ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT with a blend of 0.34 wt. % sulfur in n-heptane show 5 t o 7% more desulfurization than comparable runs with olefins present. However, this advantage is lost a t a liquid hourly space velocity of 8. These results (Figure 6) would indicate that olefins have, a t most, only a small inhibitory effect on the desulfurization process. I n all these experiments, mercaptan sulfur was completely converted t o hydrogen sulfide, while part of the thiophenic sulfur remained unreacted.
z u
B a a J
w
Acknowledgment
40
0 0
IW z
OLEFIN-FREE
FEED, 0.34%~S
The aut.hors wish t o express their appreciation t o Shell Oil Co. for permission to publish this work. Acknowledgment is also gratefully accorded t o A. F. Sartor and S. W. Kapranos for assistance in the experiments.
OLEFIN-CONTAINING FEED, 0.30%~ S
20
0
literature Cited 0
Figure 6.
2
6 8 LlOUlD HOURLY SPACE VELOCITY, vd/vol/hr
10
Desulfurization over tungsten nickel sulfide catalyst in absence of olefins
Additional experiments were performed t o define more clearly the effect of sulfur concentration of olefin hydrogenation and extent of desulfurization. Two charges containing 0.13 or 0.40 wt. % sulfur, respectively, were prepared and tested over tungsten nickel sulfide catalyst. The results are given in Table 111 and show essentially the same level of olefin saturation as t h a t obtained at 0.30 wt. % sulfur level. The sulfur reductions for the 0.30 and 0.40 wt. % sulfur charges were approximately the same (Figure 5 ) . However, for the feed containing 0.13% sulfur, about 10% greater desulfurization was obtained. I n the absence of olefins, sulfur compounds appear t o hydrogenate slightly faster a t the lower space velocities, Runs made
(1) Anderson, J., NIcAllister, S. H., Derr, E. L., and Peterson, W. H., IND. ENG.CHEM., 4 0 , 2 2 9 5 (1948). ( 2 ) Berg, L., Sumner, G. L., Jr., and Montgomery, C. W. (Gulf Research and Development Co.), U. 5.Patent 2,397,639 (.lpril 2, 1946). (3) Berg, L., Sumner, G. L., Jr., and Montgomery, C. W., ISD. ENG. CHEM.,3 8 , 7 3 4 (1946). (4) Casagrande, R. AT., Neerbott, W. K.. Sartor, 4.F., and Tramor, R. P., IND. ENG.CHEM.,4 7 , 744 (1955). (5) Egloff, G., Morrell, J. C.. Thomas, C. L., and Bloch, H. S.,J . Am. Chem. Soc., 6 1 , 3 5 7 1 (1939). (6) Hay, R. G., Montgomery, C. W.,and Coull, J., IND.ESG. CHEM.,3 7 , 3 3 5 (1945). (7) Johnston, R. W. B., Appleby, W. G., and Baker, If.O., A,iaZ. ' Chem., 2 0 , 8 0 5 (1948). (8) Young, W. G., Meier, R. L., Vinograd, J., Bollinger, H., Xaplan, L., and Linden, S. L., J . Am. Chem. Soc., 69, 2046 (1947). RECEIVED for review December 8, 1954.
QCCEPTED December 30, 1954.
Polymerization of light Olefins over Nickel Oxide-Silica-Alumina J. P. HOGAN, R. L. BANKS, W. C. LANNING,
AND
ALFRED CLARK
Phillips Pefroleum Co., Burflesville, Oklo.
Refinery cracked gas contains significant quantities of ethylene which are not recoverable by polymerization over catalysts now in commercial use. Nickel oxide on silica-alumina has been found to be highly active for this reaction, even at high ethylene dilution; the present paper describes its use for conversion of ethylene and propylene to motor fuel. The separate olefins were polymerized in continuous-flow experiments at 40' to 95' C. to investigate reaction kinetics and product compositions. In the polymerization of mixed olefins in a cracked gas, the activity and life of the catalyst were improved markedly by the recycle of butane as liquid diluent.
