GB2089779A - Synthetic zeolites - Google Patents

Abstract

Zeolites 4A have been produced having a low or virtually zero coarse fraction and an equivalent power of exchange with magnesium of or greater than 45 mg CaO/g and a coarse fraction not exceeding 2 when measured at 15 minutes stirred by the method described. Desirably they have a granulometric modulation of or greater than 85.

Description

SPECIFICATION Improvements in and relating to synthetic zeolites This invention relates to improvements in synthetic zeolites 4A having a high degree of crystallinity and a fine granulometry, particularly such as are suitable for the formulation of detergent compositions.

Belgian Patent 860,757 describes the preparation of zeolites of this type by adding to a hot (70DC) solution of a particular sodium silicate, a hot (70"C) solution of sodium aluminate containing an excess of NaOH; the silicate solution is prepared by mixing together, whilst stirring, an aqueous water-glass solution, in which the molar ratio SiO2: Na2O is 3.46, with an aqueous solution of NaOH, whereby the molar ratio drops to 1.65.

French Patent 2,096,360, on the contrary, suggest pouring the hot silicate solution into the hot aluminate solution, previously placed into a reactor, whilst Belgian Patent 862,740 describes the admixing of the two solutions, both at low temperature. According to these patents it is possible to obtain particles with a high degree of crystallinity and fine granulometry; however, the particle size distribution is not fully satisfactory.

For the purpose of formulating detergents, the particles should be so far as possible all within the range 1 to 10 microns. The particles above 10 microns display slow exchange kinetics with calcium and especially with magnesium, leave residues on the fabrics, and clog discharge pipes, whilst particles below 1 micron penetrate too deeply into the mesh of the fabrics being washed thereby causing a progressive matting of the same, and also require too long a settling time in waste water treatment tanks.

Experience has shown that best results, by way of good detergency without ecological problems, are reached only when the granulometric modulation index is sufficiently high and the coarse fraction is negligible. By the term "granulometric modulation index" (cho) is to be understood the percentage by weight of particles the size of which is from 3 to 8 microns, when the granulometric analysis is carried out with a Coulter Counter, as indicated in Belgian Patent 860,757, and by the term "coarse fraction" (a) is to be understood the percentage by weight of particles with a size greater than 10 microns.

Another drawback of the above-indicated processes is their complexity and the slow rate of the rection.

The novel zeolites 4A according to this invention have little or no coarse fraction, with an a not exceeding 2, and preferably not exceeding 1, and having an equivalent power of exchange with magnesium of or greater than 45mg. CaO/g. Desirably the coarse fraction content is substantially zero.

The zeolites of the invention may generally be produced by the process of our application no. 80/02858, which process broadly involves the addition, in a first stage, of an aqueous sodium silicate solution to an aqueous sodium aluminate solution, containing an excess of NaOH and pre-heated to a temperature from 50 to 100"C, and crystallization, in a second stage, at a temperature from 70 to 105"C, characterised in that the temperature of the silicate solution is lower by at least 20"C than that of the aluminate solution, the molar ratios SiO2: H20 and SiO2:Na2O in the silicate solution being respectively from 0.030 to 0.150 and from 1.95 to 2.30, whilst the weight ratio (t) between the reaction mother liquor and the zeolite thus formed, calculated as containing 22% by weight of water of crystallization, is from 6.5 to 20, preferably from 8 to 15. The aforesaid ration (t) may be defined in a precise way by the expression: 0.3288(gNa2O + gA1203 + gSiO2 + gH2O) - gSiSO2 gSiO2 wherein the symbols gNa2O, gAl2O3 etc. represent the quantities in grams of the reactants.

By this process it is possible to obtain zeolites 4A with a high degree of crystallinity and a fine granularity, having a granulometric modulation index (w) equal to or greater than 85 and a coarse fraction (a) equal to or less than 1 (even as low as zero). The products obtained by the process according to the invention have a very high exchange power, with respect to waters made hard by the presence of magnesium ions. The exchange with magnesium can in fact attain (in equivalent terms) the level of 45 mg CaO/g (even 50, in some cases), measured by the method described hereinafter.

