US3676522A

US3676522A - Disproportionation and isomerization for isopentane production

Info

Publication number: US3676522A
Application number: US107214A
Authority: US
Inventors: Robert P Sieg
Original assignee: Chevron Research and Technology Co
Current assignee: Chevron USA Inc
Priority date: 1971-01-18
Filing date: 1971-01-18
Publication date: 1972-07-11
Anticipated expiration: 1989-07-11

Abstract

A process for producing isopentane which comprises: (a) disproportionating a normal butane-rich fraction in a C4 disproportionation zone to obtain C3 and n-pentane; (b) disproportionating a normal hexane-rich fraction in a C6 disproportionation zone to obtain n-pentane and C7; (c) fractionating the C3, nC5 effluent and the nC5, C7 effluent to obtain nC5; and (d) isomerizing at least a portion of the normal pentane from both steps (a) and (b) in an isomerization zone to obtain isopentane. It is preferred to further integrate the disproportionation zones with the isomerization zone using common fractionation facilities.

Description

United States Patent Sieg [ 51 July 11, 1972 3,409,682 1 1/1968 Mitsche ..260/683.65

Primary Examiner-Delbert E. Gantz Assistant Examiner-G. J. Crasanakis [72] Inventor: Robert P. Sieg, Piedmont, Calif. Attorney-G. F. Magdeburger, C. J. Tonkin, A. L. Snow, F. E. [73] Assignee: Chevron Research Company, San Fran- Johnston Dawes and De jonghe v cisco, Calif. I ABSTRACT 7 [22] med 1 Jan 19 l A process for producing isopentane which comprises: (a) dis- [21] Appl. No.: 107,214 proportionating a normal butane-rich fraction in a C disproportionation zone to obtain C; and n-pentane; (b) disproportionating a normal hexane-rich fraction in a C dispropor- [52] U.S.Cl. ..260/683.65, 260/676 R tionation zone to obtain n pemane and C7; (0) fractionating [51] ....C07c 5/24, C070 9/18 the C nC effluent and the nC C effluent to obta n nC and [58] Field of Search ..260/683.65, 676 R (d) isomenzmg at least a portion of the normal pentane from both steps (a) and (b) in an isomerization zone to obtain [56] Reierences Cited isopentane. It is preferred to further integrate the dispropor- UNITED STATES PATENTS tionation zones with the isomerization zone using common fractionation facilities. 3,140,253 7/1964 Plank et al. ..260/683.65 3,392,212 7/1968 dOuville ..;.....260/676 R 8Claims, 1 Drawing Figure C3- 5 AF Y' V (L 24 c3 1 C I7 DISPROPORTIONATION /l2 m c: PRODUCT l0 2 3 14 9 6 z la l5 l6 Q /ns E ISOMERIZATION 2 4 o /3 5 8 s 2\ E C a 8 c K 5 Ce zl I o. DISPROPORTIONATION 22 v U m 20 2.9

DISPROPORTIONATION AND ISOMERIZATION FOR ISOPENTANE PRODUCTION BACKGROUND OF THE INVENTION The present invention relates to a combination process involving isomerization of saturated hydrocarbons. More particularly, the present invention relates to isomerization operated in combination with saturated hydrocarbon disproportionation, and preferably with integrated common fractionation facilities.

lsomerization is a well-known and frequently used step in petroleum refining. It enables the adjustment of the octane number upwards by converting normal paraffins, such as normal hexane, to isoparaffins, such as 2,2-dimethylbutane. A blend of various isomeric paraffins provides a gasoline which has a higher octane number than a gasoline consisting of normal paraffins. lsomerization is generally performed by passing isomerizable hydrocarbons together with hydrogen through a reaction zone containing an isomerization catalyst. The hydrogen-to-hydrocarbon mol ratio varies within a wide range, generally from 0.05:1 to :1, preferably within the range of about 0.05:1 to 2:1 for pentanes and hexanes and 0. l :1 to 1:1 for butanes. The reaction temperature will depend upon the specific hydrocarbons being isomerized and the nature and type of catalyst employed. Hydrocarbon streams consisting chiefly of pentanes and hexanes are usually isomerized at temperatures within the range of 200-900F. The isomerization, normally effected under pressure, may carried out in the liquid or vapor phase. Generally, pressures within the range of 300-1 ,000 psig have been used. A liquid hourly space velocity (LHSV), that is, the volume of liquid charged per hour per volume of catalyst, within the range of 0.5 to 10.0 and preferably within the range of about 0.75 to 4.0 is employed.

Various catalysts have been suggested for use in isomerization processes. ln general, the isomerization can be effected at low temperatures (ca. 300F.) with a Friedel-Crafts catalyst, such as aluminum chloride, or at high temperatures (ca. 750F.) with a supported metal catalyst, such as platinum on halogenated alumina or silica-alumina. Thermodynamic equilibrium for isoparaffins is more favorable at low temperatures; however, the low-temperature process has not received wide application because the Friedel-Crafts catalyst is quite corrosive and therefore expensive metals or alloys must be used. Of the high temperature isomerization processes, the noble metal catalysts such as platinum or palladium are perhaps considered to be the most effective.

