US3308053A

US3308053A - Hydrocarbon production process

Info

Publication number: US3308053A
Application number: US426583A
Authority: US
Inventors: Joe T Kelly; Alan H Peterson; Glen C Templeman
Original assignee: Marathon Oil Co
Current assignee: Marathon Oil Co
Priority date: 1965-01-19
Filing date: 1965-01-19
Publication date: 1967-03-07
Anticipated expiration: 1984-03-07

Description

March 7, 1967 J. "r. KELLY ETAL 3,308,053

HYDROCARBON PRODUCTION PROCESS Filed Janv 19. 1965 Alkylafion 5 Reactor 6 Cracker WAXY GAS OIL Hydroisom. Reactor INVENTORS JOE T KELLY BY ALAN H. PETERSON GLEN CIEMPLEM N United StatesPatent P 3,308,053 HYDRQCAREGN PRODUCTIUN PRGCESS .loe T. Kelly and Alan H. Peterson, Littleton, Cola, and

Glen C. Templeman, Findlay, @hio, assignors to Marathan (iii Company, Findlay, Ohio, a corporation of (Thin Filed .lan. 19, 1965, Ser. No. 426,583 11 Claims. (Cl. 208-67) under certain conditions, hydroisomerization of substantially straight-chain olefins containing from about 12 to about 16 carbon atoms with branched chain saturated hydrocarbons having from 4 to about 6 carbon atoms in the molecule produces good yields of a hydrocarbon having an average of less than about 2 branches per molecule, useful as a jet engine fuel having low pour point, high thermal stability, and high heat of combustion per pound. This hydroisomerization can also produce a coproduct fraction which is useful as a component in high octane gasoline.

A particularly unexpected feature of the new hydroisomerization reaction is its ability to produce the desired approximately singly branched paraffinic hydrocarbons which are valuable as jet fuels when either normal or singly branched olefins are utilized as feed materials.

In the most preferred embodiment of the present invention, the olefin starting materials are obtained by the molecular cracking of a waxy gas oil boiling above 600 F., under moderate conditions, to form a fraction containing from about C through C olefins for hydroisomerization, a second fraction containing from about C through C olefins which is alkylated with branched chain saturated hydrocarbons to produce jet engine fuels, and a third fraction containing from about C through about C olefins which may be alkylated with isobutane or other low molecular weight isoparatfins to form a conventional alkylate gasoline. As a co-product where branched chain saturated hydrocarbons having from 4 to about 6 carbon atoms are utilized in the hydroisomerization reaction, an additional product component useful in the blending of high octane gasolines is obtained.

Thus the present invention in its most preferred embodiment permits the conversion of the low value waxy gas oil streams commonly found in petroleum refineries to produce highly valuable jet engine and piston engine fuels.

By waxy gas oil is meant any distillation cut boiling above about 600 F. of a virgin crude oil or refinery stream which contains an appreciable amount of parafiinic material. A particularly satisfactory waxy gas oil for the purposes of this invention is obtained by distillation of what are commonly called waxy crudes as opposed to less suitable asphaltic crudes.

The alkylation of isobutane with propylene, butylenes, and pentenes has long been a commercial process for producing high octane gasoline stocks. This reaction exemplified below, has been studied extensively:

The product of the alkylation is, of course, a mixture of isomers rather than a single product as illustrated above. The reaction is normally carried out in the pres- 33%,953 Patented. Mar. 7, 19.67

ence of concentrated sulfuric acid or anhydrous hydrofluoric acid with a large excess (3 to 10 molars of isobutane over olefins to suppress polymerization. The present invention in its most preferred embodiment makes use of the above described conventional alkylation process as one step in an integrated, coordinated series of reactions for the preparation of engine fuels from low valued, high boiling petroleum streams.

The hydroisomerization (hydrogen transfer) reactions utilized in the process of the present invention are typified by the reaction illustrated below:

As in the case of alkylation reactions, a variety of isomeric products are formed. However, a surprising degree of specificity for methyl undecanes and trimethylpentanes is exhibited by the above reaction.

