US3230165A - Production of jet fuel - Google Patents

Description

United States Patent M 3,230,165 PRODUQTION 0F JET FUEL Guy C. Cunningham, Rolla, Mm, assiguor to Shell Gil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed June 26, 1963, Ser. No. 290,602 Claims. (Cl. 2ii889) This invention relates to a process for the production of jet fuel. More particularly, this invention relates to a process for the production of jet fuels of a high Luminometer number.

Supersonic jet aircraft capable of achieving Mach 24 speeds will probably be produced in quantity beginning about 1965. Fuels for these high Mach aircraft must meet rigid requirements as to thermal stability, density, volatility, viscosity, purity, Luminometer number and the like.

The Luminometer number (LN) of a fuel is an empirical measure of the luminosity of a flame produced by burning the fuel in a specially prescribed manner. (A detailed description of the Luminometer is available in Tentative Procedure for Operation of Luminometer, March 10, 1959, Erdco Engineering Corporation.) The luminosity in indicative of the proportion of the theoretical chemical energy which is converted to light rather than heat when the fuel is burned. A high Luminometer number (low luminosity) is important for several reasons such as: (1) Chemical energy which is converted into light does not help to expand the product gases. Thus, theoretically available chemical energy is, in a luminous combustion, only partially converted into energy of thrust of the aircraft; (2) luminosity is generally due to glowing particles of carbon which would have to be burned to CO in order to realize the maximum available heat energy of the rfuel. The fact that some of the fuel is incompletely burned means that neither the potentially available heat nor gas volume is realized; (3) erosion of the turbine blades can result from small, solid particles in a high-velocity gas-stream.

The petroleum refiner is faced with a serious problem of producing in quantity jet fuels of high Luminometer number, i.e. about 90 and preferably 100 and above. Hydrocarbon fractions boiling in the range of about 300 F. to about 600 F., preferably the kerosene fractions which boil in the range from about 325 F. to about 525 R, which are used in the production of present day jet fuels have a low Luminometer number. For example, Luminometer number of the straight-run kerosene fraction from Mixed Sour, HVI Sour, HVI Sweet and Non-Lube Sweet crudes is about 43, 68, 56, and 50, respectively.

Some degree of improvement in Luminometer number of kerosene fractions can be achieved by reducing the aromatic content of the kerosene fraction. Aromatic hydrocarbons, which are present in straight-run kerosene fractions in amounts ranging from about 10% by volume to about by volume and higher, are known to contribute to low Luminometer number of kerosene frac tions. Reduction in aromatic content of the straight-run kerosenes can be achieved through removal by such means as selective solvents or selective absorbants. This tends to reduce sulfur content of the jet fuel also since sulfur is often present in aromatic hydrocarbons, e.g., thiophene. Residual sulfur can then be removed by chemical means or by a mild hydrotreatment called hydrofining or hydrodesulfurization.

Another means to reduce aromatic content of kerosene fractions is to subject the kerosene to a relatively severe hydrogenation treatment wherein aromatics are hydrogenated to naphthenes and in addition, sulfur is removed as hydrogen sulfide. Thus, for example, hydro- 3,23,155 Patented .lan. 18, 1966 treatment of the kerosene fraction from the four crudes mentioned above increases Luminometer number from about 5 to 15 units. However, these methods are generally insufiiicent to produce high Luminometer jet fuels.

In accordance with the process of the present invention, high Luminometer number jet fuels are produced from low Luminometer number kerosenes. In the .process, a naphthene-containing kerosene fraction is contacted, together with hydrogen, with a catalyst under controlled conditions to dehydrogenate selectively naphthenes to aromatics, after which the kerosene, now enriched in aromatic content, is separated into an aromatic fraction and a non-aromatic fraction. The non-aromatic fraction, low in naphthene content, is a superior jet fuel having improved luminosity and thermal characteristics. By the process, jet fuels of at least Luminometer number can be produced from straight-run kerosenes containing aromatics and a relatively high proportion of naphthenes.

