US2397495A - Conversion of alkylated aromatic hydrocarbons - Google Patents

Description

`April 2, 1946. A. P. LIEN ETAL CONVERSION OF ALKYLATED ROMATIC HYDROOARBONS lFiled May 23, 1945 Bui mx by mmm PatentedApr. 2l,r 1946 coNvEasloN oF ALKYLATED A'aoMA'rIc 1 mmaocaaoas I 1li-unu-r P. Lien and Bernard n. Shoemaker, namv`mond; Ind., assignors to-.Standard .Oil Comf pany, Chicago, Ill., a corporation of Indiana Application May 23, 1945., SerialNo.r595,l276 (Cl. 260g-6772) 6 Claims.

This invention relates toa process for the conversion of alkyl aromatic hydrocarbons. More particularly, it relates to a processl for the conversion of alkyl aromatic hydrocarbons containing at least three carbon atoms in the alkyl group to alkyl aromatic hydrocarbons containing less than three carbon atoms inthe alkyl group, particularly ethylbenzene, by the use of a catalyst consisting essentially of hydrogen fluoride' and boron fluoride. Ethylbenzene is of great commercial importance for the manufacture of synthetic rubber,

plastics, and for many other purposes. Of the higher alkyl benzenes, cumene has found some application as a component of aviation gasoline blends but this application has been relatively in relatively pure state; in other words, to avoid the vpresence orrproduction of undesirablehydrol carbons of approximately the same .boiling range as that of the desired products.

A further object oi' our invention is to provide an improvedvmethod and means for effecting hydrocarbon conversion with hydrogen iluoridlimited. Alkyl varomatic hydrocarbonsuhaving v more than three carbon atoms in the alkyl group have found no commercial application per se, although heavy oils such as' lubricants are believed to contain such alkyl aromatic hydrocarbons.

' Of the petroleum refinery olens, ethylene and the butylenes have found extensive commercial applications. Propylene in particular, is available in relatively high purity at low cost as a byproduct oi various petroleum refinery conversions, e. g., the cracking of petroleum oils. By the invention hereinafter set forth; refinery propylene fractions and benzene can be converted to high yields of ethylbenzene, this product being heretofore made almost exclusively from benzene and ethylene. 4 v

An object of our invention is to provide a simple, efficient and relatively inexpensive process Afor producing ethylbenzene. A further object is to provide a process for thev preparation of ethylbenzene `from benzene and olens of greater molecular weight than ethylene, particularly from benzene and propylene. An additional object` of our invention is to provide a process for the simultaneous production of ethylbenzene and valuable by-products such as aviation gasoline blend'- irg stocks, toluene, ethyltoluene, diethylbenzenes, e c.

A further .object of our invention is to produce ethylbenzene andiother valuable products from 'aromatics and readily available cheap hydrocarboron fluoride catalysts 'whereby such catalysts can be used with maximum effectiveness and withv minimum losses. Afurther object is to provide an improved kmethod and means for recovering hydrogen uoride, boron fluoride and valuable aromatic hydrocarbons from the relatively spent catalyst material or complex which is .produced in the reaction./ f L Briefly, we have found that alkyl benzenes having at least three carbon atoms in the alkyl group can .be converted tovaluable lower and higher boiling products containing an unexpected plOduct in large proportion, viz.; ethylbenzene. by intimately contacting said alkyl benzenes with a catalyst consisting essentially of hydrogen fluoride and boron fluoride under conversion conditions of temperature, pressure and time. Suitable charging stocks for our process includen-propyl benzene, 'isopropylbenzena ethyltoluene, diethylbenzenes, diisopropylbenzene, isobutylbenzene and amylbenaenes. These chargingstocks can be prepared byalkylating benzene with the appropriate oleilns in the presence of alkylation catalysts. Thus. benzene can be 'alkylated with an olefin such as propylene'by th use of phosphoric acid supported on kieselguhr. The reaction is carried out at 40o-500 F., inthe presence of 0.1 to

