Title of Invention	"AN IMPROVED PROCESS FOR THE PREPARATION OF CARBON NANOTUBE FOR INDUSTRIAL APPLICATIONS"
Abstract	The process disclosed relates to the preparation of carbon nanotubes by catalytic decomposition of cycloalkane over a trimetallic oxide calyst prepared by sol-gel method, as cycloalkane being the carbon source, thereby facilitating the catalytic decomposition reaction temperature to be as low as 700-800°C.

Full Text

The present invention relates to an improved process for the preparation of carbon nanotube for industrial applications. More particularly, the present invention relates to an improved process for the preparation of carbon nanotube by the catalytic decomposition of cycloalkane on Ni-Mo-MgO catalyst. The process has enormous potential application as hydrogen storage media in electrochemical industries. It also finds application in electronics industry as micro electronic devices. Moreover, the product is envisaged to have use in chemical industries as catalyst supports in heterogeneous catalysis and solution absorption agents that has an impact on the environment management. It also finds application as recording media due to the novel magnetic properties associated therewith. As reported by Lin etal (Carbon 35, 1495-1501, 1997), carbon nanotubes are conventionally prepared by electric arc discharge, laser evaporation and catalytic decomposition of certain hydrocarbons or other organics in the presence of various supported transition metal catalyst. Choi etal (Carbon 39, 655, 2001) however observed that while the first two methods could only produce high quality nanotubes in yields suitable for limited research, they were not adoptable to industrial production. This has prompted the researchers to explore other chemical processes for viable industrial production of carbon nanotubes. Reference may be made to Gournis etal (Carbon, 40, 2641, 2002) and Hernadi etal (Zeolites 17, 416, 1996), who adopted chemical routes for the production of carbon nanotubes using metals like Fe, Co, Ni supported on zeolites, silica, alumina, graphite and metal oxides like MgO by the decomposition of hydrocarbon gases. As reported by Zang etal (Carbon 35, 1495, 1997), selection of carrier gas and catalyst in the form of ultra fine particles as well as reaction conditions used need to be taken into consideration in order to get relatively even carbon nanotubes. Liu etal (Synthetic metals, 128, 191,2002) synthesized carbon nanotubes by the catalytic decomposition of cyclohexane over Fe2O3/SiO2-AI2O3 catalyst, prepared in the form of ultra fine particles by sol-gel method, while the carrier gas H2 or N2 at a reaction temperature of 750°C introduced the carbon containing precursor cyclohexane. The main limitation associated with all these processes is that maximum gain in product weight has not been raised beyond 100%, thereby limiting its scope for commercial production. This problem has been overcome by Ning etal (Chemical Physics Letters 366, 555, 2002), who synthesized carbon nanotubes, whereby the Co-Mo-MgO catalyst was prepared by sol-gel method and methane, used as the carbon source, was introduced at a reaction temperature of about 1000°C. The major limitation associated with this process is that it poses a risk of accidents at the reaction temperature of 1000°C, at which methane is combustible. The main objective of the present invention is to provide an improved process for the preparation of carbon nanotube for industrial applications, which obviates the limitations as stated above. Another objective of the present invention is to provide a process for the preparation of carbon nanotubes at a temperature in the range of 700-800°C Yet another objective of the present invention is to prepare a Ni-Mo-MgO catalyst for catalytic decomposition of hydrocarbon. Still another objective of the present invention is to use hydrogen as the carrier gas for a carbon source. Yet another objective of the present invention is to use cycloalkane as the carbon source for producing hydrocarbon. Accordingly the present invention provides an improved process for the preparation of carbon nanotubes for industrial applications which comprises i) reacting 25-75% w/w, of nickel salt, 25-75% w/w of magnesium salt and 100-300% w/w of known gelling agent in aqueous medium at a temperature in the range of 20-40°C under stirring condition for a period of not less than 45 minutes, followed by heating the resulting saturated solution to a temperature not exceeding 120°C for a period of not less than 7hrs to get a powder, ii) adding 30-60% w/w of molybdenum salt to the powder, as