CO2 CH4 Research Articles

Gas Production Potential in Geothermal-Energy-Enhanced CH4–CO2 Swapping Processes

Carbon capture and storage has become a practice to reduce the greenhouse effect of carbon dioxide (CO2) on the global climate. Recent studies have generated increasing concerns about CO2 leakage from underground structures. This has called for more research on CH4–CO2 swapping in natural gas hydrate (NGH) reservoirs to lock CO2 in a solid state in underground structures. Because the CH4–CO2 swapping is too slow to be efficient, this study proposes to use geothermal energy to accelerate the process. This paper presents a technical feasibility analysis of using geothermal energy to assist CH4–CO2 swapping for simultaneously storing CO2 in NGH reservoirs and producing the dissociated natural gas. Mathematical models were developed to compute heat transfer from geothermal zones to NGH reservoirs. A case study was carried out using the data from an NGH reservoir in the Shenhu area, Northern South China Sea. The result of the case study indicates that heat conduction dictates the heat transfer process when the heat convection flow rate is less than 0.01 m3/s over a heat-releasing borehole length of 2,000 m. Heat convection can significantly accelerate the heat transfer inside the gas hydrate reservoir. The 15°C (designed gas hydrate dissociation temperature in the studied case) heat front will propagate to the upper and lower boundaries of the gas hydrate reservoir (39 ft or 12 m) in 220 days by heat conduction only. This time can be shortened to 140 days with the aid of a fluid convection rate of 0.005 m3/s. Geothermal heating can significantly increase the initial productivity of wells in heated gas hydrate reservoirs in CO2 swapping processes. When the gas hydrate reservoir is heated from 6 to 16°C, the fold of increase is expected to exceed five in the studied case. This study shows that CH4–CO2 swapping process using geothermal stimulation is a promising method for producing natural gas and locking CO2 permanently in NGH reservoirs. Further studies should first focus on investigations of the effect of CO2-hydrate formation on the CO2 mass transfer inside reservoirs.

Top‐down kinetic modeling from power law to elementary steps using KASTER: A methane steam reforming case study

AbstractA top‐down methodology for kinetic model construction including regression against experimental data is proposed using “KASTER.” As a case study, it is applied in the assessment of methane steam reforming (MSR) including water–gas shift (WGS) on a Ni catalyst at 923 K. The degree of detail in the reaction mechanism and the corresponding model is gradually enhanced, typically ranging from a simple power law to a microkinetic model. The reactor equations are solved transiently, preventing the numerical challenges encountered in the steady‐state solution, particularly for microkinetic models. The microkinetic variant indicated that CH4 dissociative adsorption and CO formation are kinetically relevant steps in MSR, while COOH formation is rate‐determining in WGS. However, the model providing the best balance between detail accounted for and parameter significance corresponded to a Langmuir–Hinshelwood–Hougen–Watson (LHHW) mechanism accounting for dissociative adsorption, with CO formation and COOH formation as rate‐determining steps for MSR and WGS, respectively.

Nitrilethermal synthesis of CeO2-based composite nanoparticles as Ru and Pd catalyst supports for CO2 methanation and CH4 oxidation

A one-pot and one-step solvothermal reaction in acetonitrile, termed ‘nitrilethermal’ synthesis, was developed to obtain CeO2 and CeO2-based composite nanoparticle assemblies, such as Al2O3−ZrO2, SiO2−CeO2, Y2O3−CeO2, and ZrO2−CeO2. The composites were prepared by heating a precursor solution containing Ce(NO3)3 with Al(NO3)3, Si(OEt)4, Y(NO3)3, or ZrO(NO3)2 as an oxide source and triethylene glycol as an additive in acetonitrile (or a mixed acetonitrile/ethanol solvent) at 300 °C for 10 min. Homogeneously mixed composite oxides with specific surface areas of 101−152 m2/g were obtained in all cases. The composites showed high oxygen storage capacities, with that of SiO2−CeO2 being especially high at >500 μmol-O/g. The impregnation method was used to apply the composites as supports for nanometal Ru and Pd catalysts for CO2 methanation and CH4 oxidation, respectively. Ru/SiO2−CeO2 demonstrated the slightly higher activity for CO2 methanation, while Pd/SiO2−CeO2 and Pd/Al2O3−CeO2 demonstrated superior low-temperature activities for CH4 oxidation.

