WO2009060471A2 - Microwave assisted process for synthesis of molecular sieves from pseudo and/or dry gels - Google Patents

Microwave assisted process for synthesis of molecular sieves from pseudo and/or dry gels Download PDF

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WO2009060471A2
WO2009060471A2 PCT/IN2008/000537 IN2008000537W WO2009060471A2 WO 2009060471 A2 WO2009060471 A2 WO 2009060471A2 IN 2008000537 W IN2008000537 W IN 2008000537W WO 2009060471 A2 WO2009060471 A2 WO 2009060471A2
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pseudo
optimum
range
molecular sieves
gel
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WO2009060471A3 (en
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Shivanand Pai
Bharat Lakshman Newalkar
Nettem Venkateswarlu Choudary
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Bharat Petroleum Corporation Ltd.
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B39/00—Compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites; Their preparation; After-treatment, e.g. ion-exchange or dealumination
    • C01B39/54—Phosphates, e.g. APO or SAPO compounds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B37/00—Compounds having molecular sieve properties but not having base-exchange properties
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B37/00—Compounds having molecular sieve properties but not having base-exchange properties
    • C01B37/005—Silicates, i.e. so-called metallosilicalites or metallozeosilites
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B37/00—Compounds having molecular sieve properties but not having base-exchange properties
    • C01B37/02—Crystalline silica-polymorphs, e.g. silicalites dealuminated aluminosilicate zeolites
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B39/00—Compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites; Their preparation; After-treatment, e.g. ion-exchange or dealumination
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B39/00—Compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites; Their preparation; After-treatment, e.g. ion-exchange or dealumination
    • C01B39/02—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof; Direct preparation thereof; Preparation thereof starting from a reaction mixture containing a crystalline zeolite of another type, or from preformed reactants; After-treatment thereof
    • C01B39/06—Preparation of isomorphous zeolites characterised by measures to replace the aluminium or silicon atoms in the lattice framework by atoms of other elements, i.e. by direct or secondary synthesis
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B39/00—Compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites; Their preparation; After-treatment, e.g. ion-exchange or dealumination
    • C01B39/02—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof; Direct preparation thereof; Preparation thereof starting from a reaction mixture containing a crystalline zeolite of another type, or from preformed reactants; After-treatment thereof
    • C01B39/06—Preparation of isomorphous zeolites characterised by measures to replace the aluminium or silicon atoms in the lattice framework by atoms of other elements, i.e. by direct or secondary synthesis
    • C01B39/065—Galloaluminosilicates; Group IVB- metalloaluminosilicates; Ferroaluminosilicates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/03—Catalysts comprising molecular sieves not having base-exchange properties
    • B01J29/035—Microporous crystalline materials not having base exchange properties, such as silica polymorphs, e.g. silicalites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/82—Phosphates
    • B01J29/84—Aluminophosphates containing other elements, e.g. metals, boron
    • B01J29/85—Silicoaluminophosphates [SAPO compounds]

Definitions

  • the present invention discloses a microwave assisted process for synthesis of molecular sieves from pseudo and/or dry gels with coated carbon.
  • Crystalline molecular sieves have 3 -dimensional, microporous frameworks having tetrahedrally coordinated cations [TO 4 ].
  • frameworks comprising oxygen tetrahedra of aluminium and silicon cations lead to the formation of microporous aluminosilicate framework commonly known as zeolites.
  • 3-dimensional microporous aluminophosphate (AlPOs) frameworks classified as zeo-type molecular sieves are composed of oxygen tetrahedra of Al and P cations whereas silicoaluminophosphate (SAPOs) type molecular sieves composed of oxygen tetrahedra of Si, Al and P cations.
  • AlPOs microporous aluminophosphate
  • SAPOs silicoaluminophosphate
  • Molecular sieves are classified as small, medium and large pore .molecular sieves based on their pore opening.
  • the small pore molecular sieves have pore size in between 0.4-0.5 nm.
  • Medium pore molecular sieves have pore size in between 0.5-0.6 nm whereas large pore molecular sieves have pore opening of 0.6-0.8 nm (R. Szostak, Molecular Sieves: Principles of synthesis and Identification, 2nd edition, Blackie Academic and Professional, London, 1998).
  • Molecular sieves are usually synthesized under hydrothermal conditions from a reactive gel comprising of water, aluminum, silica, germanium, and/or phosphorous sources in the presence of an organic structure directing agent, such as an organic nitrogen compound in the temperature range of 100-200 0 C wherein water molecules are believed to be acting as a filling agent during crystallization of molecular sieve.
  • an organic structure directing agent such as an organic nitrogen compound in the temperature range of 100-200 0 C wherein water molecules are believed to be acting as a filling agent during crystallization of molecular sieve.
  • Commonly used nitrogen compounds are amines, diamines and quaternary ammonium salts.
  • Such synthesis is also carried out under solvothermal conditions (EP-A-337,479) employing non-aqueous solvents such as glycols.
  • non-aqueous solvents such as glycols.
  • mineralizing agents especially fluoride ions (US patent 6,793,901) is also practiced in molecular sieve synthesis.
  • fluoride media is also reported to lead to the formation of large zeolite crystals (see Berger et.al. Microporous and Mesoporous Materials 83, (1 -3), 2005, 333-344).
  • the present invention discloses, a process for microwave-assisted synthesis of molecular sieve from pseudo and/or dry gel in the presence of carbon; a microwave absorbing aid.
  • the aforementioned and other objects of the present invention are achieved by a microwave assisted process for synthesis of molecular sieves.
  • the process eventually involves negligible and/or no water.
  • the disclosed approach involves preparation of dry gel and their coating with carbon and optimization of microwave conditions for successful synthesis of aluminosilicate, silicoaluminophosphate, silicoaluminogermante, silicogermanate, and silica based molecular sieve frameworks.
  • the present invention also discloses the methodology for calcination of crystallized frameworks for their utilization as catalyst, catalyst carrier for hydrocarbon conversion or adsorbent for separation.
  • the disclosed approach of the present invention may be utilized for synthesis of aluminosilicate, silicoaluminophosphate, silicoaluminogermante, silicogermanate, and silica molecular sieves including ITQ- 12, -13, and -32.
  • novel energy efficient microwave assisted process for synthesis of molecular sieves of the present invention utilizes carbon as an assisting aid for molecular sieve synthesis under microwave conditions.
