RU2710708C1 - Microsphere powdered aluminum hydroxide of specified dispersion and method of its production - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to chemical engineering and can be used in production of aluminum oxides and hydroxides of various modifications, aluminum salts, etc. Set task is solved by means of microspherical powdered aluminum hydroxide for preparation of catalyst supports, containing oxygen-containing compound of aluminum of formula Al₂O₃⋅nH₂O, obtained by fast partial dehydration of hydrargillite with given particle size. Powdered aluminum hydroxide contains water in an amount corresponding to the value n=0.5–2.9, and simultaneously subjected to micromilling to preset particle size and mechanochemical activation and has a chemical activity of not less than 67 %, specific surface area of not less than 120 m²/g, bulk density of 0.9–1.1 g/cm³ and preset size of particles within 5–150 mcm.

EFFECT: obtaining mechanically activated aluminum hydroxide with chemical activity of 67–72 %, specific surface area of not less than 120 m²/g, bulk density of 0,9–1,1 g/cm³ and specified particle size within 5–150 mcm.

4 cl, 1 tbl, 7 ex

Description

The invention relates to the field of chemical technology and can be used in the production of aluminum oxides and hydroxides of various modifications, aluminum salts, etc.

Hydrated aluminum oxides are widely used as intermediates for the production of aluminum salts, flame retardants, as well as granular catalysts, catalyst supports, sorbents, etc.

For the synthesis of catalysts and supports, powders of hydroxides and / or aluminum oxides of various phase composition and dispersion are used as precursors.

Known aluminum hydroxides synthesized by the technology of deposition from aluminum-containing solutions - alkaline deposition of aluminum salts or acid deposition of aluminates of alkali metals, (patent RU 2482061, IPC C01F 7/02; B82B 3/00; B82Y 40/00, publ. 05.20.2013; patent RU 2145520, IPC B01J 37/03; B01J 21/04, publ. 02/20/2000; patent RU 2362620, IPC B01J 21/04; B01J 37/03; C01F 7/02, publ. 07/27/2009). Depending on the synthesis conditions (precipitation method, pH, precipitation temperature, etc.) it is possible to obtain aluminum hydroxides of various phase composition, for example, pseudoboehmite type (patent RU 2482061, IPC C01F 7/02; B82B 3/00; B82Y 40/00, publ. May 20, 2013), a bayerite type or a mixture of pseudoboehmite and bayerite (A.S. SU 1483843, IPC C01F 7/02, publ. 09/27/1999). However, technologies for producing aluminum hydroxides based on precipitation from aluminum-containing solutions are not environmentally friendly and expensive, since they are characterized by a high consumption of chemically purified water and the formation of a large amount of polluted effluents.

The most promising modern direction in the synthesis of powders of hydroxides and / or aluminum oxides are technologies based on the amorphization of gibbsite and the subsequent processing of the amorphized product into aluminum hydroxides of various phase composition (pseudoboehmite, boehmite, bayerite, mixtures thereof).

Methods for producing amorphized aluminum hydroxide are numerous and differ in the process conditions, as well as the conditions for its subsequent processing.

A known method of amorphization of gibbsite in a stream of hot air (patent RU 2167818, IPC C01F 7/02, publ. 05/27/2001), in the pulsed heating mode in a fluidized bed of a solid carrier (patent RU 2335457, IPC C01F 7/44, publ. 10.10. 2008), in a thermally insulated chamber under the action of centrifugal forces on a heated rotating plate (patent RU 2234460, IPC C01F 7/02, publ. 20.08.2004; patent RU 2237018, IPC C01F 7/02, publ. 27.09.2004; patent RU 2237019 , IPC C01F 7/02, publ. 09/27/2004), with mechanical (A.S. SU 1330923, IPC C01F 7/02; A.S. SU 1445109, IPC C01F 7/02, publ. 11/20/1996) and / or mechanochemical activation (patent RU 2432318, IPC C01F 7/02, op Released 10/27/2011).

