US3479279A

US3479279A - Gasoline producing process

Info

Publication number: US3479279A
Application number: US574214A
Authority: US
Inventors: Jack B Pohlenz
Original assignee: Universal Oil Products Co
Current assignee: Universal Oil Products Co
Priority date: 1966-08-22
Filing date: 1966-08-22
Publication date: 1969-11-18
Anticipated expiration: 1986-11-18
Also published as: YU164967A; SE341435B; NL6711527A; FI48609B; GR34311B; YU33885B; AT285006B; ES344256A1; OA02489A; CH505885A; GB1188692A; BR6792376D0; IL28518A; DE1645822B1; DK128284B; FI48609C; NO120152B; BE710004A

Description

Nov. 18, 1969 J. B. PoHLENz GASOLINE PRODUCING PROCESS Filed Aug. 22, 196

United States Patent O 3,479,279 GASOLINE PRODUCHNG PRGCESS Jack B. Pohlenz, Arlington Heights, lil., assigner to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware Filed Aug. 22, 1966, Ser. No. 574,214 Int. Cl. ClOg 37/00, 23/02 U.S. Cl. 208--56 6 Claims ABSTRACT F THE DISCLOSURE This invention relates to the production of high octane gasoline. More specifically, this invention relates to the production of gasoline from heavy hydrocarbonaceous feeds by a route which results in higher octane numbers and higher yields. Still more specifically, this invention relates to the upgrading of a normally refractory byproduct stream from a catalytic cracker such that it may then be converted to gasoline of higher quality than directly produced from the catalytic cracker. Furthermore, this invention relates to a l-factor analysis of this upgrading step to optimize the yield and actane improvement attained when the upgraded by-product stream is converted to gasoline,

In one of its embodiments, this invention relates to a process for producing high octane gasoline which comprises: (a) hydrotreating an oil derived from a catalytic cracking zone, said oil having an average boiling point above gasoline and below heavy cycle oil and a fraction as defined in step (e) hereinbelow in the presence of hydrogen and a sulfur resistant hydrotreating catalyst in a hydrotreating reaction zone maintained at hydrotreating conditions; (b) recovering a hydrotreated normally liquid product; (c) catalytically cracking at least a portion of the hydrotreated normally liquid product in the presence of a cracking catalyst at catalytic cracking conditions; (d) recovering a high octane gasoline boiling range material produced in step (c); and (e) recovering a fraction boiling above said material produced in step (c) and returning the fraction to hydrotreating step (a).

In another of its embodiments, this invention relates to a process for the production of a first high octane gasoline and a second high octane gasoline, the F-l clear octane number of the second gasoline being at least three numbers higher than the first gasoline which comprises: (a) catalytically cracking a gas oil fresh feed and a heavy cycle oil as defined in step (c) hereinbelow in a first catalytic cracking zone maintained at catalytic cracking conditions and containing a cracking catalyst and withdrawing a product from said zone; (b) recovering the first high octane gasoline from the product of step (a); (c) recovering a heavy cycle oil from the product of step (a) and returning said heavy cycle oil to the first catalytic cracking zone; (d) recovering an oil having an average boiling point above the average boiling point of the first gasoline and below the average boiling point of the heavy cycle oil, said oil being rich in aromatics, the major single type of aromatic being J-12; (e) hydrotreating the oil of step (d) and a material as defined in step (h) hereinbelow by contacting the oil with a sulfur resistant hydrotreating catalyst in the presence nce of hydrogen at hydrotreating conditions to retain a major portion of the aromatics in said oil and said material but to produce a hydrotreated product having J-8 as the major single type of aromatic; (f) catalytically cracking at least a portion of the hydrotreated product of step (e) in a second catalytic cracking zone maintained at catalytic cracking conditions and containing a cracking catalyst; (g) recover the second high octane gasoline from step (f) having J-6 as the major single type of aromatic; (h) recovering a material having an average boiling point above the average boiling point of the second gasoline and having 1 12 as the major single type of aromatic; and (i) returning the material of step (h) to step (e).

