US2905736A

US2905736A - Isomerization of hexane

Info

Publication number: US2905736A
Application number: US675882A
Authority: US
Inventors: Donald H Belden
Original assignee: Universal Oil Products Co
Current assignee: Universal Oil Products Co
Priority date: 1957-08-02
Filing date: 1957-08-02
Publication date: 1959-09-22
Anticipated expiration: 1976-09-22

Description

S ept. 22, 1959 D. H. BELDEN IsoMERIzATIoN oF HEXANE Filed Aug. 2, 1957 xtmnxm 25N ankommt Enns@ mmh QQ 83am@ MDS Babs@ N VEN TOR.' Dona/d H. Belden A TTORNE YS.

@WSQ

N Zh um United aStates Patent" C) ISOMERIZTION 0F Donald H. Belden, Prospect Heights, Ill., assiguor, by

mesne assignments, to Universal Oil Products Company, Des Plaines, lll., a corporation of Delaware Application August 2,1951, Serial No. 675,882 f 6 Claims. (Cl. 26o-683.68)

butanes and pentanes in which process high yields` of two separate high antiknock hydrocarbon fractions are. produced. This invention also relates to a particularl series of process steps, the Vuse of which results .in maximum catalyst life and optimum product quality; These ob'- jectives are accomplished by the 'uniqueI combinationv processv of the present invention as will be set forthhereinafter.

Production of highly branched chain paraffin hydrocarbons having' high'y antilrnock properties and therefore suitable for use in automotive and'aviation fuels: is of considerable importance in the petroleum refining industry. Furthermore, the recent introduction of automobile engines of high compression ratio has necessitated the* utilization of high antiknoclc fuels, iny these. engines to obtain maximum horsepower output therefrom. Til-us the demand for higher and higher octane. number fuels has led to-the need for increased quantities of highly branched chain paraiinic hydrocarbons of high antiknock values.-

A: convenient source of such highly branched chain parafnic hydrocarbons is the catalytic isomerization of less highly branched'chain parailinicihydrocarbons. Normal butano and normal pentane have been'isomerized to' iso butane and isopentane, respectively,by various prior art processes` utilizing either liquid orvapor phase.. How-1 ever, it iswell known in the art thatA crackin-g occurs along with isomerizatiorn and that this. cracking increases with increasing molecular weight of the hydrocarbonreactant. A process of the isomerization of hexane is therefore particularly attractive when it is realized that thev hexane fraction can be converted by proper isomerization and fractionation into a high antiknock hydrocarbon fraction. It is therefore an objective of this invention toV provide such a-` process which will yield thesedesired high octane hexane isomers.

Prior art processes forthe isomerization of vsaturated hydrocarbons have taught ther-use of various catalytic agents to accelerate the desired molecular rearrangement.

at the particular operating conditions selected. Various catalytic agents which have been utilized are. metal halides such as aluminum chloride, aluminum bromide, etc.,- and these catalytic agents were activated by the Vaddition of their respective hydrogen halide. Because these catalytic agents have a very high activity factor, various disadvan-v tages resulted with the use of these agentsv inthe isom-` erization of a hexane fraction. One of-thedisadvantages is the fact that these catalytic agents notV only ac celerate isomerization reactions, but they also accelerate ICC eraclri'ngy or decomposition reactions. These decomposition reactions are particularly detrimental to the overall economics of an isomerization process since they cause the loss of a portion of the charging stock as well as in-l butane, 2-methylpentane, B-methylpentane, n-hexane,`

methylcyclopentane, benzene, and cyclohexane. Thefboil-v ing range of such a hexane fraction is from about F. to about F. By the combination process of this invention the high octane number components are selec'- tively fractionated so that only a minimum of these components are passed to the isomerization reaction zone. The isomerization reaction zone feed will be a fractioncomprising Z-methylpentane, B-mcthylpentane, normal hexane, and some methylcyclopentane. This isomeriza` tion reaction zone feed will be converted to an equilibV` rium mixture of hexane isomers which will comprise 2,2-v dimethylbutane', 2,3-dimethylbutane, Z-methylp'entane, 3- methylpentane, normal hexane, methylcyclopentane, and cyclohexane. By lthis particular-process and selective fractionation therein, two high octane number hydrocarbon products are attained, both productsI of higher octane number than the fresh feed.

