US2583739A

US2583739A - Catalytic isomerization of isoheptanes to triptane

Info

Publication number: US2583739A
Application number: US642604A
Authority: US
Inventors: Jacob D Kemp; Arthur E Stickland
Original assignee: California Research LLC
Current assignee: California Research LLC
Priority date: 1946-01-22
Filing date: 1946-01-22
Publication date: 1952-01-29
Anticipated expiration: 1969-01-29

Description

Jan. 29, 1952 J. D. KEMP ETAL 2,583,739

CATALYTIC ISOMERIZATION oF ISOHEPTANES To TRIPTANE Filed Jan. 22, 194e Patented Jan. 29, 1952 UNITED STATES PATENT OFFICE oA'rALY'rIc IsoMERIzA'rIoN 0F IsoHEP'rANEs 'ro TRIPTANE Application January 22, 1946, Serial No. 642,604

4 Claims.

The present invention relates to the produc;- tion of triptane (2,2,3-trimethylbutane) and pertains more particularly to a selective isomerization process for obtaining triptane from isoheptanes, such as methylhexanes and dimethylpentanes.

Triptane is a highly desirable fuel, since its highly branched structure gives it super-fuel characteristics exceeding that of isooctane (2,2,4- trimethylpentane). In view of the difliculty in making it, triptane has for some time been somewhat of a laboratory curiosity. More recently, due to the war pressure and demands for better aviation fuels, triptane has been made by processes which involve expensive intermediates such as Grignard reagents, Triptane made by such processes and the like, or other methods wherein only small amounts of triptane are obtained, is ordinarily too expensive for general use.

It is therefore an object of the present invention to provide an improved method of producing triptane, whereby it can be commercially obtained in large yields from isoheptane without the use of expensive intermediates or processes.

It is another object of this invention to provide a process for selectively isomerizing isoheptanes, such as methylhexanes and dimethylpentanes, to triptane without the formation of excessive amounts of side reaction products, Whereby t'riptane is relatively cheaply produced to permit its general use.

It is a further object to provide a method of obtaining a product containing a high concentration of triptane, wherein the side reaction products-'obtained therewith are valuable components of internal combustion engine fuels. such as aviation gasoline.

Further'objects and advantages of the present invention reside in special combinations of method steps, conditions and the like, as will be readily apparent from the following description of a preferred embodiment taken in reference to the drawing, which is a schematic flow diagram of one preferred embodiment of this invention.

In attaining the above objects of the present invention, isoheptanes, such as methylhexanes andv dimethylpentanes. are selectively isomerized to triptane under rather specific conditions. Thus, the isoheptanes in the presence of a sub; stantial excess of an n-parailin, e. g., propane,` in liquid form, is subjected to the action of certain liquid mixtures of hydrouoric acid and boron triiluoride at a relatively low temperature.,V It is a special feature of the present inventionto control the catalytic activity of the liquid HF, BF'a mixtures within relatively narrow limits by maintaining the BF: content at about 525% and preferably 11i-19% by Weight in the liquid mixture. By means of suchl a catalyst in combination with the other conditions set forth, a high ultimate conversion to triptane without excessive yields of side reaction or degradation products is obtained, whereas other catalysts are generally unsuitable for the present specific isoheptane isomerization for various reasons, such as low conversions, substantially complete inactivity at the desired low temperatures, excessive formation of degradation products-usually of the least useful type--such as permanent gases, e. g., methane and ethane, high catalyst consumption and cost, etc.

The isoheptanes-methylhexanes and dimethylpentanes-employed as starting materials are preferably substantially pure (i. e., above 90% concentration), although when combined with suitable n-parafns, petroleum fractions containing lower percentages, e. g., 50%,` of isoheptanes may be used. Ordinarily the isoheptane feed stock contains at least 65% by volume of methylhexanes and dimethylpentanes. As obtained from most sources, the isoheptanes are predominantly methylhexanes. Such is the case when normal heptane is isomerized to isoheptanes under optimum conditions for isoheptane formation without excessive loss to side reactions. For most convenient operation, the hydrocarbon feed material is freed of water, sulfur compounds, nitrogen bases, and other agents having deleterious action on the catalyst or imposing diiiiculties in catalyst regeneration.

