US2304183A

US2304183A - Multistage dehydroaromatization

Info

Publication number: US2304183A
Application number: US294781A
Authority: US
Inventors: Edwin T Layng; Robert F Marschner
Original assignee: MW Kellogg Co; Standard Oil Co
Current assignee: MW Kellogg Co; Standard Oil Co
Priority date: 1939-09-13
Filing date: 1939-09-13
Publication date: 1942-12-08
Anticipated expiration: 1959-12-08

Description

' genation and aromatization.

.Patented Dee. s, 1942 UNITED STAT 2,304,183 MUL'rIs'rAGE nanrnRoARoMA'rizA'rroN pany, a corporation of Delaware `Appliance september 13,1939, serial No. 294,781`

8 Claims.

This invention relates to the conversion of low knock rating naphtha into high octane number motor fuel by a multi-stage process of catalytic reforming in which there is appreciable dehydro- The object of our invention is to provide a system for obtaining maximum yields of high quality gasoline from petroleum naphtha'and to produce motor fuels of higher octane number than can possibly be produced by cracking and by thermal conversion processes.v A further object is to provide a system for obtaining maximum conversion per unit of catalyst employed or in other words, to utilize the catalyst more effectively and for much longer periods of time than has heretofore been possible.

A further object is to provide a system wherein various naphtha fractions may be most effectively and eiiiciently converted into motor fuels of high octane number and wherein the partially spent catalyst from the treating of one fraction may be effectively employed for the treating of another fraction.

A further object is to provide an improved multi-stage conversion system wherein a fractionation step is interposed between conversion stages so that the remaining stages may be operated under the particular conditions which are most effective and eicient for the production of high quality motor fuel. A further object is to provide a method and means for preventing degradation of heavy naphtha fractions by subjecting them to the severe conditions required for the forming operation. Other objects will be apparent as the detailed description of our invention proceeds. .l

It is now `known that under certain operating conditions dehydrogenation catalysts such as molybdenum oxide on alumina, chromium oxide on alumina, etc. have the remarkable and unexpected property of causing ring closure, i. e. the conversion of straight or branched chain hydrocarbons to aromatics. yIn order to prolong catalyst life for commercially feasible periods of time the reaction is effected in the presence of hydrogen, but it should not be confused with hydroforming or hydrogenation because hydrogen is produced in our process instead of being consumed. Our invention relates to improvements in the dehydro-aromatizationl process and is based on our discovery that certain naphtha fractions require different conversion conditions than other naphtha fractions. vMore specifically, we have found that the light naphtha fractions, particularly Ce and C7 hydrocarbons, require more drastic operating conditions than heavy naphtha fractions, for instance those containing predominant- -ly Ca to Cia hydrocarbons. If naphtha is treated in a single conversion zone either the light components will be insufliciently reformed or the heavy components will suffer thermal degradation.

processing of light naphtha fractions and to avoid dilution of light naphtha fractions by nonaromatizable very light naphtha. constituents such as pentanes.

A further object4 is to provide a multi-stage dehydro-aromatization system wherein different types of hydrogen impurities are produced in different stages and wherein correspondingly dierent hydrogen purification steps are employed for purifying the hydrogen produced in said different stages.

A further object is to provide a new and improved method and means for supplying the endothermic heat for the aromatization reactions.

