US3915840A

US3915840A - Process for improving the octane number of cat cracked naphtha

Info

Publication number: US3915840A
Application number: US472997A
Authority: US
Inventors: Elory M Gladrow; Walter Weissman
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1974-05-24
Filing date: 1974-05-24
Publication date: 1975-10-28
Anticipated expiration: 1992-10-28

Abstract

A process for upgrading admixtures of naphthenic and unsaturated hydrocarbon compounds by conversion of the naphthenic constituents to aromatics and hydrogenation of the unsaturated compounds with the hydrogen removed from the naphthenic compounds which comprises establishing a hydrogen transfer zone which contains a bed of fluidized coke solids particles, operated at temperature ranging from about 750*F. to about 1050*F., preferably from about 825*F. to about 1025*F., establishing a coke gasification zone which contains a bed of fluidized coke solids particles, operated at temperature ranging from about 1000*F. to about 1650*F., preferably from about 1200*F. to about 1400*F., injecting a superheated oxidizing agent into said coke gasifier in concentration sufficient to increase the surface area and activate (or reactivate) the coke solids particles, circulating the coke between said coke gasifier and said hydrogen transfer reactor, while feeding an admixture of naphthenic and unsaturated hydrocarbon compounds into said hydrogen transfer zone such that naphthenic compounds are converted to aromatic hydrocarbons and unsaturated hydrocarbons are hydrogenated by hydrogen removed from the naphthenic compounds.

Description

United States Patent Gladrow et al.

[ 1 Oct. 28, 1975 OAT CRACKED PROCESS FOR IMPROVING THE OCTANE Primary Examiner-Delbert E. Gantz NUMBER OF CAT CRACKED NAPHTHA Assistant ExaminerG. E. Schmitkons F 1 11 A. P t [75] Inventors: Elory M. Gladrow; Walter Attorney Agent or [rm L ewe yn we or Weissman, both of Baton Rouge, La, [57] ABSTRACT [73] Assignee: Exxon Research & Engineering Co., A process for upgrading admixtures of naphtheni c and Linden unsaturated hydrocarbon compounds by convers1on of the naphthenic constituents to aromatics and hydroge- Filed: May 24, 1974 nation of the unsaturated compounds with the hydro- [21] AppL No: 472 997 gen removed from the naphthenic compounds which comprises establishing a hydrogen transfer zone which contains a bed of fluidized coke solids particles, oper- U-S- Cl. ated at temperature ranging from about to about 1050F., preferably from about 825F. to about 252/445 1025F., establishing a coke gasification zone which (31-2 J C106 contains a bed of fluidized coke solids particles, oper- C10 G C103 5/1 ated at temperature ranging from about 1000F. to Fleld of Search 141, 69, 70, about 1650F., preferably from about 1200F. to 208/133, 134; 260/663 445 about 1400F. injecting a superheated oxidizing agent into said coke gasifier in concentration sufficient to References Cited increase the surface area and activate (or reactivate) UNITED STATES PATENTS the coke solids particles, circulating the coke between 2,626,286 1/1953 Voorhies et a1. 260/688 D Said Coke gasifier and Said y g transfer reactor, 2,670,322 2/1954 Krebs et a1 208/50 While feeding an admixture naphthenic and unsatu- 2,906,696 9/1959 Garbo ct a1... 208/134 rated hydrocarbon compounds into said hydrogen 3,617,505 11/1971 Cole et al. 252/444 X transfer zone such that naphthenic compounds are 3,317,874 6/1974 wenflfifberg et 252/45 converted to aromatic hydrocarbons and unsaturated 3,840,476 8/1974 Metraller 252/445 hydrocarbons are hydrogenated by hydrogen removed from the naphthenic compounds.