10% of steam to inhibit dehydration of the catalyst. Although the ratio of 'propylene to benzene in the alkylation step will aect the ratio of monoto polyalkylbenzenes, some Polyalkylbenzenes will invariably be formed and can be utilized.. along. `with the cumene,vin the conversion processy of this invention.`

-tively high boron fluoride concentrations.

v 'I'he conversion may be effected at a temperature within the approximate range of 150 to 400 l.; the higher temperatures being employed with relatively low boron fluoride concentrationsv and the lower temperatures being employed with rela- The pressure should be sufiicient to maintain substantially liquid phase conversion conditions and may and operating conditions as will enable the production and recovery of desired reaction products be within the approximate range oi about 200' to 2000 pounds per square inch. Hydrogen up to 1500 p. s. i. can be used to inhlbitundesirable side reactions such as ring fusion and to prolong catalyst life. The time of contactv will be somewhat dependent upon catalyst composition and temperature employed and may range from labout a. minute to several hours. The space velocity in a continuous reaction system may be within the approximate range of about 0.2 to 4 volumes of hydrocarbon charging stockV per hour Der Volume of catalyst in the reaction zone.

'Ihe proportion of boron fluoride to hydrogen fluoride is important. The use of too much boron iluoride results in excessive amounts of aromatics dissolving in the complex or catalystlayer which in turn requires an unduly high recycle ratio 'of complex for product and catalyst recovery. The use of too small amounts of boron uoride leaves the aromatics undissolved and outside the sphere of catalytic influence. While 2 to 20% of boron fluoride by weight, based on hydrogen fluoride, is the preferred range for maximum catalyst efl'ectiveness it should be understood that beneficial results may be obtained with the presence of only about 1% by weight of boron fluoride or an even ylesser amount thereof and in some instances benelcial results may be obtained with the Presence of even more than by weight of boron fluoride. The catalyst should be substantially but not absolutely anhydrous since a 'trace' of water (0.01 toJ 1% by weight) may improve the catalyst activity and water contents of 2 or 3% may be used.

Since boron fluoride isan expensive'reagent it is essential that its losses from the conversion system be minimized. When light hydrocarbon gases such as methane must be purged from the systemthe problemV of avoiding boron fluoride losses is considerably augmented.' In our invention we absorb the tail gases from the hot settler following the reactor and/or from the boron fluoride stripper in an absorber liquid which can be relatively cool incoming hydrogen vfluoride maintained at suillcient pressure so that the boron fluoride is absorbed orbound while hydrocarbons are substantially unabsorbed so that they can be removed' in the liquid or gaseous state. A particularly desirable absorber liquid is an intimate mixture of an aromatic hydrocarbon, such for example as diethylbenzene,1 with hydrogen fluoride because boron fluoride forms a complex with such intimate mixtures vor solutions and hence may be readily separated f romA other gases at pressures as low as atmospheric pressure.

The relatively spent catalyst material (which is a liquid mass containing catalyst complex, tarry material, dissolved catalyst components. aromatics, etc.) is reduced to Va. relatively low pressure and heated to about 90 to 200 F.. preferably 100 to 160 F., to drive oi dissolved or loosely bound hydrogen fluoride and boron fluoride, thus liberating substantial amounts .of aromatic hydrocarbons from combination with the boron fluoride hydrogen fluoride hydrocarbon complex. The heated material vis vthen allowed to settle for the separation and recovery 'of aromaticv hydrocarbons. The remaining material is then heated to a higher temperature of about 200 tov 500 F. for decomposing any complex present and thus recovering residual boron fluoride and hydrogen fluoride. s A preferred temperature range is 230 to 350 F. when the operation is carried out at substantially atmospheric pressure, higher temperatures being required when 'higher pressures are employed. The boron'fluorlde and hydrogen fluoride thus recovered can be returned to the reactor. I

Hydrogen fluoride may be recovered from the product stream by azeotropic distillation. Since no olens are employed in the charging stock the problem of removing alkyl fluorides is greatly minimized if not entirely eliminated. The product stream will consist of a relatively few hydrocarbons so that the desired products can be' readily separated from each other tionation.

