interaction of ethane and isobutylene at 1000' C., probably on account of the predominating Reaction 23 : C2H5 f C B 7
+
C2H4 f C4HS
(23)
However, vinyl radicals do appear to combine with methyl radicals to yield propylene, although hydrogen abstraction would be expected to compete readily to yield acetvlene. CH3 CH3
+ C2H3
+ C2H3+
+
C3H6
CH4
+ C2H2
(24) (25)
Acknowledgment
The author gratefully acknowledges the advice of A. C. Gasche and of W. F. Dreier in connection with the design of the
equipment. The diligent and careful experimental work of R. D. Armstrong is much appreciated. Thanks are also due E. I. Heiba and P. S. Landis for helpful discussions. literature Cited
Errede, L. A., English, W. D., Advan. Chem. Ser. No. 51, 26 (1965). Kevorkian, V., Advan. Petrol. Chem. Refining 5 , 395 (1962). Ibid., p. 406. Ibid., p. 408. Scott, E. J. Y . , IND. ENG.CHEM.PROD.RES. DEVELOP. 6, 72 (1967). Steacie, E. W. R., "Atomic and Free Radical Reactions," 2nd ed., Vol. I, p. 189, Reinhold, New York, 1954. Ibid., pp. 151, 219. Webb, L. R., Dallas, C. A,, Campbell, W. H., Ind. Eng. Chem. 54, No. 1, 28 (1962). RECEIVED for review July 11, 1966 ACCEPTEDJanuary 13, 1967
REACTION OF ALKANES WITH TOLUENE A T 800"T O 1200"C. E R I C J. Y . SCOTT M o b i l Oil Carp., Princeton, N . J .
Below 800" C. or in the absence of propane, toluene pyrolyzes to yield bibenzyl, benzene, methane, and hydrogen. Above 800" C. propane reacts with toluene to give ethylbenzene and styrene in place of bibenzyl. Ethylbenzene i s formed first and then dehydrogenated to styrene. Whereas propane promotes the pyrolysis of toluene and increases the ultimate ethylbenzene yield, it inhibits the pyrolysis of ethylbenzene and has little effect on the ultimate yield of styrene. Styrene decomposes and polymerizes to other products. Quenching retards polymerization and decomposition more than the dehydrogenation reaction, so that an improved quenching technique increases the styrene yield. Within the limits of these investigations the ultimate styrene and ethylbenzene yields are independent of reactor material. Methane, n-butane, and isobutane may b e used instead of propane as a source of methyl radicals. All of these hydrocarbons increase the ultimate ethylbenzene and styrene yields over corresponding yields in the absence of alkane. Ethane has little effect on ethylbenzene ultimate yield but enhances n-propylbenzene formation. Methane, n-butane, and isobutane yield methyl radicals, whereas ethane decomposes via ethyl radicals. Benzyl radicals are therefore believed to combine with methyl and ethyl radicals to yield ethyland n-propylbenzene, respectively.
systems a t 1000' C., free radicals combine to yield Thus methyl radicals combine with allyl radicals to form 1-butene and with methallyl radicals to form 2-methyl-I -butene. Similarly, methyl radicals combine with benzyl radicals to form ethylbenzene : N SOME
Imajor reaction products (Scott, 1967).