T
HE literature describes a number of catalysts for the polymerization of propylene to gasoline range hydrocarbons. Phosphoric acid, supported on kieselguhr (4)or quartz sand (Q), and copper pyrophosphate ( 1 1 ) are among the most important. Silica-alumina polymerizes propylene less readily and only a t relatively high temperature (15). However, none of these catalysts gives appreciable conversion of ethylene a t the process conditions ordinarily used. Ethylene has been polymerized at 250' t o 350" C. in t h e presence of phosphoric acid ( 7 ) t o give
752
products which indicate conjunct polymerization of a type different from t h a t obtained in thermal polymerization (8, 7 , 1 2 ) . Cobalt-charcoal catalysts have been used for the dimerization of ethylene (5). Bailey and Reid (1 ) discovered t h a t silica-alumina promoted with mckel oxide possessed high activity for the polymerization of ethylene, even a t room temperature, and was more active for propylene polymerization than silica-alumina alone. Furthermore, the order of decreasing rate of reaction of normal olefins,
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 4
GASOLINE PROCESSING in contrast t o t h a t observed for the usual acid-type catalysts, was found t o be as follows : ethylene, propylene, %butene, 1butene. T h e catalyst was, of course, active for the polymerization of isobutene and was used for the codimerization of isobutene with 2-butene (6). The present paper describes continuous-flow bench scale experiments on the polymerization of ethylene and propylene, separately and in admixture as cracked gas, over the nickel oxide-silica-alumina catalyst
was charged with a Hills-McCanna pump and was also passed through suitable purification equipment. The reactor consisted of a a/,-inch inside diameter by 30-inch seamless steel pipe jacketed with 2-inch inside diameter pipe. The electrically heated jacket contained liquid which was caused to boil a t a temperature fixed by the pressure of inert gas applied to the top of t h e reflux condenser. Temperatures in the catalyst bed could be controlled within 1 1 ' C. in this manner, t h e boiling liquid being water or a hydrocarbon of vapor pressure suitable for the temperature desired. T h e catalyst chamber was provided with a thermocouple well to which a wire gauze was attached as a catalyst support. The usual catalyst charge was 100 ml., giving a bed depth of 15 inches.
Cata Iys t
The silica-alumina support was prepared by impregnation of silica Hydrogel with a n aqueous solution of aluminum sulfate or nitrate, followed by washing, drying, and heating to 400' t o 500' C. in air. This material was then crushed and screened t o 14-30 mesh. The alumina content was usually 2 weight % ' b u t was not critical in t h e range of 2 to 10%. Commercial synthetic silicaalumina cracking catalyst containing about 90% silica and 10% alumina was also a satisfactory support. T h e silica-alumina support was impregnated with a n aqueous solution of nickel nitrate hexahydrate. T h e excess solution FRACTIONwas removed by filtration, and the granules LIQUID FEED were dried with agitation at about 110" C. T h e catalyst was activated in a n electrically heated stainless tube through which dry air FEED-DILUENT was passed as the temperature wa8 increased to 500' C. over a 2-hour period. T h e acti-I vation was continued for a n additional 4 ( L w i EEYFL~FU-FG OKV G~FH-~YEEL-FKET EATG-&MNS OPERATED UNDER BACK-PRESSURE? hours at 500' C. at a n air rate of 500 volumes per hour per volume of catalyst. This acFigure 1 . Polymerization apparatus tivation step decomposed all the nickel nitrate t o nickel oxide and freed the catalyst Reactor pressure was maintained by a back-pressure controller of all b u t a trace of moisture. T h e activated catalyst was then which actuated a motor