(591f) Oxidative Ethane Dehydrogenation Under Thermal and Microwave Heating over Ga/ZSM-5, Gapt/ZSM-5, and Microwave Synthesized Ga-ZSM-5

Ethane is the second largest component of natural gas, making up to 20 vol %. Although ethane is a valuable feedstock for the production of many value-added chemicals, it is often flared at the well-head to avoid the cost associated with transporting the fuel or chance of condensation of the natural gas in the pipeline. The flaring of stranded gas adds to the global issue associated with the increased release of greenhouse emissions such as CO₂. Developing uses for this ethane to eliminate the greenhouse gas emissions and increase utilization of these valuable resources. The direct catalytic oxidative dehydrogenation of ethane (ODHE) is the use of an oxidative species as a co-reactant to produce ethylene from ethane. ODHE allows for lower reaction temperature resulting in the suppression of coke and favorable thermodynamic conditions. Using a strong oxidant such as O₂ involves the dehydrogenation of ethane to ethylene, the total oxidation of ethane, and potential formation of CO_x products which can lead to lower ethylene yield and aromatics by-products. Whereas using CO₂ as a mild oxidant can prevent the overoxidation of ethane and the metal catalyst and can be more advantageous by enhancing the equilibrium conversion obtained due to the removal of hydrogen via the water gas shift mechanism.

In this study, conventional thermal heating versus microwave heating were tested for the oxidative dehydrogenation of ethane with CO₂ as the oxidative co-reactant over conventionally synthesized Ga/ZSM-5 and GaPt/ZSM-5 and a direct microwave synthesized Ga-ZSM-5 catalyst. A 2.45GHz solid-state microwave reactor system with a high-temperature mono-mode cavity was used to supply microwave irradiation to the catalyst bed during the ODHE-CO₂. The catalytic activity of the Ga/ZSM-5, GaPt/ZSM-5 and the microwave synthesized Ga-ZSM-5 were tested under 30% ethane and 30% carbon dioxide in nitrogen, at a total flow of 100 mL/min. For the thermal fixed bed reactor, the reaction temperatures tested were 450°C, 550°C, and 650°C, whereas, for the microwave fixed bed reactor, the reaction temperature was set to 450°C all for 3 hours. The fresh catalysts were further analyzed by XRD, BET, ICP-OES, NH₃-TPD to elucidate the active metal species and catalysts prior to the ODHE reaction. The spent catalysts were characterized by TGA/DTA and TEM, to determine the effect of the reaction on the catalysts. In this study, microwave heating increased the catalytic conversion of ethane and selectivity to ethylene.