Thesis
The effects of molar flux, pressure, and product gases on the stability of molybdenum carbide during steam methane reforming
Washington State University
Master of Science (MS), Washington State University
2005
Handle:
https://hdl.handle.net/2376/410
Abstract
The oxidation resistance of bulk Mo2C was tested in a plug flow reactor during steam methane reforming (SMR) at varied molar fluxes, pressures and product co-fed compositions. Lowering the total molar flux caused the oxidation temperature of Mo2C to be reduced; oxidation deactivates Mo2C. Increasing the pressure also decreased the oxidation temperature until a pressure of 5 bar is reached. Raising the pressure beyond this point yielded no further decrease in the oxidation temperature. Low molar flux and high pressure are both lower the mass transfer signifying that Mo2C is stabilized for SMR when the mass transfer is lowered. SMR product gases have been found to stabilize Mo2C. During low mass transfer conditions the concentrations of the SMR products would be expected to increase near the catalyst particles thus increasing stability. The lowest observed oxidation temperature due to molar flux and pressure effects was 875 +/- 5 °C at 0.131 mol/cm2-hr and 5 bar. Co-feeding H2 and CO was also found to lower the stable operating temperature for SMR. At low concentrations of H2 and CO, 6% to 26 %, there was a distinct deactivation temperature that was not a result of oxidation. Elevated H2 concentrations during these deactivations suggest that coke formation due to the cracking of CH4 was the cause of deactivation. An additional effect of co-feeding H2 and CO, was a depressed conversion when compared to a product free feed. This loss of conversion was due to both thermodynamic and kinetic reasons. At higher concentrations of co-fed H2 and CO, 47% and 46% respectively, there was no deactivation temperature at all. This allowed SMR to be conducted at 850 °C. That temperature is considered an important industrial benchmark because it allow for the use of conventional reactor materials. The best conversion at 850 °C was .53 +/- .0075 with 47% co-fed H2, 5 bar, and a molar flux of 0.173 mol/cm2-hr.
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Details
- Title
- The effects of molar flux, pressure, and product gases on the stability of molybdenum carbide during steam methane reforming
- Creators
- Robert Lowry McCauley
- Contributors
- William J. Thomson (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Chemical Engineering and Bioengineering, School of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; [Pullman, Washington] :
- Identifiers
- 99900525087401842
- Language
- English
- Resource Type
- Thesis