FIELD OF THE INVENTION
The present invention relates to a process for the preparation of thermally stable, high crystallite size faujasite type zeolite. The invention particularly related to a seeding composition having zero maturation time for the preparation of thermally stable, high crystallite size faujasite type zeolite
BACKGROUND OF THE INVENTION
Crystalline sodium aluminosilicate materials, which are able to distinguish molecules of slightly differing size and thus able to separate them from a mixture of gases are known as "molecular sieves" and quite often referred as "zeolites". In particular, crystalline material to be named as a "zeolite," needs to have at least one aluminum atom per unit cell, to offer catalytic activity. A number of synthetic crystalline zeolites have been prepared in the past for applications as catalysts for fluid catalytic cracking (FCC) and related operations. The most prominent and much exploited among them till date is zeolite Y. This type of zeolite with different derivatives such as NH4Y, REY, USY has been extensively used in FCC catalyst formulations.
Y Zeolite is a synthetic analog of naturally occurring zeolite named faujasite, with respect to structure. The detailed synthesis of Y zeolite from sodium aluminosilicate gels with and without aging having molar composition ratios OF H2O/Na2O: 40, Na2O/SiO2: 0.3 - 0.4, SiO2/Al2O3: 8-20 has been discussed in in Zeolite Molecular Sieves, John Wiley and Sons, D.W. Breck, 1974, pages 278-79. Further, the referred literature also refers to crystallization of zeolite Y associated with impurities such as A, X and P type of zeolites. Due to presence of impurities and unreasonably long crystallization time (50 to 144 hours), synthesis of Y type zeolite from above mentioned composition is not popular. Original synthesis procedures for Y type zeolite involves prolonged aging period followed by additional period for crystallization. In general, zeolites X and Y can be synthesized from a reaction mixture comprising soda, alumina and silica in aqueous media under alkaline conditions with crystallization time ranging from 50-144 hours. Aging of reaction mixture can reduce crystallization time to some extent. Precursor gel once prepared and heated to crystallization temperature, zeolite growth does not start instantaneously; rather it takes some time known as "induction period". Thus "Induction period" is defined as time required for providing

the conditions for "nuclei" formation. However, if analogous hydrated structure or seed is introduced to the precursor gel mixture, crystal growth occurs instantaneously over the seeds, bringing induction period to zero. Seeding not only nullify the induction period, it is an elegant technique for growing pure samples of any structure with control over crystal size at a much lower crystallization time. Seeds of zeolite X act as ideal structures for the growth of Y as both have similar structure, the only difference being silica to alumina ratio. Nuclei of zeolite X can be easily prepared at room temperature and on transferring it to a gel mixture with appropriate composition, nuclei of Y zeolite starts growing with higher silica to alumina ratio. In all the prior art processes and compositions, seed preparation technique is time consuming with maturing time varying from few hours to 24 hours. Crystallization can also be initiated by the application of organic molecules having appropriate size and geometry as templates.
US Patent No. 3,306,922 refers to synthesis of Y zeolite (Na-Y) employing quaternary ammonium ions such as tetramethy ammonium at 100 °C in 13 days. Such a process is economically not viable due to long crystallization period and additional cost involved due to template.
US Patent No. 3,433,589 refers to the synthesis of Y zeolite employing seed having following molar composition with maturing time of 24 hours at 23 °C; 1.45 Na2O : 1 A12O3: 16.3 SiO2 : 5.4 Na2SO4: 550 H2O.
US Patent No. 3,789,107 refers to a seeding composition having following molar composition for Y zeolite synthesis with aging for 24 hours at room temperature for maturity; 5-15 Na2O : 3-10 Na2SO4 : 1-4.0 A12O3 : 5-50 SiO2 : 50-500 H2O. US Patent No. 4,007,253 describes a process for the production of faujasite promoted by finely divided zeolite A.
US Patent No. 4,016,246 refers to a process for preparing faujasite zeolite employing colloidal silica as a silica source.
US Patent No. 4,166,099 and US Patent No 4,340,573 describe processes for the synthesis of faujasite type zeolite employing seed having composition; 16 Na2O : 1 A12O3 : 15 SiO2 : 400-2000 H2O with aging of seed between 2-16 hours at room temperature.
US Patent No. 4,175,059 elaborates a process for preparing a synthetic faujasite having a novel platelet-type crystalline shape with silica to alumina ratio above 2.2 by adding potassium ions to seeded faujasite synthesis slurry and heating to convert to the

