US2399765A - Isomerization of light naphtha paraffinic hydrocarbons - Google Patents

Description

B. H. SHOEMAKER ETAL May 7, 1946.

ISOMERIZATION OF LIGHT lNAPHTHA PARAFF IN IC HYDROCARBONS Filed Sept. 18, 1945 Patented May 7, 1946 ananas isoMEmzA'l'roN or LIGHT mmm ramrrmrc maocsanoNs f Bernard H. Shoemaker, Hammond, Ind., and Bernard L. Everlng, Chicago, Ill.,.assignorl to Standard Oil Company, Chicago, Ill.. a corporation of Indiana Application September 1 8; l1943, Serial No. 502,876

13 Claims.

This invention relates to the isomerization oi light naphtha paramnic hydrocarbons and itper- 4 tains more particularly to improved methods and means for isomerizing such hydrocarbons in an integrated unitary system wherein one hydrocarbon such as pentaneor butane is isomerized in the absence of added hydrogen and another hydrocarbon such as hexane or heptane is isomf erized in the presence of added hydrogen.

Although butane, pentane (with an added cracking inhibitor such as benzene) and naphthenes may be isomerized on a commercial scale (Cl. Zim-683.5)

fractionated ith the hexane isomerization products in one and the same neohexane tower so that any neohex'ane therein may be recovered and all by Friedel-Crafts type catalysts in the absence of added hydrogen, there is a-considerably greater tendency toward cracking in the caseof light normally liquid paramns such as hexanes and heavier products may be recycled to the hexane .isomerization step. Higher boiling naphthenes are eliminated from the system at the base ot a rerun tower. Thus certain products from each isomerization step serve as a part of the charge to the other isomerization step. jMaximum yields of neohexane and isopentane are obtained and the system is constantly purgedof higher boiling naphthene bottoms.

' When normal pentane is contacted under isomerization conditions with a Friedel-Crafts type catalyst and a hydrogen halide inthe absence of hydrogen and cyclic hydrocarbons 'the reaction heptanes. For isomerizing these light normally liquid hydrocarbons it has heretofore been deemed essential toemploy substantial added hydrogen pressures. This in turn 'necessitated the use of 'expensive equipment foi" withstanding .i necessary high pressures not to mention the conis chieily disproportionation and there results a product of which about one-third is butanes, onethird pentanes andorre-third hexanes and heavier.f By effecting the donversion in the presence o't a critically small amount of a cyclic liquid siderable expense of obtaining the required -hydrogen. An object of our invention is 'to materially decrease the amount of added hydrogen required for such processes and the amount and size of the necessary vhigh pressure equipment. A further object is to provide an isomerization system which will utilize catalyst more effectively and more eiliciently and which will produce larger quantities of aviation motor fuel stocks per unit of catalyst than has heretofore been possible. A further object is to obtain larger yields of neohexane and isopentane from 'a given light naphthav charge than could be produced by any prior process. A further object is to decrease capital expenditure; material requirements and operating costs of an isomerization system of given- Other objects will be apparent asths detaileddescription of our invention proceeds.

capacity.

, In practicing our linvention we isomerize nor- 4vmal pentane or butane in the absence of added hydrogen while we isomerize hexanesf'or heptanesin the presence of added hydrogen. By eliminating the use of hydrogen in the vpentane isomerization step we substantially decrease material requirements,v construction expense and operating costs. Both product streams are depentanized in one and the same depentanizer. The isopentane from both streams as well as from the original charge is separated from normal pentane in one and the same isopentane tower which l cracking inhibitor this disproportionation may be substantially repressed and ultimate isopentane yields of 85 to 90% may be obtained together with only relatively small amounts of vbutanes and Ce and heavier hydrocarbons. The preferred inhibitor is benzene in amounts of the order of .1

to 1%, e. g. about.5% Abased on charging stock.

