USE OF ANIONIC CLAY IN AN FCC PROCESS

The present invention relates to the use in a fluid catalytic cracking (FCC) process of a catalyst or catalyst additive comprising a specific type of anionic clay.

Anionic clays are layered structures corresponding to the general formula

[M _m ²⁺ M _n ³⁺ (OH) _2m+2n .](X _n/z ^z" ). bH ₂ O

wherein M ²⁺ is a divalent metal, M ³⁺ is a trivalent metal, m and n have a value such that m/n=1 to 10, preferably 1 to 6, more preferably 2 to 4, and b has a value in the range of from 0 to 10, generally a value of 2 to 6, and often a value of about 4. X is an anion with valance z, such as CO ₃ ^2" , OH ^" , or any other anion normally present in the interlayers of anionic clays. The crystal structure of anionic clays consists of positively charged layers built up of specific combinations of metal hydroxides between which there are additional anions and water molecules. Hydrotalcite is an example of a naturally occurring anionic clay in which Al is the trivalent metal, Mg is the divalent metal, and X is carbonate. Meixnerite is an anionic clay in which Al is the trivalent metal, Mg is the divalent metal, and X is hydroxyl.

In this specification, the term "anionic clay" encompasses the frequently used terms "hydrotalcite-like material" and "layered double hydroxide", which are synonymous. It further includes the various polytypes of anionic clays, such as the common 3Ri-polytype and the 3R ₂ -polytype disclosed in WO 01/012550. For more information on the various polytypes of anionic clays, reference may be had to Clay and Clay Minerals, Vol. 41 , No. 5, pages 551-557 and 558-564.

Upon mild calcination, i.e. at about 200-800 ⁰ C, anionic clays are transformed into a rehydratable mixed oxide, which in this specification is referred to as a solid

solution. These solid solutions contain a well-known memory effect whereby the exposure to water of such calcined materials results in the reformation of the anionic clay structure. Upon more severe calcination, generally above about 800 ⁰ C, a spinel structure is formed, which is not rehydratable to anionic clay anymore.

In this specification, the term "thermally treated form of anionic clay" includes both solid solutions and spinel structures.

It is known from EP 0 278 535 to use anionic clays in FCC catalysts and additives, in particular for the reduction of SO _x emissions. These anionic clays are made by (i) preparing a solution of the nitrate salts of the divalent and the trivalent metal, (ii) co-precipitating the divalent and trivalent metals using sodium hydroxide, followed by (iii) aging the resulting mixture for one hour at 65 ⁰ C and (iv) filtering and washing the precipitate with demineralized water to remove unwanted ions, such as sodium.

Sodium negatively affects the catalytic properties of zeolites. Hence, removal of sodium before the incorporation of the anionic day into the FCC catalysts or catalyst additives is important, especially if these catalysts or catalyst additives are to contain zeolite.

Another method of preparing anionic clays is disclosed in WO 99/41195 and WO 00/44671 , in which (thermally treated) aluminum trihydrate or (pseudo)boehmite is slurried with magnesium oxide or hydroxide and subsequently aged to form an anionic clay. The advantage of this process is that these aluminum and magnesium sources do not introduce unwanted anions. Furthermore, no acids, bases, or metal salts need to be added during the process, which also avoids the introduction of unwanted ions, such as Na ⁺ . Consequently, the resulting anionic clay does not need to be washed or filtered and can be dried, shaped, or added to other catalyst (additive) ingredients directly.

It has now been found that the reduction of SO _x emissions from FCC units by anionic clay-containing catalysts or catalysts additives can be further improved. This improvement is obtained by using catalysts or catalyst additives comprising a K-containing anionic clay or its thermally treated form.

Therefore, the present invention relates to the use in an FCC process of a catalyst or catalyst additive containing an anionic clay or its thermally treated form, said anionic clay comprising at least 0.5 wt% of potassium, calculated as K ₂ O and based on the weight of potassium-containing anionic clay.

The anionic clay preferably contains 1 to 30 wt% of K, more preferably 3 to 15 wt% of K (as K ₂ O).

