WO2012172560A1

WO2012172560A1 - Process for production of carbon filaments from industrial and vehicular exhaust gas

Info

Publication number: WO2012172560A1
Application number: PCT/IN2012/000105
Authority: WO
Inventors: Vivek Sahadevan NAIR
Original assignee: Nair Vivek Sahadevan
Priority date: 2011-06-13
Filing date: 2012-02-14
Publication date: 2012-12-20

Abstract

Disclosed herein is a highly economical process for large scale commercial production of carbon filaments by a low temperature synthetic method optionally under magnetic field from Industrial and Automobile flue gas emissions and flame coming from Exhaust and furnaces (boilers). The present invention further discloses a catalytic combination of alpha and gamma iron oxide magnetic nanoparticle for production of carbon filaments at low temperature.

Description

PROCESS FOR PRODUCTION OF CARBON FILAMENTS FROM INDUSTRIAL AND VEHICULAR EXHAUST GAS

TECHNICAL FIELD:

The present invention relates to highly economical process for large scale commercial production of carbon filaments by a low temperature synthetic method from Industrial and Automobile flue gas emission and flame coming from Exhaust and furnaces (boilers) thereby simultaneously reducing the flue gas (carbon) emission, reducing global warming and helping to reduce resultant climate catastrophes. The invention also relates to a novel catalytic combination of alpha and gamma iron oxide magnetic nanoparticle for production of carbon filaments.

BACKGROUND AND PRIOR ART:

Carbon fibers/filaments are forms of carbon which are known in the art and which have a diameter of, normally, from 5 to 15 micrometers. They are flexible, light in weight, thermostable, chemically inert and are good thermal and electrical conductors. They can be divided into two categories, low-modulus fibers having a Young's modulus below about 140 g Pa and high-performance fibers having a Young's modulus above about 70 g Pa and having a very high tensile strength.

Carbon nanotubes, carbon nanofibers, carbon microtubes, nanobeads etc which are allotropic forms of carbon are sought for many applications reflecting their novel mechanical, thermal and electrical properties including reinforcing, catalyst support, gas storage and electrochemical energy storage. Extensive research related to the unique mechanical and electrical behavior of carbon filaments thus has necessitated need for improved processes for preparation of carbon filaments.

The discovery of single walled carbon nanotubes (SWNT), multiwalled carbon nanotubes (MW T), carbon fibers (CF) by Iijima has started extensive research in the field due to the promising physical properties of carbon nanotubes. Single walled carbon nanotube (SWNT) is a single atom thick layer of graphite (graphene) rolled up such that the diameter is of the order of nanometers. The length to diameter ratio of these carbon filaments are of the orders of 1,000,000. Multi-walled nanotubes (MWNT) consist of multiple rolled layers (concentric tubes) of graphite. These cylindrical carbon molecules have unusual properties, which are valuable for nanotechnology, electronics, optics and other fields of material science and technology.

A number of synthetic method for production of vertically aligned carbon filaments are known from the prior art. The majority of methods of synthesis comprise formation of catalyst layer on which carbon filaments are developed followed by their purification. It is a two step process, first the production of carbon filaments and then their purification, which is not economical for industrial applications. Popular methods for obtaining such a catalyst layer are sputtering, deposition processes, such as electron beam deposition, thermal deposition and the like. Preferred process for growing carbon filaments thereon include arc discharge, laser vaporization, gas phase synthesis, CVD (Chemical Vapor Deposition) method, Plasma enhanced chemical vapor deposition vapor-phase method, Alcohol catalytic chemical vapor deposition, High Pressure CO-disproportionation process, Flame synthesis (E T. Thostenson, Z. Ren, and T. W Chou, Composites Science and Technology, Vol. 61, 2001, p. 1899-1912).

Carbon Nanotubes have also been found in the soot of Industries and places which burn Methane, benzene and ethylene, but the irregularities in size and quality is enormous due to highly uncontrolled environment.

Currently, there are three principal techniques to produce high-quality carbon filaments:

(i) Laser Ablation

(ii) Electric Arc Discharge and

(iii) Chemical Vapor Deposition (CVQ

In the laser ablation process, a pulsed laser is used to vaporize a graphite target in a high- temperature reactor while an inert gas is bled into the chamber. Nanotubes are developed on the cooler surfaces of the reactor as the vaporized carbon condenses. A water-cooled surface may be included in the system for separation and collection of the nanotubes. In the arc-method, current is passed between carbon anode and cathode in a suitable container filled with a gas. An arc is created between the electrodes, and carbon evaporates from anode and deposits on the cathode which is a mixture of different carbon nano structures. These can be subsequently separated and purified.

However, both laser ablation and electric arc discharge methods suffer the problem that it is difficult to scale-up the production of carbon filaments to industrial level.

The flame synthesis method is based on the use of controlled flame environment, where carbon atoms are formed from hydrocarbon fuels along with aerosols of metal catalyst The SWNTs grow on the metal islands. A sub monolayer film of metal (cobalt) catalyst was applied to the stainless steel by Physical Vapor Deposition (PVD). In this manner, metal islands resembling droplets were formed upon the mesh support to serve as catalyst particles. These small islands become the aerosol when exposed to flame. The reaction is carried out at 800[deg.] C. and requires purification. The hydrocarbon decomposition produces also CO/C02 contaminated hydrogen.

The CVD method is currently the only hope for large-scale production of carbon filaments. Traditionally, the catalyst for the CVD method is made either by impregnating a catalyst precursor into a powdered catalyst support, such as silica powder and alumina powder or by decomposing the precursor in the gas phase together with a carbon source at elevated temperature.

However, the production of carbon filaments by CVD method requires several conditions to be satisfied, as follows.

(i) Maintaining High Temperature-of about 860°C for the process.

(ii) Maintaining of pressure and inert atmosphere all through the cham ber.

(iii) Continuous flow of air.

(iv) Maintaining the flow of exhaust gases containing the likes of C,H2,CH 4 etc.,

In view of the wide range of high technological applications of carbon filaments , and resultant heavy demand for carbon filaments, especially in the steel making industry, the traditional method of the preparation of CNTs, the conventional materials employed and process conditions adopted thereof, have all been contributing to high cost of carbon filaments. Maintaining and satisfying all these conditions is not only costly but also difficult, thus resulting in a higher cost of carbon filaments.