Naphthenes have a weight heating value and thermal stability approaching those of paraflins and a volumetric heat of combustion approaching that of aromatics and thus are a desirable compromise between parafiins and aromatics with regard to heat of combustion. However, the presence of naphthenes in a kerosene fraction contributes to the poor luminosity characteristics of the kerosene since many naphthenes have a lower Luminometer number than paraffins. Thus, it is desirable to remove at least some of the naphthenes from the kerosene. Unlike aromatics which are easily removed from parafiins, naphthenes are extremely difficult to separate from paraflins. In the present process, naphthenes are converted to aromatic which are then separated from the paraflin hydrocarbons.

The process of the invention is particularly applicable to kerosene fractions containing a high proportion of naphthenes in the saturate fraction, such as, for example, the Mixed Sour and HVI Sour kerosenes mentioned above which have a paraflin to naphthene ratio of about 1:1 and 221, respectively. With kerosene frac tions having .a low parafiin content and a very high proportion of naphthenes, the yield of jet fuel becomes quite low. Thus, the paraflin to naphthene ratio should generally be about 1:2 and preferably about 1:1.5. However, appreciable improvement in Luminometer number can be obtained with kerosenes having a low proportion of naphthenes. In general, the paraffin to naphthene ratio should be no higher than about 5:1 and preferably 4:1.

The process of the invention can be effected with one or two conversion steps. In a two-step process, the kerosene is first desul furized to remove sulfur com pounds which are present in most if not all straight-run kerosenes, and the desulfurized kerosene is subjected to selective dehydrogenation to convert naphthenes to aromatics. While sulfur can be removed, for example, by chemical means, it is preferred to employ hydrodesui furization. In hydrodesulfurization, the sulfur-containing kerosene fraction is passed together with hydrogen over a ulfur-resistant hydrogenation catalyst. If desired, hydrocarbons boiling above and below the jet fuel boiling range, e.g. wide boiling hydrocarbon fractions, can be included in the hydrodesulfurization feed. Components outside the jet fuel boiling range can conveniently be removed subsequently by distillation. Hydrodesulfurization catalyst are well known and are commercially available and generally comprise one or more of the various Group VI and Group VIII metals, as well as the oxides and sulfides thereof, usually supported on a porous carrier. Suitable carriers are bauxite, kieselguhr, silica, alumina, alumina-silica and the like. The highly acidic carriers such as silica-alumina cracking catalysts tend to give excessive cracking, and, if used, should be treated to reduce acidity or employed under mild conditions. Particularly suitable desullfurization catalyst are cobalt or nickel in combination with molybdenum or alumina.

Desulfurization can be effected over a wide range of conditions and will vary somewhat depending upon the particular catalyst used. Temperature is in the range from about 500 to 800 F., preferably about 625 to 750 F.; pressure is in the range from about 400 to 1500 p.s.i.g., preferably 500 to 800 p.s.i.g., liquid hourly space velocity (LHSV) is about 0.5 to 5, preferably 1 to 3, and the hydrogen rate is about 500 to 10,000 standard cubic feet of H per barrel of feed (s.c.f./b.), pre ferably 1000 to 2500 s.c.f./b. Liquid hourly spaced velocity as used herein is the volumes of oil per volume of catalyst per hour. The conditions are adjusted to produce a kerosene product [fraction having a total sulfur content of less than about 25 p.p.m. w., preferably less than about 10 ppm. W. Partial hydrogenation of the aromatics or partial dehydrogenation of naphthenes can be effected in the desulfurization step although usually no deliberate attempt is made to do so. If anything, the latter is to be desired since hydrogenation of aromatics would increase the load in the (following dehydrogenation step.

The desulfurized kerosene is preferably hot stripped, for example, with hydrogen from the dehydrogenation step, to remove dissolved hydrogen sulfide and light gases, and is passed to a dehydrogenation zone. In this zone, the kerosene fraction, together with hydrogen, is con- .tacted under dehydrogenation conditions with any suitable catalyst having activity to dehydrogenate selectively naphthene to aromatics. While such catalysts may comprise a metal of Group VI and/or Group VIII and their oxides and sulfides, supported on a porous support, particularly suitable dehydrogenation catalysts are the noble metals Group VIII and particularly the highly active sulfur-sensitive platinum or alumina, with or without combined halogen, catalysts, which are widely used in the reforming of naphthas.