Catalysts and catalyst additives comprising this (thermally treated) K-containing anionic clay show increased performance in SO _x removal compared to K-free anionic clays. Furthermore, K is less detrimental to the catalytic properties of zeolites than is Na.

Further, K-containing anionic clays are easier to prepare by precipitation than K- free or Na-free anionic clays, because a K compound can be used as the base, and no washing step is required to remove undesired cations introduced by the base.

The anionic clay structure of the K-containing anionic clays suitable for use according to the present invention may be built up from various trivalent and divalent metals. Examples of suitable trivalent metals (M ³⁺ ) include Al ³⁺ , Ga ³⁺ , In ³⁺ , Bi ³⁺ , Fe ³⁺ , Cr ³⁺ , Co ³⁺ , Sc ³⁺ , La ³⁺ , Ce ³⁺ , and combinations thereof. Suitable divalent metals (M ²⁺ ) include Mg ²⁺ , Ca ²⁺ , Ba ²⁺ , Zn ²⁺ _, Mn ²⁺ , Co ²⁺ , Mo ²⁺ , Ni ²⁺ , Fe ²⁺ , Sr ²⁺ , Cu ²⁺ , and combinations thereof. Preferred metal combinations are Mg-Al, Zn-Al, Ca-Al, Ba-Al, Fe-Al, Mn-Al, and Co-Al anionic clays.

The K-containing anionic clay suitable for use according to the present invention can be prepared by various methods, some of which are exemplified here. Method 1 involves the co-precipitation of a divalent and a trivalent metal salt using a K-containing base - such as KOH, K ₂ CO ₃ , or KHCO ₃ - to form a suspension comprising a precipitate. This suspension is then aged, resulting in a suspension of anionic clay. This aging may be conducted at a temperature in the range of 25- 250 ⁰ C, preferably 50-180 ⁰ C, for 10 minutes to 48 hours, more preferably 30 minutes to 24 hours, and most preferably 1 to 6 hours. If hydrothermal aging conditions are used (i.e. above 100°C), autogenous pressure is preferably applied. The anionic clay is then dried, for instance by spray-drying, without first being separated from the remaining solution. The latter is important, because such a separation step (e.g. filtration) would remove K ions. Evidently, the anionic clay also is not washed prior to drying. Suitable salts of the divalent and trivalent metals include their nitrate, chloride, sulphate, acetate, formiate, carbonate, and hydroxycarbonate salts.

Method 2 involves the aging of a suspension comprising a divalent and a trivalent metal compound, at least one of them being water-insoluble, in the presence of a potassium salt or potassium base. Suitable potassium salts include KCI, and KNO ₃ . Suitable potassium bases include KOH, K ₂ CO ₃ , and KHCO ₃ . This aging may be conducted at a temperature in the range 25-250°C, preferably 50-18O ⁰ C, for 10 minutes to 48 hours, more preferably 30 minutes to 24 hours, and most preferably 1 to 6 hours. If hydrothermal aging conditions are used (i.e. above 100 ⁰ C), autogenous pressure is preferably applied.

The potassium salt may be introduced into the suspension as a separate compound from the slurry of divalent and trivalent metal compounds, it may be added to the divalent or the trivalent metal compound prior to combining said di- and trivalent metal compounds in the slurry, or it may already be present in the di-

or the trivalent metal compound. In the latter case, a K-doped divalent or trivalent metal compound is used.

Again, the resulting anionic clay is not separated from the liquid prior to drying, e.g. spray-drying.

Suitable trivalent metal compounds to be used in method 2 are water-insoluble compounds of the trivalent metals aluminium, gallium, indium, iron, chromium, vanadium, cobalt, vanadium, manganese, and combinations thereof. Suitable divalent metal compounds are water-insoluble compounds of the divalent metals magnesium, zinc, nickel, copper, iron, cobalt, manganese, calcium, barium, and combinations thereof.

