GB1560223A

GB1560223A - Synethesis of favjasite

Info

Publication number: GB1560223A
Application number: GB3564/77A
Authority: GB
Original assignee: WR Grace and Co
Current assignee: WR Grace and Co
Priority date: 1976-01-30
Filing date: 1977-01-28
Publication date: 1980-01-30
Also published as: IT1091561B; JPS5294899A; DE2703264A1; AU2184077A; NL7700908A; AU505874B2; FR2339571B1; ZA77535B; JPS6137206B2; FR2339571A1; CA1082671A

Description

(54) SYNTHESIS OF FAUJASITE (71) We, W. R. GRACE & CO., a Corporation organized and existing under the laws of the State of Connecticut, of 1114 Avenue of the Americas, New York, New York 10036, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be per- formed, to be particularly described in and by the following statement: The present invention relates to the production of crystalline aluminosilicate commonly referred to as zeolites or molecular sieves.More specifically the invention relates to the economic preparation of fauiasitic materials using a special technique to decrease the quantity of reactants used in this preparation and to alleviate the major pollution problems encountered with present process ing.

Fauiasite is a naturally occurring aluminosilicate zeolite. It has a characteristic X-ray structure. The synthetic materials designated zeolite X and zeolite Y by the Linde Division of Union Carbide Corporation are commonly referred to as synthetic fauiasites. Zeolite Y is described in United States Patent 3,103,007, and is generally similar to zeolite X described in United States Patent 2,882,244. The chemical formula for zeolite Y given in United States Patent 3,103,007 is as follows: 0.9+0.2 Na Ai,O: W Six2: X H O where W has a value of greater than 3 and up to about 6 and X may have a value as high as 9.

This phase of fauiasite is distinguished from the zeolite designated type X zeolite by the silica to alumina molar ratio. The silica to alumina ratio affects important physical pro peruses of the fauiasite. The synthetic fauiasite having a silica to alumina molar ratio in excess of about 4 and preferably about 5 is more thermally stable than the same material having a lower silica to alumina molar ratio. As a result high silica fauiasite is particularly useful as a catalyst ingredient or in certain selective absorbents processes where the zeolite would be expected to encounter high temperatures during regeneration.

The high-silica fauiasite (silica to alumina molar ratios above 4) can be economically prepared from a reactant solution containing soluble sodium silicates and/or metakaolin only if nucleation centres are added. These nucleation centres are amorphous materials prepared from sodium hydroxide, silica and alumina and are added to the reaction mixture as a liquid slurry.

It is desirable to decrease the amount of raw materials used in the preparation of these fauiasites both in order to reduce the cosr of raw materials, and also to eliminate excess of raw materials, especially excess of Na2O which would present a pollution problem in commercial processes.

United States Patent 3,574,538 describes a process for preparing high silica fauiasite from clay by reducing the quantity of reactants used in the process. United States Patent 3,639,099 describes a process for preparing these zeolites from synthetic materials (Na2O.

A1203, SiO2 and H20) in which the ratios of reactants are reduced.

We have found that a high purity type-Y zeolite fauiasite having a silica-to-alumina molar ratio of 3:1 to about 6:1, characterised typically by high crystallinities and high surface areas in the range of 700 to 900 m2/g as determined by nitrogen adsorption can be preDared by a process which comprises (a) preparing a gel or slurry of nucleation centres having a molar composition 12 to 19 Na.O: 1 to 10 Al.O: 12 to 19 Six2:: 220 to 900 H2O, (b) mixing said nucleation centres with a zeolite-synthesis mixture, and with aluminium sulphate to provide a crystallisation mixture having a molar composiion (excluding the composition of the nucleaion centres) within the range 1.2 to 3 Na2O: 4 to 7 sio2 A1,0,: 40 to 200 H2O, (c) heating the resultant mixture to a temperature and for a period of time sufficient to ensure cry stallisation and (d) washing, drying and recovering the product. The molar composition of the crystallisation mixture excludes the composition of the nucleation centres. It also excludes inert Na SO formed by the addition of aluminum sulfate to the Na2O-containing mixture.Thus, for every mole of SOi, added one mole Na,O is deducted from the actual reaction mixture composition to obtain an "active" reactant mole ratio which is that specified in the composition of the crystallisa tion mixture.

