US3549515A - Hydrocracking process for high end point feeds - Google Patents

Description

Dec. 22., Y1970 A. J. BRAINARD ETAL 3,549,515 HYDRocRAcKING PRocEss AFOR HIGH END POINT FEEDS Filed June 1. 1967 PATENI ATORNEY United States Patent Office Patented Dec. 22, 1970 3,549,515 HYDROCRACKING PROCESS FUR HIGH END POINT FEEDS Alan J. Braiuard, Pittsburgh, Pa., and Glen Porter Hamner, Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed June 1, 1967, Ser. No. 642,927 Int. Cl. C10g 13/00, 23/00 U.S. Cl. 208-89 8 Claims ABSTRACT OF THE DISCLOSURE High end point petroleum oils are hydrofined, then hydrocracked in two stages with fractionation following each hydrocracking stage. A bottoms fraction from the first hydrocracking stage fractionator is recycled to the hydrofiner and a bottoms fraction from the second hydrocracking stage fractionator is recycled to the second hydrocracker.

This invention relates to a process for hydrocracking high end point feeds in a two-stage process with prehydrofining of the feed. More particularly the invention relates to selective hydrocracking employing a crystalline alumino-si1icate zeolite in conjunction with a platinum group metal hydrogenation component in the first hydrocracking stage.

As the market for fuels such as motor gasoline and jet fuels increases, petroleum refiners are seeking a hydrocracking process which will efiiciently handle high end point feeds. Such a process would be designed to hydrocrack petroleum derived fractions containing at least 20 wt. percent of materials boiling above 750 F. and having an end point above 1000 F. to fuels fractions boiling in the range of C5-500 F. The process would feature high throughput, a minimum of C4 and lighter products, and a minimum of bottoms product boiling above the fuels range.

Recently, a superior hydrocracking catalyst has been introduced to commercial use which has higher activity, improved selectivity to fuels products and a better resistance to catalyst poisons. This catalyst comprises a platinum group metal, e.g. palladium incorporated with a crystalline alumino-silicate zeolite. This type of catalyst provides excellent hydrocracking results with stocks boiling in the range of about 300-750 F. However, even with the new catalyst it has not been possible to obtain both high activity and long hydrocracking runs with high end point feeds.

It has now been found that when the process streams are handled in a certain manner, high end point feeds can be hydrocracked over long periods without rapid loss of activity and selectivity.

In brief summary the invention comprises the combination of steps comprising hydrofining a high end point petroleum feedstock at mild hydrofining conditions, hydrocracking the hydroiined feed at mild conditions in the presence of a catalyst comprising a platinum group metal incorporated with a crystalline alumino-silicate zeolite, fractionating the first stage hydrocrackate to obtain a low end point second stage hydrocracking feed boiling in the range of from about 350-400" F. to about 725-775 F., and containing less than about l p.p.m. nitrogen and less than about 5 wt. percent polycylic aromatics, recycling material boiling above about 725e775 F. to the hydrofiner, hydrocracking the low end point feed in a second hydrocracking stage at mild conditions in the presence of a selective but nitrogen sensitive catalyst, recovering parafnic fuel fractions and recycling material boiling above the fuels boiling point range to extinction in the second stage hydrocracker.

Further details of the process will be described below with reference to the drawing which is a flow sheet illustrating a preferred embodiment of the invention.

The petroleum feedstock treated in the process of the invention is characterized by a greater proportion of high boiling materials than a conventional hydrocracking feed. The feed contains from 0.2-4.0 wt. percent sulfur and from 50-4000 p.p.m. nitrogen. Some of the nitrogen is in heavy organic ring compounds boiling above about 750 F. which are not hydrocracked at first pass conditions. The feed is further characterized by an aromatic content of at least 20 Wt. percent, usually in the range of 20-50 wt. percent. Many of the aromatics are polycyclic aromatics i.e., 15-30 wt. percent. Some aromatics contain sulfur and nitrogen in the ring structure. The feed boils in the gas oil boiling range, i.e., 400-l050 F. However, at least 20 wt. percent and usually 20-50 wt. percent of the feed boils at a temperature above 750 F. Most feeds have an end point above 1000 F., and thus they contain a high proportion of materials which will lay coke down on the catalyst unless measures are taken to prevent this. Specific feeds include cycle oils from thermal and catalytic cracking, coker gas oils, heavy virgin gas oils, and blends of these. The feed may also contain steam cracked fractions, coker naphtha and other fractions which must be hydrocracked under mild conditions to prevent coke formation.

