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3.4 Protonic Membranes
ОглавлениеAs previously mentioned, the impact of the CO2 emissions on Earth is triggering the energetic transition from fossil fuels to environmentally friendly energy sources. H2 is a promising energy carrier allowing the storage of chemical energy; nowadays, its main use is as a reactant for the synthesis of NH3 and CH3OH, in the refining and other industrial applications. H2 can be used in fuel cell cars, as feed into the natural gas network, and in H2/O2 fuel cells among others [66–69].
Therefore, H2 separation is an important process and its utility has been demonstrated over the past years. Pressure gradient is the main driving force for H2 separation in these type of membranes, giving a large H2 partial pressure, hydrogen will migrate across the membrane. These membranes operate at a wide range of temperatures, and they can be divided into six different types depending on their properties, temperature ranges, and H2 permeation performance. Table 3.1 shows a comparison between H2‐selective membranes.
Among these membranes, mixed protonic–electronic conductor (MPEC)‐based membranes are the most appropriate candidates for application to high‐temperature H2 (>500 °C) separation‐based processes. These membranes allow to separate H2 because of their ambipolar conductivity (electronic and protonic) when a hydrogen partial pressure difference is applied across the membrane [72–76]. This technology is the focus of many research groups worldwide because it offers the advantage of process intensification by shifting the thermodynamic equilibrium of a reaction [77–79].