CH4 Storage Research Articles

Methane and Primary Productivity in Lakes: Divergence of Temporal and Spatial Relationships

AbstractIn lakes, the production and emission of methane (CH4) have been linked to lake trophic status. However, few studies have quantified the temporal response of lake CH4 dynamics to primary productivity at the ecosystem scale or considered how the response may vary across lakes. Here, we investigate relationships between lake CH4 dynamics and ecosystem primary productivity across both space and time using data from five lakes in northern Wisconsin, USA. From 2014 to 2019, we estimated hypolimnetic CH4 storage rates for each lake using timeseries of hypolimnetic CH4 concentration through the summer season. Across all lakes and years, hypolimnetic CH4 storage ranged from <0.001 to 7.6 mmol CH4 m−2 d−1 and was positively related to the mean summer rate of gross primary productivity (GPP). However, within‐lake temporal responses to GPP diverged from the spatial relationship, and GPP was not a significant predictor of interannual variability in CH4 storage at the lake scale. Using these data, we consider how and why temporal responses may differ from spatial patterns and demonstrate how extrapolating cross‐lake relationships for prediction at the lake scale may substantially overestimate the rate of change of CH4 dynamics in response to lake primary productivity. We conclude that future predictions of lake‐mediated climate feedbacks in response to a shifting distribution of trophic status should incorporate both varying lake responses and the temporal scale of change.

Evolution of the Design of CH4 Adsorbents

In this review, the evolution of paradigm shifts in CH4 adsorbent design are discussed. The criteria used as characteristic of paradigms are first reports, systematic findings, and reports of record CH4 storage or deliverable capacity. Various paradigms were used such as the systematic design of micropore affinity and pore size, functionalization, structure optimization, high throughput in silico screening, advanced material property design which includes flexibility, intrinsic heat management, mesoporosity and ultraporosity, and process condition optimization. Here, the literature is reviewed to elucidate how the approach to CH4 adsorbent design has progressed and provide strategies that could be implemented in the future.

Experimental and simulation study of the effect of surface functional groups decoration on CH4 and H2 storage capacity of microporous carbons

The incorporation of heteroatoms (i.e. N, O, S, F) into the microporous carbon framework is proposed to affect the interactions between adsorbates and adsorbents and improve the efficiency of gas storage. We demonstrate a facile synthesis of coal-derived activated carbons (ACs) modified with oxygen and nitrogen-containing groups for CH4 and H2 storage application. The functionalised ACs showed to have a high surface area of 1617–1924 m2/g, and pore volume of 0.85–0.92 cm3/g. The AC samples prepared by pre-oxidation followed by amination possess comparatively high CH4 adsorption capacity of 13.8 to 14.2 mmol/g at 298 K and 40 bar. However, the pristine AC and the oxidised AC showed the maximum H2 adsorption capacity with 0.6 mmol/g and 0.44 mmol/g, respectively, at 20 bar and 298 K. Density functional theory (DFT) calculations were performed to study the adsorption of CH4 and H2 on the ACs with/without the surface functional groups. In agreement with the experimental results, the computational analysis showed an increase in the gas–solid interaction after surface modification. Finally, a well-known method of Grand Canonical Monte Carlo (GCMC) was used to simulate the studied gas adsorption systems and calculate the adsorption isotherms of CH4 and H2 on different ACs.

Quantitative Structure–Property Relationships from Experiments for CH4 Storage and Delivery by Metal–Organic Frameworks

Quantitative structure–property relationships (QSPRs) can be applied to metal–organic frameworks (MOFs) to allow for reasonable estimates to be made of the CH4 storage performance. QSPRs are available for CH4 storage of MOFs, but these were obtained from Grand Canonical Monte Carlo (GCMC) simulations which have come under scrutiny and of which the accuracy has been questioned. Here, QSPRs were developed from experimental data and insights are provided on how to improve storage and deliverable CH4 storage capacity based on material properties. Physical properties of MOFs, such as density, pore volume, and largest cavity diameter (LCD), and their significance for CH4 storage capacity were assessed. One relationship that was found is that CH4 gravimetric storage capacity is directly proportional to Brunauer–Emmett–Teller (BET) surface area (r2 > 90%). The QSPRs demonstrated the effect of van der Waals forces involved in CH4 adsorption. An assessment was made of the accuracy of QSPRs made by GCMC as compared to QSPRs derived from experimental data. Guidelines are provided for optimal design of MOFs, including density and pore volume. With the recent achievement of the gravimetric 2012 DOE CH4 storage target, the QSPRs presented here may allow for the prediction of structural descriptors for CH4 storage capacity and delivery.