As indicated in U.S. Pat. Nos. 2,951,888 and 3,472,912, minor amounts of sulfur compounds in the feed to isomerization processes are harmful for the typical isomerization processes. Catalysts used in typical isomerization processes include composites of a hydrogenating component on an amorphous acidic silica-alumina support and more usually 4 composites comprising halogenated alumina or aluminum,

either of which latter composites are herein referred to as halogenated aluminum catalysts.

According to U.S. Pat. No. 2,951,888, a C -C parafftnic feedstock is desulfurized to a sulphur content less than 1 ppm so that better results are achieved in hydroisomerization of the paraffinic feedstock with a catalyst selected from the group consisting of nickel, nickel-molybdenum, and palladium, supported on an acidic silica-alumina support containing 50-90 percent silica, at a temperature of 650-800F., pressure of 100-1 ,000 psig, and hydrogen-hydrocarbon mol ratio of 0.5-5.0.

U.S. Pat. No. 3,472,912 also discloses an over-all combination process .involving hydrotreating and isomerization wherein a nickel molybdenum-on-alumina catalyst is used under hydrotreating conditions to remove sulfur from C -C saturated hydrocarbons so that the hydrocarbons can be isomerized with increased life for the isomerization catalyst. Preferred isomerization catalysts according to the process of U.S. Pat. No. 3,472,912 are platinum-alumina composites activated by the addition of carbon tetrachloride (thereby resulting in a catalyst which is herein classified as a catalyst containing halogenated aluminum).

Recently, catalysts comprising either natural or synthetic crystalline aluminosilicates have been suggested for isomerization processes. Included among the crystalline aluminosilicates which have been suggested are the type X and type Y' silicates, mordenite, and layered aluminosilicates such as described in Granquist U.S. Pat. No. 3,252,757.

U.S. Pat. No. 3,507,931, titled lsomerization of Paraffinic Hydrocarbons in the Presence of a Mordenite Catalyst" discloses the isomerization of straight run distillates rich in C,,-C normal paraffins using a catalyst having a high silica-to-alumina ratio, preferably above 20:1, and operating the isomerization reaction at relatively low temperatures, such as 250-400F.

U.S. Pat. Nos. 3,280,212 and 3,301,917 also disclose hydroisomerization processes using crystalline aluminosilicate-type catalysts.

As indicated above, the present invention is directed to both isomerization and disproportionation.

The term disproportionation" is used herein to mean the conversion of hydrocarbons to new hydrocarbons of both higher and lower molecular weight. For example, butane may be disproportionated according to the reaction:

. 4 l0 a a a s m As can be seen from the above disproportionation reaction, the butane is in part converted to a higher molecular weight hydrocarbon, namely, pentane. Various processes have been suggested for converting hydrocarbons to higher molecular 7 weight hydrocarbons.

U.S. Pat. No. 1,687,890 is directed to a process of converting low-boiling-point hydrocarbons into higher-boiling-point hydrocarbons by mixing a hydrocarbon vapor with steam and then contacting the steam-hydrocarbon mixture with iron oxide at temperatures in excess of 1,112F. It is theorized in U.S. Pat. No. 1,687,890 that the following reactions may be involved to a greater or lesser extent:

1. Paraffin hydrocarbons on being brought into contact with ferric oxide at elevated temperatures are oxidized or dehydrogenated, forming unsaturated hydrocarbons.

2. Unsaturated hydrocarbons of low molecular weight polymerize into unsaturated hydrocarbons of higher molecular weight when subjected to elevated temperatures, the extent of polymerization depending upon the temperature and duration of treatment.

7. Unsaturated hydrocarbons are hydrogenated by nascent hydrogen."

Another process which has been proposed for converting hydrocarbons to higher molecular weight hydrocarbons is olefin disproportionation. Numerous methods and catalysts have been disclosed for the disproportionation of olefins. In most of these processes, the olefin is disproportionated by contacting with a catalyst such as tungsten oxide or molybdenum oxide on silica or alumina at a temperature between about l ,100 F. and at a pressure between about 15 and 1,500 psia. These prior art processes have been directed to an effective method to convert essentially only olefins, not saturated hydrocarbons, to higher molecular weight hydrocarbons by disproportionation.

For example, in U.S. Pat. No. 3,431,316, an olefin disproportionation process is disclosed, and it is stated that, if desired, parafiinic and cycloparaffinic hydrocarbons having up to 12 carbon atoms per molecule can be employed as diluents for the reaction; that is, the saturated hydrocarbons are non-reactive and merely dilute the olefins which are the reactants.

A process for the direct conversion of saturated hydrocarbons to higher molecular weight hydrocarbons would be very attractive because in many instances saturated hydrocarbons are available as a relatively cheap feedstock. For example, in

many instances, excess amounts of propane and/or butanes are available in an over-all refinery operation.

Processes which have been previously reported wherein saturated hydrocarbons are disproportionated include contact of saturated hydrocarbons with solid catalyst comprised of AlCl on A1 and contact of saturated hydrocarbons with a promoter comprised of alkyl fluoride and BF;,. The use of the AlCl solid catalyst was uneconomic because, among other reasons, the catalyst was non-regenerable. The use of alkyl fluoride and BF was unattractive because of severe corrosion, sludge formation and other operating problems.

In the past it has been the practice to convert saturated hydrocarbons, particularly normal alkanes, to olefins as a separate or distinct step and then to disproportionate the olefins to valuable higher molecular weight hydrocarbons.

