Binary Interactions in Coke Formation from Model Compounds and Asphaltenes

Abstract

The effects of binary interactions on the coke yield and cracking kinetics in mixtures of model compounds were examined to understand the interactions present in multi-component mixtures, such as petroleum residues. Eight model compounds were selected with molecular weights in the range of 398–623 g/mol and structural elements to represent components of vacuum residues, including a pyrene substituted with four alkyl groups and pyrene derivatives tethered to various heterocycles via an ethano bridge. Thermogravimetric analysis of the binary mixtures showed evidence of three distinct modes of behavior with respect to the additive sum of the mass-weighted component contributions: the coke yield was (1) equal to the additive sum, (2) less than the additive sum, or (3) greater than the additive sum. The individual behavior correlated well with the type of compounds present in the specific mixtures and can be explained in terms of three types of interactions between the mixture components: radical stability or kinetic factors, association forces between the mixture components, and matrix effects. The apparent activation energies of cracking for the mixtures, on the other hand, showed complex behavior that sometimes followed the additivity contributions of the components but, on other occasions, was outside the bounds of activation energies of the pure compounds.