The above reaction has been found to be general for isoparafiins including, among others: isobutane, isopentane, and isohexanes and for substantially straight-chain olefins, preferably alpha-olefins in the C -C range. The singly branched paraffin products are eminently suited for use as jet fuel for supersonic aircraft because of their good thermal stability, low freezing point, clean burning characteristics, and particularly because of their high heat of combustion per pound. When isobutane is used as the isoparaffin, the gasoline boiling range co-product is of excellent octane quality and similar in composition to a conventional isobutane-butylene alkylate. The number of carbon atoms in the preferred isoparaflin may be varied somewhat in order to compensate for variations in the average chain length of the C C fraction and to optimize the properties of the gasoline and jet fuel produced.

Pure normal alpha olefins are preferred as feed stocks for the present invention, but because they are more economically available, crude olefins which have been separated into the proper carbon number ranges by distillation will frequently be employed. The olefins need not be pure straight-chain (normal) olefins because, as a peculiar and valuable feature of the present invention, where a singly branched olefin is utilized in place of a preferred straight-chain olefin, the molecule will usually be singly branched. The reaction of the invention favors the formation of singly branched hydrocarbons whether or not the olefins used as raw materials are themselves branched. In general, it is preferred that the olefins have an average of less than two branches per molecule.

It is not absolutely necessary that the double bond in the olefins occur in the preferred alpha position or that the olefin feed stock being fed to the hydroisomerization reactor be composed entirely of unsaturated hydrocarbons. Substantial quantities of paraffinic hydrocarbons in the general jet fuel boiling range may be tolerated without serious interference with the hydroisomerization reaction. It is important, however, that the quantity of normal paraflins in the olefin feedstock not be sufiiciently high as to cause the fuel to have an unsatisfactorily high freezing point. Where necessary, excessive normal parrafiins may be removed in order to achieve a freezing point below about F., the preferred level for most jet fuels.

The hydroisomerization reaction of the present invention is preferably carried out in a reactor equipped for efiicient mixing and with means for removing heat. The

conditions employed are similar to those normally practiced in isobutane-butylene alkylation. The preferred acid catalyst is approximately 98% sulfuric acid but other concentrations of sulfuric acid, anhydrous hydrofluoric acid and other catalysts known to be useful for isobutane-butylene alkylation are useful in the hydroisomerization reactions. These latter catalysts include among others various aluminum chloride complexes and boron trifiuoride complexes. The catalyst to hydrocarbon volume ratio is preferably between 2:1 and 01:1 and most preferably from about 1:1 to :1. Smaller amounts of catalyst may be employed but the reaction times are then longer than those preferred for the practice of the invention.

The drawing is a schematic illustration of a preferred embodiment of the present invention wherein the hydroisomerization reaction and the alkylation reactions are performed concurrently on different fractions obtained from cracking of a waxy gas oil feedstock.

In the drawing waxy gas oil boiling within an approximate range of 600 to 1000 F. is continuously passed through a thermal cracker. Space velocity through the thermal cracking unit is from about 0.2 to 6.0 volumes per hour for each volume of internal capacity of the reactor, and is preferably from about 0.5 to about 2.0 volumes per hour. The cracker operates at a temperature of from about 800 to 1200 F. and preferably from about 1000 to 1100 F. A catalyst need not be employed, but where a catalyst is present, the temperature will preferably be from about 900 to about 1000 F. Suitable catalysts are those conventionally used for the cracking of petroleum fractions including among others: silicaalumina,v activated alumina, and molecular sieves. Catalysts will in general tend to favor production of light olefins. The contact time will be from about 1.0 to 50 and more preferably from to about seconds. Steam will be introduced into the cracking unit at a rate of about 1.5 to about 10 and preferably from about 2.5 to 5 moles of steam per mole of feed.

