GB2339774A - Synthesis of faujasite y-type zeolite from fly ash - Google Patents

Description

2339774 PROCESS FOR THE PRODUCTION OF FLYASH BASED ZEOLITE Y (FAZ-Y)

FEELD OF U14VENTION

This invention relates to a process for the production of flyash based Zeofite-Y (FAZ-Y). More particularly, this invention relates to siliceous Y type flyasb based zeolite with improved characteristics for specific apoplications as catalyst catalyst carriers or in automotive exhaust and de-NO,, catalyst. A substitute for conventional raw materials viz. Sodium silicate and aluminate results in cost effective production of Zeolite-Y with concomitant resolution of flyash disposal problem by way of recovery of high value added product.

The present invention, 'in general, relates to the production of synthetic adsorbent materials. More particularly, it relates to crystalline microporous, aluminosilicate compositions and to the hydrothermal process for preparing the same. Specifically, it relates to a process for the synthesis of highly crystalline, porous, sodium Yzeolite compositions having a Si02 /AI203 ratio varying from 2.0-4.0.

BACKGROUND OF THE RWENTION

Molecular sieves of the crystalline zeolite type are well known in the art and now comprise over 250 species of both naturally occuring and synthetic compositions. In genral, crystalline zeolites are aluminosilicates whose frameworks are formed from A104 and SiO4 tetrahedra joined by the oxygen atoms and characterized by 1 the pore openings of uniform dimensions, having significant ion-exchange capacity and being capable of reversibly desorbing an adsorbed phase which is dispersed through the internal voids of the crystal, without displacing any atoms which make up the permanent crystal structure.

Zeolite-Y is isostructural with the mineral faujasite and Zeolite-X, an aluminum rich variant of Zeolite-Y. It contains large, near'spherical cages with a free diameter of 1.3 mu. Each supercage is connected tetrahedrally liffi four neighbouring supercages via 12-membered ring windows with a crystallographic diameter of 0.74 mn. For most molecules except very bulky ones, Zeolite-Y offers a spacious cage and pore system through which they can diff-use with out hindrance. The general chemical formula of the synthetically produced, anhydrous, large pore, Zeolite-Y expressed in terms of moles may be as follows: 1.0 0.2 Na2O:AI203:nSiO2; wherein W has values from 3 to 7. These are commercially more useful as adsorbents a they have proven to be more stable at high temperature in the presence of moisture than Zeolite -X; this may be attributed to their high silica /alumina ratio.

Zeolite-Y have multifacet applications and are being best employed as catalyst in vapour phase cracking of petroleum (Weitkemp), J., Ernst S., in Chemicals in the oil industry: development and application (Ed.P.H. ogden), Royal Society of Chemistry, Cambridge, 1991), Fluid Catalytic Cracking ( Biwaaaas, J., and Maxwell, I.E., AppI.Catal, 1990 (63), 197), isornerisation of light gasoline (Maxwell, E.G. Catalysis today, 1987 (1), 385) and hydrocracking of vacuum gas oil (Ward, J.W. in 'Preparation of Catalysts' (Eds: G. Poncelet, P. Gronge and P.A.Jacobs) Studies in surface. Science and Catalysis, Elsevier, Amsterdam 2 oxford, New York< 1983 (1) 587). Treatment of wastewater with zeolite specifically with zeolite-Y are increasing world-wide; work in progress seeks to extend the use of zeolites for removal of isotopes (Dyer. A., Chem Ind., 1984, 241-245); long term disposal techniques and composites. Nevertheless, the development of material with interesting electrical, mechanical or other properties from zeolites has not often been reported in literature.

PRIOR ART REFERENCES

There are several processes available in the market for the synthesis of. Zeolite-Y. Dyer et al. has described a process for the production of zeolites, which process comprises the following steps: reactive starting materials viz; sodium silicate and aluminate taken either as freshly prepared gels or amorphous solids. relatively high pH, obtained by using an alkali metal hydroxide and or organic base. either low temperature hydrothermal conditions at atmospheric ( or low autogenous) pressures or high temperature hydrothermal conditions (where temperature is less than 3000C) are employed. a high degree of supersaturation of the components in gel phase leading to the nucleation of a large number of crystals. crystallisation time taken ranges from a few hours to several days.