In still another embodiment, this invention relates to a process for the production of high octane gasoline which comprises: (a) catalytically cracking a gas oil fresh feed, a heavy cycle oil as defined in step (c) hereinbelow and a material as defined in step (e) hereinbelow in a catalytic cracking zone maintained at catalytic cracking conditions and containing a cracking catalyst and withdrawing a product from said zone; (b) recovering a high octane gasoline from the product of step (a); (c) recovering a heavy cycle oil from the product of step (a) and returning said heavy cycle oil to step (a); (d) recovering an oil having an average boiling point above the average boiling point of the gasoline of step (b) and below the average boiling point of the heavy cycle oil of step (c), said oil being rich in aromatics, the major single type of aromatic being I-12; (e) hydrotreating the oil of step (d) by contacting the oil with a hydrotreating catalyst in the presence of hydrogen at hydrotreating conditions in a reaction zone to retain a major portion of the aromatics but convert the types of aromatics such that the major type of aromatic is J-8 and withdrawing a product material from the reaction zone; and (f) returning at least a portion of the product material to step (a).

It has been known for `many years that heavy charge stocks such as gas oil, vacuum gas oil, coker gas oils, etc., may be cracked in the presence of a cracking catalyst to produce light hydrocarbons (Cf which are rich in olens) and high octane gasoline (C5+ to about a 430 F. end point lwhich is recovered as the primary product). In addition, most catalytic crackers are operated at conditions such that a heavy product oil is produced from the reaction zone. The reaction product is introduced into a fractionator and separated therein. Typically the fractionator has an upper side cut well and a lower side cut well and is operated to remove the gasoline and light hydrocarbons overhead, a heavy cycle oil from the lower side cut well (material produced from the lower well maintained at about 550 F.), a bottoms or slurry oil (material produced from the column bottoms maintained at about 700 F.) and a refractory light oil from the upper side cut well (commonly called light cycle oil, the material produced from the upper well maintained at about 440 F.). Generally, the heavy cycle oil is recycled to the catalytic cracking zone while the slurry oil is claried whereupon it may be cracked or recovered as a fuel oil. The refractory light oil generally is not recycled to the catalytic cracking zone since it is very refractory and not readily cracked further. lt has also been taught to hydrogenate this refractory oil to improve its cracking characteristics. For example, U.S. Patent 2,671,754 shows the separate desulfurization and hydrogenation of this refractory oil. Other articles has shown general improvement in cracking characteristics of cycle oils by hydrogenation as, for example, shown in The Chemistry of Petroleum Hydrocarbons, volume III, chapter 52, pages 333 to 334. However, the prior art has failed to recognize the ultimate improvement in high qualitygasoline. Furthermore, this invention teaches the proper manner of carrying out a specific hydrotreating operation to optimize the yield and quality of the ultimately produced gasoline using the J-factor analysis. An analytical technique has been developed which permits the characterization of various types of aromatics in a hydrocarbon mixture called a J -factor analysis. It is in essence 'a mass spectrometer analysis employing a low ionizing voltage technique. The ionizing chamber is maintained at a potential of about 7 volts and the vaporized hydrocarbon mixture is introduced therein. Compounds more saturated than aromatics such as paraftins have an ionization potential above volts and these saturated compounds will not be observed on the mass spectrum since they are not ionized. The mass spectrum reveals molecular ion peaks which correspond to the molecular weight of the aromatic compound which permits characterization of these aromatics by means of the general formula CnH2nJ where I is the J factor. The following table shows the relationship between the J factor and the type of aromatic.

J-factor number: Type of aromatic hydrocarbon 6 Alkyl benzenes and benzene 8 Indanes, tetralins 10 Indenes 12 Alkyl naphthlenes and naphthlene 14 Acenaphthenes, tetrahydroanthracene 16 Acenaphthalenes, dihydroanthracenes 18 Anthracenes, phenanthrenes Using this J-factor analysis in characterizing the hydrotreating step of this invention allows for the optimum treatment of said refractory oil to produce a high quality gasoline by catalytically cracking the hydrotreated oil. Furthermore, this invention allows for substantially complete conversion of this refractory oil into high quality gasoline. It is believed that as much as 100% of this refractory oil can be converted by the process of this invention and the gasoline produced therefrom will be of higher quality (higher octane number and lower olettin content) than normal catalytically cracked gasoline.

It is an object of this invention to render the refractory oil from a catalytic cracking zone readily susceptable to further cracking.

It is another object of this invention to treat and crack said refractory oil to produce a high quality gasoline.

It is another object of this invention to treat and crack said refractory oil to produce high yields of high quality gasoline at conversions of 40 to 80% per pass.

