US3227769A

US3227769A - Manufacture of naphthalene

Info

Publication number: US3227769A
Application number: US227853A
Authority: US
Inventors: Ch In Norman Chen-Hu; William J Baral
Original assignee: Union Oil Company of California
Current assignee: Union Oil Company of California
Priority date: 1962-10-02
Filing date: 1962-10-02
Publication date: 1966-01-04
Anticipated expiration: 1983-01-04

Description

Jan. 4, 1966 NORMAN CHEN-HU CH'IN ET AL MANUFACTURE OF NAPHTHALENE Filed 0st. 2, 1962 United States Patent O 3,227,769 MANUFACTURE F NAPHTHALENE Norman Chen-Hu Chin, Fullerton, and Wiiliarn J. Baral,

Long Beach, Calif., assignors to Union Oil Company of California, Los Angeles, Calif., a corporation of California Filed Oct. 2, 1962, Ser. No. 227,853 13 Claims. (Cl. 260672) This application is a continuation-in-part of our copending application Seri-al N-o. 831,323, filed August 3, 1959, now U.S. Patent No. 3,108,063.

This invention relates to new methods for the manufacture of high purity naphthalene from certain petroleum fractions, and particularly from the heavy ends of naphtha reformates. In broad aspect, the process comprises a combination of catalytic hydrodealkylation, fractionation of the dealkylate yto recover a crude naphthalene concentrate, followed by fractional crystallization of a mixture of the naphthalene concentrate and a like-boiling fraction of the fresh feed. It has been found that, even though the like-boiling fresh feed fraction is relatively lean in naphthalene, and contains substantial amounts of alkyl benzenes, indanes and tetralins, excellent recoveries of 99+% pure naphthalene are obtainable by fractional crystallization of the mixed fractions. Moreover, by operating in this manner (rather than sending all the fresh feed through the dealkylation reactor), important econom-ies are achieved in terms -of increased eihciency of conversion to naphthalene, increased reactor capacity, and reduced hydrogen consumption per pound of total naphthalene recovered. These advantages do not accrue however, unless the fresh feed contains at least about 3%, :and preferably at least about 6%, by weight of native naphthalene. Y

In a preferred modification of the process, the fresh feedstock to the process is blended with the hydrocarbon product from the dealkylation step, and the mixture is then subjected to fractional distillation to separate at least three different liquid fractions. The lightest fraction is the light gasoline which was synthesized in the lhydrodealkylation step. The next lightest fraction is a cut which contains most of the naphthalene, both that synthesized in the dealkylation and that which was present as such in the fresh feed. This fraction is then subjected to low-temperature fractional crystallization to recover the pure naphthalene, and the mother liquor therefrom, constituting heavy gasoline is either blended into gas-oline products, or may be recycled to the hydrodealkyla- `tion zone for conversion to 400 F. end-point gasoline. The third fraction recovered from the distillation step is a cut which consists mainly of alkyl naphthalenes, both those present in the fresh feed and those which were unconverted in the hydrodealkylation step. This mixed fraction constitutes the total feed to the hydrodealkylation step. If desired, a bottoms fraction boiling above 500 F., and which may contain catalyst-deactivating materials, may be recovered as bottoms and used for fuel oil, or any other desired purpose.

From the foregoing it will be apparent that the principal object of the invention lis provide economical means for converting heavy reformate fractions, and other refractory petroleum fractions, almost entirely to Vnaphthalene and high-octane gasoline. A more specific object is to provide a dealkylation process which is economical in hydrogen consumption, and gives maximum eciency and react-or capacity per pound of naphthalene produced. Still another object is to provide novel and economical means for isolating naphthalene from both the fresh feed and the hydrode-alkylation products with Patented Jan. 4, 1966 ICC a minimum of equip-ment and processing. Other objects will be apparent from the descrip-tion which follows.

In the reforming of naphthas, .it is known that naphthalene and methyl naphthalenes are often present in the product, even though ythe feedstock may have contained no naphthalenic components. It is believed that naphthalene and methyl naphthalenes are synthesized during the reforming step by reactions of dehydrogenation and/ or dehydrocycliza-tion. As a result of these and other reactions, the effluent from most reforming processes is found to comprise from about 1% to 10% of material boiling in excess of about 400 F., even in cases where the end-point of lthe feed was as low as 385 F.

