Mineral oils: processes and products – Chemical conversion of hydrocarbons – Plural serial stages of chemical conversion
Reexamination Certificate
1999-01-08
2001-05-01
Yildirim, Bekir L. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Plural serial stages of chemical conversion
C208S097000, C208S107000, C208S142000
Reexamination Certificate
active
06224747
ABSTRACT:
BACKGROUND OF THE INVENTION
Much of refinery processing involves reaction of refinery streams in a hydrogen atmosphere. In order to maximize conversion efficiencies and to maintain catalyst life, excess hydrogen is generally used in the catalytic conversion processes, with the unreacted hydrogen being recovered, purified and repressurized for use as a recycle stream. Such recycle processes are costly, both in energy and in equipment. 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. A 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 a 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 787787 teaches hydroprocessing in parallel reactors, while hydrogen flows in series between the reactors.
U.S. Pat. No. 3,328,290 to Hengstebeck teaches combining the effluent from a hydrocracking zone with a hydrocarbon feedstock and passing the resultant combined stream through a feed-preparation zone.- A heavier liquid effluent, from the liquid effluent from the feed preparation zone, is passed, along with a separated hydrogen-containing gas, to the hydrocracking zone. Hengstebeck does not teach feeding a separate VGO stream to the hydrocracking zone.
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. 3,172,836 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. In 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, additional developments are needed for hydroconverting dissimilar refinery streams using a single hydrogen source. The present invention is directed to such a process.
SUMMARY OF THE INVENTION
In one aspect, the invention provides a method for reducing the number of reactor vessels required for hydroprocessing in a refinery. In another aspect, the invention provides a method for hydroprocessing two refinery streams using a single hydrogen supply and a single hydrogen recovery system. In another aspect, the present invention provides a method for hydrocracking a refinery stream and hydrotreating a second refinery stream in a common reactor and with a common hydrogen feed supply without poisoning the feed to the hydrocracking reaction zone with contaminants present in the feed to the hydrotreating reaction zone. In another aspect, the present invention is directed to hydroprocessing two or more dissimilar refinery streams in an integrated hydroconversion process while maintaining good catalyst life and high yields of the desired products, particularly distillate range refinery products. Such dissimilar refinery streams may originate from different refinery processes, such as a VGO, derived from the effluent of a VGO hydrotreater, which contains relatively few catalyst contaminants and/or aromatics, and an FCC cycle oil or straight run diesel, which contains substantial amounts of aromatic compounds.
The integrated hydroconversion process comprises combining a first refinery stream with a first hydrogen-rich gaseous stream to form a first feedstock; passing the first feedstock to a first reaction zone maintained at conditions sufficient to effect a boiling range conversion, to form a first reaction zone effluent comprising normally liquid phase components and normally gaseous phase components; combining the entire first reaction zone effluent with a second refinery stream, having a boiling point range below the boiling point range of the first refinery stream, to form a second feedstock; passing the second feedstock to a second reaction zone maintained at conditions sufficient for converting at least a portion of the aromatics present in the second refinery stream, to form a second reaction zone effluent; separating the second reaction zone effluent into at least one distillate fraction and a second hydrogen-rich gaseous stream; and recycling at least a portion of the second hydrogen-rich gaseous stream to the first reaction zone.
A VGO is a preferred first refinery stream, and a synthetic or straight run middle distillate is a preferred second refinery stream. A suitable synthetic middle distillate, formed by cracking a heavier stock, may contain high nitrogen levels. The second refinery stream generally boils in the middle distillate boiling range, and is hydrotreated to remove nitrogen and/or aromatics, without excessive cracking. The preferred first reaction zone contains hydrocracking catalyst, maintained at hydrocracking conditions. Likewise, the preferred second reaction zone contains hydrotreating catalyst, maintained at hydrotreating reaction conditions. In the process, the first and the second reaction zones are contained within a single reactor vessel, or in two close coupled reactor vessels, with an single integrated hydrogen supply and recovery system serving both reaction zones. The process serves to prevent contaminants present in the second refinery stream from fouling the catalyst in the first reaction zone.
A preferred process comprises combining a VGO stream with a first hydrogen-rich gaseous stream to form a first feedstock; passing the first feedstock to a hydrocracking reaction zone, maintained at hydrocracking conditions sufficient to effect a boiling range conversion, to form a hydrocracking reaction zone effluent comprising normally liquid phase components and normally gaseous phase components; combining the entire hydrocracking reaction zone effluent, at substantially the same temperature and at substantially the same temperature as the hydrocracking reaction zone, with a second refinery stream, having a boiling point range below the boiling point range of the first refinery stream, to form a second feedstock; passing the second feedstock to a hydrotreating reaction zone, maintained at hydrotreating conditions sufficient for converting at least a portion of the nitrogen compounds and at least a portion of the aromatic compounds present in the residuum stream, to form a hydrotreating reaction zone effluent; separating the hydrotreating reaction zone effluent into at least a liquid stream and a second hydrogen-rich gaseous stream; separating the liquid stream to recover at least one middle distillate stream; and recycling at least a portion of the second hydrogen-rich gaseou
Cash Dennis R.
Dahlberg Arthur J.
Chevron U.S.A. Inc.
Klaassen Alan W.
Prater Penny L.
Yildirim Bekir L.
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