US2421677A - Catalytic conversion of hydrocarbons - Google Patents

Description

A. BELCHETZ 1 CATALYTIC CONVERSION 0F HYnRocARBoNs June 3, 1947.

Filed .my 31, 1940 NN mu 'fm/vow aac/frz.

mvENroR BY 5W 23S .Quran ATTORNEY Patented June 3,`

, `2,421,677` l `CATALyricCONVERSION onnvnno- 1U` CARBONS I Y s Arnold Belchetz, Kew Gardens, N. Y., assignorto The M.W.Kellogg Company,Jersey,CityN. .l

A afcorporaton of Delaware 3 l 1 o o appiieanonlluly 31, 194e, sentirne. 348,605 v t The present invention relates tothe catalytic conversion of hydrocarbons, and more particularly,` to the conversion of straightchaln hydrocar- I bons and mixturesthereof to aromatic hydrocarbons by contacting thestraight chain compounds under suitable'reaction conditions with a catalyst capable of dehydrogenating andcyclicizing them to aromatic compounds. Initspreferred aspect,

`the invention "relates particularly to improvel ments in thetreatmentfof low anti-knock naphtha fractions having a large proportion of straight chain hydrocarbon' compounds boiling` within the `motor `fuel range to convert such compounds `to aromatichydrocarbons and thereby considerably i i? increase the anti-knock quality of the naphtha.

" f Heretofore, a. dehydro-aromatization process of .s claims. (omen-Graal Y l `considerable commercial interestland merit for y the conversionof lowf-anti-knock naphtha.. fractions boiling within, andfslightlyabove, the motorfuel range, to motor fuel ofL high aromatic duly expensive and impractical.` l y `content has beendeveloped. Pursuantfto this process-a suitable charging stock, `for, example a parafllnic naphtha of lowanti-knock quality, is l mixed with hydrogen` and contacted in the vapor phase with a suitable catalyst and under suitable reaction conditions `forfthedesired dehydro-aromatization reaction. Byfmeans of thislreaction,`

a large proportion of the straight; chain hydrocarbons is converted bydehydrogenation and cyclization to corresponding aromaticfeompounds and is` attended by a net production of hydrogen. Also, it has been proposedto effect this type of conversion by either contacting the hydrocarbons in a reaction zone containing a stationary mass or `bed of the catalyst, or by an alternative procedure' of suspending `the 'catalyst in the vapors undergoing treatment, passing the suspension through the reactionfzone,and thereafter separating the suspendedcatalyst from the vaporous reaction products. l l i l Thelatter type of operation, whilehavlng certain inherent advantagessuch as the-high degree of `intimacy of contact between the vapors ande nely divided suspendedcatalyst,` is subject to various difllculties andgdi'sadvantages which have precluded its utilization on a practical or `comlmercial scale. A general object of myinvention is the provision of a process whereby these difficulties and disadvantages are largeiyeliminated.

Among the more important obstacles which have been encountered in `attempts to practice a dehydro-aromatization processlby a procedure carbonyapors passing through the conversion zone are the following: f l l (a) `Necessity oflfsupplylng laroonsiderable endothermicheat of reaction to `the conversion zone,

`1(1)) Diillcultyl of' securingsatisfactory yields andlqualities of conversion productswithavailable catalysts when-utilizing equipmentoi a. `commerciallyfeasible size andproportions of reactants andcatalystf, l

(c) Difficulties arising out of the tendency-.of

somefof the' otherwisemore effective catalysts,

such as those comprising molybdenum compounds, toundergo reductionvduring the `conversion stage and oxidation` duringthewcatalyst regeneration staged One of the objects of: my inventionls the provision Vof a` method `for supplying the required endothermic` heat of reaction withouttutilizing conventional methods of heatexchange or heat-o transfer which have been ascertained tobe un- `visioncf a method for securing a satisfactory degree of conversionboth with respect to quantity and quality of conversion products without resort- `ing to inordlnate'ly `large equipment or proportions of reactants and catalysts at any stage of the process. l l

provision of `an improved method for preconditioning the catalyst, `particularly catalysts of the `type exhibiting a tendency-"ltotbecome reduced Y l during the `conversion stage and oxidized during i `the regeneration stage ofzthe. process whereby the `,disadvantages*arising from `such reactions, are

`an additionai object of theinventlon-ls the largely obviated;

`Various other objects, features, and advantages l fofmy invention will be apparent from a considerationof the following detailed description thereof y given in connection with the appended drawing, a

' `wherein I have illustrated.diagrammatlcally a suitable arrangement of apparatus and flow pian for the practice of the invention.

