US3384574A - Catalytic process for making a jet fuel - Google Patents

Description

May 21, 1968 R. R. HALlK ET AL CATALYTIC PROCESS FOR MAKING A JET FUEL 4 Sheets-Sheet 2 Filed July 21. 1966 LUMINOMETER NUMBER Vs. PARAFFIN CONTENT 69:32 E Eo E Paraffin Content, Z,

i A 0 W V w m m w m m H772 A. Sm/l/z m x w. R

I W F Age/1f May 21, 1968 HALlK ET AL 3,384,574

CATALYTIC PROCESS FOR MAKING A JET FUEL Filed July 21, 1966 4 Sheets-Sheet 3 RELATIONSHIP BETWEEN EQUILIBRIUM AROMATIC- NAPHTHENE RATIOS, PRESSURE AND TEMPERATURE Aromotics/Nophthene, A/N (observed) Hydrogen Pres-sure,psio

R ln/gnfo/ri FIGJII omond .Ha/

9%? A Sm/f/z Car/ I l/ S/reed Henry A. Vela/7d May 21, 1968 R. R. HALIK ETAL 3,384,574

CATALYTIC PROCESS FOR MAKING A JET FUEL Filed July 21. 1966 4 Sheets-Sheet 4 ESTIMATION OF JET FUEL FREEZE POINT FROM 370 F WEST TEXAS DATA 40 n- Poro n Lme Concentrofion Of n- Paraffin Vol F 40 IO 0 4020-30 -so -so 10 23 24 25 26 Reciprocal Freeze Point, I F PX IO; R

Raymond R Hal/k fi/fz ASnw/h Fl (5.11 Car/ 14 Sfreed I Henry R. //e/0n d- Age/7f United States Patent 3,384,574 CATALYTIC PROCESS FOR MAKING A JET FUEL Raymond R. Halik, Pitman, Henry R. Ireland, West Deptford Township, Gloucester County, Fritz A. Smith, Cherry Hill, and Carl W. Streed, Haddonfield, N..l., assignors to Mobil Oil Corporation, a corporation of New York Continuation-impart of application Ser. No. 478,526,

July 27, 1965. This application July 21, 1966, Ser.

6 Claims. (Cl. 208138) ABSTRACT OF THE DISCLOSURE The disclosure is concerned with the method of producing jet fuels from predetermined correlations represented by FIGURES I through IV in which the method includes determining from the correlation of FIGURE IV the permissible n-parafiin content of a desired freeze point jet fuel product, determining from FIGURES I and II the maximum naphthene to aromatic ratio tolerable in a product of desired heating value and luminometer number, and catalytically reforming a parafiin containing kerosine feed in accordance with the relationship represented by FIGURE III for the above predetermined naphthene/ aromatic ratio under space velocity conditions to permit 70% retention of paraffins.

This application is a continuation-in-part of application Ser. No. 478,526 filed July 27, 1965, now abandoned entitled Catalytic Process and Novel Compositions Prepared Therefrom. The present invention relates to an improved method and process for the preparation of hy drocarbon fuel compositions of desired heating value suitable for use in gas turbine engines.

In a more particular aspect, the invention relates to the method and combination of process steps for preparing from petroleum distillate fractions, high quality jet fuels under conditions to preserve paraffinic components of the distillate fractions. More specifically, the invention relates to defining a method for converting relatively high boiling hydrocarbon feed stock materials boiling in the range of kerosine type jet fuel to product rich in paraffins providing product specification luminometer number, freeze point and desired heating value.

In accordance with the method of this invention, desired paraffin rich jet fuels are prepared from petroleum hydrocarbon fractions of the kerosine type composed substantially of hydrocarbon mixtures boiling in the range of from about 350 up to about 550 F. and preferably boiling in the range of from about 375 F. up to about 525 F. Suitable hydrocarbon feeds include parafiln rich fractions boiling within the above-identified range and include virgin kerosines having an ASTM boiling range of from about 375 to about 525 F. derived from a variety of crude sources including Mid-Continent, Barco, West Texas, and Middle East (Kuwait) crudes. The feed stocks employed in the method herein described comprise kerosine type fractions containing pa-rafiins, naphthenes and aromatics in amounts of from about 30 to about 75 Weight percent paraflins, from about 20 to about 50 weight percent naph themes, and from about to about 30 Weight percent aromatics. Particularly desirable feed materials that may be upgraded by the method of this invention include straight run kerosine fractions of the following composition.

In accordance with the method of this invention, a kerosine boiling hydrocarbon fraction is subjected to a catalytic reforming treatment comprising primarily catalytic dehydrogenation and isomerization reactions under conditions selected to convert naphthenes to aromatics and hydroisomerize n-paraifins in the feed fraction under conditions directed to reduce any significant reduction of paraflins in the feed. Thereafter substantially complete removal of aromatics materials in the product of the catalytically treated mixture is effected by S0 extraction or other convenient methods to produce a desired low concentration of aromatic in the high quality jet fuel.