For example, in U.S. Pat. No. 3,431,316, saturated light hydrocarbons are cracked to form olefins, and then the olefins are separated from the cracker effluent and fed to a disproportionation zone wherein the olefins are disproportionated to higher molecular weight hydrocarbons. Thus, a separate step is used to obtain olefins because, according to the prior art, no economically feasible process is available for the direct disproportionation of saturated hydrocarbons.

U.S. Pat. No. 3,445,541 discloses a process for the dehydrogenation-disproportionation of olefins and paraffins,

using a combined dehydrogenation and disproportionation catalyst. According to U.S. Pat. No. 3,445,541, a hydrocarbon feed which is either an acyclic paraffin or acyclic olefin having three to six carbon atoms is contacted with the catalyst at conditions of temperature and pressure to promote dehydrogenation and disproportionation. It is said that the process can be carried out at temperatures between 800F. and 1,200F.; however, the lowest temperature used for processing a paraffin in accordance with any of the examples of U.S. Pat. No. 3,445,541 is 980F., and typically the temperature used is between 1,040F. and 1,125F.

The high-temperature process disclosed in U.S. Pat. No. 3,445,541 is shown therein to result in only relatively low yields of saturated higher molecular weight hydrocarbons. The U.S. Pat. No. 3,445,541 process operates with a substantial amount of olefins in the reaction zone and with about to 50 volume percent or more olefins in the effluent from the disproportionation reaction zone. U.S. Pat. No. 3,445,541 does not disclose or suggest any advantages for disproportionation of hexanes and butanes in combination with C and C isomerization.

SUMMARY OF THE INVENTION According to the present invention, a process is provided for producing isopentane which comprises: (a) disproportionating a normal butane-rich fraction in a C disproportionation zone to obtain C and n-pentane, (b) disproportionating a normal hexane-rich fraction in a C disproportionation zone to obtain n-pentane and C (c) fractionating the C nC effluent and the nC C, effluent to obtain nC and (d) isomerizing at least a portion of the normal pentane from both steps (a) and (b) in an isomerization zone to obtain isopentane.

The process of the present invention results in the production of high-octane isopentane from low-octane hexane (such as normal hexane, which has an octane rating of about 26). The isopentane which is produced in the process of the present invention has an octane rating of about 92 and is particularly useful in high-octane unleaded or low-lead-content gasolines.

lsomerization of C hydrocarbons can be used to upgrade the octane rating of normal hexane-rich hydrocarbon fractions. However, the octane can be increased only to about 70-75 (motor octane) by isomerization because the main hexane isomers produced, namely, Z-methyl pentane and 3- methyl pentane, have an octane rating of only 73 and 75, respectively. Although increasing the octane rating of a C fraction from the vicinity of about 26, which is the octane of normal hexane, to about 70-75 by isomerization to produce isohexanes represents a substantial increase, it is generally not a sufficient increase to produce high-octane gasoline components for use in unleaded or lead-free gasolines.

The C -rich hydrocarbons also have been considered as feedstocks for catalytic reforming in order to reform the C material into reasonably low volatility gasoline boiling range hydrocarbons in the octane range. However, the C hydrocarbons have been found to make a relatively unattractive feedstock for catalytic reforming processes.

Thus, it is desirable to provide a process for upgrading C rich hydrocarbon fractions into 90+ octane rating components. The process of the present invention achieves these desired results by the combination of disproportionation with isomerization. The separate normal butane and hexane disproportionation steps are particularly advantageously employed with the isomerization step in the present invention, as both the butane and the hexane disproportionation steps serve to provide a normal pentane stream from the butane and hexane feeds. The normal pentane is converted into isopentane in the isomerization zone. The isopentane has a relatively low Reid Vapor Pressure compared to butanes and a very high motor octane rating compared to hexanes, particularly compared to normal hexane.

The hexane disproportionation zone operates to produce normal pentane according to the reaction:

2 Hexane Normal Pentane Heptane The butane disproportionation step operates to produce normal pentane according to the reaction:

2 Butane Normal Pentane Propane In addition to the two disproportionation steps operating cooperatively with the isomerization step of the present invention, the disproportionation steps are also complementary to one another in the process of the present invention. The C disproportionation zone, in addition to producing normal pentane, will usually produce substantial amounts of butanes. Butane is produced in accordance with the following hexane disproportionation reaction:

Butanes have a high octane rating with normal butane having an octane rating, of about 90 and isobutane having an octane rating of about 99. However, only limited amounts of butanes can be used in motor gasolines before exceeding Reid Vapor Pressure limitations for the gasoline.

Thus, it is particularly preferred in the process of the present invention to upgrade butanes produced in the C disproportionation zone to high-octane gasoline boiling range hydrocarbons which are not as volatile as the C hydrocarbons. In accordance with a preferred embodiment of the present invention, this objective is accomplished by operation of a separate butane disproportionation zone in combination with the isomerization zone and the C disproportionation zone. The butane fed to the C disproportionation zone is at least in part derived from the butanes resulting from the C disproportionation. The butanes are disproportionated in the butane disproportionation zone to obtain increased amounts of normal pentane, which is in turn fed at least in part to the isomerization zone to produce the high-octane, relatively lowvolatility product, isopentane.

Although the butane disproportionation is preferably carried out in the same plant as the plant used for the hexane disproportionation step, usually, and preferably, separate reactors are used for the C disproportionation and the C disproportionation, respectively.