Further, EP0198558 disclose a method of preparing carbon filaments comprising exposing a suitable thermo stable support having substantially completely reduced mono crystalline metal particles to a carbon containing gas at a temperature of from about 250[deg.]C up to about 700[deg.]C to 800[deg.]C for a period of time sufficient to form carbon filaments of a desired dimension followed by removing the substrate and/or the metal particles. The metal particles disclosed in said patent is selected from ferromagnetic particles such as nickel, metallic iron, cobalt or alloys thereof. The filaments in said patent are characterized by a crystalline graphitic structure and a morphology defined by a fishbone-like arrangement of the graphite layers along the axis of the filaments.

An article titled, Carbon nanotube Synthesis via the catalytic CVD method : A review on the effect of reaction parameters by Cmar Oncel and Yuda Yurium covers the results obtained in carbon nanotube synthesis by chemical vapor deposition. Various parameters such as catalysts, supports, carbon precursors, reaction time, temperature etc used in the production of carbon nanotubes are discussed in said article.

An article titled 'Carbon synthesis of carbon Nanotubes and nanofibres' by Kenneth teo, Cahranjeet Singh et. al in encyclopedia of Nanoscience and Nanotechnology, volume X, pages 1-22 disclose the catalytic chemical vapor deposition for the preparation of carbon nanotube and nanofibres. Further, the articledisclose that branching of the carbon filament is promoted with the catalyst doped with silica or calcium.

There still remains a need to provide processes for the production of carbon filaments which is industrially feasible, cost effective and yields carbon filaments in high yield and purity. Accordingly, the inventor of the present invention has sought to provide an economical but superior alternative to redress the problems in the prior art. The inventor of the present invention has thus come up with the innovative process to produce carbon filaments at low cost by modifying the already existing conditions required for the production of carbon filaments using CVD which are found at exhaust level of the industrial plant. Commercially, this could solve not only the problem of high cost of producing carbon filaments but also bring down environmental pollution and carbon emission, leading to reduction of global warming and climate catastrophes.

The present inventor further seeks to the use of a novel catalytic combination of magnetic nanoparticles of alpha and gamma forms of iron oxide for the preparation of carbon filaments in the modified process of the instant invention.

SUMMARY OF THE INVENTION:

In view of the above, the object of the instant invention is to provide a process for the production of carbon filaments, from industrial and vehicular flue gases, which is cost effective, industrially feasible and results in high yield and purity of the carbon filaments.

The other object of the invention is to provide a novel catalytic combination of magnetic nanoparticles of alpha and gamma forms of iron oxide that enhances the growth of carbon filaments at low temperature and in particular ratio.

The carbon filaments of the current invention relates to carbon nanotubes, carbon Nanofibers, carbon microfibers, Carbon Nanorods, Carbon Nanobeads, carbon nanoparticles and such like either alone or a mixture thereof.

In an aspect, the present invention provides a catalytic combination of alpha form of Ferrous oxide (Fe203) and gamma form of ferric oxide (Fe304) magnetic nano particles in a particular ratio for the production of carbon filaments and hydrogen gas from industrial and vehicular flue gases at low temperature. The process for the production of carbon filaments is optionally carried out under magnetic field.

In another aspect, the catalytic combination of alpha form of Ferrous oxide (Fe203) and gamma form of ferric oxide (Fe304) magnetic nanoparticle is in the ratio of 1 :4, 3:7, 1 : 1, 7:3 and 4: 1.

(; In yet another aspect, the catalyst of the instant invention is embedded onto the inert substrate selected from alumina, Cement coated with Si02, Zeolite, Titanium, silicon, Glass, glass wool or ceramic brick.

Yet another aspect of the invention relates to the catalyst which is recyclable and can be used effectively for about 5 cyles.

In another aspect, the present invention relates to highly efficient, low temperature, reproducible process, optionally under magnetic field for the preparation of carbon filaments from industrial and vehicular flue gases.

In an aspect, the temperature under which the process takes places is a low temperature process and varies from 90° C to 200°C, preferably in the range of 90-150°C.

The magnetic field employed is in the range of 100 to 500 Oe and the Magnetic moment of the particle is around 30 - 40 EMU/gm.

The process of the instant invention are used for industries which gives out carbon emissions such as Rice Mills, Thermal Power stations, Petrochemical Industries, Sugar cane mills, Steel, glass and Metal processing industries etc, automobiles which can be any type of vehicles which gives out flue gases like Cars, Airbuses, Rockets, Ships, Aircrafts, Rail engines etc.

The flue gas comprises of gases such as carbon dioxide, carbon monoxide, methane, ethane, hydrocarbons, petroleum gases, nitrogen , hydrogen , water vapor, sulphur dioxide , fly ash , carbon particles, either alone or mixtures thereof.

DESCRIPTION OF DRAWINGS:

Fig. 1, Fig. 2, Fig. 3: depicts SEM analysis of Non purified Carbon Nanotubes & Microtubes.

Fig. 4, Fig. 5: depict SEM analysis of purified Carbon Nanofibers.

Fig.6, Fig. 7: depict SEM analysis of Carbon Nano-Rods. Fig. 8, Fig. 9, Fig. 10: depicts TEM analysis of Carbon Nano-Rods.

Fig. 11: depict XRD of Carbon Nano-Rods.

Figure 12: depicts CNTs that were obtained using Ferrous oxide as catalyst coated over cement substrate.

Figure 13: depicts CNTs grown over Copper slides prepared by pyrolytic spraying. Figure 14: depicts FE-SEM image of CNTs formed by using Ferrous oxide as catalyst. Figure 15: depicts FE-SEM image of CNTs formed by using Nickel catalyst tested at tested at Neyveli Lignite Corporation.

Figure 16: depict FE-SEM image of sieved CNTs produced using alpha Fe203 and gamma Fe304 magnetic nanoparticle tested at Rice Mill.

Figure 17: depict FE-SEM image of raw CNTs produced using alpha Fe203 and gamma Fe304 magnetic nanoparticle tested at Rice Mill, at Lower magnification.

Figure 18: depict FE-SEM image of purified CNTs produced using alpha Fe203 and gamma Fe304 magnetic nanoparticle tested at Rice Mill.

