US3369998A - Production of high quality jet fuels by two-stage hydrogenation - Google Patents

Description

United States Patent 3,369,998 PRODUCTION OF HIGH QUALITY JET FUELS BY TWO-STAGE HYDROGENATIQN Paul G. Bercik, Glenshaw, Pa., and Leslie D. Moore, Lisle, Ill., assignors to Gulf Researchdz Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Filed Apr. 30, 1965, Ser. No. 452,394

5 Claims. (Cl. 208-210) This invention relates to an improved process for preparing a jet fuel, particularly a superior quality et el. The development of jet engines has called for higher grade fuels. The specifications for such fuels for military uses are denominated lP-l, JP-3, JP-4, etc. They may be roughly classified as follows:

Detailed specifications for JP5 and JP6 fuels may be found in MIL-J-5624 and MIL-J-25656.

For various special purposes, it is, of course, necessary to describe intermediate or more stringent requirements. It is, therefore, not surprising that a certain tightening of specifications became necessary when lP-S jet fuel was required for use in Mach 2 jet engines.

A high speed jet aircraft builds up heat as it moves through the atmosphere. At sub-sonic speeds the heat can .be dissipated by air cooling the engine, But at the higher supersonic speeds, the heat builds up faster than it can be dissipated to the air. The most convenient reservoir for this heat is the fuel and it has become common practice to dissipate this excess in the fuel contained in aircraft fuel tanks.

Therefore, the fuel must be raised to relatively high temperatures. Unfortunately, the thermal stability of ordinary JP-S fuel was not sufficient for the heat load envisioned in the Mach 2 aircraft. At the temperatures predicted, the fuel tended to form coke and other deposits. Therefore, modifications were made in the list of specifications.

Regular JP-5 specifications were required and in addition:

(1) A minimum of 35 smoke point.

.(2) A minimum of 7S luminometer number.

(3) A higher thermal stability defined by the following test:

in a standard CFR coker, the 400 F./500 F. test run at a fuel flow rate of 3 lbs, per hour is to result in a a maximum pressure drop of five inches of mercury and a maximum deposit rating of two in 300 minutes.

It is important that fuels burn cleanly in a jet engine.

Deposits caused by poorly burning fuels decrease the efficiency of the power plant. Increased engine temperatures are caused by radiant heating. Fuels burningwith a luminous flame should also be avoided because the additional heat produced by the emitted radiation seriously damages the engine burner walls and other vital engine parts. Frequent overhaul is then necessary.

The smoke point of a fuel is a means of measuring its LII 3,309,098 Patented 1F eh.a 20, 1968 ability to burn cleanly. It is determined by a test in which a sample is burned in an enclosed lamp. with a scale. The maximum height that the flame reaches Without smoking is estimated. This number, in millimeters, is the smoke point. The test is described in ASTM D1322-59t.

The luminosity of a fuel is a measurement of the radiation of incandescent carbon particles obtained in the burning of that fuel. It is determined by the burning of fuel in a luminometer lamp and measuring the flame radiation with a photocell unit. The details of this test are described in ASTM D1740-60t.

The high temperature stability of jet fuels is measured in the fuel coker test which subjects the test fuel to temperatures and conditions similar to those occurring in aircraft engines. A fuel is pumped at a certain rate through a preheater which simulates hot fuel line sections of the engine. It then passes through a heat filter which represents small fuel passages in the hot section of the engine. The extent of the build-up as measured by pressure drop across the filter, in combination with a visual assessment of the deposit condition of the preheater, is used as an evaluation of thermal stability.

It is an objective of this invention to provide improved procedure for the manufacture of a high quality jet fuel.

It is a further object of this invention to provide procedure for the manufacture of a jet fuel meeting all JP5 and JP6 specifications.

It is also an object of this invention to provide procedure for producing a fuel meeting JP-S specifications and in addition having a minimum smoke point of 35, a minimum luminometer number of and a higher thermal stability (defined by the following test: in a standard CFR coker, the 400 F./ 500 F. test run at a fuel flow rate of 3 lbs. per hour is to result in a maximum pressure drop of five inches of mercury and a maximum deposit rating of 2.0 in 300 minutes).

It is a further object of this invention to provide procedure for manufacture of a JP-S jet fuel suitable for Mach 2 jet engines.

