Study On Coal Pyrolysis By Hydrogen Plasma To Produce Acetylene

Because of relative scarcity of oil reserves in the world, coal will again become the important raw material in chemical industry. Pyrolysis of coal in plasma, which directly produce acetylene, a kind of important chemical, can realize efficient and clean coal conversion to chemical products. To obtain reaction condition, suitable for pyrolysis of coal by plasma to produce acetylene, Gibbs free energy minimization method is applied in this paper to study C-H equilibrium system, taking C(s) into account. It is showed that in temperature range of 2800-4000K, C₂H₂ and C₂H is the main hydrocarbon in C-H equilibrium system. And quenching processing is needed to stop acetylene from dissociating. Effect of quenching process on acetylene yield is studied. It is proved that suitable quenching process can prevent acetylene from decomposing, but will not impede recombination of C₂H radicals to acetylene. As a result, the yield of acetylene will exceed its concentration in equilibrium system. Therefore, recombination of C₂H radicals is taken into account to make acetylene concentration maximized. As a result, reaction condition is obtained as C/H=1/2 and temperature range of 3200— 4100K; Then necessary quenching rate for preventing acetylene dissociating is calculated. It is showed that, with fixing rate R=0.90 as the criteria, when initial temperature ranges from 3000 to 3500K, initial quenching rate of 0.77-5.8×10⁸K/s is needed. And, considering the concrete process, water spray method is adopted in preliminary experiments. Mechanism of recombination reaction of C₂H radical to acetylene is also studied by kinetic method. It is showed that in quenching process the recombination reaction which has effect on acetylene yield is C₂H+H₂=C₂H₂+H, not that of C₂H and H. Hydrogen plasma generator system is developed and then the experimental system is set up. It is showed in preliminary experiments that acetylene is the main hydrocarbon product. And also it is proved that the experimental result of acetylene is higher than the theoretical value.