STUDY OF THE THERMAL-DEGRADATION OF HEXACHLOROBENZENE IN THE PRESENCEOF A HYDROGEN DONOR (CH4)

In this paper, laboratory results and theoretical studies concerning t he high-temperature gasphase thermal decomposition of hexachlorobenzen e in the presence of a hydrogen donor (methane) are reported. The reac tion 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 degrees C. Studies of the effect of methane concentration on the conversion of Cl-2 into HCl suggest that the oxygen concentration, the reaction duration and temperature play an important role in the c onversion of chlorine to hydrochloric acid. During pyrolysis under a n itrogen atmosphere, total conversion is reached at 1200 degrees C, wit h 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 am ounts of soot formed in the cold part of the reactor as well as to gra phitic carbon deposition on the reactor walls. In the presence of oxyg en, the chlorine conversion into hydrogen chloride is controlled by th e 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 necessa ry to work with oxygen concentrations avoiding, on one hand soot forma tion, and on the other hand, the Deacon's equilibrium displacement tow ards the formation of chlorine.