Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor(s)

Prof. Hugo de Lasa

Abstract

Nowadays and due to environmental legislations, a world-wide attention has been given towards clean transportation fuels with emphasis on sulfur contents reduction. These efforts on the other hand are challenged by the poor qualities of crude oils. The existing desulfurization technologies such as hydrodesulfurization are not capable to cope with new firm standards. Hence, it is extremely desirable to develop a catalytic desulfurization process to meet both sulfur limits and refining economics. As one aspect of this objective, it is of great importance to study and comprehend the behaviour and chemistry of individual sulfur species present in transportation fuels cuts. Zeolites namely, H-ZSM5 has shown a potential catalyst for a desulfurization process for gasoline fuel range. Acidity and shape selectivity of these zeolites make it viable for such a process eliminating the use of hydrogen.

With aiming to light diesel fraction desulfurization, this dissertation provides insights and understanding of benzothiophene sulfur species conversion over a H-ZSM5 zeolite catalyst. The H-ZSM5 particles were dispersed in an inert silica-alumina matrix to diminish possible cracking of diesel model compound (n-dodecane). This catalyst was characterized using standard techniques including: a) NH3-TPD, b) N2 adsorption, c) Particle size distribution, d) X-ray diffraction, e) SEM-EDX, and f) Pyridine FTIR. Catalytic and thermal runs were performed in the CREC Riser Simulator that mimics the industrial FCC unit. This reaction system was operated at close to atmospheric pressure, 350°C – 450°C temperatures, and 3, 5, 7 seconds reaction times. Thermal cracking was found to be negligible under the studied reaction conditions. Experimental results from catalytic runs showed a higher benzothiophene conversion over n-dodecane conversion. This was true despite the difference in benzothiophene and n-dodecane molecular sizes. The experimental results of this PhD dissertation are also supported with a molecular dynamics (MD) simulation study that studies self diffusivity of benzothiophene and n-dodecane in ZSM-5 zeolite. In addition and using the obtained experimental data, a heterogeneous kinetic model is proposed for benzothiophene conversion over H-ZSM5 catalyst. Numerical non-linear regression leads to model parameters estimations with low confidence intervals suggesting the adequacy of this kinetic model.


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