US3310594A - Method for improving the quality of aromatic compounds - Google Patents

Description

March 1967 R. E. PETERSON ETAL 3,310,594 j METHOD FOR IMPROVING THE QUALITY OF AROMATIC CQMPOUNDS Filed June 23, 1965 RODNEY E. PETERSON ELDON M. SUTPHIN United States Patent C) 3,310,594 METHOD FOR IMPROVING THE QUALITY OF AROMATIC COMPOUNDS Rodney E. Peterson, Oakmont, and Eldon M. Sutphin,

Pittsburgh, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Filed June 23, 1965, Ser. No. 466,256 Claims. (Cl. 260672) This invention relates to a method for the production of hyperpure dealkylated aromatic compounds from pctroleum-derived alkyl aromatics and more particularly, it relates to a method for producing benzene which substantially exceeds standard commercial specifications by the hydrodealkylation of petroleum-derived alkyl aromatics.

At one time a rather static benzene market was largely supplied with benzene obtained as a by-product of the well developed but stabilized coal carbonization industry. Recovery of benzene from crude petroleum in which it usually occurs as a very minor constituent was not a significant factor. However, in recent years the rapid growth in the synthesis of upgraded chemicals from benzene such as synthetic rubbers, plastics, detergents and fine chemicals has caused a rapidly increasing and fluctuating demand for benzene which could not be supplied by the coal carbonization industry.

Fortuitously, benzene has lately been produced in relatively large amounts as a by-product of the petroleum naphtha reforming process concurrently with this increasing demand. Various alkyl aromatics such as toluene and the xylenes, which are also produced in the naphtha reforming process, can be dealkylated as a further source of benzene. In this expanding market cycles of over capacity and under capacity have been a natural occurrence. These cycles are expected to continue into the future as the result of future growth and adjustments to changing economic conditions.

Concomitant with this increase in benzene usage is a demand by many users, sometimes without regard to process requirements, for benzene which surpasses the standards of established commercial specifications. In view of this fluctuating and highly competitive market for benzene, it would be most advantageous for a benzene supplier to be able to provide material of a quality that would exceed the most rigid specifications at no greater cost than lower specification material. Thus, not only could he fulfill everyusers requirements, but in periods of over capacity he could'easily sell his entire output, since users, with cost being equal, will buy the highest specification material whether or not it is required in their process. In the long run this would lead to a general upgrading of benzene and with the ready availability of a purer material should lead to new usages. In accordance with our invention a hyperpure benzene is produced from the alkyl aromatic by-products of a naphtha reforming process at no greater cost than less pure commercial grades of benzene. V

In reforming petroleum hydrocarbons a naphtha fraction is first subjected to a hydrogenation-purification step to eliminate poisons to the usually used platinum reforming catalyst. In the reforming step, conducted in the presence of an excess of hydrogen under suitable conditions of temperature and pressure, naphthenic constituents are converted to aromatics, primarily benzene, toluene, xylene and ethyl benzene. These aromatics are separated from the reformate by solvent extraction and may be distilled into exceedingly pure fractions.

Benzene is classified into a number of grades generally indicative of its purity. Nitration-grade benzene carries the most rigid standard commercial specification as set 'ice forth in ASTM D835-50. Under this specification its acid wash color, the most sensitive and significant test, must not be greater than No. 2 on the acid wash color scale. In this test a benzene sample is agitated with 96 percent sulfuric acid and the resulting color of the acid layer is compared with a set of color standards numbered from 0 through 14 with 0 being the color of distilled water.

With strict adherence to the proper processing conditions, it has been possible heretofore to make nitrationgrade benzene by the demethy-lation of toluene without any further treatment after the demethylation other than the customary separative procedures. If the demehylated product does not meet the specifications for nitrationgrade benzene, treatment with clay can bing the acid wash color down to No. 2, however, the attainment of a significantly lower number is not practically attainable by clay treatment since the clay quickly loses its effectiveness and must be frequently replaced at a prohibitive expense. Analysis of the untreated demethylation eflluent by chromatographic and mass spectroscopic analysis for color producing bodiesvor impurities has failed to identify any such substances. Notwithstanding this, we have made the surprising discovery that by an appropriate modification of the process, the resultant product will far exceed the rigid specifications for nitration-grade benzene. Our invention is in part predicated upon this discovery.

