Adsorption Of Mixtures Research Articles

IAST and GCMC predictions and experimental measurements of gas mixture adsorption on three metal–organic frameworks

IAST and GCMC predictions and experimental measurements of gas mixture adsorption on three metal–organic frameworks

Adsorption of Methane–Nitrogen mixtures with flexible Zeolitic Imidazolate Framework-7 (ZIF-7)

ZIF–7 is a pressure–regulated flexible metal–organic framework with a notably lower admission pressure for CH4 relative to N2, making it highly-prospective for curbing fugitive emissions of methane. Here, the separation of CH4 from N2 by an improved variant of ZIF–7 was studied over a range of pressures, temperatures, and compositions using multiple complementary techniques. Pure gas adsorption isotherms measured from (283 to 323) K at up to 16 MPa reveal this variant of ZIF-7 exhibits 50–60 % higher adsorption capacities for both CH4 and N2 in the large–pore phase than previous ZIF–7 samples. Binary mixture adsorption isotherms from dynamic column breakthrough experiments were consistent with those predicted from pure–gas isotherms using Ideal Adsorbed Solution Theory. Methane uptake increased significantly when the pore phase transition pressure for the mixture was reached, while the uptake of nitrogen remained small. Consequently, the equilibrium CH4-over–N2 selectivity of ZIF-7 is always larger than 5.5 and can increase to around 9, significantly above that of conventional adsorbents. Further characterisation showed the rate of the adsorption on ZIF–7 initially decreases as the pore phase transition begins before it increases significantly. Raman spectra acquired at various pressures along the adsorption isotherms revealed changes in certain vibrational modes associated with the structural change. Collectively, these observations indicate that the conceptually simple gating mechanism often used to describe the pore phase transitions in ZIF-7 in fact depends on interactions between the guest molecules and the adsorbent framework that continue to operate once the material is in the large–pore state.

How reliable is the Real Adsorbed Solution Theory (RAST) for estimating ternary mixture equilibrium in microporous host materials?

Microporous crystalline adsorbents such as zeolites, and metal-organic frameworks (MOFs) have potential use in a wide variety of separations applications. In applications such as CO2 capture, the Ideal Adsorbed Solution Theory (IAST) often fails to provide a quantitative description of mixture adsorption equilibrium especially in cation-exchanged zeolites. The failure of the IAST is ascribable to non-compliance with one or more tenets mandated by the IAST such as (a) homogeneous distribution of adsorbates within the pore landscape, (b) no preferential location of guest species, and (c) absence of molecular clustering due to say hydrogen bonding. The focus of this article is on the reliability of the Real Adsorbed Solution Theory (RAST) models for quantitative estimation of adsorption equilibrium. Configurational-Bias Monte Carlo (CBMC) simulations are undertaken to determine the adsorption equilibrium for ternary CO2/CH4/N2, CO2/CH4/C3H8, CO2/CH4/H2, and water/methanol/ethanol mixtures in NaX, LTA-4A, CHA, DDR, and MFI zeolites. Additionally, CBMC simulations of the constituent binary pairs are used to determine the Wilson or NRTL parameters, taking due account of the dependence of the activity coefficients on the spreading pressure. Use of the binary pair Wilson or NRTL parameters allows the estimation of ternary mixture adsorption equilibrium, that is tested against the CBMC data on component loadings. In all investigated guest/host combinations, the RAST provides a good estimation of ternary mixture adsorption equilibrium.

Tailored nano clay blends for enhanced dye mixture adsorption in wastewater treatment

Natural clays are eco-friendly, cost-effective, and industrially acceptable adsorbents employed in wastewater treatment. Textile effluents contains mixture of dyes where a single adsorbent often fails to treat completely. Herein, the simplest strategy for the efficient treatment of effluent with multicomponent pollutants using an tailored blend of two clay minerals has been presented. This strategy was studied using a binary blend of halloysite and montmorillonite clays (HAMT) to remove a mixture of industrial dyes, reactive Black-B (BB) and methyl red (MR) from the model effluent. Here, halloysite (HA) and montmorillonite (MT) selectively adorbs reactive black-B and methyl red respectively and could not completely treat model effluent individually whereas HAMT blend proved to be most effective. HAMT blend was prepared by convenient ultra-sonication assisted solution process and characterized using the various analytical techniques such as FT-IR, DR-UV spectra, XRD and SEM to determine structural, morphological features. Adsorption of model effluent studied as a function of pH, time, adsorbent loading and adsorbate concentration. The dye removal efficiency was remarkably enhanced when the HAMT blend was used according to the concentration of dyes present in the model effluent. The maximum dye removal efficiency was attained using HAMT (1:1) blend for effluent with an equimolar concentration of selected dyes. Similarly, HAMT (2:1) found suitable for the treatment of real textile effluent collected from local textile industries based on its assessment. This study aids in the development of a tailored adsorbent blend using conventional adsorbents for complex effluent treatment in a cost-effective way, eliminating the need for specialized materials.

