Abatement of volatile organic compounds by corona discharge. A study of the reactivity of trichloroethylene under atmospheric pressure ionization conditions

Abstract

Non-equilibrium plasma based technologies are currently being developed for the abatement of volatile organic compounds (VOCs). The promising results obtained so far encourage efforts in fundamental research to improve our knowledge of the processes involved. To gain insight into the role played by analyte-derived ionic species we have investigated the ion chemistry of trichloroethylene (TCE), a representative VOC, in air at ambient pressure by means of an atmospheric pressure chemical ionization commercial mass spectrometer. Different experimental conditions were examined with regard to the following parameters: ion source temperature, water and TCE concentrations, and extraction potential. Notably, modulation of the variable extraction potential provided a means to probe structure and reactivity of the ionic species of interest. Products resulting from TCE oxidation were observed in the analysis of both positive and negative ions. Particularly prominent is a C 2 H 2 Cl 2 O + . species, likely of enol structure, due to reaction with water. A reaction scheme is proposed based on nucleophilic addition of water to ionized TCE followed by elimination of HCl. The negative ion chemistry of TCE is dominated by Cl -and its clusters with water and TCE. At low temperature and with water in high concentration very large positive and negative ion hydrate clusters (with up to 50 water molecules) could be observed. © 1997 by John Wiley & Sons, Ltd. Received 8 July 1997; Revised 2 September 1997; Accepted 8 September 1997 Rapid. Commun. Mass Spectrom. 11, 1687-1694 (1997 Control of volatile organic compounds (VOCs) in the atmosphere is a major environmental problem due to their great proliferation and to limitations of the traditional methods of abatement (incineration, catalytic oxidation and carbon adsorption).1 Among the alternative approaches being presently developed, nonequilibrium plasma-based technologies, using either high energy electron beams or electrical discharges including corona discharges, appear particularly promising. [2][3][4] Since most of the electrical energy used for producing a non-equilibrium plasma ends up in energetic electrons rather than gas heating, this approach is particularly suited for the cost-effective treatment of large volumes of gaseous effluents containing low concentrations of VOC produced by many different manufacturing industries in which volatile organic solvents are used. The products observed under most conditions include CO, CO 2 , and, for chlorinated VOCs, HCl and Cl 2 . In some cases additional products have been detected corresponding to some intermediate stages of oxidation, such as phosgene, 1,1-dichloroethene and chloroacetylchloride from 1,1,1-trichloroethane 5 and phosgene and dichloroacetylchloride from trichloroethylene (TCE). 6 In recent publications, kinetic analysis and mechanistic interpretations have also been presented for the decomposition of representative VOCs in non-equilibrium plasma. 3,5,7 It is generally accepted that the major decay routes involve radic...

A mass spectrometry study of alkanes in air plasma at atmospheric pressure

“…Schematics of this source and of the experimental setup used for the introduction of vaporized samples were given previously [9]. The ion source is kept at near atmospheric pressure by flowing a stream of synthetic air at 4000 -5000 mL min Ϫ1 introduced through the nebulizer line, a capillary of approximately 2 mm i.d.…”

“…It was shown earlier that collision-induced dissociation (CID) experiments can be conducted in the intermediate pressure region between sampling and skimmer cones by the proper adjustment of V cone , the difference between their potentials [9]. In our experiments spectra were recorded at several different values of V cone , ranging from the lowest possible value (1-5 V) necessary to achieve an acceptable signalto-noise ratio, up to 150 V, thus providing energy-resolved mass spectral data.…”

“…However, increasing numbers of literature reports suggest that in some cases ionic initiation steps might prevail [7][8][9][10][11][12]. A major involvement of ions in nonthermal plasma chemistry is to be expected since gas-phase ion/molecule reactions are usually orders of magnitude faster than radical/molecule reactions.We have long been interested in the role played by ionic intermediates and ionic reactions in the nonthermal plasma-induced oxidation of VOCs and have used atmospheric-pressure chemical ionization mass spectrometry (APCI-MS) to detect and study the ions that are produced by corona discharges in VOC-contaminated air [9,12, 13].Saturated hydrocarbons are ideal VOC models because of their environmental relevance and the wealth Address reprint requests to Prof. …”

“…We have long been interested in the role played by ionic intermediates and ionic reactions in the nonthermal plasma-induced oxidation of VOCs and have used atmospheric-pressure chemical ionization mass spectrometry (APCI-MS) to detect and study the ions that are produced by corona discharges in VOC-contaminated air [9,12, 13].…”

“…As for the origin of such VOC-derived radicals, i.e., the nature of the initiation steps of nonthermal plasma-induced VOC decay, reactions of VOC molecules with neutrals and radicals, notably O( 3 P) and • OH, are usually envisioned. However, increasing numbers of literature reports suggest that in some cases ionic initiation steps might prevail [7][8][9][10][11][12]. A major involvement of ions in nonthermal plasma chemistry is to be expected since gas-phase ion/molecule reactions are usually orders of magnitude faster than radical/molecule reactions.…”