JPS6252787B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reducing the amount of carbon monoxide and sulfur oxides in flue gas produced in a catalyst regenerator in a fluid catalytic cracker.

Modern hydrocarbon catalytic cracking units use moving or fluidized beds of particulate catalyst. The cracking catalyst is subjected to continuous cyclic cracking reactions as well as catalyst regeneration procedures. In fluid catalytic cracking (FCC) units, the hydrocarbon feed stream is typically about 800 to 1000
contact with fluidized catalyst particles in a hydrocarbon cracking zone or reactor. Reaction of the hydrocarbons in the hydrocarbon stream at this temperature results in the deposition of carbonaceous coke on the catalyst particles. The resulting product fluid is then separated from the coked catalyst and withdrawn from the cracking zone. The coked catalyst is then stripped of volatiles and passed to a catalyst regeneration zone. In the catalyst regenerator, the coked catalyst is contacted with a gas containing a controlled amount of molecular oxygen to burn off the desired portion of the coke from the catalyst, and at the same time, the catalyst is removed from the hydrocarbons in a cracking zone. The catalyst is heated to the desired high temperature upon recontact with the stream. After regeneration, the catalyst is returned to the cracking zone where it is used to vaporize the hydrocarbons and catalyze the cracking of the hydrocarbons. Flue gas produced by combustion of coke within the catalyst regenerator is separately removed from the regenerator. This flue gas, which may be treated to remove particles and carbon monoxide, is typically released to the atmosphere. The interest in controlling pollutants in flue gases has led to the search for improved methods for controlling such pollutants, particularly sulfur oxides and carbon monoxide.

The degree of conversion achieved in an FCC cracking operation is the volume percentage of the fresh hydrocarbon feed that is converted to gasoline and lighter products during the conversion step. The gasoline end point for determining conversion is usually specified as 430〓. Conversion rate is often used to measure commercial FCC severity. For a given set of operating conditions, a more active catalyst will give a higher conversion than a less active catalyst. given
The ability to provide higher conversion rates in a FCC unit is desirable because the FCC unit thereby operates with greater flexibility. Feed throughput to the device can be increased, or alternatively, feed throughput can be held constant while higher conversion rates are maintained.

Hydrocarbon feeds processed in commercial FCC units commonly contain sulfur, commonly referred to as "feed sulfur." Approximately 2 to 10% or more of the feed sulfur in the hydrocarbon feed stream processed in the FCC unit is transferred from the feed to the catalyst particles as part of the coke formed on the catalyst particles during cracking. Always transferred. The sulfur deposited on the catalyst, here referred to as "coke sulfur", is ultimately recycled along with the coked catalyst from the conversion zone to the catalyst regenerator. In this manner, about 2 to 10% or more of the sulfur in the hydrocarbon feed is continuously pumped from the cracking zone to the catalyst regeneration zone in the coked catalyst. In the FCC catalyst regenerator, the sulfur contained in the coke is combusted with the coke carbon to produce gaseous sulfur dioxide and sulfur trioxide, which are normally present in the flue gas and removed from the regenerator. .

Most of the feed sulfur does not become coke sulfur in the cracking reactor. Instead, it is converted to normally gaseous sulfur compounds, such as hydrogen sulfide and carbon oxysulfide, or to normally liquid organosulfur compounds. These sulfur compounds are carried away with the vapor products recovered from the cracking reactor. In this way, about 90% or more feed sulfur is continuously removed from the cracking reactor in the treated and cracked hydrocarbon stream, and about 40 to 60% of this sulfur is hydrogen sulfide. It has a shape. Measures are typically taken to recover hydrogen sulfide from the effluent from the cracking reactor. Typically,
A very low molecular weight exhaust gas vapor stream is separated from the _C3 + liquid hydrocarbons in a gas recovery unit, and the exhaust gas is treated to recover hydrogen sulfide, such as by washing it with an amine solution. be done. Removing sulfur compounds, such as hydrogen sulfide, from the fluid effluent from an FCC cracking reactor is relatively easy and There is no cost. Moreover, if all the sulfur that must be recovered from the FCC operation can be recovered in a single recovery operation performed on the reactor offgas, it is possible to avoid using two separate sulfur recovery operations in the FCC unit. It could be done.

reducing the amount of oxidized sulfur in the FCC regenerator flue gas by desulfurizing the hydrocarbon feed in a separate desulfurization unit prior to cracking;
After withdrawal from the FCC regenerator, it is proposed to desulfurize the regenerator flue gas itself by conventional flue gas desulfurization procedures. Obviously, all of the above-mentioned alternatives require sophisticated external processing operations and require high expenditures in terms of invested capital and utilities.

