Catalytic J
Dehydrogenation of Gaseous Paraffins
FIGURE 1. U. 0. P. CATALYTIC DEHYDROGENATION PLANTAT RIVERSIDE
T
HE dehydrogenation of the paraffin gases t o the corresponding olefins is a problem of fundamental importance to the oil industry, because the technical problem of efficiently converting gaseous olefins into liquid motor fuel has been solved within recent years by both catalytic (“solid phosphoric”, cold and hot sulfuric acids) and purely thermal processes (8, 7 ) . Therefore, a process for the conversion of paraffins into olefins would put to good use all the paraffin gases except methane. These gases are available in enormous quantities from such sources as natural gas and gasoline, petroleum distillation gas, gas from the cracking processes, coke-oven gas, and refinery gasoline. According to one estimate (4, 6 ) , in this country alone over 500 billion cubic feet of the following are potentially available every year: ethane, about 370 billion; propane, about 120 billion; butanes, about 70 billion. A catalytic dehydrogenation process has been developed ,for converting normal and isobutane, propane, and ethane to
the corresponding olefins. The first announcement of these successful results was made in 1935 (3).
Principle of Process and Plant The process consists briefly in passing the preheated paraffin gases over a suitable catalyst. The outgoing gases contain olefins and hydrogen besides the unreacted original paraffins. The olefins are polymerized or used in alkylation, the hydrogen is separated, and the unreacted original paraffins are recycled. The plant consists essentially of a furnace, banks of catalyst reactors, and a hydrogen separation unit. Automatic controls alternate the flow of paraffin gases first through the furnace and one section of reactors and then through another, while the catalyst is being regenerated in the first section. The regeneration consists in passing automatically controlled amounts of air mixed with combustion gases or steam, to burn off the carbon on the catalyst a t a moderate combustion 268
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INDUSTRIAL AND ENGINEERING CHEMISTRY
temperature (usually below 900" C.). A feature of the process is that the length of operating cycle is short, usually of the order of one hour. Illustrations of the U. 0. P. experimental plant a t Riverside with a daily capacity of about 100,000 cubic feet of butane are given in Figure 1.
TABLE I. COMPARISON OF CATALYTIC A N D THERMAL TREATMENT TemD. Pressure 0 C; ho./sq. cm.
Contact Time
Conversion of Charm -
Conon. of ChH8 in Exit Gas
Bec.
%
%
Production Rate of CcHs" Vel.
Catalvtic for n-Butane 1 2 39 30 152 600 1 1 30 24 230 600 1 0.5 20 17 310 Thermal (6)for n-Butane 600 1 77 50 3.6 0.74 600 7 36 50 3.5 7.7 650 1 11 50 3.0 3.5 650 7 9 50 4.0 40.0 Catalytic tor Isobutane 600 1 2 41 31 156 600 1 1 31 25 239 600 1 0.6 20 17 310 Thermal (6) for Isobutane 50 18 24.1 650 1 12 650 7 12 50 14 14.5 5 Volumes of olefin (at 25' C. and 750 mm.) per volume of reaction space per hour.
The advantages of the catalytic process over purely thermal cracking are the much larger over-all yields of the corresponding olefins and a much higher reaction velocity. This is illustrated for normal and isobutane in Figure 2 and Table I. The thermal results were obtained from an article by Egloff, Thomas, and Linn (6). Even though the thermal results may be somewhat improved by the use of higher pressures and temperatures, the nonselectivity of the thermal reaction always causes them to lag behind those obtained with catalysts.
