US3150172A - Aromatic acids from petroleum fractions - Google Patents

Description

United States Patent 3,150,172 ARQMATIC ACllJ S FRQM PETRQLEUItl FRACTKGNS Qarl Serres, in, Hammond, End, and Ellis it. Fields,

Chicago, lllL, assignors to Standard till Company,

(Jhicago, ill, a corporation of Indiana No Drawing. Filed Apr. 17, 1959, er. No. 807,036

9 Claims. (Cl. Edd-52 i) This invention relates to the preparation of naphthalene carboxylic acids from readily available petroleum refinery stocks. More particularly, the invention relates to an improved process for preparing naphthalene carboxylic acids from selected fractions of catalytic reformates.

Recently, a large number of carboxylic acid derivatives of naphthalene have become of interest in the manufac ture of outstanding alkyd resins and, in ester form, as superior plasticizers. Also, certain of these naphthalene carboxylic acids are capable of forming super-polyesters which may be cold-drawn into high tensile strength fibers and films. Unfortunately, despite their superiority in certain respects to mononuclear aromatic acids such as phthalic and terephthalic acids, the naphthalene carboxylic acids are thus far of restricted commercial practicability by reason of their limited availability. Furthermore, naphthalene carboxylic acids are generally prepared by oxidation of the corresponding alkyl naphthalene, and there are two monomethyl naphthalenes, two monoethyl naphthalenes, ten dimethyl naphthalenes, and tremendous numbers of higher allcyl naphthalenes, many of which have almost identical boiling points. Thus the problem of resolving either isomeric allryl naphthalenes or isomeric naphthalene carboxylic acids to produce the pure naphthalene carboxylic acids necessary for such purposes as fiber-forming polyesters has raised an almost insurmountable technical barrier to their widespread adoption.

It has now been discovered, in accordance with the invention, that certain readily-available petroleum refinery streams may be separated by simple fractional distillation to afford selected fractions which predominate in only a small numberor even only onealkyl naphthalene. These selected fractions may then be catalytically oxidized in the liquid phase to produce exceptional yields of relatively pure naphthalene carboxylic acids. Specifically, it has now been discovered that the bottoms fraction obtained by removing gasoline-boiling-range components from a catalytically reformed naphtha, or catalytic reformate, contains only a limited number of isomeric alkyl naphthalenes, and may be resolved into selected fractions or cuts which will yield a relatively pure naphthalene carboxylic acid upon oxidation in the oxidation process set forth hereinafter. Gxidation of the selected catalytic rcformate bottoms fraction according to the inventive process is conducted by reacting that fraction with a molecular oxygen-containing gas in the liquid phase in the presence of a catalyst comprising, in conjoint presence, bromine and a heavy metal oxidation catalyst. By this oxidation, alltyl naphthalenes in the bottoms fraction are converted in high yields to the corresponding naphthalene monoor di-carboxylic acid.

It has further been discovered, however, that extreme care must be taken in preparing the catalytic rcformate bottoms fraction for oxidation. Unidentified materials, presumably hydrocarbons, which are present in reform-ate bottoms fractions which contain components having true boiling points at 200 mm. absolute pressure of above 405 F. act as powerful inhibitors to the above liquid phase oxidation process. Even a fen percent of these high boiling hydrocarbons are capable of entirely preventing the conversion of catalytic reformate bottoms fractions into recoverable naphthalene carboxylic acids.

Patented Sept. 22, 1964 ICC Catalytic reforming, as is well known, is an established process for upgrading the octane number of petroleum naphtha fractions. The charge naphtha, which may be a virgin distillate, a thermal cracked naphtha, a visbreaker naphtha, or blends of such naphthas, is processed at elevated temperatures and pressures in the presence of hydrogen gas over certain catalysts such as platinum-type catalysts comprising about (Ll-1% platinum on a high surface support material such as alumina, whereby reactions such as dehydrogenation of naphthenes to aromatics, dehydrocyclization of para'lfins to aromatics, and isomerization of normal paraffins to highly branched paraftins occur. The products of these reactions all have substantially higher octane numbers than the naphtha chargin g stock. Such naphtha charging stocks may have boiling ranges from about 100 to about 400-500 P. for a full boiling range naphtha, but present commercial practice usually dictates a feed naphtha of about ZOO-400 F. boiling range. Before subjecting. the naphtha to catalytic reforming, all or a portion of it may be pretreated over so-called hydrofining catalysts, e.g. of the cobalt-molybdate type, in admixture with hydrogen gas to saturate any olefins and decompose organic compounds of sulfur, nitrogen, and oxygen to hydrogen sulfide ammonia, and water, respectively, which in excess concentration are undesirable in the reforming operation.

