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[Display omitted] • A tubular membrane capable of capturing CO 2 /O 2 and converting propane to propylene. • Balanced conversion and selectivity. • Extended operation hours. • Mitigated overoxidation and suppressed coke formation. Combined carbon capture and conversion (3C) technologies play a vital role in our battle against global warming and climate. Using electrochemical cells for 3C is an attractive option due to their intrinsically high efficiency and selectivity. Here we report an electrochemical membrane reactor for CO 2 /O 2 capture from flue gas and instant conversion of propane to propylene over a catalyst bed. The membrane consists of a dual metal-carbonate phase, which allows CO 2 /O 2 (in 2:1 mol ratio) co-transport through the membrane. The reactor is in tubular plug-flow geometry, which enables a continuous and gradual addition of CO 2 /O 2 into a flowing propane stream along the axial length of the membrane, thus achieving an excellent balance between conversion and selectivity, while avoiding overoxidation and suppressing coking. The plug-flow membrane reactor exhibits a C 3 H 6 yield of ∼30 %, C 3 H 8 conversion of ∼35 % and C 3 H 6 selectivity of 85 % at 600 °C for an impressive 173 h of continuous operation with minimal degradation. [ABSTRACT FROM AUTHOR]

Oxidative coupling of methane (OCM), which transforms CH 4 into C 2 products (C 2 H 6 and C 2 H 4) with molecular O 2 as the oxidant, is one of the most studied direct methane conversions (DMCs). However, a major technical hurdle to the OCM process is to achieve high CH 4 conversion at high C 2 (C 2 H 6 and C 2 H 4) selectivity. One rudimentary cause for this "tradeoff" behavior is the high chemical reactivity of the products (C 2 H 6 or C 2 H 4), which can be re-oxidized by O 2. To overcome this thermodynamic challenge, minimizing the oxidizing power of the oxidant and lowering the local oxygen partial pressure are keys. In this work, we demonstrate a new membrane reactor that capture CO 2 /O 2 from a flue gas and uses it for OCM conversion. The results show that the co-captured CO 2 /O 2 mixture converts CH 4 into C 2 H 6 in the presence of a 2%Mn–5%Na 2 WO 4 /SiO 2 catalyst, followed by thermal cracking of C 2 H 6 into C 2 H 4 and H 2. The presence of CO 2 decreases the local partial pressure of O 2 , thus reducing the propensity of C 2 -products re-oxidation and leading to a higher C 2 selectivity. We show that a small button-type membrane reactor can achieve 12% C 2 yield with ∼57% C 2 -selectivity using a diluted CH 4 -Ar mixture as the feedstock. We expect higher C 2 yield with tubular plug-flow membrane reactors in the future. We also highlight the unique advantage of the membrane reactor in intensifying CO 2 capture from both flue gas and OCM purification process into one single step. A dual-phase CO 2 transport membrane for oxidative coupling of methane conversion. [Display omitted] • First demonstration of CO 2 transport membranes for oxidative coupling of methane (OCM) conversion. • Identification of CO 2 transport pathways in the membrane. • Thermodynamic analysis of main and side reactions in the OCM conversion. [ABSTRACT FROM AUTHOR]

Natural gas (NG) fired power plants emit low concentration (4–5%) of CO 2 , which presents additional technical and economic challenges to the current benchmark amine absorption technology. The newly emerged high-temperature multiphase membranes operated on molten carbonate (MC) chemistry for CO 2 capture/separation/conversion have been demonstrated with great potential to meet this challenge. In this study, we report on the CO 2 capture performance of such a membrane in tubular geometry from a mockup NG flue gas. The membrane is comprised of a mixture of Gd 0.20 Ce 0.80 O 1.95 (GDC) and MC, in which GDC forms a porous skeleton to contain MC. We show that the membrane with a dimension of 6.1 mm in outer diameter, 5.1 mm in inner diameter and 5 cm in effective length (resulting in 4 cm2 effective surface area) can achieve a CO 2 flux density of 0.46–0.55 mL/min·cm2 at 650 °C, capturing 97% pure CO 2 at a rate of 37–42% from 5%CO 2 –N 2 using moistened Ar as the sweep gas. The level of performance demonstrated by this study suites the membrane well for stationary CO 2 capture from NG power plants. [Display omitted] • Demonstration of high-performance of tubular membrane for low CO 2 capture. • Demonstration of beneficial effect of steam on CO 2 flux. • Confirmation of CO 2 –H 2 O co-transport mechanisms. [ABSTRACT FROM AUTHOR]