RU2294317C2 - Method of manufacture of high-porous cellular ceramic articles - Google Patents

Abstract

FIELD: chemical technology of high-porous ceramic materials with screen-cellular structure used as stationary carriers of block catalysts and filters.

SUBSTANCE: articles made from polyurethane with screen-cellular structure are impregnated with slip containing inert filler-electrically molten corundum or mixture of electrically molten corundum, silicon carbide, dispersed powder of aluminum oxide with addition of oxides of metals of groups II and IV of Mendeleyev's Table and polyvinyl styrene solution. Articles are dried and are treated with alumosol or aluminum chloride solution with or without introduction of active additives at pH=4±0.2, after which articles are burnt at temperature of 1450-1500°C. Porosity is increased to 93-95% at retained high strength (1.5-2 Mpa).

EFFECT: enhanced efficiency; increased porosity at retained high strength.

2 cl, 1 tbl

Description

The invention relates to the field of chemical technology of highly porous ceramic materials with a mesh-cellular structure, which can be widely used as stationary carriers of block catalysts for the conversion of natural gas, reduction of unsaturated hydrocarbons, aromatic nitro compounds, aldehydes, ketones, carboxylic acids, heterogeneous nitration of organic compounds, as well as filters for filtering metals, nozzles for mass transfer processes, high-temperature thermal insulation tion materials and other purposes.

The invented highly porous materials with a mesh-cellular structure are obtained by reproducing the structure of a foamed reticulated polyurethane by applying a ceramic powder containing a filler and sintering active alumina powder with additives in the form of a slip on various bundles, followed by burning the base and heating the remaining ceramic frame to a temperature at which a ceramic product acquires the desired properties. The total porosity of the ceramic product is 85-92% with a mesh size of 200-5000 microns with an open porosity of the bridges between the cells of 20-30%, which have a pore size of 1-2 microns. For comparison, the porosity of cellular materials obtained by extruding powder plastic masses through dies with subsequent drying and sintering is ~ 50-80%, and the channel size is 800-7000 μm.

The set of requirements for block catalysts includes primarily mechanical strength and high catalytic activity with minimal resistance to flow movement. It is noted that in terms of mechanical characteristics, cellular structures are inferior to cellular ones. At the same time, the processes of mass and heat transfer in cellular structures proceed much more efficiently, which leads to an increase in their catalytic activity.

In Russia, the development of highly porous materials according to the above method for various purposes has been going on since the beginning of the 60s, including in the Russian Engineering and Technical Center for Powder Metallurgy, Perm, under the direction of V.A. Antsiferov.

A highly porous alumina-based material with a predetermined structure of cell bridges was obtained at the Department of Ceramics and Refractories, Russian Technical University. D.I. Mendeleev prof. Lukin E.S. in 1999, from which a number of cellular catalysts with the active component of Group VIII elements (nickel, palladium) for liquid-phase hydrogenation of aromatic nitro compounds were made.

Currently, aluminosilicate materials are mainly used for the manufacture of products from highly porous ceramic materials with a mesh-cellular structure, the slip of which is applied to the reticulated polyurethane foam, and the products are squeezed from excess slip, dried to constant weight and fired at temperatures up to 1350 ° C.

Highly porous cellular ceramic material (prototype) [A.I. Kozlov, E.S. Lukin. The composition of the charge for a highly porous material with a mesh-cellular structure for catalyst carriers, RF patent No. 2233700, priority dated June 11, 2002] is obtained on the basis of a mixture of an inert filler and sintering powder of alumina with additives of any oxides of groups II and IV of the periodic table in any quantity with the addition of a binder, followed by drying of the products, burning of the organic base and firing of the ceramic frame at temperatures of 1450-1500 ° C.

The total porosity of ceramic products is 85-92% with an open porosity of the bridges between the cells of 20-30%, having a pore size of 1-2 microns.

Samples of highly porous cellular corundum withstand a static load of 0.5 to 2 MPa, depending on the composition, porosity, and heat treatment conditions.

