US2505792A

US2505792A - Cyclohexane production

Info

Publication number: US2505792A
Application number: US708048A
Authority: US
Inventors: William E Ross; Pezzaglia Philip
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1946-11-06
Filing date: 1946-11-06
Publication date: 1950-05-02
Anticipated expiration: 1967-05-02

Description

ay 2, l950 W. E. Ross ET AL CYCLHEXANE PRODUCTION Filed Nov. e, 194e 0:56:02 mmm Patented May 2, 1950 CYCLOHEXANE PRODUCTION William E. Ross. Berkeley, and Philip Pezzagla, Oakland, Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application November 6, 1946, Serial No. 708,048

Claims.

This invention relates to the production of cyclohexane. The invention relates more particularly to an improved process for the more efficient production of cyclohexane free of any substantial amount of benzene from readily available hydrocarbon mixtures comprising methylcyclopentane in admixture with contaminating amounts of benzene.

The suitability of cyclohexane as a starting or intermediate material in many of the processes wherein it is thus employed is often dependent upon the absence therein of any substantial amount of benzene. Readily available sources of cyclohexane, comprising the methylcyclopentaneand cyclohexane-containing hydrocarbon mixtures such as, for example, the naphthenic natural or straight run gasolines, etc., as Well as the cyclohexaneand methylcyclopentane-containing hydrocarbon mixtures obtained in the thermal or catalytic treatment of hydrocarbons or carbonaceous materials of naphthenic character, however, generally contain substantial amounts of benzene. Because of the complexity of composition of such hydrocarbon mixtures, the closely approximating boiling temperatures of individual components thereof and the behavior of individual components under distillation conditions, the separation therefrom by fractionation on a practical scale as practiced heretofore, of cyclohexane, or a methylcyclopentane-containing fraction substantially free of benzene, if at al1 possible, generally would be so involved and delicate an operation as to render it highly impractical. The substantially complete separation of benzene from the cyclohexane product in processes disclosed heretofore involving the conversion of benzene-contaminated methylcyclopentane to cyclohexane, by the methods of fractionation employed therein, would necessitate the rejection of the greater part of the cyclohexane produced. Resort to methods involving one or more of such steps as solvent extraction, fractional distillation and the like, although enabling the attainment of a high yield of cyclohexane, often involves initial investment costs and a complexity of operative steps greatly offsetting the apparent practicality of the process.

It is an object of the present invention to provide an improved process for the more eicient production of cyclohexane free of any substantial amount of benzene from hydrocarbon mixtures comprising methylcyclopentane and cyclohexane in admixture with benzene such as, for example, a naphthenic gasoline.

Another object of the invention is the provision of an improved process for the more eftlcient production of cyclohexane free of any substantial amount of benzene from hydrocarbon fractions comprising methylcyclopentane in admixture with benzene.

A more particular object of the invention is the provision of` an improved process for the more eiiicient production of a high purity cyclohexane, free of any substantial amount of benzene, from hydrocarbon mixtures comprising methylcyclopentane in admixture with benzene, with al minimum of operative steps and apparatus requirement thereby enabling the attainment of the improved results With a substantial saving in initial vinvestment costs. i

In accordance with the process of the invention, hydrocarbons comprising methylcyclopentane in admixture with a contaminating amount of benzene, such as, for example, a naphthenic gasoline fraction comprising methylcyclopentane, is subjected to cycloparamn isomerizing conditions, thereby converting methylcyclopentane to cyclohexane. The resulting isomerizate comprising cyclohexane is freed of the contaminating benzene originally present in the charge by fractionation in the presence of an added amount of hydrocarbons comprising normal hexane and/or methylcyclopentane in a product separating zone, to effect the separation of a vapor fraction comprising normal hexane and/or methylcyclopentane in admixture with benzene from a liquid fraction comprising cyclohexane free of any substantial amount of benzene. In processes enabling eiiicient conversion of benzene-contaminated methylcyclopentane to cyclohexane the eiiluence from the reaction zone generally contains an insuicient amount of normal hexane and/or methylcyclopentane to enable the substantially complete and eicient elimination of benzene therefrom without a substantial loss of cyclohexane. In the process of the invention, hydrocarbons comprising substantially benzenefree normal hexane and/or methylcyclopentane are added in suiiicient amount to the reactor eiiluence to enable the separation therefrom of a liquid fraction comprising substantially ben-,- zene-free cyclohexane with a minimum of loss of the desired cyclohexane. The hydrocarbons comprising substantially benzene-free normal hexane and/or methylcyclopentane added to the isomerizate in or prior to its entry into the product separating zone may be obtained from any suitable source outside of or within the system.v

