US2430096A - Plural stage catalytic and thermal conversion of hydrocarbons - Google Patents

Description

NOV-"4, 1947. w, cus 2,430,096

PLURAL STAGE CATALYTIC AND THERMAL CONVERSION OF HYDROCARBONS Filed Dec. 16, 1943 I r 4 Sheets-S heet l CHARGE c4 TALYf/c coAn/zfislo/v fir- FRAcrmA/A T/ON SELECTED (W257? FRACIZION PRODUCTS I PYROLYT/c CON VERSION ERA arm/VA no. SELECTED i arr/1? Z PRODUCTS I I CA rALYr/c V CONVERSION F76. I: l

I FRAcr/wvAr/m/ END-PRODZ)C7J W/I'MS'SS: I @371 fiarcus Nov. 4, 1947.,

W. H. BARCUS PLURAL STAGE CATALYTIC AND THERMAL CONVERSION OF HYDROCARBONS Filed Dec. 16, 1945 4 Sheets-Sheet 2 NW. 4, W47. w. H. BARCUS PLURAL STAGE CATALYTI C AND THERMAL CONVERSION OF HYDROCARBONS Fiied Dec. 16, 1945 4 sheets-shee't 5 W/TA/ESS:

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ArramvcY- Nov. 4, 1947.. w. H. BARCUS 2,430,095

PLURAL STAGE CATALYTIC AND THERMAL CONVERSION OF HYDROCARBONS Filed Dec. 16, 1943 4 Sheets-Sheet 4 bagkm Patented Nov. 4, 1947 UNITED STATES ATENT OFFICE PLURAL STAGE CATALYTIC AND THERMAL CONVERSION OF HYDROCARBONS Application December 16, 1943, Serial No. 514,444

22 Claims. 1

The present invention relates to treatment of hydrocarbons and especially composite hydrocarbon mixtures for conversion to more desirable products. More particularly, the invention is directed to a process for treating hydrocarbon mixtures, such as those derivedfrom petroleum, shale, coal or like sources, comprising a series of cooperative steps functioning in such manner as to yield products of high anti-knock value suitable for use in internal combustion engines.

The invention has particular utility in the manufacture of highest grade aviation fuels, since it provides blending stock of unusually high aromaticity whichimparts to fuel compositions containing the same certain characteristics heretofore difficult to attain to the extent desired for aviation gasoline, as well as other products useful as ingredients of fuels of this type.

It is now generally recognized that aromatic hydrocarbons are particularly desirable as a constituent of modern aircraft fuel, inthat this type of compound imparts to the fuel characteristics for satisfactory performance under socalled rich-mixture conditions as employed in operating at high power output, such as during takeoff. Other types of hydrocarbons of high anti-knock quality, such as branched-chain paralhns, generally fail to impart the characteristics desired for performance at high power consumption although they may'perform satisfactorily under lean-mixture conditions as used in low power operation such as cruising. The accelerated development in aircraft production within recent years has given rise to a critical need for large amounts of aromatic stocks suitable to provide the rich-mixture performance characteristics desired for modern aircraft fuels, and has lead to considerable investigation of possible sources and means for obtaining such stocks.

It is known that petroleum in its natural state contains aromatic hydrocarbons, usually in minor concentrations, and various methods have been proposed for recovering in sufiiciently concentrated form the aromatics of boiling range useful for aviation gasoline manufacture. It is also known that aromatic hydrocarbons are formed in the cracking of petroleum hydrocarbons, particularly in catalytic cracking, and processes employing cracking to produce aromatics and various methods of refining to obtain the aromatic stocks has been augmented to a minor extent from sources other than petroleum, the total production of such stocks has been far short of requirements.

The present invention is directed to a process for producing hydrocarbon stocks of unusually high aromaticity and in large quantities from composite hydrocarbon materials of natural or synthetic origin, and it thus provides a means of meeting rich-mixture performance specifications for aviation gasoline of highest quality. The invention also is useful in the manufacture of motor gasolne of high anti-knock quality or in the production of special products of high aromaticity as, for example, spirits or selected fractions suitable as source material for pure aromatic hy drocarbons'.

In accordance with one aspect of the invention three cooperative conversion steps are employed in the particular order of catalyticzpyrolytictcatalytic operations. A vaporizable hydrocarbon charge material containing relatively high boiling hydrocarbons is pasesd to a catalytic operation, a portion of the reaction mixture selected With respect to boiling range and composition is subjected to thermal converson conditions in a pyrolytic step, a portion of the reaction mixture from the latter operation likewise selected with respect to boiling range and composition is subjected to catalytic reaction conditions in another catalytic step and the resultant mixture is separated into products of desired boiling range including one or more products containing relatively low boiling hydrocarbons.

In more particularity and with respect to producing the aforesaid aromatic blending stock for aviation gasoline, the process comprises charging composite hydrocarbon material containing hydrocarbons of gas oil boiling range, with or without hydrocarbons of lower or higher boiling range, to an initial catalytic reaction zone maintained under conditions effective to promote a splitting reaction and therein transforming the charge into lower boiling hydrocarbons including a substantial proportion of aromatic hydrocarbons. 'The .reaction mixture from the catalytic including the transformation of non-aromatic hydrocarbons to more readily removable components. The reaction mixture from the pyrolytic zone is sent to a second fractionating zone and separated into fractions of selected boiling range,

one of which likewise contains aromatic hydrocarbons at least a considerable proportion of which boil above the aviation gasoline boiling range. This fraction is passed to the second catalytic reaction zone wherein it is subjected to conditions capable of effecting further transformation, involving the conversion of contained non-aromatic hydrocarbons either to readily removable form or to more desirable hydrocarbon compounds and the conversion of higher boiling aromatics to lower boiling aromatic hydrocarbons suitable for use in aviation gasoline. The resulting reaction mixture is passed to a third fractionating zone and separated into desired fractions including a fraction having a boi ing range suitable for aviation gasoline blending stock and having a high degree of aromaticity making it particularly desirable for this purpose. In'certain specific applications the p s i cludes subjecting other fractions obtained from the various aforesaid fractionating zones to further conversion for the production of additional amounts of highly aromatic blending stock as well as other products useful as ingredients of aviation gasoline,

In order to facilitate description of the invention there is attached hereto and made a part of this specification four sheets of drawings in which:

Figure 1 illustrates the process in simple diagrammatic form.

Figure 2 is a diagrammatic flow sheet illustrating the process in more detail.

Fi ure 3 is a diagrammatic flow sheet showing a still more detailed embodiment incorporating various refinements.

Figure 4 is a diagrammatic flow sheet illustrating another embodiment of the process including various other refinements.

As shown by Figure 1, charge oil is fed to a catalytic conversion zone, the .catalytically reacted mixture is sent to a fractionation zone and separated into fractions of desired boiling range, a selected fraction is then passed to a pyrolytic conversion zone and the resultant reaction mixture is separated into fractions in a second fractionating zone, a selected fraction from this zone is treated in a catalytic conversion operation carried out independent of the first catalytic operation and the reaction mixture from this second catalytic operation is separated into end products of desired boiling range.

