Atmospheric pressure cold plasma applied to steam reforming of small oxygenated molecules from bio-oil

Abstract

Fast Pyrolysis converts up to 75 mass % of biomass into bio-oils of which 12 mass % are small molecules with less than five carbon atoms. These molecules cannot be converted by existing technologies into green gasoline or green diesel. However, this fraction could be an excellent source for the production of hydrogen. In conventional steam reforming of oxygenated molecules, catalysts are severely deactivated by coke formation. Adding a cold plasma reactor upstream of and in cascade with a conventional steam reforming reactor could be a promising alternative to mitigate this problem. In the simplest description of cold plasma, electron avalanches become sources of free electrons that posses high directed velocities as they are accelerated in the electric field. Species more massive than the free electrons retain small kinetic energies thus the term “cold plasma'” is used to describe this state of matter. In this work, a mixture of small oxygenated molecules and water will be injected into the first (cold plasma) stage of the system. The cold plasma electron avalanches are expected to induce changes in the mechanism of reaction, affecting bond scission and conventional chemical reactions, which may enhance catalyst performance in the downstream reformer. The overall objective of this work is to observe experimentally the effect of cold plasma on the structure of small oxygenated molecules resulting from biomass fragmentation reactions and the effect that these modifications have on their tendency to form coke during steam reforming. Our working hypothesis is that the cold plasma will change the route of decomposition of small oxygenated molecules, producing intermediate species which in turn will favor the reforming process as well as reduce the formation of catalyst-deactivating carbon deposits. A prototype catalyst-based bio-oil processor that is augmented by a cold plasma reactor (CPR) has been constructed and is being evaluated. The CPR has two fuel injectors, one for water and one for the small molecules derived from bio-oils (CxHyOz). As argon carrier gas transports and mixes the two fuel injector streams the plasma reactor is held at 110 degrees C to keep all constituents in the vapor phase as they pass through a high voltage corona (cold plasma) generator consisting of an array of sharp needles that have a potential of many thousands of volts with respect to the ground plane. Injector duty cycles control the quantity of water and bio-oil molecules in the argon carrier stream.