IL28518A - Process for the production of gasoline - Google Patents

Description

TI1UJ1 |Π3 Tihni"! 'Π PATENT ATTORNEYS · , □ ' Q 1 Q 3 'DUD PATENTS AND DESIGNS ORDINANCE SPECIFICATION Process for the Production of Gasoline I/We UNIVERSAL OIL PRODUCTS COSSPAHY, a corporation duly organized under the laws of the State of ^elaware, U.S.A. , of 30 Algonquin Road, Pes Plaines, Illinois, U.S.A. do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement :- This invention relates to the production of high octane gasoline in high yields from heavy hydrocarboiaceous feeds. More specifically, this invention relates to the upgrading of refractory by-product streams from a catalytic : cracker to produce an intermediate stream that can be converted to gasoline of higher quality than that directly .produced from the catalytic cracker. Further, this invention relates to optimizing the yield and octane improvement attained when the upgraded by-product stream is converted to gasoline by use of J-factor analysis.

It has been known for many years that heavy charge stocks such as gas oil, vacuum gas oil and coker gas oils may be cracked in the presence of a cracking catalyst to produce light hydrocarbons (C^ and lighter gases which are rich in olefins) arid high octane gasoline (C^ and .higher up to o compounds boiling as high as about 221 C.) In addition, most catalytic crackers are operated at conditions such that a heavy product oil is produced from the reaction zone. The cracking reaction effluent is usually intoduced into a fractionator and separated therein. Typically the fractionator has an upper side cut outlet and a lower side cut outlet, and is operated to remove the gasoline and light hydrocarbons overhead, a heavy cycle oil from the lower side cut outlet at about 288°C, a bottom slurry oil product at about 371°C, and a refractory light oil from the upper side cut outlet (commonly called light cycle oil) at about 227°C. Generally, the heavy cycle oil is recycled to the catalytic cracking zone while the slurry oil is clarified whereupon it may be recycled and cracked, or recovered as a fuel oil. The refractory light oil generally is not recycled to the catalytic cracking zone since it cannot readily be cracked further. This light cycle oil, therefore, represents the principle yield-reducing by product. It has also been taught to hydrpgenate this refractory oil to improve its cracking characteristics (i.e. to render it less refractory). However, the prior art has failed to recognize the ultimate improvement of substantially total conversion to high quality gasoline. The present invention teaches a method of carrying out a specific hydrotreating operation whereby to optimize the .yield and quality of the ultimately produced gasoline by means of the J-factor analysis. An analytical technique has now been developed which permits identification and characterization of various types of aromaties in a hydrocarbon mixture and is called a J-factor analysis. It is in essence a mass spectrometer analysis employing a low ionizing voltage technique. The ionizing chamber of a standard mass spectrometer is maintained at a potential of about 7 volts and the vaporized hydrocarbon mixture is introduced therein. Compounds more saturated than aromaties such as paraffins have an ionization potential above 10 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, in turn, permits characterization of these aromaties by means of the general Molecular formula CnH2n_j where J 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 streams of the hydrotreatihg step of this invention allows for the optimum treatment of the refractory oil, rendering the same i best condition for prbducing a high quality gasoline by catalytic ally cracking the rest. Furthermore, this invention make's possible 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 olefin content) than normal catalytically cracked gasoline.

It is an object of this invention to render the re- i fractory oil from a catalytic cracking zone readily susceptable to further cracking to produce a high quality gasoline.

It is another object of this invention to treat and crack refractory oil to produce high yields of high quality gasoline at conversions of IO to 80% per pass, and by successive passes, to substantially completely convert the refractory oil into lighter products including a high quality gasoline.