The effluent from the thermal cracker consists predominantly of C to about C olefins plus essentially unreacted gas oil. This efiluent is fed to a distillation tower 2, where it is split into four fractions; i.e., a C C fraction which is utilized as gaseous fuel, chemical raw material, or any of the other uses to which such light hydrocarbon fractions are commonly put such as alkylation of isobutane to form alkylate gasoline; a C -C fraction which is used further in the process of the present invention as discussed below; a (I -C fraction which is also hereafter discussed as being used in the process of v the present invention; and a C and above fraction which may be further distilled and partially recycled to the thermal cracking unit. The C to C fraction fiows through a mixing T, or hatch-type mixingdevice 3 where it is mixed with isobutane or one of the other suitable paraflin fractions discussed previously. The mixture of the isoparafi'in with the C C olefins from the cracking unit then flows into the alkylation reactor 4 which operates at a temperature of about 30 to 60 P. if sulfuric acid is used as the catalyst or alternatively at from about 4 to about 140 P. if anhydrous hydrogen fluoride is used as a catalyst. In either case the catalyst to hydrocarbon volume ratio is from about 2:1 to 0.111 or more preferably from 1:1 to 0.221. The isoparafiin in the input to the alkylation reactor will be in the range of from 2 to 100 and preferably from 4 to about 10 moles of isoparaffin per mole of olefin, the substantial excess being employed to minimize polymerization.

Contact time in the alkylation reactor will be from about 1 to about 120 minutes with contact times of 5 to 30 minutes being preferred.

The efiluent from the alkylation reactor is sent through separator 5 where unreacteed isobutane is separated out and recycled back to the mixer 3. The remainder of the etiiuent is transferred to fractional dis- 4 tillation column 6 where a gasoline fraction composed primarily of C C hydrocarbons boiling from about 82 to 350 F., and a jet fuel fraction composed principally of C -C hydrocarbons boiling from about 350 to 550 F. The fractions are separated and sent to storage units for gasoline 7 and for jet fuel 8.

The C -C hydrocarbon fraction from the distillation column 2 flows through a mixer 9 where it is mixed with from 2 to about 100 and preferably from 4 to about 10 moles of isoparafiin per mole of G -C olefin. The isoparafiins fed into the mixer will be from C -C with isobutane being preferred in most instances.

The mixed (I -C olefin/isoparaffin efiiuent from the mixer flows into the hydroisomerization reactor 10 which operates at conditions generally similar to those under which the alkylation reactor operates. The temperature for the hydroisomerization reaction is from about 30 to 100 and preferably from to 90 F. The pressure is from about 0 to 500 and preferably the vapor pressure of the reactants. The catalyst is preferably sulfuric acid but hydrofluoric acid or other catalysts may be used. The volume ratio of catalyst to total hydrocarbon in the reactor is maintained at about 2:1 to 01:1 and preferably from about 1:1 to 0.2: 1. The concentration of the H 50 used is about to 105% by weight with 85 to 100% preferred and to 99% by weight especially preferred. Where hydrogen fluoride is used as the catalyst, the temperature range will be from about 4 to about 140 F. The contact time will be maintained at from about 1 to 120 and preferably from about 5 to 30 minutes.

The effluent from the hydroisomerization reactor is sent to separation zone 11 where the unreacted isoparaffins are separated out and recycled back to the mixer 9. The remainder of the product of the hydroisomerization flows to a conventional fractional distillation column 12 where a gasoline fraction consisting primarily of C to C hydrocarbons boiling in the range of 82 to 350 F. and a jet fuel fraction consisting primarily of C -C singly branched paraffinic hydrocarbons boiling in the range of 350 to 550 F., are separated. The gasoline fraction may be transferred to storage facility 7 to be mixed with the corresponding fraction from the alkylation efiiuent, or stored separately and the jet fuel fraction may be similarly sent to storage facility 8 to be blended with the corresponding fraction from the alkylation effluent or stored separately.

