US2394170A - Treatment of hydrocarbons - Google Patents

Description

Feb. 5, 1946. I A. v. GROSSE ErAL. 2,394,170

TREATMENT OF HYDROCARBONS Filed Jam a, 1940 ALIPHATEC HYDROCARBCNS DEHYDROCYCLI- ZATION: ZONE 4 GASEOUS PRoouc'rs PARAFFINIV FRESH I v RAFFINATE SOLVENT E 1 a i SOLVENT EXTRACTION ZONE I RECOVERED 9 SOLVENT 1 sEcoNp DEHYDROCYCLk ZATION ZONE a? OASEOUS PROD c L SEPARATION ZONE v l6 AROMAIC HYDROCARBONS 7 INVENTORS ARISTID V. GROSSE Patented Feb. 5, 1946 Aristid v. Grosse, Bronxville, N. Y., and William J.

Mattox, Chicago,-Ill., assignors to Universal Oil Products Company, Chicago, 111., a corporation of Delaware Application January 8, 1940, Serial No. 312,832

This'invention relates particularly to the conversion of straight chain hydrocarbons into closed chain or cyclic hydrocarbons.

More specifically it is concerned with a process involving the use of particular catalysts and specific conditions of operation in regard to temperature, pressure, and time of reaction whereby aliphatic hydrocarbons can be converted efficiently into aromatic hydrocarbons.

In the production of aromatic hydrocarbons from paramns by dehydrocyclization, certain amounts of olefinic hydrocarbons are formed simultaneously, and in the cycling of olefinic hydrocarbons, theproduct contains not only aromatic hydrocarbons but also unchanged olefins.

In each of these cases part of these olefins cannot be separated readily by fractional distillation or by solvent extraction, but they must be removed in some way if the aromatics are to be used for nitration or for other chemical work requiring pure aromatic hydrocarbons or substantially olefin-free aromatic-containing hydrocarbon mixtures. The conversion of these olefins Y to parafflns by hydrogenation or their removal by acid absorption or by oxidation are expensive operations and result inconsiderable loss of materials. The process of this invention converts these olefins into aromatics and produces a relatively high yield of substantially olefin-free aromatic hydrocarbons.

In one specific embodiment the present invention comprises a process for producing aromatic hydrocarbons from aliphatic hydrocarbons including paraflins and olefins which comprises contacting said aliphatic hydrocarbons under dehydrocyclizing conditions of temperature and' pressure with a composite comprising essentially a major proportion of a substantially inert refractory'carrier and a relatively minor proportion of an oxide of an element selected from the members of the left-hand columns of groups 4, 5, and 6 of.the periodic table to form a product containing aromatic, olefinic, and paraflinic hydrocarbonsj extracting said product by a selective solvent to separate a mixture comprising essentially oleflnic and aromatic hydrocarbons from a substantially parafilnic raflinate; recovering and recycling said solvent to further extraction use; recycling said paraifinic rafiinate to the original dehydrocycling zone; and conducting said mixture of olefinic and aromatic hydrocarbons to a second dehydrocycling zone to produce a substantially olefin-free aromatic product.

According to the present invention aliphatic or straight chain hydrocarbons having 6 or more 4 Claims. (01. zoo-eras) carbon atoms in straight chain arrangement in their structure are specifically dehydrogenated in such a way that the chain of carbon atoms undergoes ring closure with the production in the simplest case of benzene from n-hexane or n-hexene and in the case of higher molecular weight paraiiins of various alkyl derivativesof benzene. Under properly controlled conditions of temperature, pressure, and time of contact,'

very high yields of the-order of '75 to of the benzene 'or aromatic compounds are obtainable which are far in excess of any previously obtained in the art either with or without catalysts.

For the sake of illustrating and exemplifying the types of hydrocarbon conversion reactions which are specifically accelerated under thepreferred conditions by the present types of catalysts, the

following structural equations are introduced:

CH: CH

Ci cfli CH CH g 4H: s: OH: H H

C a C n-Hexane Benzene CE, C\-CH: on; cm-orn c 6 n 4H: El CH: 5 CH n-Heptane Toluene CH: C I 0%: CH:CH: C C-CHs (l: 4H: s; CHr-CH: g C-CH:

C a \C n-Oc'tene o-Xylene Ethyl benzene and oand m-xylene are also formed from n-octaneby a combination of re- I actions involving dehydrogenation, cyclization, and isomerization, but no idea is ofiered as to the probable order in which these reactions occur.