It is likewise known that these heavy ends from reformate fractions may be subjected to hydrodealkylation to synthesize and recover naphthalene. The process of this invention however goes further and provides new and novel conditions for carrying out the dealkylation, .and provides a highly economical system for the recovery and recycle of the various products.

The dealkylation feedstocks useable herein are derived by the fractionation of substantially any naphtha reformate, or other hydrocarbon fractions chemically similar thereto, eg., cracking cycle oils. To isolate the desired fraction for dealkylation, the reformate is fractionated so as to recover the heavy ends having an initial boiling point between about 350 and 450 F., preferably between about 380" and 410 F. Fractions with an initial boiling point in the preferred range will contain substantially all of the naphthalene and methyl naphthalenes in the reformate. Fractions with an initial boiling point above 450 F. will contain little of the native naphthalene, land are not suitable for use herein. For successful use herein, the feedstock should contain at least about 3% by weight of naphthalene and lat least about 10%, and preferably at least about 20%, of alkyl naphthalenes. It may also contain about 10-60% by weight of alkyl benzenes and 1-20% of alkyl ind-anes.

Reformate feedstocks may be derived from substantially any conventional reforming process. In general, such processes involve the treatment of light or heavy naphthas at temperatures of 850 to 1,000 F., pressures of 0 to 800 p.s.i.g. and space velocities of 0.2 to 5. Hydrogen is also used in the reforming process, in lamounts ranging between yabout 500 and 10,000 s.c.f. per barrel of feed. Typical catalysts useable in .the reforming step include, for example, platinum impregnated on alumina, molybdenum oxide or chromium oxide supported on alumina -or other adsorbent carrier. Any of these reforming catalysts may also be further modified by the incorporation therein of minor lamounts of other metallic promoters, or of acidizing components such as silica, iluorine or chlorine. Catalysts of this nature are well known in the art and hence need not be described in detail.

In order to obtain a reforma-te containing substantial amounts of naphthalenic components, it is preferable to start with a reformer feedstock which is rich in naphthenes and/or aromatics, and which has an end-'boiling point above about 350 F. and preferably above about 375 F. Such naphthas may comprise straight-run gasolines, cracked gasolines, coker distillates and the like. Where cracked gasolines `are used, it is preferred to prehydrogenate the feed before it is subjected to reforming.

In the dealkylation step, the preferred catalyst is made up of activated 4alumina upon which is distended a minor amount of molybdenum oxide (c g., 5 to 20%) and a smaller amount of cobalt oxide (e.g., 1 to 5%). It is further preferred that the catalyst contain a stabilizing amount of silica, e.g., about 3 to 15% by weight, which is preferably coprecipitated with the alumina. A further preference is that the catalyst should contain a minor Iamount, e.g., 0.1 to 3% by weight, of an alkali metal or an alkaline earth metal. Such metals are preferably added in the form of a hydroxide, carbonate o-r other heat decomposa'ble compound, whereby upon final calcining the alkalizing component becomes converted to a heat stable material, e.g., lan oxide, hydroxide, silicate, aluminate or the like.

To prepare catalysts of the above described nature, a hydrogel of the carrier is rst prepared, as by precipitation or coprecipitation from aqueous solutions. The hydrogel is then dried and impregnated with soluble salts of molybdenum and cobalt, either simultaneously or alternately. The alkalizing component is preferably added by a final impregnation step, but may be added at any other desired stage of manufacture. For example, it may very conveniently be mixed with an ammonium molybdate solution and impregnated simultaneously with the molybdenum. Suitable alkaline compounds for irnpregnation include, for example, sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, potassium sulfide, calcium hydroxide, etc.

It is found that the alkaline component in the catalyst functions to reduce the undesirable cracking characteristics of the catalyst, thus reducing coke laydown and light gas make. The dealkylation process conditions are also designed to reduce detrimental cracking. For this purpose, steam is added to the feed mixture in proportions ranging between about 0.2 and 5 moles thereof per mole of feedstock. Operative temperatures for the dealkylation step range between about 800 and 1,300 F., and preferably between about 900 and 1,200 F. Hydrogen is used in ratios between about 1,000 and 10,000 s.c.f. per barrel of feed, and total pressures between about 300 and 2,000 p.s.i.g. may be used. Preferred pressures range between about 750 and 1,200 p.s.i.g. Liquid hourly space velocities between about 0.2 and 5 may be used, preferably between about 0.3 and 2. Those skilled in the art will understand that the foregoing operative ranges of conditions should be properly correlated with each other to obtain optimum results.