It should be understood that although the above de scribed embodiment of the present invention utilized thermal cracking of waxy gas oils with steam, the product of suitable cracking operations according to conventional techniques and olefins obtained from such thermally cracked streams as coker distillates and visbreaker sidecuts or naphthas will also be useful in the practice of the present invention. Also, it will be recognized that the novel hydroisomerization process of the present invention can be practiced with approximately C -C olefins (preferably alpha unsaturated) which are obtained from other sources.

Example I A waxy gas oil boiling above 600 F. is cracked with steam at 1,150 P. in a laboratory size thermal cracker. No catalyst is used in the cracking step. Oil is fed at the rate of 452 g. per hour and steam at 202 g. per hour into the cracking unit with a retention time of 0.33 second. In a single pass, a 28.1 weight percent conversion is ob tained. The products are separated by distillation into cuts as follows: C through 44.5 weight percent; C through C 15.5 weight percent consisting completely of olefins; C through C 20.5 weight percent and olefins, and C C 16.9 weight percent containing 92% olefins.

The C to C cut is hydroisomerized using isobutane as the hydrogen source to produce a premium quality jet fuel and a high octane gasoline blending component. The by droisomerization is carried out in an autoclave with 99 weight percent sulfuric acid as a catalyst. The catalyst to olefin weight ratio is 5.0 and the isobutane to olefin mole ratio is 10.0. The olefin is pumped into the reactor containing the other reactants over a period of about 20 minutes and the reaction mixture is stirred for 5 minutes at the reaction temperature of 40 C. The yields obtained in the hydroisomerization reaction are gasoline, which has a boiling point to 350 F., 28 weight percent; jet fuel, which has a boiling point range from about 350 F. to 500 F., 64 weight percent; and alkylate plus polymer, which has a boiling point above 500 F., 8 weight percent. The fraction boiling above 500 F. is suitable for sale as fuel oil.

The C to C cut is converted to high quality jet fuel by alkylation with isobutane using anhydrous hydrogen fluoride as the catalyst. This reaction is carried out in a Monel autoclave using a catalyst to olefin Weight ratio of 5:1 and an isobutane to olefin mole ratio of 10:1. The alkylation reaction is run at 2 to 4 C. Addition of the olefin to the reactor containing the other reactants requires minutes. The reaction mixture is stirred for an additional 20 minutes to complete the reaction. Yields based on weight of olefin fed are gasoline (liquid to 350 F.) 50 weight percent, jet fuel (350 F. to 500 F.) 70 weight percent, and polymer (above 500 F.) 10 weight percent.

The jet fuel fraction obtained by the hydroisomerization has an average of 3.1 methyl groups (1.1 branches) per molecule and that obtained by alkylation has an average of 3.5 methyl groups (1.5 branches) per molecule. This low degree of branching is indicative of good thermal stability.

Example 11 When similar cracked waxy gas oil products are hydroisomerized using substantially anhydrous HF (containing less than 2% water by weight) at a temperature of about 50 0, products and yields are approximately as in Example I.

What is claimed is:

1. A process for the conversion of a waxy gas oil to valuable engine fuel comprising molecularly cracking under moderate conditions to obtain a product comprising substantial amounts of olefins having from about 6 to about 16 carbon atoms, separating a fraction containing from about 12 to about 16 carbon atoms per molecule, hydroisomerizing said fraction at from 20 to 80 C. in the presence of an acid catalyst with an isoparaffin of 4 to about 6 carbon atoms as the hydrogen source to form a gasoline fraction having a boiling point below about 350 F., a jet fuel fraction having a boiling point of from about 350 to 550 F., and a higher boiling fraction having a boiling point above 550 F.; separating out an approximately C to C fraction from the product of said molecular cracking, alkylating said C C fraction with a branched chain hydrocarbon containing 4 to about 6 6 carbon atoms in the presence of an acid catalyst at from 20 to C. to obtain a gasoline fraction boiling below about 350 F., a jet fuel fraction boiling from about 350 to 550 F., and a high boiling fraction boiling above 550 F.

2. The process of claim 1 wherein the branched chain hydrocarbon is isobutane, and the olefins are 6 to 16 carbon atom alpha-unsaturated olefins.

