WO2002040141A2

WO2002040141A2 - Sox catalyst

Info

Publication number: WO2002040141A2
Application number: PCT/US2001/043006
Authority: WO
Inventors: John Mccauley
Original assignee: Tricat Industries Inc.
Priority date: 2000-11-20
Filing date: 2001-11-08
Publication date: 2002-05-23
Also published as: AU2002230421A1; WO2002040141A3

Abstract

Sulfur oxides are removed in the regenerator zone and rapidly released as H2S in the reactor zone of an FCC system employing a particulate SOx catalytic/absorbent comprising Cu and/or Ag, an alkali metal oxide, MgO, V2O5 and a clay binder.

Description

SO_x CATALYST

RELATED APPLICATION

This Application claims priority from Provisional Application Serial No. 60/249,464, entitled "So_x Catalyst", the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a catalytic absorbent for sulfur oxides. The invention has particular applicability in reducing the emission of sulfur oxides during fluidized catalytic cracking of sulfur-containing hydrocarbon feedstocks.

BACKGROUND ART A major industrial challenge comprises the development of efficient methods for reducing the concentration of air pollutants, such as sulfur oxides, in waste gases, such as waste gases resulting from the processing and combustion of sulfur-containing hydrocarbon fuels. The discharge of these waste gas streams into the atmosphere is environmentally undesirable at the sulfur oxide concentrations which are frequently encountered in conventional operations. Such waste gas streams typically result, for example, from the combustion of sulfur-containing fossil fuels for the generation of heat and power, the regeneration of catalysts employed in the refining of hydrocarbon feedstocks which contain organic sulfur compounds, and the operation of Claus-type sulfur recovery units.

Two fundamental approaches have been suggested for the removal of sulfur oxides (SO_x) from a waste gas. One approach involves scrubbing the waste gas with an inexpensive alkaline material, such as lime or limestone, which reacts chemically with the SO_x yielding a non-volatile product for disposal. Unfortunately, this approach requires a large and continual supply of the alkaline scrubbing material, and the resulting reaction products can create a solid waste disposal problem of substantial magnitude. The second principal approach to the control of SO_x emission involves the use of SO_x absorbents which can be regenerated either thermally or chemically. The cyclic, FCC of heavy petroleum fractions is one of the major refining operations involved in the conversion of crude petroleum oils to valuable products, such as the fuels utilized in internal combustion engines. A typical FCC unit comprises three sections: a cracking section or reactor; a regenerator and a separation section of stripping zone. A typical FCC process involves continuous catalytically cracking of a petroleum feedstock in a reactor zone through contact with a particulate FCC catalyst at temperatures between about 400°C and about 700°C. Particulate FCC catalysts substantially deactivated by non-volatile, sulfur-containing coke deposits are separated from the reactor zone effluent and stripped of volatile deposits in a stripping zone. The stripped catalyst particles are separated from the stripping zone effluent, regenerated in a regenerator zone by combustion of the coke with an oxygen-containing gas at temperatures between about 565°C and about 790°C, and the regenerated catalyst particles returned to the reactor zone. The combustion of sulfur-containing coke results in the release of substantial amounts of SO_x to the atmosphere.

While numerous materials and composites are known to have absorbent and catalytic properties in connection with SO_x reduction, the formulation of an efficient SO_x reducing additive, e.g., catalyst and/or absorbent, in the context of an FCC system and its exigencies is fraught with problems and unpredictability.

Generally, about 45% to about 55% of the sulfur in the hydrocarbon feedstock is converted to hydrogen sulfide (H₂S) in the FCC reactor, about 35% to about 45% remains in a liquid product, and about 5% to about 10% in the coke deposited on the FCC catalyst. These amounts vary depending upon the type of hydrocarbon feedstock, rate of hydrocarbon cycle, steam stripping rate, type of FCC catalyst, reactor temperature, reactor design and other FCC system variables. Accordingly, the formulation of an effective additive for reducing SO_x emissions from an FCC system is recognized in the art as a challenging problem

