High CH4 Research Articles

A numerical study to determine proper steam-to-fuel ratio in a biogas-fueled solid oxide fuel cell for different levels of biogas methane content

It is vital to find the optimal quantity of water added to the fuel in a biogas-fueled Solid Oxide Fuel Cell (SOFC). An under-optimal water quantity can impede steam reforming reactions, while an over-optimal quantity of water (which is equivalent to reduced biogas portion) may reduce the performance of the fuel cell due to a shortage of fuel. Water production in electrochemical reactions and the carbon deposition constraint add to the complexity of water quantity optimization. The present work develops a 3D numerical model to simulate a direct biogas-fueled SOFC to find the optimal steam/biogas (S/C) ratio. Several biogas mixtures (CH4/CO2 ratios) are analyzed. For each mixture, a wide range of S/C ratios is evaluated in a wide range of voltages. It is found that the polarization curves corresponding to different S/C ratios intersect each other for a given biogas mixture. In other words, an S/C ratio can be optimal at some voltages and non-optimal at others. Based on power density maximization as an explicit criterion, the optimal S/C ratio is found to be 0.75 at low CH4 molar fractions (~50%) and 1.25 at high CH4 molar fractions (~75%).

In Situ Loading of Cu Nanocrystals on CsCuCl3 for Selective Photoreduction of CO2 to CH4.

Rational design and facile synthesis of efficient environmentally friendly all-inorganic lead-free halide perovskite catalysts are of great significance in photocatalytic CO2 reduction. Aiming at photogenerated charge carrier separation and CO2 reaction dynamics, in this paper, a CsCuCl3 /Cu nanocrystals (NCs) heterojunction catalyst is designed and synthesized via a simple acid-etching solution process by using Cu2 O as the sacrificed template. Due to the disproportionation reaction of Cu2 O induced by concentrated hydrochloric acid, Cu NCs can be deposited onto the surface of CsCuCl3 microcrystals directly and tightly. As revealed by photoelectrochemical analysis, in situ Fourier transform infrared spectra, etc., the Cu NCs contribute a lot to extracting photoelectrons of CsCuCl3 to improve the charge separation efficiency, regulating the CO2 adsorption and activation, and also stabilizing the reaction intermediates. Therefore, CsCuCl3 /Cu heterojunction exhibits a total electron consumption rate of 58.77µmol g-1 h-1 , which is 2.9-fold of that of single CsCuCl3 . Moreover, high CH4 selectivity of up to 92.7% is achieved, which is much higher than that of CsCuCl3 (50.4%) and most lead-free halide perovskite-based catalysts. This work provides an ingenious but simple strategy to rationally design cocatalysts in situ decorated perovskite catalysts for manipulating both the catalytic activity and the product selectivity.

High-capacity dynamic exclusion for highly efficient dilute C2H2 separation from CO2 and multicomponent mixture in robust ultramicroporous MOF by topology regulation

Acquiring high C2H2 adsorption capacity and effectively separating it from the most difficult-to-separate byproduct CO2 in a dilute state are crucial for obtaining high productivity/purity monomer for polymers. Here, we address this challenge through topology regulation of fluorinated ultramicroporous metal–organic framework, producing a new hydrolytically stable adsorbent, ZUL-500. Uncovered by X-ray diffraction and modeling, a more favorable spatial distribution of GeF62- anions for C2H2 recognition is realized in sql topological ZUL-500 compare to ZU-32 with the same anion and metal node but pcu topology, offering remarkably increased C2H2 affinity and amplified C2H2/CO2 affinity difference that affords a dynamic exclusion of CO2 but excellent C2H2 adsorption in fixed-bed separation even for industrial-related mixtures (up to 8 components). Excellent values were simultaneously obtained for C2H2 uptake capacity, C2H2/CO2 separation factor and C2H2 productivity, coupled with good mass transfer and recyclability, providing exceptional productivity (2.92 ∼ 3.48 mmol g−1) of high purity (≥99.6%) C2H2 from mixtures.

Do beaver ponds increase methane emissions along Arctic tundra streams?

