|Title of Invention||
"A PROCESS FOR THE PRODUCTION OF FLYASH BASED ZEOLITE-Y (FAZ-Y)
|Abstract||The present invention provides a process for production of flyash based zeolite-y (faz-y) which comprises grinding and mixing of flyash or pre-treated flyash with caustic soda in the ratios ranging between 1:0.4 - 1:1.2 to obtain a fine homogeneous fusion mixture, the said pre-treated flyash being prepared by treating flyash directly with a mineral acid , heating the said fusion mixture in an inert vessel for about 1-2 hrs to obtain a fused mass;cooling, milling and mixing of the said fused mass in distilled water for about 8-12 hrs to form a slurry;subjecting the said slurry to hydrothermal crystallization at about 90-110°C for 8 to 12 hrs to obtain FAZ-Y crystals|
|Full Text||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 its applications as catalysts / catalyst carriers in specific, as automotive exhaust and de-NOx catalysts. The use of flyash as 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 making highly crystalline, porous, sodium Y-zeolite compositions having a SiO2/Al2O3 ratio varying from 2.0-4.0.
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, the crystalline zeolites are aluminosilicate whose frameworks are formed from A1C>4 and SiC>4 tetrahedra joined by the oxygen atoms and characterized by having 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.
In the prior knowledge, the method of preparation of this zeolite phase is generally known. 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 with 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 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 : A12O3 : nSiO2; wherein 'n 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.
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 aluminium trihydrate and silicates with flyash) with concomitant resolution of flyash disposal problem.
Dyer et.al. has detailed methods for the production of zeolites. Methods currently used to prepare zeolites require :
reactive starting materials viz; sodium silicate and aluminate 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 autogeneous) pressures or high temperature hydrothermal conditions (where temperature is less than 300°C)
a high degree of supersaturation of the components in gel phase leading to the nucleation of a large number of crystals
crystallisation time from a few hours to several days.
In particular, use of flyash to synthesize zeolites have been attempted by a few researchers. The process formulated in the present invention has several advantages and are as follows:
* The modified / improved fusion step employed results in the formation of
sodium silicate and sodium aluminate, thus ascertaining the probability of
formation of zeolitic 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 homogenous
* Proper grinding and mixing of fusion mixture also avoids the formation of
glassy phase and sintering of flyash particles. This also helps in increasing
fusion temperature for better extraction of aluminosilicates 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 crystallization 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
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 (Biswas, 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 in specific 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 the literature.
In the present invention FAZ-Y was synthesised by fusing flyash (20 g) with sodium hydroxide (8-24g). A homogeneous fusion mixture was prepared by proper grinding and mixing of flyash and alkali in a ratio of about 1:1.2. This mixture was heated to at least about 500°C preferably between 550-600°C for about 1-2 hrs to obtain the fused mass. The reaction mixture was placed in inert vessel and heated to about 500-600°C. The resultant fused mass was cooled to room temperature, milled again and then stirred vigorously in water for 8-10 hrs. to obtain amorphous alumino-silicate gel. This amorphous alumino-silicate gel was then subjected to crystallisation at 90-110°C for 8-12 hrs. The solid crystalline product was then recovered by filtration, washed with water and dried at temperature of about 50-60°C.
Characterisation of FAZ-Y Calcium Binding Capacity
The Calcium Binding Capacity (CBC) of alumino-silicates was determined as follows :
1 liter of aqueous solution containing 0.5 g of CaCl2 and adjusted to a pH of 9-10 with dilute NaOH, was mixed with 1 g of alumino-silicate (FAZ-Y). The suspension was then stirred vigorously for 15 minutes at room temperature (29- 30°C). After filtration, the residual hardness of the filtrate was determined. From the difference between hardness of the original solution and filtrate the CBC is calculated as meq/lOOg. The FAZ-Y samples were dissolved in HNO3 and analysed by ICP-AES (Model : YJ24) for A1203 while SiO2 was estimated using instrumental / conventional method. Na2O was estimated using flame photometer (Mediflame - 127 with FPM compressor unit 122).
The surface morphology of the zeolite was examined by Jeol- 840-A scanning electron microscope (SEM). Powder XRD analysis was employed to monitor zeolite formation process, using CuKa as source of X-rays (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.
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.
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 negligible. Formation of zeolitic phases with maximum crystallinity was observed at 500-600°C. At higher temperature, the crystallinity gradually decreased and may be attributed to sintering of flyash to form non-crystalline glassy mass.
The trend observed for CBC as a function of fusion temperature is similar. The CBC value (140meq/100g) is quite low at 200°C while significant increase in CBC at 600°C (420meq/100g) was recorded. Beyond a temperature of 600°C there was decrease in CBC value (380 meq/l00g).
The quantitative extraction of SiO2 and Al2O3 from flyash is dependent 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 SiO2 and A1203 from flyash is useful in maintaining the high alkaline pH of the reaction system, a necessary pre- requisite.
