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. MIECs d Transport process Mass flux in a chemical potential gradient
membrane d
MIECs
Transport process
Mass flux in a chemical potential gradient
Wagner equation
ion: ionic conductivity;
e : electronic conductivity;
Dv: diffusion coefficient;
Vm: molar volume
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-.
1000K
1250K
830K P P
Bi2O3-based (B) P P B C P
Ceria-based (C) B B B B
Perovskites (P)

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

6. 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.
A0.68Sr0.3Co0.2Fe0.8O3−δ
Slope change

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

8. Membrane module design
MIECs
Membrane module design
Planar design
Tubular design

9. Applications: oxygen separation
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. Applications: dehydrogenation of light alkanes
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.
DH: dehydrogenation
HC: hydrogen combustion
O2 permeable membrane
Passivated membrane

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

12. Applications: hydrogen production from water splitting
MIECs
Applications: hydrogen production from water splitting
Water splitting coupled with syngas or alkene production
Water splitting
Syngas production
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