From Nucleation to Aerogels: The Evolution of Structure in CNT Aerosols Reactors and Methane Pyrolysis

ADAM M BOIES, Jack Peden, Shahzad Hussain, Mabel Qiao, Joe Stallard, Michael Glerum, Xiaoyu Qiu, University of Cambridge

     Abstract Number: 508
     Working Group: Carbonaceous Aerosols

Abstract
Over the last two decades, the aerosol production of bulk carbon nanotube (CNT) materials has advanced from laboratory reactors to plants capable of 5 kt/year. The commercial interest in CNT production has led to new fundamental aerosol questions that are critical to the scale and ultimate viability of CNT production. The nucleation and growth of catalyst particles within pyrolytic reaction zones of a high temperature (~1200 °C) reactor ultimately dictate the density of CNT reaction and volume-time efficiency of the process.

This presentation will discuss our emerging understanding of the role of methane pyrolysis in the presence of iron-sulfur nanoparticles that serve as sinks for C2 species which are the feedstocks of CNT growth. A new class of aerosol CNT reactors are being developed that allow optical access to study the aerosol and pyrolytic reactions via in-situ methods, such as laser induced incandescence, infrared spectroscopy and multi-photon Raman techniques. Further, these reactors provide internal methods for heating, which eliminate the need for ceramic reactor walls, opening possibilities for bespoke design of reactor geometries and catalyst precursor injection strategies.

New catalyst synthesis techniques have been developed that enable control of the size distribution of catalysts. The use of unipolar charge enables suppression of particle-particle collisions, which reduces the polydispersity of the aerosol. The subsequent growth of a dense network of CNTs results in an aerogel formation, which has been studies by atomistic and hybridized models. The nucleation of the aerogel structure is achieved by prolongment of the reorientation timescales (analogous to spherical particle coalescence) that approach the collision timescales of the CNTs. The aerogelation dynamics are of interest to a broad range of new 1D materials that are envisioned to be produced by aerosol techniques.