value in the effluent line. T h e effluent either transferred directly to the polymerization reactor under a passed t o continuous fractionating columns, which were conblanket of d r y nitrogen or stored in a container from which atfitructed of glass for single-pass experiments. For experiments mospheric moisture could be excluded. Catalysts became deinvolving recycle of liquid diluent, the columns were of steel activated if allowed to absorb as little as 0.5 weight % moisture. construction and were operated at elevated pressure. The most active polymerization catalyst contained about 4 The off-gas was analyzed for total olefins b y standard gas abweight nickel, and this concentration was obtained by t h e use sorption methods. Complete compositions were obtained in of an impregnation solution containing about 40 weight % nickel some cases by mass spectrometer analyses. Liquid polymer nitrate hexahydrate. Active catalysts were also obtained by samples were fractionated with a 13-mm. by 4-foot Hypercal impregnation of silica-alumina with solutions of nickel chloride Podbielniak column. Portions of some of the polymer samples or nickel sulfate. However, t h e activated catalyst still contained were hydrogenated before fractionation t o obtain better separaa t least a portion of the chloride or sulfate ion. tion according t o chain structure. Boiling points, refractive The polymerization activity of the nickel oxide-silica-alumina indices, and infrared scanning5 of t h e various fractions were catalyst declined at a rate determined largely by the amount and used to identify individual components and determine total polytvpe of impurities in the feed, and eventually regeneration was mer composition. required. The regeneration procedure was to strip t h e catalyst free of hydrocarbon vapors and preheat it t o combustion temperature (about 400' C.) with dry inert gas, burn off the small Propylene Polymerization amount of residual deposits a t about 500" C. with air added to the inert gas, and cool t h e catalyst ~ i t h dry regeneration gas. Experimental Procedure. The feed used was a refinery C3 After repeated regeneration, t h e nickel oxide promoter underwent stream which had been fractionated to remove all but a trace of changes which caused activity to decline, b u t the catalyst could Cf and Cq hydrocarbons. It had been caustic washed t o reduce then be restored to its initial activity b y being wet with nitric the sulfur t o about 0.001 weight %. This material contained acid solution, followed by activation in the same manner as for 23-mole yo propylene, but higher or lower concentrations were new catalyst. obtained in blends with Phillips technical propylene or propane. The propylene-propane feed was charged to the unit from a liquid feed cylinder, as shown in Figure 1, and was passed through Experimental Equipment Ascarite t o remove moisture and possibly some sulfur comA schematic flow diagram of the polymerization equipment is pounds. T h e reactor effluent passed t o a fractionating column shown in Figure 1. Gaseous feed, taken a t regulated pressure which continuously separated the polymer from the unreacted from cvlinders, was passed through the flow controller, motor Ca hydrocarbons. valve, and purification unit, and then to the top of the reactor. Operating Temperature and Pressure. Experiments in which Liquid feed, used alone or in conjunction with gaseous feed, the reaction temperature was varied from 35' t o 130' C. showed
e
-
April 1955
INDUSTRIAL AND ENGINEERING CHEMISTRY
753
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT 1000 I
I
100
I
I
a w
2
3 80
0
n
J
s
e60 L
1
!
$40-40 pz.
n w
AVERAGE PROPYLENE CONCENTRATION, MOLE% Figure 2. Propylene concentration effect on polymer formation rate. Pressure, 600 pounds per square inch gage; temperature 70' C.
