LU82383A1 - ZEOLITE CRYSTALLIZATION DURING INDUSTRIAL MANUFACTURING PROCESSES - Google Patents

Description

I '... + * Τ · ·' “''! 1 * ___. i Γ-—; r ..... ’i | The present invention relates to industrial preparation! J * i I, of crystallized sodium silico aluralhate of the zeolite A type, possi i! : having a high exchange capacity vis-à-vis calcium ions, and i iconstitué of particles having an average diameter between 2 and.

5 4 μ, 95% of the particles being in a range between 1 st B) i. , i

The main applications of zeolites are based on their well known properties of cation exchangers described for example in the "Comprehensive treatise on Inorgahic and Theoreti-jlu (cal Chemistry" by JW MELLOR, vol. VI, part. 2, Longman Editors I i! J'1925 pp. 575-579 and in particular for the sequestration of calcium ions.

I i | In order for zeolites to be used as a phosphate substitute in washing and rinsing agents, they must have as high an exchange capacity as possible while remaining in suspension in the aqueous solutions in order to avoid deposits on the laundry after washing and rinsing. It is for this reason that it is essential that the particle size is as tight as possible, preferably around an average diameter of 2 to 3 μ.

2C | | The conditions for the synthesis of zeolite A of formula i · J ^ 20, A ^ O ^ "2SÎ02" xh ^ D, where x varies from 1 to B but generally has the value 4 or 5, have been known for many years , in particular by "Ion-Exchange" of Friedrich HELFFERICH, 1962, Mc GRAW-HILL, [Book Company, chap. 2 pp. 1D-16. The conditions influencing the ^ gra-! ! 25 nullness of the zeolite formed were also studied by exem-i,

j jple in "Kinetic studies on the formation of zeolithe A" by W. MEISE

jet F.E. 5CHW0CH0W in "Molecular Sieves" 121 (1973) pp, 169-178. ^ | Numerous patents describe preparation conditions! .

jtion which vary the quality of the raw materials, the temperature, reaction temperature, the mode of addition of the reagents, etc. j | ; *; German patent application No. 25 17 21B describes in particular the use of shear forces during the study! *! pe of crystallization and the possible stage of ripening which there: ’. . *>; follows in order to obtain zeolites A with an average particle size of 35 which can go up to 6.5 U, but with sequestering power not pre-defined. j i, -! ι · ι * 2 ".

. -!. i | In its French patent application 78/35344, the application -! ! .

: j iresse describes a * process for semi-continuous preparation of zeolite il '"j jA * This consists in carrying out an instantaneous and continuous mixture jjde solutions of sodium aluminate and sodium silicate in a container in which the average residence time is between i *, I, 30 sec and 2D minutes flour form a gel whose crystallization is effected subsequently discontinuously. This process makes it possible to obtain a zeolite A whose the sequestering power is between! __l_ j11D and 120 mg Ca / g of anhydrous product, and the particle size compri-10 is between 2.9 and 6 μ, the particle size curve indicating that 9O% of the j, 1> i grains have a diameter less than 11 u.

·. | * 'i: Continuing his research in this field, ask for it -; ;

j. has developed a process for obtaining a zeolite A

... I> having a sequestering power greater than 12G mg Ca / g of anhydrous I5 product and a particularly fine and tight particle size, the i average diameter being between 2 and A μ. This product therefore proves to be particularly advantageous as sequestering Ca ++ i 11 i ions for detergents.

The process consists, after carrying out a continuous mixture | i 20 pu and instant of the two solutions, sodium aluminate and sodium silicate, to carry out the crystallization step in batch i: with sufficient stirring to maintain in suspension the zeolite A gel formed during the first step.

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The mixing of the solutions of sodium aluminate and 25% sodium licate is carried out at a temperature of between 70 and 105 ° C. with stirring as high as possible in order to obtain a gel. perfectly homogeneous This gel remains in the reactor for an average time sufficient to ensure the complete formation of the gel, that is between 30 seconds and 20 minutes. 'contribution of the two reaction solutions whose flows' I “·· j are regulated takes place in the zone of strong aspiration created by an i * | turbine whose rotation speed must be higher than 2.500'! revolutions / mn. mixing and shearing action of this turbine I ^ J is further increased if it is placed in a fixed saucer!! 1 * 35: or rotating at the same time as it.

