Methane Conversion Efficiency Research Articles

In situ generation of active ⋅OH on Co-SrTiO3 tandem catalyst for conversion of methane to methanol

Recently in <i>Chem Catalysis</i>, He and co-workers proposed the efficient conversion of methane to methanol under moderate conditions via the active O species <i>in situ</i> generated from photo-splitting of H₂O over Co-SrTiO₃ tandem catalysts. Using characterization techniques, the authors determined the intermediates and mechanism of the reaction.

Experimental investigation into stationary operated, thermochemical recuperation applied to a 200 kW industrial scale oxy-fuel furnace

Efficiency optimizations of industrial processes will play a key role in future actions reducing the global greenhouse gas emissions. This also applies to the industrial high temperature sector whereby the approach of thermochemical recuperation (TCR) is promising for such applications. The current paper thus presents the first report of experimental investigations into TCR in industrial scale (200 kW power input) and in recuperative mode with combined steam reforming and partial oxidation of methane applied inside the reactor. In contrast to previous investigations in industrial scale reported, which exclusively focused on regenerative concepts, the use of oxygen as part of the reactants plays a key role with respect to the following aspects: (I) Methane conversion: CH4 conversion rates higher than 80% were observed for all adjusted operation points. Efficient conversion of methane to syngas was thus provided by the approach. (II) Temperature control: The addition of oxygen influenced the temperature distribution inside the reactor considerably, causing an increase of the average temperature from 771°C to 801°C. Consequently, oxygen addition is an appropriate method for temperature control inside the reactor. (III) Efficiency: The furnace power input was increased by a maximum of 12.1% compared to conventional oxy-fuel combustions without TCR.

Effect of heat loss on the syngas production by fuel-rich combustion in a divergent two-layer burner

The effect of heat loss on the syngas production from partial combustion of fuel-rich in a divergent two-layer burner is numerically studied using two-dimensional model with detailed kinetics GRI-Mech 1.2. Both the radiation and wall heat losses to the surrounding are considered in the computations. It is shown that two types heat losses have different effects on the syngas production. The radiation heat loss has significant effect on the syngas temperature and the syngas temperature is dropped as radiation heat loss is increased, but it has neglected effect on the reforming efficiency and methane conversion efficiency. The wall heat loss has a comprehensive effect on the syngas production. The wall heat loss not only reduces the conversion efficiency, but also significantly decreases the syngas temperature. The effect of wall heat loss becomes weak as the equivalence is increased. The reforming efficiency drops from 0.440 to 0.424 for equivalence ratio of 2 and mixture velocity of 0.17 m/s for the predictions between adiabatic wall and non-adiabatic conditions. • Heat loss on syngas production in divergent porous burner is conducted with detailed kinetics. • Radiant heat loss to the surrounding significantly reduces the syngas temperature. • Radiant heat loss has little effect on the methane conversion efficiency and reforming efficiency. • Wall heat loss has a comprehensive effect on the reforming efficiency and syngas temperature. • Effect of wall heat loss on the syngas production becomes strong with the equivalence ratio.

High efficient thermochemical energy storage of methane reforming with carbon dioxide in cavity reactor with novel catalyst bed under concentrated sun simulator

Thermochemical energy storage performance of methane reforming with carbon dioxide in cavity reactor under concentrated sun simulator has been experimentally and numerically studied. Novel catalyst bed with Ni/Al2O3 particles and perforated quartz encapsulation is proposed to perform high bed temperature for greenhouse effect, and then chemical energy storage efficiency and total energy utilization efficiency of experimental system can respectively reach as high as 41.1% and 80.3%. As concentrated heat flux increases or reactant flow rate decreases, methane conversion rises with bed temperature increasing, while chemical energy storage efficiency first rises and then falls for larger heat loss. As inlet mole fraction of methane increases, chemical energy storage efficiency firstly increases and then drops. Numerical model of cavity reactor under concentrated heat flux is established and validated. In catalyst bed, maximum reaction rate occurs near focal point, while reverse reaction occurs near its side. With the improvement of porosity in catalyst bed, methane conversion and thermochemical storage efficiency firstly increase and then decrease, while they gradually increase with heat conductivity of bed rising. In addition, optimal concentrated heat flux, flow rate, mole fraction of methane (0.5) and bed porosity (0.6) are derived for maximum chemical energy storage efficiency.

