(737e) Optimization of Flame Reactors for Pilot-Scale Nanoparticle Manufacture

A present challenge with flame spray synthesis of nanoparticles is the translation of current laboratory-scale reactors into an industrial production environment. To achieve this goal the production rate has to be increased while maintaining constant nanoparticle characteristics in a safe and economic process. Flame spray reactor operating costs consist mainly of the employed precursor and process gases (Wegner et al., 2011). The goal here is to minimize the utilization of hydrocarbon solvents and to replace oxygen dispersion gas with air, yielding a more environmentally friendly process with better energy utilization.

The effect of preheating air and precursor streams on the spray combustion as well as product particle properties was investigated for the example of zirconia nanoparticle synthesis at rates up to 2 kg/h. Therefore, the entrained air was preheated electrically or via recovery of the process heat and the up to 100 L/min of dispersion gas were gradually exchanged by air. While a non-preheated spray flame operated with increasing levels of air did produce carbon-contaminated products or was blown out completely, the preheated system yielded stable flames and cleaner products. This is attributed to enhanced combustion kinetics and expanded flammability limits. Employing a flame enclosure allowed to confine the combustion-generated heat, further stabilized the process and allowed to preheat part of the entrainment air. Addition of steam to the flame aimed at counteracting soot formation (Dryer, 1977) but instead affected the specific surface area of product powders.

Overall, the process parameter window for stable combustion and nanoparticle formation could be broadened, process costs reduced and product quality improved by pre-conditioning of reactant streams and optimizing reactor geometry.

References:

Dryer, F. (1977). Water addition to practical combustion systems—concepts and applications. Symposium (international) on combustion, Elsevier.

Wegner, K., B. Schimmöller, B. Thiebaut, C. Fernandez and T. Rao (2011), KONA 29: 251-265