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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.

 

In this study, we simulated BZY electrolyte-supported proton-conducting solid oxide cell by coupling surface defect chemistry reaction with charged species transport. We validated the model parameters by concentration as a function of temperature, conductivity under dry and wet oxygen as a function of oxygen partial pressure and temperature. The results indicate that the high electron-hole mobility (diffusivity) is mainly responsible for the high leaking current under high temperatures. The Faradaic efficiency stays low or even negative under low operating voltage or high temperature and plateaus as the cell voltage increases. The model developed in this study is a useful tool to understand the leaking current in BZY electrolyte and provide design strategies to avoid/mitigate such significant inefficiency for water electrolysis operation. 

To meet 2050 decarbonization goals, Massachusetts will not be able to rely on carbon intensive energy sources (e.g. natural gas and gasoline) and hydrogen has been considered a replacement. To produce hydrogen without carbon emissions, renewable energy sources will be used to power electrolyzer stacks. However, renewable energy sources will also be in high demand for other energy sectors, such as automobiles and electrification. This paper estimates the amount of wind energy needed to replace natural gas with hydrogen and electrify automobiles. Comparisons are also made for a scenario in which heat pumps are used to replace natural gas. These energy sectors represent the bulk of energy consumed within Massachusetts and are of high interest to stakeholders globally. The analysis reveals the daunting amount of wind energy needed for replacement and that it is highly unlikely for hydrogen to replace natural gas in time to meet the state’s climate goals.

 

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.

 

High-temperature solid/molten-carbonate composite represent an emerging class of CO₂transport membranes to capture CO₂from flue gas with advantages in flux density and selectivity over conventional solvent/sorbent- and polymer-based counterparts. While significant technical progress in these membranes has been made in the past years, a deeper fundamental understanding of CO₂transport mechanisms is still limited. Aimed to bridge this gap, we here report a theoretical study on flux performances of four types of solid/molten-carbonate CO₂transport membranes by analytical and numerical modeling. We found that analytical and numerical results are virtually identical for solids with single charge carrier. However, for mixed conducting solids, numerical methods are preferred since analytical methods cannot solve the nonlinear local concentrations of charge carriers. Application of numerical method to a new three-phase membrane containing a mixed conducting solid, a pure electron conducting solid and molten-carbonate reveals a ∼90% increase in CO₂flux compared to the two-phase (mixed conducting solid and molten-carbonate) counterpart. The models presented here are expected to provide better fundamental insights and guidance for designing next-generation high-performance CO₂transport membranes.

 

In this work, a plain glassy carbon electrode has been investigated as a base platform to build a superoxide-ion-involved, 2-dimensional, multi-physics model to describe its oxygen reduction mechanism in caustic media. A rotating ring disk technique has been used to quantify the peroxide content and to compare the results predicted by a general multiphysics model, which was further used to extract the influencing kinetic parameters. There are three proposed models involving different mechanism combinations made up of: a sequential, single electron reduction of oxygen to superoxide, then to peroxide; a sequential two electron reduction of oxygen to peroxide followed by the final reduction to hydroxide; and a direct four electron reduction of oxygen straight to hydroxide. One model stands out to be the best description for the multistep oxygen reduction behavior of the glassy carbon electrode in 0.1 M KOH with very satisfactory results, which yields a series of important electrode kinetic transfer coefficients and exchange current densities for the elementary electrochemical reactions considered.