US3037930A - Two-stage conversion process for the production of aromatic product fractions - Google Patents

Description

June 5, 1962 H. F. MASON 3,037,930

TWO-STAGE CONVERSION PROCESS FOR THE PRODUCTION OF AROMATIC PRODUCT FRACTIONS Filed May 13, 1959 22 1.2 f MAKE-UP H2 23 Hz 2o 25 I6 a: I'- FIRST o 3 FEED V CONVERSION 1k 0 ZONE 9 g SEPARATOR 3 350F.+ f r f 27 H2 W 26\ /a 30 .21 SECOND CONVERSION ZONE 2e SEPARATOR MAKE-UP H2 INVENTOR United States Patent ce 3,037,930 TWO-STAGE CQNVERSION PROCESS FOR TIE PRODUCTION OF AROMATIC PRODUCT FRACTIONS Harold F. Mason, Berkeley, Calif., assignor to California Research Corporation, San Francisco, Calif., a corporation of Delaware Filed May 13, 1959, Ser. No. 812,883 9 Claims. (Cl. 20859) This invention relates to a process for the catalytic conversion of hydrocarbon feed stocks and, more particularly, relates to an improved process for converting such feed stocks to product fractions boiling below the feed stocks employed.

A process has recently been developed for the conversion of aromatic hydrocarbon-containing distillates having an initial boiling point of about 350 F. to high octane gasoline fractions boiling below said feed stocks. The process comprises passing such a feed stock, along with hydrogen, to a conversion zone for contact With a catalyst comprising a hydrogenating component dispersed on an active cracking support at a pressure of at least 400 p.s.i.g. and at temperatures of from about 350 F. to about 800 F. Although the process has utility with a wide variety of feed stocks, it has been found to be particularly useful in the processing of hydrocarbon feed stocks having a relatively high aromatic hydrocarbon content to produce high octane gasoline fractions boiling below about 300 F. When operating in this manner, the procedure involves separating the conversion zone efiluent into one or more normally gaseous fractions, a product gaseoline fraction boiling below about 300 F. and a bottoms fraction boiling above said gasoline fraction which is normally recycled to the conversion zone as a component of the feed.

It has now been found that the above noted process, directed to the production of high octane gasoline frac tions boiling below about 300 F., can be materially improved by the process of the present invention, it resulting in the production of a gasoline fraction having a higher octane number than heretofore considered possible.

According to the present process, an aromatic hydrocarbon-containing feed stock having an initial boiling point of about 350 F. and at least 2,000 s.c.f. of hydrogen per barrel of said feed stock, are contacted in a first conversion zone with a catalyst comprising a hydrogenating component dispersed on an active acid cracking catalyst support, said catalyst having a severity factor (as that term is hereinafter defined) in the range of about 0.1 to 2.0. The contacting step is conducted at pressures of at least 400 p.s.i.g. and at temperatures in the range of from about 350 to about 800 F. The operating conditions maintained in the first conversion zone are such that the per-pass conversion of the feed stock to hydrocarbons boiling below about 350 F. is in the range of from about 40 to 80 volume percent. The efiiuent from the first conversion zone is separated to recover at least one normally gaseous fraction, at least one aromatic hydrocarbon-containing gasoline fraction boiling below about 300 F., an intermediate fraction boiling in the range of from about 300 to 350 F., and a bottoms fraction boiling above said intermediate fraction. Said bottoms may be recycled, at least in part, to the first conversion zone. At least a portion of the intermediate fraction and at least 2,000 s.c.f. of hydrogen per barrel of the intermediate fraction are contacted in a second conversion zone with a catalyst of the same general type "as employed in the first conversion zone under such conditions of pressure and temperature within the defined operating ranges of the first conversion zone that the per-pass conversion of the intermediate fraction to hydrocarbons boiling below 3,037,030 Patented June 5, 1962 about 300 F. in the second conversion zone is in the range of from about 10 to 50 volume percent. The efilnent from the second conversion zone is then separated to recover at least one normally gaseous fraction, at least one aromatic hydrocarbon-containing gasoline fraction boiling below about 300 F., and a bottoms fraction. The 300350 F. portion of the bottoms fraction may be recycled to the second reaction zone and the 350 F.+ portion of the bottoms may be returned to the first reaction zone.

