US3436336A

US3436336A - Process for preparing low freeze point hydrocarbon fuels

Info

Publication number: US3436336A
Application number: US643924A
Authority: US
Inventors: Henry R Ireland
Original assignee: Mobil Oil Corp
Current assignee: ExxonMobil Oil Corp
Priority date: 1967-06-06
Filing date: 1967-06-06
Publication date: 1969-04-01
Anticipated expiration: 1986-04-01

Description

Luminometer Number (LN) April 1969 H. R. IRELAND 3,436,336

PROCESS FOR PREPARING LOW FREEZE POINT HYDROCARBON FUELS Filed June 6, 1967 Sheet of 2 EFFECT of AROMATIC CONTENT 0n l .N. of KEROSINE 0% Aromatics 9o 5/ Aromatics 8O 7O IO? Aroma'ncs l5% Aromahcs I v 1 I 24/ Aromatics 5O T A. Jet A; & A 1

Speclflcaflons 4O Aromaflcs 3O I l/ I 7/ 2O 3O 4O 5O 6O 7O 8O 9O Paraffin Content, Vol 7 lA/I/E/VTOH Henry/i. /re FIQUfI By v (I April 1, 1969 Filed June 6, 1967 H. R. IRELAND 3,436,336

PROCESS FOR PREPARING LOW FREEZE POINT HYDROCARBON FUELS Sheet 2 0192 ESTIMATION of JET FUEL FREEZE POINT from 370 5IO F. WEST TEXAS DATA n araffin Line F 40 3020 :0 o -lo -5o -7o I9 20 2| 22 25 26 Reciprocal Freeze Point, 1/ FPX I0: R

lA/VE/VTOR F i g u re Henry R. lre/ond Age/7f United States Patent I 3,436,336 PROCESS FOR PREPARING LOW FREEZE POINT HYDROCARBON FUELS Henry R. Ireland, West Deptford Township, Gloucester County, N.J., assignor to Mobil Oil Corporation, a corporation of New York Filed June 6, 1967, Ser. No. 643,924 Int. Cl. Cg 39/00, 23/04 US. Cl. 208-66 1 Claim ABSTRACT OF THE DISCLOSURE Hydrocarbon fuels, particularly jet fuels, are prepared by catalytically isomerizing paraffin rich, kerosine hydrocarbon fractions to form isomerates and catalytically hydrogenating the entire isomerate. Kerosine hydrocarbon fractions containing excessive sulfur, nitrogen, arsenic and/or lead are pretreated catalytically with hydrogen before isomerization.

This invention has to do with a method and process for the preparation of hydrocarbon fuel compositions. More specifically, the invention relates to a method and process for converting relatively high boiling hydrocarbon feed stock materials boiling in the range of kerosene type jet fuels and light gas oils to products rich in parafiins and having low freeze points together with desirable heating value.

Jet fuels have been prepared by a variety of processes. Generally, however, considerable loss of charge material must be accepted in order that products of specification grade can be produced. While jet fuels of requisite heating value can be so produced, the fuels invariably have undesirably high freeze points, thus necessitating incorporation of freeze point depressants (such as isoparafiin alkylates) into the products. Correspondingly, jet fuels of low freeze point have been formed but at the sacrifice of substantial quantities of the charge materials from which they are derived, to undesired products such as gases and light cracked products 5- 8)- The present invention, therefore, is directed to a method and process for overcoming one or more of such shortcomings of prior practices.

DEFINITIONS It is to be understood that several terms used in defining and describing the invention have the meanings given directly below:

Freeze point is the temperature (Fahrenheit scale) at which a hydrocarbon fraction freezes as determined by ASTM Method D2386.

Luminometer number is a measure of fuel burning characteristics as determined by ASTM Description D1740.

Heating value denotes the net heat of combustion in British thermal units per pound of a fuel burned and determined in accordance With ASTM Method D1405.