Figure 2 illustrates the process in more detail and with particular reference to its use in preparing aviation blending stock of high aromaticity. In Figure 2 gas oil, or a mixture of gas oil with lower or higher boiling hydrocarbons, enters the system through line I and is vaporized and heated to desired temperature under condi tions to prevent substantial cracking in heater 2, whence the heated vapors pass through line 3 to a catalytic reaction zone illustrated as catalytic converter 4 and therein are contacted with a catalyst effective to convert hydrocarbons contained in the charge stock to lower boiling hydrocarbons including a substantial proportion of aromatic hydrocarbons which are higher boiling than the desired end product. The reaction mixture flows from the reaction or conversion zone through line 5 to fractionator 6, wherein the mixture is separated into fractions of desired boiling range in the usual manner. In one type of operation four fractions separately are withdrawn from fractionator 6; namely, a light gasoline fraction which passes out through overhead line 1, an intermediate fraction boilin below 550 F. as, for example, within the range of 300-500" F. and preferably within the range of 300-470 F. which is withdrawn through sidestream line 8, a gas oil out which is withdrawn through sidestream line 9 and a bottoms fraction which leaves the fractionator through line in.

The intermediate fraction withdrawn from fractionator 6 through line 8 preferably is the material selected for further conversion in accordance with the invention. However, it is to be understood that, if desired, this fraction may be combined with the light gasoline fraction or that fractionator 6 may be operated in such manner as to obtain the two fractions as a single wide-boiling cut and that the mixture may be utilized as feed for the subsequent thermal conversion operation. When a separate light gaso line out is taken as illustrated in the drawing, it may be subjected to further catalytic treatment as described hereinafter for further production of products useful in aviation gasoline manufacture. The gas oil cut may be thermally cracked or used in any other desired manner and. the bottoms fraction may be utilized as fuel oil.

The aforesaid intermediate fraction, or an admixture of this material and the light gasoline hydrocarbons as the case may be, flows to a thermal or pyrolytic conversion zone illustrated as thermal converter H which may operate in liquid phase, vapor phase or mixed phase and which may comprise any known or desired type of system for effecting thermal conversion, for example, one in which the charging stock is cracked under high pressure in mainly or wholly liquid phase at a temperature just below its critical temperature, as illustrated in Patents No. 1,825,977, October 6, 1931, and No. 1,938,406, December 5, 1933, or in systems known as Cross, Dubbs, De Florez, Holmes-Manley, True Vapor Phase, Gyro, Tube and Tank, etc. Suitable operating conditions for this step of the process will depend considerably upon the particular type of thermal conversion system employed and to an extent upon the particular charge stock employed in the process. For instance, operating temperatures may vary within the range of 750 to 1200" F. and pressures may range from atmospheric to 3600 pounds per square inch gauge, or

higher. Regardless of the particular system en ployed it is desirable in any event, due to the refractory nature of the feed to this step of the process, to utilize relatively severe reaction condi tions.

The reaction mixture from thermal converter H flows through transfer line 52 to fractionator 13 wherein it is separated into fractions of desired boiling range. In one type of preferred operation three fractions are taken, consisting of distillate removed through line Hi and comprising light gasoline hydrocarbons, an intermediate sidestream cut withdrawn through line l5 comprising hydrocarbons boiling below 550 F. as, for example, within the range of 300-500 F. and preferably within the range of 300-470 l t, and a bottoms product which is withdrawn through line l6. When certain types of thermal conversion systems are employed, it is desirable to return a portion of the bottom fraction to line I 2 at a zone near the outlet from thermal converter ii in order to effect a quenching action and prevent or minimize deposition of coke in transfer line i2 and in fractionator l3, and line H is provided for this purpose, Also, in some instances, it is advantageous to return a portion of the bottom fraction by means of line l8 to the inlet of thermal converter i i in order to effect further conversion.

The sidestream fraction which flows out of fractionator i3 through line I5 is the preferred feed for the third conversion stage of the pres ent process. However, as in the case of the feed to the second conversion stage, it is to be understood that the light gasoline fraction removed through line i-l also may be included as feed either by adding it to the sidestream cut or by operating fractionator It so as to obtain the light gasoline and intermediate hydrocarbons as a single fraction. However, as more fully explained hereinafter, such method of operation usually is disadvantageous and it accordingly is preferable to charge only the intermediate fraction of selected boiling range to the final conversion step as illustrated in the drawing, This fraction flows to heater 19 wherein it is vaporized and heated to desired temperature, after which it passes through line 20 to catalytic converter 2i wherein it is brought in contact with a catalyst suitable for effecting the desired conversion reactions.

From catalytic converter .2! the reaction mixture passes through transfer line 22 to fraction-- ator 23 and therein is separated into any desired fractions. When the process is carried out primarily for producing a blending stock for aviation gasoline, a fraction taken as an overhead product through line 24 and boiling below about 360 F. (for example, having an end boiling point roughly of about 350 F.) serves as particularly suitable material for this purpose. An intermediate naphtha fraction of too high boiling range to be suitable for blending in aviation gasoline but which is useful as motor gasoline blending stock or as a special solvent of high aromaticity may be withdrawn from fractionator 23 through line 25 as a sidestream cut; for example, a naphtha fraction having an end boiling point of about 430 F. and having particularly good anti-knock characteristics may be obtained in this manner. The naphtha fraction may also be subjected to a further catalytic tr atment in a separate step as described hereinafter in connection with Figure 4 for further production of lower boiling material suitable as aviation blending stock. Hydrocarbons boiling higher than the naphtha fraction are withdrawn from the base of fractionator 23 through line 26.

In one method of operation which is particularly advantageous when the process is carried out primaril for the production of aviation blending stock, no naphtha fraction is withdrawn as an end product through line 25 but, instead, this sidestream cut is recycled, in toto, through line 2? to the entrance to heater 60 where it mixes with the fresh feed derived from the thermal operation and thence passes to catalytic converter 2i. This method of operation results in a substantial increase in yield of aviation blending stock and generally in an improvement in its rich-mixture performance characteristics. In practicing the process in this manner it is desirable progressively to increase the severity of the reaction conditions in catalytic converter 2i from the start of operation until the flow of the naphtha fraction through line 21 has reached equilibrium conditions. crease in refractory nature of the combined feed to catalytic converter 2! which occurs as the proportion of the more refractory recycled naphtha in the feed increases up to the equilibrium value.

