char and shows the effect of concentration upon the amount of ash adsorbed. The use of a 15" Brix solution gives maximum ash adsorption, and a solution more concentrated than this simply increases the difficulties and offers no advantages.
166
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Whereas it is a well-known fact that the amounts of bone char and vegetable char used in the refinery are not the same, and for this reason no comparison of the amounts of ash adsorbed can be made, it is equally true that if equal quantities of the two chars are used there is no reason to believe that the amounts of ash adsorbed will be the same. For this reason it is desirable to determine the relative ash adsorption using equal weights of the two chars and then to repeat using equal volumes. Definite volumes of bone char-namely, 5 cc., 10 cc., 15 cc., and 20 cc.-were measured in a graduated cylinder and the corresponding weights taken. Each sample was added to 500 cc. of 15' Brix solution of final molasses and refluxed for 1 hour. The ash was determined in the char as previously described. ASH ADSORBED BY EQUALVOLUMES O F BONECHAR OR NORIT Ash in Air-Dry Ash after --ASH ADSORBEDVolume Weight Char (or Norit) Testing Per cent Cc. Grams Per cent Per cent Char (or Norit) G./Cc. Bone char 0.99 0.0077 84.40 83.41 3.917 5 84.45 1.04 0.0083 83.41 10 7.835 1.05 0.0082 15 11.751 84.46 83.41 84.46 1.05 0.0082 83.41 20 15.668 Norit 0.45 0.0010 5 1.072 8.02 7.67 0.53 0.0011 10 2.144 7.57 8.10 0.67 0.0015 15 3.216 7.57 8.24 7.57 8.33 0.76 0.0016 20 4.287
It is apparent from the foregoing figures that on a volume basis bone char is approximately five times as efficient as norit in removing ash from solution. This figure is taken from the results using 20 cc. of char, as the ash adsorbed per cubic centimeter seems to have become constant a t this ratio. This series was repeated using equal weights of the chars. ASH ADSORBED BY EQUAL WEIGHTS OF BONECHAR OR NORIT Ash i n Air-Dr Ash after --ASH ADSORBED--Weight Char (or Norit7 Testing Per cent Grams Per cent Per cent Char (or Norit) G./G. Bone Char 0.98 0.009s 84.39 2 83.41 0.97 0.0097 4 83.41 84.38 0.97 0.0097 84.38 6 83.41 0.96 0.0096 84.37 8 83.41 Norit 0.60 0.0060 8.17 2 7.57 8.30 0.73 0.0073 4 7.57 0.82 0.0082 8.39 6 7.57 0.91 0.0091 8.48 8 7.57
DISCUSSION OF RESULTS The interpretation of the preceding determinations will depend somewhat on the viewpoint. The values obtained may be considered to show that norit will adsorb as much ash as bone char under conditions favorable to the latter. Taken as a whole, however, over the entire range of concentration the results are decidedly in favor of bone char. It will be observed that, although the percentage of ash adsorbed by the bone char is constant and independent of the weight of char used, the percentage of ash increases, in the case of norit, as the weight of char is increased, using a fixed amount of solution. In 500 cc. of a 15" Brix molasses solution, the total solids approximate 80 grams. In a range of from 2.5 to 10 per cent of char on total solids, bone char adsorbs a constant (0.97 per cent) amount of ash. In the same range norit increases in adsorptive power from 0.60 to 0.91 per cent. From the adsorption curves it will be found that- 10 grams of norit will remove the same amount of ash as 10 grams of bone char. This fact, if of any significance at all, seems to show that the ash adsorbed per unit weight of char is a function of the total amount of insoluble ash present in the char. Horne has shown that, in the case of bone char, the carbon present is the decolorising agent and the mineral skeleton removes the ash. It
Vol. 16, No. 2
has been suggested that on this basis 11 grams of norit containing 0.832 gram ash should show the same unit adsorption as 1 gram of bone char containing 0.834 gram ash. By extrapolating the data it is found that such is the case. Ten grams each of norit and bone char adsorb from 500 cc. of solution nearly 0.098 gram of ash. The relative efficiency of norit compared with bone char over the range of 2.5 to 12.5 per cent of char to total solids is shown by the following table: RELATIVEEBFICIENCYOF BONECHARAND NORIT Weight per 500 Cc. Efficiency Per cent Char to Solution of Norit Total Solids Grams Per cent 2.5 2 61.2 5.0 4 7.5 6 10.0 8 12.5 (extrapolated) 10
.VOlUME --
2
4
OF CHAR USED
- CC.
6
1 O f 2
8
W€/GHT OF CHAR USED - GRAMS
It will be observed that by choosing the conditions of the test, norit may be shown to be from 61 to 102 per cent as efficient as bone char in adsorbing ash from sugar solutions. Evidently, the methods of testing are at fault, and too much credence must not be placed on the results of a laboratory test of competing chars, Note.-These results are not intended to show the relative value of the two products, which were chosen simply as representative substances, but are given to indicate the variation of analytical ratings when the conditions of testing are varied. The norit was used as it is supplied to the sugarhouses, and since i t contains 1.5 per cent of water-soluble ash, the results obtained may be given an entirely different interpretation if the ash adsorbed is figured on the insoluble ash rather than on the total ash in the char. However, in light of present knowledge of the nature of ash-forming constituents, no method of distinguishing between the ash adsorbed by the char, and the ash lost to the solution from the char, is available. It is the total change in the inorganic constituents of cane juice that gives a basis for evaluating the char. Hence a carbon containing soluble ash is penalized to that extent. It is understood, however, that only factory trials will actually show the true value of a given carbon. Work in progress in this laboratory will attempt to extend the information on this subject.
