US3046219A - Recycle catalytic hydrocracking - Google Patents

Description

y 1962 F. G. CIAPETTA ETAL 3,046,219

RECYCLE CATALYTIC HYDROCRACKING 4 Sheets-Sheet 3 Filed May 14, 1959 VOLUME CYCLE STOCK //V CHARGE IOO aoT

4 2 N #GQ: 5G is VOLUME CYCLE STOCK //V CHARGE //7)/en/0r$ Fran/r C Cfape/fa Harry LCoonmdf IOO CO/VVE/FS/O/V, I/OL. (/00 RECYCLE) Af/omey 3,546,219 Patented July 24, 1962 free 3,046,219 RECYCLE CATALYTIC HYDROCRAC-KING Frank G. Ciapetta, Silver Spring, Md, and Harry L.

Coonradt, Woodbury, and William E. Garwood, Haddonfield, N.J., assignors to Socony Mobil Oil Company, Inc., a corporation of New York Filed May 14, 1959, Ser. No. 813,247 7 Claims. (Cl. 208-111) This application is a continuation-in-part of application Serial Number 491,256, filed March 1, 1955, now abancloned.

This invention relates to the catalytic cracking of petroleum hydrocarbon stocks. It is more particularly concerned with a process wherein relatively high boiling hydrocarbon fractions are converted, in the presence of platinumor palladium-containing catalysts, into valuable products.

As is well-known to those familiar with the art, the major products of a cracking operation are dry gas, butanes, pentanes, light naphtha, heavy naphtha, and cycle stock (boiling at temperatures higher than about 390 F). The light naphtha fraction usually has a rela tively high octane number (about 90-92, Fl+3 cc. TEL). On the other hand, the heavy naphtha fraction, particularly that which is obtained by cracking in the presence of hydrogen, has a relatively low octane numher (about 70-80). Accordingly, in order to produce a finished gasoline having a relatively high octane number, it has been the practice to blend the heavy naphtha fraction with the light naphtha fraction and also with butanes and pentanes in amounts limited by the mam'murn permissible vapor pressure. There is, however, a steadily increasing demand for higher octane gasolines (about 95 and higher).

As those skilled in the art will readily appreciate, such octane requirements cannot be met by the aforedescribed conventional blending operations. Accordingly, the rela tively low octane heavy naphtha fraction has been sub-. jected to reforming operations. As the increasing demand for higher octane gasolines must be satisfied largely by reforming, instead of by blending, there is a greater de mand for heavy naphtha fractions that can be reformed and a correspondingly lesser demand for light naphtha fractions that can be used for blending purposes. The light naphtha fraction is not usually subjected to a reforming operation because it produces excessive amounts of dry gas, coke, etc. The yield of gasoline obtained by reforming light naphtha, therefore, is prohibitively small. Accordingly, it will be appreciated that a cracking operation that will produce greater amounts of the heavy naphtha fraction and lesser amounts of light naphtha fractions is highly desirable.

As is Well-known to those skilled in the art, much of the material that is obtained in a cracking operation and that boils at temperatures higher than about 390 F. is a fuel oil suitable for use in Diesel engines and in domestic heating units. The burning efiiciency of this fuel oil is dependent upon its diesel indexthe higher the diesel index, the better the burning ehiciency of the fuel. It is highly desirable, therefore, to obtain a fuel oil having the highest possible diesel index.

In copending application Serial Number 825,0l6 tiled July 6, 1959, now US. 2,945,806, which was a continuation-in-part of application Serial Number 418,166, filed on March 23, 1954, now abandoned, which is a continuation-in-part of application Serial Number 351,151, filed on April 27, 1953, and now abandoned, there is disclosed a once-through process for cracking high boiling hydrocarbon fractions in the presence of hydrogen and of catalysts comprising metals of the platinum and palladium series supported upon synthetic mixed oxide carriers.

'oil having a higher diesel index.

This process can be operated to produce substantially gasoline alone or fuel oil alone, or both. At intermediate conversion levels (levels at which both naphtha and fuel oil are made), a good product distribution is obtained. The amount of dry gas is relatively small and the amounts of butanes and of pentanes produced are not in excess of those required to produce 10-pound R.V.P. (Reid vapor pressure) gasoline. Substantial yields of light and heavy naphtha are obtained and the diesel index of the fuel oil is relatively high. In view of the foregoing, however, the process would be more eflicient and its performance would be more desirable, if it could be operated to produce even less dry gas, less light naphtha, more heavy naphtha, and a fuel oil having a still higher diesel index.

It has now been found that the cracking process described in the aforementioned applications can be operated in a manner that will produce one or more of the following results: lower dry gas yield, lower yield of light naphtha, greater heavy naphtha production, and a fuel it has been discovered that these results can be obtained by a recycle operation in which the recycle ratio is controlled. As will be discussed hereinafter, however, all these desirable results are not obtained with every charge stock.

Accordingly, it is an object of this invention to provide a method for obtaining more eflicient product distribution in a cracking operation. Another object is to provide a process for cracking relatively high boiling hydrocarbon fractions that will produce, as compared with a oncethrough operation. one or more of the following results: lower dry gas yield, lower yield of light naphtha, greater heavy naphtha production, and a fuel oil having a higher diesel index. A specific object is to provide a process for cracking hydrocarbon charge stocks in the presence of hydrogen and of catalysts comprising metals of the platinum and palladium series deposited upon a synthetic composite of two or more refractory oxides which has a relatively high cracking activity, that will produce one or more of the aforementioned results. Otther objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description considered in conjunction with the drawings, in which FIGURE 1 presents a series of curves showing graphically the relationship between the temperature and the volume percent conversion into products boiling at temperatures lower than about 390 F. (LOO-recycle), and the percent conversion into fuel oil, obtained by cracking a typical, heavy gas oil in the presence of hydrogen and of a platinum-containing catalyst, both with and without the recycle operation of this invention;

FiGURE 2 presents a series of curves showing graphically the relationship between the volume percent conversion into products boiling at temperatures lower than about 390 F. GOO-recycle) and the Weight percent yield of dry gas obtained by cracking a typical, heavy gas oil in the presence of hydrogen and of a platinum-containing catalyst, both with and Without the recycle operation of this invention;

FIGURE 3 presents a series of curves showing graphically the relationship between the volume percent con version into products boiling at temperatures lower than about 390 F. (IOU-recycle) and the volume percent yield of light naphtha obtained by cracking a typical, heavy gas oil in the presence of hydrogen and .of a platinumcontaining catalyst, both with and without the recycle operation of this invention.