Beaver engineering in the Arctic tundra induces hydrologic and geomorphic changes that are favorable to methane (CH4) production. Beaver-mediated methane emissions are driven by inundation of existing vegetation, conversion from lotic to lentic systems, accumulation of organic rich sediments, elevated water tables, anaerobic conditions, and thawing permafrost. Ground-based measurements of CH4 emissions from beaver ponds in permafrost landscapes are scarce, but hyperspectral remote sensing data (AVIRIS-NG) permit mapping of ‘hotspots’ thought to represent locations of high CH4 emission. We surveyed a 429.5 km2 area in Northwestern Alaska using hyperspectral airborne imaging spectroscopy at ∼5 m pixel resolution (14.7 million observations) to examine spatial relationships between CH4 hotspots and 118 beaver ponds. AVIRIS-NG CH4 hotspots covered 0.539% (2.3 km2) of the study area, and were concentrated within 30 m of waterbodies. Comparing beaver ponds to all non-beaver waterbodies (including waterbodies >450 m from beaver-affected water), we found significantly greater CH4 hotspot occurrences around beaver ponds, extending to a distance of 60 m. We found a 51% greater CH4 hotspot occurrence ratio around beaver ponds relative to nearby non-beaver waterbodies. Dammed lake outlets showed no significant differences in CH4 hotspot ratios compared to non-beaver lakes, likely due to little change in inundation extent. The enhancement in AVIRIS-NG CH4 hotspots adjacent to beaver ponds is an example of a new disturbance regime, wrought by an ecosystem engineer, accelerating the effects of climate change in the Arctic. As beavers continue to expand into the Arctic and reshape lowland ecosystems, we expect continued wetland creation, permafrost thaw and alteration of the Arctic carbon cycle, as well as myriad physical and biological changes.

Methane and nitrous oxide emissions from rice grown on organic soils in the temperate zone

Organic soils are important carbon stocks. The conventional (dry) cultivation of these soils turns them into strong sources of greenhouse gas (GHG) emissions. For situations where restoration of natural land cover is not possible, solutions to this problem include the wet cultivation of these soils, reducing CO2 and N2O emissions. One option, paddy rice cultivation, has begun in the Swiss Central Plateau, which hitherto did not provide a suitable climate for wet rice. Wet rice is however associated with high CH4 emissions. These need to be quantified for this region, as the increased CH4 fluxes might negate the expected reductions in CO2 and N2O. Here, we quantify CH4 and N2O emissions from wet rice on organic soil with chamber measurements, in an outdoor mesocosm experiment in the Swiss Central Plateau, located in the cool temperate moist zone. We apply two water treatments (a high water table (WT) treatment, − 6 cm with mid-season drainage, and two medium WT treatments, − 11 and − 17 cm without mid-season drainage) and additionally test the use of a mineral cover layer to reduce N2O emissions. Additionally, a deeply-drained grassland treatment is used as a reference treatment. Annual CH4 emissions from rice cultivation are 6.2 g CH4.m-2.a-1 for the higher WT treatment, 6.4 g CH4.m-2.a-1 for the medium WT treatment and 2.4 g CH4.m-2.a-1 for the medium WT treatment with mineral cover. The corresponding N2O emissions are 203, 190 and 56 mg N2O-N.m-2.a-1, respectively. These results show that adding a mineral cover layer reduces annual emissions from both GHGs substantially. In total, the maximum increase in CH4 and N2O emissions resulting from rice cultivation, compared to the drained grassland treatment, is 2.3 t CO2-eq.ha-1.a-1. Expected CO2 emissions savings (derived from a literature-based model) due to a higher WT are a factor of 5–9 greater than this. We thus conclude that the cultivation of these organic soils in this region with wet rice could reduce their induced warming compared to their cultivation with (deeply drained) grassland.