In the foregoing table the structural formula of each of the primary paraflin hydrocarbons has been represented as a nearly closed ring instead of by the usual linear arrangement for the sake of indicating the possible mechanisms involved.

No attempt has been made to indicate the possible intermediate existence of mono-olefins, di-.

olefins, hexamethylenes, or alkylated hexameth-' ylenes which might result from the loss of various amounts of hydrogen. It is not known at the present vtime whether ring closure occurs at the loss of one hydrogen molecule or whether dehydrogenation of the chain carbons occurs so that the first ring compound formed is an aromatic for the manufacture of the present types of catalysts and these materials have furnished types of activated alumina which are entirely satisfactory. Precipitated trihydrates can also be dehydrated at moderately elevated temperatures to form satisfactory types of alumina. Crystallographically and X-ray spectroscopically, this most satisfactory type of alumina is referred to asgammaprimary compound as 2,3-dimethyl hexane the prinicipal resulant product is apparently o-xylene although there are concurrently produced deflnite yields of such compounds as ethyl benzene indicating an isomerization of two substituent l5 methyl groups.- In the case of nonanes which are represented by the compound 2,3,4-trimethyl hexane, there is formation not only of mesitylene but also of such compounds as methyl ethyl benzene and various propyl benzenes.

It will be seen from the foregoing that the scope of the present invention is preferably limited to the treatment of aliphatic hydrocarbons which contain at least 6 carbon atoms in straight chain arrangement, In the case of paraflin hydrocarbons containing less than 6-carbon atoms in linear arrangement, some formation of aromatics may take place due to primary isomerization reactions although obviously the extent of these will vary considerably with the type of comside reactions tends to increase and yields of the desired alkylated aromatics decrease in proportion.

While any suitable type of catalyst having dehydrogenating and cycling properties may be employed for converting parafflns into substantial yields of aromatics, according to this invention, a satisfactory catalytic material comprises a major proportion of a refractory spacing agent, carrier, or support selected from the group consisting of alumina, magnesia, silica, diatomaceous earth, and activated clay and a relatively minor proportion of an oxide of an element or a combination of oxides of-elements selected from members of the left-hand columns of groups 4, 5, and 6 of the periodic table consisting of titanium, zirconium, cerium, hafnium, and thorium; vana-' dium, columbium, and tantalum; chromium, molybdenum, tungsten, and uranium.

The carriers or supports referred to above have relatively low catalytic activities while the oxides of the elements mentioned are of relatively high catalytic activity and furnish by far the greater proportion of the observed catalytic efiects. The oxides of these several elements vary somewhat in catalytic activity in any given reaction comprised within the scope of the invention and this variation may be greater in'the case of different types of dehydrogenation and cyclization reactions.

. In regard to the preparation of alumina which is generally preferable as a carrier or support for the preparation of dehydrocycling catalysts, it may be stated that three hydrated oxides of aluminum occur in nature, to wit, hydrarqillite or gibbslte having the formula A1203.3H2O, bauxite having the formula AlzOsZHaO. and diaspore, having the formula AlaO:.H20. Of these three minerals the corresponding oxides from the trihydrated and dihydrated minerals are suitable be involved. For example, in the case of such a 1.

alumina, crystallizing in the cubic system, the length of the edge of the unit cube being about 7.90 Angstrom units. Alumina in the form of powdered corundum or prepared by dehydrating diaspore is not suitable. 1

It is best practice in the final steps of preparation 'of aluminum oxides for use in the catalyst composites to ignite them for some time at temperatures within the approximate range of 900- 1050 F. This does not correspond to complete dehydration of the hydrated oxides but gives catalytic materials of good strength and porosity so that they are able to resist for a long period of time the deteriorating effects of the service and reactivation periods to which they are'subjected.

