WO2013041501A1

WO2013041501A1 - Vanadium-antimony mixed oxide catalyst, preparation thereof and process for partial oxidation of alcohols to aldehydes

Info

Publication number: WO2013041501A1
Application number: PCT/EP2012/068290
Authority: WO
Inventors: Alexander Zipp; Alfons Drochner; Hans-Juergen Eberle; Melanie SCHUMANN; Herbert Vogel
Original assignee: Wacker Chemie Ag
Priority date: 2011-09-20
Filing date: 2012-09-18
Publication date: 2013-03-28
Also published as: DE102011083079A1

Abstract

The invention relates to a vanadium-antimony mixed oxide catalyst, to the preparation thereof and to a process for partial oxidation of alcohols to aldehydes using this catalyst. The catalyst consists of a catalytically active vanadium-antimony mixed oxide component and a silica moulding which serves as a support for the catalytically active vanadium-antimony mixed oxide component. The moulding is produced from high-purity fumed silica without addition of binders.

Description

Vanadium antimony-Misohoxid catalyst, its preparation and process for the partial oxidation of alcohols to aldehydes

The invention relates to a vanadium-antimony mixed oxide catalyst, its preparation and a process for the partial oxidation of alcohols to aldehydes using this catalyst.

For the oxidation of alcohols to aldehydes, catalysts based on silver and molybdenum oxides are known. So describe

US4584412 and US4584412 Process for the oxidation of methanol on silver catalysts. These must be operated with oxygen deficiency, therefore, a significant part of the methanol is not reacted.

US5217936 and US4829042 describe an alternative thereto, namely catalysts with molybdenum oxide or iron-molybdenum mixed oxide as the active component and method operated therewith. With these methods usually higher conversions of methanol are achieved. However, the catalytically active component molybdenum oxide or molybdenum mixed oxide forms volatile compounds under the usual reaction conditions, which are discharged from the catalytic fixed bed. The catalyst therefore loses its activity over the duration of active mass and thus also to activity. Another disadvantage of these catalysts results from the deposition of molybdenum oxides at colder sites of the reactor, combined with a continuously increasing pressure drop of the catalyst bed and thus increasing operating costs for the circulating gas. In the end, this limited temperature resistance of the catalyst also ensures that the process is not very robust against disturbances. For some time now, attempts have been made to avoid this systemic disadvantage by using alternative catalyst systems without molybdenum.

For example, WO03053556 describes a process for the oxidation of methanol on pure metal vanadates in an unsupported form. Further, it is well known that more active catalysts can be obtained by the distribution of the catalytically active components on a high surface area, porous support material. This is how Zhang et. al. (Catalis J., 2008, 260, 295-304) discloses a catalyst based on a vanadium-antimony mixed oxide on silica as support material for the partial oxidation of methanol to formaldehyde. Also this system is limited in selectivity and yield.

The object of the invention is to provide a vanadium-antimony mixed oxide catalyst with respect to the partial oxidation of alcohols higher yields of aldehydes than known vanadium-antimony mixed oxide catalysts.

The object is achieved by a catalyst consisting of a catalytic active vanadium-antimony mixed oxide and a shaped body of silica, which serves as a carrier for the catalytically active vanadium-antimony mixed oxide, characterized in that the shaped body consists of highly pure fumed silica, the was prepared without the addition of binders.

In the context of the work leading to the present invention, it was surprisingly found that in catalysts based on vanadium-antimony mixed oxides on SiO ₂ supports, the type of SiO _{2 used has} a significant influence on the partial oxidation of alcohols, namely the way that with a carrier consisting of highly pure fumed silica with a large specific surface area and a narrow pore radius distribution in the meso and macropores area even at high conversions very high selectivities (conversion x selectivity = yield) to their corresponding aldehydes to achieve. Production processes for moldings of highly pure fumed silica which are used as support material in the catalyst according to the invention are known from WO-08/071610, WO-08/08071611 and WO-08/071612. The production methods from these publications are insofar part of the present application (incorporated by reference).

WO-08/071610 and WO-08/071611 describe processes for producing high-purity support bodies from SiO ₂ by grinding and dispersion without binders or other additives,

WO 08/071612 describes a process for the production of moldings, in which the metal oxide is predispersed in water and then finely dispersed, this dispersion is subjected to a change in the pH and then shaped and dried.

The carrier moldings of the catalyst according to the invention can be present, for example, as pellets, rings, spheres, wheels, armchairs, honeycombs or any other conventional catalysts. Particularly suitable for the catalyst according to the invention are cylindrical extrudates such as pellets or rings.

By a subsequent thermal treatment of the green body properties of the catalyst support such as pore structure and mechanical stability can be adjusted specifically.