1000
I
I
I
PROPYLENE CONVERSION, PER CENT Figure 4. Propylene conversion effect on polymer composition. Pressure, 600 pounds per square inch gage; temperature, 70" C.; space velocity varied Feed
I100
PropyEene Propane
E2
Zd
E * 250
0 PROPYLENE FEED RATE, GRAMS PER LITER-HOUR Figure 3. Propylene feed rate effect on conversion and polymer formation rate. Pressure, 600 pounds per square inch gage; temperature 70' C.; Feed Propylene Propane
Mole
70
23 77
t h a t the reaction rate was highest in the range of 70" t o 93' C. Conversion declined sharply when the pseudocritical temperature, 96" C., of the feed was exceeded and the system became essentially vapor phase. Investigation of other variables was conducted at a temperature of about 70" C. and a t a pressure of 600 pounds per square inch gage, well above t h a t required t o maintain completely liquid phase. Propylene Concentration and Space Velocity. Propylene concentrations in the feed were varied from i t o 37y0in experiments a t 2, 4, a f d 8 space velocity. T h e effects of propylene concentration and space velocity on polymer production rate are shown in Figure 2. T h e logarithmic average of feed and effluent concentrations was taken as the effective concentration in t h e reactor. Rates of polymer production increased linearly with propylene concentration over the range investigated. First order 554
Mole
%
23
77
relationship between propylene concentration and rate of polymer formation was thus indicated. A similar relationship was found by Cheney and coworkers (3)for the polymerization of ethylene over cobalt-charcoal catalyst. Figure3 shows t h e effects of feed rate on conversion and polymer formation rate. T h e increase in rate of polymer formation was almost linear with respect to feed,rate t o a product rate of 500 grams polymer per hour per liter of catalyst. As t h e conversion fell below 6OO1,, t h e rate of polymer formation increased less rapidly and appeared to be leveling out a t about 800 grams per hour per liter of catalyst for this particular feed composition. Product Composition. T h e effect of once-through propylene conversion on product distribution is shown in Figure 4. At 68% conversion, the product composition in volume yo was hexenes, 72; nonenes, 19; dodecenes, 6 ; pentadecenes and heavier, 3. The hexene content of the polymer increased from 65 to 77 volume yo as once-through conversion was decreased from 83 t o 53%. The curves are extrapolated to 1 0 0 ~hexenes o in t h e polymer at zero conversion, since hexenes are assumed to be the primary reaction product and t h e trend observed over t h e limited range of conversions is consistent with t h a t assumption. T h e approximate composition of t h e hexene fraction of the propylene polymer is shown in Table I. This composition is representative of t h e hexenes in polymer made a t about 80% once-through conversion. The nonene fraction was composed mostly of dimethyl-heptenes and trimethyl-hexenes. Straightchain nonenes were present in very low concentrations. The products obtained from propylene polymerization were, in general, those which would be expected according t o t h e car-
Table I.
Composition of Hexenes in Propylene Polymer Volume, Component 2-Methyl-2-pentene 4-Methyl-2-pentene 4-Methyl-1-pentene 2- and 3-Hexene I-Hexene
INDUSTRIAL AND ENGINEERING CHEMISTRY
%
10 50 6
34 1
Vol. 47! No. 4
GASOLINE PROCESSING production of about 325 grams per hour per liter of catalyst. At the conditions of these experiments, the polymer composition by volume was 50% butenes, 16% hexenes, 137, octenes, 11% decenes, and 10% dodecenes and heavier. The polymer was free of compounds having a n odd number of carbon atoms. T h e butenes were found to consist of 5 to 10% 1-butene and 90 t o 95% 2-butene, the ratio of t r a m to cis isomers being about 2 : l . No isobutene was detected. The hexenes consisted of 60 to 70% 2-hexene and 3-hexene a t a ratio of about 2:1, and 30 to 40% 3-methyl-2-pentene and 3-methyl4-pentene at a CH,-CHz-CH, CHZ=CH-CHs ratio of about 8:1. Small amounts of 1-hexene and Z-ethyl-lbutene probably were present