Operating conditions are somewhat more severe than normally used in desulfurization and are such that generally from about 10 to 70% of the naphthenes are converted to aromatics. Dehydrogenation of naphthenes is favored by relatively high temperatures and low pressures and therefore operation is in the range from about 650 F. to 1000 F., preferably about 725900 F., and from about 200 to 600 p.s.i.g., preferably about 350 to 450 p.s.i.g. To minimize paraffin cracking, i.e. provide 95% V or more paraflin retention, high liquid hourly space velocities (LHSV) are employed, particularly with the highly active platinum-on-alumina reforming catalysts, and are in the range from about 5 to 15, preferably from about 8 to 12. Hydrogen rate is about 2000 to 10,000 s.c.f./b. Hydrogen is produced in the dehydrogenation step and can be used in the desulfurization step wherein hydrogen is consumed.

Hydrodesulfurization-dehydrogenation can be achieved in a single reaction zone and is generally preferred over the two-step process. In a single-step process, a sulfurand naphthene-containing kerosene fraction is passed, together with hydrogen, into a single hydrodesulfurization-dehydrogenation zone containing a sulfur-resistant catalyst. Since most, if not all kerosenes contain appreciable sulfur, the catalyst in a single-step process is generally limited to those which have activity for the on a carrier such as natural or processed bauxite, activated alumina, kieselguhr, and the like. A highly-acidic carrier such as silica-alumina is generaly undesirable because such a carrier tends to promote hydrocracking reactions. A preferred catalyst consists of cobalt-molybdenum or nickel-molybdenum supported on alumina.

The operating conditions for the hydrodesulfurizationdehydrogenation zone are similar to those employed in the two-step process, particularly the dehydrogenation step, and comprise a temperature in the range of from about 700 F. to about 1000 F., preferably from about 750 F. to about 900 F. (the lower temperatures are preferred to avoid product degradation); a pressure in the range of from about 200 to about 700 pounds per square inch gauge, preferably from about 400 to about 550 pounds per square inch gauge (while it is easier to dehydrogenate at lower pressures, too low a pressure results in coke deposition causing catalyst deactivation; too high a pressure results in hydrogenation reactions rather than dehydrogenation reactions); a liquid hourly space velocity to the range of from about 0.5 to about .5, preferably from about 1 to about 3; and a hydrogen rate in the range from about 500 to about 5000 s.c.f./b., preferably from about 2000 to about 4000 s.c.tf./ b. Dehydrogenation conditions are generally sufiicently severe to substantially desulfurize the kerosene, e.g. to a product sulfur content of less than 25 ppm w., and usually to less than 10 p.p.m. W.

In summary, dehydrogenation of naphthenes can be effected in a single-step or two-step process with a dehydrog'enation catalyst under controlled operating conditions which broadly are 700-1000 F. temperature, 200- 700 p.s.i.g. pressure, 0.5-l5 LHSV, and 5005000 s.c.f. Hg/b.

The hydrodesulfurized and dehydrogenated product, after it has been stabilized to remove hydrogen and light hydrocarbons, is then passed to a separation zone to remove aromatics (both aromatics originally in the hydrocarbon fraction and also those aromatics formed from the dehydrogenation of naphthenes). The separation of aromatics can be carried out by any suitable process such as adsorption on, for example, silica gel, solvent extraction, extractive distillation, etc. Very deep extraction is practiced to assure plus Luminometer number fuel, e.g. the raftinate from the extraction process should contain less than about 2% v. aromatics, preferably less than about 1% v. aromatics. Suitable solvents which are selective for aromatics include sulfur dioxide, diethylene glycol, triethylene glycol, furfural, phenol, sulfolane, and the like. Examples of preferred solvent extraction processes include sulfur dioxide extraction using from about 100% to about 200% v. sulfur dioxide and an extraction temperature in the range of from about 0 F. to -5 F.; diethylene or triethylene glycol extraction using a solvent-to-feed molar ratio of about 4:1 to about 20:1 and an extraction temperature in the range of from about 200 F. to about 350 F., and sulfolane extraction using a solvent-to-feed molar ratio of from about 2:1 to about 8:1 and an extraction temperature in the range of from about F. to about 350 F. Processes for solvent extraction of aromatics are well known and many are practiced commercially. Accordingly details of solvent extraction of aromatics need not be discussed here.

