US2583740A

US2583740A - Two-stage isomerization of n-heptane

Info

Publication number: US2583740A
Application number: US642605A
Authority: US
Inventors: Jacob D Kemp
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 STAGE ISOM'ERIZATION OF' N-HEPTANE Filed Jan. 22, 194e ,MQQR mm Wm. mi Amm Qa. \S. w Nm. A mmm. w Nm, Q @nik H 0 www HH wa. W .wmv ....WH- uw.. w M A wax M- ...W w v A @..N www un. ww. H....

invention method steps, conditions, and the like, as will be readily apparent from the following description of preferred embodiments taken in reference to Patented Jan. 29, 1952 UNITED STATESv PATENT OFFICE TWO-STAGE ISOMERIZATION OF N-HEPTANE Jacob D. Kemp, San Francisco, Calif., assigner to California Research Corporation, San Francisco, Calif., a corporation of Delaware Application January 22, 1946, Serial No. 642,605

The present invention relates to the isomerization of normal paramns to highly branched parains and pertains more particularly to the isoinerization of normal paraiiins of six to nine and especially seven to eight carbon atoms toAV isoparailins having at least two side chains.

Heretofore, -many proposals have been made for isomerizing normal paraiiins, particularly lower pounds having a lesser number of side chains, or Y low yields or conversion.

It is therefore an object of the present invention to provide an improved isomerization process for the production of high yields of highly branched parains without attendant disadvantageous high proportion of side reactions.

It is another object of the present invention i to provide an improved low temperature process for isomerizing normal parafiins having six to nine and especially seven to eight carbon atoms to isoparafins having at least two side chains and especially to isoparaiiins having at least three side chains, wherein yields of commercial importance are obtained.

Further objects and advantages of the present reside in special combinations of the drawing, which is a schematic ilow diagram of one preferred embodiment of the present invention.

, According to the present invention, it has been found that normal parains above butane and Briefly, a normal paraffin is subjected in the y' rst stage to thorough contact with an isomeriza-l y 2 Claims. (Cl. 26o-683.5)

tion catalyst of relatively low activity and short contact time in the presence of a low-boiling isoparain and preferably at a relatively high temperature (as compared to subsequent treatment) to obtain a major reaction to isomers of one side chain. In the subsequent second stage or stages the single-branched isomers, i. e.," isomers having an intermediate number of side chains or a mixture predominating in said isomers as produced in the iirst stage, are isomerized in the presence of a normal paraiiin with an isomerization catalyst of relatively higher activity, and preferably at a relatively lower temperature. While hereinafter the preferred temperatures for carrying out the separate isomerization steps are spoken of as high and low temperatures, this is meant only as relative to each other, since the present process is normally carried out at low temperatures, i. e. below approximately 150 F. or thereabouts. While the conditions of lower catalyst activity and higher temperature in the rst stage and of higher catalyst activity and lower temperature in the second or subsequent stage represents the most advantageous and superior form of the present invention, it is also contemplated that "lhus, in the broadest sense, the present invention resides in a selective stepwise isomerization process employing in the rst stage a substantial excess of a low-boiling isoparain and in the subsequent isomerizatlon treatment of the rst stage product employing a substantial excess of a liquid normal paraffin, preferably low-boiling and notably liquid propane.

By means of this process higher yields of isoparafns having` at least two side chains than have heretofore been obtained are now possible. In the present improved isomerization process the amount of material lost to side reaction is greatly reduced so that the economical production of highly useful hydrocarbons with several side chains can now be obtained. Thus, the present invention provides a selective stepwise isomerization process. The present invention is particularly important and highly advantageous for the economical production of triptane (2,2,3-trimethylbutane) from n-heptane by isomerization.

vSuitable rstarting materials for the present process include normal paraffins, such as normal hexane, normal heptane, normal octane, normal suitable.

A sired product, i.

nonane. Concentrates containing 75% to 90% or more of a particular normal parafn may be used. Petroleum fractions of relatively narrow boiling ranges, such as a heptane fraction, are especially Other fractions of non-petroleum origin, such as from Fischer-Tropsch synthesis, or the like, may be used. Substantially pure (i. e., above 90%) normal parafns are preferred. The present process is particularly and most advantageously applied to relatively pure normal heptane and normal octane. 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 diiculties in catalyst regeneration.

Suitable low-boiling isoparaiins for use in the rst isomerization stage include isobutane, isopentane, or sometimes isohexanes, or mixtures thereof. Especially preferred is isobutane or mixtures of isobutane and isopentane. The ratio of isoparaflin to normal paraffin to be isomerized is generally 0.5-5.0 to 1 by volume, usually greater than 1:1, and mostV effectively from 2 4 to 1. These isopa'rains are almost entirely unaffected in the isomerization zone, but permit a greater selectivity of isomeri'zation toward the main de- Y e., from normal heptane to methylhexane's. In some cases, although normally less desirable, mixtures of these. isoperafwith low-boiling normal parains, such as propane, normal butane, normal pentane, etc.,

may beV advantageously used, whereby a simultaneous isomerization of the low-boiling normal parafns above propane and the higher boiling' normal parafilns, e. g., heptane, takes place. These low-boiling isoand n-parains may be obtained from extraneous sources, but preferably are mainly a part of the recycle stream of the small amount of side reaction products, which may also include some isobutane and isopentane.

