Noble metal hydrocracking catalysts

Details Noble metal hydrocracking catalysts Noble metal hydrocracking catalysts

2000-03-28

2001-01-16

Dunn, Tom (Department: 1754)

Mineral oils: processes and products

Chemical conversion of hydrocarbons

Cracking

C208S111010, C502S064000, C502S066000, C502S074000, C502S079000, C502S087000

Reexamination Certificate

active

06174430

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to manufacture of noble metal hydrocracking catalysts, and the catalysts produced by the process.
BACKGROUND OF THE INVENTION
Petroleum refiners produce desirable products, such as gasoline and turbine fuel, by catalytically hydrocracking high boiling hydrocarbons into product hydrocarbons of lower average molecular weight and boiling point. Hydrocracking is generally accomplished by contacting, in an appropriate reactor vessel, a gas oil or other hydrocarbon feedstock with molecular hydrogen in the presence of a suitable hydrocracking catalyst under appropriate conditions, including an elevated temperature and an elevated pressure, such that a hydrocarbon product is obtained containing a substantial proportion of a desired product boiling in a specified range.
Often, hydrocracking is carried out in the presence of a catalyst containing sulfided Ni—W or Ni—Mo metals. However, these catalysts produce a substantial amount of aromatic content. In some application, such as for jet fuel and diesel as such or as a blend a lower amount of aromatic content is desired.
In order to obtain a lower aromatic content hydrocracked product, noble metal hydrocracking catalyst is being used. However, the conventional noble metal catalysts have a substantial gas make (C
1
to C
4
), thus lowering the desired liquid yield, i.e., within the range of from C
5
to hydrocarbons boiling at about 650° F.
It is desirable to provide a noble metal hydrocracking catalyst which will produce less gas and more liquid products under hydrocracking conditions.
SUMMARY OF THE INVENTION
A noble metal hydrocracking catalyst is provided, comprising:
a) from about 70 to about 90 weight percent of a Y zeolite, based on the catalyst having a silica to alumina mole ratio of from about 4.8 to less than 6.0, a unit cell constant within the range of about 24.50 to about 24.57, a Na
2
O level of less than or equal to about 0.2 weight percent;
b) from about 10 to about 30 weight percent, based on the catalyst of an alumina having a mercury intrusion pore volume within the range from about 0.55 to about 0.85 cc/g; and
c) from about 0.5 to 1 weight percent, based on the catalyst of a noble metal; wherein said hydrocracking catalyst have a dispersivity of the noble metal of equal or greater than about 50% by hydrogen chemisorption measurement, a surface area of kreater than or equal to 700 m
2
/g by BET surface area measurement, a compacted bulk density within the range of from about 0.40 to 0.58 g/cc, and a mercury pore volume within the range of from about 0.4 to about 0.7 ml/g.
Further, methods to prepare the noble metal hydrocracking catalyst is provided.
DETAILED DESCRIPTION OF THE INVENTION
It has been found that a noble metal hydrocracking catalyst which produces more desirable liquid product and less gas make (i.e., C
1
-C
4
hydrocarbons), preferably at most 11 weight percent can be prepared by the steps comprising:
a) ion exchanging a noble metal on a ultrastable Y zeolite powder by contacting a noble metal salt solution with the zeolite powder, preferably at a pH within the range of about 8.0 to about 8.5, for a time sufficient to exchange the noble metal ion to the zeolite to produce a noble metal containing Y zeolite powder;
b) extruding the noble metal containing-Y zeolite powder with alumina, water, at least one peptizing aid, and at least one extrusion aid to produce an extrudate; and
c) drying and calcining the extrudate at a temperature within the range of about 450° C. to about 550° C. to produce the noble metal hydrocracking catalyst.
The ultrastable Y zeolite powder useful in the invention are Y zeolite having silica to alumina mole ratio of from about 4.8, preferably from about 5.0, to below 6.0, preferably to about 5.8, more preferably to about 5.4. The unit cell constant of the powder is with the range of from about 24.50, preferably from about 24.52, to about 24.57, preferably to about 24.55. The preferred ultrastable Y zeolite powder have sodium level of less than or equal to about 0.25, preferably less than or equal to about 0.20 weight percent, calculated as Na