On the phase behaviors of CH4-CO2 binary clathrate hydrates: Two-phase and three-phase coexistences.

We develop a statistical mechanical theory on clathrate hydrates in order to explore the phase behaviors of clathrate hydrates containing two kinds of guest species and apply it to CH4-CO2 binary hydrates. The two boundaries separating water and hydrate and hydrate and guest fluid mixtures are estimated, which are extended to the lower temperature and the higher pressure region far distant from the three-phase coexisting conditions. The chemical potentials of individual guest components can be calculated from free energies of cage occupations, which are available from intermolecular interactions between host water and guest molecules. This allows us to derive all thermodynamic properties pertinent to the phase behaviors in the whole space of thermodynamic variables of temperature, pressure, and guest compositions. It is found that the phase boundaries of CH4-CO2 binary hydrates with water and with fluid mixtures locate between simple CH4 and CO2 hydrates, but the composition ratios of CH4 guests in hydrates are disproportional to those in fluid mixtures. Such differences arise from the affinities of each guest species to the large and small cages of CS-I hydrates and significantly affect occupation of each cage type, which results in a deviation of the guest composition in hydrates from that in fluid on the two-phase equilibrium conditions. The present method provides a basis for the evaluation of the efficiency of the guest CH4 replacement to CO2 at the thermodynamic limit.

Self-consistent Models of Y Dwarf Atmospheres with Water Clouds and Disequilibrium Chemistry

Y dwarfs are the coolest spectral class of brown dwarf. They have effective temperatures less than 500 K, with the coolest detection as low as ∼250 K. They make up the low-mass tail of the star formation process, and are a valuable analog to the atmospheres of giant gaseous exoplanets in a temperature range that is difficult to observe. Understanding Y dwarf atmospheric compositions and processes will thus deepen our understanding of planet and star formation and provide a stepping stone toward characterizing cool exoplanets. Their spectra are shaped predominantly by gaseous water, methane, and ammonia. At the warmer end of the Y-dwarf temperature range, spectral signatures of disequilibrium carbon monoxide have been observed. Cooler Y dwarfs could host water clouds in their atmospheres. JWST spectral observations are anticipated to provide an unprecedented level of detail for these objects, and yet published self-consistent model grids do not accurately replicate even the existing Hubble Space Telescope and ground-based observations. In this work, we present a new suite of 1D radiative-convective equilibrium models to aid in the characterization of Y-dwarf atmospheres and spectra. We compute clear, cloudy, equilibrium chemistry and disequilibrium chemistry models, providing a comprehensive suite of models in support of the impending JWST era of panchromatic Y-dwarf characterization. Comparing these models against current observations, we find that disequilibrium CH4–CO and NH3–N2 chemistry and the presence of water clouds can bring models and observations into better, though still not complete, agreement.

Selective adsorption and transport of CO2–CH4 mixture under nano-confinement

Selective adsorption and transport of CO2–CH4 mixture under nano-confinement

Synergistic improvement of carbon sequestration and crop yield by organic material addition in saline soil: A global meta-analysis

