Abstract
ABSTRACT
In this paper, laboratory results and theoretical studies concerning the high-temperature gasphase thermal decomposition of hexachlorobenzene in the presence of a hydrogen donor (methane) are reported. The reaction was studied in tubular reactors under a pressure of one bar, with mean residence times of 0.4, 1.2 and 2.4 s, in the temperature range 900-1200°C. Studies of the effect of methane concentration on the conversion of Cl2 into HCl suggest that the oxygen concentration, the reaction duration and temperature play an important role in the conversion of chlorine to hydrochloric acid. During pyrolysis under a nitrogen atmosphere, total conversion is reached at 1200°C, with a Cl/H ratio lower than 0.15, and a residence time of the order of 2 to 3 s. However, this technique is not desirable, due to important amounts of soot formed in the cold part of the reactor as well as to graphitic carbon deposition on the reactor walls.
In the presence of oxygen, the chlorine conversion into hydrogen chloride is controlled by the Deacon's equilibrium reaction. Theoretical and experimental results show that the total conversion necessitates a Cl/H value significantly lower than in the case of pyrolysis. It also shows that it is necessary to work with oxygen concentrations avoiding, on one hand soot formation, and on the other hand, the Deacon's equilibrium displacement towards the formation of chlorine.
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