In a preferred modication of the invention a suitable benzene-free hydrocarbon stream comsubstantial amount of benzene by such methodsl as fractionation as carried out on a practical methylcyclopentane admixed? with benzene. The

methylcyclopentane fraction is subjected to Vcycloparain isomerizing conditions in a cycloparan conversion zone. The methylpentane-containing fraction is subjected'to isohexane isomer'- izing conditions in a paraffinconversion zone. Normal hexane containing eiiluence from the paranin conversion is combined withy the benzenecontaminatedv cyclohexane-containing ellluence from the cyclopar'aflin conversion zone and the resulting' combined stream subjected to fractionation in a product separating zone wherein cyclohexane substantially free' or" benzene is' separated as a liquid fraction from a vapor fraction com-f prising hydrocarbons lower boiling than cyclohexane in admixture with substantially all of the' contaminant benzene. l

In order to set forth more fully the nature of the invention it will be described in detail with reference to` the attached drawing wherein the single gure represents a more or less diagrammatical, elevational View of one form of apparatus suitable for carrying out the process of the' invention. n

In accordance with the process f the invention hydrocarbons comprising open chain parafns and cy'cloparaninsV having six carbon atomsv to the molecule in admixture With benzene such as', for example, a naphthenic straight gasoline, are taken from an outside 'source and forced through line I, by means of pump 2, into" a feed fractionating Zone. The feed fractionating zone may comprise a first feed fractionator 3, Wherein the feed is subjected to fractionation to effect the separation therein of an intermediate fraction comprising. open chain parainns and cycloparafns having six carbon atoms to the molecule from higher and lower boiling hydrocarbons. ''hus a `fraction boiling in the range of, for example; from about 55C. to about 95 C. comprising open chain hexanes, methylcyclopentane and cyclohexane originallyV present in thefeed maybe separated as an intermediate fraction in fractionator 3 and removed therefrom through valved line 4.- It is to be understood that the boiling range of such intermediate fraction may vary Within the scope of the invention. A suitableyfraction is that which includes at least a substantial part of the open chain parafns and thek cycloparaf-ns having six carbon atoms to the molecule, originally present in the feed. The intermediate hexane fraction thus separated in fractionator 3 will of necessity comprise at least asubstantial part of the benzene originally present in the feed.

A hexane fraction comprising open chain hexanes, methylcyclopentane,v cyclohexane and a .contaminating amount of benzene, may be introduced into the system from any suitable source by means of valved line l'. Such a fraction introduced through line l may comprise a part or all of the hydrocarbon feed introduced into the system.

The hexane fraction is passed from line 4 into a second feed fractionator 8. In fractionator 8 the hydrocarbons are fractionated to separate a vapor fraction comprising branched chain hexanes from a liquid fraction comprising normal hexane, methylcyclopentane and` cyclohexane. The' vapor fraction separated in fractionator 8 may have a maximum boiling temperature 'f, for example, about C. and thus comprise all of the' methylpentane introduced into fractionatcr 8. The liquid fraction separated in fractionator 8 may comprise all material higher boiling, for example', than about 65 C. Thus the overhead vapor fraction separated in fractionator 8 may suitably have a boiling range of for example from about 55 C. to about 65 C., the liquid fraction may have a boiling ran-ge for example, from about 65 C?. to about 9`5 C'.

