The effects of potential model of CO2 on its bulk phase properties and adsorption on surfaces and in pores

This study investigates the adsorption and storage behaviour of CO2 in the different matrix components of shale based on a molecular simulation method. First, based on the Grand Canonical Monte Carlo (GCMC) method, we successfully established five pore models three fluid models to study the effects of temperature, pressure, pore diameter, water content, and CH4 on the adsorption of CO2. Then, based on the actual data from the shale of the Longmaxi Formation in Sichuan Basin, China, the storage capacity of CO2 in the shale is determined by calculating the density distribution of CO2 and the proportion of excess adsorbed gas. The results demonstrate that both high temperatures and water content are unfavourable for the adsorption of CO2 in the shale pores. The adsorption of CO2 increases with rising pressure while it decreases with increasing pore size. The magnitude and stability of CO2 adsorption in the pores of various matrix components is as follows: organic matter > montmorillonite > illite > kaolinite > quartz. Compared to the scenarios neglecting the adsorption of CO2, the storage capacity of CO2 decreases by 7.87%. The main finding of this study is expected to provide theoretical guidelines for CO2 adsorption storage in shale.

Gas adsorption by activated carbon (AC) is one of the common approaches applied in industries for separation and purification purposes, e.g., air purification, hydrocarbon processing, and carbon capture and storage. Understanding the preferential adsorption of the adsorbates in the gas mixture is crucial for improving separation technologies. With the develop ment of computational technology, molecular simulation is recognized as a useful tool that can be important compensation for experimental study. A uniform slit pore is commonly used for representing the AC. However, the pore structure of AC is rather complex and is composed of randomly stacked crystallites. Moreover, the confined spaces between the carbon stacks tend to be irregular-shaped. The wedge pore model was used to represent the non-uniformity of AC as its size continuously changes in the axial direction. In this regard, a systematic Monte Carlo simulation was conducted to study the adsorption of bi nary mixtures containing carbon dioxide with methane or nitrogen at the ambient temperatures (i.e., 273–298 K) in slit and wedge-shaped pores with graphitic surfaces. The results were also compared with experimental data and predicted values using Ideal Adsorbed Solution Theory (IAST). The results of the single wedge pore model agreed at low pressure for single and multicomponent adsorption of experimental data and IAST predictions, while the results of the combination of slit pore with various pore widths were also well fitted or were close to the experimental data and compared to IAST predictions. It is evident from the results that the wedge pore can be the alternative pore model for the AC to reveal some important characteristics and mechanisms for pure and mixture adsorption.

Biogas is mainly consisted of methane and carbon dioxide in the presence of other contaminants. The biogas purification by adsorption using metal-organic frameworks is getting attention due to the low-cost operation and high-efficiency process. Co-gallate was predicted to give a promising performance in CO2 and CH4 adsorption. However, the behaviours of CO2 and CH4 adsorption on Co-gallate are not well-explained. Therefore, this work is to synthesize Co-gallate and its performance was discussed in terms of adsorbed amount of CO2 and CH4. The experimental CO2 and CH4 pure adsorption isotherms were then fitted with equilibrium isotherm and kinetic models to describe the adsorption behaviours. Co-gallate offered a greater CO2 adsorption capacity than CH4 due to a stronger adsorbent-adsorbate interaction. The experimental pure adsorption isotherms were best fitted with Toth model compared to Langmuir, Freundlich and Sips models according to the values. Toth model described the CO2 adsorption was multilayer and heterogeneous. Thermodynamic property suggested the CO2 and CH4 adsorption were classified as exothermic process and physisorption. For kinetic models, pseudo-first order model brought the highest goodness-of-fit in terms of rate of adsorption compared to pseudo-second order and Elovich models. Pseudo-first order model reflects the adsorption rate is proportional to the number of vacant sites. It confirmed CO2 adsorption was more favourable than CH4, at lower temperature condition. In this work, the equilibrium isotherm and kinetic models were employed to select the best-fitted model in explaining the adsorption behaviours. Therefore, these behaviours of CO2 and CH4 adsorption on Co-gallate are useful in designing the future practical operation of CO2/CH4 gas adsorption.

Chemically modified carbonaceous adsorbents for enhanced CO2 capture: A review

Multicomponent Adsorption of Volatile Organic Compounds in the Liquid Phase: Predictive Engineering Models, Molecular Simulations and Experiments

Much research has been done on reactions of a single CO2 molecule with a graphene surface. In this paper, density functional theory calculations are used to investigate the adsorption and reaction of double CO2 on the surface of single vacancy (SV) and divacancy (DV) defect graphene. The study found that due to the mutual repulsion between CO2 and the size of the SV defect, it is difficult for two CO2 molecular to be adsorbed directly above the SV defect at the same time. Regardless of SV or DV, the adsorption of the first CO2 in the defect center will have a beneficial effect on the adsorption of the second CO2. In addition, the transition state calculation of the CO2 reaction on the DV plane was carried out, and the adsorption behavior was analyzed and studied. This in-depth study is helpful to the understanding of the reaction behavior of CO2 on graphene, and further exploration in the direction of the effective application of graphene to the reaction and adsorption of CO2. Our work explores the adsorption behavior of CO2 on graphene surfaces, the physical and chemical adsorption of double CO2 at the defect was studied and analyzed.