FIGURE 4 presents a series of curves showing graphically the relationship between the volume percent conversion into products boiling at temperatures lower than about 390 F. '(l00erecyole') and the volume percent yield of heavy naphtha obtained by cracking a typical,

heavy gas oil in the presence of hydrogen and of a platinum-containing catalyst, both with and without the recycle operation of this invention;

FIGURE presents a series of curves showing graphically the relationship between the volume percent conversion into fuel oil, the material boiling at temperatures higher than about 390 F., and the diesel index of the fuel oil obtained by cracking a typical, heavy gas oil in the presence of hydrogen and of a platinum-containing catalyst, both with and without the recycle operation of this invention;

FIGURE 6 presents the graphic relationship between the temperature and the volume percent cycle stock in the charge obtained by cracking a charge comprising a typical, heavy gas oil and varying amounts of cycle stock, in the presence of hydrogen and of a platinum-containing catalyst and under conditions that produce 50 percent conversion into products boiling at temperatures lower than about 390 F. (100-recycle);

FIGURE 7 presents the graphic relationship between the weight percent yield of dry gas and the volume percent cycle stock in the charge obtained by cracking charge stock-s comprising a typical, heavy gas oil and varying amounts of cycle stock, in the presence of hydrogen and of a platinum-containing catalyst and under conditions that produce 50 percent conversion into products boiling at temperatures lower than about 390 F. (100- recycle);

FIGURE 8 presents the graphic relationship between the volume percent cycle stock in the charge and the diesel index of the fuel oil obtained by cracking charge stocks comprising a typical, heavy gas oil and varying amounts of cycle stock, in the presence of hydrogen and of a platinum-containing catalyst and under conditions that produce 50 percent conversion into products boiling at temperatures lower than about 390 F. (100-recycle);

FIGURE 9 presents a series of curves showing graphically the relationship between the volume percent conversion into products boiling at temperatures lower than about 390 F. (100-recycle) and the weight percent yield of dry gas obtained by cracking a typical, light gas oil in the presence of hydrogen and of a platinum-containing catalyst, both with and without the recycle operation of this invention;

FIGURE 10 presents a series of curves showing graphically the relationship between the volume percent conversion into fuel oil, the material boiling at temperatures higher than about 390 F., and the diesel index of the fuel oil obtained by cracking a typical, light gas oil in the presence of hydrogen and of a platinum-containing catalyst, both with and without the recycle operation of this invention;

FIGURE 11 presents a series of curves showing graphically the relationship between the volume percent conversion into products boiling at temperatures lower than about 390 F. (100-recycle) and the weight percent yield of dry gas obtained by cracking a typical, coker gas oil in the presence of hydrogen and of a platinum-containing catalyst, both with and without the recycle operation of this invention; and

FIGURE 12 presents a series of curves showing graphically the relationship between the volume percent conversion into fuel oil, the material boiling at temperatures higher than about 390 F., and the diesel index of the fuel oil obtained by cracking a typical, coker gas oil in the presence of hydrogen and of a platinum-containing 4 F., a 50 percent point of at least about 500 F., and an end boiling point of at least about 600 F., and boiling substantially continuously between said initial boiling point and said end boiling point, with a cycle stock obtained from cracking said fraction, in which the volumetric ratio of said cycle stock to said fraction varies between about 0.1:1, respectively, and 10:1, respectively, with a catalyst comprising between about 0.05 percent and about 20 percent, by Weight of the catalyst, of at least one metal of the platinum and palladium series deposited upon a synthetic composite of at least two refractory oxides, said composite having an activity index of at least about 25, in the presence of hydrogen in amounts, expressed in molar ratio of hydrogen to hydrocarbon charge, within the range of about 2 to about 80, at a pressure above pounds per square inch gauge, at a liquid hourly space velocity within the range about 0.1 to about 10, and at a temperature above about 500 F.

Throughout the specification and the claims, the term conversion is intended to be a generic term for the amount of products boiling at temperatures lower than about 390 F. (100-recycle), of gasoline, or of fuel oil obtained in the process. It is expressed in terms of the volume percent of the initial charge which is transformed in the process. The amount of product boiling at temperatures lower than about 390 F. is obtained by subtracting the volume percent of cycle stock from 100 percent, i.e., from the initial volume of the charge. The expression (100- ecycle) is an abbreviation for 100 percent minus the volume percent recycle. Dry-gas refers to the methane, ethane, propane, and ethylene and propylene produced in a cracking process, expressed in terms of Weight percent of the initial charge. Light naphtha is the product that boils between about F. and about F. The reavy naphtha is the product that boils between about 170 F. and about 390 F. The diesel index of the fuel oil is a function of the A.P.I. gravity and the aniline number, as defined by Becker et al. in the S.A.E. Journal (Transactions), vol. 35, No. 4, p. 377. The cracking activity of a carrier is expressed in terms of the percent, by volume, of a standard hydrocarbon charge which is cracked, under specific operating conditions, in the Cat. A test. This test is described by Alexander and Shimp in National Petroleum News, 36, page R-537 (August 2, 1944). The unit for rating the cracking activity of a material is called the activity index (AL).

