The role of kinetics in the design of plasma microreactors

Abstract

Miniaturisation of plasma reactors has the potential of low power operation. In general, the electric field strength in the gap between two electrodes increases proportionate to inverse of the gap width, so that it is possible to Overcome the first ionization potential of the gas with a low voltage. However, plasmas are extinguished primarily by recombination at the walls. Wall collisions are enhanced by the greater surface area to volume ratio in microchannels, which also increases proportionate to the inverse of the gap width. If the plasma were well-mixed, then the plasma creation in the bulk would be balanced by extinction at the wall, providing no particular advantage with regard to low voltage / low power operation. However, the plasma is transferred from the bulk to the wall by ambipolar diffusion. If the operation of the plasma microreactor is essentially transient or batch, whether or not the reaction kinetics are comparable to or faster than ambipolar diffusion determines if there is a regime of operation in which a low voltage plasma discharge can generate a high yield of product. In this paper, this question is investigated with regards to the ozone formation reaction and a particular design of a microchannel plasma reactor, with parameters so chosen to arguably achieve low voltage operation. The focus of this paper is the simulation of the kinetics of the plasma reactions leading to ozone formation, which shows a time to completion that is comparable (10 -2 s) or faster than the estimate of ambipolar diffusion time at these length scales. Preliminary results of a microchip reactor are consistent with this prediction.

Degradation of pharmaceutical contaminant ibuprofen in aqueous solution by cylindrical wetted-wall corona discharge

“…Much more reactive chemical species other than hydroxyl radical can be produced, such as hydrogen peroxide, hydroperoxyl and ozone. Zimmerman et al devoted to the investigation of the ozone formation reaction in a microchannel plasma reactor [27,28]. Furthermore, shock waves and UV light formed by discharge also can be favorable during water treatment [29].…”

A kinetic model for H2 production by plasmolysis of water vapours at atmospheric pressure in a dielectric barrier discharge microchannel reactor

“…The hydrogen economy could offer advantages both in terms of lower green house gasses (GHGs) emissions and as an alternative fuel which would eventually reduce the consumption rate of fossil fuels. Hydrogen fuel produced by a renewable energy source such as wind or solar would be totally green and renewable [1,2]. For the development of the hydrogen economy it is very important to have hydrogen production processes which could produce hydrogen efficiently, at a cost comparable to that of fossil fuel and should be environment friendly [3].…”

Application of the Microbubble Enhanced Ozonolysis Technology in Biomass Utilisation

“…It was shown that in order to keep the optimal level of electrical field constant, the external applied voltage must be decreased as the dimensions of the system are reduced. The low voltage applied is a key factor for an effective reduction of plasma temperature [17]. These conditions contribute to cutting down the operating cost since the ozone generation is more effective at low temperatures.…”

“…Advantages of the DBD plasma reactor downscaling has been numerically proven with an application of COMSOL Multiphysics software [15,17]. It was shown that in order to keep the optimal level of electrical field constant, the external applied voltage must be decreased as the dimensions of the system are reduced.…”