CO2 CH4 Research Articles

Correlation Evaluation and Schematic Analysis of Influencing Factors Affecting Pore and Fracture Connectivity on the Microscale and Their Application Discussion in Coal Reservoir Based on X-ray CT Data.

The connectivity of the pore/fracture system is the key to CO2 injection and CH4 production, which is of great significance in analyzing the correlation and weight of the influencing factors affecting the connectivity on the microscale. First, the 3D reconstruction of the coal reservoir is realized. Second, the characteristic parameters of pore/fracture structures are analyzed. Next, the characteristics of absolute permeability are analyzed, and then the correlation and weight analysis of the influencing factors are realized. Finally, the schematic analysis and application discussion of the influencing factors are carried out. The results show that porosity is the key factor restricting fluid migration. The heterogeneity of the reservoir can be characterized by the volume changes of the pore/fracture, organic matter, and mineral. The interconnected pores/fractures are mainly distributed in sheets and bands. The coordination number ranges from 1 to 15. The Ferret diameter is 0-10 μm. The tortuosity is 2.27111, 1.9034, 3.98522, and 3.51516, respectively, and the Euler characteristic number is 0.931868, 0.974719, 0.921144, and 0.897697, respectively. The permeability of the SH and YW samples is higher than that of the RL and PY samples. The single weight of the influencing factor is as follows: coordination number > Ferret diameter > Euler characteristic number > porosity > tortuosity. The analysis area of the comprehensive evaluation score of the influencing factors and the permeability value can be divided into three grades. There is a positive correlation among the coordination number, the quantity equilibrium of pores and throats, and the connectivity. The shape factor gradually increases with the increase of the Ferret diameter. The reservoir permeability is indirectly characterized by the coordination number, Ferret diameter, tortuosity, Euler characteristic number, and shape factor. This study can provide new ideas for clarifying the correlation degree and weight value of the characteristic parameters and can enrich the development of 3D digital core and CO2-ECBM technology.

Energy use of biogas through chemical looping technologies with low-cost oxygen carriers

Biogas is a renewable fuel generated in the anaerobic digestion of organic material. The expansion of biogas as a bioenergy source in the next decades leads to find new ways for its energy exploitation such as the Chemical Looping technologies. In this work, a low-cost Fe-based residue was used as oxygen carrier in two processes with biogas, namely Chemical Looping Combustion (CLC) and Chemical Looping Reforming (CLR). CLC process is focused on the energy production with CO2 capture. CLC experiments showed higher methane combustion efficiency (∼86%) than those referred in literature with other low-cost Fe-based materials. CLR process is dedicated to the production of syngas or hydrogen without CO2 emissions. Ni- or Cu-based oxygen carrier had been successfully used in order to catalyse the methane reforming. Here, the Fe-based material was also used for CLR. The biogas composition facilitated dry reforming of biogas to obtain syngas. In the dry-CLR of biogas, it was possible to reach about 55% methane conversion with a yield to syngas of 1.3 mol (CO + H2)/mol CH4. A suitable management of the effluent gas is proposed to maximize CH4 conversion and syngas yield, which includes CO2 separation, H2 purification and CH4 recirculation. Both results confirm the potential of the energy use of biogas under these technologies and the promising results with the new oxygen carrier developed.

Insights by in-situ studies on the nature of highly-active hydrotalcite-based Ni-Fe catalysts for CO2 methanation

