DE102010030523A1 - Granule, useful as catalyst or catalyst carrier, comprises silicon-titanium mixed oxide powder, where the titanium comprises rutile and anatase modifications - Google Patents

Abstract

Granule comprises one or more silicon-titanium mixed oxide powders, where: the amount of titanium dioxide is 70-98 wt.% and silicon dioxide is 2-30 wt.%; (a) at room temperature, the sum of the portion of titanium dioxide and silicon dioxide is at least 98 wt.%, the titanium dioxide comprises rutile and anatase modifications and the portion of anatase modification is greater than 50%; and (b) after heating titanium dioxide at 900[deg] C for 4 hours, the portion of anatase is greater than 50% of the portion of anatase at room temperature. Granule comprises one or more silicon-titanium mixed oxide powders, where: the amount of titanium dioxide is 70-98 wt.% and silicon dioxide is 2-30 wt.%; (a) at room temperature, the sum of the portion of titanium dioxide and silicon dioxide is at least 98 wt.%, the titanium dioxide comprises rutile and anatase modifications and the portion of anatase modification is greater than 50%, the Brunauer Emmett Teller surface of the titanium dioxide is 10-200 m 2>/g and the amount of titanium dioxide with volume pore of 2-50 nm is 0-15 to less than 0.4 ml/g; and (b) after heating titanium dioxide at 900[deg] C for 4 hours, the portion of anatase is greater than 50% of the portion of anatase at room temperature; the amount of Brunauer Emmett Teller surface of the titanium dioxide is at least 60% of titanium dioxide at room temperature, and the amount of titanium dioxide with volume pore of 2-50 nm is at least 50% than the volume pore of titanium dioxide at room temperature. An independent claim is included for producing granules comprising spray-drying an aqueous dispersion comprising silicon-titanium mixed oxide powder at 200-600[deg] C.

Description

The invention relates to a granulate containing silica and titanium dioxide, which has a high stability of the BET surface area, the pore volume and the catalytic activity at high temperatures. The invention further relates to a process for the preparation of the granules and its use as a catalyst and catalyst support.

In nature, there are three titanium dioxide phases, rutile, anatase and brookite. Often anatase is the major product of various synthetic routes, such as sol-gel processes, hydrothermal processes, precipitation reactions or flame processes.

Applications of titanium dioxide as a catalyst or catalyst support require high temperatures, which lead to an irreversible conversion of anatase to rutile and thus can lead to a reduction of the catalytic, in particular the photocatalytic activity.

An improvement of this situation can be achieved, for example, by the replacement of titanium dioxide with silicon-titanium mixed oxides which have improved thermal stability of the BET surface.

Silicon-titanium mixed oxide powders can be produced, for example, by the pyrogenic route. In this case, as a rule, a mixture of silicon tetrachloride and titanium tetrachloride is hydrolyzed in a flame and / or oxidized. The flame can be generated for example by reaction of hydrogen and atmospheric oxygen. This produces the water necessary for the hydrolysis of the chlorides. So will in DE-A-2931810 claimed a silicon-titanium mixed oxide powder containing 0.1 to 9.9 wt .-% titanium dioxide. In EP-A-1553054 is a silicon-titanium mixed oxide powder having a BET surface area between 20 and 200 m ² / g and a titanium dioxide content of more than 10 wt .-% and less than 70 wt .-%, claimed. In EP-A-595 078 a silicon-titanium mixed oxide powder is claimed which contains 70 to 99 wt .-% titanium dioxide. In EP-A-1752215 discloses a silicon-titanium mixed oxide powder, having a BET surface area of 5 to 300 m ² / g and a titanium dioxide content of ≥ 99.0 wt .-% disclosed. In EP-A-1321432 discloses a flame-hydrolytically produced silicon-titanium mixed oxide powder in which the weight ratio of silica / titanium dioxide on the surface of the primary particles is greater than in the total primary particle. The weight ratio of SiO ₂ / TiO ₂ may be 0.01 to 99, based on the total primary particle, and the BET surface area may be 10 to 300 m ² / g.

In principle, these powders can all be used as catalyst or catalyst support. Especially in EP-A-595 078 disclosed powder has a relatively high stability of the BET surface under thermal treatment. However, this powder, as well as others in the prior art, have inadequate mechanical stability when used as a catalyst or catalyst support. In addition, under these conditions, a reduction of the catalytic, in particular the photocatalytic, activity can be observed, which can occur independently of the process to be catalyzed.

It was therefore the technical problem to provide a material which has good thermal and mechanical stability and high catalytic activity at high temperatures.

