Study on mechanism of C-H radicals' recombination into acetylene in the process of coal pyrolysis in hydrogen plasma

According to computation results of C-K equilibrium systems, C2H2 and C2H a re the main hydrocarbon in the C-H equilibrium system at the temperature of approximately 3500 K. Because hydrogen plasma has the advantage of high te mperature (over 3500 K), acetylene can be directly produced by coal pyrolys is in hydrogen plasma. In order to obtain high yields of acetylene, a quenc hing process is needed to fix the acetylene produced at high temperature. I t is proved that an adequate quenching rate (0.77 similar to 5.8 x 10(8) K/ s) can avoid the decomposition of acetylene, but will not prevent C2H radic als recombining into acetylene [Chem. Eng. Sci. 54 (1999) 957]. A dynamic c hemical method is employed in this paper to study the mechanism of C2H radi cals' recombination into acetylene in the quenching process. Primary experi ments have also been carried out to study the process of coal pyrolysis in hydrogen plasma. It is shown by the calculation results that: (1) the react ion that really has an effect on acetylene yield in the quenching process i s the recombination of C2H and H-2, and not that of C2H and H in traditiona l opinions; (2) if-the recombination of C2H and H-2 is taken into account, the total mass content of acetylene in the quenched gas may increase from 5 8% to 78% at the quenching rate which can prevent acetylene from decomposin g. The experimental results prove that C2H radicals really recombine into a cetylene in the quenching process. (C) 2001 Elsevier Science B.V. All right s reserved.