US3071536A - Hydrocarbon conversion process - Google Patents

Description

Jan. 1, 1963 v. E. STILES ETAL HYDROCARBON CONVERSION PROCESS 2 Sheets-Sheet 2 Filed June 21, 1956 J 2 M d 0 0 iza.

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United States Patent Ofilice 3,071,536 Patented Jan. 1, 1963 3,071,536 HYDROCARBON CONVERSION PROCESS Vernon E. Stiles and Nicholas L. Kay, Fullerton, Calif., assignors to Union Oil Company of California, Los Angeles, Calif., a corporation of California Filed June 21, 1956, Ser. No. 592,939 Claims. (Cl. 208-60) This invention relates to methods for producing maximum quantities of high octane gasoline from gas oils, or other high boiling mineral oil fractions which contain relatively large proportions of organic sulfur and/or nitrogen compounds. The process embraces a combination of catalytic hydrodesulfurization, or hydrofining, with subsequent catalytic cracking and reforming, wherein the conditions of hydrofining are specifically correlated with the cracking and reforming steps in such manner as to improve the elficiency of both the latter steps. More specifically, it has been found that certain conditions of hydrodesulfurization, or hydrofining, may be employed which will result in a total product therefrom which is substantially completely desulfurized and/or denitrogenated, while the gas oil fraction thereof is also improved for subsequent catalytic cracking, and the small proportion of gasoline-boiling-range material produced during hydrofining is also of excellent quality for reforming. The gasoline produced during hydrofining, under the conditions described, is largely or predominantly composed of the hydrocarbon fragments resulting from the hydrocracking of sulfur and nitrogen compounds in the original feed. It has been found that this gasoline, when produced under the defined conditions, is higher in naphthenes, and lower in paraflins and aromatics, than the gasoline produced under more severe conditions of hydrofining, and is higher in naphthene content than the straightrun gasoline which was originally associated with the feedstock.

It is an object of this invention to provide a combination of desulfurization, catalytic cracking, and reforming which will produce from the original feedstock a maximum quantity of high octane gasoline. A specific object is to provide conditions of desulfurization which will not only reduce the content of sulfur and nitrogen compounds, but will increase the aniline point of the gas-oil, thus im proving the product distribution obtainable from catalytic cracking, as well as producing a highly naphthenic gasoline suitable for reforming. A concomitant objective is to provide methods for pretreating catalytic cracking feedstocks in such manner as to improve the cracking efficiency thereof by raising the gasoline yield obtainable at any given conversion level, and raising the conversion level at which maximum gasoline yields are obtained. Another object is to provide means whereby the cycle oil from catalytic cracking may, if desired, be recycled substantially to extinction, resulting in a substantially complete conversion of the charge stock to high octane gasoline, coke, and light gases. Another object is to reduce the coke load on the catalyst in catalytic cracking, thereby increasing the capacity of any given cracking unit. A further object is to provide hydrofining conditions which produce highly naphthenic gasolines sufiiciently low in sulfur and nitrogen to be employed directly in reforming processes which utilize sulfur-sensitive and nitrogen-sensitive catalysts such as platinum-alumina. A further object is to minimize the consumption of hydrogen during hydrofining, thereby avoiding waste of hydrogen which would be lost on subsequent cracking of the feed. Other objects and advantages will be apparent from the more detailed description which follows.

It has been known for some time that catalytic cracking charge stocks may be subjected to various hydrogenation treatments to remove sulfur compounds, and to decrease the aromaticity, both of these effects resulting in improved cracking efficiency. Usually, in such processes, some hydrocracking of the hydrocarbon molecules occurs resulting in the production of gasoline-boiling-range material which is of very poor knock rating, due primarily to the high content of paraflins. The present invention revolves about our discovery that conditions of hydrofining, in the presence of cobalt molybdate catalysts, may be carefully controlled within narrow ranges, in such manner as to pro duce little gasoline other than the hydrocarbon fragments resulting from decomposition of sulfur and nitrogen compounds in the feed. It has been found also that the hydrocarbon fragments initially produced from the hydrocracking of sulfur and nitrogen compounds are predominantly naphthenic in character, and that by suitably adjusting the hydrofining conditions, cracking of these naphthenes to parafiins may be largely avoided. At the same time, a partial hydrogenation of polycyclic aromatic hydrocarbons in the feed occurs, all resulting in a general decrease in aromaticity of the residue boiling above the gasoline range. This residue hence forms an advantageous type of cracking stock. It has been found for example that such hydrofined residues are capable of yielding 35-40% of C -400 F. end point gasoline by volume, and these yields are moreover obtained at conversion levels of 60-70 volume percent, whereas the original untreated charge stock would be capable of producing a maximum yield of about 3 l-33 volume-percent of gasoline at a conversion level of only about 52-58 volumepercent. Moreover, the final gasoline from the catalytic cracking is found to contain less than about 5% as much sulfur as the original feed, and less than about 10% as much nitrogen. Moreover, the gasoline obtained at the maximum yield conversion level is higher in octane rating than the gasoline obtained at maximum yield conversions of the untreated feedstock.

