A micro plasma reactor for fluorinated waste gas treatment

Abstract

A microreactor based on a micro-structured electrode (MSE) system is presented. With radio frequency electric power applied to the interdigitated, comb-like capacitor structure a homogeneous plasma is driven at atmospheric pressure with low ignition voltages due to small electrode gaps. The MSE is micromachined by plating nickel onto alumina ceramics. A micromachined Foturan^® structure with inlet and outlet channels for the gas flow serves as a reaction chamber. The design of the reactor cell is arranged in a 4×4-array in a multireactor system. The performance of the reactor is modeled with computational fluid dynamics (CFD), used to improve the reactor design. Experiments show that CF₄ decomposition rates of over 70% can be achieved at atmospheric pressure.

Introduction

Up to now microreactors were mainly used because of their supreme surface to volume ratio in order to increase heat exchange and exposition effect of catalysts to media. The micro plasma reactor described in this paper makes use of very small electrode gaps between micro-structured electrodes (MSE) with an interdigitated arrangement as shown in Fig. 1 as (1). Advantages are low ignition voltages and an essentially homogeneous plasma at high pressure. The small gaps and planar geometry of the structure require micromachining via photolithography. The MSE are radio frequency (RF) driven and allow to generate large-area uniform glow discharges in He and Ne at pressures above 1500 mbar and in Ar and N₂ up to 1200 mbar. The discharges are non-thermal [1] and up to 500 mbar the plasma covers the whole electrode system. By breaking up bonds with high-energy electrons non-thermal plasma allows processing of reactions, which need more than 1000 °C in conventional thermal systems. Thus, a higher energy efficiency is given. One application which is investigated in this work is the decomposition of fluorinated waste gas as produced by semiconductor industry [2], [3].