Other dealkylation catalysts which may be used herein include the oxides and sulides of any of the Group VIB and Group VIII metals supported on an adsorbent oxide carrier. Suitable active components include for example the oxides or sulfides of tungsten, molybdenum, chromium, iron, cobalt, nickel, or mixtures thereof. These active components are supported in minor amounts (e.g., 120% by weight) upon carriers such as alumina, silica, titania, zirconia, activated clays, or the like, or mixtures thereof. In these cases also, it is preferable to add small amounts of an alkalizing component, as in the case of the preferred cobalt molybdate catalysts.

Reference is now made to the attached drawing which illustrates semi-diagrammatically a preferred adaptation of the process, but is not to he construed as limiting in scope. Fresh feed is brought in via line 2, and is cornmingled with total condensed dealkylation product from line 4 Alternatively, all or a portion of the fresh feed may be diverted via line 6 to mingle with hot, total dealkylation efliuent in line 8, thus acting as a quench oil to arrest coking in the transfer lines and heat-exchange tubes in exchanger 10. In either event, the mixture of fresh feed and reactor effluent in line 12 is admitted to light gasoline fractionating column 14, from which light gasoline boiling up to about 385-400 F. is taken overhead via line 16. This includes gasoline synthesized in the dealkylation reactors, as well as any light gasoline which may remain in the fresh feed.

The bottoms from column 14 is transferred via line 18 to naphthalene fractionating column 20, from which a crude naphthalene fraction is taken overhead via line 22 and condensed, the condensate comprising feed to the crystallizing unit to be described hereinafter. It is a surprising feature of this invention that naphthalene in Weight-percent Naphthalene 25-75 Alkyl benzenes 12-50 Tetralins 5-20 Alkyl indanes 5-20 Paraflins 0-2 Alkyl naphthalenes 0-2 Naphthenes 0-2 It will be understood that most of the impurities in this fraction are derived from the fresh feed component which is fed to the fractionating columns, for in the dealkylation effluent, most of the alkyl benzenes, alkyl tetralins and alkyl indanes are dealkylated or otherwise cracked to lower boiling materials which do not then appear in the 400-450 F. boiling range materials. If the fresh feed were not admixed and distilled with the reactor effluent, but passed directly through the dealkylator, a crude naphthalene fraction of, e.g., 9098% purity could be recovered by distillation alone. However, this entails a substantial decrease in reactor capacity and a marked increase in hydrogen consumption, and in View of the unexpected efliciency of fractional crystallization for recovering pure naphthalene from the crude mixed naphthalene fractions treated herein, the advantages of the process are found to outweigh the disadvantages in cases where the fresh feed contains suflicient native naphthalene as prescribed herein.

The bottoms from column 20, having an initial boiling point in the 420-450 F. range, is transferred via line 24 to methyl-naphthalene fractionating column 26, from which a methyl naphthalene fraction boiling between about 425 and 600 F. is taken overhead via line 28. This fraction comprises methyl naphthalenes derived from the fresh feed and unconverted methyl naphthalenes from the reactor effluent, and contains less than about 2% of naphthalene. A small bottoms fraction boiling above about 550 F. is normally withdrawn via line 30 and withdrawn from the process for use as, e.g., fuel oil, in order to prevent the build-up of catalyst-deactivating materials.

The methyl naphthalene fraction in line 28 constitutes feed to the dealkylation reactor or reactors. In the modification illustrated, four dealkylation reactors are provided in series in order to facilitate temperature control, e.g., by interstage injection of cool hydrogen. The dealkylation feed in line 28 is mingled with steam from line 29, and with fresh and recycle hydrogen from line 32, and the resulting mixture is passed via preheater 34 (where it is heated to incipient dealkylation temperatures of, e.g., 900-1,000 F.), through

dealkylation reactors

36, 38, 40 and 42, via transfer lines 44, 46 and 48. Each reactor contains a bed of granular dealkylation catalyst of the nature previously described. If desired, cool hydrogen is injected interstage Via

lines

50, 52 and 54, in order to maintain temperature levels Within the operative ranges previously specied. The average temperature rise through each reactor will normally be about 10- F.