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Π'Γ · ·: ι i The sodium silicoaluminate gel thus prepared in con-! "

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i: tinu is transferred by overflow into a second reactor fitted

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i of a system allowing the suspension of the product obtained | naked and kept at a constant temperature between 80 and 95 ° C

i! '5 in order to allow the crystallization of zeolite A. This cris-. tallization is thus carried out batchwise, the residence time in the crystallization tank being between 1 and 15 h and preferably from 4 to 7 h.

I When setting and maintaining the zeoli- j il 0! the are provided by an agitator, which rotates at a speed {} f; i; such that the tangential speeds are between 0.2 and ê! ! 'j * j ‘5 m / s. The process can also be obtained by using I; ! of ultrasound, by convection currents caused by heating - - j | local fage or by the use of jiggs.

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15 d The batch crystallization practiced under these conditions

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i tions allows you to adjust the grain size of the final product at will! ' while obtaining particularly high sequestering powers.

; | This result is obtained by acting in a coordinated manner on the para is! · Following meters = temperature, residence time, stirring speed I 1! 20 i and concentration of reagents.

. i ι! ! J Continuous gel preparation leads to properties | ; desired, on the one hand when the sodium aluminate solutions; ! are characterized by a weight ratio A ^ O ^ between i Na_0 „! i to.

| 0.5 and 1.5 with an aqueous concentration of Na_0 of between j; ! ά \ [25 'i 30 and 200 g / 1, the said solutions being obtainable, either by: j attack of alumina hydrated by a sodium hydroxide solution, or pre-j I i vated in a Bayer cycle of manufacturing d alumina, and on the other hand, when the sodium silicate solutions are characterized by | j! a SiO ^ weight ratio of between 1.5 and 3.5 with a con I '' Na_0; 1; ! 2d3D; aqueous concentration of Na_0 between 20 and 120 g / l, say j! 2 ’,! ! solutions which can be prepared from raw materials i; variable silica and soda according to economic criteria, ie I ’! -4 - | * ... ....... “I i, j. Soda, either soda and silica gel recovered from fluosilicic acid j jsresidu from a workshop for the manufacture of aluminum fluoride or hydrofluoric acid, or treatment of gases released during processing i

Itation of natural phosphates, ie sodium silicate prove-5. ; from a bauxite desilicate workshop before treatment h.

j in factories for the manufacture of alumina, either of residual silica i 'obtained during the manufacture of aluminum salts by attack by wet channeling of natural silicoaluminates such as kaolin or jargiles, or of silica obtained by thermal means, example then! î10 manufacture of magnesium, silicon-metal, or alloys of 'i! . .

•; j silicxum.

*! p The mixture resulting from the addition of these solutions of a-! 1;

; jluminate and Na silicate must have a weight ratio! ! A1? 03 between 0.5 and 1.2 and the Na ^ O content must be SiO

adjusted so that the concentration of soda in the liquor in which, after precipitation, this crystallization is carried out, is: not more than 135 g / l of NaOH, to avoid crystallization of the

Isilicoaluminates of the feldspar type inactive, but not lower than 26 g / l NaOH so that the rate of crystallization i! 2Q of zeolite A is compatible with an industrial production.

| After a time for the crystals to mature, between 1 h and 15 h, and preferably 4 to 7 h, a suspension I *; of zeolite A is obtained in the liquor described above. This suspension j: is then subjected to an appropriate solid / liquid separation (par .: - il · 25 example filtration, decantation or centrifugation).

The solid thus separated is washed with water and then dried. ! ! j j The wash water is collected and mixed with the separated liquor! . I · «j rée du solid. All this waste water is recycled so! ! j "to prepare the sodium aluminate solutions necessary for the manufacture.! 1:. 'j! Drying may cause agglomeration of the crystals.: · i.