synthetic faujasite. The said zeolite is crystallized employing seed mixture, aged to 16 hours having molar composition; 12-20 Na2O: 0.75 - 5 A12 O3: 14 - 19 SiO2: 100 -600 H2 O.
US Patent No. 4,228,137 relates to a process for an improvement in the production of zeolites, particularly of the faujasite type, employing clay based seeds derived from natural halloysite.
US Patent No. 4,340,573 relates to a seed composition of the following molar ratio; 16 Na2O: 2-9 A12O3: 15 SiO2: 500-2000 H2O.
In the above said invention, the seed is aged between 15 minutes to 96 hours at temperature between 20-80 °C.
US Patent No. 4,376,106 describes a process for producing Y-type zeolite with SiO2 /Al2Os ratio of at least 4 by employing washed gel of following molar composition as promoter; 0.993 Na2O: 1 A12O3: 3 SiO2: 78 H2O.
Preparation of this type of promoter for Y zeolite is labor intensive and time consuming. It may be seen from various examples cited therein that gel and reaction mixtures were required to be heated to 95 °C for 48 hours for obtaining Y zeolite.
US Patent No. 4,406,822 relates to a process for simultaneous production of combined X and A zeolite promoted by powdered seed of zeolite X.
US Patent No. 4,608,236 refers to the process for production of mature seed mixture obtained after aging of following molar composition for minimum of 24 hours; 9-15 Na2O: 1 A12O3: 12-18 SiO2: 180-300 H2O.
US Patent No. 4,631,262 refers to a process for enhancing of storage life of a clear solution of seeds having following molar ratios by addition of sodium silicate. The seed has been used for promoting crystallization of Y zeolite in porous microspheres of calcined clay; H2O/Na2O : 15-18, Na2O/Si02 : 0.9 - 1.1, SiO2/A12O3 : 15.5 - 19.
US Patent No.4,931,267 refers to the synthesis of faujasite like structure having silica to alumina ratio greater than 6, employing tetrapropyl ammonium and/or tetrabutyl ammonium and seed with the composition of 13.3 Na2O : 1A12O3 : 12.5 SiO2: 267 H2O.
US Patent No. 5,154,904 refers to a process for the preparation of synthetic faujasite employing seed having following composition, aged for the duration of 18-72

hours between 30-70 °C; 9-15 Na2O: 1A12O3: 9-15 SiO2: 140-260 H2O.
US Patent No. 6,284,218 refers to a process for the preparation of high crystallite size, faujasite type zeolite by employing a seeding mixture with following molar composition;
14.9 Na2O: 1A12O3: 14.38 SiO2: 319 H2O where the maturation time of about 23 hours is employed.
Further, the highest crystallite size reported therein is 1700 oA. A direct correlation between crystallite size and thermal stability of NaY zeolite has been established.
The relation between thermal stability and silica to alumina ratio of zeolite framework has been extensively discussed by Julius Scherzer ("Octane-Enhancing Zeolite FCC Catalysts", Marcel Dekker, 1990). The author has reported that thermal stability of zeolite increases with increase in silica to alumina ratio in zeolite framework. Various techniques such as thermal and hydrothermal treatment, chemical modification with EDTA and ammonium hexafluorosilicate have been described for the enhancement of silica to alumina ratio of Y zeolite framework. However, these techniques are hardware intensive and involve usage of hazardous chemicals.
From the prior art, it can be seen that thermally stable faujasite type zeolite with higher crystallite size can be synthesized by employing a combination of seed that require maturation high time and reaction mixture under conducive conditions of crystallization. Post synthesis zeolite modifications such as hydrothermal and chemical treatment that enhance thermal stability are hardware intensive and involve use of hazardous chemicals. Thus, there is a need to develop a process for the preparation of highly thermal stable faujasite type zeolite, which is simple and easy to adopt with lower processing time. The object of preparation of highly thermal stable faujasite zeolite can be realized by adopting a process described in the present invention.
Faujasite zeolite is a polycrystalline material, in which each single zeolite particle has collection of tiny single crystals, joined together with a common boundary named grain boundary. Grain boundaries are considered basically as structural defects, along which some atomic planes get terminated. At the line of termination, covalent bonds between atoms are strained. At this point, lattice atoms can be easily removed at high temperature in the presence of steam or acid, thus resulting in significant loss of crystallinity. Thus, longer the boundary length for a given unit volume of a zeolite