It is a further object of this invention to provide for a 2-step hydrogenation of straight run kerosene.

Other objects will appear later herein.

These and other objects of the invention are achieved by treating a straight run kerosene with two successive catalytic hydrogenations at carefully selected conditions with especially chosen catalysts. The first step removes sulfur and nitrogen compounds from the kerosene and the second step saturatively hydrogenates the resultant product.

This process may be used with any straight run kerosene. It has been discovered by applicants that cycle stocks are completely unsuitable as feeds for this process. It may be possible under certain conditions to manufacture a lower quality jet fuel by hydrogenation processes utilizing cycle oils. But it is not possible to manufacture the high quality jet fuel which is an objective of this invention. Included in the specification of this fuel, as indicated above, is a requirement for high luminosity numbers. These are conferred by paraflins. Any cycle oil, with boiling point in the kerosene range, will have a high aromatic content. When such a cycle oil is hydrogenated, a product of high naphthenic content is obtained. This product is marked by low luminosity numbers.

Any feed with an aromatic content higher than 50% would be competely unacceptable for this process.

If it is desired to produce a JP6 fuel, a mixture of straight-run kerosene and naphthas may be used as a charge stock.

The charge stock is submitted to a finst hydrogenation stage in order to remove sulfur and nitrogen compounds. The temperature may be between about 650 F. and 750 3 F., the pressure 500 and 1500 p.s.i.g., the liquid hourly space velocity 1.0 and 6.0. Temperatures greater than 750 F. must not be used because undesirable, excessive hydrocracking and den-itrogenation will result. The hydrogen recircul-ation rate usually will vary from about 1,500 to 10,000 standar'd cubic feet per barrel.

The catalyst employed in this first stage hydrogenation may be any of the well-known hydrorefining catalysts em ployed for hydrogen treatment of petroleum fractions for hydrodesulfurization, denitrogenation, etc. Such catalysts include metals, oxides and/or sulfides of Group VI (left column) or Group VIII. Metals of Group VI and Group VIII compounds are likewise suitable. Specific examples of satisfactory catalysts include molybdenum oxide or sulfide, tungsten oxide or sulfide, nickel oxide or sulfide, cobalt molybdate, nickel tungstate, etc. These catalysts are advantageously deposited on inert porous carriers such as activated alumina, gamma alumina, eta alumina, pseudo-boeh'mite alumina, silica-alumina cracking cat-alyst, etc. In the event that a carrier such as the last-mentioned is employed, treating temperatures only up to 715 F. can be used without excessive hy-drocracking. Between about 5 and 25% by weight of catalyst (determined as metals) is usually deposited on these carriers.

In the second stage hydrogenation, temperatures from 450 F. to 700 F. may be used. However, above 650 F. a minor amount of hydrocracking may occur. This would tend to decrease the thermal stability of the jet fuel. Consequently, a temperature range of 450 to 630 F. generally gives superior results. vPressure in the second hydrogenation stage may vary from 500 to 1500 p.s.i.g. or higher. It is especially worthwhile to make certain that the pressure does not drop significantly below 500 p.s.i.g. in combination with temperatures in the higher portions of the ranges mentioned. Such a combination will result in reforming reactions which result in formation of aromatics and thus will severely curtail quality and, to a lesser extent, yield of jet fuel. Space velocities from 1 to may be used. A space velocity of from 1 to 5 is preferred. Hydrogen may be circulated at the rate of between about 2,000 and 10,000 standard cubic feet per barrel.

The catalyst for the second hydrogenation may be either about '12 to 50% nickel, cobalt molybdenum, tungsten, or combinations of these on (gamma, eta, or pesudo-bochmite) alumina or on kieselguhr or about 0.5 to 5.0% noble metal such as platinum or palladium on the various above-described aluminas.

