US3201342A - Method of making a superior jet fuel - Google Patents

Description

K. C. BACHMAN ET AL METHOD OF MAKING A SUPERIOR JET FUEL Filed Jan. 7, 1963 Aug. 17, 1965 N I Q E E B 2 as 8 I m O I E N l 9 "-z/ 9 E E O t: f u 05 1': 2 o o- 1$g KENNETH m D 9 ORAL 9 HARRY JOHN N RIGHARD I n \WLLIAM n 9 g HENRY 9 v RICHARD n f 3 1 JAMES 0. BAGHMAN O. BEHYMER L. LANGDON E. LAWSON, JR.

0. SO OTT INVENTORS.

ATTORNEY United States Patent 3,201,342 METHQD OF MAKING A SUPERIGR JET FUEL Kenneth C. Eachman, Westfield, N1, 01ml (3. Behymer, Harry L. Langdon, John E. Lawson, Jr., Richard S. Marine, and William K. Robbins, 'Baytown, Henry H.

Rosser, Highlands, and Richard C. Russell and James G.

Scott, llaytown, Tex., assignors, by direct and mesne assignments, to Essc Research and Engineering Company, Elizabeth, N.J., a corporation of Delaware Filed Clan. 7, 1963, Ser. No. 249,658 9 Claims. (Cl. 208-89) The present invention relates to a method of making a superior jet fuel for supersonic aircraft. More particularly, the present invention relates to the production of a jet fuel for use in aircraft attaining speeds as high as Mach 3. In its most specific aspects, the invention relates to a method of making a superior fuel from a parafiinic, virgin hydrocarbon stream, utilizing a combination of specific steps, each of which must be used in order to obtain a high boiling, thermally stable jet fuel having outstanding characteristics for use in supersonic aircraft.

Specifications for supersonic aircraft fuel may be set by aircraft and jet engine manufacturers or by governmental branches. These specifications are critical since the designs of aircraft engines and air frames are based upon the specific performance characteristics which have been set with respect to the fuel specification. For a particular example of superior jet fuel for use at Mach-3 speeds, the following specifications have been set.

TABLE I Specifications for Mach-3 jet fuel Luminometer Number 100 minimum.

Freeze point 40 F. maximum. Viscosity at 30 F cs. maximum. Heat of combustion 18,900 B.t.u./ 1b., net, min. distilled 408 F. minimum.

Thermal stability at 300/500/600 (research coker) Must pass.

Many difficulties present themselves when a virgin petroleum hydrocarbon stream such as crude oil or heavy condensate is proposed as the basic source of a fuel meeting these specifications. Specifications as to luminometer number, freeze point, and heat of combustion in particular are extremely hard to satisfy when the source of the fuel is such a virgin hydrocarbon stream. Various attempts to manufacture fuels meeting the above specifications by extraction of virgin distillatcs or by blending various extracted kerosenes have been unsuccessful. However, by the practice of the present invention wherein each of the processing steps is used and wherein the Engler distillation 20% point of the jet fuel product is maintained within a critical range, a Mach-3 jet fuel can be produced which meets the desired rigorous specifications when starting from a virgin crude oil or from a heavy, natural condensate.

The present invention involves the processing sequence of a first distillation to obtain a charge stock boiling within the range of 355 F. to 510 F., followed by desulfurization, reforming, extraction, hydrofining, and adsorption, with the associated distillation steps which are required in order to obtain a final product boiling within the range of 375 F. to 495 F. and having an Engler distillation 20% point of 408 F. minimum and preferably within the range of about 410 F. to 414 F.

The present invention may be better understood by a reference to the drawing wherein a flow sheet of a preferred mode of the present invention is schematically set forth.

3,201,342 Patented Aug. 17, 1065 Referring now to the drawing, the present invention is disclosed as comprising a first step of fractionating a parafiinic feedstock such as crude oil or heavy condensates (obtained from distillate wells and the like) introduced into fractionating tower 101 by way of line 102. A low-boiling overhead stream is withdrawn by way of line 103, and a high-boiling stream is removed by way of line 104, with a heart out fraction boiling within the range of 355 F. to 510 F. being obtained by way of line 105. The heart cut is the charge stream to the processing sequence of the present invention.

