US2460852A - Isomerization of cycloparaffins of nonhydroaromatic structure - Google Patents

Description

Feb. 3, 1949- R'. N. -sHlRAs ET AL 2,460,852

ISOMERIZATION OF CYCLOPARAFFINS OF NONHYDROAROMATIC STRUCTURE Filed Oct. 18, 1946 5L, wir Wma/M Patented Feb. 8, 1949 ISMERIZATION F CYCLOPARAFFINS QF NONHYDROAROMATIC STRUCTURE Russell N. Shiras, Oakland, Alan C. Nixon, Berkeley, and Carl H. Deal, Jr., Alameda, Califg'assignors to Shell DevelopmentCom'pany, San Francisco, Calif., a corporation of vDcli'aware `ApplicationOctober 18, 1946, Serial No. 703,992

This invention relates tothe production of cycloparafns of hydroaromatic structure from hydrocarbon mixtures of relatively Wide boiling range such-fas naphthenic gasolines or fractions thereof comprising cycloparalnns of hydroaromatic structure and non-hydroaromatic structure in admixture with open chain parailin andaromatic hydrocarbons. The invention relates more particularly to an improved process for the more efficient production of cyclohexane from naphthenic gasolines and fractions thereof comprising methylcyclopen'tane and cyclohexane.

Realization of the full advantages inherent in processes relying upon cycloparamns of hydroaromaticstructure, such as, Vfor example, cyclohexane, as a starting or intermediatematerial is often dependent upon emcient practical scale production of such cycloparaiiins from the available complex hydrocarbon mixtures 'comprising them. Not only is it imperative that they be produced with high yields, but itis essential that the product obtained be of a relatively high purity and yet involve the .use of a minimum of operative steps in their production.

Sources of cycloparalnns of hydroaromatic structureinclude the available hydrocarbon mixtures such as, for example, the naphthenic, natural and straight run gasolines, etc. Other sources include hydrocarbon mixtures of naphthenic character, boiling in the gasoline boiling range obtained by fractionation of the products of the v process involving the thermal or catalytic treatment of hydrocarbons or carbonaceous materials. Eflicient production of a cycloparain of hydroaromatic structure such as, for example, cyclohexane from such readily available hydrocarbon mixtures o1" naphthenic character involves not only the problem of recovering at least a substantialpart of the cyclohexane inherently present in such mixtures, but the simultaneous conversion of the cycloparans of non-hydroaromatic structure to cycloparaiiins of hydroaro- 8 Claims. (Cl. 260-666) tion disclosed heretofore, if at all possible, is often rendered so involved and delicate an oper'- `ation as -to render it highly impractical, Resort to such expedients as the initial separation of a fraction comprising both methylcyclopentane and 'cyclohexaneI subjection of this fraction to cycloparafiln isomerizing conditions, and fractionation of the isomerizate by methods-disclosed in processes heretofore is therefore unsatisfactory.

Not only do they enable the attainment of only y relatively low conversions of cycloparafns of nonhydroaromatic structure to cycloparafns of hydroaromatic structure but` the product thereby ,obtained will generally comprise substantial amounts of contaminant materials such as aromatic hydrocarbons and open chain parafns, the boiling temperatures of which lie soclose to those of the desired cycloparains as to render their separation therefrom by such expedients as simple fractionation by methods disclosed heretofore impractical. In the production of cyclohexane from readily available naphthenic hydrocarbon.

mixtures by such methods, the ycycloparafns -produced will be contaminated with substantial amounts 'of the benzene and dimethylpentanes ,Originally present in the charge. A serious diniculty generally inherent in processes disclosed heretofore wherein benzene is unavoidably accumulated in the isomerizate is the highly disadvantageou's limitation upon the amount of unconverted material which can be recycled. For the removal of suilicient benzene to avoid an inordinate accumulation in the system requires the rejection therewith of at least a substantial part of the unconverted material constituting the recycle stream in such methods. ability of a cyclohexane as starting or intermediate material in many processes is dependent upon the absence therein to any substantial degree of benzene and dimethylpentanes, it is apparent that the "practicability of a process producing cyclo-` hexane from readily available complex naphthenic hydrocarbon mixtures relies upon the ability of the process to produce cyclohexane eiiiciently and free of any substantial amount of benzene and dimethylpentane. By the term hydroaromatic cycloparafllns, as used throughout the specifi-y cation and appended claims is meant the cycloparains having a hexamethylene ring such as,

for example, cyclohexane, and the alkyl cyclo- Since the suitstructure from hydrocarbon mixtures of relatively wide boiling range such as naphthenic gasolinas, or fractions thereof, comprising cycloparamnsot hydroaromatic and ncn-hydroaromatic structure in admixture with close boiling aromatic and open chain paraillnic hydrocarbons. i

Another object of the invention is the provision oi' an improved process for the more eillcient production oi.'` eyclohexane from hydrocarbon mixtures of relatively wide boiling range such as naphthenic gasolines.'