The cobalt molybdate catalyst employed in the hydrofining step of the process comprises a mixture of cobalt and molybdenum oxides wherein the molecular ratio of C00 to M00 is between about 0.2 and 4.0. This catalyst may be employed in unsupported form or, alternatively, it may be distended on a suitable carrier such as alumina, silica, zirconia, thoria, magnesia, magesium hydroxide, titania or any combination thereof. Of the foregoing carriers it has been found that the preferred carrier material is alumina and especially alumina containing about l%8% by weight of silica.

In the preparation of the unsupported cobalt molybdate catalyst, the catalyst can be coprecipitated by mixing aqueous solutions of, for example, cobalt nitrate and ammonium molybdate, whereby, a precipitate is formed. The precipitate is filtered, washed, dried and finally activated by heating to about 500 C. Alternatively, the cobalt molybdate may be supported on alumina by coprecipita-ting a mixture of cobalt, aluminum and molybdenum oxides. A suitable hydrogel of the three components can be prepared by adding an ammoniacal ammonium molybdate solution to an aqueous solution of cobalt and aluminum nitrates. The precipitate which results is washed, dried and activated. In still another method, a washed alumina hydrogel is suspended in an aqueous solution of cobalt nitrate and an ammoni-acal solution of ammonium molybdate is added thereto. By this means a cobalt molybdate gel is precipitated on the alumina gel carrier. Catalyst preparations similar in nature to these, and which can also be employed in this invention, have been described in US. Patents 2,369,432 and 2,325,033.

Still other methods of catalyst preparation may be employed such as by impregnating dried carrier material, e.g. an alumina-silica gel, with an ammoniacal solu tion of cobalt nitrate and ammonium molybdate. Preparations of this type are described in US. Patent 2,486,361. In yet another method for preparing impregnated cobalt molybdate catalyst, the carrier material may be first impregnated with an aqueous solution of cobalt nitrate and thereafter impregnated with an ammoniacal molybdate. Alternatively, the carrier may also be impregnated with both solutions in reverse order. Following the impregnation of the carrier by any of the foregoing methods the material is drained, dried and finally activated in substantially the same manner as is employed for the other catalysts. In the preparation of impregnated catalysts where separate solutions of cobalt and molybdenum are employed, it has been found that it is preferable to impregnate the carrier first with molybdenum, e.g., ammoniacal ammonium molybdate, and thereafter to impregnate with cobalt, e.g., aqueous cobalt nitrate, rather than in reverse order.

In yet another method for the preparation of suitable catalyst, a gel of cobalt molybdate can be prepared as described hereinbefore for the unsupported catalyst, which gel after drying and grinding can be mixed with a ground alumina, alumina-silica or other suitable carrier together with a suitable pilling lubricant or binder which mixture can then be pilled or otherwise formed into pills or larger particles and activated.

In yet another modification finely divided or ground molybdic oxide can be mixed with suitably ground carrier such as alumina, alumina-silica and the like, in the presence of a suitable lubricant or binder and thereafter pilled or otherwise formed into larger agglomerated particles. These pills or particles are then subjected to a preliminary activation by heating to 600 C., for example, and are thereafter impregnated with an aqueous solution of cobalt nitrate to deposit the cobalt thereon. After draining and drying the particles are heated to about 600 C. to form the catalyst.

It is apparent from the foregoing description of the different types of cobalt molybdate catalyst which may be employed in this invention, that we may employ either an unsupported catalyst, in which case the active agents approximate 100% of the composition, or we may employ a supported catalyst wherein the active agents, cobalt and molybdenum oxides, will generally comprise from about 7% to 22% by weight of the catalyst composition.

The conditions of hydrofining described herein are substantially non-regenerative, in that the cobalt molybdate catalyst may be employed continuously for periods ranging from several days to several months without regeneration. Eventually, however, deposits of coke and other materials will accumulate, resulting in a decrease in activity. When this occurs, the catalyst may be regenerated to substantially its initial activity by combustion with air, or dilute air-flue gas mixtures, at temperatures between about 800 and 1500 F.

