ROLE OF CATALYSIS IN PETROLEUM CHEMISTRY' High-octane Isoparaffinic Fuels Although preliminary work indicated the general nature of the sulfuric-acid-catalyzed addition of olefins to isoparaffins, attention in our earlier communication (1) was mainly directed towards the condensation of butene with isobutane, since these hydrocarbons gave the most promising results which could be easily translated to commercial operation. Other olefin-isoparaffin reactions have been studied and a brief account of some of the results obtained is given. These should be regarded as somewhat exploratory in nature. Of these reactions, the addition of propylene to isobutane and butenes to isopentane appear to offer the greatest promise. Acid requirements are, however, higher than with the butene-isobutane reactions.
HE sulfuric-acid-catalyzed addition of Cd olefins to isobutane enables a saturated material, essentially isoparaffinic and possessing a high octane number, to be obtained in one stage without recourse to polymerization or hydrogenation. Under favorable conditions more than 70 per cent of the product consists of isooctanes formed by direct addition and isomerization. Apart from neutralization and distillation to remove excess isobutane and a comparatively small amount of high-boiling material, no further
T
1 The group of papers on pages 1079-1098 were presented before the Division of Petroleum Chemistry a t the 97th Meeting of the American Chemical Sooiety, Baltimore, Md. For the firmt paper in this series, see literature citation I .
if
Production by the Addition of Olefins to Isoparaffins' S. F. BIRCH, A. E. DUNSTAN, F. A. FIDLER, F. B. PIM, AND T. TAIT Anglo-Iranian Oil Company, Ltd., Sunbury-on-Tharnes, England
treatment is necessary to obtain a suitable component for high-octane aviation fuels. Although preliminary work indicated the general nature of the reaction with regard to olefins and isoparaffins, attention has mainly been concentrated upon the condensation of butenes and isobutane, since these hydrocarbons gave the most promising results which could be easily translated to commercial operation. Other olefin-isoparaffin reactions, however, have been studied, and in the present paper it is proposed to give a brief account of some of the results obtained. These must be regarded as somewhat exploratory in nature. As previously reported (1,2 ),propylene and trimetliylethylene react with isobutane to yield saturated products consisting essentially of isoparaffins. Both olefins are produced in considerable quantities in cracking operations; but, whereas propylene must undergo some treatment such as polymerization to convert it into a gasoline product, trimethylethylene boils within the gasoline range and requires no such treatment. Furthermore , trimethylethylene possesses an excellent octane number and constitutes a valuable component of the lighter cracked gasoline fractions, and its use for other purposes would tend to impoverish the latter. The two hydrocarbons cannot therefore be regarded equally as potential olefins for 1079
INDUSTRIAL AND ENGINEERING CHEMISTRY
1080 200
.):
VOL. 31, NO. 9
to ensure the removal of the n-pentane from the product, which was accordingly taken as the material boiling between 40" and 185" C. The octane numbers reported were determined by the C. F. R. Motor Method.