In the event that the relatively high boiling feed stocks employed in the method of this invention contains materials or impurities considered deleterious to the catalyst used in the catalytic reforming treatment above referred to, the feed stocks are subjected to a pretreatment for removal or substantial reduction in concentration of such impurities. That is, feed stocks that contain a relatively high concentration of sulfur as an impurity are pretreated to reduce the sulfur concentration below about p.p.m. and preferably below about 40 p.p.m. and more usually less than about 20 parts/million. It is also desirable to effect substantially complete removal of other undesirable impurities, such as arsenic and lead in one or more pretreatment steps. In particular, when the feed stocks contain a concentration of nitrogen substantially in excess of 20 parts/million, the feed stock is pretreated to substantially reduce the nitrogen concentration thereof to a low value which is usually less than about 20 parts/million (p.p.m.) and preferably is less than about 10 parts/million. For example, a virgin kerosine fraction boiling in the range of 375-500" F. and obtained from a Mid-Continent crude may contain a concentration of sulfur up to about 1700 p.p.m.; a virgin kerosine fraction of about the same boiling range obtained from Barco crude may contain up to about 700 p.p.m.; and a similar boiling range kerosine fraction obtained from a West Texas crude may contain up to about 350 ppm. sulfur. These feed materials are therefore subjected to a suitable desulfurizing pretreatment to reduce the sulfur and any nitrogen constituents therein to not more than about 20 p.p.m. and preferably less than 20' p.p.m. To accomplish this pretreatment the feed stock is subjected to hydrodesulfurization and hydrodenitrogenation conditions by contact with a suitable catalyst (e.'g., cobalt molybdate on alumina, nickel-tungsten sulfide, chromia on alumina, and others) known in the art in the presence of hydrogen at conditions of pressure, space velocity and temperature to reduce the concentration of sulfur and nitrogen to desired values. Arsenic and lead would be simultaneously removed in such a hydropretreatment but may be separately removed by simple contact with porous alumina at reforming temperature conditions. Pretreatment of the feed stocks to remove sulfur and nitrogen compounds therefrom may be accomplished particularly by contact with a cobalt molybdate hydropretreatment catalyst within the following ranges of operating conditions.

Space velocity (LHSV) 0.5- Hydrogen partial pressure (p.s.i.g.) 130-800 Temperature, F. 675-800 Hydrogen circulation rate (s.c.f./bbl.) 190-3000 The kerosine boiling feed stock thus treated and substantially freed of undesired impurities is then subjected to the catalytic reforming treatment of this invention under conditions correlated as hereinafter described in the presence of a suitable dehydrogenation-isomerizing catalyst such that, the reactions effected will maintain a relatively high percentage of the feed paraffins, and in certain instances increase the paraffinic concentration thereof. That is, it has been found that by correlating operating conditions as described more fully hereinatfer that the relatively high boiling feed stocks can be catalytically reformed to provide a product mixture composed of hydrocarbons boiling substantially in the same range as the feed stock having a markedly reduced concentration of naphthenes while retaining a relatively high concentration of feed paraffins. It appears from the data obtained in this investigation that the main reaction is primarily dehydrogenation of naphthenes and such dehydrogenation may be made to occur in the substantial absence of paraffin cracking to substances that boil lower than the feed stock. However, even if some limited cracking of parafiins occurs, the operating conditions employed are such that the parafiinic concentration is none-the-less maintained at a very high level, possibly due to the conversion of some ring compounds in the feed stock to paraffins of corresponding carbon atoms content which boil in the range of the feed stock. Accordingly, the feed stocks employed herein are subjected to controlled catalytic dehydrogenation and catalytic isomerization under selected operating conditions that substantially completely and unexpectedly conserve the parafiinic concentration of the feed while substantially decreasing the naphthene concentration therein to aromatics. A desired paraffin rich jet fuel product fraction is obtained therefrom by removal of aromatics from the product.

Reference is made above to conservation or retention of the paraflinic concentration of the feed stock. By this sired freeze point requirements of the jet fuel to be produced, the particular feed stock employed, and other characteristics. Hence, it is not intended to exclude pro duction of catalytically treated mixtures having less than 70% retention of the paraflinic concentration of the feed stock, as the production of such catalytically treated mixtures is within the scope of this invention even though it is preferred to operate under conditions which produce no significant loss in the parafiin constituent of the feed. The invention is generally carried out under conditions to the extent of producing catalytically reformed product mixtures that retain a paraflinic concentration of at least about 70% of the parafiinic concentration of the feed stock and in most cases preferably retain more than about 80% of the paraftinic concentration of the feed stock.

Catalysts suitable for use in the reforming operation herein described include the metals of the platinum series on a suitable carrier material such as alumina. Generally, the catalyst employed should be a dehydrogenation catalyst of the platinum type having relatively little or a low cracking activity but possessing isomerizing activity at selected operating conditions. Accordingly, the catalyst may be one comprising from about 0.1 up to about 1.0 percent platinum on alumina (e.g., eta alumina) or a low activity silica-alumina base. The catalyst may also contain a halogen promotor such as chlorine or fluorine in an amount of up to about 2.0% and, preferably, in an amount less than about 1%. In a more particular aspect, the reforming catalysts contain from about 0.3 to about 0.8% platinum. However, also suitable for use herein are those catalysts which are known to possess activity for dehydrogenating naphthenes to aromatics and having a relatively low cracking activity. Examples of such catalysts include tungsten and/or nickel on kieselguhr, chromium oxide on alumina, and others.

Although the reforming conditions comprising dehydrogenation of naphthenes to aromatics and isomerization of parafiins can be varied, depending on the composition of the feed stock employed and the desired properties of the jet fuel product; the conditions of operation are correlated within the following general ranges of conditions as discussed more fully hereinafter.

Broad Preferred Space Velocity (LHSV) H /feed, s.c.f./bbl Average Temperature, F Hydrogen Pressure, p.s.i

That is, when it is desired to obtain a desired naphthene dehydrogenation without regard to eifecting any significant degree of isomerization of the normal paraffins in the feed fraction, reforming of thekerosine boiling feed may be effected within the following operating conditions.

