US2335596A - Refining of refractory hydrocarbons - Google Patents

Description

Nov. 30, 1943. v R. F. MARSCHNER REFINING' OF REFRACTORY HYDROCARBON Filed Dad. so, 1959 Patented Nov. 30, 1943 i Ranma or amac'rony r mnocanons Robert F. Mamnner, cmeasorm., minor u Standard i] Company, Chi

poration of Indiana eno, ma, a oor- Application December 30, 1939, Serial No. 311,857

s claims. (ci. 26o-.om

'I'his invention relates to the refining of refractory hydrocarbons and to the preparation from such stocks of high quality motor fuel, high solvency naphthas, condensed ring aromatic compounds and linked ring aromatic compounds.

An object of the invention is to provide an improved "method and means for refining and utilizing renery by-products containing large quantities of polymethyl-substituted polycyclic aromatics. Such hydrocarbons cannot be converted into motor fuel by the conventional cracking or reforming processes and since they are practically immune to such conversion processes they are usually .referred to as refractory stocks. One example of such refractory stock is the so-called polymer produced by the catalytic reforming or dehydro-aromatization of naphtha; the reforming product boiling above 400 or 450 F. or so-called polymer is a mixture of monoand polycyclic aromatics containing several side chains, particularly methyl groups. Similarly in cracking, particularly in catalytic cracking, the gas oil becomes more and more refractory with repeated recycling or multi-stage treatment and the final gas oil is practically worthless for further conversion; this final gas oil is a refractory stock which likewise contains large quantities of polymethyl substituted polycyclic aromatics. The invention is not limited to refractory stocks from these two sources since such stocks may likewise be obtained by the solvent extraction of various hydrocarbon mixtures or may be ob- An inspection of representative refractory stocks is as follows:

An object of the invention is to obtain valuable products from refractory hydrocarbons of the general type hereinabove indicated.

A further object is to produce from naphtha.

' gas oil or hydrocarbon charging stocks increased tained from destructive hydrogenation of car bonaceous materials, from coal tars, and from many other sources. The invention is, however, particularly applicable to the refining ot refractory cycle stocks from catalytic reforming or cracking since the utilization of such by-product material presents -a serious problem to the petroleum refining industry.

A refractory cycle stock owes its thermal stability to its condensed-ring and linked ring aromatic compound constituents. These constituents must be derivatives of relatively few aromatic compounds; naphthalene, diphenyl, phenanthrene, anthracene, with much smaller amounts of phenyl naphthalene and other higher homologues. The above-mentioned compounds contain 10-14 carbon atoms, whereas the gas oil cycle stocks contain 14-20 carbon atoms. with the difference of 3-6 carbon atoms made up mainly of methyl groups on the aromatic rings. These polycyclic aromatic hydrocarbons may, of course, contain other alkyl side chains than methyl groups, i. e. there willbe a certain number of ethyl groups, propyl groups, etc., but

a unique characteristic of such refractory hydrocarbons is the large number of methyl groups which are attached to the multi-ring structure.

yields of a motor fuel which is characterized by a high octane number, a relatively high total heat content and susceptibility to lead tetraethyl, a low acid heat number and a high stability against oxidation and gum formation. In catalytic reforming processes, catalytic aromatization, etc., considerable amounts of "benzene and toluene are formed even when heavy naphtha containing no sixand seven-carbon hydrocarbons is employed as a charging stock. Benzene, because of its low total heat content and high melting point, is not as satisfactory for an aviation fuel as dimethylor trimethyl-benzenes. Polycyclic aromatic hydrocarbons are, of course, unsuitable for motor fuel because of their low volatility. .An object of my invention is to provide an improved method and means for obtaining toluene and polymethylbenzene from refractory hydrocarbons. v

Polymethylbenzene is an outstandingly superior motor fuel. The heat of combustion of benzene is only 782 kilogram calories per gram molecular weight, while the heat of combustion of xylenes is about 1090 and of trimethylbenzene is about 1240. This means that on a weight basis (which is important from the standpoint of aviation fuels) diand trimethylbenzenes contain about 3% more heat than unsubstituted benzene; on a volume basis (important for motor fuels) diand trimethyl-benzenes contain about 6% more heat than unsubstituted benzenes.