Fabrication of the coke-resistant and easily reducible Ni/SiC catalyst for CO2 methanation

The catalytic methanation of carbon dioxide, which is a promising process for CO2 to fuels, has been extensively investigated using Ni-based catalysts due to their high CH4 selectivity, high CO2 conversion, and affordability. However, owing to its highly exothermic nature, CO2 methanation can cause severe carbon deposition and sintering effects, resulting in catalyst deactivation. This is where high thermal conductivity SiC presents itself as a viable alternative support to enhance the performance of Ni-based catalysts. In this work, Ni catalysts supported on a cheap commercial SiC were prepared by wet impregnation method with different Ni loadings and calcination temperatures. The as-prepared and spent catalysts were characterized using N2 physisorption, X-ray diffraction, H2 temperature-programmed reduction (H2-TPR), temperature-programmed oxidation (TPO) and transmission electron microscopy. H2-TPR analysis revealed that reduction at 400 °C for 15 min is enough to convert most of NiO to active Ni0 to archive the highest activity toward CO2 methanation. The catalytic performance and long-term stability of the as-prepared Ni/SiC catalysts were evaluated for CO2 methanation at stoichiometric CO2/H2 ratio of 1/4, different gas hourly space velocities, reaction temperatures, and reduction conditions. Among the synthesized catalysts, the 10%Ni/SiC-500 exhibited highest CO2 conversion (70%) and CH4 selectivity (98%) as well as stable catalytic performance for 30 h on stream at a GHSV of 20,000 h−1 and reaction temperature of 400 °C.

An Efficient Intercalation Supramolecular Structure for Photocatalytic CO2 Reduction to Ethylene Under Visible Light

AbstractPhotocatalytic CO2 reduction (CO2PR) into multi‐carbon products (especially C2H4) is a highly attractive route for global carbon cycle, however, which is seriously limited by sluggish C‐C coupling kinetics and competitive hydrogen evolution reaction (HER) and so on. Herein, the fabrication of a novel supramolecular assembly of NiAl‐Fe‐TCPP is reported by intercalating iron porphyrin (Fe‐TCPP) into NiAl‐layered double hydroxide (NiAl‐LDH), and the resultant NiAl‐Fe‐TCPP exhibit superior catalytic performance on CO2PR to C2H4 under visible light irradiation in presence of photosensitizer. A high C2H4 selectivity up to 93.4% in the carbon‐containing products with the production rate as high as 24.7 µmol h−1 can be achieved over NiAl‐Fe‐TCPP. The ex/in situ X–ray absorption spectoscopy (XAS) indicates that the electron transfer between NiAl‐LDH and Fe‐TCPP can promote the generation of low‐valence of Fe sites, resulting in the efficient production of C2H4. The spin‐polarized density functional theory (DFT) calculations find that the synergistic mechanism that CO2 molecules are activated to CO on NiAl‐LDH and then spilled to Fe‐TCPP and coupled to COCHO#, which is further reduced to C2H4, are feasible in the perspective of Gibbs free energy. Moreover, the strong host‐guest interactions between NiAl‐LDH and Fe‐TCPP lead to the promoted photocatalytic activity and superior cycle stability.

Pillar-layered metal-organic frameworks with benchmark C2H2/C2H4 and C2H6/C2H4 selectivity for one-step C2H4 production

Energy-efficient adsorptive separation shows great potential for the one-step production of high-purity ethylene (C2H4) from ternary C2 hydrocarbons. However, it remains a formidable challenge to fabricate high-performance adsorbents that exhibit simultaneous high selectivity (>2) towards acetylene/ethylene (C2H2/C2H4) and ethane/ethylene (C2H6/C2H4). Herein, we report a pillar-layered metal–organic framework, Ni(sdba)(dabco)0.5 (H2sdba = 4,4′-sulfonyldibenzoic acid; dabco = 1,4-diazabicyclo [2.2.2] octane), for preferential trapping of C2H6 and C2H2 over C2H4. The abundant accessible binding sites endow Ni(sdba)(dabco)0.5 with outstanding C2H2/C2H4 (2.28) and C2H6/C2H4 (2.47) selectivity with high C2H6 (3.15 mmol g−1) and C2H2 (4.41 mmol g−1) uptake among porous materials reported for one-step C2H4 purification. Dynamic breakthrough experiments demonstrated the feasibility of producing high-purity C2H4 (>99.9%) from C2H2/C2H6/C2H4 gas-mixtures (1/1/1 and 1/9/90, v/v/v) in a single step. Computational simulations reveal that the aromatic-rich pore spaces, which decorated with accessible interlayer uncoordinated oxygen atoms of sulfonyl groups and alkyl functionalities, can provide multiple C-H···O, C-H···π, and C-H···H interactions for selectively recognizing C2H6 and C2H2 over C2H4.