A more particular object ofthe invention is the provision of an improved process for the more eicient production of cyolohexane of`a high degrec of purity from naphthenic gasoline fractions comprising methylcyclopentane, cyclohexane, benzene and close boiling open chain parafilnic hydrocarbons.

In accordance with the process of the invention a hydrocarbon mixture of naphthenic character such as for example a naphthenic straight run gasoline is subjected to fractionation t'o separate therefrom a fraction predominating in hydrocarbons having the same number of carbon atoms to the molecule and comprising cycloparafns of non-hydroaromatic structure and cycloparains of hydroaromatic structure in admixture with close boiling aromatic -andopen chain paramns. The cycloparaflln-containing fraction thus obtained is subjected to extractive distilla- 4 tion conditions in the presence of a suitable solvent as 'described more fully below to separate therefrom cycloparaiilns of hydroaromatic and non-hydroaromatic structure free of any substantial amounts of close boiling contaminants comprising open chain parafilns and aromatic hydrocarbons. 'I'he cycloparafiins of non-hydroaromatic structure free of anysubstantial amount of aromatic and open chain paraiiins thus ob- 4 4 prising aromatic hydrocarbons. The raffinate comprising cycloparalns of non-hydroaromatic structure free of any substantial amount oi.' arcmatics is introduced into a cycloparaiiln conversion zone. In4 the conversion zone the cycloparafilns are subjected to catalytic ,cycloparailln .tained are subjected to' cyeloparamn isomerizing c,

conditions converting cycloparains of non-hydroaromatic structure to cycloparailins of hydroaromatic structure.'

` In a preferred embodiment of the invention the cycloparaln-containing fraction separated from the' naphthenic Ygasoline and including cycloparalns of hydroaromatic and non-hydroaromatic structure in admixture with close boiling contaminants comprising open chain vparailins and aromatic hydrocarbons, is subjected to an extractive distillation in a first extractive distillation zone. In the rst extractiva distillationzone a raillnate fraction comprising paralnic hydrocarbons is separated from an extract fraction comprising cycloparafilns of hydroaromatic and non-hydroaromatic structure in admixture with aromatic hydrocarbons having the same number of carbonatoms to the molecule as the cycloparafiins. The extract fraction from the first extractive distillation zone is passed into a cycloparafn separating zone wherein a vapor fraction comprising cycloparafiins of non-hydroaromatic structure andaromatic hydrocarbons is separated froml a'liqud fraction comprising cycloparalns of hydroaromtic structure free of any substantial amount of aromatics. The vapor overhead from the cycloparailin separating zone is passed into a second extractive distillation zone. In the second extractive distillation zone a railinate comprising cycloparaillns of non-hydroaromatic structure free of any substantial amount of aromatics is separated from an extract fraction comisomerizing conditions effecting the conversion ci' cycloparamns of non-hydroaromatic structure to cycloparaillns of hydroaromatlc structure having the same number of carbon atoms 'to the molecule. Eilluence from the conversion zone comprising cycloparaiilns of hydroaromatie and nonhydroaromatic structure is introducedy into the cycloparamn separating zone. As will become apparent from the following description thereof, the invention enables not only the recovery of at least a substantial part of all of the cycloparaiiln content of a cycloparafiin concentrate as cycloparamns of hydroaromatic structure, but results in the obtaining of a product of a high degree of purity, devoid of even such contaminants as aromatics of close boiling range, with a minimum of steps Vand in the absence of many of the diiflculties and complexities inherent in attempts to obtain a 'cycloparaiiln product of a similar degree of purity by 'methods available heretofore.

In order to set forth more fully the nature of the invention, it will be described in detail in its application to the production of cyclohexane of a high degree of purity, free of any substantial amounts of benzene, from hydrocarbon mixtures of naphthenlc character in the, gasoline boiling range, with reference to the attached drawing in which the single figure represents a more or less diagrammatic elevational view of a form of apparatus suitable for executing the process of the invention.