The conditions of hydrofining which may be utilized herein are in the first instance restricted as to temperature. The temperatures found effective fall within the range of about 740825 F. At below these temperatures it has been found that 'desulfurization, and especially denitrogenation, is inadequate for most purposes. Above the specified temperature range, the hydrocracking of hydrocarbons becomes an undesirable feature. The result of such hydrocracking is the production of large quantities of highly paraflinic, low octane gasoline which is not efficient reforming stock. It is therefore highly desirable to limit hydrocarbon cracking to the subsequent catalytic cracking step which is carried out in the absence of 7 hydrogen, whereby a more olefinic and aromatic gasoline of higher octane rating is produced than would have been produced by hydrocracking of the same molecules in the hydrofiner. Also, these high temperatures tend to cause cracking of the naphthenic hydrocarbons initially produced from the decomposition of sulfur and nitrogen where G is the volume-percent of synthetic gasoline produced, S is the weight-percen-tof feed sulfur which was converted, and N is the weight-percent of feed nitrogen which was converted. This equation is based upon the fundamental considerations that 1% by weight of sulfur in a heavy gas oil stock corresponds to about 12 volumepercent of sulfur compounds in such stock, and 1% of nitrogen in such a stock corresponds to about 24 volumepercent of nitrogen compounds therein. In high boiling gas oils having an end-point of for example 900l050 F., the hydrocracking of the sulfur and nitrogen compounds will ordinarily produce hydrocarbon fragments, about one-half of which will be in the gasoline boiling range. This factor varies considerably, depending upon the end-point of the feed stock. Light gas oils having an end-boiling point between about 625 and 750 F. will contain a lesser volume-percent of sulfur and nitrogen compounds corresponding to any given weight-percent of sulfur or nitrogen, but the hydrocrackiug thereof will convert the hydrocarbon residues more completely to the gasoline boiling range. Hence, the above equation is found to satisfy empirically the optimum hydrofiner gasoline yields for both light and heavy gas oils, where such gas oils are of the naphthenic type which contain between about 0.1% and 8% by weight of sulfur, and between about 0.05% and 2.0% of nitrogen.

In order to achieve the desired desulfurization, denitrogenation, gasoline quality, and gas oil quality, it is found that, for practical purposes, the pressure must be limited within the range of about 750-4000 p.s.i.g. while space velocities between about 0.5 and 7 volumes of liquid feed per volume of catalyst per hour may be employed. At pressures below about 750 p.s.i.g., dehydrogenation is favored, resulting in the production of a gasoline low in naph-thenes and high in parafiins, while the aniline point of the gas oil is improved only slightly or not at all. Pressures in excess of 4000 p.s.i.g. could theoretically be employed, but in such cases the variables of temperature and space velocity become more critical and must be controlled more precisely to give the desired results. The danger of a runaway hydrogenation reaction is present, and over-hydrogenation commonly results, the end effects of which are to decrease the arcmaticity and knock-rating of the final cracked gasoline, and consume excessive quantities of hydrogen.

Within the specified limits of temperature and pressure,

any space velocity between about 0.5 and 7 may be employed, preferably between about 1 and 5. In the preferred modification, the higher space velocities are employed in conjunction with the higher temperatures, and the lower space velocities in conjunction with the lower temperatures. a

The ratio of hydrogen to oil is not a critical factor,

except that a minimum of perhaps about 400 s.c.f. per

barrel of feed should be employed, and a practical maximum of about 10,000 s.c.f. per barrel maybe observed.

. The relationship between temperature and pressure may be defined more specifically as follows: At pressures between about 2,000 and 4,000 p.s.i.g.,-the temperature may range anywhere between 740825 F. However, at pressures between 750 and 2000 p.s.i.g., the lower temperature limit is 740 F., while the higher limit is defined by the line, P=26.6T19,920, when plotted on rectangular coordinates with P expressed in pounds per square inch gauge, and T in F. This limitation reflects the fact that at low pressures, the higher temperature ranges tend to favor cracking, and the gasoline fragments produced from the sulfur and nitrogen compounds are converted largely to paraflins. When observing the above conditions of hydrofining, it is found that as a general rule the hydrogen consumption, i.e. the hydrogen actually consumed during the reaction, is expressed empirically by the following equation:

where H is the hydrogen consumed in s.c.f. per barrel of feed, S is the sulfur converted, as weight-percent of feed, N is the nitrogen converted, as weight-percent of feed, and U represents the volume-percent of olefins present in the feed. The preferred conditions of pressure for most stocks are found to fall within the range between about 1000 and 2500 p.s.i.g.

Attached FIGURE 2 shows graphically the operative combinations of pressure and temperature. The area included within the polygon A represents the operative combinations; the preferred conditions fall within polygon B.

The product resulting from the hydrofining treatment is subjected to fractionation at a cut-point of approximately 400 F. to separate the gasoline from the gas oil residue. The gasoline is then subjected to reforming under conventional conditions, e.g. in the presence of a platinum catalyst supported on alumina, and preferably containing between about 0.5% and 8.0% by weight of combined halogen.

