US2438421A - Isomerization of paraffinic hydrocarbons - Google Patents

Description

March 23, 1948- E. E.ISENSEL ET AL 2,438,421

ISOMERIZATION 0F PARAFFINIG HYDROCARBONS Filed June 18, 1941 GASES DOPAZAFFIN FEACT l ONAT 02,5

' RECYCLED HYDZOCAEBONS SETTLEZ ILI F T ID 23 & 1 U

H EATER FEED HYDZOCAZBON NAPHTH EN E PEOMOT E2.

EUGENE SENSEL WlLUAM KSMXTH ARTHUR KGOLDSEJY Patented Mar. 23, 1948 ISOMERIZATION OF PARAFFINIC HYDRO CARBONS Eugene E. Sensel, William R. Smith, and Arthur R. Goldsby, Beacon, N. Y., assignors, by mesne assignments, to The Texas Company, a corporation of Delaware Application June 18, 1941, Serial No. 398,530

9 Claims.

This invention relates to the conversion of hydrocarbons and has to do with the isomerization of hydrocarbons to form branched chain hydrocarbons. It is applicable particularly with respect to theisomerization of saturated gasoline hydrocarbons.

Broadly, the invention contemplates effecting the reaction by subjecting the feed hydrocarbon to contact with an isomerizing catalyst in the presence of an alicyclic hydrocarbon in amount suflicient to substantially inhibitcracking of the feed hydrocarbon and deterioration of the catalyst.

One problem involved in isomerizing hydrocarbons to a relatively high yield of branched chain hydrocarbons by conversion at relatively higher temperatures is that of avoiding the occurrence of substantial cracking, and other undesirable side reactions, with formation of hydrocarbons both of lower and of higher molecular weight than the feed hydrocarbon undergoing conversion. Such cracking may also involve the formation Of unsaturated hydrocarbons which readily react with the catalyst to form undesirable complex compounds.

We have discovered that by effecting the isomerizing reaction in the presence of a naphthene hydrocarbon such as the cyclopentanes and cyclohexanes, it is possible to carry out the reaction at relatively higher temperatures than heretofore so as to obtain relatively higher conversion to branched chain hydrocarbons without substantial occurrence of cracking or other side reactions.

In accordance with this invention, normal parafiin gasoline hydrocarbons, such as butane, pentane, hexane and heptane, etc., are subjected to contact with an active metallic halide catalyst, such as aluminum chloride, in a reaction zone or zones maintained under isomerizing conditions and the reaction is effected in the presence of at least a substantial proportion of a saturated alicyclic hydrocarbon having, for example, about 3 to 20 carbon atoms per molecule, such as cyclohexane, methylcyclohexane, dimethylcyclopentane, decahydronaphthalene, etc. If desired, a mixture of alicyclic hydrocarbons may be employed such as a naphthenic fraction segregated from naphtha derived from a coastal or naphthene base crude, or such as obtained in the refining of naphthene base petroleum or fractions thereof.

The feed hydrocarbon may comprise an isoparaflin such as Z-methylpentane, for example, Where it is desired to convert the hydrocarbon to a more highly branched form such as 2,2-dimethylbutane (neohexane) i It is also contemplated that the invention may be employed to treat straight run gasoline rich in aliphatic hydrocarbons for the purpose of improvin its antiknock qualities. In such case the paraffinic gasoline is advantageously blended with a suitable proportion of naphtha or fraction relatively rich in naphthenic hydrocarbons. The resulting blend is then subjected to contact with an isomerization catalyst maintained under isomerizing conditions whereby substantial conversion of the parafiinic gasoline hydrocarbons to branched chain hydrocarbons is secured without the occurrence of substantial cracking and formation of undesirable products.

In applying the invention to the treatment of individual hydrocarbons, such as butane, pentanes, hexanes and heptanes or gasoline fractions of relatively narrow boiling range, it i advantageous to effect the isomerization reaction in the presence of a naphthene hydrocarbon of substantially different boiling temperature range, namely, in the presence of a naphthene hydrocarbon boiling either below or above the feed hydrocarbon or hydrocarbon mixture undergoing conversion. This facilitates separating the naphthene hydrocarbon from the reaction product by fractionation so that the naphthene hydrocarbon can be recycled to the reaction.

