Kinetics of petroleum pitch polymerization by gel permeation chromatography

Abstract

The thermal polymerization kinetics of petroleum pitch molecules with molecular weights (MW) between 400–2000 were studied utilizing gel permeation chromatography (GPC). Two distinctly different reaction mechanisms of the petroleum pitch were observed from the GPC curves during transformation of the pitch to mesophase and semi-coke. When mesophase is forming in the pitch, molecules in the MW range of 400–700 were the most reactive, while molecules with MW greater than 1200 were essentially unreactivc. This lack of reactivity of the larger molecules ensures that the mesophase remains highly fluid during its formation. A change in reaction mechanism occurs after the mesophase has solidified as a result of the thermal polymerization reactions. At this stage, there is an abrupt decrease in the reactivity of molecules with MW less than 1100 and the reactivity of all measured molecules is the same. This significant kinetic change is due to a physical phenomenon in which solid state reactions occur in the infusible (vitrified) polymerized pitch. The significantly reduced reaction rates occurring in petroleum pitch after vitrification are similar to the results observed for other thermosetting materials.