; This being detrimental to the good maintenance in suspension of the ".

i j! "zeolite A in the washing solution, it is then necessary to: • · *.

I carry out a selection or deagglomeration of the particles or a combination of these two operations by any suitable means.

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he * j I; Zeolite A produced by the process described above

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I have the following characteristics: '| î Λ i j- tight particle size distribution, $ 95 of the grains being located! in a range of 1 to 8 percent.

5! | - a very fine and very tight average particle size, between i 2 and 4 Ji and adjustable according to the intended use. ; an exchange capacity for calcium ions greater than! 120 mg Ca ++ per gram of anhydrous product.

- a pH of zeolite A in aqueous suspension at 1% of between jO: 10 and 11.

# j I This zeolite A is particularly suitable for the use J% j | tion in detergents to soften hard water.

; | i |; The following examples illustrate the invention without any-

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^ I sometimes limit it.

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> 15 1 EXAMPLE 1

if We prepare a sodium silicoaluminate type 2eolite A

j by continuously mixing a sodium silicate solution A with ·

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i! ! a solution B of sodium aluminate in a reactor allowing a; | j instant mix of the two solutions. The gel obtained is subjected to N 20: discontinuous ripening in a ripener.

I Solution A of sodium silicate is obtained by dis- 3. .... · I. 50 ° C solution of crystallized sodium silicate of commercial quality in 1 ml in demineralized water. It has the following characteristics: * it: j. 'vantes:] 25'! - Si0_ concentration 138 g / l

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| '| I - Na ^ O concentration 41 g / l] il - temperature = 50 ° C at the time of use'. Il j j The sodium aluminate solution B is obtained by disso-! i: lution at 104 ° C. of hydrated alumina in concentrated soda of '; ; ! l i '30' so as to obtain:!; ; not a word; i - concentration of 56 g / l ‘'! - Na 0 BO concentration g / l ä ;. , d j - temperature = 92 ° C at the time of use i. | j Solutions A and B are sent simultaneously to a reactor fitted with a turbine rotating at 8000 rpm. The solutions ; ; i i .A and B have flow rates such as the residence time in the reactor!

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I. "ΛΜ0 *" *** ^ '6 is 2 nn, the weight ratio Al ^ O ^ / SiO ^ being 1.4.

The gel thus obtained is transferred by overflow into the ripening tank. The sodium silicoaluminate is kept in suspension at 8 ° C. by using a paddle stirrer rotating at 5 to 20 revolutions / min.

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After 15 hours of ripening, the zeolite is separated by filtration then washed and dried until a product containing 20 to 22 $ of hydration water is obtained.

The zeolite thus obtained has the following properties: an X-ray diffraction diagram indicating that more than B7% of the product is zeolite A crystallized.

- a particle size characterized by:. an average particle diameter of 3.9 to 15. $ 97 for particles having less than 8 fx • 1% of particles having less than 1 p

The particle size is determined by an X-ray sedimentometer.

- a sequestering power of 121 expressed in mg of Ca per 20 gram of anhydrous product. This is measured by reacting a known amount of zeolite with an aqueous solution containing 200 mg of calcium per liter (50 ° hardness and pH 10), with vigorous stirring for 15 min at 22 ° C. Part of the calcium ions is fixed by the zeolite. After filtration and rinsing thereof, the calcium remaining in solution is measured in this filtrate by potentiometric titration using a calibrated solution of ethylenediamine tetraacetate.

- EXAMPLE 2 The following solutions are prepared according to the procedure of Example 1: - Solution A:. SiD concentration ^ 119 g / 1. Na_ü concentration 36 g / $ 1, 2 35,. temperature = 90 ° at the time of use '/ 7 i. .

