Two stage FCC process incorporating interstage hydroprocessing

Details Two stage FCC process incorporating interstage hydroprocessing Two stage FCC process incorporating interstage hydroprocessing

2001-03-16

2003-05-20

Griffin, Walter D. (Department: 1764)

Mineral oils: processes and products

Chemical conversion of hydrocarbons

Plural serial stages of chemical conversion

C208S074000, C208S072000

Reexamination Certificate

active

06565739

ABSTRACT:

BACKGROUND
The invention relates to a process for converting cycle oils produced in catalytic cracking reactions into olefinic naphthas. More particularly, the invention relates to an out-board catalytic cracking process for converting a catalytically cracked light cycle oil (also referred to herein as light cat cycle oil or LCCO) into light olefins (C
2
-C
5
) and catalysts used in such processes.
Cycle oils such as 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
-C
4
olefins and reduced concentration of multi-ring aromatics and olefins of higher molecular weight.
Hydroprocessing a cycle oil and re-cracking hydrohydrogenated cycle oil results in conversion of the cycle oil to a motor gasoline blend-stock. In some conventional processes, the hydrohydrogenated cycle oil is recycled to the FCC unit from which it was derived. In other conventional processes the hydrohydrogenated cycle oil is re-cracked in an additional catalytic cracking unit, also referred to as an outboard catalytic cracker.
Some conventional hydroprocessing processes cycle oil, such as LCCO, to partially saturate bicyclic hydrocarbons such as naphthalene to produce tetrahydronaphthalene. Hydroprocessing and subsequent LCCO re-cracking may occur in the primary reactor vessel. Hydroprocessed LCCO may also be injected into the FCC feed riser at a point downstream of feed injection to provide for feed quenching.
Unfortunately, such re-cracking of conventionally hydroprocessed LCCO results in undesirable hydrogen transfer reactions that convert species such as tetrahydronaphthalene into aromatics such as naphthalene, thereby reversing the effects of hydroprocessing and decreasing the olefin yield.
There remains a need, therefore, for new processes to increase the yield of light olefins from hydrogenated cycle oils such as LCCO.
SUMMARY OF THE INVENTION
One embodiment of the present invention comprises a fluid catalytic cracking process comprising: (a) contacting a FCC feed with a catalytic cracking catalyst in a first catalytic cracking stage under catalytic cracking conditions to produce cracked products; (b) separating at least a cycle oil fraction from the cracked products, wherein the cycle oil fraction comprises aromatics; (c) hydrogenating at least a fraction of the aromatics in the cycle oil fraction in the presence of a hydrogenating catalyst under hydrogenation conditions to form a hydrogenated cycle oil; and, (d) contacting the hydrogenated cycle oil with a catalytic cracking catalyst under catalytic cracking conditions in a second fluid catalytic cracking stage to form a second cracked product, the second fluid catalytic cracking stage being separate from the first second fluid catalytic cracking stage, wherein the catalyst of the second fluid catalytic cracking stage comprises an amorphous metal oxide catalyst having a surface area from about 5 to about 400 m
2
/g.
Another embodiment of the present invention comprises a process for catalytically cracking a cycle oil to selectively increase the yield of light olefins comprising the steps of: (a) contacting a FCC feed with a catalytic cracking catalyst under catalytic cracking conditions in a first FCC reactor to form a first cracked product, the cracked product comprising a cycle oil fraction comprising aromatic species; (b) separating the first cracked product from the catalyst of the first FCC reactor; (c) stripping the catalyst of the first FCC reactor; (d) contacting the catalyst of the first FCC reactor with a gas comprising oxygen; (e) passing the catalyst of the first FCC reactor back to the first FCC reactor; (f) separating at least a portion of the cycle oil fraction from the first cracked product; (g) hydrogenating a substantial portion of the aromatic species in the cycle oil in the presence of a hydrogenation catalyst under hydroprocessing conditions to form a substantially hydrogenated cycle oil, the hydrogenation catalyst comprising at least one Group VIII metal and at least one Group VI metal on at least one refractory support, the Group VI metal selected from the group consisting of Pt and Pd, wherein the weight of the aromatic species in the hydrogenated cycle oil is less than about 1% of the total weight of the hydrogenated cycle oil; and, (h) contacting the hydrogenated cycle oil with a catalytic cracking catalyst under catalytic cracking conditions in a separate second FCC reactor to form a second cracked product, wherein the catalyst used in the second FCC reactor comprises: (1) between about 10 and 20 wt. % of a catalyst containing a zeolite Y having a pore diameter greater than 0.7 and a unit cell size less than about 24.27 Å; (2) between about 40 and about 50 wt. % of a catalyst containing an amorphous metal oxide having a surface area between about 40 and about 400 m
2
/g; and, (3) between about 35 and about 45 wt. % of a catalyst containing an amorphous metal oxide having a surface area between about 5 and about 40 m
2
/g; (i) separating the second cracked product from the catalyst of the second FCC reactor; (j) stripping the catalyst of the second FCC reactor; (k) contacting the catalyst of the second FCC reactor with a gas comprising oxygen; and, (l) passing the catalyst of the second FCC reactor to the second FCC reactor back to the second FCC reactor.
DETAILED DESCRIPTION OF THE INVENTION
The embodiments of the present invention are based on the discovery that catalytically cracking a substantially saturated cycle oil, such as LCCO, in a FCC riser reactor results in increased conversion of the cycle oil into light olefins such as propylene. Light olefin production increases when cracking occurs in the absence of hydrogen receptor species that may be found in conventional catalytic cracking feeds such as vacuum gas oil (VGO) and other heavy hydrocarbon and hydrocarbonaceous feeds. The cycle oil is hydroprocessed to saturate a substantial portion of the aromatic species. The hydrogenated cycle oil is injected into a second FCC riser reactor that is physically separated from the primary FCC riser reactor used to convert VGO and other heavy FCC feeds. While not wishing to be bound by any theory, applicants believe that cracking the hydrogenated cycle oil in a second FCC riser reactor suppresses undesirable hydrogen transfer reactions that would otherwise occur if the cycle oil were re-cracked in the primary FCC riser reactor. Re-cracking in a second FCC reactor under cycle oil cracking conditions (i.e., conditions that exclude gas oils and residual oils from the reaction zone) substantially eliminates hydrogen transfer reactions between hydrogen donor species present in the cycle oil and hydrogen receptor species present in the VGO or residual oil because the concentration of hydrogen receptors species is decreased.
Suitable FCC feeds for the catalytic cracking process in the primary FCC riser reactor include hydrocarbonaceous oils boiling in the range of about 430° F. to about 1050° F. (480-565° C.), such as gas oil, heavy hydrocarbon 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 liquefaction processes; and mixtures thereof.
Cycle oil formation occurs in one or more conventional FCC process units under conventional FCC conditions in the presence of conventional FCC catalyst(s). Each FCC unit comprises a riser reactor having a reaction

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