US3160671A - Method for increasing the yield of recoverable monocyclic aromatic hydrocarbons in thermal hydrodealkylation processes - Google Patents

Description

United States Patent C) 3,160,671 METHOD FOR mCREASlNG 'IHE YELD F RECOVERABLE MONOCYCLEC ARGMATIC HYDRQiIARBGNS 1N THERMAL HYDRODE- ALKYLATION PROQESSES Stanford I. Feigelman, Haddonfield, N..l., and Eugene Aristotl, Newtown Square, Pa, assignors to The Atlam tic Refining Company, Philadelphia, Pa, a corporation of Pennsylvania No Drawing. Filed Mar. 16, 1961, Ser. No. 94,675 1 Claim. (Cl. 260-672) This invention relates to a method for hydrodealkylating alkylated monocyclic aromatic hydrocarbons. More particularly, this invention is concerned'with increasing the yield of recoverable monocyclic aromatic hydrocarhens in the thermal hydrodealkylation processes.

The process of subjecting hydrocarbon fractions containing alkylated monocyclic aromatic hydrocarbons to high temperatures and pressures in the presence of hydrogen in a reaction zone devoid of catalytically active material in order to hydrodealkylate the alkylated monocyclic aromatics to benzene has long been known.

The instant invention is concerned with an improvement to the aforementioned process whereby the yield of recoverable monocyclic aromatic hydrocarbons from the hydrodealkylation process is increased.

It is an object of this invention to increase the yield of recoverable monocyclic aromatic hydrocarbons in a process of thermal hydrodealkylation of an alkylated monocyclic aromatic-containing hydrocarbon fraction.

It is a further object of this invention to increase the yield of recoverable monocyclic aromatic hydrocarbons in a process of thermal hydrodealkylation of a toluenecontaining hydrocarbon fraction.

It is a further object of this invention to increase the yield of recoverable monocyclic aromatic hydrocarbons in a process of thermal hydrodealkylation of toluene.

Additional objects of this invention will be apparent from the description and claim that follow.

The present invention may be described briefly as a method for increasing the yield of recoverable monocyclic aromatic hydrocarbons, particularly benzene and toluene, from a normally liquid hydrocarbon charge fraction containing alkylatecl monocyclic aromatics in a thermal hydrodealkylation process. This is accomplished by subjecting an alkylated monocyclic aromatic hydrocarboncontaining fraction, together with diphenyl hydrocarbons, to temperatures ranging from 950 F. to l450 F. in a reaction zone devoid of catalytically active material, i.e. thermal conversion. In addition to the elevated temperatures, the feed hydrocarbons together with the added dipehnyl hydrocarbons are subjected to pressures ranging from 400 pounds per square inch to 10,000 pounds per square inch for times ranging from 1 second to 600 seconds in the presence of hydrogen in amounts ranging from 1.0 to 20.0 moles of hydrogen per mole of the normally liquid hydrocarbon charge to the reactor, i.e. both feed and diphenyl hydrocarbons, based on the average molecular Weight of these hydrocarbons charged. The unconsumed hydrogen is separated from the reactor efiluent and recycled to the reaction zone together with makeup hydrogen.

It will be noted that the recycle hydrogen may contain small amounts of normally gaseous hydrocarbons such as methane, but these hydrocarbons are not included in the calculation of the amount of normally liquid hydrocarbon charge to the reactor. The amount of hydrogen consumed by the reaction depends to a considerable degree upon the particular charge hydrocarbons employed. In general, however, this amount will be at least 1 mole of hydrogen per mole of monocyclic aromatic hydrocarbon converted. A portion or all of the diphenyl hydrocarbons contained ice in the etliuent from the reactor likewise may be recycled to the reaction zone together with any makeup diphenyl hydrocarbons that may be required for the purpose of this invention.

The diphenyl hydrocarbons suitable for use in this invention include diphenyl, methyl diphenyl, diphenyl methane, diphenylenemethane (fiuorene), dimethyl diphenyl, methyl diphenyl methane, diphenyl ethane, diphenyl benzene and similar hydrocarbons, and including mixtures of two or more of these hydrocarbons. The amount of diphenyl hydrocarbons introduced into the reaction zone along with the alkylated monocyclic aromatic hydrocarbon-containing charge may vary between 1 mole percent and 15 mole percent based on the total moles of normally liquid hydrocarbon charge to the reactor.

The liquid product of the reaction after the removal of hydrogen is further fractionated to obtain the desired benzene product and separately recover the alkylated monocyclics which can be recycled for further conversion to benzene. Thus, by recoverable monocyclic aromatic hydrocarbons is meant benzene and alkylated monocyclic aromatic hydrocarbons which can be recycled for ultimate conversion to benzene.

Although the hydrodealkylation process may be carried out within the process limits set forth above, some what narrower ranges of process conditions are preferred for optimum conversion with specific charge stocks. For example, in a preferred embodiment of this invention toluene is hydrodealkylated to benzene at temperatures ranging between 1200 F. and 1400 F. at pressures ranging between 400 p.s.i. and 800 p.s.i., in particular about 600 p.s.i., with reaction times of from 20 to 30 seconds and particularly about 25 seconds utilizing hydrogen in an amount ranging from 2.5 moles of hydrogen per mole of normally liquid hydrocarbon charge to the reactor to 6 moles of hydrogen per mole of hydrocarbon and, in particular, 4 moles of hydrogen per mole of the'normally liquid hydrocarbon charge. Under these conditions, it is preferred to employ from 2 mole percent to 7 mole percent of diphenyl hydrocarbons based on the total moles of normally liquid hydrocarbon charge to the reactor.