Referring to the drawing, a feed containing at least 50 ppm. nitrogen and at least 0.2 Wt. percent sulfur and boiling in the range of 400-1050 F. is passed by line 1 to hydrofiner 2. Hydrofining is carried out at mild conditions to avoid any substantial cracking of the feed. Hydrogen from line 3 is mixed with the feed and the reaction is preferably conducted in essentially the liquid phase with the reaction mixture passing downwardly over one or more fixed beds of a suitable hydrogenation catalyst. Typical hydrofining conditions are set forth below.

TABLE L I-IYDROFINING CONDITIONS Suitable hydrolining catalyst include salts of metals of Group VI and VIII of the Periodic Table such as the oxides and/ or sulfides of cobalt, molybdenum, iron, nickel, tungsten and mixtures thereof. The metal salts are supported on a suitable porous support material such as alumina, silica alumina, bauxite, magnesia and the like. The preferred catalyst is one containing cobalt molybdate on silica stabilized alumina.

Employing the conditions described, the nitrogen content of the feed will be reduced to less than 50 ppm. organic nitrogen. The hydrofiner efiiuent is preferably fed directly by line 4 to the first stage hydrocracker 5 without condensation of vapors or removal of HZS or NH3. In reactor S the hydrofined feed is hydrocracked at mild conditions in the presence of a crystalline alumino-silicate zeolite composited with a platinum group metal.

Because of the ability of these zeolite materials to selectively adsorb molecules on the basis of their size and shape, they have often been referred to as molecular sieves. The various types of molecular sieves may be classified according to the size of the molecules which will be rejected (i.e., not adsorbed by a particular sieve) which of course will be directly related to the diameter of the pore openings. These zeolite materials have been extensively described in the patent literature; for example,

U.S. Pats. Nos. 3,0l3,98286 describe a number of synthetic zeolites, and designate them as Zeolites A, D, $11771 LRi 66s,!) LGTJ, 6X, LY-l In general, those crystalline alumino-silicate zeolites which have been found useful in hydrocracking processes are represented by the following molar formula:

wherein M is selected from the group consisting of metal cations and hydrogen, n is its valence, and x is a number from about 1.5 to about l2. They will usually have uniform pore openings of about 6 to l5, preferably 10 to 13 angstrom units in diameter. The processes for producing these materials are well known in the art. They typically involve crystallization from reaction mixtures containing alumina, silica, alkali metal oxide, and water, all supplied by suitable source materials. A type of synthetic zeolite which has recently gained wide acceptance as a hydrocracking catalyst support because of its greater stability and higher activity is the synthetic faujasite variety, wherein x in the above formula is about 2.5 to 7, preferably 3 to 6, most preferably 4 to 5.5. The material has a crystal structure similar to the natural mineral faujasite and can be prepared by the procedure described in U.S. Pat. No. 3,130,007 ywhich refers to it as Zeolite Y. Other types of Zeolitic materials have also been found useful in hydrocracking processes. For example, synthetic mordenite has the capability of admitting aromatics into its pores, and will therefore be suitable.

For use as catalytic agents suitable in hydrocarbon conversion processes such as hydrocracking, the zeolites are usually subjected to cation exchange to reduce their alkali metal oxide content to less than about 10 wt. percent, preferably less than about 5 wt. percent. Conventionally, the alkali metal oxide content has been reduced by ion exchange treatment with solutions of ammonium salts, or salts of metals in Groups I to VIII or the rare earth metals, preferably metal in Groups II, III, IV, V, VI-B, VII-B, VIII and the rare earth metals. Mixtures of these cations have also been employed. For hydrocracking purposes, the hydrogen and/or magnesium form of these zeolites has been preferred. After suitable ion exchange, the modified crystalline zeolite is composited with a metallic hydrogenation component such as a platinum group metal for use as a hydrocracking catalyst. This may be accomplished by treatment with a platinum or palladium salt or ammonium complex, e.g. platinous tetraaminodichloride, ammonium chloroplatinate, palladium chloride, etc. Incorporation of the hydrogenation component may be accomplished by any conventional technique such as ion exchange followed by reduction, impregnation, etc. When palladium is employed, the exchanged aluminosilicate is preferably impregnated Iwith an ammoniacal solution of palladium chloride-suflcient to produce the desired amount of hydrogenation metal in the final product, and then dried and calcined at a temperature of 800 to 1000 F. Reduction of the metal is then accomplished either separately or in the hydrocracking reaction, per se. The amount of hydrogenation component may range from about 0.1 to about 25 wt. percent based on the weight of the nal product. In the case of platinum group metals, e.g. palladium, the preferred amount will be in the range of about 0.1 to 2, e.g., 0.3 to 1.0 wt. percent based on dry catalyst.

