(497a) Thomas Baron Award in Fluid-Particle Systems (Sponsored by Shell): Design of Multiphase Reactors for the Synthesis of Renewable Chemicals and Semiconductor Nanocrystals

The first part of the presentation will focus on the design of fluidized bed reactors for catalytic fast pyrolysis (CFP) of lignocellulosic biomass to renewable value-added chemicals. CFP has emerged as a very promising method for single step thermal conversion of biomass to liquid fuels and chemicals. The production of aromatics from lignocellulosic biomass using ZSM-5 catalysts was studied in a laboratory-scale bubbling fluidized bed reactor using a combination of experiments and computational fluid dynamics simulations. The operating conditions of the reactor as well as the morphology and mesoporocity of the ZSM-5 catalyst were optimized to maximize the yield and selectivity in benzene, toluene, xylene (BTX) and other aromatics and to minimize catalyst deactivation due to coking. Modeling and computer simulations of the downward flow of thermally decomposing biomass particles in the vertical feed tube of the reactor enabled the development of performance diagrams that can be used to identify operating conditions leading to rapid downward suspension flow without undesirable transitions to slow moving bed flow or reversal of the gas flow in the tube. The second part of the presentation will focus on the synthesis of semiconductor nanocrystals that exhibit size-tunable fluorescence and find applications in ultra-high color definition displays, solar energy conversion, and biosensors. We have developed novel aerosol and colloidal synthesis methods for producing II-VI compound semiconductor nanocrystals that emit in the visible part of the spectrum. The most promising synthesis method exploits the dispersed nanodomains of microemulsions and liquid crystals as microscopic templates for controlling particle size, shape, and size distribution. The mechanism of particle nucleation and growth in spherical nanodomains was studied using Kinetic Monte Carlo simulations. Generalized scaling laws were obtained that describe the growth of nanoparticles by coalescence in confined domains. The doping mechanisms and thermodynamic stability of core-shell nanocrystals were studied using Density Functional Theory calculations. Reactor configurations are being developed that are suitable for large-scale modular manufacturing of nanocrystals with narrow size distributions, while maximizing the conversion of reactants and enabling recycling of the solvents.