Pitch/coke wetting behaviour

The mechanisms of pitch/coke interactions at the mixing stage were studied by a spreading drop test, using a bed of calcined petroleum coke as substrate. For this purpose, three petroleum pitches and a binder coal–tar pitch, which was selected as a reference, were used. The results show that pitch wetting behaviour is related to both pitch surface tension and pitch viscosity. Low values of surface tension and viscosity are required for the pitch to spread and penetrate into the coke bed at temperatures below 160 °C. The non-wetting behaviour observed in some petroleum pitches was ascribed to oxidation processes, as demonstrated by the fact that the non-wetting pitch behaviour can be improved by using an inert atmosphere and/or increasing the heating rate during the spreading drop test. Additionally, the use of blends of wetting and non-wetting pitches and the addition of active surface agents contributes significantly to modifying the wetting behaviour of non-wetting pitches. From the results obtained, a relationship between surface tension–viscosity and pitch wetting behaviour was established.