In recent years carbon nanotubes have attracted a particular interest due to their unique morphology, and are therefore used widely in various applications due to their versatile mechanical and electrical properties. There is growing application of carbon nanotubes in synthesis of products such as polymer composites, conducting polymers, protecting wares, light weight sports goods, electrodes in batteries etc. Carbon nanotubes are formed by rolling of graphene sheet with sp2 carbon into seamless cylinders of nanosize dimensions. The physio-chemical properties of these carbon nanotubes depend on the structural morphology of the nanotubes.
Carbon nanotubes are classified into three categories viz. single walled, double walled and multi-walled carbon nanotubes depending on the shape and dimension of the tube. Each carbon nanotube type has unique characteristic properties due to their structural morphology. In general, carbon nanotubes with diameter as high as 5 nm are considered as single walled and types with diameter 6-100 nm diameter is considered as multiwalled nanotubes, whose inter-layer spacing is close to 0.34 nm.
U.S. Pat. No. 8,398,894 B2 discloses the method of producing carbon nanotube having desired apparent density by catalytic decomposition of gaseous mixture of ethylene and hydrogen at 650° C. using catalysts prepared by co-precipitation method.
US 20090140215 A1 patent describes the production of carbon nanotubes of 3-150 nm diameter by decomposition of ethylene as feedstock at 6500 C in the presence of H2 and Ar on supported metal catalyst which comprises mainly Co, Mn and Mo.
US2012077031 (A1) discloses the catalyst composition for the synthesis of thin multi walled carbon nanotubes having diameter of 5-20 nm using the gaseous mixture of hydrogen and carbon source selected either from saturated or unsaturated hydrocarbon having 1 to 4 carbon atoms in the temperature range of 500° C. to 900° C. The catalysts disclosed comprises the Co as main active metal along with promoters selected from Ni, Cr, Mn, Mo, W, Pb, Ti, Sn, or Cu, its oxide, or its derivative on inactive MgO support carrier using co-precipitation method under the controlled pH conditions.
EP 1 318 102 A1 describes the production of single walled/multi walled carbon nanotubes from acetylene, ethylene, butane, propane, ethane, methane using catalytic chemical vapor deposition.
CN 1443708 discloses the method of preparing the multi walled carbon nanotubes synthesis from methane feedstock using single metal and with promoter combination.
U.S. Pat. No. 8,093,176 B2 discloses the process for continuous production of catalysts for the formation of carbon nanotubes. Co, Mn and Mo are used as catalysts in different metal ratios without any support material. The hydrocarbon feedstock with carbon number C1-C4 of aliphatic and olefinic compounds used.
US 20120219490A1 describes the simultaneous production of carbon nanotubes and hydrogen from gaseous carbon source feedstock constituent of carbon and hydrogen atoms. The method deals the production of single walled carbon nanotubes and hydrogen from gaseous feedstock in the presence of vaporized metal catalyst.
U.S. Pat. No. 6,413,487 patent describes the method and apparatus for producing carbon nanotubes. The invention mainly describes the synthesis of carbon nanotubes either from CO, CH4, C2H2, C2H4 and mixtures by using Group VIII metal catalysts.
WO 2007033438 discloses the catalyst system for a multi-walled carbon nanotube production process using natural gas and mixture of methane and olefin gas.
WO 2001085612 A2 describes the process for preparing carbon nanotubes using methane, ethane, acetylene and carbon monoxide in the presence of Ni—Co catalysts.
In the above prior art, the feedstock used are gaseous hydrocarbon having carbon number in the range C1 to C4 with an objective of producing carbon nanotube. However, the above prior art have not disclosed on use of liquid hydrocarbon mixture say, crude oil or its products as feedstock with an objective of producing carbon nanotube along with mixture of hydrogen and methane, which can be used directly as a transportation fuel.
U.S. Pat. No. 6,730,284 describes the method for producing carbonaceous articles by chemical vapor deposition, wherein hydrocarbon and oxygen containing hydrocarbons and aromatic hydrocarbon are used as feed stocks by using Group I B metals and second metal selected from the group of Fe, Ni, Co, Zn and mixtures in the range of 100-11000 C operating temperature.
U.S. Pat. No. 7,160,531 disclose the process for the continuous production of aligned carbon nanotubes. The invention features the dispersion of organo metallic catalyst with liquid hydrocarbon to form a feed solution and volatilizing the feed solution. The hydrocarbon liquid contains organo metal catalyst of at least 0.5 wt. % in the dispersed state. In the disclosure, liquid organo metallic catalyst has been employed.
It is clear from the above prior art that the disclosures are related to the synthesis of carbon nanotubes from various carbonaceous raw materials particularly single molecule hydrocarbons including gases and liquid hydrocarbon as feedstock. The above prior arts disclose use of single molecules gaseous/liquid feedstock or mixture thereof for the production of carbon nanotube. Such a process is usually expensive and there is a need to find alternative methods which are more economic to produce carbon nanotubes (CNT) on a commercial scale.