US2317683A - Cyclization of hydrocarbons - Google Patents

Description

' been studied in considerable detail.

Patented Apr. 27, 1943 UNITED STATES PATENT OFFICE CYCLIZATION OF HYDBOCARBONS Bernard 8. Greensielder, Berkeley, Calif assignor to Shell Development Company. San

Francisco, Call! a corporation of Delaware No Drawing. Application February 27, 1941,

Serial No. 880,893

16 Claims. (01.269-668) hydrocarbons is, however, as by-products from the distillation of coal. Consequently; their supply is primarily dependent upon the condition of the steel and coal tar industries and is in any case limited. Aside from the myriad of uses where their application is. more or less obligatory, aromatic hydrocarbons have a great many potential uses which have been hitherto curtailed by the limited supply and relatively high prices. For example, aromatic hydrocarbons of. relatively low molecular weight have become of increasing importance for use as solvents, etc. and especially as components of liquid fuels in view of their excellent ignition characteristics. view'of these circumstances there is an urgent demand for a practical and economical process whereby aromatic hydrocarbons may be produced from other sources.

The most promising source of aromatic hydrocarbons, other than coal tar, is petroleum.

Aromatic hydrocarbons can be produced from petroleum hydrocarbons, at least theoretically, in any one of several ways, all of which have It is known. for example, that aromatic hydrocarbons are produced from non-aromatic petroleum hydrocarbons under severe thermal cracking conditions. Thus, cracked distillates obtained from high temperature 1' more or less severe cracking operations genera y contain a certain amount of aromatic hydrocarbons. This method is, however, generally impractical for the production of may be produced by the thermal treatment of light hydrocarbon gases at high temperatures according to the Fischer process. This process,

however, requires temperatures in the neighborhood of 1000 C. to 1300 C. and requires the use oi. a large number of expensive alloy reaction tubes of extremely small dimensions. The process furthermore tends to give relatively low yields oi! aromatic hydrocarbons which are predominantly of the less desired polynuclear type.

It has been found that aromatic hydrocarbonsv may be synthesized by the catalytlccyclizationdehydrogenation oi open chain hydrocarbons. This new reaction holds considerable promise in that it allows aromatic hydrocarbons to be pro-. duced in almost any desired quantities from inexpensive and readily available hydrocarbons and particularly the normal aliphatichydrocarbons which, in view of their poor ignitioncharacteristics, areleast desirable for gasoline-type fuels.- A further advantage which can-be gained bythe utilization of catalytic'cyclization is that, it naphth'enic hydrocarbons are "present in the hydrocarbon" fraction treated, these may be simultaneously dehydrog'enated to aromatic hydrocarbons, thus increasing the yield. In view of'the great possibilities aflorded by the cyclizapure aromatic hydrocarbons or highly aromatic hydrocarbon fractions in view oi the low yields, excessive production of gas and extensive treatment required to separate the aromatic hydrocarbons formed ,from olefines, diolefines I and other crackedproducts which are simultaneously formed.

It is also known that aromatic hydrocarbons tion reaction, a great deal of'workhas been done to bring this reaction into the realm of practical application. f 1 Y The production-5 1' aromatic hydrocarbons by cyclization' requires catalysts having'dehydrogenating activity. This has been considered by some to indicate that the conversion 01' open chain hydrocarbons to aromatic hydrocarbons is a multi-step reaction" involving dehydrogenation. It is therefore sometimes referred to as *cyclizanon-dehydrogenation." "dehydrogenation-cyclization" and dehydrocyclization." It is known, howeventhat the cyclization ability of a given catalyst involves more than simply its dehydrogenating ability. Although nearly all classes of dehydrogenating catalysts have been investigated with regard to their possible. cyclization activities, only a relatively few. have been iound'to exert an appreciable cyclization activity. Cyclization activity appears .to be practically confined to compounds of metals of the left-hand columns of groups IV, V and VI of the periodic table.

Of these, those of group VI and especially chromium are by far the most active.

The cycliza-tion ability of the various. cata-' lytic metal compounds is, in general, relatively little aflected by the type of compound in which the metal-is combined. Thus, for example, the

oxides, sulfides, halides, selenides, tellurides,

phosphates, manganates, molybdates, chromates, chromites, tungstates, etc. or mixtures thereof may generally be employed. Generally speaking,

erably used in the form of their oxides.

