Process for hydrocracking cycle oil

Details Process for hydrocracking cycle oil Process for hydrocracking cycle oil

1993-12-20

2001-05-01

Wood, Elizabeth (Department: 1755)

Mineral oils: processes and products

Chemical conversion of hydrocarbons

Cracking

C208S106000, C208S107000, C208S108000, C208S113000, C208S121000

Reexamination Certificate

active

06224748

ABSTRACT:

FIELD OF THE INVENTION
The process of the present invention relates to a process for hydrocracking cycle oils and other highly aromatic feeds using a catalyst comprising a hydrogenation/dehydrogenation component, such as a noble metal, and an acidic solid component comprising a Group IVB metal oxide modified with an oxyanion of a Group VIB metal.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,676,887 discloses refining of petroleum hydrocarbons to product motor fuels and other products. The process described in U.S. Pat. No. 4,676,887 operates by hydrocracking a highly aromatic feed which is produced by catalytic cracking of a suitable petroleum fraction, usually a vacuum gas oil. During the catalytic cracking the dealkylation processes characteristic of the catalytic cracking process remove alkyl groups from the polyaromatic materials in the feed to produce the gasoline as the main product together with various other higher boiling fractions. A highly aromatic distillate fraction formed in the cracking and boiling from about 400° F. to 750° F. (about 205° to 400° C.), generally referred to as cycle oil, forms a preferred feed for the subsequent hydrocracking step which converts the bicyclic aromatics (naphthalenes) in the oil under relatively mild conditions to monocyclic aromatics in the gasoline boiling range. In this way, the cycle oil from the cracking process is converted to a gasoline range product, which, being highly aromatic, has a high octane value and can therefore be incorporated directly into the refinery gasoline pool without the need for subsequent reforming. The process uses relatively mild conditions e.g., hydrogen pressure under 1000 psig, (about 7000 kPa abs) and moderate conversion coupled with an acceptably low catalyst aging rate so that long cycle durations may be obtained. Reference is made to U.S. Pat. No. 4,676,887 for a detailed description of the process.
As mentioned above, a cycle oil from the catalytic cracking step is used as the feed to the hydrocracking step and usually a light cycle oil boiling approximately in the range of 400° to 700° F. (about 205° to 400° C.) is suitable. However, if a light cut-light cycle oil with an end point of not more than about 650° F. (345° C.), preferably not more than about 600° C. (about 315° C.) is used, it is possible to operate at higher conversion levels without a concomitant increase in hydrogen pressure while still maintaining an acceptable aging rate in the catalyst. In addition, the octane rating of the hydrocracked gasoline is higher. Thus, by suitable choice of the hydrocracker feed, an extended range of operating conditions may be utilized while improving product quality. The use of the light cut light, cycle oil in this process is disclosed in U.S. Pat. No. 4,738,766, to which reference is made for a detailed disclosure of the process.
Because the hydrocracking is operated under relatively low hydrogen pressure, conversion is maintained at a relatively moderate level in order to maintain catalyst aging at an acceptable rate. One consequence of this is that the effluent from the hydrocracker contains significant quantities of unconverted material, i.e. products boiling above the gasoline boiling range. The hydrocracking step has effected a removal of a significant amount of the heteroatom containing impurities in the cycle oil feed and this is reflected by relatively low sulfur and nitrogen contents in the gasoline conversion product as well as in the higher boiling fractions. In addition, some of the higher boiling fractions have undergone hydrogenation to form more readily crackable components, and for this reason a useful aspect of the process is in the recycle of the unconverted hydrocracker bottoms to the catalytic cracking unit. A process of this type is disclosed in U.S. Pat. No. 4,789,457 to which reference is made for a detailed description of the process.
We have now found that solid acid catalysts comprising a Group IVB metal oxide modified with an oxyanion of a Group VIB metal may be used as hydrocracking catalysts for cycle oil and other highly aromatic feeds. It is an object of the present invention to provide a hydrocracking process using a catalyst which results in significant boiling range conversion of heavier cycle oil components to lighter liquids and with low production of C
1
-C
4
gases.
SUMMARY OF THE INVENTION
There is described herein a catalytic process for hydrocracking heavy, high aromatic content feeds, such as cycle oil. Processing a light cycle oil feed over a catalyst comprising a Group IVB metal oxide modified with an oxyanion of a Group VIB metal results in significant boiling range conversion, particularity of heavier cycle oil components (600° F.+) to lighter liquids. Under the hydrocracking process of the present invention only small amounts of light gases are formed. Hydrogen enrichment and preservation of the upgraded liquid products have also been found using the catalyst of the present invention.
The invention therefore includes a process for hydrocracking a hydrocarbon feedstock having an initial boiling point above about 400° F. and an aromatic content greater than about 50 wt. % comprising hydrocracking the hydrocarbon feedstock in the presence of hydrogen at a pressure of at least about 1000 psig in the presence of a catalyst composition comprising
a hydrogenation/dehydrogenation component and an acidic solid component comprising a Group IVB metal oxide modified with an oxyanion of a Group VIB metal.
DETAILED DESCRIPTION OF THE INVENTION
Feedstocks
The feed to the process is a highly aromatic stream such as a light cycle oil produced by catalytic cracking, usually by the fluid catalytic cracking (FCC) process. The feedstock will have a hydrogen content no greater than 12.5 wt. % and an API gravity no greater than about 25, usually no greater than about 20 and an aromatic content no less than about 50 wt. %. Typically the feed will have an API gravity of 5 to 25, a nitrogen content of 50 to 650 ppm and will contain 8.5 to 12.5 wt. % hydrogen. The boiling range of the feedstock will usually be from about 400 to 800° F. (205 to 370° C.), more commonly 400 to 700° F. (205 to 370° C.). Suitable feeds include, but are not limited to, light cycle oil (LCO) and heavy cycle oil (HCO) from catalytic crackers, lube extracts, and coker gas oils.
The hydrocarbon feedstock can be treated prior to hydrocracking in order to reduce or substantially eliminate its heteroatom content. As necessary or desired, the feedstock can be hydrotreated under mild or moderate hydroprocessing conditions to reduce its sulfur, nitrogen, oxygen and metal content. Generally, a hydrocarbon feedstock used in hydrocracking should have a low metals content, e.g., less than about 200 ppm, in order to avoid obstruction of the catalyst and plugging of the catalyst bed. The mild to moderate hydrotreating conditions employed include pressures of from about 2 to about 21 MPa and H
2
consumptions of from about 20 to about 280 m
3
/m
3
. Conventional hydrotreating process conditions and catalysts can be employed, e.g., those described in U.S. Pat. No. 4,283,272, the contents of which are incorporated by reference herein.
Catalyst
The catalyst used in the process of the present invention comprises an oxide of a Group IVB metal, preferably zirconia or titania. This Group IVB metal oxide is modified in two ways. According to one modification, the Group IVB metal oxide is modified with an oxyanion of a Group VIB metal, such as an oxyanion of tungsten, such as tungstate. The modification of the Group IVB metal oxide with the oxyanion of the Group VIB metal imparts acid functionality to the material. The modification of a Group IVB metal oxide, particularly, zirconia, with a Group VIB metal oxyanion, particularly tungstate, is described in U.S. Pat. No. 5,113,034; in Japanese Kokai Patent Application No. Hei 1 [1989]-288339; and in an article by K. Arata and M. Hino in
Proceedings
9
th International Congress on Catalysis,
4, 1727-1735 (1988), the entire disclosures of these publications are

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