CH3
+ C ~ H S C HF?Z C ~ H S C ~ H ~
(1)
Benzyl radicals are formed by pyrolyzing toluene a t 1000° C. I n this instance benzene and bibenzyl are the main products (Steacie, 1954, p. 189). However, if pyrolysis occurs in the presence of a source of methyl radicals such as propane, ethylbenzene is a major product and bibenzyl is reduced to negligible amounts. Reaction 1 is commercially significant, inasmuch as ethylbenzene can be readily dehydrogenated to styrene (Faith, et a/., 1965). Ethylbenzene is now manufactured by the liquid-phase reaction of ethylene and benzene, catalyzed by aluminum chloride a t 100' C. The reaction of propane with toluene might have the commercial advantage that no catalyst 72
l & E C P R O D U C T RESEARCH A N D DEVELOPMENT
is required and the reactants are cheaper. Kusunoki et al. have recently shown that a t 628' C. toluene reacts with acetone to yield mainly benzene and styrene (1963). The reaction is similar, inasmuch as acetone, like propane, is a source of methyl radicals (Scott, 1967). The reactions of p-methylbenzyl radicals with chlorocarbon radicals have been studied by Errede and Cassidy (1963). I n this report are discussed the effects of conversion, temperature, residence time, reactant ratio, quenching, reactor material, and nature of the alkane on the production of ethylbenzene and styrene from toluene. Experimental
Chemicals. Methane, ethane, isobutane, and n-butane were Matheson (c.P. grade). Helium was Airco. Ethylbenzene and styrene were obtained from Matheson Coleman & Bell. Other chemicals were as described in the previous paper (Scott, 1967). Apparatus and Procedure. The apparatus and main procedures have been described (Scott, 1967). I n some
experiments a reactor made from 446 steel was used; 446 steel contains 24.35% chromium and small amounts of manganese, silicon, carbon, phosphorus, sulfur, and nitrogen. A special method was adopted in runs designed to obtain a weight balance (see Table I ) . Liquid was condensed in two traps immersed in ice water. Sealed to the center tube of each trap was a fritted cylinder (Corning gas dispersion tube 39533, size 12EC) to condense aerosols. The condensates were combined, weighed, and analyzed by gas chromatography. Samples of ethylbenzene, styrene, and n-propylbenzene were isolated and identified by infrared spectroscopy. Exit gases were metered and analyzed by gas chromatography. I n one case a mass spectrometric analysis for hydrogen was made. I n subsequent runs a correction was made for hydrogen in the exit gas. I n all analyses, gas chromatographic areas were corrected for detector thermal response and, after correction, \yere assumed propori.iona1 to weight percentages of the components. Control runs were done a t 200' C . below the temperature required for minimum detectable reaction. Each datum in Table I corresponds to the average of a t least two high temperature runs and two control runs. Results and Discussion
Reaction of Propane and Toluene at 800' to 1200' C. T h e products obtained from the reaction of propane with toluene a t 800' to 1200' C. are consistent with the following reaction mechanism (Table I). T h e scheme is not intended to be comprehensive but only to indicate how the main products are probably formed.
+ C3Hs * C3H7 f C H I C3H7 C2H4 + CH3 H + CaHs C3H7 f HB C3H6 + fi CsHsCH2 + CH3 CsH&zHj CHa
+
+
C3H7 -+
(2) (3) (4)
(5) (1 1
-2A or
CsH5C:Hs
-
---c
- HZ
CsH5C2H3
+H C ~ H S C H* S CsHs + CH3 CsH5 + C ~ H ~ C * H BCsH6 + CsHsCH2 H + CsHsCHa * Hz f CsHsCH2 CH3 + C6H5CH3 * C H I + C ~ H ~ C H B C6HsC]&
2CsH&H2
C6&CH2
(CsHjCH2)z
2CH3 + C2H6
(6)
Table 1.
Products of Reaction of Propane with Toluene at loooo to 1100' c. Run >Vo. 7 2 3
React or Control Toluene, g. Propane, g. Temperature, ' C. Residence time, msec. Recovered,&g. Methane Ethane Ethylene ProDane Propylene Benzene Toluene Ethylbenzene Styrene Other compounds Conversion, 70 Toluene Propane Ultimate yieldsb Ethylbenzene Styrene
446 steel
446 steel
7.55
7.55 74.10
74.10 1000
1100
Inconel-600 7.71 74,49 1100
3.5
3.0
3.0
3.04 0.28 5.31 60.47 4.95
8.91
4.10
1.28
0.60
0.12
6.54 0.50 0.06 0.38
17.55 35.41 11 . O )
0.77 5.47 0.56 0.32 0.31
8.80
55.80 5.00 0,30 7.20
0.29 0.08 0.08
13.4 18.4
27.5 52.0
6.6 25.0
49.5 6.0
26.9
15.4
57,o 15.7
a Hydrogen present but not measured. DeJned as weight of toluene converted to product divided by total weight of toluene decomposed X 100.
