US3620961A - Method of producing a jet fuel - Google Patents

Abstract

Jet fuel having a low freeze point, e.g. -50* F., and high heat of combustion per gallon, e.g. at least about 124,000 B.t.u./gal., is produced by blending (1) a highly naphthenic jet fuel component having an advantageously very low freeze point but low heat of combustion on a pound basis with (2) a highly paraffinic jet fuel component having a high heat of combustion on a pound basis in excess of that desired in the blended product.

Description

United States Patent I 1 3,620,961

(72] Inventor Henry R. Ireland ISbI References Cited West Deptford Township, Gloucester UNITED STATES PATENTS County, NJ. y 1 pp No. 796,687 2,910,426 /l959 bluesenkamp et a]. 208/66 3.367.860 2/1968 Barnes ct al. u 208/ [22] PM 3 384 $14 5/1968 Halik ct al 208/15 Patented Nov. 16, 1971 [73] Assignee Mobil Oil Corporation Primary'ExaminerHerbert Levine Auornevs-Oswald G. Hayes Andrew L. Gaboriault and Carl D Farnsworth ABSTRACT: Jet fuel having a low freeze point c.g F.. [54] a g R EZ AIET FUEL and high .heat of combustion per gallon e.g. at least about 6 2 124,000 B.t.u /gal., is produced by blending 1) a highly [52] US. Cl 208/79, naphthenic jet fuel component having an advantageously very 208/15. 208/141, 208/216, 2081217 low freeze point but low heat of combustion on a pound basis [51] Int. Cl C101 1/04 with (2) a highly paraffinic jet fuel component having a high [50] Field of Search .1 208/15, 17, heat of combustion on a pound basis in excess of that desired 79, 138, 141 in the blended product. I

F NAPHTHENIG FEED C T I 2 RAFF NAT 2 4 6 o KEROS'NE EXTRACTION E c N STEP A T O R PARAFFIN FEED R so PRETREAT REFORMING ExTRAmN CH0 U DESULFURIZATION 2 SECTION STEP 7T METHOD OF PRODUCING A JET FUEL The present invention relates to the production of jet fuel. More particularly, this invention relates to the production of jet fuels having low freeze point and high energy content both on a weight basis (B.t.u./(b.) and on a volume basis (B.t.u./gal.).

As is well known, a jet fuel should have high-temperature stability, high energy content, and good handling characteristics at both low and high temperatures. An acceptable jet fuel must meet rather rigid specifications for either military or commercial use. With the passage of time, these requirements have become more demanding. For military use, there is a present need for an economical jet fuel which has a high energy content per gallon in order to increase the operating range of the aircraft, and a lower freeze point than exhibited by most prior art fuels in order to improve in air refueling of the aircraft. By way of example, a new military jet fuel specification includes the following requirements:

Gravity, API 44-50 Freeze Point, 'F,, max, 46 Heat of Combustion B.t.u.llb., min. l8,700

B.t.uJgaL, min. l24,000 Luminometer Number, min. 75 Vapor Pressure, p.s.i.a. and 300 F., max. 3.0 Aromatics, vol. max. 5.0

Thermal Stability (300/500/600'BW F.)

Pressure Change, in Hg, max. 3 Preheater Deposit Code, max.

Thermal Precipitation Test the fuel must have a heat of combustion of at least l24,000,

B.t.u./gal. eliminates many compositions which have the required heat of combustion on a pound basis. Fuels having a high A.P.l. gravity are characterized by less weight per gallon, and since the heat of combustion per gallon is based upon the weight per gallon together with the number of B.t.u. per unit weight, a low A.P.l. gravity is desirable with respect to obtaining high heat of combustion on a gallon basis. On the other hand, the heat of combustion per pound is ordinarily estimated as the product of the A.P.l. gravity and the aniline number (aniline-gravity product) so that a reduction in the ART. gravity lowers the number of B.t.u. per lb.

It is a primary object of the present invention to provide a novel jet fuel composition which is a blend of a naphthenic jet fuel component with a highly paraffinic jet fuel component, with the final product having desirable fuel properties which are intermediate between the properties of the two individual components. The naphthenic component has a low freeze point and, when employed with a relatively high freeze point paraffinic component, is used to lower the freeze point of the blended product. The naphthenic component is also used because it has a high volumetric heat of combustion. However, the naphthenic fuel component has a low heat of combustion on a pound basis, below that desired in the final product. A presently preferred paraffinic fuel component has a relatively high freeze point, and is employed primarily since it has a heat of combustion on a pound basis in excess of that desired in the blended product. By blending a naphthenic component and a paraffinic component, it is possible to obtain a jet fuel composition which will meet standards which could not be met by either the naphthenic component alone or the paraffinic component alone or by minor modification of either component,

The relative amounts of the two components which are blended varies somewhat depending upon the properties of each component and the properties desired in the final product. In general, the naphthenic component and the paraffinic component are present in a volume ratio of about 35:65 to 60:40.

It is a further object of the present invention to provide a jet fuel composition having a freeze point of a maximum of about 46 F., a heat of combustion of at least about l8,700 B.t.u./lb., and a heat of combustion of at least about l24,000 B.t.u./gal.