Known powders of hydroxides and aluminum oxides synthesized by the technology of rapid thermochemical activation of gibbsite with subsequent processing, differing in the conditions of subsequent operations and physicochemical characteristics of the products obtained (patent RU 2390495, IPC C01F 7/02, publ. 27.05.2010; patent RU 2234460, IPC C01F 7/02, published on 08/20/2004; patent RU 2335457, IPC C01F 7/44, published on 10/10/2008).

The variety of methods for producing hydroxides and aluminum oxides leads to significant differences in their properties, in particular dispersion and phase composition.

Known oxygen-containing hydrated aluminum compound of the General formula Al ₂ O ₃ ⋅nН ₂ O (patent RU 2237019, IPC C01F 7/02, publ. 09/27/2004) containing aluminum cations in the 4, 5 and 6 coordinated state with respect to oxygen, having surface of 50-450 m ² / g, amorphous or poorly crystallized or partially crystalline structure. Moreover, n = 0.01-2.99, the average particle size of the powder is from 20 to 150 microns, in thermograms this compound is characterized by the presence of an exoeffect in the temperature range of 780-850 ° C, corresponding to the ordering of the crystal structure. A method of obtaining an oxygen-containing hydrated aluminum compound consists in rapid heat-shock treatment of aluminum hydroxide at elevated temperature, followed by forced cooling. Thermal shock treatment of aluminum hydroxide is carried out in a heat-insulated chamber under the action of centrifugal forces with a thin-layer distribution of aluminum hydroxide on a rotating surface heated to a temperature of 300-1500 ° C for 0.01-10 s with the simultaneous selection of waste water vapor.

The closest technical solution to the claimed is a microspherical support for catalysts (patent RU 2271248, IPC B01J 21/04; C01F 7/02, publ. 10.03.2006), comprising an oxygen-containing aluminum compound of the formula Al ₂ O ₃ ⋅nН ₂ O of an X-ray amorphous structure, obtained by rapid partial dehydration of hydrargillite. The carrier is spheroidal particles consisting of hexagonal rods with a system of flat parallel pores corresponding to cleavage along the (001) face, the carrier contains water in an amount corresponding to a value of n = 0.5-1.0, has a particle size of 20-250 μm, the specific surface area is 80-250 m ² / g and the pore volume is 0.1-0.3 cm ³ / g. Proposed according to the invention, the carrier allows to obtain catalysts with high strength properties and high activity.

The disadvantage of the carrier is that the particle size is in a wide range (20-250 microns), therefore, it is proposed to use a laborious screening procedure to isolate narrower fractions. The carrier is mainly used for the preparation of fluidized bed catalysts. However, there are a number of catalysts, as well as carriers, sorbents, etc., which require a narrower range of particle sizes. For example, the size of the portion of the support for the hydrotreating catalyst should be in the range from 30 to 40 μm (patent RU 2472585, IPC B01J 37/02; C10G 45/08; B01J 21/02; B01J 27/20; B01J 37/04, publ. 01/20/2013). In addition, the carrier has an insufficiently high degree of rehydration.

The objective of the present invention is to obtain (without reprecipitation) chemically active amorphized aluminum hydroxides, the precursor of which is an aluminum compound obtained by the rapid dehydration of hydrargillite (gibbsite, technical alumina hydrate) having a given particle size distribution and increased chemical activity.

The problem is solved using microspherical powdered aluminum hydroxide for the preparation of catalyst supports, including an oxygen-containing aluminum compound of the formula Al ₂ O ₃ ⋅nН ₂ O obtained by the fast partial dehydration of hydrargillite with a given particle size. Powdered aluminum hydroxide contains water in an amount corresponding to a value of n = 0.5-2.9 and is simultaneously micronized to a given particle size and mechanochemical activation and has a chemical activity of at least 67%, specific surface area of at least 120 m ² / g, bulk a density of 0.9-1.1 g / cm ³ and a given particle size in the range of 5-150 microns.

