Co-generation of C2 hydrocarbons and electric power from methane in a sold oxide fuel cell type reactor

Abstract

The research studies the co-generation of C2 hydrocarbons and electiric power from methane in a solid oxide fuel cell (SOFC) reactor using La0.8Sr0.2MnO3 (LSM) as the cathode catalyst, 8 mol% yttria-stabilized zirconia (YSZ) as the electrolyte and La1.8Al0.2O3 (LaAlO) as the anode catalyst. The study is divided into 3 main parts: Investigation the behaviors of oxygen species by fuel cell type temperature-programmed desorption (FC-TPD) measurement, oxygen permeation through the LSM/YSZ/LaAlO cell and modeling of the oxidative coupling of methane (OCM) in SOFC reactor. The two oxygen species responsible for a combustion reaction and for a coupling reaction are observed as suggested in previous TPD study of the LaAlO anode catalyst powder (Tagawa et al., 2003). The increase of the applied potential during the pretreatment increases the amount of desorbed oxygen and decreases the activation energy of oxygen desorption. The oxygen permeation flux through the cell is 0.90x10-8 mol m-2 s-1 at 1173 K with the activation energy of 170 kJ mol-1. By applying an external potential, the oxygen permeation flux increases while the activation energy of oxygen permeation decreases. The oxygen permeation fluxes under methane feed in the anode side are 1-2 orders of magnitude higher than those under helium feed. A model of the oxygen permeation is proposed. In the OCM in SOFC reactor studies, both experiments and simulations are carried out. The C2 selectivity and the methane conversion are 91.7% and 23.7% at 1273 K, respectively. A mathematical model of the OCM in the SOFC reactor is developed. The plug flow condition is assumed and the kinetic rate expression with two different oxygen species is proposed. The effect of external load is investigated both by performing experiments and calculations. Methane conversion decreases with increasing the external load resistance while C2 selectivity is insignificantly affected. When operating at higher temperature and pressure, higher electric power and C2 production can be obtained. The results suggest that our SOFC system is a good reactor for C2 production; however the obtained power density is much lower than that of the conventional SOFC.