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

Accordingly, the present invention provides a process for the production of high octane gasoline from a refractory oil feed having an average boiling point above gasoline boiling range "and below .heavy cycle oil boiling range, and contain.-? ing at least \\$ volume per cent aromatics, of which the major single aromatic type is J-12, characterized by: a) hydrotreating said refractory oil in the presence of a sulfur-resistant hydrotreating catalyst at a pressure within the range of from about 27.2 to about 136 atmospheres gauge, and a temperature within the range of from about 260° to about Li¾0C., in a hydrotreating zone, b) recovering resulting normally liquid, hydrotreated product containing at least hO volume per cent aromatics, of which the majjor single aromatics type "is J-8, c) cracking at least a portion of said hydrotreated product in the presence of a cracking catalyst, d) recovering from the resulting cracked product a gasoline having an F-1 clear octane .number of at least 95, and containing at least volume per cent aromatics of which the major single aromatic type is J-6, e) and separately recovering from the cracked product a second refractory oil having an average boiling point above gasoline boiling range, and containing J-12 as the major single aromatic type.

In one 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-1 clear octane number of the second gasoline being at least three numbers higher than the first gasoline, by first catalytically cracking a gas oil fresh feed, and a heavy cycle oil, defined hereiribelow, in a first catalytic cracking zone containing ■'a cracking catalyst, and withdrawing a cracked product from said zone.

The first high octane gasoline and a heavy cycle oil are recovered from the cracked product and said heavy cycle oil is returned to the first catalytic cracking zone. A first refractory oil is also recovered from said cracked product, which oil has an average boiling point above the average boiling point of the first gasoline and below the average boiling point of the heavy cycle oil, and is rich in aromatics, the major single type of' aromatic being J-12. The first refractory oil is then combined with a second refractory oil, defined hereinbelow, and the combined stream is then hydrotreated with a sulfur resistant hydrotreating catalyst in the presence of hydrogen at hydrotreating conditions to convert a major portion! of the aromatics in said stream to a hydrotreated product having J-8 as the major single type of aromatic. At least a portion of this hydrotreated product is then cracked in a second catalytic cracking zone maintained at catalytic cracking conditions and containing a cracking catalyst. The heranbefore mentioned second high octane gasoline having J-6 as the major single type of aromatic, and the second refractory oil having J-12 as the major single type of aromatic and boiling above the average boiling point of the second gasoline are recovered from the effluent of said second cracking zone. The second, refractory oil is then recycled to the hydrotreating zone as he:rsLnbefore specified.

In another embodiment, this invention relates to a process for the production of high octane gasoline by eatalytically cracking a fresh feed gas oil, a heavy cycle oil, and a hydrotreated product as defined heieiribelow in a catalytic A high octane gasoline, a heavy cycle oil and a refracta oil having an average boiling point above the average boiling point of the gasoline and below the average boiling point of the heavy cycle oil and being rich in arpmatics, the major single type of aromatic . being J-12, are then recovered from said cracked product. The heavy cycle oil is returned to the catalytic cracker, and the refractory oil is hydrotreated to convert a major portion of the aromatics to a hydrotreated product .having J-8 as the major type of aromatic. At least a portion iof this hydrotreated product is, returned to the catalytic cracking zones as hereinabove specified.

Figure 1 shows a schematic flow schemefor one preferable embodiment of the present invention employing separate catalytic cracking zones and separators as hereinabove described.

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 hereinabove described.

As shown in Figure 1, a gas oil feed is introduced into a first catalytic cracking zone 2 through line 1. Al-though 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 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 fluidized catalyst. The fresh feed reacts under the influence 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 re- ugal actants by means such as settling, or centrifioei separation 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 and is cqntacted with additional hydrocarbon feed to repeat the process just described. It is, of course, to be understood thai' there are numerous variations in the basic catalytic cracking process which are readily apparent to those" skilled in the art. There are a large number of catalysts suitable for use in the catalytic cracking step such as silica-alumina, silica magnesia, silica zirconia, acid-ractivated clay,' crystalline catalysts, including faujasite dispersed in a silica - containing inorganic matrix, and mordenite-containing catalysts.

The amorphous silica-alumina catalysts having concentrations of from about 10 to about kO weight per cent of alumina and 90 to about 60 weight per cent of silica are preferred catalysts .

