WO2002002231A1

WO2002002231A1 - Process for manufacturing a catalyst

Info

Publication number: WO2002002231A1
Application number: PCT/EP2001/007732
Authority: WO
Inventors: Jean-Paul Schoebrechts
Original assignee: Solvay (Société Anonyme)
Priority date: 2000-07-05
Filing date: 2001-07-04
Publication date: 2002-01-10
Also published as: AU2001281960A1; FR2811244A1; FR2811244B1

Abstract

Process for manufacturing a catalyst, which can be used for oxidation and epoxidation reactions, for example using hydrogen peroxide, comprising a crystal structure based on silicon oxide, such as a zeolite, and at least one metal such as titanium, in which the crystal structure is mixed with an organic compound containing this metal, for example dichloro(dicyclo-pentadienyl)titanium.

Description

Process for manufacturing a catalyst

The present invention relates to a process for manufacturing a catalyst and to a process for manufacturing organic oxides incorporating this process.

It is know practice to manufacture catalysts for various chemical reactions by incorporating a metal into a crystal structure and more particularly into a crystal structure based on silicon oxide. This incorporation may take place during the synthesis of the crystal structure or via a subsequent treatment with an inorganic metal compound.

The first variant generally leads to a long and complex process and/or to a process requiring the use of a sophisticated structuring agent.

As regards the second variant, it is known practice (patents US-A-5 684 170 and US-A-5 374747) to treat a crystal structure based on silicon oxide (β -zeolite) with inorganic Ti compounds (TiCl₄, TiF₄). However, these compounds are extremely moisture-sensitive and liable to produce corrosive gases and they generally lead to aggregates of metal oxide not inserted into the crystal network.

The aim of the present invention is to provide a novel process which is simpler than the incorporation of metal during the synthesis of the crystal structure or which does not have the drawbacks associated with the conventional sources of metal used to treat a crystal structure which is already placed in shape. In addition, the aim consists in providing a process which makes it possible to manufacture a catalyst which has increased activity and increased selectivity in certain reactions, in particular epoxidation reactions with a peroxide. Another object is to obtain, during such epoxidations, less decomposition of the peroxide when compared with the catalysts of the prior art.

The present invention consequently relates to a process for manufacturing a catalyst comprising a crystal structure based on silicon oxide and at least one metal, in which the crystal structure is mixed with an organic compound containing this metal. The crystal structure used in the process according to the invention is, by definition, a structure which has at least one X-ray diffraction line. It is generally porous and has a pore aperture such that it promotes the circulation of certain molecules inside it. As a general rule, the pore aperture will be adapted to the size of the molecules involved in the reaction to be catalysed. Thus, for example, good results have been obtained with mesoporous crystal structures (for example MCM-41) or microporous crystal structures (zeolites) depending on the type of molecules to react. Examples which may be mentioned include zeolites, β- zeolites and USY, MOR, ZSM-5 and NaY zeolites. Some of these zeolites have only one type of pore (NaY: pore aperture of 0.74 nm) and others have two (ZSM-5: 0.53*0.56 nm and 0.51*0.55 nm; β-zeolites: 0.76*0.64 nm and 0.55*0.55 nm). The pores of these structures are generally polyhedral. In general, a crystal structure which has at least one pore aperture of greater than or equal to 0.5 nm or even greater than or equal to 0.7 nm will be chosen. The maximum pore aperture of the crystal structures according to the present invention is generally less than or equal to 30 nm, or even less than or equal to 10 nm. The process according to the present invention applies particularly to β- zeolites. The crystal structure of the process according to the present invention may be present in any solid form (powders, granules, aggregates, etc.). Generally, this crystal structure is in the form of a powder.