Conditions for catalytically reforming naphthas to obtain high octane number gasoline product and a reformate bottoms fraction for use in the inventive process herein are generally selected to produce the desired octane number product, usually an octane number of or above by ASTM research method without the addition of tetraethyl lead. The catalyst is desirably disposed in a plurality of fixed beds of catalyst particles. Reactor inlet temperatures may be between about 880 and about 1000 F., depending upon other variables to obtain the desired product octane number; pressures ranging from about 50 to about 800 pounds per square inch gage; recycle hydrogen-containing gas rates of from about 1,000 to about 10,000 standard cubic feet of hydrogen gas per 42-gallon barrel of naphtha charge; and liquid hourly space velocities, i.e. pounds of naphtha per hour per pound of catalyst, of from about 0.5 to about 5.0 may be used. Modern practice currently dictates a reformate octane level, research clear, in the -105 octane number class, which requires reactor inlet temperatures of about 940-980 F., pressures which are preferably in the range of about 150 to 450 p.s.i.g., recycle ga ratios of about 3000-6000 s.c.f./b., and liquid hourly space velocities of about 1.0- 3.0. Reforming is desirably conducted in a semi-regenerative manner, that is, a plurality of reforming zones are established in parallel flow, with interzone rehcaters to restore the desirable inlet temperatures, and a spare or swing reactor is manifolded into the piping to permit any one of the process reactors to be taken off-stream, replaced by the swing reactor, and regenerated by exposure to a controlled oxygen-containing atmosphere under combustion conditions to remove a coke-like material which deposits on the catalyst pellets as an unavoidable byproduct of the reforming reaction.

After reforming, the mixture of reformed hydrocarbons and recycle-hydrogen-containing gas is ordinarily cooled to separate liquefiable hydrocarbons as a gross liquid product from the hydrogen-containing gas for recycle. This liquid product contains a mixture of volatile hydrocarbon light ends, hydrocarbons in the gasoline boiling range, i.e. about initial boiling point to about 350420 F. final boiling point in the ASTM distillation, as Well as a higher boiling material. This higher boiling material, the amount and composition of which depending upon the naphtha charging stock distillation range and the severity of reforming, is or contains the catalytic reformate bottoms fraction or fractions which are subsequently oxidized in accordance with the present invention. This bottoms fraction is variously termed polyrner, post-gasoline, rerun bottoms, reformate botts or bottoms, etc., and is composed almost entirely (98100%) of aromatic compounds, predominantly condensed ring aromatics. It is not presently known, nor is it important, precisely how this high boiling material originates in the reforming process, but during reforming of a 200-400 F. boiling range naphtha to a severity of, say, 95l05 research octane number clear, this fraction constitutes about 15 weight percent of the charge naphtha.

The reformate bottoms fraction may be separated from gasoline boiling range hydrocarbons (either before or after stabilization of such hydrocarbons to remove light ends) by conventional fractional distillation in multi-tray distilling or rerun towers. The operation of these towers may be controlled to provide any desirable endpoint in the gasoline boiling range hydrocarbons which are taken overhead. For example, premium gasolines usually require that components blended into them all have ASTM distillation endpoints of no higher than about 400 F. or even lower, although this may be exceeded by as much as 25 or so in particular cases.

The reformate bottoms as it is taken from the rerun tower contains hydrocarbons which boil within the range suitable for providing the oxidation feedstock herein, and may contain the higher boiling hydrocarbons which act as potent oxidation inhibitors. These inhibitors, if present, must be excluded from the oxidation feedstock, and such exclusion may be conveniently accomplished by distillation in either batch or continuous distillation apparatus. According to the preferred embodiment, the reformate bottoms fraction is distilled continuously in a plurality of fractional distilling columns to separate, in serial order, (a) an extremely high boiling bottoms fraction, (b) a relatively low boiling overhead fraction, and (c) a heart out of roughly 60-90 volume percent of the reformate bottoms. This heart out may yet contain substantial amounts of high boiling oxidation inhibitors, although the heart out itself may have a relatively narrow boiling range, e.g. 458-575 F. at atmospheric pressure. The heart out is then, according to the preferred embodiment, subjected to one or more additional distillation operations to isolate one or more fractions rich in a particular alkyl naphthalene. Either an individual fraction thus obtained, a blend of two or more such fractions, or other combination of fractions predominating in one or more alkyl naphthalenes may then be selected for a particular omdation.