Amounts of benzene as low as .02% may'have a benencial. eiect in preventing disproportionation and may be employed where maximum isopenvtane production is not essential. Amounts up to 2% and higher are even more effective in inhibiting disproportionation but are usually undesirable (except perhaps in starting up proe cedures) because -increased amounts of benzene produces the charge for the pentane. isomerization step. Any Cs or heavierV hydrocarbons produced in the pentane isomerization step are impair catalyst activity and particularly in the case of aluminum chloride-hydrocarbon complexes tend toward altering the type of complex to undesirable form. Other aromatics may be employed instead of benzene vbut they are not as desirable since alkyl benzenes are even worsev thanl benzene itself in their tendency toward causing catalyst deterioration-'and the formation ofvundesirable complexes. Naphthenes may-be employed as cracking 4inhibitors in amounts about ten times as great as the required amounts 'ofjaromatics i. e.,about 1 to 10% by weight based on charge but in view of the required concentration and availability thereof, they are usuallynotas practical as benzene. It should be emphasized that the critically small amount of` benzene should be present inl the reaction zone in the charging stockwhich is undergoing `convention and not chemically combined with the aluminum chloride because our preferred complex is a complex resulting from the reaction of paraiiinic, particularly isoparailinic, hydrocarbons with aluminum halides, the naphthene complexes being satisfactory but less active and the oleilnic and aromatic complexes being undesirable.

For hexane isomerization the aromatic or naphthene `cracking inhibitors are desirable but usually they do not have to be separately added because they are present in required amounts in most virgin naphtha charging stocks. In this case, however, hydrogen pressures must be employed to maintain catalyst life and catalyst activity. By isomerizing thehexanes in a separate system from the pentanes the requirements of sired catalyst level in the hexane tower is maintained by returning complex from the bottom of both hydrogen and high pressure equipment may be greatly reduced.

An important feature of the separate isomerization steps is the savings in catalyst requirements. Make-up aluminum chloride must be continuously or intermittently added to the. pentane isomerization system in order to maintain catalyst activity at the desired level. If the bound hydrocarbon content of the complex falls below about 23% there is a tendency for aluminum chloride to be carried over with the hydrocarbon product while with hydrocarbon contents greater than 23-25% the complex selectively removes any dissolved aluminum chloride from hydrocarbon solutions so that the products leaving the reactor will not contain much more than appro ately .01% or aiuminum chioride. on the otniana, if the hydrocarbon content of the compex is permitted to increase substantially about 30 or 40%, the activity of the catalyst is markedly reduced and the amount or conversion that can be eiIected in a given unit is accordingly reduced. In the hexane system the aluminum chloride catalyst which tends to form inactive complex is continuously regenerated by the hydrogen'present i in the reactor so that' the catalyst requirements are relatively low. The inactive catalyst `from the pentane isomerization zone, which forms relatively rapidly. has heretofore been'replaced by an equivalent amount of fresh aluminum chloride or regenerated in a separate regeneration zone.

' According to our invention this inactive catalyst is regenerated by introducing it into the hexane isomerization zone. Thus owe minimize the amount of catalyst which must be withdrawn from the system by continuously circulating it between the pentane and hexane isomerization steps. Also by our invention the preferred activity level of the catalysts in the two isomerization zones tend to be automatically controlled.

By employing tower-typereactors we may maintain an activity gradient from the base to the top of each tower. Make-up aluminum chloride entersthe low point in the tower'at such a rate as to keep the hydrocarbon content of the complex at that point in thegeneral vicinity of about to 25%. In the upper part of the tower the hydrocarbon-content of the complex may be as high as to 40%. Instead of discarding all of the excess catalyst of such low activity from the system we :introduce a major' part of it to the top of the hexane isomerization tower thereby n minimizing any tendency toward aluminum chloride carry-over from the hexane reactor. As this catalyst passes downwardly in the hexane isomerization 'tower it is regenerated by hydrogen simultaneously with the isomerization of the hexanes so that by the time the complex reaches the base of the tower its hydrocarbon content may be The invention will be more clearly understood from the following detailed description of a speciilc example thereof read in conjunction with the accompanying drawing which constitutes a part of this disclosure and which is a schematic ilow diagram of a pentane-hexane isomerization system.

