US2375573A - Production of aromatic hydrocarbons - Google Patents

Description

May 8, 1945. H. H, MEIER v Y PRODUCTION OF AROMATIC HYDROCARBONS Filed Aug. 1Q, 1942 'QQ/wzf/,f/

ATTORNEY u l Patented May 8, 1945 UNITED STATES PATENT ori-Ica PuonucrroN or mnocnnno AnoMA'rrc Herbert H. Meier, Baytown, Tex., assigner-to Standard Oil Development Company, a corporation of Delaware Application August 10, 1942, Serial No. 454,232 3 Claims. (CL 2650-668) This invention relates to the preparation of aromatic hydrocarbons. It is particularly concerned with a process wherein naphthene (cycloparailin) hydrocarbons boiling in the range' between about 280 and 350 F. are converted into aromatic lhydrocarbons by catalytic dehydrogenation, and the newly formed Varomatic hydrocarbons are segregated from the unreacted charge stock by fractional distillation.

It is known that naphtha distillates derived from some crudes, for example naphthenic or asphaltic base crudes, contain appreciable quantities of aromatic hydrocarbons such as benzene, toluene, xylene, etc. 'I'he aromatic hydrocarbons are often segregated from these distillates by 4 extracting them `with a selective solvent such as SO2, furfural or other similar solvents. The extracted aromatics, after some purication such as is eiected by neutralization and/or distillation, `are then used as commercialsolvents, as-liighoctane-number gasoline blending stocks, and as the source of charge stock'in the preparation of other products. For these uses it is usually not necessary or desirable to isolate a particular aro matic hydrocarbon. Instead, itis quite satisfactial quantities of added or recycled hydrogen or in gases rich in freevhydrogen under conditions such that there is either no overall net consumption of free hydrogen or there is an voverall net production of free hydrogen.

Aromatic types of commercial solvents and high-octane-number gasoline blending agents have been prepared from broad-cutnaphtha distillates containing appreciable amounts lof naphthenes by rst subjecting the distillate to dehydrogenation treatment for conversion of the naphthenes to aromatics, and then extractingA the dehydrogenated naphtha mixture with a selective solvent, such as vS()2,Afurfural,' etc., to recover the aromatics "as an extract. The aromatic extract is then neutralized and/or distilled to ob-I tain the desired solvent or gasoline 'blending stock. In operations wherein the catalytic reforming charge stock is a broad-cut of naphtha, it is practically impossible to separate any appreciable portion of the aromatic conversion products from the unconverted charge .stock 4by fractional distillation since the conversion products boil within the .boiling range of the charge stock. The solvent extraction feature of a process of this type is not entirely satisfactory since it is complicated and requires expensive equipment. Furthermore, its use results in a 1oss\ of an appreciable amount of valuable aromatics in the form of degradation products;

I have now discovered an improved method of converting naphthene hydrocarbons present in naphtha distillates boiling in a range between ing in the presence of hydrogen. The term "catl alytic reforming shall be understood to mean a process in which hydrocarbon oils comprising naphthene hydrocarbons and boiling within the gasoline range are subjected to heat treatment at a, temperature in excess of about 500 F. and in the presence of a-suitable catalyst to produce a dehydrogenated or otherwise chemically reconstructed product of substantially higher aromaticity than the starting material, with or without an accompanying change in molecular weight. The term catalytic reforming shallbe understood to include Ichiefly dehydrogenation of the about 280 F. and 350 F. to aromatic hydrocarbons and then recovering the aromatic reaction products from the hydrocarbon reaction mixture. In accordance with my method a naphtha distillate boiling in the range between about 280 F. and 350 F. and containing appreciable-amounts of naphthene hydrocarbons is prefractionated under, emoient dlsnna'tion conditions to separate naphtha fractions having boiling ranges not greater than about 40`Fahrenheit degrees, and

` preferably between 10 to about 25 Fahrenheit de- -naphthenes but some aromatization and isomerization may also occur. The term "catalytic reforming in the presence of hydrogen shall be understood to mean a process ofcatalytic reforming carried out in the presence of substangrecs. tions are then separately subjected to catalytic reforming treatment for conversion of the naphthene hydrocarbons to aromatic hydrocarbons. Y;