Finding high-performance MOFs for effective SF6/N2 separation through high-throughput computational screening and machine learning

Abstract Given the rapidly expanding pool of synthesized and hypothetical metal–organic frameworks (MOFs), testing every single material for SF6/N2 separation by iterative experimental methods or computationally demanding molecular simulations is not practical. In this study, we integrated high-throughput computational screening and machine learning (ML) approaches to evaluate SF6/N2 mixture adsorption and separation performances of over 25 000 different types of synthesized and hypothetical MOFs (hypoMOFs), representing the largest set of structures studied for SF6/N2 separation to date. SF6/N2 mixture adsorption data that we produced for synthesized MOFs using molecular simulations were utilized to develop ML models to accurately and quickly predict SF6 and N2 uptakes, SF6/N2 selectivities, SF6 working capacities, adsorbent performance scores, and regenerabilities of both synthesized and hypoMOFs. Results showed the MOF space that we studied exhibits very high SF6/N2 selectivities in the range of 1.8–4204 at 1 bar in addition to high SF6 working capacities between 0.04–5.68 mol kg−1 at an adsorption pressure of 1 bar and desorption pressure of 0.1 bar at room temperature. The top-performing MOF adsorbents for SF6/N2 mixture separation were identified to have Zn, Cu, Ni metals; terphenyl, pyridine, naphthalene linkers; and medium pore sizes. Our comprehensive computational approach offers a highly efficient alternative to brute-force computer simulations by enabling the rapid assessment of the MOF adsorbents for SF6/N2 separation and provides molecular insights into the key structural features of the most promising adsorbents.

Qualities of Regenerated Mixtures of Adsorbents

A proposal has been presented for the regeneration of a spent sorbent mixture, comprising activated carbon (BAU-A brand) and kieselguhr (Bekogur 200 brand), in a mass ratio of 1:3. The effectiveness of the regeneration process and the potential applications of the spent sorbents were determined through X-ray phase analysis methods. The study included an investigation into the adsorption of the primary dye (methylene blue) by activated carbon and various sorbent mixtures. The observed efficiency of regeneration supports the recommendation of using a combination of kieselguhr and activated carbon sorbents for treating wastewater in food industry enterprises.

Utilizing molecular simulation, ideal adsorbed solution theory and ensemble learning algorithms to investigate adsorption and separation of sulfides on amorphous nanoporous materials

Using grand canonical Monte Carlo method, we investigated the adsorption of pure H2S and SO2 gases on amorphous materials, and the separation of CH4-H2S and CO2-SO2 mixtures. At 303 K, the optimal adsorbent for both gases was found to be HCP-Colina-id016, with 16 mmol/g. For CH4-H2S mixture, despite aCarbon-Marks-id002 exhibiting the highest selectivity (approximately 80), the H2S adsorption was low (around 1 mmol/g), while Kerogen-Coasne-id013 demonstrated a high H2S adsorption of 12 mmol/g with a selectivity of 20. In the case of CO2-SO2, HCP-Colina-id018 exhibited a SO2 selectivity exceeding 30, with a high SO2 adsorption of 12 mmol/g. The Ideal Adsorbed Solution Theory underestimated the adsorption and selectivity of both mixtures, particularly evident in CO2-SO2. Molecular simulations revealed that, for the CO2-SO2 system, CO2 underwent condensation, resulting in a sudden drop in the SO2 adsorption isotherm. However, IAST accurately predicted this abrupt change. Based on the adsorption data obtained from molecular simulations, we compared the predictive performance of four ensemble learning algorithms, namely Random Forest (RF), Gradient Boosted Decision Trees (GBDT), Extreme Gradient Boosting (XGBoost), and CatBoost, for H2S and SO2 pure gases in amorphous porous materials. The rankings were observed to be XGBoost > GBDT > RF > CatBoost.

