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liatentediluly 26,. 1938 2,124,567 PATENT OFFICE UNITED 1 STATES; ' ‘ ' ' ‘ REISSUEi-J 2424.501 CONVERSION OF HYDBOGABBONS Ariatidiv. Grease, Chicago, 11]., assignor to Uni ,veraai Oil Products Company. Chicago. 111., a corporation of Delaware - 'No'lh'awing. Application October 15, 1936. 80118] 4. JUN 25 1940 no. 105.111 4 (cl. zoo-.168) ' This invention relates‘ particularly to the con-‘_ hydrocarbon into an aromatic hydrocarbon of the version of straight chain ' hydrocarbons into closed chain or cyclic hydrocarbons. . ,4 . ' . More speci?cally, it ‘is concerned with a process 5 involving the use of special catalysts and speci?c conditions of. operation in regard to temperature,‘ ’ pressure ‘and time of reaction whereby aliphatic hydrocarbons 'can be e?iciently, converted into aromatic hydrocarbons. 10 ' ' In the straight pyrolysis. of pure hydrocarbons or hydrocarbon mixtures such as those encoun tered in fractions from petrolemor other natur ally occurring or synthetically produced hydro carbon mixtures the reactions involved which 15 produce aromatics from paraiiins and ole?ns are of an exceedingly-complicated character and con not be very readily controlled. — _ It is generally recognized that, in the thermal‘ decomposition of hydrocarboncompounds or by V 20 drocarbon mixtures of relatively narrow range that whatever intermediate reactions are involved, there is an overall loss of hydrogen, a tendency to carbon ~separatlon'and a generally wider boil ing range in the total liquid products as com 25 pared with the original chargez. Under mild cracking conditions involving relatively low tem peratures and pressures and short times of ex posure to cracking conditions it is possible to same number of carbon atoms by way of the pro gressive steps shown. If this is done it‘ is usually with very low yields which are of very little or no practical signi?cance. ‘ '. _ 5 The search for catalysts to speci?cally control and accelerate desired conversion reactions 'amonghydrocarbons has been attended with the - usual difficulties encountered in ?nding catalysts forv other types of reactions since there are no 10 basic laws or rules for predicting the effectiveness of catalytic materials and the a as a whole is in a more or less empirical state. 11 using catalysts even in connection with conversion reactions among pure hydrocarbons and_particularly in 15 connection‘ with theconversion of the relatively heavy distillates and residua which are available for cracking, there is a general tendency for the decomposition reactions to proceed at a very rapid rate, necessitating the use of extremely short time 20 factors and very accurate control of temperature and pressure to avoid too extensive decomposition. There are further di?lculties encountered. in, maintaining the e?iciency of catalysts. employedv in pyrolysis since there is usually a rapid depo- 25 sition of carbonaceous materials on their sur- ‘ faces and in their pores. _ - _ The foregoing brief review of the art of hy- ' some extent to control crackingreactions so that . drocarbon pyrolysis is given to furnish a general 30 they are limited ‘to primary decompositions and. background for indicating the improvement .in 30 there is a minimum loss of hydrogen and a max‘ such processes which is embodied in the present imum production oi’ low. boiling fractions con sisting of compounds representing the fragments of the original high molecular weight compounds. .35 .As the conditions of pyrolysis are increased in severity using higherv temperatures and higher times of exposureto 'pyrolytic' conditions, there ‘ is .a progressive increase in loss othydrogen and a large amount of secondary reactions involving 40 recombination of primary radicals to form poly mers and some cyclization toi'orm naphthenes and aromatics, but the mechanisms involved in invention, which may be applied to the treatment of pure para?in or ole?n hydrocarbons, hydro carbon mixtures containing substantial percent- . vages oi’ para?ln hydrocarbons such as relatively 35 close cut fractions producible by distilling petro leum, and analogous fractions which contain un saturated as well as saturated straight chain hy- - drocarbons, such fractions resulting from crack ing operations upon the heavier fractions of pe- 40 troleum. ‘ ' In- one speci?c embodiment the present in these cases are of so complicated a nature that veution comprises the conversion of aliphatichy very little positive information has