  • the carbon loading is ranging from 0.1-15 wt%.
  • novel energy efficient microwave assisted synthesis approach the present invention is applied for gel containing 0.1-5 wt% carbon.
  • the present invention is performed in the temperature range of 100-200 0 C, preferably 150-200 0 C, in the presence of carbon.
  • the present invention is performed for time period ranging from 1-10 days.
  • the present invention allows solid hydrogel transformation into molecular sieve with high yield, and it involves nearly complete conversion of gel to molecular sieve.
  • the present invention allows crystallization of uniform crystals with smaller particle size compared to conventional method.
  • novel energy efficient microwave assisted synthesis approach of the present invention allows the crystallization of molecular sieves at higher temperatures than that used in the hydrothermal method.
  • novel energy efficient microwave assisted synthesis approach of the present invention allows minimization of waste disposal and reduction in reactor volume.
  • time interval disclosed varied depending on the molecular sieve composition synthesized. * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
  • the synthesis time varies from 1-4 days for aluminosilicate, 1-6 days for silicogermanate, 1-5 days, silicoaluminogermante, 1-8 days for silica molecular sieve, respectively.
  • the synthesis of molecular sieves is carried out by varying microwave power.
  • the synthesis is performed in the presence of microwave power ranging from 1-1200 W; more preferably in the range of 1-300 W.
  • the synthesis of molecular sieves is performed under varying microwave ramp conditions.
  • the synthesis of molecular sieves is performed under microwave ramp conditions ranging from 5-120 mins; more preferably 45-75 mins.
  • the synthesis methodology of the present invention is applied for synthesis of silicalite-I, silicoaluminogermante (e.g. ITQ-31, -33), silica (e.g. ITQ- 12,- 13,-32), silicoaluminophosphate (SAPO-5) molecular sieves.
  • silicoaluminogermante e.g. ITQ-31, -33
  • silica e.g. ITQ- 12,- 13,-32
  • SAPO-5 silicoaluminophosphate
  • the molecular sieves synthesized as per aforementioned embodiments are calcined in air and/or nitrogen- oxygen mixture; more preferably in nitrogen-oxygen mixture at elevated temperature in the range of 500-600 0 C.
  • the molecular sieves are calcined in nitrogen-air mixture having composition ranging from 0-100 vol % of nitrogen to 0-20 vol % of oxygen.
  • the molecular are calcined in nitrogen-oxygen mixture having composition of 80:20 vol% and more preferably 98-2 vol%.
  • the calcined molecular sieves as per aforementioned embodiments are used as a catalyst and/or catalyst carrier and/or adsorbent for hydrocarbon conversions and separation, respectively.
  • FIGURE 1 XRD pattern for as-synthesized SAPO-5 phase.
  • FIGURE 2 XRD pattern for as-synthesized ITQ- 12 phase.
  • FIGURE 3 XRD pattern for as-synthesized ITQ- 13 phase.
  • FIGURE 4 XRD pattern for as-synthesized ITQ-31 phase.
  • FIGURE 5 XRD pattern for as-synthesized ITQ-33 phase.
  • FIGURE 6 XRD pattern for as-synthesized silicalite-I phase.
  • molecular sieves which can be crystallized with the present approach include framework composition of aluminosilicate, silicate-I, silicoaluminophosphate, silicoaluminogermante, silicogermanate or silica.
  • a reactive homogeneous gel having a desired composition is prepared in the presence of requisite carbon content with minimum water content.
  • the loading of carbon content is varied based on silica content in the gel composition. For example, gel containing higher silica content (in the range of 70-90 wt %) is loaded with about
  • the water level of the prepared gel is manipulated due to hydrophobic nature of the gel to achieve uniform carbon coating over the gel. Typically, water content of the gel was varied in the range of 1-10 on molar ratio basis of silica content present in the gel.
  • the gel so obtained is then subjected to microwave-hydrothermal conditions which are optimized based on the carbon content present in the reactive gel, composition and crystallization temperature.
  • the microwave conditions are varied with respect to microwave power in the range of 0-300 W and ramping time in the range of 30- 180 mins.
  • the % of applied power is adjusted according to ramping time which is basically a function of gel composition and carbon loading in the gel.
  • the crystallization time is found to be a function of gel composition, and carbon content.
  • gel comprising higher silica content found to have crystallization time up to 8-10 days whereas low silica content favored crystallization within 4 days.
  • crystallized samples are then subjected to calcination wherein samples are exposed gas mixture containing 98% nitrogen and 2% oxygen in the temperature range of 520-600 0 C depending carbon content present in the crystallized sample.
  • crystallized sample with high silica content having higher loading of carbon content is calcined at 580 0 C which is attained at three stages of 300, 500, 580 0 C, respectively.
  • the crystallinity for the crystallized as well as calcined sample is measured and confirmed using powder X-ray diffraction pattern.
  • the adsorption crystallinity for the calcined sample is measured by means of nitrogen adsorption- desorption isotherm at -196 0 C as per the ASTM method 4365 applicable for microporous solids.
  • the morphology of the sample is determined using scanning electron microscopy technique.
  • a reaction mixture is prepared by combining 7.69 grams of 85 wt.% orthophosphoric acid (H 3 PO 4 ) and 10 grams of water, to which is added 4.58 grams of a hydrated aluminum oxide, (a pseudo-boehmite phase, 74.2 wt.% Al.sub.2 O.sub.3, 25.8 wt.% H 2 O), and stirred until homogeneous.
  • a hydrated aluminum oxide (a pseudo-boehmite phase, 74.2 wt.% Al.sub.2 O.sub.3, 25.8 wt.% H 2 O)
  • To this mixture is first added 1.08 grams of 37 wt.% HCl, and then 2.16 grams of a fumed silica (92.8 wt.% SiO.sub.2, 7.2 wt.% H.sub.2 O) and the mixture is stirred until homogeneous.
  • the X-ray powder diffraction pattern (Fig. 1) of the SAPO-5 product is characterized by the following data (Table 1): This X-ray pattern and all other X-ray patterns appearing hereinafter are obtained using standard X-ray powder diffraction techniques.
  • the radiation source is a high-intensity, copper target, X-ray tube operated at 50Kv and 4OmA.
