US3287253A - Process for reforming a naphtha fraction in three stages to produce a high octane gasoline - Google Patents

Description

NOV. 22, 1966 K, w, QH JR" EI'AL 3,287,253

PROCESS FOR REFORMING A NAPHTHA FRACTION IN THREE STAGES TO PRODUCE A HIGH OCTANE GASOLINE Filed Dec. 20, 1965 Nap/lino or Hydrogen -6onfo/'ning Recycle Gas Gasoline Feed 7 DEHYDROGENATION 0F C6-R|NG NAPHTHENES Exa t Pt-On-SiO CATALYST ISOMERIZATION 0F C5-RING NAPHTHENES TO 0 R|NG NAPHTHENES a SUBSEQU'ENT DEHYDROGENATION; STAGE 2 ISOMERIZATION 0F PARAFFINS (/n/ermedio/e) Pt-On-Si0 -AI O CATALYST Chloride Containing Gompound DEHYDROCYCLIZATION 0F 3 PARAFFINS i FCHLORIDET: Pt-AI O -CI-COMPLEX CATALYST I REMOVAL I ITREATMENT I L ZL LLJ I \HIGH-PRESSURE SEPARATOR liig/z Ociane oso/ines I N VE NTORS Keir/I W. McI/enry, Jr.

Hermon 5. See/i9 ATTORNEY United States Patent 3,287,253 PROCESS FOR REFORMING A NAPHTHA FRAC- TION IN THREE STAGES T0 PRODUCE A HIGH OCTANE GASOLINE Keith W. McHenry, Jr., Park Forest, 11]., and Herman S.

Seelig, Valparaiso, 1nd,, assignors to Standard Oil Company, Chicago, Ill., a corporation of Indiana Filed Dec. 20, 1965, Ser. No. 516,746 12 Claims. (Cl. 208-65) This application is a continuation-impart of our copending US. patent application S.N. 340,604, which was filed on January 28, 1964, now abandoned.

This invention relates to the conversion of hydrocarbons and to an improved method of upgrading petroleum naphthas and gasolines to produce high-octane motor fuels. Specifically, the invention relates to an improved method for the catalytic reforming of naphtha and gasoline fractions.

Catalytic reforming, in general, is discussed by F. G. Ciapetta, R. M. Dobres and R. W. Baker in Catalysis, vol. 6, Reinhold Publishing Corp., New York, pp. 495-692 (1958). The various commercial processes are considered in this work on pages 646-687. Some of the catalytic-reforming processes provide for the regeneration of the catalyst in situ while the unit is on stream. An example of such a process is Ultraforming, which is described in the above work on pages 665-668 and by W. J. Birmingham in Petroleum Engineer, vol 26, No. 4, p. C-35 (April 1954). Such regenerative catalytic-reforming processes can successfully operate at low pressures, for example, a pressure below 400 p.s.i.g.

One of the problems encountered in catalytic reforming is the occurrence of undesirable side reactions, which result in a reduction of liquid product. The primary side reaction is cracking. Gaseous products and increased amounts of coke generally are formed from the cracking reaction. It is recognized, however, that some cracking may result in hydrocarbons that boil in the gasoline range. Although these may be desirable, a minimization or complete elimination of cracking appears to be advantageous. The smaller the amount of gas and coke formed, the greater is the yield of the desired liquid products.

While the cracking should be minimized, there are certain other reactions which occur in reforming that should be promoted. These desirable reactions, listed in order of decreasing reaction rates, are: dehydrogenation of cyclohexanes; isomerization of cyclopentanes to cyclohexanes; isomen'zation of straight-chain paraffins to branched paraffins; and dehydrocyclization of paraffins.

Maximum yields will be obtained when the desired reaction is maximized and the undesirable cracking is minimized. In the reforming process, the fastest reaction predominates in the first reactor; the next two reactions, in the intermediate reactor(s); and the slowest reaction, in the final reactor(s). Apparently no single catalyst gives the best results in all stages in a reformer, but highest yields are attained when different catalysts are used in the various reactors.