Nanoporous Fluorinated Covalent Organic Framework for Efficient C2H2/CO2 Separation with High C2H2 Uptake

Effective C2H2/CO2 separation is regarded as a crucial procedure in the C2H2 industry yet extremely challenging because of their similar physical and chemical properties. Covalent organic frameworks (COFs) have become a promising platform for gas adsorption separation, but they still suffer from unsatisfactory C2H2 adsorption capacity and selectivity. Herein, we report a nanoporous fluorine-functioned COF (TpPa-F) for C2H2/CO2 separation, which was synthesized by a mechanochemical approach with a F-containing precursor (2-fluoro-1,4-benzenediamine). A superior C2H2 adsorption capacity of 117 cm3/g (4.78 mmol/g) and a C2H2/CO2 selectivity of 3.3 at 298 K and 1 bar were achieved, which surpass most of the reported COF adsorbents in the literature. Notably, TpPa-F exhibited an extraordinary thermal stability of up to around 673 K and showed chemical robustness in organic or acidic/basic solutions. Theoretical calculations reveal the hydrogen bond interaction of C≡C–H···F, which contributes to the high C2H2 uptake and separation selectivity. This work provides a promising strategy of fluorine functionalization for enhancing the ability to recognize and separate small gas molecules in a large channel.

Precise Pore Engineering of fcu-Type Y-MOFs for One-Step C2 H4 Purification from Ternary C2 H6 /C2 H4 /C2 H2 Mixtures.

The purification of C2 H4 from C2 H6 /C2 H4 /C2 H2 mixtures is of great significance in the chemical industry for C2 H4 production but remains a daunting task. Guided by powerful reticular chemistry principles, herein a systematic study is carried out to engineer pore dimensions and pore functionality of fcu-type Y-based metal-organic frameworks (Y-MOFs) through the construction of a series of eight new structures using linear dicarboxylate linkers with different length and functional groups. This study illustrates how delicate changes in pore size and pore surface chemistry can effectively influence the adsorption preference of C2 H6 , C2 H4 , and C2 H2 by the MOFs. Importantly, clear relations between pore size/pore surface polarity and C2 adsorption selectivities of this series of MOFs are established. In particular, HIAM-326 built on a linker decorated with trifluoromethoxy group shows notably preferential adsorption of C2 H6 and C2 H2 over C2 H4 , with balanced C2 H2 /C2 H4 and C2 H6 /C2 H4 selectivities. This endows the compound with the capability of one-step purification of C2 H4 from C2 H6 /C2 H4 /C2 H2 ternary mixtures, which is validated by breakthrough measurements where high purity C2 H4 (99.9%+) can be obtained directly from the separation column. Its adsorption thermodynamics and underlying selective adsorption mechanisms are further revealed by ab initio calculations.

Construction of π back donation active site in metal-organic framework for dense packing of C2H2 and efficient C2H2/CO2 separation

