The Reaction between Methane and Steam IN THE TEMPERATURE REGION 1000° TO l l O O o C. ALVIN S. GORDON1 Central Experiment S t a t i o n , Bureau of Mines, P i t t s b u r g h , Pa.
three thin-walled porcelain tubes were inserted into the reaction space. The gaseous products were analyzed by a mass spectrometer. In all experiments a considerable volume of gas was run through the apparatus before a sample was taken. DISCUSSlON
In Figures 1 to 4,the percentages of the principal hydrocarbon product gases (on a dry basis) are plotted against the percentage of methane decomposed, for the two steam-methane mixtures and over the temperature range (lOOOo to 1100" C.) studied. Firstorder specific reaction-rate constants were calculated as previously ( 3 ) :
YCzH4i
0.601A Steam /methane= I
I A Stearn/methane= I
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m >
A
K
0
z
0
5
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w
0 K
W
a 0 A
z 2 0
5 a
0
I
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I
8
Reactor Exit Gas us. Methane Decomposed
Temperature, 1033' C.
Pressure, 1 atmosphere
I
2 4 6 METHANE DECOMPOSED, PERCENT
Figure 2.
Figure 1. Reactor Exit Gas ws. Methane Decomposed Temperature, 1007" C.
I
Preseure, 1 atmosphere
INDUSTRIAL AND ENGINEERING CHEMISTRY
1858 I
nn
" "1
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I
I.m
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4 Steam/methane = I
I A
Vol. 44, No. 8 I
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Steam/methonea I
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.40
z
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a
0'
= 0.80 s 8
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I 0
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2 METHANE
Figure 3.
.
I 4
C2 Hs
.
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6 DECOMPOSED, PERCENT
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8
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.20-
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.
.
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Pressure, 1 atmosphere
= first-order specific reaction-rate constant, see. -1
V , = rate of gas entering the reactor, cu. em. per sec. V b =
a c_
Reactor Exit Gas us. Alethane Decomposed
Temperature, 1053' C.
where k
-
a
40
volume of reactor, cc.
g
= moles of gas produced per mole of decomposed
F
= fraction of methane decomposed
methane
The rate constants increased with P, indicating a reaction of less than first order. When 0.82% acetylene, one of the reaction products, was added to pure methane, the rate of disappearance of methane more than doubled. These data, in agreement with resulk of the preceding studies, show that methane n-as decomposed aut,ocatalytically in the presence of steam as well as in its absence. Acetylene is an efficient catalyst for methane decomposition, while ethylene is relatively ineffective as a catalyst (g). As shown in Figures 1 to 4, more acetylene and less ethylene were produced from the 5 to 1 steam-methane mixtures than from the 1 to 1 mixtures for the same amount of decomposition of methane. This statement applies to the analysis of the dry product gases. In the reactor, the concentration of acetylene was larger for the 1 to 1 mixtures in all these studies, and since acetylene catalysis of methane decomposition has previously been shown to be homogeneous ($?),the 1 to 1 mixtures catalytically decomposed a larger percentage of methane in the same time. At 1007" C., the rate of methane decomposition was the same for the 1 to 1 and 5 to 1 mixtures: a t higher temperatures, the rate was faster for the 1 to 1 mixture. The faster rates were probably the result of the acetylene catalysis. At 1007" C., the difference in the rates of methane decomposition from acetylene catalysis may have been compensated by surface decomposition of methane. The acetylene percentages were smallest at this temperature. I n addition, a homogeneous rate constant increases with temperature. Both these factors resulted in a comparatively small difference in the acetylene catalysis for the 1 to 1 and 5 to 1 mixtures a t this temperature. The 5 to 1 mixture may have kept the surface freer of carbon deposits which have been shown (3)to make a less efficient surface, and the sum of the surface catalysis and acetylene catalysis may have been about equal for the 1 to 1 and 5 to 1 mixtures.
As increased concentration of %ater did not increase the overall rate of decomposition of methane or affect significantly the concentrations of the intermediate products, water must have acted as an inert diluent until a carbonaceous deposit was formed on the ~ ~ a l of l s the reactor so that the steam-carbon reaction could take place. In addition, the percentage of these oxides in the product gases n a s a maximum (about 25% of the product gases) at the shortest time of contact and fell off a t longer contact times. This behavior is to be expected Iyith a layer of carbon on the surface. The rate of production of the oxides of carbon remains constant while the rate of decomposition of methane increases (autocatalysis).
TABLE I. EFFECT O F SURFACE-VOLUME RATIO O S FORMATION OF CARBOXMOSOXIDEA N D CARBOX DIOXIDE AT 1007" C . FROX A 1 : 1 STE.OI-METHANE MIXTURE C o n t a c t Time,
Seconds
co, %
co2, %
Surface-Volume
Ratio, C m . 7 9.52 9.52 2.47 2.47
Figures 1 to 4 show that the amount of ethane was essentially constant over the range of times of contact studied, starting with the shortest time that could be reliably attained. The percentages of ethylene and acetylene increased with time of contact. At 1007" C., no acetylene m-as formed from the 1 to 1 mixture until about 0.75% methane was decomposed. These data support the earlier observation ($?)that ethane is the first product of the decomposition of methane, the other two main hydrocarbon products being formed by dehydrogenation of ethane. Increasing the surface-volume ratio produced the same general effect, as noted previously ( 2 ) . As shown in Table I, the increase in the production of the oxides of carbon was not directly proportional to the increase of the surface-volume ratio. This probably means that the steam-
August 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
carbon reaction took place in the inlet and outlet tubes of the reaction vessel as well as in the vessel itself,
1859
ACKNOWLEDGMENT
The mass-spectrometer analyses were made under the supervision of R. A. Friedel.