High contribution of methane in greenhouse gas emissions from a eutrophic lake: a mass balance synthesis

ABSTRACT Lakes are ‘hotspots’ for greenhouse gas (GHG) emissions, primarily carbon dioxide (CO2) and methane (CH4). Understanding the processes regulating GHG emissions from lakes, and their temporal variability, is essential for more accurately quantifying the role of lakes in global GHG cycles. In this study, we identified the processes that affect CO2 and CH4 concentrations in a small (0.3 km2) eutrophic monomictic lake (Okaro, New Zealand). A mass balance model was used to calculate changes in CO2 and CH4 storage in the lake as a result of internal cycling and atmospheric fluxes. To support model computations, CO2 and CH4 concentrations profiles were measured monthly over a one-year period, in addition to temperature, dissolved oxygen and chlorophyll a. Annually, Lake Okaro acted as a sink of CO2 from the atmosphere (425.4 mmol CO2 m−2 y−1) and a source of CH4 (553.4 mmol CH4 m−2 y−1) equating to a net GHG emission (diffusive fluxes of CO2 and CH4 combined) of 0.22 kg CO2-eq m−2 y−1. Although it may be viewed as conservative and applies only to diffusive fluxes, our study indicates that eutrophic lakes with high rates of primary production may act as a net source of GHGs.

Quest for an Optimal Methane Hydrate Formation in the Pores of Hydrolytically Stable Metal-Organic Frameworks.

Porous metal-organic frameworks (MOFs) capable of storing a relatively high amount of dry methane (CH4) in the adsorbed phase are largely explored; however, solid CH4 storage in confined pores of MOFs in the form of hydrates is yet to be discovered. Here we report a rational approach to form CH4 hydrates by taking advantage of the optimal pore confinement in relatively narrow cavities of hydrolytically stable MOFs. Unprecedentedly, we were able to isolate methane hydrate (MH) nanocrystals with an sI structure encapsulated inside MOF pores with an optimal cavity dimension. It was found that confined nanocrystals require cavities slightly larger than the unit cell crystal size of MHs (1.2 nm), as exemplified in the experimental case study performed on Cr-soc-MOF-1 vs smaller cavities of Y-shp-MOF-5. Under these conditions, the excess amount of methane stored in the pores of Cr-soc-MOF-1 in the form of MH was found to be ≈50% larger than the corresponding dry adsorbed amount at 10 MPa. More importantly, the pressure gradient driving the CH4 storage/delivery process could be drastically reduced compared to the conventional CH4-adsorbed phase storage on the dry Cr-soc-MOF-1 (≤3 MPa vs 10 MPa).

Tailoring the Pore Environment of a Robust Ga-MOF by Deformed [Ga3O(COO)6] Cluster for Boosting C2H2 Uptake and Separation.

The construction of superstable metal-organic frameworks (MOFs) for selective gas uptake is urgently demanded but remains a great challenge. Herein, a unique bifunctional deformed [Ga3O(COO)6] inorganic secondary building unit (SBU) generated from the desymmetrical evolution of typical triangular prismatic trinuclear cluster was first introduced, which was extended by an isosceles triangular organic linker to produce a robust Ga-MOF (SNNU-63). Remarkably, SNNU-63 can stabilize in water at 25 °C for 96 h and at 80 °C for more than 24 h, which surpasses nearly all other Ga-MOFs. The combined effects of open metal sites and hydrophobic pore environment provided by deformed [Ga3O] SBUs render SNNU-63 with high C2H2 storage capacity and efficient C2H2 and natural gas purification performance. The ideal adsorbed solution theory calculation, column breakthrough tests, and grand canonical Monte Carlo simulations demonstrate that SNNU-63 is a potential material for addressing the challenge of C2H2/CO2 and C2H2/CH4 mixture separation under ambient conditions.

