US2420883A

US2420883A - Process for the production of toluene

Info

Publication number: US2420883A
Application number: US464402A
Authority: US
Inventors: Ava J Johnson; Jr Mott Souders; John E Marsland
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1942-11-03
Filing date: 1942-11-03
Publication date: 1947-05-20
Anticipated expiration: 1964-05-20

Description

y 1947. A. J. JOHNSON ETAL PROCESS FOR THE PRODUCTION OF TOLUENE Flled Nov. 3, 1942 mm n.m muM JUL l 5 a m e V00 m AMJ m a M m .w m v May 1947. A. J. JOHNSON ETAL PROCESS FOR THE PRODUCTION OF TOLUENE Filed Nov. 3, 1942 3 Sheets-Sheet 2 Mcfl Souder5,Jn John E. Marsland. 59 Their Aflorneg'. g% &

Inventors. Ava J. Johnson- M i 1947- A. JOHNSON ETAL ,4 8

PROCESS FOR THE PRODUCTION OF TOLUENE Filed Nov. 3, 1942 5 SheetsPSheet 3 Fig. 18

Inventor's: Ava J. Johnson.

5g Their Aflorneg: g

Patented May 20, 1947 PROCESS FOR THE PRODUCTION TOLUENE Ava J. Johnson, Oakland, Mott Souders, J r., Piedmont, and John E. Marsland, Sausalito, Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application November 3, 1942, Serial hlo. 464,402

9 Claims. (01. 260-668) This invention relates to a process for the production of commercial grades of toluene suitable for nitration, etc, in a more economical manner from naphthenic petroleum dlstillates.

Toluene is one of the primary compounds upon which aromatic chemistry is based.- It is employed in large quantities as a starting material for the synthesis of a great variety of useful prod ucts such as dyestuffs, explosives, drugs, flavors, perfumes, photographic developers, plastics, intermediate chemicals, and many others. The primary source of toluene has been the distillation of coal, Consequently, the supply of toluene has been primarily dependent upon the condition of the steel and coal-tar industries-and has been thus limited. Aside from the numerous uses where its application is more or less obligatory, toluene has a great many potential uses which have been curtailed by its limited supply and rela tively high price. a consequence, considerable attention has been given to the possibility of producing toluene from other sources.

Certain processes have been perfected whereby toluene may be produced from petroleum fractions. One of these is to recover toluene from aromatic petroleum fractions, particularly cracked distillates. Certain petroleums and most highly cracked distillates contain appreciable quantities of aromatic hydrocarbons which may be recovered in the form of aromatic fractions and even relatively pure aromatic hydrocarbons by a suit-- able combination of steps involving fractionation, extraction, etc. The recovery of toluene from such distillates is, however, quite expensive. Only a small proportion of these distillates toluene and, consequently, large quantities of material must be processed in order to recover relativel small yields.

More recently, methods for the production of toluene from naphthenic distillates by catalytic dehydrogenation processes have been perfected. Thus, in one such process'a naphthenic petroleum is fractionated to separate a fraction boiling between about 205 F. and 230 F. and'the fraction is treated under dehydrogenation conditions with a dehydrogenation catalyst. tains. besides the naturally existing tcluol, toluol produced from the methyl cyclohexane which is present in appreciable quantities in such distillates. The tcluol is recovered from the dehydrogenated product by a combination of extraction and fractionation steps. In this process the yields of toluene include considerable quantities of tol uene produced from the methyl cyclohexanc by dehydrogenation.

In an improved modification of this process a fraction boiling between about 190" F, and 230 F. is separated and subjected to a catalytic isomerization treatment prior to the dehydrogenation treatment. This improved modification allows ess a fraction boiling between about 190 F. and

230 F. is separated and then divided into two fractions boiling above and below about 205 F.

' The lower boiling fraction is subjected to a selective isomerization treatment and then the two fractions are recombined and subjected to a catalytic dehydrogenation treatment.

The object of the present invention is to provide a further improved process of the described type whereby commercial grades of toluene suit- 'able for nitration may be produced from naph- This fraction contil manner.

tion isto providea ,process'wherein' substantially mid western crude petroleums.