The rst stage hydrocracking is carried out at mild conditions like those set forth below.

TABLE II.-FIRST STAGE HYD ROCRACKING CONDITIONS At these conditions 50-60 wt. percent conversion of the feed is obtained. Conventional catalysts on amorphous silica alumina bases cannot achieve these high conversions at pressures below 1500 p.s.i.g. Effluent from the first hydrocracker is passed by line 6 to high pressure separator 7. From the separator a gas stream containing H2, HZS and NH3 is recycled by lines 8 and 9 to line 3 for use in the hydroner. A portion of the recycle gas can be purged by line 10. If desired this gas can be purified by known means and recycled to one of the units. Cracked feed is passed by line 11 to the first fractionator designated by reference numeral 12. A gas and light ends stream is removed overhead from the fractionator by line 13. A naphtha fraction boiling in the range of C5-375" F. is removed by line 14. A second stage hydrocracker feed boiling in the range of 350-750 F. is passed by line 15 to second stage hydrocracker 16. The initial boiling point and the end point of the hydrocracker feed can be varied over the range of 350 to 440 F. and 700 to 750 F., respectively. The feed `will contain less than l0 p.p.m. nitrogen. A bottoms fraction boiling above the end point of the feed to hydrocracker 16, i.e., preferably above about 750 F. is recycled by line 17 and 1 to hydroiiner 2. The recycle stream contains essentially all of the heavy organic nitrogen compounds in the effluent from the first hydrocracking stage.

Hydrocracker 16 is also operated at mild hydrocracking conditions as set forth below.

TABLE IIL-SECOND STAGE I-IYDROCRACKING C ON DIT ION S Broad Preferred range rango 450-700 550-675 20D-2, 000 500-1, 500 0.2-10.0 0. .0 11g/oil ratio, s.c.f./b 2, OOO-20, 000 4, OOO-10, 000

material from the second fractionator it is also possible to use other hydrogenation metal components on the molecular sieve base. Metals of Groups VI-B and VIII-B, particularly molybdenum, tungsten, cobalt, nickel and combinations of these metals. The most preferred combinations of these metals are nickel with molybdenum and nickel with tungsten. From 10-30 wt. percent of the hydrogenation component is distended on the sieve base. The catalyst is preferably sulfided prior to use.

Eflluent from hydrocracker 16 is passed by line 18 to high pressure separator 19. A gas stream containing H2, H28 and NH3 is passed overhead from the separator by line 20 for recycle by lines 21 and 22. Makeup hydrogen is supplied by line 22. If desired a part of the recycle gas can `be purged through line 23 or the gas can be purified by known means and then recycled. Hydrocrackate is passed by line 24 to a second fractionator 25. A gas and light ends fraction is recovered overhead by line 26. A paraffinic naphtha fraction preferably boiling in the range of C5-375" F. for motor fue] is recovered by line 27. A jet fuel fraction, preferably boiling in the range of 375-500 F. is recovered by line 28. Line 29 is employed to recycle a bottoms fraction boiling above about 500 F., and is continuously recycled to the second hydrocracker. Thus, all the liquid products of the process are fuels components and all materials boiling above about 500 F., i.e., 450- 5 50 F., are recycled to extinction.

It can `be seen that the feed and the recycle stream to the second hydrocracker must be very low in heavy or- S ganic nitrogen compounds if the second stage hydrocracker catalyst must have high activity at mild hydrocracking conditions for long periods of time. According to the invention this result is accomplished by recycling a bottoms fraction containing the heavy organic nitrogen cornpounds and polycyclic aromatic coke formers lfrom the first stage hydrocracker to the hydroiiner and by operating all units at mild conditions. The process thus provides a maximum quantity of the desired fuels products from a high end point feed.