The feed stock employed as fresh feed to the first conversion zone in accordance with the subject invention may be any conventional hydrocarbon distillate fraction having a basic nitrogen content of less than 25 ppm. and having an initial boiling point of about 35 0 F., preferably boiling in the range of from about 350 to 650 F., and which also preferably contains at least 5 0 percent by volume of aromatic hydrocarbons. Such feed stocks may be of petroleum origin or they may be obtained from shale, gilsonite, coal tar or other natural sources. In this connection, the word aromatic is employed in the conventional sense to include all those hydrocarbons in corporating an aromatic nucleus which may be either unsubstituted or substituted with one or more various aliphatic or other groups. While referred to as hydrocarbons, they may also contain other atoms such as nitrogen, oxygen, sulfur and the various metals commonly found in petroleum and other distillates of natural origin.

A preferred feed stock to the first conversion zone normally meeting the criteria of boiling range, aromatic content, and nitrogen level comprises the higher boiling components of the eflluent of a catalytic reforming unit. Such efiiuents (commonly termed reformates) are conventionally produced by passing straight run, thermally cracked or catalytically cracked naphthas, along with hydrogen, through a reforming unit provided with a platinum-onalumina or molybdenum-alumina catalyst under wellknown reforming conditions. Other preferred feed stocks include concentrates rich in aromatic hydrocarbons as may be obtained by the extraction of various hydrocarbon fractions with sulfur dioxide, furfural, or the like.

One of the important variables in the conduct of the subject process which has a material effect and to that extent, permits the production of the desired gasoline products, is the control of the nitrogen content of the feed stock. As indicated, an acceptable nitrogen level expressed as basic nitrogen is about 25 ppm, although appreciable further improvement is obtained as the nitrogen content is reduced to levels below 10 ppm. When the feed stock is not already sufliciently low in nitrogen, these levels may be reached by conventional denitrification procedures, such as by hydrofining the feed stock, which involves treating the same with hydrogen at elevated temperatures and pressures in the presence of a hydrogenating catalyst which has little cracking activity and little tendency to saturate aromatics under the conditions employed. The effiuent from such pretreating steps, if satisfying the specification boiling ranges and aromatic content, may be fed directly to the first conversion zone or it may be subjected to a preliminary separation or fractionation to recover a specification feed.

The catalyst employed in both conversion zones of the subject process is a multifunctional catalyst composition comprising a hydrogenating component dispersed on an active acidic cracking support wherein the catalytic components are critically balanced to result in a catalyst severity factor of from about 0.1 to 2.0. The cracking component or support may comprise any one or more of such acidic materials as silica-alumina, silica-magnesia, silicaalurnina-zirconia composites, as well as certain acid-treated clays and similar materials. A preferred cracking support for the catalyst composition employed in the present invention is comprised of a synthetically prepared composite of silica and alumina.

The hydrogenating component of the catalyst may be selected from any one or more of the various group VI and group VIII metals, as well as' the oxides and sulfides thereof, representative materials being the oxides and sulfides of molybdenum, tungsten, chromium, and the like, and/or such metals as nickel or cobalt and the various oxides and sulfides thereof. Also suitable are'certain group I (B) or group II (B) metals, such as copper or cadmium and their oxides and sulfides. If desired, more than one hydrogenating component may be present, e.g., composites of two or more of the oxides and/ or sulfides of molybdenum, cobalt, nickel, copper, chromium and zinc,

Depending on the activity thereof, the amount of the hydrogenating-dehydrogenating component may be varied within relatively wide limits of from about 0.1 to 35%, based on the weight of the entire'catalyst composition. Within these limits, the amount of said component present should be sufiicient to provide a reasonable catalyst onstream period at required conversion levels, but insufiicient under the reaction conditions employed to eftect substantial saturation of any except highly substituted aromatic ring compounds and of any small amounts of polynuclear aromatic compounds which may be present.

The balance of catalytic components necessary to effect the desired selectivity in the multiphase reactions of the process is determined by reference to the severity factor (S,,) of the catalyst composition. This characteristic of the catalyst may be determined by subjecting the catalyst to a standardized test wherein the referencefeed stock is a trimethylbenzenasuch as pseudocumene, or an equilibrium mixture of trimethylbenzenes which may be obtained from a catalytically reformedfnaphthaQ When employing the latter trimethylbenzene concentrate, a narrow boiling fraction having a D86 distillation range from about 318 to 335 F. and a C aromatic content of at least 95 volume percent should be used. The test involves passing therreference feed stock through the test catalyst at a liquid hourlyspace velocity of 2.0 with 9,000 s".c.f. of hydrogen per barrel of feed while maintaining a catalyst temperature of 650 F. and a pressure of 1,200 p.s.i.g. This test operation is continued for a periodof time (usually about 2 to .5 hours) sufficient to stabilize,

