GB2339775A - Producing silica enriched flyash based zeolite Y - Google Patents

Description

2339775 PROCESS FOR THE PRODUCTIOX OF SILICA ENRICHED FLYASH BASED ZEOLITE

Y (FAZ- Y)

FIELD OF THE INVENTION

This application is divided from GB 9820110.6 This invention relates to a process for the production of flyash based Zeolite-Y (FAZ-Y). More particularly, this invention relates to siliceous Y type flyash based zeolite with improved characteristics for specific applications 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 of the synthesis of highly crystalline, porous, sodium Y-zeolite compositions having a S'02/A'203 ratio varying from 2.0-4.0.

BACKGROUND OF THE INVENTION

Molecular sieves of the crystalline zeolite type are well known in the art and now comprise over 250 species of both naturally occurring and synthetic compositions. In general, crystalline zeolites are 1 "'V aluminosilicates whose frameworks are formed from A10 4 and Si04 tetrahedra joined by the oxygen atoms and characterised by clik: por., openlr-s of uniform dimensloris, having si,,n[Ficam ion- exchange capackEy and being capabie of reversibly desorbing an adsor11-e,- 1 phase -.,,hlzh 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 nm. Each supercage is connected tetrahedrally Wjth four neighbouring supercages via 12-membered ring windows with a crystallographic diameter of 0.74 nm. For most molecules except very bulky ones, Zeolite-Y offers a spacious cage and pore system through which they can diffuse without Z I hindrance. The general chemical formula of the synthetically produced, anhydrous, large pore, Zeolite-Y expressed ia terms of moles may be as follows 1.0 0.2 NaZO:AI203:nSiO2; wherein V has values from 3 to 7. These are commercially more useful as adsorbents as 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 oI industry: development and application (Ed.P.H. oaden), Royal Society of Chemistry; Cambridge, 1991), Fluid Catalytic Cracking ( Biwaaaas, J., and Maxwell, I.E., Appl.Catal, 1990 (63), 197), isomerisation 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 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 zeolices for removal of isotopes (,Dyer. A., Chem Ird., t984. 241-245); Ion g 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 nere 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 autooenous) 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.

1> The said processes cause sintering of particles and the time consumed for crystallisation of FAZ-Y is significantly long.

According to the present invention, a process is provided for preparing silica enriched flyash based Zeolite-Y (FAZ-Y), comprising the steps:

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

Preferably, the calcium solution is CaCl, Preferably, the CaCl2 solution has a pH of 10-12.

Preferably, the ethylene diamine tetracetic acid has a concentration of 5-6g/30-40ml of water.

Preferably the Ca-FAZ-Y is treated with ethylene diamine tetracetic acid for 3-4 hours.

Preferably, the chelated FAZ-Y is refluxed for 8-10 hours at 100-1100C.

BRIEF DESCRIPTION OF THE 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 clearly illustrates the transformation of amorphous flyash into crystalline material.

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 at least about 500"C preferably between 550-6000C for about 1-2 hours to obtain Elie fused mass. The resultant fused mass is cooled to room ternperatur,!. milled a,lain and chtm stirred vigorously in water for 810 hours to obtain amorphous alumino-silicate gel. This solid aluminosilicate get is then subjected to crystallisation at 90-11 OC 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 50-60C.

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 A1.z03 from flyash is useful in maintaining the high alkaline pH of the reaction system, a necessary pre-requisite.

The effect of fusion temperature on zeolite formation is quite predominant and is presented in Table 4. No zeolite formation was observed at fusion temperature of 200'C 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 NaOH/flyash ratio of 0.4, leads to lower extraction efficiency of NaOH for SiO, and A1,0, 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 upto 8a) zeolite -X transforms into zeolite-A.

I The ratio of tlYash to caustic soda employ in the present invention is important. If any additional alumina such as. sodium aluminate or aluminium hydroxide is addled m tht: mixture, such addition ihifts the equilabrium oC the pr,--sent proc-ss &om [he 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.