Referring to the exemplary process-owillustrated, the charging stockk introduced through linel is suitably a naphtha fraction having a large `proportion ofstralght chain hydrocarbons of loWant-knock\qua1lty,\thatis, aliphatic hydrocarbons having from 6` to 14 carbon atomsin the carbon` chain. `'I'he naphtha is charged by v pump 2 through `gheating coil 3 in furnace 4 'wherein it is vaporlzed and heated to a temperal ture suitable for thesubsequent conversion stage.

Hydrocarbon vapors are withdrawn from the fury lwherein the catalyst is suspended in the hydrof `nace through' transfer line 5 and mixed with recycle gas containing a large proportion cfhyf ,l

drogen introduced through recycle line 6and the `A` further :object of my invention is the `prolvapor mixture then passed into the bottom of recycle gas Vand then passes upwardly through v the conversion chamber. The quantity of cata-` lyst introduced into the reaction zone is prefer-y ably maintained within definite limits pursuant to my invention as described in detail hereinafter.

In passing upwardly through the' reactor the u straight chain hydrocarbons undergo a dehydrogenation and cyclization reaction' and are largelyv converted to aromatic compounds, and altered hydrocanbon y*compounds generally, of enhanced anti-knock quality. `I have ascertained that the extent and effectiveness of the conversion is largely dependent upon the concentration of catalystyin the reactor and this concentration is preferably maintained within definitely prescribed limits pursuant to my invention as hereinaiterdescribed.

vThe conversion products are withdrawn from the ltop of reactor 1 through line I0 and vpassed 4 u t gaseous product including a large proportion oi hydrogen and light hydrocarbon gases, such as methane and ethane, is withdrawn overhead through line 5I.

Used catalyst is withdrawn from drum 'Il `by feeder I8 and introduced into a suitable means u for purgingv it of hydrocarbon vapors entrained therewith, such as stripping tower I9. Tower I9 may be provided with suitable baffles or the like to facilitate intimate contactlbetw'een the purging medium and the catalyst passing downwardly therethrough. A suitable purging medium such l as steam is introduced at the base of tower I9v through. line 20 and passes upwardly through the.

tower and exits from the top through line 2i. The purging medium is passed from line 2l into a separator 22 wherein any entrained catalyst is y c separated. Catalyst thus separated is passed by line 23 into a collecting or surge drum` 24. The purging m-ediumis withdrawn from-the top of separator 22 by line 25 and suitably may be treat- ,ed to recover its hydrocarboncontent, for example -by introduction of the mixture into line I1. vStripped catalyst is withdrawn `from the bottom of stripping towerIS :by line 26 and passed toa stripped,` used catalyst collecting or surge to a collecting or surge drum I I wherein most of l the suspended used `catalyst settles out ofthe gas stream and collects in the ibottomportion of the drum. The vapor stream i-s withdrawn from the upper part of drum I I `through line I2rand4 passed to ansuitable gas-solid separator such as cyclone 'i3 wherein residual suspended catalyst is separated and returned to the drum through line I4.'

Vaporous conversion products are withdrawn lfrom separator I3 and passed to the products` recovery system through line I1. If desired, a part of the used catalyst may be withdrawn from drum II through pipe I5 and recycled to reactor 1 by screw feeder I6 for reuse in the mixture undergoing conversion. l

The vaporous reaction products withdrawn through line I1 are cooled to a. temperature suitablefor theseparation of their condensiblecomponents from the hydrogen and normally gaseous hydrocarbons contained therein. This cooling may suitably be reffected by passing the stream through heat exchanger 60.111 heat exchange relation with the cooler recycle gas stream in line drum 24 Vby screw feeder 21. Catalyst is-wth drawn from the bottom' of drum 24 and introduced into regeneration chamber 29 by screw ,l .feeder 28.