Designing CO2 methanation catalysts that meet industrial requirements is still challenging. We report Ni-Fe hydrotalcite-derived catalysts with a wide range of Ni and Mg loadings showing that an optimised composition with Ni0.4 gives a very high CO2 conversion rate of 0.37 mmol/gcat/s at 300 °C. This catalyst is studied by in-situ APXPS and NEXAFS spectroscopies and compared with the other synthesised samples to obtain new mechanistic insights on methanation catalysts active for low-temperature (300 °C) methanation, which is an industrial requirement. Under methanation conditions, in-situ investigations revealed the presence of metallic Ni sites and low nuclearity Ni-Fe species at xNiL (Ni loading) = 21.2 mol%. These sites are oxidised on the low Ni-loaded catalyst (xNiL= 9.2 mol%). The best CO2 conversion rate and CH4 selectivity are shown at intermediate xNiL (21.2 mol%), in the presence of Mg. These superior performances are related to the high metallic surface area, dispersion, and optimal density of basic sites. The TOFCO2(turnover frequency of CO2 conversion) increases exponentially with the fractional density of basic to metallic sites (XB) from 1.1 s-1 (xNiL= 29.2 mol%) to 9.1 s-1 (xNiL= 7.6 mol%). It follows the opposite trend of the CO2 conversion rate. In-situ DRIFTS data under methanation conditions evidence that the TOFCO2at high XB is related to the presence of a formate route which is not predominant at low XB (high xNiL). A synergistic interplay of basic and metallic sites is present. This contribution provides a rationale for designing industrially competitive CO2 methanation catalysts with high catalytic activity while maintaining low Ni loading.

Visualization of CH4/CO2 hydrate dissociation and reformation during multistep depressurization assisted by pore-scale X-ray computed tomography

CH4–CO2 swapping is a promising and safe technique to produce CH4 gas and store CO2 without destabilizing hydrate-bearing sediments. However, inefficient CH4 recovery due to low CO2 diffusion prevents this technique from large-scale application. Multistep depressurization (MD) is therefore performed on CH4/CO2 hydrates after hydrate swapping to improve CO2 diffusion. This work presents pore-scale visualization of CH4/CO2 hydrates during MD by non-destructive X-ray computed tomography (CT) and combines the visual results with mixed hydrate kinetics to study hydrate morphology evolution and fluid migration. Influences of particle sizes (2–5 mm) and L-methionine (3000 ppm) on dissociation parameters were examined at reducing depletion pressures (8.5–59.4 bar) and constant temperatures (0.5–1.3 °C). The results of CT images showed enlargements of hydrate or gas phase with depletion pressures below CH4 hydrate stability pressures, complying with the pressure variations during MD. These variations of hydrate and fluid phases as well as pressure responses were the most obvious for particle size of 3 mm, resulted from good pore connectivity and relatively efficient mass transfer. L-methionine had no direct effect on CH4 production but enhanced CO2 storage, with the highest both CH4 gaseous mole fraction (86.1 mol%) and CO2 storage ratio (88.8%) at depletion pressure of 22.6 bar. This work clarified five-type pressure variations coupled with phase changes, providing firm evidence for hydrate dissociation/reformation and fluid migration that greatly affected hydrate exploitation. These understandings of varying morphologies and compositions of CH4/CO2 hydrates during MD would be applicable to help hydrate energy harvest and carbon emission mitigation.

CO2 Capture and Gas Storage Capacities Enhancement of HKUST-1 by Hybridization with Functionalized Graphene-like Materials.

The role of graphene related material (GRM) functionalization on the structural and adsorption properties of MOF-based hybrids was deepened by exploring the use of three GRMs obtained from the chemical demolition of a nanostructured carbon black. Oxidized graphene-like (GL-ox), hydrazine reduced graphene-like (GL), and amine-grafted graphene-like (GL-NH2) materials have been used for the preparation of Cu-HKUST-1 based hybrids. After a full structural characterization, the hybrid materials underwent many adsorption-desorption cycles to evaluate their capacities to capture CO2 and store CH4 at high pressure. All the MOF-based samples showed very high specific surface area (SSA) values and total pore volumes, but different pore size distributions attributed to the instauration of interactions between the MOF precursors and the specific functional groups on the GRM surface during MOF growth. All the samples showed a good affinity toward both gases (CO2 and CH4) and a comparable structural stability and integrity (possible aging was excluded). The trend of the maximum storage capacity values of the four MOF samples toward CO2 and CH4 was HKUST-1/GL-NH2 > HKUST-1 > HKUST-1/GL-ox > HKUST-1/GL. Overall, the measured CO2 and CH4 uptakes were in line with or higher than those already reported in the open literature for Cu-HKUST-1 based hybrids evaluated in similar conditions.

