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  • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
  • C04B35/62605—Treating the starting powders individually or as mixtures
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  • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
  • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
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  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/0238—Impregnation, coating or precipitation via the gaseous phase-sublimation
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  • C01G23/00—Compounds of titanium
  • C01G23/04—Oxides; Hydroxides
  • C01G23/047—Titanium dioxide
  • C01G23/07—Producing by vapour phase processes, e.g. halide oxidation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
  • B01J37/349—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of flames, plasmas or lasers
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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  • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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  • C01P2006/11—Powder tap density
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/12—Surface area
• • C—CHEMISTRY; METALLURGY
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
  • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
  • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
  • C04B2235/3231—Refractory metal oxides, their mixed metal oxides, or oxide-forming salts thereof
  • C04B2235/3232—Titanium oxides or titanates, e.g. rutile or anatase
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
  • C04B2235/50—Constituents or additives of the starting mixture chosen for their shape or used because of their shape or their physical appearance
  • C04B2235/54—Particle size related information
  • C04B2235/5409—Particle size related information expressed by specific surface values
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]

Definitions

• the present invention relates to a crystalline titanium dioxide powder having a variable sintering stability, a process for preparing the crystalline titanium dioxide powder, and a catalyst and/or a catalyst support comprising the crystalline titanium dioxide powder.
• Titanium dioxide may be produced by pyrogenic processes including flame oxidation and/or flame hydrolysis.
• a titanium dioxide precursor e.g., titanium tetrachloride
• oxygen e.g., oxygen
• flame hydrolysis titanium dioxide is formed by hydrolysis of the titanium dioxide precursor, with the requisite water for hydrolysis obtained from combustion of a fuel gas (e.g., hydrogen) with oxygen according to the following equation (2).
• a fuel gas e.g., hydrogen
• Titanium dioxide is generally present in the crystalline forms of anatase and rutile. In the references described below, the primary focus is on maximizing the proportion of anatase.
• WO 96/06803 describes a process for preparing titanium dioxide by a combination of flame oxidation and flame hydrolysis. Gaseous titanium tetrachloride and oxygen are mixed in a reaction zone and the mixture is heated in a flame produced by combustion of a hydrocarbon as a fuel gas. Titanium dioxide powder having a BET surface area of about 70-110 m 2 /g and a rutile content of less than 10% is described.
• Powder Technology, Vol. 86, No. 3, pp. 87-93 (March 1996) describes a flame oxidation process carried out in a diffusion reactor. No rutile is detected in a BET surface area of about 80-120 m 2 /g.
• DE-A-102004055165 describes a titanium dioxide powder that is prepared by flame hydrolysis and has a BET surface area of 20-200 m 2 /g.
• the anatase/rutile ratio is said to be able to be varied in a range from 2:98 to 98:2 at a given BET surface area, the examples show that the proportion of anatase clearly dominates.
• the anatase content is at least 90%.
• JP-A-10251021 describes three titanium dioxide powders obtained by flame oxidation, wherein the three titanium dioxide powders have a BET surface area of 3.2 m 2 /g, 28 m 2 /g and 101 m 2 /g and a rutile content of 97%, 32% and 15%, respectively.
• the present invention relates to a crystalline titanium dioxide powder having a variable sintering stability, a process for preparing the crystalline titanium dioxide powder, and a catalyst and/or a catalyst support comprising the crystalline titanium dioxide powder.
• An exemplary aspect of the present invention is to provide a crystalline titanium dioxide powder having a sintering stability that can be varied at a given BET surface area and a given rutile content.
• Another exemplary aspect of the present invention is to provide a crystalline titanium dioxide powder in the form of aggregated primary particles having a variable sintering stability at a BET surface area of 70-100 m 2 /g, preferably 80-90 m 2 /g, and a rutile content of greater than 10% but less than or equal to 40%, preferably 16-30%.
• a variable sintering stability is represented by titanium dioxide particles that aggregate during and/or after sintering to form larger particles thereby resulting in a decreased BET surface area.
• Representative ranges of decreased BET surface areas that constitute a variable sintering stability in accordance with the present invention include a decrease in the BET surface area of 10-90%, 15-85%, 20-80%, 25-75%, 30-70%, 35-65%, 40-60% and 45-55%, preferably 15-50%, based on the original BET surface area before sintering.
• Another exemplary aspect of the present invention is to provide a catalyst and/or a catalyst support comprising the crystalline titanium dioxide powder.
