US3201345A - Process for preparing jet fuels - Google Patents

Description

United States Patent 3,201,345 PROCESS FOR PREEARING JET FUELS Harry A. Hamilton,'Natrona Heights, Alfred M. Heuke, Springdale, and Harry C. Staui'r'er, Cheswich, Pa, assiguors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Filed June 14, 1962, Ser. No. 202,402

4 Claims. (Cl. 208-255) This invention relates to the preparation of improved jet fuels and in particular to the preparation of such fuels by a combination procedure involving hydrogenation and solvent extraction.

The jet fuels that are available commercially are not entirely satisfactory. The requirements for a satisfactory jet fuel are numerous andare quite stringent; for instance, jet fuels must be used to cool jet engines. In other words, the jet fuel is passed through preheaters integral with the jet engine in order to maintain the engine at a low temperature. Of course, the fuel is preheated in this manner, which is also desirable. However, the amount of heat which must be removed is considerable, and this means that the jet fuel must be heated to high temperatures during this preheating operation. Trouble has been encountered due to deposition of carbon in the preheaters at these high temperatures. Therefore, it is necessary to have a jet fuel which has high thermal stability. This is especially true in connection with jets employed in planes which fly at high Mach speeds where heat generation is excessive. Furthermore, jet fuelsare employed at high elevations and therefore are subjected to unusually low temperatures. This means that the jet fuel must not freeze or deposit solids at these low temperatures; otherwise filters and injecting mechanisms would become clogged. Suitably high heats of combustion, i;e., high B.t.u. content, is also a necessity. Furthermore, a goodjet fuel should burn cleanly in the jet engine. It is evident that the provision of high quality jet fuel is not a simple matter. This is particularly true if such a high quality jet fuel is to be available at a reasonable cost.

This invention has for its object to provide procedure for preparing an improved jet fuel. Another object is to provide economical procedure for preparation of a high quality jet fuel. Other objects will appear hereinafter.

These and other objects are accomplished by our in vention which includes contacting a petroleum distillate boiling in the range between about 250 and 550 F., having a freezing point below about 45 F., a viscosity at 40 F. below about 15 centistokes and composed primarily or predominantly of paraflinic and/or naphthenic hydrocarbons with hydrogen in the presence of a hydrorefining catalyst. This contacting with hydrogen takes place at elevated temperatures and pressures suitable for hydrorefining of the feed stock without substantial cracking or conversion of the feed stock into lower boiling hydrocarbons. Thereafter at least part of the so hydrogen-treated product is extracted with a preferential solvent for aromatic hydrocarbons. A superior jet fuel is recovered from the raflinate.

The feed stock to our improved process may be any petroleum fraction boiling in the range between about 250 and 550 F., provided that it has a freezing point below about 45 F., a viscosity at -40 F. below about 15 centistokes and is predominantly composed of paraffinic and/ or naphthenic hydrocarbons. Thus heavy naphtha, kerosene or a mixture of heavy naphtha and kerosene may be employed. It is advantageous to utilize distillates boiling in the above temperature range, which distillates are derived from parafiinic or naphthenic type crudes. For instance, Mid-Continental and Pennsylvania 3,201,345 Fatenied Aug. 17, 1965 type crudes are suitable sources of feed stocks. We prefor to employ feeds which boil in the range between about 330 and 515 F.

The catalyst employed in the hydrogen treatment may be any of the well-known hydrorefining catalysts employed for treatment of petroleum fractions in order to hydrogenate olefins, hydrodesulfurize, etc. Examples of such catalysts are Group Vi left hand column or Group VIII metals, oxides and sulfides. Mixtures of such Group VI and Group VH1 metal oxides and sulfides are particularly advantageous. Specific examples of suitable hydrorefining catalysts are molybdenum oxide or sulfide, tungsten oxide or sulfide, nickel oxide, nickel sulfide, cobalt molybdate, nickel tungstate, amixture of nickel sulfide and tungsten sulfide, etc. These catalysts are advantageously deposited upon an inert porous catalyst carrier such as activated alumina, the variousforms of alumina such as gamma alumina and eta alumina and deactivated silica alumina, etc. In the event that a carrier such as the last-mentioned carrier is empl0yed,.it is necessary that the cracking activity be destroyed since substantial cracking of the feed is undesirabie. Amounts of between about 5 and 25 percent by weight of hydrogenating component may be deposited on the carrier.