The liquid fraction separated in fractionator 8I is' passed therefrom through line 9 intoa third feed fractionator Ill. Within feed fractionator lilav vap'or fraction comprising substantially all of the methylcyclcpen-tane ifs separated from a liquid fraction comprising cyclohexane andi higher boilingV material. In generali, conditions are preferably controlled Within fractionator' l0 to assure the presence of substantially no dimethylpentanes in the vapor fraction separated therein. Thus the overhead vapor fraction' may preferably comprise all material boiling below about C. such as', for example, a fraction boiling in the range offroni about 55' C. to about' 7 5`C-. The liquid fraction will comprise substantially all material boiling above 75' C. such as',- for example, a fraction boiling in the range of from about 75 C.- to about 95 C. The liquid fraction thus separated comprises the greater part of the cyclohexanek introduced into the sys"-v tem and includes a minor part of the benzene originally present in the charge, and is withdrawn from fractionator lilY by means of valved line` H and eliminated from the system.A The vapor fraction separated in fractionator Ill will comprise not only substantially all of the methylcyclopentane but also the normal hexane introduced intothe system, as Well as the greater part of the benzene originally present in the charge. The proportion of the benzene originally present in the feed which will generally be included in the overhead vapor fraction of fractionator l0 will vary in accordance With the benzene content of thefeeland may range as high as from about to 90%. The relatively' small remaining portion of the benzene originally present in the feed Will be found in the overhead fraction of fractionator 8 and in the liquid fraction of fractionator ll.

From fractionator l0 the vapor fraction comprising methylcyclopentane, open chain hexanes and contaminant benzene is passed through line [3 Vinto a cycloparaifin isomerizing zone I4. Within the cycloparain isomerizing zone i4 the stream is contacted with an isomerization cata- 1 yst under cycloparaihn isomerizing conditions. Suitable isomerization catalysts comprise those containing a metal halide of the Friedel-Crafts type, particularly those comprising a halide of aluminum, such as AlCl and/or AlBra. Particularly suitable catalysts comprise the organoaluminum halide complexes', preferably a pre- 7'6 formed aluminum chloride hydrocarbon complex.

Other suitable catalysts comprise those of the molten salt type containing the aluminum chloride in admixture with one or more halide salts. The temperature in conversion zone Ill is maintained in the range of from about 20 C. to about 150D C. and preferably from about 50 C, to about 95 C. The specific temperature employed will depend to some extent upon 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. The isomerization is preferably executed in the presence of a hydrogen halide promoter, such as, for example, hydrogen chloride. The hydrogen chloride may be present in an amount of, for example, from about 0.1% to about 5% and preferably in an amount below about 1%. A greater or lesser amount of hydrogen halide may, however, be employed within the scope of the invention. Under these conditions methylcyclopentane is converted to cyclohexane within cycloparaffin isomerizing zone I4.

In a preferred method of carrying out the process of the invention, conditions within cycloparain isomerizing zone I4 are controlled to eiect the substantially selective isomerization of the methylcyclopentane, thereby leaving at least a substantial part of the normal hexane unaiected by the conditions employed. The maintenance of selective cycloparafn isomerizing conditions in cycloparain isomerizing zone I4 assures the presence of the open chain hexanes, in the eflluence from that zone in the form of normal hexane, in which form they can be utilized to aid in the removal of benzene from the cyclohexane produced. Substantially selective cycloparaflin isomerizing conditions are obtained by the use of the organo-metal halide type catalysts such as, for example, the hydrocarbon-aluminum chloride complexes at a temperature below about 80 C., for example, from about 50 C. to about 80 C. Other isomerization catalysts which may be employed to attain preferential cycloparain isomerization comprise isomerization catalysts which have been rst employed in the isomerization of parains until they no longer possess appreciable activity for paraiiin isomerization. Such catalysts include the catalyst-containing sludges formed during the isomerization of paraiins with isomerization catalysts other than the organo-metal halide complexes. Catalysts at least partly spent with respect to their ability to isomerize paraliins generally permit the utilization of somewhat higher temperatures, for example up to about 150 C.

Effluence from cycloparaflln isomerizing zone I4 is passed through line I5 into a stripping tower I6. Within stripper I6 there is separated a vapor fraction comprising hydrogen chloride from a liquid fraction comprising cyclohexane, methylcyclopentane, open chain hexanes and benzene. The Vapor fraction is recycled from stripper I6 by means of line I1 into line I3. A valved line I9 is provided for the introduction of make-up hydrogen chloride into the system.

