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Coupling and reforming of methane by means of low pressure radio-frequency plasmas

Abstract:

Non-oxidative coupling of CH<inf>4</inf>/H<inf>2</inf> mixtures was carried out by means of radio frequency (rf) glow discharges for the first time. A central composite design was employed to determine the best experimental conditions for methane transformation into higher hydrocarbons and to fit the experimental data. rf power was the factor showing the highest effect on the results while CH<inf>4</inf>/H<inf>2</inf> mole ratio showed the lowest. Conversion was 46.4% at 100 W, 0.07 mbar and CH<inf>4</inf>/H<inf>2</inf> mole ratio of 1/2. Selectivity was 56.9% for C<inf>2</inf>, 6.9% for C<inf>3</inf>, and 36.2% for C<inf>4</inf> hydrocarbons. Least squares fits of quadratic equations yielded approximating functions permitting to predict results of random experiments with errors of about 5%. The same rf system was used for the reforming of methane with CO<inf>2</inf>, O<inf>2</inf>, and steam plasmas, respectively. The highest oxidation was observed with oxygen whilst steam plasma produced the best results. H<inf>2</inf>/CO mole ratio was adjusted by setting specific experimental parameters of the latter. CO<inf>2</inf> free synthesis gas was produced at higher H<inf>2</inf>O and CH<inf>4</inf> flow rates, i.e. 0.8 mmol/h and higher power, i.e. 100 W. CO<inf>2</inf> and CO free H <inf>2</inf> was produced at 0.3 and 0.6 mmol/h flow rates of H<inf>2</inf>O and CH<inf>4</inf>, respectively, and 50 W. © 2005 Elsevier Ltd. All rights reserved.