US3057705A - High energy fuels - Google Patents

Description

Oct. 9, 1962 R. A. FRANZ ETAL 3,057,705

HIGH ENERGY FUELS Filed June 22, 1959 GAS GAS u STRAIGHT RUN GASOLINE 8 l2 CRUDE OIL CHARGE STOCK CATALYTiC 9 I 7 CRACKING CYCLE on.

LUBE STOCK SLURRY on. FLUX OIL l4 6 HIGH ENERGY FUEL AROMATIC |6 DESULFUR- |8 HYDROGEN- 20 EXTRACTION IZATION ATION INVENTOR? RAYMOND A. FRANZ EO J. LANE ATTORNEY United States Patent 3,057,705 HIGH ENERGY FUELS Raymond A. Franz and Leo J. Spillane, El Dorado, Arie, assignors to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware Filed June 22, 1959, Ser. No. 822,114 2 Claims. (Cl. 44-80) This invention relates to improved high energy fuels and in particular to fuels suitable for use in turbojet and turboprop engines.

One object of this invention is to provide a hydrocarbon fuel having substantially increased energy content per unit volume over hydrocarbon fuels of the prior art.

Another object of this invention is to provide a hydrocarbon fuel for jet engines having a heat of combustion of from 125,000 B.t.u.s to 160,000 B.t.u.s per gallon.

Another object of this invention is to provide a hydrocarbon fuel for jet engines having a heat of combustion in excess of 18,000 B.t.u.s per pound.

An additional object of this invention is to provide hydrocarbon fuels for jet engines utilizing hydrocarbon streams obtained in conventional refinery operations.

A particular object of this invention is to provide a hydrocarbon fuel for jet engines having a heat of combustion of from 125,000 B.t.u.s to 160,000 B.t.u.s per gallon and an extremely low pour point.

Additional objects will become apparent from the description of this invention.

Present jet fuels have a heat of combustion of only about 112,000 B.t.u.s per gallon. They are prepared from petroleum hydrocarbons in the naphtha and kerosene boiling range and accordingly consist largely of parafiinic hydrocarbons. Present jet fuels also have a relatively high pour point which significantly limits their applicability.

It has now been found that a mixture comprising a major portion of the hydrogenated desulfurized aromatic extract of slurry oil and a minor portion of 3-isopropylbicyclohexyl, 4-isopropylbicyclohexyl or mixtures thereof, is an extremely useful high energy fuel characterized by an exceptionally high heat of combustion and an extremely low pour point. The following examples illustrate the novel compositions of this invention:

Example I A mixture was prepared comprising 90% by weight of the hydrogenated desulfurized aromatic extract of slurry oil and by weight of a mixture of the 3-isopropylbicyclohexyl and 4-isopropylbicyclohexyl. The hydrogenated desulfurized aromatic extract of slurry oil had an initial pour point of F. The mixture prepared as described in this example had a pour point of F.

Example II A mixture was prepared comprising 80% by weight of the hydrogenated desulfurized aromatic extract of slurry oil and 20% by weight of a mixture of the 3-isopropylbicyclohexyl and 4-isopropylbicyclohexyl. The hydrogenated desulfurized aromatic extract of slurry oil had a pour point of 15 F., while the mixture prepared as described herein had a pour point of F.

Example III A mixture was prepared comprising 70% by weight of the hydrogenated desulfurized aromatic extract of slurry oil and by weight of a mixture of the I i-isopropylbicyclohexyl and 4-isopropylbicyclohexyl. The hydrogenated desulfurized aromatic extract of slurry oil had a pour point of 15 F. while the pour point of the mixture prepared as described herein had a pour point of 45 F. The hydrogenated desulfurized aromatic extract of slurry oil had a heat of combustion of 18,493 B.t.u.s per pound and 136,-

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441 B.t.u.s per gallon, a specific gravity at 20/4 C. of 0.887 and an n of 1.4837. The mixture prepared as described in this example had a heat of combustion of 18,400 B.t.u.s per pound and 136,800 B.t.u.s per gallon, a specific gravity at 20/4 C. of 0.8917 and an n of 1.4821.