The Efficiency of Pd Addition and Sr Substitution on La1−xSrxMnO3 to Remove Ventilation Air Methane in a Catalytic Flow Reversal Reactor

Ventilation air methane (VAM) is the main cause of greenhouse gas emissions in coal mining. Catalytic flow reverse reactor (CFRR) is widely used in VAM to mitigate methane emissions. In this study, palladium (Pd) and La1−xSrxMnO3 were used as catalysts in a CFRR. Different types of catalysts were prepared by loading La0.8Sr0.2MnO3, La0.9Sr0.1MnO3, and 0.1%Pd-La0.9Sr0.1MnO3 on a cordierite honeycomb reactor coated with γ-Al2O3 to compare their performances. In addition, this study compared the performance of the three catalysts in an 800 °C reactor based on different methane inlet concentrations, inlet speeds, and conversion times. The results showed: (1) 0.1% addition of Pd increased methane conversion. (2) La0.8Sr0.2MnO3 had higher efficiency at lower methane inlet concentrations, whereas La0.9Sr0.1MnO3 was more efficient at higher methane concentrations. This study demonstrates that a higher Sr loading is worth implementing only when the methane concentration of VAM is lower than 0.6%. (3) To achieve a higher methane conversion efficiency, the inlet velocity of methane should also be considered.

Highly selective oxidation of methane to formaldehyde on tungsten trioxide by lattice oxygen

Photocatalytic oxidation of methane into formaldehyde in high yield and selectivity remains a grand challenge due to the ineluctable intermediates. Here, we report that a {001}, {010} and {100} facets modified tungsten trioxide photocatalyst enables an intermediate-free oxidation of methane into formaldehyde with 99.4% selectivity. A durable formaldehyde yield of 4.61 mmol g−1 can be achieved after irradiation for 30 h. Mechanism studies disclose that surface defect and reactive lattice oxygen atom are crucial for the selectivity and productivity promotion. This work provides a valid paradigm for efficient conversion of methane to formaldehyde.

Electro Oxidation of Methane Under Ambient Conditions

Methane is one of the main components of natural gas, which is generally used as a worldwide energy source for daily and industrial activities. However, methane is also a kind of greenhouse gas, which has 30 times more global warming potential than that of CO2.[1] The severe methane leak problem has been underestimated for a long time. It was not gaining increasing attention until recently. Environmentally friendly converting methane to other value-added chemicals is attractive. The large-scale conventional methane reforming is under practical application that converts methane to methanol, but the two-steps endothermic reaction requires high energy input.[2] Effective decomposition of methane still remains challenging, due to the methane intrinsic chemical feature of high bond strength and high ionization potential. The unique symmetric structure makes it hard to break the C-H chemical bond and overcome the activation energy.[3] Several strategies have been built to achieve a lower energy consumption without CO2 emission, for example, photocatalyst technology, plasma technology, methanotrophs technology, electrosynthesis technology, etc. Among them, the electrosynthesis method stands out as the ideal one to oxidize methane to valuable oxygenates in a wide range of PH values and temperatures with an easy scale-up modular design.[4]In this report, we experimentally and theoretically explored the methane partial oxidation on FeNi(OH)x electrocatalysts under ambient conditions. The mixed transition metal hydroxide nanoplate compositions (Ni(OH)2, Fe10%Ni90%(OH)x, Fe20%Ni80%(OH)x, Fe30%Ni70%(OH)x, Fe50% Ni50%(OH)x) were synthesized by the facial hydrothermal method and characterized by SEM, TEM, HRTEM, XPS, and XRD techniques. The effect of incorporating Fe in the nickel hydroxide lamella structure was discussed. Evidently, Fe doping content modified the electrochemical property. We could manipulate the methane conversion process and promote the reaction selectivity by controlling the ratio of Fe in the prepared electrocatalysts. Of all the catalyst materials, Fe30%Ni70%(OH)x exhibited the best methane oxidation activity that greatly enhanced the catalytic performance. Electrochemical behavior studies were then developed in a three electrodes system to investigate methane activation regarding reaction time, applied potential, and methane partial pressure. The optimum electrode potential was determined, involving a key intermediate formation of methane activation. Under this potential, peroxide (NiOOH) formed, but oxygen evolution reaction (OER) onsite potential yet reached, thus the electrochemical performance could attain a relatively high methane oxidation current density and low competition with water oxidation. From cyclic voltammogram (CV) cycling evidence, a slight increase in the NiOOH anodic current and decrease in the OER oxidation peak current was observed in the presence of methane. The oxygenate products from methane electrooxidation were collected and analyzed by NMR and gas chromatograph (GC) instruments. Ethanol turned out to be the main product. The integrated design with ultrathin Fe30%Ni70%(OH)x nanosheet catalyst resulted in a maximum ethanol formation rate of 9.09 mmol/gcatalyst·h under 1.46 V vs. RHE with 87 % faradaic efficiency (FE) and 0.26 s-1 turnover frequency (TOF). In order to further understand the reaction mechanism, in situ attenuated total reflectance fourier transform infrared (ATR-FTIR) experiments and density functional theory (DFT) calculation were provided. We detected the HCO and CH3OH intermediates generated at the catalyst surface. DFT calculation with an ab initio modeling strongly supported the experimental results and rationalized the room temperature selective methane upgrading reaction pathways on Fe30%Ni70%(OH)x. We believe this fundamental work will provide insight and guidance in economically efficient methane conversion.[1] S. M. Miller et al., “Anthropogenic emissions of methane in the United States,” Proc. Natl. Acad. Sci., vol. 110, no. 50, pp. 20018–20022, Dec. 2013, doi: 10.1073/PNAS.1314392110.[2] X. D. Peng, “Analysis of the thermal efficiency limit of the steam methane reforming process,” Ind. Eng. Chem. Res., vol. 51, no. 50, pp. 16385–16392, 2012.[3] A. A. Latimer et al., “Understanding trends in C–H bond activation in heterogeneous catalysis,” Nat. Mater., vol. 16, no. 2, pp. 225–229, 2017.[4] A. H. B. Mostaghimi, T. A. Al-Attas, M. G. Kibria, and S. Siahrostami, “A review on electrocatalytic oxidation of methane to oxygenates,” J. Mater. Chem. A, vol. 8, no. 31, pp. 15575–15590, 2020. Figure 1