Figure 19: depict FE-SEM image of CNTs, formed by using Copper metal as catalyst by sputtering technique.

Figure 20: depict EDAX image of CNTs formed by using Copper metal as catalyst by sputtering technique which confirms the high content of carbon. The Si peak is formed since it was prepared over a glass substrate.

DETAILED DESCRIPTION OF THE INVENTION:

The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated and briefly described as follows.

The present invention relates to a highly economical process for large scale production of carbon filaments by a low temperature synthetic method from Industrial and Automobile gas emissions. The invention also provides a catalyst embedded onto a substrate consisting of a combination of magnetic nanoparticles of alpha and gamma forms of iron oxide for the preparation of carbon filaments. As used herein the term 'Carbon filaments' relates to carbon carbon nanotubes, carbon Nanofibers, carbon microfibers, Carbon nanorods, Carbon nanobeads, carbon nanoparticles and the like either alone or a mixture thereof disclosed in the invention.

As used herein the term 'alpha and gamma iron oxide magnetic nanoparticle' in the specification means and relates to alpha form of Ferrous oxide (Fe203) and gamma form of ferric oxide (Fe304).

As discussed above, the inventor of the present invention has focused to resolve the inherent weakness of the existing systems of producing carbon filaments which involves costly substrates, costly catalyst and very high cost of creating temperature and pressure and ambient conditions for catalytic pyrolysis. The invention further provides a novel catalytic combination of magnetic nanoparticles of alpha and gamma forms of iron oxide for the preparation of carbon filaments at low temperature.

The inventor of the present invention has also sought to drastically reduce the manufacturing cost of production of Carbon filaments, especially in Steel industry. Steel is an alloy of Iron and Carbon. The carbon in the steel gives it strength, toughness, hardness and many other properties like higher tensile strength and better young's modulus.

The existing steel manufacturing in the world employs amorphous carbon for increasing the hardness. Increasing the carbon content increases its hardness, but, however, reduces its toughness and hence, further reduces its ductility and malleability. Carbon filaments have better properties, geometry and nano-size compared to amorphous carbon and incorporation of carbon filaments into iron gives a steel of higher strength and toughness compared to the steel manufactured by conventional methods.

Carbon filaments synthesized by the present invention from the Industrial Exhaust, reduces the overall production cost to $0.05/gm with 45% purity from $90-$250/gram, depending on quality and type. The inventor of the present invention has utilized the waste heat, vacuum atmosphere and flue gas as the raw-material and consequently, has made the process economical and cheap. In fact, usage of carbon filaments even with 45% purity (impurity being Ferrous oxide catalyst and some amorphous carbon) to make steel has resulted into high quality and strength steel with the same costs involved.

The present invention comprises a novel process for the manufacture of carbon filaments from Industrial and automobile Exhausts. The production of carbon filaments are carried out in the following three phases.

Preparation of Catalytic substrate

Growing carbon filaments over the substrate

Optional Purification of the carbon filaments.

The present invention further extrapolates the Chemical Vapor deposition method performed in a laboratory CVD furnace and the uncontrolled Flame synthesis method to an existing Furnace or exhaust pipe of an Industry and Automobile on a large scale. The process of the present invention has been designed to suit the existing Industrial and automobile exhaust systems with minimal modifications to position the substrate with the catalyst. This has been achieved by preparing ideally suited template for the cultivation of carbon filaments and introducing the substrate in the path of the flue gas without modifying any of the pre-existing conditions of the exhaust pipe or furnace.

The novel features of the inventions are listed as follows.

1. Selecting novel and inert substrate hitherto not experimented or employed for.

2. Selecting high efficiency and low cost catalyst for coating over the inert substrate.

3. Loading and holding low cost inert substrate with low cost catalyst into no cost / low cost ambient condition widely available in industry, in the industrial and vehicular exhausts.

4. The process is a continuous process.

The growth of the carbon filaments with desired diameter and density depend on a number of factors such as the catalyst nanoparticles used, the carbon feedstock, the temperature, physical dimension of the catalyst particle, enthalpies for the growth of filaments on the catalyst, the amount of poisoning of the catalyst due to formation of carbon around it thus preventing the gas from reaching the catalyst particle, duration of the process, the substrate used and the like. Magnetic nanoparticles are a class of nanoparticle which can be manipulated using magnetic field. Such particles commonly consist of magnetic elements such as iron, nickel and cobalt and their chemical compounds. While nanoparticles are smaller than 1 micrometer in diameter (typically 5-500 nanometers), the larger microbeads are 0.5-500 micrometer in diameter. The magnetic nanoparticles have been the focus of much research recently because they possess attractive properties which could see potential use in catalysis, biomedicine, magnetic resonance imaging, magnetic particle imaging, data storage, environmental remediation, nanofluids, and optical filters. The physical and chemical properties of nanoparticles however depend on the synthesis method used and chemical structure. There are three different types of magnetic nanoparticles which are currently used viz. the ferrites (oxides), metallic nanoparticles, metallic with shell. The metallic nanoparticles have the great disadvantage of being pyrophoric and reactive to oxidizing agents to various degrees thus making their handling difficult and enabling unwanted side reactions.

Iron oxide nanoparticles, such as magnetite (Fe304) and hematite (a-Fe203) have been of technological and scientific interest due to their unique electrical and magnetic properties. a-Fe203 (haematite) is antiferromagnetic below -260 K (Morin transition temperature), and weak antiferromagnetic between 260 and 950 K Neel temperature. Fe304 contains both Fe2+ and Fe3+ and is ferrimagnetic.

Reducing the particle size of the iron oxide particles makes them behave as supermagnets, increases the surface area thereby enabling the production of carbon filaments in high yield. Further, the present invention aims to provide the catalyst embedded on the inert substrate that can catalyze the production of carbon filaments when exposed to any type of carbon precursor emitted out from the industrial and vehicular exhausts. The invention further refers to the catalyst which can produce the carbon filaments of desired configuration at low temperature.

