Targeted waveform enhanced plasma microreactor: Engineering Chemistry at the Interface of Microbubbles

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One class of electrochemical reaction are reactions in the plasma state. The PI and his team have been pioneering plasma microreactors that feed directly into microbubbles for the last decade. With the output of the plasma reactor entering the microbubble directly, the maximum activation is retained in the bubble, which then mediates the formation of active species on the microbubble interface. Recently, this approach has been used to catalyse the esterification reaction of free fatty acids to form esters (particularly biodiesel). More than the effectiveness of the plasma activated microbubble reaction, microbubble processing is not limited by surface area of "electrode" in quite the same way. The grand aim of this proposal is to create heterogeneous catalysis capability by tuning the plasma activated species on the gas-liquid interface of microbubbles. Conventional electrochemistry has severe issues around upscaling. Plasma microreactors, particularly those that feed into liquid media as injected microbubbles, are a class of electrochemical reactors that can potentially upscale readily. Microbubbles can have hectares of gas-liquid interface per cubic metre of liquid reactant volume, so if the (plasma)electrochemical reaction can be catalysed on the gas-liquid interface, high throughput reaction rates can be achieved in large volume, continuous flow reactors. Already achieved in pilot plant studies of anaerobic digestion is a bubble surface area flux of 0.15 hectares/sec! If even a fraction of this surface area flux is effective at mediating plasma chemical transformations, the rate of transformation processes should far exceed conventional heterogeneous reactions.This project aims to optimise how the formation of plasma-activated species is coupled to the transient operation of the plasma electronics that create the excited species that eventually react at microbubble gas-liquid interfaces. Preliminary studies show that the composition of an excited air plasma, for instance, can dramatically change with the contacting time in the reactor and the electric field applied. They also suggest that how that electric field is applied in space and time dramatically affects the chemical composition of the plasma, and consequently what chemical reactions dominate the microbubble mediated gas-liquid chemistry. The purpose of this proposal is to characterise this coupling between the time-varying plasma electronics output, as implemented with tuneable electrical engineering design, and the induced chemistry of the plasma and microbubble mediated reaction. The characterisation will be captured in computer models that permit inversion; from the desired chemical outputs, the optimum plasma electronics design, control and operating mode ("the waveform") will be predicted. In the UK plasma chemistry research is vibrant but the work is mainly centred on nuclear science, capactively coupled plasmas with applications to surface treatment (i.e. EP/K018388/1) and medical applications. Globally, several research groups are investigating tailored waveform plasmas more generally but not with specific application to chemical generation on an industrial scale. The proposed closed-loop control of tailored waveform plasma microbubble reactors offers new possibilities to increase efficiency, throughput and scale-up. This, therefore, complements the contributions from these research groups (both national and international) and so will stimulate new research and commercial opportunities. By bringing together experts from the interface of chemical engineering, electrical engineering and mathematics who, together with some eight project partners providing £160k of support, can drive a blue-skies approach to targeted waveform control of plasma reactions (using novel chemical modelling and waveform generator design) while blazing a trail for industrial adaptation to a game-changing approach to chemical production.