A suitable regeneration medium such as air; or a mixture of air and ue glas, is introduced into Ather bottom portion of regeneration Y chamber 29 through line 30 by pump-"3|Used 6, land -then further cooled in additional heat exchangers or cooler 6I. From the nal cooler 6I, the stream is passed into a high pressure gas separator 63 by line 62. The desired liquid prod-v uct is withdrawn from the bottomk of gas separator 63 by line 65, and may thereafter ibe treated .in accordance with conventional lpractice. of stabilization and the like to produce a commercial gasoline of exceptionally high anti-knock characteristics, or in any `other desired manner.

Gaseous constituents are withdrawn overhead from separator 63 through line 66, andare compressed to a. pressure suitable for the separationV catalyst `is pickedup and suspendedy inthe Vre'- generation medium and passes upwardlythrough 'y the regeneration chamber duringjwhich travel combustion of its carbonaceous content is effected A and the catalyst thereby regenerated. 'I'he regeneration products are withdrawn vfrom thetop of `the regeneration chamber through line 32 and all ora portion thereof passed by line 33 to a regenerated catalyst collecting or surge drum 34 wherein most .of the suspended catalyst is settled v out of the gas stream-and collected inthe bottom portion of the drum. Combustion or ue gases arewithdrawn overhead through'line 35Vand pass to a suitable separating system such as cyclone 36 for separation of residual catalyst entrained in the gas. the catalyst thus separated being returned Ito kdrum r34 through` line 38. .Theseparated ifiue rgas passes overhead from cyclone 36 and is withdrawn from` the process through line 39.A f

To assist in the maintenance of` the .temperature of `the regeneration zone `within required limits, it has-been found highly desirable under certain conditions to recycle cooled regenerated lcatalyst to this zone.' for absorbing a portion of the heat'of regeneration thereby preventing the temperature in the zone from exceeding the maxkirnurn or allowable safe regenerationtemperature.

and recovery of low Iboiling hydrocarbons, such f as propane and butanefpresent therein by compressor 61 and then passed lto absorbing tower .50. In tower 50 the gas is passed in countercurrent flow with an absorbing oil, suitably the u naphtha` which is to be introduced through line I, supplied at the top of the-tower throughline 68. Enriched absorbingV oil is withdrawn from the bottom of the tower throughy line 69. and la In such cases the regeneration -productsrwithdrawn throughllinee32lmay, be split, a'suitable.

fraction thus*being.by-passed-through line 10 by suitable adjustment of'valves 1I and 12. The by-passedstream is passed throughv a suitable -cooler orheat exchanger 13 whereinits temperar ture is reduced to a suitable. degree. `From cooler 13 the cooled stream-is passed by line 14 to separator 15 wherein the suspended catalyst is sepa- `v rated from the'ue gays which passes overhead through line 16. Catalyst is withdrawn from the bottom of separator 15 byline 11 and introduced into the cooled regenerated catalyst collecting or surge drum 18. vFrom drum 18 the cooled catalyst i is introduced in the required amounts to regeneration chamber 29 by screw ,feeder 19. e

The regenerated catalyst from drum 34 is preferably subjected toa purging treatment for rei moval of any oxygen-containing gases entrained or adsorbed thereon, and also in certain instances is preferably subjected to a preconditioning treate ment with a reducing gas, preferably hydrogen.

The regenerated catalyst may suitably be such as flue gas is' introduced into the bottorkrof` stripping tower 42 through line 43 `and passes upwardly throughthe tower in countercurrent e ber l in the practice of my invention are suitably illustrated bya consideration ofa typical example. In this example a low anti-knock East Texas heavy naphtha was charged through line I and *the `rcactionthe following conditions obtained: e

flow with the catalyst introduced throughfeeder 4 I, thereby stripping or displacingfrom the catalyst any detrimental oxygen-containinge` gases. The stripping medium is withdrawn `frornthe top of tower 42 through line 44 and passes to a suitable separator45 for separation of entrainedcatalyst. Catalyst thus separated is passed fromsep- `arat`or 45 into the stripped, regenerated catalyst collecting or surge drum 41 through line 4B. Cataf e lyst `is fed fromthe bottom of `stripping tower 42 into the bottom ofdrurn 41 byline 48 and screw feeder 49.