Thus, in a preferred embodiment, the present invention disclose a catalytic combination of alpha form of ferrous oxide (Fe203) and gamma form of ferric oxide (Fe304) magnetic nanoparticle for the production of carbon filaments in high yield and purity at low temperature in the range of 90-200, preferably in the range of 90~150°C The catalytic combination of alpha and gamma form of ferrous oxide magnetic nanoparticle is in the ratio of 1 :4, 3 :7, 1 : 1 , 7:3 and 4: L

In another embodiment, the process for the preparation of carbon filaments is optionally carried out in presence of magnetic field.

The catalytic combination of alpha form of ferrous oxide (Fe203) and gamma form of ferric oxide (Fe304) magnetic nanoparticles has a size of the order of 10-100 nm and behave as superparamagnets which prevents self- agglomeration since they exhibit their magnetic behavior only when an external magnetic field is applied and are thus conducive to facile alignment under relatively low magnetic fields. The catalyst is preferably used in areas of high methane or hydrogen emission.

The catalyst of the instant invention is recyclable and can be used effectively for about 5 cycles.

Alternately, the catalyst for the process of the instant invention can be selected from a group consisting of Nickel, Copper, palladium, Platinum, Cobalt, Ruthenium, Molybdenum, Silver, Gold, Aluminum, lead, titanium, Zinc, Zirconium or a mixture thereof in the form of oxides, chlorides, acetates, sulphates, carbonates, or nitrates. Accordingly, the catalytic nano sized metal or metal ' oxides are selected from CuO (Copper oxide nano particles), SnO (Tin oxide nano particles), ZnO (Zinc Oxide nano particles), Pb02 (Lead Oxide nano particles) and Nickel oxide nano particles either alone or in combination thereof.

The magnetic field employed is in the range of 100 to 500 Oe and the magnetic moment of the particle is in the range of 30 - 40 EMU/gm.

In another embodiment, the present invention provides highly efficient, low temperature, reproducible process, for the preparation of carbon filaments from industrial and vehicular flue gases, which comprises; 1. coating a combination of alpha form of ferrous oxide (Fe203) and gamma form of ferric oxide (Fe304) magnetic nanoparticle in the ratio 1 :4, 3:7, 1 : 1, 7:3 and 4: 1 over an inert substrate at about 500°C till the catalyst is impregnated onto the inert substrate;

2. inserting the coated inert substrate into the path of flue gases in a furnace/vehicular exhaust pipes through the peephole and the manhole at various temperature zones for about 5-6 minute, in absence of ash,

3. growing carbon filaments on catalytic surface at a temperature in the range of 90-200°C,

4. scrapping the carbon filaments obtained in step (3) from the substrate and regenerating the catalyst using a magnet;

5. sieving carbon filaments of step (4) through micro sieve capable of sieving up to - 100 nm; and subjecting the carbon filaments so obtained to purification.

According to the process described above, the carbon filaments obtained are carbon nanotubes, carbon Nanofibers, carbon microfibers, Carbon Nanorods, Carbon Nanobeads, carbon nanoparticles and such like either alone or a mixture thereof .

The temperature condition under which the process takes places varies from 90° C to 200°C, more preferably in the range of 90-150°C.

The process may be carried out under magnetic field applied which is applied when the substrate coated with catalyst is placed in the exhaust pipe or furnaces for the reaction to occur between Flue gas and the catalyst. The magnetic field employed is in the range of 100 to 500 Oe and the magnetic moment of the particle is in the range of 30 - 40 EMU/gm.

The catalyst is taken in different ratio to suit different Industrial and flue gas conditions. Preferably, the catalytic combination of alpha form of ferrous oxide (Fe203) and gamma form of ferric oxide (Fe304) is in the ratio of 1 :4, 3:7, 1 : 1 , 7:3 and 4: 1. The suitable inert substrate is selected from alumina, Cement coated with Si02, Zeolite, Titanium, silicon, Glass, glass wool or ceramic brick. The inert substrate is in the shape of a boat, cylinder, disc or a crucible. The substrate allows for a desirable catalyst nanoparticle -support interactions. The porous and rough nature of substrate promotes growth of carbon filaments.

The inert surface preferably used is silica layer. A cement slab of small size is prepared over which a thin layer of silica is applied. Alpha and gamma iron oxide magnetic nanoparticle is embedded onto the inert substrate by a laminar flow, calcined at about 300°C and further air dried in hot plate at 100°C or in sun light. The alpha and gamma Iron oxide magnetic nanoparticle obtained is in the size range of 10 - l OOnm.

Alpha and gamma iron oxide magnetic nanoparticle are prepared by mixing Ferric Chloride and Ferrous Sulphate in 1 : 1 mole ratio followed by heating to 100°C maintaining pH for the reaction between 8 and 14. This is followed by addition of 0.1 M Sodium Hydroxide in 10 sec under constant stirring at 180 rpm. The solution prepared is subjected to filtration and allowed to settle down for about 24 hours. The residue obtained is further coated over the inert substrate.

In another embodiment, the catalytic substrate for the production of carbon filaments can be prepared by the following methods, such as;

1. Pyrolytic spraying of metal oxides of Pb, Cu, Zn etc. the metal acetate solution is taken in the syringe and the spray pyrolysis is tuned to spray at a specific pressure to a hot plate maintained at 250-300°C.

2. Sputtering where both metal and metal oxides of Cu, Zn , Sn , Al are coated over glass and silicon substrate using dispersive sputtering.

In another embodiment, only ferrous nanoparticles are coated onto the glass and silicon substrate by sputtering method. Further, any suitable catalyst described herein above comprising of metal or metal oxide nanoparticles either alone or in combination can be coated on to the glass substrate by a process known in the art where such catalyst coated substrates are used for growing carbon filaments from flue gases. Further, the metal substrates can be used in sputtering for coating very fine mono disperse metal and metal oxide nanoparticle combinations. Acetate form of metals acting as a suitable catalyst may be employed and coated over the glass substrate that can withstand high temperature such as borosilicate.

In another preferred embodiment, alpha and gamma iron oxide magnetic nano-particles in the ratio of 1 :4, 3:7, 1 : 1, 7:3 and 4: 1 are coated over Silicon dioxide over Cement brick, alumina or wool substrate.

The thickness of the catalyst onto the inert substrate is in the range of 0.1mm to 10 mm.

The concentration of the active components i.es Iron oxide is 80% .

