CatPlasKin: The microkinetics of non-thermal plasma-assisted heterogeneous catalysis with application to the non-oxidative coupling of methane

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.

The successful implementation of the project will initiate and enable economic, academic and societal impact, based on the careful identification of all relevant stakeholders and their timely engagement at various stages of the project's path towards deployment.
There is a clear economic potential in developing a direct route to ethylene production from abundant methane, enabling alternate production routes towards polyethylene via polymerisation, but also high octane-number fuels via oligomerisation. Ethylene is a major organic commodity globally, whose demand is expected to only increase due the ever-increasing need of our society for plastics, among others. Its price is similarly bound to rise as crude oil resources continue to become scarcer leading to a clear financial drive for accessing cheaper raw materials for its production. Clear beneficiaries are hence identified in the petrochemicals and energy UK and international industries.
Using biologically-derived methane, e.g. from biogas obtained via anaerobic digestion, to produce ethylene can enable additional significant societal impact in the shape of environmental benefits, in addition to economic impact. UK has both international and domestic targets for reducing greenhouse gas emissions, under the Kyoto Protocol, the UK Climate Change Act and the EU Effort Sharing Decision. Methane represents 11% of UK greenhouse gas end-user emissions, out of which the majority originate from the agriculture (53%), waste management (32%) and energy (13%) sectors. Methane emissions form the major contribution in the agriculture sector (56%) due to the enteric fermentation from livestock, but also from manure management systems, while they dominate the waste management sector (91%), with the vast majority originating from landfill sites. Measurable methane amounts in the energy sector (5%) are emitted via leakage during natural gas distribution and during coal mining. Finally, natural gas flaring in UK-based oil platforms leads to CO2 emissions, amounting to about 3% of the total yearly UK gas production, mainly due to the lack of infrastructure for methane utilisation, while similar is the case for coal mining. The low operating temperature, high reactivity and ability to be driven by sustainable electricity can make plasma-catalytic methane upgrading a very efficient, modular and environmental solution for all above sectors.
Engagement with the related chemicals industry and with local council, agricultural and waste management authorities, SMEs active in landfill or anaerobic digestion sites related operations, Oil & Gas authorities, such the Oil & Gas Innovation Centre and the Oil & Gas Technology Centre, among others is identified as critical to ensure a fast track towards both economic and societal impact.
Academic impact is elaborated in the Academic beneficiaries section, however it is noted that plasma-catalysis is further actively investigated as a method to enhance various other processes of environmental importance. The remediation of waste gas streams via the removal of various pollutants, such as volatile organic compounds and nitrogen oxides, are primary examples of such applications. Project outcomes through the academic benefits they will bring in terms of enhanced mechanistic understanding of plasma-catalysis will further enable societal advancements through the optimisation of these environmental processes.
Societal impact is finally enabled through the project's focus on providing development opportunities to people. Besides the directly involved PDRA and PI, a substantial amount of PhD, postgraduate and undergraduate students will be working on related research topics, obtaining enhanced training and substantially benefiting from the interactions and enhanced insights of the project. In the long-term, a constant stream of young, specialised and motivated researchers is envisioned to be generated around the topic of plasma-assisted catalysis modelling.