Continuous Methane Research Articles

Molecular simulations on the continuous methane desorption in illite nanoslits

A molecular dynamics workflow to simulate the desorption–extraction of shale gas is proposed for predicting the production of shale gas. • A novel desorption–extraction MD workflow based on the EF-NEMD is proposed. • Some factors affecting the recovery are examined. • Large amount of methane in micropores is unrecoverable due to the stronger adsorption. • The recovery decline curves could be obtained in the proposed MD workflow. • Models of enhancement of recovery by pressure difference and temperature are built. Understanding microscopic process of gas desorption is important to production forecast in shale gas development. In usual simulations on the gas desorption process, the desorption occurs in a non-equilibrium state, but stops when the desorption–adsorption equilibration is reached. This is contrary to the continuous process in gas production. A workflow based on non-equilibrium molecular dynamics (NEMD) is proposed in this work to simulate the continuous desorption in the illite nanoslits by introducing an intermittent extraction into the whole process. A production curve is obtained in the workflow, and a pseudo decline-curve analysis (PDCA) can be provided in molecular simulation. The variation of desorption–extraction with pore size ( H ), temperature ( T ) and pressure difference ( ΔP ) is discussed. The attraction of illite–methane in the narrower slits is stronger than that in the wider slits. In the early stage, the extraction is dominated by the free gas in the wider slits. And in the later stage, the desorption of adsorbed gas in the narrower slits is the main process. The ΔP and T promote the desorption and extraction mainly in the early stage. The ΔP promotes the desorption in the wider slits more remarkably, while the desorption in the narrower slits is enhanced more by a higher T . The enhancement of desorption by ΔP and T in the early stage is modeled. The newly developed MD workflow and obtained PDCA model can be readily extended to study the extraction and production prediction of shale gas.

Temperature-dependant active sites for methane continuous conversion to methanol over Cu-zeolite catalysts using water as the oxidant

Methane-selective continuous conversion to methanol is highly challenged by the high CH dissociation energy and the facile over-oxidation of methane. In this work, we reported continuous methane conversion to methanol over Cu-zeolites using water as the oxidant at different reaction temperatures (200–450 °C) and found that the space–time yield (STY) of methanol depended on the reaction temperature, with a high methanol STY of 189.9 μmol/gcat./h (578.7 mmol/molCu/h) at the selectivity of 91 % on Cu-SSZ-13 being achieved at the optimal temperature of 350 °C. Increasing the reaction temperature from 200 to 350 °C resulted in the increase of the kinetic orders of methane and water for catalytic oxidation of methane. An important reason was indicated that higher reaction temperatures not only enhanced a high methane conversion rate but also triggered the reactivity of more Cu species on Cu-zeolites based on the quantification analysis of the available active sites and in-situ spectroscopic study. It was revealed that the CuxOy clusters (e.g., [Cu2(μ-O)]2+) as the active sites exhibited the reactivity at 200 °C, while the Cu(II)–OH species on 8-membered rings and the isolated Cu2+ ions on 6-membered rings presented the reactivity at higher temperatures (≥300 °C). This could be attributed to higher activation energies of Cu(II)–OH species and isolated Cu(II) sites. Besides, isotope labeling experiments indicated that the combination of methyl and hydrogen dissociated from water and methanol reforming resulted in a low methanol yield at high temperatures (≥350 °C).

Use of a swirling flow to mechanically regenerate catalysts after methane decomposition

A new device is proposed to regenerate catalysts after hydrogen production via methane decomposition. Because carbon deposition inhibits catalytic reactions, carbon removal is indispensable for continuous hydrogen production. This device generated a swirling flow by gas supplied at the top and bottom along the inner surface of a tube. The swirling flow rotated the catalyst particles in the tube. Shear stresses on the particles caused by inter-particle and particle-wall impacts led to attrition. Carbon was mechanically removed from the particles by attrition and was elutriated with the flue gas. Ten cycles of methane decomposition and catalyst regeneration were performed using reduced ilmenite as a catalyst. Carbon was clearly removed by catalyst regeneration. Stable regeneration was confirmed by examination of weight changes of the particles caused by carbon deposition and removal during the cycles. Hydrogen production increased by 10% during the cycles than during continuous methane decomposition for 4 h.