One embodiment of this invention provides a process for the isomerization of an isomerizable saturated hydro carbon fraction in the presence of hydrogen and an isom# erization catalyst which comprises introducing a saturated hydrocarbon fraction into an intermediate sectionY of a rst fractionation zone while at the same time passing av portion of a liquid phase product stream from the bottom of a second fractionation zone to the upper por.- tion ofV said first fractionation zone, passing a vapor phase saturated hydrocarbon fraction from an upper portion of said first fractionation zone to the lower portion of said second fractionation zone, removing from the bottom of said first fractionation zone an isomerization reaction'.

zone feed and introducing said feed into an isomerization reaction zone wherein low octane number saturated hydrocarbons are isomerized to higher octane number saturated hydrocarbons, passing a liquid phase eluent stream v from said isomerization reaction into anntcrmediate. portion of a second fractionation zone, removing overhead from said second fractionation zone a high octane number product enriched in isomerized hydrocarbons, passing from the bottom of said second fractionation zone a second product which is partially enriched in isomerized hydrocarbons and returning a portion of said second product to the upper portion of said first fractionation zone as aforesaid.

Another embodiment of the present invention providesy drawing from the bottom of said first fractionation zone a hydrocarbon fraction enriched in normal hexane and passmg said fractlon to an isomerization reaction zone wherein said fraction is contacted with hydrogen and said isomerization catalyst at isomerization conditions toI produce an enriched isohexane effluent fraction, introducing said isomerization effluent into an intermediate portion of a second fractionation zone, passing overhead from said second fractionation zone an isohexane enriched high octane number hydrocarbon fraction, with drawing from the bottom of said second fractionation zone a lower octane number product than the overhead product, and passing a portion of said product to the upper portion of said first fractionation zone as aforesaid.

The process of the present invention has several advantages, all interrelated. One of the advantages contained in the present process of this invention results from the particular arrangement of the selective fractionation section of the process. As stated hereinabove, the hexane fractions which are suitable for use as feed stocksA in the process of the present invention contain various hexane isomers and cyclic compounds. To produce satisfactory octane number products by the isomerization process of this invention it is necessary that a maximum amount of isomerization of the lowest octane number isomer, normal hexane, be accomplished. Another hexane isomer which occurs in these feed stocks is methylcyclopentane. This isomer has a boiling point of 161, while normal hexane boils at 156 F. From these two boiling points it is obvious that fractionation of one of these components from the other presents a difficult problem. In isomerization of hexane fractions a portion of the cyclics contained in the fresh feed is converted to non-cyclic components. The reaction zone feed must be a bottoms fraction, since Water or its oxygen equivalent, which is found in the fresh feed must be removed overhead by distillation drying since the presence of water in the reaction zone feed would tend to deactivate the isomerization catalyst. However, it is obvious that cyclic components will tend to build up in the reaction zone feed because of the higher boiling points of the cyclic compounds. In the process of the present invention where it is desired to produce two higher octane number products from one lower octane number feed stock. it has been found that cyclics build up in the reaction zone feed can be prevented by introducing the isomerization reaction'zone effluent product at an intermediate point in a fractionation zone between the withdrawal points of the two desired higher octane number products. This is contrary to what is taught in the prior art where recycle is combined with fresh feed for introduction into a fractionation zone. A critical feature of the process of the present invention is that the reaction zone liquid effluent is introduced at an intermediate point between the withdrawal points for both liquid products. By the introduction of the effluent stream at this intermediate point the quantity of cyclics in the isomerization reaction zone feed will be maintained constant since a portion of the cyclics equivalent to that introduced in the fresh feed will be drawn off at the withdrawal point of the intermediate octane number liquid product. lf the reaction zone effluent is introduced to the fractionation zone of the present process at a lower point than the withdrawal point for the intermediate octane number product, cyclic build up will occur in the process. By varying the point of introduction of the reaction zone efliuent into the intermediate portion of the fractionation zone, one can vary the octane number of the products to attain that which is desired. Another advantage of the process of the present invention is that catalyst deactivation or destruction is minimized or substantially eliminated by distillation drying of the reactor feed and rejection of small amounts of water contained therein along with the dirnethylbutanes in the overhead from the rst fractionation zone. All isomerization catalysts depend upon an acid function to accomplish the desired isomerization reaction. This acid function is destroyed or decreased by the contact of the catalyst with water. Utilization of the process of the present invention prevents this deactivation. A further advantage of the process of this invention is that by the elimination of dimethylbutanes, from the reaction zone feed, the quantity of reaction zone feed is reduced as well as the combined feed ratio and thus the total investment necessary for catalyst can be substantially reduced. Theseand other advantages will be explained more fully in the following detailed descrip- Y- tion of the process of the present invention.

