RU2218303C2 - Method to produce synthetic zeolite of a-type - Google Patents

Abstract

FIELD: chemical industry; production of synthetic zeolites of A-type. SUBSTANCE: the invention presents a method of production of synthetic zeolites of A-type, that may be used as carrying agents for catalytic agents and as adsorbents for drying and purifying of gases and for extraction of heavy metals and radionuclides from the liquid mediums. The method includes mixing of china-clay with silicon dioxide and the additive, wetting of the mixture till production of the uniform mass, molding of granules, heat treatment, hydrothermal crystallization, washing and drying. Silicon dioxide is fed in amount 1.0-5.0 mass %, in the capacity of additive at mixing they use wood meal, coke or coking active charcoal in amount of 8.1-12 mass %. Produced mixture is wetted with a solution of sodium hydroxide till its contents in the mixture is equal to 0.5-2.5 mass %. EFFECT: the method allows to improve performances of zeolite. 1 tbl

Description

 The invention relates to the production of synthetic molded zeolites, in particular type A zeolite. The obtained zeolite can be used as a catalyst carrier in the refining and petrochemical industries and as an adsorbent for drying and purifying gases and extracting heavy metal ions and radionuclides from liquid media.

 A known method of producing molded type A zeolites from a natural clay mineral - kaolin [D. Breck, Zeolite molecular sieves, M .: Mir, 1970, p. 328]. Kaolin is mixed with water until a plastic mass is formed. The mass is molded, dried and calcined until kaolin is converted to metakaolin. The ratio of silicon and aluminum oxides equal to 2 corresponds to the ratio of oxides in type A zeolite. Metakaolin granules are poured with an alkali solution, kept at room temperature and subjected to hydrothermal crystallization. The resulting product is washed from alkali and dried. The result is a zeolite-containing product.

 Pure zeolites (without kaolin admixture) cannot be obtained by this method.

The closest in technical essence to the proposed method is a method for producing synthetic zeolite type A [RF Patent 2146222, class. C 01 B 39/20, 02/11/1999]. According to the method, a natural clay mineral having a ratio of SiO ₂ : Al ₂ O ₃ = 2: 1 is mixed with carbon black, taken in an amount of 2-8 wt.%, Treated with a 3% sodium chloride solution until a plastic mass is obtained. The mass is formed into granules, dried and calcined at a temperature of 720 ^o C. After crystallization, the granules are treated with an orthophosphoric acid solution with a pH of 4-5, then the granules are dried at 180-200 ^o C.

 A significant disadvantage of this method is the low mechanical strength of the granules after calcination, which is due to the amorphization of kaolin and the burning of carbon black. As a result of the adsorption decrease in strength upon wetting the granules with a crystallization solution, a significant part of them crack and break, which reduces the yield of commercial zeolite. In addition, the use of sodium chloride and phosphoric acid in the process leads to additional pollution of the washings with chlorine ions and phosphates.

 The objective of the present invention is to increase the sorption and strength characteristics of the zeolite while increasing its yield and simplifying the technology.

 This result is achieved by a method of producing synthetic type A zeolite, including mixing the starting kaolin with an additive, moistening the mixture, forming granules, thermal activation, hydrothermal crystallization, washing and drying, according to which the starting kaolin is additionally mixed with silica taken in an amount of 1.0-5 , 0 wt.%, And an additive in the amount of 8.1-15 wt.%, Which is used as wood flour, coke or coke activated carbon, the resulting mixture is moistened with sodium hydroxide solution until it is contained in the mixture 0.5-2.5 wt.%.

 Wood flour, coke or coke activated carbon is used in powder form with a particle size of less than 100 microns. The selected amounts and dispersion of the additive provide the formation of a developed broad-porous structure of the granules during the heat treatment.

 Sodium hydroxide during the formation and drying of granules interacts with amorphous silicon dioxide to form sodium silicate, which significantly increases the strength of calcined granules and eliminates their destruction during crystallization. Excess silica provides complete alkali binding to silicate.

 As silica, a highly dispersed amorphous silica powder in a chemically active form (white carbon black) is used.

 The proposed method is as follows.

