US3231628A - Preparation of jet fuels - Google Patents

Description

United States Patent 3,231,628 PREPARATION OF JET FUELS Herman S. Bloch, Skokie, llL, assignor to Universal Oii Products Company, Des'Plaines, Ill., a corporation of Delaware No- Drawing. FiledJune 1, 1962, Ser. No. 199,244 8 Claims. (Cl. 260-666) This application is a continuation-in-part of my copending application Serial No. 783,146 filed December 29, 1958, now abandoned.

This invention relates to a process for preparing jet fuels and more particularly to a process for preparing jet fuels which have more advantageous characteristics.

The need for jet fuels is increasing at a tremendous rate due to the growing use of this type of engine in the aviation industry plus an increase in the interest in rockets. While the use of jet planes for military uses has been in efiect for a relatively long period of time, the civilian use of jet aircraft is now increasing at a rapid rate. For example, domestic airlines have just begun to use jet airliners for intracontinental and intercontinental passenger transports. Likewise, foreign airlines are also beginning to use more and more airliners powered by jet engines. As the use of jet aircraft increases, with the rigid specifications of fuel consumption compared to the pay load carried as in the case of civilian airliners, and the requirements of the military aircraft for longer range, more sustained flights, the fuel required for the jet engines must of necessity become more efficient. let engines require up to five times as much fuel per hour as a piston powered plane and, therefore, the fuel which is required to operate these engines must be highly eificient in operation. Many types of fuel are now being used to power jet engines, among which are kerosene and other hydrocarbontype fuels. The hydrocarbon fuels which are designed for jet engines and/ or for rocket use have specifications which require a high heat of combustion per pound of fuel as well as per gallon. Therefore, with both the volume and and the weight of the fuel a definite factor in the specifications, a fuel which provides a relatively higher heat of combustion will be favored over that fuel which does not provide such a high heat of combustion per pound as well as per gallon. In addition, the fuels which are required for the jet engines should have a relatively low mercaptan sulfur content and a low smoke volatility index. With regard to the latter point, the presence of aromatics in the fuel has an effect on the smoke volatility of the fuel as well as affecting the elastomers which are used as sealants on fuel tanks. These elastomers have a tendency to swell when the aromatic content of the fuel is too high and will later shrink and cause leakage to occur if a fuel which is low in aromatic content is used. Therefore, in view of all of the rigid specifications, the type of fuel which best meets all of the requirements has been found to consist of polycyclic naphthenes. Such compounds have a higher heat of combustion per pound than aromatic hydrocarbons, and a greater heat of combustion per gallon than paraffin hydrocarbons. These polycyclic naphthenes may be prepared by the catalytic hydrogenation of polycyclic aromatic hydrocarbons such as lube oil extracts, cycle stocks, etc., said hydrogenation being catalyzed by the presence of those catalysts containing nickel, cobalt, platinum, and other well known hydrogenation agents. Another source of potential jet fuels is found in feed stocks comprising hydrogenated conjunct polymers which are derived from olefinic gasoline charge stocks.

In view of the aforesaid need for jet fuels, it is an object of this invention to provide a process for the preparation of jet fuels which are more efli-cient in operation than some already in use.

A further object of this invention is to provide a process for the preparation of jet fuels which possess a higher heat of combustion per gallon of fuel than those now in use Taken in its broadest aspect one embodiment of this invention resides in a process for improving the heat of combustion of jet fuels comprising multi-ringed naphthenic hydrocarbons containing alkyl substituted cyclo-, pentano groups which comprises isomerizing said alkyl substituted cyclopentano groups to cyclohexano groups in the presence of a Friedel-Crafts catalyst at a temperature in the range of from about 0 to about 150 C., and recovering the desired product.

A further embodiment of this invention resides in a process for improving the heat of combustion of jet fuels comprising multi-ringed naphthenic hydrocarbons containing alkyl substituted cyclopentano groups which comprises isomerizing said alkyl substitutedcyclopentano groups to cyclohexano groups in the presence of an aluminum chloride catalyst at a temperature in the range of from about 25 to about C., and recovering the desired product.