The reforming step is carried out at temperatures between about 850 and 1100 F., and preferably in the range of 900 to 1000 F. A pressure in the range of about 50 to 1000 pounds per square inch is employed in conjunction with a liquid hourly space velocity between about 0.1 and 10, and preferably between about 0.4 and 2.0. Recycle hydrogen amounting to between 1000 and 10,000 cu. ft. per barrel of charge stock is introduced with the charge stock to minimize carbon deposition. Operating cycles of up to several months may be employed between regenerations.

The gas oil residue resulting from hydrofining is then subjected to any conventional type of catalytic cracking. For this purpose either fluidized, fixed bed, or mov ng bed types may be employed. Any conventional cracking catalyst may be employed as for example silica-alumina, silicazirconia, silica-magnesia, alumina-boria, acid treated clays of the montmorillonite type and the like. The cracking conditions include temperatures in the range of about 8501100 F., pressures of atmospheric to about 500 p.s.i.g., space velocities between about 0.5 and 10, and catalyst/oil ratios between about 0.5 .and 20.

Actual practice of the invention may be more readily understood by reference to the accompanying FIGURE 1, which is a schematic illustration of one modification, not intended to be limiting in scope.

The primary feed stock to the process, comprising .any mineral oil fraction boiling substantially above the gasoline range, is brought in through feed line 1, admixed with recycle hydrogen from line 2, and if desired with recycle residual oil from the subsequent cracking step which is recycled through line 3, and the mixture is then heated to the desired hydrofining temperature in heater .4, and passed into a hydrofining reactor 5 containing cobalt molybdate catalyst. The desulfurized product is then withdrawn via line 7, condensed in exchanger 8, and passed into high pressure separator 9, from which recycle hydrogen is withdrawn through line for recycle. The liquid product in separator 9 is then transferred via line 12 to low pressure separator 13, from which light hydrocarbon gases plus hydrogen sulfide and/or ammonia are withdrawn through line 14. The liquid product from separator 13 is then transferred via line 15 to a fractionating column 16.

The overhead from fractionating column 16 consists of the gasoline which was synthesized in the hydrofiner 5. This gasoline may still contain traces of H 8 and/or NH and for purposes of reforming, it may be desirable to remove those impurities by distillation or water wash ing, according to well-known techniques not herein illustrated. If the gasoline from column 16 is sufliciently pure, it is taken off through line 17 and blended with additional gasoline admitted through line 18, and with recycle hydrogen from line 20. The mixture is then preheated to reforming temperature in heater 21 and passed directly into catalytic reformer 22, containing a suitable catalyst such as granular 0.5% platinum on alumina. The products from reforming are withdrawn through line 24, cooled in exchanger 25 and admitted to high pressure separator 27. There is normally a net make of hydrogen in reformer 22, and the total hydrogenrich gases in separator 27 are withdrawn through line 28, a part thereof being recycled via line 20, while the net make of hydrogen is passed through line 2 to hydrofiner 5, to supply the hydrogen consumed. therein. If insufficient hydrogen is formed in the reforming operation, additional hydrogen may be admitted to line 2'frorn any desired source.

The liquid product in high pressure separator 27 is then passed via line 30 to low pressure separator 31, from which light gases such as methane, ethane, propane and the like, as well as small amounts of hydrogen are withdrawn through line 32 for use as fuel gas or any other desired purpose. The gasoline in separator 31 is then withdrawn through line 32 and sent to storage.

The bottoms product from fractionating column 16 consists of gasoline-free gas oil of excellent quality for catalytic cracking. This bottoms fraction is withdrawn through line 35, preheated to somewhat below cracking temperatures in heater 36, and transferred via line 37 to fluid catalytic cracker 39. Hot, regenerated catalyst from catalyst standpipe 41, at a temperature in the range of about 9001400 -F., is continuously admitted, via line 38, to cracker feed line 37, where it completes the preheating of the oil charge which was partially preheated in heater 36. As the catalyst is mixed with the oil in line 37, the oil is flash vaporized and forms a suspended fluidized catalyst-hydrocarbon mixture which is forced through line 37 into catalytic cracker 39 by the pressure maintained in the regenerator plus the force of gravity exerted on the dense catalyst in regenerator standpipe 41. In reactor 39, the catalyst settles to a definite level and forms a fluidized bed the depth of which regulates the time of reaction, and can be varied to provide the desired degree of cracking. This bed is maintamed in a fluid, turbulent condition by the entering feed vaporswhich continuously pass upwardly, thereby effectlng intimate contact of oil with catalyst and producing a substantially uniform temperature in the range of about 900-1100 F.

As cracking progresses, coke forms on the catalyst and reduces its activity. The spent catalyst laden with coke is continuously and automatically withdrawn through line 45 to spent catalyst stripper 46 where the absorbed and entrained feed vapors are stripped from the catalyst by countercurrent contact with a stripping gas admitted into standpipe 47 via line 48. Vapors from catalyst stripper 46 are continuously passed via line 50 into produce effluent line 51, which withdraws cracked products from the vapor space in the top of reactor 39. The combined mixture is then passed into a centrifugal separator 52 wherein any entrained catalyst is separated and falls through line 53 into catalyst stripper/l6.

