Catalytic Isomerization of l-IIexene J
E. A. NARAGON The Texas Company, Beacon, N . Y Experimental aata are reported on the vapor phase isomerization of 1-hexene over several fixed-bed catalysts. Analytical and test data obtained by use of fractional distillation, mass spectrometry, and octane ratings on the hydrogenated liquid products together with published equilibrium data on the hexenes have made it possible to follow the extent and Course of reactions. Activated alumina (low soda content), boria-alumina, phosphoric
acid, acid-treated Doucil and UOP cracking catalyst (Type B) were the most active catalysts tested. Approximately equilibrium mixtures of the hexenes together with some lower and higher boiling hydrocarbons were obtained over these catalysts at some temperatures in the range 500" to 900" F. Isomerization and hydrogenation both occurred when 1-hexene was treated over molybdena-boriaalumina at 600" to 775" I+'. i n the presence of hydrogen.
T
Each isomerization treatment wits carried out with a fresh batch of catalyst at atmospheric pressure except in one test where a low hydrogen pressure was used. The liquid produrtv from the isomerization treatments, with the exceptions of those obtained t o study the effect of proress period, were hydrogenated in the same equipment over f r ~ s h l yreduced molybdena-alumina catalyst that previously had been used in commercial Hpdroforming-operations. The follou~ing . - conditions were used :
HE isomerization of olefins can occur in two ways. One way involves a shift of the double bond along the carbon chain, and the other way involves chain branching. Shifting of the double bond from the one-position toward the center of the molecule results in desirable octane number improvements and provides a means of upgrading olefinic stocks such as Hydrocol (synthetic, %?) and thermally cracked gasolines (1). Chain branbhing- of one-olefins also results in desirable octane number improvements and provides a means not only of upgrading olefinic stocks but also of producing branched olefins that can be hydrogenated subsequently to high octane paraffins for Use in aviation gasoline. Previous investigators ( 3 $ 4 6, , 9 , IO) have reported work on the isomerization by chain branching of normal hexenes over a variety of catalysts. Hay, Montgomery, and Coull ( 6 ) were the only investigators who attempted quantitative analyses of the products to determine the extent of isomerization. The object of the present investigation was t o obtain data to supplement those reported b y Hay et al. (6). Several new catalysts were tested for the isomerization of 1-hexene and more detailed analytical and test data were obtained on the liquid products.
~ ~ ~ ~ ~ ~ vol,,vol.,hour ~ ' ~ ~ Hydrogen pressure, lk,.lsq. inch gage Hydrogen drawoff rate, cu. ft.jhour
~
v
Figure 1. Isothermal Fixed-Bed Unit 2490
l
575 ~ 1.0 & 400 4.0
These conditions were suitable for hydrogenating 1-hexene without 'causing isomerization, cracking, or polymerization. Also, small portions of liquid products from some of the isomekization treatments were hydrogenated over Raney nickel a~ a
EQUIPMENT AND EXPERIMENTAL PROCEDURE
A flow diagram of the fiued-bed isothermal unit used in this work is shown in Figure 1. The reactor w&s constructed of stainless steel. It had a catalyst capacity of 320 ml. (29 inches of catalyst bed in a 1-inch inside diameter tube). A perforated steel plate near the bottom of the reactor was used to hold the catalyst in place. A spiral of stainless steel tubing that served as a preheater way welded to the reactor near the top. Heat was supplied t o the reactor from three separate windings of Nichrome wire within an electric furnace and was controlled manually with Variacs. T e m p e r e tures a t the top, middle, and bottom of the catalyst bed were measured by use of iron-constantan thermocouples within a thermowell. There were t w o brine-cooled product receivers connected in parallel for alternate use. Each product receiver was surmounted by a brine-cooled h o c k b a c k condenser. A wet-test meter was connected to the outlet from the knockback condensers.
