Organic Radicals in Biomass Decomposition: Mechanisms & Dynamics

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

Organic Radicals in Biomass Decomposition: Mechanisms & Dynamics Barney Ellison (an organic chemist) and John Daily (an engineer) propose a new set of experiments to study the thermal decomposition of biomass. A) Based on Daily's fluid-dynamical modeling studies, Ellison will design and build a novel apparatus that uses a high temperature nozzle to decompose simple biomass materials such as sugars, oxygen heterocycles, and alkylaryl ethers. The hyperthermal, supersonic nozzle will be especially designed for non-volatile, biomass samples. The cracking products will be monitored simultaneously by vacuum ultraviolet photoionization mass spectroscopy and infrared absorption spectroscopy. B) Biomass gasification produces stabilized organic radicals such as propargyl and allyl which undergo bimolecular reactions that form aryl rings (C6H6). The team proposes to develop a new double resonance measurement to examine the vibrational spectra of these radicals. This novel experiment will use a coupled pair of infrared and vacuum ultraviolet lasers. The team also proposes to study the thermal decomposition of small biomass samples under controlled conditions in a high temperature, supersonic nozzle. The objective of this work is to use a mass spectrometer and infrared spectroscopy to characterize the decomposition reactions of simple sugars and oxygen heterocycles. Such experiments could provide insight to the molecular weight growth reactions that lead to the formation of tars (aromatic compounds). A major problem in all biomass gasification schemes is the presence of aromatic compounds in the biomass gas stream. Model organic compounds, such as furan or furfural, will be pyrolyzed in a hyperthermal nozzle and products will be identified and characterized in the new experiment. To make maximum use of the hyperthermal nozzle as a flow reactor requires detailed characterization of the gas flow and heat transfer characteristics. Daily will model the turbulent gas flow to characterize the hot nozzle. The design of the nozzle assembly is such that the flow chokes at the inlet orifice and again chokes at the downstream end due to friction and heat transfer. Thus the flow within the nozzle is isolated from downstream conditions, which in this case is held at vacuum conditions. Of course, the real gas flow through the nozzle is neither adiabatic, frictionless, nor uniform, and to accurately model it requires a numerical approach. Where the flow is in the continuum domain, the Navier-Stokes equations apply and can be solved using finite difference or finite element Computational Fluid Dynamics approaches. The flow downstream of the nozzle does not meet this condition, and Direct Simulation/Monte Carlo approaches are required.