14 Claims, 1 Drawing Figure l LT, arses LT. cases 1 I l I |9 I I FRAct FRACT. 65/430 as TO PRODUCT POOL 2311' I L000 37 "000 55 snssous c 5; ,8, PRODUCTS '35: ii -58 5. x 25 n-nunsrsn so cox: g newton GASIFIER REACTOR OIL FRESH FLUID SOLIDS COKE FROM FLU D COKER PRGCESS FOR IMPROVING THE OCTANE NUMBER OF CAT CRACKED NAPHTHA Processes for the production of aromatic compounds by catalytic reactions involving the transfer of hydrogen from naphthenic compounds to unsaturated hydrocarbon compounds, or hydrocarbon compounds containing nultiple bonds between carbon atoms, have been known for many years. For example, as disclosed in U.S. Pat. No. 2,626,286 to Alexis Voorhies, Jr., et a1., it is known that olefins, e.g., ethylene, propylene and l-butene, when admixed with cyclohexane, methylcyclohexane or paraffins, e.g., methylpentane, provide near-quantitative yields of benzene, toluene and methylpentenes, respectively, when contacted over a suitable catalyst at reaction conditions, e.g., an activated carbon catalyst at about 850 to 950F. The activity of the catalyst declines as the reaction proceeds but, pursuant to the teaching of this reference, can be regenerated by stripping with certain inert gases, at elevated temperatures ranging from about 1350l600F. Treatment of the carbon catalyst with steam at a temperature of about 1500F. is suggested as a preferred method of catalyst regeneration.

In U.S. Pat. No. 2,670,322 to Krebs et al. there is also described a process wherein virgin naphtha fractions in admixture with coker gases are contacted within a hydrogen transfer zone with diverse hydrogen transfer catalysts, such that naphthenic constituents in the virgin naphtha are converted to aromatic hydrocarbons and the olefinic hydrocarbons in the coker gases are converted to paraffmic hydrocarbons by the hydrogen removed from the naphthenic constituents. A fluid coking process is also described. The reformed naphtha feedstock from the hydrogen transfer zone along with a high boiling range gas oil or residuum is passed through a low temperature coking zone in which steam or other fluidizing gas may be added, prior to transmission to a fractionator to filter out any catalyst solids which may be entrained therein. The reformed naphtha feedstock from the hydrogen transfer zone is degraded in the presence of the residuum as it traverses the coking zone.

Activated carbon catalysts can be made from a variety of organic materials, e.g., wood, lignite, coal and petroleum residues, as described, e.g., in U.S. Pat. No. 2,906,696 to Garbo et al. Petroleum coke, e.g., a low surface area coke made from petroleum stocks, according to this reference, can be treated at temperatures ranging from about 1600 to 2200F. to form an activated coke catalyst of surface area ranging from about 400 m lg or greater (B.E.T.), which is suitable for reforming naphtha. Fluid coke, spherical in form, can be prepared with surface areas greater than 100 m lg by subjecting the coke to contact with steam at elevated temperatures ranging from l200 to 1400"F., and higher. A characteristic of this material is that it is relatively dense, i.e., 0.7 to 0.8 g/cc A.P.D. and, quite importantly, is highly attrition resistant. In standard Roller Attrition Tests for microspherical cracking catalysts, it is found that fluid coke attrites at a much slower rate than commercial cracking catalysts.

In fluid coking, two vessels are employed, a reactor to 1000F., and this is controlled by the flow of hot coke from the gasifier. Steam is introduced at the bottom of the reactor to fluidize the bed. Residuum feed is sprayed into the bed, being distributed over the surface of the particles to crack and vaporize therefrom, leaving a sticky residue on the particles which dries to form coke.

It is an object of the present invention to provide a new and improved fluid bed process for the continued production of usable gas and liquid products, i.e., l050F.- products, but which are particularly upgraded liquid products, notably cat (catalytic) cracked naphtha or a selected fraction thereof.

A specific object of the present invention is to provide a fluid bed process capable of utilizing added admixtures of naphthenic compounds and unsaturated hydrocarbon compounds, or compounds containing multiple bonds between carbon atoms, which admixtures are upgraded by the transfer of hydrogen from the naphthenic compounds to the more unsaturated compounds.

A more specific object is to provide a fluid bed operation wherein the naphthenes present in cat cracked naphtha, virgin naphtha, hydrocracked naphtha and the like can be fed thereto and upgraded to aromatics, thus improving the octane number of the product.