  • the diffraction pattern from the copper Ka radiation and graphite monochromator is suitably recorded by an X-ray spectrometer scintillation counter, pulse height analyzer and strip chart recorder. Flat compressed powder samples are scanned at 20 per minute, using a 2 second time constant.
  • Interplanar spacings (d) in Angstrom units are obtained from the position of the diffraction peaks expressed as 2 ⁇ where ⁇ is the Bragg angle as observed on the strip chart. Intensities are determined from the heights of diffraction peaks after subtracting background, "I 0 " being the intensity of the strongest line or peak, and "I” being the intensity of each of the other peaks.
  • the determination of the parameter 20 is subject to both human and mechanical error, which in combination, can impose an uncertainty of about .+/- 0.4° on each reported value of 2 ⁇ . This uncertainty is, also manifested in the reported values of the d-spacings, which are calculated from the 20 values. This imprecision is general throughout the art and is not sufficient to preclude the differentiation of the present crystalline materials from each other and from the compositions of the prior art.
  • Table 1 X-ray diffraction data for the as-synthesized SAPO-5 sample
  • a reactive gel comprising of 20.83g of tetraethylorthosilicate (TEOS) in 55.54g of the 1,3,5-trimethylimidazole hydroxide solution produced as per prior art under continuous mechanical stirring at 200 rpm until the ethanol and an appropriate amount of water are evaporated to yield the above gel mixture.
  • TEOS tetraethylorthosilicate
  • a solution of 2.33g of HF (48 wt % in water) and Ig of water is slowly added to the 1,3,5-trimethylimidazole silicate solution. The resultant mixture is mechanically and finally manually stirred until a homogeneous gel is formed. This gel is very thick as a consequence of the small amount of water present.
  • the formed gel is loaded with 5 wt% carbon content to obtain uniform and homogeneous distribution of carbon in the gel matrix.
  • the carbon loaded gel is autoclaved at 175 0 C for 7 days under static microwave conditions. A microwave power of 600W is applied to achieve synthesis temperature by the efid of 2.5 h.
  • the solid reaction product is recovered by filtration, washed with water, and dried in air overnight at room temperature.
  • X-ray diffraction analysis (Fig. 2) of the as-synthesized sample gives the results listed in Table 2.
  • Table 2 X-ray diffraction data for as -synthesized ITQ-12 sample
  • a siliceous reactive gel is produced by hydrolyzing 17.33g of tetraethylorthosilicate (TEOS) with 74.6g of the hexamethonium dihydroxide solution produced under continuous mechanical stirring until the ethanol and the water are evaporated to yield the above gel reaction mixture. Then, a solution of 1.94g of HF (48 wt % in water) and Ig of water is slowly added to the resultant hexamethonium silicate solution. The reaction mixture is mechanically and finally manually stirred until a homogeneous gel is formed. The resulting gel is very thick. This gel is loaded with 5 wt% of carbon to obtain uniform and homogeneous distribution of carbon in the gel matrix.
  • TEOS tetraethylorthosilicate
  • germanium oxide Aldrich, purity 99.998%
  • 24.758g of water 3.27g of N,N'-dimethyl-l,3-propanediamine (97% pure, Aldrich)
  • 12.5g of a solution of colloidal silica Lidox AS.
  • the mixture is stirred vigorously for 2 hours and when it is homogeneous, 2.59 g of hydrofluoric acid HF (48.1%, J T Baker) is added and then mixed. Finally, 5 wt% carbon content is added to obtain uniform and homogeneous distribution of carbon in the gel matrix.
  • the carbon loaded gel is autoclaved at 165 0 C. for 7 days under static microwave conditions.
  • a typical synthesis gel is produced by homogenizing gel containing colloidal silica, germanium oxide, alumina (pseudoboehmite phase), hexamethonium hydroxide and hexmethonium bromide in the presence of F " ions with minimum amount of water.
  • the final gel composition is
  • Table 5 X-ray diffraction data for as -synthesized ITQ-33 sample
  • Silicalite-I is synthesized with a batch composition of 1 SiO 2 : 0.08 (TPA)Br: 0.04 NH 4 F: 5 H 2 O.
  • a reactive gel is prepared by dissolving 4.26 g of tetrapropylammonium bromide and 0.296g of ammonium fluoride in distilled water. To this solution 12g of fumed silica is added and the mixture is stirred until it is homogenous. Finally, 5 wt% carbon content on solid content basis is added to obtain uniform and homogeneous distribution of carbon in the gel matrix.
  • the carbon loaded gel is autoclaved at 200 0 C for 7 days under static microwave conditions. A microwave power of 300W was applied to achieve synthesis temperature by the end of 2.5h.
  • the as-synthesized molecular sieves of examples 1-7 are calcined at 55O 0 C under a controlled oxygen environment for 12-18h.
  • sample is subjected to nitrogen-oxygen mixture (98-2% vol. basis) at flow rate of 300 ml/min and calcination temperature is achieved at a rate of 0.5°C/min.
  • the calcined samples are characterized for their textural and morphology properties by means of nitrogen adsorption- desorption measurements at -196 0 C (Table 7) and scanning electron microscopy.
  • the hydrogel transformation into molecular sieve in the present invention is with high yield involving nearly complete conversion of gel to molecular sieve.
  • Crystallization of molecular sieves in the present invention gives uniform crystals with smaller particle size compared to conventional method.
  • the process of the present invention allows minimization of waste disposal and reduction in reactor volume.

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Abstract

The present invention relates to microwave assisted process for the synthesis of molecular sieves from pseudo and/or dry carbon loaded gels comprising the steps of preparing pseudo and/or dry gel; carbon loading of the pseudo and/or dry gel to obtain carbon loaded pseudo and/or dry gel; treating the carbon loaded pseudo and/or dry gel at optimum microwave conditions of optimum temperature, optimum microwave power and optimum ramping time; crystallizing the product to obtain crystallized molecular sieves; and optionally calcination of crystallized molecular sieves to obtain calcined molecular seives.

