Wflm Wilfred Hoeben

Gas phase corona discharges for oxidation of phenol in an aqueous solution

A new method for the removal of harmful organic molecules from water is described. A low power corona discharge is created over the aqueous solution. Chemically active species diffuse into the water and then oxidize the target compound, which in this case is the model compound phenol. The energy consumption per removed phenol molecule is one order of magnitude lower compared to the discharge techniques that create a plasma in the water. The reaction mechanism of the conversion is shown by measuring the ozone concentration over the water, the intermediate/final oxidation products and the release of CO2 from the water. Indications are found that the discharge is more than merely an ozone generator.

Influence of gaseous atmosphere on corona-induced degradation of aqueous phenol

The phenol degradation processes by pulsed corona discharges are investigated under three kinds of discharge atmosphere (air, argon and oxygen). The temporal variations of the concentrations of phenol and the intermediate products are monitored by LIF spectroscopy. The species of the intermediate products are identified by spectral analysis. It is clarified that the oxidative gaseous reagents produced from O2 and those from H2O degrade phenol to intermediate products with comparable degradation rates. The degradation via the reagents from H2O gives rise to the formation of molecules exhibiting fluorescence at 400-500 nm, in addition to dihydroxybenzene (DHB), while the degradation via the reagents from O2 produces only DHB. The reagents from O2 play an important role in the conversion of phenol to DHB.

Oxidative degradation of toluene and limonene in air by pulsed corona technology

The oxidative degradation of two volatile organic compounds, i.e. toluene (fossil fuel based VOC) and limonene (biogenic VOC), has been studied. A hybrid pulsed power corona reactor with adjustable energy density has been utilized for degradation of ppm level target compounds in large air flows. The observed oxidation product range features an energy density-dependent spectrum of oxygen-functional hydrocarbons, which has been qualitatively discussed on the basis of literature studies. Typically, observed stable oxidation products for both target compounds are the biocompatible carboxylic acids acetic and formic acid. Measured degradation G-values are 23 nmol J−1 at 74% conversion of 70 ppm toluene and 181 nmol J−1 at 81% conversion of 10 ppm limonene.

LIF diagnostic for pulsed-corona-induced degradation of phenol in aqueous solution

LIF spectroscopy has been introduced for the in situ diagnostic of phenol degradation in the aqueous solution under pulsed-corona discharges. The applicability of LIF to the measurements of phenol concentration up to 1×10-5 mol l-1 was confirmed. The temporal variation of the absolute concentration of phenol was measured in an aqueous solution exposed by pulsed-corona discharges. This exhibited two characteristic decay times.

Pulsed Corona Demonstrator for Semi-Industrial Scale Air Purification

Although pulsed corona technology for air purification is widely investigated by the lab experiments, large-scale application has yet to be proven. Industrial systems require large flow handling and thus, high corona power. An autonomous semi-industrial scale pilot wire-cylinder type corona reactor has been constructed for air purification demonstrations. The reactor is powered by a 10-kW spark gap-based pulsed power supply, capable of generating 60-kV 100-ns wide pulses with 1-kHz repetition rate. The pulses are optionally superimposed on a 0-30-kV dc bias to enable electrostatic precipitation. The system has been successfully applied during several field and lab experiments. Conversion data as a function of energy density are presented for NOx, NH3, H2S, toluene, limonene, and fine dust removal. The system proves feasibility of large-scale air purification by pulsed corona.

Temperature and pressure effects on positive streamers in air

In this paper we investigate temperature and pressure effects on the properties of a positive pulsed streamer plasma. We use a corona plasma setup in which we vary the temperature between 303 and 773 K at atmospheric pressure and the pressure between 37.9 and 100 kPa at room temperature to achieve the same neutral gas density and compare electrical and optical (ICCD imaging) measurements carried out in both experiments.From the measurements we found that the dissipated plasma energy and the average streamer propagation velocity are both higher for the temperature experiments at the same neutral gas densities as in the pressure experiments. This suggests the existence of a specific temperature effect. A possible explanation for this effect is a higher streamer conductivity at high temperatures, as was previously found in the literature.

Partial oxidation of methane by pulsed corona discharges

Pulsed corona-induced partial oxidation of methane in humid oxygen or carbon dioxide atmospheres has been investigated for future fuel synthesis applications. The obtained product spectrum is wide, i.e. saturated, unsaturated and oxygen-functional hydrocarbons. The generally observed methane conversion levels are 6?20% at a conversion efficiency of about 100?250?nmol?J?1. The main products are ethane, ethylene and acetylene. Higher saturated hydrocarbons up to C6 have been detected. The observed oxygen-functional hydrocarbons are methanol, ethanol and lower concentrations of aldehydes, ketones, dimethylether and methylformate. Methanol seems to be exclusively produced with CH4/O2 mixtures at a maximum production efficiency of 0.35?nmol?J?1. CH4/CO2 mixtures appear to yield higher hydrocarbons. Carboxylic acids appear to be mainly present in the aqueous reactor phase, possibly together with higher molecular weight species.

Laser-induced fluorescence spectroscopy for phenol and intermediate products in aqueous solutions degraded by pulsed corona discharges above water

Laser-induced fluorescence (LIF) spectroscopy is introduced as an in situ diagnostic for phenol and intermediate products in an aqueous solution degraded by corona discharges. The complications that are inherent in applying LIF as a diagnostic for aqueous solutions are experimentally examined. The LIF intensities of phenol and the intermediate products are measured as a function of time. The absolute phenol concentration is determined. We confirm the applicability of LIF spectroscopy for monitoring phenol concentration during degradation.

Experimental Investigation on the Effect of a Microsecond Pulse and a Nanosecond Pulse on NO Removal Using a Pulsed DBD with Catalytic Materials

In this study, an experimental investigation of the removal of NO from an atmospheric air stream has been carried out with a non-thermal plasma dielectric barrier discharge reactor filled with different catalytic materials. TiO