Start-up of co-digestion of poultry litter and wheat straw in anaerobic sequencing batch reactor by gradually increasing organic loading rate: Methane production and microbial community analysis

Anaerobic co-digestion (ACoD) of poultry litter (PL) and wheat straw (WS) in an anaerobic sequencing batch reactor (ASBR) for continuous bio-energy generation was started up for the first time by gradually increasing the organic loading rate (OLR). A steady-state was reached with a daily biogas production of (13.06 ± 0.21) L and methane content of (54.38 ± 0.53) %. The subsequent regular operation achieved a daily methane yield of (100.41–188.65) mL CH4/g VS added and a total chemical oxygen demand (tCOD) removal rate of (70.3–85.9) % in the effluent under different operating parameters. The overall microbial community became more uniform, and the dominant aceticlastic methanogen of Methanosaeta was enriched after the start-up. While the microbial community was largely stable in the overall structure since the regular operation. Therefore, the start-up of the ACoD of PL and WS was successful with stable and continuous methane production.

Molecular Simulations on the Continuous Methane Desorption in Illite Nanoslits

Molecular Simulations on the Continuous Methane Desorption in Illite Nanoslits

Photochemical method for removing methane interference for improved gas analysis

Abstract. The development of laser spectroscopy has made it possible to measure minute changes in the concentrations of trace gases and their isotopic analogs. These single or even multiply substituted species occur at ratios from percent to below parts per million and contain important information concerning trace gas sources and transformations. Due to their low abundance, minimizing spectral interference from other gases in a mixture is essential. Options including traps and membranes are available to remove many specific impurities. Methods for removing CH4, however, are extremely limited as methane has low reactivity and adsorbs poorly to most materials. Here we demonstrate a novel method for CH4 removal via chlorine-initiated oxidation. Our motivation in developing the technique was to overcome methane interference in measurements of N2O isotopic analogs when using a cavity ring-down spectrometer. We describe the design and validation of a proof-of-concept device and a kinetic model to predict the dependence of the methane removal efficiency on the methane concentration [CH4], chlorine photolysis rate JCl2, chlorine concentration [Cl2] and residence time tR. The model was validated by comparison to experimental data and then used to predict the possible formation of troublesome side products and by-products including CCl4 and HCl. The removal of methane could be maintained with a peak removal efficiency >98 % for ambient levels of methane at a flow rate of 7.5 mL min−1 with [Cl2] at 50 ppm. These tests show that our method is a viable option for continuous methane scrubbing. Additional measures may be needed to avoid complications due to the introduction of Cl2 and formation of HCl. Note that the method will also oxidize most other common volatile organic compounds. The system was tested in combination with a cavity ring-down methane spectrometer, and the developed method was shown to be successful at removing methane interference.

Biologically-oriented mud volcano database: muddy_db.

Mud volcanoes (MVs) are naturally occurring hydrocarbon hotbeds with continuous methane discharge, contributing to global warming. They host microbial communities adapted to hydrocarbon oxidation. Given their research value, MVs still represent a niche topic in microbiology and are neglected by hydrocarbon-oriented research. All the data regarding MVs is sporadic and decentralized. To mitigate this problem, we built a custom Natural Language Processing pipeline (muddy_mine), and collected all the available MV data from open-access articles. Based on this data, we built the muddy_db database. The muddy_db represents the first biologically oriented database rendered as a user-friendly web app. This database includes all the relevant MV data, ranging from microbial taxonomy to hydrocarbon occurrence and geology. The muddy_mine and muddy_db tools are licensed under the GPLv3. muddy_db R Shiny web app: https://muddy-db.shinyapps.io/muddy_db/ muddy_db R package: https://github.com/TracyRage/muddy_db muddy_mine Conda package: https://github.com/TracyRage/muddy_mine.

