Mineral oils: processes and products – Chemical conversion of hydrocarbons – Plural serial stages of chemical conversion
Reexamination Certificate
1999-09-02
2001-05-29
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Plural serial stages of chemical conversion
C208S069000, C208S070000, C208S113000
Reexamination Certificate
active
06238548
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to processes for the fluidized catalytic cracking (FCC) of heavy hydrocarbon streams such as vacuum gas oil and reduced crudes. This invention relates more specifically to a method for separately reacting a traditional FCC feedstream and a gasoline feed in an FCC reaction zone.
BACKGROUND OF THE INVENTION
The fluidized catalytic cracking of hydrocarbons is the main stay process for the production of gasoline and light hydrocarbon products from heavy hydrocarbon charge stocks such as vacuum gas oils or residual feeds. Large hydrocarbon molecules, associated with the heavy hydrocarbon feed, are cracked to break the large hydrocarbon chains thereby producing lighter hydrocarbons. These lighter hydrocarbons are recovered as product and can be used directly or further processed to raise the octane barrel yield relative to the heavy hydrocarbon feed.
The basic equipment or apparatus for the fluidized catalytic cracking of hydrocarbons has been in existence since the early 1940's. The basic components of the FCC process include a reactor, a regenerator, and a catalyst stripper. The reactor includes a contact zone where the hydrocarbon feed is contacted with a particulate catalyst and a separation zone where product vapors from the cracking reaction are separated from the catalyst. Further product separation takes place in a catalyst stripper that receives catalyst from the separation zone and removes entrained hydrocarbons from the catalyst by countercurrent contact with steam or another stripping medium.
The FCC process is carried out by contacting the starting material whether it be vacuum gas oil, reduced crude, or another source of relatively high boiling hydrocarbons with a catalyst made up of a finely divided or particulate solid material. The catalyst is transported like a fluid by passing gas or vapor through it at sufficient velocity to produce a desired regime of fluid transport. Contact of the oil with the fluidized material catalyzes the cracking reaction. The cracking reaction deposits coke on the catalyst. Coke is comprised of hydrogen and carbon and can include other materials in trace quantities such as sulfur and metals that enter the process with the starting material. Coke interferes with the catalytic activity of the catalyst by blocking active sites on the catalyst surface where the cracking reactions take place. Catalyst is traditionally transferred from the stripper to a regenerator for purposes of removing the coke by oxidation with an oxygen-containing gas. An inventory of catalyst having a reduced coke content, relative to the catalyst in the stripper, hereinafter referred to as regenerated catalyst, is collected for return to the reaction zone. Oxidizing the coke from the catalyst surface releases a large amount of heat, a portion of which escapes the regenerator with gaseous products of coke oxidation generally referred to as flue gas. The balance of the heat leaves the regenerator with the regenerated catalyst. The fluidized catalyst is continuously circulated from the reaction zone to the regeneration zone and then again to the reaction zone. The fluidized catalyst, as well as providing a catalytic function, acts as a vehicle for the transfer of heat from zone to zone. Catalyst exiting the reaction zone is spoken of as being spent, i.e., partially deactivated by the deposition of coke upon the catalyst. Specific details of the various contact zones, regeneration zones, and stripping zones along with arrangements for conveying the catalyst between the various zones are well known to those skilled in the art.
The FCC unit cracks gas oil or heavier feeds into a broad range of products. Cracked vapors from the FCC reactor enter a separation zone, typically in the form of a main column, that provides a gas stream, a gasoline cut, cycle oil and heavy residual components. The gasoline cut includes both light and heavy gasoline components. A major component of the heavy gasoline fraction comprises heavy single ring aromatics.
DISCLOSURE STATEMENT
U.S. Pat. No. 3,161,582 and U.S. Pat. No. 3,847,793 teach the use of riser reaction zone that converts a first feed and discharges the converted feed into a second bed type reaction zone that treats additional more refractory feed. All of the converted feeds are recovered from a common dilute phase collection zone in the reactor.
U.S. Pat. No. 2,956,003 and U.S. Pat. No. 2,921,014 teach an FCC process and the use of a riser type reaction vessel for the conversion of an FCC feed separation of converted feed and a separate dense bed reaction vessel for the conversion of the separated bottoms stream.
U.S. Pat. No. 3,607,129 shows an apparatus for cracking a heavy FCC feedstock in a riser conversion zone, discharging the cracked product into an FCC reactor vessel, cracking hydrotreated or unhydrotreated light cycle oil in a fluidized catalyst bed in a lower portion of the reaction vessel and withdrawing the cracked products from the riser and the dense bed through a common conduit.
U.S. Pat. No. 3,776,838 shows the cracking of a naphtha stream in a fluidized catalytic cracking process.
U.S. Pat. No. 5,154,818 shows the fluidized catalytic cracking of a first lighter feed fraction in an FCC riser with spent catalyst followed by cracking of full boiling range FCC feed in a downstream section of the riser.
U.S. Pat. No. 4,032,432 teaches the conversion of C
6
and lower boiling hydrocarbon cut in a secondary conversion zone of an FCC unit using spent catalyst to form aromatics or alkyl aromatics.
U.S. Pat. No. 5,372,704 discloses an FCC arrangement for recracking FCC naphtha. The process either cracks a heavy naphtha, defined as having a boiling point range of from 300 to 425° F. or a naphtha generally which would include a full range gasoline.
U.S. Pat. No. 5,176,815 discloses the use of an isolated reaction zone in an FCC stripper for converting a primary feed and a variety of segregated secondary feeds in an FCC reaction zone. U.S. Pat. No. 5,310,477 further uses the same arrangement for the specific contacting of a heavy gasoline cut from a primary FCC reaction.
BRIEF DESCRIPTION OF THE INVENTION
An object of this invention is the cracking of a heart cut of gasoline components at low severity condition with spent catalyst to obtain a surprising increase in gasoline octane number and an increase in the yield of C
8
aromatics with little or no dry gas production.
The invention, in contrast to the art that has further converted light gasoline stream comprising C
6
and lighter hydrocarbons for upgrading and heavy gasoline fractions to improve end point conditions, processes a gasoline stream in a narrow boiling point range of from 200 to 350° F. and more preferably in a boiling point range of from 250 to 350° F. It has surprisingly and unexpectedly been found that further conversion of this specific boiling range gasoline cut at mild processing conditions with spent catalyst will dramatically increase the octane of the resulting gasoline fraction. It was further found that allowing heavy hydrocarbons into the secondary conversion with the heart cut substantially negated the positive benefits of the further conversion on the gasoline properties and in particular undid the dramatic increase in octane number.
Accordingly, in one embodiment, this invention is a process for the fluidized catalytic cracking (FCC) of an FCC feedstock and the production of a high octane gasoline and C
8
aromatics. The process comprises passing the FCC feedstock and regenerated catalyst particles to a reactor riser and transporting the catalyst and feedstock through the riser thereby converting the feedstock to a riser gaseous product stream to produce partially spent catalyst particles by the deposition of coke on the regenerated catalyst particles. A discharge end of the riser directly discharges a mixture of partially spent catalyst particles and gaseous products into a separation zone that recovers the riser gaseous products from the riser in the separation zone. The process withdraws
Upson Lawrence L.
Wesling Julie E.
Griffin Walter D.
Paschall James C.
Tolomei John G.
UOP LLC
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