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In this work, a novel structure of a hydrogen-membrane reactor coupling HI decomposition and CO2 methanation was proposed, and it was based on the adoption of silica membranes instead of metallic, according to their ever more consistent utilization as nanomaterial for hydrogen separation/purification. A 2D model was built up and the effects of feed flow rate, sweep gas flow rate and reaction pressure were examined by CFD simulation. This work well proves the feasibility and advantage of the membrane reactor that integrates HI decomposition and CO2 methanation reactions. Indeed, two membrane reactor systems were compared: on one hand, a simple membrane reactor without proceeding towards any CO2 methanation reaction; on the other hand, a membrane reactor coupling the HI decomposition with the CO2 methanation reaction. The simulations demonstrated that the hydrogen recovery in the first membrane reactor was higher than the methanation membrane reactor. This was due to the consumption of hydrogen during the CO2 methanation reaction, occurring in the permeate side of the second membrane reactor system, which lowered the amount of hydrogen recovered in the outlet streams. After model validation, this theoretical study allows one to evaluate the effect of different operating parameters on the performance of both the membrane reactors, such as the pressure variation between 1 and 5 bar, the feed flow rate between 10 and 50 mm3/s and the sweep gas flow rate between 166.6 and 833.3 mm3/s. The theoretical predictions demonstrated that the best results in terms of HI conversion were 74.5% for the methanation membrane reactor and 67% for the simple membrane reactor. [ABSTRACT FROM AUTHOR]

The modern world's major challenges, such as global warming, air pollution, and increasing energy demands, escalate the importance of sustainable development and transition toward renewables using innovative and environmentally friendly solutions, such as intensifying chemical processes, to reduce carbon footprints effectively. Aiming to enhance the process toward negative carbon emissions, this perspective explores the intensified membrane reactors for reducing the energy intensity of converting biogas into methanol, a versatile chemical feedstock, and renewable liquid fuel. Syngas and methanol synthesis processes, catalysts, and membranes were explored, and novel reactor designs were proposed. Introduction of selective membranes into the catalytic reaction zone to combine synthesis separation steps could enhance the system efficiency and intensify the process by recycling energy and materials, besides reducing costs and required energy for the separation process: the continuous harnessing of products shifts reactions toward desired species while recycling energy and materials enhances the process efficiency, and separating water from methanol reduces the required energy and costs of extra processes for methanol separation. The successful implementation of this technology holds significant promise for sustainable developments in producing chemicals and renewable fuel from renewable biogas and reducing methane and carbon dioxide emissions toward achieving carbon‐negative technologies. [ABSTRACT FROM AUTHOR]

One of the biggest environmental concerns caused by coal-fired power plants is the emission of mercury (Hg), which is toxic metal. To control the emission of Hg from coal-derived flue gas, it is important to understand the behavior and speciation of Hg as well as the interaction between Hg and solid materials in the flue gas stream. In this study, atomic-scale theoretical investigations using density functional theory (DFT) were carried out in conjunction with laboratory-scale experimental studies to investigate the adsorption behavior of Hg on hematite (α-Fe2O3). According to the DFT simulation, the adsorption energy calculation proposes that Hg physisorbs to the α-Fe2O3(0001) surface with an adsorption energy of −0.278 eV, and the subsequent Bader charge analysis confirms that Hg is slightly oxidized. In addition, Cl introduced to the Hg-adsorbed surface strengthens the Hg stability on the α-Fe2O3(0001) surface, as evidenced by a shortened Hg-surface equilibrium distance. The projected density of states (PDOS) analysis also suggests that Cl enhances the chemical bonding between the surface and the adsorbate, thereby increasing the adsorption strength. In summary, α-Fe2O3has the ability to adsorb and oxidize Hg, and this reactivity is enhanced in the presence of Cl. For the laboratory-scale experiments, three types of α-Fe2O3nanoparticles were prepared using the precursors Fe(NO3)3, Fe(ClO4)3, and FeCl3, respectively. The particle shapes varied from diamond to irregular stepped and subrounded, and particle size ranged from 20 to 500 nm depending on the precursor used. The nanoparticles had the highest surface area (84.5 m2/g) due to their highly stepped surface morphology. Packed-bed reactor Hg exposure experiments resulted in this nanoparticles adsorbing more than 300 μg Hg/g. The Hg LIII-edge extended X-ray absorption fine structure spectroscopy also indicated that HgCl2physisorbed onto the α-Fe2O3nanoparticles. Implications: Atomic-scale theoretical simulations proposes that Hg physisorbs to the α-Fe2O3(0001) surface with an adsorption energy of −0.278 eV, and the subsequent Bader charge analysis confirms that Hg is slightly oxidized. In addition, Cl introduced to the Hg-adsorbed surface strengthens the Hg stability on the α-Fe2O3(0001) surface, as evidenced by a shortened Hg-surface equilibrium distance. The PDOS analysis also suggests that Cl enhances the chemical bonding between the surface and the adsorbate, thereby increasing the adsorption strength. Following laboratory-scale experiment of Hg sorption also shows that HgCl2physisorbs onto α-Fe2O3nanoparticles which have highly stepped structure. [ABSTRACT FROM AUTHOR]