Preferred catalysts for use in both the C and the C disproportionation reaction zones are catalytic masses having a component with alkane dehydrogenation activity and a second component with olefin disproportionating activity, for example, catalytic masses comprising a Group VIII metal component and a Group VIB metal component. Particularly preferred disproportionation catalysts include catalytic masses comprising a noble metal on a refractory support and a Group VIB metal or metal compound on a refractory support, for example a catalytic mass comprising platinum on alumina and tungsten or tungsten oxide on silica. Preferred temperatures for the disproportionation of normal butane and for the disproportionation of C alkanes using the above-indicated catalytic masses are between about 400-850F. and more preferably between 650799F. Pressure maintained in the disproportionation reaction zone is preferably between atmospheric and 2,500 psia, and still more preferably between 100 and 1500 psia. In addition to the preferred relatively low temperature for hydrocarbon disproportionation, we have found that it is preferable to carry out the disproportionation reaction in the presence of no more than a few weight percent olefins, preferably less than 5 weight percent olefins. Preferred conditions for the disproportionation of saturated hydrocarbons such as butane or hexane are further discussed in commonly assigned applications Ser. Nos. 3,303 and 3,306, the disclosures of which applications are incorporated by reference into the present application.

In addition to the butane and hexane disproportionation steps of the process of the present invention cooperating to produce a normal pentane feedstock for conversion to highoctane isopentane in the isomerization step, the disproportionation step also helps insure a high-purity normal pentane feedstock to the isomerization zone as the disproportionation zones themselves require high-purity feedstocks, i.e., free of compounds such as sulfur impurities.

As indicated in U.S. Pat. Nos. 2,951,888 and 3,472,912, minor amounts of sulfur compounds in the feed to isomerization processes are harmful for the typical isomerization processes. Catalysts used in typical isomerization processes include composites of a hydrogenating component on an amorphous acidic silica-alumina support and more usually composites comprising halogenated alumina or aluminum, either of which latter composites are herein referred to as halogenated aluminum catalysts.

According to U.S. Pat. No. 2,951,888, a C -C paraffinic feedstock is desulfurized to a sulfur content less than 1 ppm so that better results are achieved in hydroisomerization of the paraffinic feedstock with a catalyst selected from the group consisting of nickel, nickel-molybdenum, and palladium, supported on an acidic silica-alumina support containing 50-90 percent silica, at a temperature of 650-800F., a pressure of 100-],000 psig, and a hydrogen/hydrocarbon mol ratio of 0.5-5.0.

U.S. Pat. No. 3,472,912 also discloses an over-all combination process involving hydrotreating and isomerization wherein a nickel-molybdenum on alumina catalyst, is used under hydrotreating conditions to remove sulfur from C -C saturated hydrocarbons so that the hydrocarbons can be isomerized with increased life for the isomerization catalyst. Preferred isomerization catalysts according to the process of U.S. Pat. No. 3,472,912 are platinum-alumina composites activated by the addition of carbon tetrachloride (thereby resulting in a catalyst which is herein classified as a catalyst containing halogenated aluminum).

Purification of the feedstock to the C disproportionation zone is necessary so that impurities such as sulfur compounds are not converted to H 8 with the consequent deactivation of the disproportionation zone catalyst. The nC -rich effluent stream from the disproportionation zones is a very excellent feedstock for isomerization using a wide variety of isomerization catalysts. A number of catalysts can also be used very advantageously in the isomerization zone of the present invention, even though they might be sensitive to small amounts of impurities such as sulfur compounds.

Commonly used halogenated aluminum-type isomerization catalysts are sensitive to sulfur impurities. However, the sulfur-sensitive halogenated aluminum-type catalysts can be used for isomerization in the process of the present invention because the disproportionation step of the present invention insures an essentially sulfur-free feed for the isomerization zone.

Halogenated aluminum-type catalysts which are sensitive to sulfur poisons but which can be used advantageously in the isomerization zone of the process of the present invention because of the high purity of the normal pentane derived from disproportionation steps include the catalysts such as used in the Butamer process described in the Oil and Gas Journal, Vol. 56, No. 13, Mar. 31, 1958, pp. 73-76, the BP isomerization process as described in Hydrocarbon Processing, Vol. 45, No. 8, Aug. 1966, pp. 168-170, and the liquid-phase isomerization process described in Hydrocarbon Processing, Vol. 42, No. 7,July 1963, pp. 125-130.

Thus, it is apparent that the process of the present invention allows for the use of a wide variety of isomerization catalysts in the isomerization zone with an expected very long life for the isomerization zone catalyst because of the high degree of purity of the normal pentane feedstock derived from the disproportionation steps preceding the isomerization zone.

Sulfur compounds present in the feed to either the C disproportionation zone or the C disproportionation zone can be removed by various hydrodesulfurization processes. For example, the sulfur can be removed by contacting the sulfurcontaminated feedstock with a catalyst such as NiMo or CoMo on alumina in the presence of hydrogen at elevated temperature and pressure to convert organic sulfur compounds to H S, which in turn can be separated from the remaining hydrocarbons.