the system, and thereafter for a time sufiicient to provide an adequate product sampler After" flashing to atmos" pheric pressure the liquid product is then fractionated to determine the volume percent of product boiling below i a 300 F., relative to feed. This is taken as the synthetic Aromatic contents of the reference feed and product. said synthetic product are determined, as by chromatographic analysis (FIAM method), and the severity fac-. tor,'S,, is calcuated from the expression: 7

where A =,volume percent aromatics in the feed, and

' ing 8,, values higher than the desired range can usually be brought into compliance by suitably adjusting the amount of the hydrogenating component present, reducingthe hydrogen partial pressure, or other: hydrogenation activity. 7 V g V Particularly good results from the standpoint ,of good selectivity and the ability to withstand repeated regener measures to reduce tion with relatively minor decreas in activity are obtained with catalysts composed of from 1 to 30% nlckel sulfide or cobalt sulfide deposited on the aforementioned synthetically prepared silica-alumina composites.

invention.

(7 .Fresh feed, as hereinbefore defined, enters the system either as a liquid, vapor or mixed liquid-vapor phase by line it) in which the feed is admixed with a recycle stream cent.

11 (described below) and hydrogen entering line 10 by lines 12, 13 and 14. The amount of hydrogen entering line 10 by line 12 is at least 2,000 standard cubic feet per barrel of total feed (including both fresh feed, as well as recycle stream 11). Normally, from about 1,000 to 2,000 s.c.f. of hydrogen are consumed in the conversion reaction per barrel of total'feed converted to synthetic product, -i.e., that boiling below the initial boiling point of the particular feed. In the present process, hydrogen streamlZ is derived from a hydrogen recycle stream 13 and a make-up hydrogen source entering the system by line 14.

The total feed and hydrogen pass from line 12 into the first conversion zone 15 which is operated at elevated pressures and temperatures. The pressure employed in converson zone 15 is in excess of about 400 p.s.i.g. and may range upwardly to as high as 5,000 p.s.i.g., with a preferred pressure range being from about 600 to 2,500 p.s.1.g.

Conversion zone 15 is maintained at reaction temperatures ranging from about 350 to about 800 F. In preferred practice, the temperature at which the conversion is initiated in a given on-stream period should be as low as possible (within the noted range and commensurate with the maintenance of the desired per-pass conversion levelsin each zone, as discussed below) since the lower the starting temperature the longer will be the duration of the on-stream period. In addition, liquid yields will be higher, and gas yields lower at the lower temperatures.

In conversion zone 15 the per-pass conversion to products boiling below the initial point of the total feed is kept within the range of from about 40 to 80 volume per- This per-pass conversion level can be maintained by correlations of, in particular, space velocities of the feed through the conversion zone and/or temperature.

Preferably, a relatively constant conversion within the 1 defined per-pass conversion level is observed. This can be accomplished by periodically increasing the catalyst temperature (within the aforenoted range) to compensate for any catalyst fouling. The natural decline in conversion level, after fairly long on-stream periods, can

, also be offset to some extent by lowering the space velocity of the feed, although this procedure is generally not as satisfactory as accomplishing the same result by temperature adjustment. Still other methods of maintaining the desired conversionlevel will suggest themselves to those skilled in the art such as by maintaining the reaction at a constant temperature and allowing the per-pass conversion to decline within the specified ranges.

The total effluent from the first conversion zone 15 is passed by line 16 into high pressure separator 17 wherein a hydrogen-rich overhead is fractionated oil? and returned as the hereinbefore noted recycle by line 13. Of course, this hydrogen recycle stream may be purified, if desired, by any suitable means. The hydrogenlean remainder of the zone 15 efiluent, preferably reduced 7 'to essentially atmospheric pressure and augmented by a recycle stream 18 (discussed below), is passed by line 19 into fractional distillation'column '(or separation zone) 20 in which separation of the feed efiluent into various fractions is accomplished. ln this particular process deg sign, a normally gaseous product, containing, for example, C hydrocarbons and lighter, is removed overhead by line '21 and passed to storage. (Obviously, the composition of this overhead fraction can be regulated to remove, for example, C s and lighter or C s and lighter.) The desired gasoline product cut boiling below about 300 F. is removed from column 20 by line 22 from which it is passed into reflux drum 23. A portion of this gasoline product is passed as reflux by line 24 from drum 23 and the remainder is passed to storage by line 25.