Description

MICROWAVE ASSISTED PROCESS FOR SYNTHESIS OF MOLECULAR SIEVES FROM PSEUDO AND/OR DRY GELS
FIELD OF INVENTION The present invention discloses a microwave assisted process for synthesis of molecular sieves from pseudo and/or dry gels with coated carbon. BACKGROUND OF INVENTION
Crystalline molecular sieves have 3 -dimensional, microporous frameworks having tetrahedrally coordinated cations [TO4]. Generally, frameworks comprising oxygen tetrahedra of aluminium and silicon cations lead to the formation of microporous aluminosilicate framework commonly known as zeolites. On the other hand, 3-dimensional microporous aluminophosphate (AlPOs) frameworks classified as zeo-type molecular sieves are composed of oxygen tetrahedra of Al and P cations whereas silicoaluminophosphate (SAPOs) type molecular sieves composed of oxygen tetrahedra of Si, Al and P cations.
Molecular sieves are classified as small, medium and large pore .molecular sieves based on their pore opening. The small pore molecular sieves have pore size in between 0.4-0.5 nm. Medium pore molecular sieves have pore size in between 0.5-0.6 nm whereas large pore molecular sieves have pore opening of 0.6-0.8 nm (R. Szostak, Molecular Sieves: Principles of synthesis and Identification, 2nd edition, Blackie Academic and Professional, London, 1998).
Wide spread application of crystalline molecular sieves in the field of petroleum processing, petrochemical, fine chemical has led to sustained research effort, both in industry and academia, for their discovery. This has resulted into synthesis of new frameworks such as SSZ-53, -59 (Burton et.al. Chemistry: a Eur. Journal 9, 5737-5748 (2003), SSZ-51 (Morris, et.al.; Chem. Mater. 2004, 16, 2844), EMM-2,-3,-8, PSU-2 (Mertens, M.M.; US pat. 2006, 7,067,095, Afeworki, M. et.al.; Chem. Mater. 2004, 18, 1705; Afeworki, M. et.al.; Micro. Meso. Mater. 2007, 103, 213; Vaughan, D. E. W. et.al. Chem. Mater. 2006, 18, 361 1) in recent times. Molecular sieves are usually synthesized under hydrothermal conditions from a reactive gel comprising of water, aluminum, silica, germanium, and/or phosphorous sources in the presence of an organic structure directing agent, such as an organic nitrogen compound in the temperature range of 100-2000C wherein water molecules are believed to be acting as a filling agent during crystallization of molecular sieve. Commonly used nitrogen compounds are amines, diamines and quaternary ammonium salts. Such synthesis is also carried out under solvothermal conditions (EP-A-337,479) employing non-aqueous solvents such as glycols. The use of mineralizing agents especially fluoride ions (US patent 6,793,901) is also practiced in molecular sieve synthesis. The use of fluoride media is also reported to lead to the formation of large zeolite crystals (see Berger et.al. Microporous and Mesoporous Materials 83, (1 -3), 2005, 333-344).
In general crystallization of molecular sieves is performed under hydrothermal conditions in the temperature range of 100-2000C which usually requires prolonged crystallization time for phase formation. This sometimes leads to the formation of thermodynamically stable dense phases such as tridymite, cristobalite, berlinite, quartz as impure phases. This is due to the metastable nature of zeolitic framework under crystallization conditions. Furthermore, conventional hydrothermal approach is often found to be energy intensive.
The microwave-assisted synthesis of molecular sieves is a relatively new area of research (Komarneni, et.al. Mater. Res. Bull. 1992, 27, 1393; Ionics 1995, 21, 95). It offers many distinct advantages over conventional synthesis. These include rapid heating to crystallization temperature due to volumetric heating, resulting in homogeneous nucleation, fast super saturation by the rapid dissolution of precipitated gels and eventually a shorter crystallization time compared to conventional autoclave heating. It is also energy efficient and economical (Geoffrey A. Tompsett, Chem. Phys. Chem. 2006, 7, 296 - 319).
Few attempts have been made to prepare molecular sieves via dry gel conversion approach wherein dry reactive gel is exposed to water vapor under hydrothermal conditions (Saha et.al. Micro.Meso.Mater. 2005, 81, 277) More recently, molecular sieve synthesis using dry and/or pseudo dry gel has led to discovery of new molecular sieve compositions and frameworks which include all silica ITQ-12 (Yang et.al.; J. Am. Chem. Soc. 2004, 126, 10403), ITQ- 13 (R. Castafieda et.al. J. Catal., 2006, 238(1) 79-87; Corma et.al. Angew. Chem.lnt. Ed. 2003, 42 (10),l 156), ITQ-32 (Cantin et.al. J. Am. Chem. Soc. 2005, 127, 1 1560) and silicoalumninogermantes such as ITQ-31 (US pat. 7025948), ITQ-33 (Nature 2006, 443, 842). These molecular sieves are synthesized under hydrothermal conditions. The present invention discloses, a process for microwave-assisted synthesis of molecular sieve from pseudo and/or dry gel in the presence of carbon; a microwave absorbing aid.
OBJECTS OF THE PRESENT INVENTION It is an important object of the present invention to provide a novel energy efficient microwave assisted process for preparing molecular sieves from gel comprising of minimum and/or no water.
In is another object of the present invention to provide a microwave assisted process for synthesis of molecular sieves from pseudo and/or dry gels which overcomes the drawbacks of the prior art processes. SUMMARY OF THE INVENTION
The aforementioned and other objects of the present invention are achieved by a microwave assisted process for synthesis of molecular sieves. The process eventually involves negligible and/or no water. The disclosed approach involves preparation of dry gel and their coating with carbon and optimization of microwave conditions for successful synthesis of aluminosilicate, silicoaluminophosphate, silicoaluminogermante, silicogermanate, and silica based molecular sieve frameworks. The present invention also discloses the methodology for calcination of crystallized frameworks for their utilization as catalyst, catalyst carrier for hydrocarbon conversion or adsorbent for separation. The disclosed approach of the present invention may be utilized for synthesis of aluminosilicate, silicoaluminophosphate, silicoaluminogermante, silicogermanate, and silica molecular sieves including ITQ- 12, -13, and -32.
In another embodiment the novel energy efficient microwave assisted process for synthesis of molecular sieves of the present invention utilizes carbon as an assisting aid for molecular sieve synthesis under microwave conditions.
In still another embodiment of the present invention the carbon loading is ranging from 0.1-15 wt%.
In yet another embodiment novel energy efficient microwave assisted synthesis approach the present invention is applied for gel containing 0.1-5 wt% carbon.
In another embodiment the present invention is performed in the temperature range of 100-200 0C, preferably 150-200 0C, in the presence of carbon.
