INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
1562
TABLE VII. DIMETHYLANILISE VAPOR COXCEXTRATIONS FOR ACETIC~CID-\~r~4TER-DI>lETHYLANILIh’E
Water in Liquid, Wt. %“
Q
(Smoothed d a t a , 1 atmosphere) Dimethylaniline i n Vapor, Wt. c/o Dimethylaniline in Liquid, Wt. % 10 20 30 50 70 3.5 5.5 10.3 22.0 4.2 6.8 15.0 9.6 5.4 8.3 14.9 10.1 9.8 6.7 12.7 16.0 8.4 11.5 17.1 14 8 18.0 10.3 13.3 16.6 12.3 15.3 17.9 18.8 17.2 14.7 18.7 19.5 17.2 19.2 18.8 19.9 19.1 19.5 19.5 19.9 19.5 19 5 19.5 20.0 19.6 19.6 20.0 19.6 19.6 19.6 20.0 19.6 19.7 19.7 20.0 19.7 19.7 19.7 19.7 20.1 19.8 20.2 19.8 19.8 19.8 19.8 20.3 19.8 19.9 19.9 20.4 19.9 20.0 20.0 20.6 20 0
BO 42.5 27.5 22.8 20.7 20.0 19.9 19.9 19.8 19.9 19.9 20.1 20.2 20.5 20.8 21.1 21.5 21.9 22.3 22.8
Dimethylaniline-free basis.
temperature (g), and interpolation can be emploged for intermediate temperatures. DISCUSSION
Figure 2 shows that the addition of dimethylaniline produces the expected effect-aiding the separation of acetic acid and water by increasing the water-acetic acid relative volatility. There is a marked effect on the volatility a t the lowest dimethylaniline concentration studied (10 weight yo in the liquid phase). This improvement occurs also at the water-rich end, where it is most needed. Further increase in dimethylaniline content t o about 50
Vol. 45, No. 7
weight % in the liquid continues to produce a steady improvement in the acid-rich end, but practically no additional change in the water-rich region. It is only a t concentrations of 70 to 90 weight % dimethylaniline that further significant effect is obtained in the water-rich region. It would appear from the data obtained that dimethylaniline in relatively smallquantities could be used as an aid in the separation of acetic acid and water by distillation. Further work on a continuously operated distillation column, using dimethylaniline as a combined extractive-azeotropic agent, would be desirable in order to check on factors of importance in a commercial installation (capacity, efficiency, corrosion, etc.). The results of such studies would provide a basis for a thorough economic evaluation of the separation process. LITERATURE CITED
(1) Cornell, L. W., and JIontonna, R. E., IND. ENG.CHEM.,25,1331 (1933). (2) Garwin, L., and Haddad, P. O., Anal. Chem., 25, 435 (1953). (3) Garwin, L., and Hutchison, K. E., IND.ESG. CHEX, 42, 727 (1950). (4) Gilmont, R., A n d . Chem., 23, 157 (1951). (5) Gilmont, R . , and Othmer, D. F., IND.ESG. CHEM.,36, 1061 (1944). (6) Hands, C. H. G., and Xorman, W-.S.,Trans. I n s t . Chem. Engrs. (London),23, 76 (1945). (7) Horsley, L. H., Anal. Chem., 19, 508 (1947). (8) LBcat, M., “L’AaBotropisme,”Brussels, Lamartin, 1918. (9) Othmer, D. F., Anal. Chem., 20, 763 (1948). (10) Othmer, D. F., Silvis, S. J., and Spiel, A., ISD.ERG.CHEM., 44, 1864 (1952). (11) Shreve, R. N., “Chemical Process Industries,” pp. 682-8. S e w York, hlcGraw-Hill Book Co., 1945. RECEIVEDfor review September 29, 1952. ACCEPTED March 10, 1953. Presented before t h e Division of Industrial and Engineering Chemistry at t h e 123rd Meeting of t h e AMERICAN CHEMICAL SOCIETY, Los Angeles. Calif.
Equilibrium in the Steam Reforming of Natural Gas H. A. DIRKSEN -4ND C. H. RIESZl Institute of Gas Technology, Chicago, ZZl.
