A thermodynamic analysis of hydrogen production via aqueous phase reforming of glycerol

Abstract

The thermodynamic analysis of glycerol (C3H8O3) aqueous phase reforming (APR) has been performed following the Gibbs free energy minimization method. The effect of the operating parameters, i.e. water to glycerol mass ratio (W/G=4−14), pressure ratio P/PH2Osat=1−2 and temperature (T=300−550K) on: i) hydrogen production, ii) CH4 production and iii) carbon formation was investigated. For the range of the examined conditions, the conversion of glycerol approached 100%. It was found that the maximum H2 selectivity reaches (1st case) the maximum stoichiometric value of 70%, while the methanation reaction (2nd case) can be reduced at high temperatures and low pressures but not eliminated, indicating that methanation is thermodynamically favored over H2 production. It was also found (3rd case) that almost 80% of the amount of glycerol is converted into carbon, while at pressure ratios P/PH2Osat≤1.4 and temperature values T>400K carbon formation can be eliminated. For all the cases studied, the optimal W/G for H2 production was found equal to 9 under thermodynamic equilibrium conditions and the best conditions to optimize H2 production and minimize CH4 and carbon formation are as follows: 450≤T≤550K, 1≤P/PH2Osat≤1.2 and 9≤W/G≤14.