The size of the particles of this crystal structure is generally not critical. However, when the mixing in the process according to the present invention is carried out in a fluid bed, particles with a mean diameter of greater than or equal to 10 μm, or better still greater than or equal to 20 μm and preferably greater than or equal to 35 μm are particularly suitable. This diameter is preferably less than or equal to 200 μm, or better still less than or equal to 150 μm and preferably less than or equal to 100 μm. Good results are obtained with a mean diameter of from 35 to 100 μm. In the case of a fluid bed, it may also prove to be advantageous to use a crystal structure with a narrow particle size distribution. The specific surface area of these crystal structures is preferably greater than or equal to 100, or even greater than or equal to 200 and preferably greater than or equal to 500 m²/g. It is generally less than or equal to 1 000, or even less than or equal to 800 and preferably less than or equal to 700 m²/g. Good results are obtained with a specific surface area of from 500 to 700 m²/g.

As regards the pore volume of these crystal structures, this volume is preferably greater than or equal to 0.1 cm³/g, or even greater than or equal to 0.2 cm³/g and preferably greater than or equal to 0.5 cm³/g. It is generally less than or equal to 5 cmVg, or even less than or equal to 3 cm³/g and preferably less than or equal to 1.5 cm³/g. Good results are obtained with a pore volume of from 0.5 to l.5 cm³/g.

The silicon oxide content of these crystal structures is generally greater than or equal to 75% and less than or equal to 100%. Generally, the crystal structure contains other compounds other than silicon oxide, and more particularly it occasionally contains alumina and optionally alkaline elements. The process according to the present invention applies more particularly to silica/alumina mixed zeolites with a silica/alumina weight ratio of greater than or equal to 5 and less than or equal to 900. In the case of mixed zeolites, and in particular those containing Al, it may prove to be advantageous to remove the Al (or the metal other than Si) as much as possible before, during or after mixing it with the organic compound containing the metal. Working in this way makes it possible to increase the activity and/or selectivity of the catalyst for certain reactions, including oxidation reactions using hydrogen peroxide. Preferably, this removal takes place before the mixing, and by any known means. It is advantageously carried out using a reductive inorganic or organic acid which allows the extraction of metal atoms from the network, as disclosed in patent US-A-5 684 170 mentioned above. Nitric acid, sulphuric acid and hydrochloric acid are suitable for this purpose. The acid titre, the duration and the demetallization temperature will be tailored so as to obtain a residual content of metal other than silicon (for example Al) of less than or equal to 0.2 mol/kg of crystal structure, or even less than or equal to 0.1 mol/kg and preferably less than or equal to 0.04 mol/kg. It may even occasionally prove to be advantageous to go down to values of less than or equal to 0.02 mol of this metal/kg of crystal structure.

The organic compound used in the process according to the present invention is preferably an organic compound of a metal chosen from Ti, Zr, Hf, V, Cr, W, Mo, Mn, Fe, Co, Ni and lanthanides. Metals chosen from Ti, Zr, Hf, V, Cr, W, Mo, Mn, Co, Ni and lanthanides are suitable. Good results have been obtained with titanium compounds. Examples which may be mentioned of organic compounds used in the process according to the present invention include organometallic compounds such as metallocenes and metal esters of the metals described above. Organometallic compounds and more particularly metallocenes give particularly advantageous results. Among these, molecules containing cyclopentadienyl groups and also at least one halogen atom fixed to the metal give good results. Among these compounds, those based on titanium give excellent results. In particular, dichloro(dicyclopentadienyl)titanium (or TiCp₂Cl₂) is advantageously used in the process according to the present invention. Good results have also been obtained with organic esters such as titanium chlorotriisopropoxide, titanium tetra-n-butoxide, titanium diisopropoxide bis(2,4-pentanedioate), titanium diisopropoxide bis(triethanolamine), 2-ethylhexyl titanate and alkanolamine titanate complexes. The organic compound containing the metal may be in liquid or solid form. When it is in solid form, it may be used in the mixture in solution or in dispersion in a solvent, which is subsequently removed by known processes (evaporation, washing, filtration, drying, etc.). Examples of such solvents which may be mentioned include C1-C9 organic solvents. They may be chlorinated aliphatic compounds (such as CC1₄, chloroform or dichloroethane), aromatic molecules (such as toluene) or alcohols (such as ethanol or methanol). It is occasionally advantageous to mix the solvent with a substance of basic nature, such as an amine (for example triethylamine).

