Catalytic Dehydroaromatization of Ethane in Microwave Reactor

Ethane is separated from shale gas to minimize condensation in natural gas pipeline. As an effective way to utilize ethane, direct non-oxidative ethane dehydroaromatization has been studied for decades. Conventionally, high reaction temperature (550-600^oC) is required to activate the hydrocarbon molecules. In this study, a microwave catalytic reactor system is used to activate ethane at temperature 200^oC lower than conventional catalytic approach. The objective of this study is to elucidate reaction mechanism in microwave-assisted ethane dehydroaromatization. The study consists of synergistically integrating microwave reaction chemistry with novel heterogeneous catalysis that selectively activates natural gas through microwave irradiation. The challenges in C-H bon activation is overcome by a combination of changing in reaction pathways, novel microwave reactor and catalysts. Specifically, the focus of the study is to ascertain reaction pathways and the catalytic function of catalyst that are sensitive to electromagnetic energy. One of the mechanisms by which the catalyst and reacting species can interact with the microwave field and provide energy to the reaction is by relaxation processes, such as dipolar or Debye processes, which involve the coupling of the radiation with dipoles in the solid catalyst. These dipoles can be defect sites (i.e. atomic vacancies) in the catalysts or dangling bonds on the surface of catalysts. From the standpoint of catalysis, dipoles on the surface can be reactant or products that would be susceptible to selective bond activation effects, which in turn can affect reaction rates.

Using ethane as the feedstock, aromatization reaction was studied in a variable frequency microwave reactor in the presence of metal promoted zeolite catalyst. The significance of microwave frequency, reaction temperature and residence time were investigated respectively. Aromatic formation can be achieved at temperature lower than 400^oC. Transmission electron microscope with energy dispersive X-ray spectroscopy, thermogravimetric analysis and other technologies were applied to characterize the metal doped catalyst. Energy economy is also calculated in this study to evaluate the feasibility of microwave operation for commercial application.