A further object is to provide a napht'ha reformlng system with maximum flexibility for the handling of different types of naphtha charging f stocks, wherein the treating conditions for the various naphtha components may be closely regulated and wherein certain fractions may be recycled to other parts of the system for increasing the overall efciency and effectiveness of the re- It appears that the first step of the dehydroaromatizaticfn is chiefly dehydrogenation and reforming. This step requires a considerable amount of added heat and we have found'that it is very important that this endothermic heat be supplied and that a substantial amount of the dehydrogenation be effected before .the hydrocarbons are subjected to the more severe aromatization step. Therefore, in accordance vwith our invention we rst heat our naphtha charging stock and contact it with a dehydrogenation catalyst preferably in the presence of added hydrogen at an Vaverage catalyst bed temperature of 850 to 1075 F., preferably about 900 F., at a pressure of about atmospheric to 450, preferably about 200 pounds per square inch, and with a space velocity of about 0.04 to 10 volumes,y preferably about l volume of liquid charge per volume of catalyst space per hour. l It should be understood that the higher space velocities are employed with the higher temperatures. The severity of operating as a space velocity of 0.5 at a temperature of 950 At constant temperature a milder treatment maybe effected by using a less active or more nearly spent catalyst or by using an increased space velocity, or both. At substantially constant space velocity severity may be increased vby using a more active catalyst or higher temperatures.

The hydrogen produced in this rst step is relatively free from methane, ethane and other hydrocarbon contaminants, but it does contain sulfur-compounds, such as HaS; such impurities may be removed by scrubbing with ethanolamine, contacting with iron oxide, etc.

The' dehydrogenated stock from the rst contacting step is next fractionated to separate two or more fractions, for example, a very light naphtha (such as pentanes) a light naphtha of about Ca 4to C carbon atoms, a heavy naphtha of about Cs to Cm carbon atoms and a fraction containing still heavier hydrocarbons. 'Ihe light naphtha may be subsequently aromatized under more severe conditions, e. g. at a temperature of about 950 to 1075 F.,preferably about 1000 F., while the heavy naphtha may be processed under milder conditions, such as about 900 to 1050 F., preferably about 975 F. The specific temperatures fwill, of course, vary with the space velocity used, and with different catalysts and different stocks,

y but generally speaking the light naphtha fraction is treated at a temperature of about 50 higher than the heavy naphtha fraction, all other conditions being equal. With the same temperature for treating the light and heavy fractions, the milder treatment may beeilected by at least doubling that space velocity. The range of space velocities in any case will be from 0.04 to 10.

The hydrogen produced by the more severe aromatization conditions is contaminated with hydrocarbons such as methane and ethane but is substantially free from sulfurv impurities. Thus a different hydrogen purification system may be employed with these stages than was employed with a hydrogen produced from the first stage.

naphtha may be subsequently treated under conditions which are optimum for that fraction.

The invention will be more clearly understood from the following detailed description read in connection with the accompanying. drawings which form a part of this speciiication and`in which similar parts are designated by like reference characters.,

Figure 1 is a flow diagram schematically illustrating a system employing xed bed catalyst chambers; and

Figure 2 is a flow diagram of another modification employing moving bed catalyst chambers.

'I'he invention is not limited to any particular naphthas'. The naphtha may be either straightrun or cracked or it may be produced by the hydrogenationof carbonaceous materials, by the catalytic conversion of carbon monoxide and hydrogen or by any other known method. In the preferred embodiment of the invention we will describe the conversion of straight-run naphtha obtained from East Texas crude. Preferably the original naphtha is straight-run or parailnic hydrocarbon which initially has a relatively low octane number.

'I'he catalyst employed in our process is preferably an oxide or a metal of group VI of the periodic table mounted on active alumina (a form of alumina obtained as a scale in aluminum ore puriflcation). About 2 to 10% of molybdenum oxide an alumina or about 8 to 40% of chromium oxide on alumina have been found to give excellent results. It should be understood, however, that the present invention is not limited to any particular An important feature of our invention is the v the product from heavy naphtha aromatization may be blended with the product from light naphtha aromatization fornal fractionation or stabilization. Alternatively, the products from light naphtha aromatization may be blended. with the unreacted heavy naphtha for a subsequent aromatization step; in this case the partially treated light naphtha requires about the same additional treatment as the heavy naphtha so that the two streams may be eiliciently processed together.

