DD227420A1 - METHOD FOR PRODUCING A PURE ZEOLITE OF TYPE A - Google Patents

Abstract

The invention relates to a process for the preparation of a pure, synthetic type A zeolite by hydrothermal treatment of a reaction mixture of acid-washed, washed phosphorus furnace slag and an alkali aluminate component, the latter containing 0.1-2% by weight of reactive dissolved alkali metal silicate. The synthesis mixture has the composition SiO2: Al2O31.3 to 2.5Na2O: SiO20.8 to 2.5H2O: Na2O20 to 80, and the hydrothermal crystallization takes place at 60 to 100C. The dissolved reactive aluminosilicate species accelerate crystallization and direct crystallization to zeolite A. The pure zeolite A is useful as an adsorbent, catalyst carrier, or as a hair binder in the detergent industry.

Description

VEB CHEMIEKOMBINAa! BITTEEFELD

2457

Process for the preparation of a pure zeolite of type A.

Field of application of the invention;

The invention relates to a process for the preparation of a pure zeolite of type A. The zeolites of type A are used as catalyst supports, selective adsorbents and as hardness binders in the detergent industry.

Characteristic of the known technical solutions

The general principle for the preparation of synthetic zeolites has long been known. It consists in the hydrothermal synthesis of the four-component system MpO-AIpO., -SiOp-HpO, where M is a monovalent cation, preferably ITa. Depending on the molar ratios of the components, the structure of the silicate component and the synthesis conditions, such as

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ζ. Β. Crystallization temperature, crystallization time, shear force, crystallization produces zeolites of different lattice types. Finally, the reaction rate is significantly influenced by the mentioned synthesis parameters. The most well-known method for the preparation of the zeolites is characterized in that amorphous gels are produced by mixing dilute solutions of alkali metal silicates (eg water glass) and alkali aluminate, from which the crystalline zeolite is formed by hydrothermal crystallization, depending on the conditions of synthesis. This is separated from the mother liquor after complete crystallization (eg, by filtration or centrifugation), washed and dried to a powder containing more or less zeolitic water. Pur zeolites with low SiO ^ content, z. B. type A, is usually commercially available water glass as raw material, while for SiO ^ -rich zeolite types silicate components with higher degree of condensation of silica, eg. As silica sol or precipitated silicas are used. Deviations from the known synthesis conditions (chemical composition of the synthesis mixture, parameters of the crystallization) can lead to the crystallization of other types of lattice. Thus zeolite A, like zeolite X, is a metastable phase and only the observance of defined reaction conditions guarantees the purity of the crystals. Impurities in stable phases are, for example, hydroxosodalite (in zeolite A) and zeolite P (in zeolite X).

In addition, an influence of the precipitation temperature, i. H. the temperature of the dilute solutions silicate and aluminate in the mixing as well as the action of shear forces during the precipitation and during the heating on the crystallization as well as

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during the crystallization on the direction and speed of crystallization detected. Furthermore, the degree of aeration of the silica in the silicate component is important. The use of highly condensed silicas as raw material for the zeolite synthesis is also possible, but in this case relatively long crystallization times are required. Although proposed measures, such as hot precipitation, high liatronlaugenüberschuß or movement of the synthesis mixture during crystallization lead to an acceleration of the formation of MSA species, however, occur in X-ray detectable impurities, stable zeolite phases, so that the purpose of the zeolites so prepared is limited. Also known is the inoculation of the synthesis mixture with already crystallized or crystallized zeolite A. The effect of finished zeolite Α crystals is unspecific (DB-OS 2 605 113). Also known is an activation of the siliceous raw material component, ζ. Β. Mahl activation (DD-PS 150 590) or the application of strong shear forces for active amorphous silica as a raw material (DE-OS 2,807,660) or the action of ultrasound. The suitability of the known possible measures depends on the silicatic raw material, its structure and its accompanying impurities. Lastly, the reuse of zeolitic mother liquors for synthesis is also known, whereby a part of the necessary caustic soda solution is made available. The principle is applicable to continuous processes with the raw materials water glass and aluminate. Thus, DE-AS 2 744 784 teaches a reuse of mother liquor, but the SiO 2 content must be below 0.09 % before further aluminate is added.

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The reuse of the mother liquor is based on environmental and economic considerations. The necessary crystallization times are more than 2 hours. Assuming active silicas in a batch process, so are Hindestkristallisationszeiten over 2 hours necessary (DE-OS 2,722,535).