The invention'will be more clearly understood by simple fracfrom the following detailed description read in s Y,

from line I'I, and introduced through line I8 at a low point in reactor I9.

The conversion may be effected in any suitable type of reactor on a batchwise, multiple batch, semi-continuous or continuous basis but we prefer to employ a continuous process with a towertype reactor and to effect the conversion by passing the charging stock upwardly through the column of catalyst maintained in the liquid phase either ,with or without mechanical agitation. 'Ihe reactor may be of the type generally used for effecting alkylation of olef'lns with isoparaillns as exemplitled'by U. S. 2,238,802 or it may be of the type described in U. S. 2,349,821 for effecting isomerization of parafllns.' It may be about 5 to feet in height and should be designed to withstand a maximum operating pressure which with the high temperatures may be as high as 2000 pounds per square inch. Before the reaction is initiated the reactor may be filled about half to three-fourths full of catalyst and heated by any conventional means to reaction temperature.

The catalyst in the reactor in this specific example is hydrogen fluoride containing 10 weight per cent (basedaon hydrogen fluoride) or boron fluoride. For each volume of hydrocarbon introduced into the reactor we may introduce between about 0.05 and 0.5, e. g., about 0.1, volume of the catalyst mixture, the bulk of this mixture being introducedw through line I1 but a portion of it being introduced through line 20. With a substantially anhydrous charging stock a trace of water may be added and/or a small amount of aqueous hydrogen fluoride through line 2| so thatproduct stream in the upper part of the reactor although some catalyst material is carried with the eilluent product stream through line 22 and cooler 23 to separator 24. Catalyst material which settles out in this -settler may be returned by lines 25 and 2G to the reactor. In this particular case the space velocity in the reactor can be'A about 1-volume of hydrocarbon charging stockl per hour per volume of catalyst in the reactor. v

The settler 2l may be operated at substan' tiallyreactor pressure and at suflicient elevation so that the'liquid catalyst may flowby gravity back to the reactor. Alternatively we may employ a pressure reducing valve in line 22 and operate the settler at a muchlower pressure, for example of the order of about 200 to 400 pounds per square inch in which casea pump will be employed in line 25. When operating vat such pressure that there is gas separation the gases are Withdrawn throughlines 21 and 28 to absorber 29. The overhead product stream passes through line to boron fluoride stripper 3| which is provided with a suitable reheating means or reboiler 3.2 at its base. Line 30 may bel provided with a suitable pressure reducing valve or pump depending upon the relative pressures in settler 24 and stripper 3i respectively. The stripper may operate at a pressure of about 200 to 300 pounds, for example about 250 pounds per square inch, and sufficient heat is supplied to insure the removal of substantially all of the boron fluoride which passes by line `33, compressor 34, and line 28 t o the base of absorber 29. We prefer to operate the stripper and absorber at such temperatures and pressures that the use of compressor 34 may be eliminated.' Make-up boron fluoride may be supplied from source 35 and introduced into the system by compressor 38to line 28.

After removal off boron fluoride the product stream passes by linel 31 to azeotropic distillation still 38 which is provided with a suitable heating means or reboiler 39 at its base and which may likewise be provided with reflux means at its top. A butane-hydrogen fluoride azeotrope. passes overhead throughline 40 through condenser 4I to settler 42 which' is operated at as low a temperature as can be obtained with available cooling water,v preferably well below 100 F. The condensed azeotrope separates into a heavier hydrogen fluoride layer which is withdrawn by line 43 to hydrogen fluoride storage tank l44. The upper butane layer is returned as reflux by line 45 and pump 48 to still 38 and eventually passes downwardly with the product stream. Any propane or .lighter gases may be vented through line 41; such gases should contain no boron fluoride but if they do they maybe compressed if necessary and introduced. through line 28 to absorber 29.