As set forth hereinabove this invention relates to a. process for the isomerization of paraflinic hydrocarbons boiling above butanes and pentanes. Hydrocarbons within the scope of the above limitation and utilizable in the process of this invention include methylcyclopentane,

cyclohexane, normal hexane, Z-methylpentane, S-methylpentane, 2-methylhexane, 3rnethy1hexane, S-ethylpentane, n-heptane, methylcyclohexane, ethylcyclohexane, noctane, Z-methylheptane, B-methylheptane, etc. The

j process of this invention is particularly applicable to the .L component.

isomerization of hexane fractions. Various sources of these hexane fractions include fractionation from straight run gasoline, straight run naphtha, natural gasoline, catalytically reformed naphtha, and catalytically reformed gasoline.

Isomerization catalysts which are utilizable within the generally broad scope of the process of the present invention are herein set forth. These catalysts include a support, an acid-acting function, and a hydrogenation The support may be selected from various diverse refractory oxides including silica, alumina, silicaalumina, silica-alumina-magnesia, silica-alumina-zirconia, silica-zirconia, etc. Depending upon the method of preparation and upon the treatment of the support thereafter, these various supports will have surface areas rangparticularly gamma-alumina having a surface area of from about 150 to about 450 square meters per gram. When gamma-alumina is utilized as the support, the acid-acting function can be added to the catalyst by the incorporation therein of what is known in the art as combined halogen. The amount of combined halogen can be varied from about 0.01 to about 8% by weight based on the alumina. 0f the various halogens which may be utilized, both iiuorine and chlorine can be used satisfactorily. Thus in an alumina type catalyst to be utilized at reaction temperatures of from about 750 to about 850 F., about 0.3% by weight of fluorine and about 0.3% by Weight chlorine may be incorporated therein. When it is desirable to utilize the catalyst at lower temperatures, for example, about 500 to about 750 F., as in the case in the preferred embodiment of the invention, the combined halogen which will be utilized along with the alumina support is fluorine, and this fluorine will be utilized in an amount of from about 2.5% to about 4.5% by weight. The composite will then have the desired hydrogenation component combined therewith. This hydrogenation component willV normally be selected from groups VI(B) and VIII of the periodic table or mixtures thereof. Such hydrogenation components include chromium, molybdenum, tungsten, iron, cobalt, nickel, and the so-called platinum group metals including platinum, palladium, ruthenium, rhodium, osmium, and iridium. Of the various hydrogenation components which may be utilized those of the platinum group metals are preferred, and of these platinum group metals, platinum itself is particularly preferred. The hydrogenation component of the catalyst of the present invention-will normally be utilized in anv amount-cf from' about 0.01% to about- 10% by weight based fonthe-weight -ofthesupport. With the preferred platinum group metals, particularly platinum, the .quantity;utilized will range from about 0.01% to about 2%. by weight. A .particularly preferred catalyst comprising platinum, combined halogen, and alumina will contain ;4% platinum, 4.0% fluorine, and alumina. Because ofV equilibrium considerations andbecause it is often desirable andor advisable -to carry out the isomerization reaction-at the lowest possible temperature, for example, from-aboutv 300 toabou-t 500 F., catalysts may also be prepared by yimpregnatingl composites such -asdeseribed hereinabove with-a metal halide of the Friedel-Crafts type For example, an kexcellent low temperatureisomcrit/:ation catalyst can beV prepared by impregnating from Yabout to vabout 20% aluminum chloride :onto a composite 1 of platinum, alumina, and combined halogen. `'Ille-@process of the presen-t invention lcan -be Aused with other .catalysts but not-necessarily with equivalent results.' Such catalystsvareV aluminum chloride sludge, aluminum bromide sludge, etc., which may be used -along with hydrogen chloride, hydrogen bromide, etc., if .so desired. VThe:isomerization processof thisinve'ntion may be carriedioutfat varying conditions of temperature, pressure, liquid hourly space velocity, and combined feed lratio. The ternperature utilized' will .generally be` dictated by the particular isomerization catalyst and thereforel tem'- peratureswill be from about..300 F-.itor about 800 F. 