Phase behavior study of hydrogen production from supercritical water reforming of glycerol

L. J. ROVETTO; A. E. ANDREATTA; E.A. BRIGNOLE

Boulder

Simposio; 18th Symposium on Thermophysical Properties; 2012

NIST

Together with the exponential increase of the biodiesel industry over the last years, a glut of glycerol, as the principal by-product of the process, is being generated. Appropriate disposal of the glycerol becomes one of the main environmental issues for biodiesel plants. Of the several options to overcome the actual situation, the thermo-chemical conversion of glycerol into a variety of valued-added products becomes an interesting alternative. Steam reforming, aqueous phase reforming and supercritical water reforming (SCWR) are currently under investigation for hydrogen production from biomass and bio-fuels derivatives. The emerging “hydrogen economy” promotes the development of these alternative hydrogen production processes in search of an efficient, clean and sustainable energy system. The compounds involved in these chemical transformations are mainly glycerol, H2O, H2, CH4, CO, CO2, in different amounts depending on the reaction route and operating conditions. This work, analyses the phase behavior of mixtures present during the conversion of glycerol into hydrogen (or syngas) in supercritical water media under different operating conditions. The Group Contribution with Association Equation of State (GCA-EoS) that takes into account self and cross-association effects of polar molecules is used to investigate the phase behavior of this system. Different phase behavior scenarios are presented following selected binary and ternary mixtures through the glycerol conversion, with increasing amounts of hydrogen in the reaction mixture. The reactor feed ratio which maximizes the hydrogen production as well as the product composition is predicted using the Gibbs free energy minimization method. The obtained results show a precedent for the possibility to extend the potential of the GCA-EoS thermodynamic model to more complex systems for hydrogen production from different raw materials.