These cyclizing metal compounds per se are, however, not generally suited for practical application due to. the fact that they quickly lose their cyclizing activity in use. In order to produce aromatic hydrocarbons in a more econom I alumina gels, activated bauxite and the like. A

particularly effective adsorptive alumina is that prepared according to the process of U. S. Patent 1,868,869 and commonly used'in the trade under the name "activated alumina.

The cyclizing metal compound and relatively inactive stabilizing compound may be employed in a wide range of proportions. In general, however, the stabilizing material functions also as a carrier material and is used in excess. Suitable catalysts may comprise, for example, an adsorptive and stabilizing carrier material supporting from 2% to 30% of a catalytically active metal in the form of a suitable compound such as an oxide, sulfide, or the like.

- These supported catalysts may be prepared in any one of several conventional manners. A convenient method comprises impregnating a suitable carrier in the form of granules or pellets of the desired size with a solution of a compound of the metal which it is desired to combine with the carrier, and then drying. The concentration of the impregnating solution used in this particular case will depend upon the solubility of the particular metal compound at the temperature of the impregnation and upon the desired concentration of the metal compound in the compound catalyst. 'I he procedure followed in drying or treating the impregnating material will vary depending upon the chemical constitution of the compound catalyst. In general, the material can be dried in air at temperatures as high as 800 C. or even higher in some cases. In other cases, it may be desirable to effect the drying with inert gases such as nitrogen, or reducing gases such as hydrogen, hydrocarbons,

etc.

active cyclizing constituentsof the combined catpregnation of the carrier "with their aqueous solutions. In such cases, the stabilizing carrier Many of the compounds hioh are desired as however, the various cyclizing metals are prefwhich can be converted to the desired metal oxide, metal sulfide or the like by calcination,

hydrogen sulfide treatment, or the like, of the impregnated material. A cyclizing metal oxidecontaining catalyst may also be obtained by precipitating a corresponding metal hydroxide on the surface of the carrier and subjecting the thus-obtained material to calcination under suitable temperature conditions.

The catalysts prepared as described are often submitted to a pretreatment rior to their use. Thus, for example, they are often heated for some hours at temperatures between about 300 C. and 600 C. in the presence of reducing gases such as hydrogen, hydrogen sulfide, hydrogen plus natural gas, etc. Such pretreatment usually improves their activity somewhat.

The process of cyclization-dehydrogenation to produce aromatic hydrocarbons using cyclizing metal compound catalysts is especially suitable for the production of aromatic hydrocarbons and relatively simple mixtures of aromatic hydrocarbons from individual hydrocarbons having prefmay be impregnated with a solution of a salt erably not more than twelve carbon atoms in an open chain and capable of being cyclized to sixmembered rings and/or hydrocarbon mixtures containing one or more of such hydrocarbons in appreciable quantities. Thus, it is applicable to the economic production of mono-nuclear aromatic hydrocarbons from hydrocarbons containing at least six and preferably not more than twelve carbon atoms in an open chain. For example, the predominant aromatic hydrocarbons i'ound in the product when treating a few of such open chain hydrocarbons are shown in the following table:

' Table I Open chain hydrocarbon Predominant aromatic hydroemployed carbons found in the reaction product N B N T A -methyl hexane Do.

Ortho xylene. Para xylene. Ortho methyl ethyl benzene. Ortho methyl propyl benzene.

Benzene.

Do. Orthoxylene.