In still another embodiment the present invention is performed for time period ranging from 1-10 days. In yet another embodiment the present invention allows solid hydrogel transformation into molecular sieve with high yield, and it involves nearly complete conversion of gel to molecular sieve.
In another embodiment the present invention allows crystallization of uniform crystals with smaller particle size compared to conventional method.
In still another embodiment novel energy efficient microwave assisted synthesis approach of the present invention allows the crystallization of molecular sieves at higher temperatures than that used in the hydrothermal method.
In yet another embodiment novel energy efficient microwave assisted synthesis approach of the present invention allows minimization of waste disposal and reduction in reactor volume.
In another embodiment of the present invention the time interval disclosed varied depending on the molecular sieve composition synthesized. **
In still another embodiment of the present invention the synthesis time, varies from 1-4 days for aluminosilicate, 1-6 days for silicogermanate, 1-5 days, silicoaluminogermante, 1-8 days for silica molecular sieve, respectively.
In yet another embodiment of the present invention the synthesis of molecular sieves is carried out by varying microwave power.
In another embodiment of the present invention the synthesis is performed in the presence of microwave power ranging from 1-1200 W; more preferably in the range of 1-300 W.
In yet another embodiment of the present invention the synthesis of molecular sieves is performed under varying microwave ramp conditions.
In still another embodiment of the present invention the synthesis of molecular sieves is performed under microwave ramp conditions ranging from 5-120 mins; more preferably 45-75 mins.
In another embodiment of the present invention the synthesis methodology of the present invention is applied for synthesis of silicalite-I, silicoaluminogermante (e.g. ITQ-31, -33), silica (e.g. ITQ- 12,- 13,-32), silicoaluminophosphate (SAPO-5) molecular sieves.
In still another embodiment of the present invention the molecular sieves synthesized as per aforementioned embodiments are calcined in air and/or nitrogen- oxygen mixture; more preferably in nitrogen-oxygen mixture at elevated temperature in the range of 500-600 0C. In yet another embodiment of the present invention the molecular sieves are calcined in nitrogen-air mixture having composition ranging from 0-100 vol % of nitrogen to 0-20 vol % of oxygen.
In another embodiment of the present invention the molecular are calcined in nitrogen-oxygen mixture having composition of 80:20 vol% and more preferably 98-2 vol%.
In still another embodiment of the present invention the calcined molecular sieves as per aforementioned embodiments are used as a catalyst and/or catalyst carrier and/or adsorbent for hydrocarbon conversions and separation, respectively. BRIEF DESCRIPTION OF THE ACOMPANYEVG DRAWINGS
FIGURE 1: XRD pattern for as-synthesized SAPO-5 phase.
FIGURE 2: XRD pattern for as-synthesized ITQ- 12 phase.
FIGURE 3: XRD pattern for as-synthesized ITQ- 13 phase.
FIGURE 4: XRD pattern for as-synthesized ITQ-31 phase. FIGURE 5: XRD pattern for as-synthesized ITQ-33 phase.
FIGURE 6: XRD pattern for as-synthesized silicalite-I phase.
DETAILED DESCRIPTION OF THE INVENTION
The microwave assisted synthesis of molecular sieves in the presence of carbon can be utilized for synthesis of molecular sieves with varied framework composition. Typically, molecular sieves which can be crystallized with the present approach include framework composition of aluminosilicate, silicate-I, silicoaluminophosphate, silicoaluminogermante, silicogermanate or silica.
Firstly, a reactive homogeneous gel having a desired composition is prepared in the presence of requisite carbon content with minimum water content. The loading of carbon content is varied based on silica content in the gel composition. For example, gel containing higher silica content (in the range of 70-90 wt %) is loaded with about
10-15 wt% of carbon whereas with those with lower silica content is loaded with 5-8 wt% of carbon based total solid content of the gel. The water level of the prepared gel is manipulated due to hydrophobic nature of the gel to achieve uniform carbon coating over the gel. Typically, water content of the gel was varied in the range of 1-10 on molar ratio basis of silica content present in the gel. The gel so obtained is then subjected to microwave-hydrothermal conditions which are optimized based on the carbon content present in the reactive gel, composition and crystallization temperature.
The microwave conditions are varied with respect to microwave power in the range of 0-300 W and ramping time in the range of 30- 180 mins. The % of applied power is adjusted according to ramping time which is basically a function of gel composition and carbon loading in the gel. The crystallization time is found to be a function of gel composition, and carbon content. Typically gel comprising higher silica content found to have crystallization time up to 8-10 days whereas low silica content favored crystallization within 4 days. Thus crystallized samples are then subjected to calcination wherein samples are exposed gas mixture containing 98% nitrogen and 2% oxygen in the temperature range of 520-600 0C depending carbon content present in the crystallized sample. For example, crystallized sample with high silica content having higher loading of carbon content is calcined at 580 0C which is attained at three stages of 300, 500, 580 0C, respectively.
The crystallinity for the crystallized as well as calcined sample is measured and confirmed using powder X-ray diffraction pattern. Likewise, *the adsorption crystallinity for the calcined sample is measured by means of nitrogen adsorption- desorption isotherm at -1960C as per the ASTM method 4365 applicable for microporous solids. The morphology of the sample is determined using scanning electron microscopy technique.
The following examples are provided to illustrate the invention and are not to be construed as limiting thereof:
Example-l Synthesis of SAPO-5
A reaction mixture is prepared by combining 7.69 grams of 85 wt.% orthophosphoric acid (H3PO4) and 10 grams of water, to which is added 4.58 grams of a hydrated aluminum oxide, (a pseudo-boehmite phase, 74.2 wt.% Al.sub.2 O.sub.3, 25.8 wt.% H2 O), and stirred until homogeneous. To this mixture is first added 1.08 grams of 37 wt.% HCl, and then 2.16 grams of a fumed silica (92.8 wt.% SiO.sub.2, 7.2 wt.% H.sub.2 O) and the mixture is stirred until homogeneous. Finally 16.30 grams of an aqueous solution of 40 wt% tetraethyl ammonium hydroxide (TEAOH) is added and the mixture obtained is stirred until homogeneous. This homogenized gel is loaded with 2 wt% carbon of solid content and dried. A portion of this reaction gel is sealed in a pressure vessel lined with polytetrafluoroethylene and heated under microwave conditions at 15O0C at autogenous pressure for 5 hours. A microwave power of 30 W is applied to achieve synthesis temperature by the end of Ih. The solid reaction product is recovered by filtration, washed with water, and dried in air overnight at room temperature.