The catalysts utilizable herein are those described in US. 2,945,806, a continuation-in-part of Serial Number 418,166, filed on March 23, 1954, now abandoned, which in turn was a continuation-in-part of application Serial Number 351,151, filed on April 27, 1953, now abandoned. Briefly, these catalysts comprise between about 0.05 percent, by Weight, and about 20 percent, by weight, of the final catalyst, preferably between about 0.1 percent and about 5 percent, by weight, of the metals of the platinum and palladium series, i.e., those having atomic numbers of 44-46, inclusive, 76-78, inclusive, supported upon synthetic composites of two or more refractory oxides. The carrier is a synthetic composite of two or more oxides of the metals of groups 11A, IILB and IVA and B of the periodic arrangement of elements [1. Chem. Ed., 16, 409 (1939)]. These synthetic composites of refractory oxides must have an activity index of at least about 25. They can also contain halogens and other materials which are known in the art as promoters for cracking catalysts, or small amounts of alkali metals that are added for the purpose of controlling the activity index of the carrier. Non-limiting examples of the composites contemplated herein include silica-alumina, silica-zirconia, silica-alumina-zirconia, silica-alumina thoria, alumina-bori-a, silica-magnesia, silica-alumina-magnesia, silicaah1min-aflu0rine, and the like. The preferred support is a synthetic composite of silica and alumina containing scream between about 1 percent, by weight, and about 90 percent, by weight, of alumina. These synthetic composites of two or more refractory oxides can be made by any of the usual methods known to those skilled in the art of catalyst manufacture. Examples of methods of preparing them are set forth in US. 2,945,806.

The following example illustrates a method of preparing a 'plat-inumcontaining catalyst utilizable in the process of this invention:

EXAMPLE 1 A synthetic silica-alumina carrier or support containing percent by weight alumina was prepared by mixing an aqueous solution of sodium silicate (containing 158 g. per liter of silica) with an equal amount of an aqueous acid solution of aluminum sulfate containing 39.4 g. Al (SO and 28.6 g. concentrated H 80 per liter. This mixture of solutions was dropped through a column of oil, wherein gelation of the hydrogel was effected in bead form. The bead hydrogel was soaked in hot water (about 120 F.) for about 3 hours. The sodium in the hydrogel was then removed by exchanging the gel with an aqueous solution of aluminum sulfate [1.5 Al (SO by weight] containing a small amount (0.2 percent by weight) of ammonium sulfate. The thus-exchanged hydrogel head was water-washed. Then, it was driedin superheated steam (about 280-340 F.) for about 3 hours and, finally, calcined at 1300 F. under a low pertial pressure of steam for about 10 hours.

The silica-alumina beads were then crushed to pass through -a l4-mesh screen and the material retained on a -mesh screen (-UJS. standard screen series) was used for catalyst preparation. Portions of the crushed, calcined carrier were then barely covered with aqueous solutions of chloroplatinic acid, of concentrations suilicient to produce the desired amount of metal in the finished catalyst. The excess solution was removed by centrifuging. The thus-impregnated carrier was then dried at 230 F. for 24 hours. The catalyst was treated with hydrogen for four hours at 400 F. Then, it was activated in hydrogen for 16 hours before it was used. The catalyst thus prepared contained 0.47 percent platinum, by weight of the catalyst, and the silica-alumina carrier had an activity index of 46.

The charge stocks utilized in the process of this invention comprise mixtures of virgin stocks with cycle stocks. As used throughout the specification and claims, the term virgin stoc means a hydrocarbon fraction that has not been subjected to the process of this invention or to the process described in the aforementioned copending application. Likewise, throughout the specification and the claims, the terms cycle stock" or recycle refer to hydrocarbon firaotions boiling at temperatures higher than about 390 F. that have been subjected to the process of this invention and are returned to the reaction zone.

The virgin stock utilizable herein are hydrocarbon fractions, having an initial boiling point of at least about 400 F., a 50 percent point of at least about 500 F. and an end boiling point of at least about 600 F. and boiling substantially continuously between said initial boiling point and said end boiling, point. Such charge stocks inelude gas oils, residual stocks, refractory cycle stocks from conventional cracking, whole topped crudes, and heavy hydrocarbon fractions derived by the destructive hydrogenation of coal, tars, pitches, asphalts, etc., such as, for example, middle. oil. a

As is well-known to those skilled in the art, the distillation of higher boiling petroleum fractions (those boiling at temperatures higher than about 750 F.) must he carried out under vacuum, in order to avoid thermal cracking. Throughout the specification and in the claims, however, the boiling temperatures are expressed in terms of the boiling point at atmospheric presure. In other words, in all instances, the boiling points of fractions distilled under vacuum have been corrected to the boiling points at atmospheric pressure.

As is well-known to those familiar with the art, the term gas oil is a broad, general term that covers a variety of stocks. Throughout the specification and in the claims, the term, unless further modified, includes any fraction distilled from petroleum which has an initial boiling point of at least about 400 F., a 50 percent point of at least about 500 F., and an end boiling point of at least about 600 F., and boiling substantially continuousiy between the initial boiling point and the end boiling point. The portion which is not distilled is considered residual stock. The exact boiling range of a gas oil, therefore, will be determined by the initial distillation temperature (initial boiling point), the 50 percent point, and by the temperature at which distillation is cut off (end boiling point).

in practice, petroleum distiliations have been made under vacuum up to temperatures as high as 11001200 F. (corrected to atmospheric pressure). Accordingly, in the broad sense, a gas oil is a petroleum fraction which boils substantially continuously between two temperatures that establish a range falling within from about 400 F. to about 11001200 F., the 50 percent point being at least about 500 F. Thus, a gas oil could boil over the entire range 4001200 F. or it could boil over a narrower range, e.g., 500-900 F.

