RU2239614C1 - Method of manufacturing ceramic filter elements - Google Patents

Abstract

FIELD: ceramics.

SUBSTANCE: preparation of membrane-type ceramic filter for selective separation of media comprises formation of intermediate bed by engobing of permeation pores in subsurface layers of coarse-pore substrate using bubbling suspension containing, in solid phase, wt %: high-fired chamotte 25-29, alumina 22-26, kaolin 9-14, sand 4-7, clay 12-18, bentonite 1-2, talk 2-3, and chalk 11-15. Operation is effected in bubbling suspension containing solid-phase natural-origin zeolite-class hydroxides and stepped heat treatment is performed with isothermal agings at moisture-removal temperature to dehydrolyze hydroxides, whereas process is ended at temperature, at which zeolite-like compounds are formed in engobed layer.

EFFECT: improved quality of ceramic filter.

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Description

The invention relates to ceramic materials science, in particular to processes for the manufacture of ceramic filter elements for the selective separation of the components of the filtered media.

In a number of technological processes of wastewater treatment, mining, pigment and gas cleaning industries, it is necessary to use filter ceramic elements of significant overall dimensions, a complex configuration with internal through or dead ends, capable of selective separation of the components of the filtered media. In the manufacture of such products, a set of technological parameters arises that determine the operational characteristics of the resulting product.

Known methods for the manufacture of ceramic filter elements, including the manufacture of a large-porous ceramic substrate and applying a finely porous membrane coating to it by engobing surface open pores or applying finely porous layers using aqueous slip systems containing ceramic materials as a dispersed phase that are identical in composition to the substrate material or complex mixtures of silicate-forming components, drying and firing (FR Patent No. 2575459, class C 04 B 38/00, 1986; SU, AS No. 1661167, class C 04 B 38/00, 1991; UA, patent No. 39564 A, class C 04 B 35/00, 2001).

A disadvantage of the known methods is the dependence of the membrane layer and its collection rate on the presence of “dead zones” in the substrate, the pore size and their distribution in the total porosity of the ceramic porous substrate, which leads to a difference in thickness of the membrane layer and a change in hydraulic resistance in the local areas of the ceramic filter element, leading degradation of product performance.

A search in patent and informational periodical publications made it possible to identify the prototype closest to the claimed object according to the technical problem being solved - a method for manufacturing ceramic filter elements, including the manufacture of a large-porous substrate and the sequential application of layers of a finely ground aqueous ceramic suspension to form a membrane coating, and before forming a membrane coating to large-porous substrate on the side opposite to the side of the application of the ceramic suspension vayut vacuum 0,15-0,7 kg / cm ^2, dried and calcined (SU, AC №1731762 A1, cl. C 04 B 38/00, 1992).

The method allows to produce small-sized objects of the simplest form, provided that the sealed devices are used in accordance with the configuration of the manufactured ceramic filter element.

The disadvantage of this method is the uneven particle size distribution and thickness of the layers deposited on substrates with large overall dimensions of the filtration surfaces, due to the sedimentation effects of particles with different specific weights in aqueous suspensions. In addition, in multilayer materials during firing, residual internal stresses arise due to different shrink coefficients, which adversely affect the heat resistance when using ceramic filter elements under unsteady thermal loads.

The objective of the invention is to develop a method of manufacturing a ceramic filter element that ensures the achievement of the purpose of the invention is to improve the quality of the membrane type ceramic filter.

This goal is achieved in contrast to the known method in that they form an intermediate layer by engobing permeable pores in the surface layers of a large-pore substrate using a sparging suspension containing components in the solid phase, wt.%:

High-worshiped fireclay 25-29

Alumina 22-26

Kaolin 9-14

Sand 4-7

Clay 12-18

Bentonite 1-2

Talcum powder 2-3

Chalk 11-15

the subsequent operation is carried out in a bubbling suspension containing in the solid phase hydroxides of natural origin of the cytolite class and stepwise heat treatment is carried out with isothermal extracts at temperatures of moisture removal, dehydrolysis of hydroxides, and the process is terminated at the temperature of formation of cytolite-like compounds in the engobed layer and cooled.

The essence of the claimed technical solution consists in a complex of operations and the sequence of their implementation, which, together with the selected chemical components, allow you to organize the specified structure of the selective membrane layer with the diameter of the channels, which are the main controlling factor to achieve the purpose of the invention

The combination of components of the engobing layer allows one to obtain a material with a cytolite-like structure, with a uniform volume distribution of small pores, with a narrow confidence interval of their sizes, and the introduction of bentonite and talc provides the synthesis of cordierite component, which increases the resistance of ceramic filter elements to unsteady heat loads.

The ratio in the engobe mixture of the components is due to the boundary conditions: the minimum content of the components does not increase the strength of the porous ceramic frame, the maximum content of the components form an excessive amount of glass phase, which reduces the stability of the ceramic porous element to non-standard thermal loads.

The introduction of a coarse porous substrate of engobe material into the porous structure of the substrate under the conditions of a bubbling suspension allows one to obtain uniformly distributed bulk porosity with a narrow-fraction pore size smaller than the pore size of the large-porous substrate and eliminate possible defects in the porous structure of the substrate.