These objects and others are achieved in accordance with the present invention which comprises establishing a hydrogen transfer zone which contains a fluidized bed of coke solids particles, operated at temperature ranging from about 750 to about 1050F., preferably from about 825 to about 1025F.,

establishing a coke gasification zone, or gasifier, which contains a fluidized bed of coke solids particles, operated at temperature ranging from about l000 to about 1650F., preferably from about l200 to about 1400F.,

injecting an oxidizing agent into said coke gasifier in concentration sufficient to increase the surface area and activate (or reactivate) the coke solids particles, preferably supplying the reaction heat for the coke gasification zone by superheating the oxidizing agent prior to inu'oducing it to the coke gasification zone, and more preferably accomplishing this superheating by a method such as mixing controlled quantities of air or oxygen and/or gaseous fuel into the oxidizing agent and passing this mixture through a combustion zone,

circulating the coke between said coke gasifier and said hydrogen transfer reactor, while feeding an admixture of naphthenic and unsaturated hydrocarbon compounds into said hydrogen transfer zone such that naphthenic compounds are converted to aromatic hydrocarbons and unsaturated hydrocarbons are hydrogenated in situ by the hydrogen u'ansferred from the naphthenic compounds.

The oxidizing agent injected into the coke gasification zone is preferably an oxygen-containing compound, or compound capable of reacting with coke to increase the surface area of the coke solids from the hydrogen transfer zone, suitably up to 1000 m lg Typical naphthenic compounds which can be fed into said hydrogen transfer zone in admixture with unsaturates are those which have normal boiling points of less than 650F., preferably less than about 450F., e.g., 3-methylcyclopentane, 1,3-dimethylcyclopentane, cyclohexane, methylcyclohexane, 1,4-dimethylcyclohexane, ethylcyclohexane, 1 ,3-diethylcyclohexane, 1,3,5-triethylcyclohexane, and the like.

Illustrative of the unsaturated compounds or hydrogen acceptors which can be fed into said hydrogen transfer zone in admixture with naphthenic compounds are olefins, diolefins and acetylenes containing from 2 to about 16 carbon atoms, preferably from about 2 to about 12 carbon atoms, e.g., ethylene, propylene, butene, 1,3-butadiene, 2-methyl-l,3butadiene, 3-methylcyclopentene, 2-ethylcyclohexene, 2,3-diethylcyclohexene, and the like. Suitable hydrogen acceptors are also provided by commercial mixtures obtained from steam cracking, coking and cat cracking units. Greater benefits are obtained with those which approach stoichiometric proportions in the sense that the hydrogen released from the naphthenes is used most completely in effecting the hydrogenation of the unsaturated hydrocarbon compounds. Suitably, the molar ratio of unsaturated hydrocarbon compounds:naphthenes in the feed to the hydrogen transfer reaction zone ranges from about 1:1 to about 5:1, and preferably from about 2:1 to about 3:1.

In a particularly desirable embodiment of this invention, a cat cracked naphtha comprising an admixture of naphthenes and olefins boiling within the range of from about 70F. to about 500F., preferably from about 80F. to about 430F., is fed into the hydrogen transfer zone along with additional light olefins, if necessary and desired, to improve its octane number. Preferably, the cat cracked naphtha is a product obtained from the reaction zone (i.e., the reactor) of a cat cracker, the feed thereto, the catalyst and the conditions of reaction of which are as follows:

The liquid product, which constitutes a preferred feed to the hydrogen transfer zone is thus one obtained at conditions very similar to those employed in the hydrogen transfer zone. The total cracked product may be fractionated to provide a light cracked gas (C, and lighter) which contains considerable olefins, a C .,/430F. cracked naphtha containing both olefins and naphthenes, a 430/650F. heating oil fraction which may contain some olefins and naphthenes, and a 650F.+ recycle oil. The C /430F. naphtha is a principal feed to the hydrogen transfer zone. The cracked gases and additional unsaturated gases from other sources are also fed to the hydrogen transfer zone. Portions or all of the 430/650F. heating oil may also be fed to the hydrogen transfer zone, if desired.

A preferred process is thus one wherein the hydrogen-transfer and gasification zones are integrated with a fluid cat cracking unit. Such a process scheme is depicted in the attached FIGURE.

Referring to the FIGURE, there is shown generally a fluid cat cracking unit comprised of a regenerator 10 and reactor 20 between which a fluidized catalyst is circulated via lines 11,12. Feed is injected into the reactor 20 via line 13, and air is injected into the regenerator via line 14. Steam is added to the stripper 15 via a line 16, and gas is removed from the stripper 15 via line 17.