The gas oils can be further roughly subdivided by overlapping boiling ranges. Thus, a light gas oil boils between about 400 F. and about 600650 F. A medium gas oil distills between about 600 650 F. and about 700- 750 F. A heavy gas oil will boil between about 600- 650 F. and about 800-900 F. A gas oil boiling between about 800850 F and about 1100-1200 F. is sometimes designated as a vacuum gas oil. It must be understood, however, that a gas oil can overlap the foregoing ranges. It can even span several ranges, i.e., include, for example, light and medium gas oils.

As mentioned hereinbefore, a residual stock is any fraction which isnot distilled. Therefore, any fraction, regardless of its initial boiling point, which includes all the heavy bottoms, such as tars, asphalts, etc., is a residual fraction. Accordingly, a residual stock can be the portion of the crude remaining undistilled at 1100- 1200 F., or it can be made up of a gas oil fraction plus the portion undistilled at 1100-1200 F. A whole topped crude, as the name implies, is the entire portion of the crude remaining after the light ends (the portion boiling up to about 400 F.) have been removed by distillation. Therefore, such a fraction includes the entire gas oil fraction (400 'F. to 11001200 F.) and the undistilled portion of the crude petroleum boiling above 1100l200 F. If it is desired, the residual fractions and the whole topped crude can be deasphalted by any means known to the art. Such treatment, however, is not necessary for charge stocks intended for use in the process of this invention.

The refractory cycle stocks are cuts of conventionally cracked stocks Which boil above the gasoline boiling range, usually, between about 400 F. and about 850 F. The refractory cycle stocks can be charged to the process of this inventionin conjunction with a fresh petroleum charge stock, or they can be charged alone to the process. The process of this invention is particularly adaptable to the cracking of sulfur-containing charge stocks. The catalysts utilizable in the process of this invention, quite unexpectedly, are not deactivated by sulfur compounds, under the conditions of the process.

The presence of even relatively small amounts of nitrogen compounds in the charge stock causes the degree of conversion which can be attained at any given temperature to decrease. Thus, the higher the nitrogen content the greater will be the temperature needed to effect a given amount of conversion. Since higher temperatures spacers are usually associated with higher dry gas production, there will usually be a greater quantity of dry gas produced when converting high nitrogen stocks to the same degree as lower nitrogen stocks.

It is, therefore, prefer-red for optimum operations that the nitrogen content of the charge stock be below about 0.1 percent by weight and still more preferably below about 0.08 percent by Weight. if desired, the nitrogen content of any charge stock may be reduced prior to its supply to the process of this invention by conventional treatment, such as acid treatment, extraction with propane or hydro-genolysis under very high pressure in contact with catalysts such as molybdenum or tungsten oxide, nickel sulfide, tungsten sulfide, cobalt molybdate, cobalt tungstate, etc.

It must be understood that all the foregoing types of virgin stock do not produce similar results when subjected to the process of this invention. In other words, all'charge stocks do not produce all, or even the same advantageous results as compared with once-through op eration, viz., lower operating temperatures, lower dry gas yield, lower light naphtha yield, higher heavy naphtha yield and a fuel oil having a higher diesel index. Some charge stocks, notably those having initial boiling points of the order of about 600650 F. or higher, and more particularly straight-run gas oils having such initial boiling points, do, indeed, produce all the foregoing advantageous results. On the other hand, other stocks, particularly light gas oils, produce only a few of them. All virgin charge stocks that are admixed with cycle stock do produce, however, fuel oils having higher diesel indexes.

The variation in results obtained with different charge stocks will become apparent to those skilled in the art from the following examples:

EXAMPLE 2 The charge stocks used in this example were a mixture containing five parts of cycle stock derived from Kuwait gas oil and one part of virgin Kuwait gas oil, a mixture containing one part of cycle stock derived from Kuwait gas oil and one part of Kuwait gas oil, and the virgin Kuwait gas oil alone. These charge stocks had the following properties:

Each mixture was subjected to cracking in the presence of hydrogen and of the catalyst described in Example 1 after the latter had reached equilibrium, i.e., had been in continuous operation for more than five days. The hydrogen pressure used was 1000 p.s.i.g., the liquid hourly space velocity was 0.5, and the molar ratio of hydrogen to oil was 40.

For purposes of comparison, portions of the virgin Kuwait gas oil, without recycle, were subjected to cracking under the same conditions, at various temperatures, and in the presence of the same catalyst used in cracking the mixtures of cycle stock with virgin Kuwait gas oil. The pertinent data are set forth in Table I.

Q Table 1 Charge s11 blend 1:1 blend cycle plus cycle Virgin Kuwait gas oil virgin plus Kuwait virgin Kuwait 0 Operating conditions:

emp, r 743 785 793 694 710 Pros-sure, p s .1 1,000 1, 000 1, 000 1,000 1,000 LrlSV 0.5 0.5 0.5 .5 0.5 111/011 ratio 40 40 40 Results:

Conversion, vol. percent. 28. 1 52. 1 60. 2 44. 4 46. 9 Dry gas, weight percent 2. 2 3. 8 5. 9 1. 6 1. 8 14) Butancs, vol. percent 4. 8 11. 0 14. 8 6. l 8. 8 Pent-e es vol. percen 4. 3 9.1 11.5 5. 4 6. 9 in, vol. percent 3. 7 7. 6 0. 7 4. 8 4. 8

23. 6 36. 3 -17. 4 38. 3 37. 2 Fuel oil, vol. percent... 71. 9 47. b 30. 8 55.6 53.1 Diesel index of fuel oil, 61.4 71.0 74. 2 68.8 20