An advantageous modification of the invention involves carrying out the reaction in a fluid type of operation wherein a substantial body of fluid containing the catalyst dissolved or suspended therein is maintained in a reaction zone with provision for continuous withdrawal of a stream of the reaction mixture and continuous recycling of the withdrawn stream to the reaction zone. Sufficient of the liquid mixture is recycled to impart thorough agitation to the reaction mixture within the reaction zone and also to permit maintaining a relatively high ratio of naphthene hydrocarbon to entering feed hydrocarbon. In this Way the ratio of naphthene hydrocarbon to feed hydrocarbon at the point of introduction of the and crosssection of the fluid mass within the reaction zone.

As an example of catalyst mixture, finely di vided aluminum chloride dissolved-or suspended in aluminum chloride-hydrocarbon compIeX'may be mentioned.

The reaction vessel or vessels may be oi: any suitable design and may, for example,- comprise vessels having provision for internal circulation of the reaction mixture such as to realize the desired conditions of high turbulence"and"high" ratio of naphthene hydrocarbon to feed: hydro= carbon undergoing conversion. These and other modifications will-be apparent upon reference to the further description ofthe invention.

The accompanying drawing comprises anew diagram illustrating one-method of carrying out the reaction. Thus freferring to the drawing a feed hydrocarbon such as n-pentane, iscontinuously drawn from a source not shown and passed through a heater I wherein it is heated to a temperature in therange about 160 to 300 F, or higher. The heated hydrocarbon is; then conducted through a pipe a-reactor 3. Likewise a naphthene hydi ocarbon. suchas cyclohexane,- is withdrawnfrom a source: not shown and introducedto the heater L I The reactor 3 comprises a vessel which maybe provided 7 with internal; mechanicalmixin gmean's and isof suiiicient capacity to=hold-a substantial body ofreactionrnixture, 7 V

The reactionvessel is ma ntained substantially filled with hydrocarbons including the catalyst, which latter may oompriseanhydrous' aluminum. chloride, for example. Provision is master the contiguousor intermittentintroduc'tion of: makeup catalystthroughan inlet 4'. k I

A suitable promoter such as hydrogen chloride is-also-introducedto the reaction f roma source not shown-througha pipe 5. g r A stream of reactionmixture is continuously drawn oft from the reactor through a pipe 6 to a settling vessel 1 whereina layer of catalyst mixture collects and is continuously withdrawn therefrom througha pipe 8, Advantage-ou'slyan additional quantity of reaction mixture is contin-ously drawn oiT- and recycled throughpi'ifle at to the reaction vessel 3. J I r The upper layer "accumulating in the; settling vessel 1 comprises reacted and unreacted hydrocarbons and cyclohexane. Thismixture is drawn off through a pip s to a f'raction ator HI whereih the cyclohexane and 'unreacted' nsrmai pentane is separated as; a liquid fraction drawn oirfrorn the bottomof the n scen it! through pipe it. Instead of recycling this residual fraction, an intermediate fractionoomprising naphthene'hy drocarbon may be drawn off as a sidestream from i'ra'ctionator it through pipe H21- and be recycled tothe'reaction, while theheav'ier' material is: discharged from the system.

withdrawing aluminum chloride and promoter. The isopentane and any lighter hydrocarbon material including promoter is drawn 01? from the top of the fractionator l and conducted to a 5 fractionator i2 wherein the gaseous material is removed as a vapor fraction and discharged through pipe IS. A liquid fraction is drawn off from the bottom of the fractionator I2 through a pipe l4 and will comprise essentially isopentane. The promoter discharged through the pipe I3 is advantageously recycledto. the'reaction vessel. Suitable provision, notishown; may be made for discharging from the system light gases or other materials tending to accumulate therein.- For example, it is advantageous to separate a butane seamen: from the light material accumulating from the reaction, either consisting essentially of isobutane or consisting of a mixture of isoand henna} butanaand' recycle this butane fraction, all or i part; through the isomerization reactiOIi: f Y 7 Likewise any hydrogen formed in the reaction nay-be recycl'edg all or in part, to the isomerization'reaction. r

