Mixed-conducting ceramic-carbonate membranes exhibiting high CO2/O2 permeation flux and stability at high temperatures

Abstract

This investigation demonstrates the feasibility to fabricate high quality ceramic-carbonate membranes based on mixed-conducting ceramics. Specifically, it is reported the simultaneous CO 2 /O 2 permeation and stability properties of membranes constituted by a combination of ceramic and carbonate phases, wherein the microstructure of the ceramic part is composed, in turn, of a mixture of fluorite and perovskite phases. These ceramics showed ionic and electronic conduction, and at the operation temperature, the carbonate phase of the membranes is in liquid state, which allows the transport of CO 3 2and O 2species via different mechanisms. To fabricate the membranes, the ceramic powders were uniaxially pressed in a disk shape. Then, an incipient sintering treatment was carried out in such a way that a highly porous ceramic was obtained. Afterwards, the piece is densified by the infiltration of molten carbonate. Characterization of the membranes was accomplished by SEM, XRD, and gas permeation techniques among others. Thermal and chemical stability under an atmosphere rich in CO 2 was evaluated. CO 2 /O 2 permeation and long-term stability measurements were conducted between 850 and 940 ℃. The best permeation-separation performance of membranes of about 1 mm thickness, showed a maximum permeance flux of about 4.46×10-7 mol•m-2 •s-1 •Pa-1 for CO 2 and 2.18×10-7 mol•m-2 •s-1 •Pa-1 for O 2 at 940 ℃. Membranes exhibited separation factor values of 150-991 and 49-511 for CO 2 /N 2 and O 2 /N 2 respectively in the studied temperature range. Despite long-term stability test showed certain microstructural changes in the membranes, no significant detriment on the permeation properties was observed along 100 h of continuous operation.

Concurrent and modulated separation of CO2 and O2 by a fluorite/perovskite‐based membrane

“…By assuming a straight pore, r is the pore radius of the support, θ is the contact angle, and γ is the molten carbonates' surface tension. Considering the biggest pore diameter observed by SEM (about 1.0 µm) for the 60CP-40PSFC sample, and following the procedure previously reported in references, 16,36,41 it can be stated that the membrane fabricated here can operate under a transmembrane pressure difference (ΔP) of about 4.2 bar without loss of the molten phase. Considering that these membranes have a high potential to be used for CO 2 separation and valorization, for example, by using a packed-bed membrane reactor configuration; then, the operating conditions are crucial.…”

“…This behavior can be attributed to both the presence of electronic conduction and the thermal activation of the ionic transport mechanisms in the ceramic material, which are directly related to the transport of species. 13,25,36 It is noticeable that the CO 2 :O 2 molar ratio change from about 2.09 at 850°C to 3.14 at 950°C. In this sense, it is important to keep in mind that Equation ( 1) is an electrochemical reaction that involves electronic conductivity; therefore, the constant CO 2 :O 2 2:1 ratio could be expected only for a metal-based membrane.…”

“…40 Finally, to determine the differential pressure in which a specific ceramic-carbonate membrane can operate, it is necessary to carry out wettability measurements. 36 Here, Figure 6 shows the obtained wettability results of a Bi 2 Y 0.3 Sm 0.2 O 3 (BYS) (Figure 6A) and the 60CP-40PSFC fluorite/perovskite dense samples (Figure 6B) against molten carbonates. Comparing the carbonate drop-profile in both samples indicates that the sample 60CP-40PSFC has excellent wettability properties against the chosen ternary molten carbonate mixture.…”

“…The observed behavior is attributed to the presence, redistribution, or even loss of the excess of carbonates that remained on the membrane surface. 13,36,40 Once the steady state was reached, a remarkably stable and simultaneous separation of CO 2 and O 2 is observed, with permeance values of 0.72 × 10 −7 and 0.26 × 10 −7 mol m −2 s −1 Pa −1 , respectively. Once again, it is remarkable that different from metal-carbonate membranes wherein the CO 2 :O 2 molar ratio in the permeate is about 2 at any temperature (according to Equation 1) in the studied fluorite/perovskite-based membrane, this ratio is to about 2.7 at 875°C.…”

“…Incorporating the carbonate phase into the porous network of the ceramic support is a critical factor that affects the performance of the final dual-phase membrane. 36,[39][40][41] On the one hand, using a ceramic material exhibiting adequate wettability properties against molten carbonate ensures the complete densification of the porous support by incorporating the carbonate. Moreover, it has been argued that the aforementioned wettability properties could help to avoid the loss of the carbonate phase during the high-temperature permeation process.…”