The X-ray powder diffraction pattern (Fig. 1) of the SAPO-5 product is characterized by the following data (Table 1): This X-ray pattern and all other X-ray patterns appearing hereinafter are obtained using standard X-ray powder diffraction techniques. The radiation source is a high-intensity, copper target, X-ray tube operated at 50Kv and 4OmA. The diffraction pattern from the copper Ka radiation and graphite monochromator is suitably recorded by an X-ray spectrometer scintillation counter, pulse height analyzer and strip chart recorder. Flat compressed powder samples are scanned at 20 per minute, using a 2 second time constant. Interplanar spacings (d) in Angstrom units are obtained from the position of the diffraction peaks expressed as 2Θ where θ is the Bragg angle as observed on the strip chart. Intensities are determined from the heights of diffraction peaks after subtracting background, "I0" being the intensity of the strongest line or peak, and "I" being the intensity of each of the other peaks.
As will be understood by those skilled in the art the determination of the parameter 20 is subject to both human and mechanical error, which in combination, can impose an uncertainty of about .+/- 0.4° on each reported value of 2Θ. This uncertainty is, also manifested in the reported values of the d-spacings, which are calculated from the 20 values. This imprecision is general throughout the art and is not sufficient to preclude the differentiation of the present crystalline materials from each other and from the compositions of the prior art.
Table 1: X-ray diffraction data for the as-synthesized SAPO-5 sample
2Θ d (A) ReI Int (%) 2Θ d (A) ReI Int ( %)
7.55 11.6 55.76 26.1 1 3.41 27.09
12.99 6.81 8.40 29.16 3.06 12.50
15.03 5.89 24.30 30.19 2.95 15.49
16.63 5.33 1.84 33.72 2.65 5.03
19.89 4.56 51.67 34.64 2.59 16.28 30
21.13 4.20 47.25 37.11 2.42 4.07
22.54 3.94 100.00 37.71 2.38 12.90
24.79 3.59 13.90 Example-2 Synthesis of ITQ-12
A reactive gel comprising of 20.83g of tetraethylorthosilicate (TEOS) in 55.54g of the 1,3,5-trimethylimidazole hydroxide solution produced as per prior art under continuous mechanical stirring at 200 rpm until the ethanol and an appropriate amount of water are evaporated to yield the above gel mixture. A solution of 2.33g of HF (48 wt % in water) and Ig of water is slowly added to the 1,3,5-trimethylimidazole silicate solution. The resultant mixture is mechanically and finally manually stirred until a homogeneous gel is formed. This gel is very thick as a consequence of the small amount of water present. The formed gel is loaded with 5 wt% carbon content to obtain uniform and homogeneous distribution of carbon in the gel matrix. The carbon loaded gel is autoclaved at 1750C for 7 days under static microwave conditions. A microwave power of 600W is applied to achieve synthesis temperature by the efid of 2.5 h. The solid reaction product is recovered by filtration, washed with water, and dried in air overnight at room temperature. X-ray diffraction analysis (Fig. 2) of the as-synthesized sample gives the results listed in Table 2. Table 2: X-ray diffraction data for as -synthesized ITQ-12 sample
2Θ d (A) ReI. Int (%) 2Θ d (A) ReI. Int (%)
10.59 8.34 49.08 25.96 3.43 38.56
13.05 6.78 23.23 26.45 3.36 45.74
15.75 5.62 100.00 27.25 3.27 15.54
17.83 4.97 7.56 29.66 3.00 4.31
19.83 4.47 8.10 31.08 2.87 13.94
20.88 4.25 17.47 31.81 2.81 12.92
21.28 4.17 12.20 33.31 2.69 10.41
21.46 4.14 7.42 33.90 2.64 8.70
22.87 3.88 13.53 34.27 2.61 4.04
23.39 3.79 16.29 35.91 2.49 3.54
23.70 3.75 4.15 36.45 2.46 2.20
24.03 3.69 12.01 39.02 2.31 2.89
25.60 3.47 15.00 39.77 2.26 4.14 Example-3 Synthesis of ITQ-13
A siliceous reactive gel is produced by hydrolyzing 17.33g of tetraethylorthosilicate (TEOS) with 74.6g of the hexamethonium dihydroxide solution produced under continuous mechanical stirring until the ethanol and the water are evaporated to yield the above gel reaction mixture. Then, a solution of 1.94g of HF (48 wt % in water) and Ig of water is slowly added to the resultant hexamethonium silicate solution. The reaction mixture is mechanically and finally manually stirred until a homogeneous gel is formed. The resulting gel is very thick. This gel is loaded with 5 wt% of carbon to obtain uniform and homogeneous distribution of carbon in the gel matrix. The carbon loaded gel is autoclaved at 1650C for 7 days under static microwave conditions. A microwave power of 300W is applied to achieve synthesis temperature by the end of 0.5 h. The solid reaction product is recovered by filtration, washed with water, and dried in air overnight at room temperature. X-ray diffraction analysis (Fig. 3) of the as-synthesized sample gives the results listed in Table 3. Table 3: X-ray diffraction data for as -synthesized ITQ-13 sample
2Θ d(A) ReI. Int (%) 2Θ d(A) ReI. Int (%)
5.20 16.96 10.60 21.05 4.21 44.43
7.06 12.49 29.98 23.04 3.86 100.00
8.03 10.99 21.05 23.75 3.74 72.69
11.22 7.87 29.06 24.37 3.65 18.81
11.91 7.42 1.34 26.59 3.35 7.99
14.35 6.16 10.07 27.72 3.22 20.19
15.51 5.71 7.99 28.49 3.13 9.47
16.09 5.50 17.73 31.13 2.87 9.10
16.65 5.32 9.81 32.09 2.79 5.12
17.10 5.18 7.76 34.36 2.61 1.81
18.91 4.69 8.21 35.62 2.52 3.50