The process can be appreciated as an even greater technical advance when it is considered that water-glass, in which the molar ratio SiO2: Na2O is about 3.46 (a product used in most of the other synthesis processes), is prepared by heating in a smelting furnace (with a considerable energy loss) a mixture of siliceous sand and sodium carbonate, while the sodium disilicate (Na2Si205) and the other silicates which can be used in the process are readily obtained in a much less complex way, directly by the hot digestion of silica in aqueous NaOH.

The rate of formation of the zeolite in the process just described is very fast and the reaction is quite flexible with regard to the operating conditions such as temperature and time, a flexibility that in general does not obtain in processes based on relatively high SiO2:Na2O ratios.

Zeolites according to the invention have been tested in some of the formulations described in Belgian Patent 860,757, in Italian Patent 1,009,446 and in US Patent 4,083,793, in each case obtaining excellent results.

To carry out the process it is found convenient to add the silicate solution to the aqueous aluminate within 15 minutes or less, and to keep the temperature of the resulting mixture during the first stage of the synthesis substantially equal to that of the aluminate solution, this latter being preferably from 70" to 75"C.

Moreover, it is also found convenient to subdivide the second (crystallization) stage into 3 substagesthe first sub-stage being characterized by the temperature being the same as that of the temperature of the first stage, the second by a temperature rising to 95 - 105"C, and the third by a substantially constant temperature between 95" and 105"C. The duration of the substages may be respectively from 30 to 60 minutes (preferably 40 to 50), from 10 to 80 minutes (preferably 15 to 40), and from 10 to 90 minutes (preferably 15 to 60).

For making or maintaining the reaction mixture homogeneous, gentle stirring is sufficient; the reaction slurry may conveniently be filtered or centrifuged in order to separate the microcrystals, and the mother liquor, after separation, may be discharged or re-cycled for the preparation of further aluminate solution.

The process may be conducted in a continuous, semi-continuous or batch mode. Batchwise operation is illustrated by way of a block diagram in Figure 1 of the accompanying drawing, whilst Figure 2 represents a variant of Figure 1; Figures 3 and 4 show graphically the most significant results of operations conducted as hereinafter exemplified with reference to Figure 1 and 2.

Referring to Figure 1 there are introduced into reactor (A), in the recited order (lines 1,2 and 3) NaOH, alumina and deionized water. The resulting aluminate solution is thereupon treated with a solution of disilicate introduced through line (4) and the reaction mixture (5) is then separated in centrifuge (B) from the mother liquors (6) which are conveyed into the collecting tank (C). The soda-rich mother liquor may be re-cycled in partial substitution of the deionized water and of the NaOH, when it is fed in through line (7). The centrifugally separated micro crystals are washed with de-ionized water (line 8) and then conveyed into tank through line (9) (D) where the cake is repulped with further de-ionized water introduced through line (10); the resulting slurry is then conveyed through line (11) into a spray dryer (E) and the resulting dry zeolite to store (F) by way of line (12).In the case of dryers of a different type, the tank (D) may be omitted.

The following Examples, of which nos. 2-4, 8, 10, and 13-16 are given for comparison purposes, illustrate how the zeolites of the invention may be prepared. It will however be appreciated that the process of our application 80/02858 will not invariably give products according to the present invention.

Example 1 Into a stainless steel reactor [reactor (A) in Figure 1], having a holding capacity of 1,200 litres, furnished with a thermostatically controlled heating system, a reflux condenser and a stirrer revolving at about 120 rpm, there were introduced 239 kg of an aqueous solution of NaOH containing 34.3% by weight of Na2O, 67 kg of hydrated aluminium oxide, containing 60% by weight of Awl203, and 585 kg of deionized water. The reaction mixture was maintained at 100"C for about 1 hour until a clear sodium was formed whose molar ratio Na2O:A1203 was 3.35, and in which the perecentage of Na2O was 9.2% by weight.