In accordance with one embodiment of the invention, a naphthenic jet fuel component containing about 60 to 89 vol. percent naphthenes, about 8 to 35 vol. percent paraffins, and less than about 5 voLpercent aromatics, and preferably less than about 3 vol. percent, is prepared by fractionating a highly naphthenic crude oil to obtain a kerosene fraction boiling in the range of about 380530 F., removing at least a substan tial portion of the aromatic hydrocarbons from it, for example by sulfur dioxide extraction, hydrotreating the resulting relatively nonaromatic liquid in the presence of a hydrotreating catalyst to remove sulfur and nitrogen compounds and olefins to thereby improve the thermal stability of the fuel, separating the resulting normally gaseous and normally liquid fractions, to obtain the desired naphthenic jet fuel component. This jet fuel component may be percolated through clay or alumina if desired. The naphthenic component is blended with a paraffinic jet fuel component processed in a particular manner and containing about 3-1 7 vol. percent naphthenes, up to about 5 vol. percent preferably, about 2-3 vol. percent aromatics, and the remainder being substantially paraffins. The paraffinic component has a heat of combustion of about l8,850l 8,960 B.t.u./lb. The paraffinic jet fuel component is prepared by first desulfurizing a kerosene fraction containing at least about 40 percent (vol.) paraffins followed by reforming at a temperature in the range of about 790 to about 870 F. under conditions to dehydrogenate and isomerize naphthenes and to isomerize normal paraffins while maintaining at least 75 percent paraffin retention, separating the normally gaseous and normally liquid fractions from the reformate thus obtained, extracting at least a substantial portion of the aromatic hydrocarbons from the liquid fraction in the reformate, for example, by sulfur dioxide extraction, to obtain a raffinatc comprising the paraffinic jet fuel component.

The naphthenic and paraffinic components processed substantially as above described are blended to form a jet fuel composition having a heat of combustion greater than 123,000 B.t.u./9al., and preferably at least about 124,000 B.t.u./9al. and a heat of combustion on a pound basis of at least about 18,700 B.t.u./lb., preferably at least 18,750 B.t.u./lb., while maintaining a freeze point having a maximum of about 46 F.

FIG. 1 diagrammatically represents a simplified process flow arrangement for preparing a jet fuel composition in ac cordance with the invention;

FIG. 2 is a graph illustrating the relationship between the A.P.l. gravity of the product and the heat of combustion of the product.

Referring now to the drawing, and more particularly to FIG. 1, a preferred embodiment of the invention will now be described.

PRODUCTION OF NAPHTHENIC FUEL COMPONENT The naphthenic fuel component of the jet fuel is prepared by fractionally distilling a suitable highly naphthenic hydrocarbon charge in a fractionator to obtain for further processing a kerosene fraction boiling within the range of about 380 to about 530 F. This naphthenic hydrocarbon charge should have a paraffin content of less than about 35 vol. percent, and preferably in the range of about 5 to 30 vol. percent paraffins. Suitable feed stocks may be, for example, a mixture of three California crudes (Cal. mix), and a stock known as Coastal A. To these may be added up to or vol. percent of Murban, Four Corners, Alaskan or Qatar stocks. Other suitable naphthenic charge stocks in the kerosene boiling range may also be employed. Suitable feed stocks have the following approximate composition and properties.

Coastal A The kerosene fraction is passed from the fractionator to an extractor. in the extractor, the liquid fraction is contacted with a suitable solvent, for example, sulfur dioxide, which is selective for removing aromatic hydrocarbons from the naphthenic charge. The conditions employed during the solvent extraction are not unusual and considered substantially conventional by those skilled in the art. Thus, when employing liquid sulfur dioxide as the solvent, the sulfur dioxide may be employed in a ratio of about 100 to about 300 vol. percent based on the fraction being extracted, and the temperature may be in the range of about 20 to 50 F.

The raffinate from the extractor is then passed through a caustic scrubber to remove residual sulfur dioxide, and then through a salt tower considered a part of the extraction step to remove residual caustic and water. It is then passed over a hydrogenation catalyst in a CHD unit where it is hydrotreated to improve its thermal stability by hydrogenation of olefins, if present, and effect removal of nitrogen and sulfur compounds and other impurities. For example, hydrogenation of pyridine to ammonia and hydrogenation of thiophene to hydrogen sul fide is effected. The CHD hydrogenation is carried out in the presence of a catalyst which may be a known catalyst employed for treatment of petroleum fractions in order to hydrogenate olefins, to hydrodesulfurize, etc. Examples of such catalysts are Group V] and Group Vlll metals, oxides and sulfides, usually supported upon an inert porous carrier such as activated alumina. Mixtures of Group VI and VIII metal oxides and sulfides are particularly advantageous. Exemplary catalyst include cobalt molybdate and nickel molybdate on alumina which are the particularly preferred catalysts of the invention.

The hydrogenation-desulfurization CHD treatment is carried out at temperatures between about 550 and about 750 F., preferably between about 580-690 F., more preferably 625675 F. and at a space velocity of up to 5.0, a hydrogen partial pressure of about 450 to 800 p.s.i.g., and a hydrogen recycle rate of about 500-3000 s.c.f./bbl. Although not illustrated on the simplified flow sheet, it will be understood that the products obtained from the hydrotreater are passed to a separator step from which hydrogen rich gas is separated for recycle, preferably after removal of hydrogen sulfide and other impurities. After stripping off light ends from the CHD treated naphthenic component, the normally liquid fraction becomes the naphthenic high B.t.u./gal., low A.P.l. gravity component of the final jet fuel blend herein produced. In some cases, it may be desirable to also percolate this processed naphthenic component through clay or bauxite or silica gel or mixtures thereof before blending it with the paraffinic component hereinafter described to produce the final jet fuel product of this invention. The naphthenic jet fuel component thus prepared contains about 60 to 89 vol. percent naphthenes, about 8 to 35 vol. percent paraffins, and preferably less than about 3 percent aromatics. It has a freeze point less than that of the freeze point desired in the final blended product and is usually in the range of less than -76 to 60 F., preferably below 68 F. The naphthenic jet fuel component has a net heat of combustion of less than about l8,700 B.t.u./pound.