The charge stream is admixed with hydrogen supplied by way of line 106 and is contacted with a hydrodesulfurization catalyst in the hydrodesulfurization zone 108. A hydrodesulfurized product is withdrawn by way of line 110 (and may be distilled in a fractionator to obtain a dry point of the overhead product of 490 F. to 500 F), admixed with hydrogen supplied by way of line 112, and subjected to catalytic reforming in the catalytic reforming zone 114.

A reformed product stream is removed by Way of line 110, preferably through a stabilizer tower (not shown), where the light ends are removed to give an IBP (initial boiling point) minimum of 300 F., and is then contacted preferably with sulfur dioxide as a solvent for aromatic hydrocarbon in the zone 118. In this step the S0 is introduced by way of line and an aromatic extract is removed by way of line 122, the paraflinic raffinate being withdrawn by way of line 124. The rafiinate is then fractionated in order to obtain an overhead fraction boiling below about 500 F., for example having an Engler FBP (final boiling point) of 480 F. to 490 F. In this distillation step the heavy polymers which are produced in the reformer 114 and/or the hydrodesulfurizer 108 are removed in the high-boiling material. For this purpose the rafiinate is introduced into distillation column 130, and a high-boiling bottoms stream, withdrawn by way of line 132 while the overhead stream, having an F-BP of about 480 F. to 490 F., is withdrawn by way of line 134.

The overhead stream 134 is admixed with hydrogen supplied by line 136 and introduced into a hydrofining zone 138, wherein the distilled raffinate is hydrofined. The hydrofined material may be fractionated to adjust the initial boiling point to about 380 F. and is then introduced into adsorption zone 142 as a final finishing step. In the adsorption zone 142, the residual aromatic compounds are removed and thermal stability of the fuel improved. The Mach-3 fuel is withdrawn by way of line 144 and may be caustic washed before or after adsorption if desired. The various distillation steps after the reforming operation must produce a final product having an Engler 20% point within the range of 410 F. to 414 F. Obviously, this may be accomplished by distillation at any of many points in the processing sequence, but preferably the 20% point is adjusted in the final distillation zone or in a distillation zone (not shown) after hydrofining in zone 138. By raising the Engler 20% point to 408 F. minimum, preferably 410 F. to 414 F., the luminometer number and heat of combustion are maximized while the freeze point is minimized, contrary to what would be expected. It normally would be expected that these values would degrade with an increasing 20% point. However, it has been found that with the 20% point within the prescribed 4 F. range, the luminometer number, freeze point, and B.t.u. ratings of the fuel are at their most desirable values, less desirable values for each being obtained at a 20% point either higher or lower than the critical range.

This is seen from the following Table II, wherein the q) changes of the luminometer number, the freeze point, and the heat of combustion are shown.

Thus, it is seen that in order to make the rigorous specifications, the Engler 20% point of the product must be maintained within the narrowly prescribed range.

In general, the processing scheme has been shown to include a prefractionation step followed by hydrodesulfurization, catalytic reforming, extraction, fractionation, hydrofining and adsorption in order to produce a superior quality Mach-3 jet fuel. The individual steps, including the variables involved therein, are discussed in sequence below.

FEEDSTOCK The oil to be used as an ultimate feedstock is obtained from a paraffinic crude such as Panhandle crude or from field condensates. The preferred crude oil will contain at least about 40% paraffins and less than about 60% aromatics plus naphthenes.

DI STILLATION The selected crude oil is then distilled in order to obtain a distillate having a boiling range from about 355 F. to about 510 F. containing from about 30 to about 50% normal paraffins, from about 10 to about 40% isoparaflins, from about 40 to about 60% aromatics plus naphthenes, and from about to about 5% olefins. The fractionation step removes high boiling, unsuitable materials from the fuel.