The solution was cooled to 70"C and in the course of 13 minutes it was treated, whilst stirring, with 209 kg of a second aqueous solution at a temperature of 7"C, containing 8.7% by weight of Na2O and 18.4% by weight of SiO2. The molar ratio SiO2: Na2O here was 2.2, a value close that of the disilicate (Na2Si2O). The quantity charged was such as to bring the weight ratios between the components of the reaction mixture to the levels: Na2O:A12O3 = 2.49, Na2O:SiO2 = 2.60, and H2O:SiO2 = 23.94.

ATo conduct the second, crystallization stage, the mixture was initially maintained, in a first sub-stage, at 70"C for 45 minutes, after which the temperature was brought up slowly to 1 OO"C during the course of 15 minutes. Finally, the mixture was heated for 90 minutes at 100"C, under atmospheric pressure and whilst being stirred gently. The precipitated solid was separated in a basket centrifuge revolving about a vertical axis [centrifuge (B) in Figure 1] and the resulting cake was then washed with deionized water until the wash water reached a pH of 11.3.An aqueous suspension containing 54 kg of the zeolite per 100 litres of suspension was then dried in a spray dryer [apparatus (E) in Figure 1j to yield a crystalline 4A zeolite of the following composition: (1.01 Na2O)(AI203)(1.98 SiO2)(4.51 H2O). Thereupon the exchange capacity of the zeolite for calcium was determined by the following method: An aqueous 0.005 molar solution of tetrahydrated calcium nitrate, that is, one having a hardness of 50 French degrees, was prepared by dissolving 1.181 g of Ca(NO3)2.4H2O in deionized water and then bringing the solution to 1 litre.To this solution was added 1 g of hydrated zeolite and the ensuing suspension was subjected to vigorous stirring for 15 minutes by a magnetic stirrer, at a temperature of 22 + 2"C. 100 ccm of this solution were then filtered on a porous septum (degree of proposity 4) and the residual concentration of Ca++ was determined by titration with a centinormal solution of the disodium salt of ethylendiaminotetraacetic acid (EDTA).The exchange capacity of the hydrated zeolite was calculated in the first instance, as mg of CaO per 1 g of zeolite, according to the formula: PS(Ca) = (50 - ccm EDTA) x 5.6, wherein by "CCM EDTA" is indicated the number of ccm of 0.01 N EDTA consumed in the titration and wherein by a hydrated zeolite is meant a product in equilibrium with a relative atmospheric moisture not below 50% at room temperature (between 15 and 30"C). The 'hydrated' zeolite was obtained by placing the filtered and washed product into an oven for 5 hours at 1050C. The dried material was then ground in a mortar and then exposed to air for not less than 3 hours, under the above indicated temperature and humidity conditions. Then, by determining the moisture content of the hydrated zeolite by calcining at 800"C for 1 hour, a correcting factor is determined for calculating the exchange capacity per gram of anhydrous product. The values indicated in Tables I to V are referred to anhydrous zeolite.

The exchange capacity in respect of magnesium is determined in a similar way by using a 0.005 molar solution of MgSO4, containing 1.232 g of MgSO4.7H2O per litre. The exchange capacity for magnesium is calculated first in mg of CaO per gram of hydrated zeolite by the formula PS(Mg) = (50 - CCM EDTA) x 5.6 and then the exchange capacity with reference to the anhydrous product (given in Tables I to V) is calculated as for calcium.

In order to evaluate the speed at which the exchange takes places, the tests were repeated with calcium and magnesium, modified in that the stirring time was reduced from 15 to 2 minutes. The kinetics of the exchange is an important datum in as much as the sequestering action of the zeolite is to be exerted in conventional washing machines usually in a short period of time, typically a few minutes; the high exchange capacity in the presence of magnesium-containing waters, set out in Table I, discloses a technical advance with respect to the results obtained so far in the art.