The molar ratios of sodium oxide to alumina and of silica to alumina in the reactant mixture are lower than normally used for a zeolite-synthesis mixture using nucleation centres, and we have found, surprisingly, that production of zeolites from such a highalumina reaction mixture (with consequent reduction in consumption of silica and soda and in the quantity of non-neutralized NaOH which has to be disposed of) is possible.

Our process is an improvement over the process disclosed in United States Patent 3,639,099 in that we can obtain identical faujasitic material from systems having ratios of reactants well below the ranges shown in this U.S. patent. Our process gives improved raw material utilizations and a significant alleviation of critical water pollution problems.

The first step of our process is the preparation of the gel or slurry of nucleation centres.

In the preferred form of our process we use nucleation centres wherein the amount of alumina. is higher, relative to the soda and silica, than previously thought to be effective.

These nucleation centre compositions prefer ably fall within the molar range of 12 to 19 Na20:2 to 10 more preferably 2 to 5 A1,0,: 12 to 19 SiOp: 220 to 900 H20 as compared to the conventional nucleation centre composi tion which is 16 Na2O: 1 A1203 :15 Six2: 320 H2O i.e. the nucleation centres preferably used in our process have maximum soda and silica contents defined by the molar composi tion: 6--9.5 Na2O:1 A1,0,:6--9.5 SiO2, and are therefore high alumina nucleation centres.

If these high alumina centres tend to gel, we have discovered that the gels can nevertheless be used effectively, preferably after dilution with water and homogenisation to slurry form.

The fauiasites of our invention cannot be pre pared from a reactant slurry having the ratios set out above without the use of nucleation centres. By using these higher alumina seeding compositions, the amount of caustic per mole of alumina added to the synthesis slurry as nucleation centres is greatly reduced, thus reducing the excess caustic in the system that is normally discharged as an effluent at the end of the process. As this caustic would have to be neutralized with acid before dis charge as an effluent, a significant saving in acid is realised, together with an overall lower salt level in the effluent.

In preparing these high alumina seed compositions, it is essential that the Na,O/Al2O, molar ratio of the slurry of nucleation centres or gel be maintained above 1.2 preferably above 1.3. Although these gels are usually aged at about 250C for 15 to 30 hours before they develop active nucleation properties, temperatures above or below 250C may also be used. However, at higher temperatures (say 600 C) shorter aging is effective (say 1 hour), and at lower temperatures longer aging is required.Similarly, as the alumina content of the nucleation centre slurry is increased, the age time of the nucleation centre slurry must also be increased, e.g. at 250 the following seed compositions (molar) have the "ripening" times shown: 16 Na2O:1.2 Al,O,:15 Six2:320 H2O need 16 hours.

16 Na2O :3.0 A1,0,:15 Six2: 320 H2O need 22 hours.

16 Nay0:7.0 At203: 15 Six,: 320 H20 need 22 hours.

The preparation of the nucleation centres normally requires a source of Na2O, a source of silica, a source of alumina and water. Preferably the source of SiO2 for preparation of the nucleation centres is sodium silicate or colloidal silica.

