Inhibition of CCl formation during the combustion of MSW gasification syngas: An experimental study on the synergism and competition between oxidation and chlorination

For the safe disposal of MSW, a four-step gasification-combustion conversion process is proposed in this work, consisting of material gasification, ash melting, syngas conversion and combustion. Based on the control method of dioxin in gasification process which has been studied previously, experiments of tar chlorination process under oxidative atmospheres were carried out in a homogeneous flow reaction system, using benzene as the tar model compound, to find a way for the inhibition of CCl formation during the syngas combustion process. Results indicated that Cl2 reacts with benzene more easily than O2 under low temperatures, and has a positive effect on both oxidative cracking and polymerization. For chlorination reactions, high temperature enhances the chlorination degree and leads to the formation of perchlorinated hydrocarbons, but also promotes the rupture of the weak CCl bonds. With the rise of temperature, hexachlorobenzene became the major product, the amounts of all chlorinated hydrocarbons decreased rapidly, and the conversion direction depended on the amount of O2. O2 generally promotes the formation of hydrogen chloride, and inhibits the chlorination of hydrocarbons. At a temperature above 900 °C, the total amount of chlorinated hydrocarbons was very low under oxidative atmospheres, even only with a equivalence ratio of 0.2. However, during the oxidation process under low temperatures, CCl can also be formed on cyclopentadienyl and 1,3-butadienyl radicals, whose chlorination products were observed. The synergistic and competitive effects between oxidation and chlorination are concluded and the major benzene conversion pathways are summarized according to the products detected.