Jet Fuels are kerosine boiling range hydrocarbon ice mixtures having properties such as given in the following typical ASTM specification D1655:

DRAWINGS Illustration of the invention is also provided with reference being made to the accompanying drawings, wherein:

FIGURE I presents a group of curves showing the effect of aromatic concentration in relation to luminometer number and parafiin concentration of kerosine-s.

FIGURE II presents a curve showing a relationship of freeze point with concentration of high freeze point components such as n-paraffins.

INVENTION In accordance with the present invention, there is provided a process for preparing a jet fuel having a freeze point below about 40 F. and a heating value in excess of about 18,400 Btu/pound, which comprises:

(1) Catalytically isomerizing a paraflin rich, kerosine boiling range hydrocarbon fraction having a freeze point of said jet fuel, having less than about 300 parts per million (p.p.m.) of sulfur, less than 10 parts per million of nitrogen, by contracting said fraction in the presence of hydrogen with a catalyst comprising between about 0.1 and about 2 percent by weight of a metal of the platinum series supported upon an alumina carrier and including up to about 2 percent by weight of chloride ion or fluoride ion, to form an isomerate, and

(2) Catalytically hydrogenating the isomerate of (1) by contacting it directly in the presence of hydrogen with a catalyst comprising a noble metal supported upon a carrier.

A particular embodiment of the invention involves use of such kerosine boiling range charge fractions having an undesirably high concentration of nitrogen or sulfur. In this embodiment, the fraction is first treated catalytically with hydrogen under conditions of temperature and space velocity selected to retain at least about percent by volume of the paraffin constituents of the charge fraction, to form a decontaminated charge fraction, which is then isomerized catalytically under the conditions defined above in (l) and the resulting isomerate is directly subjected to the catalytic hydrogenation defined above in (2).

PARAFFIN RICH, KEROSINE BOILING RANGE HYDROCARBON FRACTIONS Charge stocks for the process contemplated herein are composed substantially of hydrocarbon mixtures boiling in the range of from about 300 F. up to about 600 F., and

West Texas Mld-Contlnent Barco I Wt. v01. Wt. v01. Wt. v01.

Paraffins 30. 9 42. 7 42. 4 v 45. 1 58. 6 61.0 Naphthenes 43. 1 42. 1 43. 4 42. 33. 2 31. 8 Aromatics 17. 0 15.2 14. 3 12. 9 8. 2 7. 1

Fractions containing a relatively high concentration of sulfur as an impurity are treated catalytically with hydrogen to reduce the sulfur concentration below about 100 p.p.m., and preferably below about 40 p.p.m. and usually less than about 20 p.p.m. Correspondingly, when the charge fractions contain a concentration of nitrogen substantially in excess of 10 p.p.m., the fractions are so treated catalytically to reduce substantially the nitrogen content thereof to a low value which is usually less than about 10 p.p.m. and preferably less than 2 p.p.m. It is also desirable to efiect substantially complete removal of other undesirable impurities, such as arsenic and lead, in one or more of such catalytic steps.

For example, a virgin kerosine fraction, 375-500 F., and obtained from a Mi-d-Continent crude can contain a concentration of sulfur up to about 1700 p.p.m.; a virgin kerosine fraction, 375-500 F., obtained from Barco crude can contain up to about 700 p.p.m.; and a similar boiling range kerosine fraction obtained from a West Texas sweet crude can contain up to about 350 p.p.m. of sulfur. These charge fractions are subjected therefore to a suitable catalytic treatment with hydrogen to reduce the sulfur to not more than 100 p.p.m. and preferably less than 20 p.p.m. and any nitrogen constituents to not more than about 10 p.p.m. and preferably less than 2 p.p.m.

Kerosine fractions having desirably low concentrations of sulfur or nitrogen, need not be subjected to the catalytic treatment with hydrogen mentioned above. Representative of such fractions is a West Texas Bright Kerosine having a sulfur content of 220 p.p.m. and less than 2 p.p.m. of nitrogen.