The charging stock may be a light virgin naphtha or any other hydrocarbon charge of similar boiling range provided that it is rich in paralilns and substantially free from oleilns and excessive amounts o! aromatics. Such a charge from source l0 is fractionated by conventional means diagrammatically illustrated by column Il into a pentane-and-lighter fraction withdrawn through line i2, a hexane fraction withdrawn through line I3 and a heptane-and-heavier fraction withdrawn through line I4. All of the fractionating towers herein described are diagrammatically i1- lustrated by showing a reflux coil at the top and a reheater coil at the base but it should be understood that conventional reiiux and reboiling means are contemplated and that these diagrammatical showings are merely to simplify the drawins.

The pentane-and-lighter fraction from line I2 together with any pentanes yfrom any extraneous source I5 and product pentanes from line i6 are introduced into isopentane tower Il. Isopentaneand-lighter hydrocarbons are taken overhead through line I8 to debutanizer tower I9, the butanes and lighter hydrocarbons being removed through line 20 and the isopentane product stream being removed through line. 2 I.

The normal pentane stream leaveslthe base of isopentane tower I1 through line 22. A portion oi' this stream is passed by pump 23 throughk time to time from source 28. By employing at least two solution tanks. one may be orstream whileanother is being recharged. The amount of the charge which is passed through the solution tank and the temperature to which it is heated in heater 24 should be sufiicient to 'introand this amount and temperature can'be detery mined from the following solubility table assuming vof course that sumcient time and intireduced once more .to about 20 or 25%. The de- 75 macy of contact is employed to permit saturation and suiiicient pressure to maintain liquid phase conditions.

. Wt. per cent Lbs. oi AlCh Temperature o( AlCh per bmi dissolved of pentane assenso The lower limit or each of thesev ranges is the amount dissolved at the stated temperature, while the higher limit of each range is the amount held in solution if said solution is eiected at about F. higher than the stated temperature and then cooled thereto. The solution tanks may be operated downilow instead of uptlow and if desired a small amount of hydrogen may be employed therein for preventing complex formation, particularly at high temperatures. The resulting solution is passed by line 21 to a low point in pentane` isomerizing tower 25. 1

The remainder of the'normal pentane charge I is passed by pump 25 through heater 30 and line 3| to a, suitable distributor at the base oi' pentane isomerizer 25. Hydrogen chloride maybe introduced into the stream through line 32 in amounts within the approximate range of 2 to 10%, e. g.,

about 6% by weight, based on total charge. A

cracking inhibitor such as benzene may be introduced into line 22 from source 55 and line 34 (or into line 3| from source 33' and line 34') .in amounts of about .5% by volume based on total stock charged. y

In starting up the reaction, tower v25 may be about one-half to three-fourths lled with an aluminum chloride-hydrocarbon complex prepared by reaction of aluminum chloride in the presence or hydrogen chloride with a paramnic hydrocarbon such as a portion of the lig ph-` tha which is to undergo isomerization. suitable complex for example is that described in.

U. S. Letters Patent 2,300,249 but it should be understood that the complex may be prepared from saturated hydrocarbons generally, provided that they are substantially free from oletlns and that they do not contain excessive amounts of aromatica.

The pentane isomerization is preferably eiected at a temperature within the approximate range of 150 to 350 F., for example about 212 F., and under a pressure within the approximate range of 200 to 600 pounds' per square inch, for example about 300 pounds per square inch gauge, preferably sumcient to maintain liquid phase reaction approximate range of .3 to 3, e. g.. about 1 volume of'charging stock per hour per volume of complex inthe tower but will depend on catalyst activity and may be somewhat higher or -lower than this preferred range. The column of complex in the tower is at least 5 feet in height and I e. g.,v185 pounds per square inch gauge and at about atmCSDheric to 100 11'. temperature. `Any 4 n light hydrocarbon gases formed may be purged from the system through line since the hydro` A gen chloride under the separation conditions will remain in solution. Complex settles outof` the liquid products in the settler and will be withdrawn through line35. The remaining product stream passes over weir 40 and is introduced 4by per square inch with a top temperature of about 130 F. and a bottom temperature of about 320 F. The hydrogen chloride Vmay be returned by lines 42, 52 and 5| to the base of the isomerizer without the necessity of employing a blower or compressor. Make-up hydrogen chloride may be l l with water in system 41 and introduced through line 45 to depentanizer tower 49.

