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

• Published in: International journal of hydrogen energy Vol. 37; no. 19; pp. 14820 - 14830
• Main Authors: Díaz Alvarado, F., Gracia, F.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.2012
• Subjects: Carbon; Carbon deposits; CO2 sorption; Glycerol; Hydrogen; Oxidative steam reforming; Thermodynamics; Glycerol; Thermodynamics; Carbon deposits; CO2 sorption; Hydrogen; Oxidative steam reforming
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2012.01.158

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 °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 H2 yield. In those systems where Hydrotalcites were included as CO2 sorbent, H2 yield is maximized between 350 °C and 450 °C and S/G ratio above the stoichiometric ratio, while for CaO sorbent and no sorbent systems the maximization of H2 yield is given at 600 °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 °C and 450 °C. Those conditions maximize the H2 yield with no other product gases or carbonaceous solids. ► This is a thermodynamic study of the Oxidative Glycerol Steam Reforming. ► We have been able to represent the formation of different C-containing deposits. ► Below 450 °C the most favorable C-deposit is graphite; and above, carbon nanotubes. ► We also have represented two different CO2 sorbents and its sorption capacities. ► It is advisable to use Hydrotalcites and a temperature between 375 °C and 450 °C.