'Ifhepressure selectedfor the isomerization reactionzo'ne Willzbelow.- enough: so as.-to insure vapor operation of the isomerization reaction zone feed and this pressure will-range froml about 100A pounds Iper' square inch to about: 1000 .pounds per-squarepinch. The `liquid hourly space velo'eity-(which may bedened as the; ratio of the liquidvolume of inlet material to the volume of the reaetionspace) willrange from about 0.1 to; about l0 ormore, the onlyl-i'mitation :being that equilibrium mixtures fof-isome'rized hydrocarbons are obtained in the reactionzone "eiuentf. The combined-feed ratio (which may be defined as the total amount of fresh feed plus the 1. recycle reaction Yzone effluentfentering thereactor divided by thefquantity'of fresh'feed) will range from aboutl tov about 5 or more. In the-preferredembodi-4 ment offthe :present invention, hydrogen is utilized to minimizecracking and to maintain thesurface ofthe catalyst in a. carbonv free condition. The quantityof hydrogen utilized will range from about 0;25 to about =mols or more of hydrogen per mol of hydrocarbon. The #hydrogen consumption 4will -be exceedingly small, inz-'th'egrange of from about l30 to about 100 cubic feet prbarrel ,of hydrocarbon feeds The .process of .the present inventioncan; perhaps be bestunderstood by reference to the accompanying drawing.- whichv is a schematic diagram :ofthe process ow; Referring to Vthe .drawing of :Figure I, a saturated hydro'- carbon:;fraction `which is enriched in normal. hexane is introduced. through line 1 into an intermediate portion Off :fractionation zone- 2. The aforesaid hydrocarbon fraction is -fractionated'in'fractionation zone 2 so'that a portion ofthe branched-chain isomers contained. in the fresh feed may be passed overheadthrough'line 24. The liquid-.portion of theremaining `hydrocarbon fraction will be-.withdrawn from: the bottom .of Yfractionation. zone 2 through. line V3 and passed on to an isomerization reac= tion zone-1 for subsequent conversion to highl octane number. isomers. A rising vapor stream in fractionation zoneLZis passed 'overhead through line 24 to'the lower poi-tiongof-a second fractionation zone 12..whereintwo high octane number hydrocarbony products will be with2 drawn from saidffractionation rone .12. Ahydrocarbon fraction substantially rich-in normal hexane is withdrawn from-thebottom of fractionationzoneZ bycondit means tandis passed to a heater 4 where a vaporphase isomerization reaction zone feed is withdrawn by means` ofaconduit andcombined with a'hydrogen gas recycle stream incline 10. -The` hydrogen gas recycle-streamjs supplemented by a make up of hydrogen introduced through line 11. The combined isomerization reaction zone lfeed and hydrogen recycle gas are passed through conduit means 5 into reaction zone 6 wherein isomerizable vapor phase hydrocarbons are converted to high octane number isomers. Isomerization reaction zone efliuent is withdrawn from thebottom of reaction zone 6 through conduit means 7 and is introduced into separation zone V8 wherein a liquid phase hydrocarbon product stream is separated from a substantially pure hydrogen gas stream: The substantially pure hydrogen gas stream is withdrawn from separation zone 8 by means of conduit 10. A liquid hydrocarbon product stream `is withdrawn from the bottom of separation zone 8 by means of conduit 9 and is introduced into an intermediate portion of fractionation zone 12.

An'alternate flow of the hydrocarbon product stream after discharge from separation zone 8 is-illustrated in the drawing of FigureI wherein a conventional debu-l tanizer 28 is shown. This debutanizer isa conventional fractionation zone by means of which a light hydrocarbon gas'or low boiling cracked products are removed from the process. This removal is accomplished by the closg ing of valve 26 in line 9 and the opening of valve 27 in line 25 so that the hydrocarbon product stream passes directly from the bottom of separation zone 8 through line 9 and into the lower portion of debutanizer column 2.8.y The debutanized product is withdrawn from the bottom of column 2S by means of line 29 which is joined to line 9 by the opening of valve Y31. The light hydrocarbon gases arewithdrawn from the top of column 28 by means of line 30. I

The debutanizer column 2S is eliminated from the ow of the isomerizationreaction zone eifluent by the closing of valve 27 in line 25, the closing of valve 31 in line 29,V and the opening of valve 26 in line 9. The efuent stream now flows directly from the bottom of separation Y8 through line 9 into an intermediate portion of fractionav tion zone 12. l

