2586
INDUSTRIAL AND ENGINEERING CHEMISTRY LITERATURE CITED
(1) Bishop, J . 9., J . P h y s . Cham., 50, G (1946). ( 2 ) Davies, C . W., and Thomas, G . G., J . Chem. SOC.,1951, 2624. (3) Dippy, J. F. J., Chem. Rea., 25, 206 (1939). (4) Heilbron, I. M., "Dictionary of Organic Compounds," New York, Oxford University Press, 1934. ( 5 ) Kunin. R., and Myers, R. J., "Ion Exchange Resins," p. 59. S e w York, John Wiley & Sons, 1950. (6) Kunin, R., and Myers, R. J . , J . A m . Cham. sue., 69, 2874 (1947). (7) Lowen, W. X., Stocnner, R.W., hrgersinger, JT. J., Jr., Davidson, A. W., and Hnmo, D. N.. I b i d . , 7 3 , 2666 (1951).
Vol. 45, No. 11
(8) Peterson, S., and Jeffers, R. W., Ibid., 74, 1605 (1952). (9) Peterson, S., and Jeffers, R. W.,Trans. K e n t u c k y Acad. Sci., 13, 277 (1952). (10) Robinson, D. A., and Mills, G. F., ISD. EXG.CHFX.. 41, 221 (1949). (11) Willard, H. H., hlerritt, L. L., and Dean, J . A., "Instrumental Methods of Analysis," 2nd ed., p. 235, X e w York, D. Van PITostrandCo., 1951. HEcmwm for reviea- July 1, 1952. ACCEPTEDJuly 15, lQ.53. Based 011 the h1.S. thesis research of Elliler Gowen. Presented before the Division of Physical and Inorganic Themistry a t the 121st lIeeting of the AMERICAS CIIEMIOAL SOCIIITY, BuCfi'alo, 3.. Y .
Kinetics of Carbon Gasification by Steam J
MECHANISM OF INTERACTION OF LOW TEMPERATURE CHAR AND STEAMHYDROGEN MIXTURES AT 1600"F. 6. E. GORING', G. P. CURRAN, C. W. ZIELKE, ANI) EVERETT GORIN Research and Dsuelopment Division, Pittsburgh Consolidation Coal Co., Library, Pa.
D
IFFEREKTIAL rates of total gasification and methane formation, the determination of which was detailed in a prrvious article (S), have been correlated empirically. These corrrlations, which also furnish a quantitative basis for engineering design, serve as guides in the discussion of the char-steam kinetics mechanism. In addition to such new interpretive techniques based on the differential rate data, additional experimental data are presented on deviation from water gas shift equilibrium, methane formation, and carbon monoxide inhibition.
DEVELOPMENT OF CORRELATIONS
+
+
The diffeiential rates of total gasification (CO COS CH,) and methane formation a t 1600O F. are given in Table I with identifying values of the three independent variables of carbon burnoff, total pressure, hydrogen-steam ratio. The qualitative relationships between these rates and the three variables, based on various graphical representations, have been discussed. TOTAL GASIFICATION RATE. Fot any given burnoff, there ale right differential total gasification rates available for correlation: three rates, representing thi ee different hydrogen-steam ratios, at each of the 1- and 6-atin. pressure levels,and two ratP.5 a t 30atm. pressure. An examination of these rate data suggested an empirical method of correlation. I t was found that the total differential gasification rate may be correlated by an equation of the type:
R = Arm
Figure 1. Correlation Plot for Constant n in R = Arm
0 16
A microscopic concept, postulating a mobile surface oxygen complex, is presented to help classify the characteristics of the reaction given below. Several attempts were made to fit the rate data to correlating forms derived from mechanistic consiciwations. These attempts were unsuccessful and were abandoned since it was felt that uncertainties as to thc contributing mechanistic effects of ash constituents and, possibly, inhomogeneity of the basic carbon undermine the validity of a strictly theoretical approach. Therefore, recourse was had to empirical correlations which, although limited to certain definite ranges of the independent variables, form sound kinetic bases for design purposes and also furnish, indirectly, additional insight into the mechanism of char-steam interaction. Present address, Standard Oil Co. of Indiana. Whiting, Ind.
