Design and development of catalytic hollow fibre-based reactors for methane emission abatement under extreme conditions
Garcia Vazquez, Miguel
Natural gas is playing a key role in the decarbonisation of our energy system. This transition fuel is the cleanest fossil fuel and its combustion produces 50% less carbon dioxide than coal and 30% less than oil per unit energy generated. However, natural gas is itself a greenhouse gas responsible for a third of all global warming since pre-industrial levels. Natural gas-powered processes such as electricity production, industrial operations, residential heating and natural gas-fuelled vehicles inevitably emit small concentrations of unburned methane. Due to their low concentration (i.e. 300-1500 ppmV), these residual methane emissions have long been overlooked. As a result, there is no direct legislation addressing them and, today, an effective technology to abate these emissions is unavailable. The objective of this work is to develop a residual methane after-treatment technology that is cost-effective, long-lived and compact. The technology must be effective under real conditions and be resistant to sulfur poisoning at low temperature (i.e. 450°C), the main limitation faced by traditional precious metal-based catalysts. In order to evaluate the performance of the technology presented herein, reaction studies under real and extreme conditions as well as thorough characterisation of the materials have been fulfilled. This work has successfully underpinned the first hollow fibre after-treatment for residual methane emission abatement. This technology combines a non-precious iron and chromium oxide catalyst with a ceramic hollow fibre-based support. The developed catalyst, which is a mixture of hematite, eskolaite and traces of iron (II) chromite, has shown high resistance to sulfur poisoning during the 1000 h reaction study under sulfur dioxide concentrations 20 to 100 times larger than normal levels. Even though the catalyst was initially deactivated, it retained a third of its original activity. The long-term activity of the catalyst has been attributed to the highly sulfur-resistant eskolaite phase. In comparison, state-of-the-art precious metal-based catalysts are deactivated within hours under similar conditions. In addition, when compared to packed bed reactors, hollow fibre reactors have proven to be 3 to 5 times more efficient in terms of methane catalytic oxidation per unit mass of catalyst. Moreover, the technology has proven to be effective under real operating cycles (i.e. 10 thermal shocks) making it the ideal candidate for the development of commercial residual methane emission after-treatments. Finally, this technology has the potential to reduce an estimated 5.6 billion cubic metres annual residual methane emissions arising from electricity production, industrial and residential heating as well as transportation [1,2]. The global warming effect of these annual emissions over 20 years is equivalent to 470 billion cubic metres of carbon dioxide, a volume similar to the water volume of Lake Erie, one of the five Great Lakes of North America. Furthermore, industrialising this technology will pressure legislators to include residual methane emissions in future greenhouse gas regulations.