DD150738A5 - PROCESS FOR THE PREPARATION OF SILICOALUMINATE FROM THE ZEOLITE A-TYPE - Google Patents

Abstract

The invention relates to a process for the semi-continuous production of zeolite A-type silicoaluminate of consistent and uniform quality, wherein mixing a sodium aluminate solution and a sodium silicate solution continuously with vigorous stirring in a container in which the average residence time between 30 seconds and 20 minutes and the temperature is between 70 and 105 degrees C, whereby a gel is formed, the ripening of which then takes place intermittently for 4 to 7 hours at a temperature of 80 to 95 degrees C. The process is characterized in that the precipitated particles are kept in suspension during the tire without being impacted by shearing forces, or with shearing forces which are just needed to keep the particles in suspension.

Description

Berlin, August 22, 1980 21 ~ ^ ~ AP C 01 B / 220 621

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A process for producing a zeolite A type silicoaluminate

Field of application of the invention

The invention relates to the semi-batch large-scale production of crystallized sodium silicoaluminate zeolite A-type, which has a high exchange capacity for calsium ions and consists of particles having an average diameter between 2 and 4, wherein 95 % of the particles in a range between 1 and 8, to lie.

The main applications of zeolites are their known properties as cation exchangers, which are described, for example, in "Comprehensive Treatise on Inorganic and Theoretical Editors 1925, pp. 575-579, and in particular their ability to bind calcium ions in complexes (sequestration)."

In order for the zeolites to be used as substitutes for phosphates in detergents and dishwashing detergents, they must have the highest possible exchange capacity and still remain in suspension in the aqueous solutions in order to avoid deposits on the laundry after washing and rinsing.

For this reason, it is essential that the particle size distribution is as narrow as possible and is preferably around an average diameter of 2 to 3 μm ·

Characteristic of the most well-known technical solutions The synthesis conditions for zeolite A of the formula

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Na ₂ O, Al ₂ O ₃ . 2SiO ₂ .χH ₂ O, where χ varies from 1 to 8, but generally has a value of 4 or 5, has been known for many years, especially from "Ion-Exchange" by Friedrich Helfferich, 1962, Mc Graw-Hill Book Company, Chapter 2, pp. 10-16, The conditions affecting the particle size distribution of the zeolite formed were also studied, for example, in "Kinetic studies on the formation of zeolites A" by VV, Meise and F. "Schwochow in "Molecular Sieves" 121 (1973), p. 169-178 *

An extensive patent literature describes the production conditions, the quality of the starting materials, the reaction temperature, the manner of addition of reactants, etc. can be varied _e.

DE patent application P 25 17 218 describes, in particular, the utilization of shear forces in the course of the crystallization stage and the subsequent possible maturation stage to give zeolites A with an average particle size of up to 6.5 μm, but with an unspecified complexing capacity to obtain.

Applicant's FR patent application 78/35344 describes a process for the semicontinuous production of zeolite A. This process comprises instantaneously dissolving solutions of sodium aluminate and sodium silicate in a container in which the average residence time is between 30 seconds and 20 minutes continuously mixed and this forms a gel whose crystallization is then discontinuous. This process makes it possible to produce a zeolite A whose complexing capacity

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-Z-

is between 110 and 120 mg Ca ⁺⁺ / g of the anhydrous product and whose particles have a size in the range of 2.9 to 6 μm, the curve of particle size distribution showing that 90 % of the particles have a diameter below 11 μm .

Object of the invention

The object of the invention is to provide an improved process for the preparation of a zeolite A-type silicoaluminate, with which a product having a smaller particle diameter can be obtained,

Explanation of the essence of the invention

The invention has for its object, after continuous and instantaneous formation of two solutions, namely the sodium aluminate solution and the sodium silicate solution to carry out the crystallization discontinuously with sufficient stirring or agitation.

The process for semicontinuous production of a zeolite A-type silicoaluminate of consistent and uniform quality, in which a sodium aluminate solution and a sodium silicate solution are mixed continuously with vigorous stirring in a vessel in which the average residence time is 30 seconds to 20 minutes and the temperature is between 70 and 105 ⁰ C, wherein a gel is formed, the maturation of which is then carried out for 4 to 7 hours discontinuously at a temperature of 80 to 95 ⁰ C, is carried out according to the invention in such a way that the precipitated particles in suspension during maturation stops without

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that shearing forces are applied to them or that the shearing forces, which are just necessary to keep the particles in suspension, are brought to bear. In this case, the gel formed during the first stage of zeolite A is kept in suspension.