Adsorption characteristics and mechanisms of individual and a quinary mixture of heavy metal ions on novel CoFe2O4-BiFeO3 nanosorbents in water

Application of CoFe2O4-BiFeO3 nanocomposites (CFO-BFO NCs) in highly adsorptive removal of heavy metal ions (Pb(II), Co(II), Cu(II), Cd(II) and Zn(II)) by individual and simultanoeous adsorption were investigated for the first time in the present study. The characterization of CFO-BFO NCs were analyzed by using XRD, VSM, SEM, TEM and BET techniques. The CFO-BFO NCs powder consists of characteristic peaks of BFO and CFO without any trace of other crystalline phases; they were uniformly dispersed with a size of about 3–5 nm, much smaller than single – phase CFO (10–25 nm) and BFO (5–10 µm) with the surface area of 84.93 m2/g; remanence and coercivity were 14.33 emu/g, 1.99 emu/g and 195 Oe, respectively, significantly decreased compared to CFO but significantly increased compared to BFO. The single or simultaneous adsorption of a quinary mixture of Pb(II), Co(II), Cu(II), Cd(II) and Zn(II) on CFO-BFO NCs followed the Freundlich isotherm model and the pseudo-second-order kinetic model. Adsorption capacity of single heavy metal ions were in the order Pb(II) > Co(II) > Cu(II) > Cd(II) > Zn(II) while the simultaneous adsorption was in the order Pb(II) > Cu(II) > Co(II) > Zn(II) > Cd(II). The maximum adsorption capacities (qmax) of each ion in the case of simultaneous adsorption were smaller than that for cases of the single adsorption but the total qmax of ions mixture was much higher than the highest qmax of single adsorption. The simultaneous adsorption of heavy metal ions is the competition, the best selectivity is Pb(II) and the strongest competition is Cd(II), the adsorption ability reduces as the charge and radius of interfering cation increase and the ionic strength increases. The regeneration and reuse ability were good, while the adsorption efficiency slightly decreased over three recycles. The adsorption increased slightly as temperature increased. The adsorption process was spontaneous and endothermic. Adsorption of heavy metal ions on CFO-BFO NCs consists of both electrostatic and chemisorption. The applicability for real sample is good. Our results demonstrate that the CFO-BFO NCs is a prospective adsorbent to remove Pb(II), Co(II), Cu(II), Cd(II) and Zn(II) from aqueous environment.

Efficient adsorption of acid orange 7 from wastewater using novel bio-natural granular bentonite-sawdust-corncob (GBSC): Mixture optimization, adsorption kinetic and regeneration

The removal of dyes from industrial wastewater is one of the most environmental challenges that should be addressed through sustainable technologies. In this study, a novel green and cost-effective granular from bentonite and bio-wastes of sawdust and corncob (GBSC) was prepared for sustainable treatment of acid orange 7 (AO7) dye wastewater. The d-optimal mixture method was employed to determine the optimum combination of the GBSC in terms of dye adsorption and structure stability. Characterizations of the GBSC were investigated using SEM, XRD, FTIR and BET analyses and compared with bentonite powder (BP), modified bentonite powder (MBP), and granular modified bentonite (GMB). According to the results, a mixture of bentonite 60 wt%, sawdust 20 wt% and corncob 20 wt% at 550 °C yielded the optimal combination of the GBSC which resulted to the highest adsorption capacity 135.22 mg/g, the lowest mass loss 3.1% and maximum crushing strength 12.275 N. The kinetic and isotherm of the adsorption data were fitted well by the pseudo-second-order model and Langmuir isotherm. Our finding suggested a green circular economy model by utilizing agriculture wastes (sawdust and corncob) to synthesize GBSC for sustainable dye wastewater treatment, which offers a cost-effective adsorbent (0.907 $/g) with high regeneration (4 times reusability with 40.5% removal rate) to keep them in circulation for as long as possible.

Synthesis and Dye Adsorption Dynamics of Chitosan-Polyvinylpolypyrrolidone (PVPP) Composite.

One major environmental issue responsible for water pollution is the presence of dyes in the aquatic environment as a result of human activity, particularly the textile industry. Chitosan-Polyvinylpolypyrrolidone (PVPP) polymer composite beads were synthesized and explored for the adsorption of dyes (Bismarck brown (BB), orange G (OG), brilliant blue G (BBG), and indigo carmine (IC)) from dye solution. The CS-PVPP beads demonstrated high removal efficiency of BB (87%), OG (58%), BBG (42%), and IC (49%). The beads demonstrated a reasonable surface area of 2.203 m2/g and were negatively charged in the applicable operating pH ranges. TGA analysis showed that the polymer composite can withstand decomposition up to 400 °C, proving high stability in harsh conditions. FTIR analysis highlighted the presence of N-H amine, O-H alcohol, and S=O sulfo groups responsible for electrostatic interaction and hydrogen bonding with the dye molecules. A shift in the FTIR bands was observed on N-H and C-N stretching for the beads after dye adsorption, implying that adsorption was facilitated by hydrogen bonding and Van der Waals forces of attraction between the hydroxyl, amine, and carbonyl groups on the surface of the beads and the dye molecules. An increase in pH increased the adsorption capacity of the beads for BB while decreasing OG, BBG, and IC due to their cationic and anionic nature, respectively. While an increase in temperature did not affect the adsorption capacity of OG and BBG, it significantly improved the removal of BB and IC from the dye solution and the adsorption was thermodynamically favoured, as demonstrated by the negative Gibbs free energy at all temperatures. Adsorption of dye mixtures followed the characteristic adsorption nature of the individual dyes. The beads show great potential for applications in the treatment of dye wastewater.