The difficulties attendant upon formulating and designing an effective SO_x reducing additive in the context of an FCC system stems from various requirements and considerations, aside from the generally and considerations, aside from the generally unpredictable nature of catalytic activity. The particulate material serving as the SO_x reducing additive must be attrition-resistant to survive in an FCC environment without fragmenting. Accordingly, an effective SO_x reducing additive should have a Davison Index less than 10. An effective particulate SO_x reducing additive should not contain metal or other component which acts as a poison in the FCC regime. In addition, an effective particulate SO_x catalyst/absorbent must perform three functions: (1) oxidize SO₂ to SO₃; (2) chemisorbs SO₃: and (3) release the absorbed SO₃ as H₂S in the reactor side of an FCC system. During regeneration, sulfur in the coke is oxidized primarily to S0₂. In order for sulfate chemisorption to occur, the SO₂ must be oxidized to SO₃ which is then chemisorbed as the sulfate. As in the operational temperature of the regenerator is increased, the formation of S0₃ is less favored. Accordingly, the catalyzing function of an SO_x catalyst/absorbent is significant.

In FCC units operating with high sulfur-containing feedstocks, relatively large amounts of sulfur acceptors having a high unit capacity to adsorb SO_x are required to accomplish reductions in SO_x levels. The use of large amounts of an SO_x reducing additive results in appreciable dilution of the active FCC catalyst in the cracking reaction cycle whether the sulfur acceptor is a part of the FCC particle itself or is present as a discrete entity circulated with the FCC catalyst inventory. A basic limitation is that conditions of time and temperature for operating cyclic, FCC units, especially heat balanced FCC units, are geared to maximizing the production of desired products. Conditions established to achieve this result are by no means those that are optimum for reversibly reacting SO_x in the regenerator zone and carrying the sulfur back to the reactor for conversion at least in part to H₂S. Although SO_x reducing additives offer promise, they leave much to be desired because, inter alia, SO_x removal activity decreases rapidly with the residence time available for such SO_x reducing additives to function effectively. Thermally stable magnesium aluminate spinels, such as MgAl₂O and Mg₂Al₂O₅, are generally recognized as the SO_x catalyst/absorbent of choice for FCC systems, e.g., DESOX, a commercialized magnesium aluminate spinel.

In U.S. Patent No. 5,990,030 issued on November 23, 1999 issued to McCauley, an FCC composition to disclose containing a cracking catalyst and a SO_x additive containing an alkali metal oxide, such as Li₂O, Na₂O or K₂O and mixtures thereof. The disclosed composition constitutes an improvement of prior art composition containing SO_x additives. In U.S. Patent No. 6,129,833 issued on October 10, 2000 to McCauley, a catalyst composition is disclosed containing a SO_x additive comprising copper (Cu) and an alkali metal oxide. The entire disclosures of U.S. Patent No. 5,990,030 and U.S. Patent No. 6,129,833 are incorporated by reference herein.

There is a continuing need for an effective SO_x reducing additive, e.g., catalyst/absorbent, for. use in an FCC system which is capable of converting SO₂ to S0₃ in the regenerator zone and absorbing large quantities of SO₃ in the regenerator zone, given regenerator zone exigencies, including residence time and temperature, and further capable of effectively and rapidly liberating the absorbed SO_x in the reactor zone, given reactor zone exigencies, including residence time and temperature. There also exists a need to produce such an SO_x catalyst/absorbent in a cost-effective, efficient manner.

DISCLOSURE OF THE INVENTION

An advantage of the present invention is an SO_x catalyst/absorbent, suitable for use in an FCC system, which can be produced in a cost-effective, efficient manner.

Another advantage of the present invention is an FCC catalyst inventory comprising an FCC catalyst and an SO_x catalyst/absorbent capable of high SO_x capacity and high SO_x pickup and release rates.

A further advantage of the present invention is an FCC process employing a catalyst inventory comprising an FCC cracking catalyst and an efficient SO_x catalyst/absorbent. Additional advantages and other features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the invention. The objects and advantages of the invention may be realized and obtained as particularly pointed out in the appended claims.