3. A process for the manufacture of acyclic branched hydrocarbons with an average of less than two branches per molecule having relatively high thermal stability, low freezing point, high heat of combustion per pound, and boliing from about 300 to 550 F., comprising hydroisomerizing substantially straight-chain olefins having from 9 to about 16 carbon atoms per molecule with isoparafiins having from 4 to 6 carbon atoms per molecule in the presence of an acid catalyst selected from the group consisting of sulfuric acid and hydrogen fluoride, aluminum chloride and boron trifluoride at a temperature of about 20 to 80 C. to produce isoparafifins of the same number of carbon atoms as the olefins together with more highly branched paraflins containing twice the number of carbon atoms of the isoparaffins.

4. The process of claim 1 wherein the acid catalyst is selected from the group consisting of to about by weight H 80; and substantially anhydrous hydrogen fluoride.

5. The process of claim 1 wherein the acid catalyst is 85 to 100% by weight H 50 6. The process of claim 5 wherein the branched chain hydrocarbon is isobutane, and the olefins are 6 to 16 carbon atoms substantially alpha-unsaturated olefins.

7. The process of claim 6 wherein the gasoline fraction obtained from the hydroisomerization is blended with the gasoline fraction obtained from the alkylation and the jet fuel fraction obtained from the hydroisomerization is blended with the jet fuel fraction obtained from the alkylation.

8. The process of claim 3 wherein the acid catalyst is 85 to 100% by weight H 50 9. The process of claim 3 wherein the acid catalyst is hydrogen fluoride.

10. The process of claim 3 wherein the acid catalyst is aluminum chloride.

11. The process of claim 3 wherein the acid catalyst is boron trifluoride.

References Cited by the Examiner UNITED STATES PATENTS 2,172,228 9/1939 Van Paski 208-106 2,353,490 7/1944 Noorduyn 20871 2,391,415 12/1945 Grosse et a1. 260-68348 3,150,204 9/1964 Lawley et al 260683.59

DELBERT E. GANTZ, Primary Examiner.

ABRAHAM RIMENS, Examiner.

Claims

1. A PROCESS FOR THE CONVERSION OF A WAXY GAS OIL TO VALUABLE ENGINE FUEL COMPRISING MOLECULARLY CRACKING UNDER MODERATE CONDITIONS TO OBTAIN A PRODUCT COMPRISING SUBSTANTIAL AMOUNTS OF OLEFINS HAVING FROM ABOUT 6 TO ABOUT 16 CARBON ATOMS, SEPARATING A FRACTION CONTAINING FROM ABOUT 12 TO ABOUT 16 CARBON ATOMS PER MOLECULE, HYDROISOMERIZING SAID FRACTION AT FROM -20 TO 80*C. IN THE PRESENCE OF AN ACID CATALYST WITH AN ISOPARAFFIN OF 4 TO ABOUT 6 CARBON ATOMS AS THE HYDROGEN SOURCE TO FORM A GASOLINE FRACTION HAVING A BOILING POINT BELOW ABOUT 350*F., A JET FUEL FRACTION HAVING A BOILING POINT OF FROM ABOUT 350 TO 550*F., AND A HIGHER BOILING FRACTION HAVING A BOILING POINT ABOVE 550*F.; SEPARATING OUT AN APPROXIMATELY C7 TO C11 FRACTION FROM THE PRODUCT OF SAID MOLECULAR CRACKING, ALKYLATING SAID C7-C11 FRACTION WITH A BRANCHED CHAIN HYDROCARBON CONTAINING 4 TO ABOUT 6 CARBON ATOMS IN THE PRESENCE OF AN ACID CATALYST AT FROM -20 TO 80*C. TO OBTAIN A GASOLINE FRACTION BOILING BELOW ABOUT 350*F., A FET FUEL FRACTION BOILING FROM ABOUT 350 TO 550*F., AND A HIGH BOILING FRACTION BOILING ABOVE 550*F.