Thus, in broad scope, the process of the present invention can be applied to the disproportionation of various C -rich hydrocarbon streams, including C hydrocarbon streams containing organic sulfur impurities. However, it is particularly preferred to feed a purified low-sulfur content C -rich hydrocarbon stream to the C disproportionation zone. A purifled low-sulfur-content C -rich hydrocarbon stream which is a particularly advantageous feedstock for the C disproportionation step in the process of the present invention is a C rich cut from the effluent from a catalytic reforming process. The term catalytic reforming is used herein to refer to reforming processes wherein hydrocarbons, usually boiling in the naphtha range, are reformed by contacting the hydrocarbons with a reforming catalyst (e.g., a composite comprising platinum on alumina) at a temperature usually between about 700 and 1,000F. The C -rich cut from catalytic reforming is essentially free of sulfur impurities. Other C -rich hydrocarbon fractions can be fed to the C disproportionation zone, but in those instances where appreciable sulfur impurities are present a sulfur removal step such as hydrotreating must precede the C disproportionation reaction step.

As indicated previously, one of the particular advantages of the process of the present invention is that a wide variety of isomerization catalysts can be used in the isomerization zone but yet with long life and high activity for the isomerization catalyst due to the high purity of the normal pentane-rich feedstock derived from the disproportionation steps in the process of the present invention. However, in the process of the present invention crystalline aluminosilicate type catalysts are preferred as they can be used to obtain relatively high yields of isopentane and branched-chain C paraffms at temperatures usually about F. less than is required for a comparable isopentane yield using halogenated aluminum-type isomerization catalysts.

Thus, catalysts comprising crystalline aluminosilicates such as molecular sieves, mordenite and layered crystalline alumino-silicates are preferred. It is preferred to use one or more hydrogenation components with the crystalline aluminosilicate. Platinum and palladium are preferred hydrogenation components. Preferred catalysts comprising crystalline aluminosilicate and a hydrogenation component such as palladium or others are described in patent applications Ser. Nos. 776,733 and 839,999, which issued as U.S. Pat. 3,617,490 on Nov. 2, 1971, which applications are incorporated by reference into the present patent application, particularly those portions of the afore-identified applications disclosing catalyst compositions.

Preferred aluminosilicate-containing catalysts for use in the isomerization zone include catalysts comprising a layered clay-type aluminosilicate cracking component with 0.01 to 2.0 weight percent, based on said cracking component and calculated as the metal, of a hydrogenating component selected from platinum, palladium, iridium, ruthenium, and rhodium, and also with 0.01 to 5.0 weight percent, based on said cracking component and calculated as the metal, of a hydrogenating component selected from tungsten and chromium. Particularly preferred hydroisomerization catalysts are those as described immediately above wherein the hydrogenating components are palladium and chromium.

In the present specification, oxides and other compounds of metals are to be considered as included in reference to a metal simply as an element; i.e., chromium includes the use of chromium in compound forms such as chromium oxide.

In addition to the above-discussed integration of the disproportionation steps and the isomerization step, according to a preferred embodiment of the present invention, the isomerization zone is further integrated with the disproportionation zone by using common fractionation facilities, at least in part. The term fractionation facilities" is used herein to mean distillation columns or the like and associated equipment.

The effluent from the C C isomerization zone is usually composed primarily of isopentane, normal pentane, isohexanes and normal hexane. However, there also is present minor or small amounts of propane, isobutane, normal butane and C,* hydrocarbons. It will, of course, be understood that the amount of these secondary hydrocarbons will depend upon several factors, including the composition of the feed to the isomerization zone, the type catalyst used in the isomerization zone (some isomerization catalysts have higher per-pass conversions but lower selectivities to the desired isopentane and isohexane products), and the temperature used in the isomerization zone (higher temperatures usually resulting in more light hydrocarbons such as propane and butanes). The effluent hydrocarbons from normal hexane disproportionation and from normal butane disproportionation according to the preferred embodiments ofthe present invention using the twocomponent disproportionation catalyst usually are primarily propane, normal butane, normal pentane, normal hexane and C, hydrocarbons. However, there will also be minor or small amounts of isobutane, isopentane, and isohexane. The amounts of these isoor branched-chain hydrocarbons will increase if increased amounts ofisohexane are fed to the C disproportionation step. Thus, it is particularly advantageous to use common fractionation facilities for the isomerization zone effluent hydrocarbons and the disproportionation zone effluent hydrocarbons when substantial amounts, for example more than S or 10 weight percent, isohexane is fed to the C disproportionation zone because, in this instance, there is an increased amount of common hydrocarbons from both the isomerization zone and the disproportion zone.

The fractionation facilities required for the effluent from the isomerization zone and for the effluent from the disproportionation zones can range from one or two columns up to about eight sequential columns. For example, a propane splitter to separate propane from isobutane; an isobutane splitter to separate isobutane from normal butane*; a normal butane splitter to separate normal butane from isopentane"; an isopentane splitter to separate isopentane from n-pentane*; a normal pentane splitter to separate normal pentane from isohexane; an isohexane splitter to separate isohexane from normal hexane"; and a normal hexane splitter to separate normal hexane from C The fractionation of the aforementioned hydrocarbon cuts can be carried out in sequential separate columns or, at the other extreme, one column can be used similar to crude oil distillation with side streams being withdrawn from the column and stripped, if necessary. As indicated previously, the amounts of the various components present in the effluents from the isomerization zone and the disproportionation zone can vary. Thus, in some instances, only part of the fractionation for the two zones will be carried out in common fractionation facilities with the other part being carried out in separate fractionation facilities for the respective zones. Because there are usually substantial amounts of normal pentane and C alkanes in the effluent hydrocarbons in both the isomerization zone and the disproportionation zone, it is particularly preferred to carry out the separation of normal pentane from C alkanes in a distillation column common to both the isomerization zone and the disproportionation zone.