I T H the advent of natural gas to new and expanded markets, catalytic steam reforming of natural gas has assumed an exceptionally important role in gas manufacture. As part of a broad research program, an exploratory evaluation of carriers and promoters for nickel catalysts was made. in which some 180 tests were completed ( 3 , 4). These results could be compared accurately and on a consistent basis in several ways. A value for the conversion in a particular test could be obtained in simple fashion by the following method.
tion of 100% as the maximum conversion also provides a slight inaccuracy a t high conversion levels. To eliminate these various sources of errors, a method described by Sebastian and Riesz (6) was modified for use in this application. This method is based on the direct comparison of the volumes of the gas produced in the test and of the gas formed a t equilibrium under the test conditions:
yoconversion (by gas analysis)
where expansion is defined as the increase in gaseous volume, excluding steam, per volume of natural gas entering the system, or
1‘ o u t ~
Vi,
=
(yoCH, in outlet gas)
(yoequivalent CH, in feed gas)
100 (1)
This calculation introduced the possibility of multiplying any errors in analyzing the gas by any inconsistencies or errors in measurement of gaseous volumes (VI, and Vout). The assump1 Present address, Armour Research Foundation of Illinois Institute of Technology, Chicago, 111.
% equilibrium conversion
Expansion =
expansion,,t,,i expansion esuii. 100
= _____
A volume volume,,t~.
(2)
(3)
The equilibrium method is inherently exact and involves one less experimental determination, because it is not necessary to obtain the gas analysis. Since Sabatier and Senderens ( 5 ) first studied the methanesteam reaction, many others, including Neumann and Jacob ( 1 ) and Pease and Chesebro, ( 2 )have evaluated the equilibrium reactions. In the case of the natural gas-steam reaction, a more com-
. INDUSTRIAL AND ENGINEERING CHEMISTRY
ruiy 1953 v)
1563
4.0
9
TABLE I. EQUILIBRIUM CONSTANTS FOR WATERGAS SHIFTA N D METHANE-STEAM REACTION (7)
1160 1340 1520 1700 1880
2.204 1.374 0.9444 0.6966 0.5434
1.306 26.56 313.3 2,470 14,280
METHOD OF CALCULATION
A material balance is set up to relate reactants and products. Partial pressures are assumed to be proportional to molar concentrations. The following nomenclature was used:
3
s
I
Substances Involved in Reaction
Figure 1. Variation of Equilibrium Expansion with Temperature for Chicago Natural Gas
C Hn
0 Ha0
Molar Quantities Initial Final a b
.
W
co coa plex system is involved which requires computation of the equilibrium composition for individual gases. A short-cut procedure of calculation is described in sufficient detail for general application. GENERAL CONSIDERATIONS
In establishing the reactions of various components, some observations of a broad nature are necessary. Consideration of the equilibrium constants established carbon monoxide, carbon dioxide, hydrogen, methane, and water as the stable products at the conditions of reforming. The standard free energy of formation of ethane at 900' K. is +21,000 calories per mole, indicating an equilibrium constant approximating 10-6 for the reaction. Stabilities of the higher paraffins are even less, decreasing with chain length, and require no further consideration. Similarly, the formation of olefins is negligible for all practical purposes. The equilibrium constants of formation of carbon monoxide and carbon dioxide from carbon and oxygen are 3.195 X lo8and 6.290 X 10'8 a t 1500" K. Thus, occurrence of free oxygen a t equilibrium in this temperature range is prohibited. The chemical reactions occurring in a mixture of natural gas and steam may, therefore, be represented by the following equations.
These do not cover all possibilities, but illustrate the extremely large number of possible mechanisms. In the tests as completed it was found that no hydrocarbon other than methane remained in the gas, except possibly in the case of poor catalysts. These were of minor interest. The deposition of carbon was found to be negligible under the experimental conditions. Consideration of the simple equations CO CH,
+ HzO COz + Hz + HzO e CO + 3H2 F&
m
0
Y 5
CH4 Na
a
;z
On this basis, the carbon, hydrogen, and oxygen balances are:
c
a=x+2l+z
Hz
b
0
c=w+2x+y
=
m
+ w + 22
(16) (17)
(18)
Figure 2. Conversion of Chicago Natural Gas b y Equilibrium and by Gas Analysis Calculation
From Reactions 4 and 8, the following relationships are derived on the assumption that partial pressures are proportional to molar concentrations a t low pressures:
(4) (8)
includes all components and satisfies all requirements to be found at complete equilibrium. The actual constants used are given in Table I.