It is a special feature of the present combination of isomerization conditions to employ a large excess of an n-paraflin in liquid form, such paraiiin Vbeing soluble in the isoheptane. Other materials, such as carbon dioxide, nitrogen, etc., which have been used as gaseous additives in some isomerization processes for the purpose of imposing a gas pressure on the system, are not soluble in the present isoheptanes to an appreciable extent and are not satisfactory for the purpose of this process. Generally suitable for use in the present isoheptane lsomerization process are the hydrocarbons: ethane, propane,

The n-parafn, especially propane, is employed in substantial excess of the rest.ofthe. hydrocarbon mixture charged to Vthe isomerization zone. Thus., the ratio of n-paraiiin toisoheptanes is generally 220:1, and preferably 8-12:1

byvolume, .i..e., .the n-paraiiins. constitute 50-.85% and vpreferably.about75% ofthe reactionmixture. v.The.temperatureemployed inthe ,isomerizaltion zone isrelatively low, of theorder of. room temperature .and-below. In generaLthe temperature. is below that at whichsubstantial reaction .of a n-paraiiin occurs butsuicient to obtain satisfactory isomerization of .the isoheptanes. Preferably, atemperatureof 25-`75 F. and especially about150'F..is employed. Above this yrange, .the .-arnountof .triptane produced rapidly decreases with an attendant increase in the. amount of. sideV reactionsand/or degradation products formed, while below this range the conversion to triptane-is..unsatisfactory.

Pressure, as such, is not especiallyimportant in thepresent isomerization process and high pressures do .not appreciably increase or decrease the .isomerization to triptane. Generally, the pressure is correlated with Ithe.-natureoflthenparaiiinand the BFa content'inthe-.liquid catalyst;.that is, suiiicient .pressure'is.employedto maintain the'desiredconcentration oflBFain the liquid catalyst and the normal parafiin inlliduid form. VThe partial pressure of BF3. inthe isomerization zone is particularly,,importantsince it controls the amount of BF2 .in theactiveliquid catalyst mixture. A special advantage Yofthe present invention resides intheease of -maintaining the desired narrow Y.range .ofcatalyst activity bymeans Yof the BFrpartial pressure, since a relatively large increase in jthe ,partial pressure of BFa has a relatively small eiecton the BF3 content of the liquid catalyst. "Thus, the Bl's` partial Y pressurek provides. an .excellent way o'f'controlling the `BF3 content in the liquid cataly'stwithin the desired :narrow range, `.For example,arpartialpressure of'BFsof about'30 to 2'75 lbs/sq. in. gives a BFa content of. about'5 to 25% at 50"F. in the liquid catalystmixture. :As indicated, the total Vamount of BFS introduced into the isomerization reactor will depend upon the equilibrium pressure of BFs at the temperature employed, the ratio of liquid catalystv to hydrocarbon'a'nd upon the gas phase above the liquid-mixture. "Thus, the lower the amount of free space in the isomeriaation zone the lower the -total amount of BFs that is'required. For example, inan"isomerization'reactor there was contained 2950 cc. of gas space at 120 Rand 1850 cc. of `liquid at 50 F. under atotal absolute pressure of about 225 lbs/sq. in. A' total of 150 gms. of"BF3 was charged'of which '76.6 gms. was in the gasphase, 45.6 gms. was in the liquid catalyst phase and 27.8 gms. was in the hydrocarbon phase. The remainder of the liquid catalyst consisted of 215 gms. of HF. The partial pressure of BFa was 165 lbs/sq. in. absolute at 120 F. The liquid catalyst then contained 17.5 weight per cent of BFs.