In the second isomerization stage, the added n-paraflin is preferably a low-boiling n-parain of at least two carbon atoms, such as ethane, propane; normal butane, or normal pentane, 'or mixtures thereof. Propane is especially preferred and is found ideally suited for the isomerization of isoheptanes, mainly methylhexanes, to triptane. Higher n-'parains may likewise be employed; thus, when the original-starting material is normal heptane, the methylhexane fraction may be is'omerized in the second stage in the presence of normal heptane. These normal parafns are usually employed in excess over the stages.

Generally, any iso'merization catalyst or mixture of catalytic agents, may be used, wherein n the catalytic activity between the first and subsequent sta'ge's `can be varied. The present process usually employs catalysts comprising metal halides of the Friedel-Crafts type and hydrogen halides. ASuitable metal halides include particularly the chlorides and bromides of aluminum, and the halidesof boron, Zinc, iron, etc.,

.which may be admixed with hydrogen chloride,

hydrogen bromide or hydrogen fluoride. Also suitable are other catalyst modiers or promoters, such as water, lower alkyl halides, e. g.,

Vethyl chloride or butyl chloride, lower aliphatic alcohols, e. g., butyl alcohol, etc., secondary promoters, or admixtures of the above and the like. Likewise, complexes formed by theV combination of aluminum chloride or bromide with hydrocarbons, e. g., aluminum chloride-hydrocarbon complex from the reaction of aluminum chloride with butane during AlCla isomerization of butane, may be employed, with or without additional promoters'such as HCl or HBr. Aluminum halides may also be used with other metal halides such as halides of antimony, arsenic, zirconium, etc., or in liquid mixtures with other miscible compounds, such as nitrobenzene, ethyl ether, SO2, etc. Under some conditions, it may be advantageous for controlling catalyst activity and for depressing side reactions to provide for the presence of hydrogen. Particularly effective catalysts whose activity may be maintained at different levels are mixtures of HF and BFS, AlCls and HCl, AlBra and HBr, AlCls-hydrocarbon complexes with HCl and AlBrs-hydrocarbon complexes with HB1'. An especially preferred isomerization catalyst of the present invention is a mixture of boron trifluoride and hydrofluoric acid under sumcient pressure to maintain the desired concentration of BFa in theV liquid catalyst. Although it is preferred to use the same catalytic agents throughout the present process,

the present invention also contemplates that two dilerent catalysts may sometimes be employed in separate stages.

Relatively lower catalyst activity in the first stage as compared to the catalyst activity in the subsequent stage is determined at the same conditions. Thus, when relative catalyst activities are referred to, it is meant that the activitiesare to be compared at the same temperature, etc. According to the present invention, catalyst activity is controlled by the proportions of the ingredients in the catalyst mixture, most suitably by the concentration of promoter or more active ingredient. For example, in using aluminum halide-hydrocarbon complexes, the

catalyst activity may be increased by increasing the ratio of aluminum halide to hydrocarbon in the complex or the addition of hydrogen halide, or both; in using mixtures of boron trifluoride and hydrogen uoride, the catalyst activity may be increased by increasing the proportion of boron trilluoride in the liquid mixture; or with aluminum chloride-hydrogen chloride mixtures,

the amount of hydrogen chloride promoter may Y be increased to obtain greater catalyst activity.

The ratio of catalyst mixture to reactants depends at least in part upon the nature of the catalyst and reactants and upon the amount of relativelyV inert low-boiling isoparaffins present in theirst isomerization stage and of n-paraflins present in Ythe second isomerization stage. A large enough amount of catalyst in suitable form, either liquid or solid, is employed to yield suicient active catalyst surface to obtain the desired isomerization in a relatively short time. A constant renewal of the active catalyst surface available to the reactants is most desirable in preventing `side reactions. With the liquid type catalysts, which are preferred, the catalyst may form 5%--95% of the total liquid mixture, including the reactants, diluents, etc. When using the preferred amounts and proportions of hydrocarbons, i. e., around the middle of the ranges given, the ratio of catalyst mixture to n-parain kto be isomerized may be yfrom 0.2 to 2.0 by volume n-parafiins than for the lower n-paraifins.

=and preferably is in the vicinity-M05, espel cially with HF, BF3 mixtures;

It is especially preferable to recycle side reaction products, or like materials from extraneous sources, to each of the isomerization stages,

most desirably along with recycled, low-boiling isoparans to the rst stage and recycled normal paraihns to the subsequent stage or stages.

` The recycle of side reaction products in the second isomerization stage isparticularly important for best results.

It is a feature `of the present process that a one-pass operation in each isomerization stage, "particularly the rst stage, gives higher ultimate yields of the desired isoparains of larger number of side chains without excessivedegradation. However, incidental amounts of the desired end product in each iscmerization stage may be recycled thereto without appreciable change in over-all product yield. i

Ordinarily, only two isomerization stages are necessary; however, where isomers of three or more side chains are being produced from normal 'parains e. g., triptane from normal heptane,

the isomerizatiori treatment subsequent to the rst stage conversion to isoparaflins mainly of one side chain may be carried out in more than one stage. In most instances, a two-stage isomerization is preferable, wherein an n-parain is lsomerized in a first stage mainly to singlybranched parai'lns, e. g., n-heptane to methylhexanes, and the first stage product, e. g., methylhexanes, or a mixture of methylhexanes and dimethylpentanes, is isomerized in a second stage all the wayto the desired end product, e. g., to

triptane.