PRODUCTION OF PARAFFlNlC FUEL COMPONENT One function of the parafiinic jet fuel component comprising the jet fuel product herein described and produced is to elevate the heat of combustion in B.t.u./lb. and luminometer number of the blended final product. Thus the paraffinic component is prepared from selected petroleum hydrocarbon fractions of the kerosene type composed substantially of hydrocarbon mixtures boiling in the range from about 370 to about 550 F., preferably from about 380 to about 530 F., and containing at least about 40 weight percent paraffins. Some specific suitable feed stocks include straight run kerosene fractions of the following compositions:

The kerosene fractions described above are usually initially subjected to desulfurization and denitrogenation treatment prior to a low temperature mild catalytic refining or reforming treatment carried out under particularly correlated reaction conditions in the presence of a reforming catalyst having dehydrogenation and isomerizing activity such that the predominant reactions are dehydrogenation of naphthenes, isomerization of 5 carbon-ring to 6 carbon-ring naphthenes and isomerization of normal paraffins in the feed stock with at least 75 percent paraffins retention; that is, cracking is minimized. The resulting liquid reformate fraction after removal of gaseous constituents generally boils within the same range as the feed and is then solvent extracted to remove at least a substantial amount of the aromatics, which aromatics may be those originally present in the feed as well as those formed during the refining treatment, to provide a substantially aromatic free raffinate constituting the paraffinic jet fuel component.

As provided above, the feed stocks may be treated prior to the reforming step to remove sulfur and nitrogen impurities which would contaminate the catalysts used in the reforming step and/or which would cause corrosion problems. Thus, feed stocks containing a relatively high concentration of sulfur are preferably pretreated to reduce the sulfur concentration to not more than about 50 parts per million, along with substantially complete removal, when present, of other undesirable impurities including nitrogen, arsenic and lead. To effect this removal, the feed stock may be subjected to hydrodesulfurization by treatment with a suitable hydrodesulfurization catalyst (e.g. cobalt molybdate on alumina, nickel-tungsten sulfide, chromia on alumina etc.) in the presence of hydrogen and conditions of pressure space velocity and temperature to reduce the concentration of the aforementioned impurities. The following conditions are illustrative of those suitable for pretreatment of feed stocks of the invention and particularly for treatment ofa 375-500 E. virgin kerosene from W. Texas crude employing a cobalt molybdate hydrodesulfurization catalyst.

Space Velocity (LHSV) 2 Hydrogen Partial Pressure, p.s.i.g. 700

Temperature, F. hydrogen Circulation Rate (s.c.f./bbl.)

Space Velocity (LHSV) 0.5-l0

Hydrogen Partial Pressure 250-800 p.s.i.g.

Temperature, F. 600-800 Hydrogen Circulation Rate |90-3,000

Following the desulfurization pretreatment, the reaction products are passed to a stripper where the gaseous phase rich in hdyrogen, and containing substantially all of the hydrogen sulfide and ammonia produced in the pretreater, is stripped from the liquid phase, for example, by employing a stream of recycle gas from the reformer. The liquid phase is then passed to a multistage reformer which is diagrammatically shown in block form in FIG. I as having three stages.

In the reformer, the feed stock is subjected to mild catalytic treatment under correlated conditions to provide selective dehydrogenation of C ring naphthenes to aromatics, isomerization of alkyl C, ring naphthenes to C ring naphthenes which are then aromatized, and isomerization of normal paraffins to isoparaffins, while minimizing cracking. The conditions are correlated to obtain at least 75 percent paraffin retention, and preferably at least about 95 percent paraffin retention.

The reformer treatment conditions can be varied depending upon the particular feed stock employed, and upon the desired properties of the paraffinic fuel component to be produced, which properties are correlated with the properties of the particular naphthenic fuel component which will be blended therewith to obtain the final blended product. In general, the conditions are within the following ranges:

Space velocity (LHSV) 0.5-6 H,/feed, s.c.f.lbbl. 4,000-l0,000 Average Temperature, F. 790-870 Hydrogen Pressure, .s.i. 300-800 In the illustrated embodiment in which the catalytic treatment is carried out in three stages, in the first stage, the feed stock is treated under conditions to effect substantial naphthene isomerization and dehydrogenation with only a nominal amount of other reactions such as cracking or isomerization of parafi'ins. The temperature of the feed entering the first stage may be about 870 F. while the temperature of the fraction leaving the first stage is in the order of 790 F. since the dehydrogenation reaction consumes heat. It will be understood that reference to a three stage treatment is intended to include different catalytic reaction zones within a single reactor, or in separate reactors, each of which contains a catalyst (e.g. a bed of catalyst) with the reaction zones being interconnected by transfer lines for the passage of product from one reaction zone to the other, which transfer lines are equipped with heaters for heating the product from one reaction zone prior to its introduction into the succeeding reaction zone. In the second and third reaction zones, the conditions are regulated to achieve primarily isomerization of normal paraffins to isoparafins accompanied by some further dehydrogenation of any naphthenes which may still be present. The feed to the second reaction zone may be heated to about 830 F., and the product leaving the second reaction zone which may be at a temperature of about 810 F. is preferably again reheated, for example, to about 820 F. before introduction into the third reaction zone. The product from the third reaction zone may be at a temperature of about 810 F.

It will be understood that, for any given kerosene feed stock passed to the reformer, as the average reaction temperature employed increases from the lower to the higher. side of the stated temperature range, the space velocities generally increase within the stated range. In addition, as the catalyst ages, the temperature is generally increased at constant space velocity, or alternatively, the space velocity is decreased while maintaining a substantially constant average temperature in order to maintain a substantially constant quality of reformed product.