2
O. The surface area of the zeolite is preferably within the range of from about 750, more preferably from about 780, to about 830, to more preferably to about 810 m
2
/g. The surface area is determined by BET measurement at a relative pressure, p/p
0
, of 0.01 to 0.05.
Preferred catalysts have high total acid site concentrations (Bronsted and Lewis acid sites) of at least 650 micromoles/gram, preferably at least 680 micromoles/gram, to preferably less than 1000 micromoles/g, more preferably less than 800 micromoles/g, as measured by titration of the catalyst with pyridine, the titration of the acid sites being followed by the measuring the integrated intensities of the infrared absorption peaks in the hydroxyl group stretching region. The method for determining acid site concentrations by adsorption of ammonia at temperatures in the range 200 to 400° C. is described in the following publications: 1) M. A. Makarova and J. Dwyer,
Journal of Physical Chemistry,
1993, 97, 6337; and 2) M. A. Makarova, A. Garforth, V. L. Zholobenko, J. Dwyer, G. J. Earl and D. Rawlence in
Zeolites and Related Microporous Materials: State of the Art
1994, Studies in Surface Science and Catalysis, Vol. 84, 1994, Elsevier Science B.V., p. 365. The technique for acid site characterization with pyridine is similar to that described for ammonia in the indicated publications except for substitution of pyridine for ammonia.
The ultrastable Y zeolite (USY) used in the preparation of the catalyst of the invention can be made by at least partially ion-exchanging a sodium Y zeolite to reduce the level of sodium to about 3 weight percent of Na
2
O, based on the zeolite, by conventional ion-exchange method (ion-exchange step) then heating the zeolite in the presence of stream at a partial pressure of 0.2 to 1.0 atmospheres at a temperature range of 600 to about 800° C., (steam calcination step). The ion-exchange is typically carried out by mixing the zeolite with an aqueous solution containing a dissolved ammonium salt, such as ammonium nitrate, ammonium sulfate, ammonium chloride, and the like, then stirring the resulting slurry for between about 0.5 to about 4 hours at a temperature above ambient but less than about 100° C. For a lower level of sodium content these steps are repeated at least once. The steam calcined zeolite is then ammonium ion-exchanged again to lower the Na
2
O content to the desired range of less than about 0.20 percent. U.S. Pat. No. 5,059,567 discloses these ultrastable Y-zeolites (USY) useful for the invention, the disclosure of which is hereby incorporated by reference.
Binders useful in the invention are aluminas, such as pseudoboehmite, gamma and bayerite aluminas. These binders are readily available commercially and are used to manufacture alumina-based catalysts. LaRoche Chemicals, through its VERSAL® family of aluminas and Vista Chemical Company, through its CATAPAL® aluminas, Criterion Catalyst Company, through its HMPA aluminas, provide suitable alumina powders which can be used as binders in preparing the instant catalysts. The preferred alumina has a mercury intrusion pore volume within the range of from about 0.55, preferably from about 0.65, to about 0.85 to about 0.76 cc/g. Preferred alumina binders to be used in the preparation of the catalyst, particularly when extrusion is utilized, are the high-dispersity alumina powders. Such high-dispersity aluminas have a dispersity index of greater than 50% in a aqueous acid dispersion having an acid content of 0.4 milligram equivalents of acid (acetic) per gram of Al
2
O
3
. Such high-dispersity aluminas are exemplified by Vista's CATAPAL® D alumina and Criterion's HMPA alumina.
The noble metal salts can be palladium salts or platinum salts. The palladium salts are preferred. The palladium salts used in the invention preferably include, for example, organic amine complex salts and chloride salts such as palladium ammonium nitrate, pallad

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