On the mechanism of soot particle formation

The results of experiments on the isothermic pyrolysis of acetylene, benzen e, and diacetylene in a flow reactor near a low-temperature threshold of so ot formation are presented. Diacetylene showed a much higher ability to for m soot, coke, and tar than the other hydrocarbons. The threshold temperatur e of soot formation from diacetylene (800 K) was found to be lower than the threshold temperatures for benzene (1230 K) and acetylene (1200 K) for the same pyrolysis time (0.17 s) and equal hydrocarbon concentrations (on the basis of C atoms). The induction periods of soot formation for acetylene an d benzene at 1100-1200 K, which were estimated from experiments, correlated well with literature data extrapolated from the high-temperature region. I nvisible soot particles (0.3-0.5 mu m) and particles at different steps of carbonization were found among the products of low-temperature pyrolysis. E xperimental data were analyzed and compared within the framework of two soo t formation theories presented in the literature (the "acetylene" and "arom atic" theories). The contribution of the process of polyyne polymerization in a gas phase to the formation of a soot aerosol is discussed.