At least two additional fractions are separated in column 19; one, an intermediate fraction boiling from about 300 to 350 F., and the other the bottoms fraction. The latter is passed by line 11 to line to form part of the initial feed as hereinbefore described. The intermediate fraction is passed by line 26, along with recycle and makeup hydrogen entering line 26 by lines 27 and 28, respectively, into the second conversion zone 29. The amount of hydrogen entering conversion zone 29 by lines 27 and 28 will be within the same range as that described with respect to the hydrogen employed in the first conversion zone 15, namely, at least 2,000 s.c.f. per barrel of feed. The hydrogen in line 27 comprises a recycle stream (described below) and that in line 28 is derived from a source outside of the present process scheme.

The catalyst and the conditions employed in the second conversion zone 29 fall Within the hereinbefore defined catalyst compositions and conditions employed in the first conversion zone 15. The operating conditions and catalyst composition within zone 29 are adjusted such that the per-pass conversion of the feed to products boiling below 300 F. is from about 10 to 50 volume percent. The desired per-pass conversion level can be maintained in the same manner as that described above with respect to the first conversion zone 15. The total effluent from second conversion zone 29 is passed by line 30 intohigh pressure separator 31 wherein a hydrogen-rich recycle stream is flashed off and passed by line 27 into line 26. The remainder of the second conversion zone effluent is preferably reduced to about atmospheric pressure and passed by line 18 to line v1'9 from which it enters fractional distillation column 20 and is separated in accordance with the description above.

As noted hereinbefore, the above described flow scheme is a preferred method of conducting the subject process. However, it is obvious that many modifications can be made in the system without departing from the scope of the invention. Thus, instead of employing the common fractional distillation column 20, a number of columns or separators could be used to perform essentially the same function. In such a system, low pressure gas-liquid separators could be employed in line 19 and/or line 18 to separately remove, for example, a C to C normally gaseous fraction, or each eflluent from conversion zones and 29 could be separately fractionated. In the latter case, advantage could be taken of the fact that the portion of the efiluent from the second conversion zone 29 boiling above about 350 F. is particularly rich in C aromatics, such as durene, and these could be separated from the efiluent for chemical and other uses.

A further modification of the process involves adapting the separation section to recover xylenes. It has been found that the subject multistage conversion process is an excellent producer of xylenes which can be recovered, for example, by a further distillation of the C to 300 F. product recovered from the described process by line 25. Of course, the other various separation techniques to recover these xylene products from the conversion zone efliuents are apparent to one skilled in the art.

A still further modification of the process could employ once through operation in either or both reaction zones 15 and 29. Once through operation in zone 29 would require separate distillation of products from zones 15 and 29.

The reactions in each of the conversion zones in the present invention can be conducted by employing fixed or moving catalyst beds, fluid catalysts or slurry catalyst systems with fixed bed operations preferred. It is often possible to extend on-stream times in the conversion zones over such long periods that it becomes uneconomical to provide catalyst regeneration facilities. However, catalyst regeneration can be done, either in situ or in separate regeneration zones by conventional regeneration techniques.

Extensive experimental data covering variations in feed composition, catalyst and operating variables have been utilized in the development of a plant process design incorporating the inventive features of the subject two-stage process as well as single-stage operations where-,

in all products from the single conversion zone boiling above about 300 F. are recycled thereto. In the following table, case 1 summarizes the results that can be expected when the process described above is operated according to conditions falling within the scope of the in vention, namely, a 60 percent per-pass conversion level in the first conversion zone and a 35 percent per-pass conversion in the second conversion zone. For comparative purposes only cases 2, 3 and 4 show the results that can be expected when employing a single conversion zone at perpass conversions below 300 F. of 33, 41.5 and 60 percent, respectively. In all cases, results were predicated upon the use of the same catalyst, namely, 2.5 weight percent (of the entire catalyst) nickel as the sulfide on an active silica-alumina cracking catalyst support and upon the same fresh feed, namely, a 350 to 475 F. reformate containing 93+ percent aromatic hydrocarbons having a nitrogen content less than 25 p.p.m.

Table 1 Case No.