The effluent from nal dealkylation reactor 42 is transferred via line 8 and condenser 10 to high-pressure separator 56, from which recycle hydrogen is taken off via line 58, and condensed process water is Withdrawn via line 60. The recycle hydrogen may, if desired, be enriched or purified in a conventional purification unit 62. The high-pressure hydrocarbon condensate in separator 56 is flashed via line 64 into low-pressure separator 66, from which light hydrocarbon gases are exhausted via line 68. The low-pressure condensate in separator 66 is then transferred via lines 4 and 12 to fractionating column 14 as previously described.

The crude naphthalene fraction in line 22 is partially cooled in exchanger 72, to, eg., 13G-200 F., and is then transferred via line 74 to a crystallizer unit 74. In the modification illustrated, this unit is a continuous, scrapedsurface chiller of conventional design, and hence need not be described in detail. In general it consists of a bank of tubular conduits containing revolving peripheral blades, much as an ice cream freezer, through which the chiller feed is pumped continuously, the entire unit being in indirect heat exchange with a stream of refrigerant, not shown.

As the feed passes through the chiller unit, and the temperature becomes progressively lower, crystals of naphthalene are formed, resulting in a slurry which becomes progressively thicker. If desired, pentane, or other light hydrocarbon, or recycle mother liquor, may be added to the slurry in order to decrease viscosity. The minimum temperature reached in the chiller unit is preferably below about 40 F., and still more preferably, between about 20 and 30 F. At least about 80%, and usually at least 85-95%, of the naphthalene in the chiller feed is recovered at these temperatures, and its purity is at least about 99% after removal of mother liquor. The mother liquor ordinarily contains only about 3-8% naphthalene.

Instead of using a scraped-surface chiller unit as illustrated, it is also feasible to use one or more crystallizer holding tanks in series, in each of which a stream of naphthalene slurry is continuously recirculated through an external heat exchanger to elfect cooling. A unit of this nature -is described more particularly in our copending application Serial No. 831,323, now U.S. Patent No. 3,108,063.

The slurry efliuent from crystallizer 76 is transferred via line 78 to a conventional basket-type centrifuge 80 in which the mother liquor is separated from the naphthalene by centrifugation. The solid naphthalene which separates in centrifuge S0 may be washed near the discharge end thereof with pentane, or other light paran, added via line 82, and the resulting wash liquor is transferred via line 84 to pentane recovery column 86, from which recycle pentane is taken overhead via line 87. The bottoms from column 86 ordinarily contains about 10-15% by weight of naphthalene, and is hence recycled to chilling unit 76 via lines 89 and 74.

The washed naphthalene in centrifuge 80 is then transferred via line 88 to a steam-heated melting tank 90, and the molten naphthalene passes therefrom via line 94 to pentane stripping column 92, in which the remaining solvent is vaporized and recycled via line 96. Naphthalene is recovered as bottoms via line 98. Nahpthalene recovered in this manner is normally 99+% pure, and may be rendered substantially 100% pure with an additional pentane wash.

The mother liquor from centrifuge 80 is taken off via line 100 and is composed largely of monocyclic aromatic hydrocarbons, tetralins and indanes boiling in the 400- 450 F. range. Its naphthalene content is normally less than about 6% by weight. It constitutes an excellent heavy gasoline blending stock. If desired, however, it can be recycled to the dealkylation unit for conversion to light gasoline, and to recover the remaining naphthalene therein.

It will be apparent that the naphthalene recovered via line 98 is derived both from fresh feed and from the dealkylation product. In addition to reasons previously noted, it has been found desirable to recover fresh feed naphthalene in this manner in order to avoid unnecessary decomposition thereof during dealkylation. It is highly desirable to provide a reactor feed containing as little naphthalene as is consistent with economical removal thereof. The process of this invention provides a distinctly advantageous and economical method for recovering naphthalene from both the fresh feed and the dealkylat'i-on product whenever the fresh feed contains as much as 3% by weight of naphthalene, and preferably more than about 6%. Where the fresh feed contains less than 3% naphthalene, it is normally disadvantageous to blend it with the dealkylation product because it will then act as a mere solvent in the crystallization stage and will tend to lower ultima-te nahpthalene yields.