In the process of the present invention, the feed to the C disproportionation zone can be a normal hexane feed or a feed containing substantial amounts of isohexane in addition to normal hexane. Usually it is preferred to feed the isohexane as well as the normal hexane to the disproportionation zone so as to produce isopentane (as well as normal pentane from the normal hexane). lsopentane has a substantially higher octane than the isohexanes 2-methyl pentane and 3-methyl pentane, which are the primary isohexane products from isomerization at high temperatures (about 500-800F.) in the pentane isomerization zone.

Some of the important advantages obtained in accordance with particularly preferred embodiments of the present invention include: (I) both the C and the C disproportionation steps operate to produce a normal pentane feedstock for isomerization; (2) desulfurization of the feedstock ahead of the disproportionation step of the present invention eliminates the need for desulfurization ahead of the isomerization step; (3) in utilizing separate C, and C disproportionation reactors in the preferred embodiments as described above, the separate disproportionation steps can be operated at the best temperature, space rates and other operating conditions for their respective feeds, whereas if C, and C alkanes are interacted with one another in an averaging reaction, it is necessary to select the best compromise operating conditions; (4) in addition to the C disproportionation zone handling the problem of some C product from the C disproportionation zone, the C disproportionation zone is advantageously used to handle the problem of some C alkane product from the C disproportionation zone. Thus, each disproportionation reactor takes care of a selectivity problem for the other reactor. For example, two C s go mainly to a C and a C but they do go partly to a C and a C alkane. Conversely, two C s go mainly to a C and a C but do go partly to C and C alkanes; (5) common fractionation facilities can be used to further integrate the disproportionation zone or zones with the isomerization zone. The common fractionation facilities reduce the cost ofseparating the respective components, reduce the complexity of the combination, and make it easier to route undesired products to the proper place to convert them at least partly to the proper product to ultimately produce the desired isopentane product.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic process flow diagram illustrating preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE DRAWING Referring now more particularly to the drawing, a C -rich hydrocarbon stream is fed via lines 1 and 2 to disproportionation zone 3. The C alkanes are disproportionated to produce normal butane and heptane. Also, at least a portion of the C alkanes are usually disproportionated to produce butane and octane. Preferably, the C fraction or cut is obtained from the effluent from a catalytic reforming process. However, various other C,, fractions can be processed in the process combination of the present invention, but the C feed to the C disproportionation zone should be substantially free of sulfur compounds prior to reacting the hexanes with butanes in the dis proportionation reaction zone.

Effluent hydrocarbons are withdrawn from disproportionation zone 3 via line 4 and fed via line 6 to fractionation zone 7. The effluent hydrocarbons from disproportionation zone 3 include normal butane and normal pentane. Normal butane is removed from fractionation zone 7 via line 8 and fed to disproportionation zone 9 via line 10. The normal butane produced in disproportionation zone 3 and removed from fractionation zone 7 via line 8 may be augmented by additional normal butanes or isobutane introduced via line 11 and then line to disproportionation zone 9.

Disproportionation zone 9 converts butanes produced in zone 3 at least in part to normal pentane via the disproportionation reaction:

2 Butanes Normal Pentane Propane The normal pentane and other hydrocarbons produced in C disproportionation zone 9 are withdrawn via line 12 and fed to fractionation zone 7 via line 6. Normal pentane produced in both the C and C disproportionation zones is withdrawn from fractionation zone 7 via line 13 and isomerized in zone 14 to produce the isopentane product which is withdrawn via

lines

15 and 16 or via line 17 after fractionation in zone 7.

Thus, the C and C disproportionation zones complement each other in the production of normal pentane which is isomerized to high-octane isopentane in isomerization zone 14. The disproportionation reaction in the C and C disproportionation zones is preferably carried out in separate reactors, for example parallel reactors in a single disproportionation plant. The preferred catalyst for both disproportionation reactions is a two-component catalyst comprising an alkane dehydrogenation component and an olefin disproportionation component.

Some heavier hydrocarbons, i.e., Cf hydrocarbons, are formed in both the disproportionation zones. These heavier hydrocarbons-are withdrawn from fractionation zone 7 via line 18. The Cfihydrocarbons can be advantageously used as a feedstock for catalytic reforming to produce high-octane gasoline, for example by reforming using a platinum-rhenium on alumina catalyst. Alternately, the C-, hydrocarbons can be recycled to C disproportionation zone 3. The C? hydrocarbons are suitable feedstock for disproportionation in zone 3 to lower hydrocarbons including normal pentane.

