Patent Grant
7763164
This invention relates to the reduction of sulfur in gasoline and other petroleum products produced by a catalytic cracking process. The invention uses a specific FCCU catalyst additive. This invention relates to a novel approach to FCCU gasoline sulfur reduction. The approach uses a specified ratio of the transition metal oxides of cobalt and molybdenum to accomplish gasoline and diesel blendstock sulfur reduction. This approach also reduces emitted NOx.
Catalytic cracking is a petroleum refining process which is applied commercially on a very large scale. A majority of the refinery gasoline blending pool in the United States is produced by this process. In the catalytic cracking process heavy hydrocarbon fractions are converted into lighter products by reactions taking place at elevated temperature in the presence of a catalyst, with the majority of the conversion or cracking occurring in the vapor phase. The feedstock is thereby converted into gasoline, distillate and other liquid cracking products as well as lighter gaseous cracking products.
During catalytic cracking, heavy material, known as coke, is deposited onto the catalyst. This reduces its catalytic activity and regeneration is desired. After removal of hydrocarbons from the spent cracking catalyst, regeneration is accomplished by burning off the coke which restores the catalyst activity. The three characteristic steps of the catalytic cracking can be therefore be distinguished: a cracking step in which the hydrocarbons are converted into lighter products, a stripping step to remove hydrocarbons adsorbed on the catalyst and a regeneration step to burn off coke from the catalyst. The regenerated catalyst is then reused in the cracking step. Catalytic cracking feedstocks normally contain sulfur in the form of organic sulfur compounds such as mercaptans, sulfides and thiophenes. The products of the cracking process correspondingly tend to contain sulfur impurities even though about half of the sulfur is converted to hydrogen sulfide during the cracking process.
For modern refineries, the Fluid Catalytic Cracking Unit (FCCU) produces 40 to 60+% of the gasoline in the gasoline pool. In addition, the FCCU produces a blendstock component for diesel manufacture. Air quality regulations for these transportation fuels will require a further reduction in sulfur content as mandated by the Clean Air Act. For the FCCU process, there are two routes a refiner can utilize to further reduce the sulfur content of these transportation fuels. The first route is via a hydrotreatment process on the feedstock to the FCCU. This hydrotreatment process can by operational severity and design, remove a substantial amount of the feed sulfur to produce a gasoline sulfur content of 100 ppmw or less. The second route a refiner can take involves the use of a specialized catalyst or additive in the FCCU circulating catalyst inventory that can catalytically remove sulfur from the FCCU product distributions. Refiners may elect to use this route for both non-hydrotreated and/or hydrotreated FCCU feedstock derived from various crude sources. In addition, if a refiner utilizes the first route for desired gasoline sulfur content, when the hydrotreater is taken out of service for an outage, this specialized catalyst or additive can be utilized to minimize the increase of gasoline sulfur during the outage period.
A need exists to continue to remove SO2 gas. A need also remains in the refining industry for improved compositions and processes which minimizes the content of gas phase reduced nitrogen species and NOx emitted from a partial or complete combustion FCCU riser during an FCC process, which compositions are effective and simple to use.
Other objects and advantages of the present invention will become apparent to those skilled in the art upon a review of the following detailed description of the preferred embodiments and the accompanying drawings.
We have now found catalytic materials for use in the catalytic cracking process which are capable of improving the reduction in the sulfur content of the liquid products of the cracking process including, in particular, the gasoline and middle distillate cracking fractions. The present sulfur reduction catalysts may be used in the form of an additive catalyst in combination with the active cracking catalyst in the cracking unit, that is, in combination with the conventional major component of the circulating cracking catalyst inventory.
This invention focuses on the specialized catalyst additive for lower FCCU gasoline and diesel blendstock sulfur reduction. Compared to commercially available catalysts and additives, this invention offers the following benefits over current commercial offerings at a constant wt %. The improvements are: a significant improvement in gasoline sulfur reductions, a significant reduction in diesel blendstock component sulfur content, a significant reduction in thiophenic, benzothiophenic and di-benzothiophenic compounds, a significant increase in propylene, a significant increase in iso-butylenes, a significant increase in total pentenes with a corresponding increase in amylenes and iso-amylenes, a significant reduction in ethane, propane and butane, a significant reduction of organic sulfur compounds in the Liquefied Petroleum Gas (LPG) an increase in FCC gasoline (R+M/2) octane, a significant reduction of H2S and a reduction in flue gas NOx.