If the sulfur normally removed from the FCC unit as oxidized sulfur in the regenerator flue gas is instead removed from the cracking reactor as hydrogen sulfide entrained in the treated cracked hydrocarbons, this reaction The sulfur that is converted to vessel effluent is then
It is merely a small addition to the large amounts of hydrogen sulfide and organic sulfur that are necessarily already present in the reactor effluent. Even 5 to 15% or more hydrogen sulfide from the FCC reactor exhaust gas.
A small, if any, additional expense to remove this with currently available methods is to reduce the oxidized sulfur levels in the regenerator flue gas by separate feed desulfurization or flue gas desulfurization. significantly less than the cost of Hydrogen sulfide recovery equipment currently used in commercial FCC units typically has the ability to remove additional hydrogen sulfide from the reactor exhaust gas.
Current flue gas hydrogen sulfide recovery equipment typically removes substantially all of the sulfur typically present in the regenerator flue gas.
Any additional hydrogen sulfide that would be added to the flue gas could be treated if it were converted to hydrogen sulfide in the FCC reactor flue gas. Therefore, it is preferred to introduce feed sulfur into the cracked fluid product withdrawal path from the cracking reactor and reduce the amount of oxidized sulfur in the regenerator flue gas.

Group A metal oxides and/or carbonates such as dolomite, MgO or _CaCO3 particles
By adding it to the circulating catalyst in the FCC device,
Reducing the amount of sulfur oxide in the FCC regenerator flue gas has been proposed, for example, in US Pat. No. 3,699,037. Group A metals react with sulfur oxides in the flue gas to form sulfur-containing solid compounds.
Group A metal oxides lack physical strength and, regardless of the size of the particles introduced, they rapidly become pulverized by abrasion and are combined with catalyst fines.
Flows rapidly from FCC equipment. Therefore, the addition of dolomite and similar Group A materials must be continuous, and large quantities of the material must be used to reduce the sulfur oxide levels in the flue gas over any meaningful period of time. must be used. Reducing the amount of oxidized sulfur in the FCC regenerator flue gas by impregnating Group A metal oxides onto conventional silica-alumina decomposition catalysts has been proposed, e.g. has been done. The wear problems encountered when using unsupported Group A metals are thereby alleviated. However, Part A
Group metal oxides, such as magnesia, have been found to have an undesirable effect on the activity and selectivity of the cracking catalyst when used as a component of the cracking catalyst. The addition of Group A metals to the cracking catalyst produces particularly clear adverse results when compared to the results obtained with cracking without Group A metals: (1) The yield of liquid hydrocarbon fractions is (2) The octane number of the gasoline or naphtha fraction (boiling range 75° to 340°) is reduced considerably; typically by more than 1% by volume of the feed volume. Both of the above adverse consequences seriously undermine the economic viability of FCC disassembly operations;
Also, even complete removal of sulfur oxides from the regenerator flue gas would not compensate for the yield and octane reductions obtained by adding Group A metals to the FCC catalyst.

Although alumina has been a component of many FCC and other cracking catalysts, it is primarily chemically bonded tightly to silica. Alumina itself has low acidity and is generally considered undesirable for use as a cracking catalyst. Technically, alumina is not selective, meaning that the cracked hydrocarbon products recovered from FCC or other crackers using alumina catalysts are not the desired valuable products, but _e.g. It is known that it will contain lighter hydrocarbon gases.

currently used in most devices
The conventional type of regeneration method for FCC catalysts is the incomplete combustion type. In such systems, referred to herein as "standard regeneration," a significant amount of coke carbon remains on the regenerated catalyst that is fed from the FCC regeneration zone to the cracking zone. Typically, regenerated catalyst contains a significant amount of coke carbon, i.e. 0.2% by weight, usually about 0.25 to
Contains 0.45% carbon by weight. The flue gas withdrawn from an FCC regenerator operating in standard regeneration mode is characterized by a relatively high carbon monoxide/carbon dioxide concentration ratio. The atmosphere in most or all of the regeneration zone is generally a reducing atmosphere due to the presence of significant amounts of unburned coke carbon and carbon monoxide.