The original kaolin is mixed with amorphous silicon dioxide, taken in an amount of 1.0-5.0 wt.%, And powder of wood flour, coke or coke activated carbon with a particle size of less than 100 microns in an amount of 8.1 - 15 wt.%. An aqueous solution of sodium hydroxide is added to the dry mixture to a moisture content of 25-28%. Stirring is continued until a plastic mass suitable for molding is formed. The content of sodium hydroxide in the mixture is 0.5-2.5 wt. % The plastic mass is formed into granules with a diameter of 1.5-3 mm, the granules are dried at 100-140 ^o C for 4 hours and subjected to heat treatment at 600-700 ^o C for 1-3 hours

During heat treatment, amorphization of kaolin takes place, its transition to a chemically active form and complete burnout of the additive. X-ray amorphous granules are poured with an alkali solution and kept at room temperature for 12-18 hours. At the same time, the components of the granules interact with the solution, then they are heated to a temperature of 90-100 ^o C and held for 24-36 hours. The finished zeolite is washed from excess alkali and dried.

 The method is illustrated by the following examples.

 Example 1

230 g of kaolin (200 g of absolutely dry) are loaded into the mixer, 2 g of white carbon black are added and 16.2 g of wood flour is added, passed through a sieve with a mesh size of 100 μm. The content of white soot in the mixture is 1 wt.%, Wood flour - 8.1 wt.% (Hereinafter, the calculation for absolutely dry kaolin). The mixture is stirred for 15 minutes and 90 ml of sodium hydroxide solution containing 1 g of sodium hydroxide, which is 0.5 wt.%, Is added. The humidity of the mixture is 26%. The mixture is stirred until a plastic mass is formed, the mass is molded into granules with a diameter of 2 mm and dried at a temperature of 120 ^{° C. for} 4 hours, calcined at 620 ^{° C. for} 2 hours. 100 g of amorphous calcined granules are poured into 700 ml of a solution of sodium hydroxide with a concentration of 120 g / l. The mixture is maintained for 12 hours at 20 ^{° C.} , then the temperature is increased to 90 ^{° C.} and maintained at this temperature for 36 hours.

The resulting zeolite is washed from excess alkali, dried at 120 ^{° C. for} 4 hours and weighed. The weight of the granules due to sodium zeolite and associated moisture increased to 127 g.

 The type of crystal lattice and degree of crystallization, dynamic capacity for water vapor, pore volume by mercury porosimetry, and the strength of amorphous granules and zeolite by crushing on a Rukholtz press were determined using the X-ray phase method for the obtained sample.

 Physico-chemical characteristics of the sample are presented in the table.

 Example 2

 230 g of kaolin, 5 g of white carbon black and 24 g of coke powder are loaded into the mixer. The content of white carbon in the mixture is 2.5 wt.%, Coke - 12 wt.%. The dry mixture is stirred for 15 minutes and 95 ml of sodium hydroxide solution containing 3.0 g of sodium hydroxide, which is 1.5% by weight, are added. The moisture content of the mixture is 27%. Further operations are carried out as in example 1.

 Physico-mechanical characteristics of the sample are given in the table.

 Example 3

 230 g of kaolin, 10 g of soot and 30 g of coke activated carbon powder are loaded into the mixer. The content of white carbon in the mixture is 5 wt.%, Coke activated carbon - 15 wt.%. The mixture is stirred for 15 minutes and moistened with 105 ml of sodium hydroxide solution containing 5 g of sodium hydroxide, which is 2.5 wt.%. The humidity of the mixture is 28%. Further operations are carried out as in example 1.

 Physico-chemical characteristics of the sample are given in the table.

 In parallel, a zeolite sample prepared according to the prototype method was tested. In this case, the yield of the finished zeolite was 107 g, which is 15% lower than in the claimed method.

 A comparison of the data in the table shows that the claimed method provides for the preparation of granular type A zeolite with higher dynamic capacity and strength compared with the prototype, which ultimately leads to an increase in the yield of zeolite.

Claims (1)

A method of producing a synthetic type A zeolite, comprising mixing kaolin with an additive, moistening the mixture until a homogeneous mass is obtained, forming granules, heat treatment, hydrothermal crystallization, washing and drying, characterized in that the kaolin is further mixed with silica taken in an amount of 1.0- 5.0 wt.%, Wood flour, coke or coke activated charcoal in the amount of 8.1-15 wt.% Is used as an additive when mixing, the resulting mixture is moistened with sodium hydroxide solution until its content in the mixture is 0.5-2.5 wt.%.

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