In the conventional process without the use of nucleation centres the reaction slurry is aged at varying temperatures for periods of from 1 to 4 days. When nucleation centres are used the aging time can be substantially reduced or eliminated. The second step of our process is mixing the nucleation centres with the zeolite synthesis reaction mixture. The zeolite synthesis mixture can be prepared from a source of Na2O, a source of alumina other than aluminium sulphate, a source of silica and water. The sources of Na2O and silica are preferably the same, viz. a commercially available sodium silicate solution having a silica to sodium oxide molar ratio of about 3.2 to 1; however, sodium silicate or other ratios may be used. The sodium silicate may be diluted if desired although this dilution is not a critical part of the process. The alumina component of the synthesis mixture can be furnished by sodium aluminate or the alumina component and part of the SiO2 may be from metakaolin. After the reactant slurry is prepared it is stirred, e.g. for 5 to 15 minutes. The nucleation centres are then added. The nucleation centres may be gels and can be diluted with water to return them to their liquid slurry state and are preferably added in concentrations of 0.1 to 10% by weight of the desired product Although larger amounts of nucleation centres than 10% by weight may be added without harm, they do not substantially increase the formation rate of the product.

After the nucleation centres have been added, the slurry is desirably mixed for a period of 10 to 30 minutes to give a good dispersion of the nucleation centres in the reaction mixture.

In the process of the invention the nucleation centres, zeolite synthesis mixture and aluminium sulphate are mixed and thereby reacted to form a crystallisation mixture. The aluminium sulphate can be added to a previously prepared mixture of nucleation centres with the zeolite synthesis mixture. Alternatively, the aluminium sulphate, nucleation centres and the silica component of the zeolite synthesis mixture can be mixed together and the alumina component of the zeolite synthesis mixture (which is, of course, other than aluminium sulphate) added subsequently.

The addition of the aluminium sulphate decreases the amount of sodium oxide needed in the preparation of the zeolite and thus greatly alleviates the pollution problem that results from discarding solutions containing a relatively large amount of NaOH, that needs to be neutralized by acid.

The next step of th process is tie crystal- lisation step. In our process the crystallisa tion mixture is prepared to contain, per mole of alumina, 1 to 3 moles of Na2O, 4 to 7 moles of silica and 40 to 200 moles of water.

Preferably the crystallisation mixture has the following molar ratio of reactants: 1.6 to 2 Na2O:AI208:5 to 6.4 Six2:80 to 150 H20 (more preferably 90 to 150 H20). The cry stallization step is typically carried out for a period of 2 to 28 hours. Crystallization is normally complete in 7-16 hours. Crystallization may be carried out by heating the slurry to a temperature of from 80 to 1200C. and maintaining the slurry at that temperature. A generally preferred temperature and time is about 1000C and 4 to 26 hours. The process of crystallisa tion is followed by sampling the reaction mixture periodically to determine the surface area of the product at that time.

Our invention is illustrated by the following specific Examples. All ratios are molar; all percentages are by weight.

EXAMPLE 1 This example illustrates a method of pre paring the nucleation centres and the steps necessary for using these steps to initiate reaction. A sodium aluminate solution was prepared by dissolving 104 g. of alumina trihydrate (A1,0, . 3H2O) in a boling solution of 153 g. of sodium hydroxide in 300 ml. of water. The solution was cooled to room temperature and added with rapid stirring to a mixture of 521 g. of sodium silicate (410 Bé: Na20:3.22 Six2) in 291 ml. of water. The product set to a stiff gel within 2 min. after mixing was completed. The nucleation centres had the following oxide ratios: 16 Na20:4 Alto,: 15 SiO2 :320 H2O.These nucleation centres were prepared for use by diluting 500 g. of the nucleation centres with 352 g.

of water to form a pourable slurry having the oxide ratio of 16 Na20 :4 Al203: 15 SiO3: 640 H2O.

EXAMPLE 2 This example illustrates a method of pre paring a zeolite from a reaction slurry hav ing the following ratios of reactants: 1.9 Na2O: Al2O3 :6 SiO2: 100 H2O.

