Catalytic Non-Oxidative Coupling of Methane at Low Temperature

Catalytic Non-Oxidative Coupling of Methane at Low Temperature

Yasmeen Belhseine, Chukwuemeka Okolie and Carsten Sievers^*

Georgia Institute of Technology – School of Chemical & Biomolecular Engineering

Methane is an excellent raw material for the production of fuels and chemicals with great potential to help alleviate the ongoing pressing energy need facing the world. However, large amounts of natural gas are located in remote areas where gas transportation in pipelines is technologically challenging. Furthermore, methane has a very low energy density by volume of 10.6 kWh per cubic meter at atmospheric pressure. As a result, methane needs to be transported as a compressed gas (10 – 100 atm), which is energy intensive and expensive. Conversion of methane to more transportable products is therefore a highly desirable option which unfortunately has proven to be a very difficult problem in catalysis over the past century.

This work addresses the need for a new technology for direct methane conversion by developing catalysts for the selective activation of methane at temperatures below 500 °C. A specific aim was directed towards a direct non-oxidative coupling of methane (NOCM) into ethane and ethylene. NOCM is a thermodynamically limited reaction, affording very limited conversion of methane. However, the conversion of methane can be improved by the use of a membrane that can selectivity remove hydrogen by-products and in turn, push the reaction forward. In addition, this reaction shows great potential because it affords high selectivities of desired products due to the absence of an oxidizing agent.

Catalysts chosen for this work were selected from preliminary FTIR screening which studied the surface chemistry upon interaction with methane. Continuous flow reactions of methane in a non-oxidative environment were performed using a packed bed reactor connected to an online gas chromatograph to elucidate the products and the conversion of methane. When the reaction was run for 72 hours at 450 °C, the conversion of methane went through a maximum at 1.2%. At the start of the reaction, hydrogen was the main product, and the mole fraction of hydrogen and C₂ compounds among the products reached 56% and 44%, respectively, at the end of the reaction. The hydrogen selectivity remained higher compared to C₂ products even at the end of the reaction. In parts, this can be attributed to the dehydrogenation of ethane to ethylene, which was seen as one of the products.