While the preceding examples have illustrated the use of mixtures of 3-isopropylbicyclohexyl and 4-isopropylbicyclohexyl, similar results are obtained using either of the isomers alone. All proportions of mixtures of these isomers produce superior results in the practice of this invention.

The high energy fuels of this invention are composed of a major proportion of the hydrogenated desulfurized aromatic extract of slurry oil and a minor proportion of 3-isopropylbicyclohexyl, 4-isopropylbicyclohexyl or mixtures thereof. Particularly useful high energy fuel compositions are obtained using from about 5% to about 45% by weight of total composition of the specified isopropylbicyclohexyl isomers, and those compositions containing from about 15% to about 40% by weight of total composition of 3-isopropylbicyclohexyl, 4-isopropylbicyclohexyl or mixtures thereof, are particularly preferred.

The isopropylbicyclohexyls as utilized in the present invention are preferably made by the alkylation of biphenyl with propylene, such as by the use of aluminum chloride as the alkylation catalyst. The alkylated intermediate is then hydrogenated in order to obtain isopropylbicyclohexyl. The product thus obtained is composed almost exclusively of the 3- and 4-isomers which are used in preparing the novel high energy fuels of this invention. These two isomers may be separated if desired, but are equally useful when employed as a mixture in any proportion of the two isomers.

The utility of the hydrogenated desulfurized aromatic extract of slurry oil per se as a high energy fuel is disclosed and claimed in copending application Serial No. 817,848, filed June 3, 1959. Its method of preparation is illustrated in FIGURE 1 which represents a schematic flow diagram of a process for preparing the hydrogenated desulfurized aromatic extract of slurry oil.

In the drawing, crude oil is introduced via line 1 into topping column 2. In this column gas is taken overhead 3, straight run gasoline is removed from an upper portion 4 of the column, lube oil stock is removed from the bottom portion 5 of the column, and flux oils are removed as bottoms 6 from the column. A 300 C.600 C. charge stock is removed via line 7 from an intermediate section of the column and introduced into a catalytic cracker 8. The cracked products from the catalytic cracker are fed via line 9 into column 10 where gas is removed overhead 11, gasoline removed via line 12 from the upper portion of the column, cycle oils, a 200300 C. cut, are removed from the bottom portion of the column via line 13 and slurry oil, boiling above 300 C., is removed as column bottoms via line 14. This slurry oil generally contains about equal portions of paraffins and aromatics.

According to the process of this invention, this slurry oil is then introduced into an aromatic extraction system 15 where the aromatics are removed from the slurry oil by extraction. The overall recovery of the paraffin layer from the slurry oil in a furfural extraction amounted to 45.3% of the charge. Recovery of the aromatic oil amounted to 59.2% of the charge. The extraction was carried out in two stages, using two volumes of oil for each volume of furfural. The aromatic-furfural layer was separated and the furfural removed by distillation.

The aromatic extract of theslurry oil is then fed via line 16 to the desulfurization unit 17. In this unit, the aromatic extract is desulfurized. In a particular run the aromatic extract of slurry oil containing 4.72% sulfur was desulfurized with hydrogen over a cobalt molybdenum sulfide catalyst. An average reaction temperature of 395 C. was maintained and an average reaction pressure of 1,200 p.s.i.g. was maintained. The sulfur content of the desulfurized material was reduced to 0.07%.

In order that the subsequent hydrogenation reaction can be carried out in a manner conducive of the greatest possible hydrogenation catalyst life, it is advisable that the sulfur content of the aromatic extract of slurry oil be reduced to substantially zero. This at times may require extraordinary desulfurization techniques. For example, in a particular run it was found that the desulfurized aromatic extract of slurry oil as above described containing 0.07% sulfur could be treated with metallic sodium at 230 C. to effect complete removal of the sulfur still remaining. This significantly increased the catalyst life in the hydrogenation step.

The desulfurized aromatic extract of slurry oil is then fed via line 18 to hydrogenation system 19 wherein the material is completely hydrogenated. In a particular example, the desulfurized aromatic extract of slurry oil was hydrogenated over Raney nickel at a temperature in the range of from about 360 C. to 380 C. and a hydrogen pressure of approximately 2000 p.s.i.g. Substantially complete conversion of the aromatics to naphthenes was realized.