• a) bei Raumtemperatur
• a1) der Anteil des Titandioxides, die Modifikationen Rutil und Anatas umfasst oder aus ihnen besteht, und der Anteil an Anatas, bezogen auf den Titandioxidanteil, mehr als 50%, bevorzugt 60 bis 95%, besonders bevorzugt 65 bis 85% beträgt,
• a2) die BET-Oberfläche 10 bis 200 m²/g, bevorzugt 30 bis 150 m²/g, besonders bevorzugt 40 bis 60 m²/g, ist
• a3) das Volumen der Poren von 2 bis 50 nm 0,15 bis < 0,4 ml/g, bevorzugt 0,20 bis 0,30 ml/g ist und
• b) nach dem Erhitzen auf 900°C über einen Zeitraum von 4 Stunden
• b1) der Anteil an Anatas mehr als 50%, bevorzugt 60 bis 100%, besonders bevorzugt 65 bis 99%, des Anteiles bei Raumtemperatur ist,
• b2) die BET-Oberfläche wenigstens 60%, bevorzugt 65 bis 99%, besonders bevorzugt 75 bis 95% der BET-Oberfläche bei Raumtemperatur ist,
• b3) das Volumen der Poren von 2 bis 50 nm wenigstens 50, bevorzugt 60 bis 99%, besonders bevorzugt 70 bis 95%, des Volumens der Poren von 2 bis 50 nm bei Raumtemperatur ist.

The technical object is achieved by a granulate comprising or consisting of one or more silicon-titanium mixed oxide powders, wherein the proportion
titanium dioxide 70 to 98 wt .-%, preferably 75 to 97 wt .-%, particularly preferably 85 to 95.5 wt .-%,
on silica from 2 to 30 wt .-%, preferably 3 to 25 wt .-%, particularly preferably 4 to 15 wt .-%, is, and
wherein the sum of the proportions of at least 98 wt .-%, preferably at least 99 wt .-%, particularly preferably at least 99.5 wt .-%, in each case based on the granules and wherein

• a) at room temperature
• a1) the proportion of titanium dioxide which comprises or consists of rutile and anatase modifications and the proportion of anatase, based on the titanium dioxide content, is more than 50%, preferably 60 to 95%, particularly preferably 65 to 85%,
• a2) the BET surface area is 10 to 200 m ² / g, preferably 30 to 150 m ² / g, particularly preferably 40 to 60 m ² / g
• a3) the volume of the pores from 2 to 50 nm is 0.15 to <0.4 ml / g, preferably 0.20 to 0.30 ml / g, and
• b) after heating to 900 ° C over a period of 4 hours
• b1) the proportion of anatase is more than 50%, preferably 60 to 100%, particularly preferably 65 to 99%, of the proportion at room temperature,
• b2) the BET surface area is at least 60%, preferably 65 to 99%, particularly preferably 75 to 95% of the BET surface area at room temperature,
• b3) the volume of the pores is from 2 to 50 nm at least 50, preferably 60 to 99%, particularly preferably 70 to 95%, of the volume of the pores of 2 to 50 nm at room temperature.

Room temperature is a temperature of 23 ° C.

The granules according to the invention may preferably have an average granule diameter D ₅₀ of 10 to 200 μm. Particularly preferred is a range of 10 to 40 microns.

Another object of the invention is a process for the preparation of the granules in which an aqueous dispersion containing one or more silicon-titanium mixed oxide powder spray-dried at 200 to 600 ° C. The granules thus obtained have a very good mechanical stability and is thus ideally suited as a catalyst or catalyst support. The dispersion can be prepared by dispersion units known to the person skilled in the art. Preferably, rotor-stator units are used. The proportion of powder in the dispersion may be 1 to 30 wt .-%. In general, the proportion of powder is from 5 to 20 wt .-%. The liquid phase contains

The liquid phase of the dispersion may further comprise one or more substances which lower the viscosity of the dispersion. These can be acids or bases. Hydrochloric acid, acetic acid, potassium hydroxide, ammonia and tetraalkylammonium hydroxides may be mentioned by way of example. Such viscosity-lowering substances can be used especially when the solids content of the dispersion is high.

Ideally, pyrogenically prepared silicon-titanium mixed oxide powders are used in the process according to the invention. By pyrogenic is meant that the particles underlying the powder are obtained by means of flame hydrolysis or flame oxidation or a mixed form of both reactions. In the present case, these are so-called "co-fumed" mixed oxide powders in which the starting materials, for example silicon tetrachloride and titanium tetrachloride, are reacted together in the flame. This results in real mixed oxide particles, in contrast to physical mixtures. In the course of the reaction, primary particles are initially formed, which subsequently grow together into aggregates. The primary particles are largely or completely free of internal pores. However, the spatial arrangement of the aggregates in the granules leads to a stable for catalytic processes even under thermal treatment pore volume.

In the context of the invention, pyrogenic mixed oxide powders which contain one or more further components based on noble metals or metal oxides should also be able to be used in the process according to the invention. The proportion of these components can be up to 1 wt .-%, preferably 10 to 1000 ppm, based on the mixed oxide powder. In particular, metals and metal oxides from the group of Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Fe, Ga are used as further components , Gd, Ge, Hf, Ho, In, Ir, K, La, La, Li, Lu, Mg, Mn, Mo, Na, Nb, Nd, Ni, Os, P, Pb, Pd, Pm, Pr, Pt , Rb, Re, Rh, Ru, Sb, Sc, Sm, Sn, Sr, Ta, Tb, Tc, Tl, Tm, V, W, Y, Yb, Zn and Zr in question. Methods for producing such powders are for example DE-A-19650500 or EP-A-1785395 known.