The octane number of benzene is 97, while the octane numbers of toluenes, the xylenes and of typical trimethylbenzenes are all considerably over 100, as determined by the CFR-Motor method. The polymethylbenzenes are superior to ethylor n-propylbenzenes in octane number, indicating the material effect of the molecular configuration on knock rating properties. Thus ethylbenzene has an octane number or blending octane number of only 96 while m-xylene has a similar CFR-Motor method knock rating of 104; n-propylbenzene has a knock rating of 87 while a mixture of trimethylbenzenes has a knock rating of 109. The blending octane number of ethylbenzene is 128 as determined by the CFR-Research method, while the corresponding blending octane number of meta-xylene is 144; similarly the CFR-Research method blending octane numbers of the propylbenzenes are 128 and 137, while that of mixed trimethylbenzenes is about 150.

Conventional alkylation processes provide a satisfactory means for adding ethyl or propyl groups to benzene by means of reaction with ethylene or propylene but they are inoperative for adding methyl groups thereto. An object of my invention is to provide an improved method and means for methylating benzene or toluene.

A further object of the invention is to remove alkyl side chains, particularly methyl groups, from the polycyclic hydrocarbons present in refractory stocks so that the polycyclic hydrocarbons themselves may be then separated from each other and utilized for chemical synthesis.

A further object of the invention is to provide an improved combination of catalytic reforming and by-product utilization systems wherein not only the refractory polymer or residue is uti-'- llzed in said system, but wherein an intermediate fraction of the reformer gasoline is materially improved in the by-product utilization system and wherein hydrogen and gases produced in the reforming step are utilized to prolong catalyst activity and to augment the reaction in the byproduct conversion step. In other words, my object is to provide an integrated system for simultaneously producing a high quality motor fuel and polycyclic hydrocarbons which effective.. ly utilizes the refractory hydrocarbons produced in the reforming step.

A further object is to provide improved method and means for producing high quality motor fuel, high solvency naphtha, condensed ring aromatics and linked ring aromatic compounds from byproduct refractory petroleum stocks. Other objects will be apparent as the detailed description of the invention proceeds.

When methyl-substituted polycyclic hydrocarbons are treated with benzene and aluminum chloride under proper reaction conditions the methyl groups are transferred from the heavy polycyclic molecules to the benzene. This reaction is primarily dependent upon the amount of benzene employed; a large excess of benzene will lead to the formation of much toluene and will remove alkyl groups more or less completely from polycyclic hydrocarbons. The use of less benzene, on the other hand, will result in the production of more dimethyland trimethylbenzene but will leave many of the alkyl groups in their original Iposition on the polycyclic hydrocarbons. In practicing my invention, therefore, I prefer to effect the transfer of methyl groups to benzene in a multi-stage process-i. e. I extract the methyl groups from the polycyclic hydrocarbons by means of benzene (with aluminum chloride) in a manner analogous to the countercurrent extraction of soluble components from liquids by lmeans of selective solvents. In my first stage as fractional crystallization, distillation, etc. into fractions which consist essentially of naphthalene, anthracene, dlphenyl, etc. In certain cases it is possible to obtain individual polycyclic hydrocarbons with one or more side-chains. These fractions may be utilized 'in chemical synthesis in place of the more expensive chemicals heretofore derived from coal tar.

When the refractory stock is obtained from catalytic reforming or aromatization I may remove the benzene from the reformed naphtha and increase its value as a component of motor fuel or solvency naphtha by treating it with the reformer residue in the manner hereinabove described. .Hydrogen produced in the reforming process may be used in the treatment of the residue with benzene in order to prolong catalyst life.

The invention will lbe more clearly understood from the following detailed description read in connection with the accompanying drawing which forms a part of the specification and in which I have schematically illustrated a flow diagram of a preferred embodiment of my invention.