The liquid fraction is passed from stripper IS through line 20 into a product separating zone. The product separating Zone may comprise a fractionator 2I. Within fractionator 2l effluence from cycloparaiiin isomerizing zone I4 separated in stripper I is fractionated in the presence of added hydrocarbons comprising normal hexane and/or methylcyclopentane. The hydrocarbons comprising normal hexane and/or methylcyclopentane are introduced into the system by means of valved line 22 from any suitable outside source. The hydrocarbons thus added are free of'any substantial amount of benzene. Fractionation of eilluence from cycloparan conversion zone I 4, in fractionator 2|, in the presence of the :added hydrocarbons, enables the separation therein of a vapor fraction comprising substantially all of the material lower boiling than cyclohexane and substantially all of the benzene introduced into fractionator 2 I, from a liquid fraction comprising cyclohexane free of any substantial amount of benzene. The hydrocarbons comprising normal hexane and/or methylcyclopentane are introduced into the system through valved line 22 in an amount assuring the presence in fractionator 2I at all times of a ratio of normal hexane and/or methylcyclopentane to benzene of at least 10 to 1 and preferably at least 15 to 1, by volume. Proportions of n-hexane and/or methylcyclopentane to benzene below 10:1 in the mixture render impossible the separation of substantially all benzene from the cyclohexane without the loss of cyclohexane to a degree rendering the process highly impractical.

In a preferred modification of the invention the substantially benzene-free hydrocarbons added to the eflluence from cycloparaffin isomerizing zone I4 are obtained from the charge to the system and built up therein to suicient amount to enable a continuous removal of benzene from the cyclohexane produced with improved recovery of cyclohexane. To this effect the Vapor fraction comprising branched hexanes, separated in fractionator 8, is passed therefrom through line 24, into a paraffin isomerizing zone 25.

Hydrocarbons comprising branched hexanes free of any substantial amount of benzene obtained from any suitable source may be introduced into the system by means of valved line 23. Branched hexanes thus introduced through line 23 may constitute a part or all of the hydrocarbons charged to paraffin isomerizing zone 25.

Within paraffin isomerizing zone 25 the branched hexanes emanating from fractionator 8, and recycled from within the system, are contacted with an isomerization catalyst at isohexane isomerizing conditions, thereby converting branched hexanes to normal hexane. Isohexane isomerizing conditions employed comprises the use of a solid isomerization catalyst at a temperature in the range of from about 300c C. to about 600 C., and preferably from about 350 C. to about 450 C. Preferred solid isomerization catalysts suitable for use in the paraffin isomerization zone comprise, for example, the heavy metal sulde isomerization catalysts, in particular the suliides of the metals of the left hand side of group VI of the periodic table. Molybdenum sulfide and/or tungsten sulfide are particularly suitable catalysts. These catalysts may be used as such or in combination with inert, solid diluent or support material, as the diicultly reduclble metal oxides, for example, aluminum oxide. Hydrogen is preferably added to the isomerization charge to paraffin isomerizing zone 25. Preferred partial pressures of hydrogen to hydrocarbons lie in the range of from about 1.511 to about 8.6 :1. Hydrogen is introduced into the line 2li by means of line 26. A contact time of, for example, from about 30 to about 150 seconds has been found satisfactory. Higher or lower contact times may be used, however, within the scopeof the invention. Under the above-dened conditions branched-chain hexanes are converted efficiently4 to normal hexane within parain isomerizing zone 25.

' Elliuence from paraliin isomerizing zone 25 is passed through line 21 into suitable hydrogen separating'means indicated diagrammatically in the drawing by column 2B. In column 28 a normally gaseous fraction comprising hydrogen and optionally at least a part of the unconverted branched hexanes is separated from a liquid fraction comprising normal hexane and optionally at least a part of the unconverted branched hexanes. The vapor fraction is passed from column 28 through line 26 into line 24. A valved line 29 is provided for the introduction of make- -up hydrogen into the system.

At least a part of the liquid fraction from column 28 is passed through line 30 into line 20 to mix therein with eliluence from cycloparafn isomerizing zone i4 separated in stripper l5. Because of the low benzene content of the charge to parafn isomerizing zone 25, the liquid fraction separated in stripper 28 will comprise only small amounts of benzene, thereby rendering it particularly suitable as a source of the normal hexane-containing hydrocarbons added to the -f benzene contaminated cyclohexane stream emanating from cycloparain isomerizing zone I4.