Table II.
Effect of Propane-Toluene Ratio on Ultimate Yields
(Quartz-lined reactor) 4
5 Propane-toluene, 5 5 5 2 2 moles 1000 1100 1000 1100 Temperature, C. 900 Residence time, 1.2 1.4 1.3 1.3 1.2 msec. Conversion, % tolu22 8 22 7 1 ene Ultimate vielda Benzene 40 24 28 29 29 39 57 46 54 44 Ethylbenzene 6 0 7 16 16 Styrene 12 21 10 11 11 Others Run -To
Q
Based on toluene concerted.
(7) (8)
(9) (1 0) (11) (1 2) (1 3)
Reactions 2 to 5 are the main reactions involved in the pyrolysis of propane (Laidler et al., 1962). Similarly, Reactions 1 and 6 to 13 represent the pyrolysis of toluene (Steacie, 1954, p. 189). Toluene pyrolysis, however, is complicated by secondary processes-for example, dimethyl diphenyls as well as bibenzyl are products. I n our results "bibenzyl" may include some dimethyl diphenyls. Previous work showed that in the presence of nitrogen in place of propane, bibenzyl rather than ethylbenzcne is the major product (Table V, Scott, 1967). I n this instance, Reactions 7 to 12 predominate, However, in the presence of propane the increase in methyl radical concentration (formed by Reaction 3) favors Reaction 1 over 12. Cher, Hollingsworth, and Sicilio showed that methyl radicals react with the benzene ring a t 300' C. to yield xylenes (1966). However, the ratio of xylene to ethylbenzene decreased with increasing temperature. I n agreement with this
observation, the yield of xylenes was found to be negligible a t 1000' C . Although changing the propane-toluene ratio from zero to 2 has a marked effect on ultimate ethylbenzene and bibenzyl yields, these ultimate yields are insensitive to a further increase from 2 to 5 (runs 4 and 5, Table 11). Decreasing residence time (by increasing flow rate) decreases conversion and also the ultimate styrene yield (runs 4, 6, and 7, Table 111). This indicates that styrene is a secondary product probably derived from ethylbenzene. That ethylbenzene does in fact decompose to yield styrene was established by reaction of ethylbenzene \vith propane under comparable conditions (Table IV). .4t 1000° C. a 4370 ultimate yield of styrene was obtained. Reaction of propane \vith ethylbenzene differs from reaction with toluene in that propane inhibits rather than promotes the conversion of the aromatic. This difference in behavior may be accounted for as follows. Dehydrogenation of ethylbenzene may occur by the intramolecular Reaction 14 or by the propagation Reactions 15 and 16 (Steacie, 1954, p. 192):
VOL. 6
NO. 1
MARCH 1967
73
Table 111.
Effect of Residence Time on Ultimate Yields
(Toluene 17 mole 70;propane 83 mole yo. Quartz-lined reactor. Reactor temp. 1100" C.] R u n 'Vo. 7 6 4 Residence time, msec. 0.4 0.6 1.2 Conversion, 70 toluene 2 5 22 Ultimate yield" Benzene 27 21 28 Ethylbenzene 51 56 46 4 8 16 Styrene 18 15 10 Others
n 701
w z V 0
w
3
0
50-
z
0 0
m W
2
Based on toluene converted.
60-
W z
40-
0 -1
w Table IV.
The Reaction of Propane with Ethylbenzene at 1000° C.
(Inconel-600 reactor) Controls R u n dYo.
Reactants, mole % Propane Nitrogen Ethylbenzene Temperature, O C. Residence time, msec. Conversion, 70 Ethylbenzene Propane Ultimate yielda Styrene
8
9
95.4
...
4.6 1000 3.1
1000
...
95.4 4.6 3.1 42
18 9
...
43
37
10
W
30-
z
20
k I 53
-
I-
'3 t . .
g
l0-
95.4 4.6
I
900
3.6
0
165 10.9 0.6 0.8
1.4
20
IO
...
