US3420769A - Isoparaffinic jet fuel - Google Patents

Description

Jan.7,l969

R. S. MANNE ISOPARAFFINIC JET FUEL Filed March 20, 1967 F R ACT ION ATION CRUDE HYDROGENATION SEPARATOR ISOMERIZ ATION FRACTIONATION INVENTOR.

RICHARD S.

MANNE,

ATTORNEY.

United States Patent 3,420,769 ISOPARAFFINIC JET FUEL Richard S. Manne, Baytown, Tex., assignor to Esso Research and Engineering Company Filed Mar. 20, 1967, Ser. No. 624,358 US. Cl. 20866 Int. Cl. Cg 39/00 8 Claims ABSTRACT OF THE DISCLOSURE A 400500 F. petroleum distillate is isomerized in contact with an isomerization catalyst without substantial hydrocracking, and is thereafter hydrogenated in contact with a hydrogenation catalyst to obtain a jet fuel low in aromatic hydrocarbons.

BACKGROUND OF THE INVENTION Field of the invention Description of the prior art Stocks for producing jet fuel of acceptable quality are in short supply. Quality objectives, particularly freeze point (possibly as low as -50 F. maximum) and luminometer number (approximately 50 minimum) make it difficult to produce acceptable jet fuel Without suffering substantial value losses in processing. For example, in US. Patent 3,012,961 (Class 208, Sub. 66) the patentee Weisz discloses a method of producing a jet fuel which is high in B.t.u./ gallon in a three-step process comprising (1) hydrocracking, (2) distillation, and (3) hydrogenation. Weisz selectively hydrocracks paraffinic hydrocarbons and removes the residue, leaving a liquid product boiling above 400 F. which is substantially 100 percent aromatic in nature (column 6, lines 1315). This aromatic fraction is then hydrogenated to produce a concentrate of decalins (column 8, line 1) as the jet fuel product. The present invention avoids the losses due to hydrocracking in the Weisz process by isomerizing rather than cracking the normal paraffins in the feedstock.

SUMMARY OF THE INVENTION able to retain them in the jet fuel if possible, rather than cracking them and removing the residue as in Weisz. The present invention allows the refiner to retain the paraflins in the fuel, with a concommitant increase in quality and with the added advantage of minimizing volumetric loss during processing.

BRIEF DESCRIPTION OF THE DRAWING The present invention may be understood by reference to the drawing which is a schematic diagram of the process.

A crude oil is introduced by way of line and fractionated in a fractionating tower 101 to provide a kerosene fraction 102 which is the feedstock to the present process. This kerosene fraction is transferred by way of line 102, admixed with hydrogen introduced by way of line 104, and heated by Way of the furnace 106 before introduction by way of line 108 into an isomerization zone 110. In the isomerization zone 110 the n-paraffinic constituents in the kerosene are isomerized into isoparaffins, under conditions chosen to minimize the hydrocracking activity of the catalyst so that the final product does not suffer more than about a 10% loss of the n-paraffins due to cracking. The efiluent from the isomerization zone is transferred by way of line 112 into a separator 114, from whence hydrogen and noncondensable gases are removed by Way of line 116 while the liquid product is passed by Way of line 118, admixed with hydrogen which is introduced by way of line 120, and heated in the furnace 122 before introduction into the hydrogeneration zone 126 by way of line 124.

In the hydrogenation zone the aromatic hydrocarbons which are present in the kerosene fraction originally (as well as those which have been created by dehydrogenation of naphthenic constituents) are hydrogenated so that the resulting product contains less than 5% aromatic hydrocarbons, preferably less than 2%. The hydrogenated products are passed by way of line 128 into a separator 130 from whence hydrogen and noncondensable gases are removed by way of line 132 for suitable treatment and possible recycle, while the liquid constituents are removed by way of line 134 for fractionation if desired.

The hydrogenated product may be fractionated in a column so as to remove by way of line 142 the small amount of fragments from n-parafiins which have unavoidably been hydrocracked as an overhead lower boiling stream, while the final product is removed by way of line 144 as a superior jet fuel fraction.

DESCRIPTION OF THE PREFERRED EMBODIMENT There have been indications that shortages of kerosene and kerosene-type jet fuels might develop because of quality limitations, specifically freeze point and luminometer number (LN). If presently available, but quality deficient,

kerosene boiling range material could be upgraded to meet a goal of 50 F. maximum freeze point and 50 minimum LN, the shortage would be alleviated.