The saturate fraction (rafiinate from the extraction process), now substantially reduced in naphthene and aromatic content, is a superior jet fuel having improved luminosity and thermal characteristics. Luminometer number is at least 90, and preferably at least 100. Other components can be included with the saturate fraction to provide necessary freeze point, flash point, or other desired properties of a finished jet fuel. If desired, the saturate fraction can be further refined to improve other desired properties.

The following examples are illustrative of some of the advantages derived from the invention, but is not to be considered to limit the scope of the invention.

EXAMPLE I Table I HYD RODESULFURIZATION Catalyst Ni/Mo Co/Mo Temperature, F 650 650 700 700 700 675 075 Pressure, p.s.i.g 800 800 800 800 800 800 800 OiLscI/lobl 5,000 5,000 5,000 2, 500 5,000 5,000 5,000

The hydrotreated product was then passed into a dehydrogenation zone containing a platinum-supported catalyst (0.75% w. PL, 0.75% w. halogen, alumina). The dehydrogenation conditions were varied to show effects on product properties. Aromatics were removed from the dehydrogenated product by adsorption on silica gel. The results of the dehydrogenation and aromatics removal are shown in Table II.

Table II DEHYDROGENATION AND AROMATICS REMOVAL Feed Temperature, F 800 800 850 900 Pressure, p.s.i.g 400 400 400 400 LHSV (vol. oil/vol. catJh 5. 5 10. 9 10. 0 10. 9 Hgloil, s.e.f.!bbl 5, 500 5, 500 5, 500 5, 500 Total liquid product:

saturates, percent v- 79 62 64 59 55 Aromatics, percent v 21 38 36 41 45 Yield, percent v 96. 8 97.7 97.1 96. 0 Luminometer number of saturate 87 104. 9 102. 4 107. 6 114. 9 Aromatic content, percent v:

HEP-300 F., TBP cut 21 24 26 27 26 300-350 F., TBP cut"- 22 31 29 34 37 350-400" F., TBP cut- 35 40 400450 F., TBP out 19 40 35 40 46 450+ TBP cut 21 47 42 49 57 As may be seen from the data in Table II, the present process improves Luminomcter number beyond that obtained through conventional desulfurization followed by aromatics removal. The removal of impurities in the hydrotreating zone and the removal of aromatics from this hydrotreated product increased the Luminometer number of kerosene fraction from 45 to only 87. However, the additional step wherein the naphthenes were selectively dehydrogenated to aromatics and the subsequent removal of aromatics (including both natural and synthesized aromatics) from the dehydrogenated product markedly increased the Luminometer number of the hydrocarbon fraction to about 100. Dehydrogenation of naphthenes apparently is preferentially of the higher boiling, low Luminometer number naphthenes. The deleterious effect of naphthenes on Luminometer number can be seen by a comparison of the Luminometer number of the saturate portion of the feed to the dehydrogenation zone (87) and the saturate portion of the product from the dehydrogenation zone (greater than 102).

EXAMPLE II An HVI Sour kerosene fraction was subjected to a hydrodesulfurization dehydrogenation treatment in a single step process employing nickel-molybdenum on alumina as the catalyst. Results of the single-step, hydrodesulfurization-dehydrogenation process are shown in Table HI together with pertinent properties of the feed.

Table III SIN GLE'STEP, HYDRODESULFURIZATION- DEHYDROGENATION PROCESS Operating conditions Feed A B C D Pressure, p.s.i.g 500 500 500 500 Hiloil, s.c.f./bbl 2 700 2, 700 2, 700 2,700 LHSV (vol. oil/vol. catJhr.) 1 1 4 1 Temperature, F 760 810 810 860 Properties: Product Gravity, API. 48. 0 48. 0 47. 4 47. 9 46. 5 ASIM distillnti IBP 366 304 215 308 249 10% v. recovered. 394 383 70 384 351 50% v. recovered 428 420 410 415 404 v. recovered 470 470 462 472 458 Sulfur, p.p.m. w 610 1.7 1.4 1.4

Yields basis feed, percent v.