19.68 4.51 2.07 38.28 2.35 2.02
20.08 4.42 2.39 39.17 2.29 4.1 1 ExampIe-4 Synthesis of ITQ-31
4.35g of germanium oxide (Aldrich, purity 99.998%) is mixed with 24.758g of water, 3.27g of N,N'-dimethyl-l,3-propanediamine (97% pure, Aldrich) and 12.5g of a solution of colloidal silica (Ludox AS). The mixture is stirred vigorously for 2 hours and when it is homogeneous, 2.59 g of hydrofluoric acid HF (48.1%, J T Baker) is added and then mixed. Finally, 5 wt% carbon content is added to obtain uniform and homogeneous distribution of carbon in the gel matrix. The carbon loaded gel is autoclaved at 1650C. for 7 days under static microwave conditions. A microwave power of 300W is applied to achieve synthesis temperature by the end of 2.5 h. The solid reaction product is recovered by filtration, washed with water, and dried in air overnight at room temperature. X-ray diffraction analysis (Fig. 4) of the as-synthesized sample gives the results listed in Table 4. Table 4: X-ray diffraction data for as -synthesized ITQ-31 sample
20 d (A) ReI. Int (%) 2Θ d (A) ReI. Int (%)
10.22 8.64 100.00 28.74 3.10 6.24
14.39 6.14 7.13 29.57 3.02 4.56
16.01 5.53 6.40 31.55 2.83 7.28
18.99 4.67 26.43 32.25 2.77 10.00
20.36 4.36 5.09 32.99 2.71 14.97
22.79 3.89 46.08 33.89 2.64 14.19
23.63 3.76 38.47 34.81 2.57 3.55
24.81 3.58 16.33 37.73 2.38 2.06
26.01 3.42 3.47 38.43 2.34 2.03
Example-5 Synthesis of ITQ-33
A typical synthesis gel is produced by homogenizing gel containing colloidal silica, germanium oxide, alumina (pseudoboehmite phase), hexamethonium hydroxide and hexmethonium bromide in the presence of F" ions with minimum amount of water. The final gel composition is
0.67 SiO2: 0.33 GeO2: 0.050 Al2O3: 0.15 Hex(OH)2: 0.10 HeX(Br)2 : 0.30 HF: 1.5 H2O.
Thus obtained final gel is loaded with carbon as per example 2 and obtained gel is subjected to crystallization conditions as per example 4. The solid reaction product is recovered by filtration, washed with water, and dried in air overnight at room temperature. X-ray diffraction analysis of the as-synthesized sample gives the results listed in Table 5.
Table 5: X-ray diffraction data for as -synthesized ITQ-33 sample
2Θ d (A) ReI. Int (%)
5.33 16.54 100.00
7.76 1 1.37 6.38
9.22 9.58 7.04
9.43 9.37 9.44
10.59 8.34 2.58
12.72 6.95 3.78
13.98 6.33 1.29
15.47 5.72 5.79
16.36 5.41 2.74
18.35 4.82 2.04
19.17 4.63 4.91
20.92 4.24 4.52
22.35 3.97 3.53
23.24 3.82 8.09
24.41 3.64 7.45
25.47 3.49 5.93
26.67 3.34 4.55
28.17 3.16 5.27
30.37 2.94 0.49
35.13 2.55 0.70
38.05 2.36 0.84
ExampIe-6
Synthesis of Silicalite-I
Silicalite-I is synthesized with a batch composition of 1 SiO2: 0.08 (TPA)Br: 0.04 NH4F: 5 H2O. Typically, a reactive gel is prepared by dissolving 4.26 g of tetrapropylammonium bromide and 0.296g of ammonium fluoride in distilled water. To this solution 12g of fumed silica is added and the mixture is stirred until it is homogenous. Finally, 5 wt% carbon content on solid content basis is added to obtain uniform and homogeneous distribution of carbon in the gel matrix. The carbon loaded gel is autoclaved at 2000C for 7 days under static microwave conditions. A microwave power of 300W was applied to achieve synthesis temperature by the end of 2.5h. The solid reaction product is recovered by filtration, washed with water, and dried in air overnight at room temperature. X-ray diffraction analysis (Fig. 6) of the as-synthesized sample gives the results listed in Table 6. Table 6: X-ray diffraction data for as -synthesized Silicalite-I sample
2Θ d (A) ReI Int (%) 2Θ d (A) ReI Int (%)
7.87 11.22 100.00 28.04 3.17 2.53
8.78 10.05 68.25 29.19 3.05 1 1.42
11.82 7.48 1.85 29.89 2.98 14.15
13.17 6.71 6.41 30.40 2.94 6.08
13.83 6.39 12.82 31.19 2.86 2.61
14.83 5.97 18.69 32.13 2.78 1.70
15.42 5.74 10.28 32.75 2.73 4.33
15.51 5.70 10.83 33.43 2.67 1.15
15.87 5.53 16.17 34.38 2.61 5.55
16.44 5.38 3.67 35.08 2.55 2.49
17.24 5.14 1.59 35.67 2.51 3.45
17.71 5.00 8.68 36.10 2.48 6.53
19.15 4.62 6.23 37.52 2.39 5.20
19.88 4.46 1.93 38.76 2.32 1.29
20.29 4.37 10.05 31.19 2.86 2.61
20.77 4.27 13.80 32.13 2.78 1.70
21.69 4.09 1.72 32.75 2.73 4.33
22.20 3.99 5.61 33.43 2.67 1.15
22.98 3.86 75.14
23.31 3.81 62.20
23.63 3.76 28.64
23.89 3.72 49.88
24.36 3.65 31.84
25.53 3.49 5.59
25.83 3.45 8.68
25.88 3.44 9.70
26.90 3.31 1 1.37
Example-7
Calcination and characterization of molecular sieves
The as-synthesized molecular sieves of examples 1-7 are calcined at 55O0C under a controlled oxygen environment for 12-18h. Typically, sample is subjected to nitrogen-oxygen mixture (98-2% vol. basis) at flow rate of 300 ml/min and calcination temperature is achieved at a rate of 0.5°C/min. The calcined samples are characterized for their textural and morphology properties by means of nitrogen adsorption- desorption measurements at -1960C (Table 7) and scanning electron microscopy.
i Table 7: Textural properties of molecular sieves
Molecular sieve Surface area (m /g) Pore volume (cc/g)
SAPO-5 580 0.28
ITQ-12 720 0.28
ITQ- 13 665 0.45
Advantages of the present invention are:
1. The hydrogel transformation into molecular sieve in the present invention is with high yield involving nearly complete conversion of gel to molecular sieve.
