Process for the preparation of doped pentasil-type zeolites using a doped reactant

Description of equivalent WO 2004020335 A1

PROCESS FOR THE PREPARATION OF DOPED PENTASIL-TYPE ZEOLITES USING A DOPED REACTANT

The present invention relates to the preparation of metal-doped pentasil-type zeolites using a metal-doped reactant.

US 6,346,224 discloses the preparation of metal-doped aluminosilicates with FI topology by mixing a sodium silicate solution with an acidic metal- containing solution (e.g. an Fe-, Ni-, Zn-, or Cr-containing solution) to form a silicon-metal solution, and mixing this silicon-metal-containing solution with an aluminium-containing solution to provide a gel mixture.

This gel is crystallised under hydrothermal conditions to provide a metallo- aluminosilicate having an aluminosilicate framework with the metal incorporated therein. As the aluminium-containing mixture is basic and the silicon-metal-containing mixture is acidic, it will be clear that upon addition of the basic aluminium_^ containing solution to the acidic silicon-metal-containing solution, the metal can precipitate as hydroxide. This has a negative effect on the homogeneity of the metal distribution in the resulting zeolite.

The present invention offers a process for the preparation of metal-doped pentasil-type zeolites where the risk of precipitation of the metal dopant as a separate phase is minimised.

This process involves the following steps: a) preparing an aqueous precursor mixture comprising a silicon source and an aluminium source, at least one of these sources being doped with a rare earth metal or a transition metal of Groups Vb-Vlllb, lb, or lib of the Periodic

System, and b) thermally treating the precursor mixture to form a metal-doped pentasil-type zeolite. In this process, the silicon source and/or the aluminium source are metal- doped. This means that the desired metal compound (the dopant) has been incorporated into the silicon and/or the aluminium source before the above process is performed.

Metal-doped silicon and/or aluminium sources can be prepared by, e.g., preparing the silicon and/or the aluminium source in the presence of the desired dopant. This results in a silicon and/or an aluminium source wherein the dopant is homogeneously dispersed. Another way of doping is impregnation or ion- exchange of the silicon and/or the aluminium source with the dopant.

Hence, physical mixtures of a silicon or an aluminium source with the desired metal compound in solution or suspension - as in US 6,346,224 - are not metal- doped silicon or aluminium sources according to the above definition. It can easily be imagined that when the metal compound is introduced into an aqueous mixture via the silicon or the aluminium source (i.e.: as a metal-doped silicon or aluminium source), it is not freely present in the mixture and the risk of precipitation of the metal as a separate phase is minimised.

The dopant is a rare earth metal (e.g. Ce, La) or a transition metal of Groups Vb-Vlllb, lb, or lib of the Periodic System. Groups Vb through Vlllb are the groups represented by vanadium through nickel; Groups lb and lib are represented by Cu and Zn, respectively.

Both rare earth metals and the selected transition metals are frequently present in catalysts for hydrocarbon conversion, purification, or synthesis. For instance, Ce and V are known to improve the capability of FCC catalysts and catalyst additives to remove SOx and/or NOx compounds from regenerator gases, while the presence of V and Zn in FCC catalysts or additives improves the removal of S-compounds from the gasoline and diesel fractions of FCC. In hydro- processing catalysts Co, Mo, and W are generally applied metals, while the alkylation of hydrocarbons over solid acid catalysts applies noble metals such as Pt and Pd. In hydrocarbon synthesis, e.g. Fischer-Tropsch synthesis, Fe, Co, and Ru are desired metals. Ni and Cu are frequently used for the hydrogenation of hydrocarbons.

Examples of transition metals suitable as dopants in the process of the present invention are Mn, Fe, Cu, Ni, Zn, Mo, C, W, V, Pt, and Pd.

The dopant can be incorporated into the silicon or the aluminium source as, e.g., its oxide, hydroxide, carbonate, hydroxycarbonate, chloride, nitrate, sulfate, or phosphate.

The first step of the process according to the invention involves the preparation of an aqueous precursor mixture comprising a metal-doped silicon source and/or a metal-doped aluminium source.

Suitable aluminium sources include aluminium salts, such as Al₂(SO )₃, AICI₃, AIPO , AI₂(HP0₄)₃, and AI(H₂P0₄)₃, and water-insoluble aluminium compounds, e.g., aluminium trihydrate (AI(OH)₃) such as gibbsite and bauxite ore concentrate (BOC), thermally treated aluminium trihydrate such as flash- calcined aluminium trihydrate, (pseudo)boehmite, aluminium chlorohydrol, aluminium nitrohydrol, Si-AI cogels, and mixtures thereof. Also mixtures of one or more of these aluminium sources can be used.

It will be clear that aluminium salts cannot be doped. Hence, the term "doped aluminium source" inherently refers to a metal-doped water-insoluble aluminium source.

Doped (pseudo)boehmite, for instance, can be prepared by hydrolysis of aluminium alkoxide in the presence of the dopant, hydrolysis and precipitation of aluminium salts in the presence of the dopant, or by aging a slurry of (thermally treated) aluminium trihydrate, amorphous gel alumina, or less crystalline (pseudo)boehmite in the presence of the dopant. For more information concerning the preparation of metal-doped (pseudo)boehmite reference is made to International Patent Application Nos. WO 01/12551 , WO 01/12552, and WO 01/12554. Suitable silicon sources include sodium silicate, sodium meta-silicate, stabilised silica sols, silica gels, polysilicic acid, tetra ethylortho silicate, fumed silicas, precipitated silicas, Si-AI cogels, and mixtures thereof.

