3 years ago

Delayed Coker Coke Characterization: Correlation between Process Conditions, Coke Composition, and Morphology

Delayed Coker Coke Characterization: Correlation between
Process Conditions, Coke Composition, and Morphology
Juan Carlos Poveda-Jaramillo, Naydu P. Zambrano, Hector J. Picón, Liseth J. Duarte, Martha Eugenia Niño-Gómez, Fernando Martínez Ortega
Delayed coking is the technology most used to upgrade vacuum residue into high-value products, but in this process, secondary reactions produce coke. It is already known that the chemical and physical properties and composition of the feedstock and processing conditions affect coke morphology. Recently, a new type of morphology, called transition coke, has been described, but this morphology should be avoided because it induces operational and safety risks to delayed coking units. Several studies have attempted to understand the complex structure of this type of coke and the factors that control the different final morphologies. Therefore, the purpose of this study is to shed additional insight on the correlation between surface chemical composition and the morphology of delayed coker coke with variables of the process, such as the temperature, pressure, and elemental composition of the feedstock. All of the samples had a surface area between 1 and 4 m2/g, showing that the coke lacks porosity. Morphological classification by scanning electron microscopy (SEM) showed transition/associated shot- and sponge-type coke. From X-ray photoelectron spectroscopy (XPS), it was possible to identify heteroatoms as N, S, Si, and O on the surface of the samples. Metals were not found on the surface of the solids, despite the fact that atomic absorption (AA) and total reflection X-ray florescence (TXRF) showed elements such as Ni and V in the bulk. Solid-state nuclear magnetic resonance (ssNMR) was used to identify the aromatic and aliphatic regions and to calculate the aromaticity factor (fa) and the relationship of peri- to cata-condensed carbons, Cperi/Ccata, in the aromatic structure of the samples, giving us an idea of the condensation degree, ϕ, of the aromatic moieties. The results of this work allow us to verify that the low metal amount in the samples is related to sponge and transition coke. Thus, it is possible that this fact, in combination with the amounts of nitrogen and sulfur on the surface, could influence the formation of transition coke and that variables, such as the temperature, direct a change in morphology from transition to sponge coke.

Publisher URL: http://dx.doi.org/10.1021/acs.energyfuels.7b02788

DOI: 10.1021/acs.energyfuels.7b02788

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