45
A reaction chain corresponding to Reactions 15 and 16 cannot occur with toluene, so that in the presence of propane the faster Reactions 10 and 11 become rate-controlling and replace the much slower Reaction 7. Thus propane promotes the pyrolysis of toluene. O n the other hand, in the ethylbenzene instance, hydrogen atoms formed in Reactions 15 and 16 promote Reaction 4, so that fewer hydrogen atoms are available for continuing the ethylbenzene chain via Reaction 15. Thus ethylbenzene pyrolysis is inhibited by propane. In view of the relative insensitivity of product ultimate yields to propane-toluene ratio, propane may be regarded as a carrier gas above a ratio of 2. Thus conversion of toluene may be conveniently modified by changing the propane flow rate while the toluene flow is kept constant (Figure 1). Ethylbenzene ultimate yield decreases with increasing conversion, while the styrene ultimate yield exhibits a maximum. At low conversions styrene is formed from ethylbenzene; at high conversions it is dealkenylated to benzene. The effect of reactor material has not been rigorously studied. However, the ultimate ethylbenzene yields shown in Table I fall on the corresponding curve in Figure 1. This indicates that selectivity is essentially independent of reactor material, provided one uses a steel, Inconel-600, or quartzlined reactor. The effect of helium quenching on the reaction products is shown in Figure 2. In these runs helium at 150 p.s.i.g. was passed through a coil immersed in liquid nitrogen and expanded through a narrow stainless steel capillary (gage 33) in the exit line, 1 inch from the reactor. Flow rate was 250 cc. per minute, 1770 of the total exit gas flow. The ultimate yields of ethylbenzene and styrene are compared with those of run 11. Only at conversions of less than 10% is the selectivity for ethylbenzene increased. However, the ultimate styrene yield is increased a t all conversions. l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
30
40
50
60
70
% TOLUENE CONVERSION
15
Figure 1. Effect of conversion on ultimate product yields in the reaction of propane with toluene 0 Ethylbenzene
Based on ethylbenzene converted.
74
62
Styrene X Benzene Quartz-lined reactor Constant toluene flow Variable propane flow Reactor temperature 1 100' C. 80
0 W I-
70
Bz> 0
60 W W
z 3 -I
ez
50
0 0
m
W
a 40 m 0 J
w
w 30
k
H
5
=$
20
I-
P W
3 '0
(
% TOLUENE CONVERSION
Figure 2. Effect of helium quenching on ultimate yields of ethylbenzene and styrene Runs 11, 12, and 13
0 Ethylbenzene Styrene Helium quench No quench Inconel-600 reactor (helium quench) Propane 94.8%; toluene 5.2% Conditions for run 1 1. See Figure 3
0
-
__
ETHANE. T h e yield of ethylbenzene from a n ethanetoluene mixture is no greater than from toluene alone (runs 17 and 18, Figure 4 ) . However, the ultimate n-propylbenzene yield is 2091,, whereas none could be detected when nitrogen was the carrier. This indicates that ethyl radicals produced from ethane react with benzyl radicals.
T h e effect of helium quenching on the styrene pyrolysis was similarly tested a t 1100" C., 3.1-msec. residence time, for a mixture of 4.86% styrene and 95.14% propane. The results of four runs with and four runs without helium quenching were averaged. The conversion of styrene was reduced from 31 to 15% by quenching. These results indicate that improved quenching should increase the ultimate styrene yield in the over-all reaction of propane with toluene. The effect of temperature on ultimate product yields is shown in Figure 3. Lowering temperature increases benzene and bibenzyl ultimate yields a t the expense of ethylbenzene and styrene. If Reactions 8, 9, 11, and 12 predominate a t 800" C., the weight ratio of bibenzyl to benzene would be 2.3, corresponding to the stoichiometric equation : 3CsHaCH3
-+
CeHs f C H I
+ (C~HSCH~)?