It has been experimentally found that the heart cut described above may be separated by fractional distillation into a number of individual cuts, each predominating in a single alkyl naphthalene, if the fractionation is carefully conducted in one or more distillation towers containing a comparatively large number of fractionating trays, e.g. 30-200 trays, particularly if the distillation is conducted batchwise. Continuous distillation may of course be employed in large installations. Distillation may be carried out at any suitable pressure, e.g. mm. mercury absolute to 100 p.s.i.g. or higher, although pressures below atmospheric are conducive to finer separations. At a pressure of, say, 200 mm. mercury absolute a fraction boiling Within the range of about 360-365 F. (true boiling point methods), and representing about 10 volume percent of a typical reformate bottoms, is found to be rich in 2-methyl naphthalene. This may be oxidized in excellent yields to beta-naphthoic acid. The fraction boiling at about 365-370 F. at 200 mm. mercury contains a predominance of l-methyl naphthalene, and may be oxidized to alpha-naphthoic acid. This 365-370 fraction represents about 'volume percent of the total catalytic reformate bottoms. The fraction boiling at about 380395 F., constituting about eight percent of reformate A bottoms, is enriched in 2-methyl naphthalene and may be oxidized, either alone or in combination with the firstmentioned fraction, to beta-naphthoic acid. The fraction boiling at about 395 F., give or take about 3 F., at 200 mm. Hg is about eight percent of a typical reformate bottoms and predominates in 2,7-dimethyl naphthalene, which may be oxidized to naphthalene 2,7-dicarboxylic acid. The last useable fraction boils at about 400 (plus or minus about 3 F.), contains the 1,6-dimethyl naphthalene and is about eight percent of the reformate bot toms; it may be oxidized to naphthalene 1,6-dicarboxylic acid.

It will be understood that the reformate bottoms fractions may be oxidized either individually or in any admixture, and need not be resolved into individual closeboiling fractions. It is further understood that the boiling ranges or points set forth above of necessity are dependent on the pressure at which said ranges or points are determined. The specific pressure of 200 mm. Hg absolute has been used above for reasons of convenience and uniformity, but it is recognized by the art that the boiling point of a hydrocarbon increases with an increase in pressure and decreases with a decrease. Hence the designated distillation pressure is to be considered only as a definition of the boiling points of the respective fractions.

Components boiling above about 405 F. at 200 mm. mercury pressure contain the unidentified oxidation inhibitor, and hence reformate bottoms fractions which are not substantially free from, i.e. contain less than about 3-5 by weight, of such high boiling components cannot be oxidized in accordance with the present invention. Although the chemical nature of this inhibitor material is unknown, as little as 13 percent in an otherwise-oxidizable reformate bottoms fraction leads, instead of yields on the order of 50 mol percent or higher of naphthalene dicarboxylic acid, to only a few percent yield of dicarboxylic acid and a large amount of amorphous acidic or non-acidic material which cannot be resolved into individual components. This inhibition is set forth in Tests 1 and 2 described in a subsequent portion of this specification.

In the practice of the invention, the oxidation of alkylsubstituted naphthalenes to the corresponding naphthalene carboxylic acids may be effected by reacting such compounds with molecular oxygen, for example, air, in the conjoint presence of catalytic amounts of bromine and a heavy metal oxidation catalyst.

Metals of the group of heavy metals shown in the Periodic Chart of Elements, appearing on pages 56 and 57 of the Handbook of Chemistry, 8th edition, published by Handbook Publishers, Inc., Sandusky, Ohio (1952), have been found desirably applicable to this invention for furnishing the metal or metal ion portion of the metalbromine catalyst. Of the heavy metal group, those metals having an atomic number not greater than 84 have been found most suitable. Excellent results are obtained by the utilization of a metal having an atomic number from 23 to 28 inclusive. Particularly excellent results are obtained with one or more metals of the group consisting of manganese, cobalt, nickel, iron, chromium, vanadium, molybdenum, tungsten, tin and cerium. It has also been found that the catalytic amount of the metal may be either as a single metal or a combination of such metals. The metal may be added in elemental form, as the oxide or hydroxide, or in the form of a metal salt. For example, the metal manganese may be employed as the manganese salt of an aliphatic carboxylic acid such as manganese acetate, manganese oleate and the like, as the manganese salt of an aromatic or cycloaliphatic carboxylic acid, for example, manganese naphthenate, manganese toluate, etc., in the form of an organic complex, such as the acetylacetonate, the S-hydroxy-quinolate and the ethylene diarnine tetra-acetate, as Well as manganese salts such as the borates, halides and nitrates which are are also efficacious.