The use of different catalysts in two-stage reforming processes has been disclosed heretofore; see British Patents Nos. 775,961 and 847,728 and US. Patent No. 2,849,376. However, none of these patents disclose a process wherein specific catalysts are used in separate reforming stages to preferentially maximize or promote each of the primary desired reactions, namely the dehydrogenation "ice of cyclohexanes, the isomerization of cyclopentanes to cyclohexanes, the isomerization of normal parflins, and the dehydrocyclization of parafiins.

Our invention is an improved process for the reforming of petroleum naphthas in which the catalyst used in each of three stages is selected to promote the desired reaction for that stage in preference to other reactions. The catalyst in the first stage is selected to preferentially promote the dehydrogenation of naphthenes; the catalyst in the second stage is selected to preferentially promote the isomerization of cyclopentanes to cyclohexanes, the dehydrogenation of the cyclohexanes, and also the isomerization of parafiins; and the catalyst in the final stage is selected to preferentially promote dehydrocyclization of paraifiins to aromatics. Although reactions other than those named above may occur in each stage of the reforming process, their incidence will be less than if the catalyst used in each stage had not been selected in accordance with our invention.

Our improved method comprises contacting naphtha in an initial stage under reforming conditions with a catalyst which preferentially promotes naphthene dehydrogenation contacting in an intermediate stage under reforming conditions the efiiuent from the initial stage with a catalyst which preferentially promotes the isomerization of cyclopentanes and the subsequent dehydrogenation of the naphthenes formed thereby, and also the isomerization of normal parafiins, and contacting in a final stage under reforming conditions the effiuent from the intermediate stage with a catalyst which selectively promotes the dehydrocyclization of paraflins. The selection and use of specific catalysts in accordance with our invention provides a reforming process having a superior relationship between reformate yield and reformate octane.

The catalyst used in the initial stage may be platinum, other-noble metals, nickel, or molybdenum on a nonacidic support. A preferred non-acidic support is silica. However, other non-acidic supports, such as kieselguhr, magnesium oxide, and charcoal, can be employed. If charcoal were to be used as the support of the catalyst in the initial stage, such catalyst could not be regenerated by oxidation at high temperatures. These supports do not readily retain halo-gen, that is, no substantial amounts of a halide are retained by these supports under the reforming conditions employed. A platinum-on-silica catalyst is a preferred catalyst for this stage. The presence of hfiogen on the catalyst should be avoided to avoid formation of cracking sites. The supports should retain little or no halogens, since those small amounts of chloride which might be present in the hydrocarbon feed stock should not be picked up by the catalyst as the feed stock passes through the initial stage. The removal of halogens from the recycle gas prior to the introduction of the gas into the initial stage is advantageous. Furthermore, the dehydrogenation activity of such a catalyst is favored if the catalyst is maintained in a reduced form. Therefore, regeneration procedures should also be tailored to keep the catalyst in this reduced form. After the coke has been removed with an oxygen-containing gas, the catalyst is subjected to a hydrogen-containing gas, such as recycle gas or pure hydrogen. Since cracking is minimized in the initial stage, the regeneration of the catalyst in such stage may be held to a minimum.

Dual-site catalysts effectively promote the isomerization of the cyclopentanes to cyclohexanes and the subsequent dehydrogenation of cyclohexanes formed therefrom, as

well as the isomerization of the straight-chain paraffins. These isomerization reactions are favored-by a catalyst which is made up of platinum or other noble metal on an acidic support. Such a catalyst is used in the intermediate stage of our invention. Examples of this type of catalyst are: platinum-on-fluorided-alumina, platinu-m-on-alumina, or platinum-on-silica-alumina. Such a catalyst in the intermediate stage will only require infrequent regeneration for the purpose of removing coke, as is the case for the catalyst of the initial stage. The silica-alumina composition may be a conventional silica-alumina cracking catalyst, or it may be primarily an alumina base containing from 1 to 15 weight percent silica. A silica-alumina cracking catalyst composition is preferred as the catalyst sup port in the intermediate stage.