Typical catalytic crackin operating conditions comprise reactor temperatures of from about _|27°C up to about 5>66°C, regenerator temperatures of from about 538°C. of from about 0 atmospheres, auge h atm.g., oil-to-catalyst weight ratios of from about 1.0 to about 10.0 and combined feed ratios (ratios of fresh feed + heavy cycle oil/fresh feed) of from about 1, 1 to about 2.0. These variables may be adjusted to maintain conversions, per pass, to gasoline 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 line 3 and introduced into separator k -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 as line 8 ) and sent to a gas concentration unit, not shown, a gasoline fraction is recovered . (shown, in line 7) , a refractory oil side cut is recovered (shown in line 9) , and a heavy cycle oil side cut or bottom is recovered (shown in line 5 ) . In some cases a heavy bottoms, called slurry oil, is withdrawn from the unit(shown in line 6 ) where it may be clarified to remove catalyst particles and either recycled to zone 2 or used as fuel oil.

The refractory oil in line 9 is comingled with second refractory oil flowing in line 10: from a source described hereinafter and passed into hydrotreater 12 through line 11. The required hydrogen is intoduced into hydrotreater 12 through line 13. This hydrotreating step may be carried out by any method known to those skilled in the art of hydrotreating.

Preferably the hydrotreating catalyst is contained as a fixed bed within a reaction zone. The material in line 11 is mixed with fresh hydroge (from line 13) and recycle gas from a source described herinafter, 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 flashed 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 sulf r -resistant, that is, it possesses hydrogenation activity in the presence of sulfur compounds. A preferably catalyst comprises a silicaralumina 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 Other supports, such as alumina, silica-zirconia, silica-magnesia, faujasite, mordenite, or an inorganic oxide matrix containing at least one crystalline aluminosilicate 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 hydrotreater 12 such as temperature, pressure, liquid hourly space velocity (LHSV), and hydrogen-to-oil ratio are adjusted to selectively convert the refractory oils to a product having as the major single type of aromatic hydrocarbon J-*8 as defined hereinbefore. It has now been found that these refractory oils have J-12 as the major single type of aromatic hydrocarbon. Therefore, the above hydrotreating process variables are controlled to maximize the conversion of JT12 to J-8. It is generally preferable to maintain pressure, LHSV and hydrogen-to-oil ratio constant, and vary temperature to maximize this conversion. The initial choice of all these variables depends to a large measure on the charge stock.' Suitable pressure ranges are from about 27.2 up to about 136 atmospheres, gauge with UO.8 to 6l, 2 atm. g. being preferable. Suitable EHSV 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 : 1 to about 20 :1, with £ : 1 to l£:l being preferable. Mhen these conditions are selected, the temperature is adjusted to maximize the J-12 to J-8 conversion. For most oil fractions, temperatures within the range of from The preferable method for setting proper operating conditions is to select the independent variables (such as pressure and feed ratios), conduct a J-factor analysis of the streams flowing in lines 11 and l£ and adjust temperature to attain the maximum conversion of J-12 to J-8. If the hydrotreating conditions are too seveie the J-12 type compounds will either be converted to J-6 types or the aromatics will be saturated. Both have the undesirable effect of increasing hydrogen consumption and reducing the octane number of the gasoline when the hydrotreated oil is catalyticall cracked. If the hydro-treating conditions are not severe enough, there will be little reduction in the refractory nature of this oil. When properly hydrotreated, this material is easily catalytically cracked yielding high quality gasoline at conversions of substantially i ' 100%. The hydrotreated normally liquid product is intoduced into a second catalytic cracking zone Ik through line 15.