Atmospheric observations consistent with reported decline in the UK's methane emissions (2013–2020)

Abstract. Atmospheric measurements can be used as a tool to evaluate national greenhouse gas inventories through inverse modelling. Using 8 years of continuous methane (CH4) concentration data, this work assesses the United Kingdom's (UK) CH4 emissions over the period 2013–2020. Using two different inversion methods, we find mean emissions of 2.10 ± 0.09 and 2.12 ± 0.26 Tg yr−1 between 2013 and 2020, an overall trend of −0.05 ± 0.01 and −0.06 ± 0.04 Tg yr−2 and a 2 %–3 % decrease each year. This compares with the mean emissions of 2.23 Tg yr−1 and the trend of −0.03 Tg yr−2 (1 % annual decrease) reported in the UK's 2021 inventory between 2013 and 2019. We examine how sensitive these estimates are to various components of the inversion set-up, such as the measurement network configuration, the prior emissions estimate, the inversion method and the atmospheric transport model used. We find the decreasing trend to be due, primarily, to a reduction in emissions from England, which accounts for 70 % of the UK CH4 emissions. Comparisons during 2015 demonstrate consistency when different atmospheric transport models are used to map the relationship between sources and atmospheric observations at the aggregation level of the UK. The posterior annual national means and negative trend are found to be consistent across changes in network configuration. We show, using only two monitoring sites, that the same conclusions on mean UK emissions and negative trend would be reached as using the full six-site network, albeit with larger posterior uncertainties. However, emissions estimates from Scotland fail to converge on the same posterior under different inversion set-ups, highlighting a shortcoming of the current observation network in monitoring all of the UK. Although CH4 emissions in 2020 are estimated to have declined relative to previous years, this decrease is in line with the longer-term emissions trend and is not necessarily a response to national lockdowns.

Single photon Lidar gas imagers for practical and widespread continuous methane monitoring

The accurate and comprehensive identification and quantification of greenhouse gas (GHG) emissions is an essential part of the management and mitigation of climate change. We are developing a novel remote gas imaging sensor for the detection, visualisation, and quantification of methane emissions. The sensor uses a new technique we call Tunable Diode Lidar (TDLidar) which combines aspects of Tunable Diode Laser Absorption Spectroscopy (TDLAS) with Differential Absorption Lidar (DIAL) and Time Correlated Single Photon Counting (TCSPC) to enable remote spectroscopy and ranging with low power semiconductor diode lasers. Our first TDLidar methane sensors use diode lasers with wavelengths around the CH4 absorption line at 1.6509 μm and Peltier-cooled Single Photon Avalanche Diode (SPAD) detectors in a Random Modulation Continuous Wave (RM-CW) Lidar system. Here we characterise our TDLidar methane sensor performance with calibrated gas cells and controlled gas release trials and we demonstrate quantification of leak rates as low as 0.012 g/s and detection at distances over 90 m. The accuracy, speed, and practicality of the sensor, combined with an expectation of low-cost in volume, offers the potential that these sensors can be effectively applied for widespread continuous and autonomous monitoring of industrial methane emissions.

Atmospheric methane removal: a research agenda

Atmospheric methane removal (e.g. in situ methane oxidation to carbon dioxide) may be needed to offset continued methane release and limit the global warming contribution of this potent greenhouse gas. Because mitigating most anthropogenic emissions of methane is uncertain this century, and sudden methane releases from the Arctic or elsewhere cannot be excluded, technologies for methane removal or oxidation may be required. Carbon dioxide removal has an increasingly well-established research agenda and technological foundation. No similar framework exists for methane removal. We believe that a research agenda for negative methane emissions—‘removal' or atmospheric methane oxidation—is needed. We outline some considerations for such an agenda here, including a proposed Methane Removal Model Intercomparison Project (MR-MIP).This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 1)'.