According to the present invention, the foregoing and other advantages are achieved in part by a fluidized catalytic cracking composition comprising a particulate solid cracking catalyst for cracking a hydrocarbon feedstock and sulfur oxide (SO_x) reducing particles comprising up to about 20 wt.% Ag and/or Cu; about 20 to about 50 wt.% of an alkali metal oxide, up to about 20% of magnesium oxide (MgO), up to about 3 wt.% V₂O₅ and the remainder an inorganic support.

A further aspect of the present invention is a process for the cyclic fluidized catalytic cracking of a hydrocarbon feedstock containing organic sulfur compounds, which process comprises: cracking the hydrocarbon feedstock under fiuidizing conditions using a particulate cracking catalyst in a reactor zone, wherein the cracking catalyst is deactivated by sulfur-containing coke deposits; passing the deactivated cracking catalyst to a regenerator zone; removing the sulfur-containing coke deposits from the deactivated cracking catalyst in the regenerator zone by burning with an oxygen-containing regeneration gas, thereby forming SO_x; absorbing the sulfur oxides in the regenerator zone with a fluidizable particulate SO_x removing additive comprising an inorganic support, up to about 20 wt.% Ag and/or Cu, about 20 to about 50 wt.% alkali metal oxide, up to about 20 wt.% MgO and up to about 3 wt.% V₂O₅, the remainder an inorganic binder; and removing the absorbed SO_x from the particulate additive as a sulfur-containing gas comprising hydrogen sulfide in the reactor zone.

Additional objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to the regarded as illustrative in nature, and not as restrictive.

DESCRIPTION OF THE INVENTION It is generally recognized that the greatest deficiency of FCC SO_x additives is their limited ability to rapidly release sulfur under FCC reactor conditions. Specifically, the sulfur must be released in the reactor in a very short period of time at relativity low temperatures. Therefore, the rate at which the additive releases sulfur determines the additive's effectiveness. The present invention provides an FCC composition and methodology employing an SO_x that exhibits not only extremely high capacity for SO_x but also high SO_x pickup and release rates. The SO_x additive disclosed in U.S. Patent No. 5,990,030 constitutes a definite improvement over prior SO_x additives. However, it was observed that the release of sulfur as H S in the reactor was not always complete. Lithium oxide is a preferred metal oxide because of its low molecular weight and its high absorption capacity. Lithium oxide also has the highest release rate. However, lithium oxide is the most expensive of the alkali metal oxides. Potassium oxide exhibits a higher release rate than sodium oxide. However, the molecular weight of potassium oxide indicates that its SO_x absorption capacity is relatively low. The SO_x additive disclosed in U.S. Patent 6,129,833 contains Cu in addition to an alkali metal oxide to absorb sulfur oxide. However, under certain conditions, the absorption capacity appeared restrictive.

The present invention comprises the strategic formulation of an FCC SO_x additive exhibiting both high SO_x capacity and high SO_x pickup and release rates. The SO_x additive contains up to about 20 wt.% Cu and/or Ag, such as about 5 to about 15 wt.% Cu and/or Ag, e.g., about 10 wt.%. High concentrations of Cu or Ag improve the SO_x characteristics of the additive, but also increase costs.

The SO_x additive also contains an alkali metal oxide, such as K₂O, Li₂O or Na₂O, in an amount of about 20 wt.% to about 50 wt.%, e.g., about 35 wt.%. A high alkali metal oxide content improves the absorption capacity of the additive. However, if the ratio of the alkali metal oxide to Cu and/or Ag is too high, the release rate decreases.

The SO_x additive may also contain magnesium oxide (MgO) for increased SO_x capacity. However, the amount of magnesium oxide should be less than about 20 wt.%, such as about 7 wt.% to about 15 wt.%, e.g., about 20 wt.%, of the final product. Sulfur oxide absorbed by MgO not released in the reactor. An MgO content in excess of about 20 wt.% may adversely impact the attraction resistance of the additive.