' The stripped used catalystin certain instances is preferably subjected toa preconditioning treatment with hydrogen or other reducing gas. This lis particularly the caselwith catalysts of themolybdenum oxide type which undergo a reduction during the conversion stage `and oxidation during the` regeneration stage `of the process. This preconditioning treatment may be effected by suspending the regenerated catalyst in the recycle stream at a point in the recycle line at a sufficient distance from the reactor to permit the desired reduction by recycle gas toltake place before the charging stock is mixed therewith. I have ascertained, however. thatthis preconditioning treatment may be most` effectively practiced by pernace 4 i .e --F Temperature recycle gas in line 6`.. "?1"..` 600 Temperature regenerated catalyst in drum 8,

\ e @fr- .1150 Average inlet temperature of the naphtha,

recycle' gas and .catalyst` to chamber 1,

i ,f e F iooo Outlet temperatureof conversion products t, e leaving chamber 1----,- .F.. 900` Endothermic heat of reaction, `B.t.`u./`1b. of napntna-- `25o Pressure in chamber '1 i lbs./Ysq. ln.'ga\ f 100 `Average velocity of gas inchamber f1, e e

i, ft./sec. 3 Concentration of catalyst in chamber 1 per cu. ft. of `reaction space `lbs;j' 4 Specific heat of catalyst c `1.26 Time of contact of hydrocarbon vapors with Y catalyst c 'V sec 40 recycle gas introduced from line 6 in the propori tions of 2500 cu. ft. of recycle gas (measured at standard conditions) to vone barrelof naphtha and yregenerated catalyst of the molybdenum oxide-on-alumina-type charged to chamber 1 fromdrum 8 in the proportions,` by weight, of catalyst to naphtha of 7:1. During the course of Temperature naphtha vapors leaving fur- In `the practice of my` invention under conditions such as employed in the above example, the regenerated catalyst is supplied-to the chamber 1 at an elevated temperature somewhat above `the l fdesired average conversioni temperature and in l relatively large proportions adequate tosupply forming it in a 'separate stage andeutilizing a stream of recycle gas separate from that passed to the reactor, as shown. In accordance with this preferred procedure, a portion of the total recycle gas-withdrawn from gas separator by lines 5I and 52 is introduced into the bottom portion of a preconditioning tower `53. The gas thus introduced .picks up and suspends stripped regenerated catalyst vintroduced from drum 41 through feeder 54 and the suspension passes `upwardly through'the tower` 53` during which travel the desired preconditioning of the catalyst is effected. The suspension is withdrawn vfrom the top of tower 53 by line 55 and passed to a suitable separator 56 wherein separation of the" preconditioned catalyst is effected; The preconditioning gasis withdrawn fromseparator 56 through line 51 and` is preferably thereafter usedas fuel, or

other purposes than recycling tothe reactor 1 since it is normally too dilute in hydrogen for satisfactory utilization in the conversion step. Separated catalyst passes from separator 56 into surge drum 8 through line 58. The treatment to which the regenerated catalyst is subjected from i the time of withdrawal through line 33 and its introduction into the reactor 1 by feeder 9 are so conducted that the catalyst when introduced into the reactor retains substantially all the heat im parted during the exothermic regeneration reac- T2=required outlet temperature from `H1=total heat of the suillcient heat during the conversionlto'maintain the reactionmixture at the desired average -tem-` i perature` level. catalyst-to-oil weight ratio Amayisuitably be about '7,:1as shown in the example. Inl general, my in- 1 To produce` this resultthe vention contemplates the introduction of regenerated catalyst heated to the required elevated 'temperature in amounts `expressed in terms of catalyst-to-oil ratio by weight of about 2 to 20 andpreferably in the intermediate rangeof about 4 to 10. The desired ratio (R) may be determined applying the wherein the symbols have the following meanings, e

T1=average inlet temperature ofthe naphtha,` recycle gas and catalyst to the reactoriin FJ temp. T1 (in B. t. 11./111.)

H2=total heat of the reaction products at temp.