When using the process according to the invention, it is possible to produce a zeolite A with a complexing capacity of more than 120 mg Ca ⁺⁺ / 9 of the anhydrous product and a particularly fine and narrow particle size distribution, the mean diameter being between 2 and 4 μm. This product thus proves to be particularly advantageous as a metal complexing agent or sequestering agent of Ca ⁺ ions in wash liquors.

The mixing of the sodium aluminate and sodium silicate solutions is carried out at a temperature between 70 and 105 ° C with the greatest possible stirring, so that a completely homogeneous gel is formed. This gel remains in the reactor for an average time sufficient to ensure complete gelation, for example, for a period of 30 seconds to 20 minutes. "

The supply of the two reaction solutions, whose inflow quantities are regulated, takes place in the zone of strong suction, which is generated by a turbine whose rotational speed is above 2500 rpm. The mixing and shearing action of this turbine is further enhanced when it is placed in a vessel that is stationary or rotating simultaneously with the turbine.

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The gel of sodium silicoaluminate continuously formed in this way is converted by the upper course into a second reactor, which is provided with a system which makes it possible to keep the product obtained in suspension and to maintain a constant temperature between 80 and 95 ⁰ C upright, so that the zeolite A can crystallize "This crystallization is thus discontinuous. The residence time in the crystallization vessel is between 1 and 15 hours, preferably between 4 and 7 hours,

Since the zeolite is kept in suspension by a stirrer, the stirrer rotates at a speed such that the tangential velocity is between 0.2 and 5 m / sec. The process may also be initiated and sustained by the use of ultrasound, by convection currents caused by local heating, or by the use of marine propellers or low shear screws, jiggs, or concrete mixer drums. "

The discontinuous crystallization carried out under these conditions makes it possible to adjust the grain size of the end product as desired to obtain a particularly high sequestering ability. This result is achieved by acting in a coordinated manner on the parameters of temperature, residence time, stirring speed and concentration of the reactants.

The continuous preparation of the G _e ls gives the desired properties when the sodium aluminate on the one hand by a weight ratio of Al ₉ O-VNa ₀ O between 0.5 and 1.5 at a concentration of Na ₂ O in the V / ater be-

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30 and 200 g / l, these solutions being obtained by digestion of alumina hydrate by sodium hydroxide solution or in the production of alumina by the Bayer process, and on the other hand, the sodium silicate solutions by a weight ratio of SiO ₂ / Na ₂ O between 1 5 and 3.5 at a concentration of Na ₂ O in water between 20 and 120 g / l. These solutions can be prepared from silica and sodium hydroxide containing materials which are different depending on the economic conditions, namely sodium silicate in the form technical powder or technical sodium silicate or silica contained in sand and sodium hydroxide or sodium hydroxide and silica gel recovered from the hydrosilicofluoric acid residue of a plant for the production of aluminum fluoride or hydrofluoric acid, or from the treatment described in the preamble gaseous gases released from natural phosphates, or sodium silicate from an apparatus for deoxidizing oxides prior to treatment in plants for the production of alumina or silica, as a residue in the production of aluminum salts by digestion of natural silicoaluminates, such as kaolin or clays, by wet method or silicon dioxide thermally obtained, for example, in the production of magnesium, silicon metal or silicon alloys "

The mixture resulting from the mixing of these sodium aluminate and sodium silicate solutions must have a weight ratio of Al ₂ O ₃ / SiO _{2 of} between 0.5 and 1.2, and the Na ₂ O content must be adjusted so that the sodium hypochlorite

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solution of the liquor in which the crystallization takes place after precipitation does not exceed 135 g / l NaOH in order to avoid the crystallization of the inactive feldspar type silicoaluminates, but must not be below 26 g NaOH / l, hence the rate of crystallization of the zeolite A suitable for large-scale production «

After a ripening time of the crystals between 1 hour and 15 hours, preferably between 4 and 7 hours, a suspension of zeolite A is obtained in the liquor described above. This suspension is then subjected to a suitable separation of solid and liquid (for example by filtration, decantation or centrifuging).

