Investigations on membrane application to catalytic methylamines synthesis and kinetics of nitrous oxide decomposition on FeZSM-5.

摘要

This dissertation consists of two parts. Part A, “Preliminary Assessment of Membrane Reactors as a Means to Improve the Selectivity of Methylamines Synthesis”, includes research on methylamines synthesis from ammonia and methanol using an amorphous silica-alumina catalyst. A combined thermodynamic and kinetic analysis shows that the selectivity ratio initially observed at high methanol conversion is a kinetic ratio, not a thermodynamic ratio. In some cases in the past, this kinetic ratio has been taken to represent thermodynamic equilibrium. However, if the reaction is allowed to continue beyond the point where conversion of methanol and dimethyl ether is essentially complete, the product composition continues to change, although at a much lower rate. Eventually, the true thermodynamic selectivity ratio is obtained. A simple kinetic model was developed that captures this behavior, and this model was used to assess whether a membrane reactor might be used to alter the overall selectivity of methylamine synthesis. Four different membrane reactor configurations were considered. There were operational regimes where each configuration showed advantages, but these either occurred at low conversions or required extremely large reactors. These configurations are limited by currently available catalysts and membrane materials. The impact of membrane reactors could be increased if catalysts were developed that retained high activity during methylamine disproportionation, i.e., after all methanol had been consumed. The development of membrane materials with better permselectivities would also increase the attractiveness of membrane reactor processes.; Part B is “Promotional effects of NO in Nitrous Oxide Decomposition over FEZSM-5”. FeZSM-5 was prepared using a FeCl₃ sublimation method and a conventional solute ion-exchange method. N₂O decomposition and the effect of N₂, O₂ and NO addition in the feed were studied over thus made FeZSM-5. It has been observed that N₂O decomposition is first order with respect to N₂O. The reaction rate was very little affected by N₂ and O₂, but was greatly improved when a small amount of NO is added. The added NO did not only react with N₂O, but also promote the decomposition of N ₂O. This phenomenon was described using a six-step mechanism involving a nitrite/nitrate redox cycle. The suggested mechanism agreed with the first order reaction rate, and predicted an experimental result of isotopic labeling reported by previous literature. It is also consistent with published thermal desorption data and infrared spectroscopic results.