Pursuant to 'my invention, a relatively high lconcentration of catalyst is maintained in the` conversion zone 1 by maintaining the velocity of` the gases passing through thereactorwithin relatively low limits, for instance a `cdmcentration of "naphtha+recycle. gas `at p. risecond-as; Shown Tlf @th-emana;

thelexamplerabove. .YS spalti dfthroughathe A icles,U'and the like. gf'fthe-'ve'locityof the gases in the elownthe 'transport' velocity, slippage of y yet hfgaris'istex'nfds induced and the iconce'ntrationofcth Acataly t to unit volume of acir increased relative to ys Itounit volume of oil vapor The extent of this increase is hvelocity and increases with uur fed tthegre to dependent` ,upo

l lower;"veldeities;v and corresponding greater slipoi eacto space n locity 1 l with a relatively high concentration, forexample i l a catalyst concentration of about 12 lbs. per cu. ft. of reactor as given inthe example; however the concentration ymay be varied over a range from about 2 to 25 lbs. per cu. ft. of reactor space and preferably is maintained within the range of 6 to 16 lbs. These concentrations may be produced by maintaining the velocity of the hydrocarbon gases in the conversion chamber 'l below the transport velocity, suitably in the range of about l to 25, and preferably in the range of about 2 to rI feet per second.

The present invention does not reside in the selection or use of any particular catalyst per se, and anyv catalyst capable of catalyzing the desired dehydro-aromatization reaction may be used. As examples of suitable catalysts for use in my process, I prefer the oxides ofthe metals of the lefthand column of group 'VI of thev periodic table, particularly chromium, molybdenum and tungsten but I can also use other metallic oxides and other metallic compounds, particularly oxides of the metals of the left-hand columns of groups IV and V of the periodic table such as titanium, ceriurn, thorium and vanadium. Moreover, while these catalytic oxides can be used alone or on various supports including magnesia, I find it preferable to utilize them on alumina, particularly an Activated Alumina or on alumina gel, as a support and in general the catalytic oxide or other catalytic compound should be the minor constituent, usually from 1 to 40% by weight of the total catalyst including the support, although the optimum percentage varies, of course, with the catalyst used. It will also -be apparent that mixed catalysts can beA used, for instance a mixture of chromium oxide and molybdenum oxide alone or preferably on an alumina support, and in this case the active catalytic oxides should be o iabout 25% by weight of the total :her catalyst which can be used is agnesiumlchromite either alone or on a suitable suppoiztppreferably alumina. In fact, any aromaationgcatalyst or material that promotes the dehydrogenation and cyclization of aliphatic hydrocarbons can be used. As those skilled in the Y rt know, the etliciency of a given catalyst is argely determined by its method of preparation and consequently some catalysts give better results than others under a specic set of conditions. Such differences obviously can be overcome to some extent by suitable slight alterations in the operating conditions within the limits taught in the `present specification. Howevenof these catalystsI prefer to use a catalyst comprising molybdenum oxide supported on alumina, particularly Activated Alumina, and the molybdenum oxide should most advantageously constitute fromabout 2 to about 10% by weight of` erably employed in nely divided or powdered condition, for example, most of the catalyst should be of sufcient neness to pass a 200 mesh screen.

My preferred catalyst may be made in accordance with the following procedure:

Dissolve kilograms of ammonium para molybdate in suflicient distilled Water to yield 1500 liters of solution. Place 1500 kilograms of granular Activated Alumina in an apparatus which can be evacuated and add the molybdate solution. Agitate the mixture and then apply a vacuum pump and reduce the pressure to v30-40 millimeters of mercury. Then allow the pressure to rise to atmospheric. Lower the pressure a second time to the same level and then allow it to rise again to atmospheric pressure. Repeat this procedure a third time andthen' drain the remaining liquid from the impregnated alumina. Air-dry the latter on screens or other suitable containers using layers of about one inch in depth. At theV end of this time place the dried material in a furnace in a suitable container and heat it at atemperature of 1200 F. for one hour. Cool to atmospheric temperature, pulverize and store in closed containers until ready for use.

The pressure maintained in the conversion reactor 'l is preferably maintained at 100 lbs. gauge but satisfactory results are attainable with pressures ranging from about 50 lbs. to 450 lbs.