It is a further object of this invention to disclose a process for substantially completely converting the refractory oil from a catalytic cracker into lighter products including a high quality gasoline.

It is still further object of this invention to optimize the yield and octane number of the gasoline produced from a heavy hydrocarbonaceous charge stock by the process of this invention.

It is a more specific object of this invention to minimize hydrogen consumption in the hydrotreating step of this invention.

It is another specific object of this invention to hydrotreat refractory oils having 1 12 as the major single aromatic type to produce oils having 1 8 as the major single aromatic type.

These and other objects will become more apparent in the light of the following detailed description.

FIGURE 1 shows a schematic flow scheme for one preferable embodiment of the present invention employing separate catalytic cracking zones and separators.

FIGURE 2 shows a schematic flow scheme for a second preferable embodiment of the present invention employing a common catalytic cracking zone and separator.

As shown in FIGURE 1, as gas oil feed is introduced into a rst catalytic cracking zone Z through conduit 1.

Although this zone is shown as a box, it will be apparent to those skilled in the art of catalytic cracking that commonly used processing schemes are readily employed therein. For example, one common type of catalytic cracker is the so-called fluid catalytic cracker where hot regenerated catalyst is mixed with fresh feed and the mixture is transported to a reaction vessel containing a bed of dense fluid catalyst. The fresh feed reacts under the catalytic inuence of the catalyst to produce a wide variety of products including light hydrocarbons, gasoline, refractory oil, heavy cycle oil, slurry oil and coke. The coke generally is formed on the fluid catalyst particles. The catalyst is separated from the reactants by means such as settling, centriiical separation, etc., whereupon the reaction products are withdrawn from the reaction vessel. The catalyst containing coke is withdrawn from the reaction vessel through a stripper wherein it contacts steam to strip off a portion of the entrained oil. The steam and entrained oil are returned to the reaction vessel and the stripped catalyst is introduced into a regenerator. An oxygen containing gas stream is introduced into the regenerator and since the temperatures are sufficiently high, a portion of the coke is burned off the catalyst thereby regenerating the catalyst. The regenerated catalyst is withdrawn from the regenerator where it contacts additional hydrocarbon feed to repeat the process just described. It is, of course, to be understood that there are numerous variations in the basic catalytic cracking process and it is intended that all these variations are included in the process of my invention. There are a large number of catalysts suitable for use in the catalytic cracking step such as silica-alumina, silica magnesia, silica zirconia, acid activated clay, crystallin catalysts including faujasite dispersed in a silica-containing inorganic matrix, mordenite containing catalysts etc. The amorphous silica-alumina catalysts having concentrations of from about 10 to about 40l weight of alumina and to about 60 weights of silica are preferred catalysts.

Typical catalytic cracking operating conditions comprise reactor temperatures of from about 800 F. up to about 1050 F., regenerator temperatures of from about 1000 F. up to about 1300 F., pressures of from atmospheric up to about 50 p.s.i.g., oil to catalyst weight ratios of from about 1.0 to about 10.0 and combined feed ratios (ratios of fresh feed -1- heavy cycle oil/ fresh feed) of from about 1.1 to about 2.0. These variables, some of which are independent and some of which are dependent are adjusted to maintain conversions per pass to gasolines of from about 30% up to about 70%, and in some instances, up to about 80.0%.

The reaction products from catalytic cracking zone 2 are withdrawn through conduit 3 and introduced into separator 4. Commonly the separator is a fractionator wherein the products are separated on the basis of boiling points. Typically, a light hydrocarbon stream is withdrawn overhead (shown in conduit S) and sent to a gas concentration unit not shown, a gasoline fraction is recovered (shown in conduit 7), a refractory oil side cut is recovered (shown in conduit 9), and a heavy cycle oil side cut or bottom is recovered (shown in conduit 5). In some cases a heavy bottoms called slurry oil is withdrawn from the unit (shown in conduit 6) where it may be clarified to move catalyst particles and either recycled to zone 2 or used as fuel oil.

