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• 1. [Article] Deep desulfurization of diesel fuel using a single phase photochemical microreactor

  There is an urgent need to lower the concentration of sulfur in diesel fuels. Growing concern over environmental effects caused by burning sulfur-containing diesel has led the world to higher standards ...

  Citation × Citation Citation Abstract Copy Title: Deep desulfurization of diesel fuel using a single phase photochemical microreactor Author: Jones, Jacob Aaron There is an urgent need to lower the concentration of sulfur in diesel fuels. Growing concern over environmental effects caused by burning sulfur-containing diesel has led the world to higher standards in fuel refinement. Because of these lower standards, many techniques have been researched to remove sulfur containing compounds or otherwise reduce the sulfur content. Hydrodesulfurization remains the primary method to reduce most light sulfur-containing compounds. This process removes sulfides, sulfates, and thiols using high temperature and pressure reactions but is unable to remove aromatics and long chains containing sulfur molecules. Biodesulfurization has also been considered, utilizing microorganisms to target specific sulfur-containing compounds to remove the sulfur while leaving the high energy fuel intact. Oxidative reactions have also been considered including photocatalytic oxidation in an attempt to oxidize these aromatic compounds so that they may be removed using a polar solvent. An ultraviolet light assisted oxidative reaction occurring in a microreactor was studied. Dibenzothiophene was used as a model refractory organic compound mixed in Decane as a solvent. Dibenzothiophene undergoes a series of oxidative reactions which produce an intermediate, Dibenzothiophene Sulfoxide, and a final product, Dibenzothiophene Sulfone. This reaction only proceeds in the presence of Tert-Butyl Hydroperoxide and ultraviolet light. These reactions are reversible and an equilibrium is established between Dibenzothiophene, Dibenzothiophene Sulfoxide, and Dibenzothiophene Sulfone. The equilibrium is strongly affected by the molar ratios of the reactants. Increasing the molar ratio of Tert-Butyl Hydroperoxide to Dibenzothiophene reduces the concentration of Dibenzothiophene in the product stream or causes the reaction to shift its equilibrium towards the products. Equilibrium may not be affected by Temperature. Previous studies have shown that equilibrium concentrations have a temperature dependence. However, under the conditions of this research there was no indication of a temperature dependence. It is possible that because of the molar ratios used the reaction did not proceed appreciably regardless of temperature so the temperature dependence was not apparent. A Taylor dispersion apparatus was assembled to measure infinite dilution diffusion coefficients for Dibenzothiophene, Dibenzothiophene Sulfoxide, Dibenzothiophene Sulfone, and Tert-Butyl Hydroperoxide were measured. Values were close to those calculated using the Wilke-Chang equation. These coefficients along with measured absorption coefficients were important in developing an accurate mathematical model. A mathematical model was developed to include convective and diffusive flux, fluid transport, and reaction kinetics. COMSOL™ Multiphysics was used to numerically solve the mathematical model. Experimental data is fitted to the model to determine the reaction rate constants for each of the reversible reactions. The model was compared to previously reported data taken at 22°C and 40°C using a reactor thickness of 50 um and 100um. The model fit the data very well and can be implemented in predicting concentrations within the reactor. Title: Deep desulfurization of diesel fuel using a single phase photochemical microreactor Author: Jones, Jacob Aaron There is an urgent need to lower the concentration of sulfur in diesel fuels. Growing concern over environmental effects caused by burning sulfur-containing diesel has led the world to higher standards in fuel refinement. Because of these lower standards, many techniques have been researched to remove sulfur containing compounds or otherwise reduce the sulfur content. Hydrodesulfurization remains the primary method to reduce most light sulfur-containing compounds. This process removes sulfides, sulfates, and thiols using high temperature and pressure reactions but is unable to remove aromatics and long chains containing sulfur molecules. Biodesulfurization has also been considered, utilizing microorganisms to target specific sulfur-containing compounds to remove the sulfur while leaving the high energy fuel intact. Oxidative reactions have also been considered including photocatalytic oxidation in an attempt to oxidize these aromatic compounds so that they may be removed using a polar solvent. An ultraviolet light assisted oxidative reaction occurring in a microreactor was studied. Dibenzothiophene was used as a model refractory organic compound mixed in Decane as a solvent. Dibenzothiophene undergoes a series of oxidative reactions which produce an intermediate, Dibenzothiophene Sulfoxide, and a final product, Dibenzothiophene Sulfone. This reaction only proceeds in the presence of Tert-Butyl Hydroperoxide and ultraviolet light. These reactions are reversible and an equilibrium is established between Dibenzothiophene, Dibenzothiophene Sulfoxide, and Dibenzothiophene Sulfone. The equilibrium is strongly affected by the molar ratios of the reactants. Increasing the molar ratio of Tert-Butyl Hydroperoxide to Dibenzothiophene reduces the concentration of Dibenzothiophene in the product stream or causes the reaction to shift its equilibrium towards the products. Equilibrium may not be affected by Temperature. Previous studies have shown that equilibrium concentrations have a temperature dependence. However, under the conditions of this research there was no indication of a temperature dependence. It is possible that because of the molar ratios used the reaction did not proceed appreciably regardless of temperature so the temperature dependence was not apparent. A Taylor dispersion apparatus was assembled to measure infinite dilution diffusion coefficients for Dibenzothiophene, Dibenzothiophene Sulfoxide, Dibenzothiophene Sulfone, and Tert-Butyl Hydroperoxide were measured. Values were close to those calculated using the Wilke-Chang equation. These coefficients along with measured absorption coefficients were important in developing an accurate mathematical model. A mathematical model was developed to include convective and diffusive flux, fluid transport, and reaction kinetics. COMSOL™ Multiphysics was used to numerically solve the mathematical model. Experimental data is fitted to the model to determine the reaction rate constants for each of the reversible reactions. The model was compared to previously reported data taken at 22°C and 40°C using a reactor thickness of 50 um and 100um. The model fit the data very well and can be implemented in predicting concentrations within the reactor. Close

• 2. [Article] Oxidative desulfurization of dibenzothiophene with tert-butyl hydro peroxide in a photochemical micro-reactor

  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. ...

  Citation × Citation Citation Abstract Copy Title: Oxidative desulfurization of dibenzothiophene with tert-butyl hydro peroxide in a photochemical micro-reactor Author: Hebert, Eilleen M. 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. Title: Oxidative desulfurization of dibenzothiophene with tert-butyl hydro peroxide in a photochemical micro-reactor Author: Hebert, Eilleen M. 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. Close