CATALYTIC DECONTAMINATION OPERATION As indicated when a charge fraction contains an undesirable concentration of any one or more of sulfur, nitrogen, arsenic and lead, it is contacted with a catalyst in the presence of hydrogen to remove a substantial proportion of one or more of such contaminants. To accomplish this, the charge fraction can be subjected to hydrodesulfurization and hydrodenitrogenation conditions by contact with a suitable catalyst. Conventional catalysts can be employed, notably cobalt molybdate on alumina, nickeltungsten sulfide, and chromia on alumina. Arsenic and lead are removed simultaneously in this treatment.

Treatment of the charge fractions to remove sulfur and nitrogen compounds therefrom can be accomplished particularly by contact with a cobalt molybdate catalyst within the following ranges of operating conditions:

Hydrogen circulation rate, s.c.f./barrel of charge fraction 190-3000 Operating conditions for this treatment are selected so as to retain at least about 95 percent by volume of the parafiin constituents of the charge fraction. The etfiuent from this treatment is stripped free of hydrogen sulfide and/ or ammonia, as in a conventional distillation tower, before it is isomerized catalytically.

CATALYTIC ISOMERIZATION A kerosine boiling range fraction suitable for use directly in a catalytic isomerization step or one which has been treated catalytically with hydrogen as explained above, is subjected to a catalytic isomerization under conditions such that a relatively high percentage, at least about 70%, of the charge paraffins are retained. In some instances, an increase in paraffin concentration is realized.

By correlating operating conditions for the isomerization, an isomerate composed of hydrocarbons boiling substantially in the same range is obtained, while maintaining a relatively high concentration of charge paraffins and while reducing substantially the naphthene concentration. Although some cracking of paraflins may occur in the isomerization step, operating conditions are so selected that a desired parafiin concentration is maintained, possibly as a result of conversion of some ring compounds in the charge to paraflins of corresponding carbon atoms content boiling in the range of the charge.

With respect to conservation or retention of the parafiin concentration of the charge fraction (including a decontaminated charge fraction), it is intended that some variance can occur. The extent of the variance is dependent upon facts including the particular combination of operating conditions employed for isomerization, the desired freeze point of the jet fuel to be produced, the particular charge fraction employed, and other characteristics. It is intended, therefore, to include production of isomerates having at least about 70 percent retention of the paraffinic concentration of the charge fraction; preferred, however, are such concentrations of the order of -95 percent.

Catalysts suitable for the isomerization operation include the metals of the platinum series on a suitable carrier such as alumina, and promoted with a halogen promoter. Preferably, platinum is employed as a metal for the catalyst, and the carrier should have a relatively low cracking activity, particularly causing less than about 15 percent by volume of the isomerization charge to crack to hydrocarbons of lower molecular weight.

The catalyst can contain from about 0.1 up to about 2 percent of platinum on alumina (e.g., eta alumina) or a low activity silica-alumina base. The halogen promoter, as halide ion, is either chlorine or fluorine in an amount of up to about 2 percent; preferred concentrations are less than about 1 percent.

A particularly suitable catalyst comprises about 0.6 percent by weight of platinum on activated alumina containing about 0.55 percent by weight of chloride ion. This is a commercial catalyst, RD of Baker Sinclair.

In contrast to the effectiveness of the catalysts defined above, other catalysts recommended as catalysts for isomerizing hydrocarbons are unsuitable for use in the present process. This is demonstrated hereinafter with the following typical catalysts:

Compartive catalyst 1 is a decationized Type Y molec ular sieve containing palladium. Comparative catalyst 2 is a partially decationized, partially manganese exchanged Type Y molecular sieve containing palladium. Each catalyst was treated with hydrogen before contacted with hydrocarbon feed, following directions of the manufacturer. Chemical properties of such comparative catalysts are given below:

l5. Pd, wt. percent 0. 5=|=0.02 0. 5;!=0.02

Isomerization conditions employed are selected from the following approximate ranges:

CATALYTIC HYDROGENATION The isomerate obtained as described above is charged to a suitable hydrogenation vessel. No intermediate distillation or treatment need be applied to the isomerate efiluent. This is advantageous in that no loss of paraflin component can occur.