Model application to a lab-scale thermophilic hydrogenotrophic methanation system

The thermophilic hydrogenotrophic methanation (THM) is a well-known biochemical process by means of which hydrogen and carbon dioxide can be converted into methane. Compared to chemical catalytic methanation, THM showed an obvious advantage with a low operation cost and high flexibility. However, the THM processes are often operated with specific microorganisms, which require very specific conditions. The requirement of those specific methanogens increases the difficulty of THM operation. In this study, a modified anaerobic digestion model no. 1 (ADM1) was applied to describe the performance of a lab-scale THM system. A series of experiments were conducted to evaluate the methane conversion efficiency of THM, while a lab-scale THM system was operated at the same conditions. The model simulation showed a good data fitting performance compared to measure data after the model was calibrated with 30-day input data from the lab-scale reactor, while the mean relative error (MRE) was 14.2%. The hydrogenotrophic methanation model (HMM) was also applied for the model predictive control (MPC) test in the lab-scale reactor, where the prediction accuracy was confirmed with 10–18% MRE. The results indicated the potential of HMM to be applied further in big-scale THM processes.

Selective electrochemical oxidative coupling of methane mediated by Sr2Fe1.5Mo0.5O6-\u03b4 and its chemical stability

Efficient conversion of methane to value-added products such as olefins and aromatics has been in pursuit for the past few decades. The demand has increased further due to the recent discoveries of shale gas reserves. Oxidative and non-oxidative coupling of methane (OCM and NOCM) have been actively researched, although catalysts with commercially viable conversion rates are not yet available. Recently, {{{{{{{mathrm{Sr}}}}}}}}_2Fe_{1.5 + 0.075}Mo_{0.5}O_{6 - delta } (SFMO-075Fe) has been reported to activate methane in an electrochemical OCM (EC-OCM) set up with a C2 selectivity of 82.2%1. However, alkaline earth metal-based materials are known to suffer chemical instability in carbon-rich environments. Hence, here we evaluated the chemical stability of SFMO in carbon-rich conditions with varying oxygen concentrations at temperatures relevant for EC-OCM. SFMO-075Fe showed good methane activation properties especially at low overpotentials but suffered poor chemical stability as observed via thermogravimetric, powder XRD, and XPS measurements where SrCO3 was observed to be a major decomposition product along with SrMoO3 and MoC. Nevertheless, our study demonstrates that electrochemical methods could be used to selectively activate methane towards partial oxidation products such as ethylene at low overpotentials while higher applied biases result in the complete oxidation of methane to carbon dioxide and water.