The divalent and trivalent metal compounds are preferably used in the form of oxides, hydroxides, carbonates, and hydroxycarbonates. Examples of suitable aluminium compounds are aluminium trihydrate (including gibbsite, bayerite, and bauxite ore concentrate, BOC) and its thermally treated forms (including flash- calcined alumina), sols, amorphous alumina, and (pseudo)boehmite. Flash- calcined aluminium trihydrate may be obtained by treating aluminum trihydrate at temperatures between 800-1 ,000 ⁰ C for very short periods of time in special industrial equipment, as is described in US 4,051 ,072 and US 3,222,129. Examples of suitable magnesium compounds are MgO, Mg(OH) ₂ , hydromagnesite, magnesium carbonate, magnesium hydroxy carbonate, and magnesium bicarbonate.

Method 3 involves calcining an existing anionic clay at a temperature of 200- 800 ⁰ C, thereby forming a so-called solid solution, which can then be re-hydrated to a K-containing anionic clay by contacting this calcined anionic clay with an aqueous solution containing a potassium salt or a potassium base. This rehydration may be conducted at a temperature in the range of 25-250 ⁰ C, preferably 50-18O ⁰ C, for 10 minutes to 48 hours, more preferably 30 minutes to 24

hours, and most preferably 1 to 6 hours. If hydrothermal aging conditions are used (i.e. above 100 ⁰ C), autogenous pressure is preferably applied. Suitable potassium salts include KCI and KNO ₃ . Suitable potassium bases include KOH, K ₂ CO ₃ , and KHCO ₃ .

Method 4 involves the impregnation of an existing anionic clay with a potassium salt or base. Suitable potassium salts include KCI and KNO ₃ . Suitable potassium bases include KOH, K ₂ CO ₃ , and KHCO ₃ .

Optionally, one or more additional metal compounds may be incorporated into the K-containing anionic clay by having these metal compound(s) present during the preparation of the K-containing anionic clay, or by impregnating the K-containing anionic clay with the metal compound(s). Preferred metal compounds are Ce and/or V salts, but also other metal compounds can be introduced, such as La, Si, P, B, Ca, Ba, Fe, Cr, Ni, Mn, Ti, Zr, Cu, Zn, Mo, Sn, W, Pd, Pt, Rh, and/or Ru salts.

If desired, the anion present in the interiayers of the K-containing anionic day may be exchanged with another anion, e.g. NO ₃ ^" , OH, Cl ^" , Br ^" , I ^" , SO ₄ ^2" , SiO ₃ ^2" , CrO ₄ ^2" , BO ₃ ^2' , MnO ₄ ^' , HGaO ₃ ^2" , HVO ₄ ^2" , CIO ₄ ^" , BO ₃ ^2" , tungstates, pillaring anions such as VioO ₂₈ ^6" and Mo ₇ O ₂₄ ^6" , monocarboxylates such as acetate, dicarboxylates such as oxalate, or alkyl sulphonates such as lauryl sulphonate.

After preparation, the K-containing anionic clay may be calcined in order to obtain a thermally treated anionic clay. Mild calcination (200-800 ⁰ C) is preferred, because the use of solid solutions is preferred over the use of spinel-type structures.

It is noted that even if the additive or catalyst additive contains anionic clay upon entering the FCC unit, the anionic clay will be transformed in-situ into its thermally treated form (generally a solid solution) during processing in said unit, due to the high temperatures involved.

The catalyst additive that can be used according to the present invention preferably comprises 1-99 wt%, more preferably 20-80 wt%, and most preferably 40 to 70 wt% of (thermally treated) K-containing anionic clay, calculated as oxide and based on the total weight of additive.

This additive further comprises a binder, preferably alumina, silica, or silica- alumina, in a preferred amount of 1-99 wt%, more preferably 5-60 wt%, and most preferably 8-20 wt%, calculated as AI ₂ O ₃ and based on the total weight of additive. The additive may also comprise zeolites (such as ZSM-5 or zeolite beta) in a preferred amount of 5-30 wt% and balance kaolin.

The catalyst additive is used in the FCC process in physical admixture with an FCC catalyst. This FCC catalyst can be any conventional FCC catalyst. The FCC catalyst and the additive can be introduced into the FCC unit separately or in physical admixture.