The catalyst employed in the reformer is a dehydrogenation catalyst having selectivity for the isomerization and the dehydrogenation of naphthenes, and having low cracking activity.

For the catalytic treatment of the feed stocks embodied suitable catalysts are metals of the platinum series and particularly, platinum, on carriers such as alumina. Specific examples thereof are catalysts, of low cracking activity, comprising from about 0.1 to about 1.0 percent platinum on alumina (e.g. eta alumina) or on a low-activity silica-alumina base and which may contain a suitable halogen (e.g. chlorine) in an amount of up to about l.0 percent and, preferably, in an amount not greater than the platinum content, and preferably lower. Such catalysts that contain from about 0.3 to about 0.8 percent platinum are particularly suitable. In a broader aspect, however, suitable for use herein are catalysts which, as is known to those skilled in the art, possess activity for dehydrogenating naphthenes to aromatics and are of low cracking activity and, as further examples, such catalysts include tungsten and/or nickel on kieselguhr, chromium oxide on alumina, and others.

The reformate is passed to an extractor for reduction of the aromatic concentration, for example, by extraction with liquid sulfur dioxide. The conditions employed during the solvent extraction may be substantially the same as those employed during the corresponding step in treating the naphthenic jet fuel component, that is, when sulfur dioxide is the solvent, the sulfur dioxide may be employed in a ratio of about to about 300 vol. percent, based on the fraction being extracted, at a temperature in the range of about 20 to 50 F.

The paraffinic rafiinate obtained from the extraction step may be subjected to a relatively mild (CHD) hydrodesulfurization similar to that discussed above with respect to the naphthenic component preparation and/or percolated through a suitable material to improve its thermal stability and to yield the desired paraffinic jet fuel component which also has found use 18,850-a relatively super jet fuel meeting different specifications than those which are met by the blended product of the present application. Suitable percolation materials may be clay, bauxite, aluminas, silica gel and the like. The paraffinic jet fuel component of the invention contains about 3-17 vol. percent naphthenes, a maximum of about 5 vol. percent, preferably about 2-3 vol. percent aromatics, and has a freeze point in the order of about 40 to 45 F. and a heat of combustion of about l8,850l8,960 B.t.u./lb.

Other suitable paraffinic blending components include a hydrogenated heavy alkylate, and a paraffinic hydroisomerized product such as hydroisomerized wax or paraffinic hydrocrackate. The heavy alkylate blend stock is prepared by hydrogenating olefins in a heavy alkylate fraction boiling in the range of about 380550 F. employing processing conditions substantially the same as those described above for the hydrogenation and desulfurization of the naphthenic stock. These blend stocks have the advantage of having low freeze points. The properties of these blend stocks, and suitable hydrogenation conditions for the alkylate are set forth in the following table.

PROPERTIES OF PARAFFlNlC BLEND STOCKS 380-520 F. 37U-525 F. Heavy Hydro Alltylate crackate LHSV, v m v bis-s.0 Temperature, Fv 550 750 Product Properties Charge Product Product Gravity,APl 51.1 5l.l 52.4 Aniline Point, Fv I96 I96 177.3 Luminometer No. 85 85 Heating Value, B.t.u./lb. l8,866 [8,864 [8,917

Freeze Point, F. 76 76 76 Composition, Vol. 5

Paraffins 85.0 87.0 87.2

Olefins 2.0 Naphthenes l2.0 l2.0 ll .0 Aromatics 1.8 L0 L8 The process flow arrangement of FIG. 1 above discussed provides several variations in processing sequence which can be taken advantage of depending upon contaminating materials found in the naphthene and paraffinic components. Thus in one operating sequence of FIG. 1 herein identified as sequence A, the naphthenic product effluent of the CHD treating step may be passed by conduits 2, 4, 6 and 8 to a blending step wherein it is blended with a paraffinic product effluent of a separate CHD treating step found in conduit 22 and communicating with conduit 8 and the blending step.

On the other hand, in the preferred embodiment of FIG. I identified as sequence B," the naphthenic product effluent of the naphthenic CHD step and found in conduit 2 is combined with the paraffinic product component in conduit 16 recovered from the paraffinic SO, extraction step. That is, the paraffinic product in conduit 16 may be passed through conduit 20 containing valves 28 and 32 to conduit 14 containing valve 26 and communicating with the blending step by conduit 8 for blending with the above identified naphthene product effluent in conduit 2. It is to be noted that the paraffinic product in conduit 20 is preferably first passed through a clay or alumina percolation step 38 by way of conduit 34 containing valve 36 and the percolated product is then passed by conduit 40 containing valve 42 to conduit 20 and then to conduit 14. When employing the percolation step, valve 32 in conduit 20 will be closed.

In another embodiment, identified as sequence C, the naphthenic raffinate of an extraction step found in conduit 10 is passed by conduits l2 and 20 to be combined with the paraffinic raffinate of a separate extraction step found in conduit 16. The combined raffinates are then passed to conduit 18 containing valve 30 to CHD treatment before being recovered or passed to the blending step by conduits 22 and 8.

In still another arrangement, identified as sequence D, the paraffinic product recovered from the percolation step by conduit 40 may be combined with the naphthenic raffinate found in conduit 12 which may or may not have been percolated and the mixture thus formed passed to the blending step by way of conduits l4 and 8.

It is to be noted that the several different processing sequences above briefly outlined as sequences A," B," C" and D" are available for use with particular charge materials depending upon the extent of undesired contamination found in the respective paraffinic and naphthenic components after the aromatic removal steps. While one sequence or another may offer some economic advantage over another for particular charge material, sequence B" is preferable to the others for handling a variety of charge stock materials with a maximum of versatility. Thus sequence "B" is the preferred embodiment of this invention since it provides the versatility above referred to, permits operating the naphthenic charge CHD treating step at a lower temperature and the sequence provides a greater thermal stability to the product as measured by the TPT test.

