Kinetic analysis and catalyst development for oxidative dehydrogenation of propane with carbon dioxide

Abstract

Propylene has been widely used as a building block to produce value-added chemicals in the modern chemical industries. Regarding the production of propylene, direct dehydrogenation of propane to propylene (DDP) has been commercialized as a selective propylene production process. However, the endothermic nature of DDP constraints the thermodynamic equilibrium, limiting the equilibrium conversion of propane. The oxidative dehydrogenation of propane with carbon dioxide (ODPC) has been proposed to alleviate the constraint in the propylene production. Introduction of carbon dioxide with propane eliminates the dehydrogenated hydrogens from DDP by reacting with the carbon dioxide. The removal of hydrogen product shifts the equilibrium to product side, enhancing the equilibrium conversion of propane. Therefore, ODPC can selectively produce the propylene at relatively lower temperature than that of DDP, suggesting as an alternative for selective and efficient production of the propylene. Notably, combining the alkane dehydrogenation with the carbon dioxide reduction is regarded as an economical and eco-friendly process to produce value-added olefin and mitigate greenhouse gas emissions simultaneously.

Reaction between propane and carbon dioxide at ODPC reaction condition occurs multiple reactions, including ODPC, DDP, reverse water-gas shift reaction (RWGS), dry reforming of propane (DRP), propane cracking, and hydrogenolysis. Therefore, the analysis of reaction kinetics for ODPC is required to understand the reaction behavior of each reaction in the presence of propane and carbon dioxide. In the ODPC reaction network, the spontaneity of each reaction determines the reaction mechanism, the redox-based Mars-van Krevelen (MvK) mechanism and non-redox-based coupled reaction mechanism combining DDP and RWGS. The ODPC performance of each reaction mechanism depends on the catalyst properties, such as type of metal and support, metal species, and coordination nature of metals. Hence, catalyst design with considering the reaction mechanism is required for the development of the metal and metal oxide-based catalyst in ODPC. This thesis focused on the ODPC kinetics analysis with comprehensive kinetic model encompassing the entire ODPC reaction network, and the development of metal oxide and metal-based catalyst with considering their intrinsic properties associated with the corresponding ODPC reaction mechanism.

First, the ODPC kinetic model encompassing the entire ODPC reaction network was provided. The kinetic model was constructed based on the kinetic experiments over silica-supported chromium oxide catalyst. Estimation of kinetic parameters suggested that the activation of carbon dioxide is a rate-determining step in ODPC over silica-supported chromium oxide catalyst. Comparison of reaction rates upon the reaction condition revealed a promoting effect of carbon dioxide on the ODPC reaction rates at oxidative atmosphere.

Next, the efficient and effective strategies were proposed to develop the metal oxide-based catalysts for ODPC. An optimal ODPC catalyst composition based on the chromium and zirconium was proposed through data-driven optimization method. The machine learning model was constructed based on the in-house ODPC database. For an accurate model, the closed-loop optimization was applied. The proposed catalyst composition through data-driven optimization surpassed the ODPC performance in that of the database. Synergic effect of each element in the proposed catalyst that enhances the ODPC performance was demonstrated using the characterizations for the chromium species. Regarding the toxicity of chromium oxide, an alternative zinc-based catalyst was developed. The dispersion of supported zinc oxide species was promoted by incorporation of the molybdenum into the zirconia support, exhibiting the comparable ODPC performance with that of chromium oxide- based catalyst.

Lastly, an insight to develop the platinum-based catalyst was provided. The influence of the presence of calcium on the platinum-tin alloy was investigated that assisted to form an active platinum-tin alloy phase with highly active ODPC activity. The behavior of platinum-tin alloy under the reduction, carbon dioxide oxidation, and reaction condition was demonstrated using in-situ characterization, revealing that the calcium-assisted platinum-tin alloy inhibited the segregation at oxidative atmosphere.

This thesis provides the comprehensive ODPC kinetic model, and the efficient and effective strategies to design the metal and metal-oxide based catalyst for ODPC.