where K, and K8 are the equilibrium constants and N is the total number of moles of the equilibrium products.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1564
Rearranging Equations 16 t o 20, this system of equations can be solved in terms of z and y:
Kq
K,
- Z(U - z - y ) ( - a y2(-2a
+ b + d + 22 + 2 ~ ) '
+ b - c + 4z + 3y)Z
(21)
VOl. 45, No. 7
Figure 2. Here, experimental data (3,4)have been used to determine the actual per cent conversion of the methane equivalent of Chicago natural gas by means of Equation 2 for a large variety of conditions (abscissa). Agreement with the per cent of equilibrium conversion (ordinate) is good, as shown by the 45' line
Y
% EQUILIBRIUM CONVERSION, EOUATION 2
Figure 3.
Water-Gas Shift Reaction
through the points, and indicates that natural gas conversion proceeded with the equilibrium established throughout the range, 20
In the solution of the problem, appropriate pressure and temperature conditions are selected for values arbitrarily assigned to y, the carbon monoxide partial pressure in the equilibrium mixture. The corresponding values of the equilibrium constants are inserted and Equation 22 is solved for z,the carbon dioxide partial pretrsure. These values are altered until Equation 21 is satisfied; after that the solutions for various components are found by referring to Equations 16, 17, and 18. An alternative graphical method of solution is also possible. Equations 19 and 20 can each be rearranged to express a solution of zin terms of y, The two equations can then be plotted and the intersection of the two curves will furnish the proper values of z and y t o satisfy the equilibrium conditions. Again, substitution of these values in Equations 16, 17, and 18 will provide values for m,w, and z.
TABLE 111. EQUILIBRIUM COSCENTRATIOXS IS STEAM REFORMING OF CHICAGO SATURAL Gas Nole Ratio H,O/Natl. Gas
Thefequilibrium compositions a t unit pressure for Chicago natural gas (Table 11) admixed with 1.1, 1.2, 1.3, 1.4, 1.5, and 1.6 moles of steam per mole of natural gas have been calculated for 1160°, 1340°, 1520°, 1700", and 1880" F. The results are presented in Table 111; the calculations indicated no carbon deposition a t equilibrium under any of the stated conditions. Figure 1 demonstrates the influence of temperature and ratio of steam to natural gas on the calculated equilibrium expansion values for Chicago natural gas. A corroboration of the validity of the equilibrium conversion calculation is demonstrated in
Composition, %
coz Hz co
CHI N 2
Expansion, a V / r o l u m e Composition, ";
coi H2
CO CHI Expansion, 1 V / r olurne
S 2
Expansion, 3V,'volun1e
1.2
1.1
8.4 66.5 12.5 10.0 2.6 2.40
8.0 65.7 12.6 11.0 2.7
7.7 64.7 12.9 11.9 2.8
7.2 63.7 13.2 13.0 2.9
6.8 62.6 13.5 14.2 3.0
6.3 61.3 13.7
2.32
2.23
2.14
2.04
15.6
3.1 1.95
5.3 72.8 18.3 1.5 2.1 3.18
4.8 72.6 18.7 1.8 2.1 3.15
4.3 72.3 19.2 2.1 2.1 3.10
3.8 71.5 19.9 2.5 2.3 3.01
3.3 70.8 20.5 3.0 2.4 2.92
2.8 70.0 20.9 3.9 2.4 2.80
3.2 73.2 21.2 0.2 2.2 3.27
2.7 73.1 21.8 0.2 2.2
3 25
2.3 72.9 22.3 0.3 2.2
1.9 72.7 22.7 0.5 2.2
1.4 72.3 23.4 0.7 2.2
0.9
71.8 24.0 1.0 2.3
3 22
3 18
3.12
3.05
1.8 2.2 72.9 73.1 22.6 23.1 0.03 0.06 2.1 2.1
1.4 72.8 23.6 0.07 2.1
1.0 72.6 24.2 0.09 2.1
72.5 24.8 0.12 2.1
3.18
3.15
3.13
1700' F. Composition, COS H2
70
co
Expansion, AV/volume
80.0 6.0 3.0 1.0 10.0
1.3
1520' F. Composition. % ' CO? HI CO CHI
TABLE 11. ANALYSISOF CHICAGO NATURAL GAS %
1.4
1340' F.