The refractory oil in conduit 9 is comingled with a material flowing in conduit 10 from a source described hereinafter and passed into hydrotreater 12 through conduit 11. Hydrogen is introduced into hydrotreater 12 through conduit 13 to supply the required hydrogen. This hydrotreating step may be carried out by any method known to those skilled in the art of hydrotreating. Preferably hydrotreating catalyst is loaded in to a xed bed within a reaction zone. The material in conduit 11 is mixed with fresh hydrogen (from conduit 13) and re cycle gas from a source described hereinafter, heated and passed once through the fixed bed of catalyst. An effluent is withdrawn from the reaction zone, which is cooled and introduced into a separator. The effluent is separated into a normally liquid hydrotreated product and a normally gaseous stream. The normally gaseous stream is withdrawn from the separator by means of a recycle compressor and returned to the inlet of the reaction zone. If desired, a portion of the gaseous stream may be vented to maintain hydrogen purity although this is not generally necessary. The normally liquid product stream may be fiashed or stripped to remove dissolved gases such as hydrogen and hydrogen sulfide, although if desired, this step may be omitted.

The hydrotreating catalyst is preferably sulfur resistant, that is it possesses hydrogenation activity in the presence of sulfur compounds. A preferably catalyst comprises a silica-alumina support having at least one metal or metal compound of Group VI of the Periodic Table and one metal or metal compound of Group VIII of the Periodic Table. Especially preferable are those catalysts having tungsten and/or molybdenum along with nickel and/or cobalt on silica-alumina supports. Other supports such as alumina, silica zirconia, silica magnesia, faujasite, mordenite, inorganic oxide matrix containing at least one crystalline aluminosilicate, etc. are also suitable. Other metals besides the ones described hereinabove are also suitable as for example noble metals such as platinum or palladium. These latter catalysts are generally satisfactory without the presence of a Group VI metal.

The hydrotreating conditions employed in hydrotreate'r 12 such as temperature, pressure, LHSV, hydrogen-tooil ratio, etc. are selected to convert the refractory oils to a product having as the major single type of aromatic hydrocarbon 1 8 as defined hereinbefore. It has been found that these refractory oils have 1 12 as the major single type of aromatic hydrocarbon. Therefore, the above hydrotreating process variables are controlled to maximize the J-12 to J-S conversion reaction. It is generally preferable to maintain pressure, LHSV and hydrogen-to-oil ratio constant and vary temperature to maximize the J-12 to I-8 conversion. The initial choice of all these variables depends to a large measure on the charge stock. Suitable pressure ranges are from about 400 p.s.i.g. up to about 2000 p.s.i.g. with 600 to 900 p.s.i.g. being preferable. Suitable LHSV is from about 0.5 up to about 20 with 3 to 10 being preferable. Suitable hydrogen-to-oil mole ratios are from about 2 to about 20 `with 5 to l5 being preferable. When these conditions are selected, the temperature is adjusted to maximize the I-12 to J-8 conversion. It is expected that temperatures within the range of from about 500 F. up to about 850 F. will be em ployed. The most straight forward way to attain the proper operating conditions is to select the independent variables, conduct a J-factor analysis of the streams flowing in conduits 11 and 15 and adjust temperature to attain the maximum conversion of J-12 to 1 8. If the hydrotreating conditions are too severe, the I-12 will either be converted to I-6 or the aromatics will be saturated. This has the undesirable effect of increasing hydrogen consumption and reducing the octane number of the gasoline when the hydrotreated oil is catalytically cracked. If the hydrotreating conditions are not severe enough, there will be little improvement in the refractory nature of this oil which will make it difiicult to convert to gasoline. When properly hydrotreated, this material is easily catalytically cracked yielding high quality gasoline at 'conversion of 100%. The hydrotreated normally liquid product is introduced into a second catalytic cracking zone 14 through conduit 15. Cracking zone 14 may be a part of cracking zone Z, may be integrated Iwith zone 2 or may be an entirely separate processing unit. For example a separate stream of regenerated cracking catalyst may be mixed with the hydrotreated oil and transported into the same reaction vessel as that used for cracking zone 2. Since a major portion of the reaction occurs in the transfer line between the reaction vessel and the point wherein the regenerated catalyst and hydrotreated oil are mixed, this arrangement permits zone 14 to operate as a part of zone 2 with common separation equipment and a common regenerator. Cracking zone 14 can be integrated with zone 2 by mixing regenerated catalyst with the hydrotreated oil and introducing this mixture into a separate reaction vessel. In this case zone 14 and Zone 2 have a common regenerator but separate reaction vessels and if desired, separate separation equipment. Of course, zone 14 can be entirely independent of Zone 2 with its own reactor, stripper, regenerator, catalyst, etc. The cracking conditions employed in zone 14 are similar to those employed in zone 2 although it may be preferable in some instances to vary the conditions due to differences in charge stocks between zone 2 and zone 14 in order to optimize each cracking step. The reaction products from zone 14 are withdrawn through conduit 17 where they are introduced into separator 16. Separator 16, usually a fractionator, is employed to separate the reaction products into a light hydrocarbon portion in conduit 18 (usually sent to a gas concentration unit not shown), a second high octane gasoline stream in conduit 19 and a material referred to herein-before in conduit 10. Several unexpected results are obtained as a result of the combined effects of

