Mixed ionic electronic conductors (MIECs).

1. Mixed ionic electronic conductors (MIECs). Ceramic membranes for gas separation and chemical reactors

2. MIECs Membrane reactors Dense ceramic membranes made of MIECs have attracted interest for the realization of membrane reactors. >Mass transport by ionic diffusion through the lattice + electronic conductivity for charge compensation >Superior chemical and thermal stability in comparison to polymeric membranes; >High selectivity for oxygen and hydrogen separation; >Production of pure oygen, enriched air, hydrogen; >Selective oxidation of hydrocarbons (uniform and well-controlled O2 flux); >Splitting of oxygen containing molecules (H2O, N2O, NOx) >High fluxes; >Scalability of reactors; >Cost reduction and energy saving;  membrane reactors

3. Mass flux in a chemical potential gradient ion: ionic conductivity; e : electronic conductivity; Dv: diffusion coefficient; Vm: molar volume MIECs MIEC membrane Transport process d Wagner equation If e>> ion amb = ion ks = surface exchange reaction constant If the diffusion rate is very high (d < dc), surface oxygen exchange reactions become rate controlling.

4. MIECs Materials Most used MIECs are ABO3 perovskites with general composition BaCoxFeyZrzO3– (x+y+z=1) or La1-xSrxCoxFe1-xO3-. 1250K 1000K 830K P P Bi2O3-based (B) P P B C P Ceria-based (C) B B B B Perovskites (P)

5. MIECs Materials 900°C, 100 m BaCoxFeyZrzO3–

6. A0.68Sr0.3Co0.2Fe0.8O3−δ Slope change MIECs Materials Chemical expansion of perovskites Formation of additional oxygen vacancies at high temperature produces an increase in thermal expansion. Compatibility problems. Same or similar material for the support porous tube and active dense membrane.

7. Activation layer Dense layer Porous support layer Ba0.5Sr0.5Co0.8Fe0.2O3−δ MIECs Tubular membranes

8. Planar design MIECs Membrane module design Tubular design

9. MIECs Applications: oxygen separation (1) Using a sweep gas (steam) (2) Two-step process 5 bar 50% O2 Oxygen production: 10 mL cm-2 min-1 at 900°C

10. DH: dehydrogenation HC: hydrogen combustion MIECs Applications: dehydrogenation of light alkanes (1) Conventional catalytic thermal dehydrogenation of light alkanes suffers from low alkane conversion due to thermodynamic limitation. (2) Oxidative dehydrogenation of alkanes improve conversion efficiency but leads to byproducts. Steam suppresses coke formation. Use of MIEC membranes allows for the controlled supply of oxygen (no co-feeding) leading to high selectivity and can exploit the advantages of both methods by realizing a sequence of thermal dehydrogenation/oxydative dehydrogenation steps. O2 permeable membrane Passivated membrane

11. MIECs Applications: dehydrogenation of light alkanes Literature: conventional catalytic reactor propene ethene

12. Water splitting Syngas production Alkene production MIECs Applications: hydrogen production from water splitting Water splitting coupled with syngas or alkene production The reaction is shifted to the right even at high temperature. To increase H2 production rate, p(O2) must be very low at the opposite side of the membrane by means of an oxidation reaction. H2 production 3.1 mL cm-2 min-1 at 950°C