October 1955
INDUSTRIAL AND ENGINEERING CHEMISTRY
(13) Flumiani, G., 2. Elektrochem., 32, 221 (1926). (14) Gee, G., Trans. Faraday Soc., 34, 712 (1923). (15) Gregg, R. A., and Mayo, F. R., J. Am. Chem. SOC.,75, 3530 (1953). (16) Hayes, R. F.,U. S. Patent 2,460,105 (Jan. 25, 1949). (17) Jeu, K.,and Alyea, H. N., J . Am. Chem. SOC.,55, 575 (1933). (18) Joris, G. G., and Jungers, J. C., Bull. SOC. chim. Belg., 47, 135 (1938). (19) Jungers, J. C., and Taylor, H. S., J. Chem. Phys., 4, 94 (1936). (20) Jungers, J. C.,and Yeddanopalli, L. M., Trans. Faraday Soc., 36, 483 (1940). (21) Kharasch, M. S.,and Dannley, R. L., J. Org. Chem., 10, 406 (1945). (22) Kharasch, M. S., Jensen, E. V., and Urry, W. H., J. Am. Chem. SOC.,69, 1100 (1947). (23) Kharasch, M. S., Reinmuth, O., and Urry, W. H., Ibid., 69, 1105 (1947). (24) Mathews, J. H., and Williamson, R. V., Ibid., 45, 2575 (1923). (25) Mayo, F. R., General Electric Co., private communication. (26) Melville, H. W.,Trans. Faraday SOC.,32, 258 (1936). (27) Mosher; H. S.,and Dykstra, J. S., 126th Meeting ACS, New York, Abstracts of Papers, p. 55. (28) Olson, A. R.,and Meyers, C. H., J. Am. Chem. SOC.,48, 389 (1926). (29) Ibid., 49, 3131 (1927). (30) Oster, G., Nature, 173, 300 (1954). (31) Oster, G., Phot. Eng., 4, 173 (1953). (32) Owens, J. S., Heerema, J. H., and Stanton, G. W., U. S. Patent 2,344,781 (March 21, 1944).
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(33) Pietrusza, E.W., Sommer, L. H., and Whitmore, F. C., J . Am. Chem. Soc., 70, 484 (1948). (34) Pummerer, R., and Kehlen, H., Ber., 66, 1107 (1933). (35) Redington, L.E., J. Polymer Sci., 3, 503 (1948). (36) Renfrew, M. M., U. S. Patent 2,448,828 (Sept. 7, 1948). (37) Richards, L. M., Ibid., 2,460,105 (Jan. 25, 1949). (38) Robertson, A.,and Waters, W. A., J. Chem. SOC.,1947, p. 492. (39) Roedel, M.J., U. S. Patent 2,484,529 (Oct. 11, 1949). (40) Rogers, D. C., Ibid., 2,480,752(Aug. 30, 1949). (41) Rueggberg, W. H. C., Chernack, J., Rose, I. M., and Reid, E. E., J . Am. Chem. Soc., 70, 2292 (1948). (42) Reuggberg, W. H. C., Cook, W. A., and Reid, E. E., J . Org. Chem., 13, 110 (1948). (43) Sachs, C. S.,and Bond, J., U. S. Patent 2,505,067 (April 25, 1950). (44) Ibid., 2,505,068. (45) Ibid., 2,579,095 (Dec. 18, 1951). (46)Ibid., 2,641,576 (June 9, 1953). (47) Taylor, H.S., and Emeleus, H. S., J. Am. Chem. Soc., 53, 562 (1931). (48) Taylor, H.S., and Hill, D. G.,Ibid., 51, 2922 (1929). (49) Taylor, H. S., and Jungers, J. C., Trans. Faraday SOC.,33, 1353 (1937). (50) Toul, F.,Collection Czechoslov. Chem. Communs., 6, 163 (1934). (51) Vauehan. W. E.. and Rust. F. F.. J. Ora. Chem., 7. 472 (1942). (52) WaGzonek, S., Nelson, M. F., and TheGn, P. J., i.Am.'Chem. SOC.,73, 2806 (1951). RECEIVEDfor review November 8, 1954. ACCEPTEDJune 13,1955. Contribution 1934,California Institute of Technology.