A virgin heavy naphtha of about S50-450 F. end point is charged by pump I0 to coils II of furnace I2 and heated to a temperature of about 900 to 1100o F. under a pressure of about 200 t0 400 pounds per square inch, under which conditions it is passed by transfer line I3 to catalytic conversion chamber I4. Hydrogen from line I5 is heated in coil I6 and passed to the converter by transfer line I1, preferably about 1/2 to 8 mois of hydrogen being employed per mol of stock charged, the hydrogen preferably being heated to a somewhat higher temperature than the charging stock.

The catalyst in converter I4 is preferably a VI group metal oxide mounted on alumina, for example an activated alumina containing about 4% to 6% of molybdenum oxide. The space velocity in this chamber may be about 0.2 to 4 volumes of liquid charging stock per volume of catalyst space per hour. After the catalyst has been on-stream for 5 or 6 hours it is regenerated in the well-known manner and again placed onstream. In practice, of course, a plurality of converters will be employed but since these features form no part of the present invention they will not be described in further detail.

Gases and reaction products leave the converter through line I8 and they are passed through heat exchanger I9 and cooler 20 to hydrogen separator 2|, the hydrogen being passed by line 22 to storage tank 23. This hydrogen will of course be contaminated by gaseous hydrocarbons such as methane, ethane, etc. and although it is usually not necessary to purify it, suitable scrubbers or purification systems maybe employed for obtaining any desired degree of purity. The term "hydrogen as used herein is not limited to pure hydrogen but is intended to cover hydrogen admixed with methane, ethane, etc, The

-ber from chamber 40 through line 4|.

liquids are passed by line 24 through lfitchexchanger I3 to fractionating column 26 w is provided with suitable reflux means 28 and reboiler means 21'. Normally gaseous hydrocarbons may be withdrawn overhead through line 28, light gasoline fractions may be withdrawn through line 23, a benzene fraction through line 30 and heaviergasoline fractions through line 3|.

'I'he benzene from line 30 will, of course. contain other vhydrocarbons of approximately the same boiling range. I prefer to increase the concentration or purity of benzene in this cut before using it in subsequent steps of the process and for that purpose a solvent extraction system may be used. Selective solvents such as SO2, dichlorethyl ether, phenol, cresylic acid, chlorphenols, aniline, chloraniline, furfural, etc. mayv be employed in the conventional manner yto separate a ramnate, suitable per se for motor fuel or reformer charging stock, and an extract which consists essentially of benzene. Similarly, the refractory stock may be subjected to solvent extraction for removing non-cyclic from the polycyclic hydrocarbons in the reformer polymer or residue.

The reformer polymer" or residue is -withdrawn through line 32. This is the refractory material, i. e. the refractory hydrocarbons hereinabove referred to, the inspection of which is hereinabove set forth. The refractory hydrocarbons withdrawn through line 32 consist largely of polycyclic aromatlcs containing. a considerable number of'methyl groups along with some longer alkyl side chains and usually contains considerable amounts of polymethyl naphthalenes. These refractory hydrocarbons from line 32 are introduced through lines 33 and 36 to the first aluminum chloride reactor 35.

The benzene fractionfrom line 30 may either be introduced into line 33 through line 36, blended with finished gasoline through line 31 or withdrawn for other purposes through line 38. Benzene from outside sources may be introduced into line 33 through line 39, In reaction chamber 35 I prefer to employ about 0.5 to 10 or more volumes of K benzene per volume of refractory stock. If the purpose is to produce polymethyl benzene relatively small quantities are employed and if the purpose is to extract side chains from the polycyclic hydrocarbons relatively large volumes are used. I prefer to employ a countercurrent treating system and to employ a relatively small amount of benzene in the rst reactor, for example about 0.5 to v4 volumes of benzene per volume of reactor stock.