Cracking zone l may be a part of cracking zone 2 , may be integrated with zone 2, or may be an entirely separate processing unit. For example, a separate stream of regenerated crack-ing 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 point wherein the regenerated catalyst and hydrotreated oil are mixed and .the reaction vessel, this arrangement permits zone lh to operate' as a part of zone 2 with common separation equipment and a common regenerator. Cracking zone Ik can be integrated with zone 2 by mixing re In this case zone II4 and zone 2 have a common regenerator but separate reaction vessels and if desired, separate separation equipment. Of course, zone Ik can be entirely independent of zone 2 with its own reactor, stripper, regenerator, catalyst, and separation equipment. The cracking conditions employed in zone Ik 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 Ik in order tooptimize each cracking step. The reaction products from zone II . are withdrawn through line 17 and introduced into- separator 16. Separator l6, usually a fractionator, is employed to separate the reaction products into a light hydrocarbon portion in line 18 (usually sent to a gas concentration unit :not shown), a second high octane gasoline stream in line 19 and the second refractory oil referred to hereinbefore, in line 10. Several unexpected results are obtained as a result of the combined effects of zones 12 and ll|. ; The gasoline in line 19 is of higher quality than the gasoline of line 7. It is found that this second gasoline in line 19 is at least 3 clear octane numbers higher 7; ' than the first gasoline (in line $) . Furthermore, the second gasoline is lower in olefin content than the first .gasoline by a substantial margin, which improves its lead susceptibility and makes for a cleaner burning fuel. On the other hand, the absolute clear octane number of the second gasoline may be sufficiently high to eliminate the necessity of adding lead to improve the octane number. F-l clear octane numbers of J-factor analysis of this second gasoline reveals that the major single type of aromatic present therein is J-6, making it a preferable motor fuel. Another unexpected result is shown by examination of the unconverted oil flowing in line . A J-factor analysis indicates that the major single type of aromatic present in this unconverted oil is J-12. This means that zone lk has converted the hydrotreated material in line 15 which boils above gasoline and has J-8 as the major single aromatic type, into a gasoline having J-6 as the major single aromatic type and. a material boiling above gasoline having J-12 as the major single aromatic type. For this reason the unconverted material in line 10 is suitable for recycle to the hydrotreating step since it has a similar J-factor analysis as the first refractory oil in line 9.

Therefore, all this unconverted material may be recycled back to zone 12 and zone lU, thus allowing recycle to extinction. This means that 100$ of the material in line 9 will ultimately be converted at conversions of from about I4O to about 80$ per pass which, of course, will maximize the yield of gasoline in line 19. If desired, however, a portion of the unconverted material in ; ine 10 may be withdrawn through line IO by opening valve 39) a portion of the material in line 11 may be withdrawn through line 36 by opening valve 3½> or a portion of the material in line 1$ may be withdrawn through line 38 by opening valve 37. One or more of these alternative withdrawals can be practiced if it is desired to recover a heavier fuel than gasoline.

The process of the present invention, therefore, permits the conversions of gas oil feed stocks to gasoline and lighter materials in amounts of 90% or higher. Indeed, conversions of up to 100$ are possible by means of the process of this invention, provided the slurry oil is also cracked. Furthermore, the light hydrocarbons in lines 8 and 18 are rich in olefins, which may be used to alkylate paraffins to produce high octane isoparaffins which in turn 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 components alkyl-benzene aromatics and isoparaffins.