Graphene Oxide Protected Copper Benzene-1,3,5-Tricarboxylate for Clean Energy Gas Adsorption.

Among microporous storage materials copper benzene-1,3,5-tricarboxylate (CuBTC MOF, Cu3(BTC)2 or HKUST-1) holds the greatest potential for clean energy gases. However, its usefulness is challenged by water vapor, either in the gas to be stored or in the environment. To determine the protection potential of graphene oxide (GO) HKUST-1@GO composites containing 0–25% GO were synthesized and studied. In the highest concentration, GO was found to strongly affect HKUST-1 crystal growth in solvothermal conditions by increasing the pH of the reaction mixture. Otherwise, the GO content had practically no influence on the H2, CH4 and CO2 storage capacities, which were very similar to those from the findings of other groups. The water vapor resistance of a selected composite was compared to that of HKUST-1. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric (TG/DTG) and N2 adsorption techniques were used to monitor the changes in the crystal and pore structure. It was found that GO saves the copper–carboxyl coordination bonds by sacrificing the ester groups, formed during the solvothermal synthesis, between ethanol and the carboxyl groups on the GO sheets.

Molecular Expansion for Constructing Porous Organic Polymers with High Surface Areas and Well‐Defined Nanopores

AbstractConstruction of porous organic polymers (POPs) with high surface areas, well‐defined nanopores, and excellent stability remains extremely challenging because of the unmanageable reaction process. Until now, only a few reported POPs have Brunauer‐Emmett‐Teller (BET) surface areas (SBET) exceeding 3000 m2 g−1. Herein, we demonstrate a molecular expansion strategy to integrate high surface areas, large nanopore sizes, and outstanding stability into POPs. A series of hyper‐crosslinked conjugated polymers (HCCPs) with exceptional porosity are synthesized through this strategy. Specially, HCCP‐6 and HCCP‐11 exhibit the highest surface areas (SBET >3000 m2 g−1) and excellent total pore volumes (up to 3.98 cm3 g−1) among these HCCPs. They present decent total CH4 storage capacities of 491 and 421 mg g−1 at 80 bar and 298 K, respectively. Meanwhile, they are highly stable in harsh environments. The facile and general molecular expansion strategy would lead to improved synthetic routes of POPs for desired functions.

Molecular Expansion for Constructing Porous Organic Polymers with High Surface Areas and Well-Defined Nanopores.

Construction of porous organic polymers (POPs) with high surface areas, well-defined nanopores, and excellent stability remains extremely challenging because of the unmanageable reaction process. Until now, only a few reported POPs have Brunauer-Emmett-Teller (BET) surface areas (SBET ) exceeding 3000 m2 g-1 . Herein, we demonstrate a molecular expansion strategy to integrate high surface areas, large nanopore sizes, and outstanding stability into POPs. A series of hyper-crosslinked conjugated polymers (HCCPs) with exceptional porosity are synthesized through this strategy. Specially, HCCP-6 and HCCP-11 exhibit the highest surface areas (SBET >3000 m2 g-1 ) and excellent total pore volumes (up to 3.98 cm3 g-1 ) among these HCCPs. They present decent total CH4 storage capacities of 491 and 421 mg g-1 at 80 bar and 298 K, respectively. Meanwhile, they are highly stable in harsh environments. The facile and general molecular expansion strategy would lead to improved synthetic routes of POPs for desired functions.