The hydrogenated desulfurized aromatic extract of slurry oil is then introduced via line 20 into fractionating column 21 where approximately 90% of the product is taken overhead as high energy fuel and approximately 10% of the product discarded as bottoms.

In a typical operation, a high energy fuel was obtained having a heat of combustion of 18,493 B.t.u.s per pound and 136,441 B.t.u.s per gallon and a pour point of l F. The material had a specific gravity at 20/4 C. of 0.887 and a n of 1.4837.

Conventional catalytic hydrocarbon cracking operations, well known to those skilled in the art, can be used to prepare the heavy hydrocarbon oil streams from which the aromatics are extracted, desulfurized and then hydro genated to produce high energy hydrocarbon fuels of this invention. Silica and alumina are conventional catalysts which can be employed in the cracking step and these catalysts may be either natural or synthetic. The catalyst can be employed as a fixed bed, as a fluidized solid or as a moving bed, all of which are techniques well known to those skilled in the art. Any of the conventional feeds can be used in the catalytic cracking operation. Such feeds are usually petroleum oils containing a substantial portion boiling above 300 C. Heavy distillates boiling from 300600 C. or topped or reduced crude oils are typical feed materials. Temperatures in the range of from about 425 C. to about 500 C. are generally employed in the cracking step. Cracking pressures are generally relatively low, varying between atmospheric and 7S p.s.i.g. Most cracking operations generally employed are of the regenerative type wherein the catalyst is periodically regenerated by burning with an oxygen containing gas. The cracking operation can be carried out in a once through system in which there is no recycle and only fresh feed is charged to the unit, or a portion of the effluent can be separated therefrom by fractional distillation and returned as recycle to the feed stream to the catalytic cracker.

The products of the catalytic cracking zone or reaction are then fractionated into several fractions including a distillate fraction boiling between about 200 C. and 300 C. which is commonly called cycle oil and a bottoms fraction boiling above 300 C. which is generally referred to as slurry oil.

In preparing the high energy hydrocarbon fuels of this invention the slurry oil i dearomatized to remove therefrom aromatic hydrocarbons. This dearomatization can be carried out by any technique well known in the art but is most conveniently carried out by a solvent extraction. The manner in which this solvent extraction is carried out is not critical. Any of the known solvents suitable for this purpose can be employed to secure the desired aromatic extract. Furfural, liquid sulfur dioxide, mixtures of phenol and water, and the like are all suitable. The treatment is preferably carried out by countercurrent contact in a series of extraction stages. Furfural is particularly suited for this purpose since it can be used at relatively moderate temperatures and at moderate solvent ratios. If desired, the extraction can also be carried out through the use of solid adsorbent materials useful for this purpose.

The equipment and procedure utilized for carrying out the aromatic extraction is not a critical limitation of this invention. A variety of equipment can be employed.

The aromatic extract of slurry oil can be desulfurized by any of the techniques well known to those skilled in the art. Cobalt molybdenum sulfide, tungsten nickel sulfide, nickel sulfide, and so forth, are all suitable catalysts useful in the practice of this process. Desulfurization can be carried out at pressures ranging from p.s.i.g. up to 2000 p.s.i.g. or even higher if desired in particular circumstances. The desulfurization temperature can be varied from room temperature up to 500 C. or higher if desired. Any of the desulfurization equipment well known to those skilled in the art can be employed in this step of the process.

Any of the conventional techniques can be used to bydrogenate the desulfurized aromatic extract of slurry oil in accordance with the process of this invention. Raney nickel, palladium, platinum, etc., are all catalysts useful in this hydrogenation step. Hydrogenation pressures can be varied from 400 to 3000 p.s.i.g. or even higher if desired depending upon the particular catalyst utilized. Hydrogenation temperatures can be varied from room tem perature to 500 C. or higher, again depending upon the particular catalyst employed. Any of the conventional hydrogenation equipment with which those in the art are very familiar can be used in the practice of this step of the process.

The hydrogenated desulfurized aromatic extract of slurry oil thus obtained can be used as such as a high energy fuel. It has been found, however, that the pour point of the material can be significantly lowered if the high boiler present in the material are discarded. This can be accomplished by simple fractionation discarding up to 15% by weight of the bottoms.