Assessment of the applicability of a low-cost sensor\u2013based methane monitoring system for continuous multi-channel sampling

Systems that are made of several low-cost gas sensors with automatic gas sampling may have the potential to serve as reliable fast methane analyzers. However, there is a lack of reports about such types of systems evaluated under field conditions. Here, we developed a continuous methane monitoring system with automated gas sampling unit using low-cost gas sensors, TGS 2611 and MQ-4, that use a simple cloud-based data acquisition platform. We verified the consistency, repeatability, and reproducibility of the data obtained by TGS 2611 and MQ-4 low-cost gas sensors by measuring high- and low-concentration methane samples. The normalized root-mean-square errors (NRMSEs) of the samples with high methane concentrations, [CH4] of 3, 4, 6, and 7%, were 0.0788, 0.0696, 0.1198, and 0.0719 for the TGS 2611 sensor, respectively, and were confirmed using a gas chromatograph as a reference analyzer. The NRMSEs of the samples with low [CH4] of 0.096, 0.145, 0.193, and 0.241% measured by the TGS 2611 sensor were 0.0641, 0.1749, 0.0157, and 0.1613, whereas those NRMSEs of the same concentrations measured by the MQ-4 sensor were 0.3143, 0.5766, 0.6301, and 0.6859, respectively. Laboratory-scale anaerobic digesters were tested using the developed system. The anaerobic digesters were continuously operated for 2 months, demonstrating the potential use of sensors for detecting and monitoring methane in the field level application. This study utilized a unique way to combine the advantages of low-cost sensors and develop a reliable monitoring system by minimizing drawbacks of low-cost sensors.

Evaluation of the continuous methane production from an enzymatic agave bagasse hydrolysate in suspended (CSTR) and granular biomass systems (UASB)

Methane production from an enzymatic agave bagasse hydrolysate was evaluated in a continuous stirred tank reactor (CSTR) and in an upflow anaerobic sludge blanket reactor (UASB). The effect of different organic loading rates (OLRs) and hydraulic retention times (HRTs) on volumetric methane production rate (VMPR) was tested. To hydrolyze the bagasse, Cellulase 50XL, a food-grade enzyme, allowed a saccharification yield of lignocellulosic biomass similar to Celluclast 1.5L, which is used to treat lignocellulosic substrates. The UASB reactor operated at larger OLR (e.g., 20 g CODs/L-d) and shorter HRT (e.g., 30 h) than the CSTR (e.g., OLR of 7.3 g CODs/L-d and HRT of 66 h). The UASB achieved a VMPR of 4.5 ± 0.1 L CH4/L-d and COD removal of 94% while the CSTR had a VMPR of 1.92 ± 0.03 L CH4/L-d and COD removal of 88%. The better performance of the UASB than the CSTR can be explained by the high solid retention time (SRT) and the microbial community composition, which was less diverse than the CSTR’s community. Hydrogenotrophic methanogens were abundant in the UASB while acetoclastic methanogens dominated in the CSTR. The high VMPR obtained by the UASB reactor and the use of Cellulase 50XL can be advantageous features for future industrial application.

H2O‐Built Proton Transfer Bridge Enhances Continuous Methane Oxidation to Methanol over Cu‐BEA Zeolite

AbstractDirect oxidation of methane to methanol (DMTM) is a big challenge in C1 chemistry. We present a continuous N2O‐DMTM investigation by simultaneously introducing 10 vol % H2O into the reaction system over Cu‐BEA zeolites. Combining a D2O isotopic tracer technique and ab initio molecular dynamics (AIMD) simulation, we for the first time demonstrate that the H2O molecules can participate in the reaction through a proton transfer route, wherein the H2O molecules can build a high‐speed proton transfer bridge between the generated moieties of CH3− and OH− over the evolved mono(μ‐oxo) dicopper ([Cu‐O‐Cu]2+) active site, thereby pronouncedly boosting the CH3OH selectivity (3.1→71.6 %), productivity (16.8→242.9 μmol gcat−1 h−1) and long‐term reaction stability (10→70 h) relative to the scenario of absence of H2O. Unravelling the proton transfer of H2O over the dicopper [Cu‐O‐Cu]2+ site would substantially contribute to highly efficient catalyst designs for the continuous DMTM.

