Experimental investigation of the reverse water-gas shift reaction at high temperature and elevated pressure

Kurzfassung

To reduce the net greenhouse gas emissions to zero (COP21), several possible routes to utilize renewable sources in the energy and transport sector are discussed and investigated lately. For the air transport sector it seems likely that it will still rely on hydrocarbons in the near future. One possible process to synthesize these hydrocarbons is the power-to-liquid process. Two main steps in this process are the CO2-activation (syngas production via reverse water-gas shift reaction) and the subsequent Fischer-Tropsch process. In context of producing liquid fuels via Fischer-Tropsch, the syngas production unit has to be operated at elevated pressure up to 25 bar in order to run the process at a constant pressure level. The syngas production is an endothermic reaction which improves with higher reaction temperatures (700 °C-900 °C) due to the state of equilibrium. However, most previous studies focus on the investigation of the reverse water-gas shift reaction (rWGS) at atmospheric pressure. The pressure dependency of side reactions, like methane and carbon formation, leads to different equilibrium concentrations and therefore the pressure influence cannot be neglected. Then again, studies conducted at elevated pressure use stainless steel tubes as reactor tubes, which catalyze the reaction due to their nickel content. Therefor these experimental results combine both catalytic pathways which cannot be separated easily. In this study a novel reactor set-up is introduced, which enables to investigate heterogeneously catalyzed reactions at high temperature and elevated pressure. This setup consists of a glass tube in which the catalyst is inserted. Therefor only gas phase and catalytic reaction at the catalyst are likely to occur. The glass tube is surrounded by an electric heating wire to heat the gas to reaction temperature. On both ends of the glass tube the temperature has to be far lower than 700 °C because otherwise the wall catalysis at the stainless steel tube would falsify the results. The electric wire is wrapped in glass wool in order to isolate the reaction chamber and to prevent the outer pressure stressed stainless steel tube from high temperature impact.