Total Liquid product 93. 3 96. 4 98. 4 92. 3

Aromatics 9 12. 7 19. 3 13. 8 22. 2

N aphthenes 30 25. 7 17. 9 24. 3 14. 5

Parafiins 61 59. 0 50. 0 60. 3 55. 6

Table IV SATURATE FRACTION Feed Product B Luminometer number 108 119 Freezing point, F 22 23 Heat of combustion, B

Gross 20, 235 20, 316 18, 876 18, 956

The above data show that sufficient hydrodesulfurization and dehydrogenation can be achieved in one step to efiect significant increases in Luminometer number and heat of combustion. Luminometer number of the original feed was 67.

I claim as my invention:

1. A process for the production of jet fuel which consists essentially of passing a napht-hene-containing kerosene feed traction together with hydrogen into contact with a catalyst having dehydrogenation activity under conditions to dehydrogenate selectively naphthenes to aromatics, said conditions including a temperature in the range of about 700 to about 1000 F., a pressure of about 200 to about 700 p.s.i.g., a liquid hourly space velocity of about 0.5 to about 15, and from about 500 to about 10,000 standard cubic feet of hydrogen per barrel of feed, recovering a kerosene fraction enriched in aromatic content, separating aromatics from the kerosene fraction and recovering a non-aromatic jet fuel fraction having a Luminometer number of at least 90.

2. A process for the production of jet fuel which consists essentially of passing a kerosene feed fractioncontaining naphthenes and sulfur compounds together with hydrogen into contact with a sulfur-resistant desulfurization catalyst under desulfurization conditions, recovering a kerosene fraction having less than about 25 ppm. by weight total sulfur, passing the kerosene fraction together with hydrogen into contact with a sulfur-sensitive catalyst having dehydrogenation activity under conditions to dehydrogenate selectively naphthenes to aromatics, recovering a kerosene fraction enriched in aromatic content, separating aromatics from the aromaticenriched kerosene fraction, and recovering a non-aromatic jet -fuel fraction having a Luminometer number of at least 90.

3. A process for the production of jet fuel which consists essentially of passing a kerosene feed fraction containing naphthenes and sulfur compounds together with hydrogen into contact with a sulfur-resistant desulfurization catalyst under desulfurization conditions, recovering a kerosene fraction having less than about 10 p.p.m. by weight total sulfur, passing the kerosene fraction together with hydrogen into contact with a platinum dehydrogenation catalyst under conditions to dehydrogenate selectively naphthenes to aromatics, recovering a kerosene fraction enriched in aromatic content, separating aromatics from the aromatic enriched kerosene fraction, and recovering a non-aromatic jet fuel fraction having a Luminometer number of at least 90.

4. A process for the production of jet fuel which consists essentially of passing a kerosene feed fraction containing sulfur compounds and having a paraffin to naphthene ratio between about 1:2 and :1 together with hydrogen into contact with a sulfur-resistant desulfurization catalyst under desulfurization conditions, recovering a kerosene fraction having less than about 25 p.p.m, by weight total sulfur, passing the kerosene fraction together with hydrogen into contact with a sulfur-sensitive catalyst having dehydrogenation activity under conditions to dehydrogenate selectively naphthenes to aromatics, recovering a kerosene fraction enriched in aromatic content, separating aromatics from the aromatic-enriched kerosene fraction, and recovering a jet fuel fraction having less than 2% by volume aromatics and a Luminometer number of at least 90.

5. A process for the production of jet fuel which consists essentially of passing a kerosene feed fraction containing sulfur compounds and having a paraffin to naphthene ratio between about 1:1.5 and 4:1 together with hydrogen into contact with a sulfur-resistant desulfurization catalyst under desulfurization conditions of about 625 to 750 F., 500 to 800 p.s.i.g., 0.5 to 5 liquid hourly space velocity and 500 to 10,000 standard cubic feet of hydrogen per barrel of feed, recovering a kerosene fraction having less than about p.p.m. by weight total sulfur, passing the kerosene fraction together with hydrogen into contact with a sulfur-sensitive catalyst having dehydrogenation activity under conditions of about 725 to 900 F., 200 to 600 p.s.i.g., 5 to liquid hourly space velocity, and 2000 to 10,000 standard cubic feet of hydrogen per barrel of kerosene to dehydrogenate selectively napthenes to aromatics, recovering a kerosene fraction enriched in aromatic content, separating aromatics from the aromatic enriched kerosene fraction, and recovering a jet fuel fraction having less than about 1% by volume aromatics and a Luminometer number of at least 90.