In our process an alkyl aromatic stream such as a stream of toluene from the reformate separation is subjected to an integrated dual treatment, first hydrogenating with an excess of hydrogen under suitable conditions to demethylate the toluene and second treating in the presence of a relatively small amount of hydrogen under appropriate conditions to ensure that the product will exceed the most rigid commercial specifications. According to our process benzene can be produced with an acid Wash color as low as 0+, which is almost water white under the test. We accomplish this by immediately subjecting the demethylation efliuent to an elevated temperature and pressure in the presence of hydrogen and a solid particulate material. We do not know what direct effect, if any, that this has on the effluent other than the discovery that the benzene product obtained after the final distillation far exceeds the specifications for nitrationgrade benzene. Knowing that at least three separate purifying-hydrogenation operations as well as the associated purifying-separative procedures are involved from the original refinery distillation through this demethylation, it is wholly unexpected and highly surprising that a further treatment of this essentially pure material under these conditions would produce a strikingly superiorspecification material.

The bromine index of benzene is frequently used in commercial dealings in substitution of or to supplement the acid wash color test although it is not a part of the oflicial specifications. In typical examples the eflluent from the toluene demethylator exhibited a bromine indeX of about 20 as determined by ASTM D149l-60. This without further treatment is superior by several orders of magnitude to material produced by prior processes even after special treatment. For example, in US. Patent No. 2,701,267, crude benzene obtained by the steam distillation of wash oil used in the recovery of light oil from coal distillation gases is prepurified and then is subjected to a catalytic treatment with a large quantity of hydrogen at elevated temperature and pressure. This gives a final benzene, stated to be pure, having a bromine number of 0.2 which corresponds approximately to a bromine index of 200. It is therefore highly unexpected that the bromine index of the demthylation effluent, which is lower by a factor of about ten than the pure benzene resulting after final treatment under this patent, can be substantially reduced by our treatment. Despite this, we have made the surprising discovery that, if the demethylation efiluent is subjected to suitable conditions of temperature and pressure in the presence of a solid particulate material and a small amount of hydrogen, a benzene having a bromine index less than five and in many instances under 1.0 is produced.

The drawing illustrates an arrangement for carrying out our invention. Toluene 1 from the naphtha reformate separation admixed with recycle toluene is introduced into the system and hyperpure benzene 2 is obtained as the product. The toluene is first mixed with an excess of hydrogen 3 and the mixture heated prior to introduction into the demethylation unit 4. After demethylation, the effluent is cooled and the gases removed in gas-liquid separator 5 and in stripper 6. The benzene-rich eflluent from the stripper is treated in upgrading unit 7 to reduce the acid wash color and bromine index to an extremely low value. After gas-liquid separation in 8, the liquid effluent is separated in fractionator 9 into hyperpure benzene 2 as the main product as well as a more volatile fraction 10, unreacted toluene 11 suitable for recycling, and less volatile by-products 12. This less volatile bottoms product can be further separated into one or more of its components in a hyperpure state, if desired, including naphthalene, biphenyl, -fluorene, phenanthrene, and pyrene or this fraction may be fed into the refinery fuel oil stream.

In more specific detail the toluene-hydrogen feed is sequentially heated in heat exchangers 15 and 16 by the demethylator efiluent stream 17 and in furnace 18 fired with refinery waste gases 14 to bring the mixture to re action temperature for thermal demethylation. This reaction occurs between about 1150" and 1800 F. with 1250 to 1350 F. being the preferred range and at a pressure of about 100 to 1000 p.s.i.g., preferably in the range of 400 to 600 p.s.i.g. An excess of 1.5 to 20 mols of hydrogen per mol of hydrocarbon is generally used with the preferred molar ratio being 3 to 8 mols of hydrogen per mol of hydrocarbon. The mixture is retained in reactor 4 for sufiicient time, from one to 600 seconds and preferably from 10 to 100 seconds, to obtain the desired demthylation. This procedure as described merely represents a preferred mode of operation. Demethylation may also be performed hereunder in a catalytic reaction using a suitable dealkylation catalyst at a temperature somewhat lower, such as 1000 to 1400 F., than is used in the non-catalytic reaction.

Heat economy is effected by utilizing the hot efHuent 17 from the demthylator to sequentially heat the feed in heat exchanger 16, to heat the fractionator bottoms in heat exchanger 20, to drive the stripping column in heat exchanger 21 and to provide the initial heating of the feed stream in heat exchanger 15. After passing the stream through cooler 19 which utilizes a suitable fluid cooling stream, the gases primarily hydrogen and methane, are separated from the liquids in the gas-liquid separator 5 with final separation taking place in stripper 6. Gas and vapor streams 22 and 24 from these two units pass to the vapor recovery unit 26 from which separated liquids 27 are introduced into the upgrading unit along with the bottoms 28 from the stripper. A portion 23 of the gases from the gas-liquid separator are introduced into the upgrading unit after heating in exchanger 29 to the treating temperature.