Preferably, the powdered aluminum hydroxide consists of a fraction with a narrow distribution of powder particles selected from the following ranges: 5-15, 10-25, 25-45, 40-55, 50-70, 70-150.

Also, the problem is solved using the method of producing a microspherical powdered aluminum hydroxide, including an oxygen-containing aluminum compound obtained by the rapid partial dehydration of aluminum described above with a given particle size. In order to obtain a given particle size in the range of 5-150 μm, micromilling and mechanochemical activation of an oxygen-containing aluminum compound Al ₂ O ₃ ⋅nН ₂ O are additionally carried out simultaneously, where n = 0.5-2.9 in rotor-vortex type mills with an integrated particle classifier .

Preferably, the feed rate of the oxygen-containing aluminum compound to the rotary vortex mill is from 5 to 90 kg / m.

As the initial aluminum-containing raw materials, technical alumina hydrate (hydrargillite) is used, which has been converted into a chemically active state by thermochemical and mechanochemical activation. In particular, gibbsite from the production of Achinsk Alumina Refinery OJSC was taken as a feedstock, which is gibbsite powder with granules from 100 to 190 microns in size, with a bulk density of 1.3 g / cm ³ , specific surface area <1 m ² / g, the total pore volume <0.01 cm ³ / g, and the content of trace elements: SiO ₂ up to 0.06% wt., Na ₂ O up to 0.40% wt., Fe ₂ O ₃ up to 0.03% wt.

At the first stage, the initial technical alumina hydrate of the formula Al ₂ O ₃ ⋅ 3Н ₂ O is subjected to thermochemical activation — it is converted by rapid heat treatment into a partially dehydrated product (TGA) of the formula Al ₂ O ₃ ⋅nН ₂ O, where n = 0.5-2 , 9, having a predominantly X-ray amorphous state. Pulse heat treatment of technical alumina hydrate is carried out at a temperature of 350-900 ° C for 2-10 s. The product is cooled to a temperature below 200 ° C in a time not exceeding 10 minutes. The resulting product is characterized by a heterogeneity of quality - a wide range of particle sizes from 20 to 250 microns, specific surface area from 50 to 200 m ² / g, pore volume 0.1-0.3 cm ³ / g, and relatively low chemical activity at the level of 35-45%. The level of chemical activity determines the reactivity of the product in the hydration reactions of MTHA powders (chemical activity), which was assessed by the degree of dissolution in a 20% sodium hydroxide solution at 60 ° C for 30 min.

The heterogeneity of the quality of the obtained product makes heterogeneity in the properties of the products of its processing, and low chemical activity does not contribute to the hydration (rehydration) process. When hydrating powders, particles of different sizes undergo various changes under the same processing conditions, therefore, when hydrating powders with a narrow particle size distribution, all particles undergo the same hydrothermal influences and hydration (rehydration) is more effective.

To obtain highly dispersed, chemically active aluminum hydroxides with a certain particle size, in the second stage, the TGA product is subjected to grinding in a rotary vortex mill at specified technological parameters, which allow achieving a normalized particle size distribution.

In the chamber of a rotary vortex mill, the grinding process is carried out using a knife rapidly rotating in the horizontal plane, onto which the product enters the axial region from above. Under the knife (parallel to it), a replaceable diaphragm is fixed in the chamber. The rotation of the knife is provided through a V-belt transmission by two synchronously operating electric motors. The particle size of the finished product depends on the residence time of the starting product in the mill at a feed rate of 5 to 9 kg / min, which depends on the vacuum in the system and the diameter of the internal opening of the interchangeable diaphragm, which is set at a level of 200 to 350 mm. Mill productivity can reach 300 kg / hour of a product.