The fuels of the instant invention are eminently suitable for use in jet engines, particularly turbojet and turboprop aircraft engines.

In the operation of turbojet engines, air is withdrawn from the atmosphere into an air compressor, compressed and delivered to the combustion chamber of the engine where it is mixed with these fuels and the mixture ignited. The resulting burning mixture of the fuel and air is diluted with secondary air and expanded through a turbine which drives the air compressor. In these engines, the hot mixture i expanded in the turbine in such a manner that only sufiicient energy is extracted from the gases to operate the compressor. The remaining energy is employed to eject the gases in jet form through a jet pipe into the atmosphere and thereby produce thrust.

In using these fuels in turboprop engines, the operation is essentially the same except that the gases are almost completely expanded in the turbine, i.e., they are expanded almost down to the pressure of the surrounding atmosphere, leaving only a relatively small amount of energy to produce thrust when ejected through the jet pipe. Thus, in turboprop engines, the majority of the energy from the hot expanding gases is used to operate the compressor and the propeller and hence the thrust is obtained primarily from the latter.

In many turbojet and turboprop engines, only a single stage turbine is employed. However, more than a single stage may be employed and, if so, guide vanes are introduced between each pair of turbine wheels. After leaving the last turbine wheel, the gas enters the jet pipe and is discharged therefrom into the atmosphere.

The fuels of the instant invention may be used advantageously in the spark ignition piston-type aircraft engine, diesel engines, and turbine engines generally, but are particularly suitable for use in ramjet, turbojet and turbo prop aircraft engines. However, when the piston-type and diesel engines are employed, the fuel/air ratios are adjusted so as to achieve substantially complete combustion of the air and fuel.

The fuels of the instant invention may be blended with other materials such as gasoline, kerosene, mixtures of gasoline and kerosene, other aviation fuels, and with present hydrocarbon jet fuels to produce an improved fuel over the presently available fuel. More particularly, the fuels described herein may be added to the present aliphatic hydrocarbon jet fuels having a heat of combustion of about 112,000 B.t.u.s per gallon to raise the overall heat of combustion thereof. Moreover, the fuels described herein may be used in combination with fuel additives to obtain improved results as regards burning characteristics, etc.

The heat of combustion as given in this specification represents the heat of reaction between gaseous oxygen and liquid hydrocarbon to produce gaseous carbon dioxide and water.

What is claimed is:

1. A high energy fuel consisting essentially of the hydrogenated desulfurized aromatic extract of slurry oil, said slurry oil being the fraction boiling above 300 C. obtained in the catalytic cracking of a heavy petroleum distillate and from about 5% to about 45% by weight of total composition of an isopropylbicyclohexyl selected from the group consisting of 3-isopropylbicyclohexyl, 4- isopropylbicyclohexyl and mixtures thereof.

2. A high energy fuel consisting essentially of the hydrogenated desulfurized aromatic extract of slurry oil, said slurry oil being the fraction boiling above 300 C. obtained in the catalytic cracking of a heavy petroleum distillate and from about 15% to about 40% by weight of total composition of an isopropylbicyclohexyl selected from the group consisting of 3-isop1'opylbicyclohexyl, 4- isopropylbicyclohexyl and mixtures thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,749,225 Barnum et al June 5, 1956 2,765,617 Gluesenkamp et al Oct. 9, 1956 2,911,352 Goretta et al. Nov. 3, 1959

Claims (1)

1. A HIGH ENERGY FUEL CONSISTING ESSENTIALLY OF THE HYDROGENATED DESULFURIZED AROMATIC EXTRACT OF SLURRY OIL, SAID SLURRY OIL BEING THE FRACTION BOILING ABOVE 300* C. OBTAINED IN THE CATALYTIC CRACKING OF A HEAVY PETROLEUM DISTILLATE AND FROM ABOUT 5% TO ABOUT 45% BY WEIGHT OF TOTAL COMPOSITION OF AN ISOPROPYLBICYCLOHEXYL SELECTED FROM THE GROUP CONSISTING OF 3-ISOPROPYLBICYCLOHEXYL, 4ISOPROPYLBICYCLOHEXYL AND MIXTURES THEREOF.

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