(1)
A and n are both functions of burnoff and hydrogen-steam ratio, but are independent of the pressure in the range of 1 to 30 atm. Figure 1 illustrates the functional relationship between n and the hydrogen-steam ratio with the burnoff as a parameter. Figure
I PARAMETER OF PERCENT C GASIFIED
Figure 2.
\,so
Correlation Plot for Constant A in R = AT^
1
INDUSTRIAL AND ENGINEERING CHEMISTRY
November 1953
2 illustrates the corresponding relationship between A and the hydrogen-steam ratio. Conversely, cross plots of A and n as a function of burnoff were derived from Figures 1 and 2, but are omitted from this article. A test of the correlation is given in Figure 3, which shows the close reproduction of the experimental values of R by values calculated from the curves of Figures 6 and 7 . The correlation has limitations with respect t o the ranges of total pressure and hydrogen-steam ratio. Extrapolation beyond the ranges of these variables employed in obtaining the experimental data might be unreliable. 200
100 -80 U
50
3 40
D
0
E 30 0
2 20 IO 8 6
5
IO
20 30 4050
100
200
R (experimental) Figure 3. Test of Correlation for R
ever, permits calculation of the effects on the rates of singly varying either PH,O or PH,,thus providing the required information for mechanistic interpretations. This information is presented in graphical form (Figures 7 t o 10). None of the calculated curves shown on these plots extends beyond either of the limiting conditions of hydrogen-steam ratio (0.1 t o 1.0) or total pressure (1 to 30 atm.) which characterize the empirical correlations. Each parametric condition is represented by a conjugate pair of curves, portraying burnoffs of 10 and 40%. I n most cases the conditions were chosen so that each curve includes an experimentally measured differential point, indicated on the plots. FORMATION RATEOF CARBON MONOXIDE PLUS CARBON DIOXIDE. Figure 7 shows the effect of P H ~ on O R - RCH, a t three separate values of PH,. As the curves are on log-log coordinates, their rectangular slope at any point represents the order of R R C Hwith ~ respect to PH,Oa t that point. Most of the curves show a region of constant slope, which gradually diminishes in value as PH,O increases. The value of the constant slopes for all the curves is about 1.5, and roughly independent of both burnoff and PH,. The independence of this maximum order is interesting, but the most striking characteristic is its magnitude, as most previous investigators have reported a fractional order between 0 and 0.5 with respect t o steam (1,4 , 6) and those who correlated their data with a Langmuir-type rate expression (2,6 , 8) imply a maximum possible order of unity. The powerful inhibiting effect of hydrogen on the rate of formation of carbon oxides is illustrated graphically in Figure 8, where R - Roar is plotted on rectangular coordinates versus P Hat ~B constant value of PH,o. These curves also illustrate the increasing inhibiting effect of hydrogen at the higher burnoffs.
METHANEFORMATION RATE. It was found t h a t the differential methane formation rates could be correlated by a n equation of the same form used for the total gasification rate: R C H ~ D (T)”
*
~
DISCUSSIONS ON CHAR-STEAM INTERACTION MECHANISMS
i
15
(2)
Here again D and m are functions of burnoff and hydrogensteam ratio. The functional relationships between D and m and hydrogen-steam ratio with carbon burnoff as the parameter are shown in Figures 4 and 5. Figure 6 shows that the values of RCH,calculated from the correlation compare favorably with the experimentally determined values. Although the correlation of R C H is ~ not a s satisfying a s the analogous correlation for R, it is felt that strict adherence to its regional limitations will yield satisfactory interpolated values. These limitations are, of course, the same as those characterizing the correlation for R-namely, hydrogen-steam ratio of 0.1 to 1.0 and total pressure of 1 to 30 atm.