First Conversion Zone:

Temp, 730 730 730 730 Pressure, p.s.i.g 1,200 1,200 1, 200 1, 200 Hydrogen, s.c.f./bbl. feed 6, 400 6, 4.00 6, 400 6, 400 Per-pass conversion below 300 F., Percent 33 41. 5 6O Per-pass conversion belo 350 F., Percent 60 Recycle, F 350+ 300+ 300+ 300+ Second Conversion Zone:

Feed, boiling range, F 300-350 Temperature, F 730 Pressure, p s1 9 1, 200 Hydrogen, s.c.f./bbl. feed 6, 500 Per-pass conversion below 300 F., percenL 35 O to 300 F. Product:

F-l Clear octane No 101 98 92' Aromatics content, weight,

percent 70 66 68 47 From the table it can be seen that the two-stage process of the present invention (case 1) is capable of producing a higher octane C to 300 F. gasoline fraction than any of the single-stage operations with comparable yields of this gasoline fraction.

The references to boiling points or ranges as employed in the specification and claims are those measured in accordance with either of the ASTM distillation procedures D-86 or D-158, depending upon the reference boiling range. It is furthermore to be understood that, in respect to the designations of boiling ranges and feed and product distillation cut points, a 10 percent by volume tolerance is to be permitted in order to more closely approximate the practical limitations of industrial distillation equipment and practices.

I claim:

1. In a process for producing aromatic hydrocarboncontaining product fractions boiling below about 300 F. wherein an aromatic hydrocarbon-containing feed, containing less than 25 ppm. basic nitrogen, at least 50 percent by volume of aromatic hydrocarbons and having an initial boiling point of about 350 F., and at least 2000 s.c.f. of hydrogen per barrel of said feed are contacted in a conversion zone with a catalyst comprising a hydrm genating component dispersed on an active acid cracking catalyst support, said catalyst having a severity factor in the range of about 0.1 to 2.0, and wherein the contacting step is conducted at pressures of at least 400 p.s.i.g. and at temperatures in. the range of from about 350 to 800 F., the improved method of operation which comprises adjusting the reaction conditions in said conversion zone such that the per-pass conversion of said feed to hydrocarbons boiling below about 350 Fr is in the range of from about 40 to 80 volume percent, separating the efliuent from said conversion zone to recover at least an arc:

matic hydrocarbon-containing product fraction boiling below about 300 R, an intermediate fraction boiling in the range of from about 300 to 350 F. and a'bottoms fraction boiling above said intermediate fraction, contacting at least a portion of said intermediate fraction and at least 2000 set of hydrogen per barrel of said intermediate fraction in a second conversion zone with a catalyst of the same type as employed in the first con-' version zone under such conditions of pressure and temperature within the defined operating ranges of the first conversion zone that the per-pass conversion of said intermediate fraction to hydrocarbons boiling below about 3. The process of claim 1 wherein the efiiuent from the second conversion zone is separated to produce said product fraction and a second intermediate fraction boiling from about 300 to 350 F. and returning said second intermediate fraction to said second conversion zone.

the second conversion zone is separated to produce said product fraction and a residual fraction andrpassing said residual fraction into said first conversion zone.

5. The process of claim 1 wherein the efliuents from fraction boiling from about 300 to 350 F. and a botaromatic hydrocarbon-containing gasoline boiling below about 300F. which comprises maintaining two converjsion zones in each of which hereinafter defined hydro-- carbon fractions are contacted with hydrogen in the presence of a catalyst comprising a hydrogenating component disposed on an active acid cracking catalyst support and having a severity factor in the range of about 0.1 to 2.0,

said conversion zones each being operated at pressures of at least about 400 p.s.i.g. and at temperatures in the range of from about 350 to 800 F., contacting a feed hydrocarbon fraction having an'initial boiling point of about 350 F.' composed predominantly of aromatic hydrocarbons and' having a basic nitrogen content of less than 25 ppm. and at least 2000 s.c.f. of hydrogen per barrel of feedrwith said catalyst in the first of said conversion zones under such conditions that the per-pass conversion of said feed to hydrocarbons boiling below aboutv350 F. is in the range of from about 40 to 80 volume percent, separating the efliuent from the first conversion zone to recover at least a highly aromatic hydrocarbon-containing gasoline boiling below about 300 R, an intermediate toms fraction boiling above about 350 F., contacting said intermediate fraction and at least 2000 s.c.f. of hy- V drogen per barrel of said intermediate fraction with said catalyst in the second of said conversion zones under such conditions that the per-pass conversion of said intermediate fraction to hydrocarbons boiling below about 300 F. is in the range of from about 10m volume percent, and separating the effluent from the second conversion zonev to recover additional quantities of a highly about 300 F.

