A. Vandenbroucke

Non-thermal plasmas for non-catalytic and catalytic VOC abatement

This paper reviews recent achievements and the current status of non-thermal plasma (NTP) technology for the abatement of volatile organic compounds (VOCs). Many reactor configurations have been developed to generate a NTP at atmospheric pressure. Therefore in this review article, the principles of generating NTPs are outlined. Further on, this paper is divided in two equally important parts: plasma-alone and plasma-catalytic systems. Combination of NTP with heterogeneous catalysis has attracted increased attention in order to overcome the weaknesses of plasma-alone systems. An overview is given of the present understanding of the mechanisms involved in plasma-catalytic processes. In both parts (plasma-alone systems and plasma-catalysis), literature on the abatement of VOCs is reviewed in close detail. Special attention is given to the influence of critical process parameters on the removal process.

Decomposition of Toluene with Plasma-catalysis: A Review

Abstract Non-thermal plasma (NTP) generated at atmospheric pressure has been widely applied to abate the harmful emission of gaseous pollutants such as volatile organic compounds (VOCs). These studies have proven the existence of some drawbacks that hinder commercialization, such as a low energy efficiency and mineralization degree with the formation of undesired byproducts as a consequence. Recently, NTP has successfully been combined with catalysis in an attempt to solve these issues through complex interacting mechanisms. Toluene can be regarded as being the most frequent studied VOC for removal with plasma-catalysis on laboratory scale. Therefore, this paper aims at reviewing the current research on this model VOC.

Decomposition of Trichloroethylene with Plasma-catalysis: A review

Abstract The aim of this paper is to give a review of the research on the decomposition of trichloroethylene (TCE), a common industrial solvent, with combined use of non-thermal plasma and heterogeneous catalysis, i.e. plasma-catalysis. This air purification technique has been investigated over the last decade in an effort to overcome the disadvantages of non-thermal plasma treatment of waste air containing volatile organic compounds (VOCs). Some examples of different plasma technologies used for plasma-catalysis are given. These include the dielectric barrier discharge, the pulsed corona discharge and the atmospheric pressure glow discharge. In a plasma-catalytic hybrid system the catalyst can either be located in the discharge region or downstream of the plasma reactor. The mechanisms that drive both configurations are briefly discussed, followed by an extended literature overview of the removal of TCE with plasma-catalysis.

The HERMES recoil detector

The HERMES recoil detector is an exciting addition to the HERMES spectrometer, specifically designed to make one of the first exclusive measurements of deeply virtual Compton scattering (DVCS). DVCS is the experimentally cleanest way to access generalised parton distributions - a theoretical framework that describes the structure of the nucleon. The recoil detector utilises a silicon detector with a large dynamic range capable of reconstructing the momenta of protons in the range of 135 MeV/c to 450 MeV/c, placed directly into the HERA beam vacuum (around the HERMES target) to make both position and energy deposition measurements (for the purposes of momentum reconstruction) of the recoil protons from the process. In addition there is a scintillating fibre tracking (SET) detector placed directly outside the beam vacuum that provides both tracking information and momentum reconstruction data for protons at higher momenta. The third sub-detector is a photon detector that lies concentrically outside the SET and provides useful information on other processes for the purposes of background subtraction. Leptons involved in the interaction will be detected in the existing parts of the HERMES spectrometer. The recoil detectors silicon sub-detector was the subject of a presentation at the IEEE NSS in 2003 by Mathias Reinecke. This presentation is intended as an update on the successful development of the silicon sub-detector as well as providing more information on the impending installation of the detector into the HERMES spectrometer in November 2005

Exclusive

The Hermes experiment was built to determine the spin structure of the proton. It is already known since a long time that the proton is built out of three quarks. However, experiments have shown that the quarks itself are responsible for only about 30 % of the proton spin. The remaining parts are expected to be coming from orbital angular momenta and gluon spin. The framework of Generalized Parton Distributions (GPDs) provides access to the hitherto unknown quark orbital angular momentum. These GPDs can be probed via the measurement of so-called exclusive reactions. In these reactions the initial and final state are fully known. In the Hermes experiment 27.5 GeV beam particles are scattered off an internal gas target. To improve the measurement of exclusive reactions a recoil detector surrounding the target cell was designed and built to deremine exclusivity at the event level and to measure the kinematics of the recoiling proton. This work reports on the R&D for the readout of the silicon recoil detector. A dedicate charge injection setup, a laser test-stand and a testbeam setup are described. In modelling the GPDs exclusive pion production plays an important role. By comparing the exclusive pi^0 production rate with the exclusive pi^+ production rate, constraints can be imposed on the relative importance of the pion pole to the GPDs. Moreover, by studying pion production information about the polarized quark distribution functions can be extracted. In Hermes, the pi^0 is measured via the detection of its two decay photons in the electromagnetic calorimeter. To determine the detection capabilities of the latter device, a dedicated Monte Carlo simulation was mandatory. The simulation is based on a combination of the GEANT package and a 6-dimensional look-up table. The analysis of the Hermes data shows a small pi^0 cross section. Additionally, when examining the production ratio on the proton and neutron, a clear neutron suppression is observed for the pi^0 (and the eta) in the exclusive regime. This suppression is absent in the semi-inclusive region.

\pi^0

The total oxidation of trichloroethylene (TCE) in air at low relative humidity (RH=10%) in the presence of CO2 (520ppmv) was investigated in function of energy density using an atmospheric pressure negative DC luminescent glow discharge combined with a cryptomelane catalyst positioned downstream of the plasma reactor at a temperature of 150°C. When using Non-Thermal Plasma (NTP) alone, it is found a low COx (x=1-2) yield in agreement with the detection of gaseous polychlorinated by-products in the outlet stream as well as ozone which is an harmful pollutant. Introduction of cryptomelane enhanced trichloroethylene removal, totally inhibited plasma ozone formation and increased significantly the COx yield. The improved performances of the hybrid system were mainly ascribed to the total destruction of plasma generated ozone on cryptomelane surface to produce active oxygen species. Consequently these active oxygen species greatly enhanced the abatement of the plasma non-reacted TCE and completely destroyed the hazardous plasma generated polychlorinated intermediates. The facile redox of Mn species associated with oxygen vacancies and mobility as well as the textural properties of the catalyst might also contribute as a whole to the efficiency of the process.

production at HERMES: Detection - simulation - analysis

The decomposition of trichloroethylene (TCE) in air by non-thermal plasma was investigated with a multi-pin-to-plate direct current (DC) discharge at atmospheric pressure and room temperature. The effects of various operating parameters on the removal efficiency (RE) were examined. The experiments indicated that for low energy densities higher removal could be obtained with positive corona. For negative corona and 10 % relative humidity (RH) a maximum RE of 99.5 % could be achieved at 1100 J L-1. Formation of by-products was qualitatively analyzed in detail with FT-IR spectroscopy and mass spectrometry. Detected by-products for negative corona operated at 300 J L-1 and 10 % RH include dichloroacetylchloride, trichloroacetaldehyde, phosgene, ozone, HCl, Cl2, CO and CO2. The highest RE for TCE was achieved with a relative humidity of 19 %.