also. Hydrogenation of the octenes CH,-CH,-CH,-CHZ-CH-CH3 (1) yielded paraffins consisting of 40 to 45% 3,4-dimethylhexane, 30 to 35% 3-ethylhexane, 2 to 4% 3-CH=CH2 H+ methyl 3-ethylpentanej and about CHa-CHz-CHz-CHz-CH-CH3 --+ CH3-CHz-CHz-CHzt 20y0 n-octane. Other compounds '\y CH3-CH2-CH2-CH=CH-CH3 4- H' ('1 were no doubt present in trace quanT CH3-CH2-CH2-CH-CH2-CHa + CHs-CH2-CH=CH-CHz-CH3 H+ tities. iEthylene polymerization in thepresence of phosphoric acid has been picCorrespondingly, the branched-chain hexenes would be formed tured by Schmerling and Ipatieff as taking place by a carby the reaction of propylene with t h e secondary carbonium ion: bonium ion mechanism (IO),b u t the reverse order of reactivity of olefins over the nickel oxide-silica-alumina catalyst suggests CHa-CH-CHB CHz=CH-CH, --+ that the mechanism is different from t h a t described for the usual 4 acid-type catalysts. At any rate, the products obtained from CHs the polymerization of ethylene over nickel oxide-silica-alumina are those which would be expected from carbonium-ion reactions. CH,-&"CH,-CH-CH, (3 + The hexene fraction contained 3-methyl-2-pentene and 3-methyl1-pentene, whereas propylene dimer contained CH3 CH3 only 4-methyl- and 2-methyl-pentenes. Reactions I I H between ethylene and 2-butene would be expected CH3-CH-CH2-CH-CH3 ---+ CH,--CH-CHz-CH=CHz to give 3-methylpentenes only, regardless of which olefin formed the carbonium ion for the reaction. CH3- H--CH=CH-CHs H + (4)
bonium ion mechanism of polymerization as proposed by Whitmore (14). The fact t h a t more than a third of the hexenes fraction consisted of straight-chain hexenes indicates, however, t h a t the ratio of primary to secondary carbonium ions formed from propylene a t this temperature may be higher than has been supposed ( 8 ) . The difference in proton affinities for carbon atoms 1 and 2 is not as great in propylene as in isobutene (6). T h e formation of straight-chain hexenes from t h e primary carbonium ion of propylene could proceed as follows: +
+
L
+
i
+
+
I+
CHs 1 CH3--CH-CH1-CH2-CHa
+
\ iH3
+
+
Polymerization of Oleflns in Cracked Gas
CH,
--+
I
CH3-C=CH-CH2-CHs
The greater reactivity of branched-chain hexenes t o form nonenes and higher olefins may help t o account for t h e unexpectedly large concentration of straight-chain hexenes in the Ca fraction of the polymer. Propylene Polymer as Motor Fuel. Typical propylene polymer, consisting of 70% Cg, 20% Cg, and 10% CIZ+olefins by volume, had a n ASTM research octane rating of 90.4. With 2 ml. of tetraethyllead per gallon, the rating was 96.7. The API gravity was 62.2, and the Reid vapor pressure was 7.55 pounds per square inch absolute. An ASTM distillation gave the following points: initial, 38" C.; 50%, 90' C.; 95%, 207' C.; end point, 219" C. The total polymer was water-white, being completely free of yellow color that is typical of polymer made over unpromoted silica-alumina a t higher temperatures.
Ethylene Polymerization Experimental Procedure. Feed stock was blended from Llatheson Go. pure grade ethylene and National Cylinder Gas Co. hydrogen. Hydrogen was chosen as a diluent which would be present in cracked gas, and because it aided in the removal of impurities from the ethylene by selective hydrogenation. The experimental work reported here was done with feed containing 45 mole % ethylene and 55% hydrogen. Runs were made at 300 pounds per square inch gage and 40" C., with a feed rate of 600 standard volumes of feed gas per hour per volume of catalyst. The effluent was passed t o a dry ice trap for removal of polymer from the off-gas, which was then metered and sampled from ethylene analysis. Conversion and Product Composition. Conversion of ethylene averaged about 977" during 5-hour runs, which gave a polymer
April 1955
+
+H
+
Experimental Procedure. The feed for these experiments consisted of gas produced by the cracking of n-butane in tubular reactors. The gas had been subjected t o several compression and stripping stages and was free of material heavier than butanes. The approximate composition of this gas is shown in Table 11.
Table II.