This is accomplished by; minimizing sulfur compound formation in the FCCU riser. The cobalt and molybdenum oxides in the presence of H2S from cracked organic sulfur compounds are converted to metal sulfides. A portion of the overall sulfur reduction in the gasoline and diesel blendstock occurs by minimizing the availability of H2S to combine with olefinic compounds formed in the cracking reactions. It further is accomplished by maximizing the amount of refractory sulfur left uncracked in the slurry oil while maintaining a specified slurry oil production target. As slurry oil refractory sulfur is reduced via cracking, the various lighter cracked sulfur compounds formed are distributed or cracked “upwards” into the diesel blendstock, gasoline and LPG range products.
While this specification is described in terms of cobalt and molybdenum oxides, the invention comprises a mixture of particulate metal oxides of Group
VIB metal oxides and Group VIII metal oxides.
In the preferred embodiment, the mixture of particulate metal oxides is pulverized particulate. In another embodiment, a conventional cracking catalyst is impregnated with the additive mixture.
The file of this patent contains at least one drawing executed in color. Copies of this patent with color drawing(s) will be provided by the Patent and Trademark Office upon request and payment of necessary fee.
The present additives are used as a component of the circulating inventory of catalyst in the catalytic cracking process referred to as an FCCU process. Briefly, the FCCU process in which the heavy hydrocarbon feed containing the organosulfur compounds will be cracked to lighter products takes place by contact of the feed in a cyclic catalyst recirculation cracking process with a circulating fluidizable catalytic cracking catalyst inventory. The significant steps in the cyclic process are: (i) the feed is catalytically cracked in a catalytic cracking zone, normally a riser cracking zone, operating at catalytic cracking conditions by contacting feed with a source of hot, regenerated cracking catalyst to produce an effluent comprising cracked products and spent catalyst containing coke and strippable hydrocarbons; (ii) the effluent is discharged and separated, normally in one or more cyclones, into a vapor phase rich in cracked product and a solids rich phase comprising the spent catalyst; (iii) the vapor phase is removed as product and fractionated in the FCC main column and may be associated side columns to form liquid cracking products including gasoline; (iv) the spent catalyst is stripped, usually with steam, to remove occluded hydrocarbons from the catalyst, after which the stripped catalyst is oxidatively regenerated to produce hot, regenerated catalyst which is then recycled to the cracking zone for cracking further quantities of feed.
Slurry oil can be combined and fed to a fluid catalytic cracking unit (FCCU) to crack the hydrocarbons contained therein to smaller chained hydrocarbons, especially gasoline boiling range and heating oil. Hydrotreating prior to cracking is considered beneficial in gasoline. The gasoline is improved and a considerable amount of the sulfur will be removed which reduces SO2 emissions from FCCU itself.
The organic sulfur compounds are almost always considered to be contaminants. They hinder in downstream processing and at the very least make obnoxious SO2 gas when burned. For these reasons it is very desirable to remove these compounds. The degree of removal is dependent upon the use of the fraction. For instance, feed streams to catalytic reforming require extremely low sulfur concentrations.
The particulate additive of this invention is used in combination with an active catalytic cracking catalyst. Normally this is a faujasite such as zeolite Y and REY. Zeolite USY and REUSY also are known to process hydrocarbon feedstocks in the FCC unit to produce low-sulfur products.
The additive of this invention comprises a mixture of particulate metal oxides of Group VIB metal oxides and Group VIII metal oxides. The mixture of particulate metal oxides further comprises 5 to 30 wt. % of Group VIB metal oxides and 2 to 10 wt % of a Group VIII metal oxides. Preferably, the mixture of particulate metal oxides is pulverized particulate. Another embodiment of this invention further comprises the step of impregnating the cracking catalyst with the additive prior to catalytically cracking the petroleum feed fraction.
Preferably the Group VIB metal oxide is molybdenum oxide and the Group VIII metal oxide cobalt oxide. Preferably, the additive contains 5 to 20 wt. % of the Group VIB metal oxide and 2 to 5 wt. % of the Group VIII metal oxide.
Generally, the additive is present in an amount ranging from 1 to 25 weight percent of the weight of the cracking catalyst. Preferably, the additive is present in an amount ranging from 5 to 25 weight percent of the weight of the cracking catalyst. More preferably, the additive is present in an amount ranging from 10 to 25 weight percent of the weight of the cracking catalyst.