Granulometric analysis (using a Coulter counter) gave the results set out in Table I and shown in Figures 3 and 4. Diffractometric X-ray analysis showed a pure crystalline 4A zeolite, the interplanary distances with the corresponding indexes and intensities for the diffractogrammic peaks being as follows:: hkl d ( ) I/lo hk1 d (Â) I/lo 100 12.29 100 221.3 4.11 36.5 110 8.71 69.5 311 3.714 53 111 7.11 34.5 320 3.417 16.5 210 5.51 25.5 321 3.293 46.5 211 5.03 2 410 2.988 55.5 220 4.36 6 Example 2 With reference to Figure 2, a reactor (C), similar to the reactor (A) of Example 1, was charged with 898 kg of a recycle of mother liquor (6) consisting of a solution containing 7.99% by weight of Na2O and 0.85% by weight of Awl203. To this solution there were then added, whilst stirring (lines 1 and 2), 30 kg of a 34.3% w/w solution of Na2O and 55 kg of hydrated aluminium oxide containing 60.87% of A1203; the mixed solution was cooled down to 700C and then transferred into reactor A.Into the same were fed, by way of line 4 and in the course of 15 minutes whilst stirring, 155 kg of an aqueous solution of silicate at 1 0'C, containing 11.74% by weight of Na2O and 24.82% by weight of SiO2(molar ratio SiO2: Na2O = 2.18). The weight ratios between the components of the resulting mixture were: Na2O:AI203 = 2.44; Na2O:SiO2 = 2.61; H2O:SiO2 = 24.36. There followed crystallization, centrifuging and drying, as in Example 1, and analogous results were obtained (see Table V).

Example 3 Into the reactor (A) indicated in Example 1 there were charged 307 kg of a solution containing 29% by weight of Na2O, 67.2kg of or hydrated aluminium oxide containing 60.38% of Awl203, and 591.5 kg of deionized water. The temperature was kept at 1 000C for about 1 hour, until a clear solution resulted, in which the molar ratio Na2O:Al203 was 3.61 and in which the percentage of Na2O was 9.22% by weight. The reaction mass was then cooled to 70"C and into the reactor there were fed, in the course of 15 minutes, whilst stirring, 134.3 kg of a water-glass solution at 8"C, containing 8.24% by weight of Na2O and 28.69% by weight of SiO2, the molar ratio SiO2:Na2O being 3.6; the ratios between the components of the mixture are as set out in Table I.

There followed cyrstallization, centrifuging and drying as in Example 1, thereby obtaining the rather poor results disclosed in Table 1. This shows the need to avoid too high SiO2/Na2O ratios in the silicate solution.

In the X-ray spectrum, the peaks have a mean intensity that is lower by 10% in comparison with the product of Example 1, whilst the presence of no other crystalline compounds could be noted.

Example 4 Into the same reactor (A) as in Example 1 there were charged 243.3 kg of a solution containing 35.3% by weight of Na2O, 67.2 kg of hydrated aluminium oxide containing 60.38% by weight of A1203 and 646.2 kg of deionized water. The reaction mixture was maintained for about 1 hour at 100 C until a clear solution resulted, in which the molar ratio of Na2O:A1203 was 3.48 and the percentage of Na2O was 8.98% by weight.

The reaction mixture was then cooled to 70"C and over a period of 15 minutes, whilst stirring, there were added 143.3 kg of a silicate solution at 8"C containing 9.93% by weight of Na2O and 26.9% by weight of SiO2, in which the SiO2: Na2O molar ratio was 2.8. The weight ratios of the components of the reaction mixture are set out in Table I.

After crystallization, centrifuging and drying as in Example 1, the properties of the product, as set out in Table I, are seen to be only slightly better than those of comparative Example 3, and still far from the excellent results of Example 1,the SiO2:Na2O ratio still being too high.

Example 5: (Na2 Si2 05) Into the reactor (A) of Example 1 there were charged 227.6 kg of a solution containing 35.05% by weight of Na2O, 67.2 kg of hydrated aluminium oxide containing 60.38% by weight of A1203 and 637.9 kg of deionized water. This mixture was maintained at a temperature of 100"C for about 1 hour until a clear solution resulted in which the Na2O:A1203 molar ratio was 3.23 and in which the Na2O content was 8.55% by weight.