been evolved drocarbons including para?in and ole?n hydro 45 in spite of the large amount of experimentation ' carbons into aromatic hydrocarbons by subject- 45 which has been done and the large number of ing them at elevated temperatures of the order theories proposed; In general, however, it may of 400-700° vC. to contact for de?nite times of the be said that, starting with para?ln hydrocarbons order of 6-50 seconds with catalytic materials representing the highest degree of saturation, comprising major proportions of aluminum oxide ‘ , these compounds are changed progressively into , ole?ns, naphthenes, aromatics, and ?nally into of relatively low vcatalytic activity supporting 50 minor proportions vof oxides of elements selected ' carbon and hydrogen and other light ?xed gases. vfrom those occurring in the lefthand columns of" It is- not intended to infer from this statement Group VI of the periodic table, these oxides hav ' that any particular success has attended the con‘ 55 version of any given para?in or other aliphatic ing relatively high catalytic activity. - . According to the 'present invention aliphatic or 55 2 2,124,007 ' _It will be seen from the foregoing that the scope straight chain hydrocarbons having 6 or more of the present invention is preferably limited to carbon atoms in chain arrangement in their ' the treatment of aliphatic hydrocarbons which structure are specifically dehydrogenated in such contain at least 6 carbon atoms in ‘straight chain a way that the chain of carbon atoms undergoes arrangement. In the case of para?‘in hydrocar ring' closure vwith the production in the simplest. ' bons containing less than 6 carbon atoms in linear case of‘ benzene from n-hexane or n-hexene and arrangement, some formation of aromatics may in the case of higher molecular weight paraiiins take place due to primary isomerization reactions of various alkyl derivatives of benzene.‘ Under although obviously the extent of this will vary properly controlled conditions of- times of con-" considerably with the type of compound and the 10 tact, temperature and pressure, very high yields of the order of 75 to 90% of the benzene or aro matic compounds are obtainable which are far in conditions of operation. The process is readily applicable to parafiins from hexane up to dodec excess of any previously obtained in the art either with or without catalysts. For the sake of illus crease in molecular weight beyond this point the 10 ane and: their corresponding oleflns. With in percentage of undesirable side reactions tends to trating and exemplifying the types of hydrocar increase and yields of the desired alkylated aro bon conversion reactions which are specificallyv matics decrease in proportion.‘ _ 4 accelerated underthe preferred conditions by the According to the present invention'composite present types of catalysts, the following structural catalytic materials are employed which comprise equations are introduced: in general major proportions by weight of granu 20 15 lar activated aluminum oxide as a base catalyst or CH 20 / CH: v G1?‘ on’ CH1 ‘ on on CH CH 1:! CH: +411, CH: 4 supporting material for minor proportions of oxides of the elements in the lefthand column of CH n-hexane of relatively low catalytic activity while» the ox- ' benzene ides of the elements mentioned are of relatively C-CH: / CH1 \ 0st. 30 cal-on. on, on a. on; on, »_ on on +411’ v on n-heptane on toluene ' CH 1 ' / , \ CH: CHI-CH: 0 CHI-‘CH: a v high catalytic activity and furnish by far the ' on CH: n-octane on C-CH; CH C-CHs :2 Group VI of 'the periodic table'comprising the elements chromium, molybdenum, and tungsten. The base material comprising aluminum oxide is ‘+411, C o-xylene greater proportion of the vobserved catalytic ef 30 fects. The oxides of these several elements vary somewhat in catalytic activity in any given re-‘ action comprised within the scope 'of the inven tion and this variation may further vary in the. . v case of different types of dehydrogenation and 35 cyclization reactions. Some of. the properties of these catalytically active oxides, which are de veloped on the surface and in the pores of the alumina particles will be described in succeeding ‘paragraphs. 