zones

12 and 14. The gasoline in conduit 19 is of higher quality than the gasoline of conduit 7. It is found that this second gasoline in conduit 19 is at least 3 clear octane numbers higher than the first gasoline (in conduit 8). Furthermore, the second gasoline is lower than the first gasoline by a substantial margin in olefin content which improves its lead susceptability and makes for a cleaner burning fuel. Finally, the absolute clear octane number is sufficiently high to eliminate the necessity of having to add lead to improve the octane number. It is expected that F-1 clear octane numbers of from about 95 to about 100 will be produced in this second gasoline. J-fa-ctor analysis of this second gasoline reveals that the major single type of aromatic present therein is .T-, a preferable motor fuel. Another unexpected result is shown by examination of the unconverted oil fiowing in conduit 10. A I-factor analysis indicates that the major single type of aromatic present in this unconverted oil is I-12. This means that zone 14 has converted the hydrotreated material boiling above gasoline in conduit 15 having J-S as the major single aromatic type into a gasoline having 1 6 as the major single aromatic type and a material boiling above gasoline having I-12 as the major single aromatic type. For this reason the unconverted material in conduit 10 is suitable for recycle to the hydrotreating step since it has a similar I-factor analysis as compared to the material in conduit 9. Therefore, all this unconverted material may be recycled back to zone 12 and zone 14 which allows recycle to extinction. This means that 100% of the material in conduit 9 will ultimately be converted at conversions of from about 40 to about 80% per pass which of course will maximize the yield of gasoline in conduit 19. If desired, a portion of the unconverted material in conduit 10 may be withdrawn through conduit 40 by opening valve 39, a portion of the material in conduit 11 may be withdrawn through conduit 36 by opening valve 35 or a portion of the material in conduit 15 may be withdrawn through conduit 38 by opening valve 37. `One or more of these alternate Withdrawals can be practiced if it is desired to recover a heavier fuel than gasoline.

It is now apparent that the present invention permits the conversions of gas oil feed stocks to gasoline and lighter in amounts of or higher. Indeed, conversions of up to are possible with the process of this invention provided the slurry oil is also cracked. In this sense, this overall process has the same advantages as hydrocracking to produce gasoline from gas oils, a feat which up till now has been impossible. Furthermore, the

light hydrocarbons in conduits 8 and 18- are rich in olefins which permits alkylation with parans to produce high octane isoparafns which can be added to the total gasoline yield. When this is practiced, the present process in combination with alkylation Will produce a most desirable high octane motor fuel having as its main cornponents alkyl benzene aromatics and isoparans. Still another advantage of the present process over hydrocracking is that the butane produced by the cracking zones will be less than that required for alkylation of the C3 and C4 oleins and the vapor pressure requirements of the gasoline, whereas one of the major problems of hydrocracking is excess production of butane which puts the producer using the present process in the enviable position of buying low cost butane and selling it for high cost gasoline. Furthermore, the catalytic cracking steps and hydrotreating steps are carried at relatively low pressures, thus minimizing capital investment and operating problems. It is estimated that the conversion of a typical gas o'il by t-he process of this invention accompanied by alkylation of the olens and buying sufficient butane to satisfy alkylation and vapor pressure requirements will result in gasoline yields as rnuch as 8 or 9% higher than that produced by hydrocracking and reforming at a constant octane number.