The properties of water are of importance in many scientific disciplines such as chemistry, biology, geology, nanotechnology, and materials technology. Moreover, the adsorption of water on activated carbon (AC) is an important topic in many different areas of science and technology because water is the most common solvent in nature. The adsorption and phase behavior of polar fluids in carbon pores has been studied extensively, but our understanding of the adsorption of water on carbonaceous materials is still incomplete (1, 2, 3, 4). In recent years, a number of experimental and simulation studies of adsorption of water in pores have appeared in the literature. Some studies have assumed that the adsorption behavior of water in graphite pores is hydrophobic. Although principally hydrophobic adsorbents may contain significant numbers of adsorption centers that can interact with water, it is generally believed that the combination of weak carbon–water dispersive attractions and strong water–water associative interactions are responsible for the complex behavior of water confined in carbonaceous pores.

Understanding the adsorption mechanism is essential for developing efficient technologies to capture carbon dioxide from industrial flue gases. In this work, laboratory measurements, density functional theory calculations, and molecular dynamics simulations were employed to study CO2 adsorption and diffusion behavior in LTA-type zeolites. The CO2 adsorption isotherms measured in zeolite 5A are best described by the Toth model. Thermodynamic analysis indicates that the adsorption process is spontaneous and exothermic, with an enthalpy change of -44.04 kJ/mol, an entropy change of -115.23 J/(mol·K), and Gibbs free energy values ranging from -9.68 to -1.03 kJ/mol over the temperature range of 298-373 K. The isosteric heat of CO2 adsorption decreases from 40.35 to 21.75 kJ/mol with increasing coverage, reflecting heterogeneous interactions at Ca2+ and Na+ sites. The adsorption kinetics follow a pseudo-first-order model, with an activation energy of 2.24 kJ/mol, confirming a physisorption mechanism. The intraparticle diffusion model indicates that internal diffusion is the rate-limiting step, supported by a significant reduction in the diffusion rate. The DFT calculations demonstrated that CO2 exhibited a -35 kJ/mol more negative adsorption energy in zeolite 5A than in zeolite ITQ-29, attributable to strong interactions with Ca2+/Na+ cations in 5A that were absent in the pure silica ITQ-29 framework. The molecular dynamics simulations based on molecular force fields indicate that CO2 diffuses more rapidly in ITQ-29, with a diffusion coefficient measuring 2.54 × 10-9 m2/s at 298 K, whereas it was 1.02 × 10-9 m2/s in zeolite 5A under identical conditions. The activation energy for molecular diffusion reaches 5.54 kJ/mol in zeolite 5A, exceeding the 4.12 kJ/mol value in ITQ-29 by 33%, which accounts for the slower diffusion kinetics in zeolite 5A. There is good agreement between experimental measurements and molecular simulation results for zeolite 5A across the studied temperature and pressure ranges. This confirms the accuracy and reliability of the selected simulation parameters and allows for the study of zeolite ITQ under similar simulation conditions. This research provides insights into CO2 adsorption energetics and diffusion within LTA-type zeolite frameworks, supporting the rational design of high-performance adsorbents for industrial gas separation.

Development and application of kinetic Monte Carlo for the simulation of bulk fluids and gaseous adsorption

ABSTRACT: The use of molecular simulation to quantify gas adsorption and diffusion is needed to study the CO2 Enhanced Oil Recovery (EOR) efficiency. Favoring CO2-Oil interaction over CO2-Rock interaction depends on the strength of the interaction bond between CO2 and nanopores surface. In this study, we explored the effect of pore size and reservoir temperature on CO2 adsorption and diffusion behavior in Bakken. This comprehensive study covers the characterization of Bakken CO2-EOR using grand canonical Monte Carlo and molecular dynamic simulations. The results indicated that increasing reservoir temperature would reduce the amount of adsorbed CO2 and the adsorption kinetics of CO2 into Bakken nanopores follows a first-order Langmuir model. CO2 adsorption in Bakken nanopores was strong at low temperatures and large pore sizes. Also, high CO2 injection pressures (e.g., 55MPa) led to strong diffusion of CO2 into the nanopores. This is undesirable as high CO2 adsorption and diffusion into the walls of the nanopores would cause molecular loss of the injected CO2, consequently lower EOR efficiency. The insights gained from this work might help improve theoretical understanding of the micro behaviors of CO2 in Bakken reservoir nanopores and give valuable recommendations in CO2-EOR. 1. INTRODUCTION AND BACKGROUND In 2021, North Dakoda contributed to US oil production as second-ranked with production over 1MMbscf. Although using advanced technologies of hydraulic fracturing in unconventional reservoirs such as Bakken made higher oil production possible, the recovered production oil is only 2% of the Bakken original oil in place (OOIP). Also, maintaining production is quite challenging in unconventional reservoirs. Thus researchers are exploring the flow mechanisms to sustain oil production, including developing several enhanced oil recovery (EOR) methods such as gas injection and CO2 EOR for improving the recovery factors over the past few decades. Based on the experimental and numerical studies, one of the potential methods with a promising indication of oil incremental is CO2 EOR (Jia et al., 2018; Thakur, 2019). During a CO2 injection process, oil recovery factor can increase as a result of CO2-oil interaction. Injected gas can swell the oil and reduce viscosity leading to higher oil mobility. Also, the underground injection of captured CO2 from combustion stations has the benefits of reducing greenhouse gas emissions which makes CO2 injection a valuable process. (S. Wang, 2016). On the other hand, CO2 injection processes are not always in favor of increasing oil recovery due to the adsorption of CO2 in rock. Moreover, there is always a gap between field and simulation-predicted oil recovery (Jia et al., 2018). Therefore, it is important to investigate the effect of some common assumptions in tight reservoirs such as the ignorance of the diffusion flow mechanism and adsorption to improve oil recovery prediction.