The solid separated in this manner is washed with water and then dried. The washings are recovered and mixed into the liquor separated from the solid. "All of these residual waters are recycled to produce the sodium aluminate solutions required for the preparation.

The drying can cause agglomeration of the crystals. This agglomeration prevents zeolite A from being well kept in suspension in the caustic solution. It is therefore necessary to make a selection or to break up the agglomerates of the particles or to combine these two measures in any suitable manner.

The zeolite A produced by the process described above has the following properties:

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a) narrow grain size distribution, with 95 % of the particles ranging from 1 to 8 μm;

b) very fine and very narrow grain size between 2 and 4 μm, which is adjustable depending on the intended use;

c) exchange capacity for calcium ions above 120 mg Ca / g of anhydrous product;

d) pH of zeolite A in 1% aqueous suspension between 10 and 11 »

This zeolite A is particularly suitable for use in alkalis for softening calcareous water,

O u rd e rt a t e _s t e _s t o t e _s t o t e rs

The invention will be further elucidated by the following examples;

A zeolite A from Natriumsilicoaluminattyp is prepared as follows: A sodium silicate solution A is continuously mixed with a sodium aluminate solution B in a reactor aer enables instantaneous mixing of the two solutions. The resulting gel is subjected to the discontinuous ripening in a ripener.

The sodium silicate solution A is obtained by dissolving crystalline

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linem Sodium silicate of commercial grade obtained in deionized water at 50 ⁰ C. «It has the following characteristics:

Si0 ₂ concentration 138 g / l

Na ^ O concentration 41 g / l

Temperature at the moment of use: 50 ⁰ C

The sodium aluminate solution B is prepared by dissolving alumina hydrate in concentrated sodium hydroxide at 104 ^° C. in an amount such that a solution having the following properties is obtained:

pO concentration 56 g / l

NapO concentration 80 g / l

Temperature at the moment of use: 92 ⁰ C

Solutions A and B are simultaneously introduced into a reactor equipped with a turbine rotating at 8000 rpm. The feed amounts of solutions A and B are adjusted so that the residence time in the reactor is 2 minutes and the AlpO-z / SiOp weight ratio is 1.4.

The gel obtained in this way is transferred by upper run into a maturation container. The sodium silicoaluminate is kept by means of a paddle stirrer rotating at 20 rpm, at 80 ⁰ C in suspension.

After a ripening time of 15 hours aer Z _e olith off

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filtered and then washed and dried until a product is obtained containing 20 to 22 % water of hydration.

The zeolite obtained in this way has the following properties:

ö) An X-ray diffraction diagram showing that the product consists to more than 87 % of crystallized zeolite A.

b) A grain size characterized by the following values: average particle diameter 3.9 μm; 97 % of the particles are smaller than 8, um; 1 % of the particles is less than 1, um. The particle size is determined by the X-ray sedimentometer.

c) A sequestering capacity of 121 expressed in mg Ca / g of the anhydrous product. This value is determined as follows:

A known amount of the zeolite is reacted with a solution containing 200 mg calcium / liter (hardness 50 °, pH 10) with vigorous stirring for 15 minutes at 22 ⁰ C. Part of the calcium ions is bound by the zeolite. After the zeolite has been filtered off and rinsed, the calcium remaining in the solution is quantitatively determined in this filtrate by potentiometric titration with the aid of a suitable solution of ethylenediaminetetraacetate. «

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Example 2

In the manner described in Example 1, the following solutions are prepared:

Solution A:

Si0 ₂ concentration 119 g / 1

Na ₂ O concentration 36 g / l

Temperature at the time of use: 90 ° C ·

Solution B:

Al ₂ O_ concentration 97 g / 1

Na ₂ O concentration 99 g / 1

Temperature at the time of use: 9o ⁰ C,

Solutions A and B are simultaneously introduced into the high suction zone of a turbine disposed in a reactor. This turbine rotates at 300 rpm and is placed in a vessel that revolves around itself. This vessel consists of two plates whose concavity faces the turbine. These two plates form a space into which the two reaction solutions are introduced.