The process is also applicable for the production of poly-nuclear hydrocarbons from aikylated cyclic hydrocarbons, such as n-butyl benzene, n-amyl benzene, n-butyl eyclohexane, crotyl benzene, and the like. Of the various appllcable hydrocarbons, so that better results are, in general, obtained with normal and slightly branched hydrocarbons. Applicable hydrocarbon mixtures may also contain higher and/or lower boiling cyclizable and non-cyclizable hydrocarbons such as naphthenic hydrocarbons, paraflinic hydrocarbons, oleflnic hydrocarbons, and the like. Thus, for example, normal heptane may be cyclized in the presence of methane, ethane, ethylene, benzene, toluene, octane, 2- methyl pentane, and the like, and excellent yields of toluene obtained. I have found, however, that materially improved catalyst life and therefore operating economy can be realized when treating hydrocarbon mixtures containing lower boiling non-aromatizable hydrocarbons, if such mixtures are first treated to remove the easily dehydrogenated and non-aromatizable butanes and pentanes. Isopentane, when present in substantial concentrations in the hydrocarbon aamoes of parafllnic and oleflnic hydrocarbons in light petroleum fractions, such as gasoline, etc.. into aromatic hydrocarbons. By treating such petroleum fractions, their aromatic content is considerably increased (any hydro-aromatic hydro-. carbons which may be present are also dehydrogenated to aromatic hydrocarbons), very little cracking occurs and a stable product of low oleflne content and increased anti-knock properties is obtained. The hydrocarbon treated is preferably substantially free of water and/or compounds, such as the alcohols which form water under the reaction conditions.

The hydrocarbon or hydrocarbon mixture to be treated is preferably passed as a vapor through a bed of th catalyst supported in a suitable converter and maintained at the desired temperature by any suitable heating means. While pressures both below and above atmospheric pressure (for instance, 0.01 to 50 atm.) are applicable, the process is usually executed in practice at atmospheric pressures or thereabouts, for instance, 1 to 10 atm. r

In order to' produce the best yields of aromatic hydrocarbons and realize the maximum efllciency of the catalyst, the cyclization is usually effected at a temperature between about 350 C. and 700 C. Temperatures lower .than about 400 C. are, in general, less desirable since they require low space velocities and give low conversions. Temperatures above about 600 C. allow much higher space velocities and high conversions but are, in general, less desirable since they usually lead to cracking and carbon deposition.

The contact time required to effect the formation of aromatic hydrocarbons by catalytic cyclization-dehydrogenation of open chain hydrocarbons is usually considerably longer than that required for dehydrogenation and usually is'at least five seconds. Suitable contact times for operation in the above temperature range are, for instance, between about six seconds and two minutes. When operating within a preferred temperature range of about 450 C. to 550 C.,

optimum results are usually obtained with contact times between about six-and eighty seconds. The catalytic reaction is often executed in the presence of added hydrogen. The ratio of hydrogen to hydrocarbon may range, for example;

from up to about 5 mols per mol. The presence of hydrogen, it is found, tends to prolong the life of the catalyst by inhibiting side reactions which lead to tar and carbon formation. The use of added hydrogen is consequently of most advantage when treating complex hydrocarbon mixtures such as cracked gasoline stocks, etc..

which ordinarily tend to tarand coke up the catalyst relatively quickly. The cyclizaton reaction is, however, inhibited by excessive hydrogen pressures. When hydrogen is used, its partial pressure is therefore preferably kept below- The object of the present invention is to provide' a method whereby aromatic hydrocarbons may be produced from open chain hydrocarbons through catalytic cyclization-dehydrogenation in a more advantageous manner, more particularly by providing a method which is particularly designed to take advantage of short cycle operation and which gives increased conversions. Specific objects of the invention are to' provide an improved method for the production of aromatic hydrocarbons from single open chain hydrocarbons and simple mixtures thereof and to provide a more efllcient method for the improvement of gasoline stocks, blending stocks and other hydrocarbon fractions through the catalytic conversion of relatively less desirable open chain hydrocarbons therein to valuable aromatic hydrocarbons.

Through a lengthy investigation of catalysts with respect to their cyclization activity, it has been found that the above-described method for the catalytic cyclization of open chain hydrocarbons to aromatic hydrocarbons may be considerably improved by employing, in lieu of the conventional catalysts, catalysts which are specifically promoted for the cyclization reaction by the incorporation therein of relatively small amounts of certain promoter metals. It has been found that when certain small amounts of platinum and/or palladium are incorporated in these conventionaicyclization catalysts, as hereinafter more fully described, their cyclization activity is markedly promoted and that when such pro-.

moted catalysts are employed in otherwise'conventional cyclization processes, greatly improved yields may be obtained. The more or less specific promoting effect ofplatinum and palladium on the cyclization activity of these catalysts is contrary to expectations since these metals per'se are relatively poor cyclization catalysts. I -It has been shown, for'instance [J. Gen. Chem. (U. S.