Other objects and embodiments will be ,found in the following further detailed description of this invention.

In preparing the desired jet fuels according to the process of this invention the thermodynamics of isomerization reactions must be taken into consideration. The aforesaid thermodynamics of isomerization are such that the formation of cyclohexano groups is favored when utilizing relatively low temperatures, that is, from about 0 to about C. while the formation of substituted cyclopentano groups is favored when using relatively high temperatures, that is, above about 150 C. Furthermore, when utilizing higher temperatures and more severe conditions, treatment of alkyl substituted cyclopentano groups Will involve disproportionationi.e., transfer of an alkyl substituent such as a methyl group from one naphthene ring to another. In addition the more severe conditions which involve the use of higher temperatures will also promote ring scission with the formation of gaseous hydrocarbons and other undesirable hydrocarbons thereby radically altering the structure of the molecule which is involved in the reaction. For example, it is known in the prior art that when a single ring polyalkyl substituted naphthenic hydrocarbon is subjected to treatment at a temperature above 150 C. in the presence of certain catalytic compositions of matter, disp'roportionation' arid ring scission will occur rather than the isomerization process of the present invention in which alkyl substituted cyclopentano groups of a multi-ringed naphthenic hydrocarbonare converted to cyclohexano groups.

As hereinbefore set forth the jet fuels which possess a higher heat of combustion per pound as Well as per gallon may be prepared by passing the hydrogenated polycyclic naphthenic stocks containing alkyl substituted cyclopentano groups over a Friedel-Crafts type isomerization catalyst at a relatively low temperature, that is, temperatures ranging from about 0 to about 150 C. and preferably in a range of from about 25 to about 100 C. Under these conditions and under the influence of the particular catalyst of the type hereinafter set forth the alkyl substituted cyclopentano polycyclic cycloparaffin hydrocarbons are isomerized to a cycloheXane structure thus providing a product of greater density which has up to about 5% Patented Jan. 25, 1966 Increase in B.t.u./gal. Compound Density, D4 Relative to Compound (1),

' Percent (1) cnrfipI-ona 0.837 CH3 Examples of alkyl substituted multi-ring naphthenic hydrocarbons containing five-membered rings (CYCIOPGH': tano groups) will comprise hydrocarbons having the generic Formula I in which the various R substituents are independently selected from hydrogen and alkyl radicals containing from 1 to about carbon atomsor more, at least one R on each ring being analkyl radical, andn is a number from' 0 to about 20. V Y Specific examples of these compounds include 1,2-di (2-methylcyclopentyl)ethane, 1,2-di-(2-ethylcyclopentyl) ethane, 1,2-di-(2,3-dirnethylcyclopenty1)ethane,: 1,2-di- (2,3-diethylcyclopentyl)ethane, 1,2 di' (2,3 ,4-trimethylcyclopentyl)ethane, 1,2 di (Z-decylcylopentyl)ethane,

' absorbent support, such as, for example, alumina, or they may be suspended in a fluid medium, such as a hydrocarbon-Friedel-Crafts salt sludge. The supported catalysts are especially effective and long-lived when the support contains a small amount of a hydrogenation component, such as, for example, from about 0.05 to about 1% of platinum, and is used in the presence of hydrogen.

It is contemplated within the scope of this invention that the low temperature isomerization of multi-ring naphthenic hydrocarbons containing alkyl substituted cyclopentano groups to form cyclohexano groups may be effected in any suitable manner and may comprise either a batch or a continuous type operation. One particular type of operation which may be used is the batch type in which a quantity of the hydrogenated compounds to be isomerized is placed in an appropriate apparatus along with the desired isomerization catalyst. The apparatus is then heated to a temperature in the desired range, that is,

from about 25 to about 100. C. and maintained thereat for a predetermined residence time, at the end of which time the apparatus and contents thereof are cooled to room temperature. The reaction product is then separated from the catalyst layer and subjected to conventional means of recovery, that is, fractional distillation, etc. a