The bromine may be added in elemental, combined or ionic form. As a source of available bromine, ammonium bromide or other compounds soluble in the reaction medium may be employed. Satisfactory results have been obtained for example, with potassium bromate. Tetrabromoethane, benzyl bromide and the like may be employed if desired.

The amount of the metal catalyst employed is not critical and may be in the range of from about .01 to about by weight or more based on the aromatic reactant charged. Such catalyst may comprise a single heavy metal or a mixture of two or more heavy metal oxidation catalysts. Where the heavy metal is introduced as a bromide salt, for example, as manganese bromide, the proportions of manganese and bromine will be in their stoichiometric proportions. The ratio of metal to bromine may be varied, for example, within the range from about 1 to 10 atoms of heavy metal oxidation catalyst per atom of bromine to about 1 to 10 atoms of bromine per atom of heavy metal.

The relation of temperature and pressure should be so regulated as to provide liquid phase in the reaction Zone. Generally, the pressure may he in the range of atmospheric up to about 1500 p.s.i.g. The liquid phase may comprise all or a portion of the organic reactant or it may comprise a reaction medium in which the organic reactant is dissolved or suspended.

While a solvent need not be employed, in a preferred embodiment of the invention the oxidation is conducted in the presence of a solvent medium comprising a monocarboxylic acid having from 2 to 8 carbon atoms in the molecule. Such acids which are free of hydrogen atoms attached to tertiary carbon atoms are particularly advantageous as solvent since they have been found to be relatively stable or inert to oxidation in the reaction system. Lower saturated aliphatic monocarboxylic acids having from 2 to 4 carbon atoms in the molecule are particularly elfective solvents.

The preferred solvent is acetic acid usually employed in its glacial form. Although acetic acid is preferred, carboxylic acids such as propionic acid, butyric acid, caproic acid, benzoic acid and the like may be employed. Mixtures of these acids may be used. Where all the advantages of an acid medium are not required, other inert media may be used.

Those skilled in the art will appreciate that the amount of solvent employed will be varied over wide limits. The amount of solvent utilized is not critical but typically will be in the range of from about 0.1 to about 10, desirably 0.5 to 4 times the weight of oxidizable starting material.

As to the molecular ox gen-containing gas, there may be employed substantially 100% oxygen gas or gaseous mixtures containing lower concentrations of oxygen, for example, air. Such mixtures preferably have oxygen contents within the range of about 5% by volume to about 20% or more by volume. As such mixtures there may be employed air or air which has been diluted with gases such as nitrogen, CO and the like, or corresponding mixtures prepared from substantially pure gaseous oxygen and such inert diluents may he used. The ratio of total oxygen fed into the reaction mixture can be in the range of from about 0.5 to 50 moles or more of oxygen per mol of aromatic material.

The reaction temperature should be sufficiently high so that the desired oxidation reaction occurs and yet not so high as to cause undesirable charring or formation of tars. Thus temperatures in the range of 50-275 C. desirably from l50250 C., may be employed.

By way of illustration, a virgin naphtha charging stock is catalytically reformed in the presence of a platinumalumina catalyst (or other catalyst having dehydrocyclization activity) and the reformate product is fractionated to a gasoline boiling range material and a reformate bottoms. This bottoms is re-distilled to obtain a heart cut, which is then carefully fractionated to produce cuts or fractions suitable for the oxidation described herein.

The charge is a mixture of virgin naphtha derived from Gulf Coast, East Texas, and West Texas sweet crude oils. Before charging to the reformer, it is desulfurized over a cobalt-molybdate type catalyst, and then fractionated to exclude as a bottoms all hydrocarbons boiling above about 400 F. in the ASTM distillation. Inspections of the naphtha, the desulfurized naphtha, and tie fractionator overhead (reformer charge) are shown in Table 1 below.