Thereupon the reaction mass was cooled to 70"C and in the course of 15 minutes, whilst stirring, there was added 167.4 keg of a silicate solution at 8"C, containing 34.9% by weight of sodium silicate (Na2Si2O5), in which the molar ratio SiO2:Na2O was 2. The weight ratios between the components of the reaction mixture are as set out in Table 1.

After crystallization, centrifuging and drying as in Example 1 there were obtained a product having the properties indicated in Table 1.

Example 6 Into the reactor (A) of Example 1 there were charged 218 kg of a solution containing 35.05% by weight of Na2O, 67.2 kg of hydrated aluminium oxide containing 60.38% by weight of Awl203 and 636.6 kg of deionized water. This reaction mixture was maintained at 1 OO"C for about 1 hour, resulting in a clear solution in which the molar ratio Na2O:A12O3 was 3.11 and where the Na2O content was 8.31% by weight The reaction mixture was cooled to 70"C and into the reactor there were fed, in the course of 15 minutes, whilst stirring, 177.5 kg of a silicate solution at 8"C, containing 13.20% by weight of Na2O and 21.71% by weight of SiO2, in which the molar ratio SiO2: Na2O is 1.7.The weight ratios between the components of the reaction mixture was set out in Table II.

There then followed crystallization, centrifuging and drying as in Example 1, to give a product having the properties indicated in Table II.

Example 7 In this case Example 1 was repeated, leaving the overall composition of the reaction mixture unchanged (see Table II), but altering the composition of the starting solutions, so that in the silicate solution the ratio SiO2O:Na2O was 2.5; results are recorded in Table II.

Example 8 and 9 Example 1 was repeated, varying only the duration of the addition of silicate to aluminate; the 13 minutes of Example 1 is changed to 45 minutes for Example 8 and to 5 minutes for Example 9. The results are as set out in Table II.

Example 10 Into the reactor (A) of Example 1 there were charged 250 kg of a 35% by weight solution of Na2O, 71.5 kg of hydrated aluminium oxide containing 63.2% by weight of Awl203, and 633 kg of deionized water. The reaction mixture was heated to 100 C and held at this temperature until the hydrated aluminium oxide passed into solution. The solution was then cooled to 70"C and into it there were fed, in the course of 15 minutes and whilst stirring, 246 kg of an aqueous solution at 65 C containing 17.1% by weight of SiO2 and 8.83% by weight of Na2O, according to a molar ratio SiO2: Na2O of 2.The ratios between the components of the reaction mixture are indicated in Table lil, which also sets out the results obtained after crystallization, centrifuging and drying as in Example 1.

The high course fraction (a), amounting to 2% by weight of particles above 10 micrometers, is a sign of a poor product (and in any way less desirable in comparison with that of Example 1) and it shows the necessity of maintaining the temperature of the silicate solution below the reaction temperature.

Example 11 Example 10 was repeated, changing only the temperature of the silicate solution from 65 to 50"C. From Table III, which shows the respective data and results, there will be seen a clear improvement connected with the lowering of the temperature as indicated above; the influence of temperature is even more evident if the results of Example 10 (temp. = 65"C) are compared with the excellent results of Example 1 (temp. = 7"C).

Example 12 Example 10 was repeated, with the following modifications: (a) the temperature of the silicate solution was lowered to 23"C; (b) after the addition of the silicate to the aluminate (first stage) there was carried out the crystallization (second stage), while maintaining the temperature at 70"C for 45 minutes. Then the temperature was gradually raised from 70 to 100C in the course of 60 minutes and maintained at 1000C for a further 90 minutes.

From Table lli it will be seen that, in spite of the low modulation index (cho), the exchanging power is very high and that the coarse fraction (a) is completely absent.

Example 13 Example 10 was repeated, except for the following modifications: (a) the temperature of the silicate solution was lowered to 23"C.