H2 O-Built Proton Transfer Bridge Enhances Continuous Methane Oxidation to Methanol over Cu-BEA Zeolite.

Direct oxidation of methane to methanol (DMTM) is a big challenge in C1 chemistry. We present a continuous N2 O-DMTM investigation by simultaneously introducing 10 vol % H2 O into the reaction system over Cu-BEA zeolites. Combining a D2 O isotopic tracer technique and ab initio molecular dynamics (AIMD) simulation, we for the first time demonstrate that the H2 O molecules can participate in the reaction through a proton transfer route, wherein the H2 O molecules can build a high-speed proton transfer bridge between the generated moieties of CH3 - and OH- over the evolved mono(μ-oxo) dicopper ([Cu-O-Cu]2+ ) active site, thereby pronouncedly boosting the CH3 OH selectivity (3.1→71.6 %), productivity (16.8→242.9 μmol gcat -1 h-1 ) and long-term reaction stability (10→70 h) relative to the scenario of absence of H2 O. Unravelling the proton transfer of H2 O over the dicopper [Cu-O-Cu]2+ site would substantially contribute to highly efficient catalyst designs for the continuous DMTM.

Continuous methane to ethane conversion using gaseous oxygen on ceria-based Pd catalysts at low temperatures

Methane upgrading into more valuable chemicals has been a promising challenge. It was previously reported that highly oxidized Pd/CeO2 could produce ethane from methane. Here, we enhanced the ethane productivity by controlling oxygen mobility of the catalyst support and adding water adsorbents. Pd/Ce1-xPdxO2-y catalyst, in which Pd atom was doped at the ceria support, showed enhanced oxygen activation and oxygen transfer, improving the ethane productivity from 0.04 molC2H6/mmolSurfacePd/h in Pd/CeO2 to 0.57 molC2H6/mmolSurfacePd/h in Pd/Ce1-xPdxO2-y. In order to remove the water produced from methane oxidation, zeolite 13X was physically mixed with Pd/Ce1-xPdxO2-y. The water adsorbent could increase the ethane production significantly, especially at low temperatures. The ethane yield of 0.30 % could be obtained at 290 °C using gaseous O2 as an oxidant. This work can provide useful ways to enhance the yield of value-added products in oxidative methane conversion.

Energy efficiency and sustainability assessment for methane harvesting from Lake Kivu

Lake Kivu is a great environmental and economic resource in Rwanda. Its deep-water methane reservoir can help the country to narrow its energy supply gap. However, mishandling of the lake could lead to devastating consequences, from potable water contamination to limnic eruption. To evaluate the lake’s potential for energy harvesting, we have developed a numerical model and validated it experimentally. Based on this model, we propose an optimal methane harvesting strategy. The harvesting efficiency improvement is from 4 to 6% relative to the alternatives. While seemingly insignificant, a 1% improvement of harvesting efficiency extends the operational time of a gas power plant by ∼5%. With these improvements, the lake will sustainably supply 100 MW of electricity for up to 100 years. Potential CO2 emissions are negligible in comparison with the low-emitting developed countries. We conclude that forestry and agroforestry can mitigate CO2 emissions and reduce currently widespread deforestation. The degassed water after methane extraction poses another environmental concern. It must be reinjected at the depth of 190–250 m to minimize the environmental impacts on the lake and allow for continuous methane harvesting.

Monitoring of Flooding Characteristics with Different Methane Gas Injection Methods in Low-Permeability Heterogeneous Cores

