I
BALWANT RAI PURI, D. D. SINGH, J. NATH, and LEKH RAJ SHARMA Department of Chemistry, Panjab University, Hoshiarpur, India
Chemisorption of Oxygen on Activated Charcoal and Sorption of Acids and Bases
Treatment of activated charcoal with oxygen at temperatures varying from 100' to 600°, fixed an appreciable amount of oxygen which, on desorption at 1200°,was given out as water, carbon dioxide, and carbon monoxide. The total amount of chemisorbed oxygen and that given out as carbon dioxide was maximum at 400'. The amount and nature of the chemisorbed oxygen depended on the nature of the charcoal. The base-neutralizing capacity of charcoal was almost entirely due to chemisorbed oxygen, which on degassing at high temperatures was given out as carbon dioxide. The rest of the oxygen was not involved in base or acid adsorption b y charcoal
THE
effect of heating activated charcoal in oxygen a t different temperatures on its acid-base adsorption and other properties has been investigated (2, 3, 5, 6). Base adsorption increases with rise in temperature to a maximum a t 400" C. and decreases thereafter, whereas acid adsorption decreases to a minimum a t 400' and steadily rises to about 800'. These fundamental variations in adsorbent properties of charcoal have been
vaguely ascribed to the existence of different surface oxides of carbon characteristic of the temperature of the treatment (7-9). According to Weller and Young (70) and Wilson and Bolam (77), adsorption of strong inorganic bases is due to the presence of chemisorbed oxygen which, however, plays no part in the sorption of acids. Treatment of oxygen a t 400' fixes a maximum amount of oxygen, which corresponds with the development of maximum capacity to adsorb alkalies. However, these workers did not study the disposition of this large amount of tightly bound oxygen a t the surface of carbon nor the manner in which it influences its base-adsorption capacity. The present work was undertaken to get some information on these points.
Experimental Charcoals. Three varieties of charcoal prepared by the carbonization of recrystallized cane sugar (by pure sulfuric acid, followed by exhaustive washings with hot distilled water), coconut shells, and cotton stalks (by heating small pieces a t about 350" in a limited supply of air) were used in these investigations. Sugar charcoal was almost free of ash; the other two samples were extracted with hydrofluoric acid to lower the ash content to about 0.25%. The charcoals were then degassed a t 1200' in a resistance tube furnace to remove all types of adsorption complexes as well as tarry and pyroligneous impurities. Treatment with Oxygen. Ten grams of charcoal, activated as above, was taken in a rotating borosilicate glass
tube of 3 / h c h bore, which could be heated in a tube furnace to temperatures u p to 600'. Oxygen was led over the charcoal a t the rate of 2 liters per hour and in some experiments a t 3 liters per hour a t temperatures varying from 100' to 600' and for intervals of time varying from 1 to 24 hours. The tube was kept rotating a t the rate of 30 to 35 revolutions per minute to keep the charcoal in constant tumbling motion. Base Adsorption. Charcoal, 0.5 gram, was mixed with 80 ml. of 0.25N barium hydroxide and the suspension shaken mechanically for about 48 hours. The amount of unused alkali was determined by titrating an aliquot of the clear supernatant liquid against a standard acid solution. Acid Adsorption. One gram of charcoal was mixed with 100 ml. of 0.1N hydrochloric acid and the suspension shaken mechanically for about 48 hours. The decrease in acid concentration was determined by titrating an aliquot of the clear supernatant liquid against a standard solution of sodium hydroxide. Surface Area. Surface areas of some of the samples were calculated from the desorption branch of the water isotherms by applying the Kistler, Fischer, and Freeman equation ( 4 ) as used by Arne11 and McDermot ( 7 ) . High-Temperature Evacuation. The ~amples treated with oxygen (2-gram portions) were subjected to evacuation in a resistance tube furnace at 1200 ' and the gases were analyzed in the following sequence: Water was removed in calcium chloride tubes and carbon dioxide ir, a series of Erlenmeyer flasks containing a known amount of barium hydroxide VOL. 5 0 , NO. 7
JULY 1958
1071
Evacuation a t 1200' C. of Charcoal Treated with Oxygen at 400" C.
Table I.