A p1atinum-alumina-chloride complex catalyst is the most effective catalyst for the promotion of the dehydrocyclization of paratfins. This catalyst may be used in the final stage of our invention. This complex catalyst is discussed in detail in the McHenry et al. paper, The Nature of Platinum Dehydrocyclization Catalyst, presented at the Second International Congress on Catalysis in Paris, France, in 1960.

We have found that the platinum-alumina-chloride complex exists in both cogelled and impregnated catalysts. The two types of catalysts give comparable results; therefore, the method of catalyst preparation is not significant.

When this complex is present, the platinum on the catalyst is soluble in a dilute aqueous solution of hydrofluoric acid, the amount of complex being proportional to the amount of platinum soluble in the hydrofluoric acid solution. When no platinum exists in the complex form, all of it is found to be insoluble in the hydrofluoric acid solution. When all of the platinum exists in the complex form, all of it is soluble in the hydrofluoric acid solution.

During the use of such a catalyst under reforming condi tions, the percent of platinum in the soluble form is reduced as the complex is partially destroyed. This partially-destroyed complex can be restored by the regeneration of the catalyst in an atmosphere containing oxygen, as specified in the McHenry et al. paper, The Nature of Platinum Dehydrocyclization Catalyst.

Another catalyst that may be used in the third or final stage is one comprising a dehydrogenation component on an alumina in the matrix of which a zeolitic molecular sieve has been suspended. The dehydrogenation component may be selected from platinum, other noble metals, nickel, and molybdenum. If the third-stage catalyst comprises a support of alumina with which a ze olitic molecular sieve is admixed, the molecular sieve may be present in an amount within the range of about 0.5 to about 20 weight percent based upon said support, preferably the molecular sieve may be present in an amount within the range of about 1 to about 5 weight percent based upon said support.

Zeolitic molecular sieves are composed of porous crystalline metal alumino-silicates. The Zeolitic structure exists as a network of relatively small alumino-silicate cavities, which are interconnected by numerous smaller pores. These pores have essentially a uniform diameter at their narrowest cross section. Generally, this uniform diameter falls within the range of 4 to angstroms. Basically, the network of cavities is a rigid 3-dimensional and ionic network of silica and alumina tetrahedra. These tetrahedra are cross-linked by the sharing of oxygen atoms. Cations are included in the crystal structure to balance the electrovalence of the tetrahedra. Examples of such cations are a metal ion, an ammonium ion and a hydrogen ion. One cation may be exchanged either entirely 0 pari tially by another cation. This cation exchange is conveniently accomplished through the use of ion-exchange techniques.

Both crystalline alumino-silicate clays and amorphous alumino-silicates may be readily distinguished from the zeolites. Crystalline alumino-silicate clays, e.g., bentom'te,

have Z-dimensional structures. Amorphous aluminosilicates, e.g., a synthetic silica-alumina cracking catalyst, have random structures.

In the case of a particular zeolitic molecular sieve, the intra-crystalline pores can be varied in size by replacing at least a part of exchangeable cations with other suitable ions. Such zeolites may be used for drying purposes, for

catalytic purposes, and for hydrocarbon-type separation purposes.

Either natural or synthetic molecular sieves may be used in our proposed third-stage catalyst. Examples of natural molecular sieves are erionite, mordenite, chabazite, faujasite, gmelinite, and the calcium form of analcite.

molecular sieves. Zeolitic molecular sieves can be activated by driving out of the sieves a major portion of the water of hydration.

paring them have been presented in the chemical art,

Different tests were made in bench-scale equipment to demonstrate the effect of various catalysts on the conversion of two pure compounds. In one series of tests, the

conversion of dimethylclclopentanes, typical naphthenes, was studied. In another series, the conversion of normalheptane was investigated.