However, the said and other available methods suffer from various disadvantages. The said processes cause sintering of particles and the time consumed for crystallisation of FAZ-Y is significantly long.

3 I I I; OBJECTS OF THE PRESENT INVENTION As such, in order to overcome the said drawbacks in the said prior art processes, the applicants have developed the present novel process for the synthesis of Zeolite-Y from flyash. The main object of the invention is to use flyash as a raw material for production of zeolites. This provides an inexpensive alternate to commercially available zeolites ( as the process involves replacement of conventional aluminum trihydrate and silicate with flyash) with conconitiant resolution of flyash disposal problem.

It is an object of the present invention to provide a process for the synthesis of flyash based Zeolite-Y wherein the fusion step is modified so as to result in the formation of sodium silicate and sodium aluminate, thereby ascertaining the probability of formation of zeolitic, phases with high purity.

Another object of the invention is to provide a process wherein the fusion mixture is given proper mechanical treatment (grinding and mixing) so as to ensure complete fusion, and effective extraction of alumina / silicate from flyash. with formation of homogenous alumino-silicate gel.

It is yet another object of the present invention to provide a process for the synthesis of flyash based Zeolite-Y wherein the hydrothermal conditions employed result in the exclusive crystallisation of Zeolite-Y.

DETAELED DESCRI[PTION OF THE FqWNTION To meet the above objects, the present invention provides a novel process for the synthesis of flyash based Zeolite-Y, comprising the following steps 4 (a) forming a fine homogenous fusion mixture of flyash or pre-treated flyash with caustic soda in a weight ratio of 1:0.4 to 1:1.2, (b) heating the said fusion mixture in an inert atmosphere at about 500-6000C for about 1-2 hours to obtain a fused mass, (c) cooling, milling, and mixing of the said fused mass in distilled water for about 8-12 hours, (d) subjecting the said slurry to hydrothermal crystallisation at about 907-1100C for 8 to 12 hours to obtain FAZ-Y crystals, and (e) washing the said crystals with water and then subjecting the washed crystals to oven drying at 50-GOOC to obtain the desired FAZ-Y crystals.

Preferably, the fine homogenous fusion mixture in step (a) is formed by grinding and mixing the ingredients.

According to the present invention, the source of S'02 and A1203 used in the process described is flyash only.

In an embodiment of the invention, the flyash used is fused with solid sodium hydroxide.

In another embodiment, alum is added to flyash in flyash alum ratio of 5:1 in the mixing stage in step 1 (c) to improve the S'02/A'203 ratio.

In yet another feature of the invention, a pre treated flyash may optionally be used and in that case, the pre-treatment flyash can be prepared by treating flyash directly with a mineral acid in flyash: mineral acid ratio of 0.25:1.

In another embodiment, flyash is directly treated I - O& - - with acids in flyash: acid ratio of 0.25: 1.0 prior to the fusion step to improve the silicaalumina ratio of FAZ-Y.

The invention also provides a process for preparing silica enriched FAZ-Y which further comprises of the following steps:

- treating Na-FAZ-Y with calcium solution to obtain Ca-FAZ-Y; - treating Ca-AZ-Y with ethylene diamine tetracetic acid to obtain chelated FAZ-Y product.

- refluxing for 8-10 hours to obtain dealurninated FAZ-Y; - washing and drying the product.

Still, another feature of the invention is a process for synthesis of FZY wherein the Zeolite-Y synthesised has the following characteristics% calcium binding capacity upto 420 meq / 100g.

- average particle size (d.50) of less than 6 minons.

- crystallinity of about 90-95 - cubic crystal structure.

- specific surface area of about 550 m1/9- BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:

In the accompanying drawings:

Figure I shows that morphologically flyash is made up mainly of cenospheres and pleurospheres and is mostly amorphous.

Figure 2 shows the morphology of zeolite crystals cleariy illus=es the transformation of amorphous flyash into crystalline material.

In the present invention, FAZ-Y is synthesised by fusing flyash (20g) with sodium hydroxide (8-24g). A homogenous fusion mixture is prepared by proper grinding, and mixing of flyash and alkali in a ratio of about 1: 1 -2. This mixture is heated to 6 at least about 500'C preferably between 550-600'C for about 1-2 hours to obtain the fused mass. The resultant fused mass is cooled to room temperature, milled again and then stirred vigorously in water for 8-10 hours to obtain amorphous alumino-silicate get. This solid alumino- silicate gel is then subjected to crystallisation at 90-1 10'C for 8-12 hours to obtain FAZ-Y crystals. The solid crystalline product is then recovered by filtration, washed with water and dried at temperature of about 50-60T.