The following discussions are, at this stage, of more academic than practical interest, but should facilitate the planning of future experimental programs in carbon-steam kinetics. They contribute t o a better quantitative understanding of the gasification reaction mechanisms than has been possible in the past, mainly because of a more comprehensive representation of the pertinent variables, especially pressure. Deductions Based on Empirical Correlations. The term “mechanism,” as applied to the present discussion, may be generally defined as the separate effects of PH,O and PE, on the rates of formation of carbon monoxide plus carbon dioxide or methaneLe., R - RCH,or RcH,-from char. The experiments to obtain the differential rates were conducted (8)by systematically varying the hydrogen-steam ratio and total pressure. This means, of course, that PH,O and P Hwere ~ varied simultaneously rather than systematically, thus making it difficult t o obtain any insight into mechanism by direct examination of the measured differential rates. Use of the empirical correlations developed above, how-
2587
PARAMETER OF PERCENT
c GASIFIED
IO
E
09 08
IO
30 50
07 06 05 01
02
03
04 0 5 0.6 0 8
IO
HZ/H20 Figure 4.
Correlation Plot for Constant rn in
RCH,= D(+ METHANE FORMATION RATE. Figure 9 shows the effect of PHZO on RCH,a t two values of P H ~ The . order of R C H with ~ is in the range 0.3 to 0.6, with the highest orders respect to PH,O occurring at the higher values of P Hand/or ~ burnoff. The most significant insight into the mechanism of methane formation is provided by Figure 10, portraying the role of hydrogen. At low burnoffs, RCH,is of low positive fractional order with respect t o hydrogen, while a t high burnoffs the order varies from zero t o negative, becoming increasingly negative with increasing PH,. The above facts and other d a t a discussed below might be interpreted as indicating that methane may be formed by two independent reactions: (1) by direct hydrogenation of the char and (2) by some process involving steam. Reaction 1 is accelerated by hydrogen, while reaction 2 is inhibited by hydrogen. Some new experimental information is presented in Table I, giving the rate of formation of methane by reaction 1 using pure hydrogen as the reactant gas. Some new data are also presented for the 50% hydrogen-600fo steam series a t 30 atm. It is seen that the relative methane formation rates with pure hydrogen and hydrogen-steam mixtures at the same partial pressure of
2588
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 45, No. 11
TABLE I. DIFFERENTIAL RATESO F TOTAL GASIFICATION AND METHANE FORhfATIOii
10% Hz-QO% HzO
0.99 55 60 63 65 67 70 1.0 2.2 3.3 4.0 4.2 0.99 33 39 35 29 26 24 2.5 2.5 3.3 3.7 3.6 0.99 15.6 12.6 10.4 8.4 7.5 7.0 1.1 2.5 2.7 2.3 1.5 6.08 122 122 122 120 112 105 6.5 11.6 15.3 17.3 17.8 6.09 80 74 68 60 53 45 6.03 34 28 23 19 16 14 12.9 11.2 10.0 8.9 8.3 29.8 148 128 112 100 90 80 42 39 36 33 31 1.01 29.9 70 58 48 40 34 31 39 34 30 26 23 1.5 1.50 .. .. .. ... ... ... 1.6 0.5 '-100% H* 7.5 7.50 ... ... 9.4 4.6 100% Hz 15.0 15.1 1 2 . 8 10.8 i4:s ii:2 100% Hz a Differential methane formation rates not determinable in this series, as no direct measurement for CHI was available a t time rum were made. 0.11
1
4.2 3.2
0 30
1.03 0.12 0.30 1.01 0.32
. . . . . . . . . . . . . . .
.... ..
. . I
hydrogen is a strong function of the partial pressure of hydrogen and of the burnoff. The relative rate increases rapidly from less than 5 % of the total methane rate at 1.5-atm. hydrogen pressure and 10% burnoff t o nearly 50% of the total rate at a hydrogen partial pressure of 15 atm. and 40 to 50% burnoff.
...
..... . . . . . . .