The effect of addition of sodium chloride and seecUng to improve SiO-2 and A1203 has also been evaluated. Enrichment of Si0-2 content of flyash through ts direct acid treatment has been explored. Improvement Of Si02 content in zeolite by way of addition of alum in mixing stage to increase incorporation Of Si02 in zeolite matrix has also been evaluated. The addition of alum in the mixina 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 chanaes 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 sigpificantly upto 10 hrs. and remains constant beyond that.

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

I 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 alumino-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 meq/100 The FAZ-Y samples were dissolved HN03 and analyzed by ICPAES Nodel: YJ 24) for A1201 while SiO, was estimated using instrumental coriventional method Na,O is estimated usir,; tlarre photorneter,, Nlt. 'Iflame - 127 7 with FP,'Yf compressor unit 122). The trend observed for CBC as function of fusion temperature is similar. The CBC value (140 meq / 100g) is quite low at 200C while significant increase in CBC at 600C (420 meq / 100g) was recorded. Beyond a temperature of 600C there was decrease in CBC value (380 meq I 00g).

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 (SENA) wherein Powder XRD analysis was employed to monitor zeolite formation process, using, CuKa as source of Xrays ("Nfodel: 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.

01 In the drawinas, which are in the form of photographs. photograph I 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.

The chemical composition of flyash is detailed In Table 1. Table I Chemical composition of Flyash Component % weight (dry basis) SiO-2 61.63 A1203 25.75 Fe203 5.96 CaO 3.07 MgO 2.01 N1n304 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.

T.ible -)LZ-'(. and:omrncmal Z,:,)1te-(' S"No- CharacttriZtiO Zeolite-Y Symhesized Commercial 1. Surface area 500-550 550-600 (ml/g) 2. Exchange capacity 340-420 420 (Meq/1008) 3. Average particle size 4-5 8-10 4. Crystal strLcture Cubic Cubic SION-103 2.0-4.0 2.0-2.5 The following exarnples illustrate the influence of different parameters viz. fusion temperature, NaOK'flyash ratio, crystallisation the.,'tempera=e but does not restrict the scope of te present;nvention.

Example I

Preweighed sample of flyash (20g) and sodium hvdro-ode (24 g) were properly grinded miDed and mix,-ei to obtain a homogeneous ftision rrixture, and placed in a vessel vrt towards the reaction mix=e and heated to about 500-600'C for 1-2 hrs. The fused mass was cooled, milled and mixed thoroughly with distilled water for 8-10 hrs. The amorphous alumino-silicace 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 dn-ed at 50-60'C. The CBC and surface area of FAZ-Y is 420 meq/100g and 500- 55om2/g respectively The Si(32/A]203 ratio is around 2.0. d-spacing Values (in A') reported for ZeOlite-Y in JC?OS ile (38-238) are 14.30, 3.75, 7.46, 5 68, 4.76, 4.38, 3.77, 2.35 and 2.63. It compare3 -.veil with FAZ-Y and are as Fc1lows Table 3 d-spacing values obtained for FAZ-Y (Example 1/ Sample 1) d-spacing Relative intensity W) (0/0) 1 FAZ-Y FAZ-Y Example I Example I Sample I Sample 1 14.15 96.7 9.73 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 fusion temperature. The reaction conditions pertaining to these examples are presented in Table 4 alongwith the CBC values and SiO2/A1203 ratios.

I 13 Table 4

Variation of reaction conditions and Characteristics of FAZ-Y S. Fusion ternp. NaOH Flyash Crystallisation CBC Sio-z/ No. (1,C) (9) (9) timeAemp (meq/ Al-zO3 WC) 100g) 24 20 10/100 140 2.4 2. 600 24 20 10/100 420 2.0, 3. 800 24 20 10/100 380 1.6 FAZ-Y synthesised. at fusion temperature of 200, 600 and 800'C were designated as FAZ-Y I, FAZ-Y2 and FAZ-Y3. d-spacing values (in A) reported for ZeoUte-Y in JCPDS file (38-239) are 14.30, 8.75, 7.46, 5.68, 4.76, 4.38, 3.77, 2.85 and 2.63). It compares weU with FAZ-Y2 and FA.Z-Y3 and are as follows:

Table 5 d-ipacing values obtained ror FAZ-Y I - FAZ-Y3 (Ezarnple2/5arnple 1-3) d-spacing Relative intensity (AO) (%) FAZ-YI FAZ-Y2 FAZ-Y3 FAZ-YI FAZ-Y2 FAZ-Y3 Example 2 Example 2 Samplel Sample2 Sample3 Sample I 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 NaOfi/flyash ratio. FAZ-Y was synthesised 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-YS.