The improvement and utilization of saline soil is an important guarantee for cultivating healthy soil, ensuring global food security, and mitigating the negative impacts of climate change. Organic material addition plays a crucial role in soil improvement and remediation, soil carbon sequestration, and improving soil fertilizer and productivity. In order to explore the comprehensive impact of organic material addition on properties of saline soil (including the physical and chemical properties, nutrient fixation, crop yield, and carbon sink capacity), we conducted a global meta-analysis using data from 141 articles. We found that, soil salinization significantly reduced plant biomass (50.1 %), soil organic carbon (20.6 %), and microbial biomass carbon (36.5 %). Meanwhile, it also reduced CO2 flux (25.8 %) and CH4 flux (90.2 %) significantly. Adding organic materials to saline soil significantly increased crop yield (30.4 %), plant biomass (30.1 %), soil organic carbon (62.2 %), and microbial biomass carbon (78.2 %), but also increased CO2 flux (221.9 %) and CH4 flux (29.7 %). Considering the balance of both carbon sequestration and carbon emissions, organic material addition significantly increased the net carbon sequestration by about 5890.7 kg CO2-eq·hm−2·100 d−1 on average. Besides, the organic material addition reduced soil salinity, exchangeable sodium, and pH, and increased >0.25 mm aggregates and soil fertility. Our findings suggest that organic material addition can improve both carbon sequestration in saline soil and crop yield. Considering the huge area of saline soil around the world, this understanding is essential to reduce the saline obstacle, improve the soil carbon sink capacity, ensure food security, and increase farmland reserves.

Highly Active and Durable Rh–Mo-Based Catalyst for the NO–CO–C3H6–O2 Reaction Prepared by Using Hybrid Clustering

We developed a method for preparing catalysts by using hybrid clustering to form a high density of metal/oxide interfacial active sites. A Rh–Mo hybrid clustering catalyst was prepared by using a hybrid cluster, [(RhCp*)4Mo4O16] (Cp* = η5-C5Me5), as the precursor. The activities of the Rh–Mo catalysts toward the NO–CO–C3H6–O2 reaction depended on the mixing method (hybrid clustering > coimpregnation ≈ pristine Rh). The hybrid clustering catalyst also exhibited high durability against thermal aging at 1273 K in air. The activity and durability were attributed to the formation of a high-density of Rh/MoOx interfacial sites. The NO reduction mechanism on the hybrid clustering catalyst was different from that on typical Rh catalysts, where the key step is the N–O cleavage of adsorbed NO. The reducibility of the Rh/MoOx interfacial sites contributed to the partial oxidation of C3H6 to form acetate species, which reacted with NO+O2 to form N2 via the adsorbed NCO species. The formation of reduced Rh on Rh4Mo4/Al2O3 was not as essential as that on typical Rh catalysts; this explained the improvement in durability.

Pore-scale lattice Boltzmann simulation of CO2-CH4 displacement in shale matrix

This study couples the Navier-Stokes and multicomponent advection-diffusion equations within the lattice Boltzmann method (LBM) to innovatively simulate the CO2–CH4 displacement in nanoporous shale matrix. In the LBM simulations of CO2 injection into heterogenous CH4-saturated nanoporous media, gas movements are modeled by two separate advection-diffusion lattices driven by the velocity solved from the third Navier-Stokes lattice. Langmuir adsorption kinetics is employed at the fluid-solid interfaces to simulate the mass exchange between the bulk free space and the solid matrix. Mass transfer inside the solid matrix is considered with adsorption and diffusion parameters obtained from molecular dynamics studies. CO2 adsorption and CH4 desorption are simulated simultaneously. The coupling scheme is successfully validated for advection, diffusion, and surface adsorption. Results show that the global mass transfer process is sensitive to intra-matrix diffusion. When the solid diffusion rate is ∼10−4 of the bulk one, selectivity can significantly impact the outflux concentration. Changing the CO2 adsorption rate constant 0.1–10 times nearly has no impact on gas adsorption in the solids. In comparison, the CH4 desorption rate constant strongly correlates to the CH4 desorption pathway. Increasing the particle size under a given porosity may benefit advection and lead to fast adsorption/desorption in the solids.

Investigation of CH4/CO2 competitive adsorption-desorption mechanisms for enhanced shale gas production and carbon sequestration using nuclear magnetic resonance