, The curves shown in FIGURES 1 through 5 are based upon the data set forth in Table I. In FIGURE '1, curve 1 shows the relationship between the temperature and the volume percent conversion into products boiling at temperatures lower than about 390 F. 100-recycle) in the case in which the Kuwait gas oil alone was subjected to cracking without using recycle. Curves 2 and 3, respectively, show a similar relationship obtained by cracking the gas oil, using recycle in ratios of 1:1 and 5:1, respectively. It will be noted that much lower temperatures are required to achieve cracking at any conversion level when recycle operation is used than in the operation in which virgin feed alone is employed. It is to be noted also that with the higher recycle ratios, lower temperatures are required.

in FIGURE 2, curve 4 shows the relationship between the weight percent yield of dry gas and the volume per cent conversion into products boiling at temperatures lower than about 390 F. (100-recycle) in the case in which the virgin gas oil alone was used. Curve-s 5 and 6, respectively, show similar relationships obtained in cases in which recycle ratios of 1:1 and 5:1, respectively, were used. It is to be noted that at the same conversion 0 le el, the amount of dry gas produced in the recycle operation of this invention is considerably less than that produced in a once-through operation.

In FIGURE 3, curve 7 shows the relationship between the volume percent yield of C light naphtha and the volume percent conversion into products boiling at temperatures lower than about 390 F. (IOU-recycle) obtained in the case in which the virgin gas oil alone was subjected to cracking. Curve 8 shows a similar relationship obtained in the cases in which the recycle operation .1 of this invention was used. It will be noted that at the same conversion level, the amount of light naphtha produced in cycle operation is appreciably smaller. As has been mentioned hereinbefore, this is of considerable importance because this light naphtha does not have a 9 sufficiently high octane rating to meet the demand for high octane gasolines and, generally, it is not subjected to a reforming operation.

In FIGURE 4, curve 9 shows the relationship between the volume percent yield of heavy naphtha and the ,5 volume percent conversion into products boiling below about 390 F. (l00-recycle) in the case in which the virgin Kuwait gas oil alone was subjected to cracking. Curves 10 and 11, respectively, show similar relationships obtained in the cases in which recycle ratios of 1:1 and 5:1, respectively, were employed. It will be apparent that, as the recycle ratio is increased, the yield of heavy naphtha at any conversion level is higher. It has been found further that, from the standpoint of ease of conversion into high octane gasoline by reforming, the qualrty of this naphtha is high and that it remains subof decrease in dry gas yield is less.

stantially so at any conversion level. As this stock is one that is readily reformed into high octane gasoline, an increase in its yield is highly desirable.

In FIGURE 5, curve 12 shows the relationship between the diesel index of the fuel oil and the volume percent conversion into fuel oil boiling at temperatures higher than about 390 F. obtained by cracking the virgin Kuwait gas oil alone. Curves 13 and 14 present similar relationships obtained by using recycle ratios of 1:1 and 5:1, respectively. The considerably higher diesel indexes obtained using the process of this invention over those that can be obtained with the virgin stock alone is readily apparent. As is well-known to those skilled in the art, the burning qualities of a fuel used for diesel engines or for heating improve as the diesel index increases.

In view of the foregoing discussion, it is to be noted that, when the heavier charge stocks are used in the process of the present invention, all the advantageous results listed hereinbefore are obtained. This permits much more flexibility in operation. Thus, not only can the relative amounts of desirable and of undesirable products be controlled, but lower temperatures can be used. This means, of course, that the very heavy stocks, such as residual stocks, can be cracked at temperatures sufficiently low that coking and dry gas production are cut down considerably, resulting in increased catalyst life. The product boiling at temperatures higher than about 390 F. has a lower end boiling point than that of the charge and has a high diesel index. Accordingly, the heavier charge stocks (particularly straight-run charge stocks) having an initial boiling point of 600650 F. can be converted by the process of this invention substantially completely into gasoline having good reforming charge stock characteristics and into fuel oil having a high diesel index.

The ratio of cycle stock to virgin stock in the charge for the process of this invention must vary between well established limits, if the advantages enumerated hereinbefore are to be realized. This will be apparent from the curves set forth in FIGURES 6, 7 and 8, which have been derived from FIGURES 1, 2 and 5, respectively.

The curve in FIGURE 6 shows'the relationship between the volume percent cycle stock in the charge and the temperature at the level of 50 percent conversion into products boiling at temperatures lower than about 390 F. (100-recycle). This curve was obtained by determining, from the curves in FIGURE 1, the temperature required for 50 percent conversion using varying amounts of cycle stock (83.3%) in the feed. It will be noted that when the volume percent of cycle stock in the charge is about 50 percent (1:1 ratio), the temperature required to produce 50 percent conversion is about 60 F. lower than that required for virgin stock alone. On the other hand, at a ratio of about :1, the decrease in the temperature requirement is about F. more. At higher recycle ratios, the decrease in temperature requirement is correspondingly less.

The curve in FIGURE 7 shows the relationship between the volume percent cycle stock in the charge and the weight percent dry gas, at the level of 50 percent conversion into products boiling at temperatures lower than about 390 F. (IOO-recydle). This curve was derived from FIGURE 2 in the same manner that the curve in FIGURE '6 was derived from FIGURE 1. It will be noted that the greatest decrease in dry gas yield is obtained when the recycle ratio is increased to about 1:1. As the recycle ratio is further increased, the degree The curve in FIGURE 8 shows the relationship between the volume percent cycle stock in the charge and the diesel index of the fuel oil at the level of 50 percent conversion into fuel oil (boiling at temperatures higher than about 390 F). It was derived from FIGURE 5 in the same manner that the curves in FIGURES 6 and a 10 7 were derived from FIGURES 1 and 2, respectively. It

I will be noted that the increase in the diesel index of the fuel oil remains small until the recycle ratio is about 1:1. The curves shown in FIGURES 6, 7 and 8 indicate that very substantial advantages may be obtained in reduction of the temperatures required to effect a given conversion and in dry gas with recycle ratios as low as 0.121. To also obtain an improvement in diesel index of the fuel oil, the ratio of cycle stock to' virgin stock in the charge ordinarily should be at least about 1:1, however. The ratio of cycle stock to virgin stock can be as high as 15 :1 or higher. In practice, however, it is preferred to use cycle stock to virgin stock volume ratios varying between about 1:1 -or slightly lower and about 10:1 and higher and, more preferably, between about 1:1' and about 5:1.

