Title of Invention

"AN IMPROVED PROCESS FOR THE PREPARATION OF FILM OF MOLECULAR SIEVES"

Abstract

The present invention releases to an improved process for the preparation of films of molecular sieves. The thickness of the films prepared by the process of present invention can be monitored to a desired thickness in the range 30 to 1500 A°. The principle by which the process of present invention is developed is based on following steps. 1) Synthesis of precalcined molecular sieves by the use of tem plating agent by conventional method, 2) Formation of dispersion of molecular sieve in organic medium which spreads on aqueous surface e.g. carbon tetrachloride, chloroform, benzene, hexane,. 3) Spreading the dispersion on aqueous surface allowing the organic solvent to evaporate. In this process the dispersed particles form thin / ultra thin layer of zeolite on the surface of aqueous medium. 4) Pressurizing the layer laterally 5) Transferring the film from aqueous surface to substrate surface. 6) Calcining the layer at a temperature ranging from 300 to 800°C.

Full Text

The present invention releases to an improved process for the preparation of films of molecular sieves. The thickness of the films prepared by the process of present invention can be monitored to a desired thickness in the range 30 to 1500 A°. The films formed by this process could have applications as chemical sensors, membrane separators, catalyst, size and charge selective electrodes, thin layer chromatography, host - guest matrix etc. The conventional methods employed for the formation of molecular sieve films are 1) Immersion method / Dip method 2) Vapour phase transport 3) Laser ablation deposition 4) Self assembled multilayers The above mentioned methods and their drawbacks are discussed below. 1) Immersion method / Dip method Porous substrates / substrates are immersed in to appropriate synthesis mixtures, containing silica source, alumina source, templating agent, solvent, water and other chemicals in to pressure resistance vessel, raising the temperature slowly to appropriate temperature for hydrothermal synthesis of desired molecular sieve. During the formation of molecular sieve, the substrate gets coated by molecular sieve layer containing template. Some of the disadvantages of the method are a) morphology of the film can get affected by the substrate, b) only those substrates can be used which withstand the experimental environment of molecular sieve synthesis by hydrothermal method. 2) Vapour transport method A film of chemicals, consisting of all the constituents leading to molecular sieve, is deposited on a suitable substrate by sol-gel method. The substrate is kept in an apparatus so that under hydrothermal conditions the film is exposed to transported vapours of structure guiding agent. In the appropriate conditions of temperature, pressure and time of reaction, the gel film is converted in to molecular sieve film. The major disadvantage of this method is that, the formation of thin film of the molecular sieve is not possible . Composition of molecular sieve may not be uniform along the thickenss, particularly when the substrate used contain the molecular sieves constituents. 3) Laser ablation method / sputtering The method uses concentrated energy source, namely, laser, to transfer solid molecular sieve in to vapour form, consisting of atoms, molecules, ions and clusters. These vapours are transported to suitable substrates where they form molecular sieve film on condensation. The major disadvantages of this method are large energy requirements, vacuum requirement, difficulty in controlling the morphology of the film, most of the films are in the amorphous state when deposited and therefore postdeposition treatment is necessary to crystallize films. 4) Self assembled multilayers This technique is used in two ways to form molecular sieve films. 1) To form bonds between the substrate surface and molecular sieve films. 2) To deposit molecular sieve films.In principal, it is a construction of , multilayers assemblies by consiquitive adsorption of anionic and cationic bipolar amphiphiles and / or polyelctrolytes; the driving force being the attraction between the opposite charges. In a modification Van-Der-Waal interactions have been used as driving force. The disadvantages of this method are 1) many chemical species, other than substrate and the material of which the film is to be deposited are involved, 2) post deposition treatment is required to remove unwanted chemical species. The above methods are described in a review article Chemistry of materials, 8, 1996, 1636-1653 by Thomas Bein The main object of the present invention is to provide an improved and versatile process for the preparation of thin / ultra thin films of molecular sieves particularly the one prepared by using organic templates. The principle by which the process of present invention is developed is based on following steps. 1) Synthesis of precalcined molecular sieves by the use of templating agent by conventional method, 2) Formation of dispersion of molecular sieve in organic medium which spreads on aqueous surface e.g. carbon tetrachloride, chloroform, benzene, hexane, etc.3) Spreading the dispersion on aqueous surface allowing the organic solvent to evaporate. In this process the dispersed particles form thin / ultra thin layer of zeolite on the surface of aqueous medium. 4) pressurizing the layer laterally 5) Transferring the film from aqueous surface to substrate surface. 6) Calcining the layer at a temperature ranging from 300 to 800 °C . The molecular sieve films formed by the process of present invention may be selected from micro porous and/or mesoporous molecular sieve materials etc. which are crystallized with the help of tern plating agents. Accordingly, the present invention provides an improved process for the preparation of film of molecular sieves which comprises: a) Characterized in that dispersing powder of noncalcined molecular sieve prepared by using organic template in an organic volatile solvent such as here described capable of spreading on water, the concentration of powder in the dispersion being in the range 0.05 to 0.3 mgms/gm, b) spreading the dispersion so obtained on aqueous surface, allowing the solvent to evaporate and subject to lateral compressing the layer formed on aqueous surface by known method to form a film, c) dipping the substrate, .as herein described on which film is to be deposited vertically through the film in the water and withdrawing at a uniform rate, d) optionally repeating steps ( c ) followed