The SO_x additive may also contain a small amount of N₂O₅, up to about 3%, e.g., about 1 wt. % to about 3 wt.%, e.g., about 2 wt.%. The small amount of N O₅ improves the release of the sulfur oxide in the reactor. The SO_x additive of the present invention also comprises an inorganic binder, such as a clay. Suitable clays include bentonite, attapulgite, kaolin, hectorite, or Laponite, a synthetic clay. A suitable SO_x additive comprises about 8.5 wt.% Cu, about 9 wt.% MgO, about 36 wt.% K₂O, about 2 wt.% N₂O₅ and about 44.5 wt.% bentonite.

Another embodiment of the present invention is, therefore, a process for the cyclic fluidized catalytic cracking of a hydrocarbon feedstock containing organic sulfur compounds, which process comprises: cracking the hydrocarbon feedstock under fluidizing conditions using a particulate cracking catalyst in a reactor zone, whereby the cracking catalyst is deactivated by sulfur-containing coke deposits; passing the deactivated cracking catalyst to a regenerator zone; removing the sulfur- containing coke deposits from the deactivated cracking catalyst in the regenerator zone by burning with an oxygen containing regeneration gas, thereby forming sulfur oxides; absorbing the sulfur oxides in the regenerator zone with the inventive fluidizable particulate sulfur oxide catalyst/absorbent additive comprising up to about 20 wt.% Cu and/or Ag, about 20 to about 50 wt.% of an alkali metal oxide, such as K₂O, up to about 20 wt.% MgO, up to 3 wt.% N2O₅ and a clay binder, and removing the absorbed sulfur oxides from the sulfur oxide catalyst/absorbent as a sulfur- containing gas comprising hydrogen sulfide in the reactor zone. In various embodiments of the present invention, the SO_x catalyst/absorbent is prepared in particulate form with physical properties consistent with the requirements for effective and efficient use in an FCC system. For example, various embodiments of the particulate SO_x catalyst/absorbent of the present invention can have a bulk density of about 0.5 to about 0.9 g/cc, preferably about 0.7 to about 0.8 g/cc. Various embodiments of the particulate SO_x catalyst/absorbent of the present invention can also have a particle size of about 20 to about 180 microns, preferably about 45 to about 120 microns. In addition, various embodiments of the particulate SO_x catalyst/absorbent of the present invention can exhibit a Davison Index less than 10.

The SO_x catalyst/absorbent of the present invention can be combined in an appropriate amount with a conventional particulate FCC cracking catalyst, such any of the various crystalline aluminosilicate zeolites, for use in an FCC system. The present invention further comprises a process for the cyclic, fluidized catalytic cracking of a hydrocarbon feedstock containing organic sulfur compounds. In the inventive process, the hydrocarbon feedstock is cracked under fluidizing conditions using a catalyst inventory comprising a particulate cracking catalyst and a particulate SO_x catalyst/absorbent of the present invention in a reactor zone, wherein the cracking catalyst is deactivated by sulfur-containing coke deposits. The deactivated cracking catalyst is then transferred to a regenerator zone, wherein the sulfur-containing coke deposits on the cracking catalyst are removed with an oxygen-containing regenerating gas, thereby forming SO_x. Typically, the temperature in the reactor zone is about 400°C to about 700°C, while the temperature in the regenerator zone is about 565°C to about 790°C. A particulate SO_x catalyst/absorbent of the present invention can be prepared by various methods. In one such method, the components of the inventive SO_x catalyst/absorbent can be sequentially mixed, dried, calcined, ground and sieved.

EXAMPLES

All samples were dried at 140°C before being evaluated in the TGA. Oxidizing conditions were 730°C under 100 cc/min of 2% O₂ and 2,000 ppm SO₂ at which time a weight gain was measured. Each sample was then cooled to 525°C under N₂ gas. A gas mixture containing 5%H₂ and 95% N₂ was then passed over the sample and a weight loss was measured.

