Activated Carbon from Hydrocarbons and Chlorine G. W. STRATTON AND D. E. WINKLER' University of Kansas, Lawrence, Kans.
T
A new method for the production of an The chlorine used in these activated carbons in many activated carbon has heen developed, This experiments was a commercial grade obtained from the hfonprocesses such carbon is produced by burning hydrocarsanto Chemical Company, The as decolorizing sugar solutions, water purification, gas adsorpbans and chlorine and is activated by heathydrocarbons were commercial tion, the purification of organic ing at 1000' c. for 90 minutes. It is superior propane and butane furnished by in many respects to other currently manuthe Skelly Oil Company. chemicals and pharmaceuticals, factured activated carbons, as shown by The rate of flow of the gases etc., has led many workers to which can be used is deterseek new and better methods for determinations of iodine adsorption isomined by the size of the burner. producing this modern purifier. therms, Phenol isotherms, If the velocity of the gas is Ordinarily an activated carbon is prepared by impregnating adsorption isotherms, and gas adsorption too great, the flame will be blown out, and if the velocity is a carbonaceous material such as measurements. too low, the flame will strike wood or coal with one or more back. The ratio of chlorine to of a variety of substances such hydrocarbon is dependent upon the type of hydrocarbon as zinc chloride, alkali carbonates, sulfates, or bisulfates, sulbeing used. It was found that the ratio theoretically required furic acid, phosphoric acid, etc., followed by heating a t red for the production of carbon and hydrogen chloride was the heat. Frequently a carbon is further activated by treatment one which gave the purest carbon. I n a typical run with the a t high temperatures with steam, carbon dioxide, nitrogen, burner shown in Figure 1, butane was used a t the rate of 500 oxygen, hydrogen chloride, chlorine (1, 4, 8, 9, 11, 18, l a ) , sulfur dioxide, etc. ml. per minute and chlorine a t the rate of 2500 ml. The carbon as produced was light and fluffy and contained The production of carbon black and hydrogen chlorid; by a wide variety of chlorinated hydrocarbons. The chlorinthe combustion of chlorine and hvdrocarbons is claimed by ated derivatives made up approximately 25 Averill (9) and McGuire ( I O ) ; however, these men did not say that their carbon possessed per cent by weight of the crude carbon. The chlorinated compounds which have been any unusual adsorptive capacities. identified are carbon tetrachloride, hexachloroethane, and hexachlorobenzene. The Production of Carbon fmt two mentioned were produced in small I n these laboratories the carbon was proamounts, while the hexachlorobenzene yield was relatively large. I n addition, a small duced by the combustion of hydrocarbons amount of oil and some tarry materials were and chlorine. The water-cooled burner conformed. structed of seamless iron tubing is shown in Figure 1. The internal diameter of the inner tube was 3/g inch except a t the mouth where Activation of Carbon it was rolled down to a diameter of 6/la inch. During the purification of the carbon by The distance from the chlorine inlet to the mouth of the burner was 8 inches. This disheating in the absence of air it was observed tance was great enough to allow the two gases that increasing the time or temperature of WATER to become thoroughly mixed before they heating increased its activation. I n order INLET burned a t the mouth. The small reservoir to determine the ideal time and temperature a t the base of the burner held the chlorinated for activation, the following series of exoils which were formed before 'combustion periments was run. Samples of carbon, took place and were not carried away by the which had been dampened with Skellysolve stream of gases. By keeping the burner and dried to increase their apparent density, cooled there was less tendency for this prewere placed in No. 1 porcelain crucibles and CHLORINE INLET mature chlorination to take place within the heated a t various temperatures for different burner, and the flame was less apt to strike times. The carbon was then ground to pass back. I n operation a large rubber stopper 40-mesh screen, and its relative activity was was slipped over the water jacket down to the measured by determining its iodine number water inlet, and the top part of the burner which, in this case, represented the milliwas then inserted into a large acid-resistant grams of iodine adsorbed by 1 gram of HYDROCARBON INLET settling chamber suitable for collecting the the carbon from 100 ml. of a 0.1 N iodinecarbon. potassium iodide solution. The results FIGURE1. CHLORINE-HY- are shown in Table I and indicate that 1 Present address, Shell Development Company, temperatures around 1000° C. are best. DROCARBON BURNER Emeryville, Calif. 603 HE growing importance of
1
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INDUSTRIAL AND ENGINEERING CHEMISTRY
604
Higher temperatures are undesirable as they decrease the activation. TABLEI. EFFECTOF Temp.,
Time, Min. 30 60
c.