It is not intended to limit the invention to the precise combined fractionation of fresh feed and reactor effluent `as described above. In many cases, it will be found that the fresh feed contains little or no light gasoline, and in these cases it may be found preferable to send such feed directly to naphthalene fractionating column 20 instead of column 14, the latter then serving to fractionate light gasoline from the reactor effluent only. In still other cases, it is contemplated that an entirely separate fractionation of reactor eiuent and fresh feed may be utilized. In such cases, the fresh feed is fractionated to recover (l) a crude naphthalene fraction containing a relatively small proportion of naphthalene and relatively large amounts of alkyl benzenes as well as other hydrocarbon impuries, and (2) a raw methyl naphthalene fraction containing less than about 2% by weight of naphthalene. The reactor effluent is then fractionated, first to remove light gasoline, and then `to recover a relatively pure, crude naphthalene fraction (relatively lean in alkyl benzenes), and a methyl naphthalene recycle fraction. The recycle fraction is then blended with the raW methyl naphthalene fraction `and subjected Ito dealkylation as described. The relatively pure reactor efiiuent naphthalene fraction is then blended with the less pure fresh feed naphthalene fraction, and the mixture is subjected to fractional crystallization as described.

The following example Iis cited to illustrate the results obtainable in a specific adaptation of the process, but is not to be construed `as limiting the scope of the invention:

EXAMPLE I Fresh dealkylatz'on feed-A platinum catalyst reforrnate fraction having an ASTM boiling range of 400- 6l0 F., a gravity of 18.3 API (60 R), and the following component analysis:

Component: Weight, percent Alkyl benzenes 26.1 Naphthalene 9.4 Tetralins-Indanes 22.1 Monomethyl naphthalenes 17.8 Dimethyl naphthalenes 12.9 C13Jr components (aromatic) 8.9 Parains 2.4

Dealkylaton conditions (start of run) Catalyst 9% M003, 3% COO, 1%

NaOH impregnated on a %'vAl2O3-5% SiO2 carrier GA3 pellets). Temperature, avg. bed 1,025 F.

Pressure 1,000 p.s.i.g. Hz/oil ratio 9,000 s.c.f./B. Steam/oil mole-ratio 0.9.

L.H.S.V. 0.4.

Fractionation of fresh feed plus dealkylation eiuentfractionation products:

Column 14 overhead Light gasoline; 29.6 API,

227-400 F. ASTM boiling range.

Column 20 overhead (chiller feed) Crude naphthalene fraction; 17 API, 40S-430 F. ASTM boiling r a n g e, 49% naphthalene, 25% al k yl benzenes, 24% tetralins and indanes.

7 Column 26 overhead (dealkylation feed) Methyl naphthalene fraction; 9.7 API, 450-504 F. ASTM boiling range, 61.5% methyl naphthalene, 0.1% naphthalene.

Crystallization of naphthalene from column 20 overhead:

Approximate material balances (basis, 100,000 pounds fresh feed) Pounds Chemical hydrogen consumption 990 Light gasoline (column 14 O.H.) 17,500 Naphthalene produced (99.6% pure) 32,068 Heavy gasoline (mother liquor) 39,000 Fuel oil (column 26 Botts) 5,800 Light gases 6,622

The yield of 99.6% pure naphthalene is about 87% of theoretical, based on total naphthalene and alkyl naphthalenes in the fresh feed.

EXAMPLE II This example demonstrates the savings in hydrogen consumption brought about by the combined fractionation of fresh feed plus reactor effluent, with fractional crystallization of the crude naphthalene fraction, as compared to the case where total fresh feed is passed through the reactor, followed by fractional crystallization of the 400-435 F. product fraction.

In Example I, the chemical hydrogen consumption was about 5.4 s.c.f. per pound of naphthalene produced.

In a comparable run wherein all the fresh feed was passed through the dealkylation reactor at 1,000 F., 880 p.s.i.g., 0.49 L.H.S.V. and 6,760 s.c.f. of hydrogen per barrel of feed, the naphthalene yield was 33.6 weight-percent of the fresh feed, and the chemical hydrogen consumption was 8.4 s.c.f. per pound of naphthalene. Thus, there is a total saving in hydrogen consumption amounting to about 36% in the process of Example I, as compared to this example.

Obviously, the details of the foregoing examples may be varied considerably as to feeds, catalysts, dealkylation conditions, product recovery and recycle stream recovery without departing from the invention. The true scope of the invention is intended to be defined by the following claims.