The process of'this invention may also be effected in a' continuous type manner. Theuse of a Friedel-Crafts type catalyst of the type hereinbefore set'forth is especia ly adaptedto a fixed bed type of operation. In this operation the catalyst is disposed as a fixed bed in a reaction zone which is maintained at the proper operating conditions of temperature and pressure. The reaction zone may comprise an unpack-ed vessel or coil or may be lined with an aborbent packing material such as fire brick, dehydrated bauxite, alumina and the like. The charge stock to be isomerized 'is continuously charged thereto at aliquid hourly space velocity-in the range of from about 0.1 to about 10 or more, the liquid hourly space velocity being defined as the ,volume 1 of feed stock charged per volume of catalyst per hour, and passes over the fixed bed of catalyst in either an upward or down- Another'continuous type of operation which may be i used comprises the moving bed type in which the catalyst 1,2-di-(2-dodecylcyclopentyl)ethane, 1,2'- di (octadecylcyclopentyl)ethane, etc., 2,6-dirnethyl[ 0,3,31bicyclooctane, 2,6 diethyl[0,3,3]bicyclooctane, 2,6 dipropyl[0,3,3]bicyclooctane, 1,2,6,7 tetramethyl[0,3,3]bicyclooctane, 1 ,2,6,7-tetraethyl [0,3 ,3 bicyclooctane, 2,6Q-dioctyl [0,3 ,3] ,bicyclooctane, 2,6 dinonyl[0,3,3]bicyclooctane, 2,6 didecy1[0,3,3 ]bicyclooctane, 1 2,6-dioctadecyl [0,3,3 bicyclooctane, 2,2'-dimethylbicyclopentyl, etc. It is to be understood that the aforementionedcompounds are only representatives of the classes of compounds which may be isomerized according to the process of this invention, and that said invention is not necessarily limited thereto.

Examples of cyclohexano hydrocarbons which'will re- .sult from this isomerization of the hereinbefore mentioned alkyl substituted, multi-ringed compounds containing cyclopento groups include Decalin, 2,6-dimethyldecalin,

2,6-diethyldecalin, 1,6-dirnethyldecaJin;1,9-diethyldecalin,

1,2 di (cyclohexyl)ethane,'1,2-- di-(Z-ethylcyclohexyl) ethane,'bicyclohexyl, etc.

Friedel-Crafts type isomerization catalysts which may be used in the process of this invention include aluminum 7 chloride, aluminum bromide, zirconium chloride, ferric chloride, zinc chloride, etc. These'may be used in solid powdered form, or they may be'deposited on a solid and the reactants passconcurrently or countercurrently to each other through the reaction zone. In addition, another type of operation which may be used is the slurry type of operation in which the catalyst is carried "into the reaction zone as a slurry in the reactant. In both of the aforesaid types of reaction, as in the first continuous type of operation'whic'n was described, the reaction products are continuously withdrawn from the reaction zone, separated from the unconverted effiuent and rejcovered by conventional means,'while the unconverted efiluent is recycled to form a' portion of the feed stock.

Theiollowing examples, which, however, are not intended to limit the generally broad scope of the present invention in strict accordance therewith, are given to illustrate the process of thepresent invention.

"olefinic (polymer) gasoline. charge stock, having a boiling .point in the rangeof from about 320 .to about 450 C., 'a density of D =0.874, a molecular weight of -375, a specific dispersion of'140 and a bromine number of 167, which is indicative of four double bonds per molecule, was obtained from a fractional distillation. The .analysisof this cut which has an average formula of 27;5 47.s( n z i showed 87.34% carbon and 12.6% hydrogen,

This cut was hydrogenated at a temperature of 100 C. and an initial pressure of 1000 p.s.i.g. of hydrogen for four hours in a bomb over a nickel catalyst. The resulting product was a water-white oil having a density of D =0.854, a specific dispersion of 96.5 which is indicative of a naphthene or parafiin, a molecular Weight of 390 and a bromine number of 0. Analysis of this product disclosed 86.14% carbon and 13.82% hydrogen showing an average molecule having the empirical formula 27.5 52.5'