269
methane, and other degradation products, has been almost completely suppressed. Let us discuss chromium as a specific example. Chromic oxide was introduced in organic dehydrogenation catalysis in its early days by Ipatieff (11) and later by Sabatier (17). If, was subsequently studied in greater detail, by Lazier (18). Frey and Huppke (8) employed it in their well-known thermodynamic studies mentioned below.. However, pure chromic oxide is not suitable as a catalyst for temperatures above 400-450" C.; it rapidly loses its activity as a result of crystallization of the amorphous oxide. This loss of activity takes place in times of the order of an hour a t the temperature required for commercial operation. The deposition of the chromic oxide on major portions of y-alumina [prepared by dehydrating crystalline aluminum o-hydroxide, l ~ l ( O H ) ~allows l, the preparation of stable and very active catalysts. Other substances with a similar stable surface may be substituted for alumina. For many purposes, concentrations of less than 10 mole per cent chromic oxide are sufficient. One method of preparing the catalyst consists in impregnating or mixing activated alumina with chromium solutions. Grade-A activated alumina of the Aluminum Corporation of America is recommended. Impregnating solutions are suitably prepared by dissolving chromium trioxide (CrOJ, chromic nitrate [Cr(K03)3], or ammonium chromate [(KH4)2Cr04]or dichromate [(NH&CrpOl] in water. The quantity of solution for a given batch of carrier is adjusted in such a wag as to be completely soaked up, without leaving any drainings. The concentration of chromium compounds in these solutions is in turn adjusted to give the desired concentration of chromium oxide on the carrier. After impregnation the catalyst is dried with stirring and then heated to decompose the chromium compound, in a reducing atmosphere if desired. All of the above mentioned
Catalysts I
in
A suitable catalyst for an economic process must fulfill the following requirements: 1. It must have the ability to s lit off hydrogen selectioely without cleavage of the carbon-to-carton bond. This is a severe requirement since the energies of the bonds (Pauling's values) Linkape C-H
c-c
Electron volts 3.79 2.54
Cal./mol. 87,300 58,600
involved, favor the carbon-to-carbon cleavage. I t is intensified by the fact that high temperatures of the order of 500-750" C. must be used, since at lower temperatures the equilibrium lies almost completely on the araffin side (Table 11, A and B ) and the reaction velocities are Pow 2. It must be ea& regenerated when fouled by a carbon deposit. 3. It must have a useful life of many hundreds of hours, 4. It must be low priced. These requirements are fulfilled by selected solid catalysts containing minor molar proportions of the oxides of the transition metals of the VI (e. g., chromium and molybdenum), V (e. g., vanadium), and IV (e. g., titanium and cerium) groups of the periodic system, supported on carriers of relatively low catalytic activity (e. g., aluminum and magnesium oxides). These catalysts are highly selective and direct the conversion in accordance with the general dehydrogenation equation, CnHzn + z +CnHzn
+ HZ
under proper operating conditions. The scission of the carbon-to-carbon bond, leading to the formation of carbon,
FIGURE2. COMPARISON OF CATALYTIC ASD THERMAL TREATMENTS
INDUSTRIAL AND ENGINEERING CHEMISTRY
270
VOL. 32, XO, 2
of accuracy (19, 16). The present experimental findings are in substantial agreement with these calculations. The calculated equilibrium lines are compared with experimental results in Figure 3. Table I1 gives the equilibrium constants ( A ) , a or the degree of dehydrogenation ( B ) ,and the composition of the reaction gas (C) as functions of temperature. The calculations of Table I1 were based on the procedures of Kassel (19) and Pitzer (16); the latter assumes a hindrance in the free rotation of the carbon-carbon bond, and his results are in better agreement with those based on the third law; as Table I1 shows, the discrepancies are not important for our present purposes.
Results
I
I /DO
/WO
/zoo /OOO/TaK
-
1300
Under proper dehydrogenating conditions, over-all conversions of paraffins to the corresponding olefins of 90-95 per cent of the theoretical, or even above, are obtained. At the same time a n equal volume of practically pure (over 90 per cent) hydrogen gas, suitable for catalytic hydrogenations, is obtained as a side product. I n addition to gas analysis and physica1 properties, such as molecular weight, boiling point, and index of refraction ( 9 ) , the olefins were identified and their purity was investigated by means of chemical derivatives as follows :
I
/WO
FIGURE 3. COMPARISOX OF CALCULATED EQUILIBRIUM LINESAND EXPERIMENTAL DATA chromium compounds leave after reduction a residue of chromic oxide. For commercial use the catalyst is usually pelleted, pilled, or shaped into any convenient form.
Thermodynamics According to empirical chemical knowledge, paraffins are dehydrogenated at high temperatures whereas olefins combine with hydrogen a t low temperatures. In other words, the equilibrium of the reaction, increase in temp. CnHm+a
decrease in temp.