Composition of Cracked Gas Feed
Component Hydrogen Methane Ethylene Ethane Propylene Propane Butenes Butanes Carbon monoxide, nitrogen, acetylene, and butadiene, total
Mole
%
10 40
25 10 10
3
0.2
1.0 0.8
The compressed cracked gas was withdrawn from t h e feed cylinder through a regulator and entered the system through a flow controller and motor valve as described. I n most experiments, the gas stream was diluted with n-butane or a recycle stream composed of butane and butenes before i t entered the reactor. I n once-through operation, the reactor effluent passed to a glass fractionating column, in which t h e Cs+ polymer was removed from the off-gases. I n recycle operation, these separations were made in steel columns operated a t about 85 pounds per square inch gage, so t h a t the C4 fraction could be handled
INDUSTRIAL AND ENGINEERING CHEMISTRY
755
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT as a liquid a t room temperature and could be pumped back to t h e reactor inlet. All experiments were conducted at 500 pounds per square inch gage and a gas-feed rate of 600 standard volumes per hour per volume of catalyst. When used, liquid was charged at 4 volumes per hour per volume of catalyst.
Total olefin conversion decreased from 99 to 9G% during the course of the run. The average rate of polymer production was 360 grams per hour per liter of catalyst. The polymer composition by volume was 13% pentenes, 2 5 % hexenes, 20% heptenes, and 4170 octenes through decenes. The end point of the total polymer by ASTM distillation was 210" C., and the ASTM research octane number, unleaded, was 93.3. Feed Impurities as Catalyst Poisons
Table 111 lists t h e impurities which are catalyst poisons and which are normally encountered in t h e olefins studied. Almost without exception, those impurities which acted as catalyst poisons were absorbed quantitatively in t h e top portion of t h e bed, so t h a t the catalyst in the lower portion of the bed remained
4-O-O-Qj
I
1
WITHOUT BUTANE
HOURS ON STREAM Figure 5. Temperature effect on olefin conversion 'in cracked gas. Pressure, 500 pounds per square inch gage; space velocity, 600
Effects of Temperature and Liquid Dilution. Figure 5 shows the effect of reaction temperature on initial conversion and rate of decline in conversion in operation with cracked gas feed alone. Olefin conversion was lower initially and decreased more rapidly a t the higher temperatures. Since it seemed likely t h a t this loss of catalyst activity with time on stream was caused by the accumulation of heavy polymer on the catalyst surface, experiments were made in which liquid-phase diluent was provided by addition of butane to the olefin feed. Figure G shows a comparison of operations with and without the liquid diluent. During the run with added butane, conversion of olefins in t h e cracked gas remained constant a t 96 mole yo,in contrast .to the fairly rapid decline in conversion in the vapor-phase operation. Conversion was found t o increase slightly with reaction temperature over the range of 35' t o 75" C. in operations with butane diluent. Hydrogenation of the ethylene and propylene by the hydrogen present in the feed became appreciable a t about 75" C., both with and without butane diluent in the feed. Therefore, most experiments with this feed were conducted a t about 65' C. Butane-Butene Recycle. The use of butane as a feed diluent would involve the separation of the Cgfraction from the reactor effluent for recycle t o the reactor a t the desired rate. A considerable portion of the ethylene was converted t o butenes in once-through operation, so t h a t the butane stream contained butenes. However, since the butenes polymerized further over this catalyst, either alone or by reaction with ethylene and propylene, t h e butenes concentration in the recycle stream quickly reached a constant level a t which the rate of polymerization was equal to the rate of formation. A 100-hour run was made to obtain data on conversion and on properties of the product in butane-butenes recycle operation. Reaction conditions were 500 pounds per square inch gage and 65" t o 70' C., with feed rates of 600 standard volumes of cracked gas and 4 liquid volumes of butane-butenes per hour per volume of catalyst. T h e run was started with a butane-butenes mixture from a previous run. This mixture had reached a constant butenes content of 12 mole yo, and the composition remained fairly constant throughout the 100-hour test. Thus, all of the converted olefins went to C6+ polymer.