Generally, it has been difficult to reduce the level of carbon on the regenerated catalyst below about 0.2% by weight. Until recently, there have been few attempts to remove substantially all of the coke carbon from the catalyst, since even fairly high carbon contents have little negative effect on the activity and selectivity of amorphous silica-alumina catalysts. However, most FCC cracking catalysts used today contain zeolites or molecular sieves. It has been found that zeolite-containing catalysts typically have relatively high activity and selectivity when the coke carbon content after regeneration is relatively low. Attempts have therefore begun to reduce the coke content of regenerated FCC catalysts to very low levels, for example below 0.2% by weight.

In order to avoid air pollution, recover heat and prevent after burning, several methods have been proposed to burn almost all of the carbon monoxide to carbon dioxide during regeneration. Among the methods proposed to be used to achieve complete combustion of carbon monoxide in the FCC regenerator are: (1) controlling the amount of oxygen introduced into the regenerator;
(2) increasing the average operating temperature within the regenerator; or (3) increasing the average operating temperature within the regenerator.
Inclusion of various carbon monoxide oxidation promoters in the decomposition catalyst to promote combustion of carbon monoxide. Various solutions for the problem of carbon monoxide after-combustion,
For example, the addition of exogenous combustibles or the use of water or heat-accepting solids to absorb the heat of combustion of carbon monoxide has also been proposed.

When using traditionally commercially available carbon monoxide combustion promoters, such as group noble metals, in the FCC catalyst for complete combustion of carbon monoxide,
It has been found that it is very difficult to keep the amount of coke on the regenerated catalyst at an acceptably low level. Promoters are often found to produce sufficient CO combustion when added to catalysts;
It is not well accepted commercially because of the high levels of coke formed on the regenerated catalyst, which reduces conversion.

Complete combustion schemes, which require the temperature of the catalyst regenerator to be abnormally high to achieve complete combustion of carbon monoxide, are also not entirely satisfactory. In the afterburning method, the combustion of CO takes place substantially within the dilute phase;
Some of the heat generated by the combustion of carbon monoxide is lost in the flue gas and is also
The activity and selectivity of the FCC catalyst may be permanently affected.

Several types of addition of Group noble metals and other carbon monoxide combustion promoters to FCC systems have been proposed in the art. In US Pat. No. 2,647,860 it is proposed to add 0.1 to 1% by weight of chromic oxide to accelerate the combustion of carbon monoxide to carbon dioxide and prevent after-combustion. U.S. Pat. No. 3,364,136 contains small pore (3-5 angstroms) molecular sieves bound with transition metals of groups B, B, B, B and groups of the periodic table or compounds thereof, such as sulfides or oxides. It is proposed to use particles. Representative metals disclosed include chrome, nickel, iron,
Includes molybdenum, cobalt, platinum, palladium, copper and zinc. The metal-loaded small pore zeolite may be used in a FCC device as a physical mixture with a larger pore zeolite that is active for cracking or a cracking catalyst containing a small pore zeolite. The pore zeolite may be included in the same matrix along with the degradingly active zeolite. The small pore metal loaded zeolite is provided for the purpose of increasing the _CO2 /CO ratio in the flue gas produced in the FCC regenerator. U.S. Pat. No. 3,788,977 discloses uranium or platinum impregnated on an inorganic oxide, such as alumina, in the form of a physical mixture with an FCC catalyst or in the same amorphous substrate as the zeolite used for cracking. It is currently being proposed that it be added to the FCC system. Uranium or platinum is added to produce a gasoline fraction with a high aromatic content, and there is no discussion in the patent of the effect on carbon monoxide combustion when using the additive. In U.S. Patent No. 3,808,121, a large size carbon monoxide combustion enhancer is
It is proposed to feed the regenerator. Catalyst particles of smaller size are circulated between the FCC cracking reactor and the catalyst regenerator, while larger promoter particles remain in the regenerator due to their size. The use of carbon monoxide oxidation promoters such as cobalt, copper, nickel, manganese, copper chromites and others impregnated onto inorganic oxides such as alumina is disclosed. Belgian patent no.
No. 820181 proposes the use of catalyst particles containing platinum, palladium, iridium, rhodium, osmium, ruthenium or rhenium or mixtures or compounds thereof to promote the oxidation of carbon monoxide in an FCC catalyst regenerator. . FCC by inclusion or using catalyst during catalyst manufacture
By adding compounds of the above metals to the hydrocarbon feed to the device, active metals are added to the FCC catalyst particles in amounts ranging from trace amounts up to 100 ppm. The same patent describes that the addition of promoter metals increases the production of coke and hydrogen during cracking. Catalysts containing promoter metals can be used as is or FCC without added promoters.
It can be added in the form of a physical mixture with a decomposition catalyst.