Catalyst-free product gases are removed from separator 52 via line 54, cooled substantially to atmospheric temperature in cooler 55, and transferred via line 56 to a product 7 separator 57, from which light gases are taken oil? through line 58. The liquid product in separator 57 is withdrawn through line 59, and fractionated in distillation column 60 to recover overhead via line 61 the high quality cracked mixed with the fiuidizing gases passed via line 75' from separator 70, and admitted to centrifugal separator 76, from which flue gases are removed via line 77, and separated catalysts allowed to gravitate via line '78 into standgasoline, which may be blended with the reformed gasoline pipe 41. The regenerated catalyst in standpipe 41 is then from line 32, or otherwise utilized. allowed to drip via line 38 into charge oil line 37, by

The bottoms from column 60 comprise the refractory means of automatic control valve 80. materials which were not cracked in catalytic cracker 39, Obviously many modifications may be made in the deand this cycle oil is withdrawn through line 62. A part tails described above. The following examples are cited thereof may be withdrawn through line 64 for use as fuel 10 to illustrate the criticality of the conditions of hydrofining oil if desired. Ordinarily however, it will be found that hereinbefore described. this cycle oil is of sufiiciently high quality that it may be recycled via lines 65 and 3, to hydrofiner 5, and in this EXAMPLE I manner recycled substantially to extinction. Each pass Several hydrofining runs were conducted, employing as through the hydrofiner improves the cracking quality of feedstock a heavy gas oil which was 81.5 volume-percent the oil by effecting partial saturation of the aromatics, Straight n gas oil, and Volume Percent gh COk r thereby rendering the product susceptible to further gas oil. The original feed had an initial boiling point of catalytic cracking. The efficiency of the hydrofining 475 F. and a 50% boiling point of 720 a gravity of operation for this purpose is in fact so great that usually Sulfur 0011mm of 1-18 W igh pernot all of the cycle oil need be recycled through the hydro- Cent, a 111308611 Content of Weight P and an finer, a portion thereof, e.g. between about 25% and 75%, aniline point of 69.6 (50/50 mixture, C.). may be recycled via lines 65', 66-, 35 and 37 to catalytic This feed stock was then subjected to hydrofining over a cracker 39. The proportion of the cycle oil which is recobalt molybdate catalyst containing 9.74 weight-percent cycled through the hydrofiner should be balanced so as to M00 and Weight P r C these c mponents obtain a substantially constant aniline point of the total 29 being impregnated upon a coprecipitated silica-alumina cycle oil which is recovered in column 60. Preferably the carrier containing about 6% SiO In one series of runs, conditions of hydrofining and the proportion of cycle oil the pressure was maintained constant at 1500 p.s.i.g., the which is returned to the hydrofiner, should be so adspace velocity at 1.0, and the hydrogen rate at 3000 s.c.f. justed that the aniline point of the total cycle oil recovered 0 per barrel of feed. The results at various temperatures in column 60 is substantially the same as, or higher than, were as follows:

Table 1 Comp. of Gasoline Gas 011 Vol. Temp, Hz Con- Percent Run N0. F. sutnption, Gaso. V01. V01. N, Wt S, Wt. Aniline s.c.f./b. Yield S, Wt. Percent Percent Per- Per- Point,

Percent Naph- Arom. cent cent 50/50 C thenes 700 310 0.8 0. 03s 51 19 0. 233 0.376 76.8 744 450 4.1 0.010 49 14 0.16 0.17 78.8 768 460 0. 005 43 17 0.10 0.10 79.2 795 580 12.5 0.009 43 12 0. 094 0. 076 75.6 820 715 22.6 0. 00s 16 0. 037 0.017 69.4 840 27.5 0.006 34 1s 0. 038 0.020 65.5 866 1,020 38.9 0.007 29 20 0. 033 0.022 57.4

the aniline point of the original feed admitted through line 1. By operating in this manner the cycle oil may be recycled substantially to extinction, while at the same time there is an overall reduction in coke laydown on the cracking catalyst, as compared to the coke laydown which would occur at the same cracking conversion level of the fresh feed.

The aniline point referred to herein is a standard measure of aromaticity of hydrocarbon oils, and means the temperature at-which a 50/50 volume-percent mixture of oil and aniline becomes completely miscible. Hence, the higher the aniline point, the higher is the paraffin content ofthe oil, and the lower its aromatic content.