crystal, smaller the crystallite size and more fragile is the material for thermal/hydrothermal environment.
Defects such as stacking faults, screw defects, presence of impurity, and amorphous material in the zeolite are the major causes for their poor hydrothermal stability. Grain size or crystallite size has a direct correspondence to stacking faults. Grain size of a zeolite particle has been measured by employing the well-known Scherrer method. The grain (crystallite) size "L" of a crystal is related to half peak height width "B" in a X-ray powder diffraction pattern through a formula,
L =KX/Bcosq> where, K is Scherrer constant, A, is wave length of X-ray and 9 is angle of peak.
SUMMARY OF THE INVENTION
The present disclosure provides a process for the synthesis of faujasite type zeolite with lower crystallization time.
Further, present disclosure provides a seed composition that does not require maturing time and the reaction gel has low water and soda content.
Further, present disclosure provides a seed and reaction gel composition, application of which results in faujasite zeolite with improved physical properties such as higher crystallite size and thermal stability.
Further, present disclosure provides a process for the preparation of seed, reaction gel composition and subjecting seed gel mixture to crystallization to obtain faujasite type zeolite which is simple and easy to adopt for commercialization.
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present disclosure provides a process for preparing a synthetic faujasite zeolite with enhanced thermal stability and higher crystallite size, said process comprising;
a) blending water (HiO), a source of silica (SiC^), a source of alumina (AhOs) and Na2O, wherein F^OiNazO ranges from 10-40 moles, NaaCXSiOi ranges from 1-2.5 moles, and SiC^AhOs ranges from 1.9-5 moles to prepare a seed composition, wherein the preparation of the seed composition requires no maturation time;

b) blending water(H2O), a source of silica(SiO2), a source of alumina(Al2O3) and
Na2O, wherein H2O:Na2O ranges 30-45, Na2O:SiO2 ranges from 0.4-0.9 moles
and SiO2:Al2O3 ranges from 7-20 moles to prepare a reaction gel composition;
c) homogeneously blending the seed composition with reaction gel composition to
form a seed-reaction gel composition;
d) heating the seed- reaction gel composition to a temperature ranging from 95-
110°C for a time period ranging from 18-30 hours to obtain the synthetic faujasite
zeolite,
wherein the synthetic faujasite zeolite has a crystallite size ranging from 1950-2200°A.
An embodiment of the present disclosure relates to a source of silica is selected from a group consisting of alkaline/neutral grade sodium silicate, colloidal silica, silica gel, and precipitated silica.
Another embodiment of the present disclosure relates to a source of aluminum that is selected from a group consisting of aluminum sulfate, sodium aluminate, aluminum acetate, aluminum formate, bayrite, pseudoboehmite, alumina gel and alumina sol.
Yet another embodiment of the present disclosure relates to a preparation of the seed composition requires heating the source of silica (SiO2) to temperature ranging from 20-80 oC.
Still another embodiment of the present disclosure relates to the process of preparation of the seed composition that requires heating the source of alumina (A12O3) to the temperature ranging from 30-100oC.
Another embodiment of the present disclosure relates to the seed composition ranging from 0.5- 20 wt % that is added to the reaction gel composition.
An embodiment of the present disclosure relates to the seed composition where the synthetic faujasite zeolite having crystallinity ranging from 95-98%.
Another embodiment of the present disclosure relates to synthetic faujasite zeolite that has thermal stability to a temperature of 950°C.
An embodiment of the present disclosure relates to the process for the preparation of high crystallite size synthetic faujasite zeolite, employing a seeding