The feed rates of solutions A and B are such that the residence time in the reactor is 12 minutes and the AlpO ^ / SiOp ratio is 1.35.

The gel formed in this way is separated by upper reaches

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transferred a maturation container. The sodium silicoaluminate is kept by means of a paddle stirrer rotating at 20 rpm, at 90 ⁰ C in suspension.

After a maturation time of 5 hours, the zeolite is separated in the manner described in Example 1. This zeolite has the following properties:

a) The product consists of more than 93 % of crystallized zeolite A.

average particle diameter 3.0 μm;

99 % of the particles are smaller than 8, um; all particles are larger than 1, um,

c) sequestering capacity determined in the manner described in Example 1: 129 mg Ca / g of the non-aerated product.

Example 3

Sodium silicoaluminate is prepared in the manner described in Example 2 using the solutions described therein. Only the stirring speed in the ripening vessel is different; it is held at 140 rpm for 5 hours. After this time, the zeolite is separated in the manner described in Example 1. This zeolite has the following properties.

a) The product consists of more than 91 % of crystallized zeolite A.

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b) Grain:

average particle diameter 5.2

no particles are smaller than 1 / um

93 % of the particles are smaller than 8, um;

c) sequestering capacity, determined in the manner described in Example 1: 106 mg Ca / g of the anhydrous product.

This example illustrates that over-stirring results in poor results.

Example 4

The zeolite is prepared in the manner described in Example 2 using the solutions described therein. The only difference is the type of movement in the ripening container. The movement is achieved by exposing the liquid to the action of ultrasound. After 5 hours, the zeolite is separated in the manner described in Example 1. This zeolite has the following properties:

a) The product consists of more than 92 % of crystallized zeolite A.

b) Grain:

average particle diameter 2.4 , um ; all particles are smaller than 8 / um; 4 % of the particles are smaller than 1 .um.

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c) sequestering capacity, determined in the manner described in Example 1: 130 mg Ca / g of anhydrous product »

Example 5

The zeolite is prepared in the manner described in Example 2 using the solutions described therein. The only difference is the type of movement in the ripening container. "The movement is achieved by convection by heating the liquid at a narrow location in the lower part of the container. The resulting excess heat is removed by a arranged in the upper part of the container cooling coil, which is traversed by cold water. The average temperature in the suspension is maintained at 90 C by controlling the cooling water. After a maturation time of 5 hours, the zeolite is separated in the manner described in Example 1. This zeolite has the following properties:

a) The product consists of more than 94 % of crystallized zeolite A «

b) Grain:

average particle diameter 3.2, um;

98 % of the particles are smaller than 8, um; all particles are larger than 1, um,

c) sequestering capacity determined in the manner described in Example 1: 125 mg Ca / g of anhydrous product

Claims (6)

22, 8. 80 AP C 01 B / 220 621 GZ 57 370 18 I _ 5 _ E r eq 1, A process for the semi-continuous production of zeolite A-type silica sol of uniform and uniform quality, wherein a sodium aluminate solution and a sodium silicate solution are mixed continuously with vigorous stirring in a container in which the average boiling time is 30 seconds to 20 minutes and the temperature between 70 and 105 ⁰ C, wherein a gel is formed, the maturation of which is then carried out for 4 to 7 hours discontinuously at a temperature of 80 to 95 ⁰ C, characterized in that the precipitated particles are kept in suspension during the ripening, without that shearing forces are applied to them or that the shearing forces, which are just necessary to keep the particles in suspension, are brought to bear. 2 «method according to item 1, characterized in that the particles are kept in suspension by the action of ultrasound, Method according to item 1, characterized in that the particles are kept in suspension by the use of propulsion devices such as marine propellers or low shear screws. 4. Method according to item 1, characterized in that the particles are kept in suspension by using blades (jiggs). 22, 8. 80 APC 01 B / 220 621 GZ 57 370 18 - 16 - 5 »Method according to item 1, characterized in that the particles are kept in suspension by concrete mixer-type drums» 6. The method according to item 1, characterized in that the particles by local heating with training
of a convection current in suspension «