17:30
...
8.0 29 22
... ...
10.4
This behavior is just what one would expect if all the methane were formed by direct hydrogenation of the char. It was shown above, however, that the rate of hydrogenation of char with pure hydrogen is only a small fraction of the methane rate observed with hydrogen-steam mixtures, particularly when the total pressure is relatively low. It must be concluded, therefore, t h a t a t low pressures the bulk of the methane is formed by direct interaction of carbon and steam and t h a t the presence of hydrogen is necessary t o obtain a high ratio of
RCH~ -
R - RcH,' Distinction of Primary Products. The primary products of
I.OLPARAMETER OF PERCENT C GASIFIED-/ 0
u 0.2
0.4
0.6
0.8
1.0
1.2
the char-steam system may be defined as those gas phase components which are produced by interaction of the two reactants alone. Therefore, in view of the discussion given in the previous section, methane does not appear to be a primary product of this system, as hydrogen as well as steam is required for its formation. 50 40
30
Figure 5. Correlation Plot for Constant D in RCH,= D ( T ) ~
.
RCH In the R -RCH,
Deductions Based on Behavior of RatioA
previous qualitative discussion of the relationships between the differential gasification rates and the three independent variables (S),R and RCH,were treated separately, and no attempt was *madeto inspect the characteristics of a parameter combining the tm-o rates. The quantity RcH
, which represents the ratio
R -R C H ~
of the differential rate of methane formation t o the differential rate of carbon monoxide and carbon dioxide formation, exhibits properties which furnish an additional insight into the mechanism of methane formation.
RCH, Figure 11 shows plotted points of the ratio (calculated R -RCH, ~
from the values in Table I ) versus hydrogen-steam, with carbon burnoff a s the parameter a t a total pressure of 1 atm. It is seen t h a t the plot shows a general decrease in the ratio of RcH' for all burnoffs with decreasing hydrogen-steam ratio.
R- RCH,
Similar plots, which are not shown, were constructed a t the higher pressure levels and showed the same general behavior. It is seen from Figure 11 that for almost every pair or trio of constant burnoff points a curve may be defined which passes smoothly through the origin. These curves are not drawn, however, because their defining points are too few t o justify the common terminal behavior a t HZ/HZO = 0 on the basis of graphical construction alone.
It is clear, however, that if
RCH, is not R -RCH,
zero when the reactant is pure steam, it is a t least very smalI.
(Lo4 3 2 0
R C H (experimental) ~ Figure 6.
Test of Correlation for RCH,
It thus remains to decide whether both or only one of the carbon oxides should be classified as primary products. This question is resolvable bv considering - the behavior of two parameters new to this discussion; the water gas shift ratio exit gas compositions from the various kinetics runs, and the differential ratio of COt/CO (designated a s [ C O ~ / C O ] W 0 ) . The recourse t o direct experimental observations (integral data reported here for the first time), represented by the former parameter, is a departure from the exc]usive use of differential data which have served as the basis for discussion up to this point. DEVIATION FROM WATERGASSHIFTEQUILIBRIUM. Figure 12 shows the water gas shift ratio calculated from the series of three runs made at 1 atm. pressure with a feed gas of 25% hydrogen75% steam, plotted as a function of burnoff with initial weight of carbon in the bed as parameter. The salient features of these data are:
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
November 1953
I
0.2 03 0.5
20 30 50
IO
100
PH~O ATMOSPHERES Figure 7 . Calculated Values of R - RCH,VS. P H @ with Parameter of PH*(Atmospheres)
1. The exit gases show a drastic deviation from water gas shift equilibrium. 2. The deviation is universally on the carbon monoxide&am side of equilibrium, 3. The deviation increases with increasing burnoff, 4. The deviation becomes lesa, at any given burnoff, with increasing bed weight-i.e., longer contact time.
