Spatially resolved species and temperature profiles in the catalytic partial oxidation of methane and ethane

Catalytic Partial Oxidation (CPO) offers an efficient route to hydrogen, syngas and olefin production from a variety of traditional and renewable feedstocks. However, the CPO process is not completely understood due to the complex heat transfer, mass transfer and reaction processes going on inside one of these reactors. Extreme chemical and temperature gradients (∼200°C/mm) have made it difficult to look inside one of these reactors to gather data, which is needed to develop accurate predictive models of CPO systems. Typically reactor outlet data is used for modeling these systems, because there is not an abundance of spatially resolved data at industrially relevant conditions. Without an ability to look inside the reactor, the catalyst essentially operates as a black box making it difficult to know if models correctly predict what is occuring inside the catalyst.;With the goal of looking directly inside a catalytic partial oxidation catalyst, a technique has been developed for measuring species and temperature profiles within CPO systems. This technique is described in Chapter 3. A thin fused silica capillary (D ∼ 0.6 mm) gives access to the reactor for species and temperature measurement at industrially relevant conditions with very minimal disturbance to the reactor. This capillary is used as an access point for species and temperature sampling along the entire length of the reactor bed. Spatial resolution is estimated to be <0.3 mm as determined by the coarseness of the catalytic foam used in this thesis. Species are sampled using the capillary and quantified using a mass spectrometer or a gas chromatograph. Temperatures are determined with a fiber optic probe (D = 0.3 mm) connected to a fiber optic pyrometer giving a good estimate of the catalyst surface temperature.;Data collected using this technique is shown in Chapter 4. Experiments are performed for CPO of methane and ethane. At a C/O value of 1.0 the methane reaction proceeds in two distinct zones, first an oxidation zone is responsible for consumption of oxygen (in ∼2 mm) and fuel producing approximately equal amounts of H2, CO and H2O. A reforming zone follows in which water and methane react in steam reforming stoichiometry. The pyrometer temperature, shows a temperature maximum near the front of the catalyst due to the exothermic oxidation reactions. The temperature then quickly decreases due to the endothermic nature of steam reforming ending up very close to the adiabatic reaction temperature. The observed reaction stoichiometry indicates that methane CPO proceeds via a mixed mechanism with direct and indirect syngas formation.;Experimental data on the CPO of ethane to ethylene is also presented in Chapter 4. The ethane CPO is interesting because the system can be optimized to produce ethylene, which is a non-equilibrium product. Experiments are performed at C/O = 2.2 which is better for making ethylene. At this stoichiometry profiles indicate that hydrogen and ethylene are produced in parallel through homogeneous non-oxidative chemistry. No hydrogen is seen to be produced in the oxidation zone.;In Chapter 5 heat transfer modeling is performed to estimate the system temperature profiles in the entire reactor bed. A 1-D model is solved to estimate gas and surface temperatures which includes conduction, convection, radiation and reaction (taken from the experimental species profile data). The resulting numerical temperature profiles indicate good agreement between the simulation results and the experimental pyrometer temperature. Good agreement is achieved in terms of the value of the maximum temperature, the peak temperature location, and the temperature behavior in the front heat shield. Radiation is a significant mode of heat transfer due to the open porous structure of the catalyst and its inclusion in the model improves the agreement of the model to the experimental data.;The spatial sampling technique collects intra-catalyst data which can be directly compared against modeling results. This data can be used to validate or refine models, as seen with the heat transfer model presented in Chapter 5. This is a definite strength of spatially resolved data as compared to the bulk of data (reactor outlet data) available on CPO systems.;Although the main focus of this thesis has been the spatial sampling technique, research performed for Chapter 6 deals with a microscopy investigation of the catalyst surface. This is of interest in the context of spatially resolved data because it deals with what is occurring inside the catalyst through a close examination of the catalyst surface. This data aided in understanding how the catalyst morphology affects the catalyst system and the spatial profiles. (Abstract shortened by UMI.)...