Applicant's company and/or its affiliates purchased large quantities of particulate additives from catalyst manufacturers. This additive is used to promote the combustion of carbon monoxide during catalyst regeneration in FCC equipment.
Sold by the manufacturer for the purpose of introducing additives to mix with the FCC catalyst and circulate within the FCC unit. Applicant's company and/or its affiliates have used additives in their commercial FCC operations. One such additive was understood to include a mixture of platinum-alumina particles and silica-alumina particles.

A cracking catalyst is circulated between the cracking zone and the catalyst regeneration zone, and the sulfur-containing hydrocarbon stream is cracked in contact with the catalyst in the cracking zone, and by burning off the sulfur-containing coke from the catalyst with an oxygen-containing gas. In an embodiment of the invention in a catalytic hydrocarbon cracking process, in which a flue gas containing carbon monoxide and containing sulfur is produced in a regeneration zone, the invention provides Concerning a method for reducing the amount of sulfur oxide, the method comprises a metal selected from platinum, palladium, iridium, rhodium, osmium, ruthenium, copper and chromium, or a compound thereof, accompanied by particulate solids to promote carbon monoxide oxidation. reacting carbon monoxide with oxygen in contact with a decomposition agent (the particulate solid is physically mixed with a decomposition catalyst) to produce carbon dioxide in the regeneration zone; at least 0.5% by volume of molecular oxygen; introducing sufficient molecular oxygen into the regeneration zone to provide an atmosphere within the regeneration zone with;
sufficient coke is removed from the catalyst in the regeneration zone such that the average carbon content of the catalyst transferred from the regeneration zone to the cracking zone is less than 0.2% by weight; including a substantially silica-free alumina phase in the catalyst;
A solid containing sulfur and aluminum is produced in the catalyst in the regeneration zone by reacting the alumina present in the alumina phase in the catalyst with sulfur trioxide, and the solid containing sulfur and aluminum is It consists of removing sulfur from the catalyst and producing hydrogen sulfide in the cracking zone by contacting the hydrocarbon stream.

In conjunction with the use of a catalyst containing a separate silica-free alumina phase for reaction with oxidized sulfur in the regenerator flue gas, we have discovered that the activity of promoting the combustion of carbon monoxide is very high. The use of granular carbon monoxide combustion promoters containing high-intensity metals or compounds thereof provides a cooperative method for removing both carbon monoxide and sulfur oxides from regenerator flue gases. I found out.

The present invention is used in connection with a fluid catalytic cracking process for cracking hydrocarbon feeds. commercial
The same sulfur-containing hydrocarbon feeds normally used in FCC units can be processed in crackers using the present invention. Suitable feedstocks include, for example, gas oils, light cycle oils, heavy cycle oils, and others that typically contain about 0.1 to 10 weight percent sulfur. Sulfur may be present in the feed as thiophones, disulfides, thioethers, and others. Suitable feedstocks typically have boiling points in the range of about 400° to 1000° or more. Suitable feeds may include recycled hydrocarbons that have already been cracked.

By preheating or heat exchanging the hydrocarbon feed to approximately 600 to 750 °C prior to its introduction into the cracking zone, the cracking conditions used in the cracking or conversion step in the FCC unit are often partially reduced. Although achieved, preheating of the feed is not essential. Cracking conditions include a catalyst/hydrocarbon weight ratio of about 3-10. The weight hourly space velocity of hydrocarbons in the cracking zone is approximately 5~
Preferably, 50/hour is used. When the catalyst is fed to the regenerator, the average amount of coke contained in the catalyst after contact with the hydrocarbons in the cracking zone will depend on the carbon content of the regenerated catalyst in a particular unit as well as the specific approximately 0.5 depending partly on the thermal balance of the equipment
Preferably, from about 25% by weight.

Catalyst regeneration zones used in FCC devices employing embodiments of the present invention may be of conventional design. The gas atmosphere within the regeneration zone typically consists of a mixture of gases with varying concentrations depending on location within the regenerator. The concentration of gas also varies according to the concentration of coke on the catalyst particles entering the regenerator and also according to the amount of molecular oxygen and water vapor fed into the regenerator. Generally, the gas atmosphere within the regenerator contains 5 to 25% water vapor, varying amounts of oxygen, carbon monoxide, nitrogen, carbon dioxide, sulfur dioxide and sulfur trioxide.