As indicated in the drawing the liquid fraction drawn off from thefractionator Illthrough the pipe i i and" comprising. cyclohexane and unreacte'd pent'an'e is continuously recycled" by a pump I5'to' the reaction vessel 3. 'In addition; all or a During the operation, the naphthene may undergo isomerization, for example, cyclohexane' will be converted'to methyl 'cycl'ope'ntane. Therefore in continuous operation with recycle of the naphthenes' an equilibrium mixture of' the naphthenes' will'ultimately result and hence an equilibrium mixture-would ordinarily be recycled,

tions within the reactor 3 'and'likewise' maintain ing a high ratio'of naphthene 'toifeed' hydrocar bonundergoin'g treatment. i v V v While a single reaction vessel 3' is shown in the drawing, it is contemplated that a pluralityof of reaction and settlingstjafges. In such case the feed hydrocarbon may flow through each stageiin succession or portions of the feed may be separately introduced to succeeding stages in the system. Likewise provision may be made for con}- tinuous concurrent or countercur'ren't flowof feed hydrocarbon and catalyst mixture;

It is'und'e'r's'tood, of course, that the arrange mentcf fractionators illustrated in the drawing may be altered depending upon the particular hydroc'a'rb-ons undergoing treatment and upon the type of fractionation required. For example,

when isomerizing arelatively highboiling g'asopresence of a relatively lower boiling naphthene hydrocarbon it is necessary to rearrange the fractionators so as to segregate the naphthene hydrocarbon which is more volatile than the-resulting isomerizationproduct. 1

portion of the catalyst mixture drawnofifrom settler through the pipe a'isre'cycledjhy a pump 7 As already explai'ne'dit is advantageous to ad;

reaction vessels may be employed or a plurality.

line hydrocarbon or hydrocarbon mixture in the r It is intended also that the reaction may be effected in a reaction zone packed with a solid catalyst in lump or particle form. In such case the surplus naphthene hydrocarbon may be recirculated through a vertical reaction vessel packed with the solid catalyst or a catalyst supported upon a suitable supporting material.

Also, if desired a fluid suspension of powdered aluminum chloride in naphthene hydrocarbon or in aluminum chloride-hydrocarbon complex may be employed with a reaction tower packed with a solid inert packing material such as Raschig rings, through which tower the fluid suspension of catalyst is continuously recycled.

Besides aluminum chloride, other metallic halide catalysts may be used such as aluminum bromide, zirconium chloride, antimony chloride, or mixtures of halides such as .AlCls-SbCls. The

sults obtained by isomerlzing hydrocarbons such as pentane and hexane by contact with aluminum chloride in the presence of naphthene hydrocarbons such as cyclohexane, methylcyelohexane and dimethylcyclopentane.

A series of batch liquid phase experiments was made for the purpose of isomerizing normal pentane at a temperature of 160 F. with a reaction time of 4 hours. In each case powdered anhydrous aluminum chloride of about 200 mesh was charged to the reaction vessel to the extent of 10% by weight of the feed hydrocarbon, the reaction being promoted by the addition of a small amount of hydrogen chloride. One run was made in the absence of any naphthene, while two runs were made in which a quantity of cyclohexane was added to the reaction mixture as follows. I

Run

Per cent hydrogen chloride, by weight of feed hydrocarbon Per cent cyclohexane. by weight of feed hydrocarbon Composition of Hydrocarbon Reaction Mixture by Fractional Distillation,

per cent by weight:

Hydrocarbons of lower molecular weight than isobutane. Isobutane Normal butane. Isopentanc. Normal pentane Hydrocarbons of higher molecular weight than normal pentane including naphthene Pentane converted to lsopentane and other materials, weight per cent. Pentane converted to isopentane, Weight per cent Weight ratio of isopentane to normal pentane converted. Appearance of used catalyst 2 Red'brown liquid Dry yellow brown 8. Light yellow wet catalyst ma also comprise a solid material impregnated with metallic halide such as Porocel and aluminum chloride, charcoal and aluminum chloride, or alumina and aluminum chloride.