composition having following molar oxide ratio for constituents; namely H2O/Na2O : 10-40,Na2O/SiO2 : 1-2.5, SiO2/A12O3 : 1.9-5.
The seed composition was reacted with another reaction gel composition with following molar oxide ratio for constituents; H2O/Na2O: 20-45, Na2O/SiO2: 0.4-0.9, SiO2/A12O3: 6-15.
Further, the seed and gel mixture was subjected to crystallization from time range of 18-30 hours, with temperature range 100 + 5 oC. Crystallized products have been recovered by filtration, washed and dried.
The present disclosure provides to a process for the preparation of high crystallite size zeolite that involves usage of seed with zero maturing time. Further, the reaction gel has low water and soda content.
Another embodiment of the invention provides a seed composition with zero maturation time for preparing a synthetic faujasite zeolite having thermal stability to a temperature of 950°C and crystallinity ranging from 95-98% comprising
a. water (H2O),
b. a source of silica (SiO2),
c. a source of alumina (AlaOs) and
d. Na2O,
wherein H2O:Na2O ranges from 10-40 moles, NajOtSiOi ranges from 1-2.5 moles, and SiOziA^Os ranges from 1.9-5 moles.
A process for producing a seed composition with zero maturation time for preparing a synthetic faujasite zeolite having thermal stability to a temperature of 950°C and crystallinity ranging from 95-98% comprising blending water (F^O), a source of silica (SiCh), a source of alumina (AloC^) and Na2O, wherein H2O:Na2O ranges from 10-40 moles, Na2O:SiO2 ranges from 1-2.5 moles, and SiOiiAbOa ranges from 1.9-5 moles.
Further, the present disclosure provides a process for improving "crystallite size" thereby enhancing thermal stability of the faujasite zeolite.
The present disclosure provides a process for the preparation of a seed composition which can be instantly employed for the crystallization of faujasite type zeolite. The application of seed composition of the present disclosure to another gel

reaction composition followed by heating of the seed gel mixture results in a crystalline synthetic faujasite having higher crystallite size, thermal stability and product being free of any extraneous impurities.
The present disclosure provides a process for the crystallization of high crystallite size synthetic faujasite that involves preparation of a seeding composition which can be instantaneously employed as a mature seed to enhance step crystallization of the faujasite zeolite.
The present disclosure provides a seed and gel composition prepared by sourcing silica from alkaline/neutral grade alkaline/neutral grade sodium silicate, colloidal silica, silica gel, precipitated silica. Aluminum can be sourced from aluminum sulfate, sodium aluminate, aluminum acetate, aluminum formate, bayrite, pseudoboehmite, alumina gel or alumina sol.
The present disclosure provides a seed composition that requires no maturation time, where the seed composition is prepared by heating a source of silica to a temperature between 20-80 °C and to this hot solution of a source of alumina maintained in the temperature range 30-100 °C is added with constant stirring. The addition of source of aluminum is carried out from 10 minutes to 2 hours. The high crystallite size faujasite type zeolite is prepared by mixing 0.5-20 wt% of seed composition into another gel reaction composition, having controlled soda and water content followed by subjecting the seed gel mixture to a step of crystallization for duration 18-30 hours.
The present disclosure provides working examples which are given by way of illustration and should not be construed to limit the scope of Ihe disclosure.
EXAMPLES EXAMPLE 1: Preparing Seed composition
The example illustrates the process of preparing mature seed composition which can act as instant nucleation centers.
99 gm of sodium silicate (16.0% Na2O, 34.60% SiO2, 49.4% H2O) was diluted with 150 gm of demineralised (DM) water and heated to 80 °C. To this, 130 gm solution of sodium aluminate (25% Na2O, 11.2% A12O3, 63.8% H2O) maintained at temperature 80 °C, was added drop wise in 30 minutes with stirring, for obtaining