850 850 850 960 960 960
90
30 60 90
HEATING TIME AND
ACTIVATION
TEMPERATURE ON
Iodine
Temp.,
Time
683 773 785 735 723 930
1050
1050 1050
25 50 75 30 60 20
c.
No.
Min.'
1150 1150 1350
Iodine NO. 719 885 928 773 795 613
I n the above experiments the crucibles were placed in the hot furnace and the carbon was thus heated rapidly. I n actual practice the carbon was activated in these Iaboratories in much larger fire-clay crucibles (3 inches in diameter and 4 inches high). The covered crucibles with carbon were placed in a cold muffle furnace and heated to 1000" C. for 1.5 hours. They were then held at this temperature for an hour. The carbon produced by the latter method had an iodine number of 1100. It appears that rapid heating of the carbon is undesirable.
Comparison with Other Activated Carbons Two activated carbons prepared as described above and designated as KUl and KU2 were compared pith the following six common activated carbons: Cai bon
Use
A B C D E F
Special purifications Sugar refining Water p u ification ~ Sugar refining Water purification Special purifications
The best method for the evaluation of activated carbons is to treat Polutions containing material to be adsorbed with varying amounts of carbon and then determine the amount of material adsorbed per gram of carbon in each case. An equation which describes adsorption phenomena is that of Freundlich : 1
X/M a here X
M C K,
= = =
=
KCG
amount of solute adsorbed amount of caibon used concentration of solute after adsorption = constants
If X / M is plotted against C on logarithmic paper, a straight line results. These lines are known as adsorption isotherms and serve as an easy and rapid method for evaluating carbons. Adsorption isotherms were prepared for the eight carbons mentioned above. The three diffei ent solutions treated were of iodine, phenol, and brown sugar. I n the manufacture of activated carbon, iodine adsorption is frequently used as a control test, In general, it appears to be more indicative of the ability to remove odors and Aavois rather than color bodies ( 7 ) . Phenol adsorption is an indication of the ability of a carbon to adsorb odors and flavors (6). The experimental procedure was as follows: All carbons were dried for 3 hours in an electric oven a t 110' C. and kept in a desiccator until used. The carbons were weighed on glazed paper as rapidly as possible and transferred to 250-ml. Erlenmeyer flasks provided with close-fitting stoppers. The solutions containing the material to be adsorbed were measured a t room temperature with a 100-ml. pipet. The time of con-
Vol. 34, No. 5
tact between the solution and the carbon was 20 minutes in all cases. Each flask was vigorously shaken five times during the 20-minute period. I t was known that adsorption is a rapid process (S), but to determine whether or not equilibrium was attained in 20 minutes, samples of the solutions were treated for shorter times. In the case of iodine, equilibrium was attained in 10 minutes. Equilibrium was attained,somewhat more slowly in the phenol and brown sugar s6lutions, but no appreciable change was noticed after 20 minutes. One of the activated carbon manufacturers recommends treating colored sugar solutions with carbon for only 10 minutes (6) when making similar tests, For the determination of the iodine adsorption isotherms, a 0.040 N iodine solution mas used. This solution contained 0.508 gram of iodine and 0.762 gram of potassium iodide per 100 ml. of