Catalytic Effects of Cobalt, Iron, Nickel, and Vanadium Oxides on Steam Carbon Reaction W. M. TUDDENHAM'
AND
GEORGE RICHARD HILL
Department of Fuel Technology, University of Utah, Salt Lake City, Utah
D
URING the past 33 years the catalytic effect of metal oxides on the steam-carbon reaction has been investigated b y a number of individuals ( 1 , 8,6-9, 11-1 6). I n general all the results have been in qualitative agreement although some disagreement has existed as t o the effects of iron and aluminum oxides (6, 11, 18, 16). Iron was judged as a good catalyst by a number of workers (7, 18-14) but Taylor and Neville (16) and Long and Sykes ( 1 1 ) judged i t t o b e ineffective in increasing carbon gasification. Of the other catalysts chosen for this study cobalt was found effective b y Kroger and Melhorn (7, 8) when mixed with potassium carbonate and cupric oxide or lithium oxide and potassium oxide, and nickel was found effective b y Kroger and Melhorn (7) and b y Milner, Spivey, and Cobb (IS). While vanadium would be expected t o show catalytic activity i t was not specifically studied in any of the aforementioned work. B y and large previous experimenters have worked with relatively high catalyst concentrations and have given only fragmentary information as to temperature dependence. The purpose of this investigation was t o compare carefully the catal-ytic effects of cobalt, iron, nickel, and vanadium oxides on the steamcarbon reaction in a temperature range from the lowest temperatures practical to make measurements with the apparatus t o its upper limit, 1140' C. Catalyst concentrations as low as 0.013'% are effective in increasing the reactivity of the carbon. Some results that have a bearing on the kinetics of the system are reported. 1 Present address. Western Division Research, Kennecott Copper Corp., Salt Lake City, Utah.
EXPERIMENTAL
Apparatus and Procedure. The primary features and the arrangement of t h e apparatus are shown schematically in Figure 1. The steam generator, A , was heated b y t h e constant temperature bath, B, t o produce steam at the desired pressure. The nonsubmerged portions of the steam generator were maintained at a n elevated temperature b y means of heating coils. The steam then passed into the preheating chamber, C, and thence through the jet, D, impinging on the hot carbon, E, which was clamped in water cooled copper contacts. The temperature of the carbon was controlled b y a variable transformer and was measured with a n optical pyrometer. Some of the lower temperatures were measured with a thermocouple inserted through the sample. The reaction chamber was immersed in a circulating water bath. The excess steam was then frozen in the cold trap, F, which was cooled with a dry icepetroleum ether freezing mixture. The products of the reaction were collected in the weather balloon inside the bell jar, G, the pressure in the balloon being measured b y a Dubrovin gage. Test runs made b y passing steam over cold carbon and through the freezing chamber showed no measureable pressure build u p in G due t o steam alone. Before each run the preheating and reaction chamber as well as the balloon, bell jar, and glass tubing were evacuated to a few tenths of a micron of mercury pressure as measured b y a thermocouple gage. At the completion of a run the weather balloon was collapsed, and the gas was forced into an evacuated sample bulb. Residual gas was transferred b y means of the Toepler pump. The gas in
,
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the sample bulb was analyzed for carbon monoxide and carbon dioxide using a Fisher Precision gas analysis unit, I n performing these experiments, since the conditions for a critical orifice (2) were fulfilled, the steam velocity was controlled by the pressure in the steam generator. (To
Toepler pump and sample
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samples were heated to 200" to 400" C. with evacuation to aid in evaporation of the remaining water. After evacuation was complete the temperature was raised to 11W0C. for 25 minutes after which time it was lowered for 5 minutes, The sample was then ready for use. Estimates of the amounts deposited were obtained by ashing the samples. Measurement of the ash contents showed that the amount of bulb catalyst deposited was directly proportional to the concentration of the solution. The ash contents of Type B samples which had been treated with 0.1M solutions of the cobalt, iron, or nickel nitrates were about o.14y0. Treatment with 0.025M ammonium metavanadate produce samples with ash contents of about o.0370. GENERAL RESULTS
The basic data obtained from an experimental run were the collecting pressure a t any given time and the analysis of the collected gases for carbon monoxide and carbon dioxide. For the purpose of analyzing the data, the net reactions represented by Equations 1, 2, and 3 were assumed to be the major contributors to reaction.