Doped silica sol, for instance, can be obtained by preparing a silica sol from water glass and acid (e.g. sulfuric acid), and exchanging the sodium ions with the desired dopant. Alternatively, water glass, acid (e.g. sulfuric acid), and dopant are co-precipitated to form a metal-doped silica sol.

It is also possible to use a metal-doped Si-AI cogel as both the aluminium and the silicon source.

The amount of aluminium and silicon source present in the precursor mixture depends on the desired SAR of the resulting doped pentasil-type zeolite.

Preferably, the precursor mixture comprises a seeding material, such as a seed or template. Suitable seeding materials include faujasite-type seeds (zeolite X or Y), pentasil-type seeds (e.g. ZSM-5 seeds or zeolite beta seeds), amorphous seeds (e.g. amorphous Si-AI cogel), clays (e.g. bentonite, kaolin), milled zeolites with crystallites too small to be detected by X-ray diffraction techniques, and sols or gels containing an organic directing template like tetrapropyl ammonium hydroxide (TPAOH) or tetrapropyl ammonium bromide (TPABr). An example of such a template-containing sol is a Si-AI sol containing 0.1-10 wt% of tetrapropyl ammonium bromide. If desired, a doped seeding material is used. Suitable dopants for seeding materials are the dopants listed above as suitable for the doped aluminium source and/or the doped silicon source.

The optional dopant(s) present in the seeding material and/or the template and the dopant in the metal-doped aluminium source and/or the metal-doped silicon source may be the same or different. Preferably, the precursor mixture comprises 1-10 wt% of seeding material, based on the total solids content. It is also possible to use more than one type of seeding material.

If so desired, several other compounds may be added to the precursor mixture, such as metal (hydr)oxides, sols, gels, pore regulating agents (sugars, surfactants), clays, metal salts, acids, bases, etc. Furthermore, it is possible to mill the precursor mixture.

The precursor mixture can be shaped to form shaped bodies. Suitable shaping methods include spray-drying, pelletising, extrusion (optionally combined with kneading), beading, or any other conventional shaping method used in the catalyst and absorbent fields or combinations thereof. The amount of liquid present in the precursor mixture should be adapted to the specific shaping step to be conducted. It might be advisable to partially remove the liquid used in the precursor mixture and/or add an additional or another liquid, and/or to change the pH of the precursor mixture to make the mixture gellable and thus suitable for shaping. Additives commonly used in the different shaping methods, e.g. extrusion additives, may be added to the precursor mixture used for shaping.

The second step of the process involves thermal treatment of the precursor mixture. This thermal treatment is preferably performed at temperatures ranging from 130 to 200°C, preferably 150-180°C, for 3-60 hrs. During this step, the metal-doped pentasil-zeolite is formed by crystallisation. The thermal treatment can be conducted in one or a series of at least two reaction vessels. If more than one such vessel is used, the process is preferably conducted in a continuous mode. Using more than one reaction vessel further allows the preparation of the aqueous precursor mixture either by adding all ingredients to the first vessel or by spreading the addition of (part of the total amount of) the ingredients over the reaction vessels. The metal-doped pentasil-type zeolite resulting from the process according to the invention preferably has a SiO₂/AI₂O₃ ratio of 25-90. Typical examples of pentasil-type zeolites are ZSM-type zeolites, such as ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, zeolite beta, or zeolite boron beta. The metal-doped pentasil-type zeolite preferably contains 0.1-10 wt% of dopant, more preferably 0.1-3 wt%, and most preferably 0.5-2.5 wt%, calculated as oxide and based on the dry weight of metal-doped pentasil-type zeolite.

If so desired, the resulting metal-doped pentasil-type zeolite may be calcined and optionally ion-exchanged.

The so-formed metal-doped pentasil-type zeolite can be used in or as a catalyst composition or catalyst additive composition for, e.g. hydrogenation, dehydrogenation, catalytic cracking (FCC), alkylation reactions, hydro- desulfurisation, hydrodenitrogenation, and hydrodemetallisation.

EXAMPLES

Example 1 A silica-alumina gel (338.5 g) doped with 5 wt% RE, calculated as oxide, was added to a 30-litre stirred vessel containing 2,666 g water. Next, 2,015 g of a 98 wt% H₂S0₄ solution was added, followed by the slow addition (in 15 minutes) of 2,069 g of water glass. Next, 488.9 g of seeds slurry (prepared by mixing 51.9 gram ZSM-5 ex-AlsiPenta with 437 gram water) were added. The pH of the resulting slurry was adjusted with caustic to 10.5.

The temperature of the resulting slurry was raised to 99°C in one hour and maintained thus for another hour. The temperature was then raised to 170°C and maintained thus for 12 hours. The resulting product was dried overnight at 120°C. The powder X-ray diffraction pattern of the product indicated the formation of ZSM-5 without any traces of separate REO peaks. Hence, the rare earth metal was not precipitated as a separate phase.

Chemical analysis showed that the concentration of RE (calculated as oxide) in the ZSM-5 was 0.9 wt%.

Example 2

Example 1 was repeated, except for the addition of caustic to adjust the pH. Again, powder X-ray diffraction indicated the formation of ZSM-5 without any traces of separate REO peaks. Chemical analysis showed that the concentration of RE (calculated as oxide) in the ZSM-5 was 0.9 wt%.