An appreciable amount of oxygen i s fixed; an desorption it is evolved as water, carbon dioxide, and carbon monoxide
Time of Treatment,
Oxygen Flow, Liters/
Hours
Hour
% Loss in Weight
Gases Evolved, Cc. N.T.P./G.
co
con
HzO
1
5.23 10.14
25.14 25.49
5.55 6.39
2
19.50 27.46
38.57 39.97
10.19 14.71
4
31.37 41.25
39.13 41.31
29.40 41.64
8
44.30 51.62
41.79 43.83
16
48.33 52.10
24
55.63
Disposition of Oxygen, Mg./G. Hi0 coz co
Sugar Charcoal Nil Nil Nil Nil
Nil Nil Nil Nil
Total Oxygen,
Mg./G.
17.96 18.20
7.93 9.13
27.55 28.55
14.55 21.01
39.94 51.48
27.95 29.51
42.00 45.20
28.53 36.77
98.48 111.48
38.55 40.94
59.50 65.43
29.85 31.31
55.07 58.49
42.50 46.73
127.42 136.53
42.06 44.80
39.46 42.31
63.76 70.92
30.04 32.00
56.37 60.44
45.54 50.66
131.95 143.10
44.83
42.87
71.83
32.02
61.24
51.31
144.57
14.43
Nil
Nil
14.43
17.66
21.14
Nil
38.80
25.89 27.33 42.10 49.56
2.10
20.21
18.30
24.73
Coconut Shell Charcoal Nil Nil 14.78 Nil
29.50
30.33
21.61
0.08
21.66
30.87
0.060
52.59
35.10 38.30
33.11 36.24
31.32 33 * 57
0.11 0.13
23.65 25.88
44.74 47 * 95
0.080 0.093
68.47 73.92
16
39.60 42.70
37.84 41.23
35.28 35.92
0.15 0.18
27.03 29.45
50.40 51.31
0.117 0.128
77.55 80.89
24
44.30
41.67
36.11
0.16
29.76
51.58
0.114
81.45
Table II. Evacuation at 1200" C. of Sugar Charcoal Treated with Oxygen 400' C. i s optimum for fixation of total oxygen and removal as carbon dioxide (Rate of flow of oxygen, 2 liters/hour) Temp. of
Treatment, O
c.
100
Time,
% Loss in
Hours
Weight
5320
coz
co
Hz0
c02
co
2.30 7.12
30.25 34.84
14.56 19.78
13.72 24.33
21.61 24.89
20.80 28.26
9.80 17.38
52.21 70.53
8
29.00 31.79
36.33 39.12
17.44 21.53
36.40 48.71
25.95 27.94
24.91 30.75
76.86 93.49
16
33.47 39.93
37.08 40.19
20.35 26.28
42.15 55.97
26.48 28.71
29.07 37.54
8 16
44.37 48.33
41.79 42.06
38.55 39.46
59.50 63.76
29.85 30.04
55.07 56.37
8
16
70.41 74.93
36.37 34.49
16.38 13.34
60.31 64.12
25.98 24.64
23.40 19.06
8 16
76.34 79.12
30.29 28.57
11.87 11.02
62.73 64.77
21.56 20.41
16.93 15.76
26.00 34.80 30.11 39.98 42.50 45.54 43.08 45.80 44.81 46.26
16 300
8
500
600
Table 111.
C, %
H, %
Ss %
Ash, %
Activated sugar Before 98.59 0.67 Nil 0.11 After 84.38 0.46 Nil 0.19 Activated coconut shell Before 98.42 0.52 Nil 0.35 After 90.10 0.37 Nil 0.76 Activated cotton stalk Before 98.53 0.49 Nil 0.39 After 90.53 0.33 Nil 0.83 O Before and after treatment with oxygen at 400' C. for 16 hours.
solution. Carbon monoxide and hydrogen (if any) in the rest of the gaseous mixture were estimated ,in Orsat-Lunge gas analysis apparatus in the usual way.
127.42 131.95 92.46 89.50 83.30 82.43
Area, Sq. M./G.
0.63 14.97
303.9 317.6
0.71 8.77
183.2 191.6
Discussion
0.59 8.31
168.3 173.7
Hydrogen was found in none of the experiments. A few samples were also evacuated a t temperatures varying from 100 O to 1200'
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85.66 106.23
0, %
Surface
Description of Charcoal
Mg./G.
and the evolved gases were analyzed. UItimate Analysis. Some typical samples were analyzed on request at the National Chemical Laboratory, Poona, India, and Microanalytical Laboratory, Banbury Road, Oxford, by the usual methods of organic microanalysis. The percentage of oxygen was obtained by difference.
