Remarkable enhancement in CNT fiber synthesis by reducing convection vortex in floating catalyst chemical vapour deposition

Abstract

Synthesis of carbon nanotube fiber (CNT fiber) in a floating-catalyst chemical vapor deposition (FC-CVD) reactor suffers from very low carbon efficiency and yield. One of the major causes of poor conversion is the formation of internal convection vortex near the inlet, where catalyst particles undergo agglomeration and deactivation resulting in a significant reduction in the yield. It also lowers the average aspect ratio of the CNTs. In this work, a novel method of using an internal heating rod has been employed to reduce the convection vortex by altering the temperature gradient locally. The optimum position, temperature and size of the heating rod have been determined by computational fluid dynamics (CFD) for enhanced carbon conversion. The yield and the aspect ratio of CNT fiber, synthesized at the optimized condition have enhanced by 90% and 50%, respectively while the average ratio of D to G peak in Raman spectra (ID/IG) has reduced by 58%. For the first time, residence time distribution (RTD) analysis has been used to describe the effect of convection vortex on carbon conversion for the synthesis of CNT fiber. This work demonstrates simultaneous enhancement in yield, crystallinity and aspect ratio of the CNT fiber by reducing the convection vortex.