The spent catalyst in standpipe 47 drops through an automatically regulated valve 68 into regeneration gas line 67, throughwhich a suitable mixture of oxygen or air with title gas or steam carries the spent catalyst through regenerator return line 67 to regenerator 40. The temperature of the regeneration gas, or its oxygen content, are adjusted so that controlled burning of the coke and other deposits on the catalyst is carried out in regenerator at a substantially constant temperature level between about 900 and 1800 F. The reactivated catalyst is continuously withdrawn through line 69 and passed into flue gas separator 70, communicating with catalyst standpipe 41. Small quantities of steam or flue gas may be admitted to standpipe 41 via line 72 in order to maintain the regenerated catalyst in a fluidized condition. Flue gases from'regenerator 40 are withdrawn through line 74,

It will be noted from the above data that in runs 6 and 7, the aniline point of the gas oil product was lower than the feed, indicating a poor stock for catalytic cracking. It will be noted also that in runs 5, 6 and 7, the gasoline recovered from the hydrofining contained from 29% to 35% of naphthenes; inasmuch as the straight-run gasoline originally associated with this feed contained 41% naphthenes, it is clear that the hydrofining conditions of runs 5, 6 and 7 markedly decreased the quality of the endogenous gasoline for purposes of reforming. Most of the naphthene hydrocarbon residues initially formed were apparently cracked to paraffins, indicating that temperatures in excess of 825 C. are to be avoided, inasmuch as the gasoline produced is poor reforming stock. Moreover there is no compensating increase in octane number, in spite of the increase in aromatic content. The gasoline produced in run 7 had a leaded octane rating (F1+3 ml. TEL) of 79.8, whereas the gasoline from run 4 had a leaded octane rating of 81.8. Upon subjecting the gasoline from run 7 to reforming at 950 F. in the presence'of a 0.2% platinum-alumina catalyst a product of 93.5 leaded octane rating is obtained, while on the other hand, under the same conditions of reforming, the gasoline produced in run 4 gives a reformed gasoline of 98.0 leaded octane rating.

The conditions of run 1, while giving substantial improvement in naphthene content of the gasoline, and aniline point of the gas oil, were not suitlciently severe to give adequate desulfurization, and are hence excluded. The only runs which gave all the desired results were runs 2, 3 and 4. It may be noted that the temperature of 820 F. in run is suitable for use herein only at pressures in excess of about 1900 p.s.i.g.

A graphic correlation of the data of this example is set forth in attached FIGURE 3. From the plot of aniline point curve A, sulfur content curve B, and curves C and D defining the naphthene content of the gasolines, it will be seen that only under the conditions of temperature between 740 and 825 F. were all the desired conditions met, i.e. (1) an improvement in aniline point of the gas oil, (2) a sulfur content in the gas oil which is substantially exclusively in the flat part of the curve, and (3) the production of a gasoline product of optimum quality for reforming, i.e. one containing the minimum proportion of aromatics, and at least as high a naphthene content as the gasoline originally associated with the feed stock. All of these features indicate optimum conditions of hydrofining for the subsequent cracking of the gas oil, and subsequent reforming of the gasoline.

EXAMPLE II To show further that low pressures are not operable in combination with high temperatures, additional hydrofining runs were conducted with the same feed and catalyst, but at 800 p.s.i.g., 793 F., and 3,000 s.c.f. of hydrogen per barrel of feed. At 1.0 space velocity, the gasoline produced contained only 35 volume-percent naphthenes, and the gas oil had an aniline point of 71.2. At space velocity 2.0, the gasoline produced still contained only 35 volume-percent naphthenes, while at 3.0 space velocity the gasoline contained only 37 volumepercent naphthenes. Also, in the latter case, poor desulfurization was obtained, and the nitrogen content of the product was 0.24 weight-percent. This data shows that the high temperature range from about 800825 F. is usable for the present purposes only at pressures well above 800 p.s.i.g.

EXAMPLE III Another hydrofining run was carried out with the same feed and catalyst at 792 F., 1500 p.s.i.g, 3000 s.c.f. H per barrel of feed, but at 4.0 space velocity. The resulting product contained 5.0 volume-percent of synthetic gasoline, which was 40 volume-percent naphthenes, while the gas oil product had an aniline point of 76.4, and contained 0.19, and 0.20 weight-percent of sulfur and nitrogen respectively. This data shows that the optimum combination of results of runs 2, 3 and 4 of Example I are not dependent upon space velocity within the range herein claimed.

EXAMPLE IV This example illustrates the comparative results obtainable upon catalytic cracking of the hydrofined gas oils, as compared to cracking of the untreated gas oils.