" Hills crude.

thenic petroleum distillates in a more economical A more particular object of the invenall of the more easily convertible hydrocarbons are converted to toluene while at the same time avoiding excessive processing costs. Another more particular object of the invention is to provide a-process whereby excellent yields of toluene may be produced with a minimum consumption of catalyst, especially in the catalytic isomerization step. Still another object is to provide a process wherein the dehydrogenation may b effected with a high ratio of on'stream time to regeneration time per process cycle and wherein the catalyst may be most effectively maintained at a suitable activity for extended periods of time before it is necessary to replace it. A still further object is to provide a process wherein by recycling certain of the products the efficiency and economy of the total operation are considerably increased. Various advantages of the process, the realization of which constitute further objects of the invention, will be seen in the following more detailed description of the process and certain of its rhodifications.

The process of the invention is designed and applicable for the production of toluol from naph thenic petroleum fractions. By naphthenic petroleum fractions is meant'petroleum fractions of natural or synthetic origin containing an appreciable quantity of naphthenic hydrocarbons and parafiinic hydrocarbons having seven carbon atoms. Suitable naphthenic petroleum fractions are obtained from a large number of western and A, few typical sources are, for example, Los Angeles Basin crude, Huntington Beach crude, Dominguez Hill crude, Ventura crude, Ten Section crude and Kettlem'an The naphthenic petroleum fractions are usually in the nature of straight run gasoline fractions and are substantially free gf detrimental impurities. The process, however, provides saturated materials of unsaturated 3 naphthenic fractions as cracked stocks, reformed stocks and the like,

In one specific embodiment the process of the present invention comprises fractionating a substantially saturated naphthenic distillate into a lower boiling fraction II boiling below about 180 F.-190 F. and a higher boiling fraction III boiling above about 180 F.-190 F.; subjecting said higher boiling fraction III to a fractional distillation to separate a lower boiling fraction IV boiling below about 200 F.-212 F. and a higher boiling fraction V boiling above about 200 F.212 F.; subjecting said lower boiling fraction IV to a catalytic isomerization treatment to produce an isomerizate VI; subjecting the isomerizate VI to a fractional distillation to separate a lower boiling fraction VII boiling below about 200 F.212 F. and a higher boiling fraction VIII boiling above about 200 F.-2l2 F.; recycling a portion of said lower boiling fraction VII to the isomerization treatment with the lower boiling fraction IV; subjecting said'higher boiling fraction VIII in admixture with the abovesaid higher boiling fraction V to a fractional distillation to separate a lower boiling fraction IX boiling below about 218 F.-235 F. and a higher boiling fraction X boiling 'aboveabout 218 ,F.-235 F.; subjecting said lower boiling fraction IX per se or in admixture with a similar fraction of an unsaturatednaphthenic distillate to a catalytic dehydrogenation treatment to produce a reformate XI; subjecting said reformate XI in admixture with recycle bottoms XII to a fractional distillation to separate a lower boiling fraction XIII boiling below about 233 F.-266 F. and a higher boiling fraction XIV boiling above about 230 F.-266 F.; separating said lower boiling fraction XIII into an aromatic fraction and a non-aromatic fraction XVI by means of a selective solvent; recovering an aromatic fraction XVII from said selective solvent; subjecting said aromatic fraction XVII to a sulfuric acid refining treatment and then fractionally distilling the same to recover a lower boiling fraction consisting of substantially pure toluene and a higher boiling fraction consisting of said recycle bottoms XII.

The invention also comprises modifications and more specific embodiments of the above-outlined process which are advantageously but not necessarily employed. Thus, in one such modification the fractionation of said higher boiling fraction II is effected in the presence of recycled isomerizate VI; in another modification the recycle of said lower boiling fraction VII is reduced or eliminated and said lower boiling fraction VII is preferably subjected to further processing. These and various other preferred embodiments of the invention ar described in connection with the following more detailed description of'the process.

The outline of the process given in the preceding paragraph is amplified in the following description wherein various important features of the process are described in connection with a typical operation comprised within the scope of the invention. To assist in the description, refershoe is had to the attached drawing forming a iii part of the specification, wherein there is shown by means of diagrammatic figures one assembly of apparatus in which the process of the invention may be advantageously carried out.

In order to illustrate the various details of the process in a clear 7nd comprehensive manner without unnecessary crowding, the assembly of apparatus is divided into three sections designated Figures I, IA and IB, respectively. Referring to the drawing, Figure I, a naphthenic distillate, such as a straight run naphthenic gasoline, enters the system via line I and is pumped via pump 2 to a fractionating column 3. The fractionating column 3 is provided with the usual condenser 4, surge tank 5, recycle reflux pump 0, recycle reflux line 1, and reboiler 8. A fractionating column with these accessories constitutes a fractionating apparatus and will be simply so designated hereinafter. The conditions in the fractionating apparatus are so adjusted as to remove as an overhead product substantially all of the original distillate boiling below F.-.