Also other halogen halides besides hydrogen chloride may be used as the promoter. The promoter may be generated in situ if desired.

It is frequently desirable to remove impurities from the feed hydrocarbon prior to contact with the catalyst in order to avoid catalyst deterioration. This may beaccomplished by subjecting the feed hydrocarbon to a suitable pretreatment. For example, it may be subjected to treatment with caustic in order to remove sulfur compounds. On the other hand, the pretreatment may in- Comparing runs 1 and 2 above; it is seen that by effecting the reaction in the presence of cyclohexane a materially higher conversion to ion pentane was realized with. a greatly reduced amount of cracking, and atthe same time the catalyst had apparently suffered no deterioration. The results of run 3 indicate that with a suificiently large percentage of naphthene present the converted pentane consists almost entirel of the desired isoparaflin.

A similar series of experiments was made in which the reaction was efiected at a higher temperature, namely, 200 F'., using the same proportion of aluminum chloride to pentane charge and with the following results.

Run 4 5 3 a Per cent hydro en chloride, by weight of feed hydrocarbon Per cent cyclohexane. by weight of feed hydrocarbon Composition of Hydrocarbon Reaction Mixture by Fractional Distillation,

per cent by weight:

Hydrocarbons of lower molecular weight than isobntane Isobutane Normal butane- Isopeniane Normal pentane Hydrocarbons of Pcntane converted to isopeniane, wei ht percent- Weight ratio of isopentane to normal pentane con Appearance of used catalyst lher molecular weight than normal pentane- Pentane converted to isonentane and other materials, weight percent volve contact with weak sulfuric acid, or treatment with a solid adsorbent clay in the vapor phase or in the liquid phase to remove diolefins and also to remove sulfur compounds. Aromatic constituents may be removed from the feed hydrocarbon by treatment with sulfuric acid or with a suitable solvent. For example, the feed hydrocarbon may be subjected to contact with water at elevated temperature and pressure in order to selectively extract aromatic constituents from the feed prior to the isomerization reaction.

As indicated by the foregoing experiments substantially better conversion yields to isopentane are realized by carrying out the reaction in the presence of the cyclohexane at a temperature of 200 F. Again the results reveal that cracking is substantially eliminated by effecting the reaction in the presence of cyclohexane. So much so that the converted normal pentane is substantially entirely isopentane.

Another series of experiments was made under conditions similar to those in the preceding The following data illustrate the improved regroup, i. e., employing a temperature of 200 F.

'relatively higher temperatures; may :be' employed when effecting thereactionfini the presence iof'a naphthene such 'asmentioned above; and thereby ing results.

enabling the obtainingtot-ahigh conversion of Run- 7 8 9 Naphthene'used Cyclohexane Methylcyelohex- Dimethylcyclo- *ane V pentane concenp trate Percent naphthenej by yeightpijeed hydrocarbom 10 10 1O 1 Per cent hydrogen chlorlde by 'weight oi feed hydrocarbon 1. 2 1. l. 0

Composition oi giydrocarbon Reaction -Mixture -by Fractional Distillation,

p r' b ive s t Hydrocarbons 1:10 erxmolecular weightthanisobutane 0 0.2 elsobutane he- 1 3.3 1.0 "16.8 Normal 1511mm '0 o. 5 I'sopo'fifane 70.2 60 55.5 ,Normal penta e 1 w, 7 7 39 l1.3 Hydrocarbons olj igher molecular weightjthan normal pcntano 5. 8 g 7 J 15. 7 Pentaneeonverted to isopentanaandother-materials, per centby Weight 78. 4 65.0 75.0 Pentane converted to lsopentene, weight percent V 73. 2 60. 7' -5 7. 7 Weight ratio of isopentane to normal pentane converted 93 -93 .77 Appearanceof used-eatalyst.; Brownish yellow Wet brow-n lumpy Brown semisolid gummy solid solid complex {Dimethylcyclopentane concentrate comprising 70% naphthenes.