The purpose of fractionation zone 12 is to separate by fractional distillation the isomerization reaction zone efhuent stream to produce two separate product streams of high antilrnock hydrocarbons. The isomerization reaction zone efuent is enriched inbranched-chain isomers from the fresh feed that are introduced into fractionation zone 2 while at the same time unconverted isomerizable hydrocarbons are passed from the lower portion of rfractionation zone 12 into the upper portion of fractionation zone 2 back to the isomerization reaction zoned... A conduit 20 is provided from the lower portion of fractionation zone 12 for the withdrawal of an intermediate product of a middle octane number hydrocarbon and cyclic componentswhichare withdrawn by means of line 21. In the drawing, specification, and claims'the withdrawal is shown and discussed as a bottoms with.v-` drawal. By the use of the term bottom no intention is meant to restrict the withdrawal to the eX-act bottom of thefractionation zone but the bottom may refer to.` any lower portion of the fractionation zone. A hydro`v carbon fraction containing high octane number isomers' is passed overhead from fractionation zone 12 and withdrawn by means of conduit 13 and introduced into a cooler'lii'frorn where a liquid product stream passes to receiver 15. The highl octane number hydrocarbon prodi uct is withdrawn from receiver 15 by conduit 16 and a portion of this product is returned as reflux to fractionation ione 12 .by meansof pump 18 and conduit 19.` If .the debutanizer column 28 has been eliminated from the process flow of this invention, then the low boiling hydrocarbon gassesare removed from the process by passing said gases from receiver 15- by means of line 33l and pressure. control'valve .34. The remainingrhydro-f carbon, isomerization 'reaction` `zone product is :passed: tot

7 line 17 from where it is withdrawn as a high octane number hydrocarbon product stream.

Another modification of the invention is shown in Figure II. This modification resembles the process of Figure I except that in this instance the second fractionation zone 12 is shown superimposed and internally connected with the first fractionation zone 2, however, separate zones may be utilized within the scope of this improved process as is illustrated in Figure I.

Referring to the drawing of Figure II, a saturated hydrocarbon fraction which is enriched in normal hexane is introduced through line 101 into an intermediate portion of fractionation zone 102. As has previously been stated the aforesaid hydrocarbon fraction 101 is fractionated in this portion of fractionation zone 102 so that a portion of the branched chain isomers contained in the fresh feed may be passed to the upper portion of fractionation zone 112. The liquid portion of the remaining hydrocarbon fraction will be withdrawn from the bottom of fractionation zone 102 by means of conduit line 103 and passed on to an isomerization reaction zone for subsequent conversion to high octane number isomers. A rising vapor stream in fractionation zone 102 is passed to a lower portion of a second fractionation zone 112 wherein two separate high octane number product streams are withdrawn from said fractionation zone 112. A liquid hydrocarbon stream which has been passed through the isomerization reaction zone is introduced into an intermediate portion of fractionation zone 112 by means of line 109. The purpose of fractionation Zone 112 is to separate by fractional distillation the isomerization effluent stream to produce two separate streams of high anti-knock hydrocarbons. The isomerization reaction zone effluent is enriched in isomers from the fresh feed that is introduced into fractionation zone 102 while at the same time the unconverted isomerizable hydrocarbons are passed from the lower portion of fractionation zone 112 into the upper portion of fractionation 102 for subsequent recycle back to the isomerization reaction zone. Conduit 120 is provided from the lower portion of fractionation zone 112 for the withdrawal of intermediate product of middle octane number hydrocarbon and cyclic components that collect on collecting plate 132 and thus the return of these cyclic components to the isomerization reaction zone is substantially prevented. A hydrocarbon fraction containing high octane number isomers is passed overhead from fractionation zone 112 and is withdrawn by means of conduit 113 and` introduced into a cooler 114 from where a liquid product stream passes to receiver 115. A high octane number hydrocarbon product is withdrawn from receiver 115 by conduit 116 and a portion of this product is returned as refiux to fractionation zone 112 by means of pump 118 and line 119. The remaining hydrocarbon isomerization reaction zone product is passed to line 117 from where it is withdrawn as a high anti-knock hydrocarbon product. If the debutanizer column 28 has been eliminated from the process ow of this invention, then the low boiling hydrocarbon gases are removed from the process by passing said gases from receiver 115 by means of line 133 and pressure control valve 134.