In practicing the process as described above the two catalytic conversion steps, as well as the additional catalytic steps employed in the more explicit embodiments described below, may be carried out by any suitable or known means for effecting conversions of the type desired. The catalytic contact material may be used in situ as a stationary catalyst bed or may be permitted to flow either countercurrently to or concurrently with the hydrocarbon vapors to effect the desired reactions. Particularly suitable arrangements of apparatus employing converters of the stationary bed type in multiplicity to provide for catalyst regeneration and continuity of operation are described in U. S. Patent No. 2,078,247, issued to Eugene J. Houdry, and U. S. Patent No. 2,031,600, issued to J. W. Harrison et a1. Such arrangements have had widespread use in the industry and are particularly adaptable for carrying out each of the catalytic steps of the present inven tion. Somewhat similar operating conditions may be employed in each of the two abovedescribed catalytic conversion stages, although in general it is desirable to use more severe conditions in the second catalytic operation due to the more refractory nature of the feed to this step. When stationary catalyst beds of the type described in the aforesaid patents are utilized, suitable temperatures and pressures usually lie within the ranges of 750 F. to 1000 F. and atmospheric pressure to about 100 pounds per square inch gauge, respectively. When other types of catalytic operation are employed, temperatures ranging up to about 1100 F. may be satisfactory. In the second catalytic step, it is especially desirable to utilize a relatively high pressure since this helps promote the transforma-' tion reactions involved, particularly the transformation of olefins to other hydrocarbons. Feed rates of 8/20 (8 volumes of feed liquid per hour per 20 volumes of catalyst) to 50/20 are suitable, although lower or higher rates also may be used successfully.

Similar catalysts or contact masses may be used in each catalytic operation including the additional catalytic steps of the more refined embodiments, although the reactions which are brought about in the various steps may be dissimilar to considerable extent as more fully discussed hereinafter. Catalysts of siliceous nature having high activity are preferred. These may include blends This compensates for the in- .7 mar :fdescribed in U. S. Patents 2,078,945 and $2,078,951, issued to Eugene J..Houd ry.

The chemical reactions involved in transform- :in'gtheeharge-materials to more desirable prod- 116178 in accordance with the present invention ob- -=-viously,-are=very complicated and do not permit ofgprecise explanation. However, a consideration of .the predominant reactions effected in the ithree conversion stages is useful as an illustration of the 1 cooperative relationship of the steps .in

:producing products of enhanced value and of the .unitary nature of the process as a whole.

The .initial conversion operation carried out in catalyticconverter 4 effects a splitting reaction .in. which gas oil hydrocarbons are converted to .hydrocarbons. of lower boiling range. It has been .found that the reaction products include a considerable amount of aromatic hydrocarbons. .{I'hese aromatics, however, are predominantly of ,relatively'h-igh molecular weight, mostly boiling --above.-300 F.,-and therefore. are of too high boil- 'ing range for more than'a minor proportion rthereof torbe utilizable inaviation fuel without isubsequent treatment in accordance with the invention. -When freshgas oil is charged to the process and-asidestrea-mcut-having a boiling rangevof 300"-470"F.,for-example, is withdrawn from fractionatonfi' through line--8,-this out usual'ly will contain-25-6O per cent-aromatics, the

"remainder'being paraflins and naphthenes with iasma-ll proportion' of olefins. -When this fraction .iszsubjectedmo treatment in the thermal con- :versionvstep as: described above, the predominant .reactionseffected therein appear to comprise con- ;vers-ioni of non-aromatic. hydrocarbons, particu- .larly the paraffinichydrocarbons, to olefins and rW:mo1ecu1a-rWelghtparaffins without substan- -.tial formation of lower boiling aromatics. :A sidesstreamifraction which is then withdrawn from fractionator l3:throughline !5 and which has a y =boiling; range of 300-4-70 F., for example, usually will: contain 40-65 percent aromatics and -25 per cent olefins. Treatment of this fraction in the third conversion step as described above brings-about two types of transformation requiis-ite for obtaining desired products. One type ,zcomprises conversion of a predominant amount .oflthe'olefins to other hydrocarbon compounds ...and.involvestransformation of olefins to iso- .,para-fiins which boil in the-aviation gasoline range Fandwhichhavegood anti-knock characteristics, as well'as polymerization of olefins to higher boiling materials i which subsequently are separated 'fromthe desired products in fraotionator- 23. The other type comprises transformation of the. arcmatic hydrocarbons to aromatics of lower molecular weight, presumably by a dealkylation. reaction, thereby forming aromatics of boiling. range :suitable for aircraft fuel. In addition, this treat- .-ment'-also appears'to cause conversion of non- Reasons for certainpreferred features of the hereinbefore described method of practicing the invention are provided by the above discussion relating to the predominating chemical transformations brought about by the three conversion operations. Since a high concentration of arcmatic hydrocarbons in the products are desirable and since, in the first conversion step, only a small proportion of the aromatic hydrocarbons formed boil below 300 F., it is preferable to withdraw a light gasoline fraction from fractionator 6 through line 1 and to feed only the intermediate fraction withdrawn through line 8 to the thermal conversion step. Likewise, since the reaction mixture after thermal conversion contains no substantial amount of aromatic hydrocarbons boiling below 300 F. but does contain a considerable proportion of olefins as well as naphthenes and paraflins boiling below. this temperature, a light gasoline fraction preferably is withdrawn from fractionator 13 through line 14. This results in more efficient utilization of the catalytic equipment in the final conversion step.

A more extended application of the process is illustrated in Figure 3. As shown, charge oil entering the system through line I is heated and passed to catalytic converter 4 and the reaction mixture is separated in fractionator 6, a selected fraction preferentially boiling within the range of 300-470 F. is withdrawn through line 8 and passed to thermal converter H and the reaction mixture from the thermal conversion is separated in fractionator I3, a selected fraction likewise boiling within the preferred range of 300-470 F. is withdrawn through line I 5 and passed through heater [9 to catalytic converter 2 I, all as described in connection with Figure 2. In the present embodiment the reaction mixture from catalytic converter 2| is separated in fractionator 23 into three fractions but only two of these, namely, the overhead and bottoms fractions, are withdrawn as end products of this operation. The intermediate fraction, having a boiling range, for example, of 320-450 F., is recycled in its entirety through line 21 for further conversion. The overhead product, which has an end boiling point preferably of about 350 F., may be passed through line 24 directly to storage tank .28 for use as aviation blending stock. However, it is distinctly preferable, before sending this product to storage, first to send it through line 29 to fractionator 39 and therein to separate the C4 and C5 hydrocarbons, which are removed through overhead line 3|. It has been found that a considerable proportion of the C4 and C5 hydrocarbons are olefinic and that their removal therefore results in substantial improvement in acid-heat and also improves the rich-mixture performance characteristics.

The gasoline fraction derived from the initial catalytic step and having an end boiling point of about 350 F., for example, is passed through line 1 to heater 32 and thence, by means of line 33, to catalytic converter 36 wherein it is subjected to catalytic treatment under reaction. conditions comparable to those hcreinbefore set forth in connection with the other catalytic operations. The reaction mixture flows through line 35 to fractionator 36 and therein is separated into three fractions: namely, alight gasoline fraction of boiling range suitable for aviation base stock, for example boiling below about 310 F., whichis passed through line 3'! to storage tank 38; a bottoms fraction which is withdrawn through line 39;. and an intermediate sidestream fractionboil- 9 ing within the approximate limits of 300-4=70 P. which is removed through line 56.