Investigation of CO2 and CH4 capture from syngas in adsorption process and breakthrough modeling by modified Lattice-Boltzmann mesoscale method

A modified Lattice Boltzmann method (LBM) was developed to model and analyze the transient flow and multi-component adsorption in a dispersive packed bed column of activated carbon as a new kind of meso-scale modeling. The model using D2Q9 (two dimensions and 9 speed) lattice solves the two-dimensional space, convection-dispersion adsorption model for the CO2–CH4 mixture in rich H2 at transient condition. The sink/source term model was considered as the adsorption/desorption kinetic rate based on Extended Langmuir theory for multicomponent mixture. The mole balances in the solid phase were considered as the lumped kinetic model of adsorption-desorption reaction. The results of the developed model was presented as the flow velocity and molar fractions of the components in axial and radial directions of the bed as well as breakthrough curves of CO2 and CH4 from their mixture in H2 gas stream under pressures of 3 and 5 bar and inlet linear velocities of 0.01, 0.04, 0.08 and 0.1m/min. The breakthrough curves were validated with the experimental data and the average absolute relative deviations (AARD) were calculated for both components. In addition, the results of LBM were compared with finite difference method in which AARDs were dtermined as 3% and 8% for CO2,4% and 7% for CH4 , by LBM and FDM, respectively.

CH4 Fluxes and Their Comprehensive Greenhouse Effects with CO2 Fluxes in Direct-seeded Rice in Poyang Lake Plain

Paddy fields are complex ecosystems that both emit CH4 and absorb CO2, which plays an important role in the global water-carbon cycle and carbon budget. In this study, the CH4 fluxes and CO2 fluxes of double-cropping direct-seeded rice fields in 2020 in the Poyang Lake Plain were obtained using the eddy covariance method, and the variation characteristics, accumulation in the whole growth period, and comprehensive greenhouse effects of two greenhouse gases were quantitatively revealed. The results showed that, the double-cropping direct-seeded rice field in Poyang Lake Plain was the source of CH4 emission, and the emission during the whole growth period was 52.6 g·m-2, with an average daily emission of 0.208 g·(m2·d)-1. CH4 emission and daily average emission in the early rice season were 20.7 g·m-2 and 0.188 g·(m2·d)-1, respectively, which were lower than the emissions of 31.9 g·m-2 and 0.255 g·(m2·d)-1 in the late rice season. CH4 flux had significant seasonal variation characteristics. The strong emission period (emission peak) of CH4 was concentrated in the middle growth stage of early rice and the early growth stage of late rice. A total of 85.5% of CH4 in the early rice season and 92.1% of CH4 in the late rice season were released during the strong emission periods, and seasonal peak values were 0.638 g·(m2·d)-1 and 1.282 g·(m2·d)-1, respectively. The diurnal variation characteristics of CH4 flux showed three types:obvious unimodal type, non-obvious unimodal type, and irregular type. The strong emission period was mainly the unimodal type, and the peak values of 0.453 μmol·(m2·s)-1 in the early rice season and 0.977 μmol·(m2·s)-1 in the late rice season appeared at 14:00-15:00 and maintained a high emission rate at 12:30-16:00. The CO2 accumulation in the whole growth period of early rice and late rice was -990.4 g·m-2 and -1156.6 g·m-2, respectively, and the total was -2147.0 g·m-2. The comprehensive greenhouse effect of CH4 emission and CO2 exchange in the double-cropping paddy field was -673.6 g·m-2 (calculated using the CO2 equivalent), which showed a cooling effect. Excluding CH4 emissions when evaluating the greenhouse effect of the paddy field, the CO2 equivalent emission of 1473.4 g·m-2 would be underestimated, accounting for 68.6% of the net CO2 absorption. Considering CH4 emissions, CO2 exchanges, and carbon emissions caused by rice harvest, the two-season direct seeding paddy field in Poyang Lake Plain was the source of greenhouse gas emissions.