BLENDING OF NAPHTHENIC AND PARAFFlNlC COMPONENTS In order to achieve a blended jet fuel composition having desired properties, the naphthenic jet fuel component and the paraffinic jet fuel component are blended in a volume ratio of between about 35:65 to 60:40, and where it is intended to meet the aforementioned military specifications including the heat of combustion of about 124,000 B.t.u./gal., these components are blended within the aforementioned ranges to give a product having a gravity of about H5.5 to 470 A.P.l.

Furthermore to make the specification of 18,700 B.t.u./lb., the blended jet fuel should have a paraflin content between 50-62 vol. percent. About 50 vol. percent paraffins will make the specification when the amount of aromatics is about 2 vol. percent, this being a typical maximum aromatic content following sulfur dioxide extraction. A paraffin content of about 62 vol. percent will make the specification when the aromatics content is at its maximum permissible value of 5 vol. percent. ln addition, at least about 50 vol. percent paraffins is required in the blended jet fuel in order to give a luminometer number of 75 or better as required by the specifications.

Referring to FIG. 2, it may be seen that to make the two heat of combustion specifications, it is necessary to operate above the 18,700 B.t.u./lb. line and to the left of the 124,000 B.t.u./gallon line. However, for the blended product to have the necessary composition, the gravity must be maintained between the narrow limits of H55 to 470 A.P.l. and preferably 460 to 470 A.P.l. To meet the restrictions above identified, it is immediately clear that it is necessary to operate within the shaded area shown on E16. 2.

In addition to providing the product with a freeze point of -46 F. or less, the components should be blended to provide a product having a maximum of about 18 percent normal paraffins. It will be appreciated that, in addition to adjusting the relative amounts of the two components, the normal paraffin content of the paraffinic component may be varied by way of the treatment of the paraffinic component in the reformer to isomerize normal paraffins.

It will also be appreciated that, within permissible specifications limits, known jet fuel additives may be combined with the blended product. Such known additives include oxidation inhibitors and metal deactivators.

The invention will be more specifically described with reference to the following examples.

EXAMPLE 1 A naphthenic fuel component is prepared by introducing Cal. mix, the mixture of three California crudes as described into a fractionator and recovering a kerosene fraction boiling within the range of 380-530 F. The kerosene fraction is passed to an extractor where aromatics are removed by sulfur dioxide extraction employing a ratio of sulfur dioxide of 250 vol. percent based on the fraction being extracted and a temperature of 4 F. The raffinate from the extractor is passed to a CHD reactor where it is hydrotreated at a hydrogen pressure of 650 p.s.i.s., a LSHV of 2 v./hr./v., a hydrogen circulation rate of 500 s.c.f./bbl, and a temperature of 625 F., in the presence of a cobalt molybdate desulfurization and denitrogenation catalyst. The normally liquid fraction thus treated is percolated through clay and then recovered as the naphthenic component of the jet fuel blend.

A paraffinic fuel component is prepared from a straight run kerosene fraction which is pretreated as by desulfurization to remove impurities at a hydrogen pressure of 700 p.s.i.a., a LHSV of 2.0, a hydrogen circulation rate of 2,000 s.c.f./bbl, a temperature of 700 F., and in the presence of a cobalt molybdate hydrodesulfurization catalyst. After separation and removal of the gaseous phase in a stripper, the desulfurized normally liquid fraction is passed to the first of a three-stage reformer wherein dehydrogenation of naphthenes and isomerization of paraffins is carried out with only nominal amounts of other reactions such as cracking. The feed enters the first stage of the multistage reformer at a temperature of 870 F. and leaves at 790 F. After reheating to 830 F., the feed passes to the second zone from which it exits at 810 F., and is reheated to 820 F., for introduction into the third and last stage from which the product leaves at 810 F. The effluent of the reforming step is separated to recover a gaseous phase from the normally liquid reformate product. The normally liquid product from the reformer is passed to an extractor where aromatics are removed by sulfur dioxide extraction employing sulfur dioxide in a ratio of 250 vol. percent based on the fraction being extracted, at a temperature of 4 F. The raffinate is then percolated through bauxite to improve its thermal stability and the desired paraffinic jet fuel component is thus obtained.

The naphthenic and paraffinic components are then blended to produce a blended jet fuel composition.

The properties of three blended jet fuel compositions prepared by blending naphthenic and paraffinic components as described above are set forth in the following table.

BLENDED JET FUEL COMPOSITIONS Components Blend 1 Blend 2 Blend 3 Paraffinic component 56.5 58.5 62

vol. Naphthenic component 43.5 41.5

vol. I: Topped Naphthenic component 38 vol. b Properties Gravity, API 46.6 46.6 46.6 Aniline Point, 'F. 170.0 170.5 172.3 Total Absorption, vol. I: 2.6 3.3 30 Heating Value B.t.u.l|b. (AXG) 18,753 18,755 18,765 B.t.u./lb. (calorimeter) l8,770 18,760 18,780 B.t.u./gal. 124.050 124,060 124,130 Freeze Point, 'F. -51 51 50 Freeze Point of Paraffinic Component 'F. 40 40 -45 Freeze Point of Naphthenic Component F. -70 68 -60 Distillation, ASTM, 'F.

117p. 370 377 411 I 409 405 421 20 41B 411 424 so 433 426 437 70 447 441 449 90 476 470 476 EP 5 14 502 515 *Before blending, the naphthenic component was topped.