The fractionator overhead constitutes the charge to a commercial catalytic reforming unit employing about 0.1-1.0% platinum on alumina catalyst disposed as pellets in live fixed-bed reactors and one fixed-bed swing reactor. Reactor inlet temperatures are about 900-970 F., while the average reactor pressure is about 200-250 p.s.i.g. A recycle gas ratio of about 3,0006,000 standard cubic feet of hydrogen-containing gas per 42-gallon of charge is employed and the space velocity units of weight of oil per weight of catalyst, is about 14. In the reforming operation, naphtha taken as fractionator overhead is vaporized in a preheat furnace, combinated with hot recycle gas, and charged to the lead reactor. After passing through the lead reactor, the etlluent is reheated in an. interstage furnace in order to return the process vapors to the desired reaction temperature before charging to the next reactor. This reheating is repeated after the second, third and fourth reactors. The process vapors leaving the reactors are cooled in a series of heat exchangers comprising the reboilers and preheaters for the various towers in the fractionation sections of the plant, and are then cooled further and charged to high-pressure separator. A portion of the hydrogen-rich separator gas is compressed, heated and returned to the reactors as a recycle gas while net separator gas production is charged to an absorption system for recovery of propane, butanes, and pentanes. The high pressure separator liquid is sent to a debutanizer for removal of butanes and lighter components.

Because the dehydrocyclization reaction forms substantial amounts of reformer bottoms having higher boiling points than are usable in motor gasolines, the debutanized reformate may be treated for removal of these bottoms by rerunning in a distillation column, taking the gasoline boiling range material as an overhead reformed gasoline product and withdrawing the reformate bottoms fraction for subsequent redistillation and use in accordance with the present invention. Typical product yields from. a reforming operation conducted to provide an ASTM product octane number, research method, without TEL addition, of are shown in Table 2 below.

Inspections of debutanized gasoline and polymer or reformate bottoms obtained in this operation are shown in Table 3 below.

TABLE 3.-DEBUTANIZED GASOLINE AND RE- FORMATE BOTTOMS Gasoline Bottoms ASIM octane number:

D 908, research method, without TEL addition 100. 1 D 357, motor method, without TEL addition 87. 9 Gravity, deg. API 43. 5 9 5 Reid vapor pressure, p.s.i. 7.0 ASTM distillation, degrees Fahre Initial boiling point 106 460 IO-pereent point 180 480 30-percent point 248 500 50 pereent point 284 508 70-pereent poi.nt 314 523 QO-percent point 346 588 Final boiling point 408 700+ Hydrocarbon type, percent by volume Parqffins 22 Olefins Nsmhthenes Aromatics 75 99 The reformate bottoms fraction or polymer was continuously distilled in two towers, the first of which separated about 17 volume percent bottoms as an aromaticsrich very high boiling material, with as ASTM boiling range at atmospheric pressure of about 500670 F. The overhead was redistilled to exclude about 3% as lights, leaving about 80 volume percent of the total refonnate bottoms as usable heart cut. This heart out was transferrcd to a laboratory-scale batch distillation column packed with IOU-mesh Mr McMahon packing and having an estimated 100 theoretical plates. Once distillation was under Way, the column was operated at a top pressure of 200 mm. mercury absolute, and the column top temperatures were recorded as cut points. About 130 individual cuts were taken, each about 0.6 volume percent of the total heart out charge. The cuts were maintained in individual sample bottles, and were blended as needed. A plot showing volume percent overhead versus column top temperature shows definite plateaus corresponding to individual cuts or fractions which may be oxidized to produce the desired naphthalene carboxylic acids. In this example, the 360-365 P. fraction represented about 10 volume percent of total bottoms, the 365370 F. fraction was about 20%, the 380395 P. fraction about 8%, the 395 F. fraction about 12%, and the 401 P. fraction also about 12%.

Certain of the individual 0.6% cuts were oxidized in accordance with the invention described herein and these oxidations are described below in numbered examples. The tests are demonstrations of the inhibiting e'fitect of materials boiling above about 405 F. at 200 millimeters mercury pressure.

Example 1 In this example, a reformate bottoms fraction having a boiling point of about 363 F. (about 360-365 F.) at 200 mm. was oxidized to obtain beta-naphthoic acid.