At an average temperature of at least about 800 F., a space velocity (LHSV) of at least 0.5 is employed. At an average temperature of at least about 850 F., a space velocity (LHSV) of more than 3 is employed. At an average temperature of at least about 900 F., a space velocity (LHSV) of at least 10 is employed. At an average temperature of at least about 940 F., a

space velocity (LHSV) of more than 20 is employed.

employed.

Average temperature F about 875 Space velocity (LHSV) j 5 Total pressure p.s.i.g 500 In one embodiment of this invention, the process com prises the catalytic treatment of the relatively high boiling kerosine feed stocks in a combination of steps comprising desulfurization of the feed followed by catalytic reforming of the desulfurized feed in at least two stages wherein, in a first reforming stage, the feed stock is processed under conditions to effect primarily naphthene dehydrogenation and in a second reforming stage, conditions promoting isomerization of parafiin constituents are selected. Under some isomerizing conditions dehydrogenation of naphthenes can also be expected in the second step in a minor amount and generally is only a small fraction of that obtained in the first reforming stage. The method and process conditions selected for dehydrogenating and isomerizing as described herein can be elfected in at least two or more catalytic beds in a single reactor, or the reactions may be accomplished substantially separately in a plurality of sequentially arranged reactors. Furthermore, suitable heat exchange means for heating or cooling may be provided for adjusting the temperature of the hydrocarbon reactants between catalyst beds or between reactor zones. However, in any arrangement selected, it is important that the catalyst be arranged to the embodiment above discussed is preferably carried out under the following conditions for the first and second stages of catalyst contact.

FIRST STAGE Temperature At least about 825 F. but not more than about 925 F. as the inlet temperature of the feed.

Space velocity More than (LHSV). Pressure (total) Below 500 p.s.i.g. Catalyst As described hereinbefore, e.g.,

platinum or alumina, with or without chlorine but when present, preferably not more than 1% chlorine.

SECOND STAGE Space velocity Below 5 (LHSV). Total pressure Below 500 p.s.i.g. Inlet temperature Generally not substantially over 850 F. and at temperatures minimizing cracking under the isomerizing conditions.

Outlet temperature At least 750 F.

Catalyst E.g., platinum on alumina containing preferably not more than 1% chlorine.

Depending upon the freeze point requirements of the ultimately produced jet fuel product, the method herein described can be carried out to process feed fractions that comprise a kerosine fraction as aforedescribed blended with alkylate in blends containing up to about 40% or more by weight of alkylate. Generally speaking, and by use of a blend containing from about to about 40% by Weight of alkylate, sufficient isoparaffins may be generally present in the feed blend whereby products of sufficiently low freeze point can be obtained by subjecting the feed blend to a single stage of catalytic reforming comprising primarily naphthene-dehydrogenation conditions without need to also effect isomerization of nparafiins present in the kerosine portion of the feed blend. On the other hand, with feeds that comprise the aforedescribed kerosine fractions per se or blends thereof with, for example, less than 25% by weight of alkylate, it may be desirable to not only effect naphthene dehydrogenation but, also, substantial isomerization of n-parafiins in the kerosine portion in order to provide end products of exceptionally low and desired freeze point characteristics. Therefore, when processing low alkylate-containing blends, the process conditions may be controlled more carefully in a multi-stage catalyst bed system when it is desired to produce low freeze point products.

On the other hand, when processing a feed that comprises a kerosine fraction blended with an alkylate fraction, the alkylate fraction that is employed will have a boiling range that falls substantially within the boiling range of the kerosine fraction. It can, for purposes of illustration, be an alkylate composed substantially within the boiling range of the kerosine fraction. It can, for purposes of illustration, be an alkylate composed substantially of isoparaffins, or such alklates that contain a minor amount (e.g., 545%) naphthenes and/or small amounts of olefins (e.g., l3%). When alkylates of the latter type are used, and particularly if they also contain impurities such as sulfur and/or nitrogen, the impurities are removed sufficiently by pretreatment (e.g., hydrodesulfurization) of the alkylate feed or feed blend as discussed above prior to subjecting the feed to the naphthene-dehydrogenation reactions described herein.

Thus, in the use of blends of the kerosine fraction and alkylate, and in cases wherein the combination of the feed components is deficient in isoparafiin content (e.g., in such blends containing below 25 of alkylate), end products of exceptionally low freeze points are obtained by subjecting the feed blend preferably to two-stage of catalytic treatment under the following conditions.

FIRST STAGE Temperature At least 800 F., but not more than about 860 F. as the inlet temperature of the feed.

Space velocity More than 5 (LHSV). Pressure (total) Below 500 p.s.i.g. Catalyst As described hereinbefore, e.g.,

platinum on alumina, with or without chlorine but, when present, preferably not more than 1% chlorine.

SECOND STAGE Space velocity Below 5 (LHSV).

Total pressure Below 500 p.s.i.g.

Inlet temperature Generally not substantially above about 850 F. and at temperatures minimizing cracking.

Outlet temperature At least about 750 F.

Catalyst E.g., platinum on alumina containing preferably not more than 1.0% chlorine.

It is to be noted that when processing the alkylatecontaining feeds, lower maximum temperatures are preferred than for the alkylate free or straight run feeds because of the higher crackability of the highly branched alkylate parafiins.

From the defined catalytic treatment of the relatively high boiling feed stocks, not only is the parahinic concentration substantially conserved to provide high yields of desired components for jet fuel but, as to the catalytically treated mixture that is produced, it can be subjected to a further treatment for removal of aromatics to the extent required to provide jet fuels of high luminometer number (e.g., at least or more), excellent thermal stability, at high net heat value (e.g., at least about 18,850 B.t.u./lb.), a high boiling range (e.g., 350- 550 F.), a low vapor pressure (e.g., maximum of about 50 p.s.i.g. at 500 F.), and other desired properties including low freeze points, the latter property being largely dependent on the isoto normal-paraffins ratio in the charge stock. The term iso-parafiins as used in this discussion is meant to include all types of branched, non-cyclic parafinic irrespective of the number, location, or length of the branches. Generally speaking, the higher the ratio of iso-parafins to normal parafins, the lower will be the freeze point of the jet fuel product.