F. This lower boiling overhead fraction I is withdrawn from the system via line 9. The bottom product from the fractionating apparatus is passed via pump II and line l2 to a second fractionating pparatus 13, wherein it is fractionated in admixture with recycle distillate entering via line M. The conditions in fractionating apparatus l3 are so adjusted as to remove as an overhead product substantially all of the material boiling below 200 F.-2l2 F. The bottom product from fractionating apparatus 13 is passed via line 15 and pump 16 (Figure IA) to a fractionating apparatus ll, wherein it is fractionated in conjunction with the bottom product from fractionating apparatus l8, as will be more fully described below. Returning to Figure I, the overheadproductfrom fractionating apparatus I3 passes via line I!) to one or more isomerization reactors 2| and/or 22, wherein it is contacted underisomerization conditions with one of the known isomerization catalysts. The isomerization is effected in the vapor or liquid phase, preferably in the liquid phase in the presence of a promoter and, if desired, hydrogen. Preferred catalysts are those comprising aluminum chloride and/or aluminum bromide. Of these, aluminum chloride is preferred since it is the least expensive, easier to employ and has much less tendency than aluminum bromide to cause degradation reactions. Other acid-acting catalysts of the Friedel-Crafts type such as the chlorides of Zr. Zn, Sn, Be, Nb, Ta, Sb, B and Cd may also be employed, if desired, in conjunction with the aluminum chloride. A preferred isomerization catalyst, which has been found to be particularly suitable for the present process, is a slurry of aluminum chloride in a liquid aluminum chloride complex. Aluminum chloride (aluminum bromide may also be used) is charged to a suitable reactor 23 and reacted therein with a suitable complex-forming material added via line 24 and pump 25, preferably in the presence of hydrogen chloride added via line 26. Any of a number of known complexes may be formed. Very suitable materials with which to form the complex are, for example, smokeless kerosene, kerosene extract, cyclohexene, and aromatic hydrocarbons. The aluminum chloride is preferably added in excess, or additional aluminum chloride may be added after the desired complex is formed. The excess may, however, be very small. Th complex catalayst is withdrawn from the reactor 23, forced via pump 21 through

lines

28, 29, 3|, 32. 33, 34 and 35 to reactors 2| and 22 as required. Reactors 2| and 22 are preferably equipped with heating and mixing means (not shown) but may be of conventional design. Th mixture of hydrocarbons and fluid catalyst passes from the reactors to suitable separators 30 and 36, wherein the mixture is allowed to stratify. The heavier catalyst layer is recycled via

lines

32, 33, 34 and known promoters, such as an alkyl halide, boron I fluoride or more particularly hydrogen chloride. The promoter, preferably hydrogen chloride, is added to thesystem via lines 39, 4| and 42. The upper layer from separators 30 and 36, consisting of hydrocarbons and promotcr, passes via line 43 to a separator 44. Hydrogen chloride is withdrawn from separator 44via lines 45 and 46 and compressed via compressor 41 into a surgetank 48, wh'erein small amounts of liquefied materials are separated and intermittently withdrawn via line 49 and mixed with stock in line 5|. In order to avoid excessive dilution of the hydrogen chloride with use, a small amount of the recycled gas may be withdrawn intermittently or continuously Via line 52. The bulk of the hydrogen chloride is, however, advantageously recycled back to the reactors via lines 52, 4] and 42.

The conditions in the isomerization reactors 2| and 22 are adjusted to afford a relatively rapid clean-cut isomerization with little or no formation of fixed gases. The preferred conditions will depend upon the degree of mixing,the catalyst activity and the concentration of hydrogenchloride employed. Suitable preferred conditions, using an aluminum chloride-kerosene extract complex catalyst, are, for example, as follows:

Contact time "min" 5 to 45 Temperature F 50 to 212 Pressure atm 1 to 20 Concentration of HCl (based on the,

hydrocarbon) -per cent by weight 0.1 to 5 Instead of employing the isomerization reactors in parallel as shown, they may, if desired, be connected in series in the conventional manner with countercurrent how of the catalyst. The product from the isomerization reactor or reactors, after separation of the bulk of the hydrogen chloride in separator 44 is pumped via pump 53, line 54- of the product may also advantageously be passed 1 via lines l4 and I2 back to fractionating apparatus I3. In this way the relative efficiencies of the fractionations in fractionating apparatus l3 and I8 may be controlled. The conditions in fractionating apparatus I8 (Figure II) are so adjusted as to remove as an overhead product substantially all of the material boiling below 200 F.212 F. This overhead fraction may be handled in either one of two ways. According to one embodiment, this fraction is advantageously separated into two portions, one of which is passed via line 5| to the overhead product from fractionating column I'3. .(Figure I) and the other of which is withdrawnfrom the system via lines 5| and 61. The relative amounts of the two portions will depend upon the particular circumstances. In general, however, the portion withdrawn will range between abdut one-fourth and two-thirds of the total fraction.

According to the otherembodiment, the total drawn from the system via line 8|. I tom fractionfrom fractionating apparatus 13 is overhead product from fractionating apparatus l8 may be passed via lines 5|, G3 and 69 (Figure I) toan isomerization reactor '(I wherein it is treated as described above. Catalyst enters re- 5 actor H via line-28 and hydrogen chloride enters the reactor via line I2. The mixture of catalyst and hydrocarbon is separated and then the hydrocarbon and hydrogen chloride are separated as described above. The hydrogen chloride passes 10 via line 13 toseparator 44. The hydrocarbon phase is passed via line 15 to a caustic scrubbing system 16 (Figure IA) as previously described. The caustic washed product is passed via line 11 and surge tank 18 to a fractionating apparatus 13. 15 The conditions in fractionating apparatus" are adjusted so as to remove as an overhead product substantially all of the material boiling below 205 F.-210 F. This overhead fraction is with- The botpassed via pump 82 and line 83;to line fllwhere'it is mixed withthe bottom product from fractionating apparatus l8. The bottom fra'ctionfrom fractionating apparatus I8, alone orin admixture with the bottom fraction from fractionating apparatus 19, 'is passed via line 84 and heat exchanger 85 to fractionating apparatus l1, wherein it is fractionated in conjunction with the bottom product from .30 fractionating apparatus l3, entering via line l5 and pump I6, as previously described, and also advantageously in conjunction with extract and the bottoms from fractionating apparatus I41 entering via line 86, as will be described below. The

conditions in fractionating apparatus ll are adjusted so as to remove as an overhead product substantially all material boiling up to 218 F.- 235 F. The bottom product fromv fractionating apparatus [1 is withdrawn from the system via pump 81 and line 88. A portion of this bottom product is preferably withdrawn via line 89 to serve as a scrubbing medium, as will be described below.

l The overhead product /from fractionating ap- 45 paratus I1 is advantageously mixed with an olefinic" hydrocarbon fraction such', for instance, as

an unsaturated cracked or reformed gasoline fraction. The addition of the olefinic fraction considerably simplifies the problem of supplying the endothermic heat of the subsequent dehypresent in the added unsaturated fraction is converted into toluene. It is therefore advantageous to employ a naphthenic olefin fraction from a cracked, reformed, polyformed or similar product including the methyl cyclohexane usually present in appreciable concentrations in such distillates. Also, such unsaturated fractions usually contain appreciable concentrations of toluene and this may be most advantageously recovered by the present method since the interfering unsaturated hydrocarbons are substantially saturated in the subsequent treatment prior to the recovery step. It is therefore advantageous to employ unsaturated fractions embracing the boiling I range of about 225 F.-235 F. Advantageously mployed unsaturated fractions are, for example,