DESULFURIZA'IION The distilled fraction is submitted to hydrodesulfurization, wherein the fraction is contacted with a hydrodesulfurizing catalyst such as extruded or pilled cobalt molybdate. The temperature in the hydrodesulfization zone suitably may range from about 600 F. to about 690 F., the pressure from 150 p.s.i.g. to 300 p.s.i.g., and a hydrogen feed rate from 200 s.c.f./ bbl. to 600 s.c.f./bbl. of feed, based on pure hydrogen. The hydrogen recycle stream containing from about 60% to about 95% hydrogen may be used, in which case the amount of hydrogen recycle stream per barrel of feed will be larger than would be the case if pure hydrogen were being used.

The charge to the hydrodesulfurizing zone shall suitably involve a space velocity of from about 2.0 to about 4.0 volumes of hydrocarbon feed per volume of catalyst per hour.

In the hydrodesulfurizing step, the sulfur is removed and the sulfur content of the material is reduced from about 0.10 to 0.25% in the feed to about 0.002 to about 0.009% sulfur in the efiluent from the hydrodesulfurization unit. The H 8 and low-boiling materials produced by hydrodesulfurization may be removed by steam stripping in order to provide a more suitable feedstock for the following reforming step.

CATALYTIC REFORMING The hydrodesulfurized stream is then charged into the reforming zone and contacted with hydrogen in the presence of a reforming catalyst such as platinum on alumine, which has both aromatizing and isomerizing activity. The temperature may range from about 825 F. to about 900 F.; the pressure from 150 p.s.i.g. to 450 p.s.i.g.; the amount of hydrogen to hydrocarbon feed from 2000 s.c.f. per barrel to 7000 s.c.f. per barrel (based on pure hydrogen); and the space velocity may be from 0.2 to 2.0 v./v./hr.

In the reforming zone, the naphthenic hydrocarbons preferred treat rate is 1.5 to 3.5 v./v./hr.

are preferentially converted into aromatic hydrocarbons which makes them susceptible to extraction. It is esssential to operate the reformer at a minimum temperature of 825 F. to permit isomerization of normal to isoparafiins. While the ratio of isoto normal parailins in the feed may be as low as 0.2 to 0.5, the ratio in the finished product must be in the order of 2.0. The preceding hydrodesulfurizing step prepares the material for reforming by removing sulfur, which would interfere with the activity of the catalyst in this preferential isomerization-aromatization reaction.

EXTRACTION The reformed stream is then passed into preferably an S0 extraction zone wherein the extraction is carried out. 'For S0 the extraction must be carried out under critical conditions in order to minimize the amount of aromatics remaining in the rafiinate stream. The maximum temperature in the extraction tower may range from about 50 F. to about F., but is preferably maintained at about 65 F. A temperature gradient in the extraction tower of from about 40 F. to about 100 F. may be used, while a solvent-to-hydrocarbon ratio within the range from about 9:10 to about 2:1 volumes of solvent per volume of hydrogen may be used. By practicing the extraction step with sulfur dioxide under these conditions, a raflinate may be obtained which contains less than 3% aromatic hydrocarbon. Ammonia and phenol may be used instead of S0 extraction, but the same general temperature limits will apply.

DISTILLATION The raifinate is then submitted to after-fractionation in order to remove polymeric high-boiling materials formed in the hydrodesulfurization and/ or reforming steps, that is, those hydrocarbons which boil above about 480 F. to 500 F. This high-boiling material is deleterious because directionally it has an adverse effect on freeze point, heat content and luminometer number. It is also likely to reduce thermal stability.

The material boiling below 480 F. to 500 F. is then removed as a product suitable for the finishing steps.

