Hydroprocessing of heavy oils in membrane reactors: Experimental studies and theoretical modeling

The design of more efficient heavy-oil hydroprocessing reactors and catalysts is becoming increasingly important. This can be achieved by gaining a better fundamental understanding of heavy oils structure, transport and reactions; and by designing novel reactors. The focus in the thesis is on asphaltenes, since, they are thought to be the component primarily responsible for the poor efficiency of heavy-oil hydroprocessing reactors.; A theoretical model for asphaltene diffusion has been developed in this thesis using statistical structural models and continuum hydrodynamic theories. The asphaltene molecular structure is generated stochastically using Monte-Carlo techniques. The individual asphaltene molecules are then approximated as spheroids for the purpose of calculating their hindered diffusivities. Continuum hydrodynamic theories for hindered diffusion in-conjunction with Boundary Element Methods (BEM) are then used to calculate the individual transport coefficients of the molecules.; The efficiency of heavy-oil hydroprocessing is limited by equilibrium limited reactions, unreactive cores and retrogressive reactions which form undesirable products. Membrane reactors have the potential to increase reactant conversion and product yield, and to reduce reactor volume.; In this thesis the feasibility of using inorganic membranes for increasing the efficiency of asphaltene hydrocracking is investigated. Continuum-hydrodynamic theories of hindered transport are used to describe the flow of polydisperse macromolecular liquids through multi-layer porous membranes. The transport characteristics of the polydisperse asphaltene molecules at high temperatures through the microporous membrane strongly depend on the separation efficiency of the membrane.; The hydrocracking of asphaltenes was performed at high temperatures in a membrane reactor and in a conventional reactor. The membrane reactor generally showed marginal improvements in overall asphaltene conversion and overall maltene yields. This was because any increase in asphaltene conversion was masked by the loss of reactant asphaltene molecules through the membrane. However, membrane reactors utilizing modified membranes perform significantly better than those utilizing the original, as received, membranes. This is because the modified membranes are able to significantly reduce the loss of asphaltenes due to permeation. A membrane reactor model is used to theoretically analyze the optimum pore sizes, temperature, pressure gradient and reactor configuration needed to increase the conversions and yields.