Normal pentane is isomerized in zone 14 in the presence of hydrogen using a hydroisomerization catalyst which preferably comprises a crystalline aluminosilicate together with a hydrogenation component such as palladium or platinum. Preferred operating conditions for the C isomerization include a hydrogen gas rate in the range of 1,000 to 5,000 SCF/bbL, preferably 1,500 to 2,000 SCF/bbL; space velocities in the range of about 0.1 to 20 liquid volumes per hour of hydrocarbon feedstock per volume of catalyst, preferably 1.0 to 5.0 LHSV; temperatures in the range of about ZOO-800 F., preferably 250750 F.; and pressures within the range of atmospheric to 3,000- psig, preferably in the range of 500-800 p 1% addition to isomerizing normal pentane in zone 14, normal hexane withdrawn from the fractionation zone via line 20 can be isomerized in zone 14 by passage to zone 14 via

lines

20, 21 and 13. Because the normal pentane feedstock to isomerization zone 14 is a very high-purity feedstock, lowtemperature isomerization can be carried out particularly advantageously, for example at temperatures between about 200-500 F. to produce relatively high yields of the 2,2 dimethylbutane and 2,3-dimethylbutane hexane isomers. The latter-mentioned two isomers have a relatively high octane rating compared to the 2-methylpentane and 3-methylpentane isomers of hexane. The high-octane dimethylbutane hexane isomers are not produced in very high yield using typical hightemperature isomerization at 500 to 800 F. or hydroisomerization effective for simultaneous mild desulfurization and isomerization. Using low-temperature isomerization in zone 14. it is preferred to withdraw an isohexane stream from fractionation zone 7 as indicated in the drawing via line 22.

Using the more typical isomerization operating temperatures between 500 and 800 F., and the preferred isomerization catalyst comprising palladium, chromium, and a layered clay-type aluminosilicate, it is usually preferable to recycle both normal and isohexane from fractionation zone 7 via

lines

20, 23 and 2 to C disproportionation zone 3.

Fractionation zone 7 typically consists of three to eight distillation columns used to separate the various components obtained from both isomerization in zone 14 and disproportionation in zones 3 and 9. As indicated previously, the fractionation zone can have a varying number of distillation columns, and it is preferred to use common fractionation facilities for at least a part of the separation of effluent hydrocarbons from isomerization zone 14 and disproportionation zones 3 and 9. It is particularly preferred to carry out the fractionation of normal pentane from C alkanes in the same fractionation column for effluent hydrocarbons from disproportionation zone 3 and isomerization zone 14.

C hydrocarbons are introduced to fractionation zone 7 from several sources. A portion of the C hydrocarbon feed to disproportionation zone 3 is not converted in a single pass through disproportionation zone 3, and, as indicated previously, some C hydrocarbons are formed in disproportionation zone 9 in the disproportionation of butane.

Propane and other light gases formed in isomerization zone 14 and also in disproportionation zone 3 are removed from the effluent hydrocarbons from these two respective zones by separation in zone 8. Preferably, common fractionation facilities are used to separate the propane and other light gases generated in disproportionation zones 3 and 9 and in isomerization zone 14, particularly when the isomerization is carried out at a high temperature, for example in excess of 700 or 750 F., so as to generate substantial amounts of propane and other light hydrocarbons. When the isomerization zone is operated at relatively mild conditions, for example below 700 F., and with only one or two weight percent or less propane produced in isomerization zone 14, depropanizing the effluent hydrocarbons from the isomerization zone can advantageously be carried out separate from the depropanizing of the effluent hydrocarbons from disproportionation zones 3 and 9.

EXAMPLES Example 1 The data tabulated in Table 1 below illustrate the results obtained in disproportionating normal butane by contacting normal butane with an alkane disproportionation catalyst mass under the following conditions:

Volume of Catalyst in Reactor: 9 cubic centimeters (cc.)

Type of Catalyst:

2 cc. of0.5 wt. Pt; 0.5 wt. Re; 0.5 wt. Li on A1 0 7 cc of 8.0 wt. W0 on SiO Both types of catalyst particles were 28 to 60 Tyler mesh size.

Operating Conditions:

Temperature: 650, 700, 750, 800, 875 F.

Pressure: 900 psig Feed rate: 9 cc./hour Successive runs, of several hours each with no regeneration in between, were made at the temperatures specified, except that the catalyst was reactivated by flushing the catalyst overnight with hydrogen before the run at 875 F.

As can be seen from the date tabulated in Table l, the ultimate yield of C decreases considerably in moving from particularly preferred temperatures below 800 F. to temperatures in excess of 800 F. as, for example, temperatures as high as 875 E, where the ultimate yield of C drops to about 42 percent vs. approximately 57 percent at 750 F. More importantly, the yield of nC is seen to be greater at temperatures between 700 and 800 F. than at higher temperatures such as 875 F.

TABLE! Weight Product Yields at Various Operating Temperatures Product 650F 700F 750F 800F 875F 2 branched C.,H,. a u

I CGHIZ E branched C,H nC-,H

Z branched C H nC H E branched C H 72 branched chain in C,,--C range]" EXAMPLE 2 Using a Pd-Cr-layered aluminosilicate crystalline zeolite catalyst, a C -rich fraction free ofsulfur was isomerized at 800 psig, LHSV 1.0 and hydrogen rate 17,000 SCF/bbl. of feed, with the results as shown in Table ll.

broad application to combined C and C disproportionation to normal pentane followed by normal pentane isomerization to produce isopentane. Accordingly, the invention is not to be construed as limited to the specific embodiments or examples discussed, but only as defined in the appended claims or substantial equivalents of the claims.