Methane gas injected into reservoirs can greatly enhance oil recovery and has been widely used. However, continuous methane gas flooding has a deleterious effect on oil recovery enhancement and easily causes gas channeling in low-permeability heterogeneous reservoirs because of the low viscosity and high mobility of methane gas. This study consists of comprehensive experimental research that combines physical simulation and saturation dynamic monitoring technologies with a component analysis of produced oil to investigate the oil recovery and mobility control effects in low-permeability heterogeneous cores. First, solubility, foaming ability, and stability are used as evaluation indicators. The results show that an alcohol ethoxylate foaming agent at 1.5 wt % is suitable for reservoirs, based on the Waring blender and Ross–Miles methods combined with microscopic observation. Second, methods of methane gas with water alternating gas (WAG) injection, advanced cyclic water alternating gas (ACWAG) injection, and methane nonionic foam injection are performed on three kinds of low-permeability heterogeneous cores under reservoir conditions. The experimental results show that methane nonionic foam flooding can significantly improve oil recovery by 11–18%. Third, the residual oil saturation in the core is tested by saturation dynamic monitoring. This finding indicates that methane nonionic foam flooding reduces mobility control, effectively restrains gas channeling, increases sweep efficiency, and has the highest permeability plugging rate (82–90%) for high-permeability channels. In the stage of methane WAG and ACWAG flooding, methane gas can increase the C12–C24 components in the produced oil by 0.3–0.9%. ACWAG injection can improve the stage of no water-cut oil recovery compared with conventional WAG injection.

A potential catalyst for continuous methane partial oxidation to methanol using N2O: Cu-SSZ-39.

Continuous catalytic methanol production from methane is reported on Cu-SSZ-39 using N2O as an oxidant. Through optimization of CH4, N2O and H2O partial pressures, a methanol formation rate of 499 μmolCH3OH g-1 h-1 and a methanol selectivity of 34% is achieved.

Effectiveness of using two-stage anaerobic digestion to recover bio-energy from high strength palm oil mill effluents with simultaneous treatment

This study aimed to investigate the biohydrogen and biomethane potential of palm oil mill effluent (POME) in a two-stage anaerobic digestion (AD) system under thermophilic (55 ± 3 °C) and mesophilic (30 ± 3 °C) conditions, respectively. Among the initial loadings of 0.5 g-COD, 1.0 g-COD, or 1.5 g-COD, the best production potentials of 106.13 mL-H2/g-COD and 334.56 m L-CH4/g-CODadded, corresponding to the total energy production of 13.61 kJ/g-CODadded, were obtained from POME with an initial 0.5 g-COD loading. The investigation also revealed that the energy yield (CH4+H2) achieved from two-stage AD was approximately 38.95 % higher than single-stage anaerobic digestion (single-stage AD), where only methane energy carrier was produced. Continuous hydrogen and methane production were subsequently performed in a series of continuous stirred tank reactor (CSTR) and anaerobic horizontal baffled channel (AHBC) reactor to treat POME without external supplement. The results revealed that the highest hydrogen yield of 86 m L-H2/g-CODadded was generated at 3-day HRT, while the highest methane production was obtained from HRT over 35 days with a yield of 250.33 m L-CH4/g-CODadded. Additionally, the overall COD removal in the continuous process was approximately 66.27 %. As a highly efficient organic matter removal and higher energy recovery, the continuous two-stage AD can be further developed to industrial-scale mixed hydrogen and methane production from POME.

Wastewater-borne microalga Chlamydomonas sp.: A robust chassis for efficient biomass and biomethane production applying low-N cultivation strategy

Biogas/biomethane generation from microalgae biomass via anaerobic fermentation is increasingly gaining attention as CO2-neutral energy source. Intensive research has shown, however, that microalgae represent a rather challenging substrate for anaerobic digestion (AD) due to their high cell wall recalcitrance and unfavourable protein content. Previously, the utilization of nitrogen-limited (low-N) microalgal biomass for continuous AD-processes was demonstrated (as proof-of-concept) with remarkable biomethane productivity. The present study shows the efficient portability of the low-N cultivation/fermentation strategy on a robust, wastewater-borne microalga isolate that tolerates high temperature and light conditions and can perfectly cope with microbial contaminations. Continuous long-term anaerobic digestion was characterized by stable and efficient specific biogas and biomethane productivity (765 ± 20 and 478 ± 15 mLNg−1 volatile solids (VS) d−1, respectively), equivalent to volumetric methane productivity of 1912 mLN L−1d−1. The present work underlines the applicability of low-N-biomass of wastewater-borne, robust microalgae as mono-substrate for highly efficient continuous methane generation.