The feed stock is contacted with the hydrogen and the catalyst in any of the customary manners for the hydrogen treatment or hydrocarbons. A preferred procedure is to pass the hydrogen and vaporized hydrocarbon together through a high pressure reactor which contains a bed of the hydrofining catalyst. The hydrogen and feed may be passed downwardly or upwardly through the reactor. After passage through the reactor, the hydrogen is separated from the condensed, hydrofined hydrocarbon. It is then recycled to the reactor from which it was derived. A portion of this hydrogen is bled off and fresh or makeup hydrogen is added to maintain hydrogen purity. While the hydrogen from the first stage may be used in the second stage, it must be treated to remove ammonia and hydrogen sulfide formed in the first stage by hydrogenation of nitrogen compounds. Otherwise, adequate hydrogenation in the second stage does not take place. Distillation of the product from the second stage is usually desirable since there are usually some products formed in one or both stages which do not have the appropriate boiling point for the desired jet fuel.

Example I A virgin kerosene of West Texas origin was hydrogenated over a Peter Spence catalyst comprising 2.1% cobalt and 8.7% molybdenum supported on activated alumina. Reaction conditions were as follows:

4 Temperature F.) 665 Pressure (p.s.i.g.) 600 LSHV 4.2 Hydrogen flow (s.c.f./bbl.) 1700 The liquid hydrocarbon portion of the resultant product was saturatively hydrogenated over a prereduced, 10- 20 mesh 48% nickel on kieselguhr catalyst under the following reaction conditions:

Temperature F.) 525 Pressure (p.s.i.-g.) 1000 LSHV 1.0 Hydrogen circulation (s.c.f./bbl.) 8000 The specifications of the product fuel are set down in Table I. The specifications for the modified Mach 2 JP-5 fuel are listed alongside.

TABLE I Specifications Prodfuct o Desired, Example Rigid but not I Rigid 50% at F.)

at F.) Copper Strip Corrosion, ASTM Existent Gum, mg./ m1... Flash Point, F

Net Heat Value, B.t.u./lb 2 18, 500 18, 700 Freezing Point, F 1 55 64 Viscosity, cs. at -30 F. 1 16. 5 3 11.8 Sulfur, p.p.m l 1, 000 1. 0 Mercaptan Sulfur, p.p.m 1 1 Luminorneter Number. 2 75 89 Smoke Point 2 35 42 Water Tolerance, ml 1 l Thermal Stability, ORG Coker:

Time, minutes 300 Fuel Flow, lb./hr 3 Preheater Temperature, F 400 Filter Temperature, F- 1500 Pressure Drop, in. Hg 3. 3 Preheater Deposit 0 1 Max. 2 Min. 3 At -40 F.

The jet fuel made by this process surpasses all the modified JP-S requirements. The actual flash point was not measured but this property could be adjusted by distillation if necessary. The luminometer number of 89 and the smoke point of 42 were much better than the minimum specifications and indicative of clean flame burning, the fuel giving a 3.3 in. Hg pressure drop and no preheater deposit passed the stability requirements.

We claim:

1. The method of manufacturing a jet fuel which comprises contacting a straight-run kerosene with hydrogen in the presence of a hydrogenation catalyst formed from at least one member selected from the group consisting of nickel, cobalt, molybdenum and tungsten and oxides and sulfides thereof, on an inert porous carrier, at a temperature of 650 to 750 F., at a pressure of 500 to 1500 p.s.i.g. with a liquid hourly space velocity of 1.0 to 6.0 and a hydrogen circulation rate of 1,500 to 10,000 standard cubic feet per barrel of kerosene, contacting the resultant product with hydrogen in the presence of a catalyst which comprises a metal selected from the group consisting of nickel, cobalt, tungsten, molybdenum and the noble metals, said catalyst being supported on a porous refractory support selected from the group consisting of alumina and kieselguhr, at a temperature of 450 to 700 F. at a pressure of 500 to 1500 p.s.i.g., a liquid hourly space velocity of 1.0 to 10.0 and a hydrogen circulation rate of 2,000 to 10,000 standard cubic feet per barrel of said product of the first stage, the combination of conditions being selected to produce a superior jet fuel having a lurninometer number of at least 75.