Ultimate Analyses and Surface Areas of Charcoals" Oxygen is present as water in both charcoals
1 072
Total Oxygen,
8 16
200
400
Disposition of Oxygen, Mg./G.
Gases Evolved, Cc. N.T.P./G.
Treatment of activated charcoal with oxygen a t 400" fixes a n appreciable amount of oxygen which, on desorption (in vacuum) at 1200°, is evolved as water, carbon dioxide, and carbon monoxide (Table I). T h e amount of chemisorbed oxygen increases with increase in time of treatment as well as with rate of flow of oxygen. However, extending the
CHEMISORPTION ON CHARCOAL treatment beyond 16 hours does not increase the amount of oxygen noticeably, even though it burns off more carbon (shown by loss in weight). The effedt of temperature on the chemisorption of oxygen and its removal in different forms is shown in Table 11. I t is evident that 400' is the optimum temperature for the fixation of total oxygen as well as for its removal as carbon dioxide. The oxygen removed as carbon monoxide increases with rise in temperature u p to 400' and remains almost constant thereafter. The decrease in the carbon dioxide complex after 400' is probably due to its instability a t higher temperatures. There is one glaring difference in the disposition of oxygen in the two samples of charcoal. While in sugar charcoal an appreciable amount of chemisorbed oxygen, representing nearly 3570 of the total fixed under optimum conditions (16-hour treatment a t 400', Table I), is given off as carbon monoxide, in coconut charcoal only a small amount, representing hardly 0.15'% of the total, is given off as carbon monoxide. This was also the case with cotton stalk charcoal. An appreciable amount of oxygen is seen to be present as water in both the charcoals. This appears to be due to the presence of a small amount of hydrogen in the samples (Table 111). Evidently sugar charcoal is capable of fixing more oxygen (14.46%) than coconut shell charcoal (8.14%) under similar optimum conditions (Table I). This is probably due to the greater surface area of the former (Table 111). These values compare well with those obtained from ultimate analysis (Table 111). The same is true for cotton stalk charcoal (Tables I11 and IV). Weller and Young (70) could fix as much as 18% oxygen by an intensive treatment a t 400'. However, they did not determine its disposition and it seems highly probable that an appreciable amount of their oxygen was fixed as water, as their charcoal contained more hydrogen than those reported in this paper.
Table IV.
Amount of Alkali Adsorbed by Charcoals (Treated with Oxygen at 400' for 16 Hours) and Gases Evolved on Evacuation
Sugar charcoal fixer more oxygen than coconut shell charcoal under optimum conditions COZ Decrease Eauiv. in Ba(OH)z Temp. of B a ( 0 H h -of Adsorption, Alkali, coZ Gases Evolved on Evacuation, G./100 G. Evacua- Adsorbed, tion, Meq./ Adsorbed, Equiv., Total O c. 100 G. G./100 G. G./IOO G. COa co Ha0 0 100 300 400 500 750 900 1000 1100 1200
370.6 368.9 227.2 97.3 29.8
8.15 8.12 5.00 2.14 0.64
Nil Nil Nil
Nil
Nil Nil Nil Nil
100 300 400 500 750 900 1000 1100 1200
297.5 295.8 213.7 84.3 12.5
6.55 6.51 4.70 1.58 0.27
Nil Nil Nil Nil
Nil Nil Nil Nil
100 300 400 500 750 900 1000 1100 1200
283.6 282.9 231.3 109.6 27.7
6.24 6.22 5.09 2.41 0.61
Nil Nil Nil
Nil Nil Nil Nil
Nii
Table VI.
Sugar Charcoal Nil Nil
... 0.03 3.15 6.01 7.51 8.15 8.15 8.15 8.15
3.19 5.83 7.28 8.29 8.33 8.30 8.31
...
6.55 6.55 6.55 6.55
Cotton Stalk Charcoal Nil 0.02 Nil
...