If the product stream `withdrawn from the base of azeotropic still 38through line 48 is substantially free from alkylfluorides and hydrogen fluoride it may require no special treatment for fluoride removal. A conventional bauxite or equivalent treating system 48' is, however, prefl l 3 une ss' pentanes (which consist'chieflyI 'oristpentane) neohexane and dilsopropyl. The overhead stream is thus an exceptionally high quality aviation gasoline vblending stock `since itconsists chiefly of isopentane and neohexane.Y The overhead may, however,` contain vat least a part-ofthe methyl pentanes although we prefer to include the'methyl pentanes aswell as thenormal hex; ane in the stream whichis withdrawn from the base of tower 54 through line'58 to fractionating tower 51 which is provided with suitablereboiler Tower 51 is operated under and reflux means. such conditions as to take overhead through line 58 all hydrocarbons boiling between about 140 erably employed at. this point to insure the. re-

moval of any traces of alkyl iluorides and gen fluoride which maybe present.

The product stream is thenintroduced by line hydro- 48 into stabilizer or debutanizer tower 49 which is provided with a suitable heater or reboiler at its base and suitable reflux means 5I at its top.

' In this and other fractionating towers any conventional heating and cooling means may be employed and in practice the reflux is -usually obtained by condensing theoverhead and returning at least a part of the resulting condensate to the top of the tower. A butane stream is Withdrawn overhead through line 52 and it will consist chiefly of'isobutane, which is valuable for producing isooctane by alkylation with butenes and for other purposes. r

The stabilized or debutanized product stream then 4passes by line 53 to fractionating tower 54 which is likewise provided with a. reboiler at its base and reflux means at its top and which is operated to take overhead a fraction boiling from about 70 to 140 F., i. e., to take overhead through and about 260 F.. namely methyl pentane, normal hexane, heptanes, benzene and toluene. It will be, understood of course that if .and when toluene is a desired product itmay be separately which is provided with suitable reboiler and reflux means and from the top of which the ethylbenzene stream ls recovered through line 82. A feature of our invention is the production of ethylbenzene rather than xylenes. Any lminor amount of xylenes that maybe produced may be separated from the ethylbenzene stream by super-fractionation, azeotropic distillation or any other means. o chiefly in `the range between about 320 and 335 F. may be withdrawn as a side stream through line 82' from tower 8| for dehydrogenation to produce methylstyrene or may be recycled to vreactor I8. A diethylbenzene fraction may be recycled by line 63 via lines I3 and I4 through pump I5 and/thence through linesl I2 and I8 back to the reactor I9 or introduced by line 83' to absorption tower 29. Heavier material is preferably withdrawn from the system through line 84 thence passed through pressure reducing valve 81 to recovery drum 88 which is preferably op# erated near atmospheric pressure, for example at about 5 pounds gauge pressure and at a temperature of the order of to 160 F. Under these conditions,` hydrogen fluoride rvand dissolved or'loosely bound boron fluoride are liberated, passing overhead through line 89. This mixed effluent may pass directly through condenser 10 to receiver 1I where hydrogen fluoride is collected as a liquid and from whichy boron fluoride .may be flashed overhead through line 1I' to line 28. Liquid hydrogen fluoride maybe pumped from receiver 1I via line 12 to hydrogen fluoride storage tank 44. If there is a ltendency for moisture to accumulate in the system we may introduce the eflluent from line "89 into distillation column 13 which is provided with heating means 14 and we may take substantially anhydrous hydrogen fluoride and boron fluoride overhead through line 15 and condenser 10 to receiver 1I returning a portion lof condensate through line 18 to serve l as reflux. Aqueous hydrogen fluoride-boron iluoride may be withdrawn from the base of column l line 2 Iby'pump 19 in order to supply the desired trace of water in the reactor.

Heating of the product in drum 88 results in An ethyltoluene vfraction boiling system through line 88. Make-up hydrogen fluoride may be added to the system from source 89 to storage tank 44.