~
y
,
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1950
c - c -C-C-C.C *c-c-
e
0-C-C-0.6
C-G-C-CI
7
0-0-CaC
c-c-C-C
=+=c-c-c.c-c-
c
C-0-C-C-C
c .p- c-c-c-c-0 I
C-C-C-C=C
C-6-c-C
1) r; &
A -
C-C-C-C-C I
y
c-c=c-G I
, Two forms of activated alumina obtained from the Aluminurn Company of America: one was Grade F-1 (high soda, 0.8% maximum) and the other was Grade H-40 (R-2200 type, low soda) containing about 5% silica Three boria-activated alumina (Grade H-40, R2200) catalysts Containing 10 12.5, and 15y0 boria 5% molyhdena-lO% boria activated alumina (Grade H-40, R-2200) 10% ferric chloride activatPd alumina (Grade F-1) Two 25% zinc chloride activated alumina catalysts: one amtained Grade F-1 alumina and the other contained Grade 11-40 (R-2200) Solid phosphoric acid polymerization catalyst obtained from Universal Oil Products Com any boron phosphate-396 phosphoric acid Hyflo Super -cel ( 5 i g , Johns Manwlle) 15% boron p h o s p h a M 7 % phosphoric a c i d 4 8 % silica Acid (HC1)-treated Doucil obtained from American Doucil Company Cracking catal t T pe B, 4.3% alumina-9.4% zirconia86.2% silica og&ne$from Universal Oil Produck Company
(a,
t
G C
JIC-C-P*C
EXPERIMENTAL CONDITIONS
All catalysts with the exception of those containing zinc arid ferric chlorides were tested for the isomerization of 1-hexene at temperatures of about 50O0, 600°,750°, and 900" F. A liquid space velocity of 0.5 volume per volume per hour was used a t each temperature and in addition a few tests were made with
C I
C
Figure 2.
2491
Isomerization of 1-Hexene
check on the possibilit,y of isomerization occurring during the treatments over the molybdena-alumina catalyst. -4pproximately the same product compositions were obtained with Raney dickel as were-obtained with tho molybdena-alumina catalyst. Products from the hydrogtmation treatments were tested for unsaturation by use of bromine addition numbers. When the number waa of the order of 10 or higher, the product. was subjected to another hydrogenation treatment. If the number was between 2 and 10, the product was washed with concentrated sulfuric acid to remove the olefins. Once the bromine number was 2 or lower small samples of the final products were fractionated in high efficiency columns of the type described by Naragon and Lewis (8)to obtain Cg cuts which were analyzed by use of a mass spectrometer. The remaining portions of the final hydrogenated products were distilled to obtain the Ca cuts that were tested for motor octane ratings (A.S.T.M. D 357). The liquid products obtained to study the effect of process period were tested directly for research octane ratings (A.S.T.M. D 908) without hydrogenation or distillation. Small samples (100 ml.) of these products were hydrogenated over Raney nickel in a small bomb and then were distilled to obtain Cg cuts for mass spectrometer analysis.
80
I
/
A MOLYBDENA- BCWA - W N A A BORIA-ALUMNA
# ACID TREATED DOUCIL 0 CRACKING CATALYST-TYPE B X ACTIVATED AWMNA -GRADE H - 4 0
'
2oSO0
550
600
650 700 TEMPERATURE,
750
850
600
900
OF.
Figure 3. Motor Octane Data (A.S.T.M. D 357) on Hydrogenated Ca Cut from Isomerization of 1-Hexene
CHARGE STOCK AND CATALYSTS
The I-hexene was prepared by the dehydration of technical grade n-hexanol over activated alumina (Grade F-1) a t 800" F. in the fixed-bed isothermal unit. The alcohol was charged a t a liquid space velocity of 4 volumes per volume per hour. A fresh batch of aluminh was used for every 12 hours of operation to make certain that its activity was high. The hydrocarbon product from the dehydration was distilled in a large Stedman column having an efficiency a t total reflux of about forty theoretical plates to obtain a heart cut boiling a t 146' * 2' F. This cut, which was used in the present investigation, had the following properties: di0 0.6745; ng 1.3893; bromine addition number, 191. Hydrogenation of a portion of the fraction gave a product which boiled entirely on the n-hexane plateau and had a motor octane number (A.S.T.M. D 357) of 25. The catalysts investigated consisted of the following:
TABLE I. EQUILIBRIUM DATAON HEXENXIS(7) Hexenea
Hexanma 2,2-Dimethylbutane
8,3-Dimethyl-1-butene
Mole % a t 50OQF. 600' F. 750'F. 0.7 0.7 0.6 0.7 0.7 0.6
900" F. 0 5 0.5
2,3-Dimethylbutane
13.3 5.1 8.2
12.2 5.3 6.9
10.7 5.3 5.4
9.8 5.3 4.5
2-Methylpentane
41.1 10.9 0.9 22.5
39.9 12.8
6.8
40.5 11.8 1.0 20.4 7.3
39 1 13.7 1.5 15.8 8.1
34.4 0.5 30.8 3.1
33.7 0.9 29.5 3.3
33.0 1.3 27.7 4.0
31.7
n-Hexane 10.5 12.9 1-Hexene 0.5 0.9 2-Hexene 6.6 8.1 3-Hexene 3.4 3.9 Formed by hydrogenation from equilibrium mixtures of hexenes.
