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INDUSTRIAL AND ENGINEERING CHEMISTRY
operation. According to observation thus far made, however, the occurrence of this anhydrous salt in fresh ordinary superphosphate is not sufficiently widespread to justify the conclusion that its hydration is a common cause of superphosphate hardening.
Literature Cited (1) d'Ans, J., and Hafer, P., Angew. Chem., 50, 101-4 (1937). (2) Belopol'skil, A. P., Taperova, A. A., Serebrennikova, M. T., and Shul'gina, M. N., J . Chem. Ind. (U. S. S. R.), 14, 660-3 (1937). (3) Belopol'skil, A. P., Taperova, A. A., and Shul'gina, M. N., J . AppZied Chem. (U. S. S. R.), 12, 3-12 (in French, 13) (1939). (4) Cameron, F. K., and Bell, J. M., J. A m . Chem. SOC.,28, 1222-9 (1906). (6) Halla, P., Angew. Chem., 44, 659 (1931). (6) Hardesty, J. O., and Ross, W. H., IND.ENQ.CHEM.,29, 1283-90 (1937). (7) Ibid., 30, 668-72 (1938). (8) Hill, A. E., J . A m . Chem. Soc., 59, 2242-4 (1937). (9) Hill, W. L., and Beeson, K. C., J. Assoc. Oficial Agr. Chem., 18, 244-60 (1935).
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(10) Ibid., 19, 328-38 (1936). (11) Hill, W. L., and Hendrioks, 8. B., IND.ENQ.CHIM., 28, 440-7 (1936). (12) Hill, W. L., and Jacob, K. D., J. Assoc. Oficial AUT.Chem., 17, 487-505 (1934). (13) Hoff, J. H. van't, Armstrong, E. F., Hinrichsen, W., Weigert, F., and Just, G . , 2. physik. Chem., 45, 257-306 (1903). (14) Lehrecke, H., Chem. Fabrik, 505-7 (1933); Chem. Age (London), 37, 347-50 (1937). (15) Lehrecke, H., Tek. Tid., 65, Uppl. C., 81-5, 92-4 (1935). (16) Marshall, H. L., and Hill, W. L., IND.ENQ.CHBM.,32, 1128-36 (1940). (17) Ibid., 32, 1224-32 (1940). (18) Partridge, E. P., and White, A. H., J . Am. Chem. SOC.,51, 36070 (1929). (19) Posnjak, E., A m . J. Sci., [5] 35A, 143-71 (1938). (20) Pratolongo, U.,Ann. chim. applicata, 6, 69-112 (1916). (21) Ramsdell, L. S., and Partridge, E. P., A m . Mineral., 14, 59-74 (1929). (22) Ross, W. H., and Hardesty, J. O., Corn. Fertilizer Year Book, pp. 28-33 (1937). (23) Sanfourche, A., Bull. SOC. chim., [4] 53, 970-3 (1933). (24) Taber, W. C., J . Phus. Chem., 10, 626-9 (1906). (25) Welch, F. C., J . A m . Ceram. Soc., 6 , 1197-1207 (1923).
Active Carbon from Cottonseed Hull Bran D. M. MUSSER AND H. C. ENGEL Mellon Institute, Pittsburgh, Penna.
Laboratory experiments have demonstrated that carbons with high adsorptive capacities can be prepared from carbonized cottonseed hull bran by activation with superheated steam. The adsorption of iodine and methylene blue increases as the weight loss during activation increases. The phenol adsorption power is improved by treatment of the carbons with dilute mineral acids. The acid-extracted carbons conform to the specifications of purity and activity required for water purification and for medicinal use.