A hydrocarbon mixture of naphthen'ic character such as, for example, a naphthenic straight run gasoline, is forced from an outside source throughvvalved line l by means of pump 2 into a feed fractionating zone comprising fractionator 3. Within fractionator 3 a hexane fraction comprising methylcyclopentane and cyclohexane is separated as an intermediate fraction. The methylcyclopentane cyclohexane fraction is passed from fractlonator 3 through line 4 into a second feed fractionator 5. Fractionation within fractionator 3 is preferably controlled to concentrate substantially all of the six carbon atom cycloparailins originally present in the feed in the intermediate methylcyclopentane-cyclohexane fraction. Although the boiling range of the fraction thus obtained may vary within the scope of the invention, depending upon the particular origin of the-composition of the feed material, a hexane fractionl boiling in the range of, for example,ffrom about 65 C. to about 85 C. has been found suitable. Within fractionator 5 the hexane fraction is subjected to a second fractionation to effect the separation of a higher boiling fraction as bottoms from a vapor overhead fraction comprising cyclohexane and methylcyclopentane. Operating conditions within fractionator 5 may be controlled to include at least a substantial part of the dimethylpentanes originally present in the feed in the liquid bottoms. Bottoms from fractionator 5 are withdrawn therefrom through valved line E and may be sent to additional cycloparaiiln separating means, not shown in the drawing, to effect the recovery of any cyclohexane contained therein.

The vapor fraction is taken overhead from fractionator 5 and passed through valved line 8 a,seo,eca

of or all of the hydrocarbon charge to the system-- The overhead fraction from tower i'ractionator will comprise besides methylcyclopentane and cyclohexane a certain amount of open chain parafilns and at least a substantial part of the benzene originally present in the charge. 'I'he rst extractive distillation zone may comprise an extractive distillation column I0. Within column I0 the cycloparainconcentrate is subjected to an extraotive distillation in the presence of a suitable solvent introduced into the upper part of the column from a suitable source by means i vof line I3.

Solvents which may be employed in column I0 include any solvent material enabling the separation of open chain paraillns as a. vapor fraction from a liquid fraction comprising the solvent and the cycloparaillns under extractiva distillation conditions. vSuitable sol- J' vents comprise solvents for hydrocarbons which are higher boiling than the cycloparamns being distilled, are stable under the conditions of distillation, do not react with any of the components of the hydrocarbon feed, and which markedly increase the volatility of the open chain paralns relative to those of the cyclo. paraflins. Suitable solvents comprise, for example, the polar liquids such as for example any of the polar solvents for cycloparafilns higher boiling than cyclohexane having oxygen-, nitrogen-, or sulfur-containing polar groups such as for example phenol, benzoic acid. isobutyric acid, aniline, N-methylaniline, cyclohexylamine, N-cy- .clohexylaniline, diphenylamine, naphthylamine.

hexamethylamine diamine, benzaldehyde. furfuraldehyde, benzoic anhydride, ethylbenzoate, benzophenone,

i acetophenone, y 'cyclohexanon benzoin, benzonitrile, nitrobenzene, nitropropane,

'pentaehloroethana diphenyl ethenlacetal. acetamide, ethylphosphate, dimethylsulfolane, the alkyl-substituted sulfolaneaetc. The solvent employed may consist of a single compound or of solutions of two or more of such compounds or of aqueous solutions thereof.

Extractive distillation conditions within column I@ are controlled to eilect vthe separation of a vapor raffinate comprising open chain paramns from a liquid extract comprising the solvent, methylcyolopentane and cyclohexane. The benzene present in the charge to column i@ will be 6 tor .I are controlled so that substantially all of the cyclohexane in the charge thereto is taken overhead. This will generally result in the inclusion of a proportion oi' the dimethylpentanes in the overhead.4 Dimethylpentanes thus included in the overhead of fractionator i are separated therefrom to the degree desired in column IU of the ilrst extractive distillation zone. Inclusion of substantially all of such dimethylpentanes in the parafiinlc overhead of column I II will occasion the entrainment therewith of a certain amount of the methylcyclopentane. When methylcyclopentane is thus included to a substantial degree in the overhead from column I0 it is preferably recovered therefrom by recycling at least a part of the overhead stream from line Il through valved line .I8 -to line I leading into fractionator 3. The overhead from column Ill may be passed. in part or in its entirety, through valved line 20, to a separate fractionating zone represented in the drawing by the single fractionator 2 I. Within fractionator 2| a fraction comprising lighter boiling materials, such as open chain hexanes, is separated from a liquid higher boiling fraction comprising dimethylpentanes. Since the lower boiling of the six carbon atom cycloparafdns is readily separated by fractionation from dimethylpentane, an intermediate fraction comprising included, under extractiva distillation conditions effecting the separation of paramns from cycloparamns in the cycloparaiin extract.

