Electron driven chemistry in microreactors

Abstract

This thesis describes the development of novel process windows by the combination of atmospheric pressure plasmas with microreaction technology. In the first chapter, recent literature on microreactor technology and non-equilibirum microplasma chemistry is discussed. The focus is on microplasmas in confined microchannels for the purpose of chemical synthesis and environmental applications. Study of oxidative conversion of propane using dielectric barrier discharge in a microreactor is described. This generates a cold microplasma at atmospheric pressure and ambient temperature. Surprisingly, large amounts of products with molecular weight higher than propane, such as, C4 and C4+ were mainly observed due to C-C bond formation, in contrast to what is usually observed for this reaction when it is carried out under thermal activation, which leads to cracking products. Development of a plasma catalytic reactor based on a dielectric barrier discharge for oxidative cracking of hexane with Li/MgO based catalysts is reported. The effect of temperature, oxygen concentration, helium flow, and MgO support, and the role of Li/MgO catalysts on the conversion of hexane, and on the selectivity and yield of olefin formation are described. Direct synthesis of liquid oxygenates from partial oxidation of methane is demonstrated in a multi-phase flow, non-equilibrium plasma microreactor near 0oC at atmospheric pressure. A method for liquid-water injection into the microreactor was introduced in order to remove incomplete oxidation products such as methanol, which prevents further oxidation with excited species originating from the microplasma. In the sixth chapter, development of an in-situ CVD method for the growth of CNFs on Ni/alumina and nickel thin film catalyst coated inside a closed channel fused silica microreactor is described. Synthesis, characterization and atmospheric pressure field emission operation of tungsten oxide W18O49 nanorods is discussed. Atmospheric pressure field emission measurements in air showed a turn-on field of 3.3 V/μm, and a stable and reproducible emission current density of 28 mA/cm2. Carbon nanofibers (CNFs) and tungsten oxide nanorods have been incorporated in a continuous flow microplasma reactor to increase the reactivity and efficiency of the barrier discharge at atmospheric pressure.