The CBC and SiOJA]203 ratio obtained for FAZ-Y4, FAZ-Y5, FAZ-Y6, FAZ-Y7 and FAZ-Y8 are presented in Table 6.

Table 5

Variation of reaction conditions and characteristics of FAZ-Y Fusion temp. NaOH Flyash Crystallisation CBC SiWAI-203 No. CC) (9) (9) timeltemp (meq/100g) Ratio WC) 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 their 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 (234A), 800).

Table 7 d-ip3cing vafue3 obtained for FAZ-Y4-F.AZ-Y3 (Example 3/S3mple 1-5) d-spacing Relauve inteasay (A-) (%) FAZ-Y4 FAZ-Y5 FAZ-Y6 1FAZ-Y7 FAZ-YS FAZ-Y4 FAZ-Y5 FAZ-Y6 FAZ-Y7 FAZYS E;=mple 3 Example 3 SaMPICI UMPIC2 sample3 sample4 =mPle5 SUVW mmple2 sample3 sunple4 sample5 14.15 13.21 96.7 - 21.1 9.73 - 2?.2 - 7.44 7.46 19.3 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 2.85 2.82 4.7 100.0 15.9 35.4 2.63 - 2.65 2.57 2.0 42.6 61.5 - Example 4

Tlie swne process as mentioned in example I was repeated except for the variation in aYgallisatiOn time. The reaction conditions peftaing to &, ese examples are presented in Table 8 alongwith the CBC values and SiWA1203 ratios.

Table 3

Virlation of rraction condition and characteristics of F.AZ-Y S. Fusion temp. NaOH Flyash Crystallisation CBC SiO2/ No. (OC) (9) (9) fixneltemp (meq/100g) Ah(:

OWQ 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 121100 410 2.0 7. 550 24 20 24/100 380 2.1 T'he FAZ-Y samples ssjhesised at crystalhsa6on time of 0 hr, 2hr, 4hr, 8hr, 10hr, 12hr and 24hr were designated as FAZ-Y9, FAZ-YlO, F.AZ-YI 1, FAZ-Y12 FAZ-)(13, FAZ-Yl4 and FAZ-Y 15 respectively.

d-spacing vues reported in JCPDS file (38-238) for zeolite-Y compare well with FAZ-Y13, FAZ-Y14 and FAZ-YI5 whereas it differs significantly for FAZ-Y9, FAZ-YIO, FAZ-Y I I and FAZ-Y 12. (See Table 9 also) Example 5

The same process was repeated as described in example I except that there was a brief mi.,dng time i.e. the amorphous alumino-sificate was subjected directly to crystallizafion after mixing for a time of about 15 minutes.

Table 9 d-spacing Values Ob(ained for IFIAZ-Y9-FAZ-Y 15 (Exaniple 4/Saniple 1-7) d-spacing A Rclafivc In(ciosily Example 4 E-omplc 4 Sample Sample 2 3 4 5 6 7 1 2 3 4 5 6 7 FAZ-N'9 17AZ_y 10 FAZ-Yll FAZ-Y12 FAZ-Y13 FAZ-Y14 FAZ-Y15 FAZ-Y9 FAZ-YIO FAZ-YII FAZ-Y12 FAZ-Y13 FAZ-Y14 FAZ-YI5 11 13.8 13.79 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 - - - 203 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 4.37 4.37 - - 11.2 24.8 23.8 26.1 1 71 1 66 - 3.77 3.79 3.78 3.77 15,12 24.7 39.0 81.4 82.0 94.4 7 RR 2 R2 2.83 2.86 2.87 2.86 2.86 31.8 44.8 46.28 92.2 100.0 100.0 100.0 7 (Is 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 7"neCBC values for FAZ-Y16 and FAZ-Y17 are 420 and 'Ao -neql I rX,'g r- espwli'vely The SlOv AJ--(), rallo:ir(: is ibilows Table 10

