Scale up of a Solar Reactor for Fullerene and Nanotube Synthesis

Abstract

Conventional methods for the synthesis of fullerenes and carbon nanotubes such as laser or electric arc ablation have failed when the process is scaled up. Our ultimate goal is to scale a solar process up from 2 to 250 kW; this paper shows that our method for achieving this scale-up is valid because we were able to predict process performance variables at the 50 kW level from preliminary experimental results from 2 kW experiments. The key parameters that characterize this process are the carbon soot mass flow rate and the desired product yield. The carbon soot production rate is a function of the target temperature and this can be predicted in a straightforward way from a heat transfer model of the larger system. The yield is a more complicated function of specific reactor variables such as patterns of fluid flow, residence times at various temperatures, and the reaction chemistry, but we have found that for fullerenes it depends primarily on the concentration of carbon vapor in the carrier gas, the target temperature and the temperature distribution in the cooling zone. Using these parameters, we scaled our process up to 50 kW and compared the predicted results to the measured performance. A graphite target 6 cm in diameter was vaporized in an argon atmosphere and a reduced pressure of 120–240 hPa with a solar flux density in the range 600–920 W/cm2. Vaporization rates as high as 50 g/h were measured with a fullerene production rate equal to about 2 g/h, i.e., the expected results.