To facilitate the removal of sulfur from regenerator flue gas in a regenerator in accordance with the present invention, relatively coke-free, activated alumina-containing particles are combined with sulfur trioxide or molecular oxygen. Preferably, sulfur dioxide is contacted with the gaseous regenerator atmosphere at a location where the atmosphere contains this atmosphere. In conventionally designed regenerators, the flue gas contains the desired components and the catalyst typically contacts the flue gas at this point after a significant amount of coke has been removed. When using this type of regenerator, relatively coke-free contact between the alumina-containing particles and oxygen and sulfur dioxide or sulfur trioxide is facilitated.

According to one aspect of the invention, a carbon monoxide combustion enhancer is used within the FCC device. Carbon monoxide combustion promoters suitable for use according to the invention include the metals platinum, palladium, iridium, rhodium, osmium, ruthenium, copper and chromium or their compounds, such as oxides, sulfides, sulfates and Others. At least one of the metals or metal compounds mentioned above is used; mixtures of two or more metals are also suitable. For example, mixtures of platinum and palladium or of copper and chromium are suitable. By combining the above carbon monoxide combustion promoter metals with small amounts of other metals or metalloids, in particular rhenium, tin, germanium or lead, the effectiveness of the above promoter metals can be increased in some cases. .

The carbon monoxide combustion accelerator is prepared as follows:
Used in FCC equipment: The promoter is present in the equipment together with relatively small amounts of non-catalyst particulate solids such as alumina, silica and other particles suitable for circulation within the FCC equipment. , or the promoter comprises a small portion of the FCC catalyst particles (e.g. 5
%, preferably less than 1%), and the promoter metal is therefore present in a physical mixture with all or substantially all of the FCC catalyst.
When used as a physical mixture with the FCC catalyst, the promoter metal is preferably present as a particulate solid at a relatively high concentration. Preferably, the total amount of promoter metal added to the device is sufficient to promote combustion of most or substantially all of the carbon monoxide produced within the FCC regenerator.

Platinum is a particularly suitable promoter for use in the present method. Platinum is present on only a small percentage of the particles in the device. That is, the platinum is on a particulate solid that physically mixes with the FCC catalyst. The total amount of platinum added to the FCC device is approximately
Preferably it is between 0.01 and 100 ppm by weight, and particularly preferably between about 0.1 and 10 ppm by weight. It will be appreciated that the amount of platinum present in a given discrete particle added to the FCC device will be greater the smaller the amount of promoter-containing particles added. The concentration of platinum increases when very small amounts of particulate platinum-containing material are added to the FCC equipment.
Two weights or more may be reached if desired. However, it is preferred to keep the amount of platinum added to the particulate solid below 1% by weight of the total weight of the solid. The preferred range of use for the amount of platinum added to the discrete solid is about 0.01 to 1% by weight of the total weight of the discrete solid.

The amount of Group noble metal other than platinum generally provides a total in-system concentration, relative to the total amount of catalyst, that is about 2 to 10 times higher than that used for the platinum promoter. The amount of group metals such as palladium, iridium, etc. can thus be calculated from the above description of the concentration of platinum promoter, and at least twice as much and preferably five times as much of the other group noble metals is used. . The concentration of other Group noble metals on any separate particles within the FCC device is typically kept below about 2% by weight, desirably below about 1% by weight.

The amount of copper used as a promoter in an FCC unit is generally about 100% lower than the amount of platinum that would be used in the same unit, with respect to the total amount of catalyst used.
This corresponds to the total concentration in the device which is between 5000 times and 5000 times higher.
The concentration of copper promoter on separate particles is typically around 20% by weight
and desirably less than about 10% by weight.

The amount of chromium used as a promoter in an FCC device is generally, relative to the total amount of catalyst used,
This represents a total concentration within the device that is about 500 to about 25,000 times higher than the amount of platinum that would be used in the same device. The concentration of chromium in the chromium compound added, eg, by impregnation, onto the separate particles within the FCC device is maintained at less than about 20% by weight of the total particle weight, and desirably less than about 10% by weight.