What is claimed is: 1. In a process for converting a high end point petroleum hydrocarbon feed boiling above the gasoline range and containing nitrogen and sulfur compounds, wherein is included the steps of passing said feed to a catalytic hydrofining zone and hydrofining the feed at a temperature in the range of about 600-725 F., a pressure in the range of about 500-1500 p.s.i.g. in the presence of a hydrogen containing gas, passing the hydrofiner eliluent directly to a first hydrocracking zone and hydrocracking the feed in the presence of a hydrogen containing gas and a catalyst comprising a crystalline alumino-silicate zeolite combined with a platinum group metal at mild hydrocracking conditions including a temperature of about 600- 850 F. and a pressure of about 1000-1500 p.s.i.g.,

passing the lirst stage hydrocracking effluent to a fractionation zone, splitting the effluent into a plurality of fractions, one a suitable hydrocracking feedstock,

passing the said hydrocracking feedstock to a second hydrocracking zone and hydrocracking the feedstock in the presence of a hydrogen containing gas and a hydrocracking catalyst comprising a crystalline alumino-silicate zeolite combined with a metal selected from the group consisting of Group VI-B, Group VIII-B and mixtures thereof at mild hydrocracking conditions including a temperature in the range of about 400-650" F. and a pressure in the range of 500-1500 p.s.i.g.,

the improvement comprising providing separate and distinct distillation zones for receipt of the product from each of the hydrocracking zones,

passing the first stage hydrocracking effluent to the iirst of the fractionation zones, recovering a nitrogencontaining bottoms fraction from said lirst fractionation zone having an initial boiling point in the range of about 725-775 F.

continuously recycling said nitrogen-containing bottoms fraction directly to the said hydrofining zone,

recovering also, in the first fractionation zone, a low end point second stage hydrocracking feedstock boi1- ing in the range of 350-775" F. and containing less than p.p.m. nitrogen,

passing the said low end point second stage hydrocrackr ing feedstock to the second hydrocracking zone,

passing the hydrocracked eliiuent from the said hydrocracking zone to the second distillation zone,

recovering a relatively nitrogen free bottoms fraction from said second fractionation zone having an initial boiling point in the range of about 500 F.,

continuously recycling said relatively nitrogen free bottoms fraction directly to said second hydrocracking zone,

whereby the high end point feed, having at least about 20 Wt. percent 0f materials boiling above about 750 F., fed initially to the hydrofining zones are converted to f-uel fractions which are recovered from both fractionation zones as products.

2. Process according to claim 1 in which a major proportion of the said nitrogen compounds are heavy organic ring compounds boiling above about 750 F.

3. Process according to claim 1 in which said feed contains l5-30 wt. percent polycyclic aromatics.

4. Process according to claim 1 in which said feed is a cycle oil-gas oil mixture boiling in the range of 400 1050 F.

5. Process according to claim 1 in which the hydrogenation component of the catalyst in both hydrocracking stages is palladium.

6. The process of claim 1 wherein the high end point feed fed to the hydrofining zone is characterized as a petroleum hydrocarbon feed having an end point above l000 F. containing 50-4000 p.p.m. nitrogen and 0.2-4.0 wt. percent sulfur, and l5-30 wt. percent polycyclic aromatics.

7. The process of claim 1 wherein the catalyst of the hydrofining zone is characterized as a cobalt molybdate on silica alumina catalyst, the catalyst of the first hydrocracking zone is characterized as a crystalline aluminosilicate zeolite combined with palladium, and the catalyst of the second hydrocracking zone is characterized as a hydrocracking catalyst comprising palladium on Zeolite Y 8. The process of claim 1 wherein the fuels fractions which are recovered from the fractionation zones are char acterized as fuel fractions boiling in the range of C5 to about 500 F.

References Cited UNITED STATES PATENTS 3,203,889 8/ 1965 Pollitzer et al. 208-57 3,159,568 12/1964 Price et al. 20S-89 '3,256,177 6/1966 Tulleners et al. 208-89 DELBERT E. GANTZ, Primary Examiner R. M. BRUSKIN, Assistant Examiner u s. c1. xn. 20s-59

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