The sample oxidized had a boiling point of about 363 F. at 200 mm. Hg absolute pressure, an API gravity of 9.9, and a refractive index of 1.6046 at 20 C.; it represented 06 volume percent of the heart out. A mixture of 25 grams of the above-identified fraction, grams of glacial acetic acid, 1.2 grams of a mixture of cobalt acetate tetrahydrate and manganese acetate tetrahydrate, together with 0.5 gram ammonium bromide in 6 ml. water, was introduced into a corrosion-resistant reaction vessel. Air was passed into the vessel at 400 F. and 400 p.s.i.g. at a rate of 0.13 standard cubic foot per minute; When oxygen in the oil-gases reached 20.8 volume percent (condensable-free basis after 5.0 cubic feet of air had been introduced) oxidation was terminated and the contents of the reactor were removed. The acidic solvent was removed by evaporation and the residue dissolved in dilute sodium hydroxide solution, filtered, and the filtrate acidified with hydrochloric acid. The precipitated solid was filtered and after drying weighed 24.0 grams. It was shown to be beta-naphthoic acid by melting point (found 179183 C., literature 185 C.), neutral equivalent (found 173, theory 172) and'infra-red spectrum.

1 Example 2 In this example, a reformate bottoms fraction boiling in the range of about 365370 F. was oxidized in the liquid phase to obtain alpha-naphthoic acid.

The sample oxidized had a boiling point at 200 mm. Hg absolute of about 369 R, an API gravity of 7.2, and a refractive index at 20 C. of 1.6158. It represented 0.6 volume percent of the heart out. A mixture of 25 grams of this fraction, 150 grams of glacial acetic acid, 1.2 grams of mixed cobalt acetate tetrahydrate and manganese acetate tetrahydrate, and 0.5 gram ammonium bromide in 6 ml. water was oxidized with air at 400 p.s.i.g. at a rate of 0.13 cubic foot per minute. After the introduction of 5.5 standard cubic feet of air, oxygen in the elf-gas rose to 20.8% and the reaction was terminated. The reactor contents were cooled and removed. The acetic acid solvent was removed by evaporation on a steam bath, and the residue dissolved in dilute sodium hdyroxide solution, filtered, and acidified with hydrochloric acid to precipitate a solid acid. After drying, the solid acid weighed 25.0 grams and was shown to be alpha-naphthoic acid by the melting point (found 150- C., literature C.), neutral equivalent (found 174, theory 174) and infra-red spectrum.

Example 3 In this example, a reformer bottoms fraction having a boiling range of about 380-395 F. at 200 mm. Hg absolute pressure was oxidized in the liquid phase to prepare beta-naphthoic acid.

The sample oxidized had a boiling point of about 391 F. at 200 mm., an API gravity of 11.0, and a refractive index at 20 C. of 1.5988; it was 0.6 volume percent of the heart out. A mixture of 25 grams of this fraction, 150 grams glacial acetic acid, 1.2 grams of mixed cobalt acetate tetrahydrate and manganese acetate tetrahydrate, and 0.5 gram ammonium bromide in 6 ml. water was reacted with air at 400 F. and 400 p.s.i.g. Air was intro duced at a rate of 0.13 cubic foot per minute, and when, after 8.5 standard cubic feet of air had been admitted,

oxygen in the oli-gas returned to 20.8%, the reaction was terminated. The reactor contents were cooled and removed, after which the acetic acid was removed by evaporation on the steam bath. The residue was dissolved in dilute sodium hydroxide solution, filtered, and the filtrate acidified with hydrochloric acid. The precipitated solid was collected on a filter. After drying, the solid acid weighed 21 grams.

This solid material was worked up by redissolving it in sodium hydroxide solution, treating the solution with adsorbent charcoal, and filtering and acidifying with hydrochloric acid to precipitate the solid acids. The solid acids were then worked up by fractional crystallization from ethanol. The solid acid was found to contain 15 grams of beta naphthoic acid and 6 grams of unidentified dibasic acids. The beta naphthoic acid was identified by melting point, neutral equivalent (found 171, theory 172), and comparison of the infra-red spectrum with the spectrum of authentic beta naphthoic acid.

Example 4 In this example, a reformer bottoms fraction having a boiling range of around 395 F. at 200 mm. Hg was oxidized in the liquid phase to yield naphthalene-2,7-dicarboxylic acid.