OTTONSEED hull bran is a by-product obtained in the manufacture of hull fibers. About two million tons of cottonseed hulls are produced annually in the United States, only a fraction of which is now reduced to hull bran. Although many uses have been proposed (6) for hulls and hull bran, none except the sweeping compound (6) developed recently has shown much promise of success. At present these products are utilized principally as diluents for cottonseed meal in stock feeds. Basore and Schweickhardt (3) in 1931 examined a hull bran residue, remaining after extraction of xylose, as a raw material for the manufacture of activated carbon and reported promising results on the basis of iodine adsorption alone. They did not, however, employ the untreated hull
C
bran. So far as we are aware, this possibility has never been investigated. There are various opinions concerning the relative merits of steam, air, and other gases as activating agents. Dense, granular forms of carbon, such as coconut shell carbon, are generally produced by steam activation; but for the preparation of some powdered carbons, such as water purification grades, air is also utilized. I n Europe flue gases are widely used. The experimental work described here establishes the fact that activated carbon of excellent quality for water purification and medicinal use can readily be produced from cottonseed hull bran by steam activation.
Carbonization and Activation Divers methods have been developed for the production of active carbons. The most generally used and perhaps the most successful of these processes consists of a preliminary heating operation for the deposition of primary carbon, followed by treatment with an oxidizing gas, such as steam, air, or carbon dioxide. The first step is referred to as carbonization, the second, as activation. CARBONIZATION. An alloy steel retort fitted with a tight screw top was used for the carbonization experiments. The evolved gases escaped through a tar line attached to the to of the retort. Reasonably constant temperatures were obtainegwith an electrically controlled heating unit. The optimum conditions of processing were determined in a series of preliminary trials. Judged from the results of the phenol and iodine adsorption tests, the best carbons, irrespective of yield, were produced at 600' t o 650' C.; heat treatments at higher or lower temperatures resulted in inferior carbons. Best results were obtained when the rise from 25" to 600' C. required
DECEMBER, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
about 2 hours. The optimum time of heating at the maximum carbonization temperature was 4 hours. ACTIVATION. The carbonized hull bran was activated with steam in a cylindrical alloy steel retort incased in an electric furnace and provided with a steam inlet and a gas outIet (Figure 1). The retort was mounted on bearings by means of outside shafts. A t intervals it was turned to provide agitation during the activation process. The volume of gas evolved was measured by a wet gas meter; the data afforded an estimate of the weight loss. The temperature in all activation experiments was about 950" C.
FIGURE 1. STEAM ACTIVATIONAPPARATUS
A typical run will be described to illustrate the procedure used in this work: The retort was charged with 30 grams of carbonized hull bran, and the furnace brought to 950" C. in about one hour. Superheated steam was then passed slowly over the carbon at a rate such that the temperature of the furnace and the evolution of gas remained almost constant. The steam treatment was continued until 1.09 cubic feet (3.087 X lo4 cc.) of gas at 23" C. had been evolved. This requiTed about an hour and corresponded to a 64.7 per cent yield of activated carbon. An electrically heated stationary glazed porcelain tube ( 4 ) which was used in preliminary experiments yielded a carbon with a variable activity, probably because the product near the steam entrance was oxidized more completely than the carbon at the outlet of the tube.
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The iodine adsorption was obtained by adding 1 gram of carbon to 100 ml. of 0.1 N iodine solution, shaking mechanically for one hour, filtering, and titrating an aliquot portion of the filtrate with 0.05 N thiosulfate solution. Blank determinations were run and corrections made for the iodine which had disappeared. In the methylene blue test, 0.1 gram of carbon was added to 100 ml. of a solution containing 0.03 gram of the dye. The suspension was agitated for one hour and then filtered. The amount of methylene blue remaining was determined by a Duboscq colorimeter. The reliability of data obtained by this test has been questioned, for it has been shown that in some cases (2) completely decolorized solutions give positive tests for methylene blue, as estimated by the
I n order to evaluate the carbons produced from cottonseed hull bran, parallel determinations were run on six of the best grades of commercial activated carbons. Carbons A, B, C , E, and F are vegetable carbons produced by four leading manufacturers; D is a powdered coconut carbon. Figure 2 shows the interrelation of iodine adsorption, methylene blue adsorption, apparent density, and weight loss during activation as observed for the hull carbons. The percentage weight loss is based on the weight of carbonized material. Table I gives the data on these properties as found for the commercial carbons; values interpolated from Figure 2 are included for comparison. For each preparation it is apparent that iodine adsorption and methylene blue adsorption vary directly with the weight reduction in activation. With increased time of activation, the yield becomes lower and the hull carbon steadily shows a greater sorptive capacity for iodine and methylene blue. The highest activity is exhibited by the carbon that has been oxidized to the greatest extent in the activation process for the range of yields studied. The apparent density is also a function of activation and gradually decreases with the total weight lost by the carbon during activation. TABLEI. COMPARISON OF HULLCARBONS WITH COMMERCIAL CARBONS Carbon
% Wei,ght Loss in Activation
A B_
*.