A portion of the untreated gas oil feed of Example I was subjected to fluid catalytic cracking at a temperature of 950 F., a weight hourly space velocity of 3.06, and a catalyst/oil ratio of 8.05. Under these conditions the volume-percent conversion was 49.8, while the gasoline yield was 31.9% by volume. The gasoline contained 0.399% by Weight of sulfur and had a knock rating of 97.3 (F1+3 ml. TEL). The aniline point of the cycle oil was 51.2. The cracking catalyst employed was a synthetic silica-alumina composite containing about 85% by weight SiO The gas oil product from run 4 of Example I was then subjected to fluid catalytic cracking under conditions similar to the foregoing except that a higher space velocity of 3.8 was employed, whereby the total volume-percent conversion was 49.5. At this substantially identical conversion level, the gasoline yield was 34.4 volume-percent, and its sulfur content was only 0.037% by weight, while the knock rating was 99.3 (F-l-l-3 ml. TEL). Also, the residual cycle oil had an aniline point of 58.8, indicating substantially improved recycling characteristics.

Moreover, in the case of the untreated feed stock, it was found that 5.02 weight-percent of the feed was converted to carbon, whereas in the cracking of the hydro fined stock, only 2.81% by weight or" the feed was converted to carbon. Inasmuch as the carbon burning capacity of the catalyst regenerator is usually a severely limiting factor in catalytic cracking, it will be apparent that the marked reduction in carbon formation will materially increase the effective capacity of the catalytic cracker.

In the case of any of the gas oils produced from the preferred hydrofining operations herein described, it is found that at any given conversion level of catalytic cracking, a higher yield of gasoline is obtained, a lower yield of carbon, and a higher octane gasoline is obtained than can be obtained by cracking the untreated feedstock. These surprising advantages are achieved in addition to the expected benefit of a substantially sulfur-free and nitrogen-free product.

While the above description necessarily refers to specific modifications, there is no intention to limit the invention to the details described. The true scope of the invention is intended to be embraced by the following claims.

We claim:

1. A process for converting a feedstock consisting essentially of a distillate gas oil to high-octane gasoline, said feedstock boiling above the gasoline range and below 1050 F. and containing substantial amounts of an impurity selected from the class consisting of organic sulfur compounds and organic nitrogen compounds, which comprises first subjecting said feedstock to hydrofining in the presence of a fixed bed of cobalt molybdate catalyst supported on a carrier which is essentially activated alumina, at a space velocity between about 0.5 and 7.0, in the presence of at least about 400 s.c.f. of hydrogen per barrel of feed, and at a pressure-temperature combination falling within the polygon defined by the rectangularcoordinate lines, P=750, P=4,000, T- 740; T=825, and P=26.6T19,920, where P is pressure in p.s.i.g. and T is temperature in F., thereby efiecting substantial desulfurization, denitrogenation, and partial hydrogenation of aromatics with resultant production of a small quantity of gasoline, said gasoline being derived substantially exclusively from the decomposition of organic sulfur and nitrogen compounds, fractionating the product from said hydrofining step to recover a gasoline-boiling-range material and a gas oil residue, subjecting said gasoline fraction to catalytic reforming to improve the octane rating thereof, and subjecting said gas oil residue to catalytic cracking to produce a high octane cracked gasoline.

2. A process as defined in claim 1 wherein said catalytic cracking is carried out at a conversion level substantially higher than the maximum-gasoline-yield conversion level obtainable by catalytic cracking of said feedstock prior to hydrofining.

3. A process as defined in claim 1 wherein the product from said cracking step is subjected to fractionation to produce a gasoline fraction and a high boiling cycle oil, and a part of said cycle oil is recycled to said hydrofining step and a part thereof to said cracking step.

4. A process as defined in claim 1 wherein said reforming step is carried out in the presence of a platinumalumina reforming catalyst, and the products therefrom are separated to produce a hydrogen-rich recycle gas and a reformed gasoline fraction, recycling a portion of said hydrogen to said hydrofining step, and recycling the remaining part of said hydrogen to said reforming step.

5. A process for converting a feedstock consisting essentially of a distillate gas oil to high-octane gasoline, said feedstock boiling above the gasoline range and below 1050 F. and containing substantial amounts of an impurity selected from the class consisting of organic sulfur compounds and organic nitrogen compounds, which comprises first subjecting said feedstock to hydrofining in the presence of a fixed bed of cobalt molybdate catalyst supported on a carrier which is essentially activated alumina, at a space velocity between about 0.5 and 7.0, in the presence of at least about 406 s.c.f. of hydrogen per barrel of feed, and at a pressure-temperature combination falling within the polygon defined by the rectangular-coordinate lines, P=750, P=4000, T=740, T 825, and P=26.6T19,920, where P is pressure in p.s.i.g. and T is temperature in F, thereby effecting substantial desufurization, denitrogenation, and partial hydrogenation of aromatics with resultant production of a small quantity of gasoline, said gasoline being derived substantially exclusively from the decomposition of organic sulfur and nitrogen compounds, nfractionating the product from said hydrofining step to recover a gasoline-boiling-range material and a gas oil residue, and subjecting said gasoline fraction to catalytic reforming to improve the octane rating thereof.

6. A process as defined in claim 5 wherein said reforming is carried out in the presence of a catalyst which is essentially alumina containing a minor proportion of platinum.