15.8 1.5 9.7 4.6
18 9 2 0 11 3
2,3-Dimethyl-l-butene 2.3-Dimethyl-2-butene 2-Methyl-1-pentene 4-Methyl-1-pentene 2-Methyl-2-pentene 4-Methyl-2-pentene 3-Methyl-1-pentene 3-Methyl-2-pentene 2-Ethyl-1-butene
3-Methylpentane
1.1
18.1 7.9
2.0 25 7 4.0
5 6
2491
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 42, No. 12 DISCUSSION OF RESULTS
OF HYDROQENATED HEXENES RESULTING FROM ISOMERIZATION OF TABLE 11. C,OMPOSITION I-HEXENE OVER SEVERAL CATALYSTS
The i s o m e r i z a t i o n of 1ticxene occurs by reactions of (Liquid space velocity, 0.5 vol./vol./hour) the type shown schematically Compositio>AHydrogenated Hexeneu, Mole 7% -_ in Figure 2. Both bond shiftTeiui)., %,?-Dimethyl- 2,3-Dimettiyl2-Methyl3-MethylCatalyst F. butane butane pentane pentane n-Hexanr ing and chain branching occur. Equilibrium data 500 0.7 13.3 41.1 34.4 10.5 tn addition to the reactions 600 0.7 12.2 40.5 33.7 12.9 shown there are those which 750 0.6 10.7 89.9 33.0 15.8 900 0.5 9.8 39 I 31.7 18.9 involve the formation of cis Activated alumina dnd trans isomers. All in all 5.5 88.6 (Grade H-40) ,500 0.2 0.6 5.1 there are seventeen hekenr I ~ O 56.4 600 0.0 3 1 22.1 18.4 17.1 11 0 33.9 750 0.0 38.0 meis; mixtures of these are 22.9 32.7 900 0.0 9 4 35.0 difficult to analyze because the 8 1 21.9 18.9 55.3 .iOOU 0.8 Boria-alumina 34.5 12.7 12 1 chemical properties of the in0.0 40.7 600 h 10 7 37 7 750h 0.0 20.4 31.2 dividual isomers are similar and 27.3 31.8 7 4 33.5 900tJ 0.0 their physical propertiea, such Molybdena-boria9.3 80.2 alumina 500 0.0 0.13 9.9 as boiling points, densities, and 6 '8 27.7 34.3 600 0.0 31.2 refractive indices, are quite 7.0 31.2 27.0 34.4 750 0.4 80.3 900 0.4 1.9 9.0 8.4 close together. If the hexenes 500 0.3 32.6 12. 1 36.7 18.3 Phosphoric acid are hydrogenated t o the five 600 0.2 34.6 12.4 41..2 11.6 750 33.7 0.0 9.5 35.9 20 9 hexane isomers, however, the 78.6 900 0.8 1.4 11 . o 8.2 latter can be analyzed relitAcid-treated Doucil 500 1.8 7.6 29.1 22.6 38.9 tively easily, but such analyses 600 31.6 0.0 9.7 38.7 20.0 7.50 1.5 12.1 33.4 25.0 28.0 make it possible to follow only 900 1.0 9.9 34.2 26.4 28,d the chain branching reactions UOP cracking catalyst, and not the bond shifting 0 1 600 0.0 4 7 32.9 27.4 35.0 Type B 750 0.0 9 1 37.4 30.9 22.6 cis and trans reactions. Never900 0.0 29.3 25 7 9 4 35.6 theless, the results obtained by Catalyst contajned 15% boria. use of a hydrogenation proceb Catalyst contained 10% boria. dure can be interpreted to some extent in terms of bond shiftLIQUID TABLE 111. GAS YIELDS, LIQUIDYIELDS, AND COMPOSITION O F HYDROGENATED ing using the equilibrium data PBODUCTS FROM ISOMERIZATION OF 1-HEXENE OVER SEVERAL CATALYSTS shown in Table I for the Liquid Gas Yield Composition, Liquid Vol. yo hexenes and the data for Temp.. Cu. Ft./Litkr Recovery, Below Above hexanes formed by hydrogenF. of Charge hexanes Hexanes hexane* Catalyst wt. % 0 97 3 ating equilibrium mixtures of 300 91 0.038 Activated alumina 98 600 0.050 1 (Grade H-40) 93 6 hexenes. This is particularly 96 750 0.333 6 86 8 2.331 900 86 9 74 17 true when hexane mixtures ap500 78 0.040 Boria-alumina 2 88 10 proximating those shown in 600 89 0.070 