Vanadium and its surface oxides were studied as a potential nitrogen-selective membrane material for indirect carbon capture from coal or natural gas power plants. The effects of minor flue gas components (SO2, NO, NO2, H2O, and O2) on vanadium at 500-600 °C were investigated by thermochemical exposure in combination with X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and in situ X-ray diffraction (XRD). The results showed that SO2, NO, and NO2 are unlikely to have adsorbed on the surface vanadium oxides at 600 °C after exposure for up to 10 h, although NO and NO2 may have exhibited oxidizing effects (e.g., exposure to 250 ppmv NO/N2 resulted in an 2.4 times increase in surface V2O5 compared to exposure to just N2). We hypothesize that decomposition of surface vanadium oxides and diffusion of surface oxygen into the metal bulk are both important mechanisms affecting the composition and morphology of the vanadium membrane. The results and hypothesis suggest that the carbon capture performance of the vanadium membrane can potentially be strengthened by material and process improvements such as alloying, operating temperature reduction, and flue gas treatment. [ABSTRACT FROM AUTHOR]

Material characterization, hydrogen permeation, and separation properties of a novel ternary Pd 82 Ag 15 Y 3 membrane were evaluated by feeding single gases and several mixtures at temperature and pressure ranges of 300 – 600 °C and 1.0–3.0 bar (abs), respectively. The Pd 82 –Ag 15 –Y 3 membrane was prepared by cold rolling and was characterized by ∼38 μm of thickness. When exposed to air at different temperature and constant pressure of 1 bar, the membrane showed good thermal and chemical stability. In particular, its surface area increased from 615 μm2 at 25 °C to 685 μm2 at 500 °C indicating a potential improvement of hydrogen permeation. However, several agglomerates consisting of metal oxides were formed on the surface at the highest temperature. The temperature was -then- kept constant at 400 °C and the pressure was varied to analyze the effects of singles gases and several mixtures on the hydrogen permeation characteristics. When exposed to pure gases, such as H 2 and N 2 , the membrane showed an H 2 permeability of 9.1 × 10−11 mol m−1 s−1.Pa−0.9 and "n" value of 0.9 due to the presence of Y, while no N 2 was detected in the permeate stream, respectively. So, the membrane was considered to be completely selective towards H 2 permeation. When mixtures were used, the hydrogen permeation decreased by its original value due to the presence of other gases, such as N 2 , CH 4 , CO 2 and CO. The presence of CO particularly affected the H 2 permeating flux due to the competitive adsorption of both gases on the Pd-alloy surface. Finally, the Scanning Electron Microscope (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), Atomic Force Microscope (AFM) and X-ray diffraction (XRD) analysis were performed to observe any changes in the surface and structure of pristine and used membrane. • The Pd 82 Ag 15 Y 3 membrane showed good thermal and chemical stability when exposed to air at different temperature. • The Pd 82 Ag 15 Y 3 membrane showed higher permeability than Pd–Ag due to the presence of Y, which increased H 2 solubility. • No changes observed on the membrane's morphology with gases exposure except with O 2. • The hydrogen permeation flux decreased by 41% with CO exposure at 400 °C. [ABSTRACT FROM AUTHOR]