This product is then isomerized by treating the compound at a temperature of about 50 C. in the presence of 5% by Weight of aluminum chloride catalyst for a period of about 3 hours in a stirred autoclave, with a slow stream of hydrogen chloride bubbling through the liquid. The resultant product then shows a density of D =.887, the specific dispersion, molecular weight and bromine number remaining substantially unchanged, while the boiling range is raised by an average of about C.,

Example 11 A conjunct polymer obtained by the reaction of aluminum chloride with a polymer gasoline charge stock is treated in a manner similar to that set forth in Example I above. The cut boiling from 320 to 450 C. and having the same properties as those set forth above is hydrogenated over nickel catalyst at a temperature of 100 C. and an initial pressure of 1000 p.s.i.g. of hydrogen for four hours. The resultant water-White oil is then isomerized in the presence of two percent by weight of aluminum bromide catalyst at a temperature of approximately 35 C. for a period of 3 hours, the resultant isomers having a density of about D =.887, a higher boiling range than the unisomerized material, and a greater volumetric heat of combustion than that of the hydrogenated product before isomerization, Under these mild isomerization conditions, scarwly any cracking of the feed to gaseous and other light products occurs.

I claim as my invention:

1. A process for improving the heat of combustion of jet fuels comprising multi-ringed naphthenic hydrocarbons containing alkyl substituted cyclopentano groups which comprises isomerizing said alkyl substituted cyclopentano groups to eyclohexano groups in the presence of a Friedel- Crafts catalyst at a temperature in the range of from about 0 to about 150 C., and recovering the desired product.

2. A process for improving the heat of combustion of jet fuels comprising multi-ringed naphthenic hydrocarbons containing alkyl substituted cyclopentano groups which comprises isomerizing said alkyl substituted cyclopentano groups to cyclohexano groups in the presence of an aluminum chloride catalyst at a temperature in the range of from about 0 to about 150 C., and recovering the desired product.

3. A process for improving the heat of combustion of jet fuels comprising multi-ringed naphthenic hydrocarbons containing alkyl substituted cyclopentano groups which comprises isomerizing said alkyl substituted cyclopentano groups to cyclohexano groups in the presence of an aluminum chloride catalyst at a temperature in the range of from about 25 to about C., and recovering the desired product.

4. The process of claim 3, further characterized in that said naphthenic hydrocarbon is 2,6-dimethyl[0,3,3]bicyclooctane.

5. The process of claim 3, further characterized in that said naphthenic hydrocarbon is 2,6-diethyl[0,3,3]bicyclooctane.

6. The process of claim 3, further characterized in that said naphthenic hydrocarbon is 1,2,5,6-tetrarnethyl[0,3,3] bicyclooctane.

7. The process of claim 3, further characterized in that said naphtenic hydrocarbon is 1,2,6,7-tetraethyl[0,3,3]bicyclooctane.

8. The process of claim 3, further characterized in that said naphthenic hydrocarbon is a hydrogenated conjunct polymer derived from an olefinic charge stock.

Thomas, Anhydrous Aluminum Chloride in Organic Chemistry, page 721 relied on, Reinhold Publishing Corp., New York, 1941.

DELBERT E. GANTZ, Primary Examiner.

A'LPI-IONSO D. SULLIVAN, Examiner,

Claims (1)

1. A PROCESS FOR IMPROVING THE HEAT OF COMBUSTION OF JET FUELS COMPRISING MULTI-RINGED NAPHTHENIC HYDROCARBONS CONTAINING ALKYL SUBSTITUTED CYCLOPENTANO GROUPS WHICH COMPRISES ISOMERIZING SAID AKYL SUBSTITUTED CYCLOPENTANO GROUPS TO CYCLOHEXANO GROUPS IN THE PRESENCE OF A FRIEDELCRAFTS CATALYST AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 0* TO ABOUT 150*C., AND RECOVERING THE DESIRED PRODUCT.