The present process possesses a substantial advantage over hydrocracking processes in that the butane produced by the present cracking zones will be less than the total amount required for alkylation of the and olefins in products and for meeting the vapor pressure .requirement of the gasoline, whereas one of the major problems of hydrocracking is excess production of butane. In other words, the refiner who uses the present process is able to buy' low-cost butane and sell it as high-cost gasoline. Furthermore, the catalytic cracking steps and hydrotreating steps are effected at relatively low pressures, thus minimizing capital investment and operating problems. It is believed that the conversion of a typical gas oil by the process of this invention, accompanied by alkylation of the olefins, and buying sufficient butane to satisfy alkylation and vapor pressure requirements will Figure 2 shows an alternative preferable embodiment of the present invention having a common cracking zone and a common separator. Fresh gas oil flowing in line 21, heavy cycle oil from a source described hereinafter in line 27, and hydrotreated oil from another source described hereinafter in line 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 the art of catalytic cracking as described hereinabove with reference to zone 2 . The reaction products from zone 22 are withdrawn through line 23 and into separator 2h - Separator 2I4, usually a frac-tionator, separates the reaction products into a light hydrocarbon fraction which is sent to a gas concentration process (not shown) by means of line 26, a gasoline which is recovered from line 2i>, a refractory oil in line 29, a heavy cycle oil in line 27 and in some cases a slurry oil in line 28. The heavy cycle oil is returned through line 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 line 29 is introduced into hydrotreater 30 along with fresh hydrogen flowing in line 31. Hydrotreater 30 contains a sulf r-resistant hydrotreating catalyst in a reaction zone maintained at hydro-treating conditions. Hydrotreater 30 is operated as described hereinbefore in connection with hydrotreater 12 to convert the oil in line 29, having J- 12 as the major type of s aromatic, into a hydrotreated oil in line 32, having J-8 as the major type of aromatic. The hydrotreated oil is returned in line 32 to cracking zone 22·, It is preferable to heat and vaporize this hydrotreated oil in heater k3 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 line 2$ which therefore is a blend of ;normal catalytically cracked gasoline and the higher^quality gasoline derived' from the hydrotreated oil. If the refiner has a. market for this higher-rquality 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 line Z by opening valve i|l.

It is difficult to characterize the demarcation between the refractory oil and the gasoline and heavy cycle oil by commonly observed physical characteristics, since the split points may vary depending on charge stock, operating characteristics., and desired yields. In some cases, the end -boiling- point of the refractoy oil will vary from about 228°C„ or less to as much as 399°C, or more. The preferred manner of characterizing the refractory oil and the heavy cycle oil is the place from which each originates. As used e heiAn, heavy cycle oil is that material withdrawn from the lower side-cut outlet in the catalytic cracking unit product 8 fractionator, said outlet being maintained at about 2^8GC.

The gasoline from the catalytic cracker may be characterized by boiling point range or end point, the end point generally The light refractory oil is derived from an upper side-cut outlet of the product fractionator, said outlet beingmaintained at about 227°C. These side-cut well temperatures are for fractionator pressures of about 0, 68 to 1.02 atm.g. and if the pressure is outside this range, the temperatures will pf .course also be shifted, · ; ■ The following examples are presented to further illustrate the process of the present invention.

EXAMPLE I A gas oil charge stock was processed in a conventional catalytic cracker employing a regenerator, a reaction vessel above the regenerator, a regenerated catalyst conduit from the regenerator, a riser connected to the reaction vessel into which the hydrocarbonaceous feed passes, and a stripper for removing hydrocarbonaceous materials from the catalyst flowing from the reaction vessel to the regenerator. The reaction vessel was maintained at 507°C. resulting i a conversion of fresh feed and recycled heavy cycle oil of 5$° This resulted in a yield of coke of about 9 wt. %, a catalytically cracked gasoline of about 3h*5 volume % and a yield of and olefins of about1 9. 7 volume The cracked gasoline had an F-l clear octane! number of about 93 and. contained about 30 volume % aromatics and about 30 volume % olefins. The and olefins were alkylated with isobutane in a separate alkylation. zone to produce an alkylate gasoline yield of about 17 volume % (based on fresh feed to the catalytic cracker). Therefore, the total yield of gasoline was 51» !? volume % (3 . ÷ 17» 0) out of a conversion of 5$> which means that the efficiency, as measur In addition, a refractory oil was produced from the above described example containing about 57.6$ aromatics . A J-faotor analysis was run on this refractory oil revealing the following breakdown : J-Factor Number Volume % J-6 27.9 J-8 15.2 J-10 ' 3.3 J-12 1 0.8 J-ih 6.3 J- 16 2.6 J-18 3.9 It is thought that the actual J-6 number was lower and the actual J-12 number was higher than these numbers due to the interference in the analysis caused by sulfur^ containing molecules. When this refractory oil was subjected to a separate catalytic cracking step at a temperature of 5l0°C , the conversion was only 3Q%.