One of the more severe tests of the specification for this fuel is the Thermal Precipitation Test. This test, designated P&WA-MCLQ67 by the Pratt and Whitney Aircraft Corporation has the purpose of heating the fuel to be tested at a specified rate to 300 F., digesting the fuel at 300 F. for 2 hours, cooling the fuel at a specified rate, and determining by filtration if this heat treatment has caused precipitation on insoluble matter. The details of the test are as follows.

THERMAL PRECIPITATION TEST OF JET FUEL INSOLUBLES 1. Apparatus A. Fuel Preconditioning Unit including Fuel Reservoir and Reservoir AssemblyModel No. 2200, Erdco Engineer ing Corp. Unit shall be capable of maintaining fuel at 300 F. i F.

B. Vacuum Pump-free air capacity 33.4 liters per minute,

Model No. I406-H, Welch Mfg. Co., or equivalent.

C. Fuel Filtration Unit-Model XX 2004720, Millipore Corp.

D. Oven-capable of maintaining a temperature of 180 F.

E. Filtering Flask-4,000 ml.

11. Materials A. Filter Paper-0.45 micron pore size, 47 mm. diameter,

Type HA, Millipore Corp.

B. Precipitation Naptha-Conforming to ASTM D9l-6l,

prefiltered through 0.45 micron filter paper.

C. Aluminum foil.

D. Lint free clothConsolidated Electrodynamics Corp.,

PIN 18560 or equivalent.

E. PWA 523 Fuel Thermal Precipitation Color Standard.

F. Pentane-prefiltered through 0.45 micron filter paper.

G. Petri Dish-Millipore Corp., P/N PD 1004700.

111. Procedure A. Preparation of Test Filter Papers I. With forceps, place filter paper in the precleaned fuel filtration unit and assemble unit with filtering flask and vacuum pump. Start pump.

2. Decant three 25 ml. increments of naphtha into filtration unit. Allow each increment to filter completely through filter paper before adding the next increment.

3. Turn vacuum pump off and relieve vacuum in filtration unit.

4. With forceps, carefully remove filter paper from filtration unit and place in 180 F. 15 F. for 30 minutes.

5. With forceps, remove filter paper from oven and place in Petri dish. Close dish.

B. Preparation of Filtering Flask and Fuel Reservoir l. Flush filtering flask with 200 ml. naphtha.

2. Air dry the filtering flask.

3. Flush fuel reservoir with 400 ml. naphtha.

4. Dry the fuel reservoir interior by wiping with a lint free cloth or washing with pentane and allowing to air dry.

C. Preparation of Test Fuel and Heating Cycle Operation 1. Filter 3 gallons of test fuel through filter paper according to step A1. Discard filter paper.

2. Refilter the fuel through another filter paper. Discard filter paper. Cover fuel filtration unit with aluminum foil.

3. Place test fuel in precleaned fuel reservoir exercising care to prevent the inclusion of airborne matter.

4. Assemble reservoir assembly being careful to check and tighten water-cooling coil.

5. Close Water lnlet Valve.

6. Turn Main Power Switch On.

7. Turn Heater Selector Switch to Medium.

8. Set Temperature Controller to 300 F. Temperature of 300 F. shall be attained in l00 to 20 minutes.

9. Maintain temperature at 300 F. :5" F. for 120 minutes.

10. After lZO-minutes heating cycle, turn Heater Selector Switch to Off.

11. Open Water Inlet Valve. The fuel temperature shall drop to F. i5 F. in 30 to 45 minutes.

12. When fuel has cooled to 80 F. 15 F., close Water lnlet Valve. Disassemble fuel reservoir.

l3. Cover open reservoir with aluminum foil.

D. Filtration of Test Fuel 1. With forceps, place the prepared filter paper from A5 in the precleaned filtration unit and assemble unit with filtering flask and vacuum pump. Start pump.

2. Filter 3,785 ml. (1 gallon) of the fuel from C13 within 1 hour using a graduated cylinder taking care to prevent airborne contamination. Note: Covering the filtration unit and graduated cylinder with aluminum foil during filtration is acceptable.

. Wash the filter paper and inside walls of filtration unit with three 25 ml. increments of naphtha. Allow each increment to filter completely through filter paper before adding the next increment.

. Repeat steps A3 through A5.

. Compare colors of sample and Color Standard and report the test as darker, equal to, or cleaner than the standard.

The jet fuel blend was tested in the Thermal Precipitation Test (TPI) and it passed that test with the very good rating Shell code rating 1. Shell code rating 1 corresponds to a pass in the P&W rating system. A Shell code rating of 2 or greater corresponds to a fail in the P&W system.

EXAMPLE 2 The same naphthenic jet fuel component as that of example 1 was prepared by introducing Cal. mix, the mixture of three California crushes as described previously, into a fractionator and recovering a kerosene fraction boiling within the range of 380-530 F. The kerosene fraction thus obtained was passed to a CHD reactor where it was hydrotreated at a hydrogen pressure of 650 p.s.i.a., a LHSV of 2 v./hr./v., a hydrogen circulation rate of 500 s.c.f./bbl., a temperature of 625 F., and in the presence of the same cobalt molybdate catalyst of example 1. The normally liquid fraction is recovered and passed to an extractor where aromatics are removed by sulfur dioxide extraction employing a ratio of sulfur dioxide of 250 vol. percent based on the fraction being extracted and a temperature of 4 F. The raffinate from the extractor is then percolated through clay to obtain the desired naphthenic jet fuel component. This naphthenic component is then blended with the same paraffinic component as that of example I to produce a blended jet fuel composition.

This jet fuel blend was tested in the Thermal Precipitation Test and it failed that test with a rating of Code 2-3.