The process ofthis invention is primarily concerned- .with the conversion of substituted cyclohexanes to the corresponding substituted ben- However, it-I is recognized? that' the catalytic reforming "treatment also zene hydrocarbons.

isomerizes and dehydrogenates substituted cyclo- V' pentanes and cycloheptanes to aromatic hydro-.l

The narrow boiling range naphtha frac carbons, at least to some extent. The aromatic hydrocarbons derived from the substituted cyclopentanes and cycloheptanes have good solvent properties and high-octane-number characteristics; therefore, they are desirable products. Hence, in its broad scope, the process of this invention may be employed as a means of recovering from the hydrocarbon reaction mixture by fractional distillation aromatic hydrocarbon con- Versionl products boiling at least F. above or below the boiling points of the particular naphthene hydrocarbons from which they are derived through catalytic reforming treatment.

In order to make the process of this invention operative it is necessary to exercise care in selecting the temperature range through which the hydrocarbon charge undergoing catalytic reforming treatment boils. That is, the charge stock boiling range should be selected so that the desired aromatic conversion products boil a few degrees above or below the upper or lower limits, respectively, of the charge stock boiling range. This point can be better clarified by reference to the table which gives a comparison of the boiling n points of some of the substituted cyclohexanes boiling in the range between about 280 F. and

. 355 F. -with the corresponding substituted ben- Zel'ieS.

Table Difference in boili mi. tutti 2F" su s i u en- Bolling point, F. Zegeteltave Ito substituted side s s u e yc chain(s) hexane Substi- .substituted cycloh'xane bgfrlle Above Below 1.3,5-trimethyl 283.6 328.3 44.7 l-lllethyl, 3-ethyl 300. 5 322. 7 22. 2 I-methyl, 4ethyl 301. 9 322. 2 20. 3 l-methyl, 2ethy1 308. 6 328. 8 20. 3 [sopropyl 310. 1 08 Propyl .v r 311.0 l-methyl, 4-sopropyl. 335. l Tertiary-butyl 339. 1 ls b l 340. 2 341. 6 345. 2 347. 9 l-methyl, 4-propyl. 348. 3 l-methyl, 2propyl. 349. 0 Secondary-butyl. 354. 2

ysubstituted cyclopentanes, cyclohexanes It wm be noted from the table that i; the

catalytic reforming charge stock boils through a temperature range from about 280 F. to 315 F. and is comprised'of 1,3,5-trimethylcyclohexane, 1- methyl, 3-ethylcyclohexane, l-methyl, 4-ethylcyclohexane, 1methy1, 2-ethylcyclohexane, iso'- Dropylcyclohexane and propylcyclohexane which are converted to the corresponding substituted aromatic hydrocarbons, it is possible to separate, as a mixture of substantially pure aromatic hydrocarbons, all of the trimethyland methylethylbenzenes from the hydrocarbon reaction mixture by eicient fractional distillation, since these all boil several degrees Fahrenheit above the upper limit or the boiling rangeof the reforming charge stock. Where'a substantially pure aromatic conversion product isfnot required, such as for use as a commercial solvent or a high-octane-number blending agent, it is possible to recover all or the greater part of the propylbenzene along with the trimethylbenzene and the methylethylbenzenes without' seriously contaminating the desired product with unconverted charge stock. Itis not desirable ordinarily to recover isopropylbenzene from a catalytic vreformed charge stock boiling through the range from 280 F. to 315 F., unless it is present in an appreciable quantity, since the boiling point of the lsopropylbenzene falls well within the boiling range of the charge stock. If the catalytic reforming charge stock boils within the limit of from 300 F. to 340 F. and is comprised of methylethylcyclohexanes which the catalytic reforming treatment converts to the corresponding methylethylbenzenes, it is impossible .to separate the methylethylbenzenes from the reformed hydrocarbon mixture by fractional distillation without some contamination with unconverted charge stock 'since the `methylethylbenzenes b oil within the boiling range of the charge stock.

