Heterogeneous and homogeneous chemistry in the catalytic partial oxidation of liquid hydrocarbon feedstocks.

摘要

Catalytic partial oxidation (CPO) is emerging as an alternative process for producing high value chemicals like hydrogen or olefins. CPO is a process by which vaporized hydrocarbon fuel and oxygen are reacted over a noble metal catalyst to form high selectivities of either syngas (H2 + CO) or olefins in millisecond contact times. The CPO process has several advantages over current industrial methods used for production of these chemicals including reduced residence times, reduction of NOx emissions, and scalability over several orders of magnitude. However, before catalytic partial oxidation can be commercialized, the effects of fuel structure on product distribution and fuel conversion must be studied along with the contributions of heterogeneous and homogeneous chemistry in the reaction of heavy alkanes.; In this thesis, the relationship between heterogeneous and homogeneous chemistry in the CPO process is explored along with the effect that reactant fuel structure has on the resulting product distribution. In order to explore the effect of fuel structure, experiments are performed comparing the CPO of linear and branched alkanes. Specifically, the CPO of n-octane is compared to the CPO of i-octane (2,2,4-trimethylpentane) to explore the effects of reactant fuel chain branching on fuel conversion and product distribution. The effect of the reactant molecular weight is examined for normal alkanes ranging from molecular weights of 16 (methane) to 226 (hexadecane). The contributions of heterogeneous and homogeneous chemistry are investigated by running simulations in CHEMKIN software, performing experiments on catalyst supports that vary the relative extents of gas phase and surface kinetics, and also performing differential sphere bed experiments with both Rh and Pt metal to measure species and temperature profiles within the catalyst bed. In the end, the knowledge of the relationship between surface and gas phase chemistry and fuel structure is used to design a reactor that maximizes the yield of ethylene and other olefins produced in the CPO of n-octane.