Hydrogenation catalysts employed for contact with an isomerate in the presence of hydrogen include any type of catalyst having hydrogenation and dehydrogenation properties. Such catalysts are well known in the art The catalysts include oxides and sulfides of any metal of Group VI A of Mendeleeffs Periodic Table, or mixture thereof, typical of which are: chromium sulfide, molybdenum sulfide and tungsten sulfide. Others include oxides and sulfides of Group VIII of said Periodic Table or mixture thereof, as illustrated by: the sulfides of iron, cobalt, nickel, palladium, platinum, rhodium, osmium and iridium. Still other catalysts include mixtures of the above oxides and sulfides of the metals of Group VI A and VIII of said Periodic Table, typified by mixtures of: nickel sulfide and tungsten sulfide; cobalt sulfide and molybdenum sulfide; and nickel sulfide and molybdenum sulfide. These metals can be deposited upon adsorbent carriers such as alumina, silica-alumina and silica-zirconia. The catalyst should have substantially no cracking activity; generally, less than about percent by volume of the isomerate is cracked when in contact with such catalysts.

Preferred catalysts include those comprising at least one of the metals mentioned above, deposited upon a composite-like oxide of at least 2 of the metals of Groups III B, IV A and IV B of said Periodic Table. Additional preferred catalysts include a sulfided or unsulfided 1-8 weight percent cobalt oxide and 3-20 weight percent molybdenum trioxide on a silica-alumina or silica-zirconia base containing silica in amounts of from about 5 to about 95 weight percent.

Catalysts comprised of such metals associated with molecular sieves of selected activity can also be employed. Such catalysts are typified by those described in US. Patent No. 3,173,854.

As mentioned above, the catalysts and the carriers therefor should have little or no cracking activity. By employing such catalysts with or without such carriers, substantial cracking of parafiinic components of an isomerate is avoided or minimized. Thus, there is substantial retention of desired parafiinic components.

Pure hydrogen can be used. However, hydrogen of low purity obtained by recycle or other hydrogenating process can be used, but it is recommended that the recycle hydrogen be subjected to purification to remove some of the undesirable impurities such as water, sulfur compounds, methane and the like. The hydrogen can be circulated at a. rate in the range of from about 2000 to about 15,000 standard cubic feet (s.c.f.) per barrel of isomerate charge, and preferably 5000-7000 s.c.f./barrel of isomerate. Hydrogen consumption is generally less than about 1000, and preferably less than 500 s.c.f./barrel of isomerate.

Isomerate charge is contacted with hydrogen and a hydrogenation catalyst of the character described above, under the following approximate conditions:

Broad Preferred Temperature, F 600-700 650-650 Hydrogen Pressure p.s.l 400-1, 200 400-700 Space Velocity, LH'sv 0. 5-10 r-a Hg/lsomerate, s.c.L/bbl 2, 000-15, 000 5, 000-7, 000

The hydrogen contact can be carried out in any suitable equipment for catalytic operations. The contact can be operated batchwise. It is preferable, however, and generally more feasible to operate continuously. Accordingly, the process is adapted for operations using a fixed bed of catalyst. The process can be operated using a moving bed of catalyst wherein the hydrocarbon flow can be concurrent or countercurrent to the catalyst flow. A fluid type of operation wherein the catalyst is carried in suspension in the hydrocarbon charge can be employed.

In the contact with hydrogen, reaction conditions of temperature, pressure, space velocity and type of catalyst can be controlled such that there is substantially no conversion of the isomerate.

Following hydrogen contact, products are withdrawn from a suitable reactor and are then passed through a heat exchanger or other suitable cooling device, wherein they are cooled to temperatures at which hydrogen gas can be separated. The cooled efiluent is then passed into gas separators. Gases, primarily H are removed, and can be recycled to the isomerization or hydrogenation operations. Liquid product can be taken from the gas separators to a stripper or fractionator to remove a relatively small amount of naphtha and any light products (e.g. C and lower).