40 - It should be emphasized that in the ?eld of catalysis there have been very few rulesv evolved I In the foregoing table the structural formulas. which would enable the prediction of what ma of the primary para?ln hydrocarbons have been ~ terials would catalyze a given reaction. Most represented as a‘ nearly closed ring instead of by , of the catalytic work has been done on a purely empirical basis, even ‘though at times certain 45 the usual linear arrangement for the sake of indi cating the possible mechanisms involved. No at ‘groups of" elements or compounds have been found to be'more or less equivalent in accelerating tempt has been made to indicate the possible in termediate existence of mono-ole?nsf'diole?ns, certain types of reactions. is generally‘ preferable hexamethylenes or "'alkylated ~ hexamethyienes' so Aluminum oxide which‘ which"mi“ghtjresult from the loss of various .as a base material for the manufacture of cata- ' amounts of hydrogen.v It is not known at the I lysts for the process may be obtained from natural ' 4' present time whether ring closure occurs at the aluminum oxide minerals or ores such- as bauxite loss of one hydrogen molecule or whether dehy or carbonates such as dawsonite byfproper cal-' cination,'or it may be prepared by precipitation - drogenation of the chain carbons occurs so that 55 the ?rst ring compound formed is an aromatic of aluminum hydroxide from solutions of alumi such as benzene or one of its derivatives. ‘The num sulfate or different alums, and dehydration above three equations are of. a relatively simple ‘character indicating generally the type of reac of the . precipitate of aluminum hydroxide by heat. Usually it ‘is desirable ‘and advantageous tions involved but in the case of n-para?lns or ' to further treat it with air or other gases, or by 60 mono-ole?ns of higher molecular weight than the octane shown and in the case of branched , chain. compounds which contain various alkyl substltuent groups indifferent positions along the six-carbon atom chain, more complicated re 65 actions will be' involved. ' For example, in the case of such a primary compound as 2,3-dimethyl " :hexane the principal! resultant product is appar ently o-xylene although there are concurrently produced‘ e?nite yields 'of- such‘ compounds as _ _ . ethyl benzene indicating an isomerization of two‘ substituent methyl groups. 'In the case of other means to'activ'ate it prior to use. so _ Two hydrated oxidesof aluminum occurin na ture, to-wit:- bauxite having the formul'aAhOa.v ' ' ' 21-120 and, diaspore A12Oa.H2O. _ In both of' these oxides iron sesqui-oxide may partially replace the alumina. ‘These twominerals or corresponding oxides produced from precipitated aluminum hy- ' e ' droxide ‘ are particularly suitable, ‘for the manu facture of the present typev of catalysts and in some instances have given the best results of any of the base compounds whose .use is at present nonanes which are represented bythe compound; contemplated:v > The mineral dawsonite having " 2,3,4-trimethyl hexane, there is formation not'.. the formula Na:Al(COa) 3.2A1(OH)3 is another only of mesitylene'but also of such compounds as 75 methyl ethyl benzol and various propyl benzols. i mineral which may be used as a source'of alumi num oxide. - ' 75 - 2,124,507 3‘ It is best practice in the ?nal steps of preparing to drive off’ water and leave a aluminum oxide‘as a base catalyst to ignite it for heated of oxides on the carrier particles. '. some time at temperatures within the approxi In regard to uranium,,which is the heaviest‘ mate range of from 800-900“ C. This probably member of the present natural group of elementsdoes not correspond to complete dehydration of whose oxides are preferred as catalysts, it may‘ the hydroxide but apparently gives a catalytic merely be stated‘that while this element furnishesi material of good strength and porosity so that it is catalytic oxides having some order of catalytic _ able to resist for a long period of time the deteri orating effects of the service and regeneration 10. periods to which it is subjected. _. _ ,My investigations have also de?nitely demonstrated that the catalytic e?lciency of alumina, activity, its scarcity and cost naturally pres, cludes its extensive use in practice, . 'rIt has been found essential to. the production 10 of high yields of aromaticsfrom aliphatic. hy drocarbons when using the preferredtypes of‘ catalysts-that depending upon the aliphatic hy which has some catalytic potency in itself. is greatly improved by the presence of oxides of the ' drocarbon or mixture of preferred elements in relativelyminor amounts, hydrocarbons ‘ being ' treated, temperatures from 400Jl00° 0., should usually of the order of less than 10% by weight be employed. contact times of approximately 6 of the carrier. It is most common practice to i5 - to 50 seconds and pressures approximating at utilize catalysts comprising 2 to 5% by weight of mospherie, The use of subatmospheric pressures these oxides, particularly the lower oxides. of the order of V4 atmosphere may be bene?cial .. 