Adequate arrangements to hold the substrate in the furnace/vehicular exhaust pipes are made during substrate preparation work. To increase the sampling effect, the substrates are placed at the center of the furnace/ vehicular exhaust pipes by welding a long rod to the rod inbuilt of the substrate of present invention. Further, adequate care is taken to minimize human error in the sampling phenomena. To test the consistencies of the carbon filament production, the process is repeated which results in high consistency with a diameter of at least 26nm.

The carbon filaments obtained are scrubbed from the surface of the substrate and the catalyst can be regenerated by separation using a magnet when the catalyst is magnetic in nature or by chemical method known in the art. The carbon filaments obtained is 40% pure.

The diameter of the carbon filaments is at least 26nm and can range upto 5000nm with different catalysts. The diameter of carbon nanotubes is in the range of 26nm -lOOnm whereas the diameter of carbon nano fibers is in the range of 40-5100nm. Further, the so formed carbon filaments are purified by a process disclosed below:

1. subjecting the separated carbon filaments, with catalytic impurity, to water vapor at temperatures above 693 K wherein the debris and contaminants are either removed as C02 or easily washed away with water;

2. refluxing the oxidized sample of step (1) with 75% sulphuric acid for removal of metallic impurities;

3. dispersing the carbon filaments of step (2) in 37% hydrochloric acid and acetone in equal proportion followed by ultra -sonication for 15 min; further maintaining in the dispersion at 55°C for 2 hours;

4. cooling, filtering and washing several times with de-ionized water till the washings are neutral; and

5. separating the specific size carbon filaments by centrifuging or by chromatographic separation.

The carbon filaments obtained after purification are 95% pure.

The flue gas comprises of gases such as Carbon dioxide, Carbon monoxide, methane, ethane, hydrocarbons, petroleum gases, nitrogen, hydrogen, water vapor, sulphur dioxide, fly ash , carbon particles, either alone or mixture thereof.

In another embodiment, the catalyst comprising of a combination of alpha and gamma iron oxide is used for the preparation of carbon filaments from the emissions of Rice Mill and Sugar cane Processing Industries where the major constituent of the flue gas is Methane, while in Thermal Power stations and Petrochemical Industries the preferred catalyst is nano sized particles of Ferrous, Nickel, copper, Platinum and palladium in different metallic combinations.

Carbon filaments with the least size of 26nm are obtained for the catalyst comprising a combination of alpha form of ferrous oxide (Fe203) and gamma form of ferric oxide (Fe304), and a size range of 40-50 nm for catalyst CuO are obtained.

In an embodiment, the inert substrate of Silicon dioxide over Cement brick coated with iron oxide magnetic nanoparticle (alpha : gamma = 3:7) at 150°C produces Carbon Nanotubes & Microtubes. The Flue gas is a mixture of Methane, Carbon dioxide, Nitrogen and carbon particles etc. The best size obtained is about 26nm.

In another embodiment, carbon Nanofibers are obtained from the catalyst iron oxide magnetic nano particle(alpha : gamma = 1 : 1) coated on wool substrate at 1 10°C. The flue gas is a mixture of Methane, Carbon dioxide, Nitrogen and carbon particles etc. The size is in the range of 50nm to 5000nm.

In yet another embodiment, Carbon Nano-Rods are obtained by the process of the instant invention using iron oxide magnetic nanoparticle (alpha: gamma = 1 :4) coated on Alumina Substrate at 90 - 100°C. The size is in the range of 15nm to 50nm.

The production of hydrogen gas occurs in areas where the flue gas content is rich in methane, ethane, hydrocarbons, petrochemicals or a mixture thereof. Hydrogen gas obtained as the byproduct can be used as a potential fuel which can reduce the environmental carbon emission by 20%

Experimental

The experiments are conducted initially at laboratory level and scaled up to Pilot plant in small scale industry and further scaled up and validated to conditions in a thermal power station. Reproducibility of production of carbon filaments in all three levels are validated and optimized for commercial viability. Laboratory Preparation

L Catalyst-Substrate preparation: The metal nanoparticles to be coated on the inert substrate e.g glass can be selected from Ferrous Oxide, Copper Oxide, Zinc Oxide, Lead Oxide, Tin oxide, Nickel Oxide and copper nano particles and their combinations in various proportions, preferably alpha and gamma iron oxide magnetic nano particles in the ratio of 1 :4, 3:7, 1 : 1, 7:3 and 4: 1.

Accordingly, the glass ware is cleaned and sterilized by dipping in chromic acid solution, further washed with water, 0.5M NaOH repeatedly and alternately till the pH of glass ware is equal to pH of water. The glass ware is further rinsed with 70% IPA followed by rinsing with distilled water and further dried. Ferric Chloride and Ferrous Sulphate solutions are mixed in 1 : 1 mole ratio and heated to 100°C maintaining pH for the reaction between 8 and 14. This is followed by addition of 0.1M Sodium Hydroxide in 10 sec under constant stirring at 180 rpm. The solution is decanted to obtain alpha form of ferrous oxide and gamma form of ferric oxide magnetic nano particles. The so obtained magnetic nano particles are coated over the inert substrate (glass) by laminar flow and kept for calcination at 300°C followed by air drying at 100°C or in sunlight to assure appropriate coat.

Alternately, the glass substrates, metal substrates can be coated with the different metal or metal oxides described above and their combination by spray pyrolysis and sputtering. Acetates of metal are taken for spray pyrolysis and 99.9% pure metal discs are taken for coating the catalyst by sputtering technique.

2. Scaling up

Carbon filaments are prepared at small scale level in a rice processing industry where husk is used as a fuel. Trials are performed at 90-200°C Particles formed over the catalytic surface are etched and taken in its raw form without purification for Scanning Electron Microscopy (SEM), which yielded excellent results-in the formation of carbon filaments with a least size of 26nm. The carbon filaments synthesized are manually scrapped from the Catalytic substrate. During the process, the catalyst, alpha form of ferrous oxide (Fe203) and gamma form of ferric oxide (Fe304) nano-particles are regenerated. The catalyst is removed easily with the help of a magnet, the catalyst being magnetic. The remaining carbon filaments are optionally further purified by graining, heating at 300°C and treating with Hydrochloric acid. The carbon filaments are further analyzed using SEM and ED AX.