If the first stage accomplishes suflcient aromatization of the heavy naphtha along with the dehydrogenation reaction, the heavy naphtha may be directly blended with the very light naphtha fraction and only the light naphtha requires subsequent aromatization. As a further modincation l along this line we may recycle a part of the heavy naphtha fraction to the initial dehydrogenation y step so that' it may be aromatized as well as dehydrogenated, and we may subject only the light naphtha fraction to the more severe ,aromatization conditions.

An outstanding feature four invention4 is the.

fractionation of partially converted naphtha after the hydrogen has been removed therefrom so that each particular fraction of this partially converted catalyst but is applicable to the use of any dehydro-aromatization catalyst known to the art. The minor ingredient of the catalyst is preferably an oxide or suliide of molybdenum, chromium, tungsten or uranium or any mixture thereof mounted on bauxite, precipitatedalumina, activated alumina, alumina gel or any other suitable catalyst support. Magnesium, aluminum or zinc chromites, molybdenites, etc. may be employed since it has been found that the group VI metal is particularly active when it is in the anion. Vanadium and cerium oxides have been found to be effective for this conversion. Oxides of copper, nickel, manganese, etc. may be included to facilitate regeneration or to supplement or promote catalyst activity. Different catalysts may be used in the various steps.

The catalyst may be made by-impregnating activated alumina or other support with molybdic cipitated as a gel or the separate oxides may be mixed together as a paste, dried, extruded under pressure or pelleted and heated to a temperature of about 1000 to 1200 F. Since the preparation of the catalyst forms no part of the present invention it will not be described in further d etail.

The catalyst may be employed in fixed beds',

4 in movable beds or as a powder suspended in a gaseous stream, the conversion in all cases being in the vapor phase. The fixed bed catalysts may be positioned in tubes mounted for instance ln the convection section of a furnace or they may be positioned in a single bed or plurality of beds in vertical towers or chambers. The

A moving catalyst may be charged to the top of a tower or tube either continuously or intermittently, the spent catalyst being withdrawn from the base of the tube at substantially the same rate; in this case the reaction takes place continuously and under substantially constant conditions of temperature and pressure, the regeneration being effected outside of the conversion zone. The powdered catalyst may be fed into a rapidly moving stream of vaporized naphtha and hydrogen,.separated therefrom after reaction is completed and separately regenerated by oxygen while suspended in flue gas. Any of these specific catalyst reactors or their equivalents may be used in practicing the invention, but they will not be described in further detail. In the case of powdered catalyst the expression space velocity is not applicablethe equivalent effect is obtained by using about 1 to 5 volumes of catalyst per volume of oil and using a contact time of about 5 to 200 seconds.

Naphtha, preferably of relatively wide boiling range, is introduced by pump I to coils II.of pipe still I2 from which it is passed by transfer line I3 to catalyst chamber I4 at a temperature of about 850 to 1000" F. for example 900 F; and a pressure ranging from atmospheric to 450 pounds per square inch for example 200 pounds per square inch. The catalyst in chamber I4 is preferably about 2 to 6% molybdenum oxide on alumina, galthough as hereinabove stated, other proportions and other catalysts may be used. The hot naphtha vapors are passed over the catalyst with a space velocity of about 0.1 to 5 volumes (liquid basis) of naphtha per volume of cataylst space per hour. Although the reaction in this first catalyst chamber may` be in the" absence of added hydrogen, hydrogen may bev introduced through line I5 either with the incoming naphtha, to transfer'line I3, or directly to the catalyst chamber. In the latter be used' and while `we have shown a single column a plurality of columns, stabilizers, etc. may be used. Very light naphtha fractions, particularly pentanes, are withdrawn overhead from the fractionator through line 29, and may 'I'his fraction `includes the Ca and C1 hydrocarbons with perhaps some of the Ce hydrocarbons. Heavy naphtha with an initial boiling case the hydrogen is preferably preheated to a temperature as high or higher than the temperature of the reaction chamber. An optimum amount of hydrogen appears to be from about 0.4. to 8 mols per mol of naphtha.

