Synthesis of Carbon Nanomaterials in a Swirled Floating Catalytic Chemical Vapour Deposition Reactor for Continuous and Large Scale Production

Abstract

Carbon nanotubes (CNTs), ‘rediscovered’ (Monthioux & Kuznetsov, 2006) by Iijima as a byproduct of fullerene synthesis (Iijima, 1991), have attracted enormous scientific and technological interest. Their myriad applications in various fields since their rediscovery are no longer debatable. However, their commercial applications still depend on large scale synthesis (several thousands of tons per year) and associated cost of production. Various methods have been developed for the production of CNTs (Dresselhaus et al., 2001; Agboola et al., 2007). However, the three very useful and widespread methodologies include arc discharge, laser ablation and chemical vapour deposition (CVD) (Robertson, 2004; Agboola et al., 2007). Two key requirements revealed in these methods are as follows, (i) a carbon source, and (ii) a heat source to achieve the desired operating temperature (See & Harris, 2007). In the arc discharge, CNTs are produced from carbon vapour generated by an electric arc discharge between two graphite electrodes (with or without catalysts), under an inert gas atmosphere (Journet et al., 1997; Lee et al., 2002; Agboola et al., 2007). In the laser ablation, a piece of graphite target is vapourised by laser irradiation under an inert atmosphere (Journet & Bernier, 1998; Paradise & Goswami, 2007). As for the technique of CVD , it involves the use of an energy source such as plasma, a resistive or inductive heater, or furnace to transfer energy to a gas phase carbon source in order to produce fullerenes, CNTs and other sp2-like nanostructures (Meyyappan, 2004). As would be expected, some of these methods are more effective than others. The arc-discharge, though it produces CNTs of high quality with fewer structural defects, uses high temperature of up to 1500°C, which makes it difficult to be scaled up for commercial purposes. On the other hand, laser vaporisation method is an expensive technique because it involves high purity graphite rods and high power lasers. At the moment, the CVD methodology (or variations thereof) is the only promising process for the production of CNTs on a reasonably large-scale compared to arc-discharge and laser vaporization methods (Coleman, 2008). In addition, the process tends to produce nanotubes with fewer impurities (catalyst particles, amorphous carbon and non-tubular fullerenes) compared to other techniques (Esawi & Farag, 2007). The variants of the CVD are as a result of the means by which chemical reactions are initiated, the type of