High oxygen permeation flux of cobalt-free Cu-based ceramic dual-phase membranes

Cation-Intercalated Clay-Based Two-Dimensional Membranes for Effective Desalination and Molecule Sieving

Montmorillonite (MMT) is known as an ion-exchangeable material, and cations between MMT nanosheets are easily exchanged by other cations. In this work, Ca2+, Fe3+, and Al3+ intercalated two-dimensional MMT membranes were developed by ion exchange of pristine MMT membranes (Na+-MMT), and their ion and dye removal abilities were investigated. The d-spacings of hydrated Fe3+ intercalated MMT membrane (Fe3+-MMT) and Al3+ intercalated MMT membrane (Al3+-MMT) were decreased compared with hydrated Na+-MMT membrane due to the stronger electrostatic attraction between Fe3+/Al3+ and negatively charged MMT nanosheets. Ion and dye sieving performances were improved significantly after the intercalation of Ca2+, Fe3+, and Al3+ into MMT membranes. Al3+-MMT membrane with a thickness of 1.17 μm could exclude 94% of Na+, and its ion sieving performance remained stable during a 120-h ion sieving experiment. Moreover, the rejection rate for rhodamine B (RB) reached 94% using an Al3+-MMT membrane with a thickness of 500 nm, and a water permeance of 73 L m-2 h-1 bar-1 was achieved. The excellent ion and dye sieving performances make it promising in the application of desalination and nanofiltration.

A Review of Oxygen Carrier Materials and Related Thermochemical Redox Processes for Concentrating Solar Thermal Applications

Redox materials have been investigated for various thermochemical processing applications including solar fuel production (hydrogen, syngas), ammonia synthesis, thermochemical energy storage, and air separation/oxygen pumping, while involving concentrated solar energy as the high-temperature process heat source for solid-gas reactions. Accordingly, these materials can be processed in two-step redox cycles for thermochemical fuel production from H₂O and CO₂ splitting. In such cycles, the metal oxide is first thermally reduced when heated under concentrated solar energy. Then, the reduced material is re-oxidized with either H₂O or CO₂ to produce H₂ or CO. The mixture forms syngas that can be used for the synthesis of various hydrocarbon fuels. An alternative process involves redox systems of metal oxides/nitrides for ammonia synthesis from N₂ and H₂O based on chemical looping cycles. A metal nitride reacts with steam to form ammonia and the corresponding metal oxide. The latter is then recycled in a nitridation reaction with N₂ and a reducer. In another process, redox systems can be processed in reversible endothermal/exothermal reactions for solar thermochemical energy storage at high temperature. The reduction corresponds to the heat charge while the reverse oxidation with air leads to the heat discharge for supplying process heat to a downstream process. Similar reversible redox reactions can finally be used for oxygen separation from air, which results in separate flows of O₂ and N₂ that can be both valorized, or thermochemical oxygen pumping to absorb residual oxygen. This review deals with the different redox materials involving stoichiometric or non-stoichiometric materials applied to solar fuel production (H₂, syngas, ammonia), thermochemical energy storage, and thermochemical air separation or gas purification. The most relevant chemical looping reactions and the best performing materials acting as the oxygen carriers are identified and described, as well as the chemical reactors suitable for solar energy absorption, conversion, and storage.

Thermal Swing Reduction-Oxidation of Me(Ba, Ca, or Mg)SrCoCu Perovskites for Oxygen Separation from Air

The climate change impact associated with greenhouse gas emissions is a major global concern. This work investigates perovskite compounds for oxygen separation from air to supply oxygen to oxyfuel energy systems to abate these significant environmental impacts. The perovskites studied were Me0.5Sr0.5Co0.8Cu0.2O3−δ (MeSCC) where the A-site substitution was carried out by four different cations (Me = Ca, Mg, Sr, or Ba). SEM analysis showed the formation of small particle (<1 µm) aggregates with varying morphological features. XRD analysis confirmed that all compounds were perovskites with a hexagonal phase. Under reduction and oxidation reactions (redox), Ba and Ca substitutions resulted in the highest and lowest oxygen release, respectively. In terms of real application for oxygen separation from air, Ba substitution as BaSCC proved to be preferable due to short temperature cycles for the uptake and release of oxygen of 134 °C, contrary to Ca substitution with long and undesirable temperature cycles of 237 °C. As a result, a small air separation unit of 0.66 m3, containing 1000 kg of BaSCC, can produce 18.5 ton y−1 of pure oxygen by using a conservative heating rate of 1 °C min−1. By increasing the heating rate by a further 1 °C min−1, the oxygen production almost doubled by 16.7 ton y−1. These results strongly suggest the major advantages of short thermal cycles as novel designs for air separation. BaSCC was stable under 22 thermal cycles, and coupled with oxygen production, demonstrates the potential of this technology for oxyfuel energy systems to reduce the emission of greenhouse gases.

Effects of Bi Substitution on the Cobalt-Free 60wt.%Ce0.9Pr0.1O2−δ-40wt.%Pr0.6Sr0.4Fe1−xBixO3−δ Oxygen Transport Membranes

The mixed ionic-electronic conducting (MIEC) oxygen transport membrane (OTM) can completely selectively penetrate oxygen theoretically and can be widely used in gas separation and oxygen-enriched combustion industries. In this paper, dual-phase MIEC OTMs doped with Bi are successfully prepared by a sol-gel method with high-temperature sintering, whose chemical formulas are 60wt.%Ce0.9Pr0.1O2−δ-40wt.%Pr0.6Sr0.4Fe1−xBixO3−δ (60CPO-40PSF1−xBxO, x = 0.01, 0.025, 0.05, 0.10, 0.15, 0.20). The dual-phase structure, element content, surface morphology, oxygen permeability, and stability are studied by XRD, EDXS, SEM, and self-built devices, respectively. The optimal Bi-doped component is 60wt.%Ce0.9Pr0.1O2−δ-40wt.%Pr0.6Sr0.4Fe0.99Bi0.01O3−δ, which can maintain 0.71 and 0.62 mL·min−1·cm−2 over 50 h under He and CO2 atmospheres, respectively. The oxygen permeation flux through these Bi-doped OTMs under air/CO2 gradient is 12.7% less than that under air/He gradient, which indicates that the Bi-doped OTMs have comparable oxygen permeability and excellent CO2 tolerance.