The role of brine in gas adsorption and dissolution in kerogen nanopores for enhanced gas recovery and CO2 sequestration

Understanding storage characteristics of CH4 and CO2 in shale media is important for enhanced gas recovery and geological CO2 sequestration. This work reports a molecular simulation study of CH4 and CO2 storage behaviors in kerogen nanopores partially saturated with brine. Molecular distributions of pure CH4, pure CO2 and their mixtures in the kerogen nanopores are quantified and divided into three distinct zones: adsorption between kerogen surfaces in Zone 1, aggregation at the kerogen-brine (water) interface in Zone 2, and gas dissolved in the confined brine in Zone 3. The gas uptake is found to be affected by two different storage mechanisms: adsorption (i.e. in Zone 1) and dissolution (i.e. in Zones 2 and 3). Uptake of CH4 and CO2 decreases linearly with increasing salinity, but with different mechanisms. CH4 uptake is dominated by its adsorption in Zone 1, where its density distribution is not affected, but the available volume decreases as salinity increases. On the other hand, CO2 solubility in brine contributed by Zone 2 and Zone 3 can be comparable to its adsorption in Zone 1. As salinity increases, a significant decrease in CO2 solubility in brine is observed, besides the available volume reduction in Zone 1. For mixture sorption, the CO2 density is enhanced in the region of CH4/CO2/brine (water) interface, while that of CH4 is slightly decreased. Furthermore, increasing salinity leads to decreased amounts of recovered CH4 and sequestrated CO2. Our work provides new and important insights into enhanced gas recovery by CO2 injection and geological CO2 sequestration in shale reservoirs.

High-efficiency natural-gas storage method involving formation of gas hydrate in water/oil-cyclopentane emulsion

This study proposes a high-efficiency natural gas hydrate (NGH) storage method involving the formation of NGH in a water/oil emulsion with the addition of suitable thermodynamic additives. First, the CH4 hydrate formation conditions in a water/diesel emulsion with the addition of hydrate thermodynamic additives, including tetrabutylammonium bromide (TBAB), tetrahydrofuran (THF), and cyclopentane (CP), were measured for the first time. Interestingly, in contrast to the case of the aqueous solution, both the TBAB and THF could not promote the formation of CH4 hydrate in the water/diesel emulsion, and they exhibited a hydration inhibition effect. The CP substantially reduced the CH4 hydrate formation pressure in the water/diesel emulsion, and the resulting hydrate/diesel slurry exhibited good fluidity. The CH4 storage characteristics of the water/diesel-CP emulsion under hydrate formation conditions were systematically studied. At 276.15 K and 6 MPa, for a water/diesel-CP emulsion containing 30 wt% water cut, the CH4 storage volume (S) per unit volume water in the emulsion reached 152.32 m3/m3, with the hydrartion reaction rate was 2.27 mmol/min, which was significantly higher than that for pure water, a water-CP solution, and a single water/diesel emulsion. S increased to 163.6 when the water cut decreased to 20 wt%; the entire experimental process lasted 90 min. An increase in the temperature from 274.15 to 282.15 K had a limited influence on S, indicating the wide range of application conditions of the water/diesel-CP emulsion for the production of NGH crystals. Furthermore, in situ particle video microscope observations and focused beam reflectance measurements confirmed the good flowability of the formed CH4 hydrate/diesel slurry. Continuous production of NGHs can theoretically be achieved using the water/diesel-CP emulsion.

Facile synthesis of hybrid porous composites and its porous carbon for enhanced H2 and CH4 storage

The anticipated energy crisis due to the extensive use of limited stock fossil fuels forces the scientific society for find prompt solution for commercialization of hydrogen as a clean source of energy. Hence, convenient and efficient solid-state hydrogen storage adsorbents are required. Additionally, the safe commercialization of huge reservoir natural gas (CH4) as an on-board vehicle fuel and alternative to gasoline due to its environmentally friendly combustion is also a vital issue. To this end, in this study we report facile synthesis of polymer-based composites for H2 and CH4 uptake. The cross-linked polymer and its porous composites with activated carbon were developed through in-situ synthesis method. The mass loadings of activated carbon were varied from 7 to 20 wt%. The developed hybrid porous composites achieved high specific surface area (SSA) of 1420 m2/g and total pore volume (TPV) of 0.932 cm3/g as compared to 695 m2/g and 0.857 cm3/g for pristine porous polymer. Additionally, the porous composite was activated converted to a highly porous carbon material achieving SSA and TPV of 2679 m2/g and 1.335 cm3/g, respectively. The H2 adsorption for all developed porous materials was studied at 77 and 298 K and 20 bar achieving excess uptake of 4.4 wt% and 0.17 wt% respectively, which is comparable to the highest reported value for porous carbon. Furthermore, the developed porous materials achieved CH4 uptake of 8.15 mmol/g at 298 K and 20 bar which is also among the top reported values for porous carbon.