ILLUSTRATIVE EXAMPLES The following examples illustrate, and in no sense, limit the invention.

Example 1 A West Texas Bright Kerosine was treated as described below. The kerosine charge had the following properties:

Gravity, API 46.8 Boiling range, F. 370-522 Freeze point, F. 23 Aromatics+olefiins, percent vol. 8.2 Aniline point, F. 164.2 Luminometer No. (L.N.) 72 Heating value, B.t.u./lb. 18,725 Sulfur, p.p.m. 220 Nitrogen, p.p.m. 2

. TABLEI Operations (Charge) Pretreat Isomerization Hydrogenation Conditions:

Temp, F 700 800 550 550 550 600 610 Press, p.s.i.g 600 400 400 400 500 600 500 HSV 1. 1.5 1 2 2 2 3.5 11., s.c.f. lbbl 3,000 -6, 6,000 6,000 6,000 6,000 6,000 "370-525" F. Product 7 Yield, Vol.Percent 95 so 7 90 91 00 90 370525 F. Product (Charge) Pretreated Isomerate Jet Fuels I Properties Product Gravity, API....- v 6.8) 46.4 43.5 -40.8 46.0 46.9 467 45.9 Freeze Point, F (23) -20 -49 -50 40 44 -53 40 Arom.+0l., V01. Percen (8.2) 7.2 30.2 11.2 16.1 3.0 11.6 17.0 Anil.Pt.,F (164.2) 166.0 132.0 160 152.0 101.5 158.5 152.0 65 30 67 57 1 (71) e7 1 50 Heating Val B t.u./lb. 18,730 18,520 18,700 18,650 18,730 18,730 18,670 Sulfur, p.p.m 13 Nitrogen, p.p.m 1 1 Values estimated from Figure I.

. 1 TABLE 3 Example 2 I I No Pretreat The West Texas Bright Stock described 1n Example Operation (Charge) I 1 is isomerized without any prior pretreat with hydrogen, smemam Hydmgemtm and the resulting isomerate is hydrogenated dlrectly. 00 1 1021115: F 80 Typical results are shown in Table 2 below. g 2g? 233 1 I 2 6.000 6,000 6,000

Yield,tVol 9 percen 0 90 90 TABLE 2 a7%-525" Product 0 91' 88; Operation (Charge) Isomerization Hydrogenation :gg yrto lg kg; Z2 41 6 reeze -44 fil ig 800 600 Aron1.+0l., v01.

S {,2 500 500 percent. (8. 34. 9 17. 3 22. 7 His; 1 2 Anil. Pt., F (168.2) 129.5 160.0 147.3 f J55 ,000 ,000 370-525 F. Product Heating value y v p t 70 90+ -l (18.700) 18.460 18.660 18.580 370-525 F. Product 8 API (46 s) 37 7 44 h E t at an Fi I. Freeze Point. (23) 76 --70 g f f h 2" 2% 40 The results shown in'Table 3 reveal that the sulfur 72) 10 08 content of the kerosine charge is undesirably high such (18 730) 18 300 18,660 that it should be pretreated before'isomerization. The 220) excessive sulfur suppresses hydrogenation in the hydro- (2) genation operation, with the result that the hydrogenated Comparative Example A An Amal-Nafoora (Libyan) Kerosine having the following properties was processed in the manner described in Examples 1 and 2. The catalyst employed were those described in Example 1. Results are shown in Table 3 product has a relatively high aromatic content and a corresponding low L.N. value.

Comparative Example B 4 following, such data bei ng obtained with the West Texas Bright Kerosine earlier described in Examples 1 below, and 2.

TABLE 4 Isomerlzation Operation (Charge) Pretreat Catalyst 1 Catalyst 2 Conditions:

Temp., F 700 550 525 525 425 500 Press., p.s.l.g- 600 500 500 700 500 500 SV.--.. 2 1 1 1.9 1 9.9 H:,s.o.(.lbb1 3,000 5,240 5,180 0,000 0,000 0,050 370-525" F.

