Aluminum oxide production method

Abstract

The invention pertains to methods of producing aluminum trioxide in the form of powders or agglomerations with particles having a porous honeycomb structure, which can be used as catalyst substrates, adsorbents and filters for the chemical, food, and pharmaceutical industry. The method of production of aluminum oxide in the form of powders or agglomerations with particles having a porous honeycomb structure involves the treatment of the aluminum salt with a solution of an alkaline reagent, washing of the sediment and thermal treatment thereof. The technical result of the invention is the production of aluminum oxide in the form of separate particles with given structure and properties, specifically, with particle porosity of 60-80% and a porous structure represented by extensive parallel channels with near hexagonal packing, with dimension of the channels at the diameter of 0.3 to 1.0 micron and length up to 50 microns. For this, the aluminum salt used is crystals of aluminum chloride hexahydrate, which are treated with an excess aqueous solution of ammonia at temperature of 20-80 C. to form boehmite, and the heat treatment is done at 450-650 C. until aluminum oxide is formed.

Claims

1. A method of producing aluminum oxide in the form of powders or agglomerates having a porous honeycomb structure, the method comprising the steps of: treating an aluminum salt with an excess of a solution of an alkaline reagent at a temperature of 20-80 C. to form a sediment comprising boehmite, wherein the aluminum salt used comprises crystals of aluminum chloride hexahydrate and the solution of an alkaline reagent comprises an aqueous solution of ammonia; washing the sediment to form washed sediment; and thermally treating the washed sediment at 450-650 C. until aluminum oxide is formed.

2. The method of producing aluminum oxide of claim 1, wherein the aluminum oxide exhibits a porosity of 60-80%.

3. The method of producing aluminum oxide of claim 1, wherein the porous honeycomb structure of the aluminum oxide exhibits parallel channels with near hexagonal packing, wherein the channels each have diameters of 0.3 to 1.0 microns and lengths up to 50 microns.

Description

(1) The invention is based of the problem of developing a method of producing aluminum oxide with a honeycomb pore structure in the micron range of sizes, having low hydraulic resistance and good capacity to absorb droplet moisture.

(2) The technical result of the invention is the production of aluminum oxide in the form of separate particles with given structure and properties, specifically, with particle porosity of 60-80% and a porous structure represented by extensive parallel channels with near hexagonal packing, with dimension of the channels at the diameter of 0.3 to 1.0 micron and length up to 50 microns.

(3) The aforementioned technical effect is accomplished in that, in the method of production of aluminum oxide in the form of powders or agglomerations with particles having a porous honeycomb structure, involving the treatment of the aluminum salt with a solution of an alkaline reagent, washing of the sediment and thermal treatment thereof, the aluminum salt used is crystals of aluminum chloride hexahydrate, which are treated with an excess aqueous solution of ammonia at temperature of 20-80 C. to form boehmite, and the heat treatment is done at 450-650 C. until aluminum oxide is formed.

(4) Processing of the aluminum salt in the form of crystals of aluminum chloride hexahydrate with an excess aqueous solution of ammonia at temperature of 20-80 C. to form boehmite and heat treatment at 450-650 C. makes it possible to obtain aluminum oxide in the form of separate particles with particle porosity of 60-80% and porous structure in the form of extensive parallel channels with a near hexagonal packing, with particle dimension at the diameter of 0.3 to 1.0 micron and length up to 50 microns.

(5) In such a method of production of aluminum oxide there is no reprecipitation of hydrated aluminum compounds. The dimension of the resulting particles and, consequently, the length of the pores are dictated solely by the initial dimension of the crystals of the starting substance, aluminum chloride hexahydrate.

(6) The method for producing alumina is carried out as follows.

(7) Crystals of aluminum chloride hexahydrate are treated with a stoichiometric excess of an aqueous ammonia solution (content of NH.sub.3-25 wt. %) at a temperature of 20-80 C., which increases in the course of the process due to the exothermal effect of the reaction. The particles treated with the aqueous solution of ammonia visually preserve their external shape and the dimensions of the original crystals of aluminum chloride hexahydrate, but are constituted (according to X-ray phase analysis) of aluminum hydroxide in the polymorphic modification of boehmite (AlOOH). Thus, unlike the known methods, the aluminum hydroxide is obtained not by precipitation from aqueous solutions of aluminum salts, but by pseudomorphosis.

(8) The obtained boehmite particles are washed with water until the medium is neutral, and subjected to heat treatment at temperature of 450-650 C. for 1 hour, forming aluminum oxide.

(9) The surface morphology and cleavage of the particles of aluminum oxide according to the results of scanning electron microscopy are presented in FIGS. 1 and 2, respectively.

(10) The particles of the resulting aluminum oxide are pierced by extended parallel channels (pores) whose openings emerge onto the outer surface. The dimensions of the channels are diameter of 0.3-1.0 micron and length up to 50 microns. The porosity of the particles, determined mathematically on the basis of measurement of micrographs, is 60-80%. The aluminum oxide contains, in wt. %: Al.sub.2O.sub.3 98.6; Na.sub.2O 0.005; Fe.sub.2O.sub.3 0.01; SiO.sub.2 0.01; Cl.sup.<0.01 and has a gamma polymorphic modification, providing the highest sorptional properties of the product.

(11) In such a method of production of aluminum oxide there is no reprecipitation of hydrated aluminum compounds. Thus, the dimension of the resulting particles and, consequently, the length of the pores are dictated solely by the initial dimension of the crystals of the starting substance, aluminum chloride hexahydrate.

(12) Unlike the closest prior art and other known aluminum oxides with developed porous structure, the production of the proposed aluminum oxide is distinguished by exceptional simplicity.