fractions of aromaticand naphthene-containing unsaturated fractions boiling largely below about 23 F. and above about 205 F. The unsaturated fra tion may be added in any amount but is pref erably not added in such quantities that there is hydrogen, entering via line 95, and the mixture is subjected to a suitable dehydrogenation treatment. The dehydrogenation treatment may be effected with any of the many catalysts known to be suitable for the dehydrogenation of naphthenic hydrocarbons and may be effected in various apparatus, such as conventionally used in catalytic reforming, catalytic hydroforming, and catalytic dehydrogenation. Particularly suitable catalysts comprise the compounds, preferably the oxides, of the metals selected from the left-hand members of groups IV, V and VI of the periodic system of the elements, if desired, in conjunction with promoting-amounts of compounds, preferably the oxides, of metals selected from the group I and/or group VIII of said system. Very suitable catalysts comprise, for example, the oxides of Cr, Mo, Ti and/or V supported upon a major amount of an adsorptive carrier such as an adsorptive alumina. The dehydrogenation conditions employed will depend somewhat upon the particular catalyst. One suitable assembly of apparatus applicable with most dehydrogenation catalysts is illustrated in the attached drawing in Figure IA. The dehydrogenation system comprises two banks of catalytic converters manifolded in such a way that, while one bank is processing, the other bank may be regenerated. The converters in each bank may be connected in parallel or in series as shown. If it is assumed that the upper bank of

converters

96, 91 and 98 is processing while the lower bank of converters 99, IOI and I02is undergoing regeneration, the mixture of hydrocarbon feed and hydrogen, leaving heater 93 via line 94, is passed via manifold line I03 to converter 96. After passing through converter 9-6, the partially converted mixture is passed through heat exchanger I04, converter 91, heat exchanger I05, converter 99, manifold line I06, and heat exchanger I 01 to a separator I08. At the same time inert gas is circulated by means of compressor I09 through lines III, H2, and H3 into manifold line I03 and thence through reactor 99, heat exchanger II4, reactor IOI, heat exchanger II5, reactor I02, and line H6. The inert gas recirculation system illustrated is that described in U. S. Patent 2,262,427. Air is pumped via pump II! to lines H8 and H9 from the latter of which it is fed in controlled quantities into the recirculated inert gas stream.

The gaseous products in separator I08 are withdrawn via line I2I and divided into two portions. One portion is passed via line I22 to a cooler -I23 and low pressure separator I24 (Figure IB) and is treated as hereinafter more fully described. The other portion is compressed by compressor I25 (Figure IA) into a tower I26 and is then recycled back to the heater 93 via lin I2'I.

It is found, however, that in the present process utilizing the particular fractionation, recycle and isomerization steps described above, it is most advantageous to employ a selective catalyst of the metal sulfide type such, in particular, as a mixture of tungsten sulfide and a sulfide of a 8 metal of the iron group. A specific cataylst of this preferred type is tungsten sulfide-nickel sulfide, having a mole ratio of nickel to tungsten of from about 1:1 to 2:1. The dehydrogenation conditions employed will vary somewhat depending upon the particular catalyst employed. When employing the preferred tungsten sulfidenickel sulfide cataylst (hereinafter referred to as W-Ni sulfide catalyst) suitable preferred conditions are as follows:

Temperature F 750 to 1000 Pressure atm 5 to 75 Mole ratio of hydrogen to hydrocarbon feed- 4: 12

Liquid hourly space velocity 0.5 to 4.0

made and sulfided in the reactors by simply passing unburnt hydrogen sulfide through the system. The regeneration of the catalyst with S02 is described in more detail in copending application Serial No. 434,893. The hydrogen sulfide used for preparing the S02 may be obtained in part from the recycled hydrogen gas. Thus, the tower I26 may advantageously be the scrubbing tower of a Shell Phosphate Unit. Phosphate solution enters the tower via lines I35 and I36, and

is withdrawn via line I31 to a stripper I33 in the known manner. Hydrogen sulfide is recovered via line I3I and passed to the S02 generator I32 or drawn to storage via line I28.

The liquid product from separator I08 (Figure IA) is passed via line I39 to a low pressure separator I4I (Figure IB) wherein further quantities of gases are separated. These separated vapors are further cooled in cooler I42 and are finally passed to a third separator I43, wherein small quantities of condensible liquids are collected. The liquid product from the low pressure separator I M is passed via pump I44 and lines I45 and I46 to fractionating apparatus I41, wherein they are fractionated in conjunction with the bottom product from fractionating apparatus I48, described below. The conditions in fractionating apparatus I41 are adjusted so as to remove as an overhead product all or most of the toluene while retaining substantially all of the higher boiling products in the bottom fraction withdrawn via line I49. The economy of the fractionation steps may usually be considerably improved if this bottom product is recycled back to fractionating apparatus IT. For this purpose line I49 is shown connecting with line 86 which leads to fractionating apparatus IT.