The last-named fraction is particularly suitable charge material for still another catalytic operation in which additional quantities of aviation blending stock having even better anti-knock characteristics are produced. In this operation the fraction is passed through heater ii and line 42 to catalytic converter 33 in which rather severe reaction conditions are employed due to the refractory nature of the feed. The reaction mixture passes through line 55 to fractionator 55, from which an overhead fraction withdrawn through line 46 and a bottoms fraction withdrawn through line 4? are obtained as end products of this step. As in a previously described step, a naphtha fraction having a boiling range, for example, of 320-l50 F. is withdrawn as a sidestream cut through line 48 and all of this fraction is recycled to heater ll and thence to catalytic converter 53 in admixture with fresh feed supplied through line Gil. This results in increased yields of the desired overhead product. As described above in connection with recycling in this manner, it is desirable upon starting operation progressively to increase the severity of reaction conditions due to the increasing refractory nature of the mixed feed until equilibrium flow conditions are reached. The overhead product withdrawn through line 55 may be passed through line 24 directly to aviation blending stock storage tank 23 but, as in the case of the aviation blending stock from fractionator 23, preferably is first sent to fractionator 35 for removal of C4 and C5 hydrocarbons.

In another embodiment illustrated by Figure 4, the initial catalytic step and the succeeding thermal step conform in detail to the corresponding steps described in connection with Figure 3. Likewise the catalytic step wherein the light gasoline fraction derived from the initial catalytic operation is treated in catalytic converter 35 and the reaction mixture is separated in fractionator 36 is identical with the corresponding step of Figure 3. However, the catalytic operation immediately following the thermal step differs in that the naphtha fraction, instead of being recycled to heater is and catalytic converter 2!, is sent through line 49 to storage tank 55 for subsequent use independent of this catalytic operation. The naphtha fraction withdrawn from fractionator 36 through line 5! is passed to storage tank 52, whence, in accordance with one embodiment, it may be passed by means of line 53 to heater l9 and catalytic converter 2! for further conversion in admixture with the thermally converted feed fraction supplied through line l5. Alternatively, the naphtha fraction in storage tank 52 may be withdrawn from the system through line 54 for use as motor gasoline blending stock or other special purpose or it may be charged by means of lines 55 and 55 to heater 4! and catalytic coriverter 43 for production of additional amounts of aviation blending stock. Likewise, the naphtha fraction in storage tank 50 may be withdrawn through line 5! for special use or it may be passed through lines 58 and 56 as feed to the catalytic conversion operation, either separately or in admixture with the material from storage tank 52. Preferentially, when the two naphtha fractions are utilized as feed for the final catalytic conversion step, they are charged separately and in alternate manner to heater 4i and catalytic converter 53 since somewhat more severe reaction conditions are required to bring about the desired transformation of the naphtha from storage tank 522 than required for the naphtha from storage tank 55. The overhead fraction produced in this final catalytic operation preferably is stripped of C4 and C5 hydrocarbons in fractionator 3!] before being used as aviation blending stock.

In practicing the present invention for manuiacturing aviation gasoline blending stock it is distinctly desirable that the feed material to the thermal conversion step, in addition to having a boiling range below 550 F., contain at least 25 per cent, and preferably at least 35 per cent, of aromatic hydrocarbons boiling above 300 F. When materials containing aromatic hydrocarbons in lesser amounts are charged to the thermal conversion zone it is difficult to attain in the product the rich-mixture performance characteristics desired for aviation blending stock.

The following examples are illustrative of specific embodiments of the invention and are given only for purposes of illustration and not in limitation thereof:

Example I The present example illustrates the embodiment shown in Figure 2 without any recycling of the naphtha fraction through line 2?. A straight-run gas oil derived from a mixture of Gulf Coastal and East Texas crudes was charged to the process and subjected to reaction condi tions in catalytic converter 5 which comprised a multiplicity of catalyst chambers of the stationary catalyst bed type operating alternately in on-stream and off-stream fashion. A pressure of approximately 30 pounds per square inch gauge was maintained during on-stream operation in converter 5 and the temperature within. the catalyst bed varied from about 885 F. at the beginning of each on-stream period to about 825 F. at the end of each on-stream period. The feed rate was approximately 20/20. The reaction mixture was separated in fractionator 5 into four liquid fractions and, in addition, an uncondensible gas fraction. Yields and properties of the liquid products and charge stock were approximately as follows:

Charge Light Naphtha Gas Oil Bottoms Stock Gasoline Fraction Fraction Fraction Yield, vol. per cent of charge stock .i 29.0 13. 8 43.1 5. 5 A. P. I. gravity 30.2 58. 2 33. 5 27.9 18. 9 A. S. 'l. M. distillatio I. 13. Point, F 399 108 352 456 475 50% Point, F i 583 218 400 E30 778 End Point, F 795 338 Composition:

Vol per cent Olefins 13 Vol. per cent Aromatics. 20 Vol. per cent Para|iins+Naphtl1enes 67 Acid heat 44 Anti-knock rating:

A. S. T. M. Motor Method Octane No. (clear) 79. 5 72 1939 Research Method Octane No. (clear) 89. 5 82 aeeopeec 11; The naphtha fraction was subjected to-pyrolytic treatment in thermal converter Il-under temperatures and pressures varying, respectively from 319 F. and 960 pounds per square inch gauge at the inlet to 978 F. and 750 pounds per square inch gauge at the outlet. The reaction mixture was separated in fractionator I3 into three liquid fractions and also an uncondensible gas fraction. Yields and properties of the liquid products. were approximately asfollows:

Light Naphtha Bottoms Gasoline Fraction Fraction Yield vol. per cent of naphtha charged 15 54 A. P. l. gravity 76. 6 33. 22 2 A. S. T. M. distillation:

l. B. Point, F 78 284 389 50% Point, F. 192- 360 470 End Point, F 280 441 708 Composition:

Vol. per cent Olefins 65' 15 Vol. per cent Aromatics 0 54 Vol. per cent Paraflins+ Naphthenes 35 3L Acid heat 43 Anti-knock rating;

A. S. T. M. Motor M ethod Octane No. (clear) 77 78.5 1939 Research Method 7 Octane No. (clear) 88. 1

The resulting naphtha fraction was treated in catalytic converter 2!, which was similar in type As shown by the data listed'for the stabilized blending stock, this product was-of high quality and suitable for use in manufacture of aviation gasoline meeting-highest present-day standards.

"naphtha fraction through line 21.