20 The oxides which constitute the principal ac-‘ in that reduced pressures generally favor selec 20. tive catalytic materials may be deposited upon tive dehydrogenation reactions but on the other the surface and in the pores of the activated hand ‘moderately supe'ratmospheric pressures alumina granules by' several ‘alternate methods‘ usually of the order of less than 100 lbs. per such as for example, the ignition of nitrates squarevinch tend to increase the capacity ofcom 25 which have been adsorbed or ‘deposited from mercial plant equipment so that in‘practice a_ . aqueous solution by evaporation or by a similar balance is struck between these two factors. The ignition of precipitated hydroxides. As an al times of contact most commonly employed with ternative method though 'obviouslyless prefer n-para?lnic or mono-ole?nic hydrocarbons hav- ' ' ing from 6-12 carbon atoms tothe molecule are able, the ?nely divided oxides may be mixed‘me 30 chanically with the alumina granules ‘either in of the'order of 8-20 seconds. - It will be appreci 30' the wet or the dry condition. The point- oi’v - ated by‘ those familiarwlth the art of hydrocar-' ‘achieving the most uniform practical distrlbu- bon conversion in the presence of catalysts that the factors of temperature, pressure and .‘time tion of the oxides on the alumina should con stantly be borne in mind since the observed: cata , will frequently have to be adjusted from there 35 lytic effects evidently depend principally upon a sults of preliminary experiments to produce the surface action. . ‘_ best results in any given instance. The criterion, The element chromium has three oxides, the of the yield of aromatics will serve to'?x the trioxide CI'OQ, thedioxide CrO; andv the sesqui- - best conditions of operation. -‘ In ageneral sense oxide OM03, the last-named being readily pro duced. by heating the trioxide in hydrogen or . hydrocarbon vapors at a temperature of 250°‘ the relations between ,time, temperature and pressure are preferably. adjusted so that rather intensive conditions are employed of su?l'cient severity to insure a maximum amount of the cyclization reactions with a minimum of equimolecularv mixture of the trioxide and the;_ desired undesirable side reactions. If too short times of sesquioxide. The oxides are readily developed 45 on the surfaces and pores of alumina granules contact are employed the conversion reactions C. The dioxide has been considered‘ to be an 50 by utilizing primary solutions of chromic acid 'will not proceed‘ beyond those of simple de HaCrO; or chromium nitrate‘ Cr(NO=) a. The hydrogenation and the. yields of ole?ns and di-‘ ignition of the chromic acid, the nitrate or a ; ole?ns will predominate over those of aromatics. While the present process is particularly ap precipitated trihydroxide produces primarily the _ plicable to the production of the corresponding trioxide which is then reduced tov the sesquioxide to furnish an active catalyst for use in reactions ' of the present character. The two most important oxides of molybdenum -55 which are alternatively employed as catalysts ac'-. cording to the present invention ‘are the dioxide M00: and sesquioxide M0203. Since the reduc " tion of the trioxide by hydrogen begins at.300° C. (572° F.) and the reduction is rapid at 450°‘ 60 C. (842° F1). the e?’ective catalytic material is ‘ principally the sesquioxide. The trioxide may aromatics from‘an aliphatic hydrocarbon or a 45 50. mixture of aliphatic hydrocarbons, the invention may also be employed to produce aromaticsfrom ' aliphatic hydrocarbon mixtures such as'distillates from para?'inic or mixed base crude petroleum. In this case the aromatic character of the dis 55 tillates will-.be increased and as a rule the octane If desired and found ' number. will be higher. feasible on a basis of concentration, the aromatics produced in' the hydrocarbon mixtures may be v60 recovered as such by' distillation into fractions be added-to the active alumina carrier from a -of proper ,boiling range followed by chemical .of ammonium molybdate which are added in treatment with reagents capable of reacting se 65 amounts just requisite to wet the carrier granules lectively with them. Another method of aromatic uniformly and the mass is then dried and ignited. concentration willinvoive the ‘use of selective sol 65 solution in aqueous ammonia or from a solution The'jelement tungstenhas- three oxides: the trioxide W03, the dioxide WOzand the sesqui oxide W203. The trioxide. is readily soluble in vents such as liquid sulfur dioxide, alcohols,’ fur fural, chlorex, etc; ' _ . _ In operating the process the general procedure is to. vaporize hydrocarbons or mixtures of hy-. 