CLLn f Hz
The ethylene, from ethane, was converted into ethylene dibromide which proved to be Dure. The propylene, -from propane, gave pure propylene dibromide, free from propadiene or propyne derivatives. From n-butane an equilibrium mixture of a-butylene and cisand trans-p-butylene was obtained. On bromination, a mixture of pure 1,a-dibromo- and 2,3-dibromobutanes was obtained, with only traces, if any, of isobutylene dibromide. Near the maximum of the butane curve 1,3-butadiene appeared, in small amounts, at first, which gradually increased with contact time. The isobutylene from isobutane was identified and tested for purity by conversion into ( a ) the dibromide and ( b ) t e r t butyl alcohol (mixed melting point, --24" '2.). 3
m
(1)
is shifted toward the right by temperature increase. I n order to obtain industrially important concentrations of olefins, the temperatures employed must be rather high (above 500" C.).
I n several thermodynamic studies (8, 14, 16) approximate equilibrium constants
have been determined. The values of different workers are only in fair agreement with one another; furthermore, the range of conditions investigated covers only a part of the industrially important region. However, in recent years the physical theories of molecular structure have made important advances, and it is now possible to calculate from spectroscopic data the energy contents of the simple paraffins and olefins with a rather high degree
ITS D E P E N D E N C E ON SPACE VELOCITY, TEMPERATURE, AND AGE O F CbTALYST. I n view of the high activity of the catalysts used, the comp o s i t i o n of t h e catalyzed gas is dependent on the contact time or space velocity used. The over-all picture a t a specified temperature and pressure is as follows in the case of butanes or propane: At very
b 'sl ?
k
5
k5
93
CONTAC
+
r
TIME IN SPCONDS
FIGURE 4. YIELDOF ~ B U T Y L E N E B FROM
BUTANE
1
FEBRUARY, 1940
IKDUSTRIAL ,4ND ENGINEERING CHEMISTRY
271
by the following analyses of gases obtained from propane a t 600" C. and 1.0 atmosphere pressure, a t different contact times: -Compn. 2.7 59 20 20.5 0.0 0.0 0.5
Contact Time, Sec. Propane Propylene Hydrogen Ethylene Ethane Methane
I
~
5 - p ; -CONTACT
FIGURE 5.
%--
17.5 32 14 27.5
36 6
9 29 1 29 19
13.5
REGFNER.+T/ON w/ru ~ ~ R b ~ ~ AND y ~ A HYDRpGENl , R
@
3
of Exit Gas, Vol.
8.9 41 21 24 0.3 5 3
a
A +
,
-
All,"
ROP*E&~;
-
II
i
77M€ /ff S€C
YIELD OF ISOBUTYLENE FROM
ISOBUTANE I
high space velocities (or very short contact times) the ingoing paraffin passes through unaffected. As the space velocity is decreased (or a s , t h e contact time is prolonged), a straight dehydrogenation without any appreciable side reaction begins. It steadily increases over a certain range, then slows down and reaches a maximum. I n the vicinity of this point secondary reactions begin. The olefins are now present in high concentrations and are also accessible t o further dehydrogenation, until at very low space velocities this process reaches a natural end in carbdn and hydrogen. Before that limit is reached, methane, ethylene, and ethane appear as cleavage products of the original paraffin. This is illustrated
I
2
T I U P ?N HO:RS
___
V = % M€THAN€ ~~~
F g O M S6TART7&PE%/ODS
'
FIGURE6. CONSTANCY OF CATALYST ACTIVITY AND C o w POSITION OF CATALYZED GAS