Understanding the competitive adsorption-desorption mechanisms in shale is of fundamental significance for enhancing CH4 recovery and CO2 sequestration. This study adopted nuclear magnetic resonance to reveal the influence of CO2 on adsorption-desorption behaviors of CH4 in plug-sized samples. Three distinctive peaks were observed in the transverse relaxation time (T2) spectrum of a CH4-saturated sample, which indicated the adsorbed CH4 (0.1 ms < T2 < 1 ms), free state CH4 in pores (2 ms < T2 < 30 ms) and free state CH4 in fractures (100 ms < T2 < 1000 ms). When CH4 reached adsorption equilibration under 20 MPa, the total T2 signals of adsorbed CH4, free state CH4 in pores and free state CH4 in fractures were 565.3, 591.5 and 306.6 p. u., respectively. Subsequently, CO2 was pumped into the CH4-saturated sample under 22 MPa. When CO2–CH4 completed the competitive adsorption process, T2 signals decreased from 565.3 to 396.6 p. u. for adsorbed CH4, increased from 591.5 to 707.3 p. u. for free state CH4 in pores, and increased from 306.6 to 359.5 p. u. for free state CH4 in fractures. Afterwards, the desorption of shale sample began. CH4 concentration decreased from 79% to 55% while CO2 concentration increased from 21% to 45%. Finally, the total desorption rate of adsorbed CH4 (65%) was much higher than that without introducing CO2 (25%–40%).

The influence of irreducible water for enhancing CH4 recovery in combination of CO2 storage with CO2 injection in gas reservoirs

CO2 flooding to enhance gas recovery (CO2-EGR) with CO2 storage offers the prospects of significant environmental and economic benefits by increasing CH4 recovery while simultaneously storing CO2. Most studies ignored the interaction of water with CO2 and the formation rocks and the influence of irreducible water to enhance CH4 recovery combined with CO2 storage were poorly understood by core-flooding experiments. In this research, a numerical model of a five-spot well pattern was developed by benchmarking against the existing literature, and the model was further modified to investigate the effects of irreducible water on CO2-EGR and CO2 storage in gas reservoirs. The injected CO2 preferentially moved horizontally and gradually flowed vertically to flood CH4, making the displacement front an inclined CO2-CH4 mixing zone. The model with irreducible water changed from 0% to 40%, the CO2 sweep efficiency improved and the CH4 recovery increased by 4.37%. This could be attributed to the narrowing of the CO2-CH4 mixing zone and the change in displacement front from an inclined horizontal plane to a near arc plane with better stability. The cumulatively stored CO2 decreased by 21.24%, due to the early CO2 breakthrough and shut-in times. However, because more CO2 was dissolved in water and trapped in residual gas, the contribution of CO2 solubility trapping and CO2 residual trapping increased by 12.01% and 10.34% respectively, while CO2 structural trapping decreased by 22.86%, resulting in a significant increase in long-term storage security. Mineral reactions had a negligible influence on CO2-EGR and CO2 sequestration in the CO2 flooding process. The higher the salinity, the lower the amount of dissolved CO2, and the lower the CH4 recovery and cumulatively stored CO2, with decreased security of CO2 storage with limited impact. The higher the irreducible water saturation (Swi), the more CO2 dissolved, and the CH4 recovery and long-term storage security of CO2 improved with a reduction of cumulatively stored CO2. Changing the gas relative permeability (Krg) has a small effect for CH4 recovery and CO2 storage. This research may provide new insights into analyzing the mechanism of irreducible water on the influence of CO2-EGR and CO2 storage, laying a foundation for the optimization of CO2-EGR schemes and the implementation of field applications in water-bearing gas reservoirs with CO2 injection in the future.

Methane replacement by using CO2/C3H8 mixtures for carbon storage and enhanced methane recovery in gas hydrates

The storage of gases via hydrates formation can be enhanced with several different techniques; for instance, the addition of promoting additives helps in reducing the pressures required for the process. However, most of strategies used for gas storage cannot help during replacement processes. This article deals with the hypothesis that the usage of moderate concentrations of small – chain hydrocarbons can absolve both the purposes at the same time. In particular CO2 storage and CH4 replacement were tested with the addition of propane. Three different concentrations of propane in mixture with carbon dioxide were selected, or 0.05, 0.10 and 0.15 mf. Hydrates were formed with each of them and the results discussed in order to identify the better solution in terms of hydrates produced and, mostly, quantity of CO2 stored. The selected concentration was then used for the replacement of methane and the results discussed in order to reveal the benefits obtained in terms of both CO2 stored and CH4 recovered, in comparison with the maximum results theoretically achievable in replacement tests carried out exclusively with pure carbon dioxide.

