Mineral oils: processes and products – Chemical conversion of hydrocarbons – Plural serial stages of chemical conversion
Reexamination Certificate
1999-03-15
2001-02-20
Myers, Helane E. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Plural serial stages of chemical conversion
C208S064000, C208S079000
Reexamination Certificate
active
06190534
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improved process combination for the conversion of hydrocarbons, and more specifically for the selective upgrading of naphtha by a combination of selective olefin formation and aromatization.
2. General Background
The widespread removal of lead antiknock additive from gasoline and the rising fuel-quality demands of high-performance internal-combustion engines have compelled petroleum refiners to install new and modified processes for increased “octane,” or knock resistance, in the gasoline pool. Refiners have relied on a variety of options to upgrade the gasoline pool, including higher-severity catalytic reforming, higher FCC (fluid catalytic cracking) gasoline octane, increased alkylation of paraffins and olefins, isomerization of butanes and light naphtha and the use of oxygenated compounds.
Catalytic reforming is a major focus, as this process generally supplies 30-40% or more of the gasoline pool. Increased reforming severity to obtain higher-octane reformate generally results in higher production of fuel-value light gases and a lower yield of the desired C
5
+ reformate. Since this yield effect is magnified at higher reforming severity, workers in the art are faced with an increasingly difficult task of improving reforming catalysts and processes in order to maintain the yield of gasoline-range product.
One focus has been on the relative importance and sequence of the principal reforming reactions, e.g., dehydrogenation of naphthenes to aromatics, dehydrocyclization of paraffins to aromatics, isomerization of paraffins and naphthenes, hydrocracking of paraffins to light hydrocarbons, and formation of coke which is deposited on the catalyst. High yield of desired gasoline-range products are favored by the dehydrogenatlon, dehydrocyclization and isomerization reactions. The dual-function nature of reforming catalysts facilitates ready conversion of alkylcyclopentanes as well as cyclohexanes through isomerization in conjunction with dehydrogenation. Considering that reforming generally is effected in a series of zones containing catalyst, naphthene conversion to aromatics usually takes place principally in the first catalyst zones while paraffin dehydrocyclization and hydrocracking occurs primarily in subsequent catalyst zones.
The usual sequence of reforming reactions may be addressed advantageously through staging of catalysts containing different metals within a single reforming process unit. U.S. Pat. No. 4,929,333 (Moser et al.) teaches a germanium-containing reforming catalyst ahead of a germanium-free catalyst preferably containing rhenium and also cites other art appropriate to this concept.
Nonacidic zeolitic catalysts are known to be particularly effective for aromatization of paraffins through dehydrocyclization as well as for dehydrogenation of naphthenes. The staging of zeolitic catalysts for selected reactions also is recognized. U.S. Pat. No. 4,645,586 (Buss) teaches reforming using the sequence of a bifunctional catalyst having acid sites and containing a Group Vil metal followed by a nonacidic catalyst containing a large-pore zeolite (preferably L-zeolite) and a Group Vil metal. U.S. Pat. No. 5,037,529 (Dessau et al.) discloses dual-stage reforming the feed in the first stage with a nonacidic medium-pore zeolite containing a dehydrogenation/hydrogenation metal and Sn, In or TI, and converting first-stage effluent in the second stage with an acidic zeolite catalyst having a constraint index of 1-12.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved process combination to upgrade naphtha to gasoline. A specific object is to improve the yield of gasoline-range product from a reforming process.
This invention is based on the discovery that certain nonacidic, non-zeolitic catalysts effective for selective dehydrogenation may be combined with specified aromatization catalysts to obtain high yields of a high-octane aromatics-rich product.
A broad embodiment of the present invention is directed to the upgrading of a naphtha feedstock in a process combination comprising an olefin-forming zone containing a nonacidic, non-zeolitic catalyst comprising a platinum-group metal followed by an aromatization zone containing a catalyst comprising a platinum-group metal on a refractory inorganic oxide. Dehydrogenation is effected in the olefin-forming zone with minimal isomerization and hydrocracking, e.g., alkylcyclopentanes in the feedstock generally are not converted in this zone to a substantial extent. The olefin-forming catalyst preferably comprises a refractory inorganic oxide modified with an alkali metal; alternatively, the olefin-forming catalyst comprises a hydrotalcite. Optimally, selective olefin formation and aromatization are accomplished in the same hydrogen circuit. The process combination provides an improved yield of aromatics-rich product which usefully is blended into finished gasoline.
These as well as other objects and embodiments will become apparent from the detailed description of the invention.
REFERENCES:
patent: 4645586 (1987-02-01), Buss
patent: 4663020 (1987-05-01), Fleming
patent: 4737262 (1988-04-01), Frank et al.
patent: 4929333 (1990-05-01), Moser et al.
patent: 5037529 (1991-08-01), Dessau et al.
Myers Helane E.
Spears, Jr. John F.
Tolomei John G.
UOP LLC
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