Several catalysts were used in the dimethylcyclopentane tests. Relative rate constants were calculated from the results of these tests which had the following nominal operating conditions: 910 F., 275 p.s.i.g., 5.5 moles of:

hydrogen per mole of dimethylcyclopentane, one hour on oil, and a weight hourly space velocity of 90.

Ex-- I amples of synthetic zeolitic molecular sieves are type X, type Y, type A, type D, type L, type R, type S and type T The characteristics of both natural. and synthetic molecular sieves and the methods for pre- Rate constants Catalyst Selectivity In In kc PtAl2O3-C1 27 127 34 2. 0 Pt on SiOr-AlzOg 148 23 22 3. 0 Pt-F-AIZOJ 266 25 45 3. 8 I

The rate constant k; is the rate constant for the conversion of the dimethylcyclopentanes to aromatics, which includes the isomerization of the d imethylcyclopentanes to cyclohexanes and subsequent dehydrogenation of the cyclohexanes to aromatics; k is the rate constant for the ring opening of the dimethylcyclopentanes; and k the rate constant for the cracking of dimethylcyclo- The selectivity is the ratio pentanes to lighter material.

of k to the sum of k and k Initially the platinumalumina-chloride catalyst that was used in this series of Consequently, the platinum was in the soluble form, as mentioned above.. As the test progressed, the percentage of platinum in the solutests existed as a complex.

ble form was reduced. Here, the rate constants show that the conversion of the dimethylcyclopentanes to cycloi hexanes and subsequent conversion to aromatics were substantially promoted by all three of the catalysts, but. the concurrent reactions were promoted to a greater. ex- Oonsetent by the platinum-alumina-chloride catalyst. quently, the selectivities of the .non chlon'de catalysts were substantially greater than the chloride-containing catalyst.

The isomerization of the straight-chain parafiins is also 1 The dehydrocyclization of normal-heptane over various.

catalyst-s was studied under the following nominal operating conditions: 910 F., weight hourly space velocity However, a complex should not be formed be- Such catalysts of 1.4, 275 p.s.i.g., and 5.5 moles of hydrogen per mole of normal-heptane. Relative rate constants wer calculated for the dehydrocyclization of this parafiin and are presented below:

Rate constants for The above relative rate constants are averaged over ten-hour period-s since most of the loss of platinum-alumina-ch'loride complex occurs in the first few hours of a run. The above difference in rate constants between the catalyst with no complex and the catalyst with complex indicates the benefit which may be obtained with a complex catalyst when reasonable cycle lengths are used in commercial practice. As mentioned above, the complex is partially destroyed as a reforming run progresses, but it can be restored by the regeneration of the catalyst in an atmosphere containing oxygen. A relatively constant chloride level can be maintained by the addition of chloride to the effluent from the preceding stage prior to its entry into the stage using this catalyst.

The results from the above studies made with normalheptane indicate that the platinum-alumina-chloride-complex is the best of the catalysts studied for the promotion of the dehydrocycl-ization of paraflins. This dehydrocyclization reaction is the slowest of the reactions noted above. The platinum-alumina-chloride complex is the optimum catalyst for the final stage of the reforming system as it is the best promoter of the dehydrocyclization reactions.

The attached drawing is a diagrammatic representation of a specific embodiment of our improved method for the catalytic reforming of naphtha and gasoline fractions. The naphtha or gasoline feed that is to be upgraded is introduced into stage 1 of the reforming system. Stage 1 comprises reactor 1 which contains catalyst which preferentially promotes the dehydrogenation of cyclohexanes. In this case, a platinum-on-silica catalyst is used. The total eflluent from stage 1 is then conducted into stage 2 which comprises reactor 2. Reactor 2 contains a catalyst which promotes the isomerization reactions. For this examination, a platinum-on-silica-alumina catalyst is used. The total eflluent from stage 2 is then sent to stage 3 which comprises one or more reactors. A chloride-containing compound is added to the efiiuent from stage 2 prior to its entry into stage, 3. Each of the reactors in stage 3 contains a catalyst which will effectively promote the dehydrocyclization of parafiins. The platinum-alumina-chloride-complex catalyst is used in this stage.