Recovery through proper grazing exclusion promotes the carbon cycle and increases carbon sequestration in semiarid steppe

Grazing exclusion changes soil physical-chemical characteristics, rapidly affects microbial community composition and function, and alters biogeochemical processes, e.g., carbon (C) cycle, over time. However, the temporal dynamics of CO2 emission and CH4 uptake during grassland restoration chronosequences remain poorly understood. We investigated soil CO2 emission and CH4 uptake, the genes related to CO2 and CH4 production and reduction (cbbL, cbbM, chiA, and pmoA), and associated microbial communities under different durations of grazing exclusion (0, 7, 16, 25, and 38 years) to reveal the mechanisms and potential of soil CO2 emission and CH4 uptake in a semi-arid steppe. The results showed that a proper exclusion period could significantly improve soil physical-chemical conditions, vegetation community, and soil C-cycling. The abundance of C-cycling functional genes (cbbL, cbbM, chiA and pmoA), CH4 uptake and CO2 emission rates showed a single-peak pattern with increasing duration of grazing exclusion, peaking at 16 years and then decreasing in the period between 25 and 38 years, indicating that the effect of exclusion weakened when the exclusion period was too long. The changes in C-cycling functional genes and microbial communities are primarily influenced by aboveground net primary productivity (ANPP), and are associated with CO2, CH4, soil water content (SWC), and soil organic carbon (SOC). Structural equation modeling showed that increases in SOC content and pmoA abundance caused by an increase in ANPP accelerated CO2 emission and CH4 uptake rates, respectively. Our results provide valuable insights into the critical role of grazing exclusion in promoting grassland restoration and carbon sequestration, and have potential implications for sustainable land management practices.

Confinement effect on transport diffusivity of adsorbed CO2–CH4 mixture in coal nanopores for CO2 sequestration and enhanced CH4 recovery

The transport of CO2–CH4 mixture in coal nanopores is crucial to CO2-enhanced coalbed (CO2-ECBM) recovery, but is highly challenging on adsorption-diffusion dominated nanoscale due to the gas-surface and intermolecular interactions. Using Monte Carlo and molecular dynamics simulation, the confinement effect of nanopores with two slit widths (2 and 6 nm) on the CO2–CH4 binary diffusion in the adsorption layer are investigated. A modified computational method for multi-component transport diffusivity in the adsorption layer is proposed by incorporating the survival probability function. The results show that the transport diffusivity in the semi-confined adsorption layer shows a general decreasing tendency with the increase of pressure, while it slightly decreases when the pressure <6.4 MPa in the confined adsorption layer, following an inverse parabola trend with the maximum value at around 12 MPa. Three mechanisms are classified regarding this pressure-dependent evolution. Firstly, the collision between molecules of weaker attraction and surface dominates the transport capacity, and this collisional frequency reduces at the low-pressure region. Accompanying the pressure exceeds the critical threshold, surface diffusion becomes the primary contribution. Lastly, significant intermolecular interactions appear after the adsorption saturation. During the CO2-ECBM process, pressure drawdown is the primary method to release the adsorbed CH4, and the largest recovery ratio can reach 25.9% in 2 nm micropore and 30.1% in 6 nm mesopore. After the early CO2 injection, the transport diffusion of CH4 exceeds that of CO2, and the selectivity of CH4 over CO2 increases in the subsequent CO2 huff-n-puff cycles. The CO2–CH4 mixture under greater confinement effect manifests higher diffusion selectivity, which benefits the separation of the CO2–CH4 mixture and further contributes to the CH4 recovery.