Althoughonlyrelatively small amounts 0f side reaction products are formed in the present isomerization process as compared to the amount of 5;. degradation products obtained by using other condi'tions'of temperature, catalyst, diluent, etc.,

it is particularly important and a special feature l ofA thepresent invention to recycle Side reaction Such mixtures areLsometimesmore ad.-

,f sources to theisomerization zone.

.and hexanes, y.are employed products to 1 part of isoheptane. Preferably, the

ratio is about 1:1. However, in any event the side. reactionproducts. are employedinamounts less'. than .about 150, %V of. the n-parains, .such.. as propane. vInsome instances, it. is Y.desirable to introducealso .into the. isomerizatiorrzone v .liydrogen..and/or,.naphthenes,V such .as .cyclopentanes, cyclohexanes, etc.

lThe ratio of catalyst mixture to isoheptanes depends, at least in part, upon the activityof the liquid catalyst mixture, the amountof relatively inert n-paraflin andthe temperature .employed A large enough amount `of liquid catalystisemployed to yield sufficient active catalyst. surface to obtain the desired isomerization in a relatively short time. A constant.renewal .of the .active catalyst surface available .to .theisoheptanes most desirable in, preventing side reactions. .The

liquid catalyst may .form 5f95.%,of. the total fliqf uid mixture, including.the..isoheptanes, nparaf iin, etc. When using thepreierred .amounts .and proportions of hydrocarbons, i. e., around the middle of theranges given, the ratioofcatalyst mixture' to isoheptanemay lbe .from about.0.2.-to 2.0 by. volume .aridpreferably isv in. the, vicinity. of 1.0.

'The contacttime between the visoheptaneI and liquid HF, BFa catalyst at .isomerization conditions is preferably relatively short, such as.10-'30 minutes, more or less, rdepending inpartupon the nature of theisoheptanes charged. Thus, when the isoheptanes.are predominantly .methylhexanes, a .longer contact-time `is employed than lis used with 'dimethylpentanes as the predominant isoheptanes in thel isomerization. charge. .Likewise, with lower,catalystaotivities (i. .e.,.lower BFa. content ini. liquid catalyst) and lower tem- I ucts. vLess preferably, longer'contact'time may sometimes be tolerated when only' a'coarse dispersion of catalyst throughout the hydrocarbon feed material is achieved. y v Depending upon whetherr'nethylhex'anes"or'dimethylpentanes predominate in the is'oheptane charge and 'the `conditions employed, theconver-z sion per pass toy triptane willrvange upwards from 15% by volume'or more. Under the morepreferred conditions, ultimate conversion above z5 about 50% triptane willbe obtainedalong with production o1' other valuable gasoline components.

The mixture resulting from the above isomerization is freed of HF, BFa catalyst, n-parailin, e. g., propane, and lower boiling side reaction products, each of which may be in whole or in part recycled, discarded or regenerated, as sis applicable. The remaining crude triptane conpentanes and a small amount of hydrocarbons fraction by any suitable means, such as distilla` tion, fractional crystallization, extraction or distillation with selective solvents, etc., or combinations thereof. Most desirably, the crude triptane concentrate is subjected to fractional distillationV wherein a mixture of triptane and 2, 4-dimeth-ylpentane are separated from methylhexanes and y2,3-dimethylpentane, which latter mixture 'may` be recycled to the isomerization. Preferably the mixture of triptane and 2,4-dimethylpentane is` further separated by solvent distillation, i. e., extractive distillation, with a selective solvent such as dialkylphthalates, e. g., diethylphthalate, etc., nitroaromatics, e. g., nitrobenzene, nitrotoluene, etc., aromatic amines, e, g., aniline, etc., ketones, anhydrides, and the like.