Unaerated feeding alters the fate of dissolved methane during aerobic wastewater treatment

In municipal wastewater treatment plants, some dissolved methane can enter the aerobic bioreactors. This greenhouse gas originates from sewers and return flows from anaerobic sludge treatment. In well-mixed conventional activated sludge reactors, methane emissions are largely avoided because methane oxidizing bacteria consume a large fraction, even without optimizing for this purpose. In this work, the fate of dissolved methane is studied in aerobic granular sludge reactors, as they become increasingly popular. The influence of the characteristic design and operating conditions of these reactors are studied with a mathematical model with apparent conversion kinetics and stripping: the separation of feeding and aeration in time, a higher substrate transport resistance, a high retention time of granular biomass and a taller water column. Even for a best-case scenario combining an unrealistically low intragranule substrate transport resistance, a high retention time, a tall reactor, an extremely high influent methane concentration and no oxygen limitation, the methane conversion efficiency was only 12% when feeding and aeration were separated in time, which is lower than for continuous activated sludge reactors under typical conditions. A more rigorous model was used to confirm the limited conversion, considering the multi-species and multi-substrate biofilm kinetics, anoxic methane consumers and the high substrate concentration at the bottom during upward plug flow feeding. The observed limited methane conversion is mainly due to the high concentration that accumulates during unaerated feeding phases, which favours stripping more than conversion in the subsequent aeration phase. Based on these findings, strategies were proposed to mitigate methane emissions from wastewater treatment plants with sequentially operated reactors.

Comparative analysis of conventional steam methane reforming and PdAu membrane reactor for the hydrogen production

A comparison study between conventional and PdAu-based membrane steam methane reforming (SMR) processes for small-scale hydrogen production was conducted. Both processes were simulated using a commercial simulation software Aspen Plus. For the PdAu-based membrane reactor, a 1D pseudo-homogenous model was developed via Aspen Custom Modeler (ACM). The optimum operating pressure and temperature for the membrane SMR process are 30 bar and 550˚C. While the conventional SMR process has higher performance operating at 23 bar and 900˚C at the reforming reactor outlet. The simulation results revealed that the membrane SMR process has higher methane conversion, hydrogen yield, and process energy efficiency than the conventional SMR process. Moreover, cost analysis was conducted for both processes to study their economic feasibility. The analysis revealed that hydrogen production costs for conventional and membrane SMR processes are 4.54 and 2.87 $/kg H2 respectively.

Research progress on methane conversion coupling photocatalysis and thermocatalysis

AbstractConversion of methane into value‐added chemicals is of significance for methane utilization and industrial demand of primary chemical products. The barrier associated with the nonpolar structure of methane and the high bond energy C–H bond (4.57 eV) makes it difficult to realize methane conversion and activation under mild conditions. The photothermal synergetic strategy by combining photon energy and thermo energy provides an advanced philosophy to achieve efficient methane conversion. In this review, we overview the current pioneering studies of photothermal methane indirect conversion and present the methane direct conversion by the way of photocatalysis and thermocatalysis to provide a fundamental understanding of methane activation. Finally, we end this review with a discussion on the remaining challenges and perspectives of methane direct conversion over single‐atom catalysts via photothermal synergetic strategy.

Syntrophic co-culture of a methanotroph and heterotroph for the efficient conversion of methane to mevalonate

As the bioconversion of methane becomes increasingly important for bio-industrial and environmental applications, methanotrophs have received much attention for their ability to convert methane under ambient conditions. This includes the extensive reporting of methanotroph engineering for the conversion of methane to biochemicals. To further increase methane usability, we demonstrated a highly flexible and efficient modular approach based on a synthetic consortium of methanotrophs and heterotrophs mimicking the natural methane ecosystem to produce mevalonate (MVA) from methane. In the methane-conversion module, we used Methylococcus capsulatus Bath as a highly efficient methane biocatalyst and optimized the culture conditions for the production of high amounts of organic acids. In the MVA-synthesis module, we used Escherichia coli SBA01, an evolved strain with high organic acid tolerance and utilization ability, to convert organic acids to MVA. Using recombinant E. coli SBA01 possessing genes for the MVA pathway, 61 mg/L (0.4 mM) of MVA was successfully produced in 48 h without any addition of nutrients except methane. Our platform exhibited high stability and reproducibility with regard to cell growth and MVA production. We believe that this versatile system can be easily extended to many other value-added processes and has a variety of potential applications.