After grinding, mechanically activated aluminum hydroxide MTGA is obtained with increased chemical activity at a level of at least 67%, specific surface area of at least 120 m ² / g and normalized particle size, for example, powders with an average particle diameter of 5-15 microns, 10-25 microns, 25-45 microns, 40-55 microns, 50-70 microns, etc. According to the phase composition, the obtained MTGA powders are a multicomponent system containing predominantly amorphized aluminum hydroxide (at least 90%). The resulting products can be used as precursors for the synthesis of aluminum hydroxides of various modifications, as well as for the synthesis of various aluminum compounds - salts, aluminum oxides, etc.

The technical result is the production of mechanically activated aluminum hydroxide with a chemical activity of 67-72%), specific surface area of at least 120 m / g, bulk density of 0.9-1.1 g / cm ³ and a given particle size in the range of 5-150 microns.

To prepare the aluminum hydroxide powder, the product of partial dehydration of hydrargillite of the formula Al ₂ O ₃ ⋅nН ₂ O, where n = 0.5-2.9, is used. Pulse heat treatment of technical alumina hydrate is carried out at a temperature of 350-900 ° C for 2-10 s. The product is cooled to a temperature below 200 ° C in a time not exceeding 10 minutes. The TGA product is characterized by heterogeneity of quality - a wide range of particle sizes from 20 to 250 microns, specific surface area from 50 to 200 m ² / g, pore volume 0.1-0.3 cm ³ / g, and relatively low chemical activity at the level of 35 -45%.

The resulting product is additionally subjected to mechanochemical activation in a rotary vortex mill and receive activated aluminum hydroxide MTGA with a chemical activity of 61-12%, a specific surface area of at least 120 m ² / g and a normalized particle size in the range of 5-70 μm. The level of chemical activity determines the reactivity of the product in the hydration reactions of MTHA powders (chemical activity), which was assessed by the degree of dissolution in a 20% sodium hydroxide solution at 60 ° C for 30 min.

Example 1

TGA powder (Al ₂ O ₃ ⋅nН ₂ O, where n = 10.5) was ground in a rotary-vortex mill with a product feed rate of 9 kg / min, and a diameter of an internal opening of a replaceable diaphragm of 200 mm, which made it possible to achieve an average size particles of 5-10 microns. The characteristics of the obtained powder are shown in table 1.

Example 2

TGA powder (Al ₂ O ₃ ⋅nН ₂ O, where n = 2.9) is ground in a rotary-vortex mill with a product feed rate of 8 kg / min, and a diameter of an internal opening of a replaceable diaphragm of 220 mm, which made it possible to achieve an average size particles of 10-25 microns. The characteristics of the obtained powder are shown in table 1.

Example 3

TGA powder (Al ₂ O ₃ ⋅nН ₂ O, where n = 1.5) was ground in a rotary-vortex mill at a feed rate of 7 kg / min, with a diameter of the internal opening of the interchangeable diaphragm from 250 mm, which made it possible to achieve an average size particles of 25-45 microns. The characteristics of the obtained powder are shown in table 1.

Example 4

TGA powder (Al ₂ O ₃ ⋅nН ₂ O, where n = 2.0) is ground in a rotary vortex mill with a product feed rate of 6 kg / min, and a diameter of an internal opening of a replaceable diaphragm of 300 mm, which made it possible to achieve an average size particles of 40-55 microns. The characteristics of the obtained powder are shown in table 1.

Example 5

TGA powder (Al ₂ O ₃ ⋅nН ₂ O, where n = 0.8) is ground in a rotary vortex mill at a feed rate of 5 kg / min, with a diameter of the internal opening of the interchangeable diaphragm from 350 mm, which allowed to achieve an average size particles of 50-70 microns. The characteristics of the obtained powder are shown in table 1.

Example 6

An example demonstrates the use of an intermediate composition for the preparation of granular alumina products that can be used as carriers for catalysts, sorbents, etc.