As has been mentioned hereinbefore, when light gas oils are cracked, using the cycle operation of this invention, all the aforementioned advantageous results are not obtained. This will be apparent from the following examples:

EXAMPLE 3 The charge stocks used in this example were a mixture of equal parts,'by volume, of a virgin light East Texas gas oil with a cycle stock derived from the light East Texas gas oil, and the virgin light East Texas gas gas oil was cracked in the presence of hydrogen and of the same catalyst used in the runs described in Example 2. The run Was carried out under a hydrogen pressure of 1000 p.s.i.g., at a liquid hourly space velocity of 0.5, and using a hydrogen to oil molar ratio of 40. For comparison purposes, the virgin light East Texas gas oil alone was cracked under the same conditions and at "various temperatures, using the same catalyst. The pertinent data are set forth in Table II.

Table 11 Charge 1:1 blend of cycle plus Virgin East Texas gas virgin oil East; Texas gas oil Operating conditions:

Temp, F M0 685 700 065 Pressure, F 1,00 1 1,000 1,000 1.000 LHSV .5 0. 5 0.5 0.5 Hz/oil ratio 40 40 40 40 Results:

Conversion, vol. percent..." 13.3 49. 7 68.2 33. 6 Dry gas, weight percent 0. 4 2.1 2. 1 0. 5 Butanes, vol. percent 1. 3 5.8 8. 5 ,4. 1 Pentanes, v01. percent........ 1.0 4. 5 9. 4 3.3 Lt. naphtha, vol. percent 1.4 4.1 7.8 1. 5 Hvy. naphtha, vol percent 15.2 40.1 56.4 29.5 Fuel oil, vol. percent 86. 7 50. 3 31.8 66. 4 Diesel index of fuel oil 76. 4 83. 9 I 86. 3 '85. 7

-oils are the charge stocks.

An attempt to show the relationship graphically be tween the volume percent conversion into products boiling at temperatures lower than about 390 F. and the temperature, in the case in which the light East Texas gas oil alone is cracked and in the case of the cycle operation of this invention, produced a single curve, regardless of the type of operation. This means of course, that, with respect to the temperature of operation, the operation of this invention, when light gas oils are used, affords no advantage. Similar results were obtained in an attempt to show the relationship between the volume percent conversion into products boiling at temperatures lower than about'390 F. (lOO-recycle) on the one hand and the volume percent yield of light naphtha and the volume percent yield of heavy naphtha. The conclusion is, therefore, that there is no advantage gained from the standpoint of a decrease in light naphtha production or of an increased yield of heavy naphtha by applying the process of this invention to light gas oils.

There are, however, at least two real advantages, namely, the decreased production of dry gas and the increased diesel index of the fuel oil. This will be apparent from the curves shown in FIGURES 9 and 10. These curves are based upon the data set forth in Table II.

In FIGURE 9, curve 15 shows the relationship between the volume percent conversion into products boiling at temperatures lower than about 390 F. and the weight percent yield of dry gas produced in the case in which the "irgin light gas oil alone is cracked in the presence of hydrogen and a platinum-containing catalyst. Curve 16 shows a similar relationship in the case in which the light gas oil is cracked in the process of this invention, using a 1:1 recycle ratio. It will be apparent that in the latter the amount of dry gas produced is considerably less, particularly at the higher conversion levels.

In FIGURE 10, curve 17 shows the relationship between the volume percent conversion 'into products boiling at temperatures lower than about 390 F. and the diesel index of the fuel oil produced in the case in which the light gas oil alone is cracked. Curve 18 shows a similar relationship in the case in which the light gas .oil is cracked in the process of this invention, using a 1:1

recycle ratio. It will be noted that the process of this invention produces a fuel oil having a much higher diesel index and in better yields than can be obtained in a oncethrough operation. Thus, for example, if it is desired to produce a fuel oil having a diesel index of 85, it can be produced in about 68 volume percent yield by the process of this invention, as compared to a yield of only about 40 volume percent in the case in which no recycle operation is involved. This means, of course, that 28 volume percent more of the desired fuel oil can be obtained in the present process.

From the data set forth in Table II and the curves presented in FIGURES 9 and 10, therefore, it will be apparent to those skilled in the art that the application of the process of this invention to light gas oil is advantageous. The advantages are real and commercially valuable.

The application of the present process to light gas oils other than straight-run light gas oils, such as light coker gas oils, likewise does not produce all the advantageous results obtained as in the cases in which the heavier gas This will be apparent from the following examples:

EXAMPLE 4 The charge stocks used in this example were a mixture of equal parts, by volume, of a virgin light gas oil produced by coking a Mid-Continent residuum with a cycle stock derived from the light coker gas oil, and the virgin light Mid-Continent coker gas oil alone. These charge stocks had the following properties:

hydrogen and 0f the platinum-containing catalyst that was used in the runs described in Example 2. The hydrogen pressure was 1000 pounds per square inch gauge, the liquid hourly space velocity was 0.5, and the hydrogen to oil molar ratio was 40. For comparison purposes, the virgin light Mid-Continent coker gas oil alone was cracked at various temperatures, using the same catalyst and conditions that were used with the 1:1 blend. The pertinent data for these runs are set forth in Table III.

