Biogas, membranes and carbon dioxide capture

Biogas, which consists primarily of methane, can be obtained through the biological transformation of a large variety of organic wastes, and has drawn an increased interest within a framework of renewable energy sources. The use of gas permeation membranes for upgrading biogas (i.e., for removing carbon dioxide and hydrogen sulfide from biomethane) has been abundantly investigated and already displays practical industrial applications. A different concept, based on the use of carbon dioxide/nitrogen selective membranes, is presented in this study. The key issue is to achieve carbon capture and storage (CCS) from the flue gas of a power plant where raw biogas, together with oxygen-enriched air, is used as fuel. A CO2-concentrated flue gas is obtained, and as a result, gas permeation membranes can easily achieve carbon capture targets for post-combustion situations (90% CO2 purity and 90% capture ratio). A simulation study has shown that, based on this strategy, it is possible to acquire a very low overall energy requirement for carbon dioxide capture (less than 1 GJ per ton of recovered CO2). Such a remarkable performance can be achieved as soon as membranes show a CO2/N2 selectivity in the range of 50; a target value already reported for several polymeric materials.