OLEFIN DISPROPORTIONATION A Rtw Catahtic Process R O B E R T L . B A N K S A N D G R A N T C. B A I L E Y Phillifs Petrolrum Co
. Baitlest i l l e , Okla
A new catalytic disproportionation reaction i s described in which linear olefins of three to eight carbon atoms were converted to homologs of shorter and longer carbon chains.
Approximately equal molar quan-
tities of olefins with carbon chains shorter and longer than the feed were produced. Catalysts for the reaction consisted of molybdenum hexacarbonyl, tungsten hexacarbonyl, and molybdenum oxide supported on alumina. The disproportionation of propylene to ethylene and n-butenes using molybdena-alumina catalyst i s reported in detail. In one example at 3 2 5 " F., 450 p.s.i.g., and a space velocity of 8.5 grams of feed per hour per gram of catalyst, propylene conversion was 43% (near thermodynamic equilibrium) and efficiency to ethylene and butylene was 94%.
catalytic process linear olefins are converted to T h e disproportionation reaction \cas observed during a study of catalysts prepared from molybdenum hexacarhonyl and alumina. Reactions of olefins containing from two to eight carbon atoms \rere studied over molybdenum hexacarbonylalumina a n d molybdena-alumina catalysts prepared in the laboratory and over specially activated commercial cobalt oxide - m o l y b l e n - a l u m i n a catalyst. Disproportionation of propylene over the commercial catalyst was studied in some detail. T h e effects of molybdena content of the catalyst. temperature. space rate. and the presence of other olefins on disproportionation of propylene were examined.
Apparatus and Procedures. These studies were made in a continuous-flow system designed to operate at 200 to 1000 p.s.i.g. using a 5O-ml. or 100-ml. fixed-bed reactor (Figure 1 ) . T h e feed was pumped a t a controlled rate through a drying tube and preheater into the top of the reactor. T h e reactor was 26 inches long and was provided with a n internal thermocouple well and a catalyst support. T h e 50-ml. reactor was made from '?-inch and the 100-ml. from 1-inch stainless steel pipe. Electric furnaces controlled the temperatures of both the preheater and the reactor. T h e effluent from the bottom of the reactor passed through a back-pressure control valve and into a receiver a t dry ice temperature. T h e receiver was changed at regular intervals. generally after 30 or 60 minutes, and the effluent material collected during each interval was analyzed by chromatography. I n some cases mass spectrometer and infrared analyses were also used.
Experimental
Results and Discussion
Catalysts. Both laboratory-prepared and commercial catalysts \cere used in this investigation. Supported molybdenum hexacarbonyl was prepared by impregnating preactivated alumina, under vacuum, with molvbdenum hexacarhonyl-cyclohexane solution a t about 1 50" F. Cyclohexanc \vas removed by flushing \cith nitrogen and vacuum treatment at 250' to 290' F. T h e same procedure \cas used to prepare zupported tringrtrn heuacarbonyl. Molybdena-alumina catalysts \cere prepared in the laboratory by impregnating alumina gel, cruihed to 20-40 mesh, with aqueous .ammonium molybdate solutions. Surface area, pore volume. and average pore diameter of the unpromoted alumina were 178 s q . meters per gram, 0.48 cc. per gram. and 107 A . T h e catalysts were activated in a stream of anhydrous air at 1000" F. for 5 hours. A typical commercial cobalt oxidr-molybdena~alumina catalyst had the folloxving ph>-sicalproperties and composition :
Disproportionation Reactions. MOLYBDESLW HEXACARBOSYL-ALUMINA CATALYSTS.Propylene, 1 -butene, 1pentene, and 1-hexene \vere passed over molybdenum hexacarbonyl-alumina a t 250' F.. SO@ p.s.i.g.. and 1 to 2 \$,eight hourly space velocity (\VHS\J. Typical results are presented in Table I .
N
A NELV
I homologs of shorter and longer carbon chains.