The quantitative extraction Of Si02 and A1203 from flyash is dependeq on the amount of sodium hydroxide in the reaction system and is evident from the results presented in table 6. The residual amount of sodium hydroxide not consumed in the extraction Of Si02 and A1203 from flyash is useful in maintaining the high alkaline pH of the reaction system, a necessary prerequisite.

The effect of fusion temperature on zeolite formation is quite predominant and is presented in Table 4. No zeolite formation was obserived at fusion temperature of 2000C indicating that extraction of silicates and aluminates was neglible. Formation of zeolitic phases with maximum crystallinity was observed at 500600C. At higher temperature, the crystallinity gradually decreased and may be attributed to sintering of flyash to form non-crystalline glassy mass.

Insufficient concentration of alkali as observed for NaOI-1/flyash ratio of 0.4, leads to lower extraction efficiency of NaOH for Si02 and A1203 from flyash and also adversely effects the crystallisation process. Increase in A1203 content of reaction mixture by addition of 1.65 g of sodium aluminate leads to transformation of zeolite-Y to zeolite-X. With further increase in A1203 content ( by addition of sodium aluminate upt6 8g) zeolite -X transforms into zeolite-A.

7 q The ratio of flyash to caustic soda employ in the present invention is important. If any additional alumina such as, sodium aluminate or aluminiurn hydroxide is added to the mixture, such addition shifts the equilabrium of the present process from the formation of Zeolite-Y to Zeolite-A. Further, the temperature and the time ranges of the hydrothermal crystallisation are also critical to the present invention.

"Me effect of addition of sodium chloride and seeding to improve Si02 and A1203 has also been evaluated. Enrichment Of Si02 content of flyash through its direct acid treatment has been explored. Improvement of SiO2 content in zeolite by way of addition of alum in mixing stage to increase incorporation Of Si02 in zeolite matrix has also been evaluated. 1he addition of alum in the mixing step decreases the pH of the reaction system, thus decreasing the solubility Of Si02 in the system.

The alumino- silicate compound obtained after fusion is amorphous and changes to crystalline state when subjected to hydrothermal crystallisation.. A close scrutiny of the results presented in table 8 reveals that crystallisation time influences the zeolitic crystallinity significantly. Percent crystallinity of zeolite-Y increases significantly upto 10 hrs. and remains constant beyond that.

Calcium Binding Capacitv The Calcium Binding Capacity (CBC) of alumino-silicates is determined as follows:

1 liter of aqueous solution containing 0.5 of CaC12 and adjusted to a pH of 9-10 with dilute NaOH, is mixed with I g of alurnino-silicate (FAZ-Y). The suspension is then stirred vigorously for 15 minutes at room temperature (29-300C). After filtration, the residual hardness of the filtrate is determined. From the difference between hardness of the original solution and filtrate the CBC is calculated as 8 to meq/100 g. The FAZ-Y samples were dissolved in HN03 and analyzed by ICPAES (Model: YJ 24) for A1203 while Si02 was estimated using instrumental / conventional method Na20 is estimated using flame photometer (Mediflame - 127 with FPM compressor unit 122). The trend observed for CBC as ftinction of fusion temperature is similar. The CBC value (140 meq / 100g) is quite low at 200'C while significant increase in CBC at 600'C (420 meq / 100g) was recorded. Beyond a temperature of 600C there was decrease in CBC value (380 meq 100g).

In terms of CBC it can be said that it increases upto NaOH / flyash ratio 1.2; remains constant at NaOH / flyash ratio of 1.6, and starts decreasing with further, increase in alkali content and may be attributed to formation of undesirable product viz sodalite. The extact reason(s) for these mechanisms remain to be investigated.

The surface morphology of the zeolite has been examined by Jeol-840-A scanning electron microscope (SEM) wherein Powder XRD analysis was employed to monitor zeolite formation process, using CuKa as source of Xrays (Model: Philips PN-1830). D-spacing values reported (in A') JCPDS file (38-238) for zeolite-Y were used as standard for comparison. Specific surface area was determined using Micro-meretics-ASAP-200 analyser.