HYDROFINING The fractionated hydrocarbon is then passed to a hydrofining unit where it is contacted with hydrogen and a hydrofining catalyst such as extruded or pilled cobalt molybdate. The hydrofining step reduces the olefinic content and removes sulfur, nitrogen and polar compounds. This step is carried out at a temperature within the range from about 575 F. to about 650 F., a pressure of 250 to 350 p.s.i.g., a liquid hydrocarbon space velocity of 1.0 to 4.0 volumes of hydrocarbon per volume of catalyst per hour, and a hydrogen-to-hydrocarbon feed ratio of 500 to 1500 s.c.f./bbl. (based on pure hydrogen). The hydrofined hydrocarbon is essentially free of olefins and aromatics, but may still contain trace amounts of each component.

ABSORPTION The hydrofined fuel is then passed over an adsorbent bed having an afiinity for polar compounds, such as activated charcoal, at a treat ratio of 0.5 to 4.0 v./v./hr., whereby a thermally stable jet fuel boiling within the range of about 400 F. to 500 F. is obtained, having a heat of combustion of at least 18,900 B.t.u./lb., and otherwise meeting the specifications above set forth. A

The adsorption step removes traces of polar compounds from the fuel.

As an example of the present invention, a run utiliz ing Panhandle crude was made, and the processing sequence above set forth was generally followed. A crude fraction boiling within the range of 355 F. to 510 F. was submitted to hydrodesulfurization. The sulfur content was reduced from 1400 p.p.m. to about 50 p.p.m. by contacting the stream with 260 s.c.f. per barrel of 5 hydrogen over a cobalt molybdate catalyst at 658 F. and 255 p.s.i.g.

The hydrodesulfurized product was catalytically reformed over a platinum-on-alumina catalyst at 825 F. and 270 p.s.i.g. in the presence of 3200 s.c.f. per barrel of hydrogen and at a space velocity of 0.4 v./v./ hr.

The feed rate, was 0.4 v./v./hr. with the reactor inlet temperature 825 F. with an 85 F. temperature drop across the reactor. The hydrogen rate was 3500 s.c.f. per barrel of feed, with a pressure of 280 p.s.i.g. Conversion of naphthenes to aromatics was approximately 60% to 75% complete, with liquid yield being over 95%. The ratio of isoto normal paraffins in the product exceeded 2.0.

The reformate was then charged to an S extraction unit at a feed rate of 3200 barrels per day, to provide an S0 treat of 180%. The temperature at the bottom of the mixer tower was 15 F. to 25 F., while that at the tower top was 65 F. The aromatics content of the rafiinate obtained under these conditions was indicated to be essentially 0%. The accuracy of the testing method indicated that less than 0.5% aromatics remained.

The S0 Iaflinate was then caustic washed with 0.02 pound of NaOH per barrel of rafiinate, to 0.10 pound per barrel. The caustic washed material was hydrofined over cobalt molybdate catalyst at 615 F. to 625 F. and 300 p.s.i.g. pressure in order to saturate the 0.5 to 1% of olefins which remained in the fuel. The front end was adjusted by fractionation at the hydrofining unit.

The hydrofined fuel was then caustic washed with 30 Baum NaOH, and passed over an activated charcoal bed at about 3 v./v./hr. in order to maximize thermal sta bility. The product obtained is a fuel which boils within the range of 375 F. to 495 F. and has an Engler 20% point of about 410 F. The fuel meets all specifications of the Mach-3 jet fuel.

An analysis of the product is set forth below in Table 1H.

TABLE HI Gravity, APT 52.5 Distillation, ASTM:

IBP, F. 395 PB? 489 5% 404 406 411 416 421 427 480 Luminometer Number 117 Freeze point, F --46 Heat content, B.t.u./lb. net 18,919 Aromatics, vol. percent 0.8 lsoparaflins 59.8 Normal paraflins 28.0 Naphthenes 11.4

It was thus seen that applicants have provided a novel combination of processing steps which leads to the production of a highly useful supersonic jet fuel. The various steps must be accomplished in the order given, with the exception of the distillation step after extraction, which may be accomplished either before hydrofining or after hydrofining, but before adsorption over a polar adsorbent.

.Applicants having set forth in detail the essence of their invention, and having illustrated and set forth the best mode thereof, what is intended to be covered by Letters Patent should be limited not by the specific example given, but rather by the appended claims.