A reaction mixture was prepared by mixing 155 g. of the slurry nucleation centres des cribed above (but with the ratio 16: 1.2:15: 320) with 438 g. of a 410 Be sodium sili cate, having a silica SiO2 to NasO ratio of 3.25, and 100 g. of sodium aluminate solution containing 17.9 wt. percent Na2O and 22 wt. percent alumina. 132.5 g. of water was added to the mixture. The mixture was stir red vigorously and 193.3 g. of an alum solu tion [Al2(S04)3] containing 8.3 wt. percent of alumina was added to the mixture. The mixture was then heated at a temperature of 1000 C. After 9 hours the product was filtered, washed and evaluated.The analysis of the product was as follows: Na2O 12.8% SiO2 63.9% Al203 23.3% The silica to alumina ratio of the product was 4.65. The product had a surface area of 840 m2/g indicating a highly crystalline zeo lite, and the X-ray diffraction analysis showed an excellent pattern characteristic of zeolite Y.

EXAMPLE 3 This example illustrates the method of preparing a zeolite via a crystallisation mixture having the following ratio of reactants: 1.8 Na2O: Al2O3 :6 SiO2:100 H20.

In this preparation, 155 g. of the slurry of nucleation centres referred to in Example 2 (i.e. prepared as described in Example 1 but with a different molar ratio of Al2O, to the other components) were blended into 437 g.

of a 410 Bé sodium silicate having a silica to Na2O molar ratio of 3.25:1. 96 grams of a sodium aluminate solution containing 17.9 weight percent Na2O and 22 weight percent Awl203 were added slowly followed by the addition of 205 g. of an alum solution containing 28.06 weight percent Al2(SO4)3. After thoroughly mixing the slurry was aged for 16 hours at 1000 C. The product was cooled, filtered, washed and analysed. The analysis of the product was as follows: Na2O 12.6% Al2O3 22.2% SiO2 64.9% The product had a silica to alumina ratio of 4.96 and a nitrogen surface area of 820 m2/g.

The product had an X-ray diffraction pattern characteristic of a Y-type zeolite of high purity.

EXAMPLE 4 This example illustrates the method of preparing a faujasite via a crystallisation mixture having the composition: 1.6 Na2O: Al2O, :5.6 SiO,:100 H2O.

A slurry of nucleation centres was prepared using the general process of Example 1 to have the composition: 16 Na2O: 2 Awl203:15 SiO2: 500 1120. The slurry of nucleation centres (139 g.) was mixed with 544 g. of 410 Ba sodium silicate having a silica to sodium oxide ratio of 3.25 and 139 g. of sodium aluminate containing 18% Na2O and 22% alumina. A total of 190 g. of water was added. An alum solution was prepared to contain 8.4% Al2(SO4)3 and 240 g. of the solution was rapidly blended into the slurry.

The mixture was homogenized for a period of 15 minutes. The slurry was heated at 1000 C.

for 6 hours, filtered, washed and analysed. The product recovered was a high purity faujasitic zeolite having a silica to alumina ratio of 4.2 and a nitrogen surface area of 850 m2/g.

EXAMPLE 5 A slurry was prepared by mixing 185 g.

of the slurry of nucleation centres (as described in Example 1), 1083 g. of sodium silicate, having a Na2O to SiO2 ratio of 3.22, and 360 g of an aluminum sulphate solution containing 8.28% alumina. A sodium aluminate solution was prepared to contain 18.5% Na2O and 21% alumina and 269 g. of this solution in 369 g. of water was added to the slurry.

The resultant crystallisation mixture in slurry fonn had an oxide ratio of 1.9 Na,O: 1 Al,O,: 6 Six :100 H2O. It was heated at 1000 C. for 12 hours. The product had a surface area of 695 m2/g, a silica to alumina ratio of 4.6, and an X-ray pattern characteristic of zeolite Y.

EXAMPLE 6 In this example a slurry of nucleation centres was prepared using the process of Example 1 except that the amount of alumina trihydrate added was decreased from 104 g. to 78 g. The slurry after preparation set to a gel which was then diluted to a slurry containing 16 Na2O: 3 A1,0,:15 SiO2:640 H20. The slurry was readily pourable.

