US2381522A - Hydrocarbon conversion process - Google Patents

Description

Aug. 7., 1945.

M. M. STEWART HYDROCARBON CONVERSION PROCESS Filed March 3l, 1944 Patented Aug. 7, 1945 AUNITI-:D STATES PATENT oFFlcE 2,381,522 y maocmmou coNvnnsxoN rnocnss Meredith Marvin stewart, Beacon, N. Y., assigner to The Texas Company, New York, N. Y., a corporation of Delaware Application March 3l, 1944, Serial No. 528,830

2 Claims. (Cl. 19o-50) l l I case only small amounts of such hydrocarbons My invention relates to vhydrocarbon conversion processes, and particularly to processesfor the production of aromatic hydrocarbons of substantially motor fuel range. l

The production of -aromatic hydrocarbons such as benzene, toluene, xylenes, mesitylene, and the like, from petroleum fractions has previously been attempted in a number of different Ways. The cyclization of acyclic hydrocarbons and the dehydrogenation of .naphthenes have been pro-l posed for the production of aromatic hydrocarbons, but all such methods employ relatively low boiling charge stocks, which are expensive raw materials in view of their utility for other purposes. 4

An object 'of my presentv invention is to provide'a process for the production of aromatic hydrocarbons of substantially motor fuel range from` charge stocks comprising relatively inexpensive high boiling petroleum fractions.

A further object of my invention is to provide a method for utilizing very refractory petroleum fractions for the production of aromatic hydrocarbons of substantially motor fuel range,

Another object of my invention is to provide a process for the production of low boiling petroleum fractions of substantial aromatic content from cycle gas oils and other high boiling petroleum fractions.

Other objects and advantages of my invention will be: apparent from the following de-l scription:

The formation of aromatic hydrocarbons of substantially motor fuel range is eiected in accordance with my present invention by the indrocarbons and substantially motor fuel range cyclic hydrocarbons which are at least partially saturated, i. e., less unsaturated than aromatics.

. In this reaction, the cyclic hydrocarbons which are at least partially saturated serve as hydrogen donorsor hydrogen carriers, and are dehydrogenated simultaneously with the hydrolgenolysis (i. e., cleavage and hydrogenation) of the polycyclic aromatics to form lower boiling aromatics. In this manner aromatic hydrocarbons of substantially motor fuel range may be formed from both reactants used in the process.

The highest yields of low boiling aromatics `may be obtained if partially saturated cyclic hydrocarbons, such as cyclo-oleflns, supply all of the hydrogen for the hydrogenolysis of the polycyclic aromatics. However, partially or completely saturated cyclic vhydrocarbons may also serve merely as hydrogen carriers, in which ,-2 teraction of high boiling polycyclic aromatic hywill be required and the bulk of the hydrogen may be supplied as free gaseous hydrogen. In either case, superatmospheric pressure will favor the'hydrogenolysis reaction. Irrespective of the hydrogen source, at least two atomic weights of -hydrogen and preferably 4-10 atomic weights, should be provided in the reaction mixture per molecular weight of polycyclic aromatic hydrocarbon.

The hydrogenolysis is preferably effected with the reaction mixture substantially in ,--the` liquid phase, or with at least the polycyclic aromatic hydrocarbons in the liquid phase. tively high reaction temperatures employed, the

'pressure required to maintain a liquid phase will usually be suilicient .to obtain a favorable equilibrium in the hydrogenolysis reaction. However. a pressure above the vapor pressure of the reaction mixture may readily be provided by the introduction of hydrogen or an inert gas such as nitrogen or flue gas. In any case, the pressure should be at least lbs. per square inch,

gauge, and is preferably maintained within the range 250-500 lbs. per square inch.

The temperature for the hydrogenolysis reacl tion should be at least 600 F. in order to obtain a'reaction velocity of practical magnitude. The

upper temperature limit for the reaction should' not exceed the critical temperature of theY reaction mixture, and should not be sufficiently high to permit undue cracking of the primary' amples of each of these classes are anthracene,v

Z-amyl-n'aphthalene, and triphenylmethane. I prefer to employ compounds having a'condensed structure of three .or more rings, such as a'cenaphthene, fluorene, anthracene, phenanthrene, 'y aliphatic substituted derivatives. 'I'hese polycyclic aromatics may be employed` as pure compounds or as relatively Apure aromatic fractions,

At the rela'- pyrene, and their homologues and v if desired. However, it is vgenerally sumcient to employ any high boiling hydrocarbon fraction i which contains substantial amounts of the polycyclic aromatics. Suitable fractions of this character are cycle gas oils, i. e. recycle stocks of gas oil range which are readily obtainable from petroleum refinery crackingl operations. refractory'cycle gas oils obtained in thermal cracking to maximum gasoline yields are very satisfactory sources of polycyclic aromatics.