To wcuum gc1
w
uurn
To power supply
Figure 1.
Schematic diagram of apparatus
A = Steamgenerator B = Constant temperature bath C = Preheating chamber
-
D = Jet
CO
E &bon sample F = Cold trap
G
=
Bell jar containing balloon
Three velocities were used in these experiments. Expressed as the number of moles of steam per second issuing from the orifice, 1.0 X 10-8 sq. cm., the values were 7.2 X 10-6 moles per second, 2.6 X 10-6 moles per second, and 0.52 X 1 0 - b moles per second, respectively. The linear velocities were of the order of lo4 cm. per second. The two graphitized carbons used in these experiments were AGKS spectroscopic carbon electrodes, hereafter called Type A, and AGKSP special spectroscopic graphite electrodes, hereafter called Type B, supplied by National Carbon Co. The special spectroscopic graphite electrodes use petroleum coke flour as a raw material, and the spectroscopic carbon electrodes use a lamp black derived from coal tar oil. These raw materials are mixed with a coal tar pitch binder which carbonized during baking. The electrodes attained full graphitizing temperatures approaching 3000" C. for a sufficiently long time t o achieve the maximum crystallization possible a t that temperature with the respective starting materials (17). X-ray diffraction patterns indicated that the degrees of graphitization were similar v for the two sample types. The ash content of a typical sample of Type B carbon is 0.005% as compared with 0.02% for a typical Type A carbon sample. Spectrographic examination of the Type A material show calcium, iron, magnesium, and silicon as the major impurities while aluminum, boron, chromium, copper, and manganese are present in trace amounts. Emission lines of these impurities are either missing or only faintly visible in spectrograms of the Type B carbon. I n preparing the samples for use, 38-mm. lengths of 6-mm. carbon rod were held in a jig and two sides were carefully flattened by shaving them with a clean knife edge. These samples were then either used or treated with catalysts immediately. The catalysts were applied by soaking Type B samples in solutions of ammonium metavanadate, cobaltous nitrate, ferric nitrate, or nickelous nitrate for two or more days. Excess solution waa removed by blotting with filter paper jugt before use. The
+ HzO COz + HP c + coz % 2co
(2)
(3)
Under the& circumstances the rate of gasification is proportional to the sum of the partial pressures of carbon monoxide and carbon dioxide [P(co + co,)]. The rate of gasification of carbon may be represented by plotting P(c0 + coI) versus time. I.O
SPECIMENS
8
.
1
0.8
-1
-
c
0.6
h(
8 0
a-
0.4
0.2
0 0
40
I20
80 TIME
160
200
IMIN.1
Figure 2. Gasification curves of untreated carbon samples at 1800" c. 0
s Type A carbon 0 = Type B carbon
I n Figure 2, such plots are given for Type A and Type B carbon samples a t 1080O C. The rates of gasification so measured were not constant during the run but increased with time. I n order to determine the gasification rate a t any given time it was necessary to draw a tangent to the curve a t the point in question and to determine the slope of the tangent. Inasmuch as the com-
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October 1955
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pilations of data obtained in this study are quite voluminous, only the general results are recorded, and the reader is referred to the original work for a more detailed picture. RESULTS WITH UNTREATED SAMPLES
Rate Law. I n nearly all runs with both Type A and Type B samples, the gasification rate is a linear function of P ( c 0 + ~ 0 % ) to 0.5 mm. of Hg pressure or more. This linearity is demonstrated in Figure 3. If one considers that as the reaction proceed:, the surface roughness, and thus the number of readily attacked sites, increases, it is possible to relate the rate a t which P ( c 0 + coz) changes to the rate a t which the concentration of active centera increases. Thus, if c = the number of active sites a t any given time in thb area affected by the steam jet, c =
where a bp p b
(a
+ bp)
(4)
I
140
120 ~1
~
/
~
~
160 ~
.
Gasification pressure versus gasification rate for Type B carbon
Dashed lines indicate deviations from linearity beyond P ( c O + 001) = 0.5
80 -
Assuming that in the beginning, under a given set of conditions, the rate of gasification is proportional to the concentration of active sites
+ bp)
1080' C. 3 X 10-6 moles steam/sec. 1140O C. 0.5 X 10-6 moles steam/sec.