Ordered mesoporous Co3O4-Al2O3 bimetal oxides for CO2 hydrogenation to synthetic natural gas: Effects of surface Al2O3 distribution

The highly ordered mesoporous structures of Co3O4-Al2O3 mixed metal oxide, prepared by using a hard template of the mesoporous KIT-6, revealed a higher catalytic activity and stability for CO2 hydrogenation to synthetic methane at an optimal surface Al content with ∼6 wt% (m-CoAl(1)). The higher CO2 conversion (42.5%) and CH4 selectivity (96.7%) were attributed to the adjusted surface hydrophobicity with optimal amount of spinel CoAl2O4 phases, where the CoAl2O4 phases mainly acted as structural stabilizing components in the ordered mesoporous Co3O4-Al2O3 matrices by suppressing the aggregations of Co3O4 nanoparticles as well as by generating more hydrophobic surfaces. At an optimal surface Al2O3 content (m-CoAl(1)), the stronger interactions of Co3O4-Al2O3 were selectively formed with the help of an optimal amount of the spinel CoAl2O4 phases, which further enhanced the surface hydrophobicity and oxygen vacant sites to effectively suppress competitive adsorption of water formed by CO2 hydrogenation.

Enhancement of hollow Ni/CeO2-Co3O4 for CO2 methanation: From CO2 adsorption and activation by synergistic effects

CO2 absorption and activation play key roles in the process of CO2 methanation, but revealing the mechanism and synergistic effects are still challenges, especially in some complicated routes. Herein, an optimized hollow Ni/CeO2-Co3O4 catalyst is shown to be capable of CO2 absorption and activation, the performance could be attributed to the strong synergistic effects among each component. In addition, the respective role was verified that the Co3O4 and CeO2 contributed to the CO2 adsorption and subsequently coupled with Ni for CO2 activation. Furthermore, in-situ DRIFTS were used to demonstrate the hydrogenation mechanisms, and the promotion of CO2 absorption and CH4 selectivity was confirmed in Ni/CeO2-Co3O4. The DFT results verified the synergistic effects of the established catalysts, which could also be a universal strategy for the catalysts designation.

Thermal-Hydraulic-Mechanical Coupling Simulation of CO2 Enhanced Coalbed Methane Recovery with Regards to Low-Rank but Relatively Shallow Coal Seams

CO2 injection technology into coal seams to enhance CH4 recovery (CO2-ECBM), therefore presenting the dual benefit of greenhouse gas emission reduction and clean fossil energy development. In order to gaze into the features of CO2 injection’s influence on reservoir pressure and permeability, the Thermal-Hydraulic-Mechanical coupling mechanism of CO2 injection into the coal seam is considered for investigation. The competitive adsorption, diffusion, and seepage flowing of CO2 and CH4 as well as the dynamic evolution of fracture porosity of coal seams are considered. Fluid physical parameters are obtained by the fitting equation using MATLAB to call EOS software Refprop. Based on the Canadian CO2-ECBM project CSEMP, the numerical simulation targeting shallow low-rank coal is carried out, and the finite element method is used in the software COMSOL Multiphysics. Firstly, the direct recovery (CBM) and CO2-ECBM are compared, and it is confirmed that the injection of CO2 has a significant improvement effect on methane production. Secondly, the influence of injection pressure and temperature is discussed. Increasing the injection pressure can increase the pressure difference in the reservoir in a short time, so as to improve the CH4 production and CO2 storage. However, the increase in gas injection pressure will also lead to the rapid attenuation of near-well reservoir permeability, resulting in the weakening of injection capacity. Also, when the injection temperature increases, the CO2 concentration is relatively reduced, and the replacement effect on CH4 is weakened, resulting in a slight decrease in CBM production and CO2 storage.

