The pyrolysis and coking of n-heptane, as a model compound of hydrocarbon fuels, were investigated under supercritical conditions. The influences of temperature and Reynolds number (Re) on the cracking reactions were discussed. The conversion of n-heptane under 4.0 MPa increased evidently with temperature rising from 500 to 650 ℃. The thermal cracking and the secondary reactions of cracking products led to the increase of the precursors of coking, and finally resulted in coking seriously. Increasing the turbulence of the effluent flow could effectively inhibit coke formation. The coke samples have been characterized by the techniques of scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The analysis results showed that the filamentous coke formed during the pyrolysis of n-heptane resulted from metal catalysis and the formation of the filamentous coke might be the major factor of the carburization of the stainless steel.

Key words: hydrocarbon fuel, supercritical condition, pyrolysis, coking, carburization