InV one specic embodiment, a normal paraiiin of preferably seven or eight carbon atoms, such l as normal heptane, is isomerized toisoparains predominantly having only one side chain in a first stage by thorough contact with a catalyst mixture of relatively low activity for a short period of time in the presence of a low-boiling isothat recycled) to 1 part of n-heptane. In addition, the material being charged to the first stage isomerization` usually contains small amounts of Lside reaction products, including propane, butano,

pentane, etc., which may be `recycled together with catalyst and/or promoter. Part `of the charge includes unreacted n-heptane and may also include relatively small amounts of methylhexanes.

The catalyst in the rst stage is preferably a liquid HF, B133 mixture, containing about three i to fifteen percent, preferably for n-heptane isomerization about eight to twelve percent by weight, BFS, and the remainder HF. Generally,

a lesserproportion of BFS is used for the` higher The ratio of catalyst to n-paraiiin reactant on a volume basis in the isomerization zone may be 0.2 to 2.0 more or less and is preferably about 0.5. The feed material, including the normal paraffin to be isomerized, is thoroughly contacted with` this catalyst mixture for not longer than about thirty minutes, and preferably from ten to twenty minutes at the isomerization temperature. Thorough agitation to cbt-ain efiicent contact between the catalyst and hydrocarbon feed material is particularly important in order to permit shortest contact times, whereby the desired isomerization is attained with a minimum of degradation into side reaction products. Less preferably, longer contact times may sometimes be tolerated when only a coarse dispersion of catalyst throughout the hydrocarbon feed material is achieved. Especially favorable results are obtained when the first stage isomerzation is carried out at a relatively high temperature as compared to the subsequent isomerizatioin) of F. to 150 F., most desirably 90 F. to 125 F. Suicient pressure is employed to maintain the desired concentration of BF3 in the liquid catalyst.

The yields or conversions to the desired isomer in the first stage will depend upon the isomerizing conditions, the amount of recycled materials, etc., as well as the nature of the n-parafn being treated. Usually above about 35% of the n-parafn charged will be converted to the isomer having only one side chain.

The resultant rst stage isomerization product may be separated into unreacted n-parafn, e. g., n-heptane, and an isoparaffin concentrate of, or a fraction predominating in, isomers of only one side chain, e. g., methylhexanes. Also, the

vsmall amount of side reaction products and residual catalyst may be separated for disposal, or recycled in whole or preferably in part. The isoparaflin concentrate generally conta-ins at least 65%, and preferably more than 80%, of isoparaiiins. Usually,` a concentrate of substantially pure (i. e., above 90% concentration by volume) isoparafiins is obtained, either in a primary separation, or, if necessary, in a secondary operation. The isoparains in the concentrate are mostly (i. e., 70% or 75% or more) singly-branched isomers. For example, under the preferred isomerization conditions with n-heptane as starting material, the rst stage isoheptane concentrate or fraction generally contains at least to or more of methylhexanes. It is most advantageous to minimize the amount of unreacted n-parafl'in in the isoparaffin concentrate, and it is preferable to recycle some singly-branched isoparaiin along with the unreacted n-parafn rather than use as feed material to the second isomerization stage an isoparafiin concentrate containing appreciable amounts of the unreacted n-paraiiin.` i

The separation of the isoparaiiin concentrate from the rst step reaction product mixture may be carried out in any suitable manner, such as by fractional distillation, solvent extraction, dash distillation, azeotropic distillation, extractive distillation, etc., or combinations thereof, in suitable apparatus, such as one or more packed or plate columns, or the like.

The concentrate or fraction of isomers predominantly of one side chain, e. g., methylhexanes, is subjected `in the second. isomerization step to the action of an isomerization catalyst mixture of increased activity, e. g., a liquid HF, BFa catalyst mixture containing a greater amount of BF3 than in therst stage.. Thus, the preferred BFs, HF mixture in the second isomerization reactor contains 5% to 25% BF3, preferably for heptane isomerization 13% to 19% BF3, under sufiicient pressure to maintainV the catalyst substantially in liquid forni. On a volume basis the ratio of catalyst to isoparaftin re- 4actant may be 0.2 to 2.0 more or less, :and is preferably about 1.0.

In the second isomerization stage, it is espe- "Il cially important that the isoparafn feed matebeing isomerized is about 2-20 to 1;

amount of n-parafn, such as propane, is ordi- Vthe recycled side products.

`frgtscymo il rial be subjected to the isomerization conditions `in the presence of a substantial amount of an n- .paraim preferably a low-boiling n-paraiin, in

The isoparaffin stage.

products Vas may be separated from the desired end product are Vrecycled or added to the feed materialv to the second isomerization stage.

