Membrane separation processes for argon plasma gas recovery

  • Membranprozesse zur Argon-Plasmagas-Rückgewinnung

Harlacher, Thomas; Wessling, Matthias (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2014)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2013

Abstract

A mixture of argon and hydrogen is used as plasma gas in a thermal plasma synthesis for the production of silicon carbide. Next to argon and hydrogen, the exhaust gas of the ceramic synthesis contains carbon monoxide. Since argon is an expensive gas, the plasma gas needs to be recycled. For this purpose, the carbon monoxide has to be removed from the exhaust gas. The applicability of a membrane based gas separation process for this separation task was investigated in this study. A process route combining a water-gas shift reaction with a subsequent gas separation was identified as the most promising route based on an experimental screening of commercial polymer membranes. Experimental data were also applied for the validation of a gas permeation model in a commercial equation-oriented modeling environment. This model was implemented in a commercial process simulations software. In the gas permeation unit the carbon dioxide and hydrogen resulting from the water gas shift have to be separated. In the two-stage membrane process the application of different membrane materials (polyimide, PEO based Polyactive) and the adaptation of the membrane areas in the two stages allow an independent adjustment of the hydrogen and carbon dioxide concentrations in the product stream. After compensating the argon losses caused by the gas treatment process, the recycled gas stream complies with the stream composition required for the plasma gas. Hybrid processes were investigated as an alternative to the membrane stand alone process. The techno-economic analysis of the different processes indicated the advantageousness of the membrane-stand-alone process and a hybrid process combining a chemical absorption and a membrane unit. The gas stream at the outlet of the water gas shift reactor is saturated with water. Therefore, the influence of water vapor on the membrane separation performance had to be investigated. The simulation model was extended and validated by experimental data for saturated feed gas streams. Depending on the feed pressure an up to 50% higher membrane area demand was determined, while the achievable argon recovery remained nearly unchanged.

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