Facile and efficient synthesis of ordered mesoporous MIL-53(Al)-derived Ni catalysts with improved activity in CO2 methanation

A novel and feasible way to obtain MIL-53(Al)-derived Ni catalysts for CO2 methanation is presented. The sacrificial MIL-53(Al) was obtained by a less time and energy-consuming hydrothermal synthesis, at 190 °C, 12 h (compared to 220 °C, 72 h), at no expense on the structural and textural properties. The as-synthesized (as) and activated (lt) forms of MIL-53(Al) were derived at 600 °C to give amorphous mesoporous MIL-53(Al)-derived alumina, AlMIL-53(as) and AlMIL-53(lt), respectively. The subsequent Ni(10 wt%) catalysts obtained by impregnation were investigated by XRD, N2 physisorption, TPR, TEM, H2-TPD, and CO2-TPD. It was found that Ni/AlMIL-53 catalysts have an ordered mesoporous structure (5–10 nm), uniform distribution of round-shaped Ni nanoparticles (4–5 nm), aligned within the pores of the MIL-53(Al)-derived alumina, and an enhanced H2 and CO2 adsorption capacity compared to Ni/Al(com). Thus, Ni/AlMIL-53(as) reveals a H2 adsorption capacity 2 times larger than Ni/AlMIL-53(lt), and 4 times larger than for Ni/Al(com). This was explained by the largest dispersion of small Ni nanoparticles (∼4.2 nm), but also by an additional amount of H2 available on the catalyst, as revealed by control TPD tests. Also, Ni/AlMIL-53(as) showed a judicious distribution among weak and medium basic sites. These features made Ni/AlMIL-53(as) the best performing catalyst in CO2 methanation (200–500 °C, CO2/H2/Ar=1/4/1, 36 Lg-1h-1), with 70% CO2 conversion and 95% CH4 selectivity, at 400 °C. All catalysts showed stable CO2 conversion and CH4 selectivity over 24 h time on stream, with no evident deactivation due to Ni sintering or C deposition, the catalytic performance decreasing in the series Ni/AlMIL-53(as)>Ni/AlMIL-53(lt)>Ni/Al(com).

Defect engineering by steam treatment over Pt/CeO2 catalyst promoting C–H activation in partial oxidation of methane

Reducible oxides such as ceria have been certified to significantly enhance the catalytic activity of redox reactions. In this study, Pt/CeO2 catalyst was treated with steam, a good deal of hydroxyl groups came into being on surface to form Pt–OH species, thus achieving a high degree of Pt dispersion. The results of O2-TPD, XPS, Raman and EPR indicated that the dissociation of steam at surface vacancy was in favor of activation and removal of lattice oxygen and generation of oxygen vacancies. DFT calculation and in situ DRIFTS results showed that the oxygen vacancy was favorable for activating C–H bond in methane. The Pt/CeO2–H2O catalyst with abundant oxygen vacancies presented outstanding catalytic activity than that of Pt/CeO2, the CH4 conversion rate, CO and H2 selectivity was 62%, 60% and 58%, respectively. What's more, defective engineering promoting methane partial oxidation can be extended to all kinds of redox reactions.

A High-pressure Filled Ice in the H2O–CO2–CH4 System, with Possible Consequences for the CO2–CH4 Biosignature Pair

Here we constrain the speciation of carbon that may outgas in ocean exoplanets. Ocean exoplanets likely have at least a few percent by mass of water, which is sufficient to build a high-pressure ice layer between a rocky interior and the outer hydrosphere. We study the possible formation of a filled ice in the ternary system H2O–CO2–CH4. The incorporation of CH4 and CO2 in filled ice would be an important mechanism for transporting carbon across a high-pressure ice mantle into the atmosphere. The CH4–CO2 pair is also important as a potential biosignature. We find that a filled ice in the system H2O–CO2–CH4 is possible though enriched in CH4. CO2 cannot account for more than 15% by mole of the carbon content of the filled ice. Such a filled ice is less dense than an overlying ocean and would therefore discharge into the ocean, depressurize, and outgas its carbon content into the atmosphere. A high-pressure, water-rich mantle in ocean worlds may therefore support the transport of carbon from the interior into the atmosphere. More than 75% by mole of this carbon would be reduced. As long as CH4 exists/is produced in the interior and the ice mantle convects, thus transporting chemical species outward, a flux of carbon enriched in CH4 would outgas. If this persists over geological time it would negate atmospheric sinks for CH4, and explain low concentrations of atmospheric CO2. If the contrary is correct than the interior of the planet may be oxidizing.