These four features are characteristic of every series of runs made in this study. It is clear from ( I ) , (8), and ( 4 ) that the rate of the water gas shift reaction is slow, and is certainly not of a higher order of magnitude then the gasification rates. This generalization, which is supported by the data of Hinshelwood and coworkers (0, is a necessary step in the argument developed below. It is also clear, from 2, that carbon monoxide is a primary product. BEHAVIOR OF THE RATIO [ C O ~ / C O ] ~ V 0. The quantity (CO2/CO)w o is the ratio of the differential rates of formation of the specified components and is a function only of the intensive variables of temperature, pressure, hydrogen-steam ratio, and carbon burnoff. It may be evaluated by means of the graphical
extrapolation technique (S),utilizing experimentally observed values of CO&O. The validity of using the extrapolation technique for this purpose may be established by an argument similar t o that presented originally (3) in connection with the determination of differential rates of total gasification and methane formation from experimentally observed integral gasification rates. Figure 13 illustrates application of the extrapolation technique t o the ratio of carbon dioxide to carbon monoxide for a typical series of three runs, made a t 1 atm. pressure and a n inlet gas of 60% hydrogen-50% steam. The curves are selected cross plots, at burnoffs a t 10, 20, and 30%, obtained from a primary plot of CO2/CO ratio versus burqoff with bed weight as parameter. The values of ( C 0 2 / C O ) ~ 0, obtained from the ordinate intercepts of the Figure 13 curves, are listed in Table 11, along with the results of similar extrapolations made for six other series of runs a t 1600' F. The most significant characteristic of the values given in Table I1 is a general one-namely, that they are almost all nonzero. This means that the incipient rate of appearance of both oxides is of the same order of magnitude over wide ranges of the three independent variables, and that the formation of carbon dioxide results from either one or the other of the following classical alternatives: (1) Carbon dioxide is formed bv the direct interaction of steam and carbon and is thus a primary product like carbon monoxide, or (2) carbon dioxide is not a primary product but arises from consecutive reactions, involving water gas shifting of the primary carbon monoxide.
-
80
-
-
2589
30 20
IO
* I
0
E
5
3 2
0.1
I I I I IIIII 0.2 0 3 0.5 I
I I I II IIII 2 3 5 10
I I I Ij 20 50
ATMOSPHERES Figure 9. Calculated Values of RCH4 us. PH& with Parameter of P H (Atmospheres) ~ 90
c
50 40
30
20
0
IO
I2 5 4
3 2
0
1
2
3
4
5
6
7
8
PH, ATMOSPHERES Figure 8. Auxiliary Plot of R - Rcn, vs. PH,at 5.4 Atmospheres Steam
' X
I 01
0.2 0.3
0.6
I
2
3
5
IO
PH, ATMOSPHERES Figure 10. Calculated Values of RCH4 US. PHt with Parameter of P H (Atmospheres) ~
2590
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 45, No. 11
PERCENT C GASIFIED 0.4
A 00032 0 00058
0.7
0.3
0.2
05
04
0.I
03
0
0.2
0.4.
