Conversion of propane to propylene in a proton-conducting fuel cell.

摘要

Using proton-conducting fuel cells for propane dehydrogenation to produce propylene is a novel process having many interesting characteristics, which combines the continuous chemical process to produce value-added propylene with electrical power generation. Although a lot of efforts have been made to demonstrate this process experimentally, no success has been achieved because of challenges in finding suitable proton-conducting electrolytes and compatible electrodes operating at intermediate temperatures (800°C). In this thesis, the feasibility of conversion of propane to propylene in a proton-conducting fuel cell was studied by developing suitable fuel cell components.;LiNaSO4 and the perovskite type of oxide, Y-doped BaCeO 3, was investigated for use as proton conducting electrolyte in the fuel cells. Thermodynamic analysis and experimental results indicated LiNaSO 4 was not stable in the fuel cell for propane dehydrogenation and the proton conductivity of LiNaSO4 only accounts for 5-10% of total ion conductivity. Y-doped BaCeO3 presents high proton conductivity and good chemical stability over 120 h tests coupled with suitable fuel cell set-up design. Thus, the feasibility of conversion of propane to propylene in a fuel cell based on this perovskite oxide with platinum as anode and cathode catalysts was investigated. The feasibility was proven with high product selectivity to propylene and good fuel cell performances. It was also showed that the electrochemical reaction of propane dehydrogenation was in competition with other side reactions caused by the gas species (H2, C2H 6, C2H4, etc.), which were the products of non-electrochemical reactions (e.g. thermal cracking) in the anode chamber. The hydrogen oxidation reaction was a predominant side electrochemical reaction.;Chromium (III) oxide synthesized by sol-gel method showed high activity for electrochemical propane dehydrogenation, and the maximum power density of about 110 mW/cm2 was achieved at 700°C as well as propylene selectivity up to 95%.;Carbon deposition during the process of propane dehydrogenation in the fuel cell was a problem, as the carbon poisoned the anode catalysts leading to deactivation of anode catalysts and deterioration of the product distribution. Compared to open circuit conditions, carbon deposition can be dramatically reduced with a local electrical field on the anode catalyst under the current flow conditions.