Example II This example also illustrates the embodiment shown in Figure 2 but with recycling of the total The naphtha fraction derived from the thermal operation and conforming substantially to that shown in Example I was fed to heater l9 and treated in cat- .alytic converter 2i. All of the naphtha fraction withdrawn through the sidestream line from fractionator 23-was recycled through line 21 to give; as charge to the operation, an admixture of recycled naphtha and the-fresh feed. A pressure of 55-60 pounds per square inch gauge and a temperature varying from 885 F; to 835 F. were maintained in catalytic converter 2|. The fresh feed rate was 11.7/ 0 and the combined feed rate was 15.7/20. Cland C5 hydrocarbons were removed'from the overhead product and a stabilized blendingv stock thereby was obtained. Properties and yields of the charge materials and the liquid products were approximately as follows:

Charge w Stabilized Blending Bottoms Fresh Recycled Total Stock Fraction Feed Naphtha Feed Yield, vol. per cent of fresh feed 100 134 55.4 W 11.4 A P. I. gravi 33. 5 32. 5 33. 3 36.6 15. 5 A'.=S. l. M. distillation:

I. B. Point, F. 284 50% Point, F 360 End Point, F 441 Composition:

' Vol. per cent olefins 15 Vol. per cent aromatics 54 Vol. per cent parafiins-l-naphthenes 3i Acid heat; 43

Antl-lmock rating; AFB-3C: plus 4 ml.

TEL/gal.

1 Calculated from test on 50:50 blend with aviation base stock? to catalytic converter 4, at a pressure of approximately. pounds per square inch-gauge. and .a.

temperature varying from 910 F. at thebeginning of on-stream operation to 845 at the end of the on-stream period. A ieedrate of 15.7 was utilized. The reaction'mixture was separated in fractionator 23 into three fractions. The overhead fraction was subjected to distillation effecting removal of C4 and part of the C5 hydro carbons, thereby producing. a stabilized aviation blending stock. Yields and properties of the products were approximately as follows:

Stabilized Blending Naphtha Bottoms Stock Fraction Fraction Yield, vol. per cent of naphtha charged. 56.6. A. P. I. gravit 40.7 A. S. 'I. M. distillation:

I. B. Point, F 121 50% Point, F 29e End Point, F... 356. Composition:

Vol. per cent Olefins 2 Vol. per cent Aromatics Vol. per cent Parafiins-l-Naphthenes. 28"

Acid heat Anti-knock rating: AFD-3C: plus 4 ml. TEL/gal 1o -II s+a+i (IMEr,=255) 1 Calculated from test on 50z5oblend-with aviation basestockp Example III respectively, of the on-stream period. The feed 10 rate was 36.7/20. The reaction mixture was separated in fractionator 36 into three liquid fractions. Yields and properties of these as well as of the light gasoline charge are shown in the following tabulation:

l4 ploy a minor proportion, for instance per cent, in the blend in order that the usual distillation specifications for aircraft fuel may be met. Such minor proportions usually bring about the desired improvement in rich-mixture performance characteristics.

' Although it has been stated above that the various catalytic conversion steps may be carried out by any of the known means for eifecting such conversions, it is not meant to imply that the various types of catalytic operation are exact equivalents, since the different methods may differ toan extent in effectiveness in promoting the various transformation reactions involved in the process. For example, in the catalytic step imme- Charge Overhead Fraction giggg: gggg gg Yield, vol. per cent of charge 100 75.0 10.9 4. 0 A. P. I. gravity 59.5 65.1, A. S. T. M. distillation:

I. B. Point, F 103 50% Point, F 216 End Point, F 300 Composition:

Vol. per cent Olefins 26 Vol. per cent Aromatics 19 Vol. per cent Paraffins+Naphthenes 55 Acid heat 80 Anti-knock rating:

AFD-lC: plus 4 ml. TEL/gal 88.5 99.0

AFD-3C: plus 4 ml. TEL/gal S+0.45 (IMEP=l8l.5)

As shown by the tests, the overhead fraction was particularly suitable as aviation base stock. The naphtha fraction was passed through line 40 to catalytic converter 43 wherein it was subjected to catalytic conversion under a pressure of approximately 65 pounds per square inch gauge and a temperatrue varying from 890 F. to 850 F, at the beginning and end, respectively, of the onstream period. All of the naphtha fraction separated from the reaction mixture in fractionator 45 was recycled through line 48 to heater ll and catalytic converter 43, so that the only liquid fractions obtained as end products were the overhead and bottoms. The charge rate to catalytic converter 43 was 13.1/ based on the fresh feed 45 from line 50 or 15.7/20 based on the combined fresh feed and recycled naphtha. Yields and properties of the two end products as well as of the recycled naphtha were as follows:

dium is employed to regulate the catalyst temperature and the only gain or loss of heat in the catalytic zone is that due to the temperature difference between inlet and outlet reactant streams, may be used to advantage in certain respects. The choice of type of catalytic operation also may be governed by considerations not directly connected with the present process, such as the proper integration of the process with other refinery operations. For example, the method com- Recycled Bottoms Naphtha Overhead Fraction 1 Fraction Yield, vol. per cent of fresh charge. 9.9 A. P. I. gravity 31. 3 20.1 A. S. T. M. distillation:

I. B. Point, F 310 352 Point, F." 348 428 End Point, F" 421 760+ Composition:

Vol. per cent olefins 1 Vol. per cent aromatics 88 Vol. per cent paraflins-i-naphll thenes. Acid heat Anti-knock rating:

AFD-IC: plus 4 ml. TEL/gal. 100 AFB-3C: plus 4ml. TEL/gal... S+8.6 2 (IMEP=275) 1 After removal of light ends in fractionator 30. 2 Calculated from 50:50 blend with aviation base stock.

The data tabulated for the overhead fraction show it to be excellent aviation blending stock.

The aviation blending stock prepared in accordance with the present invention may be utilized in any suitable or desired proportion as an ingredient of aircraft fuel. However, when it is prepared so as to contain a substantial amount of hydrocarbons boiling above 300 F. as in the monly referred to as the fluid catalyst method, in which vapor containing particles of finely divided catalyst suspended therein is passed through a reaction zone to effect the desired conversion, tends to produce a greater proportion of butylenes in the gaseous conversion products whereas the stationary bed method tends to produce a greater proportion of isobutane. It therespecific examples presented, it is desirable to emfore may be desirable to choose the type of cata- 1'5 lyticioperation *orr such-.basisasto; compensate for: aideficiency of .either butylenestor. isobutane from. other. refinery operations and so obtain: a :proper. balance. .between [these componentsas feed tc;a:. separateralkylation process. Again; since aelighta gasoline fraction is produced in thefirsticata: lytic'stage andthis fraction maybe subsequently treated catalytically in order'toproduce aviation basestock, it may bedesirable to chocseior'the initialcstep themethodof operation whichrpro: duces the best quality light gasoline. fraction for Y such? purpose.