We claim:

1. A process for the manufacture of naphthalene from a petroleum feed stock boiling above about 350 F., and containing at least about by weight of alkyl naphthalenes, at least about 3% by weight of naphthalene, and between about 10-60% by weight of alkyl benzenes, which comprises:

(A) subjecting said feedstock to fractional distillation to recover (1) a crude naphthalene fraction boiling between about 385 and 450 F., and containing a substantial proportion of alkyl benzenes, and (2) a raw methyl naphthalene fraction boiling between about 425 and 600 F., and containing methyl naphthalenes and less than about 2% by Weight of naphthalene;

(B) subjecting said raw methyl naphthalene fraction plus added hydrogen and steam to hydrodealkylation at a temperature above about 900 F., a pressure below about 2,000 p.s.i.g. and in the presence of a dealkylation catalyst, and recovering a partially dealkylated hydrocarbon product therefrom;

(C) fractionating said hydrocarbon product to recover (l) a crude naphthalene fraction boiling between about 385 and 450 F., and (2) a recycle methyl naphthalene fraction boiling between about 425 and 600 F. and containing methyl naphthalenes and less than about 2% by weight of naphthalene;

(D) subjecting said recycle methyl naphthalene fraction to dealkylation step (B) in admixture with said raw methyl naphthalene fraction;

(E) subjecting said crude naphthalene fraction from step (A) in admiXture with the crude naphthalene fraction from step (C) to fractional crystallization at a temperature below about 40 F., and suiciently low to effect crystallization of at least about of the total naphthalene in the mixture; and

(F) subjecting the crude naphthalene recovered from step (E) to washing with a lower paratiin hydrocarbon to produce 99}% pure naphthalene.

2. A process as defined in `claim 1 wherein said dealkylation catalyst consists essentially of 1) a minor proportion of a hydrogenating component selected from the class consisting of the oxides and sulfides of Group VIB and Group VIII metals, (2.) a minor proportion of an alkaline component selected from the class consisting of heat-stable alkali metal and alkaline earth metal cornpounds, and (3) a major proportion of a carrier which is essentially activated alumina.

3. A process as defined in claim 2 wherein said hydrogenating component is a mixture of the oxides of cobalt and molybdenum.

4. A process as defined in claim 1 wherein said petroleum feedstock is a catalytic reformate fraction boiling between about 400 and 600 F.

5. A process as defined in claim 1 wherein a highoctane light gasoline fraction is also recovered in said fractionation step (C).

6. A process as defined in claim 1 wherein the mixed blend of crude naphthalene fractions which is subjected to fractional crystallization step (E) contains by Weight about 2575% naphthalene, 12-50% alkyl benzenes, and about 10-40% of alkyl indanes plus tetralins.

7. A process for the manufacture of naphthalene from a petroleum feedstock boiling above about 350 F. and containing at least about 10% by weight of alkyl naphthalenes, at least about 3% by weight of naphthalene, and between about 10-60% by weight of alkyl benzenes, which comprises:

(A) maintaining a catalytic hydrodealkylation zone utilizing as feed thereto a methyl naphthalene fraction produced as hereinafter defined, and recovering a partially dealkylated hydrocarbon product therefrom;

(B) blending `said partially dealkylated hydrocarbon product with said petroleum feedstock;

(C) subjecting the resulting blend to fractional distillation to recover (l) a relatively naphthalene-rich fraction boiling between about 385 and 450 F., and containing a substantial proportion of alkyl benzenes, and (2) a heavier methyl naphthalene fraction relatively lean in naphthalene and boiling above about 425 F.;

(D) subjecting said methyl naphthalene fraction plus added hydrogen and steam to hydrodealkylation in said hydrodealkylation zone of step (A), in contact with a dealkylation catalyst at a temperature above about 900 F. and a pressure below about 2,000 p.s.i.g.; and

(E) subjecting said naphthalene-rich fraction to frac- 'tional crystallization at a temperature below about 40 F., and su'iciently low to effect crystallization of at least about 80% of the total naphthalene in the fraction; and

(F) subjecting the crude naphthalene recovered from step E to washing with a lower paraflin hydrocarbon to produce 99+% pure naphthalene.

8. A process as dened in claim 7 wherein said dealkylation catalyst consists essentially of 1) a minor proportion of a hydrogenating component selected from the class consisting of the oxides and suldes of Group VIB and Group VIII metals, (2) a minor proportion of an alkaline component selected from the class consisting of heat-stable alkali metal and alkaline earth metal compounds, and (3) a major proportion of a carrier which is essentially activated alumina.

9. A process as dened in claim 7 wherein said hydrogenating component is a mixture of the oxides of cobalt and molybdenum.

10. A process as defined in claim 7 wherein said petroleum feedstock is a catalytic reformate fraction boiling between about 400 and 600 F.