\ '- Solution B: ί. concentration of A1_D_ 97 g / 1 \ i c J · * li. Na ^ O concentration 99 g / 1 | , temperature = 90 ° at the time of use 5 Solutions A and B are sent simultaneously to the high suction zone of a turbine located in a reactor. This turbine rotating at 300 rpm is placed in a saucer rotating on itself. This saucer is made up of two plates whose concavity is directed towards the turbine. These two plates 10 determine a volume into which the two solutions are injected! . reactionary.

jî. . Solutions A and B have flow rates such that the residence time in the reactor is 12 min, the ratio being 1.35.

The gel thus obtained is transferred by overflow into a ripening tank. The sodium silicoaluminate is kept in suspension at 90 ° C. by using a paddle stirrer rotating at <2D revolutions / min.

After 5 hours of ripening, the zeolite is separated according to the same methods as those of Example 1.

The zeolite thus obtained has the following properties: - more than 93% of the product is zeolite A cristalis-! sée.

- grain size characterized by: 25. average particle diameter 3.0 μ. 99% of the particles having less than 8 μ. all these particles being greater than 1 μ - sequestering power determined according to the operating mode || described in Example 1 = 129 mg Ca / g of anhydrous product Ι 30 - EXAMPLE 3

The preparation of sodium silicoaluminate is carried out with the solutions and according to the procedure described in Example 2.

The only difference is the stirring speed in the ripener. j 35 This is maintained at 140 rpm for 5 hours.

t / 'At the end of this time, the zeolite is separated according to the same methods as those of Example 1.

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The zeolite thus obtained has the following properties: - more than 91% of the product is de- zeolite A crystallized 5 - particle size distribution characterized by: * • mean particle diameter 5.2 μ • 93% of the particles have less than 8 μ • no particle has less than 1 μ 10 - sequestering power determined according to the procedure described in example 1 = 106 mg Ca / g of anhydrous product "♦

This example shows that too much agitation leads to - bad - results.

15 - EXAMPLE 4

The zeolite is prepared with the solutions and according to the procedure described in Example 2.

The only difference is the agitation mode in the mOrisseur. This is achieved by subjecting the liquid to ultrasound.

After 5 hours, the zeolite is separated according to the same methods as those of Example 1.

The zeolite thus obtained has the following properties: - more than 92% of the product is zeolite A crystallized 25 - particle size distribution characterized by • average particle diameter 2.4 μ • all the particles have less than 8 μ * · 4 . & particles have less than 1 μ - sequestering power determined according to the procedure 30 described in Example 1 = 13D mg Ca / g of anhydrous product.

- EXAMPLE 5

The zeolite is prepared with the solutions and according to the procedures described in Example 2. *

The only difference is the agitation mode in the mOrisseur. This is obtained by convection by subjecting the liquid to very localized heating at the bottom of the tank, the excess calories supplied being evacuated by a coil of cold water located in the upper part of the tank. the eu $ e.

Λ: The average temperature in the suspension is maintained Ί at 90 ° C by regulation on the cooling water.

d j | 5 After 5 hours of ripening, the zeolite is separated:! according to the same profcédês as those of Example 1.

| ! ! j The zeolite thus obtained has the following * properties: i j * · iΐ · - more than 94% of the product is zeolite A crystal- I ...

; - lrsee | 10 - particle size distribution characterized by, · average particle diameter 3.2 p, '· $ 98 of the particles have a size less than 8 μ I ~~ "all these particles have more than 1 μ 15 - sequestering power determined according to the operating mode 'described in Example 1 = 125 mg Ca / g of anhydrous product.

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Claims (1)

4.- Method according to claim 1 wherein the maintenance in suspension is ensured by the use of jiggs. 5. - The method of claim 1 wherein the maintenance in suspension is provided by concrete type rollers. • "6.- The method of claim 1 wherein the maintenance in suspension is provided by local heating creating convection currents. 7." Silicoaluminate type zeolite A of which 95% of the crystals are in a range from 1 to 8 μ, the average being between 2 and 4 μ, and having a sequestering capacity greater than 120 mg of cal-% cium per gram of anhydrous product. 'Λ \ XK \ \ \ .Λ: i; \, \ .__' 'v \, \. ♦ <