It is apparent `that the present process and any step thereof can be carried out either continuously or batchwise, or combinations of batchwise and `continuous treatments may be used. In the isomerization any suitable apparatus providing thorough contact between the catalyst mixture, the various ingredients of the feed material, including recycle products and added n-parains, may be employed. For example, combinations of mechanically driven agitators, such as turbo mixers with settlers, used either singly or in series or parallel, packed columns adapted from concurrent or countercurrent flow, or coil reactors which may contain mixing jet nozzles, or the like, may be used. Since it is particularly important inthe present process to attain thorough contact between the liquid HF, BF3 catalyst mixture and isoheptanes, it is preferred to use contacting devices, such asturbo mixers or other relatively high speed agitator and baffle arrange- 'ments wherein the catalyst is quickly and finely dispersed throughout the hydrocarbon charge.

The material forming the isomerization reactor, or reactors, and other apparatus, especially that whichis in contact with the HF, BF3 catalyst, is ordinarily substantially inert, such as Monel, nickel, Hastalloy, etc., so that no reaction of HF and/or BFa takes place with the apparatus material to form substances inhibiting the isomerization reaction or to form excessive amounts of contaminants. Many suitable types of apparatus can be constructed readily by one skilled `in the art, but the invention is now further illustrated and may be better understood by reference to the schematic drawing showing one preferred. embodiment of the present invention and wherein, for the sake of simplicity and clarity, there have been omitted certain details, such as pumps, valves, pressuring means, coolers, heat exchangers, reiiux systems, etc.

In an embodiment of the preferred continuous process flow of the present invention as shown in the drawing, the feed isoheptane comprising mainly either methylhexanes and/or dimethylpentanes are introduced into isomerization reactor II! through line I I along with an n-parafn, e. g., propane, via lines I2 and I3, recycledma- Vterial via lines I3 and I4, and HF, BFr catalyst mixturethrough line I5. s The reaction mixture in the isomerization reactor I0 is constituted in accordance with the ranges given hereinabove as obtained from added or recycled materials. For example, the reaction mixture may 'contain 1 volume of the isoheptanes: methylhexanes and/or dimethylpentanes, 8 `volumes of propane, 1 volume of side reaction products including butanes, pentanes and hexanes, and 1.5 volumes of a liquid HF, BFr; catalyst mixture containing about 13-19 by weight of BF3. This reaction mixture is thoroughly agitated within the isomerization reactor I 0 at about 50 F. andl under about 105-175 lbs/sq. in. partial pressure of BFa, allowing about 15 minutes contact time. The isomerization product mixture including HF, BRa and hydrocarbon leaves the isomerization reactor IIl'and passes to line I8 into settler I9, `wherein a separation into ahydrocarbon phase and a catalyst phase takes place. The catalyst phase may bein whole or in part either recycled through lines 20 and I5 to the isomerization reactor I0 or passed to dispcsal line 2| for rejection of suitable regeneration. Fresh catalyst or any component thereof as required to maintain the quantity' and ratio of HF to BFa in the liquid catalyst, may be added to the isomerization system through line 22.

The hydrocarbon phase contains triptane, dimethylpentanes, methylhexanes, some catalyst materials and asmall amount of side reaction products such as butanes, pentanes and hexanes. This hydrocarbon phase passes through line 25 to a suitable separator, such as depropanizer 28 wherein propane and lower boiling material including HF and BF; are removed for recycle through lines 21 and I3 to the isomerizaton re'-z actor I0. Material boiling higher than. propane passes from depropanizer 26 to line 29 to a further separator, such as dehexanizer 3D, for separation into two fractions: one containing materials boiling below the heptanes, such as a small amount of side reaction products, inc luding butanes, pentanes and hexanes, and asecond fraction containing the heptanes and 'small amounts of higher boiling materials. The lower boiling fraction discharges from dehexanizer 30 through line 3I `from whence it may be recycled to the isomerization reactor I0 through lines I3 and II or to other disposal through line 32, or both. In general, although the` side reaction product hydrocarbons together with the mixture of propane, HF and BFS, may be recycled to the isomerization reactor I0, the separation between the HF, BFa mixture and the hydrocarbons may be effected in any suitable manner whereby Aal1 or part of each of the separated portions may be recycled or disposed of in other ways. Thus,I part of the HF, BF3 mixture may pass to a suitable catalyst regeneration, and the hydrocarbons, other than that required for recycle, may be used for blending in gasoline, since these hydrocarbons are valuable gasoline components.