CONCLUSIONS
LITERATURE CITED
The reaction between methane and steam in the temperature range 1000' to 1100" c- is probably a m k h a t i o n of the decomposition of methane and of the steam-carbon reaction. is formed " a Of the decomposition^ behaves as an inert gas.
(1) Gordon, A.
(2) Gordon, A.
s., INn.
ENtr. CHE~., 38, ,18-20
S., J. Am.
(1946).
Chem. SOC.,70, 395-401 (1948).
RECEIVBD for review October 27, 1951. ACCEPTED April 26, 1952. Contribution from the Synthetic Fuels Research Branch, Bureau of Mines, Bruceton, Pa.
Composition of Virgin, Thermal, and Catalytic Naphthas from Mid-continent Petroleum WILLIAM E. CADY, ROBERT F. MARSCHNER, AND WENDELL P. CROPPER Standard Oil Co. (Indiana), Whiting, Ind.
D
URING the past two decades, knowledge of the composition of the 5- to 10-carbon hydrocarbons in the lowest-boiling third of petroleum has become extensive. Techniques for the analysis of virgin naphthas have been developed to the point of being routine. The established techniques are somewhat less suitable for cracked naphthas because of the greater number and complexity of the hydrocarbons, especially olefins, that are present. Less progress has been made in determining the composition of the 10- to 20-carbon hydrocarbons in the middle-boiling third of petroleum. The task of analyzing any such mixture is colossal, and only a few n-alkanes and aromatics have been isolated and identified. Extensive analyses of these intermediate hydrocarbons must await better separation and identification methods, as well as the synthesis of many pure hydrocarbons and the determination of their physical properties. The analysis of the hydrocarbons with more than 20 carbons per molecule in the highest-boiling third of petroleum is a t present limited to characterization by general hydrocarbon types or to determination of per cent of carbon in rings and side chains. Not even the ring systems that predominate are known. Complete and specific analyses of these complex mixtures as such will never be accomplished. However, the analysis of the products of cracking of these complex mixtures may be helpful in extending the knowledge of their original composition. The considerable literature data on the composition of cracked
. 4
EXPERIMENTAL
The naphthas were produced from mid-continent stocks by commercial refinery operations. The virgin naphtha was the residue from a depropanizing column handling a sweetened composite of light naphthas and liquefied gases. The thermal naphtha was the distilled residue from a debutanizing tower handling a composite of naphthas absorbed from the gases produced by several thermal cracking units operating a t 480" C. The catalytic naphtha, likewise a debutanized absorption naphtha, was produced over natural ON COMPOSITION OF CRACKED N A P H T H A S TABLE I. LITERATURE catalyst at 470 O C. in a single fluid catalytic crackAuthor Naphtha Scope (Number of Carbon A t o m ) ing unit. Inspection data for these naphthas are Individual paraffinsOlefins (6 andand 7) paraffins (4 and5); Thermal Bates (1942) (') included in Table 11. The percentages of each Catalytic (fixed bed) Streiff and Rossini Catalytic (fixed bed and Aromatics (7 to 9) ; individual aromatics carbon number in each naphtha are included (1943) ($9) fluid) (fluid)" Starr et al. (1947) ($1) Catalytic I n ividual hydrocarbons (4 to 8 ) ; hyhere for convenience. A11 compositions in this drocarbon classes (9) paper are expressed as liquid volume per cent. Hydrocarbon classes (5 to 9) Rampton (1949) (18) Griswold and Walkey Catalytic (moving bed) Individual hydrocarbons (6) The scheme of fsactionation employed has been (1949) (18) Glasgow et az. (1949) Catalytic (fixed bed) Hydrocarbon classes (5 to 10); in&described (16). The first step was a large scale vidual paraffina and naphthenes (4) (5 to 7) fractionation of several gallons of each total Hydrocarbon classes (5 to 11) Wilson (1950) ($6) Thermal (coker) b naphtha. Distillate was recombined by carbon Individual hydrocarbons (4 to 8) Melpolder et al. (1952) Catalytio (fluid) ( i r) number into gallon blends. These were super0 From Tinsley East Texas Coastal, and Mirando petroleum. fractionated through more efficient columns into b From Santa Maria Valley'petroleum. small fractions with a boiling range of 2' C. er
p
*
naphthas derived from the heavier two-thirds of petroleum consist for the most part of isolated analyses. As may be seen from the variety of petroleums, cracking methods, and analytical treatments summarized in Table I, the results can be correlated only with difficulty. Bates et al. (3) compared East Texas virgin naphtha with the paraffinic portions of thermal and catalytic cracked naphthas from East Texas gas oil, but a comparison of extensive analyses of virgin and cracked naphthas derived from a single type of petroleum has been lacking. The present paper presents the compositions of the light naphthas obtained by three different processes from mid-continent petroleum. The.first of these was a virgin distillate representing the lightest 20% of the petroleum. The second was a cracked naphtha obtained by the thermal cracking of the heaviest 70%. The third was a cracked naphtha obtained by the catalytic cracking of the 30 to 70% fraction. These naphthas together account for almost half of the mid-continent crude petroleum studied.