.u decomposition of the loosely bound boron fluoride-hydrogen fluoride complex and by removal ofthe iiuorlde components and of excess hydrogen iiuoride solvent the aromatic hydrocarbons are thrown out of solution. The residue in drum 68, consisting of. aromatic hydrocarbons and more-firmly-bound fluoride complex, is with- .drawn through line 80 to settler 8l wherein an upper aromatic layer ymay be recovered from the lower complex layer and passedby line 82, pump 83 and a bauxite system 82' for fluoride removal lto line 56. By removing boron uoride and hydrogen fluoride from the spent catalyst material and employing the settling or separation step a A considerable amount of aromatic hydrocarbons is recovered which would otherwise`be lost. The

Cil

larger the ratio of boron fluoride to hydrogen l,

' fluoride which is employed in the reactor thev larger will be the amount vof aromatics recovered in settler 8l. y

Thecomplex and tarry material which settles out in settler 8|.is withdrawn through line 84 to drum 85 which is provided with heating means 86. This drum is operated at about atmospheric pressure and at a temperature of the order of 230 to 350 F. or more underwhich conditions the complex is decomposed and boron` uoride and hydrogen iiuoride are liberated. d. The liberated boron iiuoride and hydrogen uoride may be compressed by compressor 81 and returned by lines and I8 to reactor I9, but is preferably` introduced through line 20' tothe base of abi.

sorber 29, the latter arrangement offering the advantage of providing better control on the amount and composition of catalyst entering the reactor. A tarry residue is withdrawn from the Hydrogen fluoride is pumped from this storage such complex formation toremove boron fluoride,

it may be separated from extraneous gases at atmospheric pressure, s0 that compressor 81 may be eliminated as well as compressor l3l.

An eiective method of operation is to introduce enough diethylbenzene fromline 63' to the upper part of .absorber 29 to maintain a liquid hydrocarbon layer above the acid level in the absorber. Intimate mixing can be obtained by spraying hydrouoric acid laterally or downwardly into .this diethylbenzene layer (or by.` any other means).

so that any boron fluoride not absorbed in the lower part of tower 29 will react with the intimate mixture in the top thereof to yform complex and be positively prevented from leaving the absorber with extraneous gases. The resulting complex is scrubbed out of the mixture .by incoming hydrogen'fluoride and carried as a solution therein with the catalyst leaving the absorber through line I1.

Results obtainable by'V our invention are shown by a batch run wherein 3.1 mols each of benzene and cumene, 331 grams of hydrogen uoride and l y 33 grams of boron trifiuoride were introduced into a bomb provided with stirring mechanism and ref acted at a temperature of 334 F. for 50 minutes under a pressure which rose to` about 860 -p. s. i.

during' thereaction period. Practically no hydrocarbon gases lighter than propane were produced and the amount of complex formed wasv estimated to be about 6.5 grams per mol vof cumene charged. In a similar run employing aluminum chloride-hydrogen chloride, the red oil complex amounted to 28.3 grams perY mol of cumene charged or morthan 4 times'the amount 0i complex that was produced in our hydrogen ilubride-boron fluoride run. vThis islan extremely important advantage of our invention becau'se it eiects enormous savings in charging stock and tank by pump 99 and passed by line 9| to the upper part of absorber 29 which may operate at a pressure whichV may be ,as high as 1000 poundsv per square in ch and in this particular examplel may operate at about 240 pounds per square inch.

At such pressures and at the relatively lowA temperature of the order of about V100 F. or lower the boron fiuoride'is absorbed in or chemically 1 bound to the hydrogen nuorid but the hydrocarbon gasesare unabs'orbed therein and may be vented from the top o f the absorber Vthrough line 92. By this means, losses of boron fluoride are substantially prevented while the system is being purged from methane and any other `light f gases' which may tend to accumulate therein. It should be understood that make-up hydrogen fluoride. may be introduced directly into the top of the absorber and that line 43 and/or 12 may likewise lead to-the absorber rather than to am hydrogen iiuoride storage tank. Y

Our invention is not limited to the use of hydrogen fluoride as the absorptionmedium, but it is important to note that absorption systems of the type used for hydrogen, chloride in isomerization 'plants are not suitable for boron fluoride recovery, particularly since it is desirable to vent'any propane through line 92 rather thanV from line 41.