The associated fluid bed unit is comprised of a hydrogen transfer reactor 30 and a coke gasifier vessel 40, and coke is circulated between the vessels via lines 31,32. Makeup coke solids, supplied from a first coker, delayed coker, or otherwise, are introduced into the coke gasifier 40 via gasifier inlet line 33 along with an oxygen-containing compound, preferably steam or carbon dioxide, which is introduced via line 34.

Product from the cat cracker reactor 20 is introduced, via line 18, into a fractionating tower l9 and split into light gases, C /43OF. naphtha and light and heavy cat cycle oils. The C /430F. naphtha which is removed from fractionator 19 via line 21, is admixed with a light olefin stream introduced via line 22 into line 21 and fed via line 32 into the hydrogen transfer reactor 30.

Effluent from hydrogen transfer reactor 30 is fed via line 35 into a fractionator 36 and split into a light gas fraction and a liquid fraction of increased octane value which is withdrawn from fractionator 36 via line 37 and fed to the product pool. Stack gas from regenerator 10 of the cat cracker unit which contains a sulfur dioxide pollutant, if desired, can be fed via line 23 into an auxiliary vessel 41, into which oxygen or air is injected via line 42, and combusted to form a superheated mixture which is then fed via line 43 into the coke gasifier 40 wherein it provides oxidizing agents in the form of steam and CO for the gasification zone. The reduction of S0 to H 8 which occurs in the gasification zone is exothermic and thereby also provides part of the heat required for that zone. The sulfur dioxide is reduced primarily to hydrogen sulfide. The hydrogen sulfide can be efficiently recovered in the form of sulfur by well known processes. The result is that atmospheric pollutants are recoverable in a form which has economic value. Gaseous products, e.g., carbon monoxide, hydrogen, hydrogen sulfide, and the like, are removed from coke gasifier 40 via line 38.

In the following examples, a total liquid overhead product from a conventional cat cracking operation is used as the feedstock for a simulated second-stage operation.

EXAMPLES 1 AND 2 In these examples, PCC-Type BP activated carbon granules were used as the catalyst in the hydrogen transfer reactor. The naphtha feed introduced into the hydrogen transfer reactor was a 65F. stabilized cat cracked product (Davison XZ-36 catalyst used in the cat cracking stage) of which 47% by weight was in the 65-430F. boiling range. The aromatic content of the naphtha fraction was determined by a combination of silica gel separation and MS spectrometry and found to be about 13.9 wt.% of the total feed. The olefin added to the 65430F. naphtha was C 14 which was fed at a rate calculated to provide 3 mols of l-I-acceptor for each mol of cyclo C and cyclo C naphthene in the feed.

The runs were conducted in the hydrogen transfer reactor at 985 and 1020F. initial temperature. Because of the endothermic nature of the cracking operation, actual catalyst bed temperatures averaged about 965F. and 1000F. during the 2-minute process period.

In the run conducted in the hydrogen transfer reactor at 985F. initial temperature and a feed rate of 15.0 W/Hr./W, conversion to 430F. material was 90.5 wt.%. The aromatic content of the naphtha was raised to 19.6 wt.% based on feed. In the run conducted in the hydrogen transfer reactor at 1020F. initial temperature and a feed rate of 15.0 W/Hr./W, conversion to 430F. material was 89.3 wt.%. The aromatic content of the naphtha was raised to 18.6 wt.% based on feed. In both runs, the increased aromatics content of the naphtha indicates a substantial increase in the octane number of the naphtha over that obtained in conventional single-stage operation.

The H-transfer reactions were occurring in which C 11,, was being converted to C H was ascertained from the data which showed that about 148 CF/B C l-I was formed in the run at 985F., and 161 CF/B C H was formed in the run at 1020F. Normally, the C I-I yield in a conventional single-stage cracking operation is in the range of 15-25 CF/B.

EXAMPLE 3 In this example, the PCC-Type BP activated carbon granules were impregnated with 6.0% K (as K CO oven dried at 300F., to improve the gasification kinetics of the coke deposited during the hydrogen transfer stage.