The hydrogen treatment described may be carried out at a temperature of between about 500 and 800 F. and preferably between 600 and 725 F. A pressure of about to 2000 p.s.i.g. and preferably 500 to 1000 p.s.i.g. is employed. The temperature and pressure conditions are so selected that hydrogenation conditions prevail in the reactor and so that there is hydrogenation of deleterious substances present in the feed stock. These deleterious substances are not all elucidated, but they appear to be primarily gum-forming materials, olefins, sulfur compounds, nitrogen compounds, etc. While pressures higher than 2000 p.s.i.g. may be used with entirely satisfactory results, there is no particular advantage in such higher pressures and, of course, they are more costly to employ. A liquid hourly space velocity of between about 0.2 and 10.0 and preferably between about 1 and 4- is employed. A hydrogen recycle rate of between about 5000 and 10,000 s.c.f./bbl. and preferably between about 1000 and 3000 s.c.f./bbl. is utilized.

The abovementioned feed stock is contacted with the hydrogen and the catalyst in any customary manner for hydrorefining of hydrocarbons. The most usual procedure for this type of operation is to pass the hydrogen and vaporized hydrocarbon together through a high pressure reactor which contains a body of solid pieces of the hydrorefining catalyst. The hydrogen and feed may be passed downwardly through the hydrorefining reactor or upfiow therethrough. After passage through the reactor, the hydrogen is separated from the condensed hydrorefined hydrocarbon and is recycled for re-use in known fashion.

It is advantageous at this stage to distill the hydrocarbon product from the hydrogen treatment. If the original feed stock contained only components boiling in the range of the desired jet fuel, then after the hydrogen treatment the hydrogen-treated product can. simply be subjected to a low-cost topping operation to remove the small amount of volatile material formed during the hydrogen treatment. It is, of course, feasible to employ other procedures. For instance, an original charge stock boiling over a broader range than the desired jet fuel can be hydrogenrefined, and then the desired jet fuel separated from the hydrogen-treated product. An alternative, but less desirable procedure, is to directly extract the hydrogen-treated distillate and then separate the jet fuel portion therefrom.

We have found that any solvent which preferentially removes aromatic hydrocarbons is useful for improving the hydrogen-treated fraction in regard to jet fuel charaoteristics. We do not know what materials are extracted by these solvents, but we have found that these solvents remove materials which are present in the hydrogentreated fraction which have a deleterious effect on the jet fuel properties. These are not necessarily aromatic hydrocarbons as is pointed out above. Furfural is a preferred solvent for this purpose. However, examples of other suitable solvents are diethylene glycol, dimethyl sul-foxide, ace-tonitrile and sulfur dioxide.

The solvent extraction is carried out in the same manner as employed in the petroleum industry for solvent refining of petroleum fractions to remove aromatic constituents. The solvent ratios customarily employed for such solvent extractions may also be used. In connection with the solvents mentioned above, a solvent to oil ratio of :1 to 3.0 and a temperature of 70 to 150 F.; a solvent to oil ratio of 0.5 to 5.0 and a temperature of 100 to 170 F.; a solvent to oil ratio of 0.2 to 10.0 and a temperature of 70 to 170 F.; a solvent to oil ratio of 0.1 to 10.0 and a temperature of 40 to 140 F;. and a solvent to oil ratio of 0.1 to 3.0 and a temperature of 20 to30 F. advantageously would be used for furfural, diethylene glycol, dimethyl sulfoxide, acetonitrile and sulfur dioxide respectively. With other solvents, the solvent to petroleum fraction ratio should preferably be adjusted so that the maximum yield of jet fuel is obtained having the desired specification-s.