'Ihe precise conditions in reaction chamber I4 will vary with differences in catalyst, in charging stock and with desired results but generally speaking, an average temperature of about 925 F. is suitable for a space velocity of about 1 volume of liquid per volume of catalyst space per hour and 2 mols of hydrogen per mol of naphtha. Higher temperatures may be used with higher space velocities. The endothermic heat of dehydrogenation is quite considerable and unless additional heat is supplied to compensate for radiation and for this endothermic heat of reaction there will be a considerable temperature drop between the inlet and outlet of the catalyst chamber.

Products and gases from catalyst chamber I4 are passed through line- I6, heat exchanger I1 and cooler I8 to hydrogen separating d rum I9 which is'preferably maintained at substantiallyio through line 25.

Liquids from separator I9 are withdrawn by pump 26 through exchanger I1 wherein they are revaporized and introduced by line 21 into fractionating column 28. It should be understood that any conventional fractionating system may point of' 200 to 250 F. and an end point of abOUt 350 t0 403 F. iS Withdrawn through line- 3I, this fraction containing the Cs and Cio hydrocarbons with some Ca and perhaps Cn and C12 hydrocarbons. may be Ywithdrawn as a bottom through line 32 and may have an initial boiling point of about 350 to 450 F. and a final boiling point of about 450 F. or higher.

In our preferred examples we have illustrated the separate treatment of two or three vnaphtha fractions but it should 'be understood that a much larger number of fractions may thus be separately treated. Cu hydrocarbons are more difficulty aromatizable than C fz, C1 are more diillcultly aromati'zable than Ca, Cs than C9, etc. but the difference in the required severity of treatment gradually diminishes with hydrocarbons of higher and higher molecular weights. Thus our light naphtha may consist essentially of Ca hydrocarbons, a'heavier fraction may consist essentially of C1 hydrocarbons, a heavier fraction may consist essentially of Ca hydrocarbons, etc. Alternatively. when the light naphtha consists essentially of Cs hydrocarbons, the next heavier fraction mayincludew to Cs and the next heavier from Ca to Cio. etc.

While the ease of aromatization, and consequently the mildness of the aromatization conditions, gradually increases with the molecular weight of the hydrocarbons, we have found that the tendency toward volatility increase is much greater in the case of heavier hydrocarbons than in the case of lightvhydrocarbons. .When Cs to Ci: hydrocarbons are aromatized there is a pronounced tendency toward increase in volatility. Such a tendency is appreciable with Cs to C9 hydrocarbons and it is only very'slight in the case' of Cs and C1 hydrocarbons. 'I'his tendency toward the increase of volatility is a further cogent reason for the separate treatment of specific hydrocarbon fractions.

While we have referred to Cs hydrocarbons, C2i-C1 hydrocarbons, etc. and while in our examples we have given certain general boiling ranges,

vit should be understood that close fractidiation is not essential in the practice of our invention. When separately treating a Cn-C'z and' di Cr-Ca fraction, respectively, it is important that thef as aviation gasoline, high solvency naphtha,'

safety fuel, high knock rating motor fuel-` etc. Aromatization of the Ci-Ca fraction, for instance, produces a high solvency naphtha of exceptional quality, the aromatization of heavy phtha produces anexceptionally high grade 'a ation safety An extra heavy naphtha eral flexibility of operation.

The very light naphtha from line 29 is intro- I duced through line 33 directly to the final fractionatlng tower or stabilizer 34, thus avoiding the necessity of reheating it with materials undergoing aromatlzation, and avoiding undesirable dilution of those fractions which are to undergo aromatizatlon.