INDUSTRIAL APPLICATION ON LARGE SCALE

Further experiments are carried out at Thermal Power Station- 1, NLC, Neyveli, a Central government undertaking, wherein different temperature zones ranging from 1200°C- 150°C to carry out trials were available. The experiments also yielded results in the formation of carbon filaments with the size of at least 26nm and can range upto 5000nm for different catalysts.

Different substrates (both glass and cement scaffold) coated with catalyst are inserted into⁴' the furnace through the peephole and the manhole, using long rods welded to the iron projection inbuilt in our substrates.

The resultant samples are analyzed at the high resolution SEM facility available at Jawaharlal Nehru University (JNU), New Delhi. While some of the samples are analyzed with Energy Dispersive X-ray Analyzer (ED AX) for advanced study and analysis.

Procedure

1) Inert substrate: Cement substrate covered with a layer of Si02

a) Sand covered cement substrate is coated with alpha form of ferrous oxide (Fe203) and gamma form of ferric oxide (Fe304) magnetic nanoparticles in the ratio of 1 :4, 3:7, 1 : 1, 7:3 and 4: 1.

Solution form of the catalysts are coated over the sand covered cement substrate and kept in muffle furnace at 500°C till the catalyst impregnated in the Si0₂ pockets.

Alternately, glass substrates, metal substrates can be coated with the different metal or metal oxides described above and their combination by spray pyrolysis and Magnetron sputtering. Acetate form of metals acting as suitable catalysts are taken and coated over the glass substrates which can withstand high temperature (borosilicates). 99.9% pure metal discs are taken for coating the catalyst by sputtering technique.

2) Adequate arrangements to hold the substrates in the furnace are made during the substrate preparation work.

3) To increase the sampling effect, the substrates are placed at the centre of the furnace & Exhaust pipes by welding a long rod to the rod inbuilt in the substrate. Adequate care is taken to minimize human error in the sampling phenomena.

4) The catalyst-substrate is exposed to the flue gas emission at varying temperature zones ranging from 1200°C-150°C for a period of 5-6 minutes.

5) To test the consistency of the carbon filaments produced, experiments are repeated resulting in high consistency with at least 26nm.

In the process, the samples are kept for 5 - 6 minutes. The time is optimized taking into consideration various factors like Flue gas flow rate, temperature of the flue gas and the substrate - Catalyst combination.

The flue gas flow rate is of 68,500m3/hour. The size of substrate is kept small as the substrate is manually inserted into the man-hole and peep hole. Preferably, the substrate used has a size of 15 x 15 and is square in shape. The Amount of flue gas used depends on various factors i.e. the time when flue gas is accessed as it varies throughout the day depending on the firing and activation stages, the site in the boiler where the flue gas is accessed as it varies the volume of flue gas, the temperature, flow rate of the flue gas and finally on the size & shape of the substrate and concentration of the catalyst.

Maximum use of the flue gas is made by increasing the size of substrate and making it cylindrical. Further, the cylindrical surface is coated with the catalyst. According to the type of boiler and optimizing the conditions for maximum exposure of substrate to the flue gas by automated continuous process, maximum amount of flue gas is utilized in the boiler.

Since the presence of ash in the whole system varies throughout the day, the duration of operation of the boiler is selected when the fly ash blown out of the boiler is minimum. The presence of ash hides the catalysts exposed area towards carbon dioxide, carbon monoxide, methane and hydrogen, but due to the velocity of the flue gas and high flame in the boiler, the ash is carried away with the bulk and its interference with the process is thus reduced.

In areas where the catalytic substrate is placed after the electrostatic precipitator or cyclone separator, the interference due to ash is highly reduced. Hence, during the large scale implementation of the present technology, a small improvisation in the furnace/vehicular exhaust pipe by installation of a small electrostatic precipitator completely solves the problem of ash interference.

Further, the growth mode of carbon filaments depends on the size of the catalyst, the substrate pore size where the catalyst is placed and its exposure to flue gas. The substrate pore size is in the range of 20m²/g - 42m²/g.

According to the following conditions of the instant invention, in an embodiment, random parallel and intertwined CNTs for Iron oxide Magnetic Nanoparticle coated over Silica - Cement substrate exposed to flue gas at 100 - 400°C yields CNTs which are observed to have Y-Junction in their structures.

Variation in the conditions like using only Ferrous oxide nanoparticle has resulted in production of "Carbon Nanobeads" produced at lower temperature of 250°C.

Using different types of catalysts like Copper oxide nanoparticles, Nickel oxide nanoparticles, Titanium oxide nanoparticles and their various combinations coated over glass and quartz substrate by sputtering & Spray Pyrolysis produces different patterns of CNTs with different physical and electrical properties. in an embodiment, the inert substrate of Silicon dioxide over Cement brick coated with iron oxide magnetic nanoparticle (alpha : gamma = 3:7) at 150°C produces Carbon Nanotubes & Microtubes. The Flue gas is a mixture of Methane, Carbon dioxide, Nitrogen and carbon particles etc. The best size obtained is about 27nm. (Fig. 1 , Fig. 2, Fig. 3- non-purified)

In another embodiment, carbon Nanofibers are obtained from the catalyst iron oxide magnetic nanoparticle (alpha : gamma = 1 : 1) coated on wool substrate at 110°C. The flue gas is a mixture of Methane, Carbon dioxide, Nitrogen and carbon particles etc. The size is in the range of 50nm to 5000nm. (Fig 4, fig 5- purified)

In yet another embodiment, Carbon Nano-Rods are obtained by the process of the instant invention using iron oxide magnetic nanoparticle (alpha: gamma = 1 :4) coated on Alumina Substrate at 90 - 100°C. The size is in the range of 15nm to 50nm.(SEM analysis: Fig.6 , Fig. 7; TEM analysis: Fig. 8, Fig. 9, Fig. 10; XRD : Fig. 1 1 )

Higher yield and purity of carbon filaments is obtained using alumina boat shaped crucibles as the substrates (Figs. 6 - 10 shows very pure aligned 1-D (one dimensional) Carbon Nanorods).

PURIFICATION OF RAW CARBON FILAMENTS:

The carbon filaments obtained are sieved through micro sieve of l OOnm. The separated carbon filaments having the catalytic particles are further subjected to following process.