(b) the aluminate solution contained 90.8 kg more water while the silicate solution correspondingly containing 90.8 kg less water. In other words, the overall ratios between the components (Na2O, Al203, SiO2, H20) were kept unchanged but the process was started from a more concentrated silicate solution in which the molar ratio SiO2:H2O rose to 0.138 (in Example 10 the ratio was 0.069).

From Table III it will be seen that the product had a satisfactory exchange power and an excellent modulation index with a coarse fraction (a = 1) at the limit of acceptability.

Example 14 Example 10 was repeated with the following modifications: (a) the temperature of the silicate solution was lowered to 25"C; (b) the solution of aluminate contained 103 kg of water more, while the silicate solution correspondingly contained 103 kg less of water, whereby the molar ratio SiO2: H20, in the silicate solution, rose to 0.159.

The poor results (Table IV) show that a low concentration of silica in the feeding solution, is essential for the synthesis of zeolites of high quality.

Example 15 Example 14 was repeated with the modification that the temperature of the silicate solution was raised to 65"C, whereby its viscosity fell to about one fourth of the starting value (at 25"C). Instead of obtaining better and acceptable results, as might have been expected, it was found (Table IV) that the product had a power of exchange with calcium inferior to that of the product of Example 14, and granulometric parameters almost as poor as those of the preceding example; this shows the importance of the dilution perse of the silicate solution and excludes the possibility that the poor results of Example 14 resulted from a viscosity effect.

Example 16 Example 15 shows that the dilution of the silicate solution is a critical and necessary factor. The present example shows that the appropriate dilution must be associated with sufficiently low SiO2: Na2O ratios.

To this end, an aluminate solution, prepared with 276.6 kg of a 35% by weight solution of Na2O, 71.5kg of hydrated aluminium oxide containing 63.2% by weight of A1203 and 640.4 kg of deionized H2O, was heated up to 70"C and to it were added, in the course of 15 minutes and whilst stirring, 211.2 kg of a silicate solution at 23"C, containing 19.9% by weight of SiO2 and 5.9% by weight of Na2O, the molar ratio SiO2: Na2O amounting to 3.5. The mixture was worked up as in Example 1 and yielded a lower quality product that showed a high coarse fraction content (a = 4; Table IV).

Example 17 Into a heat-insulated reactor with a holding capacity of 70 m3 and fitted with a stirrer and external heating (by means of a recycle pump and an exchanger), there were introduced 12,320 kg of a 35.5% by weight solution of Na2O, 3,680kg of or hydrated aluminium oxide containing 61.3% by weight of A1203 and 17,120 kg of deionized H2O. This reaction mixture was then heated up to 1 OO"C until dissolution of the alumina was complete. Thereupon 14,620 kg of deionized H2O were fed in, and the temperature accordingly fell to 750C.

At this point there were added, in the course of 15 minutes and whilst stirring, 12,240kg of or an aqueous solution of silicate containing 17.16% by weight of SiO2 and 8.61% by weight of Na2O, at 22"C; the temperature was maintained for 45 minutes at 75"C and was then gradually brought up in the course of 60 minutes to 98"C. The mixture was held at 980C for 1 hour, after which it was filtered, washed and dried, the product having the properties set out in Table IV.

Example 18 Into the reactor described in Example 17 there were introduced 12,700 kg of a solution containing 35.5% by weight of Na2O, together with 3,610 kg of hydrated aluminium oxide containing 61.3% by weight of A1203 and 17,760 kg of deionized H2O. The mixture was heated up to 1000C, until dissolution of the alumina was complete, after which there were fed in 14,940 kg of deionized H2O, in consequence of which the temperature dropped to 750C. At this point there were fed in, during the course of 15 minutes 11,500 kg of a silicate solution containing 18.40% by weight of SlO2 and 8.70% by weight of Na2O, at 23"C.

The temperature was maintained at 750C for a period of 45 minutes and was then gradually brought up to 98"C over 20 minutes; the reaction mixture was then left for 30 minutes at 980C after which it was filtered, and the product was washed and dried.

The excellent results obtained are as set out in Table V.