Light naphtha, from line 30 is introduced to coils 35 or pipe still 36 and thence through transfer line 31 to catalyst chamber 30 which may contain the same type of-catalyst employed inchamber I4,A but which is operated under much mor severe conditions. The temperatures in transfer line 31 may be higher than the average temperature in chamber 38. The average temperature in the catalyst chamber 38 may range from about 925 to 1075 F., for example 1000 F.vwith a space velocity of about 0.04 to 2 or 3 Volumes of liquid dehydrogenated light naphtha F. but lmaybe in the range of 875l to 1075" F., for example 980 F. Hydrogen may be introduced either to line 3l, line 49 or chamber 59 through line 5I in amounts of about 0.4 to 8, for example about 2 ,mols of'hydrogen per mol of heavy naphtha. The pressure in chamber 50 should -be about 30 to 450, for example 200 pounds per square inch and the space velocity may be in the range of 0.04 to or 0.2 to 5 for example 1.0 volume of liquid heavy naphtha per volume of catalyst space per hour, the same type of catalyst being employed as is employed in chambers I4 and 38 respectively.

Products and gases from chamber 50 are introduced through heat exchanger 52 and cooler 53 into hydrogen separator 54 which is preferably at about reaction pressure and at a temperature of about to 105 F. Hydrogen is withper volume of catalyst space per hour, for example 0.5. Hydrogen is introduced either into line 30, line 31 or catalyst chamber 38 through line 39, preferably about 0.4 to 8, for example about 3 mols of hydrogen being added per mol of light naphtha. The amount of hydrogen so introducedy may be varied throughout a fairly wide range and the purity of the hydrogen is preferably above 80%, although it may be as low as 50 or 60%. As above stated, this hydrogen is preferably preheated before being introduced into the transfer line or catalyst chamber.

The reaction products and gases from light naphtha conversion chamber 38 are withdrawn through heat exchanger 40 and cooler 4l to hydrogen separator 42 which is preferably maintained at reaction pressure and at a temperature of about 35 to 105 F. The hydrogen is withdrawn through line 43 and the excess can be withdrawn from the system through line 43a.

Liquid products from separator 42 are passed through heat exchanger 40 and thence either through line 44 to the final gasoline fractionating means 34, or through line 45 for admixture with heavy naphtha in line 3l or through line 4B for admixture with stock entering coils II. A pump corresponding to pump 26 may of course be employed in the liquid line from separator 42 when the liquid is to be passed to a zone of higher pressure.

Heavy naphtha from line 3| may be passed directly to line 33 and final gasoline fractionator or stabilizer 34, particularly when the first treatment in chamber I4 has. effected suiiicient aromatization to improve its octane number to the required extent. Usually, however, we prefer drawn through line 55.

The liquid products from the separator are withdrawn through exchanger 52 and passed by line 56 to line 33 and fractionator or stabilizer 34 or a portion may be passed through line 51 to coils I I.

A portion of the heavy naphtha from line 32 a lcommon system 34 from which Cs and lighter hydrocarbons are withdrawn through line 30. gasoline fractions through line 6I and fractions heavier than gasoline through line 62. The heavier-than-gasoline fraction from line 62 may be recycled to coils II through line 63 or may be withdrawn through line 64 to storage or for conversion in other systems.

Hydrogen from

lines

43 and 55 lis picked up by compressor 65 and passed to a system B6 for the separation of hydrocarbon gases therefrom.-

This system may be a conventional scrubbing tower employing a liquid hydrocarbon scrubbing liquid such as liquefied butane, hexane, naphtha, gas oil, etc. Alternatively, the separation of h ydrogen from hydrocarbons may be effected by refrigeration processes such as those taught by Claude or Linde. Any particular hydrocarbon separation system may be used and it will therefore not be described in further detail. Hydrogen thus freed from hydrocarbon gases, preferably above '70% pure, is then passed to hydrogen storage tank 24.

From storage tank 24 hydrogen is passed through coils 61 in pipe still 68 to line E9 which is in turn connected to lines I5, 5I and 39. It

`should be understood that. the hydrogen for each 41 and 61 may be placed in such positions in this furnace that they will receive the required amount of heat. Similarly, the conversion chambers may be mounted in the convection portions of the furnace and/or hot ue gases from the furnaces or from the regeneration system may be passed in contact with the conversion chambers.