The liquid fraction comprising cyclohexane free of any substantial amount of benzene is taken from the lower part of fractionator 2l and passed through line 33 into a fractionator 34. Within fractionator 34 there is separated a vapor fraction consisting essentially only of cyclohexane substantially free of benzene, and a liquid fraction comprising any material higher boiling than cyclohexane which may have entered cycloparafiin isomerizing zone I4 or may have been formed within the system. The vapor fraction is taken overhead from fractionator 34 by means of valved line 35 and eliminated from the system as a nal product. The liquid fraction is separated from fractionatcr 34 through valved line 35.

The vapor fraction separated in fractionator 2l comprising normal hexane, methylcyclopentane, benzene and isohexane, is passed therefrom through

lines

38 and 39 into a fractionator 40. Within fractionator 40 there is separated a liquid fraction comprising methylcyclopentane, normal hexane and benzene and a vapor fraction comprising isohexanes substantially free of benzene. The liquid fraction is taken from fractionator 40 by means of valved line 4|. At least a portion of the hydrocarbon stream passing through line 4| is recycled through valved line 42 into line l' leading into the feed fractionating zone. hydrocarbons recycled through line 42 may be passed in part, or entirety, into valved line 43 leading into line I3 passing directly to the cycloparafiin isomerizing zone.

The vapor fraction separated within fractionator 4E! is taken overhead therefrom through valved line 45 and passed at least in part into line 24 leading to paraffin isomerizing zone 25. Valved line 46 is provided for the elimination of any portion of the overhead vapor fraction flowing through line 45 from the system.

A portion of the liquid bottoms from column 28 may be by-passed continuously or intermittently from line 30, through valved line 3S directly into fractionator 40. The amount of hydrocarbons by-passed through line 39 from line 3B, as well as the amount of hydrocarbons eliminated from the system through line 46, is controlled to avoid the accumulation of benzene to any substantial degree within the parafn isomer- The It is seen that when conversion of normal hexe ane to isohexanes is effected in cycloparain isomerizing zone I4, the isohexanes so formed, themselves of little use in the separation of benzene, will be comprised in the substantially benzenefree overhead from fractionator 40, whence they are recycled to paraffin isomerizing zone 25 to be converted therein to normal hexane.

The process of the invention enables the eilicient production of high purity cyclohexane having a benzene content as low as below about 0.1% from readily available naphthenic gasolines, the benzene content of which gasolines may often range as high as about 6% and higher. The invention thus provides a highly eiiicient process for the economical production of substantially benzene-free cyclohexane from benzene-contaminated hydrocarbon mixtures comprising methylcyclopentane wherein separation of benzene-free cyclohexane is obtained within the system with the use of substantially only practical fractionating means to effect the removal of benzene from admixture with cyclohexane.

The following example is illustrative of the practical scale production of substantially benzene-free cyclohexane from benzene-contaminated naphthenic gasoline:

Eample Straight run gasoline was subjected to fractionation in a rst feed fractionator to separate therefrom a hexane fraction boiling in the range of from 35 C. to 90 C. and containing 20.5% branched hexanes, 20% normal hexane, 19% methylcyclopentane, 9.5% cyclohexane and 3.5% benzene by volume. The hexane fraction thus obtained was subjected to further fractionation to separate therefrom a branched hexane fraction (A) boiling in the range of from 55 to 65 C. and containing branched hexanes, 15.7/ normal hexane and 1.3% benzene; and an intermediate fraction (B) boiling in the range of from 65 C. to 75 C. containing 39% normal hexane,

9% branched hexanes, 43.5% methylcyclopentane, no readily determinable amount of cyclohexane and 8% benzene. The benzene contents of fraction (A) and fraction (B) represented 6%- and 87.5%, respectively, of the total benzene content of the entire hexane fraction.

Intermediate fraction (B) was isomerized by contact with an aluminum-chloride hydrocarbon complex catalyst at a temperature of 80 C. in the presence of hydrogen chloride added in an amount equal to 0.9% by weight of the feed, at a contact time of 29 minutes. A conversion of methylcyclopentane to cyclohexane of 75% was obtained. Conversion of normal hexane in the fraction to branched hexanes amounted to 40%.

Branched hexane fraction (A) was isomerized by contact with a molybdenum sulfide catalyst at a temperature of 400 C., 20 atmospheres pressure, with a contact time of 80 seconds in the presence of added hydrogen. A conversion of branched hexanes to normal hexane of 67% of the theoretical was attained. Eiiiuence from the cycloparaiiin isomerizing zone, freed of hydrogen chloride, and the eiiiuence from the parain isomerizing zone, freed of hydrogen, are combined and introduced into a product fractionator. A liquid fraction consisting essentially of cyclohexane is separated in the product fractionator from a vapor fraction comprising the open chain hexanes, methylcyclopentane and benzene.