The upgrading of present stocks to meet the LN and freezing point requirement should preferably be done with a minimal loss of volume in the requisite treatment for such improvement. The LN can be improved by extraction to remove the aromatic, but this reduces substantially the volume of the hydrocarbon stream available as a jet fuel. Likewise, the n-parafiins can be removed from the kerosene range stocks, and the freezing point lowered, by contact with molecular sieves or cracking, but this again reduces the volume which is available as a jet fuel and deprives the resulting fuel of the even-burning characteristics which the paraffinic content can provide.

The present invention improves both the luminometer number and the freeze point characteristics of the kerosene range feedstocks by isomerizing the kerosene boiling range material without substantial hydrocracking, under conditions chosen to minimize cracking, and then subjecting the isomerized material to hydrogenation to saturate aromatic hydrocarbons. Unexpectedly, it has been found that the isomerization pretreatment enhances the susceptability of the materials to hydrogenation so that the aromatics content of the hydrogenated product can be substantially reduced under relatively mild conditions of hydrogenation. The use of mild hydrogenation is important in reducing the pressure specifications which must be met, thereby minimizing the cost of plant investment.

Kerosene feedstock The feedstock for the present process is a jet-quality deficient kerosene. The kerosene feedstock may suitably boil within the range of 300-550 F., and may contain from 20 to 50 volume precent naphthenes, from 20 to 50 volume percent aromatics, from to 30 volume percent n-parafiins, and from to 40 volume percent isoparafiins. An inspection of a representative kerosene feedstock is given below in Table I.

TABLE I.EXE1\IPLARY KEROSENE FEEDSTOCK Freeze, F. 32 RI, 25 C. 1.4696 n-Paraflins, percent 18 Isoparafiins, percent 23 Naphthenes, percent 29 Aromatics, percent 30 IBP, F. 366 10%, F. 404 F. 418 50%, F. 450 90%, F. 500 FBP, F. 530

By advertence to Table I, it is seen that a typical feedstock for use in the present invention has a luminometer number of 29, far below the 50 minimum which is required. Also, the freeze point of 32 F. is far too high as compared to the --50 F. minimum which is desired. As will be discussed hereinafter, the present invention allows the production of a jet fuel having a luminometer number of about 6080 and with a freeze point of about -55 to 60 F., while suffering only about a 5-15 volume percent loss in volume due to cracking during the isomerization step.

Isomerization The first step of the present invention is liquid phase isomerization, which may be suitably accomplished in contact with a catalyst such as platinum on alumina. Suitable catalysts will include metals of Group VI and Group VIII of the Periodic Table, their oxides and sulfides, which may be supported on materials such as alumina, natural or processed bauxite, kieselguhr, etc. When using platinum, 03-06% platinum on alumina is preferred. A halogen promoter may be employed, but is not essential.

The conditions of isomerization will depend upon the specific catalyst which is to be employed, but will be chosen to minimize the cracking activity of the catalyst so that isomerization of the n-paraffin can be accomplished without substantial losses due to cracking.

When using the preferred platinum-on-alumina catalyst, these conditions may include from 800 F. to 1000 F. (preferably 875 F.), a pressure of 150 to 500 psig. (preferably 300 p.s.i.g.), a liquid hourly spaced velocity (LHSV) from 0.2 to 2 v./v./hr. (preferably 1 to 1.5 v./v./hr.), and a hydrogen feed rate of from 2000 to 10,000 s.c.f./b. (preferably 5000 s.c.f./b.).

The conditions are chosen so as to obtain an isomerized product containing at least volume percent paraffinic hydro-carbons (at least 15% isoparaffins) while suffering no more than a 15 volume percent loss of the feedstock due to cracking of the paraffins into constituents which boil below the boiling range of the feedstock.

Hydrogenation The hydrogenation step may be accomplished in contact with a suitable hydrogenation catalyst, such as the platinum-on-alumina catalyst preferred for use in the isomerization zone. Other suitable catalysts may be chosen from the group consisting of nickel, cobalt and iron. These catalysts may be supported on materials such as alumina, silica, magnesia, kieselguhr, zirconia, etc.

For the preferred platinum-on-alumina catalyst, hydrogenation conditions will include a temperature from 400 to 800 F. (preferably 500 F.), a pressure from 200 to 2000 p.s.i.g. (preferably 800 p.s.i.g.), a liquid hourly space velocity (LHSV) from 0.3 to 3 v./v./hr. (preferably 0.5 v./v./hr.), and a hydrogen treat rate of from 500 to 10,000 s.c.f./b. (preferably 5000 s.c.f./b.).

