Enhanced Representation of Thermal Cracking Chemistry in the Context of Bitumen Partial Upgrading

A detailed modeling framework to describe thermal cracking reactions during bitumen partial upgrading on a molecular basis is put forward in this study. The first block of the framework describes the molecular composition of a whole bitumen feedstock using statistical distributions in conjunction with structural descriptors for hydrocarbon classes, including solubility parameters to distinguish asphaltene components. The creation of a molecular ensemble mimicking the bitumen feedstock is accomplished via Monte Carlo simulation using input information from bulk property measurements and advanced analytical methods. This ensemble of molecules forms the starting point of the conversion model, which is the second block. Thermal cracking chemistry is organized in terms of reaction families, such as carbon-carbon bond cracking, sulfur-carbon bond cracking, dehydrogenation, and condensation, and the reactivity parameters are approximated using structure-reactivity correlations. Because of its considerable size, the reaction network is generated on the fly by means of a kinetic Monte Carlo algorithm, whereby molecule cracking reactions progress one by one over time. Reactivity parameters are tuned against an experimental data set generated in a visbreaking pilot plant. Besides describing the evolution of yield structure under different cracking severities, the model is able to track changes in API gravity, asphaltene content, and molecular distributions. Most importantly, the model explains how the different molecular reaction pathways impact product properties relevant to bitumen partial upgrading and provides directional predictions into other aspects of these technologies, such as product solubility and formation of olefins.