S. R.) 9, 496 (1939)] that with a platinum cata lyst the conversions of parafiln hydrocarbons to aromatic hydrocarbons are only in the range of 1% to 6%. Furthermore, the amounts of platinum and/or palladium required as promoters are quite small. and far less than needed for even a poor cyclization. Furthermore, this promoting. effect is practically confined-to these metals.

Other metals of group VIII of the periodic sys-' tem are not equivalent. Ofithe materials which have beenfound to act as specific-promoters for cyclization, namely. platinum and/or palladium,

platinum is preferred. v p

The .quantity of promoter metal or mixtureof promoter metals'incorporatedin the cyclization catalyst in order to exhibit the desired promoter 7 promoting a cyclization catalyst with platinum," for instance, it may be impregnated, with asuitable solution of] platinum chloride. Other soluble salts of platinum and/or palladium may also I be employed. Thus, for example, in the case of platinum one may impregnate'the cyclization catalyst with'fsuitable solutions of salts such as ammonium platinum chloride, alkali platinum chloride,-barium platinum cyanide, etc. The impregnate'd solutions may be prepared with either water or alcohol, or mixtures thereof. In impregnating the cyclization catalyst with such solutions of promoter salts, it is preferable to employ solutions of such concentrations that the entireimp'regnating solution is taken up by the catalyst. Inthis way catalysts having uniform and predetermined compositions may be most easily prepared without loss of valuable promoter salts, displacement, or the like.

. The catalyst impregnated with the solution of the promoter substance may be treated in the manners conventional in making platinum or palladiumcatalysts to convert the impregnated promoter compound to the metal. Thus, for example, the impregnated catalyst may be dried at 5(R C.-150 C. and finally heated to, for instance, 450%. The catalyst may then, if desired, be pretreated with a reducing gas as described above.

The platinum and/or palladium promoters employed in these catalysts, it is found, act altocargoes is applied to a cyclizing metal compound supported upon an alumina carrier than when it is gether differently than when employed as catalysts per se. For instance, it is known that platinum and palladium are notoriously susceptible to poisoning by sulfur and similar catalyst poisons. When employed as promoters for cyclizing metal compounds in the cyclization of open chain hydrocarbons, however, it is found that such catalyst poisons have no apparent adverse effect. Thus, for example, a catalyst promoted by platinum can be used in the cyclization of open chain hydrocarbons with sulfur as mercaptan or hydrogen sulfide actually added to the feed without impairing the cyclizing activity. It is found, however, that the activity of the cyclizing catalysts is adversely affected by sulfates in the catalyst mass. When promoting cyclizing catalysts with platinum or palladium, therefore, it is preferable that soluble sulfates, if these are present in appreciable concentrations, be first removed. Also, the' impregnating solutions are preferably substantially sulfate-free. Thus, for example, when impregnating a suitable carrier with chromium oxide, superior results may be obtained by employing chromic acid or chromium nitrate which has been purified to remove sulfate impurities. Alkali metal compounds (except the sulfates), on the otherhand, are not usually detrimental. In fact, it is found that small amounts of potassium or potassium compounds (other than the sulfate) are beneficial and that catalysts containing potassium (preferably 5% to 15% of the amount of metal in the cyclizing metal compound) along with the platinum and/or palladium are somewhat superior. Sodium, when present in appreciable concentrations, is known to exert a poisoning action on cyclizing catalysts. In small amounts, however, its presence may be ignored.

While the property of platinum and palladium to selectively promote cyclization appears to be general to all cyclizing metal compounds it is not equivalent in all catalysts. It appears to depend somewhat both upon the specific cyclizing metal compound promoted and upon the carrier material employed. In general, the promoter effect is most pronounced with metal compounds having the strongest cyclizing activity. Thus, the platinum and/or palladium promoters may be most advantageously employed with a supported chromium oxide catalyst. The reason for the difference in promoting action caused by the carrier material is not understood. It is, however, very clearly evident. It is found that the promoter effect is more pronounced when the promoter type.

supported upon other conventional carriers. Fur- 'thermore, all alumina carriers are not equivalent.