The yields showed that 7.5 wt . % coke was produced, 20.1 volume % gasoline was produced and a yield of and olefins of about 5.0 was produced. - Alkylation of these olefins with isobutane resulted in an alkylate yield of 8.8 volume %. The total gasoline yield, including alkylate, was 28.9 volume %, indicating an efficiency of 76.1$. The catalytically cracked gasoline showed an olefin concentration of about 13 volume %.

The same refractory oil was subjected to controlled hydrotreating at a. pressure of 5k . h atm. g., a LHSV of 2, a hydrogen circulation rate of 0.$3h Standard Cubic Meter per Liter (SCML;) and a temperature of 399°C , with a catalyst containing nickel and molybdenum.

The hydrotreated oil' contained about aromatics and had the following J-f ctor analysis: J-Factor- Number Volume % J-6 Ih .k J-8 70.9 J- 10 5.1 J-12 h . 9 J-I 3.U J-16 1.0 J-18- 0.3 Thus, it can be readil seen that the hydrotreati.ng step had converted an oil having J-12 as its major aromatic component into a hydrotreated oil having J^8 as its major aromatic component. The sulfur compounds were also substantially removed and therefore the J-factor analysis is substantially accurate. This hydrotreated oil was subjected to a separate catalytic cracking step at a temperature of li96°C., res lting .in a conversion of about The yields from this operation show that 3.1 wt„$ coke was produced, UO.O volume % gasoline was produced and a yield of and olefins of 7.2 volume % was produced. Alkylation of the olefins with isobutane resulted in an alkylate gasoline yield of about 12. 7' volume %. The total gasoline yield, including alkylate,, was 52 .7 volume %, indicating an efficiency of 9$. %, The catalytically cracked gasoline contained about 60 volume % aromatics and only 3 volume % olefins and had an F-1 clear octane number of 97. A J-factor analysis was run on the catalytic cracking gasoline and showed the following results: J-Factor Number ' Volume % J-6 78. 7 J-8 13.0 J- 10 1.1 J-12 7.1 J-l 0.1 and no detectable J-l8; Comparison of the gasoline produced by the catalytic cracking of the hydrotreated refractory oil with the normal catalytically cracked gasoline is tabulated below.

Gasoline from Gasoline from Hydrotreated Gas Ojl Refractory Oil F-l Clear Octane Number 93 97 Olefin content, % 30 3 Aromatics content, % 30 60 Gasoline yield including alkylate 51.5 52.7 Efficiency as % of ' conversion 93.6 95.8 Coke make, wt. % ! 9.0 ■3.1 Temperature requirement at 55% conversion 507°c. 96°c All these comparisons clearly show substantial improvement in product quality, product yield and process operation, using the process of the present invention. Comparison of the results of the catalytic cracking of the unhydrotreated refractory oil and the hydrotreated oil show that the gasoline produced from the latter oil was of better quality (contains 10$ less olefins) and resulted in an operation that permitted high gasoline yield and high efficiency.

The unconverted material from the catalytic cracking of the hydrotreated oil which contained about 60 volume % aromatics was subjected to a J-factor analysis yielding the followr-"ing analysis: J-Factor Number Volume % J-6 6.U J-8 19,9 J-10 2.7 J-12 8.U J-lU 6.8 J-16 2.7 J-18 3.7 It should be noted that this material is very similar to the original refractory oil which means that recycle of this material to the hydrotreater followed by catalytic cracking will readily convert this material into gasoline at about the same , conversion level as that of refractory oil. It should also be noted that the catalytic cracking of the hydrotreated oil results in a gasoline rich in J-6 and an unconverted material rich in J- 12. In other words, the catalytic cracking step has made J-12 compounds as well as J-6 compounds from J-8 compounds, a most unexpected result.