Acyclic components of such high boiling fractions undergo cracking in my process, simultaneously with the hydrogenolysis of the aromatic components. y

The hydrocarbons which may be used as hydrogendonors or hydrogen carriers in this reaction comprise the partially or completely sat- Highly urated cyclic hydrocarbons of substantially motor fuel range. The cycloparains and cycloolens having iiv or six carbon atom rings are examples of this class .of compounds. I generally prefer to employ hydrocarbons having six carbon atom rings, i. e., the hydro-aromatics. The various hydrogenated derivatives of benzene, toluene, the xylenes, mesitylene, isopropyl benzene, and

naphthalene, are examples of suitable compounds of this type. Similarly to the polycyclic aromatics, the cycloparaflins or cyclo-olens may be employed in my process in the form of pure compounds or relatively pure fractions, if desired. However, any hydrocarbon mixtures containing substantial amounts of cycloparains or cyclooleflns may be used for this purpose. bon mixtures such as naphthenic petroleum fractions are most advantageous from a cost standpoint, and I prefer to employ a naphthenic `straight run or distillate naphtha. or equivalent petroleum fraction.

'I'he ratio-of cycloparafiins -or cyclo-olens to polycyclic aromatics in the reactionA mixture should be suiciently high to provide adequate hydrogen for the hydrogenolysis. If no egaseous hydrogen is employed in conjunction with the hydrogen donor hydrocarbons, the concentration of the latter is preferably substantially in excess of the equivalent concentration of poly-r' tact with the gaseous hydrogen and` with the liquid polycyclic aromatics for efficient hydrogen transfer. Only a minor fraction of the concentration requred to supply all of the hydrogen will be sufficient for this method of operation.

The hydrogenolysis reaction may be effected merely by contacting the hydrogen-donor cyclic hydrocarbons, or gaseous hydrogen and hydrogen-carrier cyclic hydrocarbons, with the liquid polycyclic aromatic hydrocarbons at the reaction temperature. The reaction may be carried out continuously or by batch methods, as desired, and various types of apparatus may be employed for either type of operation. A directflred preheater of the pipe still type, in conjunction with a relatively large capacity reaction vessel or soaker," will serve for continuous operation with reaction mixtures which are substantially completely in the liquid phase. For reaction mixtures containing gaseous hydrogen, or in which the hydrogen donor hydrocarbons are largely in the vapor Hydrocar- 'completely in the liquid phase.

phase. other types ot apparatus are desirable in order to secure adequate contact of the :gas and liquid phases. Tubular reactorsoperated with turbulent ow, or tower reactors employing countercurrent flow of the gasfand liquid phases, may be used for continuous operation.

A preferred method of continuous operation with the charge hydrocarbons substantially completely in the liquid phase is illustrated diagrammatically in the accompanying drawing. As may be seen from this now diagram, a mixture of a light naphthenic petroleum fraction and a heavy fraction containing polycyclic aromatics is charged to a preheater l where it is heated to the reaction temperature, e. g., 850 F. The mixture then passes to a reaction vessel or soaker 2, having s'uicient volume to provide a residence time of 2-3 hours. 'lhereaction pressure in the high to maintain the hydrocarbons substantially Hydrogen, or recycled process gas supplied by compressor 3 may be utilized to increase the reaction pressure above the vapor pressure of the hydrocarbon mixture, if desired.

The reaction mixture drawn from the reactor 2 is suitably charged to a primary fractionator 4, at sufficiently reduced pressure toeiect continuous distillation, taking overhead the hydrocarbons of motor fuel range and lighter.

The primary fractionator is suitably adapted to permit the withdrawal of a recyclehigh boiling fraction as aside stream, vwhich may then be mixed with the high boiling' aromatic charge as shown in the drawing. When operating in this manner, any tarry reaction products formed in the process may be separately withdrawn as bottoms from the primary fractionator.