c:
D
..
.. ..
Apparent Density 0.61 0.31
% ' Iz Adsorption 68.3 43.6
0 . 2 51
55.0 96.9
0.48
% Methylene Blue Adsorp tion 35.0 29.0 33.0 99.8
FIGURE 2. RELATIONOF VARIOUS PROPERTIES OF HULLCARBONS TESTS.The adsorption values for phenol, iodine, and methylene blue were used to indicate the effect of increasing degrees of oxidation and of subsidiary activating processes, such as acid leaching, on the sorptive capacity of the carbon for different types of adsorbates. The phenol adsorption was estimated by the colorimetric procedure (1) recommended by the American Water Works Association. Dibromoquinonechlorimide was employed as the indicator in a solution of pH 9.2.
Hull carbons which readily adsorbed iodine and methylene blue were found to be comparatively inactive as phenol adsorbents. Phenol values determined a t several different weight losses of the preparations were in each case greater than 50. Preliminary experiments indicated that an acid treatment of the carbon subsequent to activation enhanced the adsorbing power for phenol. The procedure consisted in boiling the
INDUSTRIAL AND ENGINEERING CHEMISTRY
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VOL. 32,NO. 12
The primary carbon produced in the carbonization of the air-dried starting material amounts to about 30 per cent of the hull bran. The yield obtained in the activation process depends upon the type of carbon desired. A product with strong phenol-adsorbing properties may be produced from carbonized hull bran in 65-70 per cent yields. A carbon which readily adsorbs iodine and methylene blue requires further TABLE11. HULLCARBONS ACID-WASHED AFTER ACTIVATION oxidation and may be obtained in about 40 per cent yield. Hull % Weight Carbon Loss in Apparent Phenol The over-all recovery of active carbon, on the basis of the No. Activation Density Value air-dried hull bran, therefore varies from 12 to 20 per cent. 17 20 0.73 66.7 Preliminary examination seemed to indicate that the acid16 35 0.71 37.5 13 39 0.70 36.7 washed activated carbons would be suitable for pharmaceu15 44 0.68 36.0 tical use. Therefore, samples 12, 13, and 17 (Table 11) were 12 58 0.59 27.3 18 62 0.61 41.0 evaluated according to the specifications set forth in the U. S. Pharmacopeia (8) in respect to the following criteria: ash content, acid-soluble substances, volatile substances, completeness of carbonization, chlorides, sulfates, sulfides, Further experimentation revealed that a significant incyanogen compounds, heavy metals, strychnine sulfate adcrease in the phenol adsorbing capacity can be effected by a sorption, and methylthionine chloride adsorption. Typical is, before and double acid extraction of the carbon-that results are recorded in Table IV. after activation. Data on representative hull carbons prepared by this procedure are recorded in Table 111; the improvement in phenol adsorption effected by the double washing is clearly seen by comparing the samples in this series with TABLEIV. CONFORMANCE TO U. S. P. REQUIREMENTS the approximately corresponding carbons in Table 11. The Hull u. 8. P. values for the commercial grades of active carbons, which Carbon Limit were analyzed as received, are included for comparison. Volatile substances, % 5.0 15 hull carbon in 4 per cent hydrochloric acid for 10 minutes, washing in water, oven drying, and finally grinding in a mortar and pestle (power-driven) until it passed a 200-mesh screen. Typical results are given in Table 11.