The higher boiling heptane fraction leaving the dehexanizer 30 passes through line 34 into heptane fractionator 35. Therein the heptane fraction is separated into a lower boiling crude triptane concentrate `containing ZA-dimethylpentane, and a higher boiling fraction, containing mainly 2,3-dimethylpentane and methylhexanes. The latter fraction or bottoms may be withdrawn through line 3Il and recycled to isomerization reactor III through lines I4 and II. If desired, all, or preferablyonly part, ofthe bottoms may be further separated by passing' 'f1-assenso t'anes, Afsuchfas! octane. etc., 'may be. removed throughxlne l.l,fthe.heptanes passing through 'fline 42 'to `recyclepline M. The heptane frac- Jtionator r351is preferably` a. distillation column, or

columnspeither packed, itray,r or bubble cap type,

'easierseparationztbetween triptane` and 2,-4-dimethylpentane ontheonehand `andthe remain- -ingisoheptaneson "the .other hand; in contradistinction, when `isobutane 'instead of lpro'pane is :used fas lthe'principalA diluent in the isom'eriza- .tion zoneappreciable amounts of these kneo carbon atom dimethylpentanes' are formed under :conditions for production of comparable amounts of'triptane. #Thiscis illustrated by the heptane .analyses inthe following tablet A B C Pincipallililfent. Propane- Eropane Vlfsobutane Vol. pcrcentdiluentin ed 75 25 75 '.Contact time,min l. "15 l5 90 Temperature, F l 50 .50 50 Infra-redi'analysis, heptane fraci .tionVvvoL-:perrcent:

V"Triptane 17.2 16.5, 11.8 l :2;2'diniethylpentanar. nil U. 8' 5. 5 .3,3-dimethylpentaner. ynil 1.3 9.7 '2`;3dimetliylpentane.. 12. l11.2 10.2 2,4-dimethylpentapc.- '2554` 23.8 20:5 2fmei'lhylhexane.- 27.8f 28.29- 27.1 if-methylhexgane" l 17. 2 17. 5 ,15. 2 VNEthylpen'tane. 'nil 4nil nil .Normalheptane nil` ni] l nil vrThe'triptane concentrateleaving heptane fracti'ona'tor 35 through'line 45 contains about 40% or more triptane and the remainder almost en'- ti'relyf Zilli-dimethylperitane. Although `this tripztane'concentrate 'has a fairly 'high octane numberjandmay thus be us'e'd'as'su'ch for aviation fuel', it is more preferable to separate further to get at least .-80% anolmost desirably substantially pure '-(i.* Je., rabove 90%) triptane. 'Due tothe closenessin lboilingl point 'of triptane and '2A-di; methylpentaneg'.fractional distillation cannot orf-'- dinarilybe used. A suitable method of 'separatluriinvolves the vuse of Iselective Solvents. Thus .thetriptane concentrate may be passed through through une .t3v toa-.suitable separatorzmffraetionator 55, wherein triptane is removedfftrom the-solvent and Apasses out v'through.l'ine56. The remaining solvent 'isrecycled through lineiI-to distillation column 50.

' The. triptane Vthus Obtained may he fof 'about concentration but 'is usually in 'the vicinity vofi-% or above. `If 'further puricationisvrequiredit is usuallysuitable to employ fractional 4'crystallization whereby triptane may bereadily :crystallized VfromtheV mixture.

.By means of the above describedpreferred process flow of the present invention `high yields can be obtained'rfrom isoheptane byfisomerization. Thev over-al1 conversion to triptane is 'in the 1vicinity of 50% orhigher, the remainder consisting mainly of valuable gasoline components. Thus, -for .the rst time, Vtriptane ris produced in goed yields by` isomerization. As;il1ustrative of the sabove :described pro-cess the following ,example 'is given:

.Isoheptane isomefizatz'on Conditions:

Temperature 50F. Contact time'n 1 5 min. Catalyst (liquid) 19% BFz, 81% HF Ratio catalyst to total hydrocarbons 14:86 `by vol.