Generally, the additive has a particle size ranging from 1 nm to 900 nm. Preferably the additive has a particle sizing ranging from 50 nm to 800 nm. More preferably, the additive has a particle size ranging from 100 nm to 700 nm.
In cracking carbo-metallic feedstocks in accordance with FCC processes, the regeneration gas may be any gas which can provide oxygen to convert carbon to carbon oxides. Air is highly suitable for this purpose in view of its ready availability. The amount of air required per pound of coke for combustion depends upon the desired carbon dioxide to carbon monoxide ratio in the effluent gases and upon the amount of other combustible materials present in the coke, such as hydrogen, sulfur, nitrogen and other elements capable of forming gaseous oxides at regenerator conditions.
The regenerator is operated at temperatures in the range of about 1000.degree to 1600.degree. F., preferably 1275.degree. to 1450.degree. F., to achieve adequate combustion while keeping catalyst temperature below those at which significant catalyst degradation can occur. In order to control these temperatures, it is necessary to control the rate of burning which in turn can be controlled at lest in part by the relative amounts of oxidizing gas and carbon introduced into the regeneration zone per unit time.
The catalyst of this invention, with or without the metal additive is charged to a FCCU unit of the type outlined in
At such time that containment metals on the catalyst becomes intolerable high such that catalyst activity and selectivity declines, additional catalyst and additive can be added and deactivated catalyst withdrawn at addition-withdrawal point 9 into the dense bed 13 of regenerator 12 and/or or at addition-withdrawal point 7 into regenerated catalyst standpipe 16. Addition-withdrawal points 7 and 9 can be utilized to add virgin catalysts containing one or more metal additives of the invention.
The additive generally contains 5 to 30 wt. % of a Group VIB metal, oxide and 2 to 10 wt. % of a Group VIII metal oxide and alumina. In the following Examples, the additive contained 5 to 20 wt. % of molybdenum and 2 to 5 wt. % of cobalt.
To demonstrate this invention, a ground Cobalt oxide-Moly oxide hydrotreating, catalyst was introduced to the laboratory FCC catalyst evaluation testing unit as an additive. The protocol used to evaluate this invention is identical to the protocol and conditions used to evaluate commercially available gasoline sulfur reducing catalysts. The additive was combined with a conventional zeolite catalyst. The following summarizes the test data and results at constant conversion weight percent and shows:
In the above protocols, the additive is typically used in an amount from about 0.1 to about 10 weight percent of the inventory in the FCCU. Preferably, the amount will be from about 0.5 to about 5 weight percent. About 2 weight percent represents a norm for most practical purposes. The additive may be added in the conventional manner, with make-up to the regenerator or by any other convenient method. The additive remains active for sulfur removal for extended periods of time although very high sulfur feeds may result in loss of sulfur removal activity in shorter times.
The effect of the present additives is to reduce the sulfur content of liquid cracking products, especially the light and heavy gasoline fractions, although reductions are also noted in the light cycle oil, making them more suitable for use as a diesel or home heating oil blend component. The significant reduction in H2S will also have a benefit on downstream processing units where H2S is removed via caustic and amine treatment. The lower H2S load on these units will improve unit efficiency and debottleneck capacity. The sulfur removed in the FCC is absorbed as a metal sulfide and released as Sox in the regenerator.
The ability of the additives of the invention to convert NOx in a FCCU regenerator operated in a partial or complete burn mode also may be determined. The key performance measurement in this test is the NOx conversion. It is desirable to have high NOx conversion for a wide range of O2 and CO amounts. The activity of the compositions for converting NOx to nitrogen under various O2 levels, in the reducing/oxidizing conditions possible in a regenerator operating in partial or complete burn are possible due to the oxygen storage capability of the additive. No other nitrogen oxides like N2O or NO2 were detected.
Specific compositions, methods, or embodiments discussed are intended to be only illustrative of the invention disclosed by this specification. Variation on these compositions, methods, or embodiments are readily apparent to a person of skill in the art based upon the teachings of this specification and are therefore intended to be included as part of the inventions disclosed herein.
The above detailed description of the present invention is given for explanatory purposes. It will be apparent to those skilled in the art that numerous changes and modifications can be made without departing from the scope of the invention. Accordingly, the whole of the foregoing description is to be construed in an illustrative and not a limitative sense, the scope of the invention being defined solely by the appended claims.
This application is a conversion of and claims the benefit of U.S. provisional patent application Ser. No. 60/798,267 filed May 4, 2006.
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| Number | Date | Country | |
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| 60798267 | May 2006 | US |