The hexane stream from line i3l is introduced by pump 55 into the top of hydrogen chloride introduced at the base of this tower through line at the rate of about 50 to .300, e. g., about 200 cubic reet per barrel of stock charged. The complex for the hexane isomerizing tower may be that which is produced in the pentane isomerizins tower or it may be initially prepared lfrom vsuitable hydrocarbons as hereinabove described.

Make-upaluminum chloride may be introduced Thus'a portionof the solution from tanks 25 may be passed by line 5I to surge tank 52, and it may 'Y be introduced into the higher pressure conversion conditions. r'I'he rate of ow may be within the zone in tower 55 by means of pump 53 and line 54. vThe pentane thus introduced into tower 55 e is isomerized along with the hexanes, and the resulting isopentane is recovered in our fractionation system. Usually only 'a small amount ofv make-up aluminum chloride, ii any, has to be in l It should be understood that instead of employ- A ing only one isomerizing tower in eitheroor both isomerizing `steps we may employ 4two or more towers either in series or in parallel and we may employ higher temperatures in the first tower than in the second. The hexane isomerization .temperature should be within the approximate range of about 150 to 350 F., e. g., about 250 F. 'I'he pressure should be of the order of about 500 4to 1500 pounds per square inch, e. g.,about 850 pounds per square inch. The total space velocity -maybe'of the order oi' about .2 to'4 volumes of line 40a into 'strippin' column 4| which may oper.-

ate at a. gauge pressure slightly above'300 pounds charging stock per' hourV per volume of complex in the total contacting zone and we prefer to employ columns of atleast 5 ieet in height and preferably about 20 to 30 feet in height.

Any complex which -does not settle back to the column from the liquid'products in the upper part of tower 55 are taken overhead through line 55 isomerizer tower 58. Bettler 1 0 is preferably operated from about atmospheric temperature to 100 F. and at a suillclent pressure so that gases may to the pentane tower 2 8' we may Pass complex from the base of tower 58 by line 93a to settler 93h, return hexanesto tower 58 through line 93o and transfer hexane-free complex through lines 83d and 93 back to tower 28. Some catalyst will have to be discarded from the system and such discard is effected through line 94. The catalyst rerun tower 8|. Any hydrocarbons boiling above about 175 F. are removed from the system as naphthene bottoms through line 82 and may be employed as motor fuel components or as a charging stock for hydroforming or aromatization in pentanizer B9 through line 8 to neohexane towerl 85. The neohexane product stream is drawn from the top of tower 85 through line 8G. Other hexanes (chiefly methyl pentanes) with a small amount of naphthenes are recycled from the base of tower 85 through line 81 to the top of absorber i.

The continuous introduction of make-up'aluminum chloride solution at the base of pentane tower 28 is at such a rate as to maintain a catalyst activity at the base of the tower corresponding to a bound hydrocarbon content in the general vicinity of to 25%. Atthe top of tower 28 the catalyst activity may be considerably lower corresponding to a hydrocarbon content of the a order o! about 30 to 50% Since complex is con- A tinuously being formed from make-up catalyst in the tower it is necessary that complex be continuously removed in order that a substantially constant complex liquid level be maintained in tower 28. Catalyst may thus be removed from the upper part of tower 28 to a trap 8G for separating any product or unconverted hydrocarbons therefrom, such product oru'nconverted hydrocarbons being returnedto the tower through line 90a or introduced to settler 31. Liquid complex may then be introduced by pump 9| through line 92 to the upper part of tower 58. We may. however. dispense with trap 90 and simply rely on the product stream leaving through line to carry a suilicient amount of entrained complex to maintain the column of complex at the desired level in tower 28. A part of the settled catalyst from line 39 may be discarded, but most of it may be introduced by pumpll' and 92 to the upper part 'of tower 58. 4