0.6
0.8
1.0
1.2 0.2
Figure 11. RcH*/(R - RCHJ us. Hz/H20 a t I Atmosphere
01
However, the applicability of alternative 2 would require that the rate of t.he water gas shift reaction be several orders of magnitude greater than t.he carbon gasification reaction; otherxvise the secondarily formed carbon dioxide could not contribute t o the ratio (CO?/CO)w 0 . As it has been sholvn (above) that the rates of the water gas shift and gasification reactions in the charsteam system are of the same order of magnitude, it follows that alternative 2 is not applicable and that carbon dioxide is a primary product. POSSIBLE FORMATION MECHANISJI FOR CARBON OXIDES. The distinction of the primary product,s has little value in itself, unless this knowledge leads to a n improved concept of the carbonsteam interaction mechanism. As the evolution of such a generalized concept Tvould require considerably more experimental evidence than is available a t present, the discussion below is limited to broad outlines of t,he basic ideas. The existence of a carbon-oxygen complex on carbon surfaces undergoing gasification by steam, carbon dioxide, or oxygen has been experimentally demonstrated, both directly ( 7 ) and indirectly (6). Quantitative removal of this complex from the carbon surface may be effected by the action of carbon monoxide or hydrogen, yielding, respectively, carbon dioxide or steam. The mechanism discussed here is based on t'he assumption that the oxygen complex possesses anot,her characteristic property-that the oxygen atoms retained on the surface are capable of random movement thereon. This concept of mobility of adsorbed or chemisorbed substances has been applied t,o kinetic discussions of various other heterogeneous systems. Its application to the carbon-steam system permits postulation of a reasonable mechanism for the primary formation of carbon dioxide-by the collision, on the carbon surface, of two mobile oxygen atoms. The following three equations would then describe carbon oxide farmat.ion:
0
L
-
"p!: Gas
Composition
HAO% Hz-50% Hz-75% H2-75% Hn-90% Hz-90% Hr50%
Ha0 HzO HzO
sure, Atm. 1
6
1
Hz0
30
HzO Hz0
6
Hz0
1
30
Per Cent Carbon Burned 10 20 30 40 50 Observed Ratios
30 40 Calculated Ratios
0 . 4 2 0 . 2 6 0.08 0.05 0.03 0.03 0 . 2 2 0.09 0.06 0 . 0 4 0:03 0 . 0 5 0 . 0 3 0 . 6 2 0.37 0.18 0 . 1 1 0.10 0.12 0.09 1.05 0.50 0.30 0.30 0.30 0.30 0 . 2 1 0.43 0.34 0 . 2 6 0.19 0.15 0 . 2 6 0 . 2 1 1.05 0.60 0.40 0.30 0 . 2 5 0.40 0.30 , . 0.00 0.00 0.00 0.00 0 . 0 7 0.04
IO
20
30
40
50
60
PERCENT CARBON GASIFIED Figure 12. Deviation of Exit Gases from Water Gas Shift Equilibrium for 25% Hydrogen-75% Steam Series a t 1 Atmosphere
-
c ( 0 ) + c ( 0 ) coz + c
(6)
It is possible oii the basis of this mechanism, assuming that methane formation is a completely independent reaction, t o predict by calculation the ratio of carbon dioxide t o carbon monoxide. On the basis of the above assuniptions and the additional assumption of a uniform surface, one can obtain Equation 7 for the predicted ratio by the standard methods of kinetic analysis.
(7) This equation involves only one arbitrary constant-4k~/k$,which can be determined from one experimental point. The value of CO?/CO a t other experimental conditions may then he calculated. The value. of CO,/CO in this may are given in Table I1 a t two values of the burnoff-namely, 30 and 40%. It is seen that a fairly close fit is obtained between the calculated and observed values. The theory predicts that at constant burnoff the CO,/CO ratio should decr?aie whenever (I? - R c H ~de) 0.8
I PERCENT C GASIFIED
0
20
40
60
80
100
INSTANTANEOUS WEIGHT OF C IN LB. ATOMS x 104
BED,
Figure 13. Extrapolation Plot for Carbon DioxideCarbon Monoxide Ratio i n 5 0 q Hydrogen-500Jo ~ Steam Series at 1 Atmosphere
2591
INDUSTRIAL AND ENGINEERING CHEMISTRY
November 1953
1
*
INLET PARTIAL PRESSURE. ATMOSPHERES
H1
0.50 4.54
X
0
"TAL
0.49
c0 o- c 0 q
I
0.18 0.13 0.45 BED WEIGHT FOR BOTH RUNS,
0.012LB. ATOMS C
4
10
20
30
40
0-
50
Figure 15.