A slurry was prepared by mixing 246 g.

of the nucleation centres prepared as described above with 1069 g. of sodium silicate having a Na2O to SiO2 ratio of 3.22. A sodium aluminate solution was prepared to contain 18.5 /c Na2O and 21% alumina. This solution (264 g.) was added to the silicate and nucleation centre slurry mixture. Then 384 g. of aluminum sulphate solution containing 8.28% alumina in 318 g. of water was added.

The resultant crystallisation mixture having the following ratios of oxides: 1.9 Na,O: Awl203 :6 Six2: 100 H20 was heated at 1000C.

for 12 hours. The product recovered had a silica to alumina ratio of 4.4, a surface area of 797 m2/g, and an X-ray pattern characteristic of zeolite Y.

EXAMPLE 7 In this example a gel of nucleation centres was prepared using the process described in Example 1 except that the amount of alumina trihydrate added was decreased to 52 g. The product had the oxide ratio of 16 Na2O: 2 A1,0,:15 SiO2: 320 H2O. The nucleation centres were used to prepare a synthetic faujasite by adding the nucleation centres as a gel, without dilution, to a zeolite synthesis slurry. The slurry was prepared by mixing 32 g. of the nucleation centres which corresponds to 1.25 weight percent of the total slurry alumina, to 820 g. of sodium silicate having an Na2O to SiO2 ratio of 3.22.A sodium aluminate solution was prepared to contain 18A% Na2O and 20.3% Al2O,, and 224 g. of this solution was mixed with the sodium silicate.

An aluminum sulphate solution was pre pared to contain 8.37% alumina and 259 g. of this solution was added to the slurry along with 348 g. of water. The resultant crystallisation mixture slurry having an oxide ratio of 1.9 Na2O: Al2O3: 6 SiO2: 100 HZO was heated for 10 hours at 1000 C. The product recovered had a silica to alumina ratio of 4.1 a surface area 700 m2/g and gave an X-ray diffraction pattern characteristic of zeolite Y.

This example demonstrates that a relatively small amount of nucleation centres gives a good yield of the product.

EXAMPLE 8 This example illustrates the scale up of the process to a pilot plant.

A gel of nucleation centres was prepared to contain 16 NaY:1.2 Al2O3:15 Six2:320 H2O. This gel (6.8 lbs.) was blended with 18.9 lbs. of 410 Bé sodium silicate solution having an SiO2 to Na2O ratio of 3.22. This resultant slurry along with 0.6 U.S. gallon of water was added to a 6 U.S. gallon steam jacketed kettle equipped with a mixer. The mixture was blended and 4.6 Ibs. of sodium aluminate solution containing 18.4% Na2O and 24.3% Aloha was added with rapid mixing. After completion of the aluminate addition, 8.9 lbs. of aluminum sulphate solution containing 8.37% alumina was added with rapid mixing. The ratio of reactants of the resultant crystallisation mixture slurry was 1.9 Na2O : Al2O3 :6 SiO2:100 H2O. The slurry was heated to boiling, and the mixer was turned off 15 minutes after the slurry boiled.

After 13 hours of reaction at boiling temperature the product was recovered. The product had the following chemical composition: A1203 23.4% SiO2 63.7% Na2O 13.3% The product had a SiO2 to A1203 ratio of 4.62, a surface area of 772 m2/g and an ray pattern characteristic of zeolite Y.

EXAMPLE 9 This illustrates the use of a crystallisation mixture slurry of the oxide ratio 2.0 Na2O: 1 Auk0,:7 SiO2:110 H20 to synthesize an NaY zeolite. It was prepared by mixing 310 g. of a gel of nucleation centres (prepared as in Example 8), 1042 g. 410 Ba sodium silicate solution (Na2O: 3.22 SiO2 weight ratio), 186 g. sodium aluminate solution (18.5% Na2O; 21.0% Al2Os), 450 g.

aluminum sulphate solution (8.4% Alto,), and 272 g. water. The resultant crystallisation mixture was heated to 100+30C. for 12 hours.

The product was a well crystallized NaY faujasite having a nitrogen surface area of 843 m2/g and a unit cell size of 24.65, which corresponds to a SiO2/AI203 ratio of 5.1 on the scale established by D. W. Breck and E.