Temperature and soil moisture control CO2 flux and CH4 oxidation in urban ecosystems

Climate-driven shifts in soil temperature and soil moisture are crucial factors that control the ecosystem-atmosphere greenhouse gas (GHG) balance. In the present study, the relationship between CO2, CH4 fluxes and soil moisture content and temperature sensitivity was examined in three dominating types of urban ecosystems: grassland, city park and arable land. The analysis was based on the field measurements at biweekly intervals over a year using a static closed chamber method in Wroclaw urban area, Poland. The observed patterns of land-atmosphere CO2 and CH4 exchange varied across land cover types and were strongly influenced by seasonal variations in temperature and soil water content. Emission of CO2 from grassland and the city park was two times higher than from the arable land. The calculated CH4 oxidation rate was one and half times higher (p < 0.05) under grassland and the city park as compared to arable land.The estimated Q10 values ranged between 1.68 and 1.79 for CO2 and from 1.26 to 1.49 for CH4, depending on the ecosystem type. The temperature sensitivity of soil respiration decreased when the temperature was above 24.5 °C across the moisture gradient from 20 to 25 % m/v. Results suggest that despite the urban areas with agricultural land use revealed the lowest CO2 fluxes compared to grassland and city park, the former showed the lowest seasonal mean CH4 oxidation. This indicates that with ongoing warming, the higher Q10 of CO2 production vs. CH4 oxidation will further shift the carbon balance towards the source and this shift will be especially critical for arable lands in urban areas.

Carbon conversion by Methanococcus maripaludis S2 under diazotrophy and a revised genome-scale metabolic model

Methanococcus maripaludis can utilize CO2 as the sole carbon source. Since N2 is a major component of most flue gases, understanding its impact on the cellular behaviours of M. maripaludis is critical. Here, we studied CO2 conversion by M. maripaludis S2 in minimal media with ammonium or N2 as the sole nitrogen source. N2-grown cultures exhibited a long lag phase, prolonged growth phase, and lower cell density compared to ammonium. At any specific growth rate, the CO2 intake and CH4 evolution fluxes were higher for N2 than ammonium, suggesting that N2 is a better nitrogen source for carbon conversion to CH4. The flux measurements were used to improve a genome-scale metabolic model existing in the literature. The revised model iMR557 has a coverage of 32% open reading frames and includes new pathways. iMR557 was used to illustrate flux distributions under different conditions and successfully replicate the previously reported acetate dissimilation.

Enhanced performance of La1-xFeO3-δ oxygen carrier via A-site cation defect engineering for chemical looping dry reforming of methane

Chemical looping is a process-intensification tool that focuses on the fields of fossil fuel combustion, CO2 capture, hydrocarbon valorization, energy storage, and other energy-related and environmental-related areas. Perovskite-structured LaFeO3, a typical oxygen storage material, shows great potential for chemical looping partial oxidation and H2O/CO2 splitting. Here, we report a simple and efficient strategy to enhance catalytic activity by tuning A-site cation defects in perovskites via a sol-gel method. Systematically studies show that A-site cation defects affect both the physical and chemical properties. With the A-site cation defect engineering, the crystallite size of the La1-xFeO3-δ perovskites is reduced. The catalytic performance for CH4 oxidation and CO2 splitting is enhanced with increasing oxygen vacancy concentration. The La0.93FeO3-δ oxygen carrier exhibits the highest catalytic performance with 88% CO selectivity and 90% methane conversion at 750 °C. In addition, the La0.93FeO3-δ shows higher stability in the successive CH4 partial oxidation/CO2 splitting redox cycles, with almost unchanged CH4 conversion and CO selectivity. All these results demonstrate that the strategy of adjustment of different molar ratios of A/B site in perovskite metal oxides can effectively regulate the oxygen vacancy concentration.

Dry reforming of methane using bimetallic Pt–Ni/Ti-SBA-15: Effect of Si/Ti ratio on catalytic activity and stability