In the following example a natural gasoline fraction comprising mixed hexanes and boiling the range 137 to 156 F. was subjected to isomerization in a'batch liquid phase operation using aluminum chloride and hydrogen chloride at a temperature or about 200 to 210 F. The aluminum chlorideiaimounted to 10%'- by weight of the hexane feed, *While the hy'drogen chloride amounted. to 3% -byweight fithe-feed. Run 11 was made in the presence of *cyclohexane amounting tof-1-0%by-weig-ht of the hexane feed. Run 10' was1 ma:deiiinithe *:absence of the naphthene hydrocarbon. The ihydrocarbcn product obtainedzinreaclrsrun' was fractionated to produce a Cs: fractiona and fithe two 10s fractions were tested forantik-nock characteristics :with the follow ingifresults c. F. R. M. Octane Number-- l M ftithouttetraethyl lead-addi 7 82.2.

1011.. "Withaddition orz QeL TELn, 96.0. NVithaddition-of 4cc.-I -EL 1-. Isooctane plus piece-T L. O.53cc.T-EL.

Thus, the product obtained in run 11 exhibited a higher clearoctanenumber and a. greater lead susceptibility. For example, with the addition of A cc. of tetraethyl lead it possessed an octane number equivalent to that of pure'iso-octane containing 0.2 :cc. of the 1ead2compound, while the product from'run 10 with a similar addition or lead compound had an octane-number of only -The product from run 11 was found to contain parailinto isoparafifin without substantial cracking;

The products or' any portion thereofproduced in the above described isomerization reaction may be subjected to further refining or' processfrom the fractionator l0 comprising isopentane.

and promoter -may --be passed directly to an alkylation unit f or the. pro duction of' :safety 1 fuel. The 'alkylation o'perationmay i'nvolve'reaction of isopentanewith'an olefin'such as triisobutylene in the presence' of a n a-luminumrchloride catalyst. On the other hand, "it is conterriplated that the entire reaction .aprcd-uct frfomthe isomerizat-ion operation may 'beipassed- :directly' to an alkylation reaction depending upon the type of final prodnot desired. e

The feed to the :isomerization reaction may comprise normal paraifin hydrocarbons or a. mixture of normal and-isoparaiiin -hydrocarbons incl-ud-ing pentanes hexanes, :heptanes and-the like. Obviously many :modifications and variations of the :invention,-as hereinbeiore set *forth, may be made Without departing from the spirit and. scope thereof, and therefore only such limitations should be imposed as are indicated in theappended claims.

We claim: a v 1. In a process forisomerizingnormal;pentahe, the steps comprisingrpasslng normalpentane'to a reaction zone containing an "aluminum halide isomerization catalyst maintained inthe I rese-nce of hydrogen chloride-at a temperaturein the.

range to 200 Fssuch that :normal pentane is converted in relatively: large "amount to 180- ment and sufficient to substantially inhibit cra'ck- 7 .ing of the pentaneduringcontact with the catalyst, and withdrawing'ir'om the. reactionzone a hydrocarbon 1 mixture comprising =isope'ntane.

2..A continuous methodfor isomeriaing nor 7 7 taining. an 7 aluminum halide isomerization catalyst under isomerizing conditions at ample-vetted temperature not in excess of about 300 F. such that the isomerization reaction is normally accompanied by substantial hydrocarbon cracking, continuously passing to said reaction zone feed hydrocarbons consisting essentially of normal parafiins, effecting contact between said normal .paraffins and the catalyst in the presence of an amount of added naphthene hydrocarbon relatively small compared to the paraifin hydrocarbons undergoing conversion in the reaction zone, introducing the added naphthene hydrocarbon to the reaction zone in an amount sufiicient to inhibitsubstantially said hydrocarbon cracking but insuificient to prevent isomerization of said normal paraffin hydrocarbons to a substantial extent, effecting substantial isomerization of normal paraffins during passage through the reaction zone, and continuously withdrawing from the reaction zone isomerized paraflin hydrocarbons.