1.15 3.83 5.63 6.24 6.24 6.24 6.24
1.31 4.17 6.05 6.84 6.83 6.90 6.89
168.7 201.7 227.3 348.8 105.9 89.3
12.56 10.86 6.44 3.23 18.57 22.35
Nil Nil
Nil Nil
2.54 3.09 3.49 3.55 3.58 3.62 3.60
4.58 6.98 8.90 11.88 12.84 13.95 14.31
Nil Nil
Nil Nil
2.12 2.78 2.98 3.27 3.29 3.26 3.31
0.015 0.018 0.022 0.022
6.93 7.04 7.03 7.06
Nil Nil Nil Nil 0.017 0.024 0.029 0.034 0.037
3.02 5.66 7.42 7.95 8.05 8.01 8.09
Nil Nil
Nil Nil
1.92 2.04 2.83 2.91 2.93 3.01 2.97
2.66 4.84 6.92 7.45 7.58 7.69 7.67
Base Adsorption of Charcoal Is Equivalent to Carbon Dioxide Evolved on Degassing at 1200'
Charcoal Sugar
O
Treatment with Oxygen c. L./hr. Hours
100
8 16 8 16 8 16 1 2 4 8 16 1 2 4 8 16 24
200 300 400
Table V. Base Adsorption Capacity of Sugar Charcoal Rises on Treatment with Oxygen for 16 Hours
100 200 300 400 500 600
0.89 4.73 6.31 8.22 8.86
Coconut Shell Charcoal Nil Nil Nil 0.04 Nil Nil 1.85 1.57 Nil 4.70 4.39 Nil 6.28 6.57
(Rate of flow of oxygen, 2 liters/hour) Temp. of Adsorption Adsorption Treatment, of Ba(OH)a, of HCI, O C. Meq./100 G. Meq./lO-O G .
Nil Nil Nil Nil
500
8 16 8 16
600
Coconut shell
400
2
2 4 8 16 24 8
16
coz
BdOWz Adsorbed, Meq./100 G.
Evolved, Meq./100 G.
122.7 168.7 149.3 201.7 173.4 227.3 44.1 81.9 253.1 331.7 348.8 52.1 122.2 274.7 356.7 370.6 371.5 105.0 131.6 105.9 97.9 89.3
130.0 176.6 155.7 192.2 181.7 234.6 49.5 90.9 262.5 344.2 352.3 57.0 131.3 282.5 365.5 377.8 382.2 119.1 146.2 119.1 106.0 98.5
120.3 177.9 261.1 293.7 301.9 280.3 297.6
131.9 192.8 279.6 315.0 322.4 299 7 320.7
VOL. 50, NO. 7
JULY 1 9 5 8
1073
,
Acid-Base Adsorption. The baseadsorption capacity of charcoal is seen (Table V) to rise appreciably on treatment with oxygen at different temperatures to a maximum value at 400’ and to decrease thereafter. The acid adsorption capacity, which is very much lower in magnitude, follows the reverse order, being minimum at 400’. These facts have been reported (2, 3. 5, 6 ) , but no satisfactory explanation appears to have been offered. I t was thought of interest to correlate the capacity of charcoal to neutralize alkalies with the amount of carbon dioxide evolved from it on high temperature evacuation. The latter values expressed in milliequivalents per 100 grams are compared with the corresponding barium hydroxide values in Table VI in the case of the samples of charcoal described in Tables I and 11. I n most cases the amount of alkali neutralized by charcoal is almost exactly equivalent to the amount of carbon dioxide evolved from it on degassing at 1200’. This shows that the acid character as well as the base-adsorption capacity of charcoal is almost entirely due to the presence of the carbon dioxide complex contained in it. Charcoal activated in oxygen at 400’ contains the maximum amount of this complex and therefore it has maximum base-adsorption capacity. The amount of this complex decreases on treatment with oxygen a t higher temperatures and the base adsorption capacity decreases CorrespondingIy. The acid adsorption by charcoal increases when the carbon dioxide complex decreases, obviously because the charcoal surface is then less acidic. While the acid was adsorbed reversibly, as it could be removed almost completely by repeated washings with water, the alkali was adsorbed irreversibly, as very little of it could be removed in this manner. The charcoal samples treated with oxygen (3 liters per hour) at 400’ for 16 hours were subjected to evacuation a t temperatures varying from 100’ to 1200°, starting with a fresh sample a t each temperature. The amounts of gases evolved, together with the amounts of barium hydroxide neutralized by the residual samples, after evacuation a t the various temperatures. are recorded in Table IV. The evolution of water and carbon dioxide starts on evacuation in the 300’ to 400’ temperature range and is almost complete a t 750’. Carbon monoxide is evolved (in appreciable amounts) only from sugar charcoal; its evolution commences a t 750’ and appears to be complete at about 1200’. The capacity of charcoal to react with alkali decreases with increase in the temperature of evacuation and the decrease a t a particular temperature is almost equivalent to the amount of carbon dioxide eliminated from the
