I
HARMON
M. KNIGHT and JOE T. KELLY
Research and Development Department, American
Oil Co., Texas City, Tex.
Preparation of Diisopropyl Using Salt Hydrate-Boron Trifluoride Complex Catalysts These new catalysts bypass many of the difficulties encountered with known catalysts
D~ISOPROPYL
or 2,3-dimethylbutane is a particularly valuable gasoline component because of its high Research octane rating of 103, its high lead susceptibility, and its excellent volatility. I t can be produced by the alkylation of isobutane with ethylene using various FriedelCrafts catalysts. Aluminum chloridehydrocarbon complexes ( 7 , 77, 20, 22), aluminum bromide (4, 74. 75), and boron trifluoride complexed with phosphoric acid (2, 6, 27), water (5, 70, 77, 18, 7Y), hydrogen fluoride (76, 23), and with a mixture of hydrogen fluoride and water ( 3 ) have all been reported as ethylene alkylation catalysts. All of these, however. present handling a n d corrosion problems and have rather short life. I n most cases, these catalysts are not effective below room temperatures, primarily because of viscosity characteristics ; alkylation at higher temperatures is accompanied by disproportionation and isomerization. Isomerization results in conversion of the primary product, diisopropyl, to relatively low-octane methylpentancs, while disproportionation causes decreased yields and high catalyst consumption. An effective solid catalyst was sought which could be used at loiv temperatures and thus avoid undesirable side reactions without creating mixing problems due to changes in catalyst viscosity. Certain hydrated salts, when used with boron trifluoride, were found to be active alkylation catalysts. For high activity, a n excess of boron trifluoride is required over that needed to form a 1 to 1 molar complex with the water of hydration. Alkylation with an iron(II1) pyrophoqphate hydrate-boron trifluoride catalyst, under preferred conditions, gives 260 to 27070 (wt.) total alkylate based on ethylene charged. Total alkylate product has a Research octane of 100 to 101 ; the hexane fraction. which is
97 to 99y0 2,3-dimethylbutane, rates almost 103. Experimental
Catalysts. Iron(II1) pyrophosphate was prepared from sodium pyrophosphate and iron(II1) nitrate using the following procedure. To a solution containing 25 ml. of concentrated nitric acid and 1000 grams of reagent grade iron(II1) nitrate nonahydrate [Fe(iY03)39H20] in about 15 liters of distilled water was slowly added, with stirring, 300 grams of technical grade sodium pyrophosphate (NalP20,) (\'ictor Chemical Works). A freshly prepared solution of S grams of flocculating agent (Separan 2610, Dow Chemical Co.) in 1000 ml. of hot, distilled water was added rapidly to cause coagulation of the salt crystals. After settling, the mixture was filtered and washed with hot, distilled water and then with absolute methanol. T h e salt was then dried at 85' to 90' C. for about 15 hours, after which it was ground to a powder and analyzed for water content. It was then dried carefully a t 110' C . to the desired hydrate level. Other pyrophosphates were prepared similarly. Salts other than the pyrophozphates were purchased and used after drying for 20 hours a t 110' C. Procedure. Catalyst screening was carried out in batch experiments: 90 grams of hydrated salt was charged to a dry, 4-liter carbon steel bomb. The bomb was evacuated, and 1 kg. of a dried 3 to 1 molar blend of isobutane and ethylene was added, followed by 90 grams of boron trifluoride. T h e mixture was rocked for 20 hours, after which a liquid sample was drawn rapidly through activated alumina to remove dissolved boron trifluoride and salt particles. This sample was distilled on
a Podbielniak column to obtain a hexane fraction for analysis by mass spectronietry. In some instances, the total product was water-washed and then fractionated for determination of product distribution and octane ratings. In the study of reaction variables, a 5-liter carbon steel stirred vessel, jacketed for temperature control, was used. First, 200 grams of salt was added to the reactor, and it was evacuated; then 1600 grams of technical grade iaobutane (Phillips Petroleum Co.) was added and 200 grams of anhydrous boron trifluoride (Harshaw Chemical Co. and Allied Chemical and Dye Corp.) pressured in. Reactor contents were mixed for 1 hour a t about 25' C. to assure complete complex formation, after which the temperature was adjusted to that desired for the alkylation reaction. Approximately 1SO grams of technical grade ethylene was added over a period of 1 to 4 hours through a porous metal dizk near the reactor bottom. After the ethylene was added, reactor contents were stirred for an additional half hour. and then the salt was allowed to settle. T h e hydrocarbon product was removed and waterwashed. Samples were taken for Podbielniak analyses, and the remainder of the product was depentanized on a Hyper-Cal column. The drpentanized product was distilled to 177' C . overhead temperature using a one-plate column to obtain an overhead fraction for octane determinations.