In the drawings, which are in the form of photographs, photograph 1 depicts that morphologically flyash is made up mainly of cenospheres and pleurospheres and is mostly amorphous. Photograph 2 depicts the morphology of zeolite crystals and clearly illustrates the transformation of amorphous flyash into crystalline material.

9 The chemical composition of flyash is detailed in Table 1. Table 1 Chemical composition of Flyash Component % weight (dry basis) Si02 61.63 A1203 25.75 Fe203 5.96 CaO 3.07 MgO 2.01 MnA 0.15 Sulphites Nil Na2O '0. 15 K20 0.17 Comparative analysis of FAZ-Y sample synthesised at optimal conditions and commercially available Zeolite-Y is provided in Table 2. It is evident from the results that the synthesised FAZ-Y matches quite well with the commercially procured zeolite sample. The estimated cost of production is considerably less than the commercial Zeolite-Y due to use of flyash as a source of silica and alumina.

- 10 Table 2

Comparative characteristics of FAZ-Y and commercial Zeolite-Y S.No. Characteristics Zeolite-Y Synthesized Commercial Surface area 500-550 550-600 2. Exchange capacity 340-420 420 (meq/100g) 3. Average particle size 4-5 8-10 (00) (micron) 4. Crystal structure Cubic Cubic 5. SiO2/Al203 2.0-4.0 2.0-2.5 The following examples illustrate the influence of different parameters viz. fusion temperature, NaOIVflyash ratio, crystallisation timettemperature but does not restrict the scope of the present invention. These examples also suggest the best mode of carrying out the invention.

Example I

Preweighed sample of flyash (20g) and sodium hydroxide (24 g) were properly grinded milled and mixed to obtain a homqses fusion mixture, and placed in a vessel ftiert towards the reaction mixture and heated to about 500-6000C for 1-2 hrs. The fused mass was cooled, milled and mixed thoroughly with distilled water for 8-10 hrs. The amorphous aluminosificate gel was then subjected to crystallisation for 8-12 hrs at about 90- 1 100C. The solid crystalline product was recovered by filtration, washed with water and oven dried at 50-WC. The CBC and surface area of FAZ-Y is 420 meq/100g and 500-550m/g respectively. The SiO2/Al203 ratio is around 2.0. d-spacing values (in A) reported for Zeolite-Y in JCPDS file (38-238) are 14.30, 8.75, 7.46, 5.68, 4.76, 4.38, 3.77, 2.85 and 2.63. It compares well with FAZ-Y and are as follows:

Table 3 d-spacing values obtained for FAZ-Y (Example I/ Sample 1) d-spacing Relative intensity (A) FAZ-Y FAZ-Y Example I Example I Sunple I Sample I 14.15 96.7 8.73 27.2 7.46 20.7 5.69 42.7 4.78 12.6 4.39 24.8 3.79 81.4 2.87 100,0 2.65 42.6 Example 2

The same process as mentioned in example I was repeated except for the variation in Rision temperature. The reaction conditions pertaining to these examples are presented in Table 4 alongwith the CBC values and SiWA1203 ratios.

12 Table 4

Variation of reaction conditions and Characteristics of FAZ-Y S. Fusion temp. NaOH Flyash CrjstaUisation CBC SiO2/ No. CC) (9) (9) timeltemp (meq/ A12% 100g) 1. 200 24 20 10/100 140 2.4 600 24 20 10/100 420 2.0.

800 24 20 10/100 380 1.6 FAZ-Y synthesised at fusion temperature of 200, 600 and 8000C were designated as FAZ-YI, FAZ-Y2 and FAZ-Y3. d-spacing values (in A") reported for Zeolite-Y in JCPDS file (38-238) are 14.30, 8.75, 7.46, 5.68, 4.76, 4.38, 3.77, 2.85 and 2.63. It compares well with FAZ-Y2 and FAZ-Y3 and are as follows:

13 Aw- Table 5 d-spacing values obtained for FAZ-VI-FAZ-Y3 (Exam ple2/Sample 1-3) d-spacing Relative intensity W) (0/0) FAZ-YI FAZ-Y2 FAZ-Y3 FAZ-YI FAZ-Y2 FAZ-Y3 Example 2 Example 2 Samplel Sample2 Sample3 Samplel Sample2 Sample3 13.82 14.15 14.0 38.4 96.7 83.5 8.63 8.73 8.67 11.4 27.2 25.9' 7.39 7.46 7.42 13.8 20.7 21.5 5.64 5.69 5.66 33.3 42.7 45.9 4.74 4.78 4.76 14.77 12.6 12.6 4.36 4.39 4.37 24.7 24.8 24.9 3.77 3.79 3.78 72.9 81.4 83.1 2.86 2.87 2.86 100.0 100.0 100.0 2.64 2.65 2.64 38.9 42.6 39.4 Example 3

The same process as mentioned in example I was repeated except for the variation in NaOfUflyash ratio. FAZ-Y was syntix-sised at different NaOH/flyash ratios of 0.4, 0.8, 1.2, 1.6 and 2.0; the samples so obtained were designated as FAZ-Y4, FAZ- Y5, FAZ-Y6, FAZ-Y7 and FAZ-Y8.

The CBC and SiO2/AI203 ratio obtained for FAZ-Y4, FAZ-Y5, FAZ-Y6, FAZ-Y7 and FAZ-Y8 are presented in Table 6.

14- Table 6

Variation of reaction conditions and characteristics of FAZ-Y S. Fusion temp. NaOH Flyash Crystallisation CBC SiO2/A1203 No. (1,C) (9) (9) timettemp (meq/100g) Ratio (hrs/OC) 1. 550 8 20 10/100 160 2.4 2. 550 16 20 10/100 260 2.2 3. 550 24 20 10/100 420 2.0 4. 550 32 20 10/100 340 1.6 5. 550 40 20 10/100 240 0.86 d-spacing values (Table 7) obtained for FAZ-Y6 compare well with the zeolite-Y reported in JCPDS file (38-238); whereas it differs significantly for FAZ-Y7 and FAZ-Y8. XRD patterns for FAZ-Y4 and FAZ-Y5 indicate thew amorphous nature. The XRD patterns for FAZ-Y7 and FAZ-Y8 match closely with that for sodalite, hydrate (Sidheswaran, P., Bhat, N, A, Indian Journal of Chemistry, 1995 (34A), 800).

Table 7 d-spacing values obtained for FAZ-Y4-FAZ-YS (Example 3/Sample 1-5) d-spacing kelative intensity (AO) FAZ-Y4 FAZ-Y5 FAZ-Y6 FAZ-Y7 FAZ-Y8 FAZ-Y4 FAZ-Y5 FAZ-Y6 FAZ-Y7 FAZ-Y8 Example 3 Example 3 samplel sample2 sample3 sample,4 sample5 samplel sample2 sample3 sample4 sample5 14.15 13.21 96.7 - 21.1 - 8.73 - 27.2 - - 7.44 7.46 18.3 20.7 - - 5.69 - 42.7 - 4.78 4.86 - 12.6 2.6 - 4.39 - - 24.8 - - 3.79 3.75 - 81.4 3.7 - 2.85 2.87 2.95 2.82 4.7 - 100.0 15.9 35.4 2.63 - 2.65 2.57 2.0 - 42.6 61.5 Example 4

The swne process as mentioned m example I was repeated except for the variation m crystallwhon tune The reaction conditions pettaining to these examples are presented in Table 8 alongwith the CDC values and SiO2/AlA ratios.

16 Table 8

Variation of reaction condition and characteristics of FAZ-Y S. Fusion temp. NaOH Flyash Crystallisation CBC SiO2/ No. (OC) (9) (9) time/temp (meq/100g) A1203 WC) 1 550 24 20 0/100 160 1.8 2. 550 24 20 2/100 240 1.9 3. 550 24 20 4/100 200 1.9.

4. 550 24 20 8/100 380 1.9 5. 550 24 20 10/100 420 2.0 6. 550 24 20 12/100 410 2.0 7. 550 24 20 24/100 380 2.1 The FAZ-Y samples Tfnthesised at crystallisation time of 0 hr, 2hr, 4hr, 8hr, 10hr, 12hr and 24hr were designated as FAZ-Y9, FAZ-YIO, FAZ-Yll, FAZ- Y12 FAZ-Y13, FAZ-Y14 and FAZ-Y15 respectively.

d-spacing values reported in JCPDS Me (38-238) for zeolite-Y compare well with FAZ-Y13, FAZ-Y14 and FAZ-Y15 whereas it differs significantly for FAZ-Y9, FAZ-YIO, FAZ-YI I and FAZ-Y12. (See Table 9 also) Exaniple 5 The same process was repeated as described in example I except that there was a brief mixing time i.e. the amorphous alun-tino-silicate was subjected directly to crystallization after mixing for a time of about 15 minutes.

