CO2CAP · Carbon dioxide capture

Final Activity Report Summary - CO2CAP (Carbon dioxide capture)

The main objective of the project focused on the capture of carbon dioxide from the combustion of methane with the oxygen contained in air as it occurs in conventional power stations. The carbon dioxide produced can be captured in a pure form and used in chemical processes such as the production of methanol or captured and sequestered underground. This combined power generation with carbon dioxide capture system has been termed 'advanced zero emissions power plant'. The membrane system employed provided a gas-tight barrier between the air and the methane but under an oxygen partial pressure difference (or more accurately a gradient in oxygen activity) oxygen can pass through the membrane while nitrogen is excluded thereby also preventing the formation of dangerous oxides of nitrogen (NOx). In addition, this separation also has a safety aspect preventing dangerous mixtures of oxygen and methane from occurring and preventing explosions. The system offers the chance to obtain oxygen from the air, a process that is economically attractive. The material chosen to perform this role was a metal oxide ceramic comprising of lanthanum, strontium, cobalt and iron (specific chemical formula La0.6Sr0.4Co0.2Fe0.8O3, abbreviated 'LSCF6428') with a cubic perovskite crystal structure. Material of this type with mixed conductivity are well known to possess catalytic activity, adding further simplicity of design i.e., membrane and catalyst in one component. The novel aspect of this system was that the membrane was in the form of fine hollow fibres of diameter 1mm with an open internal diameter of around 0.7 mm. The fibres employed in this study were of length 30 cm and provided by our collaborators at the department of chemical engineering, Imperial College London. The hollow fibres offer the opportunity to have a reactor with a high surface area for a given reactor size, providing another economic and practical advantage. To this ends an easy to use reactor design had to be devised that minimised leaks from the outside atmosphere while allowing a number of essential experiments to be done namely: leak testing, oxygen permeation testing and finally the methane combustion reaction. The main achievement was that we were able to show that such a material could be used and was stable over a period of 24 hours when exposed to low concentrations of methane and oxygen at temperatures up to 850 degrees Celsius. The combustion of methane process was monitored over this period and the production of carbon dioxide and the simultaneous depletion of methane was observed. At the same time the integrity of the membrane was monitored by looking for the presence of nitrogen in the gas exiting the reactor module. The presence of nitrogen would indicate degradation of the membrane. Only trace amounts of nitrogen were observed and were attributed to imperfect sealing of the various components of the reactor module.

Data: CORDIS, © European Union