Charge to reactor:

1000 bbls/day Aisoheptanes consisting of about 80% methylhex'anes and the reremainder principally ldimethylpentanes 2440 bbls/day Visoheptanes recycled '18400 bbls/day propane recycled 1225 bbls/day isobutane recycled 980 bbls/day pentanes recycled 980 bbls/day hexanes recycled.

Product from reactor:

18400 bbls/day propane v2440 bbls/day isoheptanes vtriptane) 500 bbls/dayitriptane v.1381 bbls/day isobutane 1046 bbls/day pentanes 1055 bbls/day hexanes 29 `bhls/d'ayheavy oils from acidpha'se 192 bbls/day octanes and heavier.

(other than carbon phase from settler I9 passed directly 'into' dehexanizer '30, in which case it is preferablefto separate by suitable means the dehexanizer'overhead material into HF, BFa `mixture and hydrocar-icons for' example, in order to' obtain "more controlled recycle operation. A

In lthe above described triptane production process it may sometimes be advisableinstead 'of separating the triptane concentrate by extractive distillation, to subject this mixture of triptane and 2-,4-dimethylpentane to' a vselective' isfmie'ri-v zation process whereby the latter is isomerized to 2,3-dimethylpentane and methylhexanes, which are relatively easily separated by fractional distillation from triptane. For example, 1 part of a triptane concentrate is vigorously agitated for a short time (about 15 minutes) at approximately 50 F. with -about 0.2 to 2.0 parts by weight of an isomerization catalyst consisting of 0.1 to preferably about 1%, by weight of BFs in the liquid catalyst and the remainder HF. The hydrocarbon phase separated from the liquid catalyst is fractionally distilled to remove the 2,3-dimethylpentane and methylhexanes which may be recycled to the isomerization reactor I0. The low boiling triptane concentrate thereby obtained contains less than half as much 2,4-dimethylpentane as prior to the selective isomerization process above described. Thus, for example, a triptane concentrate containing about 20% 2,4- dimethylpentane when so treated yields a new triptane fraction containing less than and usually below 5% 2,4-dimethylpentane.

As pointed out or indicated hereinabove, the process of the present invention provides an especially advantageous method of producing triptane in large yields at relatively low cost. Further, practical contact times are obtainable in. the operation in liquid phase at relatively low temperatures. The amount of side reaction is small and high concentration of triptane is obtained due at least in part to both specific isomerization to triptane compared to isomerization to other neocarbon atom heptanes and favorable thermodynamic equilibrium. This is made possible by the use of liquid n-parailin, especially propane, as the diluent, whereby the catalyst, of any given composition which is correl-ated with a given activity level, has a maximum activity since propane and the like do not occupy active catalyst centers on the catalyst surface as occurs when other agents are used as the principal diluents.

We claim:

1. A method for the production of triptane by the isomerization of isoheptane concentrates comprised of a major portion of the methyl hexanes and a minor portion of the dimethyl pentanes which comprises intimately contacting a mixture of one volume of isoheptane concentrate, 220 volumes of liquid propane and 0.5-3 volumes of hydrocarbons obtained as sidereaction products in said isomerization with 0.2-2 volumes of a liquid isomerization catalyst mixture containing about 5-25% by weight of BFa and the remainder HF at a temperature of 25J/5 F. for about 10-30 minutes, separating from the reaction product mixture an isoheptane concentrate containing substantially all of the triptane formed in the course of the reaction, separating from the isoheptane product concentrate a triptane concentrate containing 2,4- trimethylpetane as the principal diluent, subjecting the triptane concentrate to extractive distillation in the presence of diethylphthalate as a selective solvent, recovering from the extractive distillation step a mixture of triptane and diethylphthalate, and separating therefrom a triptane concentrate containing at least 80% triptane.

