On the use of supported ceria membranes for oxyfuel process/syngas production

Multilayered Ceramic Membrane with Ion Conducting Thin Layer Induced by Interface Reaction for Stable Hydrogen Production

Conventional methods for fabricating multilayered ceramic membranes with ion conducting dense thin layers are often cumbersome, costly, and limited by poor adhesion between layers. Inspired by the architectural structure of the rooted grasses in soil, here, we report an interface-reaction-induced reassembly approach for the direct fabrication of Ce_0.9 Gd_0.1 O_2-δ (CGO) thin layers rooted in the parent multilayered ceramic membranes by only one firing step. The CGO dense layers are very thin, and adhered strongly to the parent support layer, ensuring low ionic transport resistance and structural integrity of the multilayered membranes. When using as an oxygen permeable membrane for upgrading fossil-fuel-derived hydrogen, it shows very long durability in harsh conditions containing H₂ O, CH₄ , H₂ , CO₂ and H₂ S. Furthermore, our approach is highly scalable and applicable to a wide variety of ion conducting thin layers, including Y_0.08 Zr_0.92 O_2-δ , Ce_0.9 Sm_0.1 O_2-δ and Ce_0.9 Pr_0.1 O_2-δ .

High-Performance Microchanneled Asymmetric Gd(0.1)Ce(0.9)O(1.95-δ)-La(0.6)Sr(0.4)FeO(3-δ)-Based Membranes for Oxygen Separation

A microchanneled asymmetric dual phase composite membrane of 70 vol % Gd(0.1)Ce(0.9)O(1.95-δ)-30 vol % La(0.6)Sr(0.4)FeO(3-δ) (CGO-LSF) was fabricated by a "one step" phase-inversion tape casting. The sample consists of a thin dense membrane (100 μm) and a porous substrate including "finger-like" microchannels. The oxygen permeation flux through the membrane with and without catalytic surface layers was investigated under a variety of oxygen partial pressure gradients. At 900 °C, the oxygen permeation flux of the bare membrane was 1.6 (STP) ml cm(-2) min(-1) for the air/He-case and 10.10 (STP) ml cm(-2) min(-1) for the air/CO-case. Oxygen flux measurements as well as electrical conductivity relaxation show that the oxygen flux through the bare membrane without catalyst is limited by the oxygen surface exchange. The surface exchange can be enhanced by introduction of catalyst on the membrane surface. An increase of the oxygen flux of ∼1.49 (STP) mL cm(-2) min(-1) at 900 °C was observed when catalyst is added for the air/He-case. Mass transfer polarization through the finger-like support was confirmed to be negligible, which benefits the overall performance. A stable flux of 7.00 (STP) ml cm(-2) min(-1) was observed between air/CO/CO2 over 200 h at 850 °C. Partial surface decomposition was observed on the permeate side exposed to CO, in line with predictions from thermodynamic calculations. In a mixture of CO, CO2, H2, and H2O at similar oxygen activity the material will according to the calculation not decompose. The microchanneled asymmetric CGO-LSF membranes show high oxygen permeability and chemical stability under a range of technologically relevant oxygen potential gradients.

Novel Approach for Developing Dual-Phase Ceramic Membranes for Oxygen Separation through Beneficial Phase Reaction

A novel method based on beneficial phase reaction for developing composite membranes with high oxygen permeation flux and favorable stability was proposed in this work. Various Ce0.8Sm0.2O2-δ (SDC) + SrCO3+Co3O4 powders with different SDC contents were successfully fabricated into membranes through high temperature phase reaction. The X-ray diffraction (XRD) measurements suggest that the solid-state reaction between the SDC, SrCO3 and Co3O4 oxides occurred at the temperature for membrane sintering, leading to the formation of a highly conductive tetragonal perovskite phase SmxSr1-xCoO3-δ. The morphology and elemental distribution of the dual-phase membranes were characterized using back scattered scanning electron microscopy and energy dispersive X-ray spectroscopy (BSEM-EDX). The oxygen bulk diffusivity and surface exchange properties of the materials were investigated via the electrical conductivity relaxation technique, which supported the formation of conductive phases. The SDC+20 wt % SrCO3+10.89 wt % Co3O4 membrane exhibited the highest permeation flux among the others, reaching 0.93 mL cm(-2) min(-1) [STP = standard temperature and pressure] under an air/helium gradient at 900 °C for a membrane with a thickness of 0.5 mm. In addition, the oxygen permeation flux remained stable during the long-time test. The results demonstrate the beneficial phase reaction as a practical method for the development of high-performance dual-phase ceramic membranes.