After the solvent extraction has been completed, the ratfinate is subjected to treatment for removal of residual solvent. The most advantageous procedure for such removal will depend upon the solvent employed. In the case of furfural, conventional distillation or azeotropic distillation is preferred. After removal of residual solvent, the product constitutes the desired high quality jet fuel. Of course, if the original feed stock to the hydrogen treatment did not have the desired boiling range for the jet fuel to be prepared or if the small amount of volatile materials formed during hydrogen treatment were not removed after the hydrogen treatment, then a distillation step is required after the solvent extraction to separate the desired jet fuel, i.e., the jet fuel having the required boiling range.

EXAMPLE A West Texas kerosene having the characteristics shown in Table I was contacted with hydrogen in the presence of a nickel-cobalt-molybdenum-oxide catalyst deposited upon activated alumina at a temperature of 650 F.; a pressure of 600 p.s.i.g.; a liquid hourly space velocity of 5.0; and a hydrogen recycle rate of between 1500 and 1800 s.c.f./bbl. The hydrogen employed was 88 percent pure obtained from a hydroreforming operation. The resulting product was topped to remove components boiling below 325 F. and was then extracted with furfural in a ratio of one part furfural to four parts kerosene in a 15 stage Schiebel column at a temperature of 160 F. Thereafter the kerosene was subjected to distillation to remove residual furfural. The product which was obtained in a yield of 90 percent had the properties shown in Table II.

Table I Gravity, API 42.6 Freezing point, F. 68.0 Viscosity at 40 F.: C 11.76 Aromatics, vol. percent 19.1 Olefins, vol. percent 1.4 Sulfur, total wt. percent 0,448 Mercaptan sulfur, wt. percent 0.12 Nitrogen, wt. percent 0.003 Distillation Initial boiling point, F 314 End point, F. 497 5 364 373 4 Table l-Continued DistillationContinued End point, F.:

Table II.-Pr0duct Gravity, API 44.7 Lbs/gal. 6.69 Viscosity at 40 F.: C 11.18 Freezing point, F. -59 Sulfur, wt. percent 0.015

Mercaptans sulfur, wt. percent 0.0005

1. The process for preparing a jet fuel which comprises cont-acting a petroleum distillate having a freezing point below about -45 F., a viscosity at 40 F. below about 15 centistokes, which includes substantial amounts of hydrocarbons boiling in the range between about 250 and 550 F. which are composed predominantly of a member of the group consisting of parafinic and naphthenic hydrocarbons, with hydrogen in the presence of a hydrorefining catalyst at a temperature between about 500 and 800 F. at a pressure between about and 2000 p.s.i.g. and at a liquid hourly space velocity between about 0.2 and 10, said reaction conditions being selected within the specified ranges to result in the hydrogenation of the gum-forming materials present in the feed stock without substantial conversion of the petroleum distillate into lower boiling hydrocarbons, and without substantial saturation of aromatic compounds, extracting deposit-inducing substances from the hydrogenated product with a solvent selected from the group consisting of furfural, diethylene glycol, dimethyl sulfoxide, acetonitrile, and sulfur dioxide, and recovering a jet fuel from the rafiinate.

2. The process for preparing a jet fuel which comprises contacting a petroleum distillate having a freezing point below about -45 F., a viscosity at -40 F. below about 15 centistokes, boiling in the heavy naphthakerosene range and composed predominantly of a member of the group consisting of parafiinic and naphthenic hydrocarbons, with hydrogen in the presence of a mixed Group VI-Group VIII hydrogenation catalyst deposited upon an inert porous carrier at a temperature between about 500 and 800 F. at a pressure between about 100 and 2000 p.s.i.g. and at a liquid hourly space velocity between about 0.2 and 10, said reaction conditions being selected within the specified ranges to result in the hydrogenation of the gum-forming materials present in the feed stock without substantial conversion of the petroleum,

distillate into lower boiling hydrocarbons, and without substantial saturation of aromatic compounds, extracting deposit-inducing substances from the hydrogenated product with furfu-ral and recovering a jet fuel from the rafiinate.