For the preparation of high quality jet fuels, the product mixture obtained from the catalytic dehydrogenationisomerizing reforming treatment herein described in subjected to processing conditions selected for removal of aromatics to provide an aromatic-rich phase separate from a parafin-rich phase comprising the desired high quality jet fuel. Thus, for example, a reduction in the aromatic concentration of the naphthene depleted product mixture can be effected by solvent extraction, as by extraction with S0 at a liquid S0 ratio of from about 50 to about 300 volume percent based on the product mixture, at an operating temperature of from about -20 to 50 F.

The method and process herein described provides a heretofore unknown high degree of flexibility for the production of jet fuels adapted to meet a wide variety of specific property requirements. For purposes of clearly illustrating the method of this invention, specific embodiments are described hereinafter by the examples presented and reference to the drawings provided herewith.

FIGURE I presents curves showing a relationship between heating value and paraflin content of the jet fuel having different aromatic concentrations.

FIGURE II presents a group of curves showing a relationship of luminometer number with paraffin content of jet fuel having different aromatic concentrations.

FIGURE III presents a family of curves which establishes a relationship of equilibrium aromatic-naphthene ratios, with operating pressures and temperatures.

FIGURE IV presents a curve establishing a relationship of freeze point with concentration of high freeze point components such as n-parafiins.

The combination of conditions in terms of temperature, space velocity and hydrogen partial pressure disclosed herein were determined at least in part from a raw kerosine, derived from Barco crude, containing about 700 p.p.rn. sulfur and p.p.rn. nitrogen which was pretreated at the conditions of 700 F., 800 p.s.i.g., 4 LHSV and 1100 s.c.f./bbl. hydrogen circulation with a cobalt molybdate on alumina catalyst whereby the sulfur concentration was reduced to 13 p.p.rn. The thuspretreated kerosine fraction boiling in the range of about 350-510 F. was then processed under a variety of operating conditions with a catalyst comprising 0.6% platinum on eta alumina and containing about 0.6% chlorine. Following such a catalytic treatment, the product mixture was distilled to remove material boiling below about 375 F. and thereafter percolated through a bed of silica gel for substantially quantitative removal of aromatics to provide highly paraffinic efliuents useful as high quality jet fuels of relatively high boiling range.

In further illustration of embodiments of this invention, the following Table I sets forth data obtained by subjecting a Barco kerosine (350510 F.), pretreated as per the aforesaid to reduce the sulfur concentration to 13 p.p.rn., to the conditions shown with use of a In the following Table II, data are set forth for the analysis of kerosine fractions boiling in the range of about 375-500 F. from each of several different crudes. The analysis of the product obtained from a catalytic treatment thereof as embodied herein, and properties of a raifinate (jet fuel) obtained from S0 extraction of the catalytically treated product boiling in the range of about 375-500 F. are presented.

CONDITIONS FOR CATALYTIC TREATMENT Catalyst: platinum on eta alumina percent 0.6

Average temperature F 850 Space velocity (LHSV) 20 Total pressure, p.s.i.g 450 TABLE II Virgin Kerosine Mid- West Conti- Barco, Texas, nent, Weight Weight Weight percent percent percent Feed Stock:

Parafiins 39. 9 42. 4 58. 6 Naphthenes 43. 1 43. 3 33. 2 Aromatres. 17.0 14. 3 8. 2

8. 4 9. 2 9. 0 375-500 F. Fraction:

Paraifins 39.1 41. 0 56.9 N aphthenes 4. 1 3. 7 2. 8 Aromatics 48. 4 46. 1 31. 3

Ralfinate from S0; extraction of 375 500 F. fraction:

Gravity 52. 5 53 54 Luminometer N0 110 116 124 Net Heat of Combustion (B.t.u./lb.) 18, 920 18, 925 18, 935

catalyst containing 0.6% platinum on eta alumina and It is pp r from thfi data 5615 forth In Table II that 0.6% chlorine. by the defined catalytic reforming treatment of the 375- TABLE I Run Numbers 1 2 3 4 5 6 7 8 (A) Treatment Conditions in Presence of Platinum Catalyst:

Temperature 860 900 860 800 650 750 940 000 Total Pressure (p.s.i.g.) 500 600 500 200 53 105 500 500 Hydrogen, partial press e, p.s.i- 455 445 445 180 48 95 450 455 LHSV 20 30 10 20 15 3 Hydrogen circulation 6,020 5,010 5, 095 5,535 5,630 5, 875 5,555 5, 940 Yield, V01. Percent, from Treatment (A):

375+ F. fraction 1 89.2 86.1 92.0 95.4 95.7 97.2 66.6 61.9 375+ F. paralfins 2 102 98 104 108 103 108 50 Jet Fuels Produced by quantitative removal of aromatics from product from Treatment (A) by silica gel adsorption:

Gravity,API 53.4 51.1 50 5 49.0 50.7 54.7

Flash Point, F Freeze Point, F Luminometer No. -i=5 Net Heat of Combustion (Btu. Vapor Pressure (p.s.i.) at 500 F 1 Based on 375+ F. fraction in charge stock. 2 Based on 375+ F. paraflins in charge stock.