2. Crystallization of molecular sieves in the present invention gives uniform crystals with smaller particle size compared to conventional method.
3. The process of the present invention allows minimization of waste disposal and reduction in reactor volume.

Claims

We claim:
1. A microwave assisted process for the synthesis of molecular sieves from pseudo and/or dry carbon loaded gels comprising the steps:
a) preparing pseudo and/or dry gel such as hereinbefore described; b) carbon loading of said pseudo and/or dry gel to obtain carbon loaded pseudo and/or dry gel; c) treating said carbon loaded pseudo and/or dry gel at optimum microwave conditions of optimum temperature, optimum microwave power and optimum ramping time; d) crystallizing the product obtained from step c) to obtain crystallized molecular sieves.
2. The process as claimed in claim 1 wherein said pseudo and/or dry gel is a homogeneous gel comprising no water or water in the range of 1-10 on molar ratio basis of silica content present in the gel.
3. The process as claimed in claim 1 wherein said carbon loading is in the range of 0.1-15 wt%.
4. The process as claimed in claim 3 wherein said carbon loading is in the range of 0.1-5 wt% carbon.
5. The process as claimed in claim 1 wherein said optimum temperature comprises a temperature range of 100-200 0C.
6. The process as claimed in claim 5 wherein said optimum temperature is preferably in the range of 150-200 0C.
7. The process as claimed in claim 1 wherein said optimum microwave power ranges from 1-1200 W.
8. The process as claimed in claim 7 wherein said optimum microwave power is preferably in the range of 1-300 W.
9. The process as claimed in claim 1 wherein said optimum ramping time is in the range of 5-120 mins.
10. The process as claimed in claim 9 wherein said optimum ramping time is preferably in the range of 45-75 mins.
11. The process as claimed in claim 1 wherein said crystallizing is performed for a time period ranging from 1-10 days.
12. The process as claimed in any preceding claims wherein said molecular sieves are selected from a group comprising of aluminosilicate, silicate-I, silicoaluminophosphate, silicoaluminogermante, silicogermanate or silica based molecular sieve framework.
13. The process as claimed in claim 12 wherein said silicoaluminophosphate is SAPO-5.
14. The process as claimed in claim 12 wherein said silicoaluminogermante is ITQ- 31, ITQ -33.
15. The process as claimed in claim 12 wherein said silica based molecular sieve framework is ITQ- 12, ITQ- 13 and ITQ-32.
16. The process as claimed in claim 11 wherein said time period is 1-4 days for aluminosilicate, 1-6 days for silicogermanate, 1-5 days for silicoaluminogermante and 1-8 days for silica molecular sieve.
17. A microwave assisted process for the synthesis of molecular sieves from pseudo and/or dry carbon loaded gels comprising the steps: a. preparing pseudo and/or dry gel wherein said gel is homogeneous gel comprising no water or water in the range of 1-10 on molar ratio basis of silica content present in the gel; b. carbon loading of said pseudo and/or dry gel to obtain carbon loaded pseudo and/or dry gel wherein said carbon loading is in the range of 0.1-
15 wt% preferably in the range of 0.1 -5 wt% carbon; c. treating said carbon loaded pseudo and/or dry gel at optimum microwave conditions of optimum temperature of 100-200 0C preferably 150-200 0C, optimum microwave power in the range of 1-1200 W preferably in the range of 1 -300 W and optimum ramping time is in the range of 5-120 mins preferably in the range of 45-75 mins; d. crystallizing the product obtained from step c) to obtain crystallized molecular sieves wherein said crystallizing is performed for a time period ranging from 1-10 days.
18. The process as claimed in claims 1 or 17 wherein crystallized molecular sieves are subjected to calcination to obtain calcined molecular seives.
19. A microwave assisted process for the synthesis of molecular sieves from pseudo and/or dry carbon loaded gels comprising the steps: a. preparing pseudo and/or dry gel such as hereinbefore described; b. carbon loading of said pseudo and/or dry gel to obtain carbon loaded pseudo and/or dry gel; c. treating said carbon loaded pseudo and/or dry gel at optimum microwave conditions of optimum temperature, optimum microwave power and optimum ramping time; d. crystallizing the product obtained from step c) to obtain crystallized molecular sieves; e. calcination of crystallized molecular sieves to obtain calcined molecular seives.
20. The process as claimed in claims 18 or 19 wherein said calcination is performed in air and/or nitrogen-oxygen mixture.
21. The process as claimed in claim 20 wherein said calcination is performed in nitrogen-oxygen mixture at elevated temperature in the range of 300-600 0C.
22. The process as claimed in claim 21 wherein said calcination is performed in nitrogen-oxygen mixture preferably at a temperature in the range of 500-600 0C.
23. The process as claimed in any of the preceding claims 18 to 22 wherein said calcination is performed in nitrogen-oxygen mixture having composition ranging from 0-100 vol % of nitrogen to 0-20 vol % of oxygen.
24. The process as claimed in any of the preceding claims 18 to 23 wherein said calcination is performed in nitrogen-oxygen mixture having composition of 80:20 vol%.
25. The process as claimed in claim 24 wherein said calcination is performed in nitrogen-oxygen mixture having composition 98:2 vol%.
26. Use of molecular sieves obtained by the process as disclosed in any of the preceding claims as a catalyst, catalyst carrier, adsorbent for hydrocarbon conversions, separation or combinations thereof.
27. Molecular sieves prepared by the microwave assisted process as claimed in any of the preceding claims.
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CN113165893A (en) * 2018-12-11 2021-07-23 埃克森美孚研究工程公司 EMM-41 compositions, methods of manufacture, and uses thereof
CN113165893B (en) * 2018-12-11 2024-06-11 埃克森美孚科技工程公司 EMM-41 compositions, methods of manufacture and uses thereof
CN112110454A (en) * 2020-09-25 2020-12-22 浙江浙能技术研究院有限公司 Microwave-assisted synthesis method for rapidly synthesizing SSZ-13 molecular sieve
CN114644347A (en) * 2020-12-17 2022-06-21 中国石油化工股份有限公司 SAPO-20 molecular sieve and preparation method thereof
CN114014336A (en) * 2021-11-30 2022-02-08 大连理工大学 Method for synthesizing SAPO-37 molecular sieve

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