The vapor fraction is taken from the product fractionator and subjected to a separate fractionation to separate therefrom a vapor fraction comprising open chain hexanes, containing less than 1.5% benzene, from a liquid fraction comprising methylcyclopentane, open chain hexanes and benzene. The open chain hexane vapor fraction is recycled to the paraflin isomerizing zone and a portion of the liquid fraction is recycled continuously to the cycloparaiiin isomerizing zone.

Re-running of the liquid cyclohexane fraction;

withdrawn from the product fractionator to separate material higher boiling than cyclohexane therefrom resulted in obtaining a cyclohexane fraction consisting of 99-1-% cyclohexane, containing less than 0.1% of benzene, having a specic gravity /4 (vac.) of 0.7781 and a refractive index 20/d of 1.4260.

The invention claimed is:

1. The process for the production of cyclohexane substantially free of benzene from a hydrocarbon fraction comprising methylcyclopentane in admixture with open chain hexanes of normal and branched structure and benzene, which comprises fractionating said hydrocarbon fraction in a feed fractionating zone to separate therefrom a higher boiling fraction comprising methylcyclopentane in admixture with benzene and a lower boiling fraction comprising branched chain hexanes, said higher boiling fraction containing an insuicient amount of open chain hexanes to enable the substantially complete separation by practical fractionating means of ysubstantially benzene-free cyclohexane from the -isomerizate obtained by subjecting said higher gboiling fraction to methylcyclopentane isomerizing conditions, contacting said higher boiling fraction with an aluminum chloride isomeriza- ,tion catalyst in a cycloparafiin conversion zone at ya temperature of from about 20 C. to about 150 C., thereby converting methylcyclopentane A:to cyclohexane in said cycloparanin conversion zone, contacting said branched chain hexane fraction with a metal sulfide isomerization catalyst in a paraffin conversion zone at a temperature of from about 300 C. to about 600 C., thereby converting branched chain hexanes to normal hexane in said paraffin conversion zone, passing effluence from the cycloparafn conversion zone into a product fractionating zone, passing eiiiuence from said paran conversion zone into said product fractionating zone at a rate assuring the presence of a ratio of normal hexane to benzene in excess of 10:1 by volume in said product fractionating zone, and separating substantially benzene-free cyclohexane from a fraction comprising methylcyclopentane, open chain hexanes and benzene in said product fractionating zone.

2. The process for the production of cyclohexane substantially free of benzene from a hydrocarbon mixture comprising methylcyclopentane in admixture with open chain hexanes of normal and branched structure and benzene, which comprises fractionating said hydrocarbon mixture in a free fractionating zone to separate 'therefrom a higher boiling fraction comprising methylcyclopentane in admixture with benzene and a lower boiling fraction comprising branched chain hexanes, said higher boiling fraction containing an insucient amount of open chain hexanes to enable the substantially complete separation by practical fractionating means of substantially benzene-free cyclohexane from the isomerizate obtained by subjecting said. higher boiling fraction to methylcyclopentane isomerizing conditions, contacting said higher boiling fraction with an aluminum chloride isolmerization catalyst in a cycloparaiiin conversion zone at cycloparain isomerizing conditions, thereby converting methylcyclopentane to cyclohexane in said cycloparan conversion zone, contacting said branched chain hexane fraction with a metal sulfide isomerization catalyst in a paraffin con- Version Zone at a temperature of from about 300 C. to about 600 C., thereby converting branched chain hexanes to normal hexane in said parafn conversion zone, passing efiiuence from the cycloparaffin conversion zone into a product fractionating zone, passing efiiuence from said paraffin conversion Zone into said product fractionating zone at a rate assuring the presence of a ratio of normal hexane to benzene in excess of 10:1 by Volume in said product fractionating zone, and separating substantially benzene-free cyclohexane from a fraction comprising methylcyclopentane. open chain hexanes and benzene in said product fractionating zone.

