Bi-Directional Catalyst Injection in Floating Catalyst Chemical Vapour Deposition for Enhanced Carbon Nanotube Fiber Yield

Carbon nanotube fiber (CNT fiber) synthesized through floating catalyst chemical vapour deposition (FC-CVD) is one of the strongest man-made fibers ever synthesized. The poor carbon conversion in the FC-CVD process is one of the major hurdles in its commercial deployment. In this work, we have employed a novel method of bi-directional catalyst injection where catalysts were injected from both inlet and outlet sides of the reactor. The injection of the catalyst from the outlet into the reactor reaction zone was possible by a backflow caused by the convection vortex as predicted by the computational fluid dynamics (CFD) analysis. Bi-directional catalyst injection was able to enhance the carbon conversion by 53 % compared to conventional uni-directional injection. CNT fibers obtained in bi-directional catalyst injection are a mixture of multi-walled (MW) and single-walled (SW) CNTs whereas uni-directional catalyst injection resulted in MWCNTs only. The average ID/IG ratio and the average CNT dimensions were similar in both uni-directional and bi-directional catalyst injection. The amorphous carbon content was lower for bi-directional catalyst injection. A mechanism for the improvement of carbon conversion in bi-direction catalyst injection has been proposed