Example I One specific example of the operation of the process of this invention in the presence of a catalyst comprising platinum, aluminum, and combined halogen is herewith described.

The process is carried out similar to that set forth hereinabove with reference to Figure i and the catalyst utilized comprises alumina containing 0.4% platinum and about 4.5% combined tiuorine.

' This example illustrates the isomerization of a hexane fraction having a boiling range of from about 30 C. to about 90 C. The composition of this hexane fraction is as follows: cyclopentane, 0.8%; 2,2-dimethylbutane,

1.7%; 2,3-dimethylbutane, 5.1%; 2-methylpentane', 25.8%; S-methylpentane, 16%; normal hexane, 39.4%; methylcyclopentane, 6.2%; cyclohexane, 2.9%; and nor.- mal heptane, 2.1%. Referring again to the drawing of Figure I this hexane fraction in the quantity of 432 mols per hour is passed as a liquid through line 1 into an intermediate portion of fractionation zone 2. The aforesaid hexane fraction is fractionated in this portion of fractionation zone 2 so that a portion of the branched chain isomers contained in the fresh feed may be passed overhead. A rising vapor stream in fractionation zone 2 is passed to the lower portion of a second fractionation zone 12 by conduit means 24 wherein two separate high octane number products will be withdrawn from said fractionation zone 12. A portion of the isomerization reaction zone effluent is withdrawn from the bottom of said fractionation zone 12 by means of line 20 and passed to the upperportion of said fractionation zone 2 by means of pump 22 and line 23. This effluent fraction is combined with fresh feed introduced into fractionation zone 2 for the further fractionation of the combined feed so that a.; isomerization reaction zone feed is prepared which contains an equilibrium quantity of cyclic components and an increased quantity of isomerizable hydrocarbons.

The isomerization reaction zone feed is withdrawn from the bottom of fractionation zone 2 by means of line 3. The isomerization reaction zone feed is charged at the rate of 480 mols per hour to a heater 4 and this feed comprises 9 mols per hour of 2,3-dimethyl butane, 80 mols per hour of Z-methylpentane, 77 mols per hour of 3-methylpcntane, 203 mols per hour of normal hexane, 60 mols per hour of methylcyclopentane, 18 mols per hour of cyclohexane, and 33 mols per hour of normal heptane. The cornbined feed ratio which has been hereinabove defined is 1.1 in this particular example. The aforesaid isomerization reaction zone feed is introduced into heater 4 and is substantially vaporized therein and withdrawn from said heater at a temperature of 600 F. The substantially vaporized isomerization reaction zone feed is Withdrawn from heater 4 through line S at a temperature of 600 F. and is combined with a hydrogen recycle gas stream line 10, the hydrogen recycle gas rate being high enough so that a mol ratio of combined hydrocarbon feed to mols of hydrogen gas is 2. This is accomplished by recycling the hydrogen from the separation zone 8 to the isomerization reaction zone 6. A small amount of substantially pure make up hydrogen is added to the system through line 11 to compensate for the hydrogen used up in the reaction and that which is removed as dissolved gas. The reaction is carried out at a pressure of 550 pounds per square inch in vapor phase at a liquid hourly space velocity of 2. As set forth hereinabove isomerization of the reaction zone feed is accomplished in reaction zone 6 in the presence of the hereinabove described catalyst and results in the production of 480 mols per hour of reaction zone effluent containing 56 mols per hour of 2,2-dimethylbutane, 31 mols per hour of 2,3-dimethy1- butane, 121 mols per hour of Z-methylpentane, 82 mols per hour of 3-methylpent'ane, 82 mols of normal hexane, 64 mols of methylcyclopentane, 10 mols per hour of cyclohexane, and 34 mols of heptane.

The isomerization reaction zone eiuent is withdrawn from reactor 6 by means of line 7 and passed to a separator 8 wherein a separation of liquid hydrocarbon and recycle hydrogen gas is attained. The hydrogen recycle gas is passed overhead from separator 8 by means of conduit 10 which joins the combined feed to the isomerization reaction zone in line 5. The isomerization reaction zone efuent is withdrawn from separator 8 by means of conduit 9 and in this particular case is passed to a debutanizer column 28 wherein the low boiling hydrocarbon gases are passed overhead from said debu-l tanizer column 28 it is necessary that valve 26 in line 9 be closed and the valve 25 in line 27 and valve 3,1 in line 29 be opened. In this manner a debutanized product-may `benwithdrawn tr'omr-y column28 by meansl of line .129 andV passedvthrough valve'SI which joins Vsaid debutanized product to line 9.