Catalyst is introduced into the reaction chge amount of anhydrous aluminum chloride employed may vary throughout considerable range, such as from 1% to 50%', but I prefer to employ about 2% to 20%, say 10%, based on total liquid reactants. The time of reaction may vary from a few minutes to 0.5 to hours, but if the preferred "extraction" procedure is followed, the time may be 1-4 hours in the rst step and 2-6 hours in the second. The temperature may be from about room temperature to 200 or 300 F. a temperature near the reflux temperature vof the benzene solution being convenient. During the reaction the liquids and catalyst are maintained in intimate contact with each other by means of a mechanical stirrer (not shown); heating or cooling coils will, of course, be emplOyed for maintaining the desired temperature. Customarily it is--desirable to heat the mixture means of pump 6I and line 52;

Suitable l to reaction temperature, whereupon the exothermic reaction makes moderate cooling desirable.

The treatment may beeifected continuously or vbatchwise in accordance with conventional methods. Since AlCl: ractions and the apparatus for and methods of conducting them lare well-knowny they will ot be described in detail and are diagrammatically illustrated on the drawing. HC1 or other promoting agent may be used for increasing catalyst activity or catalyst life. The products of the reaction may be water washed or otherwise freed from HC1 or other contaminants. Where hydrogen is used for increasing catalyst activity and life conventional systems will, of course, be employed for separating hydrogen, as well as normally gaseous hydrocarbons, methyl chloride, etc. from l,the reaction products. Detailed descriptions of all of these well-known expediente would only confuse the drawings, and for the purpose of clarity such detailed descriptions of known expedients will be omitted.

Spent catalyst may be withdrawn from the system through line 42 and the vreaction products after being freed from catalyst are With- Vdrawn through line 43 to fractionating column 44 which is provided with suitable reflux means 45-and reboiler means 46. Unreacted benzol is taken overhead through line 41 to benzene storage tank 48. Toluene is withdrawn through side stream 43 and it may be recycled through lines and 5| to line 34 and reactor 35. Alternatively, the toluene may be separately recovered or it may be passed through lines 52, 53 and 54 to gasoline storage tank 55. Xylenes may he recovered through side stream 56 and trimethylbenzenes through line 51. These side streams may likewise be separately withdrawn or passed via lines 52, 53 and 54 to gasoline storage.

The partially dealkylated refractory stock is withdrawn from the base of fractionating column 44 through line 58 and cooler 59 and introduced into second aluminum chloride reaction chamber 60. Benzene from storage tank 48 is introduced into this second reaction chamber by reactor my purpose is to remove as many as possible of the methyl groups and alkyl side chains from the polycyclic components of the partially dealkylated refractory stock, therefore `I employ from 5 to 15 volumes of benzene per volume of refractory stock. The reaction condltions in chamber ,60 are similar to those in reaction chamber 35, although somewhat higher temperatures and longer reaction time, as well as more catalyst (based upon the refractory material) may be employed. Aluminum chloride from hopper 63 is introduced into the chamber through valved line 64 and spent catalyst is removed therefrom through line 65.

The products from the second reaction chamber, after being freed from catalyst material, are Withdrawn through line 66 to fractionating column 61 provided with reflux means 68 and reboiler' means 69. Unreacted benzol is taken overhead through line 10 and either introduced through line 1I to benzene storage tank 48 or recycled through lines 12, 5l and 34 to reaction chamber 35. Additional benzene may be introduced into the system through line 13.

Toluene and perhaps some Xylenes are withdrawn through side stream 14 and may either be passed through lines 15, 5| or 34 to the first In the second reactor enables the removal of most methyl groups and alkyl side chains from the polycyclic hydrocarbons in the refractory stock. It should be understood, however, that any number of treating steps may be employed when two steps are not suillcient to obtain polycyclic aromatica of the desired degree of purity. These polycyclic compounds are withdrawn from the base of fractionator 81 through line 'I1 to a suitable separation system 18 wherein the naphthalene, anthracene, dlphenyl, etc. (which still may contain one or more methyl groups) may be separated from each other by distillation, crystallization or other conventional methods.

