Converting Carbon Dioxide into Value Added Chemicals via Low Temperature Atmospheric Pressure Plasmas

Carbon dioxide is a waste product produced extensively by modern everyday life. In order to combat the growing threat of climate change atmospheric carbon dioxide levels need to be reduced and controlled. If waste carbon dioxide can be converted effectively and efficiently on a commercial basis into valuable chemicals atmospheric carbon dioxide levels can be controlled in a financially viable and potentially appealing manner. Carbon monoxide is a valuable feedstock for the chemical industry and as a base for synthesising renewable fuels. It is currently produced using high temperatures and pressures. Utilising the non-equilibrium nature of low temperature plasmas to convert carbon dioxide is of growing interest.

Radio-frequency atmospheric pressure plasmas are well known for their ability to produce chemical species at low gas temperatures with high scalability for industrial processes and low operating powers. However, they have not been extensively
studied for their application in converting carbon dioxide. The aim of this work was to study the effectiveness of radio-frequency atmospheric pressure plasmas for converting carbon dioxide into value added chemicals and the underlying mechanisms that cause dissociation in order to better understand how to improve the process.

In order to determine the level of conversion of carbon monoxide the Fourier transform infra-red spectroscopy diagnostic was used and the power deposited in the plasma was measured to calculate the energy efficiency of the dissociation. A global model was also developed to provide a greater understanding of the reaction pathways that lead to the conversion of carbon dioxide. The predictions made by the model were then tested using two-photon absorption laser induced fluorescence by measuring both the densities of atomic oxygen and carbon monoxide and comparing them to the model predictions. Finally the ability to utilise the plasma produced carbon monoxide was studied in order to determine how viable these plasmas would be for commercial use. High yields of over 98% were obtained at the expense of energy efficiency; a maximum energy efficiency of 9% was also obtained.