Mineral oils: processes and products – Chemical conversion of hydrocarbons – Plural serial stages of chemical conversion
Reexamination Certificate
2002-10-02
2004-11-02
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Plural serial stages of chemical conversion
C208S067000, C208S075000, C208S076000, C208S077000
Reexamination Certificate
active
06811682
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for converting cycle oils produced in catalytic cracking reactions into olefin and naphtha. More particularly, the invention relates to a process for converting a catalytically cracked cycle oil such as heavy cycle oil (“HCO” or “HCCO”), light cycle oil (“LCO” or “LCCO”), and mixtures thereof into olefins and naphthas using a zeolite catalyst.
BACKGROUND OF THE INVENTION
Cycle oils such as HCCO and LCCO produced in fluidized catalytic cracking (“FCC”) reactions contain two-ring aromatic species such as naphthalene. The need for blendstocks for forming low emissions fuels has created an increased demand for FCC products that contain a diminished concentration of multi-ring aromatics. There is also an increased demand for FCC products containing light olefins that may be separated for use in alkylation, oligomerization, polymerization, and MTBE and ETBE synthesis processes. There is a particular need for low emissions, high octane FCC products having an increased concentration of C
2
to C
4
olefins and a reduced concentration of multi-ring aromatics and olefins of higher molecular weight.
A high octane gasoline may be formed conventionally by hydrotreating an FCC cycle oil and then re-cracking hydrotreated cycle oil. The hydrotreated cycle oil may be recycled to the FCC unit from which it was derived, or it may be re-cracked in an additional catalytic cracking unit.
In such conventional processes, hydrotreating a cycle oil such as LCCO partially saturates bicyclic aromatics such as naphthalene to produce, for example, tetrahydronaphthalene and alkyl-substituted derivatives thereof (collectively referred to herein as (“tetralins”). Hydrotreatment and subsequent cycle oil re-cracking may occur in the primary FCC reactor. Hydrotreated cycle oil may also be injected into the FCC feed riser upstream or downstream of primary feed injection. In another conventional process, hydrotreated cycle oil is recycled with a hydrotreated naphtha, and both are injected into the primary riser reactor at a point upstream of primary feed injection.
Unfortunately, such re-cracking of hydrotreated LCCO results in undesirable hydrogen transfer reactions that convert species such as tetralins into polynuclear aromatics such as naphthalene.
There remains a need, therefore, for new processes for forming naphtha and olefin from hydrotreated cycle oils.
SUMMARY OF THE INVENTION
In one embodiment, the invention is a method for catalytically cracking a primary feed comprising:
(a) injecting the primary feed into an FCC riser reactor having at least a first reaction zone and a second reaction zone upstream of the first reaction zone, the primary feed being injected into the first reaction zone;
(b) cracking the primary feed in the first reaction zone under primary feed catalytic cracking conditions in the presence of a catalytically effective amount of a zeolite-containing catalytic cracking catalyst in order to form a cracked product;
(c) separating at least a cycle oil from the cracked product and then processing the cycle oil in the presence of a catalytically effective amount of a hydroprocessing catalyst under hydroprocessing conditions in order to form a hydroprocessed cycle oil having an increased concentration of tetralins;
(d) injecting the hydroprocessed cycle oil into the second reaction zone; and
(e) cracking the hydroprocessed cycle oil under cycle oil catalytic cracking conditions in the presence of the catalytic cracking catalyst.
In another embodiment, the invention is a cracked product formed in accordance with such a process.
DETAILED DESCRIPTION OF THE INVENTION
The invention is based on the discovery that recycling a hydrotreated cycle oil such as HCCO and LCCO to an FCC reaction zone in the presence of a catalytically effective amount of an appropriate FCC catalyst results in increased propylene production when the cycle oil injection is along the feed riser at a point upstream of gas oil or residual oil feed injection. It is believed that injecting the cycle oil into the FCC reaction zone in the presence of an appropriate FCC catalyst and at a point upstream of gas oil or residual oil injection suppresses undesirable hydrogen transfer reactions by re-cracking potential hydrogen donors present in the cycle oil before such donors can contact the primary feed.
Preferred hydrocarbonaceous feeds (i.e. the primary feed) for the catalytic cracking process described herein include naphtha, hydrocarbonaceous oils boiling in the range of about 430° F. (220° C.) to about 1050° F. (565° C.), such as gas oil; heavy hydrocarbonaceous oils comprising materials boiling above 1050° F. (565° C.); heavy and reduced petroleum crude oil; petroleum atmospheric distillation bottoms; petroleum vacuum distillation bottoms; pitch, asphalt, bitumen, other heavy hydrocarbon residues; tar sand oils; shale oil; liquid products derived from coal and natural gas, and mixtures thereof.
The preferred cracking process may be performed in one or more conventional FCC process units. Each unit comprises a riser reactor having a first reaction zone and a second reaction zone upstream of the first reaction zone, a stripping zone, a catalyst regeneration zone, and at least one separation zone.
The primary feed is conducted to the riser reactor where it is injected into the first reaction zone wherein the primary feed contacts a flowing source of hot, regenerated catalyst. The hot catalyst vaporizes and cracks the feed at a temperature from about 450° C. to 650° C., preferably from about 500° C. to 600° C. The cracking reaction deposits carbonaceous hydrocarbons, or coke, on the catalyst, thereby deactivating the catalyst. The cracked products may be separated from the coked catalyst and a portion of the cracked products may be conducted to a separator such as a fractionator. At least a cycle oil fraction, preferably an LCCO fraction, is separated from the cracked products in the separation zone. Other fractions that may be separated from the cracked products include light olefin fractions and naphtha fractions.
Light olefins separated from the process may be used as feeds for processes such as oligimerization, polymerization, co-polymerization, ter-polymerization, and related processes (hereinafter “polymerization”) in order to form macromolecules. Such light olefins may be polymerized both alone and in combination with other species, in accordance with polymerization methods known in the art. In some cases it may be desirable to separate, concentrate, purify, upgrade, or otherwise process the light olefins prior to polymerization. Propylene and ethylene are preferred polymerization feeds. Polypropylene and polyethylene are preferred polymerization products made therefrom.
Preferably, the coked catalyst flows through the stripping zone where volatiles are stripped from the catalyst particles with a stripping material such as steam. The stripping may be preformed under low severity conditions in order to retain a greater fraction of adsorbed hydrocarbons for heat balance. The stripped catalyst is then conducted to the regeneration zone where it is regenerated by burning coke on the catalyst in the presence of an oxygen containing gas, preferably air. Decoking restores catalyst activity and simultaneously heats the catalyst to, e.g., 650° C. to 800° C. The hot catalyst is then recycled to the riser reactor at a point near or just upstream of the second reaction zone. Flue gas formed by burning coke in the regenerator may be treated for removal of particulates and for conversion of carbon monoxide, after which the flue gas is normally discharged into the atmosphere.
Preferably, at least a portion of the cycle oil is hydroprocessed in the presence of a hydroprocessing catalyst under hydroprocessing conditions in order to form a cycle oil having a significant amount of tetralins. At least a portion of the hydroprocessed cycle oil is conducted to the riser reactor and injected into the second reaction zone. The hydroprocessing may occur in one or more hydroprocessing
Daage Michel
Klein Darryl P.
Stuntz Gordon F.
Swan, III George A.
Touvelle Michele S.
ExxonMobil Research and Engineering Company
Griffin Walter D.
Kliebert Jeremy J.
Singleton Wilson Erika
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