For the runs shown in Table 1, Run Nos. 1-6, inclusive were carried out under correlated conditions selected for a high conservation of paraflins, as shown by the values of 98 to 108 volume percent shown for the yield of 375+ F. parafiins from the catalytic treatment A. It is further apparent from the data in Table I that such high conservation of parafiins in such a relatively high boiling range was obtained along with a relatively high yield of the 375+ F. fraction from the catalytic treatment. On the other hand, and as is evident from the data shown for Runs Nos. 7 and 8, relatively low yields were obtained for the 375+ F. fraction from the catalytic treatment and paraffin retention of only about 50-54 volume percent occurred. Such results evidence the substantial loss of parafiins in the desired boiling range of at least 375 F. by use of operating condtions falling outside of the boundary limits herein defined.

Example I A 390 to 490 F. boiling range fraction, distilled from a West Texas crude, was pretreated over a hydrodesulphurization catalyst (chromia on alumina) at an average temperature of about 740 F., p.s.i.g. total pressure,

9 130 p.s.i.g. hydrogen partial pressure and 0.6 LHSV whereby the sulfur concentration was reduced from about 300 p.p.m. to about 2 p.p.m. The pretreated stock thus obtained was then catalytically reformed with a 0.35% platinum on eta alumina catalyst in an adiabatic reactor system under conditions shown in the following Table III. From such a catalytic reforming treatment, liquid product in the 375+ F. range was obtained in a 78.5 volume percent yield based on the amount of charge to the pretreater with a paraffin retention of at least 75.2 volume percent.

The effluent from the above catalytic reforming treatment was then distilled to obtain a 390+ F. fraction which was then contacted at about 40 F. with S in the proportion of 200 parts S0 to 100 parts of the effluent to remove aromatics therefrom. The S0 rafiinate, containing 2% aromatics, was then percolated through bauxite. The following Table III contains data for the conditions of the catalytic reforming treatment and the properties of the S0 rafiinate (390+ F.) following percolation through the bauxite.

TABLE III First Second Third Reactor Reactor Reactor Catalytic Treatment Conditions:

Temperature, F.:

Reactor Inlet 850 811 832 Reactor Outlet. 811 798 825 Total pressure, p.s.i.g. 400 400 400 HzHpartial pressure, p.s.Lg... 330 330 330 L SV 7.6 2.2 2.2 Hz Circ., s.c.t/bbl 9,0009,800

Properties of 390+" F. cut after Bauxite Percolation:

Gravity APT 52.7 ASTM ist., F.:

EP 493 Luminometer No 116 Freeze Pt., F -37 Net Heat of Combustion, B.t.u./

Flash Point, F 1Z2 Vapor pressure at 500 F., p.s.i.g High Temp. Erdco Stability Test Preheater Deposit Code 1 A Hg 0. 9

Run No 1 2 3 4 Feed Stock Barco West Kuwait Mid- Texas Continent Catalytic Treatment Conditions:

Temperature 862 862 860 860 Pressure, p.s.i.g 500 500 500 250 LHSV 10 10 10 15 Properties of 375+ F. Jet Fuel from Silica Gel Treatment:

Luminometer No 122 134 131 116 Net Heat of Combustion (B.t.u./lb.) 18, 960 18, 975 18,975 18. 942

Example III A West Texas raw kerosene was pretreated over a hydrodesulfurization catalyst comprising chromia on alumina promoted with molybdena at 800 F., 170 p.s.i.g.,

5 0.8 LHSV and a hydrogen circulation rate of 695 s.c.f./

bbl. The pretreated stock was then treated over a 0.35% platinum on alumina catalyst in an adiabatic reactor at the following conditions:

The product from such a treatment was distilled to ob tain a 360-520 F. fraction from which aromatics were removed by silica gel absorption to produce a paraffinrich phase having a freeze point of 28 F. By comparison, a sample of the raw kerosene percolated over silica gel to remove aromatics had a freeze point of -16 F. Data pertaining to this specific example are set forth in the following Table IV.

TABLE IV Stock Untreated Pretreated Catalytically Raw Charge Stock Treated Kerosene (hydrode- (Platinum suliun'zed) Catalyst) Yield of 360+ F. cut., V01. Percent l 100 94.1 93.1 Volume yield of 360+ F. parafiins 100 102 Analysis of 360-520 F. Jet Fuel from above stocks: 2

Freezing Point, F 16 -28 Paraifins, Vol. Percent 65. 4 84. 7 Naphthencs (monocyclic plus dicyli 34. 5 15. 2 Aromatic, Vol. Percent 0. 1 0. 1

1 Base. 2 Aromatics removed by silica gel.

Example IV Example 11 A Gach Saran kerosene charge stock (boiling range 370490 F.) was pretreated over CoMo-Al hydrodesulfurization catalyst whereby the sulfur concentration of the charge stock was reduced from 4700 p.p.m. to 8 p.p.m. and the nitrogen concentration was reduced from p.p.m. to about 1 p.p.m. The pretreated charge stock was then treated over a platinum on alumina catalyst at 800 F., 370 p.s.i. (hydrogen partial pressure) and 1.5 LHSV. From such a treatment there was obtained a liquid product, the 375+ F. fractionof which was in- 86.6 volume percent yield with a 90% volume percent conservation of paraffins.