In a preferred embodiment, the shaped body consists of highly pure fumed silica with a large specific surface area and a narrow distribution of pore radii in the region of the meso- and macropores. Preference is given to a specific surface area of 30 to 500 m ² g ^-1 . The specific surface area was determined by nitrogen physisorption according to BET. In a particularly preferred embodiment, the shaped body has a specific surface area of greater than 200 m ² g ^-1 , up to 500 m ² g ^-1 , a defined pore structure with a very narrow monomodal pore radius distribution in the range between 5 and 30 nm, preferably between 10 and 20 nm and has less than 1% micropores and is characterized by a high proportion

Mesopores on the total pore volume of over 75%, preferably over 90%, with the remainder to 100 vol.% Formed by macropores. Micropores are pores having a diameter of less than 2 nm, mesopores are pores having a diameter of from 2 to 50 nm, and macropores are pores having a diameter of greater than 50 nm. The pore volume is determined by means of mercury porosimetry.

Preferably, the high-purity fumed silica has a total content of impurities of less than 100 ppm.

Preferably, the shaped body of fumed silica has a total content of impurities of less than 50 ppm.

Impurities are preferably to be understood as meaning the alkali metals, as well as the elements Ca, Ti, Al, Fe, Ni, Cr, S. The catalyst of the invention preferably has a content of vanadium oxide (as V ₂ O ₅ ) of 0.1 to 20 wt .-%, preferably 5 to 15 wt .-% and a content of antimony oxide (as Sb ₂ O ₅ ) of 0, From 1 to 40% by weight, preferably from 10 to 25% by weight. The application of the components described can be carried out by customary methods of preparing heterogeneous catalysts, for example, the methods known as impregnation, precipitation, ligand exchange offer. In a particularly preferred embodiment, the preparation of the catalyst by impregnation of the support materials with solutions of compounds of the active metals and other components of the catalyst. Possible solvents for the impregnation are water and organic solvents such as, for example, methanol, ethanol, propanol, acetone, dimethyl ether, tetrahydrofuran, acetonitrile and dimethylformamide. Particularly preferred for the process is the use of water or ethanol for the application of the components. The amount of solution is usually greater than or equal to the pore volume of the Trägerformkör- to be impregnated.

In a further embodiment of the catalyst, precursors of the active metal and the promoters are added ready during the production process of the support materials and subjected to shaping therewith. This approach is particularly advantageous because the application of larger amounts of active component in conventional impregnation must be done sequentially in several steps. In the catalyst shown here, the required amounts of the precursor of the active metal can be added in a single production step, which significantly simplifies the preparation of the catalyst.

The invention further relates to a process for heterogeneously catalyzed partial oxidation of aliphatic alcohols their corresponding aldehydes, in which a catalyst according to the invention is used.

Preferably, by means of the process according to the invention, aliphatic alcohols having 1 to 10 carbon atoms are converted to their corresponding aldehydes, with particular preference methanol being converted to formaldehyde.

The conversion of the alcohols to the corresponding aldehydes using the catalyst according to the invention is preferably carried out at a reaction temperature of 100 to 700 ° C, preferably 250 to 600 ° C, more preferably 300 to 450 ° C and at a reaction pressure of 0 to 2 MPa , preferably 0 to 1 MPa, more preferably 0 to 0.2 MPa.

The reaction can be carried out in all common reactor types for carrying out heterogeneously catalyzed gas phase reactions, e.g. In fixed bed reactors or fluidized bed reactors, the process is preferably carried out in fixed bed reactors.

The process is operated with simple passage of the reaction gases through the reactor or as a recycle gas process, preferably the process is operated as a recycle gas process. Preferably, the catalytic reaction of the reactants is carried out diluted in an inert gas. The inert gas used is preferably nitrogen, helium or argon, particularly preferably nitrogen. The content of the reaction gases at the reactor inlet of alcohol is preferably between 1 to 20 mol%, more preferably 2 to 15 mol%, particularly preferably 5 to 12 mol%. The content of the reaction gases at the reactor inlet of oxygen is preferably between 1 to 20 mol%, particularly preferably 2 to 15 mol%, particularly preferably 5 to 12 mol%. The process preferably takes place with a volume flow of reaction gases corresponding to a volume-related space time of 100 to 10,000 NL gas per liter of catalyst and h, preferably 500 to 5,000 NL gas per liter of catalyst and h, more preferably 1,000 to 2,500 NL gas per liter of catalyst and h.