CHI N2
(Average of mass spectrometer determinations)
1.5
1160O F.
x2
DISCUSSION OF RESULTS
1.6
2.6 73.2 22.1 0.02 2.1 3.26
3.23
3.20
0.5
1880' F. Composition, % CO? H2
co
2.2 73.0 22.7
N2
2.1
CHI Expansion, AV/volume
0.0
3.22
1.8 73.0 23.1 O.O+ 2.1
1.6 72.9 23.5 O.O+ 2.1
3.22
3.20
1.1 72.8 24.0
o.o+ 2.1
3.1'8
0.8 72.7 24.4 O.O+ 2.1
3.17
0.4 72.6 24.9 O.O+
2.1
3.15
1565
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
July 1953
reaction is extremely large, as shown in Figure 4. Thus, the water gas shift reaction, CO HzO CO2 Hz, is indicated to be the fastest of the reactions occurring, whereas the methane decomposition reaction, CH, HQO+ CO 3H2, is the ratecontrolling step. Conversions close to 10070 w e r e o b t a i n e d with many nickel-periclase catalysts and with promoted nickel catalysts on various carriers at high reaction rates (3000 hours-1, space velocity) (3, 4).
IO000
*
1000
* bj
100 I
I
I
..
.....:. .
.. !. *'
I
+
*.
.-p.
+
+
+
' ,
ACKNOWLEDGMENT
. ....,:
I
..
I
I
0.01
'
..
I
I
I
I
I
I
The work described was conducted in Project CPR-7 as part of the PAR plan under t h e sponsorship of the Gas Production R e s e a r c h Committee of the American G a s A s s o c i a t i o n , whose permission to publish this work is gratefully acknowledged. The authors are indebted to J. J. s. Sebastian, Bureau of Mines, Morgantown, W. Va., for suggesting the alternative approach t o the g r a p h i c a l m e t h o d of solution. LITERATURE CITED
(1) Neumann, B., and EXPERIMENTAL DATA FROM LITERATURE REFERENCES 3a4 Jacob, K., Z . Elektrochem., 30, 557 (1924). (2) Pease, R. N., and 0.001 Chesebro, P . R., J . Am. Chem. SOC., % E O U l L l B R l U M CONVERSION, EOUATION ( 2 ) 50, 1464 (1928). (3) Riesz, C. H., DirkFigure 4. Methanation Reaction sen, H. A., and P l e t i c k a , W. J., A m e r i c a n Gas Association Production and Chemical Conference, New York, to 100%. Random scattering of the data indicates that Equations May 26-29, 1952. 9, 11, 13, and 15 are not initial reaction steps, since this would (4) Riesz, C. H., Dirksen, H. A., and Pleticka, W. J., Inst. Gas Techcause displacement to the right of the conversion values obnology, Research Bull. 20 (October 1952). served by gas analysis in Figure 2. (5) Sabatier, P., and Senderens, J. B., Compt. Tend., 134, 514 (1902). The reasonably constant mass law values (shown by the or(6) Sebastian, J. J. S., and Riesz, C. H., IND.ENG.CHEM.,43, 860 dinate in Figure 3 ) determined that the water gas shift equilib(1951). rium was maintained throughout the experimental tests. The (7) Wagman, D. D., Kilpatrick, J. E., Taylor, W. J., Pitzer, K. S., scattering of values below the theoretical equilibrium constant in and Rossini, F. D . , Natl. Bur. Standards, Reseakch Paper the range, 20 to 60% equilibrium conversion, may be caused by inRP1634 (February 1945).
4
accuracies in temperature control of the catalyst bed in deviating from 1700' F. a t high input rates. However, in striking contrast, the departure from equilibrium attributable to the methane-steam
RECBIVED for review October 27, 1952. ACCEPTED April 11, 1963. Presented before the Division of Gas and Fuel Chemistry at the 122nd MeetCHEMICAL SOCIETY, Atlantic City, Pi. J. ing of the AMERICAN