7. A process as defined in claim 5 wherein said reforming step is carried out in the presence of a platinumalumina reforming catalyst, and the products therefrom are separated to produce a hydrogen-rich recycle gas, and a reformed gasoline fraction, recycling a portion of said hydrogen to said hydrofining step, and recycling the remaining part of said hydrogen to said reforming step.

8. A process for converting a feedstock consisting essentially of a distillate gas oil to high-octane gasoline, said feedstock boiling above the gasoline range and below 1050 F. and containing substantial amounts of an impurity selected from the class consisting of organic sulfur compounds and organic nitrogen compounds, which oomprises first subjecting said feedstock to hydrofining in the presence of a fixed bed of cobalt molybdate catalyst supported on a carrier which is essentially activated alumina, at a space velocity between about 0.5 and 7.0, in the presence of at least about 400 s.c.f. of hydrogen per barrel of feed, and at a pressure-temperature combination falling within the polygon defined by the rectangular-coordinate lines, P:750, P=()0, T=740, T=825, and P=26.6T- 19,920, Where P is pressure in p.s.i.g. and T is temperature in F., thereby effecting substantial desulfurization, denitrogenation, and partial hydrogenation of aromatics with resultant production of a small quantity of gasoline, said gasoline being derived substantially exclusively from the decomposition of organic sulfur and nitrogen compounds, fractionating the product from said hydrofining step to recover a gasoline-boiling-range material and a gas oil residue, and subjecting said gas oil residue to catalytic cracking to produce a high octane cracked gasoline.

9. A process as defined in claim 8 wherein said catalytic cracking is carried out at a conversion level substantially higher than the maximum-gasoline-yield conversion level obtainable by catalytic cracking of said feedstock prior to hydroiining.

10. A process as defined in claim 8 wherein the product from said cracking step is subjected to fractionation to produce a gasoline fraction and a high boiling cycle oil, and a part of said cycle oil is recycled to said hydrofrning step and a part thereof to said cracking step.

References Cited in the file of this patent UNITED STATES PATENTS 2,600,931 Slater June 17, 1952 2,642,381 Dickinson June 16, 1953 2,755,225 Porter et al July 17, 1956 2,768,936 Anderson et al. Oct. 30, 1956 2,769,769 Tyson Nov 6, 1956 2,772,212 Seyfried Nov. 27, 1956

Claims (1)

1. A PROCESS FOR CONVERTING A FEEDSTOCK CONSISTING ESSENTIALLY OF A DISTILLATE GAS OIL TO HIGH-OCTANE GASOLINE, SAID FEEDSTOCK BOILING ABOVE THE GASOLINE RANGE AND BELOW 1050*F. AND CONTAINING SUBSTANTIAL AMOUNTS OF AN IMPURITY SELECTED FROM THE CLASS CONSISTING OF ORGANIC SULFUR COMPOUNDS AND ORGANIC NITROGEN COMPOUNDS, WHICH COMPRISES FIRST SUBJECTING SAID FEEDSTOCK TO HYDROFINING IN THE PRESENCE OF A FIXED BED OF COBALT MOLYBDATE CATALYST SUPPORTED ON A CARRIER WHICH IS ESSENTIALLY ACTIVATED ALUMINA, AT A SPACE VELOCITY BETWEEN ABOUT 0.5 AND 7.0, IN THE PRESENCE OF AT LEAST ABOUT 400 S.C.F. OF HYDROGEN PER BARREL OF FEED, AND AT A PRESSURE-TEMPERATURE COMBINATION FALLING WITHIN THE POLYGON DEFINED BY THE RECTANGULARCOORDINATE LINES, P=750, P=4,000, T=740, T=825, AND P=26.6T-19,920, WHERE P IS PRESSURE IN P.S.I.G. AND T IS TEMPERATURE IN *F., THEREBY EFFECTING SUBSTANTIAL DESULFURIZATION, DENITROGENATION, AND PARTIAL HYDROGENATION OF AROMATICS WITH RESULTANT PRODUCTION OF A SMALL QUANTITY OF GASOLINE, SAID GASOLINE BEING DERIVED SUBSTANTIALLY EXCLUSIVELY FROM THE DECOMPOSITION OF ORGANIC SULFUR AND NITROGEN COMPOUNDS, FRACTIONATING THE PRODUCT FROM SAID HYDROFINING STEP TO RECOVER A GASOLINE-BOILING-RANGE MATERIAL AND A GAS OIL RESIDUE, SUBJECTING SAID GASOLINE FRACTION TO CATALYTIC REFORMING TO IMPROVE THE OCTANE RATING THEREOF, AND SUBJECTING SAID GAS OIL RESIDUE TO CATALYTIC CRACKING TO PRODUCE A HIGH OCTANE CRACKED GASOLINE.

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