This upgrading operation is broadly carried .out at about 150 to 600 F., at 100 to 1000 p.s.i.g., at a liquid hourly space velocity of 1 to 20 volumes of liquid per hour per volume of solid particulate material, and using 10 to 1000 s.c.f./bbl. of hydrogen of to 100 percent purity. Preferred conditions for operation are 200 to 500 F., 300 to 500 p.s.i.g., a liquid hourly space velocity of 1 to 8 and 50 to 500 s.c.f./bbl. of hydrogen of 50 to 100 percent purity. Suitable solid particulate mate- 4. rials for use in the upgrading unit include the metals, metal oxides and sulfided metals of Group VI (left column) and Group VIII of the Periodic Table, alone or in admixture, distended on non-acidic supports. These include nickelcobalt-molybdenum, cobalt-molybdenum, sulfided nickel, sulfided tungsten-nickel, sulfided tungsten on such nonacidic carriers as alumina, clay, and kieselguhr and the like. Primary process control is effected by varying the liquid hourly space velocity. After gas-liquid separation in 8, the stream 30 is fractionated into super specification benzene and the other previously described fractions.

The gases 31 from the gas-liquid separator 8 are passed to the vapor recovery unit 26 and treated with the other gas streams. A mixture 32 consisting essentially of hydrogen and methane are recycled through compressor 34 for reuse in the system. A small side stream 35 is bled off and makeup hydrogen 36 is added to the recycle stream to maintain the concentration of hydrogen in the system at a desired level.

The following is a specific example of the operation of the invention in which hyperpure benzene is produced from toluene. Fifteen thousand lbs./hr. toluene from the reformate extraction which includes a relatively small proportion of recycle toluene from the fractionator is combined with a mixed stream of reformer off-gas and recycle hydrogen having a net hydrogen content of about 75 mol percent to form a hydrogen to toluene mol ratio of 3.5 to 1. This mixture is preheated to about 1170 to 1250 F. and charged to the demethylator operating at a pressure of about 460 p.s.i.g. Two reactors in. series are used with cooling between stages to maintain the desired temperature of reaction. After a total contact time of about 40 seconds, the demethylated efitluent is quenched by heat exchange with the input stream. After cooling the efiluent stream in the manner previously indicated, the gases are separated in the gas-liquid separator operating at F. and 400 p.s.i.g. with final separation occurring in the stripper operated at 450 F. and 310 p.s.i.g.

These stripper bottoms are fed directly to the treating unit at a rate of 4 liquid volumes per hour per volume of solid particulate material together with 200 s.c.f. of gas-liquid separator off-gas containing about 50 percent hydrogen per barrel of liquid feed. The treating unit is operated at a temperature of 450 F. and 350 p.s.i.g. The solid particulate material in the treating unit is a presulfided mixture containing 2.3 percent nickel, 1.4 percent cobalt, and 9.2 percent molybdenum supported on alumina. After separation from the gases, the liquid efiluent from the treating unit is fractionated to produce 10,700 pounds of hyperpure benzene per hour. The following is a representative analysis of this operation:

It is of interest to note that the improvement in'acid wash color does not show up until fractionation has been accomplished while the improvement in bromine index does not appear to be significantly improved by frac-. tionation.

Of particular significance is the beneficial results obtainable at low rates of hydrogen feed to the treating unit. Higher hydrogen feed rates to the treating unit than those indicated, although not detrimental to our process, are wihout particular advantage. Of further significance are the excellent results obtained after long usage of the solid particulate material. In many runs over the range of preferred conditions of operationthe benzene product consistently displayed an acid wash color of 1- or better and a bromine index under 5, indicating good tolerance to reasonable variations in operation.

It is of critical importance to the successful economical utilization of our process that it be integrated into an energy conserving system as described. Although toluene was specifically described as the feed material, other petroleum-derived materials are also suitable including xylene, ethyl benzene and other monoalkyl and polyalkyl benzene compounds alone or in admixture with toluene. These aromatic compounds are also converted to hyperspecification benzene at high conversion efficiency and good selectivity. In addition, this process can be used to produce hyperpure dealkylated polynuclear aromatic compounds, such as naphthalene, from the corresponding alkylated polynuclear compounds.

It is to be understood that the above disclosure is by way of specific example and that numerous modifications and variations are available to those of ordinary skill in the art without departing from the true spirit and scope of our invention.

We claim:

1. A process for improving the quality of dealkylated aromatic compounds which comprises heating a compo sition selected from the group consisting of an alkyl aromatic compound and a mixture of alkyl aromatic compounds and about a 1.5 to 20 molar excess of hydrogen to a temperature and pressure between about 1000 to 1800 F. and 100 to 1000 p.s.i.g. for about one to 600 seconds, separating the gases from the liquid effiuent, subjecting the substantially sulfur-free liquid efiluent to a temperature and pressure between about 150 to 600 F. and 100 to 1000 p.s.i.g. in the presence of about to 1000 s.c.-f. of hydrogen per barrel of liquid efiluent and a solid particulate material selected from the group consisting of metals, metal oxides and sulfided metals of Group VI (left column) and Group VIII of the Periodic Table, and mixtures thereof, distended on a non-acidic support, and separating the treated effluent into fractions of hyperpure dealkylated aromatic compounds.