A microporous aluminum-based metal-organic framework for high methane, hydrogen, and carbon dioxide storage

We report a microporous aluminum-based metal-organic framework (MOF), BUT-22 for high methane (CH4), hydrogen (H2), and carbon dioxide (CO2) storage. At 296 K and 80 bar, BUT-22 exhibits a high gravimetric CH4 storage capacity of 530 cm3 (STP)/g (0.379 g/g). BUT-22 also has a high gravimetric H2 storage capacity of 12 wt.% at 100 bar and 77 K. In addition, the CO2 adsorption studies revealed that BUT-22 exhibits a high absolute gravimetric CO2 uptake of 1.7 g/g at 296 K and 40 bar.

Investigation of tuning behavior of trimethylene oxide hydrate with guest methane molecule and its critical guest concentration

Due to the promising storage capacity for CH4, the method of natural gas storage and transportation using solid gas hydrate is recognized as an alternative to conventional liquefied natural gas process. To make this alternative more viable, however, it is necessary to further shift the formation temperature and pressure of natural gas hydrate closer to ambient conditions. Although there is a trade-off between storing more CH4 and mitigating the formation conditions, it is known that adding specific liquid molecules such as tetrahydrofuran, as a secondary guest to CH4 hydrate could lead to favorable thermodynamic stability while still affording promising CH4 storage capacity via a mechanism known as the tuning phenomenon. Here, this study focused on trimethylene oxide (TMO) + CH4 hydrate to reveal its unique guest occupation patterns for potential application to natural gas storage and transportation. The occurrence of the tuning behavior on the TMO + CH4 hydrate was observed for the first time. Most importantly, the tuning factor referred to as the CH4 occupation ratio between the large and small cages of sII hydrate, exhibited a value of 0.73 at the critical guest concentration, which is the largest value reported to date. The phase equilibria of the TMO + CH4 hydrate were provided for TMO concentrations ranging from 1.0 to 5.56 mol%. The spectroscopic data obtained from synchrotron HRPD, dispersive Raman, and 13C solid-state HPDEC MAS NMR spectrometry provided experimental evidence of the distinct enclathration characteristics of CH4 and TMO molecules during the tuning phenomenon. These findings provide fundamental knowledge on the tuning effect and lend useful insights for designing and developing gas hydrate-based natural gas storage and transportation process.

Formation of CH4 Hydrate in a Mesoporous Metal-Organic Framework MIL-101: Mechanistic Insights from Microsecond Molecular Dynamics Simulations.

The formation of CH4 hydrate in a mesoporous metal-organic framework MIL-101 is investigated by microsecond molecular dynamics simulations. CH4 hydrate is observed to form preferentially in the outer space of MIL-101 cavities rather than inside the cavities; only when the hydrate formation is nearly complete in the outer space can stable hydrate form in MIL-101 cavities. The underlying reason is revealed to be the easy dissociation of small hydrate clusters formed in the nanospace of the cavities, because of the diffusion of CH4 molecules out of the cavities into the outer space. Compared with dry MIL-101, the CH4 storage capacity of H2O-saturated MIL-101 is drastically reduced as the cavities are occupied by H2O. When oversaturated with H2O, however, extra H2O molecules in the outer space of the cavities can form considerable CH4 hydrate, significantly promoting CH4 storage capacity. This study provides important mechanistic insights into the formation mechanism and process of CH4 hydrate in MIL-101 and will facilitate the design of emerging materials for energy storage.