The constancy of the catalyst activity and the composition of the catalyzed gas during two cycles a t set conditions is illustrated in Figure 6. A section corresponding to 10 hours, with an air regeneration after 4.75 hours, is shown from a life test with Dropane a t a catalyst temperature of 600" C., 1.00 airnosphere pressure, and a contact time of 2.65 seconds. Under proper operating conditions the performance of the catalyst remains practically undiminished for over 1000 hours. TABLE 11. DATAON THE DEHYDROGENATION REACTION AS FUNCTIONS OF TEMPERATURE (18, 16) The amount of dehydrogenation or the acTemp. -Ethane----Propane--Butan-1sobutanetivity is practically constant after short con' K. (7. Kassel Pitrer Kassel Pitrer Kassel Pitzer Kassel Pitrer secutive oxidations of the carbon. The percentage A. Equilibrium Constants, Kp = ' c ( ~ ! ~ ~i n~Atm. " , of hydrogen (20.5) practically equals that of ~. .. . propylene (19.5), as it should in straight dehy673 400 0,000105 0.000105 0.00133 0.00210 0.00325 0.0075 0.00410 0.0093 700 427 0.00025 0.000275 0.00338 0.00501 0.00817 0.0170 0.0100 0.0209 drogenation. A trace of methane-0.5-1 per 723 450 0.00066 0.00059 0.0074 0.0102 0.0170 0.033 0.0205 0.040 0.0315 0.040 0.0725 0.118 0.0860 0.145 773 500 0.00325 0.0026 cent-and a trace of carbon on the catalyst 0.120 0.142 823 550 0.0132 0.010 0.270 0.375 0.305 0.455 (which is evidenced by the slight excess of 0.940 1.25 0.388 0.421 0.840 1.08 873 600 0.0465 0.033 2.55 3.05 1.08 1.12 2.34 2.70 923 650 0.143 0.094 hydrogen) are due to secondary reactions. The 6.20 6.70 2.72 2.63 5.80 6.10 973 700 0.382 0.240 4.28 4.07 1000 727 0.64 0.383 9.25 9.20 10.00 10.1 rest of the gas-i. e., 60 volume per cent-is R. a = Degree of Dehydrogenation at 1 Atrn. unreacted propane, which on recycling gives an 0.0580 0.0706 0.0900 0.0129 0.0995 0.143 700 427 0.0158 0.0166 over-all yield of over 95 per cent propylene. 0,1748 0.1961 0.2600 0,3249 0,2814 0,3559 773 500 0,0569 0.0509 0.5287 0.5443 0.6757 0.7206 0.6961 0.7454 873 600 0.2108 0.1787 The process and the catalysts used are covered 1000 727 0.625 0.900 0.896 0.950 0.954 0.953 0.950 0.526 by patents (U. S. 2,167,650, etc.) and pending apC. z % Olefins = yo Hydrogen in Equilibrium Mixture 1% Paraffins = (100 - 22)%1 plications in the United States and in foreign 700 427 1.6 1.6 5.5 6.5 8.3 11.4 9.1 12.5 14.9 16.4 20.6 22.0 26.3 773 500 5.4 4.9 24.5 countries. Subsequent to the presentation of 34.6 35.3 40.3 873 600 17.4 15.2 41.9 41.0 42.7 this paper, parallel results were published by 1000 727 38.5 47.4 47.3 34.5 48.7 48.7 48.7 48.7 Burgin, Groll, and Roberts ( I ) . E
212
INDUSTRIAL AND E N G I N E E R I K G CHEMISTRY
Acknowledgments Acknowledgment is due to the late Hans Tropsch for his earlier and parallel contributions in this field. Thanks are due to Gustav Egloff, J. C. Morrell, L. S. Kassel, and Jack Sherman for many valuable discussions and help in calculations and particularly to J. M. hlavity, W. J. hlattox, and M. W. Cox for continuous enthusiastic cooperation and assistance in experimentation.
Literature Cited Burgin, J., Groll, H., and Roberts, R. M., Natl. Petroleum News, 30, NO.36, R-1432 (1938) ; Oil GUSJ.,37, NO. 17, 48 (1938). Burk, R. E., “Polymerization”, A. C. S. Monograph 75, New York, Reinhold Pub. Corp., 1937. Egloff, Gustav, Proc. Am. Petroleum Inst., 111, 16, 137-8 (1935). Egloff, Gustav, “Reactions of Pure Hydrocarbons”, A. C. S. Monograph 73, p. 6, New York, Reinhold Pub. Corp., 1937. Egloff, Gustav, Schaad, R. E., and Lowry, C. D., Jr., J . Phys. Chem., 34, 1619 (1930). Egloff, Gustav, Thomas, C. L., and Linn, C. B., IKD.ENG. CHEY.,28, 1283 (1936).
VOL. 32, NO. 2
(7) Ellis, Carleton, “Chemistry of Petroleum Derivatives”. Vol. 11, pp. 631-75, Reinhold Pub. Corp., 1937. (8) Frey, F. E., and Huppke, W. F., IND. ENG.CHEX.,2 5 , 5 4 (1933). (9) Grosse, A. V., J. Am. Chem. SOC.,59, 2739 (1937).