For simplicity we have shown one conversion chamber I4, one chamber 50 and one chamber 33,

but it will be understood that a plurality cf chambers will be used in each instance, some chambers being on stream while others are undergoing regeneration. The catalyst in 38 after becoming partially spent may be used in place of catalyst in 50 on 'heavy naphtha. The regeneration per se is effected by the well-known expedient of burning carbonaceous material from the catalyst by means of carefully regulated amounts of oxygen in flue gas at the same time reconverting to oxides any suldes formed from the catalytic oxides. gases must be suciently low so that the hot spot or combustion zone which traverses the chamber during regeneration will not reach a temperature higher than about 1100 or 1200 F. In the nal stages of regeneration ..higher oxygen concentrationsaremployed to insure complete removal of carbon and the required oxidation of the catalyst. Prior and subsequent to regeneration the system will, of course, be purged with flue gas, steam, impure hydrogen or some other inert gas. Relatively impure hydrogen is particularly suitable for purging after the regeneration step because it tends to recondition the catalyst for further use. The regeneration or purging gases in each chamber may be introduced through line 10 and withdrawn through line 1|.

In Figure 2 we have shown a modification of our invention as applied to a movingbd catalyst and a detailed description of this gure is' not necessary since thel same reference characters are employed as were employed in connection with Figure 1. In this system the fresh catalyst is introduced into chamber A and after it has been held in this chamber for about', 2 to 20 hours, preferably about 5 to 10 hours, it is transferred to Initially the oxygen content of the hot stood that the naphtha stocks'may be segregated y according to chemical composition as well as ac'- cording to boiling ranges. In this case fractionator 38 would be replaced by a solvent",extractlon system, the raffinate going to line 30 and the extract to line 3 I.. The naphtha may be separated by selective solvents into a relatively paraffinc fraction which may be subjected to the severe operat- 'ing conditions hereinabove described in connec. tion with light naphtha, and into relatively naphy thenic fractions which may take the place of the heavy'naphtha hereinabove described. Also while operating tower 38 as a fractionator as originally described, naphtha rainate from an extraction system may be introduced into line 30 from some outside source through line 12. A naphtha extract from a solvent extraction system maybe introduced into line 3| from an outside source through line 13. The naphtha is preferably subjected to the'initial treatment in chamber I4 before it is subjected to the solvent extraction system.

Instead of solvent extraction we may separater j the initially treated naphtha by fractional crystallization and then introduce the more paraifinic X fraction or fractions into the system through line involves a fractionation by distillation between chamber B. After a similar holding time the k conversion stages, it should be understood that this fractionation may be effected by any known f produce relatively diilicultly aromatizable fractions and easily aromatizable fractions, respectively. 1 Y

The invention has been described in considerable detail but it should be understood that We do not limit ourselves to such details except as dcflned by thnffollowing claims.

We claim:

A may be operated at about 900 F., chamber' B under more severe conditions, for example at about 950 to l050 F. and chamber C under conditions of intermediate severity for example, at

about 950 to 1000 F. In this case it will be noted that the fresh catalyst is employed under relativelymild conditions for the dehydrogenation step and that the catalyst used for aromatization of light naphtha is less spent than the catalyst employed for aromatization of heavy naphtha. Since the catalyst in chamber C is more nearly spent than that in chamber B, the reaction conditions in chambers B and C may be substantially the same while still retaining greater catalyst activity for light naphtha than 1. The method of converting low knock rating naphtha into high quality motor fuel in a multistage dehydro-aromatization system, which method comprises contacting said naphtha at a temperature of about 850 to 1000 F. with a dehydrogenation catalyst, separating hydrogen from the dehydrogenated products, fractionating the dehydrogenated products into an easily aromatizable fraction and a dificultly' aromatizable fraction, respectively, contacting the difllcultly aromatizable fraction with an aromatizing catalyst at a temperature of aboutv 900 to .l075 F. at a pressure of about 30 to 450 pounds per square inch and in the presence of about 0.4 tos8 mois of hydrogen with a space velocity of about 0.04 to 3 volumes of liquid hydrocarbon feed per volume of catalyst 0 space per hour, contacting said easily aromatizable fraction with an aromatizing catalyst at a temperature of about 900 to 1000 F. under apressure of about 30 to 450 pounds persquare inch in the presence of about 0.4 to 8 mols of hydrogen per mol of hydrocarbon and With a space velocity of about 0.2 to 5 volumes o f liquid hydrocarbon` further steps of removing sulfur compounds from the hydrogen separated after the first contacting step, separating the hydrocarbon gases from the hydrogen removed after the aromatizing steps,