The separation of C2H2/CO2 is very important but still a great challenge in industry because of their very similar molecular sizes and physical properties. Considering that CuI site can form both π complex interactions and π back donation interactions with C2H2, herein, we achieved high C2H2 packing density and efficient C2H2/CO2 separation by anchoring CuI ions with synergistic dual-pyrazol sites of MOF-303. The adsorption experiments show that the resulting CuI@MOF-303 could quickly adsorb C2H2 in the low-pressure region, and the C2H2 packing density is up to 477.9 g/L at 1 bar and 298 K, which is higher than any reported adsorbents. The density functional theory calculations show that π back donation of CuI site in CuI@MOF-303 can strengthen the interaction between CuI@MOF-303 and C2H2 by providing electrons from d orbitals of CuI site to the unoccupied antibonding π* orbital of C2H2 molecule. In addition, the C2H2/CO2 selectivity of CuI@MOF-303 at 1 bar is 25.9, which is 6.0 times of the original MOF-303. Breakthrough experiments show that CuI@MOF-303 has good separation performance for C2H2/CO2 gas mixtures, featuring both high C2H2 uptake and high separation factor of 10.6. Satisfyingly, fuel-grade C2H2 (purity ＞ 98.2 %, 82.83 cm3/cm3) can be obtained after desorption. Moreover, CuI@MOF-303 also has good C2H2 adsorption cycle stability and C2H2/CO2 separation regeneration ability, which indicates that it has great potential in industrial C2H2 purification.

Tailoring Carbon Deposits on a Single-Crystal Cobalt Catalyst for Fischer–Tropsch Synthesis without Further Reduction: The Role of Surface Carbon and Penetrating Carbon

The preparation of Fischer–Tropsch synthesis (FTS) catalysts that exhibit excellent catalytic performance and are suitable for direct use in a fixed-bed reactor without further reduction is crucial in industrial applications. However, only marginal progress has been made with respect to the preparation of cobalt-based FTS catalysts owing to tendency of metallic cobalt to oxidize easily; this tendency necessitates the activation of these catalysts via reduction despite having undergone reduction treatment during their preparation. Herein, this problem has been addressed by tuning the carbon deposits (surface C and penetrating C) on the surface of a single-crystal cobalt catalyst. Screen-like surface C on a catalyst pretreated with 5% CO (p-Co–CO) exhibits diffusion suppression and chemical inertness to oxidizing gas, thus preventing the oxidation of metallic cobalt and resulting simultaneously in high activity and low CH4 selectivity (7.2%) without requiring further reduction. Moreover, the exact role of surface C and penetrating C deposited on cobalt catalysts in the FTS performance is explored. Both surface C and penetrating C enhance the activity of the cobalt catalyst but with opposite effects on the FTS selectivity. Surface C improves the adsorption ability of bridged-type CO and the formation of long-chain hydrocarbons, whereas penetrating C is conducive to adsorbing linear CO and increases undesired CH4 selectivity. This study clarifies the effect of deposited carbon on the FTS reaction and provides insights into the design of high-performance nonconventional FTS catalysts that do not require further reduction.

Engineering the Interface and Interaction Structure on Highly Coke-Resistant Ni/CeO2-Al2O3 Catalyst for Dry Reforming of Methane

Designing and tailoring metal-support interaction in Ni-based catalysts with plentiful interfacial sites is of significant interest for achieving a targeted catalytic performance in dry reforming of methane (DRM), but remains as a challenging task. In this work, Ni/Al2O3 and Ni/CeO2-Al2O3 catalysts with the same strong metal-support interaction (SMSI) but distinct interface structure are developed by an improved evaporation-induced self-assembly method using pseudobohemite gel as aluminum source. Ni/CeO2-Al2O3 exhibits superior catalytic activity and stability in DRM in comparison with Ni/Al2O3. The highest CH4 and CO2 conversion reaches at 71.4% and 82.1% for Ni/CeO2-Al2O3, which are higher than that of 64.3% and 75.6% for Ni/Al2O3 at 700 °C. The SMSI effect in Ni/CeO2-Al2O3 provides more active interfacial sites with less coke deposition, and promotes the generation of active formate species which are the key intermediates for DRM. The findings of the present work could possibly pave the way for fabricating catalysts with SMSI strategy for efficient heterogeneous catalysis.