It is found that the promoting effect of platinum and/or palladium is much more pronounced when the alumina carrier material consists essentially of or contains appreciable quantities of alumina alpha-monohydrate. Such a material is Activated Alumina. Activated Alumina" is a particular form or kind of alumina prepared from the scaly deposits formed in the Fickes- Sherwin modification of the Bayer process, according to the process described in U. 8. Patent 1,868,869.

The cyclization-dehydrogenation of open chain hydrocarbons using catalysts promoted with platinum and/or palladium, according to the process of the present invention, is illustrated in the following'examples. These examples, which are in'the nature of selected carefully executed comparable experiments carried out under favorable conditions with a few typical catalysts and with a simple representative hydrocarbon rather than illustrations of suitable applications of the process with a wide variety of catalysts and hydrocarbon stocks, were chosen for the purpose of illustrating and emphasizing various aspects of the promoting effect discussed above and should not be consideredas limiting the invention in any way. I

Example I Excellent cyclization catalysts of the conventional type having the following compositions Or (as chromium 23:? Support Per cent "Activated alumina do -.-.do

were employed under the following nearly optimum conditions Temperature=490 C. Pressure=1 atmosphere Liquid hourly space velocity==0.33

for the cyclization-dehydrogenation of pure normal heptane to toluene. The conversions to toluene obtained initially, at the maximum, and after five hours of operation are given in the following table:

Conversions Time Catalyst Catalyst Catalyst 183 184 185 Per cent Per cent Per cent Initial Maximum conversion Five hours Example II p A quantity of catalyst having the same composition as catalyst 184 described above was impregnated with 0.17% platinum (catalyst 176). as 0.087% platinum about doubled the conver- This platinum-promoted catalyst was appliedfor sions to toluene obtained in a process period of the cyclization-dehydrogenation of normal hepten hours. It is also seen that, although the contane under the same conditions as those 'of Exversions obtained in both'cases with the proample I. The conversions to toluene obtained 5 moted catalyst were much higher than those obwere as follows (the results obtained with catalyst tained with the unpromoted catalyst, the bromine 184 are included for comparison): numbers of the products were lower. This is unexpected and is due to the fact that the platinum Conversions promoter is quite specificand is primarily efiec- Time tive in increasing the cyclization activity of the Catalyst Catalyst catalyst- 170 184 Example V Perm! pm Several comparable chromium oxide-alumina eggg: y :3 cyclization catalysts were prepared and some Five hours 50 41 were promoted for cyclization with small amounts of platinum. Their active component From this example it is seen that by promoting P were as a conventional cyclization-dehydrogenation catalyst with a small amount of platinum, much Chromium better yields of aromatics may be obtained. Catamm oxide Plath Example I]! 0 An excellent cyclization-dehydrogenation cat-. 3,; 8%: 8- zn 8 96 alyst (No. 57) of the conventional type prepared fig 0.39? 0.0427 Pt. by impre n n n adsorptive alumina w :4"C;:: 3233 ,zfiiiii 312 9 71915.

10.5% chromium (as chromium oxide) wasused in the cyclization-dehydrogenation of pure normal heptane under the following nearly optimum conditions:

Temperature=490 C.--

Pressure=10 atmospheres Diluent=Hydrogen, 1 moi/3 mois heptane .Contact time=70 seconds These catalysts were used for the cyclizationdehydrogenation of normalheptane under the following conditions:

Temperature=490 C. Pressure=l atmosphere Liquid hourly space velocity=0.33

The initial conversions, maximum conversions, The following results w p and average conversions over the first 7 10,

Average conversion to toluene and 25 hours are given in the following table:

over the first ten hours=7% Bromine number of the product=11 M 40 Initial axi- Average conversion over When the "hydrogen diluent was replaced with Catalyst No. OOnVetmum nitrogen in a comparable experiment, the folsion 7 hrs, 1 mm 25 hm lowing results were obtained:

Average conversion to toluene Pericmt Per cent Per cent -41 7 a1 over the first ten hours=12% 230.6 46.9 33.4

Bromine number'of the product=14 5 3 2 These experiments illustrate the results obtain- 2; g

able under favorable conditions with one of the best prior art cyclization catalysts for medium time cycle operation. The distinct retardation of the cyclization reaction caused by the 2% atmospheres partialpressure of hydrogen is readily apparent.