EXAMPLE 3 The same naphthenic component as that of examples I and 2 was CHD-treated, So -extracted and percolated in that sequence as in the case of example 2 except that the CHD conditions were 650 p.s.i.a., a LHSV of l v./hr./v., a hydrogen circulation rate of 1,000 s.c.f./bbl., and a temperature of 650" F. The naphthenic component thus treated was blended with the paraffinic component in the same way as example 2. This jet fuel on TP Testing was rated as a Code 1-2 borderline failure. This was the best rating achieved in a series of tests in which the Cal. mix kerosene was treated at varying CHD conditions followed by aromatics extraction and percolation.

The significant differences between examples I and 2 are as follows: In example 1, SO, extraction preceded CHD treatment and in example 2, SO, extraction followed CHD treatment. Thus, the comparison of examples 1 and 2 shows that aromatics extraction before CHD hydrogen treatment produces a jet fuel blend having a better TPT rating than the reverse sequence represented by example 2. in addition, the comparison between examples I and 3 shows that using the sequence of aromatics extraction before CHD hydrogen treatment permits obtaining good TPT ratings using lower temperatures and hydrogen circulations in the hydrogen treatment step than in the case of hydrogen treatment before aromatics extraction.

EXAMPLE 4 A naphthenic fuel component is prepared by introducing Cal. mix, the mixture of three California crudes as described previously in admixture with four corners crude in a minor amount, into a fractionator and recovering a kerosene fraction boiling within the range of 380-530 F. The kerosene fraction is passed to an extractor where aromatics are removed by sulfur dioxide extraction employing a ratio of sulfur dioxide of 250 vol. percent based on the fraction being extracted and a temperature of F. The raffinate from the extractor is passed to a CHD reactor where it is hydrotreated at a hydrogen pressure of 650 p.s.i.a., a LHSV of 1.3 v./hr./v., a hydrogen circulation rate of l,500 s.c.f./bbl., a temperature of 645 F., in the presence of a cobalt molybdate desulfurization and denitrogenation catalyst. The normally liquid fraction thus treated is recovered as the naphthenic component of the jet fuel blend.

A paraffinic fuel component is prepared from a straight run kerosene fraction which is pretreated as by desulfurization to remove impurities at a hydrogen pressure of 700 p.s.i.a., a LHSV of 2.0, a hydrogen circulation rate of 2,000 s.d.f./bbl., a temperature of 700' F., and in the presence of a cobalt molybdate hydrodesulfurization catalyst. After separation and removal of the gaseous phase in a stripper, the desulfurized normally liquid fraction is passed to the first of a three-stage reformer wherein dehydrogenation of naphthenes and isomerization of paraffins is carried out with only nominal amounts of other reactions such as cracking. The feed enters the first stage of the multistage reformer at a temperature of 870 F. and leaves at 790 F. After reheating to 830 F., the feed passes to the second zone from which it exits at 8l0 F., and is reheated to 820 F., for introduction into the third and last stage from which the product leaves at 8 [0 F. The effluent of the reforming step is separated to recover a gaseous phase from the normally liquid reformate product. The normally liquid product from the reformer is passed to an extractor where aromatics are removed by sulfur dioxide extraction employing sulfur dioxide in a ratio of 250 vol. percent based on the fraction being extracted, at a temperature of 10 F. The raffinate is then percolated through clay to improve its ther mal stability and the desired paraffmic jet fuel component is thus obtained.

The naphthenic and paraffinic components are than blended to produce a blended jet fuel composition having an A.P.l. gravity of 46.3. The properties of this jet fuel composition are shown in table I.

TABLE 1 Test Test Results Gravity,'APl 46.3 Distillation Temperature, F.

Initial Boiling Point 383 10% Evaporated 407 20% Evaporated 4l0 50% Evaporated 434 Evaporated 48l End Point 522 Residue, Vol. I: L0 Loss Vol.% L0 Existent Gum, mg.ll00 ml. 0.4 Total Potential Residue, l6 hr. aging,

mgJlOO ml. 0.5 Sulfur, wt. 0.02 Mercaptan Sulfur, wt. 0.000l Aromatics, vol. 1.8 Flash Point, F., PMCC I58 Freezing Point, F. 50 Copper Strip Corrosion, 2hr.at2l2F. l

Net Heat of Combustion B.t.u./lb. 18,735 B.t.u./gal. l24,l38 Luminometer No. 87 Water Reaction, Interface Rating lb Water Separometer Index Modified 94 Thermal Stabilit'y: CRC Fuel Coker (300/500/600) Pressure Change, Inches Hg 0.6 Preheater Deposit Code 2 Vapor Pressure, p.s.i.a.

at 300 F. 2.65 at 500 F. 44.0 Thermal Precipitation Test- PdrWA-MCLQ 67 Pass Fuel System Icing Inhibitor, vol. l: 0.1 l Particulate Matter, mgJgal. 0.5

It is to be noted from table I that this blended jet fuel product passed the Thermal Precipitation Test (TPT) with a rating of Code 1.

Having thus provided a general description of the improved method and combination of processing steps to be practiced by this invention and provided examples in support thereof, it is to be understood that no undue restrictions are to be imposed by reason thereof.

lclaim:

l. A method for producing a jet fuel product having a heat of combustion equal to or greater than 124,000 B.t.u./gal. and 18,700 B.t.u./lb. which comprises (a) processing a naphthenic rich charge boiling from about 380 to about 530 F. through the combination of aromatic extraction followed by catalytic hydrodesulfurization so as to produce a naphthenic jet-fuelboiling component containing less than 35 vol. percent paraffins, volume percent aromatics and 50 p.p.m. of sulfur, (b) processing a paraffin rich charge material boiling in the range of 370 F. to about 550 F. comprising at least about 40 vol. percent paraffins, and less than 50 p.p.m. of sulfur by catalytic reforming under isomerizing conditions to maximize paraffin retention, and produce after extraction of aromatics therefrom a reformed paraffinic jet fuel component containing less than about 17 vol. percent naphthenes and less than 5 vol. percent aromatics which will produce upon selected blending with the above naphthenic component, (c) a jet fuel product blend having a gravity in the range of about 45.5 to about 47 A.P.l., and a paraffin content in excess of about 50 vol. percent.