The hydrogenation conditions are chosen to maximize hydrogenation of the aromatic constituents, some of which may have been formed during the isomerization step. The product from the hydrogenation should contain less than 5% aromatic hydrocarbons, preferably less than 2% (by volume), and will comprise at least 25 volume percent paraflinic hydrocarbons, including at least 15 volume percent isoparaffins. Thus, it is seen that all of the paraflinic hydrocarbons in the isomerized product remain in the hydrogenated product. The hydrogenated product boils within the range from 300 F. to 500 F.

In order to illustrate the present invention, a number of runs were made wherein the exemplary kerosene feedstock shown in Table I was first subjected to isomerization in contact with a 0.6% platinum-on-alumina catalyst, at 875 F., 300 p.s.i.g., v./v./hr., and 5000 s.c.f.b./b. This product was then hydrogenated in contact with 0.6% platinum-on-alumina catalyst, at 500 F., 900 -p.s.i.g., 0.5 v./v./hr., and 5000 s.c.f./b. of hydrogen. The results of this run are summarized below in Table II.

TABLE II.IMPROVEMENT OF LN AND FREEZE POINT Operating Conditions Isomerization Hydrogenation Catalyst 0.6% Platinum 0.6% Platinum on lumina. on Alumina. Temperature... 875 Pressure 300 p.s.i.g 900 p.s.i.g. Space velocity, LHSV... 1.25 v./v./hr 0.5 v./v./hr. Hydrogen rate 5,000 s.c.fJb 5,000 s.c.fJb.

Stream Data Feed Isom. Prod. Hydr. Prod.

LN 29. 2 13. 8 69. 7 Freeze Point, F 32 72 70 Hydrocarbon Analysis:

Isopara 22.8 28. 5 n-Parafl'ins 17. 1 8. 2 97. 5

By advertence to Table II it is seen that the luminometer number of the kerosene feedstock was increased from 29.2 in the feed to 69.7 in the hydrogenated product. The freeze point was improved from a 32 F. to -70 F. Note that this was accomplished by isomerizing the nparaflins in the feedstock, which were reduced from 17.1% to 8.2% while the isoparaffins increased from 22.8% to 28.5%. Note that the naphthenes in the feedstock were dehydrogenated in the isomerization zone to form aromatics, but that in the final hydrogenation product only 0.5 volume percent aromatics were present. Loss of feedstock was only about 5 volume percent. Thus, a superior jet fuel is produced in the two-step process.

In order to show that the hydrogenation susceptibility of the kerosene fraction was unexpectedly improved by the isomerization step, runs were made wherein the feedstock without isomerization was contacted with a platinum-on-alumina catalyst under hydrogenation conditions, and these results compared to the hydrogenation of the isomerized product, using the same feedstock for the isomerization step. The results of these runs are shown below in Table III.

TABLE III.IMPROVED HYDROGENATION By reference to Table III, it is seen that the raw feedstock contained 29.5% aromatic hydrocarbons, which was reduced by hydrogenation at the standard operating conditions to only 0.6 volume percent in Run I. The isomerized ieedstock into the hydrogenation zone in this case contained about 52% aromatic hydrocarbons, due to the dehydroaromatization activity in the isomerization zone. The hydrogenation accomplished in a reduction in aromatic hydrocarbons of about 92%. Comparing this with the hydrogenation of the untreated feedstock in Run II, it is seen that the product contained 25.5% aromatics. Compared to the feed stock (which contained only 29.5% aromatics) it is seen that the reduction in aromatic hydrocarbons without the isomerization step was only about The hydrogenation was carried out under the identical conditions employed in Run I. Thus, the enhancement of hydrogenation eflicacy is clear.

Attention is also directed to the fact that the hydrogenation step was carried out under 400 pounds pressure, at a temperature of only 500 F. These mild hydrogenation conditions allow the use of equipment in the hydrogenating units which is much less expensive than that which is required for operation at-900 pounds and at elevated temperatures. The distillation data presented on the raw feed and on the Run II product demonstrate that the product was corrected to essentially the same boiling range as the feed, This was done by the removal of 5 volume percent of the total reactor effluent by distillation. This 5% is the measure of the loss by cracking to lower than feed boiling range, since little if an gas is formed in the reaction.

Having disclosed in detail the essence of the present invention, and having given several specific examples thereof as preferred embodiments, what is desired to be protected by Letters Patent should be limited by the following claims.