M. Flanigen (Molecular Sieves, Society of the Chemical Industry, 1968, pages 4760).

EXAMPLE 10 The more complete utilization of reactant chemicals and the lower effluent produced in our process over that taught in U.S. Patent 3,639,099 is illustrated as follows. In order to synthesize 464 g. (one mole) NaY faujasite (mole ratio Na2O : Al2O, :5 SiO2) from a synthesis slurry using the slurry oxide ratio of 3.0 Na2O:1.0 Al2O2 :9 SiO2:130 H20 (as taught by U.S. Patent 3,639,099), there must be produced an effluent which contains the following amounts of Na2O and SiO2.

Mole Oxides In Slurry Na2O Al20, SiO2 11,0 Synthesis Slurry 3.0 1.0 9.0 130 less NaY product 1.0 1.0 5.0 Effluent Oxides 2.0 - 4.0 Thus 2 moles of Na2O (124 g.) Na2O) as free alkali) and 4 moles of SiO2 (240 g.) appear in the effluent in order to synthesize 464 g. (one mole) of NaY.

In our improved process the effluent is greatly reduced, the quantity of effluent for the production of a one mole of NaY is as shown below (data based on Example 8).

Mole Oxides In Slurry Na2O Awl203 SiO2 H20 Synthesis Slurry 1.8 1.0 6.0 100 less NaY product 1.0 1.0 5.0 Effluent Oxides 0.8 - 1.0 Thus only 0.8 mole Na2O (50 g. Na2O as free alkali) and 1 mole SiO2 (60 g.) appear in the effluent in order to synthesize one mole (464 g.) of NaY. This shows that our process is more efficient in utilization of chemicals and in reduction of effluent from the synthesis of the Y type faujasite zeolite than earlier processes.

WHAT WE CLAIM IS: 1. A process for preparing a crystalline aluminosilicate having the faujasitic structure and a silica to alumina molar ratio of 2 to about 6 which comprises (a) preparing a gel or slurry of nucleation centres having a molar composition 12 to 19 Na2O:l to 10 Al203: 12 to 19 SiO2: 220 to 900 H20, (b) mixing said nucleation centres with a zeolite-synthesis mixture, and with aluminium sulphate to provide a crystallisation mixture having a molar composition (excluding the composition of the nucleation centres) within the range 1.2 to 3 Na2O:4 to 7 SiO2:Al2O3:40 to 200 H20), (c) heating the resultant mixture to a temperature and for a period of time sufficient to ensure crystallisation and (d) washing, drying and recovering the product.

2. A process according to claim 1, wherein the proportion of nucleation centres added in step (b) is 0.1 to 10 percent by weight of the zeolite synthesis mixture.

3. A process according to claim 1 or 2, in which in step (c) the mixture is heated at a temperature of about 1000C for 4 to 26 hours.

4. A process according to any preceding claim wherein the zeolite synthesis mixture is prepared as a slurry from a source of Nazi, a source of alumina other than aluminium sulphate, a source of silica and water.

5. A process according to claim 4, wherein the source of at least part of the silica content of the zeolite synthesis mixture is sodium silicate.