The efliuent from stage 3 is then sent to a high-pressure separator where the hydrogen-containing gas is separated from the liquid product. The hydrogen-containing gas is recycled to stage 1 after it has undergone a conventional treatment for the removal of chloride, or a portion of it without chloride removal may be returned to stage 3, or the entire flow of gas may be recycled Without chloride removal to stage 1. Chloride removal is preferred. The liquid product then sent to a conventional reforming product-recovery system where the liquid product is stabilized.

For the initial stage of our improved process the platinum-on-silica catalyst may be prepared as Catalyst F was prepared in Example 6 of British Patent 790,476. Suitable operating conditions for this stage are weight hourly space velocity of 5-100, a hydrogen to hydrocarbon mole ratio of about 3:1 to about 10:1, a catalyst bed temperature of 800 to 1050 F., and a pressure of 250 to 600 p.s.i.g.

The platinum-on-silica-alumina catalyst used in the second stage is similar to the catalyst prepared by F. G.

6 Ciapetta in U.S. Patent 2,550,531. The operating conditions are weight hourly space velocity of 1 to 20, a hydrogen to hydrocarbon mole ratio of about 3:1 to 10:1, a catalyst bed temperature of 850 to 1050 F. and a pressure of to 350 p.s.i.g.

The catalyst in the final stage of the specific embodiment of our invention is a catalyst that is prepared from alumina sol by adding chloroplatinic acid and gelling with ammonia as described by L. Heard,'et al. in U.S. Patent 2,659,701, assigned to the Standard Oil Company (Indiana). The alumina sol is prepared as described by L. Heard in U.S. Patent Reissue 22,196. Suitable operating conditions for the final stage of our reforming process are a weight hour space velocity of 1 to 10, a hydrogen to hydrocarbon mole ratio of from 3:1 to 10:1, a catalyst bed temperature of 850 to 1050 F. and a pressure of 150 to 350 p.s.i.g. Frequent regeneration of the catalyst in this final stage is required to maintain the desired complex. Chloride addition to the gas stream entering this stage during the regeneration treatment may be performed. V

The use of this specific embodiment of our invention in which a particular catalyst is used for a particular reaction is not to limit this invention, but any suitable catalyst which will preferentially promote that specific reaction may be used in place of the designated catalyst in the particular stage of the reforming system. Conditions that may be used in our reforming scheme are con ditions that are included in those shown in the prior art to be effective for each particular catalyst. Stage 3 need not necessarily consist of two reactors; for some reforming situations, only one reactor may be sufiicient for this stage.

From the foregoing description it should be apparent that there is provided in accordance with our invention an improved process for the reforming of naphthas and gasolines. As will be evident to those skilled in the art, various modifications or equivalents of this invention can be made or followed without departing from the spirit or scope thereof.

We claim:

1. In a process for reforming petroleum hydrocarbons boiling in the gasoline and naphtha ranges by passing preheated hydrocarbon vapors and recycled hydrogencontaining gas through a plurality of stages under reforming conditions, the improvement which results in greater product selectivity and which comprises contacting in an initial stage under reforming conditions the preheated hydrocarbons and recycled hydrogen-containing gas with a catalyst which comprises a dehydrogenation component on a halogen-non-retaining, non-acidic support and which promotes the dehydrogenation of naphthenes; contacting in an intermediate stage under reforming conditions the effluent from said initial stage with a catalyst which comprises a dehydrogenation component on an acidic support and which promotes the isomerization of cyclopentanes, the dehydrogenation of resultant cyclohexanes, and the isomerization of paraffins; contacting in a final stage the efiiuent from said intermediate stage under reforming conditions with a catalyst which comprises a dehydrogenation component on an alumina-containing support and which promotes the dehydrocyclization of parafiins; separating the total efiluent from said final stage into hydrogen-containing gas and high-octane liquid products; and recycling at least a part of said hydrogen-containing gas to said initial stage.