The overhead product from fractionating apparatus I4! is mixed with the liquid products from the separators I24 and I43 and the mixture subjected to a suitable treatment to recover toluene. A preferred method is by extractive distillation in the known manner. Thus, the mixture is passed via line I5I to an extractive distillation column I52, wherein it is distilled in conjunction with a higher boiling polar solvent, entering via line I53. Non-aromatic impurities are removed overhead via line I54. The extract phase is removed via line I55 and passed to a stripping column I 56, wherein-the toluene is separated from the solvent. The solvent is recycled back to the extractive distillation column I52 via line I53. The toluene is removed as an overhead product from column I56 via line I51. This material consisting essentially of toluene but containing small amounts of impurities is treated with sulfuric acid in tank I58 (and, if desired, caustic-washed in means not shown). The treated product is withdrawn to a settling tank 159 and is then passed via line I 6| to a final fractionating apparatus I48. In fractionating apparatus I48 the conditions are adjusted to recover as an overhead product substantially pure toluene, containing substantially no higher boiling product. This product is removed from the system via line I62. The bottom product from fractionating apparatus I48 contains toluene contaminated with higher boiling products. This fraction is advantageously passed via line I back to fractionating column The above-described combination of steps effected in apparatus I41, I52, I56 and I48 constitutes a particularly advantageous preferred embodiment of the invention. By employing the described recycle the maximum purity of the toluene may be maintained with a minimum of fractionation costs. Another advantageous preferredembo'diment of the process affording maximum yields with low recovery costs lies in the described method of separating the normally. liquid products from the gases in the product from the dehydrogenation reactors. According to a preferred embodiment, the gaseous fraction separated in separator I24 (Figure IB) is passed to a column I63, wherein it is scrubbed with a portion of the bottom product from fractionating apparatus l'I (Figure IA). The scrubbing liquid is then passed via line 86 to fractionating apparatus I'I, wherein it'is fractionated in conjunction with the bottom product from fractionating pparatus l3. Another important feature of the described process is the described recycle of a portion of the overhead product from fractionating apparatus I8 to the overhead product from fractionating apparatus l3 in combination with the passage of the bottom product from the fractionating apparatus I3 to the fractionating apparatus II. Another important feature of the process is the addition of an, olefinic fraction, preferably containing methyl cyclohexane and/or toluene, to the overhead product from fractionating apparatus II. By the described combination of recycles in conjunction with the described preferred dehydrogenation treatment substantially all of the more easily converted components of the feed are converted to toluene with a, minimum cost of separation.

The process of the invention as described above, it will be seen, comprises a plurality of unit operations, which in themselves are known, com bined with specific fractionations and novel recycles in such a manner as to afford a novel process which, when applied to the particular type of petroleum distillates described, afiord a more advantageous and economical production of substantially pure toluene. unit operations such as fractionation, isomerization, dehydrogenation, catalyst regeneration, extraction of toluenefrom aromatic distillates, and the like are concerned, these may be operated in any of the known suitable manners with the various known expedients and apparatus and are not limited to the specific embodiments illustrated and described. In a few cases, however, certain embodiments of these known unit processes have been found to be most advantageous when employed in the present combination of steps, and these are more particularly pointed out above and in certain of the more specific claimed embodiments.

What is claimed is:

1. A process for the production of commercial grades of toluene suitable for nitration from naphthenic petroleum distillates which comprises the combination of steps of fractionating a substantiallysaturated naphthenic petroleum distillate I into a lower boiling fraction II boiling below about 180 F.-190 F. and a higher boiling fraction III boiling above about 180 F.-190 F., subjectingsaid higher boiling fraction to a fractional distillation to separate a lower boiling fraction IV boiling below about 200 1 2-212 F. and a higher boiling fraction V boiling above about200 F.-212 F., subjecting said lower boiling fraction IV to a catalytic isomerization treatment under isomerization conditions with an aluminum chloride isomerization catalyst to produce an isomerizate VI, subjecting isomerizate VI to a fractional distillation to separate a lower boiling fraction VII boiling below about 200 F' -212 F. and a higher boiling fractio VIII boiling above about 200 F.-212 F., subjecting said higher boiling fraction VIII in admixture with the abovesaid higher boiling fraction V and in admixture with a recycled bottom fraction XIV specified below and in admixture with a. recycled fraction X specified below to a fractional distillation to 5 separate a lower boiling fraction IX boiling below matic fraction XI fixed gases including hydrogen,