solution. The iodine solution was treated with decreasing amounts of carbon as described above. The equilibrium mixture was then filtered through a 12-cm. Whatman filter paper without the use of a filter aid. The first 10 ml. of filtrate were discarded, and 50 ml. of the remainder were titrated with a 0.0509 N sodium thiosulfate solution, using starch as an indicator. Each milliliter of sodium thiosulfate was equivalent to 0.00643 gram of iodine. The concentration, C, of the solute remaining in equilibrium with the carbon was therefore equal to the number of milliliters of sodium thiosulfate solution used, times 0.00643, times 2. The value of X was equal to 0.508 minus C. Results are given in Table I1 and Figure 2. TABLE 11. IODINE ADSORPTIONDATA Carbon KU 1
C , Grams Iodine Not Adsorbed 0,0039 0.0120 0.05X
0.222
X,Grams Iodine Adsorbed 0,504 0.496 0.452 0.286
M , Grama Carbon Used 0.800 0.600 0,400 0.200
x/>w
Grams d d i n e Adsorbed/ Gram Carbon 0.630 0,826
1.13 1.43
xu2
0.0081 0.0323 0.125 0.293
0.500
0,800
0.800 0.400 0.200
0.625 0.793 0.957 1.074
A
0.0423 0.0725 0.129 0.256
0.466 0.435 0,379 0,252
1,000 0.750 0.500 0.250
0.466 0.581 0.767
B
0.0355 0.102 0.228 0.365
0.473 0,406 0.280 0.143
1.000 0.750 0.500 0.250
0.473 0.541
C
0.0092 0.0448 0.156 0.307
0.499 0.463 0.352 0.201
1,000 0.750 0.600 0.260
0.499 0.618 0,703 0.803
D
0.0044 0,0151 0,0182 0.258
0.504 0.493 0.427 0.250
i.noo
0.500
0,504 0.657 0.854
0.101 0.166
0,407 0.342 0.237 0.144
E
0.251
0.364
F
0.0080
0.0293 0.114 0.276
0.476 0.383 0.215
0.500 0.479 0.394 0.232
0.760
0.250
1,007
0.560
0.572
1.000
1.000
0.407 0.456 0.514 0.576
1.000 0.750
0.500 0,639 0.788 0.928
0.750 0.500 0.250 0.500
0.250
For the determination of the phenol adsorption isotherms, a 0.025 N phenol solution in water (0.235 gram of phenol per 100 ml. of solution) was used. The phenol solution was treated with decreasing amounts of carbon as described above, and the equilibrium mixture was filtered through a 12-cm. Whatman filter paper without filter aid. The phenol which was in equilibrium with the carbon was determined by the bromide-bromate method. Twenty-five milliliters of the
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INDUSTRIAL AND ENGINEERING CHEMISTRY
filtrate were transferred to a 250-ml. glass-stoppered bottle and diluted to 100 ml. An excess of the bromide-bromate solution, containing 2.784 grams of potassium bromate and 10 grams of potassium bromide per liter of solution, was added along with 10 ml. of 4 N sulfuric acid. The bromidebromate solution was measured with a pipet, and the amount added was varied from 25 to 50 ml., depending upon the amount of carbon which had been used and upon its activation. A large excess of bromine must not be present; otherwise the results are apt to be erratic. After thoroughly mixing, 15 minutes were allowed for the reaction to go to completion. An excess of potassium iodide solution was then added and the liberated iodine was titrated with 0.0958 N sodium thiosulfate solution, using starch as an indicator. If the free bromine found by the titration with thiosulfate sohtion is subtracted from the total available free bromine in the bromide-bromate solution added, the amount of bromine which went to form tribromophenol is obtained. This value is then directly related to C, the concentration of phenol in the solution in equilibrium with the carbon. The value of X is then equal to 0.235 minus C. Results are given in Table I11 and Figure 3.