The catalytic dehydrogenating efficiency of alumina is greatly improved by the presence of oxides of the preferred elements in relatively minor amounts. The oxides which constitute the rincipal active catalytic materials may be deposited upon the surface and in the pores of the activated alumina granules by several alternative methods, suchas, for example, the ignition .of nitrates which have been absorbed or deposited from aqueous solution by evaporation or by a similar ignition of precipitated hydroxides. As an alternative method, though obviously less preferable, thefinely divided oxides may be mixed mechanically with the alumina granules either in the wet or dry condition. The point of achieving the most uniform practical distribution of the oxides on the alumina should constantly be borne in mind since the observed catalytic effects evidently depend principally upon surface action.

While dehydrogenation of aliphatic hydrocarbons may be effected in the presence of a large number of carriers supporting members of a relatively large group of oxides as hereinabove indicated, oxides of a few metals of this group have been found, in general, to be more useful than others either as individual oxides, as mixtures of oxides of.a particular metal, or as mixtures of any combination of oxides of the elements vanadium, chromium, and molybdenum. Methods of preparing dehydrogenating and cycling catalysts containing oxides of these elements are described in later paragraphs of this specification. The oxide of vanadium which results from the ignition of the nitrate, the .hydroxide, or the carbonate is principally the pentoxide V205 which is reduced by hydrogen to form the tetroxide V204. or the corresponding dioxide V0: and then to the sesquioxide V203. In any case the primary deposition of vanadium compounds upon alumina granules may be made-by the use of the soluble vanadyl sulfate or the nitrate and also solutions of ammonium and alkali metal vanadates may be employed, which furnish alkaline residues on ignition. It is probable that the sesquioxide is the principal compound which accounts for the catalytic activity observed with vanadium catalystsin reactions of the present character.

The element chromium has three oxides, the trioxide (310:, the dioxide CrOa, and the sesquioxide Cl'aOs, the last named being readily pro-- duoed by heating the trioxide in hydrogen or pheric.

it'drocarbon vapors at a temperature of 480 F. l'he dioxide has been considered to be an equimolecular mixture of the trioxide and the sesqui oxide. The oxides are readily developed on the surfaces and pores of alumina or'other carrier granules by utilizing primary solutions of chromic acid H2CrO4 or chromium nitrate Cr(NOa)a. The

vent by the addition of another material, as water,

- which renders the solvent and extracted oil muignition of the chromic acid, the nitrate, or the precipitated trihydroxide produces primarilyithe trioxide which is then reduced to the sesquioxide to furnish an active catalyst for use in reactions of the present character.

The two most important oxides of molybdenum trioxide by hydrogen begins at about 570 F. and I the reduction is rapid at 840 F'. the effective catalytic 'material is principally the sesquioxide. The trioxide may be added to the active alumina carrier from a solution in aqueous ammonia or from a solution of ammonium molybdate which is added in amounts just requisite to wet the carrier granules uniformly and the mass is then dried and calcined.

It has been found essential in the production of high yields of aromatic from parafllnic and olefinic hydrocarbons when using the preferred types of dehydrocyclization catalysts that, depending upon the aliphatic hydrocarbon or mixture of aliphatic hydrocarbons being treated, temperatures from 850 to 1200 F. should be employed, contact times of approximately 0.1 to 60 seconds, and pressures approximating atmos- The use of sub-atmospheric pressure of the order of atmosphere may be beneficial in that reduced pressure generally favors selective" dehydrogenation reactions, but on the other hand moderately superatmospheric pressure usually of the order pf less than 100 pounds per square inch, increases the capacity of commercial plant equipment, so that in practice a balance is struck between these two factors.

It will be appreciated by those familiar 'with the art of hydrocarbon conversion in the presence of catalysts that the factors of temperature, pressure, and time will frequently need to be adjusted upon the basis of preliminary experiments to produce the .best results in any given' instances The criterion of the yield of aromatics will serve to fix the best conditions of operation and in general the relations between temperature, pressure, and time are adjusted preferably so that rather intensive conditions are employed of suflicient severity to insure a maximum amount of the desired cyclization reactions with a mini- 7 mum of undesirable side reactions. If the times of catalytic contact employed are too short the conversion reactions may not proceed beyond those of simple dehydrogenation and the yields of olefins and diolefins will predominate over those of aromatics. I

Among the solvents which maybe used. for separating products of dehydrocyclization reactions into mixtures comprising essentially aromatic and olefinic hydrocarbons from paraffinic hydrocarbons. are sulphur dioxide, furfural, nitrobenzene,

phenol, icresol, ,Bfi-dichloroethylether, methylcarbitol, and others which have selective solvent effects and which are capable of being recovered by one of several well known methods. Such methods of solvent recovery include distillation tualiy immiscible.