The introduction into the open surface pores of naturally occurring hydroxides of a ziolitic class from a bubbling suspension is aimed at, as in the previous operation, and, in addition, allows to obtain a membrane layer with minimal hydraulic resistance, with a pore size for the selective retention of components of a given fraction from the filtered medium.

Isothermal holdings during heat treatment are designed to implement mild conditions that do not lead to the formation of bubbles, channels or microcracks during the removal of physically sorbed and crystallographic water and the most complete passage of physicochemical processes in the engobed layer at the temperature of formation of cytolite-like compounds.

An example implementation of the method.

1. The proposed method was used for the manufacture of hollow, ceramic sector-type elements with an outlet pipe and a total filter surface of 5000 cm ² .

2. For the implementation of the process used:

2.1. Porous ceramic elements, processed in accordance with the requirements of the drawing for sector-type products.

2.2. High-baked fireclay.

2.3. Kaolin Prosyanovsky.

2.4. Alumina PS, α-Al ₂ O ₃ 96%.

2.5. Sand Avdeevsky.

2.6. Clay VGO-1.

2.7. Bentonite Bulgarian.

2.8 Talc of Anot.

2.9. Chalk Raigorodsky.

2.10. Ziolite with a natrolite structure.

2.11. Water is tap.

3. The processes of applying filter materials were preceded by the operation of the preparation of slip suspensions.

For engobing used a mixture of components, wt.%:

Highly burnt fireclay 27

Kaolin 14.5

Alumina 24

Sand 5.5

Clay 15

Bentonite 1.5

Talc 2.5

Chalk 13

The components were mixed dry in a Z-shaped mixer, and subsequent homogenization was carried out by co-grinding the components in a vibrating mill to a specific surface of 800–900 cm ² / g. A slip system was obtained by mixing with water to obtain a suspension with a specific gravity of 1.4 g / cm ³ . An identical method was used to obtain a slip suspension containing zeolite class hydroxide - natrolite with a specific gravity of 1.65 g / cm ³ .

4. In a 200-meter capacity container containing a suspension with engobe material, air was supplied from the air distribution system from below and a porous sector element, a substrate, was immersed, the internal volume of which was connected to the vacuum system through the outlet pipe. The process was carried out for 2-3 s. With a vacuum of 90 Pa. Then the workpiece was removed and left for 5-7 s. under vacuum to remove excess moisture and seal the engobing layer.

5. Then, the preform was transferred to a container containing a bubbling suspension with natrolite, kept for 10-15 s at a vacuum of ≈20 Pa. After removing the preform, heat treatment was carried out in air.

6. The first isothermal exposure was carried out at a temperature of 80-90 ° C for 5 hours, the second exposure was carried out at 250-300 ° C for 2 hours, then the temperature was brought to 900-1000 ° C and the exposure was carried out for 3 hours.

The end of the heat treatment process was carried out at a temperature of 1300 ± 50 ° C for 3 hours and was cooled together with the furnace.

7. According to the proposed method was made a pilot batch of products in the amount of 12 pieces. The material and the filter elements themselves were subjected to control by standard methods in accordance with GOST.

The chemical composition of the engobe layer material is made by chemical, spectrographic, and atomic absorption methods. The analysis of the phase composition was performed by the x-ray method. Based on the analysis, it was found that the engobing material is a solid solution of anorite CaAl ₂ Si ₂ O ₃ and a mixture of analogues of (Na, Zi) leucite KAlSi ₃ O ₈ , in which half of the Na ions are replaced by K, Zi, part of the Ca ions are replaced by Mg and Ba , Fe and Cr ions replace Al, and Ti replace Si. The presence of isomorphic impurities leads to a distortion of the material’s crystalline lattice, which leads to the presence of a large number of various kinds of dislocations that increase the ion-exchange activity of typical molecular sieve zeolites.

Thus, the ceramic filter element plays the role of:

- mechanical filter;

- adsorption absorber;

- molecular sieve;

- ion exchange material.

Characteristics of ceramic filter elements are presented in the table.

These tables show that the proposed method allows to obtain the structure of products with a minimum acceptable range of properties that guarantee the stability of the quality of the products obtained, to expand the functionality for operational characteristics. The increased permeability and strength of the porous structure can increase the working pressure of the filtration and regeneration, and therefore the performance of the filtering systems as a whole, the inventive method is carried out on standard processing equipment with the possibility of organizing, at the stage of applying layers in sparging ceramic suspensions, production lines using control and regulatory devices manufactured by domestic industry.

Claims (1)

A method of manufacturing ceramic filter elements, including the manufacture of a large-porous substrate, the sequential deposition of layers of a finely ground ceramic suspension using a vacuum applied to the large-porous substrate from the side opposite to the ceramic suspension, drying and calcining, characterized in that they form an intermediate layer by engobing the permeable pores in the surface layers of a large-porous substrate using a bubbling suspension containing in solid AZE components, wt.%: Highly burnt fireclay 25-29 Alumina 22-26 Kaolin 9-14 Sand 4-7 Clay 12-18 Bentonite 1-2 Talcum powder 2-3 Chalk 11-15 prepare a suspension containing zeolite class naturally occurring hydroxides in the solid phase, apply it to the substrate, and then carry out stepwise heat treatment with isothermal extracts at temperatures of moisture removal, dehydrolysis of hydroxides, and the process is terminated at the temperature of formation of zeolite-like compounds in the engobed layer and cool.