The carbon filaments are treated with water vapor at temperatures above 693 which very effectively reduces amorphous carbon debris and metallic contaminants without introducing defects in carbon filament structure. The debris and contaminants are further either removed as C0₂ or easily washed away with water in an additional step.

Oxidized sample is then refluxed with 75% Sulphuric acid for removal of metallic impurities. 400 ml mixture of 37% hydrochloric acid and acetone in equal proportion is prepared and lOOmg of carbon filament is dispersed in it followed by ultra-sonication for 15 min. The dispersion is kept at 55°C for 2 hours. The sample is cooled, filtered and washed several times with de-ionized water till the washings are neutral. Pure carbon filaments of purity 95% are obtained.

Characterization Technique

The resultant carbon filaments are confirmed and the sample analyzed using Field Emission Scanning Electron Microscope (FE-SEM), Transmission Electron Microscope (TEM) and Energy Dispersive X-ray Analyzer (EDAX). The data obtained using FE- SEM is interpreted in order to confirm the presence of nano sized carbon tubes. While TEM is used to study the 3D morphology of the tubes, EDAX is used for finding the constituents of the sample and to confirm the presence of Carbon.

The SEM analysis report indicated the presence of CNTs with the least size of 26nm (nanometres) for the alpha Fe203 and gamma Fe304 magnetic nanoparticle coated substrates and a size range of 40-50nm for CuO substrate. Figure 12 to Figure 20 shows the SEM image of various samples.

DETAILS OF PHYSICAL PROPERTIES OF PREPARED CARBON FILAMENTS

For CNTs produced from alpha and gamma form of Iron oxide Magnetic Nanoparticle in particular ratio of 3:7; 1 : 1 ; and 1 :4 coated over Silica - Cement substrate:

The Young's modulus of the SWNTs is appx. lTPa, the tensile strength is 10 - 40GPa and it can withstand a pressure of 28GPa without deformation.

The Young's modulus of the MWNTs is appx. 0.7TPa, the tensile strength is 60 - 140GPa and it can withstand a pressure of 52GPa without deformation.

The formation of Y- Junction is very useful phenomena found and its influence in the electrical and its electro-magnetic property will bear very good commercial potential of this invention.

The different allotropic forms of the carbon filaments such as carbon nanotubes, carbon Nanofibers, carbon microfibers, Carbon Nanorods, Carbon Nanobeads, carbon nanoparticles etc. are obtained by the instant process by optimizing the operational conditions such as using appropriate catalyst, temperature conditions, substrate used , the flue gas content and the industry source.

The inventor of the present invention has thus come up with the innovative process to product Carbon filaments at low cost by modifying the already existing conditions required for the production of Carbon filaments. The modified process of the present invention provides carbon capture from the exhaust and furnace level of the industrial plant and Automobiles. Commercially, this solves not only the problem of high cost of producing Carbon filaments but also brings down environmental pollution and carbon emission by more than 40%, leading to reduction of global warming and climate catastrophes. Hydrogen gas formed as a by-product which when used as a fuel reduces the environmental carbon emission by 20%. The process further provides production of pure carbon filaments that are ready to be used in composite Industries sector (70% of the entire Carbon nanotube market).The advantages of the process is summarized below:

1. It is a low temperature, continuous synthesis process. The operating temperature is 90°C - 200°C.

2. The catalyst is recyclable and can be used effectively for 5 cycles.

3. Flue gas having any carbon content can be used for this process.

4. Yet major advantage of the invention is its applicability to any type of Industrial Exhaust and Furnaces without any change in the actual process of the Industry as also with any type of Automobiles or Vehicles like Cars, Ships and Airbuses.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative examples and that the present invention may be embodied in other specific forms without departing from the essential attributes thereof, and it is therefore desired that the present embodiments and examples be considered in all respects as illustrative and not restrictive. Examples:

Example 1: Preparation of alpha and gamma form of Iron oxide magnetic nanoparticle inert substrate.

The glass ware is cleaned and sterilized by dipping in chromic acid solution, further washed with water, 0.5M NaOH repeatedly and alternately till the pH of glass ware is equal to pH of water. The glass ware is further rinsed with 70% IPA followed by rinsing with distilled water and further dried. (0.1 M) solution of Ferric Chloride and (0.1 M ) solution of Ferrous sulphate are mixed in 1 : 1 mole ratio and heated to 100°C maintaining pH for the reaction between 8 and 14. This is followed by addition of 0.1M Sodium Hydroxide in 10 sec under constant stirring at 180 rpm. The solution is decanted to obtain alpha form of ferrous oxide and gamma form of ferric oxide magnetic nano particles.

Example 2: Coating of the alpha and gamma form of Iron oxide magnetic nanoparticle on inert substrate.

The magnetic nano particles of alpha and gamma form of iron oxide (obtained from example 1) are coated over the inert substrate by laminar flow and subjected to calcination at 300°C followed by air drying at 100°C to obtain appropriate coat.

Example 3: Preparation of Carbon Nanotubes

Iron oxide magnetic nanoparticle (alpha: gamma in the ratio of 3 :7) are coated over silicon dioxide coated over cement brick(obtained from example 2) are introduced at the center of the furnace of the exhaust of the Rice Mill by welding a long -rod to the rod inbuilt in the substrate. Optimal conditions of the furnace are set followed by subjecting the substrate to flue gas emission containing methane, carbon dioxide, Nitrogen and carbon particles at the flow rate of 68,500m3/hour from rice mill at 150°C for about 5 minutes to obtain the product. Carbon nanotubes of the size 27nm are obtained.

Example 4: Preparation of Carbon Nanofibres

Iron oxide magnetic nanoparticle (alpha: gamma in the ratio of 1 : 1) coated over wool substrate (obtained from example 2) are introduced at the center of the furnace of the exhaust of the Rice Mill by welding a long rod to the rod inbuilt in the substrate. Optimal conditions of the furnace are set followed by subjecting the substrate to flue gas emission containing methane, carbon dioxide, Nitrogen and carbon particles at the flow rate of 68,500m³/hour from rice mill at 1 10°C to obtain the product.