The properties and composition of the charge stock, the catalytically treated liquid product (375+ F.), and the catalytically treated product from which aromatics were removed by silica gel absorption are set forth below:

Catalytieally Treated Charge Stock Raw Charge Stock Before silica After silica gel treatment gel treatment Composition (v01. percent):

Paraflins, 40.4 41. 9 85. 7 Olefins, 1.9 0. 6 (l) Aromatics, 22.0 49. 4 (1) Naphthenes, 35.7. 8. 14. 3 Paraffin Distribution (vol. per nt 0 8 1. 3 2. 9 Cir 5.8--- 5.7 11.5 C12: 15.0.- 15.9 32. 8 Cu, 12.4" 12. 2 24. 4 C14, 5.6.-- 5. 2 10. 2 C15, 1 6 1.6 2.5 Cm 0. 6 Distillation (A STM) IBP, 371.. .392 5%, 399 407 405. 410 41 414. 427- 432 90%, 457-. 477 EP, 498 Luminator N 114 Freeze point, F 45 Heating Value (B .t.u./lb) 18, 920

1 Nil.

Example V A 368 to 473 F. boiling range fraction, distilled from a Barco virgin kerosene, was pretreated with a cobalt molybdate hydrodesulfurization catalyst at 700 F., 800 p.s.i.g. hydrogen pressure and 4.0 LHSV whereby the fraction was reduced in nitrogen concentration to 2 p.p.m. and sulfur to 6 p.p.m. The pretreated fraction was then treated over a 0.6% platinum on eta alumina catalyst at 900 F., 10 LHSV, 250 p.s.i.g. pressure and a ratio of H /feed of 20 (molzmol). Such a treatment resulted in substantial conversion of naphthenes in the feed stock to aromatics with a paraffin retention of about By extraction of aromatics from the thus-treated product mixture by silica gel, a parafiin-rich rafiinate was obtained that had a luminometer number of 120.

In reference to the jet fuels produced by the method of this invention, and in the defined high yields from the relatively high boiling feed stocks as described hereinbefore, the following is a typical analysis (mass spectrographic) of a jet fuel produced by the process embodied herein from a West Texas kerosene having a boiling range of from about 390 to about 490 F. by treatment over a 0.35% platinum on eta alumina catalyst followed by substantial but not complete removal of aromatics by S0 absorption. Such a jet fuel consists essentially of C to C paraffins, naphthenes and not more than 5 vol. percent aromatics.

CARBON 1N0. DISTRIBUTION, VOL. PERCENT Paraffins:

C 10.8 C 30.4 C 30.0 C 9.9 C 2.4

a 2-7 C 0.3 C 0.2 C19 0.2 Naphthenes 7.6 Aromatics 4.9 Misc. 0.6

A typical analysis of a jet fuel, prepared in the manner 12 of the jet fuel for which the foregoing analysis is set forth, except that the feed stock had an initial boiling point of about 375 F. and aromatics were substantially quantitatively removed by silica gel adsorption, is as follows:

As shown, and although such a product contains a small amount of C paraffins and C paraffins, it consists essentially of paraflins in the C to C range and napthenes. Thus, in general, the jet fuels embodied herein are substantially composed with respect to paratfins to those of C and higher carbon atom-containing parafiins and may or may not contain some C paraffins. When present, however, the C paraffins do not usually exceed about 5 volume percent. Such jet fuels are further characterized by being devoid of or substantially devoid of C and lower parafiins. Howeved, if C parafi'ins are present, they are present in relatively small amount (e.g., not more than 2% and more specifically not more than about 1%) which may be due to phase equilibrium in carryover in a distillation operation employed in the process. In general, the jet fuels embodied herein have a net heat of combustion of at least about 18,800 b.t.u./lb. and comprise a mixture of paraflins, naphthenes and aromatics in which the aromatics concentration is less than 10 volume percent and usually less than about 5 volume percent.

Example VI The catalytically treated and silica gel extracted product of Example IV above presented was given a subsequent treatment over a 0.35% platinum on alumina catalyst under isomerization conditions of:

Temperature, F. 800 Pressure, p.s.i.g 350 LHSV, v./v./hr 1 This further isomerization step significantly lowered the n-paraffin content, and thus the freeze point. Under these conditions, additional dehydrogenation of retained napthenes was also experienced. The results of this specific example are shown in the following table:

Example VII The kinetics of three reactions of prime interest (naphthene dehydrogenation, isomerization of normal paratfins, and paraffin hydrocracking) were obtained under catalytic reforming treatment of a hydrodesulfurized West Texas kerosine passed in contact with a fresh catalyst comprised of 0.6% platinum on eta alumina. Using reciprocal LHSV (units of v./v./hr. or just hr.-

I 3 as a measure of time in the rate constant, k, the following values were obtained:

Naphthene Isomer- Paraffin Reaction Dehydroization Hydrogenation cracking k 850 F., hr. 60 2. 8 0. 36 Activation Energy, KcaL/gr. mol. 3O 41 57 Example VIII In order to show that use of conditions of high temperature without sufficiently high space velocity result in a very substantial loss of paraiiins in the desired boiling ranges, the following data are set forth for runs using 0.6% platinum on alumina catalyst with a 350- F. boiling range Barco kerosene pretreated to a sulfur concentration of about 13 p p.m.

Untreated Run No. Charge Stock Reaction Conditions:

Temperature, F 942 940 Pressure, p.s.i.g 500 560 LHSV 3 5 H Circulation, s.c.t./bh1 7, 170 4, 906 Yields:

D13 Gas (wt. percent) 10.9 6. 7 Butanes (vol. percent) 7.1 I. 7 Pentanes (vol. percent) 4. 9 5. 6 (36-375 13. (vol. percent) 16.4 43. o 36.8 375+ F. cut (vol. percent) 83.6 33.2 43. 6 Composition of 375+ F. cut vol. percent,

on feed:

Parailins 37. 7 4. 2 9. 9 Naphthenes. 35. l 0.2 0. 4 Aromatics 10. 8 28.8 33. 3 Retention of 375+ I Parafiins, vol.

percent 100 11 24 As shown by such data, and as compared to the paraffin concentration in the 375+ F. fraction of the feed stock, a parafiin retention of only 11 and 24 volume percent, respectively, occurred for the runs carried out at relatively high temperatures but without use of a substantially high space velocity.