The overhead from the primary fractionator 4 comprises lowboiling aromatics formed by the dehydrogenation of the naphthenes and the hy- I drogenolysis of the polycyclic aromatics in the charge mixture, together with liquid and gaseous products from the thermal cracking of other components of the high boiling charge stock. This mixture may then be fractionated by any of the usual methods. In `the modication shown, the overhead from fractionator 4 is charged to a secondary fractionator 5 from which the overhead fraction passes to condenser 6 and gas separator 1. The liquid condensate withdrawn`4 from the separator 1 comprises a light aromatic motor fuel fraction which may be further stabilized and nished by conventional methods.. The bottoms from the secondary frac- Ationator 5 comprise a. heavy aromatic naphtha which may be sweetened and further treated as desired for blending in motor fuels or for use as an industrial solvent.

My invention will be further illustrated by the following specific example:

` i Eample 'and approximately 116 F. aniline point in a ratio of about two volumes of naphthenic distillate per volume of gas oil. The combined feed is charged through a pipe-still heater where the liquid temperature is raised to about 850 F. The heated charge, at a pressure of about 450 lbs. per square inch, then lpasses through a reascissa action vessel or "soaker," the ilow rates being adjusted t maintain a highliquid level in the reaction vessel with an average residence time of approximately 90 minutes. The product stream from the soaker charged to a tar stripper to separate tarry products and to recover a gas oil side stream for recycling. The overhead from the tar stripper is then stabilized and fractionated to obtain a 320 F. end point motor fuel blending stock and a heavy aromatic naphtha suitable for industrial solvent uses. The light product is incorporated in an isopentanealkylate-straight run gasoline base' stock, in a concentration of approximately 20% by volume,

. to produce an aviation grade motor fuel of superior rich mixture anti-knock characteristics.

It is to be understood, of course, that the above example is merely illustrative, and does not limit the scope of my invention. Other charge stocks may be substituted for those specified in the example, and the reaction conditions may be varied in accordance with the .foregoing description. My processv is applicable to the hydrogenolysis of any polycyclic aromatic hydrocarbon, and any such hydrocarbon or fraction may be incorporated in the feed in any thermal reforming process employing a hydro-aromatic or naphthenic naphtha charge stock. The use of any equivalents or modifications of procedure which would naturally occur to those skilled in the art is included in the scope of my invention. Only such limitations should be imposedy on the scope of this invention as are indicated in the appended claims.

1. A process for the production of aromatic hydrocarbons of motor fuel range from gas oil produced by cracking mineral oil, said gas oil containing in substantial amount, polycyclic aromatic hydrocarbons having a condensed structure of at least 3 rings, which comprises passing said gas oil through a conversion zone, introducing to said zone cyclic paraiiin and olefin hydrocarbons having 6 carbon atom rings,

providing in the resulting reaction mixture during passage through the reaction zone 4 to 10 atomic weights of hydrogen per molecular weight of polycyclic aromatic hydrocarbons, maintaining the conversion zone at a temperature in the range 750 to 850 F. and under a pressure suiiicient to maintain the feed hydro-l carbons substantially in liquid phase, maintaining a hydrocarbon vresidence time within the conversion zone of about 2 to 3 hours, discharging products of reaction from the conversion zone, separating from said discharged products a gaseous fraction and a gasoline fraction rich in' aromatic hydrocarbons and recycling said gas fraction at least in part to said conversion zone.

2; A process for the production of aromatic hydrocarbons of motor fuel range from gas oil produced by cracking mineral oil, said gas oil containing, in substantial amount, polycyclic aromatic hydrocarbons having a condensed structure of at least 3 rings which comprises passing said gas oil characterized by having an A. P. I. gravity of about 28 and an aniline point of-about 116 through a conversion zone, introducing to said zone a naphtha fraction boiling in the range about 200 to 225 F. and containing about 26% naphthenes by volume, adding said naphtha to the conversion zone in the proportion of about 2.volumes per volume of gas oil, maintaining the conversion zone at a temperature in the range 750 to 850 F. and under a pressure sufficient to maintain the feed hydrocarbons substantially in liquid phase, maintaining a. hydrocarbon residence time within the conversion zone of about 90 minutes, discharg-

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