2. The method of manufacturing a jet fuel which comprises contacting a straight-run kerosene with hydrogen in the presence of a hydrogenation catalyst formed from at least one member selected from the group consisting of nickel, cobalt, molybdenum and tungsten and oxides and sulfides thereof, on an inert porous carrier at a temperature of 650 to 750 F., at a pressure of 500 to 1500 p.s.i.g. with a liquid hourly space velocity of 1.0 to 6.0, and a hydrogen circulation rate of 1,500 to 10,000 standard cubic feet per barrel of kerosene and cocurrently contacting the resultant product with hydrogen in the presence of a catalyst which comprises a metal selected from the group consisting of nickel, cobalt, tungsten, molybdenum and the noble metals, said catalyst supported on a porous refractory support selected from the group consisting of alumina and kieselguhr at a temperature of 450 to 630 F. at a pressure of 500 to 1500 p.s.i.g., a liquid hourly space velocity of 1.0 to 5.0 and a hydrogen circulation rate of 2,000 to 10,000 standard cubic feet per barrel of said product of the first stage, the combination of conditions being selected to produce a superior jet fuel having a luminometer number of at least 75.

3. The method of manufacturing a jet fuel which comprises contacting a straight-run kerosene with hydrogen in the presence of a cobalt-molybdenum catalyst at a temperature of 650 to 750 F., at a pressure of 500 to 1500 p.s.i.g. with a liquid hourly space velocity of 1.0 to 6.0, and a hydrogen circulation rate of 1,500 to 10,000 standard cubic feet per barrel of kerosene and contacting the resultant product with hydrogen in the presence of a catalyst comprising a metal selected from the group consisting of nickel, cobalt, tungsten, molybdenum and the noble metals, said catalyst supported on a porous refractory support selected from the group consisting of alumina and kieselguhr at a temperature of 450 to 630 F. at a pressure of 500 to 1500 p.s.i.g., a liquid hourly space velocity of 1.0 to 5.0 and a hydrogen circulation rate of 2,000 to 10,000 standard cubic feet per barrel of said product of the first stage, the combination of conditions being selected to produce a superior jet fuel having a luminometer number of at least 75.

4. The method set forth in claim 3 wherein the second stage catalyst comprises nickel.

5. The method set forth in claim 1 wherein the second stage catalyst is 12 to percent nickel on kieselguhr.

References Cited UNITED STATES PATENTS 3,077,733 2/1963 Axe et al. 260667 3,147,210 9/1964 Hass et al. 260667 3,201,342 8/1965 Bachman et al. 260-667 3,236,764 2/1966 Den Herder et al. 260-667 3,304,338 2/1967 Parish 260-667 SAMUEL P. JONES, Primary Examiner.

DELBERT E. GANTZ, Examiner.

Claims (1)

1. THE METHOD OF MANUFACTURING A JET FUEL WHICH COMPRISES CONTACTING A STRAIGHT-RUN KEROSENE WITH HYDROGEN IN THE PRESENCE OF A HYDROGENATION CATALYST FORMED FROM AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF NICKEL, COBLAT, MOLYHBDENUM AND TUNGSTEN AND OXIDES AND SULFIDES THEREOF, ON AN INERT POROUS CARRIER, AT A TEMPERATURE OF 650 TO 750*F., AT A PRESSURE OF 500 TO 1500 P.S.I.G. WITH A LIQUID HOURLY SPACE VELOCITY OF 1.0 TO 6.0 AND A HYDROGEN CIRCULATION RATE OF 1,500 TO 10,000 STANDARD CUBIC FEET PER BARREL OF KEROSENE, CONTACTING THE RESULTANT PRODUCT WITH HYDROGEN IN THE PRESENCE OF A CATALYST WHICH COMPRISES A METAL SELECTED FROM THE GROUP CONSISTING OF NICKEL, COBALT, TUNGSTEN, MOLYBDENUM AND THE NOBLE METALS, SAID CATALYST BEING SUPPORTED ON A POROUS REFRACTORY SUPPORT SELECTED FROM THE GROUP CONSISTING OF ALUMINA AND KIESELGUHR, AT A TEMPERATURE OF 450 TO 750*F. AT A PRESSURE OF 500 TO 1500 P.S.I.G., A LIQUID HOURLY SPACE VELOCITY OF 1.0 TO 10.0 AND A HYDROGEN CIRCULATION RATE OF 2,000 TO 10,000 STANDARD CUBIC FEED PER BARREL OF SAID PRODUCT OF THE FIRST STAGE, THE COMBINATION OF CONDITIONS BEING SELECTED TO PRODUCE A SUPERIOR JET FUEL HAVING A LUMINOMETER NUMBER OF AT LEAST 75.