Example 19 Example 10 was repeated except for the following modifications: (a) temperature of the silicate solution was reduced to 220C; (b) the solution of the aluminate contained 150 kg less of H2O while the silicate solution contained 150 kg more of H2O, so the degree of dilution of the silicate solution reached to a high level (in fact the molar ratio SiO2:H20 amounted to only 0.038).

The less satisfactory results, as set out in Table V, show that whilst a too low dilution is detrimental for the purposes of the synthesis (Examples 13 and 14), this Example has a SiO2:H2O molar ratio approaching that of the high dilution limit.

Example 20 Into the reactor of Example 1 there were charged 255 kg of a solution containing 35.5% by weight of Na2O, 72.89 kg of hydrated aluminium oxide containing 63.21% by weight of Al203 and 740 kg of deionized water.

The whole mixture was then heated up to and held at 100"C until dissolution of the alumina was complete.

The mixture was then cooled to 70"C and then, in the course of 15 minutes it was treated with 148 kg of a solution containing 28.76% by weight of SiO2 and 14% by weight of Na2O, corresponding to a molar ratio SiO2:Na2O = 2.1, at 21"C. Other data and results are as set out in Table V.

TABLE I Characteristics Ex. 1 Ex. 3 Ex. 4 Ex. 5 SiO2: Na2O in the sili cate solution 2,2 3,6 2,8 2,0 mixing time (in minutes) 13 15 15 15 ratios in the: Na2O:A1203 2,49 2,47 2,47 2,47 reaction mix- Na2O:SiO2 2,60 2,60 2,60 2,59 ture H2O:SiO2 23,94 23,89 23,89 23,91 Power of exchange: stirr. for 15 min. Ca++ 177 163 173 175 stirr. for 15 min. Mg++ 45 29,5 28 45 stirr.for2min. Ca++ 145 123 137 145,5 stirr.for2min.Mg++ 16 13,5 14 24 granulometry: < 2um 2,5% 1% 1,5% 3% < 3lim 13% 4% 8,5% 21,5% < 5lim 68% 26% 50% 89% < 8lim 98,5% 69% 85% 98% < 10Fm 100% 83% 90% 99% Coarse fraction (a) 0 17 10 1 Modulation (o) 85,5 65 76,5 76,5 TABLE II Characteristics Ex. 6 Ex. 7 Ex. 8 Ex. 9 SiO2:Na2O in the silicate solution 1,7 2,5 2,2 2,2 mixing time (in minutes) 15 13 45 5 Ratios in the: Na2O:Ai203 2,47 2,49 2,49 2,49 reaction mix.Na2O:SiO2 2,60 2,60 2,60 2,60 H2O:SiO2 23,90 23,94 23,94 23,94 Exchange power: stirr. 15 minutes Ca++ 175,5 175 166 172,5 stirr. 15 minutes Mg++ 45,5 45 42.5 50 stirr.2 minutes Ca++ 148,5 145,5 140 152 stirr.2 minutes Mg++ 20,5 20,5 17 22,5 granulometry: < 2lim 3% 2% 1% 2,5% < 3 m 28% 14% 9% 17% < 5Rm 83% 80% 72% 85% < 8Fam 97,5% 97% 98% 97% < 10 m 98,5% 98,5% 98% 99% 98% Coarse fraction (a) 1,5 2 1 2 Modulation (#) 69,5 83 89 80 TABLE III Characteristics Ex. 10 Ex. 11 Ex. 12 Ex. 13 SiO2:Na2O (silicate solut.) 2,0 2,0 2,0 2,0 SiO2:H20 (silicate solut.) 0,069 0,069 0,069 0,138 Temp. (silicate solut.) 65 C 50 C 23 C 23 C Mixing time (in minutes) 15 15 15 15 Ratios in the:: Na2o:Al2o3 2,42 see see see reaction mix- Na2O:SiO2 2,60 example example example ture H2O:SiO2 23,87 10 10 10 Duration of second sub- see ex.