MTGA powders obtained in examples 4 and 3, with particle sizes of 40-55 μm and 25-45 μm, respectively, are subjected to separate hydration with solutions of nitric acid in reactors with a heating jacket and a propeller-type mixer. Hydration is carried out at atmospheric pressure and temperatures of 65-95 ° C, at pH = 5-9 for 0.5-10 hours, with the ratio of liquid to solid phase (3-6): 1. After hydration is completed, the suspension of aluminum hydroxide enters the drum vacuum filters, where the suspension is separated into a liquid phase and a wet mass with a moisture content of not more than 60%.

Part of the wet mass obtained after hydration of MTGA powder with a particle size of 25-45 μm is subjected to drying in a drying plant for pasty products in a stream of hot air at a temperature of 80 to 130 ° C and a vacuum in the dryer in the range from minus 1.5 to minus 0 , 5 kPa. The result is an aluminum hydroxide powder with a specific surface area of 255 m ² / g.

Part of the wet mass obtained after hydration of MTGA powder with a particle size of 25-45 μm is subjected to heat treatment at temperatures of 250-350 ° C to obtain a transition alumina powder with a specific surface area of 298 m ² / g and bulk density of 0.57 g / cm ³ .

At the stage of preparation of the molding mass, the composition is prepared by mixing the obtained intermediates in the following ratio: 30% wet weight of aluminum hydroxide with a particle size of 40-55 μm, 50% aluminum hydroxide powder with a particle size of 25-45 μm and 20% transition aluminum oxide powder, and additionally, acids (organic or inorganic) are added to plasticize the mass, porous structure additives, and metal modifying compounds can be added if necessary.

The mass is plasticized, fed into a screw granulator and granules are obtained. Granules can be formed in the form of cuttings with a diameter of 2 to 12 mm, spheres from 2 to 15 mm, a trefoil, a ring, etc.

Example 7 (prototype).

The carrier is prepared using hydrargillite obtained from nepheline raw materials by sintering with soda and limestone in the form of a powder of spheroid particles from hexagonal rods of 20-250 μm in size with the properties shown in table 1. It is subjected to rapid partial dehydration at a temperature of 500 ° C for 1 sec The result is an oxygen-containing aluminum compound of the formula Al ₂ O ₃ ⋅nН ₂ O, where n = 0.5, which consists of spheroid particles consisting of hexagonal rods with a system of flat parallel pores, which is sieved to obtain a certain particle size of 70-250 microns. The carrier has a pore volume of 0.1 cm ³ / g specific surface area of 80 m ² / g and contains compounds of silicon, iron, sodium.

The data are presented in table 1.

The carrier has a chemical activity of 62%.

Example 6 shows that the products obtained can be used as precursors for the synthesis of aluminum hydroxides of various modifications, as well as for the synthesis of various aluminum compounds - salts, aluminum oxides, etc.

Claims (4)

1. Microspherical powdered aluminum hydroxide for the preparation of catalyst supports, including an oxygen-containing aluminum compound of the formula Al ₂ O ₃ ⋅nН ₂ O obtained by the rapid partial dehydration of hydrargillite with a given particle size, characterized in that it contains water in an amount corresponding to n = 0,5-2,9 and simultaneously subjected to a predetermined micronized, particle size and mechanical activation, and has a reactivity of not lower than 67%, specific surface area below 120 m ² / g, bulk w density of 0.9-1.1 g / cm ³ and a predetermined particle size in the range 5-150 microns. 2. Powdered aluminum hydroxide according to claim 1, characterized in that it consists of a fraction with a narrow distribution of powder particles selected from the following ranges: 5-15, 10-25, 25-45, 40-55, 50-70, 70 -150. 3. The method of producing a microspherical powdered aluminum hydroxide according to claim 1 or 2, in which to obtain a given particle size in the range of 5-150 μm, micromilling and mechanochemical activation of the oxygen-containing aluminum compound Al ₂ O ₃ ⋅nН ₂ О, where n = 0 , 5-2.9, in rotor-vortex type mills with an integrated particle classifier. 4. The method according to claim 3, characterized in that the feed rate of the oxygen-containing aluminum compounds in the rotary vortex mill is from 5 to 90 kg / m