The sample oxidized had a boiling point of about 396 F. at 200 mm. Hg, an API gravity of 11.2, and a refractive index of 1.6051. This fraction represented 1.2 volume percent of the heart cut. A mixture of 25 grams of the reformate bottoms fraction, 150 grams glacial acetic acid, 1.2 grams of mixed cobalt acetate tetrahydrate and manganese acetate tetrahydrate, and 0.5 gram ammonium bromide in 6 ml. water was heated in a reactor at 400 F. while air at 400 p.s.i.g. was passed into the reactor at the rate of 0.13 cubic foot per minute. After 6.5 standard cubic feet of air had been used, the reaction was terminated and the reactor contents were then allowed .to cool and were subsequently withdrawn. The acetic acid solvent was removed by evaporation on the steam bath, and the residue dissolved in dilute sodium hydroxide solution, filtered, the filtrate acidified with hydrochloric acid, and the precipitated solid cooled on a filter. After drying, the solid acid weighed 21 grams and had a neutral equivalent of 116. Theory for naphthalene dicarboxylic acids is 108. This product was dissolved in 450 cc. hot ethanol, and on cooling yielded a precipitate amounting to 10-15% by weight of the total product. This precipitated material was shown to be naphthalene 2,7-dicarboxylic acid by comparing its infrared spectrum with the spectrum of authentic 2,7dicarboxylic acid.

Example 5 In this example, a reformate bottoms fraction boiling around 400 F. at 200 mm. Hg was oxidized to prepare naphthalene-1,6-dicarboxylic acid.

This sample had a boiling point of 401 F. at 200 mm. Hg, an API gravity of 9.7, a refractive index of 1.6082 at 20 C., and represented 0.6 volume percent of the heart cut. A mixture of 25 grams of bottoms fraction, 150 grams acetic acid, 1.2 grams cobalt and manganese acetate tetrahydrates, and 0.5 gram ammonium bromide in 6 ml. water was heated in a reactor at 400 F. while air at 400 p.s.i.g. was passed through the reaction mixture at a rate of 0.13 standard cubic foot per minute. When 8.0 cubic feet of air had been introduced, oxygen in the off-gas returned to 20.8% and the reaction was terminated. The reactor contents were removed and cooled, the acetic acid solvent was removed by evaporation on a steam bath, and the residue dissolved in dilute sodium hydroxide solution, filtered, and the filtrate acidified with hydrochloric acid to precipitate a solid acid product. This solid acid weighed 32 grams (80 weight percent yield) and had a neutral equivalent of 116 (theory for a naphthaiene dicarboxylic acid is 108). The infra-red spectrum of this acid was essentially identical to the spectrum of authentic naphthalene 1,6-dicarboxylic acid. The infrared spectrum was not changed after treatment with charcoal and crystallization from ethanol. The infra-red spectrum of the dimethyl ester of this product was also essentially identical with the spectrum of a dimethyl ester of authentic naphthalene 1,6-dicarboxylic acid.

TEST 1 In this test, a reformate bottoms fraction composed of hydrocarbons boiling above 405 F. was oxidized in the liquid phase, and gave a black, syrupy mass which could not be worked up.

The cut oxidized had a boiling point of 408 F. at 200 mm. Hg, an API gravity of 9.6, and a refractive index of 1.6129 at 20 C. It represented 0.6 volume percent of the heart cut. A mixture of 25 grams of this high boiling material, grams glacial acetic acid, 1.2 grams mixed cobalt and manganese acetate tetrahydrates, and 0.5 gram ammonium bromide in 6 ml. water was heated at 400 F. while air at 400 p.s.i.g. was passed through the mixture at the rate of 0.13 cubic foot per minute. After completion of the reaction, the acetic acid solvent was removed by evaporation on a steam bath to yield a black, syrupy mass which could not be worked up or separated by conventional means into pure components. By chromatographic analysis, it was found that this syrupy mass contained about 9.0 grams of methyl naphthoic acids and 8.0 grams of one or more naphthalene dicarboxylic acids, plus unidentified neutral resinous products.

In a modification of the above test, a second portion of the 408 F. boiling range reformate bottoms cut was re peatedly crystallized from ethanol to furnish about 60 Weight percent of substantially pure 2,3-dimethyl naphthalene (by infra-red analysis). This was oxidized under conditions duplicating those of the test and yielded 2,3- dicarboxylic acid in 63 mole percent yield. Thus it is evident that a minor quantity of some material in bottoms fraction boiling above 405 F. exerts a powerful inhibition on the oxidation reaction.

TEST 2 To further demonstrate the inhibiting action of materials boiling above 405 F. at 200 mm. Hg, an additional test was conducted using a mixture of 10 grams of the fraction successfully oxidized in Example 4, 10 grams of the fraction successfully oxidized in Example 5, and 10 grams of the reformate bottoms fraction boiling at 408 F. and which would not oxidize in Test 1. Recalling that the reformate bottoms fraction in Test 1 contained only 40% of unidentified inhibiting material, the blend of fractions herein employed contained at most only 13.3% inhibitor.