The isomerization reaction zone eiiiuent is introduced by meansVr off-conduit9 into the intermediate lportion of fractionation zonelZ. ,A separation of two high octane number hydrocarbon fractions is maintained in fractionation zone 12 so-that-the-quantityofhigh octane number hydrocarbon being passed overhead' from said fractionationczone I2 is-149 molsper hour which contains 5'3 mols per hour of 2,2-dimethylbutane, 18 mols per hour of 2,3-dimethy1butane, 47 mols per hour of Z-methylpentane, 15 mols per hour of 3-methylpentane, 4 mols per hour of normal hexane, and 2 mols per hour of methylclyclopentane. This high octane number hydrocarbon product is withdrawn from the top of fractionation zone 12 by means of conduit 13 and passed to a cooler 14 and then to a receiver 15. The product in receiver 15 is then withdrawn `from the bottom by means of conduit 16 and a portion of said high octane number hydrocarbon is returned as reux by means of pump 1S and conduit 19 to the upper portion of said fractionation zone 12 while the remainder, 149 mols per hour, is withdrawn as high octane number hydrocarbon product by means of line 17. The particular octane number obtained in this product stream that is withdrawn by means of line 17 is 98 F-l-i-3 cc.

Further fractionation is effected in fractionation zone 12 so that a product stream of the quantity of 275 mols per hour is withdrawn from the lower portion of fractionation zone 12 by means of conduit line 20. The product stream withdrawn through line 20 contains 8 mols per hour of 2,2-dimethylbutane, 23 mols per hour of 2,3-dimethylbutane, 103 mols per hour of 2methyl pentane, 58 mols per hour of S-methylpentane, 48 mols per hour of normal hexane, 27 mols per hour of methylcyclopentane, 3 mols per hour of cyclohexane, and 8 mols per hour of normal heptane. The octane rating of the aforesaid hydrocarbon fraction in this particular case is 90 F-1-1-3 cc. A sufficient quantity of the product stream withdrawn from line 20 is returned by means of pump 22 and line 23 to the upper portion of fractionation zone 2 so that the combined feed ratio of 1.1 is maintained. In addition, however, to maintaining this combined feed ratio the particular arrangement of fractionation zone 12 and fractionation zone 2 is such that the cyclics rejected from the process through line 20 permits the lower boiling isomerizable hydrocarbons to combine with the fresh feed that is introduced through line 1 into said fractionation zone 2 and thus provide a desirable isomerization reaction zone feed. Without this cyclics rejection this process would be inoperative since the cyclics could build up in the isomerization reaction zone feed to a point where they would simply back out all of the fresh feed.

The particular operating conditions used in fractionation zone 2 are such that the bottom temperature of fractionation zone 2 is of the order of about 250 F. while the top temperature of said fractionation zone 2 is of the order of 235 F. The operating conditions maintained in fractionation zone 12 are such that the bottom temperature of said fractionation zone 12 is of the or`der of about 235 F. and the upper temperature of said fractionation zone 12 is of the order of 190 F. While the pressure maintained on both fractionation zone 2 and fractionation zone 12 is of the order of about 45 pounds per square inch.

I claim as my invention:

1. A process for the isomerization of an isomerizable saturated hydrocarbon fraction which comprises introducing said saturated hydrocarbon fraction into a first fractionation zone while at the same time passing a liquid phase product stream from the bottom of a second fractionation zone to the upper portion of said first fractionation zone, passing a vapor phase saturated hydrocarbon 10 fractionffrom anuppen portion of .said rstfractionation zone t to the lower?r portion of. Isaid second fractionation zone, .removing :fronti the bottom of said first fractiona-1 tion zonef..-a.n;ison:te1:ization.reaction zone feed and vintroducing.- said feed into.V an'isomerization reaction; zone*v wherein low octanenum-ber saturatedhydrocarbons are isomerizedto `higher octane knumber saturated `hydrof carbons, passing a `liquid phase'Y efiluent stream from said isomerization reaction'` zone into an `intermediate portion of said. second :fractionation V zone, y.removing overhead from said second fractionation zone a high octane number product enriched in isomerized hydrocarbons and recovering the same, passing from the bottom of said second fractionation zone a second product which is partially enriched in isomerized hydrocarbons and returning a portion of said second product to the upper portion of said first fractionation zone as aforesaid and recovering another portion thereof.