2. The method of claim I wherein the naphthenic component is blended with the paraffinic component in a volume ratio between about 35:65 to about 60:40.

3. The method of claim 1 wherein the paraffin rich reformate component recovered after removal of aromatics therefrom is blended with the naphthenic component after aromatic removal and the blend thus formed is then hydrogenated to remove undesired sulfur constituents.

4. The method of claim 1 wherein the naphthenic jet fuel charge material is blended with the paraffin rich jet fuel reformate product before treatment to remove aromatic and sulfur bodies.

5. The method of claim 1 wherein the parafi'inic jet fuel component recovered from the aromatic removal step is percolated through a solid adsorbent material before blending with the hdyrogenated naphthenic rich jet fuel component.

6. A method for producing ajet fuel product having a heat of combustion equal to or greater than l24,000 B.t.u./gal. and an A.P.l. gravity in the range of 45.5 to 47 which comprises (a) processing a naphthenic rich charge containing less than 35 vol. percent paraffins and boiling in the range of 380 to 530 F. by the steps of aromatic removal followed by hydrogenation thereof sufficient to remove sulfur bodies to at least about 50 ppm. to form a naphthenic product material containing from about 60 to about 89 vol. percent naphthenes, (b) processing a desulfurized paraffin rich jet fuel boiling range material through catalytic reforming under conditions to efiect dehydrogenation of naphthenes, isomerization of C carbon ring and C carbon ring naphthenes and isomerization of n-paraffins to produce a paraffin rich jet fuel product which will have after removal of aromatics a heat of combustion in the range of about l8,850 to about l8,960 B.t.u./!b. and a freeze point of the order of about -40 to about --45 and (c) blending the naphthenic product material with the above produced paraffin rich jet fuel product in a volume ratio selected to produce a blended jet fuel product in a volume ratio selected to produce a blended jet fuel product having a paraffin content above 50 vol. percent and a heat of combustion equal to or greater than 18,700 B.t.u./lb. and an A.P.l. gravity in the range of 46 to 47.

i t B UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Dated January 3, 1972 Patent No. 3,

Inventor(s) HENRY R. IRELAND It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Abstract,

Column Column Column Column Column Column Column Column Column Column Column Column Column Column Column Column (SEAL) Attest:

EDWARD M.PLETCHER,JR.

10, line After line 1 "50F" should be -50F-- line line

line

line

line

line

line

line

line

line

line

line

line

lino

line Ml After "/6oo delete "13w" "Btu/ sl should be --Btu/gallon-- "Btu/9gal" should be --Btu/gallon-- "500E" should be --500F- After "use" delete --l8,850-- After "18,850" insert "11.0" should be under "Product" column "HF.5" should be 45.5"

"111 .5" should be +5.5--

After 'described" insert --previously-- should be --p.s.l.a.--

"p. s .i. s.

"lh should be 1132-- should be 11" is; not in exact position under colu "15F" insert --oven- J to 20" should be "100 to Signed and sealed this 6th day of June 1972.

Attesting Officer ROBERT GOTTSCIIALK Commissioner of Pate

Claims (5)

1. 2. The method of claim 1 wherein the naphthenic component is blended with the paraffinic component in a volume ratio between about 35:65 to about 60:40.
2. 3. The method of claim 1 wherein the paraffin rich reformate component recovered after removal of aromatics therefrom is blended with the naphthenic component after aromatic removal and the blend thus formed is then hydrogenated to remove undesired sulfur constituents.
3. 4. The method of claim 1 wherein the naphthenic jet fuel charge material is blended with the paraffin rich jet fuel reformate product before treatment to remove aromatic and sulfur bodies.
4. 5. The method of claim 1 wherein the paraffinic jet fuel component recovered from the aromatic removal step is percolated through a solid adsorbent material before blending with the hdyrogenated naphthenic rich jet fuel component.
5. 6. A method for producing a jet fuel product having a heat of combustion equal to or greater than 124,000 B.t.u./gal. and an A.P.I. gravity in the range of 45.5 to 47 which comprises (a) processing a naphthenic rich charge containing less than 35 vol. percent paraffins and boiling in the range of 380* to 530* F. by the steps of aromatic removal followed by hydrogenation thereof sufficient to remove sulfur bodies to at least about 50 p.p.m. to form a naphthenic product material containing from about 60 to about 89 vol. percent naphthenes, (b) processing a desulfurized paraffin rich jet fuel boiling range material through catalytic reforming under conditions to effect dehydrogenation of naphthenes, isomerization of C5 carbon ring and C6 carbon ring naphthenes and isomerization of n-paraffins to produce a paraffin rich jet fuel product which will have after removal of aromatics a heat of combustion in the range of about 18,850 to about 18,960 B.t.u./lb. and a freeze point of the order of about -40 to about -45 and (c) blending the naphthenic product material with the above produced paraffin rich jet fuel product in a volume ratio selected to produce a blended jet fuel product having a paraffin content above 50 vol. percent and a heat of combustion equal to or greater than 18,700 B.t.u./lb. and an A.P.I. gravity in the range of 46 to 47.

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