Free Solvent Volume Correlation with Pyrolytic Coke Formation

摘要

Petroleum residua can be modeled as ordered systems of polar asphal- tenes dispersed in a lower polarity solvent phase, held together by interme- diate polarity resins. Vacuum distillation processes and the coking of thE vacuum residua require significant heat input. When a residuum is heated above the temperature at which pyrolysis begins (350"C), there is typically an induction period before coke formation begins (1,2). To minimize fouling of heat exchangers due to undesired coking, distillation heating is stopped sooner than need be, resulting in less than maximum product yield. Two new Coking Indexes have been developed for measuring the proximity to thE coke formation onset in thermal treatment (3). These are based on floccula- tion titration data and the solubility of heptane asphaltenes in cyclohexane. Coking onset appears to coincide with the depletion of resin-type asphaltene solubilizing components in residua, resulting in a bimodal system. This is consistent with observations of the formation of a neophase at the onset of coke formation (4). Using the Coking Indexes can allow distillation to be continued to the verge, but not beyond the onset of coke formation, resulting in significant increases in distillate yield while minimizing the risk of fouling.