However, according to an advantageous variant of the present invention, the mixing of the organic compound containing the metal with the crystal structure is performed by dry mixing, i.e. in the absence of a significant amount of a solvent for the said organic compound. The mixing is preferably carried out in the absence of any solvent.

, The amount of organic compound introduced into the mixture is such that the metal will be present in the catalyst in a proportion of 1 g/kg or more, or even 5 g/kg or more and preferably 10 g/kg or more. The amount of metal present in the catalyst is advantageously less than or equal to 100 g/kg, or even less than or equal to 30 g/kg and preferably less than or equal to 20 g/kg. Good results are obtained with an amount of from 10 to 20 g/kg.

When the mixing is carried out in the presence of a solvent, the temperature of the mixture is preferably greater than or equal to 15°C, or even greater than or equal to 20°C, and preferably less than or equal to 40°C, or even less than or equal to 25°C. This temperature is generally less than the boiling point of the solvent at atmospheric pressure. When dry mixing is carried out, the' temperature of the mixture is preferably greater than or equal to 50°C, or even greater than or equal to 90°C and preferably greater than or equal to 100°C. This temperature is preferably less than or equal to 400°C, or even less than or equal to 325°C and preferably less than or equal to 310°C. When dry mixing is carried out, the temperature of this mixing operation may be greater than the melting point of the organic compound (or T_m).

The mixing operation may be carried out at atmospheric pressure or under an autogenous pressure (i.e. in a closed medium, optionally with prior application of vacuum, and leaving the pressure to change freely as a function of the temperature and of the gaseous compounds evolved by the mixture).

The mixing operation is preferably carried out in the absence of water and oxygen. It is preferably carried out under inert atmosphere (nitrogen, helium or argon). The mixing operation may be carried out with stirring. This stirring may be obtained by any known means.

Any type of mixer is suitable for carrying out this mixing: it may be a static mixer fitted with a stirrer, a rotary mixer or rotary oven, a fluid bed, etc.

Finally, the crystal structure and the solvent, where appropriate, are advantageously dried prior to mixing with the organic compound, this drying being performed by any known means (for example by heating for the crystal structure, and by molecular sieving for the solvent). The maximum admissible amount of water is generally less than or equal to 5 mol%, ideally less than or equal to 1 mol% and preferably less than or equal to 0.5 mol% of the amount of the organic compound used, so as to avoid partial hydrolysis of this compound, which would lead to aggregates of metal oxide not inserted into the crystal network.

The mixture obtained by the process according to the present invention may be used without modification or after a post-treatment. This post-treatment is advantageously a heat treatment at high temperature (calcination) in order to allow the removal of certain organic molecules not participating in, or even inconveniencing the reaction to be catalysed: The temperature at which this treatment takes place is preferably greater than or equal to 400°C, or even greater than or equal to 500°C. This temperature is preferably less than or equal to 800°C, or even less than or equal to 600°C. A temperature in the region of 550°C is suitable for use.

The duration of this post-treatment is advantageously greater than or equal to 1 h, or even greater than or equal to 5 h. This duration is preferably less than or equal to 24 h, or even less than or equal to 15 h. A duration of about 10 h is suitable for use. This post-treatment may be carried out under an oxidative atmosphere. It is generally carried out under an atmosphere containing oxygen.

The thermal post-treatment described above may be followed by another treatment with a weak base (for example LiOAc) in order to neutralize the acid sites present in the crystal structure which are liable to disrupt certain reactions, such as epoxidation reactions with a peroxide, for example. Such a treatment applied to a Ti-β-zeolite used for the epoxidation of olefins is disclosed in patent US-A-5 684 170 mentioned above.

' The catalysts obtained by the process according to the present invention are particularly suitable for oxidation reactions between an oxidizable organic substrate and a peroxide.

The catalysts obtained by the process according to the present invention are most particularly suitable for epoxidation reactions of olefins using hydrogen peroxide. In this case, the crystal structure will preferably be a β-zeolite freed of Al, as described above.