2. A process for the production of benzene having an acid wash color less than No. 2 which comprises heating a mixture of toluene and about a 3 to 8 molar excess of hydrogen to a temperature and pressure between about 1100 to 1350 F. and 400 to 600 p.s.i.g. for about 10 to 100 seconds, cooling the effluent and separating the eflluent gases from the liquid effluent, subjecting the substantially sulfur-free liquid efiluent at a temperature and pres- 3. 'A method in accordance with claim 1 in which hyperspecification benzene is separated from the treated efiluent.

4. A method in accordance with claim 1 in which the alkyl aromatic compound is toluene and hyperspecification benzene is separated from the treated efiluent.

5. A method in accordance with claim 1 in which the liquid etfiuent is subjected to a temperature and pressure between about 200 and 500 F. and 300 to 500 p.s.i.g.

in the presence of about 50 to 500 s.c.f. of hydrogen per barrel of liquid efiluent at the rate of 1:1 to 8:1 volumes of liquid effluent per hour per volume of solid particulate material.

6. A method in accordance with claim 5 in which byperpure benzene is separated from the treated eflluent.

7. A process for the production of hyperpure benzene which comprises subjecting a substantially sulfur-free benzene product to a temperature and pressure between about 150 to 600 F. and to 1,000 p.s.ig. in the presence of about 10 to 1,000 s.c.f. of hydrogen pe-r ba-rrel of benzene and a solid particulate material selected from the group consisting of metals, metal oxides and sulfided metals of Group VI (left column) and Group VIII of the Periodic Table, and mixtures thereof, distended on a non-acidic support, and separating hyperpu-re benzene from the treated efiluent.

8. A process for improving the acid wash color of benzene which comprises subjecting substantially sulfurfree benzene having an acid wash color after distillation greater than No. 2 on the acid wash color scale to a temperature and pressure between about to 600 F. and 100 to 1,000 p.s.i.g. in the presence of about 10 to 1,000 s.c.f. of hydrogen per barrel of benzene and a solid particulate material selected from the group consisting of, metals, metal oxides and sulfided metals of Group VI (left column) and Group VIII of the Periodic Table, and mixtures thereof, distended on a non-acidic support, and separating benzene havinga reduced acid wash color from the treated efiluent.

9. Aprocess in accordance with claim 8 in which the benzene feed possesses an acid wash color between about No. 2 and No. 6 and hyperspecification benzene having an acid wash colorless than about No. 2 is separated from the treated efiluen-t.

10. A process in accordance with claim 8 in which the benzene is subjected to a temperature and pressure between about 200 to 500 F. and 300 to 500 p.s.i.g. in the presence of said solid particulate material and about 50 to 500 s.c.f. of hydrogen per barrel of liquid efiluent.

References Cited by the Examiner UNITED STATES PATENTS 2,876,268 3/1959 Ciapetta et al. 260-674 2,957,925 10/1960 Oettinger 260-674 3,150,196 9/1964 Mason 260-672 3,213,150 10/1965 Cabbage .1..... 260-672 3,222,410 12/1965 Swanson 260-672 DELBERT E. GANTZ, Primary Examiner.

G. E. SCHMITKONS, Assistant Examiner.

Claims (1)

1. A PROCESS FOR IMPROVING THE QUALITY OF DEALKYLATED AROMATIC COMPOUNDS WHICH COMPRISES HEATING A COMPOSITION SELECTED FROM THE GROUP CONSISTING OF AN ALKYL AROMATIC COMPOUND AND A MIXTURE OF ALKYL AROMATIC COMPOUNDS AND ABOUT A 1.5 TO 20 MOLAR EXCESS OF HYDROGEN TO A TEMPERATURE AND PRESSURE BETWEEN ABOUT 1000* TO 1800*F. AND 100 TO 1000 P.S.I.G. FOR ABOUT ONE TO 600 SECONDS, SEPARATING GASES FROM THE LIQUID EFFLUENT, SUBJECTING THE SUBSTANTIALLY SULFUR-FREE LIQUID EFFLUENT TO A TEMPERATURE AND PRESSURE BETWEEN ABOUT 150* TO 600* F. AND 100 TO 1000 P.S.I.G. IN THE PRESENCE OF ABOUT 10 TO 1000 S.C.F. OF HYDROGEN PER BARREL OF LIQUID EFFLUENT AND A SOLID PARTICULATE MATERIAL SELECTED FROM THE GROUP CONSISTING OF METALS, METAL OXIDES AND SULFIDED METALS OF

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