From these results it is seen that, although concentrations of platinum promoter as small as 0.3 of the chromium concentration in the catalyst (catalyst 233) are efiective in materially increasing the initial conversion, such amounts do Example IV not produce the optimum promotion even for fairly sh rt ycle peration (compare for eximilar to the above-described catg gg zgg i 133% chromium as ample, the average conversions over the first 7 mium oxide) was impregnated r hours). A concentration Of platinum Of about platinum (catalyst 232). This promoted catalyst the chromlum tion (catalyst 232) gives much greater conversions in short in lo ed for the c clization of normal hep- 6 n e un del the same co r iditions as shown in Ex- 0 cycle operatlonr is appmximately 25% efficient in 7 -hour cycles and is even definite] u io am ollows. y 5 per r ample m The results obt ed were as I in 10-hour cycles. Over about 25 hours the aver- Average conv rsion t toluene age conversions are about equal. Catalyst 176 over the first ten hours=1'l% 65 containingabout 1.5% platinum -(based on the Bromine number=9 amount of chromium in the chromium oxide) when the hydrogen diluent was replaced by an gives much superior nv rsi ns in Short cycle equal amount of nitrogen, the results obtained Operation. 7 /2-hour cycle operation and 10-hour were as follows; cycle operation, and even the average conversion obtained in 25-hour cycle operation are improved.

Aver e conversion to toluene Example V therefore clearly illustrates the e'flfect over the first t n h0111'$=31% of the concentration of promoter and the ad- Bromine numb r= vantageous results made possible by the present It is seen that, by comparing Examples III and method, especially when using short cycle opera- IV, the promotion of the catalyst with as little 7: tion.

Example VI A conventional chromium oxide-alumina cycli- Temperature=490 C., Pressure=1 atmosphere Liquid hourly space velocity=0.33

Conversions to toluene obtained initially, at the maximum and the average obtained over the first 7 V2, 10 and 25 hours of operation are given in the following table. The results obtained with a comparable catalyst to which no palladium promoter was added are given for comparison.

Non- Palladium- Conversion to toluene promoted promoted catalyst catalyst 25 hours average.

It is seen from these results that palladium is essentially as effective a promoter for cyclizationdehydrogenation as platinum. The initial conversions obtained with palladium-promoted catalysts are slightly lower, but the averages in medium cycle operation are equal to, if not slightly better than, those obtained with platinumpromoted catalysts. Other elements of Group VIII are not equivalent to platinum and/or palladium in their promoting eflect. Cobalt, for instance, when applied to the above catalyst 57 (0.08%) under conditions comparable with those of Example VI afiords average conversions of only 41.7%, 39.8% and 30.4% for the first 7%,10 and 25 hours, respectively. Nickel and ruthenium act similarly. 7

Example VII Two comparable experiments were made using the above-described catalyst 234 (containing 0.085% Pt) in which the normal heptane feed was altered by the addition 01' 0.05% and 0.25%, respectively. of sulfur in the form of diethyl sulfide. The deviations of the conversion curves for both of the experiments from those obtained with pure normal heptane feed with the same catalyst were within the limits of error of the measurements. The experiment with the heptane having the higher suliur content, in tact, gave slightly better conversions than were obtained with the sulfur-tree teed.

The advantage of the present process over the prior art process such as described above is that," due to the specific promoting effect of the specified quantities of platinum and/or palladium on oyclizing metal compound catalysts, greatly improved conversions may be obtained. As is illustrated in the above examples, the improved conversions are particularly pronounced in the initial operating stages, i. 'e. during the first few hours of processing after each regeneration. The present process is therefore especially advantageous in that it allows the cyclization to be ef- Iected with much higher conversions with short cycle operation. The exceptional advantage of the present process in short cycle operation will be more clearly evident from the following consideratipns:

- (1) In catalytic cyclization it is a general rule that catalysts which show the highest cyclization activity decline in activity taster than those having lower activities. This refers to the temporary loss of activity which is caused by the deposition on the catalyst of small amounts of carbonaceous deposits and is probably due to the fact that the amount of carbonaceous deposits formed is more or less proportional to the amount of reaction catalyzed. As a result, in the initial stages of operation, i. e. in the first 2-10 hours after any regeneration, the superiority of the promoted catalyst over the non-promoted catalyst is greater than after long periods or operation.