(10) Grosse, A. V.,Morrell, J. C., and Mattox, W. J., IND.ENQ.
CHEM.,to be published. (11) Ipatieff, V. N., Bar., 34, 3589 (1901); 35, 1047 (1902); J . RuS3. Phys. Chem. Sac., 34, 182 (1902); 40, 500 (1908). (12) Kassel, L. S., J . Chem. Physics, 4, 276, 438 (1936). (13) Lazier, W. A., and Vaughen, J. V., J. Am. Chem. SOC.,54, 3080 (19321. (14) Marek, L. F., and Paul, R. E., IND. EXQ.CHEM.,2 6 , 4 5 4 (1934); Marek, L. F., McCluer, TVV. B., Ibid., 23, 878 (1931). (15) Pease, R. N.,and Durgan, E. S., J . Am. Chem. SOC.,50, 2715 (1928); 52, 1262 (1930). (16) Piteer, K. S., J . Chem. Physics, 5, 473 (1937). (17) Sabatier, P., and Mailhe, A., Bull. SOC. chim., [4] 1, 107, 341, 524, 733 (1907); Compt. rend., 146, 1376 (1908); 147, 16, 106 (1909); 148, 1734 (1909); Ann. chim. phys., [ 8 ] 20, 289, 302 (1910).
PRESENTED before the Dirision of Organic Chemistry a t the 96th Meeting of the Smeriortn Chemical Society, Milwaukee, Wis.
Reactions of Maleic Anhvdride with Abietic Acid and Rosin A. G. HOVEY AND T. S. HODGINS, Reichhold Chemicals, Inc., Detroit, Mich.
Contrast is made of results where rosin is used instead of the pure precipitated abietic acid previously discussed in the study of the structure of abietic acid, and of the addition products formed by qbietic acid with maleic anhydride. Although the existing theoretical data on the reaction of resinic acids with maleic anhydride which exist in abundance are valuable, commercial operations have to be carried out with rosin. Much of the theoretical work previously done was performed on freshly prepared abietic acid on which no oxidation had taken place if it could possibly be prevented. On the other hand, industry has to use rosin that may or may not have undergone a certain degree of oxidation.
formation of abietic acid occurs in rosin under the influence of heat or treatment with acids (11). Ruzicka and Meyer (33) obtained approximately 90 per cent yields of abietic acid by vacuum distilling rosin at low pressures and 200-210° C., and suggested that the formation of abietic acid from rosin involved isomerism. Much d E culty has arisen in the studies of the structure of rosin acids due (a) t o the fact that abietic acid is only one of many pos(Table I), (b) to sible isomers of the general formula CZ~H3002 the marked tendency of these isomers to oxidize, and ( c ) to their tendency to form mixed crystals. The presence of resene is said to act as a positive catalyst for oxidation (20). Until recently ( I d , 14, 15, SO) it was considered that pyroabietic acid was one of these isomers into which even the relatively stable abietic acid was changed by heating.
TUDIES of the composition of rosin and of the structure of the resin acids were stimulated by early success in improving on the properties of nature’s product by “liming” or by esterifying. The acidic characteristics of rosin, recognized over a century ago (6),have been widely utilized in the manufacture of driers and other rosin soaps for many industrial purposes. Although abietic acid is not an original constituent of the tree secretions and is apparently not present to an appreciable extent even in virgin rosin, the
The resin acids existent as primary constituents of oleoresins of conifers have been designated as sapinic acids (18). Fleck and Palkin ( I S ) suggested that, in addition to the three methods previously used for isomerization of these labile resin acids-i. e., acid treatment, heat without chemical agents, and ultraviolet light-isomerism could also be promoted by other catalysts. Although it was formerly thought that rosin consisted principally of abietic acid anhydride, Fonrobert (16, 17)
S
TABLE I. ISOXERS OF THE FORMULA C20H8002 Acid
LAbietic (avlvic) “l-Pimario“ (1Sapietic) d-Pimaria (alpha) Proabietic
M. P..
C. 171-173 O
152 212-214 159-160
Specifio Rotation in Abs. Aloohol About -looo
Reference (1.9) Sohulz method
-282’ 740 11.5’
++