scrubbing at least a portion of said fixed gases including hydrogen with a portion of said higher boiling fraction X and subjecting the higherboilv recycled hydrogen with a tungsten sulfide-nickel In so far as the known ing fraction X used in said scrubbing to the above-said fractionation in com'unction with said higher boiling fractions VIII, V and XIV, subjecting the aromatic fraction XI to a fractional ,distillation in admixture with recycled bottoms XII specified below toseparate a lower boiling fraction XIII boiling below about 233 F. -26 F. and said higher boiling recycled bottom fraction XIV boiling above about 230 F.-266 F., separating said lower boiling fraction XIII into an arcmatic fraction XV and a non-aromatic fraction XVI, subjecting said aromatic fraction XVv to a sulfuric acid refining treatment and then fractionally distilling the same to recover a lower boiling fraction XVII consisting of substantially pure toluene and a higher boiling fraction consisting of said recycle bottom fraction XII.

2. Process according to claim 1 in which the dehydrogenation is effected in the presence of sulfide catalyst under the following conditions:

Temperature F 750 to 1000 Pressure atmospheres 5 to '75 M01' ratio of hydrogen to hydrocarbon feed 4:1 to 12:1 Liquid hourly space velocity 0.5 to 4 3. In a process for the production of commer cial grades of toluene suitable for nitration from naphthenic petroleum distillates which comprises separating from a naphthenic petroleum distillate a fraction comprising alkyl pentamethylene hydrocarbons, isomerizing said alkyl pentamethylene hydrocarbons to methyl cyclohexane, dehydrogenating the methyl cyclohexane so produced to toluene and recovering substantially pure toluene from the dehydrogenated product, the improvement which comprises the combination of steps of separating from a naphthenic petroleum distillate a fraction III boiling above about 180 F.-l90 F., subjecting said fraction III to a fractional distillation to separate a lower boiling fraction IV boiling below about 200 F.-212 F. and a higher boiling fraction V boiling above about 200 F.-212 F., subjecting said lower boiling fraction IV to a catalytic isomerization treatment under isomerization conditions with an aluminum chloride isomerization catalyst to produce an isomerizate VI, subjecting the isomerizate VI to a fractional distillation to separate a lower boiling fraction VII boiling below about 200 F.- 212 F. and a higher boiling fraction VIII boiling above about 200 F.-212 F., and subjecting said higher boiling fraction VIII in conjunction with said higher boiling fraction V to a fractional distillation to separate a lower boiling fraction IX boiling below about 218 F.-235 F. and a higher boiling fraction X boiling above about 218 F.-235 F.

4. Process according to claim 3 in which the isomerization treatment is effected with a slurry of aluminum chloride in an aluminum chloride complex under the following conditions:

Hydrocarbon-catalyst phase ratio 1:1 to :1

5. In a process for the production of commercial grades of toluene suitable for nitration from naphthenic petroleum distillates which comprises separating from a naphthenic petroleum distillate a fraction comprising alkyl pentamethylene hydrocarbons, isomerizing said alkyl pentamethylene hydrocarbons to methyl cyclohexane, dehydrogenating the methy1 cyclohexane so produced to toluene and recovering substantially pure toluene from the dehydrogenated product, the improvement which comprises the combination of steps of separating from a naphthenic petroleum distillate a fraction III boiling above about 180 F.-190 F., subjecting said fraction III to a fractional distillation to separate a lower boiling fraction IV boiling below about 200 F.-212 F. and a higher boiling fraction V boilingabove about 200 F.-212 F., subjecting said lower boiling fraction IV in conjunction with a. portion of fraction VII specified below to a catalytic isomerization treatment under isomerization conditions with an aluminum chloride isomerization catalyst to produce an isomerizate VI, subjecting the isomerizate VI to a fractional distillation to separate a lower boiling fraction VII boiling below about 200 F.-212 F. and a higher boiling fraction VIII boiling above about 200 F.-212 R, recycling at least a portion of said lower boiling fraction VII to the isomerization treatment with the lower boiling fraction IV and subjecting said higher boiling fraction VIII in conjunction with said higher boiling fraction V to a fractional distillation to separate a lower boiling fraction IX boiling below about 218 F=235 F. and a higher boiling fraction X boiling above about 218 F.235 F.