Another object of the invention is the use of the granules as a catalyst or catalyst support, especially in those processes in which water vapor is present or arises.

Examples

Analytical procedures

The pore volume of the pores from 2 to 50 nm is determined by the BJH method DIN 66134 certainly. The BET surface will decrease DIN 66131 certainly. The determination of the Anatasanteiles by X-ray diffraction.

feedstock

Based on the in US 5268337 disclosed method is a silicon-titanium mixed oxide powder P1 having a content of SiO ₂ of 5 wt .-% of TiO ₂ from 94.7 to 95.0 wt .-%, a BET surface area of 50 m ² / g and an anatase content of 66%. In addition to SiO ₂ and TiO ₂ , P1 may also contain proportions of chloride and optionally further impurities caused by the purity of the starting materials.

Production of a granulate

1.50 kg of P1 are dispersed in 10 kg of water by means of an Ultraturrax DI 25 over a period of 15 minutes at a speed of 20,000 rpm. The dispersion is then spray dried by means of a disk atomizer at 380 ° C and the resulting granules G1 deposited on a filter.

G1 has approximately the same values as P1 with respect to the SiO ₂ content, the TiO ₂ content, the BET surface area and the anatase content. The average granule diameter is 30 μm.

Stability of the pore volume

2.5 g of G1 are exposed to a certain temperature in an alumina boat in a muffle open over a period of 4 hours. The temperatures are 600 ° C, 700 ° C, 800 ° C and 900 ° C. In the investigation of the properties of the granules under hydrothermal conditions, a device is used, in which the granules are in an oven, through which a water vapor saturated gas stream is passed at a pressure of 1.1 bar. The absolute humidity is controlled to a value of 100 ± 15 g H ₂ O / m ³ gas flow.

Result

The table shows that in G1, the pore volume of the pores from 2 to 50 nm, the BET surface area and the anatase content at temperatures under thermal and hydrothermal load only insignificantly decreases.

G1 thus shows optimum properties for use as a catalyst and catalyst support, namely a high stability of the pore volume, a high stability of the BET surface area and a high stability of the anatase phase relevant for catalytic processes. Table 1: Substance parameters under thermal and hydrothermal load thermal load hydrothermal load VP _{(2-50 nm)} * [cm ³ / g] BET [m ² / g] Anatas [%] VP _{(2-50 nm)} [cm ³ / g] BET [m ² / g] Anatas [%] 23 ° C 0.24 50 67 0.24 50 67 600 ° C 0.22 50 67 0.21 50 67 700 ° C 0.22 50 67 0.21 47 67 800 ° C 0.21 48 66 0.21 47 66 900 ° C 0.20 38 67 0.20 39 66 * VP _{(2-50 nm)} = pore volume of the pores with a diameter of 2 to 50 nm

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 2931810 A [0005]
• EP 1553054A [0005]
• EP 595078 A [0005, 0006]
• EP 1752215A [0005]
• EP 1321432A [0005]
• DE 19650500 A [0014]
• EP 1785395A [0014]
• US 5268337 [0017]

Cited non-patent literature

• DIN 66134 [0016]
• DIN 66131 [0016]

Claims (7)

Granules comprising or consisting of one or more silicon-titanium mixed oxide powders, wherein the proportion of titanium dioxide 70 to 98 wt .-%, of silica from 2 to 30 wt .-%, and wherein the sum of the shares at least 98 wt a) the proportion of titanium dioxide comprising or consisting of rutile and anatase modifications and the proportion of anatase, relative to the titanium dioxide content, is more than 50%, a2) the BET surface area is 10 to 200 m ² / g a3) the volume of the pores is from 2 to 50 nm 0.15 to <0.4 ml / g and b) after heating to 900 ° C over a period of time b1) the content of anatase is more than 50% of the content at room temperature, b2) the BET surface area is at least 60% of the BET surface area at room temperature, b3) the volume of the pores is from 2 to 50 nm at least 50% the volume of the pores is from 2 to 50 nm at room temperature. Granules according to claim 1, characterized in that the average granule diameter D _{50 is} 10 to 200 μm. Process for producing the granulate according to claims 1 or 2, characterized in that an aqueous dispersion containing one or more silicon-titanium mixed oxide powders is spray-dried at 200 to 600 ° C. A method according to claim 3, characterized in that the proportion of powder in the dispersion is 1 to 30 wt .-%. Process according to claims 3 or 4, characterized in that the liquid phase of the dispersion contains one or more viscosity-lowering substances. Process according to claims 3 to 5, characterized in that pyrogenically prepared silicon-titanium mixed oxide powders are used. Use of the granulate according to claims 1 or 2 as catalyst or catalyst support.