Thermodynamic Phase Equilibrium Composition Determination of Ethanol Steam Reforming by Direct Minimization of Gibbs Free Energy Using Peng-Robinson Property Method

Abstract

Abstract Thermodynamic equilibrium analysis of ethanol steam reforming was carried out by direct minimization of Gibbs free energy method using Aspen Plus (V8.8). Equilibrium compositions of each species were analysed for temperatures ranging from 873 to 1173K, steam-to-ethanol molar ratios (S/C) of 2:1 -6:1 and pressure at 1atm. Due to high temperature and reduction of CO2, there is shift in equilibrium which resulted to increase in hydrogen formation. The predominant reactions which contributed to the increase in hydrogen formation are incomplete ethanol steam reforming, ethanol decomposition, methane steam reforming and water-gas shift reaction, which in turn make H2/CO ratio significant, with regard to steam-to-ethanol feed ratio of 6. Methane formation is negligible when the reforming is operated between 1093K and 1173K for all the steam-to-ethanol molar feed ratios. This implies that higher carbon deposition (4.17×10-23 kmol/s) observed at 1173K with respect to steam-to-ethanol molar feed ratio 2 could be due to methane decomposition, Boudouard reaction and CO2 reduction. However, the least rate of carbon deposition is 2.48×10-23 kmol/s relating to feed ratio 6 at 1173K, which implies that high carbon formation is significant at temperature above 1173K and steam-to-ethanol molar feed ratio 2. In view of the high H2/CO ratio attained within the considered temperatures (873-1173K) and steam-to-ethanol molar feed ratio of 6, the syngas is recommended to be used for electricity generation via solid oxide fuel cell.