A size-dependent thermodynamic model for coke crystallites: the carbon-sulfur system up to 2500 K (2227 °C)

A model is presented for the development of the thermodn. functions of enthalpy, entropy, and Gibbs energy for the elements carbon and sulfur in coke crystallites.  The crystallites of various degrees of graphitization may be described by crystallite length La and crystallite height Lc.  This carbon​/sulfur model has been developed using concepts similar to those in the carbon​/hydrogen model for coke crystallites.  The major model parameters are derived from reported thermodn. properties.  Approx. 75 pct of the model parameters for the carbon​/hydrogen and carbon​/sulfur system are parameters common to both systems.  The resulting crystallite size (La) constrained in the carbon​/sulfur phase diagram, computed by a Gibbs energy minimization technique, is presented for 1 atm and temps. between 1500 K and 2500 K (1227 °C and 2227 °C)​.  A very good agreement is obtained between the predicted thermal desulfurization of petroleum cokes and critically assessed exptl. data.  The removal of sulfur from coke crystallites is predicted to occur mostly between 1600 K and 1850 K (1327 °C and 1577 °C) at 1 atm, depending on the La value.  The precision in the predictive calcns. and the transferability of the model parameters are two aspects that tend to support the usefulness and the theor. basis of the entire approach.