70 aqueous ammonia from which it may be de posited upon active alumina granules and it is drocarbons and after heating the, vapors to a ' ordinarily reduced preliminary to service by the vsuitable temperature within the ranges previously action’ of hydrogen at a red heat. Tungstic acids speci?ed, to pass them through'stationary masses may be precipitated from aqueous solution to of granular :catalytic materialin- vertical cylin 75 form the hydrated oxides’ and these may be . dricah treating columns 0 vbanks ‘of catalyst containing tubes in parallel connection. ' Since 4-. 2,124,567 ‘ i the reactions vare» endothermic it , which had been developed on the carrier-particles I ' may be neces by the ignition of chromium nitrate and the‘ re sary to apply some heat externally to maintain duction of the primary trioxide by hydrogen at the best reaction temperature. After passing a temperature of_250-3G0° C. The hexane frac-‘ through the catalytic zone theproducts are sub tion was passed through a bed of this cat'al'ystat mitted to fractionationvto recover cuts or frac a temperature of 525° C., atmospheric pressure tions containing the desired aromatic ‘product and a time of contact of 20 seconds to produce ‘with the separation of. ?xed gases, unconverted _ a once-through yield -of about 47%. The ?nal hydrocarbons and. heavier residual materials, yield after recycling unconverted-hexane several which may be disposed of in any suitable manner. 10 depending upon their composition. The overall yield of aromatics may be increased by recycling the unconverted straight chain hydrocarbons to further treatment with fresh material, although ' 10, times was above 90% as previously stated. Example '11 f In this case n-heptane was converted to toluene this is a more or less obvious expedient and not speci?cally characteristic of the/present invention. utilizing a catalyst supporting molybdenumpxe ides on the preferred alumina base. The catalyst 15 was made by utilizing a solution of ammonium" It is an important feature of the present proc- . molybdate in an excess of ammonia and adding ess that the vapors undergoing dehydrogenation the concentrated solution to about three times its _ should be free from all but traces of water vapor since the presence of any substantial amounts of weight of granular alumina particles followed by steam ‘reduces the catalytic selectivity of the and ammonia and leave a residue of the trioxide. Before ‘service the particles were treated with hydrogen at about 450° C. to reduce a material composite catalyst to a marked degree. . In. view of the empirical state of the catalytic art, it is not intended to submit a complete explanation ‘of the reasons for the deleterious in?uence of water'vapor on the course of the ‘present type of catalyzed reactions, but it may be suggested that the action of‘the steam may be to cause a partial hydration of alumina and some of the catalytic oxides due to preferential adsorption‘ so that in effect the hydrocarbons are prevented from reaching or being adsorbed by the catalyti cally active surface‘. . careful mixing and calcining to drive o? water v20 portion of the trioxidev to lower'oxides such as the sesquioxide. effective in removing hydrogen from chain com pounds in such a way that cyclization may be promoted without removal of hydrogen from end - . 25 . particles at a temperature of 555°v C'., atmospheric pressure and 13 seconds contact time to produce a yield of approximately 50% of toluene on a once-through basis, this yield being ?nally raised so to about 80% by complete recycling of uncon verted material. _ The present types of catalysts are particularly . , n-I-Ieptane.was passed over a'bed of the catalyst Example III - v This example is given to illustrate the direct formation of toluene from n-heptene, which con version was accomplished using the catalyst simi lar to that described under-Example II, a temper as carbon atoms so that both end and side alkyl groups may appear as substituents in benzene ’ ature of 510° C., atmospheric pressure and a time rings and it has been found