6. A process for the production of jet fuel which consists essentially of passing a napthene-containing kerosene feed fraction together with hydrogen into contact with a desulfurization-dehydrogenation catalyst at a temperature in the range from about 700 to about 1000 F., a pressure in the range from about 200 to about 700 p.s.i.g., a liquid hourly space velocity of about 0.5 to 5, and from about 500 to about 5000 standard cubic feet per barrel of kerosene feed, recovering a kerosene fraction enriched in aromatic content, separating aromatics from the aromatic-enriched kerosene fraction, and recovering a nonaromatic jet fuel fraction having a Luminometer number of at least 90.

7. The process according to claim 6 wherein the catalyst is selected from the group consisting of cobalt-molybdenum and nickel-molybdenum.

8. The process according to claim 6 wherein the naphthene-containing kerosene feed fraction has a parafiin to naphthene ratio between about 1:2 and 5 :1 and the nonaromatic jet fuel fraction has an aromatic content less than 2% by volume.

9. A process for the production of jet fuel which consists essentially of passing a hydrocarbon feed fraction containing naphthenes and sulfur compounds together with hydrogen into contact with a sulfur-resistant desulfurization catalyst under desulfurization conditions, recovering a kerosene fraction having less than about 10 ppm, by weight total sulfur, passing the kerosene fraction together with hydrogen into contact with a platinum dehydrogenation catalyst at a temperature in the range from about 750 to 1000 F., a pressure in the range from about 200 to 600 p.s.i.g., a liquid hourly space velocity of from about 5 to 15, and a hydrogen rate of from about 2000 to 10,000 standard cubic feet per barrel of kerosene, recovering a kerosene fraction enriched in aromatic content, separating aromatics from the aromatic enriched kerosene by means of a solvent selective for aromatics, and recovering a non-aromatic jet fuel fraction having a Luminometer number of at least 90.

10. The process according to claim 9 wherein the hydrocarbon feed fraction has a parafiin to naphthene ratio of between about 1:15 and 4: 1 and the non-aromatic jet fuel fraction has an aromatic content less than about 1% by volume.

References Cited by the Examiner UNITED STATES PATENTS 2,945,802 7/ 1960 Ciapetta et al 20815 3,015,549 1/1962 Ciapetta et al 20815 3,110,661 11/1963 Franz 208-89 3,125,503 3/1964 Kerr et a1 20815 DE-LBERT E. GANTZ, Primary Examiner.

ALPHONSO D. SULLIVAN, PAUL M. COUGHLAN,

Examiners.

S. P. I ONES, Assistant Examiner.

Claims (1)

1. 3. A PROCESS FOR THE PRODUCTION OF JET FUEL WHICH CONSISTS ESSENTIALLY OF PASSING A KEROSENE FEED FRACTION CONTAINING NAPHTHENES AND SULFUR COMPOUNDS TOGETHER WITH HYDROGEN INTO CONTACT WITH A SULFUR-RESISTANT DESULFURIZATION CATALYST UNDER DESULFURIZATION CONDITIONS, RECOVERING A KEROSENE FRACTION HAVING LESS THAN ABOUT 10 P.P.M. BY WEIGHT TOTAL SULFUR, PASSING THE KEROSENE FRACTION TOGETHER WITH HYDROGEN INTO CONTACT WITH A PLATINUM DEHYDROGENATION CATALYST UNDER CONDITIONS TO DEHYDROGENATE SELECTIVELY NAPHTHENES TO AROMATICS, RECOVERING A KEROSENE FRACTION ENRICHED IN AROMATIC CONTENT, SEPARATING AROMATICS FROM THE AROMATIC ENRICHED KEROSENE FRACTION, AND RECOVERING A NON-AROMATIC JET FUEL FRACTION HAVING A LUMINOMETER NUMBER OF AT LEAST 90.