Rational Design of Heterogeneous Catalysts and Process Conditions for Non-oxidative Methane Upgrading

Abstract

As finite crude oil resources are rapidly consumed, the pressure to implement alternative technologies to replace current petroleum refining processes has pushed researchers to explore methane, the primary component of natural gas, as a hydrocarbon feedstock for fuel and chemical production. The low cost and increased supply of natural gas, along with the high H:C ratio of methane provide an opportunity for economically viable production of value-added fuels and chemicals with a lower carbon footprint. However, the low polarity and high kinetic inertness of methane create both kinetic and thermodynamic technological challenges in upcycling to higher hydrocarbons. Innovative new catalysts and processes are needed to enable the conversion of methane or natural gas in the era of shifting feedstocks for fuel and chemical production. The research in this dissertation focuses on direct non-oxidative methane conversion (DNMC), one of the most promising pathways for upgrading methane into C2 (i.e., ethane, ethylene and acetylene) and aromatic (i.e., benzene and naphthalene) hydrocarbons with hydrogen co-product. Compared to the current state-of-the-art methane upgrading based on a multi-step process, e.g., gasification or steam methane reforming to produce syngas, followed by FT higher hydrocarbon synthesis, the DNMC can produce valuable olefin and aromatic hydrocarbons in one step. The reaction, however, is currently challenged by high energy input, low conversion, low selectivity and poor catalyst durability, due to the highly endothermic reaction nature and coke deposition. This dissertation targets to solve these challenges via novel catalyst design and development, process condition optimization and process simulation for DNMC for one-step methane upgrading. The catalyst innovation is based on the concept of single-atom (SA) catalysis, the most active new frontier in heterogeneous catalysis since 2011. The absence of metal atom ensembles in SA catalysts mitigates coke formation during methane activation. The single atom metal catalysts in silica matrix were synthesized by various protocols for this purpose. A collection of characterizations was done to understand the physiochemical properties of the as-prepared catalysts. The process conditions influence contributions of heterogeneous surface and/or gas phase reactions in DNMC. The reaction was set at different conditions to reveal these inherent working mechanisms. Lastly, the technoeconomic implications of the DNMC over single atom catalysis processes were evaluated by process simulation. By using principles of thermodynamics, kinetics, and transport phenomena concurrently with AspenPLUS V10 software, this dissertation assesses energy efficiency and economic feasibility and proposed process design optimization parameters.