'I'he amount of added hydrogen or recycle gas introduced through line 6 in the practice of my invention may be expressed as the number of mols of hydrogen per mol of charge calculated on the basis of the mean molecular weight of charge which for the East Texas heavy naphtha used in the illustrated example was in the vicinity of 120. The practice of my process will usually require the addition of hydrogen in amount ranging from between 0.5 to 9 and preferably about 2 to 3 mols of hydrogen per mol of hydrocarbons charged.

version temperature in vapors of the aliphatic hydrocarbons, passing the suspension upwardly through a, conversion zone at a velocity within the range of about 1 to 3 feet per second under catalyst-to-hydrocarbons, by Weight, of about 2-20 to 1 so as to supply the endothermic heat of reaction without supplying extraneous heat to the reaction mixture to any substantial extent.

2. A processfor the conversion of aliphatic hydrocarbons to aromatic hydrocarbons which comprises suspending a powdered dehydrogenating version mixture and each other, splittingthe and cyclicizing catalyst of suflicient fineness that most of it passes a 200-mesh screen previously heated to a temperature approximating the conversion temperature in vaporsof the aliphatic hydrocarbons, passing the suspension upwardly through a conversion zone at a velocity within the u range of about 1 to 3 feet per second under superatmospheric pressure and at elevated temperatures suitable largelyto dehydrogenate and cyclicize the aliphatic hydrocarbons to aromatic compounds, .and maintaining the `proportions of heated catalyst and hydrocarbons introduced to the conversion zone within limits in terms of catalyst-to-hydrocarbons, by weight, of about 4-10 to 1 so as to supply the endothermic heat of reaction without supplying extraneous heat' to the` reaction mixture to any substantial extent.

3. A process for the conversion of aliphatic hydrocarbons to aromatic hydrocarbons which cornprises suspending a powdered dehydrogenating and cyclicizing catalyst of sulcient neness that most of it passes a 200-mesh screen and previously heated to a temperature approximating the conversion temperature, in vapors of the aliphatic hydrocarbons, passing the vapors upwardly through a conversion zone at a velocity within the range of about 1 to 3 feet per second under superatmospheric pressure and at elevated ternperatures suitable to largely dehydrogenate and cyclicize the aliphatic hydrocarbons to aromatic compounds, and maintaining the proportions ofV heated catalyst and hydrocarbon reactants intro' duced to the conversion zone within sucn limits as to supply the endothermic heat of reaction without supplying extraneous heat to the reaction mixture to any substantial extent and Withinthe range of about 2-20 parts of catalyst to 1 part of said reactants by weight, the said maintained velocity of the hydrocarbon vapors through said conversion zone being such as to produce a relatively great concentration of catalyst in said zone.

4. A process for the conversion of aliphatic hydrocarbons i to aromatic hydrocarbons, which comprises suspending a powdered dehydrogenating and cyclicizing catalyst of suicient rlneness that most of it passes a 200-mesh screen and previously heated to a temperature approximating the conversion temperature in vapors of the aliphatic hydrocarbons, passing the vapors upw'ardly through a conversion zone within the range of about l to 3 feet per second in the presence of added hydrogen and under superatmospheric pressure and elevated temperatures suitable largely to dehydrogenate and cyclicize the aliphatic hydrocarbons to aromatic compounds and hydrogen, the proportions of heated catalyst and reactants introduced to the conversion zone 10 i being maintained within such limits as to supply the endothermic heat of reaction without supplying extraneous heat to the reaction mixture to any substantial extent and within the range of 2 to v20 parts of catalyst to l part of reactants by weight, withdrawing the conversion products and separating the used catalystand hydrogen pro-- duced, from the other components of the constream of hydrogen and utilizing one portion `to precondition theused catalyst `for reuse and the other portion as theadded hydrogen present in the conversion stage. t

5. rA process for the conversion of aliphatic hydrocarbons to aromatic hydrocarbons which comprises heating and vaporizing said aliphatcyhydrocarbo'ns to a temperature suitable for conversion, suspending a powdered dehydrogenating and cyclicizing catalyst of suflicient ilneness that most of itpasses a 200 mesh screen and previously Y to a temperature approximating the -conversion temperaturein said vapors of the aliheated phatic hydrocarbons, passing `the vapors' upwardi ly through a ,conversion zone at a velocity within the 'range of about 1 to 3 feet per second under superatmospheric pressure and at elevated temperatures suitable to largely dehydrogenate and cyclicize the aliphatic hydrocarbons to aromatic compounds, and maintaining the proportions of"` heated catalyst and hydrocarbon reactants introduced tothe conversion zone withinsuch limits as to supply the endothermic heat of rezatction` without supplying extraneous heat to the reaction t mixture to any substantial extent and within the i range of about 2-20 parts of-catalyst to 1 part of said reactants by weight, the said maintained velocity of the hydrocarbon vapors through said conversion zone being such as to produce a relatively great concentration of catalyst in said zone.