that under proper of contact of approximately 20 seconds. The 40 operating conditions they do not tendto promote once-through yield of toluene was ‘76% and the any great amount of undesirable side reactions ultimate yield was in the neighborhood of 93 - leading to' the'deposition of carbonor carbona ceous materials and for this reason show reac tivity over relatively ‘long periods of time. ‘When their activity begins to diminish‘ after a period of service, it is readily regenerated by the simple expedient of oxidizingwith air or other oxidizing gas at a_ moderately elevated temperature, usually within the range employed in the dehydrogena .0 tion and cyclizationreactions. This oxidation effectively removes traces of carbon deposits which contaminate the surface of the particles and decrease their e?iciency. It is characteristic of the present types of catalysts that they may 95% by recycling unconverted ole?n. _ Example v1V To prepare thecatalyst'an ammonlacal aqueQ 45 ous solution of tungsten trioxide was used to 'de- . posit the trioxide upon an activated alumina. After reduction with hydrogen, analyses showed there was. present from 4-5% of mixed tungsten , oxides. , 1 50' ‘ ' Using the above catalystthevapors of n-hep- tane were treated at a temperature of 560° ‘0., substantially atmospheric pressure, and 15 seg/ onds contact time to produce aHyieldsofW46%' of toluene on a once throughbasi's which was ?nally 55 .- be repeatedly regenerated with only a very grad brought to'about a r16% ultimate yield after sev ual loss of catalytic efficiency. recyclings of unconverted charge. During oxidation with air or other/oxidizing eral The foregoing speci?cation and examples show gas mixture in regenerating partly spent matew , clearly the character of the invention ‘and the rial, there is evidence to indicate that the lower res'ults'to be expected in its application to all 60 oxides are to a large extent, if not completely, 60 - oxidized to higher oxides which combine with phatic. hydrocarbons, ~although neither section is intended to be unduly limiting. aluminum oxide to form aluminum salts of vari I claim as-my invention: ' _ able composition. Later. these salts are decomé l. A process for the production of aromatic posed by contact with reducing gases in the ?rst \hydrocarbons from aliphatic hydrocarbons’ of 65 stages of service ‘to reform the loweroxides and regenerate the real catalyst and hence thecata-' from six to twelve carbon atoms, which comprises . lytic activity. ' ' ' Example I In this example an ultimate yield of 'over 90% benzol was produced by the catalytic conversion ,of an n-hexane. fraction‘ obtained-from a highly dehydrogenating and cyclicizing the aliphatic hydrocarbon byssubjectionto a temperature of the order of 400 to ‘700° C. for a period of about _ 6 to 50 seconds, in the presence of, an aluminum 70 a oxide catalyst containing a relatively small amountof an oxide of a metal fromthe left. hand para?ln'ic crude petroleum by close fractionation.’ ,column of Group 'VI' of -the periodic table and . selected from the class consisting. of chromium,‘ The catalyst comprised an alumina base support75 ing about 4% by weight of chromium sesquioxide ' molybdenum,v tungsten ‘and uranium. , . ‘ ' 75 2,124,007 2. A~process for the production of aromatic hydrocarbons from aliphatic hydrocarbons of from six to twelve carbon atoms, which c0m-, prises dehydrogenating and cyclicizing theoali phatic hydrocarbon by subjection to a tempera ture of the order of 400 to 700° C. for a period oi.’ about 6 to 50 seconds, in the presence of an aluminum oxide catalyst containing a relatively small amount of an oxide oi.’ chromium. 10 3. A process for the production of aromatic hy drocarbons from aliphatic hydrocarbons of from six to. twelve carbon atoms, which comprises de hydrogenating and cyclicizlng the aliphatic hy drocarbon by subjection to a temperature otthe v 5 order 01' 400 to 700° C. for a period'o! about 6 to 50 seconds,‘ in the presence 0! an aluminum oxide catalyst containing, a relatively small amount of an oxide of molydenum. 4. A process for the production of aromatic hy drocarbons irom aliphatic hydrocarbons of from six to twelve carbon atoms, which comprises def hydrogenating and cyclicizing the aliphatic hy drocarbon by subjection td a temperature of the order ot’400 to IZ00“ C. for a period or about 6 to 50 seconds, in the presence of an aluminum oxide catalyst containing a relatively vsmall amount of an oxide of tungsten. - ' ' ,ARISTID V. GROSSE, .