FIGURE 2 shown an alternate preferable embodiment of the present invention having a common cracking zone and a common separator. Fresh gas oil flowing in conduit 21, heavy cycle oil from a source described hereinafter in conduit 27 and hydrotreated oil from a source described hereinafter in conduit 32 are introduced into catalytic cracking zone 22 maintained at catalytic cracking conditions and containing a cracking catalyst. Cracking zone 22 may be any type of cracking process known to those skilled in t-he art of catalytic cracking as described with reference to zone 2 hereinbefore. The reaction products from zone 22 are withdrawn through conduit 23 and into separator 24. Separator 24, usually a factionator, separates the reaction products into a light hydrocarbon fraction which is sent to a gas concentration process not shown by means of conduit 26, a gasoline which is recovered @from conduit 2S, a refractory oil in conduit 29, a heavy cycle oil in conduit 27 and in some cases a slurry oil in conduit 28. The heavy cycle oil is returned through conduit 27 to cracking zone 22 as described hereinbefore. The slurry oil is clarified and may be recovered as a fuel oil or recycled to cracking zone 22. The refractory oil flowing in conduit 29 is introduced into hydrotreater 30 along with fresh hydrogen flowing in conduit 31. Hydrotreater 30 contains a sulfur resistant hydrotreating catalyst in a reaction zone maintained at hydrotreating conditions. Hydrotreater 30 is operated as described in the operation of hydrotreater 12 hereinbefore to convert the oil in conduit 29 having l-12 as the major type of aromatic into a hydrotreated oil in conduit 32, having l-8 as the major type of aromatic. The hydrotreated oil is returned in conduit 32 to cracking zone 22. It is preferable to heat and vaporize this hydrotreated oil in heater 43 before contacting said hydrotreated oil with regenerated cracking catalyst. It should be noted that the only gasoline stream produced in this embodiment is flowing in conduit which therefore is a blend of normal catalytic cracker gasoline and the higher quality gasoline derived from the hydrotreated oil. If a rener has a market for this higher quality gasoline, it would then be preferable to employ a separate catalytic cracking zone and separation facilities. Also, if desired, a light fuel oil can be withdrawn through lconduit 42 by opening valve 41.

It is difficult to characterize the split points between the light refractory oil and the gasoline and heavy cycle oil by commonly observed physical characteristics since this split point varies depending on charge stock, operating characteristics, desired yields, etc. In some cases, the end point of the light refractory oil will vary from about 55 0 F. or less to as much as 750 F. or more. The most preferable manner of characterizing the light refractory oil and the heavy cycle oil is the place from which each originate. As used herein heavy cycle oil is that material withdrawn from the lower side cut well in the catalytic cracking main column fractionator, said well being maintained at about 550 F. The gasoline from the catalytic cracker may be characterized by boiling point range or end point, the end point generally being within the range of from 350 F. up to. about 450 F. and typically about 430 F. The light refractory oil is therefore the material boiling between the gasoline and the heavy cycle oil. The light refractory oil is derived from an upper side cut well in the main column fractionator said well being maintained at about 440 F. These side cut well temperatures are for fractionator pressures of about 10 to 15 p.s.i.g. and if the pressure is outside this range, the well temperatures will of course also be shifted.

The following examples are presented to further illustrate the process of the present invention.

EXAMPLE I A conventional catalytic cracker employing a regenerator, a reaction vessel above the regenerator, a regenerated catalyst conduit from the regenerator, a riser into which the regenerated catalyst flows and into which the hydrocarbonaceous feed passes connected to the reaction vessel and a stripper from the reaction vessel to the regenerator is run on a gas oil charge stock. The reaction vessel is maintained at 945 F. resulting in a conversion of fresh feed and recycled heavy cycle oil of 55%. This results in a yield of coke of about 9l wt. percent, a catalytic cracking gasoline of about 34.5 volume percent and a C3 and C4 olen content of about 9.7 volume percent. The catalytic cracked gasoline has an F-l clear octane number of about 93 and contains about 30 volume percent aromatics and about 30 volume percent olens. The C3 and C4 olens are alkylated with isobutane in a separate alkylation zone to produce an alkylate gasoline in yields of about 17 volume percent (based on fresh feed to the catalytic cracker). Therefore, the total yield of gasoline is 51.5 volume percent (34.5-147.0) out of a conversion of 55% which means that the efficiency measured by percent of conversion which yields gasoline is 93.6 (51.5/55).