The purity of the resulting zeolite is determined by the impurities and the degree of condensation of the silica component.

Object of the invention

The aim of the invention is the production of X-ray-pure zeolites of type A with minimal crystallization time.

Explanation of the essence of the invention

The invention has the object of reacting siliceous secondary raw materials in direct synthesis with alkaline aluminate solution to X-ray pure zeolites.

It has been found that pure zeolites of type A are obtained at a high rate of crystallization when the alkaline aluminate component contains 0.1-2% by weight of reactive, dissolved alkali metal silicate, and those obtained from the acid-washed and washed phosphorus-containing slag and the alkaline aluminate reactive component containing reactive alkali metal silicate existing synthesis mixture of hydrothermal ^ crystallization are subjected.

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A reaction of the acid-washed and washed phosphorus furnace slag with alkaline aluminate solution without the inventive content of reactive, dissolved Alkalialumososilat leads to a zeolite A, the impurities, eg. B. hydroxosodalite contains. In addition, much longer crystallization times are required.

The dissolved, reactive alkali metal aluminosilicate in the aluminate component is characterized in that it can be detected by precipitation at temperatures below 10 C and this precipitate contains at least 30 % crystalline fractions. The aluminosilicate phases thus introduced act both as crystallization accelerators in the zeolite synthesis and as true crystallization directors, so that after-compared to the known zeolite A synthesis - shortened reaction times, X-ray zeolite A is produced. In this case, zeolite A crystallizes from a synthesis mixture of the composition

SiO ₂ : Al ₂ O ₃ = '1.3 to 2.5 Me ₂ O: SiO ₂ = 0.8 to 2.5 H _o 0: Ha ₀ O = 20 to 80

L ₂ ,

by hydrothermal treatment at 65 to 98 C from. The acid-soaked phosphor slag to be used is contaminated as follows:

TiO ₂ : 1.1%

PeO ₃ : 0.2 %,

CaO: 1.7 %

MgO: 0.1 %

P ₂ O ₅ : 0.9 %

Cl ", K ₂ O, C ©, Cr in traces.

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In particular, the content of Brdalkalioxiden in the reaction mixture leads to the formation of foreign phases in the hydrothermal crystallization. By the method according to the invention, however, there is a direction to pure zeolite A at crystallization times of one hour at 90 C.

The reactive, dissolved alkali metal aluminosilicate may advantageously be introduced from a zeolite mother liquor into the aluminate by using as the aluminate component a mixture of filtered, still hot mother liquor and aluminate solution.

Ausführun, g; sbeisT3iel

336 g of phosphorus furnace slag säuregelaugte washed with stirring with a solution of 774 ml of Na-aluminate and 540 ml of a 0.5 mass -% reactive offset dissolved Ifatriumalumosilicat the composition Ha ₂ O · AIPO ^ ^# 2.1 siop containing 2 m UaOH. In this case, a reaction mixture of the composition produced 1.7 SiO ₂ * Al ₂ O ₃ · 3.9 ITa ₂ O · 136 H ₂ O. The reaction mixture was stirred v / ith 15 min at room temperature. And then 50 min. Bei.90 ⁰ C hydrothermally crystallized. After filtering off and washing the reaction product, a zeolite X which is pure by X-ray analysis is obtained with an adsorption capacity of 22.3 Ma-SS H ₂ O at 0.6 Torr water vapor pressure. In a parallel experiment, the same synthesis mixture, but without content of reactive, dissolved sodium aluminosilicate, crystallized. The adsorption capacity after 50 min. Crystallization is only 4.4% by mass H ₂ O.

Claims (2)

- 7 - 2457 invention claim A process for the preparation of a pure zeolite of type A by crystallisation of a reaction mixture of the composition SiO ₀ : Al ₀ O- = 1.3 to 2.5 C. Na ₀ O: SiO ₀ = 0.8 to 2.5 CL H ₂ O: Na ₂ O = 20 to 80, at 60 to 100 ⁰ G under hydrothermal conditions, characterized in that a mineralsauer leached, washed Kiosphorofenschlacke used as the silicate and a 0.1 to 2% by mass of reactive, dissolved sodium aluminosilicate containing sodium aluminate as aluminate component. 2. The method according to item 1, characterized in that the aluminate component consists partly of molecular sieve mother liquor.