Chemical composition of Examples:

Example 1 31% K₂O, 21% Mg, 2% V₂O₅, 46% clay Example 2 5% Cu, 5% Li₂O, 28% K₂O, 19% MgO, 2% V₂O₅, 41% clay Example 3 5% Cu, 5% Li₂O, 35% K₂O, 10% MgO, 2% V₂O₅, 43% clay Example 4 39% K₂O, 10% MgO, 2% V₂O₅, 49% clay Example 5 8% Cu, 36% K₂O, 9% MgO, 2% V₂O₅, 45% clay

Table 1

TGA Results of Sampl es

Sample: Regenerator conditions Reactor conditions

Wt/% gain rate t . % loss rate (wt%/min) (wt.%/min)

Example 1 56 1.0 0.3 0.2

Example 2 71 1.0 1.8 0.2

Example 3 60 0.9 2.2 0.4

Example 4 40 1.1 0.4 0.1

Example 5 46 1.3 5.0 3.0

DESOX 37 1.1 0.4 0.3

As can be seen from Table 1, samples that contain alkali metal oxide have a greater absorption of So_x than DESOX under regenerator conditions. Under reactor conditions, samples containing copper, release greater quantities of SO_x and at a greater rate than samples not containing copper.

In embodiments of the present invention, stabilizing agents can be added to enhance the desirable properties of compositions comprising silver and copper. In general, other Group IIA oxides can be added as stabilizing agents, e.g., calcium incorporated as calcium oxide. Silver with the proper stabilizing agent demonstrates properties similar to copper. Materials containing MnO, CoO, ZnO, Fe₂O₃, or other transition metal oxides form sulfides as a portion of their composition under reducing conditions. The presence of copper or silver shifts the reducing products to oxides, thereby releasing sulfur.

The SO_x catalyst/absorbent of the present invention enjoys utility in various applications wherein SO_x reduction is desired, but has particular utility in an FCC environment for absorbing SO_x as SO₃ in the regenerator zone and releasing absorbed SO_x in the reactor zone of an FCC system. The inventive SO_x catalyst can, therefore, be used in any of various FCC systems as part of the catalyst inventory together with any of various conventional FCC cracking catalysts, including aluminosilicate zeolites.

Claims

WHAT IS CLAIMED IS:

1. A fluidized catalytic cracking composition, comprising: a particulate cracking catalyst for cracking a hydrocarbon feedstock; and a particulate sulfur oxide catalyst/absorbent additive comprising up to about 20 wt.% copper

(Cu) and/or silver (Ag), about 20 to about 50 wt.% of an alkali metal oxide selected from the group consisting of lithium oxide, sodium oxide, potassium oxide, and mixtures thereof, up to about 20 wt.% magnesium oxide (MgO), up to about 3 wt.% V₂0₅, the balance an inorganic binder.

2. The composition comprising according to claim 1, about 5 to about 15 wt.% of Cu or Ag, about 35 wt.% of the alkali metal oxide, about 7 to about 15 wt. % of MgO, about 1 to about 3 wt.% V₂0₅, and the balance a clay binder selected from the group consisting of bentonite, attapulgite, kaolin, hectorite and Laponite.

3. The composition according to claim 2, comprising about 10 wt.% Cu, about 35 wt.% K₂0, about 10 wt.% MgO, about 2 wt.% V₂0_5>, the balance of clay.

4. A process for the cyclic fluidized catalytic cracking of a hydrocarbon feedstock containing organic sulfur compounds, which process comprises: cracking the hydrocarbon feedstock under fluidizing conditions using a particulate cracking catalyst in a reactor zone, whereby the cracking catalyst is deactivated by sulfur-containing coke deposits; passing the deactivated cracking catalyst to a regenerator zone; removing the sulfur-contianing coke deposits from the deactivated cracking catalyst in the regenerator zone by burning with an oxygen containing regeneration gas, thereby forming sulfur oxides; absorbing the sulfur oxides in the regenerator zone with a fluidizable particulate sulfur oxide catalyst/absorbent additive according to claim 1; and removing the absorbed sulfur oxide from the particulate sulfur oxide reducing additive as a sulfur-containing gas comprising hydrogen sulfϊde in the reactor zone.

5. The process according to claim 4, employing the particulate sulfur oxide reducing additive set forth in claim 2 having a bulk density of about 0.5 to about 0.9 g/cc, a particle size of about 20 to about 180 microns and a Davison Index less than 10.

6. The process according to claim 5, employing the sulfur oxide catalyst/absorbent additive according to claim 3.