The vapor ramnate fraction is taken overhead i from column i0 by means of valved line id. The

liquid extract fraction ls taken from the lower part of column Iii and passed through line IS into a stripping zone comprising still I@ wherein the cycloparans comprising methylcyclopentanel and cyclohexane in admixture with benzene are separated as a vapor fraction from a. liquid fraction comprising the solvent. Lean solvent is returned from still i8 to the upper part of column l0 by means of valved line I3.

`The process of the invention enables substantially complete recovery of the six carbon atom cycloparafllns originally present in the feed. In a preferred method of effecting such substantially complete recovery of all the six carbon atom cyclopa'raiilns in the feed, conditions in fractionaamount of dimethylpentane is separated in fractionator 2i and removed therefrom by means of line 22.

Overhead from stripper I6 comprising methylcyclopntane, .cyclohexane and'benzene, free of any substantial amount of dimethylpentanes, is passed through line. 24 into a cyclopa'ramn separating zone. 4When operating the process with the passage ofl overhead from column Ill to fractlonator 2i. the methyloyclopentane withdrawn from fractionator 2l' through line 22, is passed in part or entirety into line 2t to combine therein with the cycloparajiin overhead from stripper it. f The cycloparafn separating zone may comlprise a. fractionator 25. fraction comprising cyclohexane is separated from a vapor fraction comprising methylcyclopentane and benzene. The liquid fraction comprising cyclohexane is withdrawn from fractionator 25 by means o f valved line 2t and eliminated from the system as a nal product. The vapor fraction comprising methyloyclopentane and benzene is withdrawn'overhead from fractionator 2t and passed through valved line '2t into a second extractiva distillation zone. The second extractive distillation zone may comprise an extractiva distillation column 29. Within column 2Q the hydrocarbon stream is distilled in the presence of a suitable solvent which is introduced into the upper part of the column by means of line 3G. Extractive distillation conditions are controlled within column 30 to effect the separation of a railinate vapor overhead comprising methylcyclopentane free of any substantial amount of benzene from a liquid extract fraction comprising solvent and benzene. Suitable solvents for use in column 29 comprise those set forth for the separation of cycloparamns from open chain paraihns in column I0. Thus good results are attained by the use ofphenol or any other polar solvent for benzene which is higher boiling than benzene and stable under the operating conditions, to effect the indicated separation of methylcyclopentane from benzene.

The vapor fraction comprising methylcyclopentane free of any substantial amount of ben- In fractionator 25 a solvent is passed from extractiva distillation column '29 through line 3l into a stripper 32. Within stripper 32 benzene is stripped from the sol` vent and eliminated as overhead therefrom through line 33. Lean solvent is Withdrawn froml stripper I6 and passed through line 30 to column 28.

It ls thus seen that the process of the invention enables not only the substantially complete recovery of cyclohexane free of any substantial amount of benzene from the charge, .but provides for the separation of a methylcyciopentane charge for the conversion zone which is also free of any substantial amount of benzene. Modification may obviously be made within the scope of the invention without departing from the spirit and scope thereof. Thus if desired the cycloparaln-rich solvent withdrawn from column i may be stripped of only the methylcyciopentane in stripper i6. Additional solvent may then be introduced from an outside source by means of valved line l1. The substantially pure methylcyclopentane thus obtained overhead from stripper I6 may be passed directly to the conversion zone. To this effect a valved line 31 is provided drocarbon complex. Other y suitable catalysts comprise those of the molten salt type containing the aluminum chloride in admixture with one or more halide salts. The temperature in the conversion zone 40 is maintained in the range of from about 20 C. to about 150 C. and preferably from about 50 C. to about 95 C. The specific temperature employed will be dependent to some extent vupon the particular catalyst employed. When utilizing a preformed aluminum chloride hydrocarbon complex as the catalyst a temperature in the range of from about 65 C. to about 85 C; is somewhat preferred. A hydrogen halide promoter, such as for example hydrogen chloride,

is preferably introduced into reactor 40 by meansv of line 42. The hydrogen chloride may be introduced in an amount of, for example, from about 0.1% to about 5% and preferably in an amount enabling the passage of hydrocarbons from line 24 into line 35 leading to the conversion zone. When thus taking only methylcyciopentane overhead in stripper I6, the solvent now still containing cyclohexane as well as benzene is drawn therefrom through line i3 and by-passed through a valved line 38 to suitable cyclohexane and benzene recovery means not shown in the drawing. Such recovery means may comprise one or more separate stripping zones as well as one or more separate solvent extraction or extractive distillation zones. When the benzene is thus diverted from the system through line 38 and no benzene is sent to the cycloparafiin separating column 25, the benzene-free overhead from column 25 may be passed directly to the conversion zone by means of valved lines 28, 34, 36 and 35.

