As mentioned, CO2 can be used as raw material for the synthesis of sev­eral chemicals [99]. Moreover, if CO2 is concentrated or separated by a membrane system exhibiting high CO2 permeation and permselectivity, this open up the possibility to develop a continuous process of membrane reaction to simultaneously capture and chemically convert CO2. For exam­ple, if the membrane is able to separate CO2 at intermediate and even high temperatures, it can be used for the design of a membrane reactor for the production and purification of hydrogen and syngas. Syngas is a gaseous fuel with a main chemical composition of CO, H2, CO2, and CH4. Syngas can be used as feedstock for the synthesis of several other clean fuels such as H2, methanol, ethanol, diesel and other hydrocarbons synthesized via the Fischer-Tropsch process [100-104].

Among the different processes for the synthesis of syngas and hydro­gen, CO2 methane reforming Eq. (11) and the water-gas shift reaction (WGS) Eq. (12) are the most promising options.

CH4 + CO2 ~ 2CO + 2H2 (11)

CO + H2O ~ CO2 + H2 (12)

Figure 6 schematizes the membrane reactor concept considering the two reactions described above. Figure 6A shows a membrane reactor for dry reforming of methane to produce syngas at temperatures between 700 and 800 °C. Figure 6B illustrates the use of ceramic oxide membranes for hydrogen purification by separating the CO2 from water-gas shift products at about 550 °C. Additionally, Figure 6B shows the possibility of using a ceramic sorbent to chemically trap the permeate CO2 and therefore en­hance the CO2 permeation process by reducing the concentration of CO2 in the permeate side.

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