C2Hj
+ CgHs C?Hb
-+
-+
CzHs
C2H4
+ Hz
+
C6HsC3H7
(20)
(17)
Inasmuch as the experimental value is close to unity, some benzyl radicals are disappearing by reactions other than Reaction 12. As the temperature increases, Reaction 12 reverses, less bibenzyl is formed, and more benzyl radicals are available to combine with methyl radicals to form ethylbenzene by Reaction 1. Reactions of Alkanes with Toluene at 1100" C. Propane was chosen initially as a hydrocarbon methyl radical source because it is known to decompose partially to yield methyl radicals as indicated by Reactions 2 to 5. Other possible sources are methane, n-butane, and isobutane. Ethane chain propagation involves not methyl radicals but ethyl radicals and hydrogen atoms:
H
+ CsHsCHz
The effect of conversion on ultimate yields is shown in Figure 4. n-Propylbenzene decomposes, probably by demethanation to styrene, more readily than ethylbenzene. R-BUTAXE.R u n 20 indicates that appreciable ultimate yields of both ethyl and n-propylbenzene are found.
a w
w9 1
x
(1 8)
+H
I
(1 9 )
W
3 10
T h e results of experiments using hydrocarbons other than propane for radical sources are shown in Table V and Figure 4. METHANE.Substituting methane for nitrogen as carrier gas reduces bibenzyl and promotes ethylbenzene formation (runs 1 4 and 15). A considerable amount of benzene is formed in both runs, indicating that extensive demethylation of toluene occurs. T h e analogous reaction with carbon tetrachloride in place (of methane was found to yield mainly p,p'-dichlorostyrene formed by dehydrohalogenation of p , p', p"-trichloroethylbenzene. Similar findings have been reported by Errede and Cassidy for the reaction of p-xylene with carbon tetrachloride (1 963).
19 20 21
22 23 24
Alkane Methane Methane Ethane Ethane Ethane Propane n-Butane 50% Propane 50% n-Butane Isobutane 6070 Propane 40y0 Propylene Propane
15
10
20
25
30
5
% TOLUENE CONVERSION
Figure 3. Effect of temperature on ultimate product yieldsreaction of propane with toluene Run 1 1 0 Ethylbenzene 0 Styrene X Benzene 0 Bibenzyl Quartz-lined reactor Propane 83%; toluene 17%
llOOo C. (Quartz-lined reactor) Residence ~~l~~~~ Wt. yo Ultimate Yield Based on Toluene Converted Reactant, Mole 70 Time, Conver- EthylToluene Alkane Nz Msec. sion, benzene Styrene Benzene Others 18.0 82.0 ... 2.6 3 40 7 40 Bibenzyl 10 18.0 ... 82.0 2.6 5 6 3 43 Bibenzyl 40 5.8 94.2 ... 0.6 25 12 10 57 n-Propylbenzene 13 ... 0.4 6 12 7 45 n-Propylbenzene 20 4.0 96.0 ... 96.0 0.4 1 17 3 35 n-Propylbenzene 0 4.0 Bibenzyl 45 Table V.
Run No. 14 15 16 17 18
RESIDENCE TIME Imsec.) TEMPERATURE ('C1
12 I100 5
0
Reactions of Alkanes with Toluene at
14.0 14.0 7.4
86.0 86.0 92.6
... ... *..
1.4 1.o 0.5
21 13 4
44 51 60
18 15 8
24 19 13
10.0 17.0
90.0 83.0
...
*..
0.7 1.2
10 17
61 38
10 11
21 32
17.0
83.0
...
1.2
18
46
16
27
VOL. 6 NO. 1
...
n-Propylbenzene 10 n-Propylbenzene 11
...
...
... MARCH 1967
75
butyl radicals would be expected to decompose to ethyl and methyl radicals, respectively: n c
+ CzH4 CHI + C3Hs
CH~CHZCH~C -+ HC?Hj ~
(21)
CH3CHzCHCHz
(22)
+
ISOBUTANE. Isobutane reacts with toluene to give a high ultimate yield of 60Yc a t 10% conversion (run 22). Isobutane also gives a more specific distribution of alkyl benzenes than propane. Whereas propane to some extent yields ethyl radicals which can form n-propylbenzene, no ethyl radicals can be formed directly from isobutane. Methyl radicals in this instance may be formed either from isobutane directly by C-C bond scission or from isobutyl radicals: CHzCH(CH3)z -+ CH3
+ C3Hs
(23)
Acknowledgment
I acknowledge the careful work of R. D. Armstrong, who assisted me in the experiments described in this paper, and thank E. I. Heiba and P. S. Landis for helpful discussions. Literature Cited 0
20
IC
30
40
50
60
70
% TOLUENE CONVERSION
Figure 4. Effect of conversion on ultimate product yieldsreaction of ethane with toluene
0
Ethylbenzene
0 n-Propylbenzene 0 Styrene X Benzene Quartz-lined reactor Constant toluene flow Variable ethane flow Reactor temperature 1 100’ C.