For many purposes it is unnecessary to effect a sharp fractionation of these materials as mixtures of polycyclic hydrocarbons maybe advantageously employed as a heat transfer medium or as a source material for fixed amines for dyes, mixed phenols for plastics, mixed halides for insulation purposes, mixed sulfonic acids for various purposes, etc. Such hydrocarbon 4derivatives are often more readily separaiiad than the parent hydrocarbons themselves.

For example, the mixed polycyclic hydrocarbons may be chlorinated to the extent of about 20% to 70% by weight and may be fractionated either before or after chlorination to produce viscous products which may range from liquids to waxy solids and which are similar in physical and chemical properties to chlorinated naphthalene, chlorinated diphenyl, etc. Such chlorination products are useful in small quantities as addition agents to mineral oilsfor improving their stability, gravity, pour point, viscosity, extreme pressure lubricant properties, etc. Also the chlorinated products may be used as heat exchange media, for electrical insulation, etc.

Instead of halogenating the mixed polycyclic hydrocarbons they may be nondestructively hydrogenated to give acondensed naphthenic hydrocarbon mixture particularly valuable as aV Diesel fuel or medicinal oil. Alternatively. they may be destructively hydrogenated for the production of motor fuel.

This mixture of polycyclic hydrocarbons can also be converted by known methods into an exceedingly cheap commercial dye or coloring agent. In this process the mixture may be treated with sulfuric acid, nitric acid or chlorine and unreacted hydrocarbons may be recycled for Q da NOz,SOxOH,Cl No. 0,011,01

Since the polycyclic hydrocarbons constitute mixtures of components each of which is more or less alkylated. the color of the resulting dyes is usually black; other colors may be obtained however, by fractionating the polycyclic mixture before treatment. By converting a part of the polycyclic aromatics to mixed phenols or amines and converting an equivalent part` to diazonium chlorides the two product mixtures may be reacted to give a brown to black dye which is very -cheap as compared with dyes made from pure organic compounds.

While the above processes for treating polycyclic aromatics are applicable to unfractionated mixtures, I prefer to fractionate the dealkylated polycyclic compounds; since the alkyl derivatives of these compounds have a much lower melting point than unsubstituted cyclics, fractionation by distillation and freezing is advantageous. The above treating processes may, of course, be applied to the refractory stocks themselves but an important feature of my invention is the utilization of the alkyl groups, particularly methyl groups present in such refractory stock for the production of valuable hydrocarbons such as toluene, Xylene, etc.

In the above description where reference is made to side streams of toluene, xylene, trimethyl benzene, etc. it should be understood that these streams contain mixtures of hydrocarbons, particularly in the case of the xylenes and other polymethyl benzenes. It is usually unnecessary tosharply fractionate these polymethyl benzenes since the mixtures as produced are extremely valuable components of motor fuels, particularly for special aviation fuels, as well as for high solvency naphthas, etc.

Since the refractory stock may contain some paraillnic components as well as substituted polycyclic hydrocarbons, the activity of the catalyst in the reaction chambers may be somewhat extended if these reaction chambers are maintained under a hydrogen pressure of from about 50 to 500 pounds per square inch. Since hydrogen is produced in the catalytic reforming reaction and since the source of hydrogen under pressure is maintained in said system, I may maintain this hydrogen pressure in the aluminum chloride re` actors by simply connecting those reactors with hydrogen storage tank 23.

While I have described in detail the refiningI of a refractory stock produced from catalytic reforming it should be understood that the refractory hydrocarbons may be obtained from other sources. Cracking furnishes an important source of such refractory stock-a desirable stock is one which has been recycled at least twice and preferably four or five times through a cracking process in which the cracking per pass is at least 20% in the ilrst pass,

The refractory stock may be further treated in one or more of several ways before subjecting it to the aluminum chloride treatment. It may be solvent extracted with a selective solvent such as sulfur dioxide, giving a raffinate which may suitably be returned to the cracking process and an extract which is highly suitable for dealkylation by the process hereinabove described. Many crudes contain polymethyl polycyclic hydrocarbons which can be separated from other components of the crude by distillation and solvent extraction. Products from such crudes or' from other sources may be dehydrogenated for the purpose of converting condensed cycloalkane derivatives suc h as alkyldecalins to the corresponding aromatic hydrocarbons such as alkylnaphthalenes prior to subjecting them to thealuminum chloride dealkylation process hereinabove described.