6. In a process for the production of commercial grades of toluene suitable for nitration from naphthenic petroleum distillates which comprises separating from a naphthenic petroleum distillate a fraction comprising alkyl pentamethylene h drocarbons, isomerizing said alkyl pentam thylene hydrocarbons to methyl cyclohexane, dehydrogenating the methyl cyclohexane so produce to toluene and recovering substantially pure oluene from the dehydrogenated product, the improvement which comprises the combination of steps of separating from a naphthenic petroleum ,distillate a fraction III boiling above about 180 F.-l F., subjecting said fraction III in admixture with recycled isomerizate VI mentionedxbelow to a fractional distillation to separate a lower boiling fraction IV boiling below about 200 F.-2l2 F. and a higher boiling fraction V boiling above about 200 F.-212 F., subjecting said lower boiling fraction IV to a catalytic isomerization treatment under isomerization conditions with an aluminum chloride isomerization catalyst to produce an isomerizate VI, combining a portion of said isomerizate VI with said fraction III, subjecting the remainder of said isomerizate VI to a fractional distillation to separate a lower boiling fraction VII boiling below about 200 F.-2l2 F. and a higher boiling fraction VIII boiling above about 200 F.212 F., and subjecting said higher boiling fraction VIII in conjunction with said higher boiling fraction V to a fractional distillation to separate a lower boiling fraction IX boiling below about 218 F.235 F. and a higher boiling fraction X boiling above about 218 F.-,-235 F.

7. In a process for the production of commercial grades of toluene suitable for nitration from naphthenic petroleum distillates which comprise! separating from a naphthenic petroleum distillate a fraction comprising alkyl pentamethylene hydrocarbons, isomerizing said alkyl pentamethylene hydrocarbons to methyl cyclohexane, dehydrogenating the methyl cyclohexane so produced to toluene and recovering substantially pure toluene from the dehydrogenated product, the improvement which comprises the combination of steps of fractionating the isomerized feed prior to the dehydrogenation treatment into a lower boiling fraction IX boiling below about 218 F.-235 F. and a higher boiling fraction X boiling above about 218 F.-235 F., subjecting said lower boiling fraction IX to a catalytic dehydrogenation treatment to produce an aromatic fraction XI, separating from the aromatic fraction XI fixed gases including hydrogen, scrubbing at least a portion of said fixed gases including hydrogen with a portion of said higher boiling fraction X, and subjecting the higher boiling fraction X used in said scrubbing to the above-said fractionation to produce said fractions IX and X.

8. In a process for the production of commercial grades of toluene suitable for nitration from naphthenic petroleum distillates which comprises separating from a naphthenic petroleum distillate a fraction comprising alkyl pentamethylene hydrocarbons, isomerizing said alkyl pentamethylene hydrocarbons to methyl cyclohexane, dehydrogenating the methyl cyclohexane so produced to toluene and recovering substantially pure toluene from the dehydrogenated product, the improvement which comprises the combination of steps of fractionating the isomerized product prior to the dehydrogenation treatment in conjunction with a higher boiling fraction XIV specified below into a lower boiling fraction IX boiling below about 218 F.-235 F. and a higher boiling fraction X boiling above about 218 F.-235 F., subjecting said lower boilingfraction IX to a catalytic dehydrogenation treatment to produce an aromatic fraction XI, subjecting the aromatic fraction XI to a fractional distillation to separate a lower boiling fraction XIII boiling below about 233 F.-266 F. and said higher boiling fraction XIV boiling above about 230 F.266 F.

9. In a process for the production of commerclal grades of toluene suitable for nitration from naphthenic petroleum distillates which comprises separating from a naphthenic petroleum distillate a fraction comprising alky1 pentamethylene hydrocarbons, isomerizing said alkyl pentamethylene hydrocarbons to methyl -cyclohexane, dehydrogenating the methyl cyclohexane so produced to toluene and recovering substantially pure toluene from the dehydrogenation product, the improvement which comprises the combination of steps of subjecting the aromatic fraction XI produced by the dehydrogenation treatment to a fractional distillation in admixture with a recycled bottom fraction XII specified below to separate a lower boiling fraction cycled bottom fraction XII.

AVA J. JOHNSON. I MQTT SOUDERS, JR.

JOHN E. MARSLAND.

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

UNITED STATES PATENTS Number Name Date 2,249,337 Vlsser et al. July 15, 1941 2,291,254 Pines et al July 28, 1942 2,288,866 Hoog July 7, 1942 2,299,716 van Peski Oct. 20, 1942