Y Thus,in treating heptanes, it is mos'tdesirable to recycle the'side reaction products, such as iso butane, pentanes, and hexanes, to a second isomerization stage.V Further, if desired, n-parafns,

e. g., low-boiling normal parains, such as normal butane or propane, produced as side products in the first isomerization stage may be introduced as .part of the added n-parafn in the second isomerization stage. Preferably, the ratio of nparains and recycled side products to parains the narily in considerably greater proportion than Thus, for example, in aheptane isomerization using propane, a pre- `ferred feed mixture to the second isomerization stage comprises about 1 volume of isoheptanes, about 8 volumes of propane, and about 1 volume of other recycled materials, including side reaction products, such as butanes, pentanes, and

r hexanes.

The temperature in the second isomerization 'step is preferably relatively low, such as below 75 F. usually between 25 F. and 60 F. or lower.

Generally, the temperature is maintained so that Yonly the isoparains, e. g., methylhexanes and dimethylpentanes, are isomerized without substantial effect on the relatively inert n-parafdns, such as 4isornerizatiorrof butano, etc. d

Although the contact time in the second step is not as critical as in the rst isomerization step, a relatively short'contact time of about fifteen to thirty minutes or more with vigorous agitation may be employed, the longer times being used for the lower temperatures of isomerization or less eflcient mixing. VDepending upon the nature of the singlybranched isomers and the Yhighly branched chain isoparaflins desired and the conditions employed, the conversion per pass to the desired product will range upwards from by volume-'or more. Under the more preferred conditions in the second isomerization stage, ultimate conversions above about 50% will be obtained along with the production of other valuable gasoline components.

As in the irst isomerization stage, the reaction Vproducts may be separated into the desired products by any suitable means, such as distillation, fractional crystallization, extraction or distillation with selective solvents, etc., or combinaetc., aromatic amines, e. g.,.aniline, etc., ketones,

anhydrides, and the like.

It apparent that the processof the present linvention and any'step thereof can be carried out either continuously or batchwise, or combinations of batchwise and continuous treatmentmay be'used .In the isomerizationstages any suitable apparatus providing thorough contact between the catalyst mixture and the various in- `gredientsof the feed material, including recycled products and other added material, may be employed; ^For example, combinations of mechanically driven ag-itators, such as turbo mixerswith settlers, used either singly or in series or parallel, packed column adapted for concurrent or countercurrent flow, coil reactors, or the like, maybe used. Since it is particularly important in the present process to attain thorough'contact between the catalyst and hydrocarbon .mixture, it is preferred to use contactingdevices, such as turbo mixers or other relatively high speed agitator and ballie arrangements, wherein the catalyst is quickly and nely dispersed throughout the hydrocarbon mixture. The material forming the isomerization reactor, or reactors, and other apparatus, especially that which in 4contact with the HF, BFs catalysitis ordinarily substantially inert, such as Monel, nickel, Hastalloy, etc., so that no reaction of HF and/or BF3` takes place with the vapparatus material to form substances inhibiting theisomerizaton reaction or to form Vexcessive amounts of contaminants. `Many suitable types of apparatus can be constructed readily by one skilled in the art, but the invention will now be described `in reference to an illustrative preferred process Vflow shown schematically inthe drawing, wherein for the sake `of simplicity and clarity there have been omitted certain details, such as pumps, valves, pressuring means, coolers, .heat exchangers, reflux systems, etc.

Referring to the figure showing one preferred embodiment of a continuous flow process of the present invention, normal heptane and isobutane in a 1:3 ratio together with recycled material mentioned hereinbelow are introduced through `lines H and l2 .respectively into a .rst stage isomerization reactor i0, which Ymay bea turbo mixer operated to achieve a tine dispersion of .catalyst 'throughout `the hydrocarbon'- mixture.

The temperature within the isomerization reactor |10 is maintained at about 100" F. An HF,

IBFB catalyst mixture is also introduced into the isomerization reactor i0 Ythrough line t3 at a ratesufficient to give a liquid catalyst of about `8 to 12% BFa by weight and a'liquid catalyst to 'normal heptane ratio of about 0.5 on a volumeV basis. Thetotal amount of BF3 introduced into the reactor will depend upon the equilibrium pressure of BFa at the temperature employed, the V ratio of liquid catalyst .to .hydrocarbon and the gas space above the liquid mixture. Thus, sufcient pressure, such as 100-400 lbs./sq.in.V of

BF?. is used tomaintain the desired concentration of BFs in the liquid catalyst. For example, a total of about 25% BFs based by weight on'the HF, BF3 mixture was introduced into an isomer- When, as is preferred, a thorough contact be.

tween the catalyst and hydrocarbon mixture 1s quickly attained `in the reactor I0, the rates Aof flow of hydrocarbons and catalyst are gauged-to give a contact time in the isomerization reactor of about fifteen minutes.

A mixture of catalyst and hydrocarbons discharges from reactor I through line I5 into settler I6, wherein a separation into a hydrocarbon phase and a catalyst phase takes place. Ordinarily, at least part of the catalyst phase is recirculated to the reactor I0 through lines I'I and I3. Part cf the catalyst may be withdrawn through line I8 for regeneration or other disposal.