Effects of different microbial pretreatments on the anaerobic digestion of giant grass under anaerobic and microaerobic conditions

Microbial pretreatment to lignocellulosic biomass for anaerobic digestion (AD) has achieved increased attention; however, the low efficiency and unclear mechanism of oxygen parameter affecting this process performance limit its practical application. In this study, five readily available microbial consortia were developed to analyze the influences of various oxygen concentrations during pretreatment process upon methane conversion efficiency and microbiota within AD of giant grass. Results found that anaerobic pretreatment by liquid or straw composting inoculant, along with microaerobic pretreatment by cow manure at 10 mL/g VS oxygen concentration, obtained 23.1%, 24.4%, and 16.0% higher methane yields (275.3, 279.8, and 265.3 mL/g VS) than corresponding untreated group, respectively. Microbial community analyses showed that microbial responses to oxygen varied significantly with microbial consortium, which consequently caused different AD performances. The findings will enrich theoretical knowledge of microbial pretreatment and provide a technological guidance for efficient utilization of giant grass and other lignocellulosic biomasses.

Electrochemical Oxidative Coupling of Methane to Produce Higher Hydrocarbons Using Sr2Fe1.5Mo0.5O6-Δ Electrocatalysts

Efficient conversion of methane to value added products such as olefins and aromatics has been in pursuit for the past several decades. The demand has increased further due to the recent discoveries of shale gas reserves (1). Oxidative and non-oxidative coupling of methane (OCM and NOCM) has been actively researched although commercially viable conversion rates have not been achieved with any catalyst yet. Electrochemical OCM is gaining attention due to its ability to control the oxide ion flux that will help reduce the over-oxidation of methane while also helping to activate methane. Recently, (SFMO-075Fe) has been reported to activate methane with a C2 product selectivity of 82.2% (2). However, alkaline earth metal-based materials are known to suffer chemical instability in carbon rich environments at elevated operating temperatures. Hence, we evaluated the chemical stability of SFMO-075Fe and SFMO in carbon rich conditions at temperatures relevance for EC-OCM. SFMO-075 showed wonderful methane activation properties but suffered poor chemical stability as observed in thermogravimetric and powder XRD measurements. XPS and XRD measurements revealed that SrCO3 as the major product along with MoC when SFMO is exposed to methane at 900°C. We further found that methane could be selectively activated towards partial oxidation products such as ethylene at low overpotentials while higher applied biases results in complete oxidation of methane to carbon dioxide and water. We report in this presentation our findings with SFMO along with potential benefits of EC-OCM for methane activation. References Schwach, X. Pan, and X. Bao, “Direct Conversion of Methane to Value-Added Chemicals over Heterogeneous Catalysts: Challenges and Prospects,” Chem. Rev., 117, 8497, 2017.Zhu, S. Hou, X. Hu, J. Lu, F. Chen, and K. Xie, “Electrochemical conversion of methane to ethylene in a solid oxide electrolyzer,” Nat. Commun., 10, 1173, 2019.

Syngas production by methane-rich combustion in a divergent burner of porous media

The superadiabatic combustion in porous media contributes to the efficient conversion of methane to syngas. In this paper, a divergent packed bed burner of two-layer was proposed to obtain the characteristics of methane partial oxidation. The divergent angle, interface location and pellet diameter were used to study the temperature and species distributions. Results indicate that the upper limit of velocity gradually decreased as the equivalence ratio increased and the limit of the divergent burner is obviously higher than that of the cylindrical one. The increasing of the divergent angle within a certain range enhances the methane conversion and the 15° shows the best among the selected five angles. The mole fractions of H2 and CO gradually decrease when the interface locations move from the cylindrical region to the divergent one. As the equivalence ratio increased from 1.3 to 3.5, the yields of H2 and CO and the energy conversion efficiency of syngas increase first and then decrease, and the maximum efficiency of 45.9% appears at the equivalence ratio of 2.0. The divergent region weakens the influence of inlet velocities and contributes to the stability of reforming reactions.