Percent 95 69 80 84 83 83 370-525 F. Product Gravity, API- 47. 1 49. 1 48. 1 48. 1 48.8 48. 1 Freeze Point, (23) -17 -14 14 15 -17 Atom. +01.,Vol. (8.2) 9.2 5.7 7.2 6.2 1.3 4.2

Percent.

L.N (72) V 84 74 He ating/Ealue, (18, 730) 18,680 18, 790 18,770 18,770 18, 810 18,880

1 Estimated.

From results shown in Examples 1, 2 and Comparative Example A, above, it is clear that hydrogenation alone causes an insignificant change, if any, in freeze point. Therefore, hydrogenation of the isomerates as shown in Comparative Example B does not affect the freeze point. Such products are unsuitable for use as jet fuels.

Referring now to FIGURE I, it will be noted that a higher L.N. characterizes a kerosine of lower aromatic content and higher paraffin content. FIGURE II shows a single straight line curve which establishes a relationship between concentration of n-paraffins in the product and the freeze point of the product. This relationship is particularly useful in identifying the process requirements for producing a jet fuel for reasons given below.

From FIGURE I is determined that, in order to produce a product of at least 70, the product must have at at least about 40% paraffins when as much as 5% aromatics are in the product. FIGURE II reveals that, in order to meet a -40 F. freeze point, a jet fuel product should not have substantially more than about 23 volume percent of n-paraflins. That is, the sum of the concentrations of low freeze point constituents such as isoparaffins and cycloparafiins must be at least about 77 volume percent so that when combined with the n-paraffin material, the final product will meet the 40 F. freeze point requirement. However, from FIGURE I it was determined that the parafiin concentration of the final product should be at least 40% and since only about 23 volume percent of this can be n-paraffins, it is essential that about 17 percent of the paraflins must be isoparaflins to meet the product requirements.

Having thus given a general description of the process and means of this invention and provided by way of example specific embodiments thereof, it is to be understood that no undue restrictions are to be imposed by reason thereof, and minor modifications may be made thereto without departing from the scope thereof.

What is claimed is:

1. A process for preparing a jet fuel having a freeze point below about -40 F. and a heating value in excess of about 18,400 B.t.u./pound, which comprises:

(l) contacting a paraflin rich, kerosine boiling range hydrocarbon fraction having a freeze point at least about 5 F. higher than the freeze point of said jet fuel, containing about 40 to weight percent paraflins, 20 to 50 weight percent naphthenes, 5 to 30 weight percent aromatics, and contaminated with at least one of sulfur and nitrogen, in the presence of hydrogen, with a catalyst suitable for hydrodesulfurization and hydrodenitrogenation under conditions of temperature and space velocity selected to retain at least about percent by Nolume of the parafiin constituents of the fraction, to form a decontaminated charge fraction,

(2) catalytically isomerizing the decontaminated charge fraction of (1) by contacting the decontaminated charge fraction at a temperature of about 750 F. to 850 F. in the presence of hydrogen with a catalyst comprising between about 0.1 and about 2 percent by weight of a metal of the platinum series supported upon an alumina carrier and including up to about 2 percent by weight of chloride ion or fluoride ion, to form an isomerate with conservation of parafiins, and

(3) catalytically hydrogenating the isomerate of (2) by contacting it directly in the presence of hydrogen with a catalyst having hydrogenation and dehydrogenation properties and substantially no cracking activity.

References Cited UNITED STATES PATENTS 3,012,961 12/1961 Weisz 208-15 3,328,289 6/1967 Streed 20815 FOREIGN PATENTS 870,474 6/1961 Great Britain.

HERBERT LEVINE, Primary Examiner.

US. Cl. X.R. 208-15, 89, 141, 143

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,436,336 April 1, 196

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:

Column 2, lines 32 and 33, "having a freeze point of said jet fuel" should read having a freeze point at least about 5 F. higher than the freeze point of said jet fuel Signed and sealed this 14th day of April 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR

Attesting Officer Commissioner of Patents