CONCLUSION The results obtained in the foregoing experiments show that: (1) increasing the time of heating of char in solution also increases the amount of ash adsorbed, (2) adsorption is greater when dealing with higher concentrations of sugar solution than with rather dilute solutions, (3) volume for volume bone black will remove more ash than norit under the same conditions, and (4)weight for weight norit under certain conditions is just as effective as bone char, though in general the bone char is the more efficient. These statements are not to be taken as final generalizations, but merely as tentative suggestions subject to modification. It. is thought that the diverging opinions found in print may be due to several causes: (1) ignition of char to ash a t
February, 1924
INDUSTRIAL AND ENGINEERING CHEMISTRY
too high a temperature, (2) use of too dilute testing solution, (3) the solution and char were not heated together for sufficient time, and (4)the chars were tested in some cases on
167
the volume basis and in other cases on the weight basis, using a t the same time widely varying ratios of char to total solids.
. The True Dry Substance Content of Beet Molasses1 By R. G . Gustavson and J. A. Pierce UNIVERSITY OF
DENV&R,D E N V E R , COLO.
temperature of from 100” TANDARD methods Surfur dioxide, carbon dioxide, ammonia, iodoform-producing to 105” C. might be mainof determining the true substances, and a n unidentified oil distil from the molasses when tained, was employed. A dry substance content dried under conditions approximately similar to those employed in large Liebig condenser, of beet sugar juices, and determining dry substance under the method recommended by the mounted vertically, premore particularly of molasAssociation of Oficial Agricultural Chemists. The fotal percenfage served a constant boiling ses, presuppose that, when of these compounds, othe) than water and oil, passing o$ is 1.965. point by preventing the subjected to a uniform heat A t a temperature approximating 104” C. an amido constituent of evaporation of the water in of from 100” to 105” C., the molasses decomposes with liberation of ammonia. the solution. nothing passes off but water. I t is suggested that these results will explain in part the variation Instead of the aluminium Since an accurate knowlexisting between dry substance content as found by the refractometer dish used in the standard edge of the Percentage of and byoven drying. method, a flask of about 75dry substance is necessary ml. capacity was employed. in formulating the degree of “true purity” in the original substance, any doubt that This modification was suggested by Paul M. Grissinger, rethe standard method is accurate leads to the corollary doubt search chemist with the Great Western Sugar Company, with the statement that experiments have indicated that glass that the figures obtained by the formula and aluminium vessels give identical results. 100s p =Three small holes were bored through the door of the oven P to permit the insertion of a plain glass tube, a thermometer, are correct. The method recommended by the Association and a soda-lime bulb. All three had entrance to the disof Official Agricultural Chemists, usually known as the tilling flask through a tightly fitting rubber stopper. The “Standard Method,” is so generally accepted by sugar chem- thermometer bulb was inserted into the mass of sand and ists tha,t it is considered by most of them to be exact. Very molasses, since preliminary experiments showed that the little literature on the subject can be found in any published interior of the mixture did not reach the temperature of the treatises on sugar analysis. &ken2 states that “the use of empty part of the flask for a t least 20 minutes when the latter the vacuum oven to determine whether there might he some registered 105’ C. A small soda-lime bulb was used to predecomposition of the less stable constituents of beet mo- vent the ingress of carbon dioxide from the air. The other lasses at 105” C . did not indicate that any such decomposi- end of the plain tube was attached to a small Liebig condenser. tion took place.” To the authors this is not a satisfying The receiving vessels consisted, a t various times, of a conclusion. 200-ml. flask containing 50 ml. of distilled water, a similar Lack of data on dry substance determinations, the reali- flask containing 50 ml. of 0.1 N sulfuric acid, a similar flask zation that factory processes of manufacture indicate the pos- containing 50 ml. of 0.1 N sodium hydroxide, one containing sible volatilization of carbon dioxide and sulfur dioxide, 50 ml. of saturated bromine water, and a potash bulb of the and tho fact that the analyses of Wiley and Browne3 show usual type. Protection by means of calcium chloride tubes the presence in molasses of comparatively unstable amido was employed a t necessary points. A bent tube attached compounds were the reasons for the series of experiments to the discharge end of the Liebig condenser was kept a t all described herein. times below the surface of the solution in the flasks as in the Kjeldahl method. A suction apparatus of sufficient strength DESCRIPTION OF APPARATUS AND MATERIAL to neutralize the pressure in the train of apparatus was used Stroiig efforts were made to parallel as closely as possible continuously, and regulated to maintain as closely as possible the conditions existing when molasses is dried by the standard a pressure of one atmosphere. method. The fact, however, that the volatile fraction and The material investigated was a molasses known as “standnot the residue was the object under investigation made it ard molasses,” from a factory whose ltme rock and water necessary to employ a still and a series of flasks and bulbs to were of sufficient purity to result in a product considered to be collect the distillate. This train of apparatus resulted in the typical. It had a Brix of 93.2” and a slight negative alkaformation of atmospheric conditions different from those linity. Dry substance by the refractometer was 79.2 per cent. found in the standard method, and it was necessary to counThe sand employed was prepared by the standard method teract this effect. The authors believe that in all essentials of sifting, treating with hydrochloric acid to remove soluble the conditions of drying the substance were exactly as they iron, washing, and drying on a hot plate. Sand between 40 would have been under the official method. and 60 mesh was used exclusively. A small, double-walled drying oven, containing in the jacket tt glycerol solution of such a strength that a constant EXPERIMENTAL
S
1
Received July 11, 1923.
* THISJOURNAL, 1 Sherman,
18, 979 (1920). “Food Products,” 1914, yp. 421, 427,431.
Sand and a known quantity of molasses were mixed in proportions of about 25 to 1. Great care was taken to make