Surface area. sq. meters/g. 284 Pore volume, c c . j g . 0.58 Pore diameter, '4.82 Bulk density. g./'cc. 0 . 6 1 Size (extrudates). inch ,'IO
Composition, wt. 7c c o0 3 4 MoOa 11.0 A 1 2 0 8 85.6
T h e catalyst \vas activated with air a t 1000" or 110O0 F. for .i hours beforr u c r . Feed Stocks. Phillips pure grade or technical grade hydrocarbons \cere dried over activated alumina. T h e liquid feeds were degassed b>-heating to the boiling point. I n some tests propane. isobutane. or n-pentane \cas used a s diluent. Most of the studicr on prop)-lvne disproportionation were m a d e with a 60 pro~)vlene40 propanv blend. 170
l&EC PRODUCT RESEARCH A N D DEVELOPMENT
Table I.
Disproportionation of Various Olefins over Molybdenum Hexacarbonyl-Alumina Catalyst
ConLersion. % Product distribution, mole
Propylene
I-Butene
I-Pentene
I-Herene
25
10
60
54
42
8
2
5
8
23
55
84 16
33 6'
52 48
rr
Ethylene Propylene Butenes Pentenes Hevenes CI Butene distribution. 1 -Butene
+
2-Butene
Pentene distribution. c1-Pentene 2-Pentene Isopentene
5 100
2
98
52 40 8
Conversions ranged from 10% for 1-butene to 60y0 for 1pentene. Yields of olefins with chain length shorter than the feed were 40 to 50'moles per 100 moles of converted feed as compared to 50 to 60 moles of longer chain olefins. T h e shorter chain olefins contained appreciable amounts of alphaolefins ; the longer chain products were predominantly internal olefins. No indication of polymerization as a primary reaction was observed (product distributions showed no peaks a t carbon numbers which were multiples of the feed). Ethylene was converted at low yields to a product containing cyclopropane and methylcyclopropane. In one test a t 280' F.. 500 p.s.i.g., and 250 v . ~ v . , ' h r . ethylene , conversion was 2.77, and the product contained 8 weight 7, cyclopropane and 12 weight methylcyclopropane. TUSCSTEN HEXACARBONYL CATALYSTS.'Tungsten hexacarbonyl on alumina. when activated. was an olefin disproportionation catalyst. I n tests with 1-butene and I-pentene feeds, disproportionation conversions were 7 and 447,. respectively. COBALTOXIDE-MOLYBDENA-ALUMINA CATALYST.Disproportionation of propylene. 1-butene, 2-butene; 1-pentene. 2pentene, 1-hexene. and 1-octene over cobalt oxide-molybdena-alumina catalyst was investigated over a temperature range of 200' to 570' F., a t 450 p.s.i.g. and 3 to 4 weight hourly space velocity (Figure 2 ) . T h e rates of conversion were highest a t 300' to 400' F. The maximum conversions in some cases were limited by thermodynamic equilibriums-for example: the equilibrium disproportionation of propylene is about 40%. Alpha-olefins disproportionated more rapidly than the corresponding beta-olefins. These catalysts have some activity for double-bond isomerization. Figure 3 shows the per cent of feed isomerized in these experiments. This precludes exact comparison of reaction rates of different isomers as feed and influences isomer distribution in the product. T h e distributions of the disproportionation products were not appreciably affected by temperature. However, a t the higher temperatures hydrogenation of the olefins started to become significant. Distributions of the disproportionation products obtained from propylene, 1-hexene, and 1-octene a t 325' F. are presented in Figure 4. Similar data obtained from 1butene and 2-butene are presented in Figure 5. .4pproximately equal molar quantities of olefins with chains shorter and longer than the feed were produced. Ratios of trans-2-butene to cis-2-butene in the reactor effluents are shown in Table 11. Similar data for 2-pentene are shown in Table 111. The ratio of trans-2-butene to &-%-butene was near the equilibrium value, calculated a t 0 p.s.i.g.. in disproportionation of propylene or 2-pentene. The ratio was less than equilibrium value in disproportionation of 1-pentene a t 200' F. T h e trans to cis ratio of 2-butene from 1-butene isomerization was
Table II,
Ratio of trans-2-Butene to cis-2-Butene in Reactor Effluent
Temperature of Test, F. Olejin Feed 200 225 320-325 390-400 Propylene 2.15 1.95 1.78 0.96 1.24 1.49 1-Butene 0.46 2.21 2.21 2-Butenea 2.31 2.0 I-Pentrne 1.o 1.8 2-Pentene 2.0 1 .9 2.2 2.0 Equilibrium ratio* 2 . 4 Ratio in 2-butene feed: 5.36. * At 0p.s.i.g.