6. A process for the conversion of aliphatic hydrocarbons to aromatic compounds, which comprises suspending a powdered dehydrogenating and cyclicizing catalyst of sufficient neness i that most of it passes a 200mesh screen and previously heated to a temperature approximating the conversion temperature in a mixture oi' added hydrogen and vapors of the aliphatic hydrocari bons, the feed weight ratio of the hydrocarbon reactants to the catalyst being maintained within i such limits as to supply the endothermic heat of reaction without supplyingextraneous heat to the reaction mixture `to any substantial extent u and within the range of about 220:1, passing the gases upwardly through a conversion zone at a velocity within the range of about 1 to Sieet per second under superatmospheric pressureandat an elevated temperature suitable largely to dehydrogenate and cyclicize the aliphatic hydrocarbons in said conversion zone and within limits sufficient to produce a concentration of catalyst in said zone of between about 2 to 25 pounds per cubic foot of conversion space.

7. A continuous process forvthe conversion of a low octane `naphtha to a highly aromatic high octane motor fuel, which comprises introducing a mixture of added hydrogen and vapors of said low octane naphtha and a-nely divided dehydrogenating and cyclicizing catalyst of suillclent neness that most of-it passes a 200 mesh screen and previously heated to mating the conversion temperature in a feed weight ratio of about 2 to 20 parts of catalyst to 1 part of naphtha into a catalytic conversion Zone maintained under superatmospheric presa temperature approxisure and at an elevated temperature, and passing the vaporous reactants upwardly through said conversion zone at a velocity maintained within the range of about 1 to 3 feet persecond to, provide a concentration of said finely divided' catalyst in said conversion zone of not less than sixy naphltha in the presence of a catalyst comprising an oxideof a metal included in the left-hand column of group VI of the periodic table to con-A vert constituents of said naphtha to aromatic compounds, the improvement which comprises flowing the naphtha in the vapor phase at `a relatively lowvelocity within the range of about 1 to 3 feet per second upwardly through a catalytic conversion zone maintained at an elevated temperature. suitable for the desired conversion,

continuously introducing said catalyst in powdered condition of suflicient fineness that most of it passes a 200 mesh screen and Previously heated to a temperature approximating the conversion temperature into said conversion zone at a rate in proportion to the hydrocarbons introduced withinthe range of about 2 to 20 parts of catalyst to 1 part of naphtha by weight whereby the catalyst particles are circulated in the vapors undergoing conversion through the conversion zone and a relatively high concentration of cata- Y 12 lyst particles is maintained in said zone, the feed weight ratio of the hydrocarbon reactants to the hot catalyst being maintained within the above limits at a value effective to supply the endothermic heat of reaction without supplying extraneous heat to the reaction mixture to any substantial extent.

REFERENCES CITED The following references are of record in the' le of this patent:

UNITED STATES PATENTS Number Name Date 1,799,858 Miller Apr. 7, 1931 1,873,783 Osterstrom et al. Aug. 23, 1932 2,039,904 Hill` May 5, 1936 2,216,470 Forney Y Oct.' 1, 1940 2,124,586 Morrell et al.- July 26,1938 2,172,535 Grosse et al Sept. 12, 1939 1,913,940 Mittasch et al. June 13, 1933 2,183,591 Schulze Dec. 19, 1939 2,231,424 Huppke Feb. 11, -1941 2,259,486 Carpenter Oct. 21, 1941 2,239,801 Voorhees Apr. 29, 1941 2,270,715 Layng et al Jan. 20, 1942 2,289,329 Prickett` July 7l 1942 2,322,019 Hemminger June 15, 1943 2,253,486 Belchetz Aug. 19, 1941 FOREIGN PATENTS Number Country Date 411,477 Great Britain June 4, 1934 l ARNOLD BELCHETZ.

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