WHAT IS CLAIMED IS:

1. A process for producing isopentane which comprises:

a. disproportionating a normal butane-rich fraction in a C disproportionation zone to obtain C and n-pentane;

b. disproportionating a normal hexane-rich fraction in a C disproportionation zone to obtain n-pentane and C c. fractionating the C n-pentane effluent of step (a) and the n-pentane, C-, effluent of step (b) to obtain said npentane and d. isomerizing at least a portion of the normal pentane derived from both steps (a) and (b) in an isomerization zone to obtain isopentane. 2. A process in accordance with claim 1 wherein common fractionation facilities are used at least in part for effluent hydrocarbons from the disproportionation zones and the isomerization zone. I

3. A process in accordance with claim 1 wherein the same fractionation column is used for the fractionation of normal pentane from C alkanes present as a mixture in effluent hydrocarbons from both the isomerization zone and the C disproportionation zone.

4. A process in accordance with claim 1 wherein the isomerization catalyst comprises palladium or platinum with a crystalline aluminosilicate.

5. A process in accordance with claim 1 wherein the isomerization catalyst comprises 0.05 to 5.0 weight percent palladium and 0.05 to 5.0 weight percent chromium on a layered clay-type crystalline aluminosilicate.

6. A process in accordance with claim 1 wherein the normal butane and the normal hexane disproportionation reactions are carried out at a temperature between 400 and 850 F. using a catalyst comprising a noble metal on an alumina support and a Group VlB metal compound on a silica support.

7. A process in accordance with claim 1 wherein the normal butane and normal hexane disproportionation reactions are carried out by a process comprising contacting the C alkanes with a catalytic mass comprising platinum on alumina and tungsten or tungsten oxide on silica at a temperature between TABLE IL-ISOMERIZATION OFSYNTHETIC NAPHTHA Catalyst temperature, F.

'lotal cracked prod.

I Wt. percent 0. 0. 49 U. 53 0. 63 0. 98 1. 33 1. 87 2. 74 3. 66 5. 36 7. 41 l). 30 13. 92

ISO-(1., 14. 36 14. 15 l5. 65 16. 37 17. 30 22. 07 25. 41 28. 48 36. 80 32. 48 30. 71 30. 35 20. 13 29. 34

n-(I l 32. 56 35. 75 35. 66 34. 16 32. 65 27. 37 25. 03 22. 71 20. 19. 4O 17. 44 17. 33 17. 03 17. 26

2,2-(linl0lllyl butane s 0. 46 6. 61 0. 93 2. 11 2. 3. 52 4. 26 4. 27 5. 31 5. 56 5. 40 4. 9O

2,3-dlm0tl1yl butane" 0. 75 1. 00 1. 33 1. 98 2. 25 2. 40 2. 48 2. 56 2. 6O 2. 67 2. 54 2. 3E) 2-metliyl pentane 10. 96 13.17 13. 38 14. 44 15. 33 15. 38 14. 97 14. 66 13. 98 13. 41 13. 51 13. 72 12. 99 12. 28 3-metliyl pentane 11. 47 10. 22 9. 99 10. 23 10. 66 10. 73 16. 52 1U. 19 ll. 89 9. 46 J. 62 ll. 69 9. 28 8. 79 n-Co 21. 54 17. 20 15. 74 14. 47 13. 17 10. 62 ll. 98 9. 45 9. 24 8. 99 ll, 22 l). 12 9. 0O 8, 44 Methyl cyelopentane 2. 47 4. 74 5. 63 6. 19 6. 68 7. 07 6. 28 5. 64 5. 22 4. 64 4. 73 3. 69 3. 73 2. 42 Benzene- 0. 79 Cyelohexane 5.83 3. 73 3. 03 2. 03 1. 51 1. 28 1. 22 0. 82 0.82 0. 66 0. 83 0. 46 1. 05 0. 26

Although various embodiments of the invention have been about 650 and 850 F. and a pressure between about 100 psia described, it is to be understood that they are meant to be iland 1,500 psia.

lustrative only and not limiting. Certain features may be changed without departing from the spirit or scope of the present invention. It is apparent that the present invention has

Claims

2. A process in accordance with claim 1 wherein common fractionation facilities are used at least in part for effluent hydrocarbons from the disproportionation zones and the isomerization zone.
3. A process in accordance with claim 1 wherein the same fractionation column is used for the fractionation of normal pentane from C6 alkanes present as a mixture in effluent hydrocarbons from both the isomerization zone and the C6 disproportionation zone.
4. A process in accordance with claim 1 wherein the isomerization catalyst comprises palladium or platinum with a crystalline aluminosilicate.
5. A process in accordance with claim 1 wherein the isomerization catalyst comprises 0.05 to 5.0 weight percent palladium and 0.05 to 5.0 weight percent chromium on a layered clay-type crystalline aluminosilicate.
6. A process in accordance with claim 1 wherein the normal butane and the normal hexane disproportionation reactions are carried out at a temperature between 400* and 850* F. using a catalyst comprising a noble metal on an alumina support and a Group VIB metal compound on a silica support.
7. A process in accordance with claim 1 wherein the normal butane and normal hexane disproportionation reactions are carried out by a process comprising contacting the C6 alkanes with a catalytic mass comprising platinum on alumina and tungsten or tungsten oxide on silica at a temperature between about 650* and 850* F. and a pressure between about 100 psia and 1,500 psia.
8. A process in accordance with claim 7 wherein the olefin concentration in the disproportionation reaction zone is maintained below about 5 volume percent.