The climate and compositional variation of the highly eccentric planet HD 80606 b – the rise and fall of carbon monoxide and elemental sulfur

ABSTRACTThe gas giant HD 80606 b has a highly eccentric orbit (e ∼ 0.93). The variation due to the rapid shift of stellar irradiation provides a unique opportunity to probe the physical and chemical timescales and to study the interplay between climate dynamics and atmospheric chemistry. In this work, we present integrated models to study the atmospheric responses and the underlying physical and chemical mechanisms of HD 80606 b. We first run 3D general circulation models (GCMs) to establish the atmospheric thermal and dynamical structures for different atmospheric metallicities and internal heat. Based on the GCM output, we then adopted a 1D time-dependent photochemical model to investigate the compositional variation along the eccentric orbit. The transition of the circulation patterns of HD 80606 b matched the dynamics regimes in previous works. Our photochemical models show that efficient vertical mixing leads to deep quench levels of the major carbon and nitrogen species and the quenching behaviour does not change throughout the eccentric orbit. Instead, photolysis is the main driver of the time-dependent chemistry. While CH4 dominates over CO through most of the orbits, a transient state of [CO]/[CH4] > 1 after periastron is confirmed for all metallicity and internal heat cases. The upcoming JWST Cycle 1 GO program will be able to track this real-time CH4–CO conversion and infer the chemical timescale. Furthermore, sulfur species initiated by sudden heating and photochemical forcing exhibit both short-term and long-term cycles, opening an interesting avenue for detecting sulfur on exoplanets.

Substitution and oxygen vacancy double defects on Bi2MoO6 induced efficient conversion of CO2 and highly selective production of CH4

A series of novel iodine substitution and oxygen vacancy double defects Bi2MoO6 nanosheets for enhanced photocatalytic reduction of CO2 is reported, which exhibited superior CO2 photocatalytic activity and CH4 selectivity under full solar spectrum illumination. Bi2MoO6-I2 (the molar ratio of I to Mo is 0.13) has the highest photocatalytic activity, its CO yield is 2.0 times that of pure Bi2MoO6, the CH4 yield is 12.2 times that of pure Bi2MoO6, and the CH4 selectivity reaches 5.3 times that of pure Bi2MoO6. Its structure and physicochemical properties were investigated by material characterizations, photoelectrochemical tests and DFT calculations. The enhancement in CO2 conversion and CH4 selectivity benefit from: (1) Larger specific surface areas and smaller nanosheets thicknesses facilitate carrier migration; (2) More suitable band structure promotes the reduction of CO2; (3) Insertion of impurity energy levels in the band gap enables efficient jumping of photogenerated electrons; (4) Double defects contribute to efficient CO2 adsorption and activation; (5) Promoting highly selective conversion of CO2 to CH4 by optimising the formation energy of reaction intermediates.

Displacement Characteristics of CO2 to CH4 in Heterogeneous Surface Slit Pores

Studying the CO2–CH4 displacement process is of great importance to understand the CO2-enhanced shale gas recovery technology. However, most studies have focused on the gas behavior in the reservoir during the dominant stage of competitive adsorption after CO2 injection, as well as the shale gas recovery, displacement efficiency, and gas separation after displacement, while less attention has been paid to the gas behavior during the initial period of displacement. A CO2–CH4 displacement model that can provide a continuous pressure gradient in the displacement direction and a stable back-pressure at the pore outlet was developed based on a heterogeneous surface pore. The model was divided into three areas: CO2 injection area, pore area, and back-pressure area. Molecular dynamics simulations were used to study the effects of depressurization exploitation and injection pressure on the displacement behavior at the initial period of the displacement process under different reservoir conditions. It was found that the displacement process always starts from the CH4 reverse flow stage and then experiences the injection pressure action stage and positive displacement stage in sequence. Moreover, the extent of CH4 reverse flow directly affects the system development process and the final displacement efficiency. A small system presorption pressure and a large injection pressure are beneficial to the displacement. It is believed that the reservoir pressure should be dropped to the lowest possible level during depressurization exploitation, and the CO2 injection pressure needs to be selected by considering displacement efficiency, reservoir safety, and economic cost. The CO2 occupies the adsorption sites near graphene faster than that near montmorillonite (MMT) in the direction of displacement, while the CH4 desorption is faster near MMT. Therefore, it cannot be concluded that the displacement process near graphene is ahead of MMT. It is considered that the gas desorption/adsorption behavior near the graphene dominates the displacement process in terms of gas amount, while the fluctuation near MMT with time and injection pressure directly affects the gas adsorption variation in the pore space from the trend.