6 78 16 Table I are obtained by isom750 85 0.671 15 71 14 900 63 1.332 12 73 15 erizing hexenes and sub500 95 0.036 Molybdena-boria-alumina 0 95 5 sequently hydrogenating the 97 603 0.224 2 88 10 89 products as i t can be assumed 750 1.969 4 88 8 79 5.256 900 3 88 9 that such mixtures are formed 500 91 0.083 Phosphoric acid 3 82 15 from equilibrium mixtures of 600 87 0.053 5 91 4 750 98 0.115 4 93 3 the hexenes. This assumption 95 0.652 900 5 92 3 is used in the interpretation of 500 0.012 Acid-treated Doucil 2 the following data: 83 15 600 97 0.062 4 76 20 0.296 750 88 13 77 10 Activated alumina (Grade 3.403 900 66 11 71 18 H-40), boria-alumina, molybti00 97 0.030 Cracking catalyst, Type B 2 82 16 dena-boria-alumina, phos92 750 0.293 5 70 25 2,160 900 82 10 71 19 phoric a c i d , a c i d - t r c a t e d Doucil, and UOP cracking catalyst (Type B ) were the most active catalysts tested. space velocities of 0.1 and 1.0 volume per volume per hour. In Using these catalysts, mixtures of hexanes approximating those formed from equilibrium mixtures of hexenes were produced at general, the space velocity of 0.5 volume per volume per hour was the most satisfactory since at any one temperature more cracking Some temperatures the rarlge 500" to 9000 F. as shown in and polymerization occurred with the space velocity of 0.1 Table 11. Octane data on the mixtures of hexanes produced with volume per volume per hour and less isomerization occurred with these catalysts together with octane data on the hythe 'pace Of per volume per hour' The drogenated hexene equilibrium mixtures are plotted in Figure 3 . durations of the tests varied with the space velocities as follows: The same conclusions cltn be dravvn from these data as are drawl, 10 hours for 0.5; 20 hours for 0.1 ; and 6 hours for 1.0 volume per from the data in Table 11, volume per hour. In addition to the isomerization reactions there are side reacT h e catalysts containing zinc and ferric chlorides were tested at temperatures below the melting points of these compoundstiOnS, such as cracking and polymerization, which occur over from about 300" t o 500" F. A small amount of a nitrogenthese catalysts. Information on these reactions can be obtained hydrogen chloride mixture was charged continuously along with by inspection of the gas yields, liquid yields, and the over-all the 1-hexene over the zinc chloride-alumina catalyst. compositions of the hydrogenated liquid products that are sum-
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1950
2493
TABLE V. EFFECTOF PROCESS PERIOD ON ISOMERIZATION OF PERIOD ON ISOMERIZATION OF TABLE IV. EFFECTOF PROCESS ~ - H E X E NOVER E PHOSPHORIC ACIDCATALYST ~ - H E X E N OVER E 12.501, BORIAACTIVATED ALUMINA Charge Temperature, F. Liquid space velocity, vol./ vol./hour Gas yield, cu. ft./liter of charge Li uid isomerizate s e x e n e charged, wt. Research octane B o . (A.S.T.M. D 908) Clear 0.5 ml. TEL/gal. 1.0 ml. TEL/gal. + 3 . 0 ml. TEL/gal.
++
0-10 603
Process Periods, Hours 10-20 20-30 30-40 40-50 805 605 606 604
0.5
0.5
0.6
0.5
0.5
0.057
0.042
0.036
0.133
0.037
97
99
99
97
99
95
96 98 99 100
97 99 99 100
95 98 98 99
97 98 99
... 99
100
...