Combined DFT and MD simulation approach for the study of SO2 and CO2 adsorption on graphite (111) surface in aqueous medium

CO2 sequestration (CS) into the shale formations can reduce not only carbon emissions but also enhance gas recovery (EGR). The adsorption and diffusion behaviour of CO2 and CH4 on kerogens with different maturity play a crucial role in CS-EGR as they determine the efficiency of CO2 storage and energy recovery. In this work, GCMC and MD simulations were performed to investigate the adsorption and diffusion behaviour of CO2 and CH4 on kerogen models at different grades of maturity. It indicated that, in the same maturity, the CO2 adsorption capacity was more significant than that of CH4. With increasing maturity, the adsorption capacity and diffusion rate increased. With the increase of water contents, the swelling ratio of kerogens increased, and the adsorption capacity and the diffusion coefficients of CH4 and CO2 decreased. However, the adsorption selectivity of CO2 over CH4 significantly increased. H2O and CO2 molecules both preferred to adsorb on functional groups of oxygen, nitrogen and sulfur. This study consolidated our hypothesis that an injected CO2 to shale gas and oil formations contributed positively to enhanced energy recovery owing to the difference in adsorption and diffusion behaviour of CH4 and CO2 in kerogens with different maturity in gas and oil reservoirs.

Unusual adsorption and desorption behaviors of NO and CO on nanoporous nickel phosphate VSB-5: In situ FT-IR and TPD study

Flexible metal-organic frameworks (MOFs) have attracted much attention as selective gas adsorption and storage. This report describes boron doping in zeolitic imidazolate framework-7 (B-ZIF-7), which exhibits reversible phase transition during CO2 adsorption/desorption. We have successfully prepared B-ZIF-7 coordination networks using boron-bridged benzimidazolate (B(bim)4-) as organic ligands. Powder X-ray diffraction (PXRD) measurements and infrared spectroscopy revealed that B-ZIF-7 has a crystal structure similar to that of ZIF-7 while containing boron bridging in the coordination network. Since B-ZIF-7 forms a cationic coordination network, the guest anions are encapsulated within the pore. CO2 adsorption/desorption measurements at 300 K showed that B-ZIF-7(NO3), which contains nitrate ions (NO3-) as guest anions in its pores, exhibits a S-shaped CO2 adsorption/desorption isotherm, which is characteristic of gate-opening type MOFs. Compared with ZIF-7, B-ZIF-7(NO3) has superior CO2 adsorption capacity in the low-pressure and superior CO2 storage capacity. The CO2 adsorption and desorption behavior of B-ZIF-7(NO3) was analyzed by in situ temperature-controlled PXRD measurements and thermogravimetric analysis under a CO2 atmosphere, and a reversible phase transition was observed. We have also successfully prepared B-ZIF-7(Cl) and B-ZIF-7(OTf) (OTf = CF3SO3-) with different guest anions. The CO2 adsorption/desorption behaviors of B-ZIF-7(Cl) and B-ZIF-7(OTf) were significantly different from those of B-ZIF-7(NO3) and ZIF-7. B-ZIF-7(Cl) showed gate opening at a higher pressure than ZIF-7, and B-ZIF-7(OTf) did not show S-shaped CO2 adsorption isotherm and showed adsorption behavior in micropores. These results indicate that the CO2 adsorption behavior of B-ZIF-7 depends on the interaction between the guest anions and CO2 molecules or the cationic framework and the bulkiness of the guest anions. Boron doping in a coordination network with boron-bridged imidazolate ligands is a promising strategy to increase the gas adsorption capability of porous materials.

Characterization of Cabot BP280 with argon and nitrogen adsorption at temperatures above and below the triple point – Energetic vs Structural heterogeneities