Results a n d Discussion Definition of the Catalysts. A large number of hydrated salts were tested as alkylation catalysts, using the screening procedure. They varied widely in performance, with some showing essentially no activity. Some of the active salts are shown in Table I. VOL. 51, NO. 1 1
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270
W
I-
?
8
2
230
I
I
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IO
15
20
WT.%
WATER
OF
1 25
HYDRATION
A
80'
40
-lo
b
I
30
.-
REACTION TEMP. ('CJ
Table I. Boron Trifluoride Is Active with a Large Variety of Hydrated Salts Ca+ Alkylate Yield, Compound Wt. yo" Fe4(P20;) r 4 H ~ 0 Als(P3Olo)a~10Hz0 Fe~(Sn03)~.3HzO Mg,Pz0;.3HzO CO~(ASO~)Z.~HZO BeS0~2Hz0 KzH2Sbz0;.4HzO
232 223 179 196 181 191 167
Based on ethylene charged.
The importance of water of hydration was determined by testing several anhydrous salts. These were relatively inactive. This is shown in Table 11, with runs in which both anhydrous and hydrated cobalt and nickel pyrophosphates were used. T o determine the role of water of hydration, the relationship between amount of boron trifluoride absorbed by different hydrated salts and their degree of hydration was established. It was found that 1 mole of boron trifluoride is absorbed per mole of water of hydration regardless of the degree of hydration of
Table 11.
Salt Used
Cb
a given salt. thus indicating that boron trifluoride forms a 1 to 1 complex with the water. The resulting complexes are free-flowing powders which produce fumes of boron trifluoride when exposed to moist air. Screening runs were all made with boron trifluoride in excess of that required to give 1 mole of boron trifluoride per mole of water of hydration. Therefore, activities of solid complexes, \vith molar equivalents of boron trifluoride and water, were checked. For this study, the solid complex of boron trifluoride and iron(II1) pyrophosphate nonahydrate was preformed. and then less strongly held boron trifluoride was removed by evacuation. The weight of boron trifluoride retained in the salt was equivalent to 1 mole per mole of water of hydration unless the evacuation was prolonged. \Vhen this solid boron trifluoride-salt hydrate complex was used in bomb runs essentially no reaction occurred, even after 20 hours of contact. These data show that water of hydration is required for an active catalyst and that boron trifluoride in molar excess of the water is needed for high catalytic activity. Variable Studies. The iron(II1) pyrophosphate hydrate-boron wifluoride
Only Hydrated Salts Are Active Yields, Wt. %" C3 15 110 10 110
1 356
4Figure 1. Lower reaction temperatures increase diisopropyl yields and octane ratings
INDUSTRIAL AND ENGINEERINGCHEMISTRY
c 7
+
20 78 9 98
Total 35 188 19 2 08
Conversion, %
...
100
...