I claim:

1. A method of producing a superior jet fuel which comprises sequentially (1) catalytically isomerizing a quality-deficient kerosene with-out hydrocracking more than 15 volume percent thereof into components boiling lower than said kerosene, to obtain an isomerized product containing at least 25 volume percent parafi'inic hydrocarbons including at least 15 volume percent isoparaffins, and thereafter (2) catalytically hydrogenating said isomerized product to obtain a hydrogenated product boiling within the range from 300 F. to 500 P. which contains less than 5 volume percent aromatics and contains all of said paraffinic hydrocarbons.

2. A method in accordance with claim 1 wherein both the isomerization step and the hydrogenation step are carried out in contact with platinum on alumina.

3. A method in accordance with claim 1 wherein said isomerization catalyst is platinum on alumina under liq mid phase isomerization conditions including a temperature from 800 to 1000 F.,

a pressure from to 500 p.s.i.g.,

a LHSV from 0.2 to 2.0 v./v./hr., and

a hydrogen feed rate from 2000 to 10,000 s.c.f./ b.

4. A method in accordance with claim 3 wherein said hydrogenation catalyst is platinum on alumina and said hydrogenation conditions include a temperature from 400 to 800 F.,

a pressure from 200 to 2000 p.s.i.g.,

a LHSV from 0.3 to 3 v./v./hr., and

a hydrogen feed rate from 5.00 to 10,000 s.c.f./ b.

5. A method in accordance with claim 4 wherein kerosene boils within the range of 300 to 500 F. and contains from 10 to 30 volume percent n-parafiins,

from 15 to 40 volume percent isoparaffins,

from 20 to 50 volume percent aromatics, and

from 20 to 50 volume percent naphthenes.

6. A method of producing a superior jet fuel which comprises in an isomerization zone, contacting a hydrocarbon mixture comprising 10 to 30 volume percent n-paraffins, 20 to 50 volume percent aromatics, and 20 to 50 volume percent naphthenes and boiling within the range from 300 to 550 F. with an isomerization catalyst chosen from the group consisting of the metals of Group VI and Group VIII of the Periodic Table, their oxides and sulfides, and admixtures thereof, under liquid phase isomerization conditions including a temperature from 800 to 1000 F., a pressure from 150 to 500 p.s.i.g., a space velocity from 0.2 to 2 v./v./hr., and a hydrogen rate from 2000 to 10,000 s.c.f./ b. said conditions being chosen to minimize hydrocracking so that not more than 15 volume percent of said hydrocarbon mixture is hydrocracked, whereby an isomerized product stream is obtained which contains at least 25 volume percent paraffinic hydrocarbons, including at least 15 volume percent is-oparafiins,

and, in a hydrogenation zone, contacting said isomerized product stream with a hydrogenation catalyst chosen from the group consisting of platinum, cobalt, and iron,

under liquid phase hydrogenation conditions including a temperature from 400 to 500 F.,

a pressure from 200 to 2000 p.s.i.g.,

a space velocity from 0.3 to 3 v./v./hr., and

a hydrogen treat rate from 500 to 10,000 s.c.f./b.

whereby a hydrogenated product is obtained boiling substantially within the range from 300 to 500 F. and comprising at least 25 volume percent paraffinic hydrocarbons,

including at least 15 volume percent isoparafiins,

and

less than 5 volume percent aromatics.

7. A method of producing a superior jet fuel which comprises sequentially subjecting a hydrocarbon stream boiling substantially within the range from 366 to 530 F. and containing [from 10 to 30 volume percent n-paratfins, from 20 to 50 volume percent aromatics, and from 20 to 50 volume percent naphthenes first to dehydroisomerization in contact with a platinumon-alumina catalyst at a temperature of about 875 F. a pressure of about 300 p.s.i.g., a LHSV from about 0.3 to about 3 v./v./hr., and hydrogen feed rate of about 5000 s.c.f./b.,

and then to hydrogenation in contact with a platinumon-alumina catalyst 7 and then to hydrogenation in contact with a platinumon-alumina catalyst at a temperature from 400 to 800 F., a pressure from about 200 to about 1000 psig. a LHSV from about 0.3 to about 3 v./v./hr., and

a hydrogen feed rate from about 500 to 10,000

s.c.f./b., to obtain a hydrogenated product boiling within the range from 356 to 530 F. and containing about 97.5 volume percent paraflrns and naphthenes, and about 0.5 volume percent aromatics. -8. A method in accordance with claim 7 wherein the hydrogenation conditions include a temperature of about 500 F.

References Cited UNITED STATES PATENTS 9/1961 Haney 208l44 12/1961 Weisz 20866 DELBERT E. GANTZ, Primary Examiner.

US. Cl. X.R.

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