Having regard to the foregoing text, the present invention also relates to a process for manufacturing organic oxides by reaction between an oxidizable organic substrate and a peroxide, in which a catalyst is manufactured by means of the process described above, and it is then used during the reaction between the oxidizable organic substrate and the peroxide. The present invention also relates to such a process in which the oxidation reaction is an epoxidation reaction, the oxidizable organic substrate is an olefin and the peroxide is hydrogen peroxide.

In the case of such epoxidation reactions, a diluent chosen from water, alcohols, ketones and nitriles, and mixtures thereof, is often used. Nitriles are preferred. The nitrile diluent generally contains up to 10 carbon atoms and preferably from 1 to 6 carbon atoms. Examples which may be mentioned are acetonitrile and propionitrile. Acetonitrile is preferred.

The total amount of diluent which may be used in the process according to the invention is generally greater than or equal to 35% by weight of the reaction medium, in particular greater than or equal to 60% by weight and better still greater than or equal to 75% by weight. This amount is generally less than or equal to 99% by weight and in particular less than or equal to 95% by weight. The molar ratio between the amounts of olefin and of peroxide compound that are used in the process according to the invention is generally greater than or equal to 0.1, in particular greater than or equal to 1 and preferably greater than or equal to 4. This molar ratio is usually less than or equal to 100, in particular less than or equal to 50 and preferably less than or equal to 25.

The peroxide compound is advantageously, used in the form of an aqueous solution. In general, the aqueous solution contains at least 10% by weight of peroxide compound, in particular at least 20% by weight. It usually contains not more than 70% by weight of peroxide compound and in particular not more than 50% by weight.

The temperature of the reaction between the olefin and the peroxide compound may range from 10°C to 100°C. The temperature may be greater than or equal to 25°C and preferably greater than or equal to 45°C. A temperature of greater than or equal to 50°C is most particularly preferred. The reaction temperature is preferably less than 80°C.

The reaction between the olefin and the peroxide compound may take place at atmospheric pressure. It may also be performed under pressure. The peroxide compounds which may be used in the process according to the invention are peroxide compounds containing one or more peroxide functions (-OOH) which may release active oxygen and which are capable of carrying out an epoxidation. Hydrogen peroxide and peroxide compounds which may produce hydrogen peroxide under the conditions of the epoxidation reaction are suitable for use. Hydrogen peroxide is preferred.

The oxirane (or product of the epoxidation) which may be prepared by the process according to the invention is an organic compound comprising a group corresponding to the general formula;

The oxirane generally contains from 2 to 30 carbon atoms and preferably from 3 to 16 carbon atoms. The oxiranes which may be prepared advantageously by the process according to the invention are 1,2-epoxypropane, l,2-epoxy-3- chloropropane and 1,2-epoxyalkanes containing from 4 to 16 carbon atoms.

The olefins which are suitable in the process according to the invention generally contain from 2 to 30 carbon atoms and preferably 3 to 16 carbon atoms. Propylene, allyl chloride and α-olefins containing from 4 to 16 carbon atoms are suitable for use. The reaction between the olefin and the peroxide compound may take place in any type of reactor.

The catalysts according to the present invention may also be used for polymerization reactions, in particular of olefins and more particularly of ethylene and C3-C20 α-olefins. In this case, a thermal post-treatment is generally not required with the choice of a metallocene as active compound. The olefins which may be polymerized with the catalysts obtained by the process according to the present invention are preferably ethylene and propylene, optionally with a comonomer. The present invention is illustrated in a non-limiting manner by the examples which follow:

Comparative Example CI: direct synthesis of a Ti-β-zeolite 1.170 g of tetrabutyl orthotitanate or TBOT and 10.0 ml of isopropanol dried over 4A molecular sieves were successively added, under nitrogen, to a 100 ml polyethylene flask equipped with a magnetic bar, and the mixture was heated at 35°C for 30 minutes under nitrogen.