A mixture of 30 grams of the above described blended fraction, 150 grams acetic acid, 1.2 grams mixed cobalt and manganese acetate tetrahydrates, and 0.5 gram ammonium bromide in 6 ml. water was heated at 400 F. While air at 400 p.s.i.g. was passed through the mixture at a rate of 0.13 cubic foot per minute. When oxygen in the oft-gas returned to 20.8%, the reactor contents were cooled and removed. The acetic acid solvent was removed by evaporation on the steam bath. Work-up gave 7.0 grams of unreacted hydrocarbon, 7.0 grams of nonacidic black tar, and 22.0 grants of black acidic syrup which could not be resolved into crystallizable acid products.

From the foregoing presentation it is apparent then that the inventive process provides an outstanding method for preparing naphthalene carboxylic acids. The charging stock is readily available, and will become even more obtainable as automobile octane number requirements demand increased catalytic reforming severity. Thus the outstanding plasticizers, pesticides, resins, and polyester fibers which are based on naphthalene carboxylic acids and which heretofore had been of limited commercial utility by reason of their unavailability may now become important products of commerce.

We claim:

1. In a process for the preparation or" a naphthalene carboxylic acid wherein a catalytic reformate bottoms fraction is reacted with molecular oxygen-containing gas in the liquid phase and in the presence of a catalyst comprising in conjoint presence bromine and a heavy metal oxidation catalyst, the improvement of the step, prior to such reaction, of separating from said catalytic reformate bottoms fraction those hydrocarbons having a true boiling point at 200 mm. Hg absolute pressure of above 405 F. whereby inhibition of the oxidation reaction is avoided.

2. Process of claim 1 wherein said catalytic reformate bottoms fraction has a true boiling range at 200 mm. Hg absolute pressure of about 360365 F., and the naphtha- 1 1 lene carboxylic acid thus prepared is beta-naphthoic acid.

3. Process of claim 1 wherein said catalytic reformate bottoms fraction has a true boiling range at 200 mm. Hg absolute of about 365-370 F., and the naphthalene carboxylic acid thus prepared is alpha-naphthoic acid.

4. Process of claim 1 wherein said catalytic reformate bottoms fraction has a true boiling range at 200 mm. Hg absolute pressure of about 380-395 F. and the naphthalene carboxylic acid thus prepared is beta-naphthoic acid.

5. Process of claim 1 wherein said catalytic reformate bottoms fraction is a mixture of two such fractions having true boiling ranges at 200 mm. Hg absolute pressure of about 360-365 F. and about 380-695 F, and the naphthalene carboXylic acid thus prepared is beta-naphthoic acid.

6. Process of claim 1 wherein said catalytic reformate bottoms fraction has a true boiling range at 200 mm. Hg absolute pressure of about 395 F., and the naphthalene carboxylic acid thus prepared is naphthalene-2,7-dicarboxylic acid.

7. Process of claim 1 wherein said catalytic reformate bottoms fraction has a true boiling range at 200 mm. Hg absolute pressure of about 401 F., and the naphthalene carboxylic acid thus prepared is naphthalene-1,6-dicarboxylic acid.

8. Process of claim 1 wherein said heavy metal oxida tion catalyst has an atomic number of 23 to 28, inclusive.

9. Process of claim 1 wherein said heavy metal is selected from the group consisting of manganese, cobalt, and mixtures thereof. 7 i 7 References Cited in the file of this patent UNITED STATES PATENTS V Smith Aug. 17, 1954'

Claims (1)

1. IN A PROCESS FOR THE PREPARATION OF A NAPHTHALENE CARBOXYLIC ACID WHEREIN A CATALYTIC REFORMATE BOTTOMS FRACTION IS REACTED WITH MOLECULAR OXYGEN-CONTAINING GAS IN THE LIQUID PHASE AND IN THE PRESENCE OF A CATALYST COMPRISING IN CONJOINT PRESENCE BROMINE AND A HEAVY METAL OXIDATION CATALYST, THE IMPROVEMENT OF THE STEP, PRIOR TO SUCH REACTION, OF SEPARATING FROM SAID CATALYTIC REFORMATE BOTTOMS FRACTION THOSE HYDROCARBONS HAVING A TRUE BOILING POINT AT 200 MM. HG ABSOLUTE PRESSURE OF ABOVE 405*F. WHEREBY INHIBITION OF THE OXIDATION REACTION IS AVOIDED.