When methylcyclopentane is passed from fractionator 2i -through valved line 22, such methylcyclopentane stream may also be introduced directly into the conversion zone. To this effect a valved line 39 is provided to enable the passage of methylcyclopentane from line 22 into line 35. An outstanding feature of the process of the invention is the elcient separation of benzene from cyclohexane. The separation of benzene from cyclohexane is greatly aided in column 25 by the presence therein of substantial amounts of methylcyclopentane which is taken overhead with the benzene. The passage of methyicyclopentane, even though free of benzene, from line 22, through line 24, into fractionator 25, may he resorted to to obtain the additional advantage of its presence upon the emcient separation of benzene from cyclohexane.

The conversion zone may comprise one or more reaction vessels such as for example, a reactor 40, provided with suitable stirring means 4l. Within reactor d0 the methylcyclopentane is contacted with an isomerization catalyst under cycloparamn isomerizing conditions. Suitable catalysts comprise those containing a metal halide of the Friedel-Crafts type, particularly those comprising a halide of aluminum, such as AlCis and/ orAlBra. Particularly suitable catalysts comprise the organo-aluminum yhalide complexes. preferably a, preformed aluminum chloride hybelow about 1%. A greater or lesser amount of hydrogen halide may, however, be introduced into the reaction zone within the vscope of the invention. Under these conditions methylcyclopentane is converted to cyclohexane within reactor 40.

Efiiuence from reactor 40 comprising cyclohexane, and uri-converted methylcyclohexane, entrained catalyst and hydrogen halide, is passed through line 43 into a catalyst separating zone, such as a separator 44. Within separator 44 a catalyst layer is separated from a supernatant hydrocarbon layer. Catalyst is passed from separator through line 45 to reactor 40. The hydrocarbon layer is passed from separator 44', through line 5B, into an accumulator 41. Liquid comprising cycloparaffins and dissolved hydrogen chloride is passed from accumulator 41 through line 48 into a stripping tower 49. Within stripper l there is separated a vapor overhead comprising hydrogen halide which is recycled through valved lines 5i and s2 to the conversion zone. A valved line 52 is provided for the introduction of makeup hydrogen chloride into the system.

A liquid fraction comprising cyciohexane and unconverted methylcyclopentane is taken from the lower part of stripper 49 and passed through line 56 into fractionator 25. To aid in avoiding the accumulation of light materials within the systeml wit-hout loss of valuable cycloparaifins, a part of the overhead from fractionator 25 may be passed intermittently or continuously from line 28, through line34, into line 8 leading to the first extractiva distillation column i0.

A further signal advantage of the process of the invention resides in the ability to employ a total recycle from the isomerization zone therein. Due to 'the substantially complete elimination of benzene from the reactor charge without loss of any substantiai amount of cyoioparafiins from the system, all of the methylcyclopentane content of the reactor emuence is returned to the reaction zone, thereby attaining substantially complete conversion to cyclohexane of all methylcyclopentane charged to the process and its recovery as a benzene-free product. The invention therefore eliminates the diiicuities often inherent in processes disclosed heretofore, wherein at least .a substantial portionof the cycloparaiiin-containing recycle stream must be sacrificed to effect the elimination of sumcient benzene to prevent its accumulation Within the system.-

The foliowlng example is illustrative of the practical scale production of high. purity, benzene-freecyclohexane from a. naphthenic straight run gasoline in accordance with the process of the invention:

9 Example In a continuous plant scale operation 8200 barrels of straight run naphthenic gasoline contains ing 7.1% of methylcyclopentane, 2.73% of cycloane, 4.5%. benzene and 2.28% dimethylpentanes,

the remainder of the concentrate consisting essentially of lower boiling and higher boiling paramns.