In the use of acid extraction (e.g., oleum) for aromatic-removal, it may often be necessary to further treat the extracted product to effect additional removal of aromatics. For such a purpose, a suitable method involves subjecting the parafiin-rich phase from the acid extraction to hydrogenation for conversion of the remaining small amount of aromatics to naphthenes. A suitable combination of conditions for such a treatment is as follows:

Pressure, p.s.i.g. (total) 500 or higher. Space velocity LHSV 1.

H charge hydrocarbons (mol ratio) 16 (approx) H /charge hydrocarbons (s.c.f./bbl.) 10,000. Temperature, F. 500.

Catalyst: hydrogenation catalyst e.g., platinum on cta or gamma alumina As used herein, luminometer number is determined in accordance with the method of test, set forth in AST M Description D174060T.

It will be apparent to those skilled in the art, that in a process as herein described for the production of jet fuels of defined boiling range, as for example, an initial boiling point of at least 350 F., or at least 375 F., that any lower boiling material that may be formed during the process may be removed by conventional means, such as by distillation, in any of several stages of the process. Removal of such low boiling materials may be carried out by subjecting the product, from the catalytic reforming step for conversion of naphthenes to aromatics or after the second catalytic isomerizing step, to distillation to strip out the undesired materials that boil below the initial boiling point of the desired jet fuel.

In certain instances freeze point depressants may be added to lower the freeze point and, for this purpose, isoparaflins such as alkylates that boil within the boiling range of the jet fuel can be used. The addition of isoparaffins for lowering the freeze point can be made to the feed stock, to the jet fuel product or to an intermediate stage of the process herein described.

In the present process, use of an adsorbent such as silica gel for aromatic removal usually does not require further processing of the product jet fuel as the paraffin rich efiluent therefrom is generally of exceptionally desirable characteristics with respect to luminometer number and thermal stability. Similarly, in the use of S0 for aromatic removal, further processing of the raffinate from such an operation is generally not required. However, a further treatment of the S0 raffinate, such as with an adsorbent clay, or catalytic hydrogenation may be used to improve thermal stability by removal of residual contaminants that tend to decrease thermal stabi-lity.

Referring now to FIGURE I, the data obtained in this investigation were accumulated and developed to produce the self-explanatory curves presented in the figure which show the change in heating value of jet fuels as their paraffin and aromatic content is varied. The curves in FIGURE I (and FIGURES IIIV) were established for fuels having a nominal boiling range of 350500 F. For fuels of significantly different boiling ranges, the curves would be similar but displaced with respect to the abscissus. FIGURE II, on the other hand, shows the variation in luminometer number obtained as the paraflin content varies for three different aromatic products. The figure is essentially self-explanatory in showing that a higher LN is obtainable as the aromatics are reduced in the product and the higher the paraffin content, the higher will be the (LN) luminometer number.

FIGURE III presents .an accumulation of data arranged to provide a family of curves which permit establishing a relationship between equilibrium aromatic-nap'hthene ratio, hydrogen pressure and temperature of the reforming operation to effect the desired change in composition to produce a desired jet fuel product. The relationships established by the curves presented in FIGURE III show that to obtain a given arom'atic/naphthene ratio, different hydrogen pressure conditions are required for different reaction temperature conditions.

FIGURE IV entitled Effect of n-Parafiin Concentration on Freeze Point for 375-500 F. Boiling Kerosene Fraction shows a single straight line curve which establishes a relationship between concentration of n-paratfins in the product and the freeze point of the product. This relationship is particularly useful in identifying the process requirements for producing a jet fuel for the reasons more fully explained below.

In accordance with one specific embodiment of this invention the curves above-identified are employed in the following illustration to identify the procedure for producing a desired lOOLN jet fuel boiling in the range of from about 350 F. to about 500 F. and having for example, a freeze point of about -40 F. and a heating value of about 18,900 B.t.u./lb. From FIGURE 1, we determine that a jet fuel of about 18,900 Btu/lb. heating value must have a paraffin content of at least if there is as much as 2% of aromatics in the jet fuel product. From FIGURE II, we also determine that to produce a product having an LN of that the product must have at least about 82% paraffins when as much as 2% aromatics is in the product. Therefore, from these two figures we now know that a jet fuel product of at least 85% will be suitable to produce a 100+ LN product having a heating value of 18,900 B.t.u./lb. Turning now to FIGURE IV we determine that the jet fuel product suitable to meet a -40 F. freeze point should not have substantially greater than about 23 volume percent of normal parafiins. That is, the sum of the concentrations of low freeze point constituents such as isoparaffins must be at least about 77 volume percent so that when combined with the n-paraifin material, the final product will meet the 40 F. freeze point requirement. However, from FIGURES I and II we determined that the paraffin concentration of the final product must be at least 85% and since only about 23 volume percent of this can be nparafiins, it is thus essentially that about 62% of the as above described or (3) a combination of (1) and (2) above. By the above discussion we have been able to identify the requirements of the product components with the aid of FIGURES I, II and IV.

To produce the product thus identified, applicants have found and identified a relationship of operating condition that when properly correlated will produce the product desired. Accordingly, a further embodiment of this invention is directed to identify the method and operating procedure one employs for producing a product such as above-identified.