91
94
...
89
0.0 12.8 41.8 35.4 9.8 0.2
0.0 10.9 38.0 33.2 17.7 0.2
0.0 4.6 47.3 31.1 17.0 0.0
0.0 10.6 39.4 36.4 13.4 0.2
0.0 10.2 36.3 33.2 20.3
0.0
ISOMERIZATION OF ~ - H E X E N OVER E MOLYBDENABORIA-ACTIVATED ALUMINA IN PRESENCE OF HYDROGEN
Temperature, F. Hydrogen'pressure, lb./s inch age Liauid space velocity, v%./vol.$hour GSS drawoff rate. cu. ft./hour Liquid recovery, wt. % ' Bromine addition No. of liquid product Hydrogenated liquid product Portion boiling below Ca cut vol. % Pqrtion boiling above Ca c u i , vol. % Cscut vol Motor o;?tane (A.S.T.M. D 357) Composition by mass spectrometer analysis, mole yo 2.2-Dimethylbutane 2,3-Dimethylbutane 2-Methylpentane 3-Methylpentane n-Hexane Residue
Teat 1 501 200 0.5 2.1 91.5 165 0 11 89 32 0.5
0.1 6.7
5.5
86.8 0.4
Test 2 614 200 0.5 1.9 92.3 41 6 14
80
57
0.4 5.9 31.3 20.3 40.5 1.6
Test 3 776 200 0.5 2.1 92.5 5
Hydrogenated liquid isomerizate cs cut, yo!. % of total Composition of Cs cut, mole % ' 2,2-Dimethylbutane 2,3-Dimethylbutane 2-Methylpentane 3-Methylpentane n-Hexane Residue
OF
marized in Table 111. These data are only approximate but, nevertheless, are useful in indicating trends. Inasmuch a~ boria-alumina and phosphoric acid were found to be active isomerization catalysts at 600" F., two tests were made to determine the effect of process time over these catalysts. Results of these tests are given in Tables I V and v. The activity of the boria-alumina catalyst fluctuated somewhat but remained good over a period of 50 hours whereas the activity of the phosphoric acid catalyst markedly decreased. The effect of hydrogen on the isomerization of 1-hexene over the mloybdena-boria-alumina catalyst a t temperatures of about 500", 600", and 775' F. was determined by making three tests; the resulta of these tests are shown in Table VI. Both isomerization and hydrogenation occurred a t temperatures of 600' and 775" F. The zinc chloride-alumina catalysts with added hydrogen chloride had some activity for the isomerization of 1-hexene even at the low temperatures of 300"to 500' F. as shown by the data in Table VII. Ferric chloride-alumina without hydrogen chloride a t 320" and 410" F. had about the same activity as that shown in Table VI1 for the zinc chloride-alumina (Grade H-40)a t similar temperatures. Activated alumina (Grade F-1) showed little activity for the isomerization of 1-hexene. The amounts of branched chain hexanes in the hydrogenated Ce cuts of the liquid products from tests with this catalyst were found to vary from 3 to 14'% as the temperature was varied from 500" to 900' F. The supported boron phosphate-phosphoric acid catalysts also showed little activity and gave results similar to those of the activated alumina (Grade F-1).
1.0
1.0
1.0
0.040
0.038
0.031. 0.035
97
110
101
98
97 99 100 Is0 0.06
94 96 98 98
98 98 99 100
92
93
95
95
97
0.0 10.1 37.1 31.6 20.1 1.1
0.0
0.0 5.5 28.6 24.0 41.8 0.2
0.0 3.9 23.1 20.4 52.4 0.2
1.4 24.7 20.1 53.3 0.5
6.1 28.9 24.0 40.8 0.2
1.0
100 96 98 99 99
0.0
HYDROGEN CHLORIDE
Temperature e F. Nt HC1 (1 1) charge rate, cu. ft./hour Liquid space velocity, vol./ vol./hour Grade activated alumina used
+
Test 1 318
Test 2 408
Test 3 318
Test 4 Test 5 406 507
0.015
0.015
0.015
0.015
0.015
0.5 F-1
0.5
F-1
0.5 H-40
1.0 H-40
0.5 H-40
98.2 0.02
92.3 0.04
98.1
