Predicting coke formation tendencies

New coking indexes were developed to measure how near a pyrolysis system is to coke formation during the coke formation induction period. These are based on an asphaltene flocculation titration and the cyclohexane soluble portion of heptane asphaltenes. Coking indexes were determined for five residua before and after pyrolysis for 60 and 90 min at 400°C. The coking indexes appear to be universal for all the materials studied. The theoretical basis is based on the dispersed particle solution model of residua structure. Coking onset is coincidental with the destruction of the ordered structure and the formation of a bimodal system. Nuclear magnetic resonance (NMR) imaging showed the presence of two and three phase systems in the toluene soluble portions of residua pyrolyzed for 90 min. Results also show that initial coke formation can be related to the free solvent volume. A relationship was observed between free solvent volume and the amount of initial coke make at 400°C. The results provide a new tool for ranking residua, gauging proximity to coke formation, predicting initial coke make tendencies.