DD227415A1 - PROCESS FOR THE PREPARATION OF PURE ZEOLITE A - Google Patents

Abstract

The invention relates to a process for the preparation of pure, synthetic zeolites of the type A by hydrothermal treatment of a reaction mixture of gelled or unreacted SiO 2 material obtained in the process of ferrosilicon production and separated from cyclones and an alkali aluminate component, the latter being 0.1-2 Ma. % reactive dissolved alkali metal aluminosilicate. The synthesis mixture has the composition SiO2: Al2O31.32.5Na2O: SiO20.82.5H2O: Na2O2080 and the hydrothermal crystallization takes place at 60-100. The dissolved reactive aluminosilicate species of crystallization to zeolite A. The pure zeolite A can be used as adsorbent, catalyst carrier or in the detergent industry as a hair binder.

Description

Process for the preparation of pure zeolite A

Field of application of the invention

The invention relates to a process for the preparation of pure zeolites 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 Na. Depending on the molar ratios of the components, the structure of the silicate component and the conditions of synthesis, e.g. Crystallization temperature, crystallization time, shear force, arise in the crystallization of zeolites of different lattice types. Finally, the reaction rate is significantly influenced by the mentioned synthesis parameters.

The most well-known method of preparing the zeolites is characterized by preparing dilute solutions of alkali silicates (e.g., water glass) and alkali aluminate with amorphous gels from which the crystalline zeolite is formed by hydrothermal crystallization depending on the conditions of the synthesis. This is separated after completion of the crystallization of the mother liquor

(e.g., by filtration or centrifugation), and dried to a powder containing more or less zeolitic water.

Pure zeolites with a low SiO 2 content, eg type A, usually serves as a raw material for commercially available water glass, while for SiO _? -rich zeolite types find silicate components with a higher degree of condensation of the silica, for example silica sol or precipitated silicas.

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. the temperature of the dilute solutions silicate and aluminate in the mixing and the action of shear forces during the precipitation and during the heating to the crystallization temperature and during the crystallization on the direction and speed of crystallization detected.

Furthermore, the degree of aggregation 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 Uatronlaugenüberschuß or movement of the synthesis mixture during crystallization lead to an acceleration of the formation of MSA species, however, occur in X-ray detectable contamination of stable zeolite phases, so that the intended use of zeolites thus prepared is limited , Also known is the

Inoculation of the synthesis mixture with already crystallized or crystallized zeolite A. The effect of finished zeolite A crystals is unspecific (DE-OS 2605113). Also known is an activation of the siliceous raw material component, zS Mahlaktivierung (DD-PS 150590) or the application of high shear forces for active amorphous silica as a raw material (DE-OS 2807660) or the action of ultrasound. The suitability of the known possible measures depends on the siliceous raw material, its structure and its structure. 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 2744784 teaches a reuse of mother liquor, but the SiOp content must be below 0.09 % before further aluminate is added · The reuse of the mother liquor is made for economic and environmental considerations. The necessary crystallization times are more than 2 hours · If one starts from active silicas in a discontinuous process, then minimum crystallization times over 2 hours are necessary (DE-OS 2722535).

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 is based on the object silicic acid-containing secondary raw materials in direct synthesis with alkaline aluminate

Solution to rö'ntgenographisch pure zeolites implement. The objective can be met according to the invention with a high crystallization rate when the alkaline aluminate component is 0.1-2 Ma. contains -% reactive, dissolved alkali metal silicate and consisting of the annealed or unannealed, in the process of 3 errosiliciumherstellung and deposited from cyclones SiOG-Abprodukt, hereinafter referred SiOp substance, and the reactive, dissolved Alkalialumosilicat containing alkaline Aluminatkomponente existing synthesis mixture of the hydrothermal Are subjected to crystallization.

A reaction of the SiO 2 material with an alkaline aluminate solution without the inventive content of reactive, dissolved alkali metal silicate leads to a zeolite A which contains impurities, for example hydroxo-dodithium. 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 ⁰ C and this leaching product 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 - 2, 5 Me ₂ O : SiO ₂ = 0 ,8th - 2, 5 H ₂ O : ITa ₂ O = 20 - 80

by hydrothermal treatment at 65 - 98 ⁰ C from.

The SiO ₂ -Stoff the subject invention includes carbon-containing and other impurities which may be removed by calcination at temperatures above 500 ⁰ G and can be used as raw material for zeolite synthesis by annealing.

If the process according to the invention takes place without annealing, the synthesized zeolite must be freed from the impurities by subsequent annealing. In particular, the content of alkaline earth oxides in the reaction mixture leads to the formation of frenide 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 can advantageously be introduced from a zeolite mother liquor into the aluminate by using as the aluminate component a solution of hot-filtered, still hot mother liquor and aluminate solution.

Embodiment .

340 g of an annealed at 550 ⁰ C SiOg-substance were added with stirring with a solution of 774 ml Ha-aluminate and 540 ml of a 0.5 wt .-% reactive dissolved Hatriuraalumosilicat the composition Ha ^ ₂ O Al ₂ O., * 2 , 1 SiO 2 containing 2 m ITaOH added. This gave a reaction mixture of the composition 1.7 SiO ₂ -Al ₂ O - 3.9 ITa ₂ O «136 HgO. The reaction mixture was stirred at room temperature for 15 minutes and then hydrolyzed for 50 minutes at 90 ^° C. After filtering off and washing the reaction product was a X-ray zeolite pure A with an adsorption capacity of 22.6 Ma. -% 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 was crystallized. The adsorption capacity after crystallization for 60 min was only 2.7 Ma. -% H ₂ O. A maximum adsorption capacity of 19.8 Ma .- ^ H ₂ O was reached after 180 min.

Claims (3)

invention claim 1. A process for the preparation of pure zeolite A by crystallization of a reaction mixture of the composition at 60 to 100 ⁰ C under hydrothermal conditions, characterized in that a obtained in the process of Ferrosiliciumherstellung and deposited from cyclones SiO ₂ -Abprodukt with a 0.1 to _S 2 Ma .-% reactive, dissolved sodium trichloroaluminate solution containing sodium are mixed together. 2. Method, according to item 1, characterized in that the Hatriumaluminatlösung consists partially of molecular sieve mother liquor. 3 · Process according to the items 1 to 2, characterized in that the S1O ₃ -Abprodukt is annealed at 500 to 600 ⁰ C before the zeolite synthesis.