. 0 We claim: 1. A process of making a jet fuel which comprises: fractionating a parafiinic crude oil stream to obtain a charge stream boiling Within the range of 355 F.

' to 510 F.;

contacting said charge stream with hydrogen and a hydrodesulfurization catalyst under hydrodesulfurization conditions to obtain a desulfurized stream containing less than 0.01% sulfur by Weight;

contacting said desulfurized stream with hydrogen and a reforming catalyst at a temperature from 825 F. to 900 F, a pressure from 150 p.s.i.g. to 450 p.s.i.g., and a space velocity from 0.2 to 2.0 v./v./hr., whereby naphthene aromatization and normal parafiin isomerization are maximized in obtaining a reformed stream; extracting substantially all of the aromatic hydrocarbons from said reformed stream by contact with a solvent for aromatic hydrocarbons to obtain a rafiinate containing less than 3% aromatic hydrocarbons;

hydrofining said railinate by contact with hydrogen and a hydrofining catalyst under hydrofining conditions to obtain a hydrofined product; and

contacting said hydrofined product with an adsorbent for polar compounds to obtain a thermally stable jet fuel;

said jet fuel being subjected to at least one fractionation step during the course of said process whereby the Engler distillation 20% point thereof is within the range of 408 F. to 414 F. and the fuel boils within the range of 375 F. to 495 F.

2. A process in accordance with claim 1 wherein the hydrodesulfurization catalyst is cobalt molybdate, and said hydrodesulfurization conditions comprise a temperature within the range of 600 F. to 690 F., a pressure within the range from 150 p.s.i.g. to 300 p.s.i.g., and a space velocity of 2 to 4 v./v./h1'.

3. A process in accordance with claim 1 wherein said reforming catalyst is platinum on alumina.

4. A process in accordance with claim 1 wherein the solvent for aromatic hydrocarbons is chosen from the group consisting of S0 N11 and phenol.

5. A process in accordance with claim 1 wherein the solvent for aromatic hydrocarbons is S0 and the extraction is accomplished at a solvent-to-hydrocarbon ratio from 9:10 to 2:1 in an extraction zone at a maximum temperature from 50 F. to F. and a maximum temperature gradient across said Zone from 40 F. to 100 F.

6. A method in accordance with claim 2 wherein the reforming catalyst is platinum on alumina.

'7. A method as in claim 6 wherein the solvent for aromatic hydrocarbons is S0 and the extraction is accomplished at a solvent-to-hydrocarbon ratio of from 9:10 to 2:1 in an extraction zone at a maximum temperature from 50 F. to 100 F. and a maximum temperature gradient across said zone from 40 F. to 100 F.

8. A method as in claim '6 wherein the hydrofining catalyst is cobalt molybdate, and said hydrofining conditions comprise a temperature from 575 F. to 650 F a pressure from 250 p.s.i.g. to 350 p.s.i.g., a space velocity from 1.0 to 4.0 v./v./hr., and a hydrogen-to-hydrocarbon ratio from 500 to 1500 s.c.f./bbl.

9. A process of making a jet fuel which comprises:

fractionating a parafi'inic crude oil stream to obtain a charge stream boiling within the range of 355 F. to 510 F. and comprising from 30 to 50% normal parafiins, from 10 to 40% isoparaflins, from 40 to 60% aromatic and naphthenic hydrocarbons, and from 0 to 5% olefins;

contacting said charge stream with from 200 to 600 s.c.f. of hydrogen per barrel of charge stream in the presence of a cobalt molybdate hydrodesulfurization catalyst, at a temperature from 600 F. to 690 F., a pressure of p.s.i.g. to 300 p.s.i.g., and a space velocity of 2 to 4 v./v./hr., whereby there is obtained a desulfurized stream containing less than 0.01% sulfur;