The Carbon nano fibres are further treated with water vapor at temperature above 693 K followed by further washing with water at the same temperature to eliminate debris and contaminants. The Oxidized sample is then refluxed with 75% Sulphuric acid for emoval of metallic impurities. To the 400 ml mixture of 37% hydrochloric acid and acetone in equal proportion is dispersed lOOmg of carbon nanofibres followed by ultra-sonication for 15 min. The dispersion is kept at 55°C for 2 hours. The sample is cooled, filtered and washed several times with de-ionized water till the washings are neutral to obtain pure carbon nnaofibres^'. The size of the purified carbon nanofibre is 50nm to 5000nm.

Example 5: Preparation of Carbon Nanorods

Iron oxide magnetic nanoparticle (alpha: gamma in the ratio of 1 :4) coated over alumina substrate (obtained from example 2) are introduced at the center of the furnace of the exhaust of the Rice Mill by welding a long rod to the rod inbuilt in the substrate. Optimal conditions of the furnace are set followed by subjecting the substrate to flue gas emission containing methane, carbon dioxide, Nitrogen and carbon particles at the flow rate of 68,500m³/hour from rice mill at 90-100°C to obtain the product. The size of the carbon nanorods is 25nm to 55nm.

Claims

I claim,

1. A recyclable catalytic composition comprising a combination of alpha form of ferrous oxide and gamma form of ferric oxide magnetic nanoparticle in the ratio 1 :4, 3:7, 1 :1, 7:3 and 4: 1 embedded onto the inert substrate for the conversion of industrial and vehicular flue gases into carbon filaments at low temperature and optionally under magnetic field.

2. The catalyst composition according to claim 1, wherein the temperature is in the range of 90°C-200°C.

3. The catalyst composition according to claim 1, wherein the temperature is in the range of 90°C-150°C.

4. The catalyst composition according to claim 1, wherein the carbon filaments comprises carbon nanotubes, carbon Nanofibers, carbon microfibers, Carbon Nanorods, Carbon Nanobeads, carbon nanoparticles and such like either alone or a mixture thereof.

5. The catalyst composition according to claim 1 , wherein the catalyst particle size is in the range of 10- 1 OOnm.

6. The catalyst composition according to claim 1, wherein the magnetic field employed is in the range of 100 to 500 Oe.

7. The catalyst composition according to claim 1 , wherein the inert substrate selected from alumina, Cement coated with Si02, Zeolite, Titanium, silicon, Glass , glass wool or ceramic brick.

8. The catalyst composition according to claim 1, wherein the flue gas comprises carbon dioxide, carbon monoxide, methane, ethane, hydrocarbons, petroleum gases, nitrogen , hydrogen , water vapor, sulphur dioxide , fly ash , carbon particles, either alone or mixture thereof.

9. The catalyst composition according to claim 1, wherein the catalyst (alpha : gamma = 3:7) coated on the inert substrate of Silicon dioxide over Cement brick at 150°C to yield Carbon Nanotubes & Microtubes.

10. The catalyst composition according to claim 1, wherein the catalyst (alpha : gamma = 1 : 1) coated on wool substrate at 1 10°C yields Carbon Nanofibers.

11. The catalyst composition according to claim 1, wherein the catalyst (alpha : gamma = 1 :4) coated on alumina at 90-100°C yields Carbon Nano-Rods.

12. A highly efficient, low temperature, reproducible process optionally under magnetic field for the conversion of industrial and vehicular flue gases into carbon filaments, comprises;

a. coating a combination of alpha form of ferrous oxide (Fe203) and gamma form of ferric oxide (Fe304) magnetic nanoparticle in the ratio 1 :4, 3:7, 1 : 1, 7:3 and 4: 1 over an inert substrate at about 500°C till the catalyst is impregnated into the inert substrate;

b. inserting the coated inert substrate into the path of flue gases in a furnace/ vehicular exhaust pipes through the peephole and the manhole at various temperature zones for about 5-6 minute, in absence of ash;

c. growing carbon filaments on catalytic surface at a temperature in the range of 90-200°C,

d. scrapping the carbon filaments obtained in step (c) from the substrate and regenerating the catalyst using a magnet;

e. sieving carbon filaments of step (d) through micro sieve capable of sieving up to 100 nm; and subjecting the carbon filaments so obtained to purification.

13. The process according to claim 12, is a continuous process/batch process.

14. The catalyst composition according to claiml2, wherein the temperature is in the range of 90°C-200°C.

15. The catalyst composition according to claiml4, wherein the temperature is in the range of 90°C-150°C.

16. The catalyst composition according to claiml2, wherein the magnetic field employed is in the range of 100 to 500 Oe.

17. The process according to claim 12, wherein the carbon filaments is selected from carbon nanotubes, carbon Nanofibers, carbon microfibers, Carbon Nanorods, Carbon Nanobeads, carbon nanoparticles and such like either alone or a mixture thereof.

18. The process according to claim 17, wherein the carbon filaments have a diameter of at least 26nm.

19. The process according to claim 12, wherein the inert substrate is selected from alumina, Cement coated with Si02, Zeolite, Titanium, silicon, Glass , glass wool or ceramic brick.

20. The process according to claim 12, wherein the flue gas comprises Carbon dioxide, Carbon monoxide, methane, ethane, hydrocarbons, petroleum gases, nitrogen , hydrogen , water vapor, sulphur dioxide , fly ash , carbon particles, either alone or mixture thereof.

21. The process according to claim 12, wherein, said process yields Carbon Nanotubes & Microtubes on the magnetic nanoparticle catalyst Ferrous and ferric oxide ( alpha : gamma = 3:7) coated on the inert substrate of Silicon dioxide over Cement brick at 150°C .

22. The highly efficient, low temperature, reproducible process according to claim 12, wherein, said process yields Carbon Nanotubes & Microtubes on the magnetic nanoparticle catalyst Ferrous and ferric oxide (alpha : gamma = 1 : 1 ) coated on wool substrate at 1 10°C

23. The highly efficient, low temperature, reproducible process according to claim 12, wherein, said process yields Carbon Nanotubes & Microtubes on the magnetic nanoparticle catalyst Ferrous and ferric oxide (alpha : gamma = 1 :4) coated on alumina at 90-100°C.

24. The highly efficient, low temperature, reproducible process according to claim 12, wherein ash interference in step (b) eliminated by installation of electrostatic precipitator.