EXAMPLE II Equipment is used substantially as shown in Figure 2, the light hydrocarbons being 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 catalytically cracked gasoline to produce an overall gasoline yield (at a vapor pressure of 0.68 atm.g. ) of above about 90' volume %, with F-1 clear octane number above about 95. The hydrotreater is maintained at conditions to maximize the conversion of the J-12 in line 29 into J-8 in line 32. Heater 3 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 refractory oil derived from a catalytic cracking zone contain at least li volume % aromatics with the largest single type of aromatic being J-12. The hydrotreating step is preferably carried out on said refractory oil to produce a product having at least h volume ■% aromatics with the largest single type of aromatic being J-8. This when cracked will result in the production of a gasoline having at least about hS% aromatics and a F-l clear octane number of about 95.

Claims (11)

HAVING NOW particularly described and ascertained the nature of our said invention and in what manner the same is to he performed, we declare that what we claim is

1. A process for the production of high octane gasoline from a refractory oil feed having an average boiling point above gasoline boiling range and below heavy cycle oil boiling "range, and containing at least k5 volume per cent aromatics, of which the major single aromatic type is J---12, characterized by: a) hydrotreating said refractory oil in the presence . of a sulfur-resistant hydrotreating catalyst at a pressure within the range of from about 27.2 to about 136 atmospheres gauge, and a temperature within the range of from about 260 to about kSh°C, in a hydro- treating zone, b) recovering resulting normally liquid, hydro- treated product containing at least kO volume per cent aromatics, of which the major single aromatics type is J-8, e) cracking at least a portion of said hydro-treated- product in the presence of a cracking catalyst, d) recovering from the resulting cracked product a .. . . ' ' i ' . gasoline- having- an F-l clear octane number of at least 95, and: containing at least US volume per cent aromatics of which the.ma or single aromatic type is J-6, e) and^separately recovering from the cracked product a second refractory oil having an average boiling point above gasoline boiling range, and containing J-12 as the major single aromatic type.

2. The process of claim 1, further characterized in that at least a portion of the second refractory oil recovered from the cracked product is returned to the hydrotreating zone.

3. The process of either of claims 1 or 2, further characterized in that the refractory oil feed is derived from a fresh gas oil stream by cracking said gas oil in the presence of a cracking catalyst, and recovering from the resulting cracked product, at least a heavy cycle oil, a gasoline, and said refractory oil feed.

4. U. The process of claim 3, further characterized in that the heavy cycle oil is recycled and subjected to cracking with the fresh gas oil stream.

5. £. The process of either of claims 3 or k, further characterized in that the fresh gas oil stream and the hydro-treated product stream are cracked in separate cracking zones.

6. The process of claim $, further characterized in that the gasoline resulting from the cracking of the hydro-treated product has an F-l clear octane number of at least three numbers higher than that of the gasoline resulting from the catalytic cracking of the fresh gas oil stream.

7. The process of either of claims 3 or I4. further .characterized in that the fresh gas oil stream is cracked in the same cracking zone as the hydrotreated product stream.

8. The process of any of claims 1 to 7, further characterized in that light hydrocarbons are produced by the cracking of the hydrotreated product and the fresh gas oil, an olefinic fraction containing 3 to 1; carbon atoms per molecule is recovered from said light hydrocarbons,: is reacted with, iso-butane, and resulting alkylate gasoline is recovered.

9. The process of any. of claims 1 to 8, further characterized in that the hydrotreating catalyst comprises at least one catalytically active component selected from the metals of Group VI and Group VIII of the periodic table,, and compounds thereof, composited with a silica alumina support ■material.

10. The process of claim 9, further characterized in that at least one catalytically active component is selected from tungsten, molybdenum, nickel, cobalt and compounds thereof. octane

11. A process for the production of high line substantially as hereinbefore described. Bated this 16th day of August, 1967 For thef pplican s DR. BBMS QfLD COM & CO