mature seed solution with composition expressed in moles as; 5.11 Na2O : 1 A12C>3 : 3.74SiO2: 102H2O.
EXAMPLE 2
Preparation of high crystallite size faujasite type zeolite
1143 gm of sodium silicate (16.0% Na2O, 34.60% SiO2, 49.1% H2O) was diluted with 288 gm of DM water. To this, sodium hydroxide solution prepared by dissolving 81 gm sodium hydroxide pellets (77.5% Na2O, 22.5% H2O) in 252 gm of DM water was added under stirring. A solution containing 399 gm hydrated aluminum sulfate [A12(SO4)3, 16 H2O (16.17% A12O3)] dissolved in 792 gm of DM water was added drop wise to the sodium silicate-alkali solution with constant stirring to obtain a thick gel. The thick gel was divided into three equal parts and each part was added with 2 wt%, 4 wt% and 6 wt% of seed, weight based on volatile free basis of batch size and stirred for five minutes. Batches containing 2 wt%, 4 wt% and 6 wt% of seed were respectively designated as 2(a), 2(b) and 2(c). Seed- reaction gel composition was held at 100 + 2 °C, for 23 hours in a boiling water bath, while contents were stirred once in three hours. Crystallized products were filtered out. The zeolite cake was washed with boiling DM water till the pH of the filtrate came down to 9, and then dried at 110°C for 16 hours to obtain dry products having 12 wt% moisture. Thus oven dried products were characterized for surface area, X-ray crystallinity with unit cell size, crystallite size and thermal stability and the results of analysis are shown below.
Physico-chemical properties of synthetic faujasite zeolites prepared employing instant seed composition.

(Table Remove)
EXAMPLE 3:
Preparation of high crystallite size faujasite type zeolite with reaction gel composition having composition expressed as moles as, 6.26 Na2O: 1A12O3*. 10.34 SiO2: 1.01 SO4: 140.7 H2O
381 gm of sodium silicate (16.0% Na2O, 34.60% SiO2, 49.1% H2O) was diluted with 96 gm of DM water. To this, sodium hydroxide solution prepared by dissolving 27 gm sodium hydroxide pellets (77.5% Na2O, 22.5% H2O) in 50 gm of DM water was added under stirring. A solution containing 133 gm hydrated aluminum sulfate [A12(SO4)3, 16 H2O (16.17% A12O3)] dissolved in 133 gm of DM water was added drop wise to the sodium silicate-alkali solution with constant stirring to obtain a thick gel. To the thick gel 48 gm of freshly prepared seed as per example of present invention was added under stirring. Seed-reaction gel composition was held at 100 + 2°C, for 23 hours in a boiling water bath, while contents were stirred once in three hours. Crystallized product was filtered out. The zeolite cake was washed with boiling DM water till the pH of the filtrate came down to 9, and then dried at 110°C for 16 hours to obtain a dry products having 12 wt% moisture. Thus oven-dried product was characterized by different techniques. Surface area of the product was measured as 680 m2/gm; crystallinity was measured as 92% with unit cell 24.67 °A. Crystallite size was measured as 2030°A. DTA analysis of sample showed crystallinity loss at 925 °C.
EXAMPLE 4
Preparation of high crystallite size faujasite type zeolite with reaction gel composition having composition expressed as moles as, 5.54 Na2O: lAl2Oa: 10.34 SiO2:l.01 SO4: 135.4 H2O
381 gm of sodium silicate (16.0% Na2O, 34.60% SiO2, 49.1% H2O) was diluted with 96 gm of DM water. To this, sodium hydroxide solution prepared by dissolving 15 gm sodium hydroxide pellets (77.5% Na2O, 22.5% H2O) in 30 gm of DM water was added under stirring. A solution containing 133 gm hydrated aluminum sulfate [A12(SO4)3, 16 H2O (16.17% A12O3)] dissolved in 133 gm of DM water was added drop wise to the sodium silicate-alkali solution with constant stirring to obtain a thick gel. To the thick gel 48 gm of freshly prepared seed as per example of present invention was added under stirring. Seed-reaction gel composition was subjected to crystallization with conditions similar to that under example 3 and synthetic product was characterized.
Surface area of the product was measured as 685 m2/gm; crystallinity was measured as 92% with unit cell 24.66°'A. Crystallite size was measured as 2050°A. DTA analysis of sample showed crystallinity loss at 935 °C.
EXAMPLE 5: Product employing seed prepared as per U.S. Pat. No.6, 284,218 with and without maturing
Experiment of example under 2(b), was repeated except for in place of seed under example 1 of present invention was replaced with seed prepared as per US Patent No. 6,284,218. Crystallized product was designated as 5(a). Another product designated as 5(b) was prepared by employing seed prepared as per U.S Patent. No. 6, 284,218 without aging (aging time zero hours). A third product designated as 5(c) was prepared with a procedure exactly similar to that explained under example 2 of U.S Patent 6,284,218. The characterization results of the products are shown below under table 2.
(Table Remove)