In addition, a light refractory oil is produced from the above described example containing about 57.6% aromatics. A I-factor analysis is run on this light refractory oil revealing the following breakdown: l-6-27.9%; J-8- 15.2%; L10-3.3%; ]-12-40.8%; F14-6.3%; J-16- 2.6%; and, I-18-3.9%. It is thought that the actual I6 number is lower and the actual J-12 number is higher than these numbers due to the interference in the analysis with sulfur containing molecules. This refractory oil is subjected to a separate catalytic cracking step and even though temperatures of 950 F. are employed, the conversion is only 38%. The yields show that 7.5 wt. percent coke is produced, 20.1 volume percent gasoline is produced and a C3 and C4 olen yield of about 5.0 is produced. Alkylation of these olefins with isobutane results in an alkylate yield of 8.8 volume percent. The total gasoline yield including alkylate is 28.9 volume percent with an efficiency measured by percent of conversion of 76.1. The catalytic cracking gasoline shows an olefin concentration of about 13 volume percent.

The same light refractory oil is subjected to controlled hydrotreating at a pressure of 800 p.s.ri.g., a LHSV of 2, a hydrogen circulation rate of 3000 s.c.f./bbl. and a temperature of 750 F., with a catalyst containing nickel and molybdenum. The hydrotreated oil contains about 55.8% aromatics and has the following l-factor analysis: J-6-14.4%; I-8-70.9%; L10-5.1%; L12-4.9%; J-14-3.4%; I-16-1.0% and L18-0.3%. Thus, it can be readily seen that by the hydrotreating step has converted an oil having l-12 as its major aromatic component into a hydrotreated oil having J-8 as its major aromatic component. The sulfur compounds are also substantially removed and therefore the I-factor analysis is substantially correct. 'Ihis hydrotreated oil is subjected to a separate catalytic cracking step at a temperature f 925 F. resulting in a conversion of about 55%. The yields from this operation show that 3.1 wt. percent coke is produced, 40.0 volume percent gasoline is produced and a C3 and C4 olefin yield of 7.2 volume percent is produced. Alkylation of the olens with isobutane results in an alkylate gasoline yield of about 12.7 volume percent. The total gasoline yield including alkylate is 52.7 volume percent with an eiciency measured by percent of conversion of 95.8. The catalytic cracking gasoline contains about 60 volume percent aromatics and only 3 volume percent olens and has an F-l clear octane number of 97. A J-factor analysis is run on the catalytic cracking gasoline and shows the following results: 1 6- 78.7%; I-8--13.0%; L10-1.1%; L12-7.1%; I-14- 0.1%; J-16-0.l% and no detectable J-18. Comparison of the gasoline produced by the catalytic cracking of the hydrotreated light refractory oil with comparison of the normal catalytic cracking gasoline is tabulated below.

All these comparisons clearly show the substantial improvement in product quality, product yield and improved process operation. Comparison of the results of the catalytic cracking of the unhydrotreated light refractory oil and the hydrotreated oil show that the latter gasoline is of `better quality (contains 10% less olefins) and results in an operation where it is possible to attain high gasoline yield and high efficiency.

The unconverted material from the catalytic cracking of the hydrotreated oil which contains about 60 volume percent aromatics is subjected to a J-factor analysis yielding the following analysis: I-6-6.4%; I-8-l9.9%; L10-2.7%; L12-58.4%; J14-6.8%; J-16-2.7%; and, J-18-3.7%. It should be noted that this material is very similar to the original light refractory oil which means that recycle of this material to the hydrotreated followed by catalytic cracking will readily convert this material into gasoline at about the same conversion level as that of fresh light refractory oil. It should also be noted that the catalytic cracking of the hydrotreated oil results in a gasoline rich in 1 6 and an unconverted material rich in I-12. In other words, the catalytic cracking step has made J-12 compounds as well as 1 6 compounds from J-S compounds a most unexpected result.

EXAMPLE II Equipment is arranged substantially as shown in FIG- URE 2 and the light hydrocarbons are sent to a gas concentration unit and finally into an alkylation unit. Cracking zone 22 is operated at about a conversion of 55% and a 5% slurry oil is withdrawn from the process. The alkylate gasoline is combined with the catalytic cracking gasoline to produce an overall 10` lb. RVP gasoline yield of above about 90 volume percent with the F-l clear octane number above about 95. The hydrotreater is maintained at conditions to maximize the conversion of the 1 12 in conduit 29 into J-8 in conduit 32. Heater 43 is used to vaporize the recycled hydrotreated oil before the oil is returned to zone 22. This process is operated stably over long periods of time With no loss in gasoline yield or quality.

It is preferable for the production of high quality gasoline by the process of this invention that the light refractory oil derived from a cata-lytic cracking zone contain at least 45 volume percent aromatics with the major single type of aromatic being J-12. The hydrotreating step is preferably carried out on said light refractory oil to produce a product having at least 40 volume percent aromatics with the major single type of aromatic being J-S. This will result in the production of a gasoline having at least about 45% aromatics and a F-1 clear octane number of about 95.