V"tion of maction conditions and char2cteri3tic3 of FAZ-Y Sr. Fusion T=V. N&OH Flyash Nfidng 74ne CqvAlbsation CBC Sio NO. (OC) rain dMettemp. (maq/1009) Al-Oj hr/'C 1 530 24 20 15 10/100 420 1.9 (with 5g of NaCI) 3 550 24 20 15 10/100 340 1.9 d-spacing values reported for Zeolite-Y in JCPDS file (38-238) compare well with FAZ-Y!6 and FAZ-Y17 and are as follows:

Table I I d-spacing values obtained for FAZ-Y16-F.AZ-Y17(EYample5 / Simple 1-2) d-spacing Relative Intensity A N FAZ-Yl6 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 - 5.67 565 35.9 4.26 4.76 4.75 13.7 3.73 4.38 4.37 25.6 4.85 3.78 3.76 100.0 100.0 187 2.86 77.9 22 9. 5 2.64 2.64 26.0 22.1 Example 6

71he %sicr -oto of flyash and iedlun hydrox;de was repeated as desclllbed n example The Eised mass,,as cooled, MI'lled and Mixed thorougly with distilled water for 10 hrs with sinUtaneous addition of alum solution (5%). The amorphous alumino-silicate gel was then subjected to crystallisation fbr & 12 hrs at about 90-11 OC. The solid cryvaine product was recovered by fihrafion washed with water and oven dried at SO- 60'C. The CBC observed is 340 meq/100g. d-spacing values reported for FAZ-YI8 in JCPDS Ede (38- 238) are 14.30, 8.75, 7.46, 5.68, 4.76, 4.3 8, 3.77, 2.85 and 2.63. It compares with FAZ-Y 19 and are as fbHows Table 12 d-spacing values obtained for FAZ-YI8 (Example 61 Sample 1) d-spacing Relative Intensity AO (0/0) FAZ-Y18 FAZ-Ylg Example 6 Example 6 Sample I Sample 1 14.20 98.0 8.75 27 4. 1 7.47 20.5 5.70 41.9 4.79 14.5 4.40 2 7. 5 3.79 93.8 2.87 100.0 2.65 46.1 Example 7

Flyash was -reated 1.14th hydrochloric acid (6-34,or [0-24 hrs at about 100-1 IO'C. The acid treated flyash slurry was cooled and Eltered. The solid product was washed with water and dried at about 110- 1200C.

Tw add treated flya3h. so obtained was fized with sodium homde as described in ccample I. The fized mass was cooled, znMed and mmed thorougWy with &Oed water for 1-2 hm 1"he amorphous alunino-sUicate gel was then subjected to crystaHisation for 8-12 bfs at about 90-1 WC. The solid crystalline product was recovered by filtration, washed with water and oven dried at 50-WC. ne CBC is 280 meq1lOO & d-spacing values reported for Zeolite-Y in JCPDS file (38-238) compare well with FAZ-Y19 and are as Mows:

Table 13 d-spacing values obtained for FAZ-Y19 (Example 7 /Sample 1) d-spacing Relative Intensity AO (%) 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 4.77 141.8 4.37 23.7 3.79 75.25 3.32 100.0 2.87 79.0 2.65 30.3 n tw present inventwn, the swe process as waltioned in example I was repeated e.XcWt for addLt-LOnal dealmlmtlm step using chelatim technique - 7he sofid FAZ-Y obtained as per the pmcen of aample I was Uested with CaCh Mkidea at Ia. 12 PH to obtain Ca Evdmpd FAZ-Y form (Ca-FAZ-Y) Tw Ca- FAZ-y W25 Awthc Mated wkh EDrrA wk=a (WO40ml of wxw) and s&red coa=w fbr 34 hm The rewtion inb=re was dun refluxed for about 9- 10 brs at 100-1 IOOC- The sofid ayzilfiw Mduct was recovemd by fik=,oa and wasbed dwougWy to obtain modified / dealwmnated Zee-Y I"m acis 24o mw/ioo& d-spacing vakies rworted for Zeo&e-Y in JCPDS file (38-238) compare weD with FAZ-Y uA are as fbDows:

Table 14 d-spacing values obtained for FAZ-Y20 (Example 8 / Sample 1) d-spacing Relative btensity 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 92.5 3.32 99.5 2.87 100.0 2.65 42.8 -M e P,-ovldes an inexpensive alternate to:Ornrnercial grade zeallEe-Y. 71!,! 1.- C"ecw/e 3ubsciruce or zhtt preparation oC Molecular sieves / catalyst, Zeolite composites / membranes, Abrasive tools and brake Uners and CaWyst carriers.

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

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

5. High value utilisation of flyash.

In addition to the above, the process has the following advantages:

The modified / improved fusion step employed results in the formation of sodium silicate and sodium aluminate, thus ascertaining thj! probability of formation of zeolite phases with high purity. Proper mechanical treatment (aginding and mixing) of fusion mixture ensures complete fusion, and effective extraction of alumina silica from flyash with formation of homaenous alumino-silicate an e 1.

Proper grnding and mixing, of Fusion mixture also avoids the formation of glassy phase and sintering of flyash particles. This also heIP3 in increasing fusion,emperature for better extraction of alui=osilicates 57om flyash, without sintering of particles 7he 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.

The crystallinity of FAZ-Y is significantly high (90-95 %), which is important for its possible industrial application as catalysts / catalyst carrier.

Claims (6)

CLAIMS: -

1. A process for preparing silica enriched flyash based zeolite-Y (FAZ-Y), comprising the steps: 5 (a) treating Na-FAZ-Y with calcium solution to obtain Ca-FAZ-Y; (b) treating Ca-FAZ-Y with ethylene diamine tetracetic acid to obtain chelated FAZ-Y product; (c) refluxing for 8-10 hours to obtain dealuminated FAZ-Y; and (d) washing and drying the product.

2. A process as claimed in claim 1, wherein the calcium solution is CaCl,

3. A process as claimed in claim 2, wherein the CaCl2 solution has a pH of 10-12.

4. A process as claimed in any preceding claim, wherein the ethylene diamine tetracetic acid has a concentration of 5-6g/30-40ml of water.

5. A process as claimed in any preceding claim, wherein the Ca-FAZ-Y is treated with ethylene diamine tetracetic acid for 3-4 hours.

I 4 Z7-

6. A process as claimed in any preceding claim, wherein the chelated FAZ- Y is refluxed for 8-10 hours at 100-1100C.

5. A process as claimed in any preceding claim, wherein the Ca-FAZ-Y is treated with ethylene diamine tetracetic acid for 3-4 hours.

6. A process as claimed in any preceding claim, wherein the chelated FAZ-Y is refluxed for 8-10 hours at 100-1100C.

Al Amendments to the claima have been filed as follows 1. A process for preparing silica enriched flyash based zeolite-Y (FAZ-Y), comprising the steps of:

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 500OC-6000C to obtain a fused mass; C) cooling, milling and mixing said fused mass in distilled water; d) subjecting the said slurry to hydrothermal crystallisation to obtain FAZ-Y crystals; e) treating FAZ-Y with calcium solution to obtain Ca-FAZ-Y; f) treating Ca-FAZ-Y with ethylene diamine tetracetic acid to obtain chelated FAZ-Y product; g) refluxing for B-10 hours to obtain dealuminated FAZ-Y; and h) washing and drying the product.

2. A process as claimed in claim 1, wherein the calcium solution is CaCl..

3. A process as claimed in claim 2, wherein the CaCl2 solution has a pH of 10-12.

4. A process as claimed in any preceding claim, wherein the ethylene diamine tetracetic acid has a concentration of 5-6g/30-40ml of water.