From the results of characterization, it can be concluded that seed prepared as per U.S. Pat. No.6, 284,218 needs maturing time without which seed cannot promote crystallization of faujasite type crystalline phase. Further, faujasite type zeolite prepared as per referred example has lower crystallite size 1700A, inferior thermal stability of 875°C, in comparison to stability between 905-940°C, for a zeolite prepared as per process of present invention.

We claim:
1. A process for preparing a synthetic faujasite zeolite with enhanced thermal
stability and higher crystallite size, said process comprising;
a) blending water (H2O), a source of silica (SiO2), a source of alumina (Al2O3)
and Na2O, wherein H2O:Na2O ranges from 10-40 moles, Na2O:SiO2ranges
from 1-2.5 moles, and SiO2 :Al2 O3 ranges1.9-5 moles to prepare a seed
composition, wherein the preparation of the seed composition requires no
maturation time;
b) blending water(H2O), a source of silica(SiO2), a source of alumina(Al2O3)
and Na2O, wherein H2O:Na2O ranges 30-45 moles, Na2O:SiO2 ranges from
0.4-0.9 moles and SiO2 :Al2O3 ranges from 7-20 moles to prepare a reaction
gel composition;
c) homogeneously blending the seed composition with reaction gel composition
to form a seed-reaction gel composition; and
d) heating the seed- reaction gel composition to a temperature ranging from 95-
110°C for a time period ranging from 18-30 hours to obtain the synthetic
faujasite zeolite, wherein the synthetic faujasite zeolite has a crystallite size
ranging from 1950- 2200°A.

2. The process as claimed in claim 1, wherein the source of silica is selected from a
group consisting of alkaline/neutral grade sodium silicate, colloidal silica, silica
gel, and precipitated silica.
3. The process as claimed in claim 1, wherein the source of aluminum is selected
from a group consisting of aluminum sulfate, sodium aluminate, aluminum
acetate, aluminum formate, bayrite, pseudoboehmite, alumina gel and alumina
sol.
4. The process as claimed in claim 1, wherein the preparation of the seed
composition requires heating the source of silica (SiO2) to temperature ranging
from 20-80 °C.
5. The process as claimed in claim 1, wherein the preparation of the seed
composition requires heating the source of alumina (Al2O3) to the temperature
ranging from 3 0-100°C.
6. The process as claimed in claim 1, wherein the seed composition ranging from 0.5-
20 wt % is added to the reaction gel composition.

7. The process as claimed in claim 1, wherein the synthetic faujasite zeolite having
crystallinity ranging from 95-98%.
8. The process as claimed in claim 1, wherein the synthetic faujasite zeolite having
thermal stability to a temperature of 950°C.
9. A seed composition with zero maturation time for preparing a synthetic faujasite
zeolite having thermal stability to a temperature of 950°C and crystallinity ranging
from 95-98% comprising
a. water (H2O),
b. a source of silica (SiO2),
c. a source of alumina (Al2O3), and
d. Na2O,
wherein H2O:Na2O ranges from 10-40 moles, Na2O:SiO2 ranges from 1-2.5 moles, and SiO2 :Al2O3ranges from 1.9-5 moles.
10. A process for producing a seed composition with zero maturation time for preparing
a synthetic faujasite zeolite having thermal stability to a temperature of 950°C and
crystallinity ranging from 95-98% comprising blending water (H2O), a source of
silica (SiO2), a source of alumina (Al2O3) and Na2O, wherein H2O:Na2O ranges
from 10-40 moles, Na2O:.SiO2 ranges from 1-2.5 moles, and SiO2:Al2O3 ranges
from 1.9-5 moles.