Direct conversion of methane into ethylene through the oxidative coupling of methane (OCM) is a technically important reaction. However, conventional co-fed fixed-bed OCM reactors still face serious challenges in conversion and selectivity. In this paper, we apply a finite element model to simulate OCM reaction in a plug-flow CO2/O2transport membrane (CTM) reactor with a directly captured CO2and O2mixture as a soft oxidizer. The CTM is made of three phases: molten carbonate, 20% Sm-doped CeO2, and LiNiO2. The membrane parameters are first validated by CO2/O2flux data obtained from CTM experiments. The OCM reaction is then simulated along the length of tubular plug-flow reactors filled with a La2O3-CaO-modified CeO2catalyst bed, while a mixture of CO2/O2is gradually added through the wall of the tubular membrane. A 12-step OCM kinetic mechanism is considered in the model for the catalyst bed and validated by data obtained from a co-fed fixed-bed reactor. The modeled results indicate a much-improved OCM performance by membrane reactor in terms of C2-yield and CH4conversion rate over the state-of-the-art, co-fed, fixed-bed reactor. The model further reveals that improved performance is fundamentally rooted in the gradual methane conversion with CO2/O2offered by the plug-flow membrane reactor.
Direct nonoxidative methane conversion (DNMC) transforms CH4to higher (C2+) hydrocarbons and H2in a single step, but its utility is challenged by low CH4 equilibrium conversion, carbon deposition (coking), and its endothermic reaction energy requirement. This work reports a heat‐exchanged autothermal H2‐permeable tubular membrane reactor composed of a thin mixed ionic‐electronic conducting SrCe0.7Zr0.2Eu0.1O3–
- NSF-PAR ID:
- 10448026
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Energy Materials
- Volume:
- 11
- Issue:
- 46
- ISSN:
- 1614-6832
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
-
more » « less
To cut CO2emissions, we propose to directly convert shale gas into value-added products with a new H2/O2co-transport membrane (HOTM) reactor. A Multiphysics model has been built to simulate the membrane and the catalytic bed with parameters obtained from experimental validation. The model was used to compare C2 yield and CH4conversion rate between the membrane reactor and the state-of-the-art fixed-bed reactor with the same dimensions and operating conditions. The results indicate that (1) the membrane reactor is more efficient in consuming CH4for a given amount of fed O2. (2) The C2 selectivity of the membrane reactor is higher due to the gradual addition of O2into the reactor. (3) The current proposed membrane reactor can have a decent proton molar flux density but most of the proton molar flux will contribute to producing H2O on the feed side under the current operating conditions. The paper for the first-time projects the performance of the membrane reactor for combined H2O/H2removal and C2 production. It could be used as important guidance for experimentalists to design next generation natural gas conversion reactors.
-
more » « less
Commercial proton exchange membrane heavy-duty fuel cell vehicles will require a five-fold increase in durability compared to current state-of-the art light-duty fuel cell vehicles. We describe a new composite membrane that incorporates silicotungstic heteroply acid (HPA),
α -K8SiW11O40▪13H2O, a radical decomposition catalyst and when acid-exchanged can potentially conduct protons. The HPA was covalently bound to a terpolymer of tetrafluoroethylene, vinylidene fluoride, and sulfonyl fluoride containing monomer (1,1,2,2,3,3,4,4-octafluoro-4-((1,2,2-trifluorovinyl)oxy)butane-1-sulfonyl fluoride) by dehydrofluorination followed by addition of diethyl (4-hydroxyphenyl) phosphonate, giving a perfluorosulfonic acid-vinylidene fluoride-heteropoly acid (PFSA-VDF-HPA). A composite membrane was fabricated using a blend of the PFSA-VDF-HPA and the 800EW 3M perfluoro sulfonic acid polymer. The bottom liner-side of the membrane tended to have a higher proportion of HPA moieties compared to the air-side as gravity caused the higher mass density PFSA-VDF-HPA to settle. The composite membrane was shown to have less swelling, more hydrophobic properties, and higher crystallinity than the pure PFSA membrane. The proton conductivity of the membrane was 0.130 ± 0.03 S cm−1at 80 °C and 95% RH. Impressively, when the membrane with HPA-rich side was facing the anode, the membrane survived more than 800 h under accelerated stress test conditions of open-circuit voltage, 90 °C and 30% RH. -
null (Ed.)To directly use a CO 2 –CH 4 gas mixture for power and CO co-production by proton-conducting solid oxide fuel cells (H-SOFCs), a layer of in situ reduced La 0.6 Sr 0.2 Cr 0.85 Ni 0.15 O 3−δ (LSCrN@Ni) is fabricated on a Ni–BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3−δ (BZCYYb) anode-supported H-SOFC (H-DASC) for on-cell CO 2 dry reforming of CH 4 (DRC). For demonstrating the effectiveness of LSCrN@Ni, a cell without adding the LSCrN@Ni catalyst (H-CASC) is also studied comparatively. Fueled with H 2 , both H-CASC and H-DASC show similar stable performance with a maximum power density ranging from 0.360 to 0.816 W cm −2 at temperatures between 550 and 700 °C. When CO 2 –CH 4 is used as the fuel, the performance and stability of H-CASC decreases considerably with a maximum power density of 0.287 W cm −2 at 700 °C and a sharp drop in cell voltage from the initial 0.49 to 0.10 V within 20 h at 0.6 A cm −2 . In contrast, H-DASC demonstrates a maximum power density of 0.605 W cm −2 and a stable cell voltage above 0.65 V for 65 h. This is attributed to highly efficient on-cell DRC by LSCrN@Ni.more » « less
-
Membrane reactors (MR) are known for their ability to improve the selectivity and yield of chemical reactions. In this paper, a novel high-pressure MR employing a liquid sweep was applied to the methanol synthesis (MeS) reaction, aiming to increase the per single-pass conversion. For carrying-out the reaction, an asymmetric ceramic membrane was modified with a silylating agent in order to render its pore surface hydrophobic. A commercial MeS catalyst was used for the reaction, loaded in the MR shell-side, while the tube-side was swept with a high boiling point organic solvent with high solubility towards methanol. The membrane reactor was studied under a variety of experimental conditions (different pressures, temperatures, space times, and liquid sweep flow rates) and showed improved carbon conversion when compared to the conventional packed-bed reactor operating under the same conditions.more » « less
