Destruction of carbon tetrachloride in the presence of hydrogen-supplying compounds with ionisation and catalytic oxidation: Part 2. Methane as hydrogen font

The performance of methane (CH₄) as hydrogen donor molecule for the deep and clean oxidation of tetracloromethane (CCl₄) has been experimented. The oxidation of CCl₄–CH₄ admixtures were performed by catalytic combustion with and without pre-catalytic actions (i.e. ionisation/ozonisation) over manganese oxide based catalyst. The extent of CCl₄ and CH₄ combustion was controlled by quantitative determinations of both CO₂ and HCl formed and of CCl₄ and CH₄ converted. Experiments were performed in the 100–500 °C reaction interval in a continuous reaction line at laboratory scale. Fixed CCl₄ concentration (2000 ppmv) with/without CH₄ addition to air constituted the feed. Methane was added to the feedstream in variable concentration (1000–3000 ppmv), the obtained organic mixtures had H/Cl atomic ratios (R_H/Cl) from 0.5 to 1.5. Comparing the tests of ionisation/ozonisation (I/O) of pure CCl₄ streams and CCl₄–CH₄ admixtures, the efficiency of the hydrogen donor role of CH₄ was evidenced. The residue CH₄ concentration was not affected by the residence time (14–42 s) in the ionisation reactor while the residue concentration of CCl₄ decreased by increasing it. A first-order rate equation in CCl₄ concentration was found to represent the ionisation process both in the absence and in the presence of hydrocarbon. On the manganese oxide catalyst, CCl₄ catalytic combustion (CC) was not remarkably influenced by CH₄ presence. CCl₄ destruction by catalytic combustion assisted with ionisation (IOCC) gave rise to higher HCl yield in comparison with conventional combustion. The HCl formation increased with increasing the R_H/Cl value both in the I/O and IOCC experiments, while the CO₂ formation lightly decreased for high R_H/Cl in the CC and IOCC experiments due to incomplete oxidation of CH₄.