Mineral oils: processes and products – Chemical conversion of hydrocarbons – With preliminary treatment of feed
Reexamination Certificate
1999-01-08
2001-01-30
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
With preliminary treatment of feed
C208S086000, C208S108000, C208S211000, C208S212000
Reexamination Certificate
active
06179995
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to an integrated process for upgrading a residuum feedstock by hydrotreating and hydrocracking using a common hydrogen supply system.
Some progress has been made in developing methods for using a single hydrogen loop in a two-stage reaction process. U.S. Pat. No. 5,009,768 teaches hydrodemetallizing a high-residual vacuum gas oil and hydroconverting the product from the first reaction zone at deep denitrogenation conditions in a second reaction zone. Cycle oil from an FCC may be added to the feed to the second reaction zone. U.S. Pat. No. 4,283,271 and U.S. Pat. No. 4,283,272 teach processes for making lubricating oil which include passing a suitable hydrocarbon feed and hydrogen sequentially through a hydrocracking zone, a catalytic dewaxing zone and a hydrotreating zone, all at high pressure and in that order, with purification of the hydrogen gas prior to passage to the dewaxing zone.
EP 787,787 discloses a hydroprocess in parallel reactors, with hydrogen flowing in series between the reactors. Effluent from a first reaction zone is separated into a first hydrogen rich gaseous stream and a first hydroprocessed product stream. The first hydrogen rich gaseous stream is shown as being used as quench for a second reaction zone. The first hydrogen rich gaseous stream is also combined with a second hydrocarbon feedstock and fed to the second reaction zone, at a lower hydrogen partial pressure than is the first reaction zone. Effluent from the second reaction zone is separated, the second hydrogen rich gaseous stream being recycled to the first reaction zone, both as a quench stream and as a reactant in combination with a first hydrocarbon feedstock.
Other methods have been proposed for separating partially reacted reactants within a reactor, removing one of the reacting streams (generally either a liquid or a vapor stream) and continuing reaction of the remaining stream. For example, U.S. Pat. No. 5,403,469 teaches a two-stage hydrocracking process, with denitrification being accomplished in the first conversion zone and cracking conversion being accomplished in the second conversion zone. U.S. Pat. No. 3,172,836, a liquid-vapor separation zone is located between two catalyst beds for withdrawing a normally gaseous fraction and a normally liquid fraction from a first catalyst bed. The normally gaseous fraction, along with a second normally liquid fraction, is then passed downwardly through a second catalyst bed. The normally liquid fraction passed through the second catalyst bed may be a liquid fraction recovered from a distillation of the effluent from the first catalyst bed. In U.S. Pat. No. 4,615,789 a liquid/vapor separator is utilized between catalyst beds to remove liquid from between the beds and permit vapor separated by the separator to pass through catalyst beds below the separator.
U.S. Pat. No. 5,603,824 teaches a reactor having at least a top bed containing a hydrocracking catalyst and a bottom bed containing a dewaxing catalyst. A hydrocarbon feed mixture is separated, with the heavier stream being hydrocracked in the top bed of the reactor and the lighter stream combined with the effluent from the top bed and the combination catalytically dewaxed in the bottom bed.
However, further improvements for reducing refinery operating costs using common hydrogen supply systems are desired.
SUMMARY OF THE INVENTION
Residuum feedstocks typically contain significant amounts of sulfur, nitrogen and highly unsaturated complex molecules termed “asphaltenes”. The residuum feedstocks may also contain metal compounds, e.g. nickel and vanadium in particular with sometimes lesser amounts of other metals such as calcium, magnesium and iron. These contaminants are detrimental to many refinery processes, and especially to many catalytic processes. Therefore, it is imperative that these contaminants be removed from the residua prior to further processing, and that downstream catalysts not be degraded by contact with these contaminants.
The present invention is directed to a process for upgrading a residuum petroleum feedstock to useful finished products such as fuels or lubricating oil base stocks. In such a process, a number of upgrading steps are generally required. Hydrotreating, for example, removes metals from the feedstock, saturates olefins and aromatics, converts asphaltenes and removes sulfur and nitrogen. Specialized catalysts are required for converting the complex residuum molecules, many of which contain these contaminants. Asphaltenes are large, complex, asphaltic-type molecules with relatively low solubility, particularly in conversion products from a residuum conversion process. During processing, unconverted asphaltenes tend to precipitate and form plugs and obstructions in process equipment, in process lines, and on catalyst surfaces.
For processing a residuum to make fuels or lubricating oil base stocks, it is desirable to further reduce the molecular weight of a hydrotreated residuum by hydrocracking. However, residual amounts of asphaltenes in the hydrotreated residuum, or carried over in the hydrogen recovered from a residuum hydrotreating unit, quickly deactivate the hydrocracking catalyst, making conventional hydrocracking of a hydrotreated residuum difficult and expensive.
This problem is frequently addressed in conventional process by providing separate and distinct processes hydrotreating and hydrocracking processes, each with an independent and separate hydrogen system. Each system includes hydrogen recovery from the reactor effluent, hydrogen purification to remove ammonia, hydrogen sulfide and other contaminants, and hydrogen compression to return the hydrogen to reactor pressure for recycle. Having the two independent systems addresses the catalyst contamination problem, but at high equipment and operating cost.
It is desirable to have an integrated system for hydrotreating and hydrocracking a residuum feedstock at reduced risk of contaminating the hydrocracking catalyst while avoiding the duplication of a dual hydrogen recycle and recovery system.
Accordingly, the present invention is directed to an integrated hydroconversion process comprising:
contacting a residuum feedstock with a hydrogen-rich gaseous stream in a hydrotreating reaction zone to form a hydrotreated liquid product having reduced asphaltene content and a gaseous hydrotreater effluent;
fractionating the hydrotreated liquid product to recover at least a desulfurized VGO fraction;
contacting a VGO feed with a gaseous hydrocracker feed stream in a hydrocracking reaction zone, at hydrocracking conditions sufficient to effect a boiling range conversion of the VGO feed, to produce at least the hydrogen-rich gaseous stream and a liquid hydrocrackate;
passing the hydrogen-rich gaseous stream to the hydrotreating reaction zone for contacting with the residuum feedstock;
fractionating the liquid hydrocrackate to recover at least a VGO product stream; and
combining the desulfurized VGO fraction with at least a portion of VGO product stream to form the VGO feed for contacting in the hydrocracking reaction zone.
In a preferred process, the hydrotreated gaseous effluent is purified in a recycle gas purifier to produce a purified recycle gas. The purified recycle gas is available as one of the sources of the gaseous hydrocracker feed stream, as one of the sources of quench fluid for the hydrotreating reaction zone, and/or as one of the sources of quench fluid for the hydrocracking reaction zone.
In the preferred process the hydrogen-rich gaseous stream recovered from the hydrocracking reaction zone is passed to the hydrotreating reaction zone at substantially the same temperature and at substantially the same pressure as the hydrocracking reaction zone. Under operating conditions such that the hydrotreating reaction zone is maintained at a temperature below that of the hydrocracking reaction zone and/or at a pressure below that of the hydrocracking reaction zone, the hydrogen-rich gaseous stream, in this preferred process, is reduced in tempera
Armstrong Martin J.
Cash Dennis R.
Chevron U.S.A. Inc.
Griffin Walter D.
Klaassen Alan W.
Nguyen Tam M.
Prater Penny L.
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