Residua coke formation predictability maps

Abstract

The dispersed particle solution model of petroleum residua structure was used to develop predictors for pyrolytic coke formation. Coking Indexes were developed in prior years that measure how near a pyrolysis system is to coke formation during the coke formation induction period. These have been demonstrated to be universally applicable for residua regardless of the source of the material. Coking onset is coincidental with the destruction of the ordered structure and the formation of a multi-phase system. The amount of coke initially formed appears to be a function of the free solvent volume of the original residua. In the current work, three-dimensional coke make predictability maps were developed at 400, 450 and 500 °C for four residua with nominal H/C atomic ratios of 1.4. The maps relate residence time and free solvent volume to the amount of coke formed at a particular pyrolysis temperature. Coke formation reactions can be modeled with zero-order kinetics which occur in two stages. The first stage produces 22.5–27.0 wt% coke with activation energies ranging from 22,000 to 38,000 cal/mol. The second stage continues the reaction to completion, producing 58.1–63.6 wt% coke with activation energies ranging from 54,000 to 83,000 cal/mol. The activation energies correlate with the original residua free solvent volumes. The results provide a new tool for ranking residua, gauging proximity to coke formation, and predicting initial coke make tendencies.