• the present invention provides a crystalline titanium dioxide powder in the form of aggregated primary particles having a variable sintering stability at a BET surface area of 70-100 m 2 /g and a rutile content of greater than 10% but less than or equal to 40%.
• variable sintering stability is represented by titanium dioxide particles that aggregate during and/or after sintering to form larger particles thereby resulting in a decreased BET surface area.
• Representative ranges of decreased BET surface areas that constitute a variable sintering stability in accordance with the present invention include a decrease in the BET surface area of 10-90%, 15-85%, 20-80%, 25-75%, 30-70%, 35-65%, 40-60% and 45-55%, preferably 15-50%, based on the original BET surface area before sintering.
• the BET surface area of the crystalline titanium dioxide powder is 70-100 m 2 /g, 75-95 m 2 /g or 80-90 m 2 /g.
• the BET surface area of the crystalline titanium dioxide powder is preferably 80-90 m 2 /g.
• the rutile content of the crystalline titanium dioxide powder is greater than 10% but less than or equal to 40%, 15-35% or 20-30%.
• the rutile content of the crystalline titanium dioxide powder is preferably 16-30%.
• the rutile content is based on the percentage of crystalline rutile relative to the sum of the crystalline forms of rutile and anatase which add up to 100%.
• the crystalline titanium dioxide powder having a variable sintering stability in accordance with the present invention generally does not contain further crystalline forms of titanium dioxide (e.g., titanium dioxide (B) or brookite) that can be detected in X-ray diffraction patterns.
• the present invention also provides a crystalline titanium dioxide powder in the form of aggregated primary particles having a variable sintering stability at a BET surface area of 80-90 m 2 /g and a rutile content of 16-30%.
• Primary particles are understood to include particles that are initially formed in the reaction, which can subsequently grow together to form aggregates during the course of the reaction.
• Aggregates are understood to include primary particles of similar structure and size that have grown together, with the surface area of the aggregate being smaller than that of the sum of the surface areas of the individual, isolated primary particles.
• a plurality of aggregates and/or individual primary particles can also be combined to form agglomerates, wherein the aggregates and/or primary particles are in point contact with one another. Agglomerates can be broken up by the introduction of energy as a function of the degree to which the aggregates and/or particles are combined.
• the proportion of aggregates and/or agglomerates having an average particle diameter of more than 45 ⁇ m in the crystalline titanium dioxide powder of the present invention is 0.0001-0.05 wt. %, 0.001-0.01 wt. % or 0.002-0.005 wt. %.
• the crystalline titanium dioxide powder of the present invention may further comprise one or more residues of chloride.
• the crystalline titanium dioxide powder of the present invention preferably has a chloride content of less than 0.1 wt. %.
• the crystalline titanium dioxide powder preferably has a chloride content of 0.01-0.05 wt. %.
• the tamped density of the crystalline titanium dioxide powder of the present invention is not particularly limited.
• the crystalline titanium dioxide powder of the present invention advantageously has a tamped density of 20-200 g/L, 30-190 g/L, 40-180 g/L, 50-170 g/L, 60-160 g/L, 70-150 g/L, 80-140 g/L, 90-130 g/L or 100-120 g/L.
• a tamped density of 30-120 g/L is particularly preferred.
• the present invention also provides a process for preparing a crystalline titanium dioxide (TiO 2 ) powder, wherein the process comprises:
• TiCl 4 titanium tetrachloride
• H 2 hydrogen
• a primary air introducing a titanium tetrachloride (TiCl 4 ) vapor and, separately therefrom, hydrogen (H 2 ) and a primary air into a mixing chamber to produce a gaseous mixture, wherein the primary air comprises air and/or oxygen enriched air;
• the relative amounts of TiCl 4 vapor, hydrogen and primary air are selected to provide crystalline TiO 2 powder having a BET surface area of 70-100 m 2 /g and a rutile content of greater than 10% but less than or equal to 40%,
• factor A has a value of 0.1-0.4 ⁇ 10 5 g/m 2 or 0.2-0.3 ⁇ 10 5 g/m 2 in accordance within the following formula:
• TiCl 4 , H 2 , primary air and gaseous mixture are in units of kmol/h
• BET surface area is in units of m 2 /g
• factor A is in units of 10 5 g/m 2 .
• the total gas comprises a gaseous mixture comprising titanium tetrachloride vapor, hydrogen, and a primary air, which comprises air and/or oxygen enriched air.
• the gaseous mixture may further comprise a secondary air, which comprises air and/or oxygen enriched air.