Table III Charge 1:1 blend of cycle stock Virgin light Mid-C0ntiand virgin nent coker gas oil Mid-Continent coker gas oil Conditions:

Temp, F 750 795 780 Pressure, p.s.i.g. 1, 000 1, 000 1,000 1,000 LHSV .5 0.5 0.5 0. 5 Hz/Oil ratio 40 40 40 40 Results:

Conversion, vol. percent. 25. 8 43. 2 66. 5 62. 5 Dry gas, weight percent 1. 5 2. 5 4. 2 3. 6 Butanes, vol. percent.-- 2. 6 6. 5 11.8 10.6 Pentanes, vol. percent 1. 4 4. 9 10.0 6. 7 Lt. naphtha, vol. percent 2. 7 4. 7 9.8 11.2 Hvy. naphtha, v01. percent. 24. 8 35. 5 46. 6 44.1 Fuel oil, vol. percent 74. 2 5G. 8 33. 5 37. 5 Diesel index of fuel oil... 62.1 61. 8 59. 5 72.6

As was noted in the case of the light East Texas gas oil, the cycle operation with the light coker gas oil did not produce all the advantageous results listed hereinbefore. Thus, at any given conversion level, the temperature, the yield of light naphtha, and the yield of heavy naphtha were substantially the same, both in once-through operation and in the cycle operation. There were, however, substantial advantages from the standpoint of lowered dry gas yield and higher diesel index of the fuel oil, in the case in which the cycle operation was used. This will be apparent from the curves in FIGURES 11 and 12. These curves are based upon the data set forth in Table III.

In FIGURE 11, curve 19 shows the relationship between the volume percent conversion into products boiling at temperatures lower than about 390 F. l00-recycle) and the Weight percent of dry gas produced when the virgin light Mid-Continent coker gas oil was cracked in the presence of the platinum-containing catalyst. Curve 20 shows a similar relationship obtained in the case in which the 1:1 blend of cycle stock and virgin coker gas oil was cracked. It will be apparent that considerably less dry gas is produced in the case in which the cracking is carried out in accordance with this invention.

In FIGURE 12, curve 21 shows the relationship between the volume percent conversion into products boiling at temperatures lower than about 390 F. (lOO-recycle) and the diesel index of the fuel oil produced in the case in which the virgin light Mid-Continent coker gas oil was cracked in the presence of the platinum-containing catalyst. Curve 22' shows a similar relationship obtained in the case in which the 1:1 blend of cycle stock and virgin light coker gas oil was cracked. it will be noted that the diesel index of the fuel oil produced by the cycle operation of this invention is much higher than that of the fuel oil produced in a one-through operation.

It will be apparent, therefore, that there are real and distinct advantages in using the process of this invention. In the case of the light gas oils, straight-run or coker, two advantageous results are obtained. In the case of the heavier gas oils, on the other hand, there are a number of advantages over once-through operation, viz., lower operating temperatures, lower dry gas yield, lower light naphtha yield, higher yield of heavy naphtha, and a higher diesel index in the fuel oil.

In so far as is known there is nothing critical about the reaction temperature at which the process of this invention is carried out and it is believed operable at any temperatures, conventional in the art, at which hydrocracking, with a net consumption of hydrogen, will occur. Of course, the reaction temperature should not generally exceed the minimum temperature at which the charge is converted completely into naphtha, since higher temperatures can only crack the naphtha boiling range. material into lower boiling hydrocarbons, including dry gas. For the reaction to proceed at an acceptable rate, it is usually necessary that the reaction temperature exceed about 500 F. Preferably, the reaction temperature should be within the range about 500 F. to about 825 F. and still more preferably within the range 650 F. to about 825 F.

Likewise, in so far as is known, there is nothing critical about the hydrogen pressure employed in this invention and it will operate with any hydrogen pressures which etfect hydrocracking with a net consumption of hydrogen by the charge stock. Very high hydrogen pressures, however, make it necessary to employ very expensive heavy walled reactors. It is, therefore, preferable that the hydrogen pressure be within the range 100 to 2500 pounds per square inch gauge (p.s.i.g.).

The liquid hourly space velocity of the reactant employed in this invention will generally be within the range about 0.1 to about 10 and preferably 0.1 to about 4 voltunes of reactant (measured as 60 F. liquid) per volume of catalyst per hour. The molar ratio of hydrogen to hydrocarbon usually will be within the range about 2 to about 80 and preferably about 5 to about 50.

The process of this invention can be carried out using conventional apparatus and schemes for eifecting recycle operation in catalytic cracking. As the catalyst remains active over long periods of time before it must be regenerated, the operation is advantageously carried out using a fixed bed of catalyst. Other techniques, however, can be used, such as, the moving bed technique or the fluid technique.

Although the present invention has been described with preferred embodiments, it is to be understood that modifications and variations may be resorted to, without departing from the spirit and scope of this invention, as those skilled in the art will readily understand. Such variations and modifications are considered to be within the purview and scope of the appended claims.