The catalyst was tested at 1020F. initial cracking temperature, with added C I-I and the same feed as used in the preceding examples. Conversion to 430F. material was 84.2%. The aromatic yield in the 430F. naphtha was 14.1 wt.%, based on feed, this indicating some improvement in the naphtha octane number. The C H yield was 124 CF/B, indicating substantial H-transfer but apparently this catalyst is less selective in forming aromatics than the activated carbon catalyst described in the preceding examples.

It is apparent that various modifications and changes can be made without departing from the spirit and scope of the present invention.

Having described the invention, what is claimed is:

I. A process for upgrading admixtures of naphthenic and unsaturated hydrocarbon compounds by conversion of the naphthenic constituents to aromatics and hydrogenation of the unsaturated compounds with the hydrogen removed from the naphthenic compounds which comprises establishing a hydrogen transfer zone which contains a bed of fluidized coke solids particles operated at temperature ranging from about 750F. to about 1050F.,

establishing a coke gasification zone which contains a bed of fluidized coke solids particles operated at temperature ranging from about 1000F. to about 1650F.,

injecting an oxidizing agent into said coke gasification zone in concentration sufficient to increase the surface area and activate (or reactivate) the coke solids particles,

circulating the coke between said coke gasification zone and said hydrogen transfer zone, while feeding the admixture of naphthenic and unsaturated hydrocarbon compounds into said hydrogen transfer zone.

2. The process of claim 1 wherein the hydrogen transfer zone is operated at temperatures ranging from about 825 to about 1020F.

3. The process of claim 1 wherein the coke gasification zone is operated at temperatures ranging from about 1200F. to about 1400F.

4. The process of claim 1 wherein the oxidizing agent is steam or carbon dioxide, or both.

5. The process of claim 1 wherein the circulated coke is of surface area ranging from about 25 m /g to about 1000 m g.

6. The process of claim 1 wherein the circulated coke is of surface area ranging from about m /g to about 650 m /g.

7. The process of claim 1 wherein the naphthenic compounds, contained in admixture with the unsaturated hydrocarbon compounds, are of boiling point ranging below about 650F.

8. The process of claim 1 wherein the naphthenic compounds, contained in admixture with the unsaturated hydrocarbon compounds, are of boiling point ranging below about 450F.

9. The process of claim 1 wherein the unsaturated compounds, contained in admixture with the naphthenic compounds, contain from 2 to about 16 carbon atoms.

10. The process of claim 1 wherein the unsaturated compounds, contained in admixture with the naphthenic compounds, contain from 2 to about 12 carbon atoms.

11. The process of claim 1 wherein the molar ratio of unsaturated hydrocarbon compoundsznaphthenes in the admixture constituting the feed ranges from about 1:1 to about 5:1.

12. The process of claim 1 wherein the molar ratio of unsaturated hydrocarbon compoundsznaphthenes in the admixture constituting the feed ranges from about 2:1 to about 3:1.

13. The process of claim 11 wherein the naphthene portion of the admixture comprises a C /430F. cut from a cat cracker.

14. A process for upgrading admixtures of naphthenic and unsaturated hydrocarbon compounds by conversion of the naphthenic constituents to aromatics and hydrogenation of the unsaturated compounds with the hydrogen removed from the naphthenic compounds which comprises the combination of a hydrogen transfer zone which contains a bed of fluidized coke solids particles, operated at temperature ranging from about 750 to about 1050F.,

a coke gasification zone which contains a bed of fluidized coke solids particles, operated at temperature ranging from about 1000 to about 1650F., coke being circulated between said hydrogen transfer zone and said coke gasification zone,

a cat cracking zone within which a gas oil boiling in about the 550F.1050F. range is fed at a rate of about 1-40 V/V/l-Ir., and cracked at a temperature 7 8 ranging from about 850-1000F. and at a pressure bon compounds:C /430F. naphtha of from about ranging from about -50 psig, and cracked, to pro- 1:1 to about 5: duce a C's/430 naphtha fracuon and feeding said admixture into said hydrogen transadmixing said C /430F. naphtha fraction from said cat cracking zone with unsaturated hydrocarbon 5 compounds in molar ratio of unsaturated hydrocarfer zone.