2. Process of claim 1 wherein the hydrogen-containing gas being recycled to said initial stage is subjected to a treatment for chloride removal prior to its introduction into said initial stage.

3. Process of claim 1 wherein a chloride-containing compound is added to the eflluent from said intermediate stage prior to its introduction into said final stage to maintain the desired chloride-level of the catalyst in said final stage.

4. Process of claim 1 wherein the catalyst in said initial stage is a platinum-on-silica catalyst. 5. Process of claim 1 wherein the catalyst in said intermediate stage is a platinum-on-silica-alumina catalyst.-

6. Process of claim 1 wherein the catalyst in said intermediate stage is a platinum-on-fluorided-alumina catalyst.

7. Process of claim 1 wherein the catalyst in said initial stage and the catalyst in said intermediate stage are regenerated infrequently for coke removal only.

8. Process of claim 1 wherein at least a part of said hydrogen-containing gas is recycled to said final stage without a treatment for chloride removal.

9. Process of claim 1 wherein the catalyst in said final stage is regenerated frequently.

10. Process of claim 1 wherein the catalyst in said final stage comprises platinum and chlorine on an alumina support.

11. Process. of claim 1 wherein the catalyst in said final stage comprises a platinum-alumina-chloride complex.

12. Process of claim 9 wherein a halogen-containing compound is added to the regeneration gases to the final stage during regeneration.

References Cited by the Examiner UNITED STATES PATENTS 2,969,319 l/ 1961 Sasnowski et a1. 208--65 3,007,862 11/4361 Patten et a1. 208-65 DELBERT E; GANTZ, Primary Examiner.

A. RIMENS, Assistant Examiner.

Claims (1)

1. IN A PROCESS FOR REFORMING PETROLEUM HYDROCARBONS BOILING IN THE GASOLINE AND NAPHTHA RANGE BY PASSING PREHEATED HYDROCARBON VAPORS AND RECYCLED HYDROGENCONTAINING GAS THROUGH A PLURALITY OF STAGES UNDER REFORMING CONDITIONS, THE IMPROVEMENT WHICH RESULTS IN GREATER PRODUCT SELECTIVITY AND WHICH COMPRISES CONTACTING IN AN INITIAL STAGE UNDER REFORMING CONDITIONS THE PREHEATED HYDROCARBONS AND RECYCLED HYDROCARBON-CONTAINING GAS WITH A CATALYST WHICH COMPRISES A DEHYDROGENATION COMPONENT ON A HALOGEN-NON-RETAINING, NON-ACIDIC SUPPORT AND WHICH PROMOTES THE DEHYDROGENATION OF NAPHTHENES; CONTACTING IN AN INTERMEDIATE STAGE UNDER REFORMING CONDITIONS THE EFFLUENT FROM SAID INITIAL STAGE WITH A CATALYST WHICH COMPRISES A DEHYDROGENATION COMPONENT ON AN ACIDIC SUPPORT AND WHICH PROMOTES THE ISOMERIZATION OF CYCLOPENTANES, THE DEHYDROGENATION OF RESULTANT CYCLOHEXANES, AND THE ISOMERIZATION OF PARAFFINS; CONTACTING IN A FINAL STAGE THE EFFLUENT FROM SAID INTERMEDIATE STAGE UNDER REFORMING CONDITIONS WITH A CATALYST WHICH COMPRISES A DEHYDROGENATION COMPONENT ON AN ALUMINA-CONTAINING SUPPORT AND WHICH PROMOTES THE DE-

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