2. A method for the production of triptane by the isomerizaton of isoheptane concentrate comprised of a major portion of the methyl hexanes and a minor portion of the dimethyl pentanes which comprises intimately contacting one volume of isoheptane concentrate, 6-12 volumes of liquid propane, and 0.5-3 volumes of hydrocarbons obtained as side reaction products in said isomerization with 0.2-2 volumes of a liquid isomerization catalyst mixture containing 5-25% by weight of BFa and the remainder HF at a temperature of -'75 F. for about 10-30 minutes, separating from the reaction product mixture an isoheptane concentrate containing substantially all of the triptane formed in the course of the reaction, separating from the reaction product ischeptane concentrate, a triptane concentrate containing 2,4-dimethylpentane as the principal diluent, vigorously agitating one volume of the triptane concentrate with 0.2-2 volumes of a liquid isomerization catalyst mixture containing ill-5% by weight of BFS and the remainder HF for a short period of time at about 50 F., whereby the 2,4-dimethylpentane is selectively isomerized to methyl hexanes and 2,3- dimethylpentane and thereafter separating triptane from the reaction product by fractional distillation.

3, In a process for the production of triptane by the catalytic isomerization of isoheptanes the improved method which comprises contacting a liquid feed consisting predominantly of methyl hexanes and dimethyl pentanes with a liquid iscmerization catalyst consisting of HF and BFs and containing about 5-25% by Weight of BFS at a temperature of 25 F. to 75 F., effecting said catalyst contacting step in the presence of 6-12 volumes of liquid propane per volume of feed whereby the formation of undesired side reaction products especially 2,2 and 3,3 dimethyl pentane is substantially reduced.

4. A method for the production of triptane by selective isomerization of isoheptanes which comprises intimately contacting one volume of a liquid feed consisting predominantly of methyl hexanes and dimethyl pentanes with 0.2 to 2 volumes of a liquid isomerization catalyst consisting of HF and BF3 and containing .E3-25% by weight of BFa at 60 F. for a period of 10 to 30 minutes, effecting said catalyst contacting step in the presence of about 6 to 12 volumes of liquid propane whereby the formation of 2,2 and 3,3 dimethyl pentane is substantially reduced.

JACOB D. KEMP. ARTHUR E. STICKLAND.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,266,012 DOuville et al. Dec. 16, 1941 2,325,122 Ipatieff et al. July 27, 1943 2,402,807 Egloif June 25, 1946 2,408,752 Burk Oct. 8, 1946 2,408,753 Burk Oct. 8, 1946 2,418,023 Frey Mar. 25, 1947 2,423,045 Passino et al June: 24, 1947 2,443,607 Evering June 28, 1948 2,461,568 Richmond Feb. l5, 1949 FOREIGN PATENTS Number Country Date 24,044 India May 25, 1937

Claims

3. IN A PROCESS FOR THE PRODUCTION OF TRIPTANE BY THE CATALYTIC ISOMERIZATION OF ISOHEPTANES THE IMPROVED METHOD WHICH COMPRISES CONTACTING A LIQUID FEED CONSISTING PREDOMINANTILY OF METHOD HEXANES AND DIMETHYL PENTANES WITH A LIQUID ISOMERIZATION CATALYST CONSISTING OF HF AND BF3 AND CONTAINING ABOUT 5-25% BY WEIGHT OF BF3 AT A TEMPERATURE OF 25* F. TO 75* F., EFFECTING SAID CATALYST CONTACTING STEP IN THE PRESENCE OF 6-12 VOLUMES OF LIQUID PROPANE PER VOLUME OF FEED WHEREBY THE FORMATION OF UNDESIRED SIDE REACTION PRODUCTS ESPECIALLY 2,2 AND 3,3 DIMETHYL PENTANE IS SUBSTANTIALLY REDUCED.