Claims

1. A PROCESS FOR UPGRADING A ADMIXTURES OF NAPHETHIC AND UNSATURATED HYDROGEN COMPOUNDS BY CONVERSATION OF THE NAPHTHENIC CONTITUENTS TO AROMATICS AND HYDROGENARATION OF THE UNSATURATED COMPOUNDS WITH THE HYDROGEN REMOVED FROM THE NAPHTHENIC COMPOUNDS WHICH COMPRISES ESTABLISHING A HYDROGEN TRANSFER ZONE WHICH CONTAINS A BED OF FLUIDIZED COKE SOLIDS PARTICLES OPERATED AT TEMPERATURE RANGING FROM ABOUT 750*F TO ABOUT 1050*F, ESTABLISHING A COKE GASTERIFICATION ZONE WHICH CONTAINS A BED OF FLUIDIZED COKE SOLIDS PARTICLES OPERATED AT TEMPERATURE RANGING FROM ABOUT 1000*F. TO ABOUT 1650*F, INJECTING AN OXIDIZING AGENT INTO SAID COKE GASIFICATION ZONE IN CONCENTRATION SUFFICIENT TO INCREASE THE SURFACE AREA AND ACTIVATE (OR REACTIVATE) THE COKE SOLIDS PARTICLES, CIRCLUATING THE COKE BETWEEN SAID COKE GASIFICATION ZONE AND SAID HYDROGEN TRANSFER ZONE, WHILE FEEDING THE ADMIXTURE OF NAPHTHENIC AND UNSATURATED HYDROCARBON COMPOUNDS INTO SAID HYDROGEN TRANSFER ZONE.

2. The process oF claim 1 wherein the hydrogen transfer zone is operated at temperatures ranging from about 825* to about 1020*F.

3. The process of claim 1 wherein the coke gasification zone is operated at temperatures ranging from about 1200*F. to about 1400*F.

5. The process of claim 1 wherein the circulated coke is of surface area ranging from about 25 m2/g to about 1000 m2/g.

6. The process of claim 1 wherein the circulated coke is of surface area ranging from about 100 m2/g to about 650 m2/g.

7. The process of claim 1 wherein the naphthenic compounds, contained in admixture with the unsaturated hydrocarbon compounds, are of boiling point ranging below about 650*F.

8. The process of claim 1 wherein the naphthenic compounds, contained in admixture with the unsaturated hydrocarbon compounds, are of boiling point ranging below about 450*F.

11. The process of claim 1 wherein the molar ratio of unsaturated hydrocarbon compounds:naphthenes in the admixture constituting the feed ranges from about 1:1 to about 5:1.

12. The process of claim 1 wherein the molar ratio of unsaturated hydrocarbon compounds:naphthenes in the admixture constituting the feed ranges from about 2:1 to about 3:1.

13. The process of claim 11 wherein the naphthene portion of the admixture comprises a C5/430*F. cut from a cat cracker.

14. A process for upgrading admixtures of naphthenic and unsaturated hydrocarbon compounds by conversion of the naphthenic constituents to aromatics and hydrogenation of the unsaturated compounds with the hydrogen removed from the naphthenic compounds which comprises the combination of a hydrogen transfer zone which contains a bed of fluidized coke solids particles, operated at temperature ranging from about 750* to about 1050*F., a coke gasification zone which contains a bed of fluidized coke solids particles, operated at temperature ranging from about 1000* to about 1650*F., coke being circulated between said hydrogen transfer zone and said coke gasification zone, injecting an oxidizing agent into said coke gasification zone in concentration sufficient to increase the surface area and activate (or reactivate) the coke solids particles, a cat cracking zone within which a gas oil boiling in about the 550*F.-1050*F. range is fed at a rate of about 1-40 V/V/Hr., and cracked at a temperature ranging from about 850*-1000*F. and at a pressure ranging from about 0-50 psig, and cracked, to produce a C5/430*F. naphtha fraction, admixing said C5/430*F. naphtha fraction from said cat cracking zone with unsaturated hydrocarbon compounds in molar ratio of unsaturated hydrocarbon compounds:C5/430*F. naphtha of from about 1:1 to about 5:1, and feeding said admixture into said hydrogen transfer zone.