z
0
5 3 5
K
E
1.0 .7
8
g0
.4
0 v)
5 .2 C-EQUILIBRIUM CONCENTRATION OF IODINE
Mg. OF IODINE PER 100 ml OF TREATED SOLUTION
KU 1
B
TABLE 111. PHENOL ADSORPTION DATA X Grams Phenol Adsorbed 0.200 0.170 0.124 0.068
M, Grams Carbon Used 1,000 0.750 0.500 0.250
Grams Ph)enol Adsorbed/ Gram Carbon 0.200 0.227 0.248 0,272
XU2
0.0635 0.0983 0.142 0.187
0.171 0.137 0.093 0.048
1.000 0.750 0.500 0 250
0.171 0.183 0.186 0.192
A
0.0932 0.116 0.151 0.189
0.142 0.119 0.084 0.046
1.000 0.750 0.500 0.250
0.142 0.159 0.168 0.184
B
0.0980 0.140 0.160
0.183
0 137 0.095 0 075 0.052
1.500 1.000 0.750 0.500
0.0913 0.095 0.100 0.104
C
0.0647 0.113 0.140 0.170 0.202
0.170 0.122 0.095 0.065 0.033
1,500 1.000 0.750 0.500 0.250
0.113 0.122 0.127 0.130 0.132
D
0.0646 0.0967 0.138 0.184
0.170 0.138 0.097 0.051
1.000 0.750 0.500 0.250
0.170 0.184 0.194 0.204
E
0.113 0.166 0.185 0.200 0.217
0.122 0.069 0.050 0.035 0 018
2.000 1.000 0.750 0.500 0.250
0.0610 0.0690 0.0667 0.0700 0.0720
0.0767 0.108 0.145 0.188
0.158 0.127 0.090 0.047
1 000 0.750 0.500 0.250
0.158 0.169 0.180 0.188
Carbon XU1
F
KU2
x/M
C, Grams Phenol Not Adsorbed 0.0350 0.0646 0.111 0.167
Since the sugar industry does not have a standard color solution, a solution containing 150 grams of brown sugar per liter was used in these laboratories for the .determination of the color adsorption isotherms. This colored solution, which was assigned the value of 150 color units, was treated with decreasing amounts of carbon. I n the case of the sugar solutions, the stoppered flasks containing the carbon and the solution were placed in a water bath kept a t 70" C. The flasks were shaken as previously described, and a t the end of 20 minutes when equilibrium had been attained, the solutions were filtered through a 12-cm. Whatman filter paper until sparkling clear. No filter aid was used. After the solutions cooled to room temperature, the color remaining was determined by measuring the percentage transmittance
C B
E
C-EQUILIBRIUM CONCENTRATION OF PHENOL
..
Mg. OF PHENOL PER loo mi. OF TREATED SOLUTION N
__
-
C-EQUILIBRIUM CONCENTRATION OF COLOR
FIGURE 2 (Top). IODINE ADSORPTION ISOTHERMS FIGURE 8 (Center). PHENOL ADSORPTION ISOTHERMS FIGURE 4 (Bottom). COLORADSORPTION ISOTHERMS
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INDUSTRIAL AND ENGINEERING CHEMISTRY
606
of light of 4500 A. through the sugar solutions compared to distilled water. The percentage transmittance was determined with a Cenco-Sheard spectrophotelometer. The values of X and C in Freundlich's equation were calculated from the percentage transmittance by the following relation: Ill0 =
The above expression can be written: In
Z Io
=
-kdC
In
5I
=
kdC
Since the distance was constant in this work, a new constant K can be substituted for kd. Solving the above equation for C and changing to logarithms to the base 10, C =
2.303 log Io/I
K
I n order to evaluate the constant, the above equation was solved for K and measurements of Io/I were made on three solutions containing, respectively, 50, 100, and 150 grams of brown sugar per liter of solution or 50, 100, and 150 color units, respectively. The value of K was found to be 0.0054. The color units remaining after carbon treatment could be determined from the follow-ing expression : Z C = 426 log 2
Z
The value of X was then equal to 150 minus C. Results are given in Table IV and Figure 4. TABLE IV Carbon
C Color Urhts Not Adsorbed
Carbon Cooonut Coeonut KU2 XU granular
GASADSORPTIOSMEASUREMENTS
Meeh Size
c---Gram/Gram Propane adsorbed
Propane retained
20 40 40 10-30
o:io9 0.155 0.184
0:OO
0100
of CarbonChlorine adsorbed 0.383 0.403 0.471 0.583
Chlorine retained o:i2 0:il
e-kdC
where I = intensity of light emerging from solution Zo = intensity of light entering solution e = base of natural logarithms k = a constant d = distance light travels through solution C = concentration of colored substance in solution
or
TABLE V.