1074
charcoal a t that temperature (columns 4 and 5, Table IV). The agreement is striking in the case of sugar charcoal, which was almost free from ash. I n the case of the other two samples, the amount of the carbon dioxide given out a t a particular temperature (column 5) is somewhat larger than the corresponding decrease in the amount of alkali neutralized (column 4). This small difference appears to be due to some extra amount of carbon dioxide formed by oxidation of charcoal at high temperature by the small amount of silica and other metallic oxide ash contained in the samples. It may, therefore, be concluded that base-adsorption capacity of activated charcoal treated with oxygen is almost entirely owing to that part of the chemisorbed oxygen which decomposes on degassing a t high temperatures to give carbon dioxide. The view of some workers ( 7 7 ) , that all or almost all of the chemisorbed oxygen is involved in the sorption of bases from aqueous solution, is not substantiated. This also explains why IVelier and Young (70) could not properly correlate sorption of bases by charcoal with total oxygen. The observations recorded here indicate the importance of determining the disposition of the chemisorbed oxygen in evaluating charcoals and in understanding their behavior toward bases and acids. literature Cited (1) Arnell, J. C., McDermot, H. L., J . Phys. Chem. 5 8 , 492 (1954). (2) King, A., J . Chem. Sac. 1936, 1688. (3) Ibid., 1937, 1489. (4) Kistler, S. S., Fischer, E. A., Freeman, I. R., J. Am. Chem. Sac. 65, 1909 (1943’1. Kdlthoff, I. M., Ibid., 54,4473 (1932). Kruyt, H. R., de Kadt, G. S., Kallaid 2.47, 44 (1929). Lepin, L., Physik. 2. Sowjetunion 4, 282 (1933). Schilov, N., Shatunovska, H., Z . Physik. Chem., A150, 31 (1930). Schilov. N.. Shatunovska. H.. Chmutov, K., ibid., A149, 21’1 (1’930). Weller, S.: Young, T. F., J . Am. Chem. Sac. 70,4155 (1948). Wilson, J. H., Bolam, T. R., J . CalloidSci. 5, 550 (1950).
RECEIVED for review October 25, 1957 ACCEPTEDJanuary 9, 1958
Cor rect ions Hydraulically Driven Pumps The article, “Hydraulically Driven Pumps,” by D. H. Newhall [IND.ENG. CHEM.49, 1949 (1957)l has several discrepancies. I n Figure 1, the first portion of the sub-
INDUSTRIAL A N D ENGINEERING CHEMISTRY
caption following “Neglecting friction,”
a and p should not be subscripts but Pa = A p The subcaption P should read:
Low pressure piston of area, A Figure 3 caption should read: This double-acting pump, including low pressure system, gives essentially a continuous uniform flow except for crossover of valves (Figure 8,B).
On page 1953. Figure 7 , A should be inserted before The scheme and B before The hydraulic circuit.
On page 1954, Figure 8,A and B should be inserted before Single-acting pump and Double-acting pump, respectively. I n Figure 9, the diagonal lines should have the following figures added to the end of their lines. DA 7 should have 10 DA 4 should have 5
A New High Pressure Technique In the article on “A New High Pressure Technique” by D. H. Newhall [IND.ENG. CHEW 49, 1991 (1957)J the caption to Figure 2 should read: Simple free piston gage, calibrating a Bourdon gage I n Figure 3, the arrow from C should not point to the packing ring but to the re-entrant cylinder just below it.
Analysis of Porous Thermal Insulating Materials I n the correspondence on this subject [IND.ENG. CHEM.49, 1936 (November 19 57) ] misprints have caused two parts to be confusing. The correct versions are given below. The first sentence in the note of D. A. de Vries should read : An article on the heat transfer in porous thermal insulating materials was published by Topper (70). The last par1 of L. Topper’s reply should read: Using his symbols, when E ~ / E O is 0.1, Equation 4 gives E / E O = 0.49, while de = 0.47. Vries’ Table I1 gives E , / Q (de Vries states that-differences between the formulas proposed by me and Topper’s formula increase with increasing difference of B ~ / E S from 1, in particular for el/eO > 1. The small difference in the sample given by Topper is therefore not a t all surprising.)