Engineering enhanced anaerobic digestion: Benefits of ethanol fermentation pretreatment for boosting direct interspecies electron transfer

Conversion of organic wastes to methane via anaerobic digestion has been practiced for more than 160 years. However, the technical bottlenecks derived from the thermodynamic limitations of interspecies hydrogen/formate transfer (IHT/IFT) between syntrophs and methanogens resulting in the slow fermentation rate, low methane conversion efficiency and poor stability of system still limit its large-scale application. No engineering strategy to speed up IHT/IFT for dramatically changing the performances of anaerobic digestion has been developed. However, recent studies documented that simply pretreating organic wastes to produce ethanol could effectively accelerate and stabilize anaerobic digestion. This may be linked to the promotion of direct interspecies electron transfer (DIET), an alternative working mode that no longer requires hydrogen or formate as an electron carrier. Further information on how this strategy affects the function of methanogenic communities to clarify its advantages is required. In this study, we summarized the evidence that pretreating organic wastes to produce ethanol enhanced anaerobic digestion, discussed the link between ethanol and DIET, and emphasized how this strategy would be better applied in the future.

Utilization of Polyhydroxybutyrate (PHB) as intracellular reducing power for methanol production to alleviate the reliance on external energy sources by Methylocystis hirsuta

Methanol production is a promising biotechnology for the valorization of methane into a higher value product using methanotrophic bacteria. A major challenge facing the methane to methanol conversion is the need for external electron donor. As intracellular polyhydroxybutyrate (PHB) storage seems a prominent solution to circumvent such a challenge. In this study, a PHB accumulating methanotrophic strain i.e. Methylocystis hirsuta was employed to investigate the potential of coupling PHB consumption with methanol production. In addition, diversified batch experiments were performed to evaluate the optimum cultivation conditions for methanotrophs to increase methanol production. It was attained that the highest methanol concentrations were observed for cells harvested after shorter cultivation periods regardless their PHB content. Moreover, increasing formate concentrations had a negative effect on PHB consumption which was completely hindered at formate concentrations above 100 mM. Meanwhile, cells depending on PHB solely were able to produce up to 124 ± 6 mg/L which was improved upon adjusting the growth, PHB accumulation and methanol production periods at which it reached 241 ± 15 mg/L. PHB-rich cells supplied with only 25 mM formate was able to produce methanol concentration of 399 ± 15 mg/L. Interestingly, this is similar to the methanol produced using PHB-lacking cells incubated in a medium having 100 mM of formate. Moreover, PHB-rich cells with only 25 mM formate had higher methane conversion efficiency (69 ± 6%) compared to PHB-lacking cells with 100 mM formate (54 ± 4%). Further studies are required to improve the methanol productivity of this process.

Facile synthesis of N-doped carbon supported iron species for highly efficient methane conversion with H2O2 at ambient temperature

A series of N-doped carbon supported highly-dispersed Fe catalysts are prepared, and their catalytic performances for the direct conversion of methane to CH3OH and HCOOH with by-product CO2 are tested at ambient temperature. The nitrogen doping can greatly improve the metal-support interaction, and anchor the Fe species on the support. The catalytic activity of the catalyst is further enhanced by the modification of hydroxylamine hydrochloride. The optimized 2.5 wt%Fe/NC−HH catalyst shows 475 μmol/gcat for CH3OH and 832 μmol/gcat for HCOOH after 1 h reaction. The effect of the type of nitrogen species on the catalytic performance of the catalyst has been studied in detail. In addition, other transition metals (Ni, Co, Cu and Mn) as active centers have been also studied, and none of them is effective for the conversion of methane. Additionally, it is found that the methane conversion over the prepared catalysts proceed via a radical mechanism.

Atmosphere-Pressure Methane Oxidation to Methyl Trifluoroacetate Enabled by a Porous Organic Polymer-Supported Single-Site Palladium Catalyst

The efficient conversion of methane into methanol at low temperature under low pressure remains a great challenge largely because of the inertness and poor solubility of methane. Herein, we report ...