A variety of charge stocks may be employed for conversion by thermal hydrodealkylation in accordance with the instant invention. It is necessary, however, that such charge stocks contain alkylated monocyclic aromatic hydrocarbons in order that the purposes of the invention may be realized, namely, increasing the yield of recoverable monocyclic aromatic hydrocarbons in a thermal hydrodealkylation process.

Charge stocks which contain these compounds and which may be utilized in the process of this invention include virgin or straight-run hydrocarbon distillate fractions, furnace oil fractions boiling between about 300 F. and 650 F. resulting from the catalytic cracking or" a petroleum gas oil fraction, fractions obtained by the catalytic reforming of hydrocarbons, coal tar aromatic fractions and alkylated benzene hydrocarbons obtained as a result of the alkylation of benzene to produce a starting material for alkyl aryl sulfonate production. The alkylated monocyclic aromatic hydrocarbons include toluene, the Xylenes, ethyl benzene, trimethyl benzene such as mesitylene, higher alkylated benzenes wherein the alkyl group may contain from 6 to 12 carbon atoms or more and wherein the benzene ring may have additional alkyl side chains. It will be understood, of course, that with certain types of higher alkylated monocyclic aromatics wherein there are several side chains on the ring or where the side chain may be long it may not be possible to convert the alkylated monocyclic into benzene in a single pass. In accordance with this invention, however, the yield of recoverable monocyclic aromatics is increased with the result that the ultimate conversion to benzene is increased, since the alkylated product from any single pass may be recycled.

The following example is provided to illustrate a specific embodiment of the invention.

EXAMPLE Two continuous alkylation runs were carried out in a tubular reactor which was devoid of catalytically active material. The charge composition, reaction conditions, and products obtained are set forth in the table.

Table Run 1st 2d Charge Toluene-100 Toluene-96.9

mole percent mole percent;

Diphenyl- 3.1 mole percent Reaction conditions:

Temperature, F 1, 296 1, 290 Pressure, p.s.i 600 000 Reaction time, seen 21. 2 21. 2 Mole ratio, H22 Hydrocarbon.. 4. 0 4.1 Monocyclic aromatics recovered in the product, mole percent:

Benzene 73. 3 37. 1 Toluene 22. 2 28. 9

It will be seen that in the run where no diphenyl was employed 95.5 mole percent recovery of benzene and toluene was obtained, showing that 4.5 mole percent monocyclic ring compounds were lost. In the second run wherein diphenyl was used the charge contained 96.9 percent toluene and a recovery of benzene and toluene of 96.0 mole percent was obtained showing that apparently only 0.9 mole percent of monocyclic ring compounds were lost. However, it was found by analysis that 0.45 mole percent of the diphenyl was lost which would correspond to a production of 0.9 mole percent benzene so that the corrected value of monocyclic aromatics lost amounted to 1.8 percent. Thus, by comparing the runs it is apparent that by introducing diphenyl into the reaction zone an increase of 2.7 mole percent of recoverable monocyclic aromatic compounds was obtained. Since toluene is recycled to extinction in a commercial process it will be seen quite readily that in a recycle operation if an increase of 2. percent of recoverable aromatics is obtained per pass, the instant invention provides a method of markedly increasing the total recovery of benzene in a hydrodealkylation process.

We claim:

In a process for hydrodealkylating alkylated monocyclic aromatic hydrocarbons in an alkylated monocyclic aromatic-containing hydrocarbon fraction wherein such fraction is subjected to thermal conversion in a reaction zone devoid of catalytically active material in the presence of hydrogen at a temperature ranging from 950 F. to 1450 F. at a pressure ranging from 400 pounds per square inch to 10,000 pounds per square inch for a time ranging from 1 second to 600 seconds with the amount of hydrogen ranging from 1.0 to 20.0 moles of hydrogen per mole of the normally liquid hydrocarbon charge, the improvement which comprises increasing the yield of recoverable monocyclic aromatic hydrocarbons by introducing diphenyl into the reaction zone together with the alkylated monocyclic aromatic-containing hydrocarbon fraction, said diphenyl being in an amount ranging from 1 mole percent to 15 mole percent based on the total moles of normally liquid hydrocarbon charge to the reaction zone, and recovering the monocyclic aromatic hydrocarbons.

References Cited in the file of this patent UNITED STATES PATENTS 1,230,975 Alexander June 26, 1917 2,335,596 Marschner Nov. 30, 1943 2,739,991 Hervert Mar. 27, 1956 2,929,775 Aristofi et al. Mar. 22, 1960 UNITED STATES- PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,160,671 December 8, 1964 Sta'nf ordfL, Eeigelm'an er; 'al. It is hereby certified. that err or appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 8 for- R2," ead 2.7

Signed and sealed this 20th day of'April 1965.

(SEAL) Attest:

ERNEST W. SWIDER- I EDWARD J BRENNER Attesting Officer Commissioner of Patents Notice of Adverse Decision in Interference In Interference No. 95,417 involving Patent No. 3,160,671, S. I. Feigelman and E. Aristofi, METHOD FOR INCREASING THE YIELD OF RECOV- ERABLE MONOCYCLIC AROMATIC HYDROCARBONS IN THER- MAL HYDRODEALKYLATION PROCESSES, final judgment adverse to the patentees was rendered June 14, 1973, as to claim 1.

[Ofiicz'al Gazette July 2, 1,974.]