(2) Cyclization catalysts 'do not, in general, exhibit their maximum activity immediately upon being put on-stream but require a certain 'induction period (generally in the order of 1-8 hours), during which lower than optimum conversions are obtained. The promoted catalysts used in the process of the present invention, on the other hand, afiord maximum conversions almost immediately upon being put on-stream, i. e. in the process 01 the present invention the induction period is substantially absent. As a result of these two factors the initial conversions to aromatic hydrocarbons obtainable in the present process are often several times as high as those obtained by prior art methods, and conversions over short cycle periods are much superior. The average conversions over long cycle periods, although superior to those using prior art cyclization catalysts, are not superior in the outstanding degree that they are in short cycle operation.

I claim as my invention:

1. Process for the production 01 aromatic nydrocarbons from aliphatic hydrocarbons having from six to twelve carbon atoms which comprises contacting the aliphatic hydrocarbon under cyclizing conditions with a solid compound catalyst consisting essentially of iromabout 2% --i'rom six to twelve carbon atoms which comprises contacting the aliphatic hydrocarbon under cyclizing conditions with a solid compound catalyst consisting essentially of a cyclizing oxide of a metal selected from the left-hand column of group VI of the periodic table supported upon a major proportion of a stabilizing carrier consisting essentially of alumina alpha monohydrate and promoted with about 0.2% to 2% (based on the amount of metal in the cyclizing compound) of a metal selected from the group consisting of platinum and palladium.

3. Process for the production-,0! aromatic hydrocarbons from aliphatic hydrocarbons having from six to twelve carbon atoms which comprises contacting the aliphatic hydrocarbon under cyclizing conditions with a solid compound catalyst consisting essentially of a cyclizing oxide of a metal selected from the left-hand column of group VI of the periodic table supported upon a major proportion of an adsorptive alumina and promoted with about 0.2% to 2% (based on the amount of metal in the cyclizing compound) of U from six to twelve-carbon atoms which comprises Wlth from about 0.2% to 2% aamosa contacting the aliphatic hydrocarbon under cyclizing conditions with a solid compound catalyst consisting essentially of from about 2% to 30% chromium as chromium oxide supported upon a stabilizing carrier or relatively low catalytic activity and promoted withabout .07% to .2% of platinum.

5. Process for the production of aromatic hydrocarbons from aliphatic hydrocarbons having from six to twelve carbon atoms which comprises contacting the aliphatic hydrocarbon under cyclizing conditions with a solid compound catalyst consisting essentially of a cyclizing compound of chromium supported upon a major proportion of a stabilizing carrier of relatively low catalytic activity and promoted with from about 0.2% td2% (based' on the amount of metal in the cyclizing compound) of. platinum.

6. Process for the production of aromatic hydrocarbons from aliphatic hydrocarbons having from six to twelve carbon atoms which comprises contacting the aliphatic hydrocarbon under cyclizing conditions with a solid compound catalyst consisting essentially of a cyclizing compound oi a metal selected from the left-hand column of group VI of the periodic table supported upon a major proportion of a stabilizing carrier of relatively low catalytic activity and promoted (based on the amount of metal in the cyclizing compound) of platinum.

7. Process for the production of aromatic hydrocarbons from aliphatic hydrocarbons having from six to'twelve carbon atoms which comprises contacting the aliphatic hydrocarbon under cyclizing conditions with a solid compound catalyst consisting essentially of chromium oxide supported upon a major proportion of a stabilizing carrier of relatively low catalytic activity and promoted with about 0.2% to 2% (based on the amount of metal in the cyclizing compound) of a metal selected fromthe group consisting of platinum and palladium.

8. Process for the production of aromatic hydrocarbons from aliphatic hydrocarbons having from six to twelve carbon atoms which comprises contacting the aliphatic hydrocarbon under cyclizing conditions with a solid compound catalyst consisting essentially of a cyclizing oxide of a metal selected from the left-hand column of group VI of the periodic table supported upon a major proportion of a stabilizing carrier of relatively low catalytic activity and promoted with about 0.2%.to 2% (based on the amount of metal in the cyclizing compound) of a metal selected from the group consisting of platinum and palladium.