96
system was one of the most effective of the catalyst systems tested, and for this reason it was studied extensively. For this work a stirred reactor was used, and ethylene was added slowly as previously described. This resulted in high internal isobutane to ethylene ratios which reduced heavy alkylate and polymer formation and thus gave higher over-all alkylate yields than obtained in the screening runs. Factors were sought which would further increase product quality by reducing the isomerization of 2.3-dimethylbutane to the less valuable methylpentanes and by increasing the yield of hexanes a t the expense of the relatively low octane heavy alkylate. The latter point is extremely important. as an increase in selectivity for hexanes not only increases over-all yield based on ethylene but also increases the octane rating of the total alkylate. Reaction temperature was one of the most important variables. Runs were made in the -20' to 30' C. range, using the complex of iron(II1) pyrophosphate nonahydrate and excess boron trifluoride. Changes in temperatures over this narrow range had little effect on over-all yields and conversions but had a large effect on composition of the hexane fraction and on octane quality (Figure 1). T h e 2,3-dimethylbutane content of the hexane fraction increased from 90 to 9770 with a corresponding octane increase of 3.5 units. Octane rating of the C S alkylate was also higher a t lower temperatures, indicating less isomerization. The striking feature is the high concentration of dimethylbutanes in the hexane fraction obtained a t the lower temperatures. The degree of hydration of the salt affected the selectivity of the catalyst for hexane alkylate in preference to heavy
P R E P A R A T I O N OF D I I S O P R O P Y L Table Ill. Moles
of H20/
Moles of Salt
6.0 8.0 a
If the dimer form of boron trifluoride is more electrophilic than the monomer, the 2 to 1 complex would ionize to a greater extent and therefore be a stronger acid catalyst. This is proposed as a possible explanation to the inactivity of the solid complex in the absence of free boron trifluoride and the high activity obtained under boron trifluoride pressure.
Under Preferred Conditions Excellent Yields of High Purity Diisopropyl M a y be Obtained" Alkylate DistributionC Yield Ethvlene 2.3Research Cbf, Reacting, Dimethyl- 2-Methyl- 3-Nethyloctane Wt. %* % C'j butane pentane pentane C,' Cst 266 263
99 100
72.4 70.5
0.0 0.0
0.3 0.0
1.0
1.4
26.3 28.1
100.9 100.8
Isobutanejolefin molar ratio, 4 8 ; BFI salt weight ratio, 1.3; total time, 3 hrs.; temp., * Based on ethylene charged. e Yapor fractometer analyses.
30' F.
alkylate. Results of runs made with varying water of hydration but a constant ratio of salt to boron trifluoride are shown in Figure 2. The lower hydrates gave higher yields of hexanes and therefore increased total alkylate yields. Octane ratings followed this same trend. It was concluded from other variable studies that increasing the isobutane to olefin ratio increases the selectivity of the product for hexane alkylate. Reaction times of 1 hour were sufficient in equipment used, but longer contact was not detrimental. Activity increases with increasing amounts of boron trifluoride in excess of that required to form a 1 to 1 molar boron trifluoride-water complex. For ethylene alkylation Jvhen there is no excess boron trifluoride, the catalyst is essentially inactive, as mentioned previously. while with a 50 mole % excess, activity- is high. After consideration of the variables, runs were made under preferred conditions. Results shown in Table I11 are typical of those obtained with carefully prepared iron(II1) pyrophosphate dried to 6 to 8 moles of hydrate water. With higher isobutane to olefin ratios, even higher yields and octane ratings would be expected. Mechanism
Because the salts studied retain 1 mole of boron trifluoride per mole of hydrate water at atmospheric pressure, it seems likely that they act in a manner similar to boron trifluoride monohydrate, which is known to be active for ethylene alkylation and which is reported to ionize as shown below (7) : BF3.HsO + (BF30H)-
+ H+
T h e alkylation reaction could then be expected to be initiated by a proton
released from the hydrate water and to proceed by the Schmerling mechanism (8). One thing that requires explanation is the need for excess boron trifluoride for high activity. This, however, is not unique for the boron trifluoride-salt hydrate systems. Clayton and Eastham (73) showed that, with boron trifluoridewater, isomerization rate of 2-butene is dependent on both boron trifluoride and boron trifluoride-water concentrations. They found that (BF3)2.H20 as the catalyst satisfied the kinetics of the reaction. Burwell, Elkin, and Shields (72) showed that, in alkylation of benzene with sec-butyl methyl ether. reaction rate is appreciable only with excess boron trifluoride. h'elson and Brown ( 9 ) credited increased activity obtained with excess boron trifluoride to the formation of a singly bridged dimer as shown, where AV represents a nucleophilic compound : F
They suggest that boron trifluoride dimer is much more electrophilic than monomer. The dimer theory can explain the requirement for excess boron trifluoride in the salt hydrate system as illustrated below where M represents the metal salt. (The exact method by which the water is held in the salt is not known, but likely it is as a n aquo complex with the cation.) Here a rather low degree of ionization is expected for the 1 to 1 boron trifluoride-water complex, as indicated. This complex, however, is believed to be in equilibrium with the 2 to 1 complex and this equilibrium would be expected to be dependent on boron trifluoride partial pressure.