Enhanced Carbon Storage Process from Flue Gas Streams Using Rice Husk Silica Nanoparticles: An Approach in Shallow Coal Bed Methane Reservoirs

Carbon capture and storage (CCS) is considered a key process to reach net-zero emission by the 2050 aim of limiting global warming. Coal bed methane (CBM) is considered potential geological reservoirs for underground CCS due to the CO2–CH4 exchange feasibility by adsorptive phenomena. Global implementation has been focused only on deep reservoirs to provide methane recovery. Thus, this work proposes a modified CCS process based on silica nanoparticle inclusion for shallow CBM reservoirs (<300 m). The nanomaterials were evaluated at high pressure in two main stages including i) CO2 sorption on a single CO2 stream and ii) CO2 selectivity on a flue gas stream (N2–CO2 mixture). This work includes silica nanomaterial synthesized from rice husk as agro-waste sources with better technical-economic feasibility framed in a circular economy to reduce costs and maximize the use of available resources. Rice husk silica (RSi) nanoparticles were doped with 1.0, 3.0, and 5.0 wt % of urea (Si–U), diethylamine (Si-DE), triethylamine (Si-TE), and ethylenediamine (Si-EM) to enhance the CO2 sorption. First, CO2 sorption was evaluated at 30 °C and between 0.084 and 3 MPa using a CO2 stream to determine the best-doped amount of each N-source. Then, the best nanoparticles were used to impregnate CBM at 10 and 20 wt %, and the subsequent CO2 storage on the flue gas stream (70% v/v N2 and 30% v/v CO2) was done. The results showed that CO2 sorption on RSi increases with the N-group coating in the order RSi-DE < RSi-TE < RSi-U < RSi-EM. Also, the best-doped amount for each N-source was 3 wt %. For CBM impregnation, the nanofluid containing 20 wt % of RSi-EM3 presented the best yield increasing the CO2 sorption from 0.05 to 0.75 mmol g–1, meaning an increase of more than 1000% in the sorption capacity.

Pressure broadening in Raman spectra of CH4–N2, CH4–CO2, and CH4–C2H6 gas mixtures

Different molecular environments change the spectrum of a given gas sample involved in a mixture compared to the spectrum of a pure gas. It is necessary to account for this effect to improve the accuracy of the analysis of the natural gas composition by Raman spectroscopy. First, the change in the main components of natural gas (methane, nitrogen, carbon dioxide, and ethane) must be considered. This work is devoted to the mutual influence of CH4–N2, CH4–CO2, and CH4–C2H6 on their characteristic Raman bands in the range of 300–2500 cm−1. The half-width and asymmetry of the Q branches of N2, CO2, and C2H6 as a function of methane concentration were obtained in the range of 1–50 bar. The averaged broadening coefficients of the rotational-vibrational lines of the ν2 band of CH4 perturbed by N2, CO2, and C2H6 are measured. A high-sensitivity spectrometer with a resolution of 0.5 cm−1 based on spontaneous Raman scattering was used to obtain reliable results. The algorithm and all the necessary parameters for simulating the effect of various molecular environments on the Raman bands of the main components of natural gas are presented.