As an initial step of the process, the composition of the kerosene feed with respect to parafiins, naphthenes and aromatics must be determined. Having thus made this determination and identified the characteristics of the product required we determine from FIGURE I the paraffin-naphthene ratio permissible in the final product having about 2% aromatics therein. From FIGURE I we determine the naphthene concentration to be about 13% and thus, the paraflin/naphthene ratio to be 85/13 or about 6.5.

As indicated above, the kerosene feed to be processed is evaluated to determine its paraffin, naphthene and aromatic content. Assuming that we determine that the feed comprises 40% parafiins we can determine from the above parafiin-napht-hene ratio to what extent'the naphthenes in the feed must be reduced to produce the 6.5 ratio above determined. With 40% parafiins in the feed we find by the above relationship that the naphthene content must be reduced to about 6.1%. This determination also establishes the aromatic content of the product after the catalytic treatment and before aromatic extraction, as about 53.9 and therefore the aromatic/naphthene ratio as 53.9/ 6.1 or about 8.9 as a minimum value. Having thus determined to what extent the feed needs to be reformed by dehydration of naphthenes to produce a product having an aromatic/naphthene ratio of about 8.9 we now determine from FIGURE III the pressure-temperature relationship required to produce such a product. It will be observed from FIGURE III that the correlated operating conditions to produce the above aromatic/naphthene ratio are as follows: H2 pressure must not be In accordance with the correlations shown in FIGURE 4 it can be determined that to obtain the desired -40 F.

freeze point of this example, that the n-parafiin content should be no more than about 23% in the product fuel or 27% of the paraffin fraction. Referring thus to our example for a raw, untreated feed containing 40% total 16 :paraffins, if the n-paratfin content is thus more than about 27% x 40% or about 10.8% normal parafiins, isomerization of the feed will be required under the conditions hereinbefore set forth. It is obvious that the greater the concentration of normal parafiins in the feed, the greater Will be the amount of isomerization required.

Having thus provided a general description of the invention and presented several examples in support thereof, it is to be understood that no undue limitations are to be imposed by reason thereof except as defined by the following claims.

We claim:

1. A method for producing jet fuels of desired freeze point and heating value which comprises: determining from the correlation represented by FIGURE IV the permissible n-paraffin content of a kerosine boiling range hydrocarbon to provide a product of desired freezepoint; determining from the correlations represented by FIG- URES I and II the maximum concentrations of naphthenes and/or aromatics permissible in the finished jet fuel product to maintain as a minimum a predetermined heating value and luminometer number desired, having thus determined the paraflinmaphthene-aromatic product distribution, determining the aromatic/naphthene ratio required in the etlluent of a catalytic dehydrogenationisomerization step and then catalytically reforming a parafiin rich kerosine boiling range feed in accordance with the relationship of conditions provided in the equilibrium correlation represented by FIGURE III for the above determined aromatic/naphthenic ratio at a space velocity chosen to retain at least about 70% of the parafiins and removing aromatics from the reformed efiiuent to provide the product distribution above determined.

2. The method of claim 1 wherein the dehydrogenation of the hydrocarbon feed is accompanied with isomerization of n-paraifins in an amount sufiicient to provide the product with a desired freeze point, the degree of isomerization required being determined by the freeze point correlation represented by FIGURE IV.

3. The method of claim 1 wherein the first catalytic treatment is primarily dehydrogenation of naphthenes and wherein isomerization of parafiin hydrocarbons is accomplished in a downstream stage of catalytic treatment at suitably correlated temperature and space velocity conditions, and the extent of isomerization effected being sufficiently severe such that the normal parafiins are reduced to below about 30% of the total parafiin content.

4. A method for producing a kerosine boiling range jet fuel having a freeze point below about 40 F. and a B.t.u./lb. heating value in excess of 18,900 which comprises: determining from FIGURE IV the maximum permissible amount of n-parafiin allowed in the product to meet said freeze point requirements, determining from correlations represented in FIGURES I and II the permissible parafiin-naphthene-aromatic content to satisfy desired product requirements of heating value and a luminometer number of at least 90, having thus made the above determinations, determining the required naphthene to aromatic ratio in the product effluent of a catalytic dehydrogenation-isomerization conversion of the kerosine boiling feed, thereafter catalytically dehydrogenating naphthenes in said feed in accordance with the temperature and pressure correlation of FIGURE III to obtain said required product efiluent naphthene to aromatic ratio, maintaining isomerizing conditions in a least one downstream stage of said catalytc treatment to permit obtaining the above determined n-paraffin limit employing a space velocity in each of said dehydrogenating and isomerizing operations to retain at least about 70% of the paraifins and removing aromatics fromthe product of said catalytic treatment to produce the above determined permissible paraffin-naphthene-aromatic content of said product.

5. The method of claim 4 wherein alkylate product boiling in the kerosine boiling range is employed with the 3,384,574 17 18 ker'osine boiling feed to provde the jet fuel product de- OTHER REFERENCES sired.

6. The method of claim 1 wherein sufficient alkylate POPOViCh et Fuels, Lubricants PP- 156-163,

is blended with the product of the catalytic dehydrogen- J n Wiley and Sons.

ation step to produce the desired jet fuel product. 5 Paushkin, The Chemical Composition and Properties of Fuels for Jet Propulsion (Chapter II, part 4), pp. 53-64 References Cited (1962), Pergamon Press. UNITED STATES PATENTS 3,110,661 11/ 1963 Franz 208--60 HERBERT LEVINE, Primary Examiner. 3,117,073 1/1964 Hertwig et a1 20865 10 FOREIGN PATENTS 870,474 6/1961 Great Britain.

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