H F
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L
EI*
F
J
Acknowledgment
The authors are grateful to the management of American Oil Co. for encouraging the publication of this work. literature Cited
(1) .4lden, R. C., Frey, F. E., Hepp, H . T., McReynolds, L. A., Oil Gas J . 44, No. 40, 70 (1946). (2) Axe, W. N. (to Phillips Petroleum Co.), L.S. Patent 2,404,897 (July 30, 1946). (3) Axe, W. N., Schulze, W. A , , IKD. ENG.CHEM.39, 1273 (1947). (4) Baker, C. 0. (to Socony-Vacuum Oil Co., Inc.), U. S. Patent 2,530,143 (Nov. 14, 1950). (5) Beyerstedt, F. .J. (to Standard Oil Development Co.), Zbid., 2,284,554(May 26,1942). (6) Beyerstedt, F. J. (to Standard Oil Development Co.), Zbid.,2,363,222(Nov. 21, 1_, 9 A,A',. I
(7) Brooks, B. T., Board, C. E., Kurtz, S. S.: Jr., Schmerling, L., "The Chemis. try of Petroleum Hydrocarbons," Vol11, p. 250, Reinhold, New York. 1955. (8) Zbid.,Vol. 111, pp. 372--3. ( 9 ) Zbid., p. 522. (10) Bruner, F. H. (to The Texas Co.), U. S. Patent 2,363,116 (Nov. 21, 1944). (11) Bruner, F. H., Clarke, L. A . , Sawyer, R. L. (toTheTexasCo.),Ibid.,2,345,095 (March 28, 1944). (12) Burwell, K. L., Jr., Elkin, L. M., Shields, A. D., J . Am. Chrm. Sac. 74, 4567 (1952). (13) Clayton, J. M.: Eastham, A. M.?Ibid., 79, 5368 (1957). 4) Gorin, M. H . (to Socony-Vacuum Oil Co., Inc.), U. S. Patent 2,401,925 (June 11: 1946). 5) Gorin. M. H., Swerdloff, W. (to Socony-Vacuum Oil Co., Inc.), Ibid., 2,412,143 (Dec. 3, 1946). 6) Grosse, A . V., Linn, C. B. (to Universal Oil Products Co.). Zbid.. 2.411.992 iDec. 3. 1946). 7) Holloway, C., Jr., Bonnell, W. S., IND.ENG.CHEM.38, 1231 (1946). (18) Meinert, R, N. ( t o Standard Oil Development Co.), U. S. Patent 2,348,637 (May 9,1944). (19) Miller, P. (to Standard Catalytic Co.), Zbid., 2,398,908 (April 23, 1946). (20) Pines, H., Grosse, A. V., Ipatieff, V. N., J . Am. Chem. SOC.64, 33 (1942). (21) Schulze, W. A. (to Phillips Petroleum Co.), U. S. Patent 2,378,040 (June 12, 1945). (22) Thompson, R. B., Chenicek, J. A., IND.END.CHEM.40, 1265 (1948). (23) Vermillion, H. E. (to The Texas Co.), U. S. Patent 2,452,166 (Oct. 26, 1948). _
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RECEIVED for review January 22, 1959 ACCEPTED June 1, 1959 Division of Petroleum Chemistry, 135th Meeting, .4CS, Boston, Mass., April 1959. VOL. 51, NO. 1 1
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