17' Table 9 d-spacing Values Obtained for FAZ-Y9-FAZ-YI5 (Example 4/Sample 1-7) d-spacing AO Relative Intensity (1/o) Example 4 Example 4 Sample Sample 2 3 4 5 6 7 1 2 3 4 5 6 7 FAZ-Y9 FAZ-YIO FAZ-YI1 FAZ-Y12 FAZ-Y13 FAZ-Y14 FAZ-YI5 FAZ-Y9 FAZ-YIO FAZ- YlI EAZ-Y12 FAZ-Y13 FAZ-Y14FAZ-YI5 14.34 12,9 13.9 13.78 14.15 14.0 14.0 12.2 64.2 31.28 40.6 96.7 76.6 84.6 - - - - 8.73 8.68 8.66 - - - - 27.2 22.5 22.7 - 7.46 7.42 7.39 - - 20.7 21,50 21.1 - 5.66 5.69 5.66 5.66 - 16.2 42.7 42.7 44.2 - 4.75 4.78 4.76 4.76 - 8.2 12.5 11.9 13.5 - - - 4.36 4.39 437 4.37 - - 11.2 24.8 23.8 26.1 3.73 3.66 - 3.77 3.79 3.78 3.77 15.12 243 - 39,0 81.4 82.0 84.4 2.88 2.82 2.83 2.86 2.87 2.86 2.86 31.8 44.8 46.28 92.2 100.0 100.0 100.0 2.69 2.68 2.66 2.64 2.65 2.64 2.64 20.4 25.9 24.67 39.0 42.6 42.6 41.2 The CBC values for FAZ-Y 16 and FAZ-Y 17 are 420 and 340 meq/ I OOg respectively. The SiO2/A]203 ratio are as follows:

Table 10

Variation of reaction conditions and characteristics of FAZ-Y Sr. Fusion Temp. NaOH Flyash h4ixing Tune CrfsWlisation CBC SiO2/ No. (OC) Min. tilneftalp. (meqtlOOg) A1203 hr/OC 1 550 24 20 15 10/100 420 1.9 (with 5g of Naa) 3 550 24 20 15 10/100 340 1.8 d-spacing values reported for ZeoUte-Y in JCPDS file (38-238) compare well with FAZ-Y16 and FAZ-Y17 and are as follows:

Table 11 d-spacing values obtained for FAZ-YI6-FAZ-YI7(Example5 / Sample 1-2) d-spacing Relative Intensity A (0/0) FAZ-Y16 FAZ-Y17 FAZ-Y16 FAZ-Y17 Example 5 Example 5 Samplel Sample2 Sample I Sample 2 14.0 14.31 44.0 14.40 8.67 8.34 13.3 3.97 7.42 - 10.6 - 5.67 5.65 35.9 4.26 4.76 4.75 13.7 3.73 4.38 4.37 25.6 4.85 3.78 3.76 100.0 100.0 2.87 2.86 77.9 29.5 2.64 2.64 26.0 22.1 Example 6

The fusion step of flyash and sodium hydroxide was repeated- as described in example 1, The fused mass was cooled, mifled and mixed thoroughly with distilled water for 10 hrs with simultaneous addition of alum solution (5%). The amorphous alumino-sUicate gel was then subjected to crystall.isation for 8- 12 hrs at about 90-11 OIC. The solid crystaffine product was recovered by fiftration washed with water and oven dried at 50- 60'C. The CBC observed is 340 meq/100g. d-spacing values reported for FAZ-Y18 in JCPDS file (38-238) are 14.30, 8.75, 7.46, 5.68, 4.76,4.38,3.77, 2.85 and 2.63. It.compares with FAZ-Y18 and are as follows:

Table 12 d-spacing values obtained for FAZ-YI8 (Example 61 Sample 1) d-spacing Relative Intmsity M (0/0) FAZ-Y18 FAZ-Y18 Example 6 Example 6 Sample I Sample I 14.20 98.0 8.75 24.1 7.47 20.5 5.70 41.9 4.79 14.5 4.40 27.5 3.79 83.8 2.87 100.0 2.65 46.1 Example 7

Flyash was treated with hydrochloric acid (6-8N) for 10-24 hrs, at about 100- 11 OOC. The acid treated flyash slurry was cooled and filtered. The solid product was washed with water and dried at about 110- 1200C.