Insufficient concentration of alkali, as observed for NaOH/flyash ratio of 0.4, leads to lower extraction efficiency of NaOH for SiO2 and A12O3 from flyash and also adversely affects the crystallisation process. Increase in A12O3 content of reaction mixture by addition of 1.65g of sodium aluminate leads to transformation of zeolite-Y to zeolite-X. With further increase in A12O3 content (by addition of sodium aluminate upto 8 g) zeolite-X transforms into zeolite-A. In terms of CBC it can be said that it increases upto NaOH/flyash ratio of 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 exact reason (s) for these mechanisms remain to be investigated.
The alumino-silicate compound obtained after fusion is amorphous and changes to crystalline state when subjected to hydrothermal crystallization. A close scrutiny of the results presented in Table 8 reveals that crystallization time influences the zeolitic crystallinity significantly. Percent crystallinity opf zeolite-Y increases significantly upto 10 hrs and remains constant beyond that.
The effect of addition of sodium chloride and seeding to improve SiO2/Al2O3 has also been evaluated. Enrichment of SiO2 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 SiCh in zeolite matrix has also been evaluated. The addition of alum in the mixing step decreases the pH of the reaction system, thus decreasing the solubility of SiC>2 in the system.
Accordingly the present invention provides, a process for production of flyash based zeolite-Y (FAZ) which comprises the following steps :
a) grinding and mixing of flyash or pre-treated flyash with caustic soda in the ratios
ranging between 1:0.4 - 1:1.2 to obtain a fine homogeneous fusion mixture, the
said pre-treated flyash being prepared by treating flyash directly with a mineral
acid in flyash : mineral acid ratio of 0.25 : 1 to obtain pre-treated fly-ash;
b) heating the said fusion mixture in an inert vessel at about 500-600°C for about 1-2
hrs to obtain a fused mass;
c) cooling, milling and mixing of the said fused mass in distilled water for about 8-12
hrs to form a slurry;
d) subjecting the said slurry to hydrothermal crystallization at about 90-110 C for 8 to
12 hrs to obtain FAZ-Y crystals ;
e) washing the said crystals with water and then subjecting the washed crystals to
oven drying at 50-60°C to obtain the desired FAZ-Y crystals comprising
characteristics of calcium binding capacity upto 420meq/100g, specific surface
area of about 550 m2/g, average particle size (d50) of less than 6 micron,
crystallinity of about 90-95% and having cubic crystal structure.
The chemical composition of flyash is detailed in Table 1.
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.
Chemical Composition of flyash
Table 2 Comparative characteristics of FAZ-Y and commercial Zeolite-Y
The following examples illustrate the influence of different parameters viz. fusion temperature, NaOH/flyash ratio, crystallisation time/temperature but does not restrict the scope of the present invention. These examples also suggest the best mode of carrying out the invention.
Preweighed sample of flyash (20g) and sodium hydroxide (24 g) were properly grinded / milled and mixed to obtain a homogeneous fusion mixture, and placed in a vessel inert towards the reaction mixture 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-silicate gel was then subjected to crystallisation for 8-12 hrs at about 90- 110°C. The solid crystalline product was recovered by filtration, washed with water and oven dried at 50-60°C. The CBC and surface area of FAZ-Y is 420 meq/lOOg and 500-550m2/g respectively. The SiO2/Al2O3 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 3d-spacing values obtained for FAZ-Y (Example 1/ Sample 1)
The same process as mentioned in example 1 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/Al2O3 ratios.
Table 4 Variation of reaction conditions and Characteristics of FAZ-Y
FAZ-Y synthesised at fusion temperature of 200, 600 and 800°C were designated as FAZ-Y1, 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 :
Table 5d-spacing values obtained for FAZ-Y1-FAZ-Y3 (Example2/Sample 1-3)
The same process as mentioned in example 1 was repeated except for the variation in NaOH/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-Y8.
The CBC and SiO2/Al2O3 ratio obtained for FAZ-Y4, FAZ-Y5, FAZ-Y6, FAZ-Y7 and FAZ-Y8 are presented in Table 6.
Table 6 Variation of reaction conditions and characteristics of FAZ-Y
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 (34A), 800).
Table 7 d-spacing values obtained for FAZ-Y4-FAZ-Y8 (Example 3/Sample 1-5)
The same process as mentioned in example 1 was repeated except for the variation in crystallisation time. The reaction conditions pertaining to these examples are presented in Table 8 alongwith the CBC values and SiO2/Al2O3 ratios.
Table 8 Variation of reaction condition and characteristics of
The FAZ-Y samples synthesised at crystallisation time of 0 hr, 2hr, 4hr, 8hr, lOhr, 12hr and 24hr were designated as FAZ-Y9, FAZ-Y10, FAZ-Y11, FAZ-Y12 FAZ-Y13, FAZ-Y14 and FAZ-Y15 respectively.
d-spacing values reported in JCPDS file (38-238) for zeolite-Y compare well with FAZ-Y13, FAZ-Y14 and FAZ-Y15 whereas it differs significantly for FAZ-Y9, FAZ-Y10, FAZ-Y11 and FAZ-Y12 (See Table 9 also).