Although: the. flow sheets. show, a multiplicity of-rcatalytic zones, in actual practicethepvariousrconversions. may be. and preferably are carried.; out with a minimum amount'of catalytic equipment by utilizing blocked outoperation. In operating in this mannerone catalytic unit is utilized to efiect a number of the various conversions by charging first one feed fraction over -areasonably extended time period and then another. Fractions produced in the various operations and which are intended'for further conversion are collected separately in storage tanks and later utilized as feed as desired. In ,prace ticing the invention on commercial scale the catalytic steps including all those in the more specifically illustrated forms of the process conveniently may be carried out with two catalytic units, one continuouslycharging the fresh. gas. oil andthe other handling the various other cata lyticconversions in blocked-out? operation, The present process when carried out inthismanner permits more efiicient utilization of j catalytic equipment and production of greateramounts of' aviation fuel for a given amount of catalytic ca: pacity than heretofore possible.

I do not herein claim the process, described. as being practiced in the apparatus diagrammed in Fig. 3, as the same forms the subject matter of a divisional application, Ser. No. 72.311 94 filed JanuaryZO, 1947;

What I claim and, desire to protect b'y Letters Patent is:

1. In. the production of lowerboilinghydrocarbons of high aromaticity the steps ofcatalyticah ly cracking a composite higher boiling hydrocare bon charge. to, produce a hydrocarbon,mixture containing a substantial proportion of high boiling aromatics, selecting from the reaction mixture a fraction containing at least 25 per cent of: high boiling aromatics, thermally vcraclringsaizL fraction without substantial admixture with hydrocarbons derived from any other operation to transform non-aromatics contained therein to chemically different hydrocarbon compounds including olefins, selecting from the reaction mixture resulting solely from thermally cracking said fraction a fraction containing at least 40' per cent of high boiling aromatics and a minor percentage of olefins, catalytically reacting the last-named fraction in an independent zone the presence of a cracking type catalyst to transform high boiling aromatics to lower boiling aromatics and reduce materially the olefin content, and separating from the mixture resulting from e ast; at lyt eact o act on: ontainin atl stfi e nt i idl w o inea omatics. 1 as, the; desired product.

r The processdefi edinm 1 hIQi i 2Qm; the mix ur -r sult n mmth -J st ata t gree nt q genes s. na-r t in n tha h h; are: at c ty il .mainlx: bo -t e actionc tainin th ower o l n roma ics. andein whicbz senaratedmaphtha. is. atalytic-a ly reactants.zthesreactionzmixtureresultin -solely: rqm therin an independenhzone in,,the presence of a cracking type catalyst to produce lower boiling aromatics and fa flOlllthe: reaction mixture obtained from th'e independent zone a fraction is separated containing a substantial proportion of said lower boilingaromatics.

3.". The process defined in claim. 1 '2 wherein a naphtha fraction boilingmainly above the fraction :containingthe. lower boiling. aromatics also is separatedfrom the reaction. mixture. obtained from the last catalytic reaction zcne and at least. a-substantial proportion of such separated.naphav tha fractioniis recycledtosaid catalytic reaction; zone.-.

4. In the production of lowerrboiling;.hydr0ecarbons of high aromaticity the steps of cata-- lytically cracking a composite higher boiling hydrocarbon charge to produce a hydrocarbon mixture containing a substantial'proportion of high: boiling aromatics; selecting fromuthe react on mixture 2. fraction boiling; below, 550?'F, and containing a substantial proportionofaromaticsboiling above300? F., thermallycracking said gfraction alone to transform non-aromatics contained therein to. chemically different, hy-

drocarbon compounds includingolefins, selecting from the reaction mixture resulting solely from thermally-cracking said fraction;.a fraction boiling below 550 F. and containing a substantial proportion of. aromatics boiling above 300 F; andfa minor percentage of ;olefin s,- catalytically reacting the lastenamed fraction'in an. independent zone in the presence ofa cracking typecatalyst to transfor'm the high-boiling' aromatics tolowei boiling aromatics and reduce-materiallythe olefin content; and separating -from-- the mixture resulting from thelast catalytic re-- acti n a fraction containing a, high concentratienpf, saidglower boiling aromatics as the-desired product.

5; The process defined in claim '4 whereimirom the mixture resulting fromthe last catalytic, reqtion. on s se arated. a ap ha of ieh maticity boiling mainlynhcve the fraction containing the lower boiling. aromatics and in which such separated naphtha .is catalytically l reacted;

independent. zone in the presence. of-a cracking type catalyst-to produce lower boiling; aromatics and 'from the reaction mixture obtained from the independent zone a fraction is separated. containing a substantial proportion of saidlowerbailingaromatioa- 6. The process defined ingclaim 4 whereinsa naphtha fraction boiling mainly above the fraction containingthe lower boiling aromatics also-- is separated from-the reaction mixture obtained from the last catalytic reaction zone and atleast asubstantialproportion of such separated naphtha fraction is recycled to said catalytic reaction zone.

'7: In the production of lower boilinghydrocan. I bons -of,.high'aromaticity the steps ofcatalytical- 1y cracking a composite higher boiling hydrocarbon charge to produce a hydrocarbon mixture containing a substantial proportion of high boiling aromatics, selecting from the reaction mixture-a.riraq ion-be l n .-pre l m a tly in th limit-51.0 9 ;?F;-;1 Q iend: containin a substant al; proporti ns 0i alt nat on thermall ackin aid. inaction; wi ho u .t n i l.a

trewit. L YQ YD a ZD RS: der iz d: ro n r- .neration tatran iorm.nonr rom t cscom ta 3. thei achem callr i fe ent.h dmcar: on omnounds=.-in ndins 'olefins, s lectine.: rom;

mally cracking said fraction a fraction boiling predominantly within the limits of 300 F. to 470 F. and containing a substantial proportion of aromatics and a minor percentage of olefins, catalytically reacting the last-named fraction in an independent zone in the presence of a cracking type catalyst to transform the high boiling aromatics to lower boiling aromatics and reduce materially the olefin content, and separating from the mixture resulting from the last catalytic reaction a fraction boiling below 360 F. and containing a high concentration of said lower boiling aromatics as the desired product.

8. Ihe process defined in claim '7 wherein a naphtha fraction boiling mainly above the fraction containing the lower boiling aromatics also is separated from the reaction mixture obtained from the last-named catalytic reaction zone and at least a substantial proportion of said fraction is recycled to the feed to said zone for further conversion.

9. The process defined in claim 7 wherein C4 and Cs hydrocarbons are removed from the fraction separated from the last-named reaction mix ture thereby to yield a product improved with respect to acid-heat and rich-mixture performance characteristics.

10. In the production of lower boiling hydrocarbons of high aromaticity suitable for use as aviation blending stock the steps of catalytically cracking a composite higher boiling hydrocarbon charge to produce a hydrocarbon mixture containing a substantial proportion of high boiling aromatics boiling above 300 F., selecting from the mixture a fraction boiling predominantly within the limits of 300 F. to 470 F, and containing 25-60 per cent aromatics, thermally cracking said fraction without substantial admixture with hydrocarbons derived from any other operation to transform nonaromatics contained therein to chemically different hydrocarbon compounds including olefins, selecting from the reaction mixture resulting solely from thermally cracking said fraction a fraction boiling predominantly within the limits of 300 F. to 470 F, and containing 40 to 65 per cent of aromatics and a minor percentage of olefins, catalytically reacting the lastnamed fraction in an independent zone in the presence of a cracking type catalyst to transform the high boiling aromatics to lower boiling aromatics and reduce materially the olefin content, and separating from the mixture resulting from the last catalytic reaction a fraction boiling below about 360 F. and containing 65-85 per cent aromatics as the desired product.