As illustrative of the rst stage isomerization, a batchwise experimental run was carried out at 100 F. and 15 minutes contact time in a reactor of 4.8 liter volume and under 267 lbs/sq. in. absolute pressure, giving a BFg partial pressure of about 182 lbs/sq. in. absolute and about 11.7 weight percent of BFa in the liquid catalyst phase, as follows:

Rim- A Charge to reactor, grams:

BF3 162 Propane 15 Isobutane 597 Normal butane 28 Normal heptane 270 05+ product recovered, grams 1 260 2,2,3-trimethylbutane 2.9 3,3-dimethylpentane 1.3 2,3-dimethylpentane 9.1 2,4-dimethylpentane 16.2 2-methylhexane 44.2 B-methylhexane 28.0 Normal heptane 151.1 Octanes 7.3 Heptanes lost 1 10.0

l 1 Includes losses through side reactions 'and mechanical osses.

The hydrocarbon phase leaving the settler I6 is a mixture of methylhexanes, dimethylpentanes (in a ratio of about 1 to 4-5 with the methylhexanes), isobutane, some unreacted normal heptane, some HF and BF3, and relatively small amounts of side reaction products, such as propane, butanes, pentanes, etc. This mixture passes through line 20, preferably rst to a recycle rectiiier 2I, wherein conditions are maintained to remove everything boiling up to but not including heptanes. The mixture of HF, BF3, isobutane, and lower-boiling side reaction products may be recycled in whole or in part through lines 22 and I2 to the rst stage isomerization reactor I0. In some instances, it is desirable to pass the whole or part of this low-boiling mixture through line 24, to a suitable vessel or column, called for convenience, iirst stage depropanizer 25. Therein materials boiling below isobutane and thus including HF, BFz, and propane are separated from isobutane which is recycled to the reactor I0 through

lines

26, 22 and I2. The lower boiling materials, i. e., HF, BFs, and propane, leave depropanizer 25 through line 21 and may be discarded or disposed of, such as for example as mentioned hereinbelow.

The heptanes, including methylhexanes, dimethylpentanes and unreacted `normal heptane which are substantially free of lower boiling materials, pass from recycle rectifier 2l through line 30 to a suitable separator, such as heptane still 3 I. Therein a separation between unreacted normal heptane and isoheptanes is effected, the normal heptane recycling at least` in part through line 32 to first stage isomerization reactor I0.

Preferably, the heptane still 3| is a fractional distillation column of a sucient number of theoretical plates for an eflicient separation between normal heptane and isoheptanes. The present process is most effective when the overhead from the separation in heptane still 3| contains little or no n-heptane and thus the bottoms withdrawn for recirculation may contain some methylhexanes. Although the heptane still 3I ls shown as a single column or unit, two or more columns may be used in a conventional multistage fractionation with intermediate recycle streams to obtain an isoheptane concentrate of at least 60% and preferably above 90% of isoheptanes.

The iirst stage isoheptanes comprising mainly methylhexanes and leaving still 3I through line 35, are introduced into the second isomerization stage reactor 40 through line 4I. Propane or other, preferably low-boiling, normal parain in about 8:1 ratio with the isoheptane is likewise introduced through lines 42 and 4I into isomerization reactor 40. Preferably recycle streams including propane, some catalyst, dimethylpentanes, unreacted methylhexanes, and side reaction products (i. e., butanes, pentanes, and hexanes) are added via

lines

44 and 45 to flow into reactor 40 as described hereinbelow. Sufcient side reaction products may be recycled to give a ratio of them to isoheptanes of about 1:1. Part of the propane introduced into second stage isomerization reactor 40 may be supplied from the reaction products from the first stage isomerization; thus, at least part of the propane together with HF and BF3 separated in rst stage depropanizer 25 maybe directed into the second stage isomerization reactor 40, and for this purpose line 48 from depropanizer overhead line 21 connects with pro pane line 42.

Catalyst is introduced into second stage isomerization reactor through line 50 and may comprise either in whole or in part either fresh catalyst from line 5I or recycled catlyst from line 52. The preferred HF, BF; catalyst mixture in reactor 40 contains about 13 to 19% by weight, and sufficient catalyst is introduced to maintain a catalyst to isoheptane ratio of about 1.0 on a volume basis. The pressure in the isomerization reactor 40 is at least suflicient to keep the desired concentration of BFs in the liquid catalyst and the propane mainly in liquid form. With thorough agitation the contact time between the cata lyst and hydrocarbons in the isomerization reactor 40 is about fteen to twenty minutes, and the temperature is maintained at about 50 F.

The catalyst and hydrocarbon mixture leaving the second stage isomerization reactor 40 passes through line to settler 56, wherein a separation into a hydrocarbon phase and a catalyst phase takes place. The catalyst phase may be in whole or in part either recycled through line 52 to the reactor 40 or passed through disposal line 57 for rejection or suitable regeneration.

As illustrative of the second stage isomeriza# tion, batchwise experimental runs at 50 F. and l5 minutes contact time were carried out in a reactor of 4.8 liters volume. In Run B, the total pressure was 245 lbs/sq. in. absolute, giving a BFs partial pressure of about 158 lbs/sq. in. and about 17.0 weight percent of BFs in the liquid catalyst phase. In Run C, the total pressure was 225 lbs/sq. in. absolute, giving a BF3 partial 5 pressure of about 163 ibs/sain. and about 17.5%

geen@ ,y lr Y B133 1n the liquid catalyst phase. The charge and product composition was as follows:

Run No B C 1 Chargeto reactor, grams:

HF 2l5 215 BF5 156 150 Ethane 13 Propane 643 318 Isobutane. 7 87 Normal butane. 4 Pentancs 119 Hexanes 126 2,3-dimethylpentane `277' 272 05+ Product Recovered, grams 207 487 Pen nes 25. 1 106. i Hexanes 44. 2 2,2,3-trimethylbutane (triptanc) 14. 5 2,2-dimethylpentane 0. 6 3,3-dimethylpentaneL 1. 1 2,3-din1ethylpentane. 10. 9 2,4-dimethylpentane. 2l. 2 2-methylhexane 25. 7 3-methylhexane 16. 4 Normal heptane 1.3 Octanes+ 45. 9r Weight of heptane recovered, gra 91. 7` Weight of heptane lost, grams 185 Ratio o heptanes lost to triptane formed 12. 8

1 The totalpressure was 2101bs./sq. in. gauge, giving a BFa partial pressure of 163 lbs/sq. m.

2 Both losses through side reactions and mechanical losscs are included.

Vremoved for recycle through lines 62 Vand 44 to second stage reactor li. Material b-oiling higher than Vpropane passes from depropanizer 6i through line V65 to a further separator, such as a dehexanizer 66, for separattionV intoY two fractions: one containing materials boiling helow heptanes, such as kthe small amounts of side reaction products including butanes, pentanes, and hexanes, and a second fraction` containing the heptanes and small amounts ofhigherr boiling materials. The lower boiling fraction discharges from dehexanizer 66 through line 6l, from whence it Vmay be. recycled to the second stage reactor lil through lines 44 and M or to other disposal throughline [i8V or both. In general, although side reaction products, such as butanes, pentanes, and hexanes, togetherwith the mixture of recovered propane, HF' and BF may be recycled to the second stage reactor 46, a separation of the HF, B133 mixture from the hydrocarbons may be eiected in any suitable manner, whereby all or part of each of the separated portions may be recycled or disposed of in other ways. Thus, part ofthe HF, BFs mixture may pass to a Vsuitable catalyst regeneration, and the hydrocarbons other than that required. for recycle may be used for blending in 'gasolines The higher boiling. heptane fraction leaving dehexanizer 'passes through line 'i6 into isoheptane fractionator ll. Therein, the heptane fraction is separated into a lower boiling triptane concentrate containing 2,4-dimethylpen- Vtaneand a higher boiling fraction containing Y through line '43 to rerun still 8), lwherein small til' fifi

amounts of heavier tanes,rsuch as octanes, etc., may be removed through line 8i, the heptanes passing throughy line 82 to recycle line 45; Thefractionator ll is preferably a distillation column or columns,v

suremay be maintained. Thel almost negligibler amount of 2,2-dimethylpentane and 3,3-dimethylpentane formed will be found in the triptane concentrate and the heptane fractionator bottoms, respectively. It is one of the advantages of the present invention as preferably applied to triptane production from n-heptane that the use of an n-parain, particularly propane, in the second isomerization stage causes little orV noiormation of 2,2-dimethylpentane and 3,3-dimethylpentane, thereby permitting a better separation between triptane and 2,4-diinethylpentane on one hand and the remaining ischeptanes on the other hand; however, when isobutane instead of propane is used as the principal diluent in the second isomerization stage, appreciable amounts of these neo-carbon atom dimethylpentanes are formed partly at the expense of triptane production.

The triptane concentrate leaving heptane fractionator 'il through line 85 contains about 40% or more triptane and the remainder almost entirely 2,4-dimethylpentane. Although thisV triptane concentrate has a fairly high octane number and may thus be used as such'for aviation fuel, it is more preferable to separate further to get at least and most desirably substantially pure (i. e., above triptane. Due to the closeness in boiling points of triptane and 2,4-dimethylpentane Yfractional distillation cannot ordinarilybe used. A suitable method of separation involves the use of selective solvents.

Thus, the triptane concentrate may be passed through line 86 to an extractive distillation system. For example, in the schematic extractive distillation system shown, triptane concentrate is introducedinto the middle portion of a suitable column 96 while a selective solvent, such as diethylphthalate, is introduced through line 9| into the upper portion. Substantially all or at least a principal amountof the 2,4-dimethylpentane together with any 2,2-dimethylpentane present is taken overhead through line 92 and recycled through lines d5 and 4l to the second stage isomerization reactor 4B. A mixture of triptane and solvent along with small amounts of 2,4-dirnethylpentane is withdrawn Vand passed through line t3 to a suitable separator or fractioner $24, wherein triptane-is removed from the solvent and passes out through line 95. Ihe remaining solvent is recycled through line 9| to distillation column 60.

The triptane thus obtained may beV of about 86% concentration but is usually in the Vicinity of 90% Aor above. If further puriiication is required, it is usually suitable to employ fractional crystallization, whereby triptane may bereadily crystallized from the mixture.