However, if the methylethylcylohexanes are present in appreciable quantities in the catalytic reforming charge stock, it is possible to separate from the reformed hydrocarbon mixture a fraction boiling between about 320 and 330 F. which is sufficiently high in aromatic content to be employed as a commercial solvent or as a gasoline blending agent. In general, the narrower Ythe boiling range of the reforming charge stock, the easier it is to recover the conversion products by fractional distillation and the higher will be their purity or their aromatic content.

The process of this invention may be more fully understood by reference to the attached drawing which is a diagrammatical flow plan 0f a preferred embodiment.

Referring to the drawing, numeral I designates a supply of hydrocarbon oil boiling in the naphtha boiling range and which contains an appreciable quantity of naphthenev hydrocarbons, such `as the and cycloheptanes. Pump 2 withdraws oil from tank I through line 3 and forces it through line 4 into distillation means 5. 4Distillation means 45 comprises any suitable number of highly efdcient fractionating units which are collectively capable of separating from the charge oil a fraction boiling fbelow about 280 F. and a fraction boiling above 350 F., both of which are discardedfrom the system, and which is also capable of separating the constituents boiling in the range between about 280 and 350 F. into any suitable number of distillate fractions having desirable boiling ranges not greater than about 40 F. For pur-'- passed't intermediate storge tank 8, a cut boiling between 315 and 340 F. which is passed to intermediate storage tank I0 by means of line 9, a cut boiling between 340 and 350 F. which is A removed to intermediate storage tank I2 through liner II, and a cut boiling above 350 F. which is discarded from the system by means of line' I3.

In successive order, the narrow-boiling-range oils in tanks 8, I0 and I2 may be separately withdrawn through lines I4, I 5 and I6, respectively. by means of pump I1 and forced through line I8.

Numeral I9 designates a supply of hydrogen or a gas rich in free hydrogen. Hydrogen or hydro-A wherein it is heated to a temperature suitable for maintaining the desired temperature in the reacsuldes of molydenum,

tion zone 24 in which it is presently to be introduced by means of line 23. If desired,the oil and the hydrogen may be heated separately instead of being heated in admixture with eacn other. The oil-hydrogen mixture is heated in means 22 to a temperature which is from 100 to 150 F. above the average temperature maintained in reaction zone 24.

Reaction zone 24 is provided lwith a catalyst material24a which is capable of catalytically reforming the oil in th'e presence of hydrogen. Suitable materials for. this purpose comprise aluminum oxide in any of its various forms such as bauxite, acid treated bauxite, aluminum hydrate, alumina gel, activated alumina, partially or completely peptized alumina or alumina gels, silicaalumina gels, and hydroiiuoric acid treated alumina, together with from 1 to 50% by weight of an oxide or sulfide of a metal of the.IV,V, VI, or

VIII groups of the periodic system. Especially suitable catalysts are. activated alumina mixed or impregnated with` from 1 to 20% of oxides or chromium, tungsten, vanadium, cobalt or nickel. i

Reaction zone 24 is maintained at a temperature between 850 and 1,000 F, and under a pressure between slightly above atmospheric pressure and about 600 lbs. per sq. in., preferably between and`,400 lbs. per sq. inch. The oil is passed through the reaction zone at a relatively low rate, usually between 0.1 and 3.0, preferably between 0.5 and 1.5 vol. 'of liquid oil per vol. of catalyst per hour. Thequantity of gas passed through the reaction zone along with the 4oil should be between 1000 and-6000 cua ft. per barrel of oil, anci'thsl gas should containv between 30 and 90 mol per centof free hydrogen.