?%-%uble substances, gram Completeness of carbonization (NaOH extn.)
TABLE111. HULLCARBONS ACID-WASHED BEFORE ACTIVATION Carbon No.
A C F E D
% Weight Loss in Activation
.. .. ..
..
*.
Apparent Density
0.61 0.31 0.52 0.41 0.48
AND AFTER
Phenol Value
37.5 30.0 19.0 20.9 22.5
The increased phenol adsorption brought about by treatment of the hull carbon with dilute acids is.probably the result of several factors. The acid wash removes the sulfur-containing compounds, ash, and alkaline mineral components present in the activated carbons. The removal of these ingredients effects a loss of about 6 per cent, based on the weight of the activated carbon. The purified materials would therefore be expected to exhibit greater adsorptive capacity. The treatment with acids effects, in addition to the increase in carbon content, a change in the polarity of the active carbon. The boiling acid neutralizes the alkaline ash components of the activated carbon; accordingly it shifts the pH value and tends to make i t more electropositive. This change would therefore favor the increased adsorption of the negatively charged substances. The acid-treated carbons were washed repeatedly in hot water and then oven-dried at 105’ C. The pH of aqueous extracts of the dried carbons was determined (portable glass electrode) with the following results: unwashed carbon, 9.9; active carbon produced from carbonized hulls which were washed in 4 per cent hydrochloric acid, 9.8; and carbon washed in 4 per cent hydrochloric acid after activation, 7.0. The ash content of the latter carbon was equal to 2.8 per cent. The apparent density of the carbonized hulls was 0.92 while that of the acid-washed material corresponded to 0.85.
Chloride6 (AgCl), gram Sulfates (BaSOd, gram Sulfides (PbS) Cyanogen compounds (Turnbull’s blue) Heavv metals (UreciDitable as sulfides).. eram _ Adsoiptive power (sirychnine sulfate) Adsorptive power, g . methyl thionine chloride adsorbed/g. carbon
2.8 0.005 Filtrate colorless 0.0084 0.0000 Negative Negative Complete
4 0.035 Filtrate colorlesa 0.0258 0.0279 Negative Negative 0 0006 Complete
0.1066
0.0750
0,0000
It is evident that activated carbon can be prepared from cottonseed hull bran which will fall well within the U. S. P. requirements. Acid-extracted activated carbons obtained from this source would therefore be entirely suitable for medicinal usage as well as for water purification. Literature Cited (1) Am. Water Works Assoc., Comm. Rept. on Specifications and Tests for Powdered Activated Carbon, J . Am. Water Worlcs Assoc., 30, 1133 (1938). (2) Barrett, E. P., Mellon Inst., private communication. (3) Basore and Schweickhardt, Bull. Alabama Polytech. Inst., No. 2, 29 (1931). (4) Fieldner, Hall, and Galloway, U. S. Bur. Mines, Tech. Paper 479 (1930). (5) Musser and Nickerson, IND. ENQ.CHEM.,31, 1229 (1939). (6) Olcott, Soap, 14, 105 (1938). (7) Rosin, Beal, and Ssalkowski, J. Am. Pharm. Assoc., 24, 630 (1935). ( 8 ) U. S. Pharmacopoeia XI, 2nd supplement, Philadelphia, J. B. Lippincott Co., 1939. CONTRIBUTION from the Cotton Research Foundation Fellowship a t Mellon Institute.
Correction-Spirit
Varnishes
Through an unfortunate error the footnote a t the bottom of page 1539, of the November, 1940, issue, states that one of the authors, I. W. Hutchison, Jr., is the Dow Chemical Company Fellow at the University of Kentucky. This, of course, should have read the “University of Louisville”, where the work was carried out.
