Methane is an abundant material that presents huge potential as a feedstock for chemicals synthesis. It is widely available as the major constituent of natural gas, but becomes also increasingly more obtainable from sustainable sources, such as biogas and landfill gas, and unconventional sources, such as shale gas, coalbed methane and methane hydrates. Moreover, it has more than 25 times higher 100-year global warming potential to that of CO2, so the need to develop efficient methane utilization methods towards value-added products is more than clear.
Among many uses, methane has been identified as a very promising raw material for the production of ethylene. The latter is the most widely produced base chemical, used e.g. for polymers, but its production depends on crude oil, generating the vast majority of CO2 process emissions in the UK chemical industry. In fact, under the Kyoto Protocol and the UK Climate Change Act, UK has specific international and domestic targets for reducing greenhouse gas emissions. 11% of these are represented by methane originating from agriculture, waste management and the energy industry, hence the production of ethylene from methane can be a promising process with multiple benefits for these sectors.
The high temperatures needed, though, for the activation of the stable methane molecule via thermal-catalysis, in conjunction with the use of oxidants to facilitate thermodynamically favourable routes, result in significant amounts of undesired carbon oxide by-products in the currently applied upgrading methods.
The combination of non-thermal plasma with catalysis has recently emerged as a promising technology to enable catalysts to operate at low temperatures. In non-thermal plasmas, the overall gas temperature is as low as ambient, however electrons are highly energetic resulting in collisions that easily break down molecule bonds, producing various reactive species like free radicals, excited states and ions that participate in subsequent reactions. The strong non-equilibrium character of these plasmas has been shown to even allow thermodynamically unfavourable reactions to occur under ambient conditions.
Being able to carry out direct methane coupling towards ethylene at low temperatures at non-oxidative conditions would present significant benefits, ranging from carbon oxides-free products to drastically reduced energy requirements and would enable alternate production routes towards polymers and high octane-number fuels. Combining the high reactivity of plasma with the high selectivity of the catalytic surface has a huge potential to unravel these benefits, which can further be enhanced by the use of sustainable electricity for the generation of the plasma.
Nonetheless, the interaction between non-thermal plasma and catalysts is a highly complex phenomenon. There has been a considerable amount of experimental work aimed at understanding the underlying elementary processes, however most mechanistic details are not yet elucidated. The combination of experimental, theoretical and modelling studies is needed to gain a more fundamental insight.
Microkinetic modelling is proposed as a novel approach to enhance the understanding and enable the optimisation of plasma-assisted heterogeneous catalytic reaction systems. With support from BASF, UK and a carefully designed experimental program, the novelty of the proposed project lies on the, for the first time, systematic consideration of all elementary reaction processes taking place in the plasma phase and on the catalyst surface and the explicit description of the interactions among them. The project is very timely, addressing topics in EPSRC's portfolio in relation to energy efficiency and alternative fuels and sources of chemicals. Successful implementation will result in the development of predictive computational tools that can be used to accelerate the design of new processes, reducing the needs for experimentation and associated costs.
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