The introduction of'this complex containing 30 to 50% hydrocarbon in the upper part of tower 58 minimizes any tendency for aluminum chloride carry-over through line 85. 'I'he complex introduced through line 92 gradually ows downwardly in tower 58'and during the course of its flow it is hydrogenated and thus regenerated so that. by the time it reaches the bottom oi' tower 5B its hydrocarbon content may be decreased t0 approximately 20 to 25%. Complex from the base oi' tower 58 may then be returned through line 93 back to a low point in pentane lsomeriaer` 28. To avoid possibility ot hexanes nding'their way withdrawn from the system is the least active catalyst. A large amount of the catalyst may be continuously recirculated from the pentane tower to the hexane tower and thence back to the pentane tower for alternate operation in the presence and absence of hydrogen. This recirculation effects marked savings in the required amount of make-up aluminum chloride, it minimizes the amount of complex which must be withdrawn from the system and disposed of and it likewise minimizes hydrogen chloride losses.

`In a pentane isomerization system small amounts of hexanes are formed and in the hexane isomerizationLsystem small amounts of pentanes are formed. Our system provides not only for common product fractionators but for a fractionation system which permits a portion of the product's from each conversion system to be combined with the charge entering the other conversion system. This integrated unitary system thus results in maximum productionof isopentane and neo'hexane, minimum catalyst requirements and operating costs and exceptionally small losses on account of complex discard. The pentane-hexane charge is converted substantially lquantitatively into isopentane and neohexane together with small amounts of butanes and lighter hydrocarbons and small amounts of naphthene bottoms suitable for hydroforming. Our system gives a greater yield of higlquality aviation motor fuel 4blending stocks :from4 a given pentane-hexane derstood that this example is given by way of illustration'and that it is not limitative. Other modifications and alternative operating conditions will be apparent to those skilled in the art from the above detailed description. The prin' ciples of our invention with appropriate modcations are equally adaptable to the isomerization of butane and hexanes or'butanes together with mixed pentanes and hexanes. In the latter 'system n-butane is isomerized in the absence of hydrogen with a liquid aluminum chloride complex and the spent complex is pumped to the pentanehexane unit operating in the-presence of hydrogen where-the spent catalyst is regenerated as it isomerizes the latter feed. The -changes in the fractionation columns and the lines will be apparent to those skilled in the art in the light of the above disclosure.

In another modication of our process the naphthenic bottoms from the common fractionationl are employed as a cracking inhibitor in the pentane isomerization step. The naphthenic bottoms may be used in entirety or may be fractionated to produce a' cyclohexane and/or a methylcyclohexane rich traction for such use when operating the pentane reactor as an isomerlzation reactor.

, An alternative method is to operate the pen- A The ditions consists principally oi about equal volumes of butanes, pentanes and hexanes. The product is fractionated together with the hexane isomerization product in the common fractionation system, the n-pentane fraction being re- 'cycled to the pentane reactor and the less branched hexanes recycled to the hexane reactor operating in the presence oi hydrogen. 'Such a mode oi operation, together with hexane isomerization in the Presence of added hydrogen, makes it possible for us to convert n-pentano `into butano (principally isobutane), isopentane and neohexane.l The overall production of neohexane by this method of operation is greater than the production of neohexane when operating the pentane reactor in the presence of an inhibitor.

second column or nume aluminum omorldc-paraillnic hydrocarbon complex in the presence of Features of the invention are applicable when catalysts other than aluminum chloride-hydrocarbon complexes are employed. For example,v any Friedel-Crafts or hydrogen halide type of catalyst may be employed under conditions suitable for the particular catalyst in accordance with the general principles set forth in connection with the above examples ofour invention hereinabove described. 'We claim:

1.v The method of isomerizing paramn hydrocarbons of the pentane-hexane boiling range which method comprises separating said hydrocarbons into a pentane .traction and a hexane fraction, removing isopentane and lighter hydrocarbons from the pentane fraction, contacting the hydrogen chloride, introducing hydrogen at a low point in said second column at the rate oi about 50 to 250 cubic feet per barrel of stock charged thereto, maintaining said second column at a' temperature within the approximate range oi 150 to 350 F. and under a' pressure within vthe approximate range of 500 to 1500 pounds per square inch, introducing a solution oi.' make-up aluminum chloride in at least a part ofthe pentane fraction introduced into said rst column whereby complex is formed in said ilrst column, withdrawing complex from an upper part of said rst column at such a rate as to maintain a substantially constant complex level therein. introducing the withdrawn complex into an upper part of the'second column whereby said'complex is regenerated as it passes from the upper part of said second column K to the lower part thereof and transferring catalyst from the lower part of said second column to a lower part of said nrst column.