21.50 g of tetraethyl orthosilicate or TEOS and then 44 g of an aqueous 22.4% by weight solution of 4,4'-trimethylenebis(N-benzyl-N- methylpiperidinium) dihydroxide or R(OH₂) were successively introduced into a 100 ml polyethylene flask equipped with a magnetic bar. The mixture was stirred at room temperature until a clear solution was obtained.

The solution of TBOT in isopropanol cooled to room temperature was then added under nitrogen to the mixture of TEOS and R(OH)₂ (flow rate of 20 ml/h) and the mixture was left stirring for 30 minutes at room temperature. 14.6 g of the R(OH)₂ solution were then added under nitrogen and with stirring and the solution was brought to 85°C under a stream of nitrogen over 3 h so as to remove the isopropanol and the alcohols formed by hydrolysis of the Si and Ti esters. ₎

' Two portions of 10 ml of water were added after 1 and 2 h so as to limit the reduction in volume due to the removal of the alcohols. After 3 h, 67.8 g of water were added. The composition of the gel at this stage was 1 Si - 0.033 Ti - 0.28 R(OH)₂ - 60 H₂O.

The gel was transferred into a 120 ml Teflon-lined Parr bomb and heated at 135°C for 9 days with stirring. The solid was then separated from the mother liquor by ultracentrifugation

(13 000 rpm - 15 min), resuspended twice in deionized water and recentrifuged. It was then dried at 110°C for 16 h in a ventilated oven and then calcined in air at 550°C for l0 h.

The β crystal structure was confirmed by X-ray and the results of the analyses carried out on this zeolite are given in Table 1 below. Example 2: mixture of an aluminium-depleted β-zeolite and of a titanocene in the presence of a solvent a. Removal of aluminium:

50.00 g of a commercial β zeolite (CU Chemie Uetikon AG, ZEOCAT® PB/60 H, SiO₂/Al₂O₃ = 66.6 mol/mol, 13.1 g Al/kg) and 1 000 ml of 14 N HNO₃ (65%) were introduced into a one-litre conical flask equipped with a magnetic bar.

The suspension was heated with stirring at 80°C for 4 h and was then cooled and filtered and the solid collected was washed with demineralized water to neutral pH. This solid was dried overnight at 175°C in a ventilated oven. The above set of operations was repeated twice. The solid was then calcined in air at 550°C for 10 h.

The residual Al content was 0.7 g/kg (SiO₂/Al₂O₃ = 1 280 mol/mol). The crystallographic structure was not modified by the treatment. b. Mixing: 3.00 g of the zeolite freed of aluminium according to the procedure described above were introduced into a 500 ml conical flask purged beforehand with dry nitrogen, equipped with a magnetic bar and on which was mounted a 3- way tap. The system was brought to 120°C and maintained under vacuum (3 mbar) for 1 h and then cooled under nitrogen. 120 ml of CHC1₃ dried over 4 A molecular sieves were then added and the suspension was stirred at room temperature.

0.92 g of TiCp Cl was introduced into a 250 ml conical flask purged beforehand with dry nitrogen, equipped with a magnetic bar and on which was mounted a 3 -way tap, followed by addition of 120 ml of CHCI3 dried over 4 A molecular sieves.

This solution was then added under nitrogen to the zeolite suspension and the mixture was stirred for 0.5 h at room temperature.

30.0 g of triethylamine dried over 4 A molecular sieves were then added under nitrogen and the system was kept stirring for 2 h at room temperature. The suspension obtained was filtered under nitrogen and the solid collected was washed, under nitrogen, with 3 times 50 ml of CHCI₃ dried over 4 A molecular sieves and was then dried under vacuum at 120°C overnight and then calcined in air for 10 h at 550°C.

The β crystal structure was confirmed by X-ray and the results of the analyses carried out on this zeolite are given in Table 1 below. Example 3: dry mixing of an aluminium-depleted β -zeolite and of a titanocene

4.00 g of the β-zeolite freed of aluminium according to the procedure described above were introduced into a Pyrex reaction tube.