obtained in step (i), followed by heating the resulting product to a temperature of 700 - 800°C for not less than 5 hours to obtain Ni-MO-MgO catalyst, iii) passing hydrogen gas at a rate of not less than 100 ml per minute through 0.1-0.5% w/v, based on the weight of Ni-MO-MgO catalyst, of known cycloalkane solution for a period of not less than 30 minutes followed by passing the resulting hydrocarbon gas through the Ni-MO-MgO catalyst, as obtained in step (ii), at 700 - 800°C and subsequent adjusting of temperature of not exceeding 100°C by passing nitrogen gas to obtain carbon nanotube, iv) subjecting the carbon nanotube, as formed in step (iii), to conventional washing followed by drying by known method at a temperature not exceeding 150°C to get pure carbon nanotube. In an embodiment of the present invention, the nickel salt used may be selected from nickel nitrate, nickel chloride.nickel sulphate In another embodiment of the present invention, the magnesium salt used may be selected from magnesium oxide, magnesium nitrate,magnesium chloride In yet another embodiment of the present invention, the known gelling agent used may be selected from citric acid, urea,polyvinyl alcohol. In still another embodiment of the present invention, the molybdenum salt used may be selected from ammonium molybdate,molybdenum powder. In yet another embodiment of the present invention, the known cycloalkane used may be selected from cyclobutane, cyclopropane,cyclohexane. The process of the present invention is described below in detail. 25-75% w/w, of nickel salt, 25-75% w/w of magnesium salt and 100-300% w/w of known gelling agent are mixed in water under stirring condition. The reaction is continued for a period of not less than 45 minutes at a temperature in the range of 20-40°C. The resulting saturated solution is heated to a temperature not exceeding 120°C for a period of not less than 7hrs to get a pale green powder. 30-60% w/w of molybdenum salt is then added to this powder and the resulting mixture is heated to a temperature of 700 - 800°C for not less than 5 hours to obtain Ni-MO-MgO catalyst. Gaseous hydrogen is passed at a rate of 100 ml per minute through a known cycloalkane solution for a period of not less than 30 minutes. The amount of the cycloalkane ranges between 0.1-0.5% w/v, on the weight of the Ni-MO-MgO catalyst. The resulting hydrocarbon gas is passed through the Ni-MO-MgO catalyst, maintained at a temperature in the range of 700 - 800°C, whereby carbon nanotube is formed in impure form. The temperature is finally adjusted at not more than 100°C by passing nitrogen gas to avoid formation of amorphous carbons in the system. The impure carbon nanotube is purified by conventional washing, which is done with water and diluted nitric acid. The product is finally air dried at a temperature not exceeding 150°C to get pure carbon nanotubes. The inventive step of the present invention lies in using cycloalkane as the carbon source, thereby facilitating the growth of carbon nanotube at a temperature as low as 700-800°C by using trimetallic oxide catalyst. The following examples are given by way if illustration only and therefore should not be construed to limit the scope of the present invention. Example 1 0.25g of nickel nitrate was dissolved in water with 0.25g of magnesium oxide and 1g of citric acid to form a saturated solution by magnetic stirring for 45 minutes at 20°C. This solution was heated for a period of 7 hrs at 120°C to get a powder. 0.3g of ammonium molybdate was added to the powder obtained and was mixed manually. This was heated at 700°C for 5hrs in air to obtain the Ni-Mo-MgO catalyst. 0.015g of Ni-Mo-MgO catalyst was loaded into the reaction chamber and kept in the furnace. The temperature of reaction chamber was raised from room temperature to 700°C. Soon after the temperature reached 700°C, pure hydrogen gas at the rate of 100ml per min passed through cyclohexane solution was fed into the reaction chamber containing the catalyst for 30 minutes which resulted in the formation of carbon nanotube. The reaction chamber was then cooled by passing nitrogen gas. The grown carbon nanotube was washed with dilute nitric acid and water to get them in the pure form. Example 2 0.50g of nickel nitrate was dissolved in water with 0.50g of magnesium oxide and 2g of citric acid to form a saturated solution by magnetic stirring for 1 hr at 30°C. This solution was heated for a period of 8 hrs at 110°C to get a powder. 0.45g of ammonium molybdate was added to the powder obtained and was mixed manually. This was heated at 750°C for 8 hrs in air to obtain the Ni-Mo-MgO catalyst. 