11. A process as dened in claim 7 wherein a highoctane light gasoline fraction is also recovered in said fractionation step (C).

12. A process as defined in claim 7 wherein the naphthalene-rich fraction which is subjected to fractional crystallization step (E) contains by weight about 25-75% naphthalene, 12-50% alkyl benzenes, and about 10-40% of alkyl indanes plus tetralins.

13. A fractional crystallization process for the recovery of naphthalene from a petroleum feedstock consisting essentially of a mixture of a non-dealkylated petroleum fraction boiling between about 400 and 450 F., and a dealkylated petroleum fraction boiling between about 400 and 450 F., said feedstock containing by weight about -75% naphthalene, 12-50% alkyl benzenes and about l0-40% of alkyl indanes plus tetralins, which comprises chilling said petroleum feedstock to a temperature below about F., and suciently low to crystallize at least about of the naphthalene contained therein, recovering and washing the naphthalene crystals with a lower paraffin to produce naphthalene crystals of 99+% purity.

References Cited by the Examiner UNITED STATES PATENTS 2,823,241 2/1958 Bennett et al 260-674 2,858,348 10/1958 BoSmajian et al 260-674 3,055,956 9/1962 Paulsen 260-674 DELBERT E. GANTZ, Primary Examiner. ALPHONSO D. SULLIVAN, Examiner.

Claims

1. A PROCESS FOR THE MANUFACTURE OF NAPHTHALENE FROM A PETROLEUM FEED STOCK BOILING ABOVE 350*F., AND CONTAINING AT LEAST ABOUT 10% BY WEIGHT OF ALKYL NAPHTHALENES, AT LEAST ABOUT 3% BY WEIGHT OF NAPTHTHALENE, AND BETWEEN ABOUT 10-60% BY WEIGHT OF ALKYL BENZENES, WHICH COMPRISES: (A) SUBJECTING SAID FEEDSTOCK TO FRACTIONAL DISTILLATION TO RECOVER (1) A CRUDE NAPHTHALENE FRACTION BOILING BETWEEN ABOUT 385* AND 450*F., AND CONTAINING A SUBSTANTIAL PROPORTION OF ALKYL BENZENES, AND (2) A RAW METHYL NAPHTHALENE FRACTION BOILING BETWEEN ABOUT 425* AND 600*F., AND CONTAINING METHYL NAPHTHALENES AND LESS THAN ABOUT 2% BY WEIGHT OF NAPHTHALENE; (B) SUBJECTING SAID RAW METHYL NAPHTHALENE FRACTION PLUS ADDED HYDROGEN AND STEAM TO HYDORDEALKYLATION AT A TEMPERATURE ABOVE ABOUT 900*F., A PRESSURE BELOW ABOUT 2,000 P.S.I.G. AND IN THE PRESENCE OF A DEALKYLATION CATALYST, AND RECOVERING A PARTIALLY DEALKYLATED HYDROCARBON PRODUCT THEREFROM; (C) FRACTIONATING SAID HYDROCARBON PRODUCT TO RECOVER (1) A CRUDE NAPHATHALENE FRACTION BOILING BETWEEN ABOUT 385* AND 450*F., AND (2) A RECYCLE METHYL NAPHTHALENE FRACTION BOILING BETWEEN ABOUT 425* AND 600*F. AND CONTAINING METHYL NAPHTHALENES AND LESS THAN ABOUT 2% BY WEIGHT OF NAPHTHALENE; (D) SUBJECTING SAID RECYCLE METHYL NAPHTHALENE FRACTION TO DEALKYLATION STEP (B) IN ADMIXTURE WITH SAID RAW METHYL NAPHTHALENE FRACTION; (E) SUBJECTING SAID CRUDE NAPHTHALENE FRACTION FROM STEP (A) IN ADMIXTURE WITH THE CRUDE NAPHTHALENE FRACTION FROM STEP (C) TO FRACTIONAL CRYSTALLIZATION AT A TEMPERATURE BELOW ABOUT 40*F., AND SUFFICIENTLY LOW TO EFFECT CRYSTALLIZATION OF AT LEAST ABOUT 80% OF THE TOTAL NAPHTHALENE IN THE MIXTURE; AND (F) SUBJECTING THE CRUDE NAPHTHALENE RECOVERED FROM STEP (E) TO WASHING WITH A LOWER PARAFFIN HYDROCARBON TO PRODUCE 99+% PURE NAPHTHALENE.