3. The method according to claim 2 in which the added naphthene hydrocarbon is present in the reaction zone to the extent of about to 25% by weight oi the reactant hydrocarbon within the reaction zone.

4. The method according to claim 2 in which the added naphthene hydrocarbon is one having from about 3 to 20 carbon atoms per molecule.

5. The method according to claim 2 in which the added naphthene hydrocarbon is cyclohexane.

6. A continuous method for isomerizing normal parafiin hydrocarbons which are normally free from naphthene hydrocarbons comprising maintaining an isomerization reaction zone containing aluminum halide isomerization catalyst under isomerizing conditions at an elevated temperature not in excess of about 300 F. such that the isomerization reaction is normally accompanied by substantial hydrocarbon cracking, continuously passing to said reaction zone a hydrocarbon consisting essentially of normal parafflns, efiecting contact between said paraflin hydrocarbons and the catalyst in the presence of an added relatively small amount of naphthene hydrocarbon of substantially different boiling temperature range than the paraflins undergoing conversion, introducing the added naphthene hydrocarbon to the reaction in an amount sufiicient to inhibit substantially said hydrocarbon cracking but insufiicient to prevent isomerization of said normal paraifin hydrocarbons to a substantial extent, effecting substantial isomerization of the normal parafiins during passage through the reaction zone, continuously withdrawing a stream of hydrocarbon reaction mixture from the reaction zone, subjecting the withdrawn bydrocarbons to fractionation to separate therefrom a fraction comprising isomerized hydrocarbons and a fraction comprising said naphthene hydrocarbons, and continuously recycling said naphthene hydrocarbon fraction to the reaction zone.

7. A process for isomerizing hydrocarbons which comprises passing a natural gasoline fraction boiling in the range about 137 to 156 F. to a reaction zone containing aluminum chloride 10 maintained in the presence of hydrogen chloride at a temperature of about 200 to 210 F., eiiecting contact between said gasoline fraction and the aluminum chloride in the presence of added cyclohexane amounting to about 10% by 'weight of said gasoline fraction such that cracking of the gasoline fraction is substantially inhibited and such that the new product comprises a substantial amount of 2,2-dimethylbutane, and with, drawing from the reaction zone a hydrocarbon mixture comprising isomerized hydrocarbons including said 2,2-di-methylbutane.

8. In the process for the isomerization of an isomerizable normal paraffin having from 5 to 6 carbon atoms with an aluminum halide catalyst at an elevated temperature below about 266 F. at which degradation would normally take place, the improvement which comprises recycling through the isomerizing zone a mixture of interisomerizable pentamethylene and hexamethylene cycloparaffin hydrocarbons in an amount sufficient to inhibit substantially said degradation, whereby selective isomerization of the normal parafiin hydrocarbon is efiected.

9. In the process for the isomerization of an isomerizable normal paraifin hydrocarbon having from 5 to 6 carbon atoms with an aluminum halide catalyst at an elevated temperature below about 266 F. at which degradation would normally take place, the improvement which comprises adding to the hydrocarbon to be isomerized a cycloparaflin hydrocarbon chosen from the group consisting of cyclopentane, cyclohexane, and their methylated derivatives, in an amount sufiicient to inhibit substantially said degradation, whereby isomerization of the normal paraffin hydrocarbon is effected without substantial degradation.

EUGENE E. SENSEL. WILLIAM R. SMITH. ARTHUR R. GOLDSBY.

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

UNITED STATES PATENTS Number Name Date 2,220,092 Evering et al Nov. 5, 1940 2,249,337 Visser et al July 15, 1941 2,250,410 van Peski July 22, 1941 2,280,710 Lynch Apr. 21, 1942 2,288,866 Hoog July 7, 1942 2,299,716 van Peski Oct. 20, 1942 2,300,249 Evering et al Oct. 27, 1942 2,303,083 Kuhl Nov. 24, 1942 2,308,792 Thomas Jan. 19, 1943 2,313,054 de Simo et al. Mar. 9, 1943 OTHER REFERENCES Ind. & Eng. Chemistry, July 1932, pages 814 to 818.

Nat. Pet. News, Feb. 12, 1936, page 36.

Images