For the purpose of illustrating the process of the present invention, the attached drawing shows diagrammatically a typical process flow for producing aromatic hydrocarbons from paraflinic hydrocarbons containing a chain of 6-12 carbon atoms per molecule.

Referring to the drawing an aliphatic hydrocarbon iraction comprising essentially paraflins and oleflns containing 6l2 carbon atoms per molecule is introduced through line i to dehydro- -cyclization zone 2 which may comprise a chamber or a plurality of'chambers containing a granular dehydrocycling catalyst maintained under conditions of temperature, pressure, and time adequate to effect substantial formation of aromatic hydrocarbons and relatively minor production of olefinic hydrocarbons bydehydrogenation and cycling reactions. Dehydrocyclization zone 2 may also infrom which gaseous products are discharged throu h line 5. I

Normally liquid hydrocai bo'ns consisting of paraflins, oleflns, and aromatics are conducted from separation zone 4 through line 6- to extraction zone I in which a mixture of aromatic and olefinic hydrocarbons is extracted from paraflinic hydrocarbons. This extraction of aromatic-and olefinic hydrocarbons from paraflinic hydrocarbons may be made elther by batch or continuous processes although from the standpoint of eiliciency the method of counterflow extraction is preferable in common operations. The details of the batch and counter-flow procedures are generally well known in common practice and need not be enlarged upon here since they form no special feature of the present invention.

From extraction zone 1 a railinate comprising essentially paraflinic hydrocarbons isconducted through line 8 and recycled by way of line I to further treatment in dehydrocyclization zone 2.

Before this ramnate is recycled it may be necessary to remove relatively small amounts of solvent contained therein. For example when sulphur dioxide is the solvent it may be desirable to wash the raiiinate with water and/or caustic soda solution and dry the same before it is returned to further dehydrocycling treatment.

From solvent extraction zone I the solution containing dissolved olefins and aromatic hydrocarbons may be withdrawn through line 9 to separation zone I ii in which the hydrocarbons are separated from the solvent. Recovered solvent is conducted from separation zone It through line i I and recycled through line 6 to further use in extraction zone 1. Fresh solvent may be introduced to line 6 as desired through line l2, while used'and recovered solvent may be withdrawn from line H by way of line l3. The nature of separation zone i0 is dependent upon the solvent where the extracted oil and the solvent boil within different ranges, and the precipitation of the solemployed. In case the preferred solvent is sulphur dioxide, it may be separated by fractional distillation from the aromatic and olefinic hydro-- the hydrocarbon product to remove -the relatively small amounts of solvent present.

The mixture of aromatic and olefinic hydrocarbons separated from the selective solvent in separation zone I is conducted thence through line ll to a second dehydrocycling zone containing granular dehydrocycling catalystand operated at conditions of temperature, pressure, and time adequate to efiect substantially'complete conversion to aromatics of the olefinic, hydrocarbons present in the product obtained from the first dehydrocyclization step. Thus the aromaticolefinic extract containing relatively minor proportions of olefins is subjected to further cycling in contact with essentially the same type of dehydrocyclization catalyst such as 2-25% chromium sesquioxide on alumina at a temperature gaseous products are discharged through line It and substantially pure aromatic hydrocarbons are withdrawn through line l9 to storage.

The catalytic process herein described makes possible the conversion of aliphatic hydrocarbons into pure aromatics or aromatic mixtures which are free from oieflns and suitable for nitration or for other chemical reactions or uses where-olefins are objectionable. Also by this process the olefins contained in the products Of the first cyclization stage are converted further to aromatics in the second stage so that the yield of aromatic hydrocarbons is increased considerably over that obtainable by dehydrocyclization in a single stage.