The ceramic suspension used for molding has a low viscosity and high fluidity, which allows it to be uniformly applied to the structural elements of the mesh-preform. The fixing of the ceramic layer on the surface of the polymer matrix occurs during the drying process when removing moisture contained in the adhesive, and in the final form the workpiece already has some mechanical strength. Typically, such suspensions contain a refractory powder having a particle size of 1-5 μm, flux and alloying powders of the same dispersion level, 40-60% of a dispersed medium, rheological substances (usually bentonite), as well as organic adhesives. However, the low content of suspensions and, as a result, the low strength of highly porous material after firing, not exceeding 1 MPa for porosity of more than 85%, remains a big problem, so it is necessary to choose the right adhesive and rheological additives and their concentrations for the specific oxide composition of the suspension and the polyurethane foam used.

The most promising way is the introduction into the ceramic suspension of adhesives that can form a film on the surface of organic foam, which burns out without residue along with the matrix material. For these purposes, substances such as dextrin, carboxymethyl cellulose, polyvinyl alcohol (PVA) are used. It is noted that in the presence of a PVA slip in the liquid phase, the use of traditional thinners (such as acids and alkalis) is excluded due to the negative effect of the pH of the medium on the rheological characteristics of the aqueous polymer solution (PVA can coagulate and lose the properties of the adhesive additive).

In the manufacture of samples of aluminum oxide with an organic adhesive additive based on PVA, it was found that treatment with a solution of aluminum chloride of dried samples leads to their darkening after subsequent drying; the samples after firing practically have no shrinkage and do not undergo deformation. This is due to the fact that the PVA on the surface of the samples under the influence of the acidic medium of a solution of aluminum chloride turns into a simple polyvinyl alcohol ether, which has high adhesion to various surfaces and a higher temperature of destruction than PVA. This allows you to maximize the squeezing of the excess ceramic slip from the impregnated polyurethane samples, which ensures an increase in porosity of ceramic products after firing up to 93-95% while maintaining high strength in the absence of shrinkage and deformation and preserving the shape of products of complex configuration. The increase in porosity can significantly reduce gas and hydroresistance to a moving stream.

The aim of the invention is to increase porosity to 93-95% while maintaining high strength (up to 1.5-2 MPa), which, in the absence of shrinkage and deformation during firing, ensures the preservation of the shape and size of large-sized products and products of complex shape with a significant reduction in gas and hydraulic resistance ceramics (up to the level of 2-3 mm of water. Art. at a length of 100 mm).

The technical result is achieved by the fact that polyurethane products with a mesh-cellular structure after impregnation with a slip consisting of an inert filler in the form of electrofused corundum or a mixture of electrofused corundum and silicon carbide and dispersed aluminum oxide powder with additives of metal oxides of groups II and IV of the periodic table are subjected squeezing excess slurry to the maximum extent, drying to remove moisture and impart strength, treatment with a solution of aluminosol or aluminum chloride without or with the introduction of elements in active additives at pH 4 ± 0.2 with subsequent additional drying, firing to burn polyurethane and obtain ceramic products with a given mesh-cell structure and properties.

After applying aluminosol to the products, followed by calcining to develop the surface of the carrier and applying the catalytically active element, the resulting catalyst can be used in a wide variety of chemical processes.

The compositions and properties of samples of catalyst supports according to the proposed method are shown in the table.

Claims (1)

A method of manufacturing highly porous ceramic products with a mesh-cellular structure using the method of impregnating a polymer matrix with a slip, consisting of an inert filler - electrofused corundum or a mixture of electrofused corundum and silicon carbide, dispersed aluminum oxide powder with additives of metal oxides of groups II and IY of the Mendeleev table and a PVA solution followed by drying and firing to remove the organic component and obtain ceramics with a given structure and properties, characterized in that for increased I porosity reducing gas and hydraulic resistance and ensure accurate shape and dimensions of large products of complex configuration and the dried product after the impregnation of the slurry was subjected to solution treatment alyumozolya or aluminum chloride, with or without the introduction of chlorides supplements elements at pH 4 ± 0,2.