Nutrient release and flux dynamics of CO2, CH4, and N2O in a coastal peatland driven by actively induced rewetting with brackish water from the Baltic Sea

Abstract. The rewetting of drained peatlands supports long-term nutrient removal in addition to reducing emissions of carbon dioxide (CO2) and nitrous oxide (N2O). However, rewetting may lead to short-term nutrient leaching into adjacent water and high methane (CH4) emissions. The consequences of rewetting with brackish water on nutrient and greenhouse gas (GHG) fluxes remain unclear, although beneficial effects such as lower CH4 emissions seem likely. Therefore, we studied the actively induced rewetting of a coastal peatland with brackish water, by comparing pre- and post-rewetting data from the peatland and the adjacent bay. Both the potential transport of nutrients into adjacent coastal water and the shift in GHG fluxes (CO2, CH4, and N2O) accompanying the change from drained to inundated conditions were analyzed based on measurements of the surface water concentrations of nutrients (dissolved inorganic nitrogen, DIN, and phosphate, PO43-), oxygen (O2), components of the CO2 system, CH4, and N2O together with manual closed-chamber measurements of GHG fluxes. Our results revealed higher nutrient concentrations in the rewetted peatland than in the adjacent bay, indicating that nutrients leached out of the peat and were exported to the bay. A comparison of DIN concentrations of the bay with those of an unaffected reference station showed a significant increase after rewetting. The maximum estimated nutrient export (mean ± 95 % confidence level) out of the peatland was calculated to be 33.8 ± 9.6 t yr−1 for DIN-N and 0.24 ± 0.29 t yr−1 for PO4-P, depending on the endmember (bay vs. reference station). The peatland was also a source of GHG in the first year after rewetting. However, the spatial and temporal variability decreased, and high CH4 emissions, as reported for freshwater rewetting, did not occur. CO2 fluxes (mean ± SD) decreased slightly from 0.29 ± 0.82 g m−2 h−1 (pre-rewetting) to 0.26 ± 0.29 g m−2 h−1 (post-rewetting). The availability of organic matter (OM) and dissolved nutrients were likely the most important drivers of continued CO2 production. Pre-rewetting CH4 fluxes ranged from 0.13 ± 1.01 mg m−2 h−1 (drained land site) to 11.4 ± 37.5 mg m−2 h−1 (ditch). After rewetting, CH4 fluxes on the formerly dry land increased by 1 order of magnitude (1.74 ± 7.59 mg m−2 h−1), whereas fluxes from the former ditch decreased to 8.5 ± 26.9 mg m−2 h−1. These comparatively low CH4 fluxes can likely be attributed to the suppression of methanogenesis and oxidation of CH4 by the available O2 and sulfate in the rewetted peatland, which serve as alternative electron acceptors. The post-rewetting N2O flux was low, with an annual mean of 0.02 ± 0.07 mg m−2 h−1. Our results suggest that rewetted coastal peatlands could account for high, currently unmonitored, nutrient inputs into adjacent coastal water, at least on a short timescale such as a few years. However, rewetting with brackish water may decrease GHG emissions and might be favored over freshwater rewetting in order to reduce CH4 emissions.

Coal char supported Ni catalysts prepared for CO2 methanation by hydrogenation

Catalytic CO2 methanation is a potential solution for conversion of CO2 into valuable products, and the catalyst plays a crucial role on the CO2 conversion and CH4 selectivity. However, some details involved in the CO2 methanation over the carbon supported Ni catalysts are not yet fully understood. In this work, commercial coal char (CC) supported Ni catalysts were designed and prepared by two different methods (impregnation-thermal treatment method and thermal treatment-impregnation method) for CO2 methanation. Effects of the preparation conditions (including the thermal treatment temperature and time, the mass ratio of CC:Ni and the preparation method), as well as the reaction temperature of CO2 methanation, were investigated on the catalyst morphology, reducibility, structure and catalytic performance. Fibrous Ni-CC catalyst is achieved and shows high CO2 conversion (72.9%–100%) and CH4 selectivity (>99.0%) during the 600-min methanation process. Adverse changes of the catalyst surface and textural properties, reducibility, particle size and morphology are the potential factors leading to the catalyst deactivation, and possible solutions resistant to the deactivation were analyzed and discussed. The CO2 methanation mechanism with the CO route was proposed based on the oxidation-reduction cycle of Ni in this work.