Photocatalytic methanol and methane production using captured CO2 from coal-fired power plants. Part I - a Life Cycle Assessment

In order to reduce climate-related CO2 emissions from coal-fired power plants CO2 can be captured and stored. Alternatively, CO2 can also be used as resource for new products. One way to use CO2 from flue gases is a photocatalytic conversion of CO2 to methanol or methane using dye-sensitized semiconductors according to the overall equations (1) and (2): CO2 + 2 H2O + solar energy -> CH3OH + 1.5 O-2 (1); CO2 + 2 H2O -> CH4 + 2 O-2 (2). These photocatalytic processes have been investigated within the research project Solar2Fuel (S2F), clarifying the technical requirements, economic conditions and ecological impacts of the concepts. This paper evaluates the energetic and ecological prospects of the two photocatalytic S2F concepts in comparison to conventional technologies for power generation and methanol/methane production. The study uses the Life Cycle Assessment method to determine ecological effects and to identify weak points of the concepts. Results of global warming potential indicate that the S2F concept has the potential to reduce CO2 emissions in comparison to conventional power generation and methanol/methane production. But the S2F concept needs large amounts of water in regions which suffer from water shortages. Furthermore, distillation of methanol produced by photocatalysis has been identified as a weak point with respect to energetic and ecological impacts. Hence, the methane producing S2F concept shows a better ecological performance than the S2F methanol process. (C) 2014 Elsevier Ltd. All rights reserved.