`By means of the above-described preferred` process iiow of the present invention, high yields of triptane can be obtained from n-heptane by valuable gasoline components. V'l`-lr1u's',for the material boiling above hepi First stage someriaation Conditions:

Temperature=l F. Contact time==15 min. Catalyst (lquid)=% BFa, 90% HF Ratio of catalyst to total hydrocarbons=14 :86

by volume Charge: 1000 B. /D. (barrels per day) fresh n-heptane 1780 B. /D. n-heptane recycled 8350 B./D. isobutanerecycled Product:

1000 B./D. isoheptanes 1780 unreacted n-heptane 8350 BJD. isobutane 0.75 B./D. heavy oils from acid phase Second stage isomerization Conditions:

Temperature=50 F. Contact time=15 min. i Catalyst (liquid) :19% BFs. 81% HF Ratio catalyst to total hydrocarbons=14z86 by volume Charge:

1000 B./D. isoheptanes from first stage. 2440 B. D. isoheptanes recycled 18400 B./D. propane recycled 1225 B./D. isobutane 980 B. /D. pentanes 980 B./D. hexanes Product:

18400 B. /D propane 2440 B./D. isoheptane (other than trlptane) 500 B./D. triptane i 1381 B./D. isobutane 1046 B./D. pentanes 1055 B. /D. hexanes 29 B,/D. heavy oils from acid phase 192 B. /D. octanes and heavier Although the above described process flow and example represent illustrations of a preferred embodiment of the present invention, it will be readily appreciated that many modifications and changes may be made without departing from the Y spirit and scope of the present invention as deiiined by the claims hereinbelow. Thus, while ordinarily two separate reactors will be used for, the isomerization stages, these may in some circumstances be incorporated into one unit, tower or contactor with intermediate separations and recycle streams.

Further, instead of using the preferred propane as the principal diluent in the second isomerization stage, other n-parafiins, preferably low-boiling, may be employed, in which case the second stage depropanizer 6| will not ordinarily be operated at least as such. In the event n-heptane is employed in the second isomerization stage o'f a triptane process, the second stage depropanizer 6| may be omitted, and lthe hydrocarbon phase from settler 55 passed directly into dehexanizer 6B, in which case it is preferable to separaterby suitable means the dehexanizer overhead materrial into HF, BF3 mixture and hydrocarbons, for example, in order to obtain more controlled recycle operation.

Instead of substantially pure r1-parai3ins,.las` starting materials for the present process, substantially pure, or fractions containing singly branched-chain higher parafilns, such as methylhexanes, methylheptanes, methyloctanes, methylnonanes, etc. may be employed. Likewise, in some cases mixtures of nand iso-paraiiins may be used to advantage, inwhich event the mixtures are preferably introduced into the system in such mannerthat a fractional separation takes place before the feed enters the isomerization zones. For example, when a heptane fraction containing some isoheptanes, such as about 10% to 30% or more of methylhexanes, constitutes the fresh feed to the first isomerization stage instead of substantially pure n-heptane in the above process, it is preferable to introduce such heptane fraction into the heptane still 3l rather than directly into isomerization reactor IU.

` In the above described triptane production process, it may sometimes be advisable instead of separating the triptane concentrate by extractive distillation, to subject this mixture of triptane -and 2,4-dimethylpentane to a selective isomerization 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, such as about l5 minutes, at approximately 50 F. with about 0.2-2.0 parts by weight of an isomerization catalyst consisting of 0.1% to 5%, preferably about 1%, by Weight of BF3 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 methylhexane, which may be recycled to the second stage isomerlzation. The low-boiling triptane concentrate thereby obtained contains less than half as much 2,4-dimethylpentane. Thus, for example, aitriptane concentrate containing about 20% 2,4-dimethylpentane when so treated yields a new triptane fraction containing less than about 10% 2,4-di1nethylpentane.

Although the present process is especially and preferably applicable to n-heptane isomerization, other n-parafiins, such as hexane, octane and nonanes, may be advantageously treated according to the present invention. When the higher n-parailins are isomerized, it is usually more desirable to use somewhat lower catalyst activities or lower temperatures, or both. However, it is an essential feature that the first stage isomerization be carried out in the presence of a substantial amount of an isoparain and preferably an isomerization catalyst of relatively low activity and the subsequent isomerizatlon of the first stage isomers be carried out in the presence of a substantial amount of a liquid n-parain and preferably an isomerization catalyst of 'high activity (said catalyst activities being compared at 4 the same conditions).

While the `especially preferred catalyst consists of HF and BF3 and generally the present process `is most effectively carried out therewith, other catalysts as mentioned hereinabove may sometimes be used to advantage. As illustrative thereof, the conditions of isomerization. may be in the vicinity of those given in the following examples:

Example 1.-An aluminum chloride-hydrocarbon complex containing about to 75% by weight AlCla and 35% to 25% hydrocarbon, such as is formed in butane isomerization, is employed in the present stepwise isomerization process, wherein the general conditions in the stages may be as follows:

VVabove'for that of the second stage.

, In the rst stage, Witna temperature of 75 F.

to 125 F. and a contact time of five to Vforty-rive minutes, the aluminum chloride-hydrocarboncomplexcontains about 0.5 to 15 mol percent of withY an HC1 partial pressure of about fifteen/tol three hundred pounds per square inch..

Other conditions, such as of ratios of catalyst and diluents to the hydrocarbon being isomerized, etc., Will be generally of the order of the ranges given hereinabove in connection with the preferred HF, B123 liquid catalyst mixture.V f

Example 2.-An aluminum bromide-hydrocarbon complexmay be employed under the general illustrative conditions `set out above for aluminum chloride-hydrocarbon complex.v

-As hereinbefore mentioned, the catalyst activities and temperature in one or both of the isomerizationstages may be varied from thev ranges given for the preferred general embodiment, While retaining at least part of the advantages ofthe present invention.