Cher, M., Hollingsworth, C. S., Sicilio, F., J . Phys. Chem. 70, 877 (1966). Errede, L. A , , Cassidy, J. P., Ibid., 67, 69 (1963); J. Org, Chem. 28, 1059 (1963). Faith, W.L., Keyes, D. B., Clark, R. L., “Industrial Chemicals,” 3rd ed., p. 733, Wiley, New York, 1965. Kusunoki, Y., Nakamura, M., Nakamura, J., Tsutsumi, S. (to Yawata Chemical Industry Co.), Japan. Patent 22,573 (Oct. 24, 1963). Laidler, K. J., Sagert, N. H., Wojciechowski, B. W., Proc. Roy. Soc. 270A, 242, 254 (1962). Scott, E. J. Y., IND.ENG.CHEM.PROD.RES. DEVELOP. 6, 67 (1967). Steacie, E. \V. R., “Atomic and Free Radical Reactions,” 2nd ed., Vol. I, p. 189, Reinhold, New York, 1954. Ibid., p. 192.
n-Butane thus behaves like ethane and propane, inasmuch as both methyl and ethyl radicals are formed. n-Butyl and sec-
RECEIVED for review July 11, 1966 ACCEPTEDJanuary 13, 1967
HYDROISOMERIZATION OF OLEFINS J .
C. P L A T T E E U W , H . D E R U I T E R , ’
D. VAN ZOONEN,2 AND H . W.
KOUWENHOVEN
Koninklijke/Shell-Laboratorium, Amsterdam (Shell Research N . V.), Holland
is a process for the conversion of linear olefins into branched paraffins, a suitable catalyst being nickel sulfide on silica-alumina (Frye et al., 1963; Platteeuw and Choufoer, 1961, 1962, 1964). This reaction is characterized by the fact that the ratio of iso- to normal paraffins in the product is appreciably higher than predicted by the thermodynamic iso-to-normal equilibrium ratios of either the olefins or paraffins. Thus the product mixture is highly branched and saturated, qualities very desirable in a gasoline. T o obtain a clearer understanding of the mechanism of hydroisomerization, studies have been carried out with model compounds as well as with olefinic mixtures from refinery streams. T o gain a n insight into the role of the nickel sulfide component, the behavior of silica-alumina as such and with YDROISOMERIZATION
Present address, Compagnie de Raffinage Shell Berre, France. Present address, Bataafse Internationale Petroleum Maatschappij, N.V., The Hague, Holland. 1
2
76
IbEC P R O D U C T RESEARCH A N D DEVELOPMENT
various loadings of nickel sulfide was investigated. In the latter case, the degree of dispersion of nickel sulfide on the silica-alumina carrier was varied and its effects were studied. Experimental
Feedstocks. T h e model compounds, obtained from the Phillips Petroleum Co., were 1-butene and 2-butene, 1,3butadiene, and 1-hexene, pure grade. A light catalytically cracked gasoline with a final boiling point of 100” C. was used in the larger-scale experiments. I t had a bromine number of 109 grams per 100 grams of product, and consisted of 30 weight % paraffins, 59 weight % olefins, 9 weight 7 0 naphthenes, and 2 weight ’% aromatics. Catalysts. The silica-alumina-containing samples were prepared from Ketjen MS 3A, a low-alumina fluid cracking catalyst (13 weight % A1~03,87 weight % %On). Prior to use this material was washed with deionized water to remove ammonia and dried at 120” C. for 17 hours. Nickel was placed on the silica-alumina base thus treated by the following methods :