The following example is introduced to show results obtainable in the operation of the process although these data are not presented with the intention of limiting unduly the broad scope of the invention.

A mixture of '75 mole per cent paraffinic and 25 mole per cent oleflnic hydrocarbons boiling within the range of 150-400" F. was passed at 1050 F.

under atmospheric pressure through-a tube containing a layer of 3 x 3 mm. pellets formed from a composite consisting of 12% chromium sesquioxide and 88% activated alumina. When the hydrocarbon mixture was charged at a rate corresponding to an average contact time of 2 seconds, the product of this treatment contained 60% aromatics, 20% olefins, and 20% paraflins. The parafllns, separated from the oleiins and aromatics by extraction with liquid sulphur dioxide, were recycled to the original dehydrocyclization zone while the extracted hydrocarbons after removal and re-use of the sulphur dioxide solvent were conducted to a second catalyst reactor containing another portion of the 12% chromium sesquioxide on alumina catalyst at 1150 F. under atmospheric pressure using a charging rate corresponding to an average contact time of 5 seconds. The latter treatment gave relatively small amounts of hydrogen and other gaseous products and produced a normally liquid aromatic fraction substantially free from olefinic hydrocarbons and suitable for nitration use.

The foregoing specification and example show clearly the character of the invention and the results to be expected in its application to all- I phatic hydrocarbons including paramns and olefins although neither section is unduly limiting.

We claim as our invention;

l. A rocess for the production of aromatic hydrocarbons from aliphatic hydrocarbons havin 6-12. carbonatoms to the molecule which com-. prises subjecting the hydrocarbon to contact with a dehydrocycling catalyst under dehydrocyclin conditions of temperature and pressure, subjecting the resulting conversion products comprising aromatics, olefins and parafllns to the action 01 a solvent to effect the separation of a parafllnic rafinate an n extract comprisingcleflns and aromatics, and subjecting said extract to contact with a separate dehydrocycling catalyst under independently controlled conditions of temperature and pressure to form a substantially olefinfree aromatic product.

2. The process or claim l further characterized in that said railinate is subjected to further treat! ment in contact with the first mentioned dehydrocycling catalyst.

v3. A process for producing a substantially oleiln-free aromatic hydrocarbon fraction which comprises contacting aliphatic hydrocarbons including paraflins and oleflns of 6-12 carbon atoms per molecule with a dehydrocycling catalyst at a temperature in the approximate range of 850-1200 F. under a pressure from substantially atmospheric to approximately pounds per square inch to form a product comprising essentially aromatic, olefinic, and parafiinic' hydrocarbons; extracting said product by a selective solvent to separate a substantially paramnic raffinate from a mixture comprising essentially ole- .finic and aromatic hydrocarbons; recycling s'aid rafiinate to contact with the original dehydrocycling catalyst; and subjecting said mixture of olefinic and aromatic, hydrocarbons to contact with a separate dehydrccycling catalyst under independently controlled conditions of temperature and pressure to produce a substantially olefin-free aromatic product.

4. A process for producing a substantially olefin-free aromatic hydrocarbon fraction which comprises contacting aliphatic hydrocarbons including paraifins and olefins of 6-12 carbon atoms per molecule at a'temperature in the approximate range of 8501200 F. under a pressure from substantially atmospheric to approximately 100 pounds per square inch for a time of contact of the approximate order of 0.1-60 seconds with a composite of 98-75% by weight of activated alumina and 2-25% by weight of chromium sesquioxide to form a product comprising essentially aromatic, olefinic, and paraillnic hydrocarbons; extracting said product by liquid sulphur dioxide to separate a substantially paraifinic raflinate from a mixture comprising essentially olefinic and aromatic hydrocarbons; recycling said raffinate to contact with the original dehydrocycllng catalyst; and subjecting said mixture of olefinic and aromatic hydrocarbons at a temperature in the approximate range of 850-1200" F. under substantially atmospheric pressure for a time in the approximate range, of 1-100 seconds to contact with a separate composite of 98-75% by weight of activated alumina and 2-25% by weight of chromium sesquioxide to produce a substantially olefin-free aromatic product.

ARIS'I'ID V. GROSSE. WIILIAM J. MATTOX.

intended to be

Images