The Cs cycloparafiln concentrate thus obtained is subjected to a first extractive distillation in the presence of phenol as the solvent to separate an overhead railinate consisting essentially of paraiiins from a liquid bottoms extract consist- -ing essentially of solvent, cycloparafln and aromatics. .'I'herich extract-containing solvent is stripped to obtain an extract fraction consisting essentially of methylcyclopentane, cyclohexanev and benzene, substantially free= of paraillns, which i-s passed into a cycloparaftln fractionator into which the hydrocarbon efliuent from the subsequent reaction zone is also introduced. In the cycloparaiiin fractionator a-vapor overhead containing methylcyclopentane and aromatics is separated from a liquid bottoms fraction consisting essentially of benzene-free cyclohexane. The overhead from the cycloparain fractionator The invention claimed is:

1. The process for the Vproduction of cyclohexane free of any substantial amount of benzene from naphthen-ic gasoline which comprises separating av fraction comprising methylcyclopentane and cyclohexane in admixture with close boiling open chain parailins andbenzene from said gasoline, subjecting said fraction to extractivedistillation in -a iirst extractive distillation zone, separating a raflinate fraction comprising paralns from an extract fraction comprising methylcyclohexane, cyclohexane and benzene in y said iirst extractive distillation zone, passing said extract fractionfrom said rst extractive dis-v tillation zone into a cycloparain fractionating zone, separating a vapor fraction comprising methylcyclopentane and benzene from a liquid fraction comprising cyclohexane free of any substantial amount of benzene in said cycloparafiin fractionating zone, passing said vapor fraction from said cycloparan fractionating zone into af second extractive distillation zone, separating a rainate fraction comprising methylcyclopentane free of any substantialamount of benzene from an extract `fraction comprising benzene in said second extractive distillation zone, contacting said rafiinate from said second extractive distillation zone with an isomerizatiqn `catalyst at methylcyclopentane isomerizing conditions in a conversion zone, thereby converting methylcyclopentane 'to cyclohexane in said concontains '7.5% normal hexane, 84.07% methylcyclopentane, 0.9% cyclohexane and 6.07% ben- I y resulting in the obtaining of a substantially benzene-free railinate containing 8% normal hexane, 89.4% methylcyclopentane and 1% cycloe hexane. Benzene 'is stripped from lthe rich phenol solvent and recovered as 99.8% pure benzene. The benzene-free raffinate from the second extractive distillation zone is subjected to cycloparaflin isomerizing conditions by contact with an aluminum chloride-hydrocarbon complex at a temperature of 80 C. and in the presence of a 0.4% HC1. The hydrocarbon components of the reactor eiiiuent containing 40.7% methylcyclopentane and 48.7% of cyclohexane are passed directly into the cycloparafiin fractionator. Benzene-free liquid bottoms having a v91.5% by volume content of cyclohexane is drawn as the bottoms fraction from the cycloparaiiin fractionator. Redistillation of this cyclohexane fraction results in a benzene-free cyclohexane of 95% purity. 87% of the combined methylcyclopentane and cyclohexane originally present in the gasoline charge to the system is standing of the invention have been omitted from th`e drawing. Fractionatlng zones depicted in the drawing by single fractionators may com'- prise the use of more than one fractionator in the execution of the invention on a practical'- scale.

version zone, passing eliluence from said conversion zone into said cycloparafiin fractionating zone, and withdrawing said liquid fraction consisting essentially of cyclohexane free of any substantial amount ofi benzene from said cycloparailin fractionating zone. 7

2. The process for the production of cyclohexane free of any substantial amount of benzene from naphthenic gasoline which comprises separating a fraction comprising methylcyclopentane and cyclohexane in admixture with close boiling open chain parafnsand benzene from said gasoline, subjecting said fraction to extractive distillation in a first extractive distillation zone, separating a raflinate fraction comprising parailns from an extract fraction comprising methylcyclohexane,.cyclohexane and benzene in said first extractive distillation zone, passing said extract fraction from said rst extractive distillation zone into a cycloparailn fraction-ating zone, separating a vapor fraction comprising methylcyclopentane and benzene from a liquid fraction comprising cyclohexane free of any substantial amount of benzene in said cycloparaiiin fractionating zone," passing said vaporA fraction from said cycloparan fraetionating zone into a second extractive distillation zone, separating a raiiinate fraction comprising methylcyclopentane free of any substantial amount-0f benzene from an extract fraction comprising benzene in said second extractive distillation zone, contacting said raffinate from said second extractive distillation zone with an laluminum chloride isom-v erization catalyst at methylcyclopentane'isomerizing conditions in a conversion zone, thereby said conversion zone into saidcycloparaiiin fraci tionating zone, and withdrawing said liquid fraction consisting essentially of cyclohexane free of any substantial Vamount of benzene from said cycloparaflin fractionating zone.