The same process was repeated as described in example 1 except that there was a brief mixing time i.e. the amorphous alumino-silicate was subjected directly to crystallization after mixing for a time of about 15 minutes.
d-spacing Values Obtained for FAZ-Y9-FAZ-Y15 (Example 4/Sample 1-7)
The CBC values for FAZ-Y16 and FAZ-Y17 are 420 and 340 meq/lOOg respectively. The Os ratio are as follows :
Variation of reaction conditions and characteristics of FAZ-Y
d-spacing values reported for Zeolite-Y in JCPDS file (38-238) compare well with FAZ-Y16 and FAZ-Y17 and are as follows :
Table 11d-spacing values obtained for FAZ-Y16-FAZ-Y17(Example5 / Sample 1-2)
The fusion step of flyash and sodium hydroxide was repeated, as described in example 1. The fbsed mass was cooled, milled and mixed thoroughly with distilled water for 10 hrs with simultaneous addition of alum solution (5%). The amorphous alumino-silicate gel was then subjected to crystallisation for 8- 12 hrs at about 90-110°C. The solid crystalline product was recovered by filtration washed with water and oven dried at 50- 60°C. The CBC observed is 340 meq/lOOg. 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-Y18 (Example 6/ Sample 1)
Flyash was treated with hydrochloric acid (6-8N) for 10-24 hrs at about 100-110°C. The acid treated flyash slurry was cooled and filtered. The solid product was washed with water and dried at about 110-120°C.
The acid treated flyash so obtained was fused with sodium hydroxide as described in example 1. The fused mass was cooled, milled and mixed thoroughly with distilled water for 1-2 hrs. The amorphous alumino-silicate gel was then subjected to crystallisation for 8-12 hrs at about 90-110°C. The solid crystalline product was recovered by filtration, washed with water and oven dried at 50-60°C. The CBC is 280 meq/100 g. d-spacing values reported for Zeolite-Y in JCPDS file (38-238) compare well with FAZ-Y19 and are as follows:Table 13 d-spacing values obtained for FAZ-Y19 (Example 7 / Sample 1)
The same process as mentioned in example 1 was repeated except for additional dealumination step using chelation technique.
The solid FAZ-Y obtained as per the process of example 1 was treated with CaCl2 solution at 10-12 pH to obtain Ca Exchanged FAZ-Y form (Ca-FAZ-Y) The Ca-FAZ-Y was further treated with EDTA solution (5-6g/30-40ml of water) and stirred continuously for 3-4 hrs. The reaction mixture was then refluxed for about 8- 10 hrs at 100-110°C. The solid crystalline product was recovered by filtration and washed thoroughly to obtain modified / dealuminated Zeolite-Y. The CBC is 240 meq/lOOg. d-spacing values reported for Zeolite-Y in JCPDS file (38-238) compare well with FAZ-Y and are as follows:
Table 14 d-spacing values obtained for FAZ-Y20 (Example 8 / Sample 1)
Main advantages of FAZ-Y Synthesis
1. 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 partially the adverse environmental effects envisaged for flyash
5. High value utilisation of flyash
1. A process for production of flyash based zeolite-Y (FAZ-Y) which comprises the following steps:
a) grinding and mixing of flyash or pre-treated flyash with caustic soda in the
ratios ranging between 1:0.4 - 1:1.2 to obtain a fine homogeneous fusion
mixture, the said pre-treated flyash being prepared by treating flyash
directly with a mineral acid in flyash : mineral acid ratio of 0.25 : 1 to obtain
b) heating the said fusion mixture in an inert vessel at about 500-600°C for
about 1-2 hrs to obtain a fused mass;
c) cooling, milling and mixing of the said fused mass in distilled water for
about 8-12 hrs to form a slurry;
d) subjecting the said slurry to hydrothermal crystallization at about 90-110°C
for 8 to 12 hrs to obtain FAZ-Y crystals
e) washing the said crystals with water and then subjecting the washed crystals
to oven drying at 50-60°C to obtain the desired FAZ-Y crystals comprising
characteristics of calcium binding capacity upto 420meq/100g, specific
surface area of about 550 m2/g, average particle size (d50) of less than 6
micron. Crystallinity of about 90-95% and having cubic crystal structure.
2 A process for the production of flyash based Zeolite Y (FAZ-Y) substantially
as herein described with reference to the examples.
|Indian Patent Application Number||2163/DEL/1998|
|PG Journal Number||13/2008|
|Date of Filing||24-Jul-1998|
|Name of Patentee||COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG, NEW DELHI - 110 001, INDIA|
|PCT International Classification Number||C01B 39/14|
|PCT International Application Number||N/A|
|PCT International Filing date|