CATALYTIC STEAM REFORMING OF BIOMASS-DERIVED OXYGENATES - ACETIC-ACIDAND HYDROXYACETALDEHYDE

Biomass can be pyrolytically converted in high yields (similar to 70 w t.%) into vapors (or oils when condensed) composed mainly of oxygenate d organic compounds. Using a fixed-bed microreactor interfaced with a molecular beam mass spectrometer (MBMS), we have been studying the cat alytic steam reforming of model oxygen-containing compounds present in biomass pyrolysis vapors. This MBMS sampling system is unique in its rapid, real-time, and universal detection of gaseous and condensible p roducts. In this paper, we present results for steam reforming of acet ic acid (HAc) and hydroxyacetaldehyde (HAA), two major products derive d from the pyrolysis of carbohydrates in biomass. We propose mechanism s to couple the thermal decomposition and steam reforming reactions of these compounds. Both HAc and HAA undergo rapid thermal decomposition ; complete steam reforming of these two model compounds can be achieve d with commercial Ni-based catalysts. HAc forms coke on the catalyst s urface, which is subsequently gasified by steam. The proposed mechanis m for this coke formation involves an adsorbed acetate species that de carboxylates to form the coke precursor, (CH1-3)(abs), and also ketene , a dehydration product of HAc, that decomposes to form (CH1,2)(abs). The reforming of HAA by steam does not involve any detectable intermed iate and proceeds smoothly to a complete breakdown to CO and H-2 on th e catalyst surface.