means which will produce fractions which will` tha with the -aromatized gasoline.

`heating the hydrogen which has thus been-separated from sulfur and hydrocarbon impurities in Vseparate systems and recycling said heated hydrogen to said aromatizing steps.

3. The method of converting naphtha into high A.

quality motor fuel in a multi-stagefdehydro-aromatization system which comprises catalyticaliy dehydrogenating said naphtha, fractionating the dehydrogenated naphtha into a light naphtha and a heavy naphtha, heating said light naphtha and contacting it with an aromatizing catalyst at a temperature of about 900 to 1075 F. and a pressure o f about 30 to 450 pounds per square inch in thev presence of about- .4 to .8 mois of hydrogen per mol of naphtha andwith a space velocity of about 0.04 to 3 volumes of liquid v.light naphtha per volume of catalyst space per hour, heating said heavy naphtha and contacting it withl an aromatizing catalyst at temperature of about 900 to 1075 and a pressure of about 30 to 450 pounds per square inch in the presence of about .4 to 8 mola of hydrogen per molof heavy naphtha and with a space velocity of about 0.04 to 10 volumes .of liquid heavy naphtha ,per volume of catalyst space per hour, and recovering aromatized gasoline from hydrogen 'and from products which are respectively llghterand heavier than said. aromatized gasoline.

4. The method of claim 3 which includes the further step of separating a very light'naphtha fraction from the light naphtha and heavy naphtha respectively-prior to the aromatization of the latter naphthas, and blending the very light :mph-

5. The method of claim 3 wherein the light naphtha is contacted with aromatizing catalyst at a temperature approximately 50 degrees higher than' the temperature at which the heavy naphtha is contacted with aromatizing catalyst.

6. The method o1' clairn 3 wherein'the light 'naphtha is contacted with aromatizing catalyst at a substantially lower spacev velocity than the space velocity at which the heavy naphtha is contacted with aromatizing catalyst. j

7. The method ofl claim 3 whereinthe light naphtha is contacted with aromatizing catalyst under more severe operating conditions than those 'under which the hea`vy naphtha is' contacted with aromatizing catalyst.

s. The method cf converting nephtha into high quality motor fuel in a multi-stage dehydroaromatization system which method comprises catalytically dehydrogenating said naphtha, fractionating the dehydrogenated naphtha into alight naphtha fraction consisting essentially of Ce tp Cs hydrocarbons, a lighter naphtha fraction consisting essentially of C4 to Ce hydrocarbons and a heavynaphtha fraction consisting essentially of Ca to Cia hydrocarbons, heating the light naphtha.l

fraction consisting essentially of Ca to Ca hydrocarbons and contacting it with an aromatizing catalyst at a temperature of about 900 to 1075 EF'. under a pressure of about. to 450 pounds per square-inch in the presence of about .4 to 8 mols of hydrogen per mol of naphtha and with a space velocity of about .04 to 3 volumes of light naphtha per volume of catalyst space per hour, blending the catalytically aromatized dehydrogenated light naphtha fraction with the dehydrogenated lighter naphtha fraction and the'dehydrogenated heavy vnaphtha fraction and separating a motor fuel of the gasoline boiling range from said blend.

EDWIN T. LAYNG.

F'. MARSCHNER.