Modeling of a continuous rotary reactor for carbon nanotube synthesis by catalytic chemical vapor deposition: Influence of heat exchanges and temperature profile

摘要

The influence of the reaction exothermicity has been taken into account for the modeling of a continuous inclined mobile-bed rotating reactor for carbon nanotube synthesis by the CCVD method using ethylene as carbon source. The optimal temperature to maximize the productivity and to avoid the formation of soot and tars is equal to 700 °C with ethylene. In small scale reactors, the heat exchange between the carbon nanotube growing bed and the atmosphere of the furnace surrounding the reactor is efficient enough to evacuate the heat released by the reaction and to keep the temperature constant along the reactor. However, for higher production capacity reactors, the global heat released by reaction increases, and the heat exchange has to be efficient enough to evacuate the heat released by the reaction. Otherwise, one may observe a runaway phenomenon. So the heat released by reaction influences the temperature profile through the reactor and heat exchanges have to be taken into account to model the axial temperature profile. The model has been validated with data obtained on two industrial reactors equipped with heating systems belonging four distinct heating zones with the same length providing an adequate control of the temperature in the reactor. To avoid a too high reaction speed, possibly leading to excessive heat release and to hot point responsible of cracking of ethylene and of reactor fouling by tars and soot deposition in the first reactor sections, the feed temperature of the reacting gas has to be fixed at a value lower or equal to 650 °C.