stage 15' 15' 60' 10 Power of exchange: Stirr.for15min. Ca++ 170 175 175,5 172,5 stirr.for15min. Mg++ 44 47 52 42 stirr.for2min. Ca++ 132.5 137.5 158 129 stirr. for 2 min. Mg++ 3.5 3.5 23 3.5 granulometry: < 2Fm 2,5% 4% 4% 0,5% < 3lim 16% 16% 28% 6,5% < 5ym 71,5% 87% 92,5% 41% < 8Fm 96% 97% 99,5% 94% < 10 m 98% 98,5% 100% 99% Coarse fraction (a) 2 1,5 0 1 Modulation (co) 80 81 71,5 87,5 TABLE IV Characteristics Ex. 14 Ex. 15 Ex. 16 Ex. 17 SiO2:Na2O(silicatesolu.) 2,0 2,0 3,5 2,1 SiO2:H2O(silicate solu.) 0,159 0,159 0.080 0,069 Temp. (silicate solu.) 25 C 65 C 23 C 22 C Mixing time (in minutes) 15 15 15 15 Ratios in the: Na2O::A12O3 see see 2,42 2,41 reaction mix- Na2O:SiO2 example example 2,60 2,58 ture H2O:SiO2 10 10 23,87 23,90 Duration of second sub- see ex. see ex. see ex.

stage 10 10 10 60' Power of exchange: Stirr.i5minutes: Ca++ 170 168 174,5 175 stirr. 15 minutes Mg++ 21 38 42 51 Stirr. 2 minutes Ca++ 123.5 125,5 126 156 stirr. 2 minutes Mg++ 0 0,5 14 20 granulometry: < 2Fm 1% 1% 1,5% 3% < 3Fm 4% 3,5% 15% 28,5% < 5Fm 25,5% 23,5% 74% 91,5% < 8Fm 68% 71,5% 94% 99,0% < 101lm 86% 89,5% 96% 100% Coarse fraction (a) 14 10,5 4 0 Modulation (#) 64 68 79 70,5 TABLE V Characteristics Ex. 18 Ex. 19 Ex. 20 Ex. 2 SiO2:Na2O (silicate solu.) 2,2 2,0 2,1 2,18 SiO2::H2O (silicatesolu.) 0,076 0,038 0,151 0,117 Temper. (silicatesolut.) 23 C 22 C 21 C 10 C Mixing time (in minutes) 15 15 15 15 Ratios in the: Na2O:A12O3 2,49 see 2,42 2,44 reaction mix- Na2O:SiO2 2,60 example 2,61 2,61 ture H2O:SiO2 23,95 10 23,87 24,36 Duration of the second sub-stage 20' 15' 60' 15' Power of exchange: Stirr. 15 minutes: Ca++ 176 167 174 176 stirr. 15 minutes Mg++ 46 31 41 43 Stirr.2minutes: Ca++ 142 121 147.5 144 stirr.2minutes Mg++ 14 13.5 15 21.5 granulometry: < 2,Lt 3% 1% 3% 1,5% < 3lim 14% 3.5% 11% 9% ( 5,etm 70% 37% 47,5% 71% < 8,etm 99% 89% 94% 98% < 10Ftm 100% 96.5% 98,5% 99% Coarse fraction (a) 0 3.5 1,5 1 Modulation ((0) 85 85.5 83 89

Claims (7)

1. Zeolites 4A having an equivalent power of exchange with magnesium of or greater than 45mg CaO/g and a coarse fraction not exceeding 2 when measured at 15 minutes stirring by the method hereinbefore described.

2. Zeolites according to Claim 1 in which said coarse fraction does not exceed 1.

3. Zeolites according to Claim 1 in which said coarse fraction is substantially zero.

4. Zeolites according to Claim 1,2 or 3 having an index of granulometric modulation of or not greater than 85.

5. Zeolites according to any preceding Claim having an equivalent exchange power with magnesium of orgreaterthan 50mg CaO/g.

6. Zeolites according to any preceding Claim when prepared by a process as claimed in our application 80/02858.

7. Zeolites according to Claim 1 substantially as described in any of the foregoing Examples 1, 5-7, 9, 11, 12,17or18.