. 3. The method oi producing isopentane and. neohexane from c hydrocarbons of the pentane-hexane boiling range. which method comprises producing separate hexane and normal `pentane charging stocks, contacting said normal pentane charging .stock with a :Elrst column of halide isomerization catalyst in the absence of substantial amounts or addedfhydrogen' but iu' J the presence oi a small amount oi a cyclicliquid remaining normal pentane in the absence of any t substantial amount oi.' added Ahydrogen but in the presence of a small amount or a cyclic cracking inhibitor with a column of a halide isomerization catalyst under conditions of temperature, pressure and space velocity to give isomerization asthe main reaction in a pentane contacting acne, re'- moving catalyst fromthe products of the contacting step, contacting said hexanefraction with a hydrogen chloride containing gas stream for absorbing hydrogen chloride therefrom, contacting the hexane together with absorbed hydrogen chloride with a second column .of halide isornerizu.;`

tion catalyst in a hexane contacting zone under substantial hydrogen pressure and under conditions ot temperature, pressure and space velocity to eilect isomerization as the main reaction. separating catalyst and a hydrogen chloride gas stream from products leaving the hexane contacting step, returning said gas stream to said cracking inhibitor under conditions effective for lsomerization. contacting said hexanecharging stock with a second column of halide isomerization catalyst in the presence of added hydrogen in amounts or at least cubic reet per barrel of stock charged and under conditions enective for isomerization, separating heavierthanhexane hydrocarbons from the products from the second column contacting step. combining the ro-` of hexanes therein.

absorption' step, removing from. said product stream hydrocarbons which boil substantially-J above about 175 F.. combining the remainder of the product` stream .with the pentane isomerization product stream, depentanizing the combined productsK and introducing said pentanes to said isopentane removal step.- tractionating the depen tanized products to separate fneohcxane from carbons of the pentane-hexane boiling range which method comprises iractionating a charg-l `ing stock containing pentanes and hexanes but substantially free from oleflns to obtain a pentane fraction and a hexane fraction, introducing said pentane fraction at a low point in a column o! liquid aluminumchlorlde Paramnic hydrocarbon complex in the presence otra small amount of a liquid cyclic hydrocarbon cracking inhibitor and heavier hydrocarbons and returningsaid heavier l Vhydrocarbons `to said hexane contacting step.` 4 2. The method of isomerizing paraillnic hydro- 4. The method oi' claim 3 which includesthe' step of adding benzene in amounts within the ap- -proximate range oi' .02 to 2% to the normal pentane charging stock .contacted with said nrst co1- umn. of halide' isomerization catalyst;

. 5. The method of claim 3 which includes the, further step of transferring catalyst from said second column back to saidiirst column.'`

6.' The method of isomeri'zing a plurality of diiierent paramnic-hydrocarbons o! the 'light comprises naphtha boiling range which method fractionating a charging stock containing said hydrocarbons to obtain' a ilrst fraction of paraillnic hydrocarbons isomerizabl in the absence in the absence o! substantial amountsl or added hydrogen,- contacting said hexane fraction with a of added hydrogen and a second fraction of said hydrocarbonsto be isomerized in the presence oi' addedhydrogem contacting'said first fraction with a nrst column of liquid halide isomerization catalyst bydispersing said fraction at the base of said column o! liquidcatalyst and passing said dispersed hydrocarbons upwardly through said column oi' catalyst in the absence oi any substantial amount ofuadded hydrogen chloride-hydrocarbon and under conditions for effecting isomerizetion,V contacting said second fraction with a second column of liquid halide isomerization catalyst by dispersing said second fraction at a low point in said column and passing the dispersed hydrocarbons upwardly therein in the presence of added hydrogen in amounts of at least 50 cubicfeet per barrel in said second fraction charged and under conditions ior effecting isomerization, removing liquid catalyst from products leaving the upper part ot said ilrst column, introducing at least a substantial amount oi said removed liquid catalyst at an upper point in said second column and returning liquid catalyst from the lower part of said second column back to said first column.