The promoter metal or metal compound can be added to a separate particulate solid that is physically mixed with the FCC catalyst as it circulates through the device. The granular solid to be mixed with the catalyst is mixed with the catalyst and FCC in the granular form.
It may be any material suitable for circulation within the device. Particularly suitable materials are porous inorganic oxides such as alumina and silica, or silica
Mixtures of two or more inorganic oxides such as alumina, natural and synthetic clays and the like, crystalline aluminosilicate zeolites, and others. Gamma alumina is particularly good. The promoter metal may be added to the particulate solid in any suitable manner, such as by impregnation or ionization, or to a precursor of the particulate solid, such as by co-precipitation from an aqueous solution with an inorganic oxide precursor sol. It's fine. Particulate solids may be shaped into particles of suitable size for use in the FCC apparatus by conventional methods such as spray drying, grinding larger particles to the desired size, and the like.

A particulate solid containing at least one promoter metal or metal compound of the type described above can be mixed with the FCC catalyst body prior to charging the catalyst to the FCC device. Similarly, particulate solids containing promoters can be added to the FCC device in desired amounts separately from the catalyst.

When promoter metals are used in the system, and especially when promoter metals are present in relatively high concentrations in the form of particulate solids physically mixed with the decomposition catalyst, all carbon monoxide in the catalyst regenerator is Preferably, at least the majority of the combustion takes place in the dense catalyst phase region within the regenerator. The dense catalyst phase region means that the catalyst concentration is at least
means an area that is 10 pounds per cubic foot.

When using a separate particulate promoter physically mixed with the cracking catalyst, a minimum content of molecular oxygen of at least 0.5% by volume and preferably at least 1.0% by volume is maintained in the atmosphere within the regenerator. In addition, sufficient oxygen must be introduced into the regeneration zone within the FCC device.
The lowest concentration of molecular oxygen is usually found in the flue gas exiting the regeneration zone.

When using a separate particulate promoter that is physically mixed with the cracking catalyst, sufficient carbon within the regeneration zone is used such that the average concentration of carbon in the regenerated catalyst that is recycled from the regeneration zone to the cracking zone is less than 0.2% by weight. A large amount of coke must be burnt off the catalyst.

In accordance with another aspect of the invention, sulfur oxides are removed from the flue gas in the FCC regeneration zone by reacting sulfur trioxide with alumina in the regeneration zone. The alumina used in the reaction is contained as a separate alumina phase in the catalyst used in the FCC device;
Alternatively, it is contained in a significant portion of the catalyst particles used within the device. Suitable alumina is 40% by weight
Preferably, it is not tightly bound to more silica and is substantially free of tightly bound silica. The alumina, which forms a separate phase in the catalyst, contains on average about 50 to 5000 ppm by weight of "reactive alumina," as determined by treating the catalyst particles containing the alumina phase according to the following steps: If so,
Suitable for use in this method: (1) A gas mixture stream containing by volume 10% water, 1% hydrogen sulfide, 10% hydrogen and 79% nitrogen at a temperature of 1200 °C and atmospheric pressure. , continuously passed over the catalyst particles until the weight of the solid particles is substantially constant; (2) containing by volume 10% water, 15% carbon dioxide, 2% oxygen and 73% nitrogen; The solid obtained from step (1) above is heated at a temperature of 1200 °C and atmospheric pressure until the weight of the solid particles becomes substantially constant (the weight of the particles at this time is "Wa"). and (3) a stream of a gas mixture containing 0.05% by weight of sulfur dioxide, plus the same proportions of the same gas as used in step (2) above, at a temperature of 1200°C.
and at atmospheric pressure, over the solid particles obtained from step (2) above until the weight of the solid particles becomes substantially constant (the weight of the solid particles at this time is designated as "Ws").

The weight fraction "Xa" of reactive alumina in the solid particles is determined by the following formula: Xa = Ws-Wa/Wa x molecular weight of alumina/3 x molecular weight of sulfur trioxide. FCC used
Catalysts, especially catalysts that contain a large amount of alumina in their total composition, contain at least a small amount of a separate alumina phase containing reactive alumina. On the other hand, many alumina-containing catalysts are substantially free of any reactive alumina. Most, if not all, conventional catalysts contain both silica and alumina, and we have noticed that the absence of reactive alumina in many of the alumina-containing catalysts means that no reactive alumina is present in the catalyst. This is believed to be the result of a tight bond between silica and alumina. Therefore, the alumina phase must be substantially silica-free in order to contain alumina suitable for reaction with the sulfur trioxide in the regenerator flue gas.