Ordinarily I prefer to employ residues of cycle stocks from catalytic cracking, reforming or aromatization since residues from these processes are available in large quantities and their disposal presents a serious problem to petroleum reners.

While I have described a preferred embodiment of the invention it should be understood that I do not limit myself to any of the above details since many modifications of the invention will be apparent to those skilled in the art from the above description.

I claim:

1. The method of dealkylating refractory hydrocarbons containing polymethyl, polycyclic aromatics which comprises rst treating said refractory stock with a small amount of benzene in the presence of aluminum chloride to produce polymethyl benzene and partially dealkylated refractory hydrocarbons and subsequently treating the partially dealkylated refractory hydrocarbons with a large amount of benzene in the presence of aluminum chloride for effecting the removal of alkyl groups which were not removed in the first treatment step.

2. The method of countercurrently treating polyalkyl polycyclic hydrocarbons with benzene for obtaining toluene, polymethylbenzenes and dealkylated polycyclic hydrocarbons, respectively, which method comprises treating the polyalkyl, polycyclic hydrocarbons with about 1/2 to 4 volumes of benzene in the presence of aluminum chloride in the first treating step, separating the unreacted benzene and alkylbenzenes from partially dealkylated, polycyclic hydrocarbons, subsequently treating the partially dealkylated, polycyclic hydrocarbons with about 5 to 15 volumes of benzene in the presence of aluminum chloride in a second treating step, and removing unreacted benzene and methylated benzenes, respectively, from the products resulting from said second treating step.

3. In a combination system for the catalytic reforming of naphtha wherein hydrogen and refractory stock are produced, the hydrogen being stored under pressure, and for the dealkylation of said refractory stock by means of benzene in the presence of aluminum chloride, the method of extending the catalyst life in the dealkylation system which comprises operatively connecting the dealkylation system with said hydrogen storage, whereby the hydrogen produced in the reforming system exerts a hydrogen pressure in the dealkylation system for prolonging dealkylation catalyst life.

4. A hydrocarbon conversion process which comprises catalytically reforming naphtha in the presence of a catalyst containing a group VI metal oxide under temperature, pressure and space velocity conditions for producing hydrogen,

reformed gasoline and a refractory stock containing large amounts of polymethyl polycyclic aromatics, separating said refractory stock from said reformed gasoline, contacting said separated refractory stock with a monocyclic hydrocarbon in the presence of an aluminum chloride catalyst, prolonging the aluminum chloride catalyst life by introducing into said contacting step at least a part of the hydrogen produced in said reforming step, maintaining reaction conditions in said contacting step for transferring methyl groups from said refractory stock to said monocyclic hydrocarbon and separating the methylated monocyclic hydrocarbon from the demethylated refractory stock.

5. A hydrocarbon conversion process which comprises catalytically refroming naphtha in the presence of a catalyst containing a group VI metal oxide under temperature, pressure and space velocity conditions for producing hydrogen, reformed gasoline, and a refractory stock containing large amounts of polymethyl polycyclic aromatics, separating said refractory stock from said reformed gasoline and lighter products, contacting said separated refractory stock with a monocyclic hydrocarbon in the presence of an aluminum chloride catalyst, maintaining reaction conditions in said contacting 'step for transferring methyl groups from said refractory stock to said monocyclic hydrocarbon, and separating the methylated monocyclic hydrocarbon from the demethylated refractory stock.A

6. The method of claim 5 wherein the refractory stock is characterized by approximately'the following specifications; A. P. I. gravity approximately 10, Saybolt viscosity at 100 F. approximately 34 seconds, refractive index approximately 1.59, aniline point below 40 F., initial boiling point at least about 415 F., 90% point less than 600 F.

ROBERT F. MARSCHNIR.

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