Inserting Amide into NOTT-101 to Sharply Enhance Volumetric and Gravimetric Methane Storage Working Capacity.

Amide-functionalized NJU-Bai45 exhibits high volumetric and gravimetric CH4 working capacities of 190 cm3 cm-3 and 298 cm3 g-1 (from 5.8 to 65 bar), higher than that of the similar NJU-Bai43 (187 cm3 cm-3 and 292 cm3 g-1). This finding indicates that nitrogen-functionalized aromatic ring may not always play a positive role in amide-MOF for CH4 storage.

Flexible nanoporous activated carbon cloth for achieving high H2, CH4, and CO2 storage capacities and selective CO2/CH4 separation

Innovative tools are needed for the synthesis of smart, new, efficient, and safe nanoporous carbon materials for energy gas storage. Here, a flexible nanoporous activated carbon cloth was developed. Polypyrrole nanoparticles were polymerized in dispersed form on commercial viscose rayon cloth fiber surfaces. Then, the material was carbonized and activated by physical and chemical activation methods applied individually. Chemical activation conditions were varied and optimized. This produced a high porosity flexible nanoporous carbon textile with a surface area of ~2000 m2 g−1, total pore volume of 0.85 cm3 g−1, and high nitrogen content. The new flexible nanoporous carbon cloth achieved superior H2 and CH4 storage capacities and CO2 capture compared to so-far-reported activated carbon cloth, and values were comparable to or higher than those reported for powder activated carbons. Excess H2 uptake values were 4.0 and 0.173 wt% at 77 K and 298 K at 20 bar, respectively, and CH4 storage amounted to 7.5 mmol g−1 at 20 bar and 298 K, which is among the highest reported values for porous carbon materials. CO2 uptake values were 4.2 and 14.3 mmol g−1 at 1 and 20 bar at 298 K, respectively, which are values superior to those previously reported for activated carbon cloth. Hence, the flexible nanoporous activated carbon cloth is effective for greenhouse gas (i.e., CO2) uptake during post- and pre-combustion conditions. Separation selectivity for CO2/CH4 binary mixtures was evaluated based on the ideal adsorbed solution theory (IAST) model and a high value of 15.9 was achieved.

A fluorinated Zr-based MOF of high porosity for high CH4 storage

An organic linker H2FBDA (H2FBDA = (2E, 2′E)-3,3'-(2-fluoro-1,4-phenylene) diacrylic acid) with the electron-withdrawing fluoro-group, has been applied to construct a Zr-based metal-organic framework, the ZJU-800 (ZJU = Zhejiang University). ZJU-800, derived from UiO-66 and isostructural with NU-801, is explored for high-pressure methane storage capacity of 10.0 mmol/g at 65 bar and room temperature, with good thermal and water stability. It is shown that the amount of methane uptake is 61.2% higher than that of UiO-66 at 35 bar.

Enhanced CH4 storage in hydrates with the presence of sucrose stearate

Clathrate hydrate is a promising option for gas storage and transportation. Sucrose stearate, an environmentally friendly chemical, was studied in CH4 hydrate formation process to evaluate its effect on gas storage of CH4 hydrate. The experiment was conducted systematically with four different sucrose stearate concentrations at three various initial pressures. The experimental data were employed to calculate the normalized hydrate formation rate and equilibrium time based on chemical affinity. The results indicated that the presence of sucrose stearate significantly enhanced the CH4 hydrate formation rate and storage when initial pressure was higher than 5.0 MPa. In addition, Raman spectroscopic analysis was performed to examine the hydrate structure and obtain the theoretical storage capacity. The spectra demonstrated that sucrose stearate decreased the hydration number with not changing CH4 hydrate’s structure. The theoretical storage capacity and the energy value were increased by about 2.59%. Combing all the results, sucrose stearate was a good kinetic promoter for CH4 hydrate formation. The systems with sucrose stearate at low concentration and high concentration were suggested for designing gas storage process and fast hydrate formation process, respectively.