756
"" 0
4 6 0 HOURS ON STREAM Figure 6. Liquid diluent effect on olefin conversion in cracked gas. Pressure, 500 pounds per square inch gage; temperature, 65OC.;space velocity, 600 gas plus 4 liquid n-butane
2
active until the absorptive capacity of the entire bed was consumed. I n tests with feed containing poisons, it was easy to follow the progressive poisoning of the bed with a thermocouple probe, since the point of maximum temperature rise produced by the highly exothermic polymerization reaction moved downward at the rate a t which t h e catalyst was being poisoned. I n operation a t moderate space velocity t h e percentage conversion of olefin in t h e feed did not fall appreciably until more than half the bed had been poisoned.
Table 111.
Feed Impurity Poisons of Nickel Oxide-SilicaAlumina Catalyst
Impurity Acetylene Carbon monoxide Oxygen Sulfur compounds Water vapor Butadiene Carbon dioxide
Poisoning Effects Severe Severe Moderate Moderate Moderate Moderate Slight
The effect of the impurities listed in Table 111 a s causing moderate t o severe poisoning was apparently not reversible, as indicated by t h e fact t h a t t h e activity of t h e poisoned catalyst did not recover t o any large extent after removal of the poison from the feed. However, the catalyst was readily regenerated by combustion of any deposits which accumulated.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47 No. 4
GASOLINE PROCESSING literature Cited (1)
(2) (3) (4)
(5) (6)
Bailey, G. C., and Reid, J. A. (Phillips Petroleum C o . ) , U. S. Patents 2,581,228 (Jan. 1, 1952) and 2,605,940 (Aug. 12, 1952). Burk, R. E., Baldwin, B. G., and Whitacre, C. H., IND.ENG. CHEM.,29, 32630 (1937). Cheney, H. A., McAllister, S. H., Fountain, E. E., Anderson, J., and Peterson, W. H., Ibid., 42, 2580-6 (1950). Egloff, G., and Weinert, P. C., World Petroleum Congr., Proc. 3rd Congr., Hague, 1951, Sect. IV, p. 201. Evans, A. G., and Polanyi, M., J . Chem. SOC., 1947, p. 252. Hogan, J. P. (Phillips Petroleum Co.), U. S. Patent 2,642,467 (June 16, 1953).
(7) Ipatieff, V. N., and Pines, H., IND. ENG. CHEM.,27, 1364-9 (1935). (8) Langlois, G. E., Ibid., 45, 1470-6 (1953). (9) Langlois, G. E., arid Walkey, J. E., World Petroleum Congr., Proc. 3rd Congr., Hague, 1951, Sect. IV, p, 191. (10) Schmerling, Louis, and Ipatieff, V. N., "Advances in Catalysis," Vol. 11, p. 65, ilcademic Press, New York, 1950. (11) Steffens, J. H., Zimmerman, XI. U., and Laituri, iM. J., Chem. Eng. Progr., 45, 269 (1949). (12) Storch, H. H., J . Am. Chem. SOC.,57, 2598-601 (1935). (13) Thomas, C. L., IND.ENG.CHEM.,37, 543-5 (1945). (14) Whitmore, F. C., Ibid., 26, 94 (1934). RECEIVED for review September 10, 1954.
$CCEPTED January 11, 1955.
Dehydroalkylation of Aromatics with lsoparaffins JOE T. KELLY
AND
ROBERT J. LEE,
Pan American Refining Corp., Texas Cify, rex.
The alkylation of aromatic hydrocarbons by isobutane in the presence of olefins has been studied in considerable detail. By this reaction, tert-butyl aromatics can be prepared in good yield and high purity. The olefins are found to act primarily as hydrogen acceptors under acidcatalyzed conditions at 0" to 30" C. when excess isobutane is employed and an alkylatable aromatic i s present in the system. The olefins are thereby converted to paraffins rather than alkylating the isobutane or the aromatic. In the case of Cq and higher normal olefins, hydrogen transfer and saturation of the olefin i s accompanied by isomerization of the carbon skeletoni.e., hydroisomerization-so that a branched chain paraffin is produced. A carbonium ion mechanism i s presented which i s in accord with the experimental facts and the products produced.