3. The process for preparing a jet fuel which comprises contacting a petrol-cum distillate having a freezing point below about 45 F., a viscosity at -40 F. below about 15 centistokes, boiling in the heavy naphthakerosene range and composed predominantly of a member of the group consisting of parafiinic and naphthenic hydrocarbons with hydrogen in the presence of a cobaltmolybdenum catalyst deposited upon activated alumina at a temperature between about 600 and 725 F. at a a pressure between about 500 and 1000 p.s.i.g. and at a liquid hourly space velocity between about 1 and 4, said reaction conditions being selected within the specified ranges to result in the hydrogenation of the gum-forming materials present in the feed stock without substantial conversion of the petroleum distillate into lower boiling hydrocarbons, and without substantial saturation of aromatic compounds, extracting deposit-inducing substances from the hydrogenated product with furfural and recovering a jet fuel from the raffinate.

4. The process for preparing a jet fuel which cornprises contacting a petroleum distillate, having a freezing point below about 45 F., a viscosity at 40 F.

6 below about 15 centistokes, having a boiling range between about 330 and 515 F, and composed predominantly of a member of the group consisting of paraifinic and naph-thenic hydrocarbons, with hydrogen in the presence of a cobalt-molybdenum-alumina catalyst at a temperature between about 600 and 725 F. at a pres- References Cited by the Examiner UNITED STATES PATENTS 2,731,506 l/56 Love et a1. 260683.9 2,846,358 8/58 Bieber et a1. 208-212 2,967,204 1/61 Beuther et al. 260-667 3,077,733 2/63 Axe et a1, 208212 3,098,106 7/ 63 Edwards 260-467 AL-PHONSO D. SULLIVAN, Primary Examiner.

Claims (1)

1. THE PROCESS FOR PREPARNG A JET FUEL WHICH COMPRISES CONTACTING A PETROLEUM DISTILLATE HAVING A FREEZING POINT BELOW ABOUT -45*F., A VISCOSITY AT -40*F. BELOW ABOUT 15 CENTISTOKES, WHICH INCLUDES SUBSTANTIAL AMOUNTS OF HYDROCARBONS BOILING IN THE RANGE BETWEEN ABOUT 250 AND 550*F. WHICH ARE COMPOSED PREDOMINANTLY OF A MEMBER OF THE GROUP CONSISTING OF PARAFINIC AND NAPHTHENIC HYDROCARBONS, WITH THE HYDROGEN IN THE PRESENCE OF A HYDROREFINING CATALYST AT A TEMPERATURE BETWEEN ABOUT 500 AND 800*F. AT A PRESSURE BETWEEN ABOUT 100 AND 2000 P.S.I.G. AND AT A LIQUID HOURLY SPACE VELOCITY BETWEEN ABOUT 0.2 AND 10, SAID REACTION CONDITIONS BEING SELECTED WITHIN THE SPECIFIED RANGES TO RESULT IN THE HYDROGENATION OF THE GUM-FORMING MATERIALS PRESENT IN THE FEED STOCK WITHOUT SUBSTANTIAL CONVERSION OF THE PETROLEUM DISTILLATE INTO LOWER BOILING HYDROCARBONS, AND WITHOUT SUBSTANTIAL SATURATION OF AROMATIC COMPOUNDS, EXTRACTING DEPOSIT-INDUCING SUBSTANCES FROM THE HYDROGENATED PRODUCT WITH A SOLVENT SELECTED FROM TEH GROUP CONSITING OF FURFURAL, DIETHYLENE GLYCOL, DIMETHYL SULFOXIDE, ACETONITRILE, AND SULFUR DIOXIDE, AND RECOVERING A JET FUEL FROM THE RAFFINATE.