3. The process for the production of cyclohexane substantially free oi benzene from a hydrocarbon mixture comprising a methylcyclopentane in admixture with open chain hexanes of normal and branched structure and benzene, which comprises fractionating said hydrocarbon `mixture in a feed fractionating zone to separate therefrom a higher boiling fraction comprising methylcyclopentane in admixture with benzene and a lower boiling fraction comprising branched chain hexanes, said higher boiling fraction containing an insuicient amount of open chain hexanes to enable the substantially complete separation by practical fractionating meansof substantially benzene-free cyclohexane from the isomerizate obtained by subjecting said higher boiling fraction to methylcyclopentane isomerizing conditions, contacting said higher boiling fraction with an isomerization catalyst catalyzing the cycloparailn isomerizing reaction in a cycloparain conversion zone at cycloparaiiin isomerizing conditions, thereby converting methylcyclopentane to cyclohexane in said cycloparaiiin conversion zone, contacting said branched chain hexane fraction with an isomerization catalyst catalyzing the parain isomerizing reaction in a parafn conversion zone at isohexane isornerizing conditions, thereby converting branched chain hexanes to normal hexane in said paran conversion zone, passing eifluence from the cycloparafn conversion zone into a product fractionating zone, passing effluence from said paran conversion zone into said product fraotionating zone at a rate assuring the presence of a ratio of normal hexane to benzene in excess of 10:1 by volume in said product fractionating zone, and separating substantially benzene-free cyclohexane from a fraction comprising methylcyclopentane, open chain hexanes and benzene in said product fractionating zone.

4. The process for the production of cyclohexane substantially free of benzene from a hydrocarbon fraction comprising methylcyclopen- 11 tane in admixture With open chain hexanes of normal and branched structure and benzene, which comprises fractionating said hydrocarbon fraction in a feed fractionating zone to separate therefrom a higher boiling fraction comprising methylcyclopentane in admixture with benzene and a lower boiling fraction comprising branched chain hexanes, said higher boiling fraction con taining an insufficient amount of open chain hexanes to enable the substantially complete 4separation by practical fractionating means of substantially benzene-free cyclohexane from the `isomerizate obtained by subjecting said higher boiling fraction to methylcyclopentane isomerizing conditions, contacting said higher boiling fraction with an aluminum chloride isomerization catalyst in a Acycloparafiln conversion zone at a temperature of from about 20 C. to about 150 C., thereby converting methylcyclopentane to cyclohexane in said cycloparaiiin conversion zone, contacting said branched-chain hexane fraction with a metal sulde isomerization catalyst in a paraffin conversion zone at a temperature of from about 300 C. to about 600 C., thereby converting branched chain hexanes to normal hexane in .said paralin conversion Zone, passing eiiluence from the cycloparan conversion Zone into a rst product fractionating zone passing efuence from ysaid paraffin conversion zone into said rst product ractionating zone at a rate assuring the .presence of a ratio of normal hexane to benzene in excess of :1 by volume in said iirst product fractionating zone, separating a vapor fraction comprising fmethylcyclopentane, branched and normal hexanes and benzene from liquid bottoms consisting essentially of substantially benzeneffree cyclohexane in said rst product fractionating zone, passing said Vapor fraction from said first product fractionating zone into a second V,product fractionating zone, separating a vapor fraction comprising branched chain hexanes from a liquid fraction comprising methylcyclopentane, normal hexane andbenzene in said second prod- -uct Iiractionating zone, and passing at least a part of said vapor fraction from said second product fractionating zone to said parain conversion Zone.

5.. The process for the production of cyclohexane substantially free of benzene from a hydrocarbon mixture comprising methylcyclopentane in admixture with open chain hexanes of normal and branched structure and benzene, which comprises fractionating said hydrocarbon mixture in a feed liractionating zone to separate therefrom a higher boiling fraction comprising methylcyclopentane in admixture with benzene and a lower boiling fraction comprising branched chain hexanes, said higher boiling fraction containing an insufficient amount of Open chain hexanes to enable the substantially complete separaton by practical fractionating means of substantially benzene-free cyclohexane from the isomerizate obtained by subjecting said higher boiling fraction to methylcyclopentane isomerizing conditions, contacting said higher boiling fraction with an isomerization catalyst catalyzing the paran isomerizing reaction in a cycloparafn conversion zone at cycloparafn isomerizing conditions, thereby converting methylcyclopentane to cyclohexane in said cycloparaiiin converysion zone, contacting said branched chainhexane fraction with an isomerization catalyst catalyzing i,

tially benzene-free cyclohexane in said rst product fractionating zone, passing said vapor fracJ tion from said first product fractionating zone into a second product fractnating zone, sepa.- rating a Vapor fraction comprising branched chain hexanes from a liquid vfraction comprising methylcyclopentane, normal hexane and benzene in said second product iractionating Zone, and passing at least a part of said vapor fractn from said second product fractionating Zone to said parallin conversion zone.

