PETR 42 |
| The average chemical structure of asphaltenes present in a vacuum resid feed is related to the morphology of the coke that is produced in a delayed coker (shot coke vs. sponge coke). A combination of solid-state 13C NMR, X-ray Photoelectron Spectroscopy (XPS), and elemental abundance was used to characterize the average chemical structure of several n-heptane asphaltenes from shot coke and sponge coke producing vacuum resid feeds. The chemical structural properties of the asphaltenes are discussed in relation to the coke morphology produced from the parent resid. Feeds with higher solubility parameter asphaltene PNA cores tend to produce a shot coke morphology. Air oxidation of vacuum resid delayed coker feeds promotes formation of anisotropic shot coke. The combination of the Microcarbon Residue Test (MCRT) on a feed to the delayed coker followed by cross-polarized light optical microscopy on the coke produced in the MCRT is a predictive test for the morphology of the coke formed in delayed cokers. Sponge coke forming feeds produce cokes with highly anisotropic (ordered) 10-60 µm flow domains, whereas shot coke forming feeds produce cokes with a less anisotropic mosaic structure of 1-10 µm. Air oxidation increases both the asphaltene content, and the polarity of the asphaltenes by increasing the organic oxygen heteroatom content of the asphaltenes in vacuum resid feeds. The higher solubility parameter of the oxidized asphaltenes favors phase separation from the hydrocarbon matrix and leads to shot coke formation. |
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Symposium Honoring Martin Gorbaty
8:20 AM-11:55 AM, Monday, August 20, 2007 Boston Park Plaza -- Plaza Ballroom, Oral
Division of Petroleum Chemistry |