The acid treated flyash so obtained was fized with sodium hydroxide as described in earnple, 1. 11e fused mass was cooled, milled and mixed thoroughly with distilled water for 1-2 brs. The amorphous aluminosilicate gel was then subjected to crystaUisation for 8-12 bFs at about 90-1 10T. 11e, solid crystalline product was recovered by fikration, washed with water and oven dried at SO-WC. The CBC is 280 meq/100 & dqxcing values reported fbr Zeolite-Y in JCPDS file (38-239) compare well with FAZ-Y19 and are as follows:

Table 13 &spacing values obtained for FAZ-Y19 (Example 7 / Sample 1) d-spacing Relative Intensity M (0/0) FAZ-Y19 FAZ-Y19 Example 7 Example 7 Sample I Sample 1 14.07 56.20 8.70 14.35 7.43 13.49 5.67 32.0 4.77 11.8 4.37 23.7 3.78 75.25 3.32 100.0 2.87 79.0 2.65 30.3 21 Example 8

The same process as mentioned in example I was repeated except for additional dealumination step using chelation technique.

Ile soUd FAZ-Y obtained as per the process of example I was treated with CaC12 soMon at 10- 12 pH to obtain Ca Exchanged FAZ-Y fbrm (Ca-FAZ-Y) The Ca-FAZ-Y was fiuther treated with EDTA soWon (5-60040n-A of water) and stirred continuously for 3-4 hrs. The reaction mbcture was fl= refluxed for about 8- 10 brs at 100- 11 OC, The soNd crystaffine product was recovered by filu-&on and washed thorougMy to obtain modified / deahmunated ZeoOe-Y. The CBC is 240 meq/100& d-spacing values reported for Zeo&e-Y in JCPDS file (38-238) compare weD with FAZ-Y and are as Mows:

Table 14 d-spacing values obtained for FAZ-Y20 (Example 8 / Sample 1) d-spacing Relative Imensity A (0/0) FAZ-Y20 FAZ-Y20 Example 8 Example 8 Sample I Sample I 14.16 98.8 8.74 20.4 7.45 20.5 5.69 41.4 4.77 14.4 4.39 28.5 3.79 82.1; 3.32 99.5 2.87 100.0 2.65 42.8 22 Main advantages of FAZ-Y Synthesis I Provides an inexpensive alternate to commercial grade zeolite-Y. 2. Provides effective substitute for the preparation of Molecular sieves / catalyst, - Zeolite composites / membranes, - Abrasive tools and brake liners and - Catalyst carriers.

3. Economically viable and technically non-tedious process (eliminates tedious process of preparing gels/sols etc.).

4. Tackles at least pardafly the adverse environmental effects envisaged for flyash.

5. 11igh value utilisation of flyash.

In addition to the above, the process formulated in the present invention has the following advantages:

The modified / improved fusion step employed results in the formation of sodium silicate and sodium aluminate, thus ascertaining the probability of formation of zeolite phases with high purity. Proper mechanical treatment (grinding and mixing) of fusion mixture ensures complete fusion, and effective extraction of alumina silica from flyash with formation of homgenous alumino-sflicate gel.

Proper grinding and mixing of fusion mixture also avoids the formation of glassy pahse and sintering of flyash particles. This also 2-3 helps in increasing fusion temperature for better extraction of aluimnosilicates from flyash, without sintering of particles The hydrothermal conditions 'employed results in the crystallisation of flyash based Zeolite-Y exclusively.

High concentration of alkali and promoters in the form of trace elements and certain salts provides conditions for faster crystallisation of FAZ-Y.

TIle crystallinity of FAZ-Y is significantly high (90-95 O/o), which is important for its possible industrial application as catalysts / catalst carrier.