by calcining at 300 to 800°C till template is completely removed to get film of molecular sieve. In one of the embodiments of the present invention, the molecular sieves used in the process of present invention may be selected from zeolites, mesoporous materials which are crystallized with the help of templating agents. In another embodiment the volatile solvents used may be selected from solvents having spreading coefficient in the range of 8 to 18 dynes/cm exemplified by carbon tetrachloride, chloroform, benzene, n-hexane and their mixtures. In yet another embodiment, the substrates used in the process of invention can be selected from metals, ceramics, glass, quartz, alumina, titania , porous substrates made thereof. The process of the present invention is described herein below by examples which are illustratative and should not be construed to limit the scope of present invention in any manner. Example 1 0.1 mgms of precalcined Hexagonal Mesoporous Silica (HMS) powder is ground. It is dispersed in 5 ml of carbon tetrachloride and stirred for 10 min. Two drops of dispersion are spread on the surface of aqueous phase contained in teflon tray of 45 cms times 15 cms times 2 cms size. Carbon tetrachloride is allowed to evaporate. A layer of HMS formed on the surface of water is laterally compressed with the help of oleic acid piston and teflon thread barrier, (pressure ~30 dynes / cm.) The substrate, a glass slide, is dipped and withdrawn at constant rate of 1 cm / min. in the compartment having HMS layer on the surface. In this process the layer gets coated on glass substrate. The coating operation is repeated 15 times to get thicker coating. The film, thus formed is subjected to calcination at a temperature of 500 ° C for 8 hrs. in constant flow of air. Example 2 0.26 mgms of precalcined ferririte powder is ground. It is dispersed in 5 ml of chloroform and stirred for 10 min. Two drops of dispersion are spread on the surface of aqueous phase contained in teflon tray of 45 cms times 15 cms times 2 cms size. Carbon tetrachloride is allowed to evaporate. A layer of ferririte formed on the surface of water is laterally compressed with the help of oleic acid piston and teflon thread barrier, (pressure -30 dynes / cm.) The substrate, a glass slide, is dipped and withdrawn at constant rate of 1 cm / min. in the compartement having ferririte layer on the surface. In this process the layer gets coated on glass substrate. The coating operation is repeated 15 times to get thicker coating. The film, thus formed is subjected to calcination at a temperature of 550 ° C for 8 hrs. in constant flow of air. Example 3 0.15 mgms of precalcined ZSM 5 powder is ground. It is dispersed in 5 nil of benzene and stirred for 10 min. Two drops of dispersion are spread on the surface of aqueous phase contained in teflon tray of 45 cms times 15 cms times 2 cms size. Carbon tetrachloride is allowed to evaporate. A layer of ZSM5 formed on the surface of water is laterally compressed with the help of oleic acid piston and teflon thread barrier, (pressure -30 dynes / cm.) The substrate, a glass slide, is dipped and withdrawn at constant rate of 1 cm / min. in the compartement having ZSM5 layer on the surface. In this process the layer gets coated on glass substrate. The coating operation is repeated 15 times to get thicker coating. The film, thus formed is subjected to calcination at a temperature of 580 ° C for 8 hrs. in constant flow of air. Example 4 0.2 mgms of precalcined SAPO powder is ground. It is dispersed in 5 ml of n-hexane and stirred for 10 min. Two drops of dispersion are spread on the surface of aqueous phase contained in teflon tray of 45 cms times 15 cms times 2 cms size. Carbon tetrachloride is allowed to evaporate. A layer of SAPO formed on the surface of water is laterally compressed with the help of oleic acid piston and teflon thread barrier, (pressure ~ 30 dynes / cm.) The substrate, a glass slide, is dipped and withdrawn at constant rate of 1 cm / min. in the compartement having SAPO layer on the surface. In this process the layer gets coated on glass substrate. The coating operation is repeated 15 times to get thicker coating. The film, thus formed is subjected to calcination at a temperature of 550 ° C for 8 hrs. in constant flow of air. The main advantages of the present invention are l)This is a common method of thin film formation of molecular sieves which are conventionally synthesized by the use of organic template. 2) The method does not require any sophisticated equipment. 3) The procedure is simple and the method is low cost. 4) The morphology of the deposited material does not get affected during the process of thin film formation. 5) The thickness of films can be monitored. We Claim: 1. An improved process for the preparation of film of molecular sieves which comprises: a) Characterized in that dispersing powder of noncalcined molecular sieve prepared by using organic template in an organic volatile solvent such as here described capable of spreading on water, the concentration of powder in the dispersion being in the range 0.05 to 0.3 mgms/gm, b) spreading the dispersion so obtained on aqueous surface, allowing the solvent to evaporate and subject to lateral compressing the layer formed on aqueous surface by known method to form a film, c) dipping the substrate, as herein described on which film is to be deposited vertically through the film in the water and withdrawing at a uniform rate, d) optionally repeating steps (c ) followed by calcining at 300 to 800°C till template is completely removed to get film of molecular sieve. 2. A process as claimed in claim 1, wherein the said molecular sieve is selected from zeolites such as ZSM-5, Beta, ferrierite and mesoporous materials hexagonal meso porous silica, Mobile crystalline material -MCM-41. 3. A process as claimed in claims 1 and 2, wherein the said organic volatile solvent is selected from carbon tetrachloride, chloroform, benzene, n-hexane and their mixtures. 4. A process as claimed in claims 1 to 3, wherein the said substrates is selected from metals, ceramics, glass, quartz, alumina. 5. A process for the preparation of films of molecular sieves described substantially in claims 1 to 4, hereinbefore and illustrated with reference to the examples contained therein.

Documents:

987-del-2000-abstract.pdf

987-del-2000-claims.pdf

987-del-2000-correspondence-others.pdf

987-del-2000-correspondence-po.pdf

987-del-2000-description (complete).pdf

987-del-2000-form-1.pdf

987-del-2000-form-19.pdf

987-del-2000-form-2.pdf

987-del-2000-form-3.pdf