Oxidative steam reforming of glycerol for hydrogen production: Thermodynamic analysis including different carbon deposits representation and CO2 adsorption

Glycerol production is associated with growing biodiesel industry, and because of its poor fuel skills it has been signed as a candidate for hydrogen production by Steam Reforming (SR). In various reforming reaction systems, many different types of Carbon deposits have been reported, but this variety has not been incorporated in thermodynamic studies as previous studies have represented carbon deposits only as Graphite. This work proposes a new representation including Graphite, Carbon Nanotubes, Amorphous, and Polymeric carbon for Glycerol Reforming systems. The study also includes an analysis of CO2 sorption effects, comparing Hydrotalcites and CaO as sorbents, with their respective variation of sorption capacity with temperature. All thermodynamic analysis is performed by Gibbs free energy minimization, following an algorithm for discrete nonlinear minimization. The extended representation of carbon deposits reveals the existence of two regions: below 450 degrees C the most favorable carbonaceous solid type is graphite; and above, carbon nanotubes. The use of CO2 sorbents in Glycerol Reforming systems shifts the equilibrium to products, increasing H-2 yield. In those systems where Hydrotalcites were included as CO2 sorbent, H-2 yield is maximized between 350 degrees C and 450 degrees C and S/G ratio above the stoichiometric ratio, while for CaO sorbent and no sorbent systems the maximization of H-2 yield is given at 600 degrees C and S/G = 10. From the thermodynamic analysis, once the O/G ratio has been chosen according to energetic consideration, it is advisable to carry out the Glycerol Reforming reaction with at least a stoichiometric S/G ratio, the addition of enough mass of Hydrotalcites for stoichiometric CO2 sorption and a temperature between 375 degrees C and 450 degrees C. Those conditions maximize the H-2 yield with no other product gases or carbonaceous solids. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.