=
= 1140' C. 3 X 10-b moles steam/sec.
(5)
Aceording to Equation 5, a plot of dp/dt versus p should result in a straight line with slope equal to kb, b times the specific rate constant, and intercept equal to ka. This corresponds with the results observed for the untreated samples of Type A and Type B carbon, and has been interpreted to mean that the gasification rate of the untreated samples was first order with respect t o the concentration of available active sites in the presence of excess carbon. Table I contains values of ka, kb, and b / a obtained for the two types of carbon a t various temperatures. It was not possible to get absolute values of a or b from the experimental data.
Table I.
100
lo4
I
d i
Figure 3.
the original number of sites available additional number formed by gasification = pressure of the carbon gasified, P(CO+ coz) = proportionality constant
kc = k ( a
80
00
40
dP(C0 + COZ)
= =
9 = dt
20
C
TREATED GRAPHITE SAMPLES
Rate Curves. I n Figure 4 are shown curves of P(co + cos) versus time for treated graphite samples a t 1100' C. The gasification of the sample treated with ammonium metavanadate (NHIVO~)proceeded a t a constant rate whereas with iron, cobalt, and nickel, the rates increased with time in a manner somewhat similar to that of the untreated Type B carbon. Further investigation showed that the changes in gasification rate exhibited by the treated samples were not linear functions OfP(C0
+ cod.
Experimental Values of kb, ka, and b / a for Untreated Carbon Samples Temperature,
Carbon A A A A A A A B
B
c.
1110"
1095 1080 1065 1050 1035 1020 1140 1110
kb 0.027 0.050 0.026 0.023 0.017 0.012
Ra
2.9 7.5 4.9 6.0 3.2 3.5
0.0091
0.018 0.014 0.011
B 1080 This run was apparently out of control.
b/ a
0.0012 0.0012 0.0011
2.5 15 12 10 I
1 0
0
1
I
"
2
A
6
I
8 riME
HEATS O F ACTIVATION
If one assumes that the b term is not temperature dependent, the slope of a plot of log k b / T versus 1 / T should be equal to
- AH"/2.303R Analyzing the experimental data in this manner for the two types of carbon gave heats of activation of 72 kcal. per mole for the Type A and 36 kcal. per mole for the Type B carbon. Carbon Monoxide: Carbon Dioxide Ratio. The level of carbon dioxide in the products obtained using Type A samples was generally higher than was obtained with Type B samples. Previous workers ( 4 )have pointed out that the reaction
CO
+ HzO F? COz + H B
(2) is catalyzed by impurities such as were present in relatively large amounts in the Type A carbon samples.
' IO
'
I
iz
iviN
16
l
>6
18
LC
I
Figure 4. Gasification curves of treated Type B samples a t 1100' C. 1 = Iron treated, 0.14% ash 2 = Cobalt treated. 0.14% ash 3 Nickel treated, 0.14% ash 4 = Vanadium treated, 0.3% ash
-
I n experimental runs a t lower temperatures, both iron and vanadium treated samples showed evidence of having been poisoned, probably by adsorption of one or more of the reaction products. The effect is shown in Figure 5 for vanadium. No such phenomenon was noted for cobalt and nickel. Judging from the observations of previous investigators, the adsorbed product was probably hydrogen. This poisoning effect was shown to be reversible by repeating the experiments with the same sample after re-evacuating the apparatus while heating the carbon t o the temperature in question.
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Rate Law. The order of reaction with respect t o the amount of carbon gasified is zero for vanadium-treated samples up t o those pressures a t which poisoning sets in. For samples treated with cobalt, 'iron, or nickel, the order appears t o change in an undetermined manner, tending toward zero order as reaction proceeds in a number of cases.
"O
Vol. 41, No, 10
Table 111. Carbon Monoxide: Carbon Dioxide Values with Treated and Untreated Type B Carbon Samples
%
CO: C o t Values Average Range
Temperature Range, O C.
Treatment Untreated 0.1M Co(NO8): 0 1M Fe NO:): 0:1M NifNO:)r 0.02M NHtVO:
1080-1140 555-1100 590-1100 580-1100 975-1100
57 39 240 4 94
-
14-91 236-62 78-512