9. Process for the production of aromatic hydrocarbons from aliphatic hydrocarbons having from six to twelve carbon atoms which comprises contacting the aliphatic hydrocarbon under cyclizing conditions with a solid compound catalyst consisting essentially of a cyclizing oxide of a metal selected from the left-hand columns of groups IV, V and VI of the periodic table supported upon a major proportion of a stabilizing carrier of relatively low catalytic activity and promoted with about 0.2% to 2% '(based on the amount of metal in the cyclizing compound) of a metal selected from the group consisting of platinum and palladium.

10. Process for the production of aromatic hydrocarbons from aliphatic hydrocarbons having from six to twelve carbon atoms which comder cyclizing conditions with a solid compound catalyst consisting essentially of a cyclizing compound of chromium supported upon amajor proportion of a stabilizing carrier, of relatively low catalytic activity and promoted withabout to 2% (based on the amount 01 metal in the cyclizing compound) oi a metal selected from the group consisting of platinum and palladium.

11. Process for the production of aromatic hydrocarbons from aliphatic hydrocarbons having from six to twelvecarbon atoms which comprises contacting the aliphatic hydrocarbon under cyclizing conditions with a solid compound catalyst consisting essentially of a cyclizing compound of a metal selected from the left-hand column of group VI of the periodic table supported upon a major proportion of a stabilizing carrier of relatively low catalytic activity and promoted with about 0.2% to 2% (based on the amount 01 metal in the cyclizing compound) of a metal selected from the group consisting of platinum and palladium.

12. Process for the production of aromatic hydrocarbons from aliphatic hydrocarbons having from six to twelve carbon atoms which comprises contacting the aliphatic hydrocarbon under cyclizing conditions with a solid compound catalyst consisting essentially of a cyclizing compound of a metal selected from the left-hand columns of groups IV, V and VI of the periodic table supported upon a major proporion of a stabilizing carrier of relatively low catalytic activity and promoted with about 0.2% to 2% (based on the amount of metal in the cyclizing compound) of a metal selected from the group consisting of platinum and palladium.

13. Process for the production of aromatic hydrocarbons from aliphatic hydrocarbons having from 6 to 12 carbon atoms which comprises contacting the aliphatic hydrocarbon under cyclizing conditions with a solid compound catalyst con sisting essentially of a cyclizing compound of a metal selected from the left-hand columns of groups IV, V and VI of the periodic table supported upon a major proportion of a stabilizing carrier consisting essentially of alumina alpha monohydrate and promoted with about 0.2% to prises contacting the aliphatic hydrocarbon un- 76 2% based on the amount of metal in the cyclizing compound) of a metal selected from the group consisting of platinum and palladium.

14.. Process for the production of aromatic hydrocarbons from aliphatic hydrocarbons having from 6 to 12 carbon atoms which comprises contacting the aliphatic hydrocarbon under cyclizing conditions with a solid compound catalyst consisting essentially of a cyclizing oxide of a metal selected from the left-hand columns of groups IV, V and VI of the periodic table supported upon a major-proportion of a stabilizing carrier consisting essentially of alumina alpha monohydrate and promoted with about 0.2% to 2% (based on the amount of metal in the cyclizing compound) of a metal selected from the group consisting of platinum and palladium.

15. Process for the production of aromatic hydrocarbons from aliphatic hydrocarbons having from 6 to 12 carbon atoms which comprises contacting the aliphatic hydrocarbon under cyclizing conditions with a solid compound catalyst,

consisting essentially of a cyclizing compo d of chromium supported upon a major prop ion of a stabilizing carrier consisting essenti of alumina alpha monohydrate and promoted with about 0.2% to 2% (based on the amount ofmetal in the cyclizing compound) or a metal selected from the group consistingof platinum and cameos consisting essentially of chromium oxide supported upon a major proportion of a stabilizing carrier consisting essentially of alumina alpha monohydrate and promoted with about 0.2% to 2% (based on the amount of chromium) 01' a 'metal selected from the group consisting of platinum and palladium.

- BERNARD S. GREENSFELDER.