3. The process for the production of cyclopar ailins of hydroaromatic structure free oi' any sub-l .tionating zone, and'withdrawing said liquid-fracstantial amount of aromatic hydrocarbons from a naphthenic gasoline which comprises separating a fraction comprising cycloparamns of hydro- ,I

aromatic and non-hydroaromatic structure in admixture with close boiling open chain pax'aln `and aromatic hydrocarbons from said gasoline.

fractionating zone, separating a vapor fraction,

comprising cycloparains of non-hydroaromatic structure and close boiling aromatic hydrocarbons from a liquid fraction consisting essentially of cycloparaillns of hydroaromatic structure free of any substantial amount of aromatic hydrocar- -bons in said cycloparain fractionating zone, passing said Vapor fraction from said cycloparailln fractionating zone into a second extrae-tive distillation zone, separating a railinate fraction comprising cyoloparalns .of non-hydroaromatic tion consisting essentially of cyclohexane tree ot any substantial amount of benzene from said cycloparafiln fractionating zone.

5. The process for the production of cyclohexane free of any substantial amount of benzeneni Irom a hydrocarbon fraction comprising methylcyclopentane and cyclohexane in admixture with close boiling open chain paramns and benzene, which comprises subjecting said fraction to extractive distillation in a rst eXtractive-fdistiilation zone, separating a raffinate fraction comprising parailins from an extract fraction comprising methylcyclohexane, cyclohexane and benzene in said rst extractive distillation, zone, passing said extract fraction from said first extractive distillationzone into a cycloparafiin i'ractionating zone, separating a vapor fraction comprising methylcyclopentane` and benzene from a liquid fraction comprising cyclohexane free of any substantial amount of benzene in said structure free of any substantial amount of aromatic hydrocarbons from an extract fraction comprisingaromatic hydrocarbons in said second extractiva distillation zone, contacting said raiiinate fraction from said second extractive distillation zone with an isomer-ization catalyst at cycloparain isomerizing conditions in a conversion zone, thereby converting cycloparamns of a non-hydroaromatic structure to cycloparailins of vane free of any substantial amount of benzene from a hydrocarbon fraction comprising methylcyclopentane and cyclohexane in admixture with close boiling open chain paraiiins and benzene, which comprises subjecting said fraction to extractive distillation in a first extractiva distillation zone, separating a railinate fraction comprising parafiins from an extract fraction comprising methylcyclohexane, cyclohexane and benzene in said rst extractive distillation zone, passing said extract fraction from said first extractive distillation zone into a cycloparaflin fractionating zone, separating a vapor fraction comprising methylcyclopentane and benzene from a liquid fraction comprising cyclohexane. free of any substantial amount of benzene in said cycloparamn fractionating zone, passing said vapor fraction from said cycloparailin fractionating z one into a second' extractive distillation zone,

separating a railinate fraction comprising methylcyclopentane free of any substantial amount of benzene from an extract fraction comprising benzene in said second extractive distillation zone. contacting said raffinate from said second extractive distillation zone with an isorerization catalyst at methylcyclopentane isomerizing conditions in a conversion zone, thereby converting methylcyclopentane 4to cyclohexane in said conversion zone, passing eiiluence from said conversion zone into said cycloparaffin fraccycloparailn fractionating zone, passing said vapor traction from said cycloparailln fractionating zone into a second extractive distillation zone, separating a raillnate fraction comprising methylcyclopentane free of any substantial amount of benzene from an extract fraction 'comprising benzene in said second extractive distillation zone, contacting'said raiilnate from said second extractive distillation zone with an aluminum halide isomerization catalyst at methylcyclopentane isomerizing conditions in a conversion zone, .thereby converting methylcyclopentane to cyclohexane in said conversion zone, passing eflluence from said conversion zone into said cycloparafiin fractionating zone, and withdrawing said liquid fraction consistingessentially of cyclohexane free of any substantial amount of benzene from said cycloparailn fractionating zone.

