Mineral oils: processes and products – Chemical conversion of hydrocarbons – Plural serial stages of chemical conversion
Reexamination Certificate
1999-10-21
2001-11-13
Myers, Helane E. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Plural serial stages of chemical conversion
C208S089000, C208S209000
Reexamination Certificate
active
06315889
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a hydrocarbon conversion process referred to in the art as hydrocracking which is used commercially in petroleum refineries to reduce the average molecular weight of heavy or middle fractions of crude oil. The invention more directly relates to an integrated hydrotreating/hydrocracking process which has a specific product separation arrangement. The invention is specifically related to separation of the effluent of a hydrocarbon conversion zone using an augmented high pressure separator upstream of a conventional high pressure separator to allow the division of the hydrotreating reaction zone effluent into recycled and recovered fractions.
BACKGROUND OF THE INVENTION
Large quantities of petroleum derived hydrocarbons are converted into higher value hydrocarbon fractions used as motor fuel by a refining process referred to as hydrocracking. In this process the heavy feed is contacted with a fixed bed of a solid catalyst in the presence of hydrogen at conditions of high temperature and pressure. This results in a substantial portion of the molecules of the feed stream being broken down into molecules of smaller size and greater volatility. The high economic value of petroleum fuels derived from these smaller molecules has led to extensive development of both hydrocracking catalysts and hydrocracking process technology.
The raw petroleum fractions typically charged to a hydrocracking process contain significant amounts of organic sulfur and nitrogen. The sulfur and nitrogen must be removed to meet modern fuel specifications. Removal or reduction of the sulfur and nitrogen is also beneficial to the operation of a hydrocracking reactor. The sulfur and nitrogen is removed by a process referred to as hydrotreating. Due to the similarity of the process conditions employed in hydrotreating and hydrocracking the two processes are often integrated into a single overall process unit having separate sequential reactors dedicated to the two reactions and a common product recovery section.
RELATED ART
Both hydrotreating and hydrocracking are widely practiced commercial processes. The very significant economic utility of the hydrocracking process has resulted in a large effort devoted to the improvement of the process and to the development of better catalysts for use in the process. A general review and classification of different hydrocracking process flow schemes and a description of hydrocracking catalysts is provided at pages 174-183 of the book entitled,
Hydrocracking Science and Technology
authored by Julius Scherzer and A. J. Gruia published in 1996 by Marcel Dekker, Inc. FIGS. 10.2, 10.3 and 10.5 show hydrotreating reactors upstream of the hydrocracking reactor and general process flows. As noted therein it is an established practice to first pass a hydrocracking unit feed stream into a hydrotreating reactor in order to reduce the level of sulfur and nitrogen tied up in the target petroleum molecules. Some form of separation may be employed between the hydrotreating reactor and the hydrocracking reactor to reduce the amount of hydrogen sulfide carried over to the hydrocracking reactor with the hydrocarbon phase.
The high pressures employed in hydrocracking has prompted efforts to conserve the pressure of any portion of the hydrocracking effluent which is to be recycled and to also limit reductions in pressure as a separation mechanism to the product recovery section of the process. The effluent of a high pressure reactor such as a hydrocracking reactor therefore typically flows into a vessel referred to as a high pressure separator (HPS), which operates at a pressure close to the outlet pressure of the reaction zone. High pressure separators are classified as “hot” or “cold” depending on whether the effluent stream is cooled significantly prior to passage into the HPS.
U.S. Pat. No. 3,260,663 issued to T. V. Inwood et al, illustrates the passage of the effluent of an initial hydrotreater 8 into a separator 14 which may be operated at close to the conditions employed in the hydrotreater. The separator contains trays 24, and hydrogen may be charged to the bottom of the separator via line 28. A vapor-phase comprising 650° F.-minus hydrocarbons and hydrogen and a liquid phase stream are removed from the separator and passed into separate hydrocracking zones. The effluent of both hydrocracking reactors shown in the reference is handled in a more conventional manner with the effluent first flowing into a HPS and then the liquid from the HPS flowing into a low pressure separator 66.
The art also includes more complicated separation schemes employing multiple separators. For instance, U.S. Pat. No. 3,471,397 issued to J. T. Fortman et al illustrates the use of a HPS, a hot flash separator and a cold separator. U.S. Pat. No. 3,733,260 issued to J. A. Davies et al shows the use of a hot separator, a hot flash separator, a old separator and a cold flash separator. This reference also illustrates the practice of treating the recycle hydrogen gas stream to remove hydrogen sulfide.
SUMMARY OF THE INVENTION
The invention is a combined sequential hydrotreating and hydrocracking process. The flow scheme of the invention employs two high pressure separators in series to separate the effluent of a hydrotreating reactor in order to provide controlled division of heavy hydrocarbons between a high conversion hydrocracking zone and the product recovery zone of the process. A variable portion of the hydrotreater effluent is thereby bypassed around the hydrocracking zone allowing controlled overall conversion and production of an upgraded “unconverted” bottoms product stream.
A broad embodiment of the invention my be characterized as an integrated hydrocarbon conversion process which employs both a hydrocracking reactor and a hydrotreating reactor, which process comprises passing a feed stream comprising hydrocarbons having boiling points above 700° F. and hydrogen into a hydrotreating reaction zone operated at hydrotreating conditions and producing a hydrotreating reaction zone effluent stream comprising hydrogen, hydrogen sulfide, and unconverted feed components having boiling points above about 700° F.; separating the hydrotreating reaction zone effluent stream in a first high pressure separation zone into a vapor-phase light fraction comprising hydrocarbons having boiling points below about 700° F., and a liquid-phase heavy fraction comprising hydrocarbons having boiling points above about 700° F.; separating the light fraction in a second high pressure separation zone into a recycle gas stream and a liquid process stream; passing a first portion of the heavy fraction, the liquid process stream and hydrogen into a hydrocracking reaction zone operated at hydrocracking conditions, and producing a hydrocracking reaction zone effluent stream; passing the remaining second portion of the heavy fraction and the hydrocracking reaction zone effluent stream into a product recovery zone, and recovering at least one distillate hydrocarbon product stream.
REFERENCES:
patent: 3779897 (1973-12-01), Wrench et al.
Anderle Christopher J.
Gala Hemant B.
Thakkar Vasant P.
Myers Helane E.
Spears, Jr. John F.
Tolomei John G.
UOP LLC
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