The following examples serve to further explain the invention:

Example 1 (comparative example)

Production of carrier material from precipitated silica

A mixture consisting of 50.0 g precipitated silica, available under the name Perkasil * SM 614 from Grace Davison and 1.0 g methyl hydroxyethyl cellulose, available as Walocel from Dow Chemical and 1.0 g microcrystalline cellulose under the name Microcel at Blanver Farmoquimica Ltda.A and 126.2 g distilled water was mixed in a kneading machine (Hermann Linden Maschinenfabrik GmbH & Co. KG) for 30 minutes and then extruded through a piston extruder into shaped bodies. These moldings were for 4 days at room temperature, which is to be understood in the context of the present invention, 23 ° C, and dried for 1 day at 45 ° C and then sintered at 600 ° C (at 1 K / min to 100 ° C, for 2 hours hold at 5 K / min at 600 ° C, hold for 6 h). The carrier material produced in this way has a BET specific surface area of 158 m ² g ^-1 and a pore volume of 1.79 mL g ^-1 .

Preparation of catalyst

To prepare the catalyst, the support material was treated twice with an amount corresponding to the pore volume of a solvent. solution of 4.0% by weight of ammonium vanadate and 1.3% by weight of oxalic acid in water at room temperature and dried for 1 h at 50 ° C. and 3500 Pa and a further 12 h at 40 ° C. The resulting solid was impregnated with a volume corresponding to the pore volume of a solution of 33.3 wt .-% antimony chloride (SbCl ₃ ) in ethanol and dried for 1 h at 45 ° C and 3500 Pa and a further 12 h at 40 ° C. The solid was then impregnated with a volume corresponding to the pore volume of a solution of 10.0% by weight of ammonia in water at room temperature and again dried for 1 h at 45 ° C and 3500 Pa and for a further 12 h at 40 ° C. The precursor thus obtained was then heated under a stream of air (100 NmL min ^-1 ) at 2 K min ^-1 to 600 ° C. (2 K min ^-1 ) and calcined at this temperature for a further 4 h.

The catalyst prepared in this way had a content of V ₂ O ₅ of 5.9% by weight and a content of Sb ₂ O ₅ of 19.8% by weight.

Catalytic test

For examination, the described catalyst was adjusted by milling and fractional sieving to a particle size distribution of 200 to 450 μm and 100 mg thereof with 50 NmL / min of a gas mixture consisting of 4.3 mol% methanol and 4.3 mol% oxygen in argon in a quartz glass reactor with 4 mm inner diameter at a temperature of 425 ° C for the reaction. The analysis of the products was carried out by mass analysis. The results achieved with the catalyst were:

Example 2 (Inventive Catalyst) Preparation of support material

The support materials of fumed silica were prepared as described in WO028071612, Example 21. The support material has a BET specific surface area of 203 m ^a g ^-1 and a pore volume of 0.76 mL g ^-1 .

The preparation of the catalyst based on this support material and its catalytic test for the oxidation of methanol were identical to Example 1. The results achieved with the catalyst were:

The example clearly shows that using high-purity pyrogenic silica as support material, the achievable yield of formaldehyde is higher than in the comparative example on precipitated silica.

Claims

claims

1. Catalyst consisting of a catalytically active vanadium-antimony mixed oxide and a shaped body of silica, which serves as a carrier for the catalytically active vanadium-antimony mixed oxide, characterized in that the shaped body consists of highly pure pyrogenic silicic acid and without the addition of Binders was produced.

2. A catalyst according to claim 1, characterized in that the shaped body of highly pure fumed silica having a specific surface area of 30 to 500 m ² / g and a defined pore structure with a monomodal pore radius distribution in the range between 5 and 30 nm, preferably between 10 and 20 nm and has less than 1% of micropores and is characterized by a proportion of mesopores in the total pore volume of over 75%, preferably over 90%, the remainder to 100 vol.% Formed by macropores.

3. A catalyst according to claim 1 or 2, characterized in that the shaped body of highly pure fumed silica has a total content of impurities of less than 100 ppm.

4. A catalyst according to claim 1, 2 or 3, characterized in that it has a content of vanadium oxide (as V ₂ O ₅ ) of 0.1 to 20 wt .-%, preferably 5 to 15 wt .-% and a content of Antimony oxide (as Sb ₂ O ₅ ) from 0.1 to 40 wt .-%, preferably 10 to 25 wt .-%.

5. A process for preparing a catalyst according to any one of claims 1 to 4, characterized in that the catalytically active components to the high-purity pyrogenic Silica in a conventional manner, for example, central impregnation, precipitation, ligand exchange is applied.

6. A process for the heterogeneously catalyzed partial oxidation of aliphatic alcohols to their corresponding aldehydes, characterized in that a catalyst according to claim 1 is used.

7. The method according to claim 6, characterized in that aliphatic alcohols having 1-10 C-atoms to the corresponding aldehydes, preferably methanol is converted to formaldehyde.

8. The method according to claim 6 or 7, characterized in that the reaction at a reaction temperature of 100 to 700 ° C, preferably 250 to 600 ° C, more preferably 300 to 450 ° C and at a reaction pressure of 0 to 2 MPa, preferably 0 to 1 MPa, more preferably 0 to 0.2 MPa.