0.035g of Ni-Mo-MgO catalyst was loaded into the reaction chamber and kept in the furnace. The temperature of reaction chamber was raised from room temperature to 750°C. Soon after the temperature reached 750°C, pure hydrogen gas at the rate of 120ml per min passed through cyclohexane solution was fed into the reaction chamber containing the catalyst for 45 minutes which resulted in the formation of carbon nanotubes. The reaction chamber was then cooled by passing nitrogen gas. The grown carbon nanotubes was washed with dilute nitric acid and water to get them in the pure form. Example 3 0.75g of nickel nitrate was dissolved in water with 0.75g of magnesium oxide and 3g of citric acid to form a saturated solution by magnetic stirring for 75 minutes at 40°C. This solution was heated for a period of 10 hrs at 115°C to get a powder. 0.6g of ammonium molybdate was added to the powder obtained and was mixed manually. This was heated at 800°C for 10 hrs in air to obtain the Ni-Mo-MgO catalyst. 0.075g of Ni-Mo-MgO catalyst was loaded into the reaction chamber and kept in the furnace. The temperature of reaction chamber was raised from room temperature to 800°C. Soon after the temperature reached 800°C, pure hydrogen gas at the rate of 130ml per min passed through cyclohexane solution was fed into the reaction chamber containing the catalyst for 60 minutes which resulted in the formation of carbon nanotubes. The reaction chamber was then cooled by passing nitrogen gas. The grown carbon nanotubes was washed with dilute nitric acid and water to get them in the pure form. The main advantages of the present invention are the following. 1. Large-scale nanotubes can be produced by this process. 2. The cost of the process is comparatively low than the other preparation processes. 3. The use of cyclohexane as a carbon source makes the process simpler and safe. 4. The addition of molybdenum enhances the growth of carbon nanotubes. 5. The growth temperature is only about 700 - 800°C. 6. The carbon nanotubes are rope shaped and obtained in bulk. WE CLAIM 1. An improved process for the preparation of carbon nanotube for industrial applications, which comprises : i) reacting 25-75% w/w, of nickel salt, 25-75% w/w of magnesium salt and 100-300% w/w of known gelling agent in aqueous medium at a temperature in the range of 20-40°C under stirring condition for a period up to 45 minutes, followed by heating the resulting saturated solution to a temperature up to 120°C for a period up to 7hrs to get a powder, ii) adding 30-60% w/w of molybdenum salt to the powder, as obtained in step (i), followed by heating the resulting product to a temperature of 700 - 800°C up to 5 hours to obtain Ni-MO-MgO catalyst, iii) passing hydrogen gas at a rate of not less than 100 ml per minute through 0.1-0.5% w/v, based on the weight of Ni-MO-MgO catalyst, of known cycloalkane solution for a period up to 30 minutes followed by passing of the resulting hydrocarbon gas through the Ni-MO-MgO catalyst, as obtained in step (ii), at 700 - 800°C and subsequent adjusting of temperature up to 100°C by passing nitrogen gas to obtain carbon nanotube iv) subjecting the carbon nanotube, as formed in step (iii), to conventional washing followed by drying by known method at a temperature up to 150°C to get pure carbon nanotube. 2. An improved process, as claimed in Claim 1, wherein the nickel salt used is selected from nickel nitrate nickel nitrate, nickel chloride, nickel sulphate. 3. An improved process, as claimed in Claims 1 and 2, wherein the magnesium salt used is selected from magnesium oxide, magnesium nitrate, magnesium chloride. 4. An improved process, as claimed in Claims 1 to 3, wherein the known gelling agent used is selected from citric acid, urea, polyvinyl alcohol. 5. An improved process, as claimed in Claims 1 to 4, wherein the molybdenum salt used is selected from ammonium molybdate, molybdenum powder. 6. An improved process, as claimed in Claims 1 to 5, wherein the known cycloalkane used is selected from cyclobutane, cyclopropane, cyclohexane. 7. An improved process for the preparation of carbon nanotube for industrial applications, substantially as herein described with reference to the examples.

Documents:

316-del-2004-abstract.pdf

316-del-2004-Claims-(29-11-2010).pdf

316-del-2004-claims.pdf

316-del-2004-Correspondence-Others-(29-11-2010).pdf

316-del-2004-correspondnece-others.pdf

316-del-2004-correspondnece-po.pdf

316-del-2004-description (complete).pdf

316-del-2004-form-1.pdf

316-del-2004-form-18.pdf

316-del-2004-form-2.pdf

316-del-2004-form-3.pdf

316-del-2004-form-5.pdf