Single-site decorated copper enables energy- and carbon-efficient CO2 methanation in acidic conditions

Renewable CH4 produced from electrocatalytic CO2 reduction is viewed as a sustainable and versatile energy carrier, compatible with existing infrastructure. However, conventional alkaline and neutral CO2-to-CH4 systems suffer CO2 loss to carbonates, and recovering the lost CO2 requires input energy exceeding the heating value of the produced CH4. Here we pursue CH4-selective electrocatalysis in acidic conditions via a coordination method, stabilizing free Cu ions by bonding Cu with multidentate donor sites. We find that hexadentate donor sites in ethylenediaminetetraacetic acid enable the chelation of Cu ions, regulating Cu cluster size and forming Cu-N/O single sites that achieve high CH4 selectivity in acidic conditions. We report a CH4 Faradaic efficiency of 71% (at 100 mA cm−2) with <3% loss in total input CO2 that results in an overall energy intensity (254 GJ/tonne CH4), half that of existing electroproduction routes.

High-rate and selective conversion of CO2 from aqueous solutions to hydrocarbons

Electrochemical carbon dioxide (CO2) conversion to hydrocarbon fuels, such as methane (CH4), offers a promising solution for the long-term and large-scale storage of renewable electricity. To enable this technology, CO2-to-CH4 conversion must achieve high selectivity and energy efficiency at high currents. Here, we report an electrochemical conversion system that features proton-bicarbonate-CO2 mass transport management coupled with an in-situ copper (Cu) activation strategy to achieve high CH4 selectivity at high currents. We find that open matrix Cu electrodes sustain sufficient local CO2 concentration by combining both dissolved CO2 and in-situ generated CO2 from the bicarbonate. In-situ Cu activation through alternating current operation renders and maintains the catalyst highly selective towards CH4. The combination of these strategies leads to CH4 Faradaic efficiencies of over 70% in a wide current density range (100 – 750 mA cm-2) that is stable for at least 12 h at a current density of 500 mA cm-2. The system also delivers a CH4 concentration of 23.5% in the gas product stream.

Numerical study on pollutant emissions characteristics and chemical and physical exergy analysis in Mild combustion

This analytical study appraises the emission characteristics of different pollutants such as CO and NOX as well as conducting chemical and physical exergy analyses on conventional and Mild combustion regimes. The RANS turbulence approach and the k-ε RNG model were utilized in this study to simulate turbulence, whereas the eddy dissipation concept (EDC) model and the GRI–Mech 2.11 chemical mechanism were adopted to treat the turbulence-chemistry interaction. This study evaluated local and global pollutant emissions and exergy efficiency along the reacting jet and explored the effects of temperature and chemical species on the physical and chemical exergies in MILD combustion in comparison to conventional combustion. It is found that the overall exergy efficiency of MILD combustion rises by 1, 3, and 4% for oxygen mass fractions of 3, 6, and 9% in hot oxidizer coflow, with the NOx emissions are 81, 72, and 55% lower than conventional combustion, respectively. Chemical exergy is greater than physical exergy near the fuel nozzle due to high CH4 and H2 concentrations. Chemical exergy reduces along the burner due to chemical reactions, while physical exergy increases due to the increased temperature. However, owing to the trade-off between these two exergies along the flame jet, the total exergy approaches a constant value at large distances from the burner. The maximum total exergy occurs at a distance of 0.12 m from the fuel nozzle, with chemical exergy accounting for 83% of the total exergy. In the outlet (0.5 m from the fuel nozzle), chemical exergy accounts only for 30% of the total exergy. It can also be concluded that the exergy is stabilized at a distance of 0.3 m from the nozzle (60% of the domain length). Despite a higher local CO emission in conventional combustion than in MILD combustion, the CO emission substantially decreases at a smaller distance from the nozzle in conventional combustion due to the high O2 concentration.