' 3'5 4. The process of claim 1 wherein the eifiuent from both conversion zones are separated in a common fractional distillation zone.

v 6. The process of claim 1 wherein aXylene-containing fraction is recovered from at least one of the product fractions boiling below about 300 F.

7. A process for producing maximum yields of highly aromatic hydrocarbon-containing gasoline boiling below 8. The process of claim 7 wherein at least a portion of said bottoms fraction is passed into said first conversion zone.

9. The process of claim 7 wherein the eflduents from said conversion zones are separated in a common fractional distillation section.

7 References Cited inthe file of this patent UNITED STATES PATENTS 2,464,539 Voorhies et al. Mar. 15, 1949 2 ,885,346 'Kearby er al. May 5, 1959 2,945,801 Ciapetta et al. July 19, 1960 FOREIGN PATENTS 596,434 Great Britain Jan. 5, 1948

Claims (1)

1. IN A PROCESS FOR PRODUCING AROMATIC HYDROCARBONCONTAINING PRODUCT FRACTIONS BOILING BELOW ABOUT 300*F. WHEREIN AN AROMATIC HYDROCARBON-CONTAINING FEED, CONTAINING LESS THAN 25 P.P.M. BASIC NITROGEN, AT LEAST 50 PERCENT BY VOLUME OF AROMATIC HYDROCARBONS AND HAVING AN INITIAL BOILING POINT OF ABOUT 350*F., AND AT LEAST 2000 S.C.F. OF HYDROGEN PER BARREL OF SAID FEED ARE CONTRACTED IN A CONVERSION ZONE WITH A CATALYST COMPRISING A HYDROGENATING COMPONENT DISPERSED ON AN ACTIVE ACID CRACKING CATALYST SUPPORT, SAID CATALYST HAVING A SEVERITY FACTOR IN THE RANGE OF ABOUT 0.1 TO 2.0, AND WHEREIN THE CONTACTING STEP IS CONDUCTED AT PRESSURES OF AT LEAST 400 P.S.I.G. AND AT TEMPERATURES IN THE RANGE OF FROM ANOUT 350* TO 800* F., THE IMPROVED METHOD OF OPERATION WHICH COMPRISES ADJUSTING THE REACTION CONDITIONS IN SAID CONVERSION ZONE SUCH THAT THE PER-PASS CONVERSION ZONE CARBONS BOILING BELOW ABOUT 350*F. IS IN THE RANGE OF FROM ABOUT 40 TO 80 VOLUME PERCENT, SEPARATING THE EFFUENT FROM SAID CONVERSION ZONE TO RECOVER AT LEAST AN AROMATIC HYDROCARBON-CONTAINING PRODUCT FRACTION BOILING BELOW ABOUT 300*F., AN INTERMEDIATE FRACTION BOILING IN THE RANGE OF FROM ABOUT 300* TO 350*F. AND A BOTTOMS FRACTION BOILING ABOVE SAID INTERMEDIATE FRACTION, CONTACTING AT LEAST A PORTION OF SAID INTERMEDIATE FRACTION AND AT LEAST 2000 S.C.F. OF HYDROGEN PER BARREL OF SAID INTERMEDIATE FRACTION IN A SECOND CONVERSION ZONE WITH A CATALYST OF THE SAME TYPE AS EMPLOYED IN THE FIRST CONVERSION ZONE UNDER SUCH CONDITIONS OF PRESSURE AND TEMPERATURE WITHIN THE DEFINED OPERATING RANGES OF THE FIRST CONVERSION ZONE THAT THE PER-PASS CONVERSION OF SAID INTERMEDIATE FRACTION TO HYHDROCARBONS BOILING BELOW ABOUT 300*F. IN SAID SECOND CONVERSION ZONE TO RECOVER OF FROM ABOUT 10 TO 50 VOLUME PERCENT, AND SEPARATING THE EFFUENT FROM SAID SECOND CONVERSION ZONE TO RECOVER THE AROMATIC HYDROCARBON-CONTAINING PRODUCT FRACTION BOILING BELOW ABOUT 300*F. PRODUCED IN SAID SECOND CONVERSION ZONE.

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