Most cracking catalysts contain 50% or more by weight of silica, which tends to bond tightly with the alumina making it relatively inert with respect to reaction with sulfur oxides.

Catalysts containing relatively large amounts of alumina present as a separate phase (free alumina) can be prepared by using starting materials containing 50% to 60% or more alumina or alumina precursors and at least some amount of separate alumina. It can be produced by making catalysts from materials such as clays, which are known to contain free alumina. A separate alumina phase or reactive alumina may be added to the prefabricated catalyst by impregnation, but
We have found that alumina cannot be successfully added to a silica-containing catalyst unless the catalyst has first been heated to a temperature of from 1000° to about 1500°C, preferably from 1000° to 1400°C.

Apart from the requirement that the catalyst should include a separate, substantially silica-free alumina phase,
The process of the invention imposes no special restrictions on the type of cracking catalyst that can be used. Preferred catalysts are those containing 1 to 50% by weight of a zeolite crystalline aluminosilicate, such as a type X zeolite or a type Y zeolite, bound to a porous, heat-resistant substrate such as one or more inorganic oxides. The sodium cations in the zeolite component of the catalyst are preferably ion-exchanged with rare earth or hydrogen cations to enhance the activity and stability of the catalyst.

The alumina in the catalyst particles reacts with sulfur trioxide or sulfur dioxide and oxygen in the FCC catalyst regenerator to form at least one solid compound containing sulfur and aluminum, such as sulfate of aluminum. In this way, sulfur oxides are removed from the regenerator atmosphere and are therefore not in the flue gas and emitted from the regenerator.

A catalyst containing solid aluminum- and sulfur-containing materials is fed to a cracking zone within the FCC unit.
In the cracking zone, alumina is regenerated in the catalyst and hydrogen sulfide is produced by contacting a sulfur-containing catalyst with the hydrocarbon stream being treated in the cracking zone. In addition to producing hydrogen sulfide, the reaction of the sulfur- and aluminum-containing solids with the hydrocarbon feed will produce other sulfur compounds in fluid form, such as carbon oxysulfide, organic sulfides, and others. The resulting fluid sulfur compounds exit the cracking zone as part of the cracked hydrocarbon stream, along with the fluid sulfur compounds produced directly from the sulfur in the hydrocarbon feed. The exhaust gases that are subsequently separated from the cracked hydrocarbon stream are therefore treated with hydrogen sulfide, which is produced directly from the sulfur in the feed, and by reacting the sulfur- and aluminum-containing solids with the hydrocarbon stream in the cracking zone. Contains hydrogen sulfide produced.

Catalysts containing a separate alumina phase containing alumina to be reacted with sulfur trioxide in the regenerator may contain promoter metals such as platinum, palladium, iridium, rhodium, osmium, It is essential to the operation of this invention that it must be substantially free of any of ruthenium, copper and chromium or compounds of these metals. The presence of these metals or their compounds in catalyst particles containing an alumina phase containing alumina to be used for reaction with oxidized sulfur means that even small amounts of solid sulfur may be present in the FCC regenerator where carbon monoxide is present. - It has been found that there is a practical harm to the ability of alumina to produce containing substances. Therefore, when these metals are present on catalyst particles containing alumina that are to react with sulfur trioxide, the desired reaction of sulfur trioxide to react to form a solid is inhibited and the object of the present invention is However, more sulfur oxides are present in the regenerator flue gas and exit the FCC regenerator. Therefore, although the metal promoters disclosed herein are essential to the operation of the present invention, they must be used in particulate solid form as a physical mixture with a catalyst containing a separate alumina phase that reacts with the sulfur oxide. Therefore, the promoter metal is
Must be on a separate particle physically mixed with the FCC catalyst.

The following illustrative embodiments describe preferred embodiments of the operation of the invention.

Using conventional FCC equipment and a commercially available type of zeolite-containing equilibrium cracking catalyst containing an average of 180 ppm by weight of reactive alumina in a separate alumina phase, boiling points ranging from about 580〓 to about Approximately 19,000 barrels/day of hydrocarbon feed with 1,100 liters is cracked. The hydrocarbon feed contains approximately 0.8% feed sulfur by weight. The cracking zone inlet used is a combination of a riser cracking method and a dense bed cracking method. The digestion conditions used include approximately
A reaction temperature of 920 °C, a hydrocarbon polymerization space velocity of about 5/hr, and a conversion of about 85% (defined as feed converted to components lighter than 430 °C) are included. Spent catalyst
The average amount of coke on the catalyst is about 1.5% by weight
It is. The coke on the spent catalyst contains approximately 0.7% by weight sulfur.