contacting said desulfurized stream with from 2000 to 7000 s.c.f. of hydrogen per barrel of desulfurized stream in the presence of platinum on alumina reforming catalyst, at a temperature from 825 F. to 900 F., a pressure from 150 p.s.i.g. to 450 p.s.i.g., and a space velocity from 0.2 to 2.0 v./v./hr., whereby naphthene aromatization and normal paratfin isomerization are maximized in obtaining a reformed stream;

extracting substantially all of the aromatic hydrocarbons from said reformed stream by contact with from 0.9 to 2.0 volumes of S per volume of reformed stream in an extraction zone at a maximum temperature from 50 F. to 100 F. and a temperature gradient across said zone of 40 F. to 100 F where by there is obtained a rafiinate containing less than 3% aromatic hydrocarbons;

fractionating said raifinate to obtain a rafiinate fraction boiling below 480 F.;

hydrofining said raflinate fraction by contact with a cobalt molybdate hydrofining catalyst and from 500 to 1500 s.c.f. of hydrogen per barrel of raffinate fraction at a temperature from 575 F. to 650 F., a pressure from 250 p.s.i.g. to 350 p.s.i.g., and a liquid hydrocarbon space velocity of 1.0 to 4.0 v./v./hr., whereby an essentially olefinand aromatic hydrocarbon-free hydrofined product is obtained;

fractionating said hydrofined product to obtain a hydrofined fraction boiling below 480 F. and having an Engler distillation 20% point of 410 F. to 414 F.; and

contacting said hydrofined fraction with activated charcoal at a space velocity of 0.5 to 4.0 v./v./hr.,

whereby there is obtained a jet fuel having a luminorneter number of at least 100, a heat of combustion of at least 18,900 B.t.u./lb., a maximum viscosity at F. of 15 centistokes, and a maximum freezing point of F.

References Cited by the Examiner UNITED STATES PATENTS 2,478,916 8/49 Haensel et al 208-138 2,691,623 10/54 Hartley 208-138 3,001,932 9/61 Pietsch 208211 3,012,961 12/61 Weisz 260667 3,077,733 2/63 Axe et al 260667 3,125,503 3/64 Kerr et a1 208143 25 ALPHONSO D. SULLIVAN, Primary Examiner.

Claims (1)

1. A PROCESS OF MAKING A JET FUEL WHICH COMPRISES: FRACTIONATING FRACTIONATING A PARAFFINIC CRUDE OIL STREAM TO OBTAIN A CHARGE STREAM BOILING WITHIN THE RANGE OF 355*F. TO 510*F.; CONTACTING SAID CHARGE STREAM WITH HYDROGEN AND A DHYDODESULFURIZATION CATALYST UNDER HYDRODESULFURIZATION CONDITIONS TO OBTAIN A DESULFURIZED STREAM CONTAINING LESS THAN 0.01% SULFUR BY WEIGHT; CONTACTING SAID DESULFURIZED STREAM WITH HYDROGEN AND A REFORMING CATALYST AT A TEMPERATURE FROM 825*F. TO 900*F., A PRESSURE FROM 150 P.S.I.G. TO 450 P.S.I.G., AND A SPACE VELOCITY FROM 0.2 TO 2.0 V./V./HR., WHEREBY NAPHTHENE AROMATIZATION AND NORMAL PARAFFIN ISOMERIZATION ARE MAXIMIZED IN OBTAINING A REFORMED STREAM; EXTRACTING SUBSTANTIALLY ALL OF THE AROMATIC HYDROCARBONS FROM SAID REFORMED STREAM BY CONTACT WITH A SOLVENT FOR AROMATIC HYDROCARBONS TO OBTAIN A RAFFINATE CONTAINING LESS THAN 3% AROMATIC HYDROCARBONS; HYDROFINING SAID RAFFINATE BY CONTACT WITH HYDROGEN AND A HYDROFINING CATALYST UNDER HYDROFINING CONDITIONS TO OBTAIN A HYDROFINED PRODUCT; AND CONTACTING SAID HYDROFINED PRODUCT WITH AN ADSORBENT FOR POLAR COMPOUNDS TO OBTAIN A THEREMALLY STABLE JET FUEL;

Images