DRY ICE-ACETONE OATH'
PUMP/-
SCALES
Figure 1. Experimental unit for p.s.i.g. operation
200- to 1000-
70
n 0. 0
n
+ z Y 30-
a
n. W
20 -
0
200
300
500
400
600
TEMPERATURE, F.
Figure 2. Effect of temperature on disproportionation conversion
Table 111.
Ratio of trans-2-Pentene to cis-2-Pentene in Reactor Effluent
Temperature of Tcst, a F. 25.5 ,320-325 390--~?00 5 7 0 ~~
570
OlrJin Feed
200
1.80 1.49
Propylene 1-Butene 2-Butene 1-Pentene 2-Pentene" Equilibrium ratiob
2.0 3.0 1.2 3.8 1.6
2.5
VOL. 3
NO. 3
1.5 1.8 1.7
a
3.0 2.4 2.6 2.2 2.7 1.5 1.5 Ratio in 2-pentenefeed: 5.7. * A t Op.s.i.g.
3.4 2.4
1.8 2.1
2.4
1.4
SEPTEMBER 1964
2.1 2.2 1.3
171
...~
far belo\< the equilibriurn ratio. indicating the mechanism for isomerization favors cis formation The ratio of tron.r-2-prntene to izr-2-pentene \vas highcr t h a n t h r cquilibriurn ratio in disproportionation of prop)-lenc or butriies. 'The trail.: to cis ratio of 2-pentene from 1 -prntene isomerizatioti \vas less than thc. equilitriurn value a t the lower teiiipet-aturc a n d higher at the higher trmperatures. Propylene Disproportionation Studies. CATALYSTS. 7'he eift.ct of rnolybdena content of the catalyst was studied on laboi-ator! -prepared inol~-h(lcna-alurninacatalysts containing IICJIII 0.1~) to 13,25; nioiybdrna. Propylene conversions Lvere highest Lvith 7 to 125; niolybdena catalvsts. L\'hen teinperatui-e \\-a$ increased step\viw from 15O0 to 550' 1'. propylene ions incrrased \ \ ith increasing temperature to a maxirnuiri vaiue for cach c a t a l p and then in some caws decreased \q.irh f i i r t h ~ rincrt.asr in temperature. '1 he addition of 2 to 4$1 cobalt oxide to molybdena-alumina catal>sts reduced cokr formation. but apparently did not affect the initial ac.ti\,ity of the catalyst. REACT i o & 'I'I:MPF KA'I'CKE. Analyses of the products from di~proportionatic,nof propylene over cobalt oxide-molybdena-alurnina catal!-sts a t various temperatures are sho\in in Table
i- --T
_-
40
o.
-
20'0
400
300.
600
500
TEMPERATURE, F.
I\..
Figure 3. Effect of temperature on isomerization
v\ \
I F E E D ! 10 PROPYLENE
I
L
Propylene conversion incrrased lvith temperature from l-,V\: at 200' € . to 42.657 a t 400' F.. and then decreased to 1 4 . 6 7 a t 5-0" F. At 40(i0F. the conversion was near the a p p a r r n t equilibrium conversion for the reaction :
~
I-HEXENE
I
1
I
CHANGE I N NUMBER OF CARBON ATOMS
Figure 4.
Distribution of disproportionation products
Table IV.
At 3 2 5 a F., 4 5 0 p.s.i.g. a n d 4 W H S V with propylene, 1-hexene, a n d 1 -octene feeds
5O
t
I
I
2 propylene 9ethylene
+ 2-butene
'I'hr efficiencies of converted prop)-lene to ethylene and butenes \ v e x highest at the lower temperatures. A t the higher temperatures. in addition to the increase in material above C + hydrogenation of propylene to propane started to become qigniticant. SPACI:R.ATE. T h e effects of space rate at 325' F. and 4 5 0 p.s.i.g. \\.ith I)rop~-lenc.-i)ropaIiefeed containing GO and 99Yc propvlrne are sho\in in Table \'. Prop)-lene conversions a t 4 and 8.5 IVHSV w w e near the apparent disproportionation equilibrium conLrersioi1, ~ L I Idecreased at higher space rates. of equilibrium conversion \vas obtained. Similar con\-er---
Ethylene 1 -Butene tr uns-2-Butene cis-2-Butene Ci Residue B. 39.3 Space rate, \CHSV Propylene conversion,
+
C''
I