A one-pot hydrothermal technique was used to make a series of Ti-incorporated mesoporous SBA-15 with varying Si/Ti ratios. The synthesized mesoporous materials were modified by introducing Ni (9%) as active metal and Pt (0.5%) as promoter using nickel nitrate and chloroplatinic acid, respectively, as metal precursors through incipient wetness impregnation method. All the catalysts and supports were characterized by X-ray diffraction, BET surface area, Fourier Transform–Infrared spectroscopy, UV–Visible diffuse reflectance spectroscopy, H2–temperature-programmed reduction, NH3–temperature-programmed desorption, transmission electron microscopy, and thermogravimetric analysis. The catalysts were subjected to dry reforming of methane using CH4/CO2 (molar feed ratio of 1:1) with a gas hourly space velocity (GHSV) of 36,000 mL. g−1. h−1 at a temperature range of 400–800 °C. The characterization results confirmed the incorporation of titanium ions in the SBA-15 matrix. However, Si/Ti loadings of 10 and 20 exhibited low extra-framework anatase phase titania levels, and high surface acidity. Among the subjected catalysts, Pt–Ni/Ti-SBA-15 (Si/Ti = 10) showed higher catalytic activity (CH4 = 84% and CO2 = 91%) with a H2/CO ratio of 3.6 after an 8 h reaction, and exhibited higher stability and coke tolerance than the bare catalysts and other modified Pt–Ni/Ti-SBA-15 catalysts. The characterization results of spent catalysts also confirmed low coke deposition on titanium-incorporated catalysts. The remarkable performance of the Pt–Ni/Ti-SBA-15 towards CH4 conversion and CO2 conversion may be related to strong metal–support interaction, presence of strong and weak acid sites, well-dispersed active metals and bi-metallic interaction.

Catalytic non-thermal milli-pulse plasma for methanation of CO2 without carbon deposition and catalyst deactivation

Catalytic routes for upgrading CO2 through Sabatier reaction CO2+4H2→CH4+2H2O have been studied for decades. To avoid water adsorption and catalyst aging, the process must be operated at 300–400 °C, which subsequently causes carbon deposition and catalyst deactivation. Non-thermal plasma is a promising approach to overcoming the barriers associated with CO2 dissociation and conversion, and avoid the carbon deposition observed in a traditional Sabatier reaction. This study elucidated; 1) the impacts of reactor geometry and plasma condition on plasma discharge; 2) the synergism between active site (Ni and Co) and catalyst support; and 3) the impact of catalyst promoter (Ru) on CO2 conversion, methanation yield, and selectivity. The physics and chemistry of plasma were investigated in 6 different reactor geometries using 28 different catalysts. The plasma physics was discussed as a function of discharge characteristics, capacitance properties, reduced electric field, power consumption, and reactor temperature. CO2 conversion, CH4 yield, and CH4/(CO + CH4) selectivity are reported and compared with those under thermo-catalysis at 400 °C. In addition, carbon deposition on the surface of high-voltage electrodes as a result of Joule heating was investigated. In contrast to γAl2O3, CO selectivity was dominant in SiO2-supported catalysts. In terms of active sites, the following trend was observed for CO2 conversion, methanation, and yield: Ru > Ni > Co. The addition of Ru promoter played a more prominent role in enhancing CH4/(CO + CH4) selectivity, other than production yield or conversion. Except for SiO2-Ni15 and SiO2-Co15, all the catalysts showed a higher methane yield in plasma discharge at 150–170 °C than thermal conversion at 400 °C.

Numerical study on the influence of temperature on CO2-ECBM

CO2-ECBM can not only improve the production of CBM, but also contribute to CO2 geological sequestration, which has multiple economic effects. In this paper, COMSOL simulation software was used to conduct numerical simulation studies on the 3# coal seams in Qinshui Basin. A fully coupled model of coal deformation, gas flow and migration, and thermal transfer was established to evaluate the effect of temperature on the production of CBM by CO2 injection. The results indicates that temperature is a key factor affecting CH4 production and CO2 storage. Increasing injection temperature can significantly accelerate the process of gas displacement and the CO2 storage is more sensitive to temperature than the CH4 production. In contrast, both the CH4 production and the CO2 storage decrease with the increase of initial temperature of coal seam and the permeability will decrease faster. With the increase of injection time, the effective influence radius of displacement increases, but the increment of influence radius decreases gradually. The lower the initial temperature of the coal seam, the larger the influence radius, the influence radius increases as a whole with the increase of time. Low Young's modulus or high Poisson's ratio can effectively increase CO2 storage and CH4 production.