COLOR ADSORPTION DATA
x,Color
Units Adsorbed
M , Grams Carbon Used
X/lM, Color Units Adsorbed/ Gram Carbon
KU 1
39 43 51
111 107 99
1.000 0.750 0.500
111 143 200
XU2
62 74 85 107
88 76 65 43
1.000 0.750 0.500 0.250
88 101 130 172
A
23 31 44 71
127 119 106
79
1.000 0.750 0.500 0.250
127 158 212 316
B
85 91 101 118
65 59 49 32
1.500 1.100 0.700 0.250
43 54 70 128
C
102 107 111 117
48 43 39 33
1.000 0.750 0.500 0.250
48 57 78 132
D
39 51 62 92
111 99 88 58
1.000 0.750 0.500
0.250
111 132 176 232
E
110 120 130
40 30 20
1.000 0.500 0.250
40 60 80
F
34 42 51 81
116 108 89 69
1.000 0.750 0.500 0.250
116 144 178 276
Gas Adsorption Measurements Not all activated carbons are suitable for gas adsorption purposes. Coconut charcoal has long been recognized as the most efficient in this field, and it has found extensive use in gas masks. Measurements were carried out in these laboratories to determine if the K U carbon had gas adsorption capacities equal to that of coconut charcoal obtained from the War Department. The experimental procedure was as follou7s: The activated carbon was placed in a specially constructed U-tube provided with a ground-glass joint, which facilitated emptying and filling, and with a stopcock on either end. The adsorption tube was weighed empty and then filled with carbon, and the lower portion of the adsorption tube which contained the carbon was heated 30 minutes a t 400' C. under 1 mm. pressure. The stopcocks were closed and the tube was reweighed when cool. The difference in weight, after correcting for the lack of air in the tube a t the second weighing, gave the weight of the carbon. The gas to be adsorbed was then allowed to flow through the carbon until equilibrium had been attained, at which time the tube was again weighed to get the weight of the adsorbed gas; corrections were made for the gas in the gas space of the adsorption tube. To determine the retention of the gas by the carbon, the adsorption tube and its contents were again heated 30 minutes at 400" C. under 1mm. pressure. The stopcocks were closed and the tube was reweighed when cool. Results are given in Table V. Carbon Black for Rubber Carbon black for use in rubber has also been made in these laboratories by burning hydrocarbons and chlorine. It is produced in the same manner as described in the first part of the article. The purification of the carbon must be carried out at a lower temperature than is required for activation. A carbon free from chlorine can be produced by heating at 600' C. for 35 minutes and allowing natural gas to pass over it during heating and while cooling to 200" C. Carbon made by this method meets the requirements of the rubber industry in regard to pH, volatile matter, acetone extract, moisture content, and diphenylguanidine adsorption. Samples of KU carbon black were compared on a weight for weight basis with channel black. The tests, carried out by the Firestone Tire & Rubber Company, showed that the rubber cured with the K U carbon black had greater stress at 400 per cent elongation, lower tensile strength a t break, and lower percentage elongation a t break than rubber cured with channel black. Literature Cited (1) Adier, R., Brit. P a t e n t , 340,202 (1929). (2) Averill, C. C:, U. S. P a t e n t 1,238,734 (1917). (3) Blowski, A. A., and Ban, J. H . , IND.ENG.C H R M . ,18, 32-42 (1926). (4) Chaney, N. K., U. S. P a t e n t s 1,497,543 and 1,499,908 (1924). (5) Darco Corp., Laboratory Manual for Use in Analyzing and Testing Decolorizing Carbon, 1936. ( 6 ) Helbig, W. A., J . Am. Water V'orks Assoc., 30, 1226-33 (1938). (7) Industrial Chemical Sales Co., "The Modern Purifier", 1937 (8) Janneck, J., and Engel, H . , German P a t e n t 533,936 (1928) (9) Klar, R., and Miller, A., 2. physik. Chem., A169,297-304 ( 1 9 3 4 ) . (10) McGuire, 3. A., U. S. Patent 1,498,924 (1824). (11) Morrell, J. C . , Ibid., 1,712,930 and 1,713,347 (1929). (12) Naugle, J. J., G e i m a n P a t e n t 500,582 (1926). (13) Sohober, O., Ibid., 488,779 (1926).