The system was brought to 120°C and maintained under vacuum (3 mbar) for one hour, and then cooled under nitrogen.

0.31 g of TiCp₂Cl₂ was then introduced under nitrogen, into the tube. The tube was placed under vacuum (3 mbar) and sealed. It was then rotated at 60 rpm in a horizontal oven. The oven was brought to 300°C over 1 h, maintained at this temperature for 4 h and then heated at 310°C overnight. After cooling, the tube was opened and the solid obtained was calcined in air at 550°C for l0 h.

The β crystal structure was confirmed by X-ray and the results of the analyses on this zeolite are given in Table 1 below.

The solids obtained in Examples 1 to 3 were used in the epoxidation reaction of 1 -hexene with hydrogen peroxide, under the following conditions.

38.4 g of acetonitrile (0.935 mol), 12.6 g of 1-hexene (0.150 mol) and an amount of solid such that the Ti content in the final reaction medium is 8.5 meq Ti/kg are introduced into a jacketed Pyrex reactor equipped with a paddle stirrer and on which is mounted a condenser cooled to -20°C. The suspension is stirred at 750 rpm. Helium is introduced at a flow rate of 6N 1/h via a sintered tube and the temperature of the medium is brought to 50°C. After 15 min, the helium flow rate is reduced to IN 1/h and 3.3 g of a 38.8 wt% hydrogen peroxide solution (0.038 mol) are added over 20 min.

The hydrogen peroxide content is determined by iodometry after 30, 60, 90, 120 and 240 min. The liquid phase containing the 1,2-epoxyhexane (HO) and the 1,2-hexanediol is analysed by gas chromatography at the end of the test. The oxygen content in the flushing helium is assayed continuously using an oxygen analyser.

The results are collated in Table 1. Table 1

1: yield = mass of solid recovered after calcination, relative to that calculated ,on the basis of the Si and Ti precursors used and

. expressed in the form of oxides 2: selectivities relative to the hydrogen peroxide consumed, at total conversion of the latter. n.d. = not detected

Claims

1. Process for manufacturing a catalyst comprising a crystal structure based on silicon oxide and at least one metal, characterized in that the crystal structure is mixed with an organic compound containing this metal.

2. Process according to Claim 1, in which the crystal structure and the organic compound containing the metal are dry-mixed.

3. Process according to claim 1, in which the mixing is carried out in the presence of a solvent chosen from aliphatic chlorinated solvents, aromatic solvents and alcohols.

4. Process according to any one of the preceding Claims, in which, when the mixing is carried out in the presence of a solvent, the temperature of the mixture is between 15°C and the boiling point of the solvent at atmospheric pressure, and when dry mixing is carried out, the temperature of the mixture is between 50°C and 400°C.

5. Process according to any one of the preceding claims, in which the organic compound containing the metal is first mixed with the crystal structure and this mixture is then subjected to a calcination at a temperature of from 400°C to 800°C.

6. Process according to any one of the preceding claims, in which the crystal structure is a zeolite.

7. Process according to Claim 6, in which the zeolite is a β zeolite.

8. Process according to any one of the preceding claims, in which the crystal structure contains less than 5 g of Al/kg.

9. Process according to any one of the preceding claims, in which the metal is chosen from Ti, Zr, Hf, V, Cr, W, Mo, Mn, Co, Ni and lanthanides.

10. Process according to claim 9, in which the organic compound contains titanium.

11. Process according to any one of the preceding claims, in which the organic compound is a metallocene.

12. Process according to Claim 10 or 11, in which the organic compound is dichloro(dicyclopentadienyl)titanium.

13. Process for manufacturing organic oxides by reaction between an oxidizable organic substrate and a peroxide, characterized in that a catalyst is manufactured by means of the process described in any one of the preceding claims, and this catalyst is then used during the reaction between the organic substrate and the peroxide.

14. Process according to the preceding claim, in which the oxidation reaction is an epoxidation reaction, the oxidizable organic substrate is an olefin and the peroxide is hydrogen peroxide.