11. In the production of lower boiling hydrocarbons of high aromaticity suitable for use as aviation blending stock the steps of catalytically cracking a composite higher boiling hydrocarbon charge to produce a hydrocarbon mixture containing a substantial proportion of aromatics boiling above 300 F., selecting from the reaction mixture a fraction containing at least 25 per cent of high boiling aromatics boiling within the limits independent zone in the presence of a cracking type catalyst to transform the high boiling aromatics to aromatics boiling below 360 F. and reduce materially the olefin content, and separating from the mixture resulting from the last catalytic reaction a fraction containing at least 65 per cent of said lower boiling aromatics as the desired product.

12. In the production of lower boiling hydrocarbons of high aromaticity suitable for use as aviation blending stock the steps of catalytically cracking a composite higher boiling hydrocarbon charge to produce a hydrocarbon mixture containing a substantial proportion of aromatics boiling above 300 F., selecting from the reaction mixture a fraction containing 25 to per cent of aromatics boiling within the limits of 300 F. to 470 F., thermally cracking said fraction without substantial admixture with hydrocarbons derived from any other operation to transform nonaromatics contained therein to chemically difierent hydrocarbon compounds including olefins, selecting from the reaction mixture resulting solely from thermally cracking said fraction a fraction boiling within the limits of 300 F. to 470 F. and containing at least 40 per cent of aromatics and a minor percentage of olefins, catalytically reacting the last-named fraction in an independent zone in the presence of a cracking type catalyst to transform the high boiling aromatics to aromatics boiling below 360 F. and reduce materially the olefin content, and separating from the mixture resulting from the last catalytic reaction a fraction containing at least per cent of said lower boiling aromatics as the desired product.

13. In the production of lower boiling hydrocarbons suitable for aviation gasoline manufacture the steps of catalytically cracking a composite hydrocarbon charge boiling predominantly in the gas oil boiling range to produce a hydrocarbon mixture containing a substantial pro portion of high boiling aromatics, selecting from the reaction mixture a light gasoline fraction and a naphtha fraction boiling mainly above the gasoline fraction and containing said high boiling aromatics, thermally cracking the naphtha fraction to transform non-aromatics to chemically difierent hydrocarbon compounds and selecting from the resulting reaction mixture a second naphtha fraction of similar boiling range containing the high boiling aromatics, catalytically reacting said second naphtha fraction in a second catalytic conversion zone in the presence of a cracking type catalyst to transform aromatics contained therein to lower boiling aromatics, separating from the reaction mixture resulting from the second catalytic reaction a gasoline of high aromaticity boiling mainly below 350 1 and having rich-mixture performance characteristics suitable for aviation blending stock and a naphtha fraction of high aromaticity boiling mainly above said gasoline, catalytically reacting the light gasoline fraction from the first catalytic operation in a third catalytic conversion zone in the presence of a cracking type catalyst to produce additional high boiling aromatics, selecting from the reaction mixture resulting from the third catalytic conversion zone a gasoline fraction boiling mainly below 310 F. having lean mixture performance characteristics and suitable for use as aviation base stock and a highly aromatic naphtha fraction boiling mainly above said gasoline fraction, mixing the last-named naphtha fraction with the naphtha fraction from the secand catalytic conversion zone and catalytically reacting the mixture in a fourth catalytic conversion zone in the presence of a cracking type catalyst to produce lower boiling aromatics, separating from the reaction mixture resulting from the fourth catalytic conversion zone a gasoline fraction of high aromaticity boiling mainly below 350 F. to thereby yield further amounts of product having rich-mixture performance characteristics; suitable for aviation blending stock.

14. In the production of lower boiling hydrocarbons suitable for aviation gasoline manufacture' the steps of catalytically cracking a compQ ite hydrocarbon charg boiling predominantly in th as-oil boiling range to produce a hydrocarbon mixture containing a substantial proportion of high boiling aromatics, selecting from the reaction mixture a light gasoline fraction and a naphtha fraction boiling mainly above the gasoline fraction and containing said high boiling aroma-tics, thermally cracking the naphtha fraction to transform non-aromatics to chemically difierent hydrocarbon compounds and selecting from the resulting reaction mixture a second naphtha fraction of similar boiling range containing the high boiling aromatics, catalytically reacting the second naphtha fraction in a second catalytic conversion zone in the presence of a cracking type catalyst to transform aromatics to; lower boiling aromatics, separating from the reaction mixture resulting from the second catalytic reaction a gasoline fraction of high aromaticity boilingmainly below 350 F. and having; rich-mixture performance characteristics suitable for aviation blending stock and a third naphtha fraction of high aromaticity boiling mainly above said gasoline fraction, catalytically reacting the third naphtha fraction in a third catalytic conversion zone in the presence of a cracking type catalyst to transform aromatics contained therein to lower boiling aromatics, selecting' from the reaction mixture resulting from the third catalytic conversion zone a gasoline fraction of high aromaticity' boiling mainly below 350 F. to thereby yield further amounts of product having rich-mixture performance characteristics suitable foraviation blending stock, catalytically reacting the light gasoline fraction from the first catalytic conversion zone in a fourth catalytic conversion zone in the presence of a cracking type catalyst to further produce high boiling aromatics, selecting from the-reaction mixture resulting from the fourth catalytic conversion zone a gasoline fraction boiling mainly below 310 F. having lean mixture performance characteristics suitable for aviation base stock and a highly aromatic fourth naphtha fraction boiling mainly abovethe gasoline fraction and mixing at least a substantial proportion of the fouith naphtha fractionwith the second naphtha fraction to thereby form mixed feed for the second catalytic conversion zone.

15. In the production of lower boiling hydrocarbons of high aromaticity the steps of thermally cracking a composite hydrocarbon material the predominant part of which boils within the range of 300-500" F. and containing not less than 25 per cent ofaromatics boiling above 300 F. to transform a substantial part of the non-aromatics to chemically different hydrocarbon compounds including olefins without substantial A transformation of higher boiling aromatics to lower-boiling aromatics, selecting from the reaction mixture resulting from the thermal operation: an intermediate, fraction, the predominant part of which boils within the range of 300-500" F., catalytically reacting said intermediate fraction alone in the presence of a cracking type catalyst to transform the higher boiling aromatics to lower boiling aromatics including aromatics boiling below 300 F. and greatly reduce the percentage of olefins, then separating from the reaction mixture resulting from the catalytic operation a lower boiling fraction containing substantially all the aromatics boiling below 300 F.