6. A process according to claim 4 or 5, wherein the source of alumina is sodium aluminate.

7. A process according to claim 5, wherein

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. A1203 23.4% SiO2 63.7% Na2O 13.3% The product had a SiO2 to A1203 ratio of 4.62, a surface area of 772 m2/g and an ray pattern characteristic of zeolite Y. EXAMPLE 9 This illustrates the use of a crystallisation mixture slurry of the oxide ratio 2.0 Na2O: 1 Auk0,:7 SiO2:110 H20 to synthesize an NaY zeolite. It was prepared by mixing 310 g. of a gel of nucleation centres (prepared as in Example 8), 1042 g. 410 Ba sodium silicate solution (Na2O: 3.22 SiO2 weight ratio), 186 g. sodium aluminate solution (18.5% Na2O; 21.0% Al2Os), 450 g. aluminum sulphate solution (8.4% Alto,), and 272 g. water. The resultant crystallisation mixture was heated to 100+30C. for 12 hours. The product was a well crystallized NaY faujasite having a nitrogen surface area of 843 m2/g and a unit cell size of 24.65, which corresponds to a SiO2/AI203 ratio of 5.1 on the scale established by D. W. Breck and E. M. Flanigen (Molecular Sieves, Society of the Chemical Industry, 1968, pages 4760). EXAMPLE 10 The more complete utilization of reactant chemicals and the lower effluent produced in our process over that taught in U.S. Patent 3,639,099 is illustrated as follows. In order to synthesize 464 g. (one mole) NaY faujasite (mole ratio Na2O : Al2O, :5 SiO2) from a synthesis slurry using the slurry oxide ratio of 3.0 Na2O:1.0 Al2O2 :9 SiO2:130 H20 (as taught by U.S. Patent 3,639,099), there must be produced an effluent which contains the following amounts of Na2O and SiO2. Mole Oxides In Slurry Na2O Al20, SiO2 11,0 Synthesis Slurry 3.0 1.0 9.0 130 less NaY product 1.0 1.0 5.0 Effluent Oxides 2.0 - 4.0 Thus 2 moles of Na2O (124 g.) Na2O) as free alkali) and 4 moles of SiO2 (240 g.) appear in the effluent in order to synthesize 464 g. (one mole) of NaY. In our improved process the effluent is greatly reduced, the quantity of effluent for the production of a one mole of NaY is as shown below (data based on Example 8). Mole Oxides In Slurry Na2O Awl203 SiO2 H20 Synthesis Slurry 1.8 1.0 6.0 100 less NaY product 1.0 1.0 5.0 Effluent Oxides 0.8 - 1.0 Thus only 0.8 mole Na2O (50 g. Na2O as free alkali) and 1 mole SiO2 (60 g.) appear in the effluent in order to synthesize one mole (464 g.) of NaY. This shows that our process is more efficient in utilization of chemicals and in reduction of effluent from the synthesis of the Y type faujasite zeolite than earlier processes. WHAT WE CLAIM IS:

1. A process for preparing a crystalline aluminosilicate having the faujasitic structure and a silica to alumina molar ratio of 2 to about 6 which comprises (a) preparing a gel or slurry of nucleation centres having a molar composition 12 to 19 Na2O:l to 10 Al203: 12 to 19 SiO2: 220 to 900 H20, (b) mixing said nucleation centres with a zeolite-synthesis mixture, and with aluminium sulphate to provide a crystallisation mixture having a molar composition (excluding the composition of the nucleation centres) within the range 1.2 to 3 Na2O:4 to 7 SiO2:Al2O3:40 to 200 H20), (c) heating the resultant mixture to a temperature and for a period of time sufficient to ensure crystallisation and (d) washing, drying and recovering the product.

7. A process according to claim 5, wherein

the zeolite synthesis mixture is prepared from sodium silicate and sodium aluminate, as the source of the Na2O content and a source also of silica and aluminum.

8. A process according to any preceding claim, wherein the proportions of ingredients employed provide a crystallisation mixture which had the following molar ratios of constituents: 1.6 to 2 Na2O: A1203: 5 to 6 Si02: 80 to 1501120.

9. A process according to any preceding claim, wherein the nucleation centres have the oxide molar ratio 12 to 19 Na20 :2 to 5 Al20,:12 to 19 SiO2.

10. A process according to any preceding claim, wherein the nucleation centres are prepared from sodium silicate or colloidal silicate, as the source of the silica content.

11. A process according to any preceding claim wherein the nucleation centres are prepared as a slurry obtained by diluting a gel.

12. A process according to claim 1, substantially as hereinbefore described in any one of Examples 2 to 9.

13. Zeolites of the faujasitic structure when produced by a method according to any preceding ciao