The vproducts of reaction leave reaction zonel 24 throughline 25, and flow through a cooling means 26 before being discharged into separator means 21 wherein gaseous and liquid products may be separated. The gaseous products,l which consists ,principally of hydrogen and relatively small amounts of low molecular weight hydrocarbons such as methane, ethane, and propane, are removed from separating means 21 through line 23 and may beA returned by means of compressor 2s directly to hydrogen'supply tank I9. As an alternative procedure, the gaseous products may be recycled directly to the system by means of lines' 28 and 30. Where desirable,la

'substantial portion of the hydrocarbon2 con-I stituents may be removed from the gaseous prod# ucts before returning the latter to the system. In this latter case,l the gaseous products may be passed through line 3| which is provided with a and converted material will be removed as over` head by line 36 and as bottoms by line 31;

Ihe following example illustrates the application of the process of this invention to the preparation of aromatic hydrocarbons for use as solvents or high-,octane-number blending agents.

Example A naphtha fraction boiling from 280 F. to 350 F. and containing appreciable quantities of naphthene hydrocarbons is distilled under emcient fractionating conditions to obtain a out boiling from about 280 F. to 315 F., a Vcut -boiling from about 315 F. to 340'F., and a cut boiling from about 340 F. to 350 F. These lnarrow. boiling naphtha cuts are separately subjected to catalytic reforming treatment in the presence of hydrogen under the following conditions:

Average catalyst temperature -F 913 Pressure pounds per square inclir..l 200 Oil feed rate, volumes of liquid oil per volume of catalyst per hour Recycle gas rate, cubic feet per barrel of oiL. 2,600 Per cent H2 in recyc1e gas 4 Length of reaction cycle -bours- 6 The liquid pmdccts secured from the catalytic treatment of these various narrow boiling fractions are separately distilled under eflicient fractionating conditions to obtain aromatic fractions boiling above the boiling range of their respective reforming charge stocks. The aromatic content of the conversion products separated in this manner is in the order of 85 per cent and higher.

. Having fully described and illustrated 'the practice of the present invention, what Il desire to claim is:

` I claim: i

1. A process of treating a hydrocarbon distillate boiling in the range of 280 to 350 F. and containing appreciableiquantitics of naphthenes comprising the steps" ofv distilling said fraction to obtain a first out boiling from 280 to 315 F..

va secondcut boiling from 315 to 340 F. and a third cut boiling from 340 to 350 F., separately scrubber 32 for removal of the undesired hydrocarbon constituents. Scrubber 32 may be any means suitable for the purpose of separating hydrogen from mixtures of the same with hydrocarbons. Perhaps the most convenient method is .to scrub the gaseous products with a light hydrocarbon oil under' conditions such that hydrocarbon constituents but substantially no hydrogen will be Vabsorbed from the gaseous products.4 Gas may be removed from the system through `vent' line The liquidv'products separating in separating means 21 are removed through line 34 and introduced into fractionating means '35 wherein conversion products are separated from the charge stock. In most instances the converted products boil above the boiling range of the charge stock and accordingly are removed by line 31 whilethe unchanged charge stock is reheating and reacti'ig each cut in a reaction zone in the presence of hydrogen and a dehydrogenation catalyst and .under temperature and pres-V sure conditions suitable for converting naphthenes to aromatics and passing the products of said reaction zone to a distillation zone to Aobtain fractions containing a major portion of aromatics and fractions containing a major portion of unconverted hydrocarbons.

2. A method of processing hydrocarbons com` prising the steps of subjecting a naphtha fraction containing appreciable quantities of napthene hydrocarbons and boiling from 280 to 350 F. to distillation to separate the naphtha into a first cut boiling from 280 to 315 F., a second cut boiling from 315 to 340 F. and a third cut boiling from 340 to 350 F., separately mixing'each of said cuts with hydrogen to obtain mixtures,

separately passing each of said mixtures through Catalyst Mixture of 4aluminum .A

' and molydenum oxides a. heater to raise the temperature thereof above 850 F. and to a reaction zone where they are vmaintained in the presence of a dehydrogenation catalyst and under conditions suitable for converting substantial amounts of naphthene hydrocarbons to aromatic hydrocarbons, removing the products of reaction from the reaction zone,

cooling them,separating gaseous products from liquid products and fractionating the liquid products by distillation to obtain, fractions comprising major amounts of aromatic hydrocarbons and major amounts of unconverted hydrocarbons.

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