-7
Propylene and Isobutane
I60 ja0l
CURVESPLATE COLFIGURE 1 (above). DISTILLATION UMN) O F LIQUIDPRODUCrS FROM ADDITION O F PROPYLENE AND ISOBUTANE CURVE (%-PLATE COLFIGURE2 (below). DISTILLATION UMN)OF LIQUIDPRODUCT FROM ADDITION OF TRIMETHYLETHYLENE AND
ISOBUTANE
C4HlO : C ~ H I O 1 : 1
acid condensation. Obviously the conversion of propylene into a saturated high-octane product suitable for use in aviation fuels would constitute a great advance and would offer considerable advantages over simple polymerization since the latter process produces unsaturated polymers suitable only for use in motor fuels. The use of trimethylethylene and other pentenes must be determined by factors, depending upon market conditions, such as volatility, the demand for saturated hi'gh-octane material, and so on. Similar conditions obtain with regard to the use of isopentane in place of isobutane as isoparaffin. The experimental procedure followed in general that previously described ( I ) , the olefin being slowly added to the vigorously agitated acid-isoparaffin mixture in an autoclave. Except when otherwise stated, the reaction was carried out a t 20" C. with 97 per cent acid. The portion boiling between 27" and 185" C. was taken as the product for purposes of calculating the yield based upon the olefin taken, except in reactions involving isopentane. Since a cut containing 95 per cent isopentane was employed for the latter, it was necessary
1
(
Preliminary attempts to induce propylene to react with isobutane under conditions similar to those employed during the early experimental work with the butenes (i. e., 97 per cent acid and equimolecular ratios of olefin and isoparaffin) resulted in a considerable increase in the volume of the acid due to the formation of isopropyl sulfuric esters and little or no addition. On the removal of the unchanged isobutane from the hydrocarbon layer, only a small amount of high-boiling unsaturated material remained, largely composed of propylene polymers and hydropolymers. Dilution of the acid furnished a small quantity of highly unsaturated oil similar in properties and odor to that originally described by Ormandy and Craven and formed as the result of the hydropolymerization of the propylene (6). This oil was considered by them to contain triolefins (of. Ipatiev and Pines, 6). Modification of reaction conditions by raising the temperature and increasing the acid concentration to 30" C. and 100.6 per cent, respectively, appreciably reduced the ester formation, and a fair yield of the addition product was obtained. Later the higher temperature was found to be unnecessary with the stronger acid, and a return was made to the original temperature of 20" C. The product was found to have a low bromine number and to contain appreciable proportions of isoheptanes boiling a t approximabely 80" and 90" C. The octane number of the gasoline fraction boiling between 27" and 185" C. was 82.5. Increasing the isobutane-propylene ratio in the reaction mixture to 4 : l was found to have a pronounced beneficial effect in improving the product both in yield and octane number (Table I). The acid requirements, as shown by the drop in free acid concentration from 101.7 to 92.4 per cent were excessive, however. Of particular interest was the change in boiling range of the product as shown both by the A. 5. T. M. distillation and the fractionation curves (Figure 1). Under favorable reaction conditions 90 per cent of the product distilled below 140" C. Of this, the major portion consisted of the isoheptanes already mentioned and boiling a t approximately 80" and 90" C., which, from their physical properties, appeared to consist mainly of 2,Pdimethyl- and 2,3-dimethylpentanes1 respectively. Small but definite fractions were also obtained a t 58-61', 99-loo", and 108-114" C.; in the first of these, the isohexane fraction, 2,3-dimethylbutane, was readily identified by the formation of its solid dibromo derivative on bromination in sunlight (4). The material boiling a t 99-100" C. was shown from the physical properties to consist solely of 2,2,4-trimethylpentane; the less definite fraction a t 108-114" C. consisted of other isooctanes. The presence of 2,2,4-trimethylpentane in the products of this reaction is of considerable interest since i t would seem to indicate that, under the conditions of reaction, isobutane becomes partly dehydrogenated to isobutene which then condenses with more i ~ o b u t a n e . ~This would appear to be confirmed by the presence of the isomeric isooctane fraction boiling between 108" and 114" C. since such isomers invariably accompany the formation of 2,2,4-trimethylpentane from isobutene and isobutane under these conditions. The addition of propylene to isobutane is thus capable of producing in good yield a valuable material of high octane 8
The amount of the isolictanes formed rules out the possibility t h a t these derived from butenes present as "impurities" in the starting materials.
were
SEPTEMBER, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLEI.
Run number Isoparaffin: Weight taken, grams Olefin: Weight taken, grams 1soparaffin:olefin ratio Acid volume, cc. Free acid concentration: Start, % End. % Crude produet:'" on olefin taken g e c i f i c gravity at 15.6O.C. Bromine number (Francis) 4 . S. T. M. distillation, c.: Initial b. p. 2 per cent 5 10 20 30 40
Specific gravity at 15.6',C. Bromine number (Francis) Octane number (C. F . R . Motor Method): Neat Plus 1 cc. tetraethyllead per Imp. gal.
RESULTS
202 Isobutane 3240 Propylene 535 4:l 1600
100.6
101.7 92.4
150 0.708 1
215 0.685 162O C.) ( > 1 6 0 ° C.) 0.775 Specific gravity at 15.6O.C. 0.774 0.786 0.785 0.787 0.780 0.760 Bromine number (Francis) 2.5