We claim:

1. A process for cracking hydrocarbon fractions that has at least one of the following advantages over a oncethrough operation: lower operating temperatures, lower dry gas yield, lower light naphtha yield, higher heavy naphtha yield, and a fuel oil having a higher diesel index, which comprises contacting a mixture of a hydrocarbon fraction having an initial boiling point of at least about 400 F., a 50 percent point of at least about 500 F. and an end-boiling point of at least about 600 F. and boiling substantially continuously between said initial boiling point and said end-boiling point with a cycle stock which is obtained from hydrocracking said initial hydrocarbon i4 fraction and which boils at temperatures higher than about 390 F., in which the volumetric ratio of said cycle stock to said hydrocarbon fraction ranges from about 1:1, respectively, to about 10:1, respectively, with a catalyst comprising about 0.05 percent to about 20- percent, by weight of the catalyst, of at least one metal of the platinum and palladium series deposited upon a synthetic composite of oxides ofat leasttwo metals of the groups HA, 111B and 1V ofthe periodic arrangement of the elements, having an activity index of greater than 25, in the presence of hydrogen in amounts, expressed in a molar ratio of hydrogen to hydrocarbon charge, ranging from about 2 to about 80, pressures of about pounds per square inch gauge to about 2500 pounds per square inch gauge, at a liquid hourly space velocity ranging from about 0.1 to about 10, and at temperatures of about 500 F. to about 825 F.

2. A process for cracking hydrocarbon fractions that has at least one of the following advantages over a oncethrongh operation: lower operating temperatures, lower dry gas yield, lower light naphtha yield, higher heavy naphtha yield, and a fuel oil having a higher diesel index, which comprises contacting a mixture of a petroleum gas oil having an initial boiling point of at least about 400 F., a 50 percent point of at least about 500 F., and an end-boiling point of at least about 600 F., and boiling substantially continuously between said initial boiling point and said end-boiling point, and containing less than about 0.08 percent nitrogen, by weight, with a cycle stock which is obtained from hydrocracking said gas oil, and which boils at temperatures higher than about 390 F, in which the volumetric ratio of said cycle stock to said gas oil ranges from about 1:1, respectively, to about 5:1, respectively, with a catalyst comprising about 0.1 percent to about 5 percent, by weight of the catalyst, of platinum deposited upon a synthetic composite of silica and alumina having an activity index of at least about 28, in the presence of hydrogen in amounts, expressed in a molar ratio of hydrogen to hydrocarbon charge, ranging from about 5 to about 50, pressures ranging from about 350 pounds per square inch gauge to about 2000 pounds per square inch gauge, at a liquid hourly space velocity ranging from about 0.1 to about 4, and at temperatures of about 650 F. to about 835 F.

3. A process for hydrocracking hydrocarbon fractions that has at least one of the following advantages over a once-through operation: lower operating temperatures, lower dry gas yield, lower light naphtha yield, higher heavy naphtha yield, and a fuel oil having a higher diesel index, which comprises contacting a mixture of a hydrocarbon fraction having an initial boiling point of at least about 400 F., a 50 percent point of at least about 500 F. and an end-boiling point of at least about 600 F. and boiling substantially continuously between said initial boiling point and said end-boiling point with a cycle stock which is obtained from hydrocracking said initial hydrocarbon fraction, and which boils above about 390 F., in which the volumetric ratio of said cycle stock to said initial fraction is Within the range of about 0.1 1, respectively, to about 10:1, respectively, with a catalyst comprising about 0.05 percent to about 20 percent, by weight of the catalyst, of at least one metal of the platinum and palladium series deposited upon a synthetic composite of oxides of at least two elements of the groups IIA, lIIB and IV of the periodic arrangement of the elements, having an activity index of greater than 25, in the presence of hydrogen under reaction conditions which produce a a net consumption of hydrogen during the reaction, which conditions include a molar ratio of hydrogen to hydrocarbon charge within the range of about 2 to about 80, a hydrogen pressure above about 100 pounds per square inch gauge, a liquid hourly space velocity within the range of about 0.1 to about 10, and temperatures above about 500 F.

4. The process of claim 3 wherein the hydrocarbon 15 fraction has an initial boiling point of at least about 600 F.

5. The process of claim 3 wherein the volumetric ratio of cycle stock to hydrocarbon fraction contacted is Within the range of about 1:1, respectively, to about 10:1, respectively.

6. The process of claim 3 wherein the activity index of the base of the catalyst is at least 28.

7. The process of claim 6 wherein the hydrocarbon fraction has an initial boiling'point of at least about References titted in the file of this patent UNITED STATES PATENTS Johnson et a1. July 16, 1957 Boedeker et a1. Dec. 2, 1958 Haensel et a1 Sept. 29, 1959 Ciapetta July 19, 1960

Claims (1)

1. A PROCESS FOR CRACKING HYDROCARBON FRACTIONS THAT HAS AT LEAST ONE OF THE FOLLOWING ADVNTAGES OVER A ONCETHROUGH OPERATION: LOWER OPERATING TEMPERATURES, LOWER DRY GAS YIELD, LOWER LIGHT NAPHTHA YIELD, HIGHER HEAVY NAPHTHA YIELD, AND A FUEL OIL HAVING A HIGHER DIESEL INDEX WHICH COMPRISES CONTACTING A MIXTURE OF A HYDROCARBON FRACTION HAVING AN INITIAL BOILING POINT OF AT LEAST ABOUT 400*F., A 50 PERCENT POINT OF AT LEAST ABOUT 500*F.AND AN END-BOILING POINT OF AT LEAST ABOUT 600*F. AND BOLING SUBSTANTIALLY CONTINUOUSLY BETWEEN SAID INITIAL BOILING POINT AND SAID END-BOILING POINT WITH A CYCLE STOCK WHICH IS OBTAINED FROM HYDROCRACKING SAID INITIAL HYDROCARBON FRACTION AND WHICH BOILS AT TEMPERATURES HIGHER THAN ABOUT 390*F., IN WHICH THE VOLUMETRIC RATIO OF SAID CYCLE STOCK TO SAID HYDROCARBON FRACTION RANGES FROM ABOUT 1:1, RESPECTIVELY, TO ABOUT 10:1, RESPECTIVELY, WITH A CATALYST COMPRISING ABOUT 0.05 PERCENT TO ABOUT 20 PERCENT, BY WEIGHT OF THE CATALYST, OF AT LEAST ONE METAL OF THE PLATI-

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