Thus, in some instances, where a greater production of side reaction products can be tolerated, i. e., where the side reaction products can be economically or readily utilized, such as for blending in aviation fuel or for other purposes, either or both higher catalyst activities and higher temperatures may be employed in one or both `isomerization stages. For example, the activity ofthe catalyst in the rrst stage may even approach orrexceed that of the catalyst in the second stage, and/or the temperature in theV second stage may be raised to about that of the ilrst stage or higher. Generally, the catalyst activities will not exceed those indicated herein- Ordinarily, under the above criterion the catalyst activity in the rst stage Will not be as critical as in the second stage and thusr can be raised With a consequent increase in conversion. It 1s to be underv stood that such modifications will bemade with due correlation with the nature of the hydrocarn-parain diluents are used in order to avoid excessive side reactionsproducing undesirable ma,- terials.Y feature to carry out the rst stage isomerization in the presence' of a substantial excess of a lowboiling isoparaiiin and the subsequent isomerization ofthe first stage productor fraction thereof inthe presence of a substantial excess of an n-parain, especially propane, in liquid form.

- I claim: Y y

1; Av process for isomerizing n-heptane which comprises intimately contacting one Vvolume of In any event, it remains an essential je() Number Name Y Date 2,266,012 DOuville et al Dec. 16, 1941 2,325,1 22 Ipatielf et al July 27, 1943 V2,339,849 Goldsby et al Jan. 25, 1944 2,402,807 Egloff June 25, 1946 2,408,752 Burk Oct. 8, 1946 2,417,698 McAllister et al.V Mar. 18, 1947 2,418,023 Frey Mar. 25, 1947 2,423,045 Passino et al June 24, 1947 2,443,606 Y Douviiie et a1. June 22, 1948 2,443,607 Evering June 22, 1948 2,443,608 Evering et al. June 22, 1948 2,446,998 Burk f Aug. 17, 1948 y2,461,545, Hepp Feb. 15, 1949 2,461,568 Richmond V Feb. 15,1949

Y FOREIGN PATENTS K Number 1 Country Date 24,044 India May 25, 1,937

Y n-heptane and 2` to'4 volumes of iso-butane with atleast `'0.2 volume of a liquid isomerization catalyst consisting of HF and 842% by weight of BFS,

art-.a temperature in the range of -125" F. for a period not exceeding- 30 minutes, separating from the isomerization product an iso-heptane concentrate Vcomrirised of methyl hexanes and dimethyl pentanes, intimately contacting one volume of said iso-heptane concentrate with at least 0.2 volume of a liquid isomerization catalyst consisting of'HF and containing'from 13-19% by Weightof BFs at a temperature of 25-60 F. for a period not exceeding 30 minutes and in the presence of 6 to 12 volumes of liquid propane whereby theformation of 2,2- and 3,3-dimethyl pentanes is substantially reducedand producing an isom'erizationv product containing substantial proportions of triptane. y

2. A process for isomerizing n-heptane which comprises intimately `contacting one Volume of n-heptane and 2 to 4 volumes o iso-butane with at least'0.2 `volume of a liquid isomerization catalyst consisting of HF and 8-12% by weight of BFa at a temperature in the range of 90125 F. for a period not exceeding 30 minutes, separating from the isomerization product an iso-heptane concentrate comprised ofY methyl hexanes and dimethylV pentanes, intimately contacting one volume of said iso-heptane concentrate with at least 0.2 volume of a liquid isomerization catalyst consisting of HF and containing from l13-'19% n REFERENCES CITED The following references are of record in the .'le of this patent:

UNITED STATES PATENTS

Claims

1. A PROCESS FOR ISOMERIZING N-HEPTANE WHICH COMPRISES INTIMATELY CONTACTING ONE VOLUME OF N-HEPTANE AND 2 TO 4 VOLUMES OF ISO-BUTANE WITH AT LEAST 0.2 VOLUME OF A LIQUID ISOMERIZATION CATALYST CONSISTING OF HF AND 8-12% BY WEIGHT OF BF3 AT A TEMPERATURE IN THE RANGE OF 90-125* F. FOR A PERIOD NOT EXCEEDING 30 MINUTES, SEPARATING FROM THE ISOMERIZATION PRODUCT AN ISO-HEPTANE CONCENTRATE COMPRISED OF METHYL HEXANES AND DIMETHYL PENTANES, INTIMATELY CONTACTING ONE VOLUME OF SAID ISO-HEPTANE CONCENTRATE WITH AT LEAST 0.2 VOLUME OF A LIQUID ISOMERIZATION CATALYST CONSISTING OF HF AND CONTAINING FROM 13-19% BY WEIGHT OF BF3 AT A TEMPERATURE OF 05-60* F. FOR A PERIOD OF NOT EXCEEDING 30 MINUTES AND IN THE PRESENCE OF 6 TO 12 VOLUMES OF LIQUID PROPANE WHEREBY THE FORMATION OF 2,2- AND 3,3-DIMETHYL PENTANES IS SUBSTANTIALLY REDUCED, AND PRODUCING AN ISOMERIZATION PRODUCT CONTAINING SUBSTANTIAL PROPORTIONS OF TRIPTANE.