Figure 14. Effect of Carbon Monoxide on Carbon Oxide Formation Rate
creases, The only gross violation of this predicted trend is the zero value of the CO,/CO ratio a t 50% hydrogen-50% steam and 30 atm. The above exception may be related to the high methane formation rate under the above conditions, which vitiates the assumption of independence of the two rates R ROH,and RcH,. Although the above mechanism was useful in interpreting the observed CO,/CO ratio, it was not found applicable in correlating R - R C Hitself ~ as function of the variables of the system. Carbon Monoxide Inhibition. The data of Hinshelwood et al. showed that carbon monoxide had no measurable inhibiting effect on the carbon-steam interaction rate. It was felt, however, that the present investigation should include at least a cursory check of this point, since the type of carbon being studied is different from that used by the previous workers. The results support their conclusion, but also revealed an important corollary phenomenon. The pertinent data were obtained from a single gasification experiment, using a feed gas containing carbon monoxide. In order to ensure control of the carbon monoxide partial pressure entering the bed, a four-component feed gas was used at a water gas shift ratio corresponding to 1600' F. equilibrium (see Figures 14 and 15 for values of component pressures). Otherwise the metered concentrations would have been altered by water gas shifting on the stainless steel surfaces of the heated feed lines upstream of the fluid bed. The partial pressures of hydrogen and steam in this feed gas were made to approximate, as closely as possible. the feed gas for. a routine kinetics run. The initial weight of carbon in the bed was also duplicated. Therefore, comparisons of the specific integral rates of carbon monoxide plus carbon dioxide formation and the specific integral methane formation rates from the two runs gave a semiquantitative insight into the effect of carbon monoxide on char-steam kinetics. Figures 14 and 16 show these comparisons. The scattering of the data points, in Figure 14, for the carbon monoxide addition run is explainable by the relative lack of precision in measuring carbon monoxide plus carbon dioxide formation rates for this run, since these rates had to be calculated from the difference between the quantities of these components entering and leaving the bed. Because of this scattering, no attempt was made t o draw a curve through the carbon monoxide addition run points. It i s clear, however, that over the depicted burnoff range of 0 to 40% the points fell close to the curve for the routine hydrogen-steam run. It is concluded, therefore, that carbon monoxide has negligible effect on carbon monoxide plus carbon dioxide formation rate. There is no data-scattering problem in Figure 15, as, since methane was not a feed gas component, calculation of methane
-
L
#
10
20
30
40
50
PER CENT CARBON GAS1FI ED
PERCENT CARBON GASIFIED
Effect of Carbon Monoxide on Methane Formation Rate
formation did not require taking the difference between similar numbers. The comparative curves give clear evidence of carbon monoxide inhibition of the methane formation rate. The effect is relatively small, although measurable, up to about 20% burnoff. Beyond this point, however, the inhibition becomes increasingly greater and the trends of the curves imply the existence of even more pronounced effects a t burnoffs outside the range of the data. NOMENCLATURE
lb. atoms C lb. atoms C minute lb. moles CH R C H=~ differential methane formation, Ib. atomR minute = total pressure, atmospheres = rate constant for Reaction 6, l/minute = rate constant for Reaction 5 , I/minute
R
= total differential gasification rate,
LITERATURE CITED
Chang, T. H., Sc. D. thesis in chemical engineering, Massachusetts Institute of Technology, 1950. Gadsby, J., Hinshelwood, C. N., and Sykes, K. W., Proc. R o g . Soc. London, 187,129-51 (1946). Goring, G. E., Curran, G . P., Tarbox, R. P., and Gorin, E., IND.ENG.CHEM., 44,1057 (1952). Graham, H. S., Sc. D. thesis in chemical engineering, Massachusetts Institute of Technology, 1947. Key, A., Gas Research Board, Publ. 40 (July 1948). Long, F. J., and Sykes, K. W., Proc. Roy. SOC. (London), 193A, 377-99 (1948). Marsh, J. F., Inst. Gas. Engrs.. Bull. 393 (November 1951). Warner, B. R., J . Am. Chem. Soc., 66,1306-9 (1944). RECEIVED for review October 24, 1952. ACCEPTED June 17, 1953. Presented before t h e Division of Gas and Fuel Chemistry, AMERICAN CHEMMICAL SOCIETY, Pittsburgh, Pa., April 1953.
