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Adsorption equilibrium isotherms of CO2, CH4, and mixtures of CO2/CH4 on shale sampled from Nanchuan, southeastern Sichuan Basin, were measured at 278, 298, and 318 K by an accurate gravimetric method. The adsorption equilibrium data of CO2 and CH4 were fitted using both the virial model and the Brunauer–Emmett–Teller (BET) model, and the isotherms of CO2/CH4 mixtures were fitted by an extended BET model. On the basis of adsorption data, the adsorption selectivity factors for CO2 over CH4 (αCO2/CH4 ) and thermodynamic parameters were estimated. Nanchuan shale was characterized with a high total organic carbon (TOC), having inorganic minerals and wide pore size distribution ranges. The adsorption heat, negative Gibbs free energy change, and negative surface potential of CO2 are larger than those of CH4, and the entropy loss of CO2 is larger than that of CH4, suggesting that adsorbed CO2 is in a more highly ordered arrangement than CH4 on shale. αCO2/CH4 values at different temperatures are all larger than 2.5.

Graphite is one of the most attractive anode materials due to its low cost, environmental friendliness, and high energy density for potassium ion batteries (PIBs). However, the severe capacity fade of graphite anodes in traditional KPF6-based electrolyte hinders its practical applications. Here, we demonstrate that the cycling stability of graphite anodes can be significantly improved by regulating the coordination of solvent molecules with KPF6 via a high-temperature precycling step. In addition to the solvents being electrochemically stable against reduction, a stable and uniform organic-rich passivation layer also forms on the graphite anodes after high-temperature precycling. Consequently, the PIBs with graphite anodes could operate for more than 500 cycles at 50 mA g–1 with a reversible capacity of about 220 mAh g–1 and an average Coulombic efficiency greater than 99%. Furthermore, full batteries based on Prussian blue cathodes and high-temperature precycled graphite anodes also exhibit excellent performance. Molecular dynamics simulations were performed to explore the solvation chemistry of the electrolytes used in this study.

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A new tetrazolate zeolite-like framework with a diamond topology, UTSA-49, was synthesized. UTSA-49 shows high selectivity for CO2/CH4 and CO2/N2 indicating a synergistic effect of the suitable pore size/shape and functional groups.

Knowledge of the kinetics of adsorption of CO2 and CH4 on shales is essential for the optimization of the technique of enhanced gas recovery by CO2 injection. In this paper, the experiments of adsorption kinetics of CO2 and CH4 on marine Wufeng (WF) shale and continental Yanchang (YC) shale at 318, 338, and 358 K over the pressure range of 3.0–8.0 MPa were conducted by a volumetric method. Results show that the adsorption processes of CH4 and CO2 on the shales can be described as an initial rapid adsorption stage and a slow sorption stage. The unipore model can simulate the kinetics data of CO2 and CH4 well. The diffusion coefficient (D) of gas increases with the increase of pressure. High temperatures will help to improve the diffusivities of CO2 and CH4. The order of magnitude of D of CO2 and CH4 on the two samples is 10–11 m2/s. The diffusion activation energies (E a) of CO2 and CH4 on YC shale are 3.37 and 10.15 kJ/mol, respectively, and E a of CO2 and CH4 on WF shale are 1.33 and 3.56 kJ/mol, respectively. The E a value of CH4 greater than that of CO2 indicates that CH4 diffusion in shale formation is more difficult and needs to jump a higher potential barrier. There is a positive correlation of pressure with the adsorption rates of CO2 and CH4. As the temperature enhances, the gas adsorption rate reduces. The ratios of D of CO2, CH4, and N2 are 1.42:1.15:1.00 on YC shale and 1.72:1.38:1.00 on WF shale. The adsorption rates of CO2, CH4, and N2 on the shales exhibit a decreasing trend.

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In this paper, the experiments of enhanced shale gas recovery by the injections of CO2, N2, and CO2/N2 mixture gases were carried out in a fixed bed setup to investigate the influence of the types of displacing fluid on CH4 recovery and gas flow dynamics. Investigation results show that when taking CO2 or N2 as displacement agent, the Coats–Smith dispersion–capacitance model can give an excellent simulated result to the breakthrough curves of CO2 and N2. The injection of N2 leads to the shortest breakthrough time (t b) of injected gas and the lowest recovery of CH4 product (R CH4‑product), while injecting CO2 into shale formations results in the longest t b of injected gas and the highest R CH4‑product with a relatively sharp displacement front. The differences of dispersion coefficient (K D) and the flowing fraction of pore space (F v) in the Coats–Smith dispersion–capacitance model are the underlying reasons for the distinct behaviors of CO2 injection and N2 injection. With increasing CO2 mole fraction in CO2/N2 mixture gases, R CH4‑product rises. The injection of 50:50/N2:CO2 mixture gases exhibits the biggest enhancement degree of N2 concentration during the displacement process. The injection of a N2-rich mixture can significantly prolong t b of CO2 and help to sequestrate injected CO2 over a long-term. For the transport of CO2 in reservoir, F v increases and K D and the mass transfer coefficient between mobile and immobile regions (K m) decreases with increasing N2 concentration in binary gas mixture, revealing that N2 can hinder the diffusion of CO2 into the micropore system to displace CH4. The fluctuation range of flow rate of injected gas (F injected‑gas) and the CO2 storage amount (V storage‑CO2) enhance as CO2 mole fraction in mixture raises. In order to optimize R CH4‑product, V storage‑CO2, and CO2 sequestration time, the selection of displacing fluid and the ratio of CO2/N2 mixture gases should be taken into consideration.