'7. The method of isomerizing a plurality of diierent paranic hydrocarbons of the light naphtha boiling lrange which method comprises fractionating a charging stock containing said hydrocarbons to obtain a first fraction of paraflnic hydrocarbons isomerizable in thel absence of added hydrogen and a second fraction of said hydrocarbons to be isomerized in the presence of added hydrogen, contacting said flrst fraction with a first column'of liquid aluminum chloride- .hydrocarbon complex isomerization catalyst by dispersing said fraction at the base of said column of liquid catalyst and passing said dipsersed hydrocarbons upwardly through said column of catalyst in the absence of any substantial amount of added hydrogen and under conditions for eecting isomerizatlon, contacting said second fraction with a second column of liquid aluminum complex isomerization catalyst by dispersing said second fraction at a low point in said col and passing the dispersed hydrocarbons upwardly therein in the presence of added hydrogen in amounts of at least 50 cubic feet per barrel in said second fraction charged and under conditions for eecting isomerization, introducing relatively active catalyst complex from a low point in the second column to a low point in the rst column. removing .catalyst complex from a high point in said first column, returning at least a part of said removed catalyst complex to a high point in said' second column and adding make-up aluminum chloride to catalyst complex in at least one of lsaid columns.

8. The method of isomerizing a pluralityl of\ paraiilnic hydrocarbon fractions of which a ilrst fraction is isomerizable in the absence of added hydrogen and a. second traction requires the presence of added hydrogen in the isomerization step. which method comprises dispersing said irst fraction at a low point in a rst'column ot liquid aluminum chloride paraillnic hydrocarbon complex and passing the dispersed hydrocarbons upwardly through said column in the presence o!y hydrogen chloride but in the absence of added hydrogen under conditions for effecting isomerization, dispersing said second fraction at a low point in a second column of liquid aluminum chloride parailinic hydrocarbon complex and passing said dispersed hydrocarbon upwardly in said second column in the presence of substantial amounts of added hydrogen and hydrogen chloride under conditions for eil'ecting isomerization. separating relatively spent complex from products leaving the upper part of said rst column. discarding a part of said separated complex, intro.. ducing another part of said separated complex at an upper point in said second column and returning complex from the lower part oi said second column back to said ilrst column.

9. The method of claim 8 which includes the further step of adding make-up aluminum chloride to both columns as a solution in a part of said first fraction.

l0. The method of claim 8 wherein the rst fraction consists' essentially of pentane and the second fraction consists essentially of hexanes.

1l. The method of claim 8 wherein the rst fraction consists essentially of butane and the second fraction is a normally liquid paraiilnic hydrocarbon lower boiling than heptane.

l2. In a process wherein a iirst parailnic hydrocarbon stream' higher boiling than propane and lower boiling than hexane is isomerized in a first column of aluminum chloride-hydrocarbon complex under isomerization conditions in the presence of hydrogen chloride and in the absence of any substantial amount of added hydrogen. and a second parainic hydrocarbon stream higher boiling than pentane 'and lower boiling than octane is isomerized in a second column of aluminum chloride-hydrocarbon complex under isomerlzation conditions in the presence of hydro- 4gen chloride, in the absence of the first hydrocarbon stream, and in the presence of a substantial amount of added hydrogen, the method of minimizing the amount of 'required make-up aluminum chloride which comprises transferring relatively spent complex from the upper part of said rst column to said second column so that the transferred catalyst may be regenerated simultaneously with the isomerization effected in said second column and transferring active complex from the lower part of said second column back to said rst column.

i3. The method of claim 12 which includes the steps of transferring complex from an upper part of the first column vto an upper part of the second column and transferring complex from a lower part of the second column to a lower part of the first column.

BERNARD H. SHOEMAKER. BERNARD L. EVERING.

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