Characteristics of methane emissions from alpine thermokarst lakes on the Tibetan Plateau

Understanding methane (CH4) emission from thermokarst lakes is crucial for predicting the impacts of abrupt thaw on the permafrost carbon-climate feedback. However, observational evidence, especially from high-altitude permafrost regions, is still scarce. Here, by combining field surveys, radio- and stable-carbon isotopic analyses, and metagenomic sequencing, we present multiple characteristics of CH4 emissions from 120 thermokarst lakes in 30 clusters along a 1100 km transect on the Tibetan Plateau. We find that thermokarst lakes have high CH4 emissions during the ice-free period (13.4 ± 1.5 mmol m−2 d−1; mean ± standard error) across this alpine permafrost region. Ebullition constitutes 84% of CH4 emissions, which are fueled primarily by young carbon decomposition through the hydrogenotrophic pathway. The relative abundances of methanogenic genes correspond to the observed CH4 fluxes. Overall, multiple parameters obtained in this study provide benchmarks for better predicting the strength of permafrost carbon-climate feedback in high-altitude permafrost regions.

Chemically and biologically driven carbon transformation flow in MSW leachate treated by a high-solids anaerobic membrane bioreactor system

Carbon transformation is important for an anaerobic process but is often overlooked when using an anaerobic membrane bioreactor (AnMBR). Material flow in an AnMBR treating calcium-rich MSW leachate was thus quantitatively investigated to illustrate how chemical and biological factors affect carbon transformation. The results show that a remarkable amount of carbon in the leachate was degraded, with 50.1% of it should be converted into CH4 and 37.7% of it into CO2. However, a much smaller value of 40.6% and 14.2% were experimentally obtained. Chemical analysis indicated that the precipitation of calcium carbonate captured 1.23 g/day of carbon. At the same time, about 23.2 g/L HCO3− and 16.6 mg/L CH4 (both as carbon) were dissolved in the liquid. Those features facilitated the high CH4 (74%) content in biogas. A carbon transformation model was therefore established and showed carbon flow into the gas, liquid, and solid phases, respectively. Carbon existed in biogas, permeate, and discharged sludge was also obtained.

Experimental investigation of hydrogen-intensified synthetic natural gas production via biomass gasification: a technical comparison of different production pathways

A sustainable and secure energy supply requires alternative concepts for energy generation. Utilizing biomass to produce synthetic natural gas (SNG) allows the synthesis of a currently widely used energy carrier on a renewable basis. The additional integration of hydrogen increases the carbon utilization of the biomass. This study experimentally investigates and compares the production of raw-SNG in three novel process chain configurations combining the advanced dual fluidized bed (DFB) gasification technology, gas cleaning units, and a fluidized bed methanation reactor. The three process chains comprise the direct methanation of DFB product gas, a hybrid route with hydrogen addition to the DFB product gas, and the methanation of a hydrogen-enriched product gas generated through DFB gasification with in situ CO2 removal (SER process). The direct methanation of the DFB product gas yielded a raw-SNG CH4 content of 40 vol.-%db at 360 °C and atmospheric pressure conditions. Through the integration of external hydrogen in a hybrid process, the carbon utilization of the biomass could be increased from 37% to around 70% at an unchanged cold gas efficiency of 58–59%. Via the SER process, a high raw-SNG CH4 content of 70 vol.-%db was achieved at an increased cold gas efficiency of 66% without the need for external hydrogen. Finally, a comparison points out the main advantages of the process configurations and provides a decision basis for novel SNG production pathways.

Highly Efficient Synthesis of High‐Value Olefins from Syngas over Layered Fe‐Mn/Magadiite Catalyst

AbstractThe simultaneous realization of high olefin/paraffin (O/P) ratio and low CH4 selectivity has always been a bottleneck for the conversion of syngas to high‐value olefins (HVOs). Magadiite (MAG) is a layered silicate material with active SiOH, which increases the interlayer charge density and ion‐exchange ability. Herein, a MAG‐supported, Mn‐modified Fe3O4 microsphere catalyst exhibits excellent CO conversion of 76.5 % and HVO selectivity, with a high O/P ratio of 5.02 and low CH4 selectivity of 16.1 % for conversion of syngas to HVOs. The layered structure of the MAG support promotes dispersion of the active centers and the Mn promoter improves the basic properties of the catalyst. Moreover, the Mn promoter and MAG support have a synergistic effect, which promotes CO dissociation and suppresses H2 adsorption, thereby resulting in high HVO selectivity and low CH4 selectivity.