2. A process for the isomerization of hexane which comprises introducing a normal hexane liquid stream into an intermediate portion of a first fractionation zone while at the same time passing a liquid phase product stream from the bottom of a second fractionation zone to the upper section of said first fractionation zone, passing isohexanes from an upper portion of said first fractionation zone and introducing the same into the lower portion of said second fractionation zone, withdrawing from the bottom of said first fractionation zone a hydrocarbon fraction enriched in normal hexane and passing said fraction to an isomerization reaction zone wherein said fraction is contacted with hydrogen and an isomerization catalyst at isomerization conditions to produce an enriched isohexane eiuent fraction, introducing said isomerization efuent into an intermediate portion of said second fractionation zone, passing overhead from said second fractionation zone an isohexane enriched high octane number hydrocarbon product and recovering the same, withdrawing from the bottom of said second fractionation zone a lower octane number product than the overhead product and passing a portion of said product to the upper portion of said first fractionation zone as aforesaid and recovering another portion thereof.

3. A process for the isomerization of hexane in the presence of hydrogen and an isomerization catalyst comprising alumina, platinum, and combined halogen, which comprises introducing a normal hexane liquid stream into an intermediate portion of a first fractionation zone while at the same time passing a liquid phase product stream from the bottom of a second fractionation zone to the upper portion of said first fractionation zone, passing isohexanes from an upper portion of said first fractionation zone and introducing the same into a lower portion of said second fractionation zone, withdrawing from the bottom of said first fractionation zone a hydrocarbon fraction enriched in normal hexane and passing said fraction to an isomerization reaction zone wherein said fraction is contacted with hydrogen and said isomerization catalyst, said isomerization reaction zone being maintained at a temperature of from about 300 F. to about 850 F. and at a pressure of from about 100 to about 1000 pounds per square inch and wherein said enriched normal hexane fraction is isomerized in the presence of said catalyst and hydrogen at a liquid hourly space velocity of from about 0.1 to about 10 to an equilibrium mixture of hexane hydrocarbons, introducing said equilibrium mixture into an intermediate portion of said second fractionation zone, passing overhead from said second fractionation zone an isohexane enriched high octane number hydrocarbon product and recovering the same, withdrawing from the bottom of said second fractionation zone a lower octane number product than the overhead product, and passing a portion of said product to the upper portion of said first fractionation zone as aforesaid and recovering another portion thereof.

4. The process of claim 3 further characterized in that 111 the' catalyst comprises alumina, from about 0.1% to about 2%' by weight thereof of platinum, and from about 0.1% .to about 8% by weight thereof of combined halogen.

5. The process of claim 4 further characterized in that the combined halogen is a mixture of chlorine and fluorine in an amount of from about 0.3% to about 0.7% by weight, and the isomerizaton is carried out at a temperature of from about 750 to about 850 F.

6. The process of claim 4 further characterized in that the combined halogen is uorne in an amount of from about 2.5 to about 4.5%V by weight, and the process is carried out at a temperature of from about500 to aboutY References Cited in the le of this patent UNITED STATES PATENTS

Claims

2. A PROCESS FOR THE ISOMERIZATION OF HEXANE WHICH COMPRISES INTRODUCING A NORMAL HEXANE LIQUID STREAM INTO AN INTERMEDIATE PORTION OF A FIRST FRACTION ZONE WHILE AT THE SAME TIME PASSING A LIQUID PHASE PRODUCT STREAM FROM THE BOTTOM OF A SECOND FRACTIONATION ZONE TO THE UPPER SECTION OF SAID FIRST FRACTIONATION ZONE TO THE HEXANES FROM AN UPPER PORTION OF SAID FIRST FRACTIONATION ZONE AND INTRODUCING THE SAME INTO THE LOWER PORTION OF SAID SECOND FRACTIONATION ZONE, WITHDRAWING FROM THE BOTTOM OF SAID FIRST FRACTIONATION ZONE A HYDROCARBON FRACTION ENRICHED IN NORMAL HEXANE AND PASSING SAID FRACTION TO AN ISOMERIZATION REACTION ZONE WHEREIN SAID FRACTION IS CONTACTED WITH HYDROGEN AND AN ISOMERIZATION