• Titanium tetrachloride is preferably vaporized at temperatures of less than 200° C., for example 136° C.
• the process of the present invention may also be carried out with in addition to the primary air, a secondary air being introduced into the mixing chamber and/or ignited in the burner and burned into the reaction chamber, wherein the volume ratio of primary air to secondary air is 10:0.1, 7.25:0.2, 4.5:0.3 or 1.75:0.4.
• the flame is preferably burned into a reaction chamber that is sealed off from the surrounding air.
• the process of the present invention may be carried out with the primary air and/or the secondary air being enriched with oxygen.
• the process of the present invention may be carried out with the primary air and/or the secondary air being preheated to a temperature of 50-500° C., 100-450° C., 150-400° C., 200-350° C. or 250-300° C.
• Titanium dioxide prepared by flame hydrolysis in accordance with the present invention may be obtained by introducing gaseous starting materials in a stoichiometric amount such that the amount of hydrogen introduced is at least sufficient to react with the chloride of titanium tetrachloride to form hydrochloric acid.
• the amount of hydrogen required for this reaction is referred to as the stoichiometric amount of hydrogen.
• the ratio of the amount of hydrogen introduced to the stoichiometric amount of hydrogen required is referred to as gamma ( ⁇ ) in accordance with the following equation:
• the process of the present invention is carried out at a gamma ( ⁇ ) value of 1-9, 2-8, 3-7 or 4-6.
• Titanium dioxide prepared by flame hydrolysis in accordance with the present invention may be obtained by introducing gaseous starting materials in a stoichiometric amount such that the amount of oxygen introduced, for example as a primary air and/or a secondary air, is at least sufficient to react with the titanium of titanium tetrachloride to form titanium dioxide and convert any excess unreacted hydrogen into water.
• the amount of oxygen required for this reaction is referred to as the stoichiometric amount of oxygen.
• the ratio of the amount of oxygen introduced to the stoichiometric amount of oxygen required is referred to as lambda ( ⁇ ) in accordance with the following equation:
• the process of the present invention is carried out at a lambda ( ⁇ ) value of 1-9, 2-8, 3-7 or 4-6.
• the process of the present invention may further comprise steam treating the crystalline TiO 2 powder, after separating the crystalline TiO 2 powder from the gaseous substances, with steam and an optional air.
• the steam treating may be carried out at a temperature of 250-750° C., 300-700° C., 350-650° C., 400-600° C. or 450-550° C.
• Steam treating serves a number of purposes, including for example, removing unreacted chloride from the surface of the crystalline TiO 2 powder and/or reducing the number of agglomerates.
• the process of the present invention may be carried out by continuously treating the crystalline TiO 2 powder, from which the gaseous substances have been separated off, with steam and optional air, which is/are flowing in a concurrent or countercurrent direction.
• the present invention also provides a catalyst and/or a catalyst support comprising the crystalline titanium dioxide powder having a variable sintering stability.
• the crystalline titanium dioxide powder having a variable sintering stability in accordance with the present invention may also be used in the ceramics industry.
• the BET surface area was determined in accordance with DIN 66131.
• the tamped density was determined by a method based on DIN ISO 787/XI K 5101/18 (not sieved).
• the bulk density was determined in accordance with DIN ISO 787/XI.
• the pH was determined by a method based on DIN ISO 787/IX, ASTM D 1280, JIS K 5101/24.
• the proportion of particles larger than 45 ⁇ m was determined in accordance with DIN ISO 787/XVIII, JIS K 5101/20.
• Determination of the chloride content within the crystalline titanium dioxide powder of the present invention was carried out at follows: 0.3 g of the crystalline titanium dioxide powder was admixed with 20 mL of a 20% sodium hydroxide solution (analytical reagent), dissolved and introduced while stirring into 15 mL of cooled nitric acid (HNO 3 ). The chloride content of the solution was titrated with a silver nitrate (AgNO 3 ) solution at a concentration of 0.1 mol/L or 0.01 mol/L.
• Examples 2 to 5 were carried out in a manner analogous to that described in Example 1.
• the respective amounts of the starting materials, the BET surface area and the rutile content of the crystalline titanium dioxide powders thus obtained are reported in Table 1.
• Comparative Example 11 is a titanium dioxide powder commercially available from Evonik Degussa under the registered trademark Aeroxide® TiO 2 P25.
• Comparative Example 12 is a titanium dioxide powder commercially available from Evonik Degussa under the registered trademark Aeroxide® TiO 2 VP P90.

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• 2007
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