T
HIS paper describes t h e alkylation of aromatic hydrocarbons
%
by isoparaffins in t h e presence of a n olefinic hydrogen acceptor. Primary emphasis has been on t h e alkylation of benzene and toluene with isobutane t o produce tert-butyl aromatics. Excess isobutane is required as alkylating agent under acid catalyzed conditions a t 0' t o 30" C. Olefins must be present t o accept hydrogen in order for t h e reaction to proceed. T h e reaction is therefore termed dehydroalkylation. T h e olefins are converted to paraffins by t h e hydrogen transfer reaction involved in dehydroalkylation. I n t h e case of C4 and higher n-olefins, hydrogen transfer and saturation of t h e olefin is accompanied b y simultaneous isomerization of t h e carbon skeleton-Le., hydroisomerization-so t h a t a branched chain paraffin is produced. Studies of numerous reaction combinations indicate that isobutane is converted to tert-butyl ions which alkylate t h e aromatic. By this process, p-di-tert-butylbenzene and isoparaffins can be produced in near quantitative yields from a reaction mixture consisting of isobutane, benzene, and olefins. Similarly, tert-butyltoluene is obtained from toluene. Yields of tert-butylated aroinatics and hydroisomerized products vary considerably, depending on t h e structure of t h e olefin hydrogen acceptor and t h e catalyst. D a t a are presented on a variety of olefins using sylfuric acid, boron fluoride monohydrate (BF3. HzO), and hydrogen fluoride catalysts. On t h e basis of these results, a carbonium ion mechanism has been developed which is in accord with t h e experimental facts and t h e products produced. T h e dehydroalkylation reaction may be illustrated by equation presented herewith. T h e over-all result may be pictured as t h e reaction of isobutane with a n aromatic (in this case toluene), with a net transfer of t h e tert-hydrogen from isobutane and a hydrogen from t h e aromatic t o t h e olefin. tert-Butyltoluene and a paraffin are t h e major products. T h e reaction is thus seen t o involve dehydroalkylation in contrast t o t h e conventional alkylation of a n aromatic b y a n olefin. However, a n olefin is necessary as hydrogen acceptor;
*
April 1955
in t h e abeence of olefin, no reaction of isobutane and toluene could be induced with these acid catalysts. Literature references t o the direct alkylation of aromatics with olefins are voluminous. However, t h e alkylation of aromatics with isoparaffins by a hydrogen transfer reaction was first reported by Condon and Matuszak in 1948 ( 4 ) , and subsequently in a Condon patent ( 3 ) . Condon and Matuszak described experiments in which t h e relative rates of alkylation of benzene and isobutane were studied, by reacting mixtures of benzene in excess isobutane with propylene. Their major products were direct olefin alkylation products, namely isopropylbenzenes. However, some dehydroalkylation was evidenced by moderate yields of mono-tert-butylbenzene and terl-butyl-isopropylbensene. Since no isobutylene was charged to this reaction, the krt-butyl aromatics must have been formed from isobutane through a hydrogen transfer reaction. I n the present work, dehydroalkylation becomes the major reaction, and the competing reactions of direct olefin alkylation become of minor importance when the reaction is carried out with excess isobutane and with certain combinations of catalysts and olefin types. Further, even when a n-olefin is used as hydrogen acceptor, it is converted to isoparaffins almost t o t h e exclusion of n-paraffins. However, the yields are generally lower when using a n-olefin as hydrogen acceptor, and with some catalysts the yields are much loner than obtained with branched chain olefins. CH CH3-C-?
FH3
+
t
CH3 ISOBUTANE
TOLUENE
G3
4-
IOOC
CHJ-CH-CH=CH-CH~-
OLEFIN
ACID CATALYST
CH3 CH3-hH-CHz-CHz-CH3
CHJ-C-CH~ CH3
2 - M E T H Y LPENTANE
t - B U T Y LTOLUENE
INDUSTRIAL AND ENGINEERING CHEMISTRY
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