I claim as my invention:

1. A process for the production of high octane gasoline which comprises:

(a) cata-lytically cracking a gas oil fresh feed and a product material as defined in step (d) hereinbelow in a catalytic cracking zone maintained at catalytic cracking conditions and containing a cracking catalyst and withdrawing a product from said zone;

(b) recovering a high octane gasoline from the product of step (a);

(c) recovering an oil having an average boiling point above the average boiling point of the gasoline of step (b), said oil being rich in aromatics, the major single type of aromatic being I-12;

(d) hydrotreating the oil of step (c) by contacting the oil with a hydrotreating catalyst in the presence of hydrogen at hydrotreating conditions in a reaction zone to retain a major portion of the aromatics but convert the types of aromatics such that the major type of aromatic is J-8 and withdrawing a product material from the reaction zone; and

(e) returning at least a portion of said product material to step (a).

2. The process of claim 1 further characterized in that the hydrotreating catalyst comprises a silica-alumina support having at least one Group VI metal or metal compound and at least one Group VIII metal or metal compound deposited on the support.

3. The process of claim 2, further characterized in that the Group VI metal is selected from the group consisting of molybdenum and tungsten and the Group VIII metal is nickel.

4. A process for the production of high octane gasoline which comprises:

(a) catalytical-ly cracking a gas oil fresh feed, a heavy cycle oil as defined in step (c) hereinbelow and a material as defined in step (e) hereinbelow in a catalytic cracking zone maintained at catalytic cracking conditions and containing a cracking catalyst and withdrawing a product from said zone;

(b) recovering a high octane gasoline from the product of step (a);

(c) recovering a heavy cycle oil from the product of step (a) and returning said heavy cycle oil to Step (a);

(d) recovering an oil having an average boiling point above the average boiling point of the gasoline of step (b) and below the average boiling point of the heavy cycle oil of step (c), said oil being rich in aromatics, the major single type of aromatic being J-12;

(e) hydrotreating the oil of step (d) by contacting the oil with a hydrotreating catalyst in the presence of hydrogen at hydrotreating conditions in a reaction zone to retain a major portion of the aromatics but convert the types of aromatics such that the major type of armatic is 1 8 and withdrawing a product material from the reaction zone; and

(f) returning at least a portion of the product material to step (a).

5. The process of claim 4, further characterized in that the entire product material withdrawn from step (e) is returned to step (a).

6. A process for the production of high octane gasoline which comprises:

(a) catalytically Icracking a gas oil fresh feed, a heavy cycle oil and a material as dened in step (g) hereinbelow in at least one catalytic cracking zone maintained at catalytic cracking conditions and containing a cracking catalyst;

(b) recovering at least one light hydrocarbon stream product from step (a) and concentrating this product to produce a fraction therefrom substantially having from about 3 to about 4 carbon atoms per molecule;

(c) alkylating the concentrated fraction along With isobutane to produce an alkylate gasoline;

(d) separating at least one high octane gasoline stream from step (a);

(e) recovering a heavy cycle oil stream from step (a) and returning said heavy cycle oil to step (a);

(f) recovering from step (a) an oil having an average boiling point above the average boiling point of the gasoline of step (d) and below the average boiling point of the heavy cycle oil of step (e), said oil being rich in aromatics, the major single type of aromatic being J-12;

(g) hydrotreating the oil of step (f) by contacting the oi-l with a hydrotreating catalyst in the presence of hydrogen at hydrotreating conditions in a reaction Zone to retain a major portion of the aromatics but convert the types of aromatics such that the major single type of aromatic is J-8 and withdrawing a product material from the reaction zone;

(h) returning the material of step (g) to step (3);

and

(i) recovering the gasoline streams of steps (c) and steps (d).

References Cited UNITED STATES PATENTS 3,245,900 4/ 1966 Paterson 208-56 2,370,533 2/1945 Gershinowitz 196-49 2,431,243 11/ 1947 Greensfelder et al. 196-52 3,168,461 2/1965 Russell et al. 208--89 3,240,840 3/1966 Goble et al. 260-683.47

DELBERT E. GANTZ, Primary Examiner T. H. YOUNG, Assistant Examiner