Enhanced oxygen separation through robust freeze-cast bilayered dual-phase membranes

Dual-phase oxygen-permeable asymmetric membranes with enhanced oxygen permeation were prepared by combining freeze-casting, screen-printing, and constraint-sintering techniques. The membranes were evaluated under oxyfuel operating conditions. The prepared membranes are composed of an original ice-templated La(0.6)Sr(0.4)Co(0.2)Fe(0.8)O(3-δ) support with hierarchically oriented porosity and a top fully densified bilayered coating comprising a 10 μm-thick La(0.6)Sr(0.4)Co(0.2)Fe(0.8)O(3-δ) layer and a top protective 8 μm-thick layer made of an optimized NiFe2O4/Ce(0.8)Tb(0.2)O(2-δ) composite synthesized by the one-pot Pechini method. Preliminary analysis confirmed the thermochemical compatibility of the three involved phases at high temperature without any additional phase detected. This membrane exhibited a promising oxygen permeation value of 4.8 mL min(-1)  cm(-2) at 1000 °C upon using Ar and air as the sweep and feed gases, respectively. Mimicking oxyfuel operating conditions by switching argon to pure CO2 as a sweep gas at 1000 °C and air as feed enabled an oxygen flux value of 5.6 mL min(-1)  cm(-2) to be reached. Finally, under the same conditions and increasing the oxygen partial pressure to 0.1 MPa in the feed, the oxygen permeation reached 12 mL min(-1)  cm(-2). The influence of CO2 content in the sweep gas was studied and its reversible and positive effect over oxygen permeation at temperatures equal to or above 950 °C was revealed. Finally, the membrane stability over a period of 150 h under CO2-rich sweep gas showed a low degradation rate of 2.4×10(-2)  mL min(-1)  cm(-2) per day.

A novel CO2-stable dual phase membrane with high oxygen permeability

A good combination of high CO₂ stability and high oxygen permeability is obtained for the novel CP–PSFC dual phase membrane.

Ethylene production by ODHE in catalytically modified Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) membrane reactors

Process intensification by the integration of membranes and high-temperature reactors offers several advantages with regard to conventional process schemes, that is, energy saving, safe operation, reduced plant/unit size, and higher process performance, for example, higher productivity, catalytic activity, selectivity, or stability. We present the study of oxidative dehydrogenation of ethane at 850 °C on a catalytic membrane reactor based on a mixed ionic-electronic conducting membrane. The surface of the membrane made of Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) has been activated by using different porous catalytic layers based on perovskites. The layer was deposited by screen printing, and the porosity and thickness was studied for the catalyst composition. The different catalyst formulations are based on partial substitution of A- and B-site atoms of doped strontium ferrite/cobaltites (A(0.6)Sr(0.4)Co(0.5)Fe(0.5)O(3-δ) and Ba(0.6)Sr(0.4)BO(3-δ)) and were synthesized by an ethylenediaminetetraacetic acid-citrate complexation route. The use of a disk-shaped membrane in the reactor enabled the direct contact of gaseous oxygen and hydrocarbons to be avoided, and thus, the ethylene content increased. High ethylene yields (up to ≈81 %) were obtained by using a catalytic coating based on Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ), which included macropores produced by the addition of graphite platelets into the screen-printing ink. The promising catalytic results obtained with this catalytically modified membrane reactor are attributed to the combination of 1) the high activity, as a result of the high temperature and oxygen species diffusing through the membrane; 2) the control of oxygen dosing and the low concentration of molecules in the gas phase; and 3) suitable fluid dynamics, which enables appropriate feed contact with the membrane and the rapid removal of products.