Semester

Fall

Date of Graduation

2021

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Chemical and Biomedical Engineering

Committee Chair

Jianli Hu

Committee Member

Debangsu Bhattacharyya

Committee Member

Xingbo Liu

Committee Member

Charter Stinespring

Committee Member

Dushyant Shekhawat

Abstract

Stranded gas is a raw gas mixture of volatile hydrocarbons where the main composition is methane. The producers flare the stranded gas at the site because the cost of collecting and transporting the gas is higher than the value of the gas itself. To reduce the waste of this natural resource, it is worthwhile to utilize the on-site stranded natural gas as feedstock to produce value-added chemicals without emitting greenhouse gas. Direct natural gas conversion process is more desirable because of lower capital investment. Methane and ethane, the two major components of natural gas, are very stable molecules that usually require high temperature and a catalyst to achieve a decent single-pass conversion. Meanwhile, under high temperature, the light alkane molecules are likely to collapse into carbon and hydrogen gas. The carbon will cover the catalyst's surface, which causes deactivation. These two issues make natural gas upgrading very challenging.

In this dissertation, a novel cyclic regeneration process was developed to investigate the metal-doped ZSM-5 catalyst deactivation mechanism on direct ethane conversion. The results show that metal agglomeration was another main cause of deactivation other than coke deposition; and using lower concentration of oxygen to regenerate the catalyst can better recover the catalyst activity. Microwave technology was applied to assist the catalytic natural gas conversion process. Under the microwave radiation, significant enhancement in ethane conversion to aromatics was achieved at a temperature as low as 400 °C. Methane conversion can also be improved under microwave radiation at a low bulk temperature, indicating accelerated methane activation over the metal site and hence suggesting a “hot spot” on the metal site despite much lower catalyst bulk temperature measured in the microwave reactor. However, lower selectivity towards aromatics was observed and this is due to the lower relative temperature of the zeolite compare with the metal sites. Other than the hot spot formation, the microwave radiation also brings non-thermal effects which affect catalytic performance. The dissertation advances finite-element modelling approaches to study the non-thermal effects of microwave radiation on direct methane conversion process. The simulation results show an inconsistent electric field distribution on the catalyst particle surface and the existence of local ultra-high electric field between spherical catalyst particles. With the presence of the electric field, methane activation is possible without forming plasma due to the molecule polarization and deformation effects induced by the microwave radiation. Hence, the methane conversion can be improved at a much lower bulk temperature.

Embargo Reason

Publication Pending

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