The K-containing anionic clay-containing catalyst that can be used according to the present invention preferably comprises 0.1-50 wt%, more preferably 1-30 wt%, and most preferably 3 -15 wt% of (thermally treated) K-containing anionic clay, calculated as oxide and based on the total weight of the catalyst.

This catalyst further comprises conventional FCC catalyst ingredients. Hence, it contains a binder or matrix material, preferably alumina, silica, and/or silica- alumina, in a preferred amount of less than 50 wt%, more preferably 5 to 40 wt%, and most preferably 20 - 30 wt%, calculated as oxide and based on the total weight of the catalyst. It further contains a faujasite zeolite, e.g. zeolite Y, zeolite USY, or rare-earth metal exchanged zeolite Y or USY (RE-Y, RE-USY), in a preferred amount of 5-50 wt%, more preferably 10-30 wt%, and balance kaolin. In addition, it may contain other ingredients, such as ZSM-5, modified ZSM-5, and/or zeolite beta, and/or additives such as Ce and/or V.

The catalyst and the catalyst additive to be used according to the present invention can be prepared by slurrying the (thermally treated) K-containing anionic clay and the other ingredients of the catalyst or the additive, followed by shaping, e.g., spray-drying, the slurry to form particles. This spray-drying may optionally be followed by a calcination step.

Before addition to the slurry, the (thermally treated) K-containing anionic clay may be milled in order to decrease its particle size. Alternatively, the slurry containing the (thermally treated) K-containing anionic clay and other ingredients of the catalyst or the additive is milled. "Milling" is defined as any method that results in a reduction of the particle size. Such a particle size reduction can at the same time result in the formation of reactive surfaces and/or heating of the particles. Instruments that can be used for milling include ball mills, high-shear mixers, colloid mixers, and electrical transducers that can introduce ultrasound waves into a slurry. Low-shear mixing, i.e. stirring that is performed essentially to keep the ingredients in suspension, is not regarded as "milling".

The use of (thermally treated) K-containing anionic clays in fluid catalytic cracking processes leads to reduced SO _x and/or NO _x emissions from the FCC regenerator and/or the production of sulphur- and/or nitrogen-lean fuels (e.g. gasoline, diesel).

EXAMPLES

Example 1 A K-containing anionic clay was prepared by slurrying precipitated boehmite alumina and MgO in a molar ratio Mg/AI of 2, resulting in a slurry with a solids content of 10 wt%. The slurry was aged at 85 ⁰ C for 4 hours and subsequently spray-dried to form microspheres.

These microspheres were calcined at 600 ⁰ C for 1 hour and then rehydrated by slurrying in a 0.1 molar potassium hydroxide solution for 1 hour at 80°C. The resulting K-containing anionic clay contained 3.6 wt% K (as K ₂ O), measured by X-Ray Fluorescence Spectroscopy (XRF).

Comparative Example 2

Example 2 was repeated, except that the calcined anionic clay was rehydrated in the absence of potassium. The resulting product was an Mg-Al anionic clay substantially free of K.

Example 3

The products of Example 1 and Comparative Example 2 were tested for their SO _x reducing ability in FCC processes using the thermographimetric test described in Ind. Eng. Chem. Res. Vol. 27 (1988) pp. 1356-1360. 30 mg of the product sample was heated under nitrogen at 700 ⁰ C for 30 minutes. Next, the nitrogen was replaced by a gas containing 0.32% SO ₂ , 2.0% O ₂ , and balance N ₂ with a flow rate of 200 ml/min. After 30 minutes the SOz-containing gas was replaced by nitrogen and the temperature was reduced to 650°C. After 15 minutes nitrogen was replaced by pure H ₂ and this condition was maintained for 20 minutes. This cycle was repeated 3 times. The sample's SO _x uptake during hydrogen treatment was measured as the sample's weight change (in %). The SO _x uptake of these cycles is shown in Table I.

Table I - SO _x uptake (% weight increase) by the products of Example 1 and Comparative Example 2

Cycle No. Example 1 Comparative Example 2

_ __ __

2 4.18 1.58

3 3.36 1.14

This Table shows that K-containing anionic clays have a higher SO _x uptake than anionic clay substantially free of K.