| Feedstocks to hydrocracking units are generally conventional straight-run heavy gas oils. However, the heavy gas oils produced in residuum-upgrading processes such as coker gas oils are becoming important feedstocks for the hydrocracking units. Also, the interest in the processing feedstocks from different origins, such as tar sands, is growing. As the feedstocks become more complicated, a methodology to predict the conversion of feedstocks and yields of liquid and gas fractions in the hydrocracking units become more and more important.; Data on the successive hydrotreating and hydrocracking of a range of heavy gas oil feedstocks were collected using a micro-reactor apparatus. A simple overall hydrocracking model for heavy gas oils based on measurable properties of feedstocks, including models of the hydrotreating section and the hydrocracking section, was established to predict the conversion of heavy gas oils. The apparent cracking kinetics in the hydrotreating section were represented as a combination of hydrodesulfurization and hydrogenation of aromatics. In the hydrocracking section, the cracking rate constant was represented by a Langmuir-Hinshelwood model where the rate constant was only a function of the nitrogen content of feedstocks. A novel lumped hydrocracking model of heavy gas oil was also established to predict the yields of liquid and gas fractions. The model showed that the nitrogen compounds influenced not only crackability but also cracking route of heavy gas oil by the selective adsorption on the acid sites of the hydrocracking catalyst.; Another novel hydrocracking model was established for transitions due to switching feedstock. The model was based on the steady state model, continuous-stirred tank reactor model, the liquid hold-up, and the desorption rate constant for nitrogen compounds from the acid sites of zeolite-based hydrocracking catalysts. The model suggested that the nitrogen exchange adsorbed on the catalysts would be much slower than the nitrogen exchange in the liquid phase during switching feedstocks. Finally, a hydrocracking model based on high performance liquid chromatography and field ionization mass spectrometry analyses was established to investigate the hydrocracking pathways on a molecular level. The model showed the difficulty of the hydrogenation of monocyclic aromatics and the cracking of saturates and alkyl substituents. |
