Page 175 - New Trends in Green Construction

AN ARGON NON-THERMAL MICROWAVE PLASMA FOR TREATMENT OF BETX CONTAMINATED WATER VIA OH RADICAL OXIDATION
Enrique Casado, M. Carmen García, Dorota A. Krawczyk and Antonio Rodero
Keywords: OH radicals, CG-MS, Plasma, Fluorimetry, OES. 1. Introduction
In the last years, the use and design of plasma reactors capable to produce reactive oxygen and nitrogen species has become a main task in the development of both environmental and bio- medical applications. In this work, a non-thermal microwave argon jet has been used for water treatment, with a small xylene layer on the surface of the water which is oxidized via OH radicals. OH radicals play an important role in the degradation of aromatics. Products resulting from the plasma-xylene interaction were identified and quantified using Gas Chromatography – Mass Spectrometry (CG-MS) analysis under different plasma conditions: microwave power, argon flow rate, treatment time and geometry.
Rate production of OH using fluorimetry and plasma characterization using Optical Emission Spectroscopy (OES) have also been performed under different conditions.
2. Materials and method
The generation of the argon plasma was performed using a surfatron microwave power coupling device [Moisan, 1992]. In the present case, a T-shaped quartz tube (1.5 and 4mm of inner and outer diameter) with one of its ends opened to the air was used (Fig. 1). With this configuration the plasma column goes down and approach the water. All the liquid samples were placed in cylinder shaped glass containers (2 cm diameter and 4 cm high) containing 4 ml of miliQ water and 1 ml of Xylene.
Solutions of toluene treated with this plasma reactor were analyzed using CG-MS (Thermo Finnigan, Thermo-Quest Trace CG/MS- Trace DSQ) in order to see the oxidation products from Xylene and OH radicals.
OH radicals generation rate was measured from the fluorometric
method proposed by Newton and Milligan [Newton, 2006] based on the use of 3-Coumarin Carboxylic acid dissolved in water. A PTI, Quanta Master 40 UC/VIS Steady State Spectrofluorometer was used.
3. Results and conclusions
Products resulting from the plasma-xylene interaction (oxidation of Xylene) were identified and quantified using CG-MS analysis. In this case, Benzyl radicals Tolualdehyde, 2,6-Xylenol and 2,3-Xylenol were identified in the chromatograms. These products came from xylene oxidation and have been previously studied [Zhao, 2005]. Fig. 2 shows relative changes in these products content for different microwave powers (30, 50, 70 and 90 W), Ar gas flows (0.9, 1.1, 1.4, 1.7 and 2 L/min), treatment times (1, 1.5, 2 and 2.5 min) and distance of sample to plasma (from 0.5 to 4.5 cm). For the three first parameters, a linear dependence was found. This means that it is
New Trends in Green Construction
Fig. 1: Photo of plasma and sample
175