ADVANCED REACTION ENGINEERING FOR THE NONOXIDATIVE VALORIZATION OF METHANE

Abstract

Non-oxidative methane conversion (NMC) represents a promising pathway that directly transforms methane into higher hydrocarbons such as ethane, ethylene, acetylene, aromatics, and hydrogen in a single-step synthesis. This process holds particular appeal due to its potential for remote operation and its status as a carbon-neutral process, given that it does not produce carbon dioxide in the product effluent. As such, NMC could serve as a viable alternative to existing multi-step, energy-intensive processes like the Fischer-Tropsch synthesis and liquid petroleum gas production. Despite its potential, NMC faces significant challenges. The thermodynamic stability of methane, attributed to its strong C-H bonds, poses a considerable obstacle. Other challenges include low selectivity towards desired products, rapid catalyst deactivation, and kinetic hindrance, all of which complicate the process. As of now, these challenges have prevented the development of a commercially viable NMC process. This dissertation aims at overcoming these hurdles to unlock the full potential of NMC, paving the way for a more efficient and sustainable method of methane conversion from the perspective of both catalyst design and reaction engineering. The impact of hydrogen activation on NMC using a hydrogen-permeable SrCe0.8Zr0.2O3-δ (SCZO) perovskite oxide material over the iron/silica catalyst was explored. The SCZO oxide, with its mixed ionic and electronic conductivity, facilitates H2 activation into protons and electrons. The SCZO's ability to absorb H2 in-situ lowers its local concentration, promoted the improvement of NMC reaction thanks to the Le Chaterlie’s principle. To further improve the NMC reaction performance, an innovative autothermal catalytic wall reactor (ACWR) designed for self-sustaining NMC with high hydrocarbon product yield (>21% C2 & >27% Aromatics) and minimal coke formation. The system, potentially powered by combusting the sole co-product H2, offers a self-sustained and negative neutral operation of NMC. Further operando studies via Spatial Resolved Capillary Inlet Mass Spectrometry (SpaciMS) have demonstrated that the increased local concentration and the volcanic axial concentration profile of ethylene within the ACWR highlight its effectiveness in comparison to traditional reactor designs. With the detection of a higher ethylene concentration near the reactor wall, SpaciMS studies have also provided experimental evidence that ethylene is a surface product of the Fe/SiO2 catalyst. A novel Pulsed Heating and Quenching (PHQ) thermochemical synthesis technique was applied to methane pyrolysis to demonstrate high selectivity to valuable C2 products. The technique's salient features include rapid activation of reactants at high temperatures for increased rates and conversions, and precise control over the heating process, enhancing the selectivity of desired products.