2-4

Claims (7)

CLAIMS:

1. A process for the synthesis of flyash based zeolite-Y (FAZ-Y), the said process comprising the following steps:

(a) forming a fine homogenous fusion mixture of flyash or pre-treated flyash with caustic soda in a weight ratio of 1:0.4 to 1:1.2, (b) heating the said fusion mixture in an invert atmosphere at about 500-6000C for about 1-2 hours to obtain a fused mass, (c) cooling, milling, and mixing of the said fused mass in distilled water for about 8-12 hours, (d) subjecting the said slurry to hydrothermal crystallisation at about 90-1100C for 8 to 12 hours to obtain FAZ-7 crystals, (e) washing the said crystals with water and then subjecting the washed crystals to oven drying at 50-600C to obtain the desired FAZ-Y crystals.

2. A process as claimed in claim 1, wherein the fine homogenous fusion mixture in step (a) is formed by grinding and mixing the ingredients.

3. A process as claimed in claim 1, wherein flyash in step (a) may optionally be replaced by a pre treated flyash and in this case, the said pre treated flyash being prepared by treating flyash directly with a mineral acid in flyash: mineral acid ratio of 0.25:1.

V7

4. A process as claimed in claim 1, wherein the source of Si02 and A1.03 is flyash.

5. A process as claimed in claim 1, wherein the flyash is fused with solid sodium hydroxide.

6. A process as claimed in claim 1, wherein alum is added in a flyash: alum ratio of 5:1 in the mixing stage in step 1 (c) to improve the S'02 and A1203 7. A process as claimed in claim 1, wherein flyash is directly treated with acids in flyash: acid ratio of 0.25-1.0 prior to fusion step to improve the silica alumina ratio of FAZ-Y.

8'. A process for preparing silica enriched FAZ-Y which further comprises of the following steps:

treating Na-FAZ-Y with calcium solution to obtain Ca-FAZ-Y; treating Ca-AZ-Y with ethylene diamine tetracetic acid to obtain chelated FAZ-Y product; refluxing for 8-10 hours to obtain dealuminated FAZ-Y; washing and drying the product.

9. A process for preparing FAZ-Y as claimed in claim 1, wherein said FAX-Y having following characteristics:

calcium binding capacity up to 420 meq/100g.

average particle size (d5o) of less than 6 minons.

"(e-ZA.

crystallinity of about 90-95%.

cubic crystal structure.

specific surface area of about 550 m2/g.

Amendments to the claims have been filed as follows 1. A process for the synthesis of flyash based zeolite-Y (FAZ-Y), the said process comprising the following steps:

(a) forming a fine homogenous fusion mixture of flyash or pre-treated flyash with caustic soda in a weight ratio of 1:0.4 to 1:1.2; (b) heating the said fusion mixture in an inert atmosphere at 500-6000C for 1-2 hours to obtain a fused mass; (c) cooling, milling, and mixing of the said fused mass in distilled water for 8-12 hours; (d) subjecting the said slurry to hydrothermal crystallisation at 90-1100C for 8 to 12 hours to obtain FAZ-Y crystals; (e) washing the said crystals with water and then subjecting the washed crystals to oven drying at 50-GOOC to obtain the desired FAZ Y crystals.

2. A process as claimed in claim 1, wherein the fine homogenous fusion mixture in step (a) is formed by grinding and mixing the ingredients.

3. A process as claimed in claim 1, wherein flyash in step (a) is replaced by a pre-treated flyash and in this case, the said pre-treated flyash being prepared by treating flyash directly with a mineral acid in flyash: mineral acid ratio of 0.25:1.

4. A process as claimed in claim 1, wherein the flyash comprises S'02 and A1203 - 5. A process as claimed in claim 1, wherein alum is added in a flyash: alum ratio of 5:1 in the mixing stage in step 1 (c) to improve the SiO, and A1203 - 6. A process as claimed in claim 1, wherein flyash is directly treated with acids in flyash: acid ratio of 0.25:1.0 prior to fusion step to improve the silica alumina ratio of FAZ-Y.

7. A process for preparing FAZ-Y as claimed in claim 1, wherein said FAZ-Y having following characteristics:

- calcium binding capacity up to 420 meq/100g.

- average particle size (d5o) of less than 6 microns.

- crystallinity of 90-95%.

- cubic crystal structure.

- specific surface area of 550 M2/g.