The amount of carbon on the regenerated catalyst is about 0.5% by weight.
The flue gas leaving the catalyst regenerator is approximately 650 volumes
ppm sulfur oxide (calculated as sulfur dioxide), approximately 0.3
% oxygen by volume, and has a CO/CO ₂ ratio of approximately 0.6. The catalyst regeneration conditions used in the regeneration zone are temperatures of approx.
Including 1200〓. The catalyst is continuously circulated between the cracking zone and the regeneration zone at a rate of approximately 16 tons/min. The total amount of catalyst retained in the system is approximately 180 tons.

According to the invention, impregnated on an alumina support
Sixty pounds of particles containing 0.6% by weight platinum are introduced for circulation in the FCC unit along with the catalyst. The introduction of platinum-alumina particles then continues at a rate of about 7 pounds/day. This keeps the amount of platinum added to the system at an equilibrium level of about 5 ppm by weight with respect to the total amount of catalyst present in the system. Most of the carbon monoxide is combusted in the dense catalyst phase region within the regenerator. Sufficient oxygen is added to the regenerator to provide at least 1.0% by volume oxygen in the regenerator atmosphere. A sufficient amount of coke is burned off from the cracking catalyst in the regenerator such that the regenerated catalyst recycled from the regenerator to the cracking reactor contains on average no more than 0.2% by weight of carbon. Platinum - Alumina - Carbon oxide -
After addition of the combustion promoter, the CO/CO ₂ and sulfur oxide levels of the flue gas exiting the regeneration zone are measured. The CO concentration is found to decrease significantly from 500 to 1500 ppm by volume, while the level of oxidized sulfur, calculated as _SO2 , is found to decrease to below 200 ppm by volume. The amount of carbon on the regenerated catalyst is about 0.5% by weight.

As can be seen from the above illustrative embodiments, the method of the present invention provides a simple method for suppressing the amount of both carbon monoxide and sulfur oxides present in the flue gas withdrawn from an FCC catalyst regenerator. Provide an economical way.

Many modifications, variations and equivalents of the embodiments illustrated above will be apparent to those skilled in the art and are intended to be encompassed within the scope of the appended claims. There is.

Claims (1)

[Scope of Claims] 1. A cracking catalyst is circulated between a cracking zone and a catalyst regeneration zone, and a sulfur-containing hydrocarbon stream is cracked in contact with the catalyst in the cracking zone, and the catalyst is decomposed with an oxygen-containing gas. In a catalytic hydrocarbon cracking process in which sulfur-containing flue gas is produced in a regeneration zone by burning off sulfur-containing coke from monoxide in the regeneration zone by contacting with an accompanying carbon monoxide oxidation promoter containing a metal or metal compound selected from platinum, palladium, iridium, rhodium, osmium, ruthenium, copper and chromium. (b) introducing into the regeneration zone sufficient molecular oxygen to provide an atmosphere within the regeneration zone having a molecular oxygen concentration of at least 0.5% by volume; (c) sufficiently removing coke from said catalyst in said regeneration zone such that the average carbon content in said catalyst sent from said regeneration zone to said cracking zone is less than 0.2% by weight; (d) said metal or (e) by reacting sulfur trioxide with the alumina present in the alumina phase in the catalyst; producing sulfur- and aluminum-containing solids in the catalyst in the regeneration zone; (f) contacting the sulfur- and aluminum-containing solids with the hydrocarbon stream in the catalyst in the cracking zone; A method of reducing the amount of carbon monoxide and sulfur oxides in a flue gas comprising removing sulfur from a gas and producing hydrogen sulfide. 2 Regarding catalysts, calculated based on elemental metals.
The method of paragraph 1 above, wherein sufficient particulate solid is mixed with the catalyst to provide 0.1 to 100 ppm by weight of metal. 3. The method of item 2 above, wherein the carbon monoxide oxidation promoter contains 0.01 to 5% by weight of metal, calculated on an elemental metal basis. 4. The method of paragraph 1 above, wherein sufficient molecular oxygen is introduced into the regeneration zone to provide an atmosphere with a molecular oxygen concentration of at least 1.0% by volume.