Application To Solid Biomass
Reactive flash volatilization of solid particles composed of cellulose, starch, lignin, Quaking Aspen (Populus tremuloides) wood chips, and polyethylene was demonstrated in 2007 in the scientific journal Angewandte Chemie. Particles of cellulose were completely converted to syngas (H2 and CO) and combustion products (H2O and CO2) in as little as 30 milliseconds. Catalytic reforming of all materials occurred without the requirement of an external heat source while operating at 500–900 °C. Under optimal conditions, 50% of all atomic hydrogen and 50% of all atomic carbon can be converted to molecular H2 and carbon monoxide in as little time as 30 milliseconds. Reaction chemistry was demonstrated on both a Rh-Ce/alumina catalyst and a Ni-Ce/alumina catalyst.
A publication in the scientific journal Green Chemistry demonstrated that the process of reactive flash volatilization can be considered a combination of several other global chemistries occurring through thermal and chemical integration. As shown in the diagram at the right, the initial pyrolysis chemistry occurs when the biomass particle (green) physically contacts the hot catalyst (orange). Volatile organic compounds (VOCs) flow into the catalyst with oxygen, adsorb on Rh atoms, and react to form combustion products (H2O and CO2) and syngas (H2 and CO). After this initial chemistry, three main global reactions occur. Combustion products react catalytically with syngas by the water-gas shift reaction. Also, volatile organics react catalytically with steam (H2O) to form new combustion products and syngas. Finally, the volatile organics can crack homogeneously in the gas phase to form smaller volatile organics.
The operating temperature has been shown to vary within the catalyst length while also being a strong function of the biomass-to-oxygen ratio. An experimental examination has shown that the heat required to thermally fracture biomass was generated within the catalyst bed by surface oxidation reactions. The temperature profile (and reaction temperature) was shown to be extremely important to prevent the formation of carbon at equilibrium. Very fast conversion has been attributed to high operating temperatures, but the maximum cellulose processing rate has not been determined. However, catalytic partial oxidation of volatile organic compounds has shown that complete conversion can occur in less than 10 milliseconds.
Read more about this topic: Reactive Flash Volatilization
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