16. In the production of lower boiling hydrocarbons of high aromaticity, the steps of thermally cracking a composite hydrocarbon material the predominant part of which boils within the range of 300-500 F. and containing not less than 25 per cent aromatics boiling above 300' F. to transform a substantial part of the nonearomatics to chemically different hydrocarbon compounds including olefins and without substantial transformation of higher boiling aromatics to lower boiling aromatics, selecting from the reaction mixture resulting from the thermal operation an intermediate fraction the predominant part of which boils within the range of 300-500 F., catalytically reacting said intermediate fraction alone in the presence of a cracking type catalyst to greatly reduce the percentage of olefms and to transform higher boiling aromatics to lower boiling aromatics thereby to produce a mixture of a relatively large fraction of hydrocarbons boiling mainly below 350 F. and containing a major per centage of aromatics and a relatively small fraction of hydrocarbons boiling mainly above 350 F. and also containing a major percentage of arcmatics, then separating from the last-mentioned reaction mixture the fraction containing the lower boiling product of high aromaticity,

1'7. The process defined in claim 16 which comprises catalytically reacting the fraction boiling mainly above 350 F. in the presence of a cracking type catalyst to transform the higher boiling aromatics contained therein to lower boiling aromatics thereby to increase both the amount of lower boiling hydrocarbons of high aromaticity and the percentage of aromatics contained in the low boiling product.

18. The process of producing from a hydrocarbon charging stock boiling mainly within the range of 400-800 F. and relatively poor in arcmatics a lower boiling hydrocarbon aviation blending stock the major portion of which consists of aromatics, which comprises catalytically cracking the charging stock to produce a reaction mixture containing aromatics boiling above 300 F., separating from the reaction mixture resulting from the catalytic operation a fraction boiling mainly below 300 F., and a fraction boiling mainly within the range of 300500 F. and containing over 25 per cent aromatics, thermally reacting the last-named fraction without substantial admixture with hydrocarbons derived from any other source to produce a substantial percentage of olefins without substantial transformation of contained aromatics to lower boiling aromatics, separating from the reaction mixture resulting solely from thermally cracking said lastnamed fraction a fraction boiling mainly below 300 F. and containing substantially no aromatics and a fraction boiling mainly within the range of 300-500 F. and containing a high percentage of aromatics, and catalytically reacting this lastnamed fraction in an independent zone in the presence of a cracking type catalyst to greatly reduce the percentage of olefins and to produce aromatics boiling below 350 F., then separating;

from the reaction mixture resulting from the second catalytic reaction a fraction boiling mainly below 350 F. of which aromatics comprise the major part.

19. The process defined in claim 18 comprising also subjecting the fraction boiling mainly below 300 F. which was separated from the reaction mixture resulting from the first catalytic operation to a further independent catalytic reaction in the presence of a cracking type catalyst to produce aromatics boiling above 300 F., separating from the reaction mixture resulting from this catalytic operation a lighter fraction, a heavier fraction and an intermediate fraction boiling mainly within the range of 300-470 F. and containing a major percentage of aromatics, independently catalytically reacting the intermediate fraction in the presence of a cracking type catalyst to transform higher boiling aromatics to aromatics boiling below 350 F., then separating from the reaction mixture resulting from this catalytic operation a fraction boiling mainly below 350 F. of whicharomatics comprise a ma jor part.

20. The process of producing a blending stock for gasoline nearly free of olefins and which contains a major proportion of aromatic hydrocarbons and a minor proportion of paraffins and naphthenes, which comprises producing, by catalytic cracking, from a hydrocarbon fraction having a boiling range mainly within the range 400- 800 F., a hydrocarbon mixture a fraction of which boils mainly within the range of 300-470 F. and contains between 25 and 60 per cent relatively high boiling aromatic hydrocarbons boiling mainly above 300 F., then fractionating said mixture to separate said fraction, then, by thermally cracking said fraction, without substantial admixture with other hydrocarbons, transforming non-aromatic hydrocarbons contained therein to chemically different hydrocarbons including olefins and producing a hydrocarbon mixture a fraction of which boils mainly within the range of 300-470 F. and contains a higher percentage, between 40 and 65 per cent, than the first-named fraction, of aromatic hydrocarbons boiling mainly above 300 F., then fractionating the last-named mixture to separate the lastnamed fraction, then by catalytically reacting the last-named fraction in the presence of a cracking type catalyst, without substantial admixture with other hydrocarbons and separately from and independent of the first-named catalytic cracking step, transforming higher boiling aromatics to lower boiling aromatics and greatly reducing the olefin content, and then separating from the mixture resulting from the lastnamed catalytic reaction a fraction containing a higher percentage, between 65 and 85 per cent, of aromatics than the second-named fraction a high proportion of which aromatics boil below 300 F.

21. Process according to claim 20 comprising also producing in. the first-named catalytic operation a gasoline fraction boiling mainly below 300 F., then by catalytically reacting this gasoline fraction in the presence of a cracking type catalyst and in an independent catalytic operaromatics boiling below 300 F., and separating from the resulting reaction mixture a fraction boiling mainly below 360 F. of which aromatics comprise a major part.

22. The process of producing a blending stock for gasoline nearly free of olefins and which contains a major proportion of aromatic hydrocarbons and a minor proportion of parafiins and naphthenes) from a starting material boiling mainly within the range of 300-470 F. and containing between 25 and 60 per cent relatively high boiling aromatic hydrocarbons boiling mainly above 300 F., which comprises transforming, by thermally cracking said starting material without substantial admixture with other hydrocarbons,

non-aromatic hydrocarbons contained therein to chemically different hydrocarbons including olefins and producing a hydrocarbon mixture a fraction of which boil mainly within the range of 300-470 F. and contains a higher percentage,

between 40 and 65 per cent, than the starting material, of aromatic hydrocarbons boiling mainly above 300 F.,then fractionating this mixture to separate said fraction, then by catalytically reacting said fraction in the presence of a cracking type catalyst without substantial admixture with other hydrocarbons, transforming higher boiling aromatics to lower boiling aromatics and greatly reducing the olefin content, and then separating from the mixture resulting from said catalytic reaction a fraction containing a higher percentage, between 65 and per cent, of aromatics than the first-named fraction a high proportion of which aromatics boil below 300 F.

- WILLIAM HERMAN BARCUS.

. REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,248,357 Kanhofer July 8, 1941 2,270,071 McGrew Jan. 13, 1942 2,297,775 Kanhofer Oct. 6, 1942 2,304,189 McGrew Dec. 8, 1942 2,342,080 Kalichevsky Feb. 15, 1944 2,345,995 Warrick Apr. 4, 1944 2,347,216 Peterkin Apr. 25, 1944 2,333,625 Angell Nov. 9, 1943 2,337,630 Thomas Dec. 28, 1943 2,345,129 Kuhn Mar. 28, 1944 2,352,025 Seguy June 20, 1944 2,360,622 Roetheli Oct. 17, 1944 2,367,527 Ridgway Jan. 16, 1945 1,441,341 Govers Jan. 9, 1923 2,370,533 Gershinowitz Feb. 27, 1945

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