WTLLIAM E. ROSS.

PHILP PEZZAGLIA.

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

UNITED STATES PATENTS Number Name Date 2,288,866 I-Ioog July 7, 1942 Y2,382,446 Ross et al Aug. 14, 1945 2,392,398 McMillan et al Jan. 8, 1946 2,399,927 Howes et al Mar. 7, 1946 2,415,066 Ross et al Jan. 28, 1947 2,417,699 McAllister et al Mar. 18, 1947 OTHER REFERENCES Ser. No. 323,410, van Peski (A. P. C.) pub. Apr. ,20, 1943.

Claims

3. THE PROCESS FOR THE PRODUCTION FO CYCLOHEXANE SUBSTANTIALLY FREE OF BENZENE FROM A HYDROCARBON MIXTURE COMPRISING A METHYLCYCLOPENTANE IN ADMIXTURE WITH OPEN CHAIN HEXANES OF NORMAL AND BRANCHED STRUCTURE AND BENZENE, WHICH COMPRISES FRACTIONATING SAID HYDROCARBON MIXTURE IN A FEED FRACTIONATING ZONE TO SEPARATE THEREFROM A HIGHER BOILING FRACTION COMPRISING METHLCYLOPENTANE IN ADMIXTURE WITH BENZENE AND A LOWER BOILING FRACTION COMPRISING BRANCHED CHAIN HEXANES, SAID HIGHER BOILING FRACTION CONTAINING AN INSUFFICIENT AMOUNT OF OPEN CHAIN HEXANES TO ENABLE THE SUBSTANTIALLY COMPLETE SEPARATION BY PRACTICAL FRACTIONATING MEANS OF SUBSTANTIALLY BENZENE-FREE CYCLOHEXANE FROM THE ISOMERIZATE OBTAINED BY SUBJECTING SAID HIGHER BOILING FRACTION TO METHYLCYCLOPENTANE ISOMERIZING CONDITIONS, CONTACTING SAID HIGHER BOILING FRACTION WITH AN ISOMERIZATION CATALYST CATALYZING THE CYCLOPARAFFIN ISOMERIZING REACTION IN A CYCLOPARAFFIN CONVERSION ZONE AT CYCLOPARAFFIN ISOMERIZING CONDITIONS, THEREBY CONVERTING METHYLCYCLOPENTANE TO CYCLOHEXANE IN SAID CYCLOPARAFFIN CONVERSION ZONE, CONTACTING SAID BRANCHED CHAIN HEXANE FRACTION WITH AN ISOMERIZATION CATALYST CATALYZING THE PARAFFIN ISOMERIZING REACTION IN A PARAFFIN CONVERSION ZONE AT ISOHEXANE ISOMERIZING CONDITIONS, THEREBY CONVERTING BRANCHED CHAIN HEXANES TO NORMAL HEXANE IN SAID PARAFFIN CONVERSION ZONE, PASSING EFFLUENCE FROM THE CYCLOPARAFFIN CONVERSION ZONE INTO A PRODUCT FRACTIONATING ZONE, PASSING EFFLUENCE FROM AID PARAFFIN CONVERSION ZONE INTO SAID PRODUCT FRACTIONATING ZONE AT A RATE ASSURING THE PRESENCE OF A RATIO OF NORMAL HEXANE TO BENZENE IN EXCESS OF 10:1 BY VOLUME IN SAID PRODUCT FRACTIONATING ZONE, AND SEPARATING SUBSTANTIALLY BENZENE-FREE CYCLOHEXANE FROM A FRACTION COMPRISING METHYLCYCLOPENTANE, OPEN CHAIN HEXANES AND BENZENE IN SAID PRODUCT FRACTIONATING ZONE.