6. The .process for the production of cycloparans of hydroaromatic structure free of any substantial amount of aromatic hydrocarbons from a hydrocarbon fraction comprising cycloparailns of hydroaromatic and non-hydroaro-- matic structure in admixture with close boiling open chain paraiin and aromatic hydrocarbons, which comprises subjecting said fraction to extractive distillation in a first extractlve distillation zone, separating a ramnate, fraction comprising parainns from an extract fraction comprising cycloparafiins of hydroaromatic and nonhydroaromatic structure in admixture with close boiling aromatic hydrocarbons in said rst extractive distillation zone, passing said extract fraction from said first extractive distillation zone into a cycloparafn fractionating zone, separating a vapor fraction comprising cycloparamns of non-hydroaromatic structure and close boiling aromatic hydrocarbons from a liquid fraction consisting essentially of cycloparaiilns of hydroaromatic structure free of any substantial amount of aromatic hydrocarbons in said cycloparafiin fractionating zone, passing said vapor fraction from said cycloparailln fractionating zone into a second extractiva distillation zone, separating a raffinate fraction comprising cycloparaflins of non-hydroaromatic structure free of any substantial amount of aromatic hydrocarbons-from an extract fraction comprising aromatic hydrocarbons in said second extractive distillation zone with an isomerization catalyst at cyclopa-ramn isomerizing conditions in a conversion zone, thereby converting cycloparaiins of non-hydroaromatic structure to cycloparaiilns of hydroaromatic structure in said 13 conversion zone, passing etiluence from said conversion zone into said cycloparaiiin fractionating zone, and withdrawing said liquid fraction consisting essentially of cycloparaiiins of hydroaromatic structure free of any substantial amount of aromatic hydrocarbons from said cycloparailln fractionating zone.

7. The process for the production of cyclohexane free of any substantial amount of ben-y zene from a hydrocarbon fraction comprising methylcyclopentane and cyclohexane in admixture with close boiling open chain paraillns and benzene which comprises subjecting' said fraction to extractive distillation in a first extractive distillation zone, separating a raiiinate fraction comprising paraiiins and methylcyclopentane from an extract fraction comprising methylcyclohexane, cyclohexane and benzene in said rst extractive distillation zone, passing said -rafiinate fraction from said iirst extractive distillation zone into a methylcyclopentane fractionating zone, separating a fraction comprising methylcyclopentane from a fraction comprising paraiiins in said methylcyclopentane fractionating zone, passing said extract fraction from said first extractive distillationzone and said methylcyclopentane fraction from said methylcyclopentane 'fractionating zone into a cycloparaiiin fractionating zone, separating `a vapor fraction comprising methylcyclopentane and benzene from a liquid fraction comprising cyclohexane free of any substantial amount of benzene in said cycloparain fractionating zone, passing said vapor fraction from said cycloparaiiin fractionating zone into a second extractive distillation zone, separating a rafilnate fraction cornprising methylcyclopentane free of any substantial-amount of benzene from an extract fraction comprising benzene in said second extractive distillation zone, contacting said raiilnate from said second extractive distillation zone with an isomerization catalyst at methylcyclopentane isomerizing conditions in a conversion zone, thereby converting methylcyclopentane to cyclohexane in said conversion zone, passing eiiiuence from said conversion zone into said cycloparaiiin fractionating zone, and withdrawing said liquid iraction consisting essentially of cyclohexane free of any substantial amount of benzene 'from said cycloparaiiln fractionating zone.

8. The process for the production of cyclohexane free of any substantial amount oi' benzene from a hydrocarbon fraction comprising methylcyclopentane and cyclohexane in admixture with close boiling open` chain parafilns and benzene which comprises subjecting said fraction to extractive distillation in a first extractiva distiliation zone, separating a raiiinate fraction comprising paraiiins and methylcyclopentane from an extract fraction comprising methylcyclohexane, cyclohexane and benzene in said rst extractiva distillation zone, passing said raffinate fraction from said first extractiva distillation zone into a methylcyclopentane 'fractionating zone, separating a fraction comprising methylcyclopentane from a fraction comprising paraiiins in said methylcyclopentane fractionating zone, passing said extract fraction from said iirst extractive distillation zone into a cycloparailln fractionating zone, separating a vapor fraction comprising methylcyclopentane and 'benzene from aliquid fraction comprising cyclohexane vfre'e of` anyy substantial amount of benzene in said cycloparamn fractionating zone, passing said vapor fractionfrom said cycloparaiiln fractionating zone into a second extractive distillation zone, separating a rafnnate iraction comprising methylcyclopentane free of any substantial amount `of benzene from an extract fraction comprising benzene in said second extractive distillation zone, contacting said rafnate from said second extractive distillation zone and said methylcyclopentane fraction from 'said methylcyclopentane fractionating zone with' an isomerization catalyst at methylcyclopentane isomerizing conditions in a conversion zone,

thereby converting methylcyclopentane to cyclo` REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date `2,288,126 Dunn et ai.' June 30, 1942 2,299,716 Van Peski Oct. 20, 1942 2,306,253 McMillan Dec. 22, 1942 2,382,446 Ross et al. (A) Aug. 14, 1945 2,396,331 Marschner Mar. 12, 1946 2,415,066 Ross et a1. (B) Jan. 28,

OTHER REFERENCES 'Brame et namur. Inst. Pet. Tech., vpi, 1a, soa-811mm). s

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