appears that boron iiuoride chemically reacts with such mixture to form a complex which is soluble in liquid hydrogen iluoride. By utilizing We have discovered that-a most` .effective absorbent for boron lfluoride is an intimate mixture rsolution of an aromatic hydro.-

carbon such as toluene, ethyl-toluene, diethyl benzene, or the like' with hydrogen uoride. It

' -Volume per cent Low boiling- 2.3 Benzene 24.7 Y'Tol'uene 17.6 Ethylbenzene 24.7 Ethyltoluene 1 9.4.

catalyst requirements, moreover, our catalyst may be always quantitatively recovered while the aluminum chloride complex can not'be recovered by any practical method., In our process, the recovered hydrocarbons consisted of 14.5 weight per cent condensible normally gaseous hydrocarbons and 85.5 weight per cent of normally liquid hydrov .Although benzene lwasfancied with the' feed, it

did not actually take partinthe reaction. Therefore, based on the cu'menecharged, the following distribution of the liquid products is obtained:

The relative freedom of the ethylbenzene fraction from xylenes is noteworthy.

It should be noted that under the reaction conditions as here used, there were indications of over-treatment, such as the appearance of. a low boiling liquid fraction and the presence of n-butane in the condensibles fraction. Therefore, under milder conditions, a still more favorable distribution of products would be expected than that outlined above, especially as regards the production of condensibles and the ratio 'roi isobutane to propane in the condensibles fraction. It will, of course, be appreciated that a considerably higher ultimate yield of ethylbenzene may be obtained by recycling ethyltoluene, diethylbenzene, andhigher boiling fractions to the conversion process. y

- While we have described a preferred example of our invention in considerable detail it should be understood that our invention is not limited to the specic system or the particular conditions therein recited since many modiiications and alternativeuconditions will be apparent from the above description to those skilled in the art. In some instances,l for example. it may be desirable to hydrolyze the complex withdrawn from `the bottom of settler 8| through line u instead of subjecting it to hydrogen fluoride-boron iluoride recovery. The complex withdrawn through line Il is a mobile liquid, brlght'blue in color. It is Per cent byy volume Ethylbenzene 9.4-8 5 m-Xylene 3.2 o-Xylene None p-Xylene 0.6

; riod of time sumcient to effect substantial con.

insoluble in both hexane and benzene but after f treatment with water, is soluble in these solvents. The hydrolyzed product has drying oil propertiesandmaybeutilizedfortheproductionofa dryingoil or plastic materials instead of for the recovery of hydrogen nuoride and boron fluoride.

We claim: l. A method for producing ethylbenzene which comprises intimately contacting an alkyl benzene containing at least three carbon atoms in the alkyl group with a catalyst consisting essentially of hy- -drogen fluoride and boron fluoride under elevated conversion conditions of temperature and pressure for a time suillcient to effect substantial conversion, and separating ethylben'zene from the conversion products.

2. The method of claim l wherein the alkyl benbene is isopropylbenzene.

3. The method of claim 1 wherein the alkyl benzene is'diisopropylbenzene.

4, A hydrocarbon conversion process which comprises intimately contacting an alkyl benzene containing at least three lcarbon atoms in the alkyl. group in a conversion zone with a catalyst consisting essentially of hydrogen fluoride promoted by about 2 to about 20% by weight of boron nuoride at a temperature in the range oi about 150 to about 400 F. under suilicient pressure to maintain liquid phase conversion conditions for a period of time sufficient to eiect substantial conversion.

5. The method of claim 4 wherein the alkyl benzene is isopropylbenzene.

6. A Vmethod for producing ethylbenzene which comprises intimately contacting isopropylbenzene in a conversion zone with a catalyst consisting essentially 4of hydrogen iluoride promoted by about 2 to about 20% by weight of boron fluoride at a temperature' in the range of about 150 to about 400 F. under suiilcient pressure to maintain liquid phase conversion conditions for a peversion, removing conversion products from the conversion' zone, separatingthylbenzene and higher boiling conversion products and recycling the last named products to the conversion zone.

ARTHUR P. LIEN. BERNARDRBHOEMAKER.

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