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Sulfur content in fuels is an increasingly critical environmental issue. Hydrodesulfurization removes sulfur from hydrocarbons; however, further desulfurization is necessary in fuels. New methods are required. In this study, micro-scaled single phase oxidative desulfurization is explored. An ultraviolet light-assisted micro-reactor is introduced for desulfurization of dibenzothiophene.
Dibenzothiophene is mixed with decane and oxidant, tert-butyl hydro peroxide. The mixture forms a thin layer inside the micro-reactor which has a rectangular window to facilitate ultraviolet light irradiation. Thin spacers, 100 μm and 50 μm, establish fluid thickness within the micro-channel. Ultraviolet light reacts with oxidant to create hydroxyl radicals and convert dibenzothiophene to sulfoxides and sulfones. These products are easily extracted. The overall desulfurization process is a pseudo first-order reaction.
Experiments using the 100 micron spacer are conducted at steady state conditions and three temperatures; 22 oC, 40 oC, and 60 oC. For the 50 micron spacer, temperature conditions were 22 oC and 40 oC. Micro-reactor residence times range from 2 to 30 seconds. The desulfurization study includes a comparison between theoretical model and experimental results, significance of spacer thickness, significance of temperature, and comparison between outcomes of this study to those obtained from other researchers.
A mathematical model of the micro-reaction system is developed to predict dibenzothiophene conversion. The model includes convection, diffusion, and pseudo first order reaction kinetics in the presence of ultraviolet light. The model is solved numerically using COMSOL software. Experimental data is fitted to the model equations to determine the pseudo first order reaction rate constant. The dibenzothiophene reaction rate constants are 7.76*10-4 s-1 and 1.47*10-3 s-1 at temperatures of 22 oC and 40 oC, respectively. The mathematical model fit the experimental data well and therefore, may be used to predict concentrations within the micro-reactor for various operating conditions.
Overall, desulfurization of dibenzothiophene using tert-butyl hydro peroxide and ultraviolet light-assisted micro-reactor was more efficient compared to other processes. The micro-reactor was capable of achieving 79 % conversion in about 30 seconds, thus reducing the sulfur content from 125 ppm to about 30 ppm. |
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