Non-Idealities in adsorption thermodynamics for CO2 capture from humid natural gas using CALF-20

The focus of this article is on CO2 capture from natural gas under humid conditions using CALF-20. Configurational-Bias Monte Carlo (CBMC) simulations are used to investigate adsorption of CO2/CH4/H2O mixtures in CALF-20 with varying relative humidities in the bulk gas phase. The CBMC simulations reveal that the mixture adsorption equilibrium shows strong deviations from the estimations of the Ideal Adsorbed Solution Theory (IAST). CBMC simulations for mixture adsorption of the constituent binary pairs, CH4/H2O, and CO2/H2O, reveal that the origin of thermodynamic non-idealities stem from segregated nature of the adsorbed phase and inhomogeneous distribution of guest adsorbates within the pore landscape of CALF-20. The extent and nature of the segregation depends strongly on the % relative humidity of the bulk gas mixture.The important message that emerges from this investigation is the need to incorporate the Real Adsorbed Solution Theory (RAST) for quantitative modelling of fixed-bed adsorbers in natural gas purification with CALF-20.

Competitive Adsorption of 4-Hydroxybenzaldehyde and Toluene onto High Silica Zeolites

To evaluate the ability of zeolites to remove natural low molecular organic substances, p-hydroxybenzaldehyde (p-HBA), a phenolic compound derived from lignin, was chosen as a representative of naturally occurring dissolved organic substances. Two distinct high-silica zeolite materials, namely ZSM-5 and Y, were utilised for the study, and the adsorption process was investigated under a wide range of conditions. It has been observed that p-HBA is adsorbed by both zeolites, and the pH significantly impacts the adsorption of p-HBA, particularly within the low concentration range, while exerting minimal influence on the saturation capacity. For both zeolites, various isotherm models were assessed to accurately describe the adsorption data obtained from aqueous solutions of p-HBA. In addition, to comprehend the selectivity of the adsorbents towards natural organic substances and xenobiotics, the competitive adsorption of mixtures of p-HBA and toluene (TOL) was investigated. The zeolite’s saturation capacity for p-HBA diminishes with increasing contaminant concentration. Conversely, the adsorption of toluene remains minimally affected by p-HBA, and it has been demonstrated that toluene can displace adsorbed p-HBA from the zeolites’ sites. This finding has been confirmed by diffractometric study that indicates that TOL and p-HBA occupy “the same” adsorption sites. Furthermore, Rietveld refinements reveal the formation of p-HBA complexes interacting with the framework and stabilising the guest structures within the zeolite porosity. The results obtained are important for the selection of proper adsorbent for the removal of hydrocarbons in environmental application (natural waters).

Pure Component and Binary Mixture Adsorption of Light Alkanes and Alkenes on Zeolite NaX at Low Temperatures: Influence of Chain Length.

In this study, the separation of short-chain alkane/alkene pairs by fixed-bed adsorption on zeolite NaX at low temperatures is investigated. Experiments are carried out with pure components and mixtures of ethane/ethene, propane/propene, and n-butane/1-butene in the temperature range between -75 and +40 °C and partial pressures up to 450 Pa. For a short chain length, much stronger adsorption of the alkene is observed. In contrast, with an increase in chain length, the isotherms of alkanes and alkenes of the same chain length become more similar. In addition, a greater influence of temperature on capacity is seen, the shorter the chain length is. In binary mixtures, a strong competition occurs at high total loadings with the alkene displacing the alkane. A characteristic curve is formed for the selectivity in the mixture, which shifts to higher temperatures with an increase in the chain length.

The Gibbs and Butler Equations and the Surface Activity of Dilute Aqueous Solutions of Strong and Weak Linear Polyelectrolyte-Surfactant Mixtures: The Roles of Surface Composition and Polydispersity.

In a previous paper, we applied a combination of direct measurements of both surface tension and surface excess in conjunction with the Gibbs equation to explain features of the adsorption and surface tension of mixtures of surfactants and strong linear polyelectrolytes at the air-water interface. This paper extends that model by including (i) the restrictions of the Butler equation for the behavior of the surface tension of mixed systems and (ii) the surface behavior of surfactant and linear weak polyelectrolyte mixtures, for which the inclusion of measurements of the surface excess and composition is shown to be particularly important. In addition, a closer examination of earlier data at higher concentrations provides evidence that the surface layering that is often observed in polyelectrolyte-surfactant systems is also an average equilibrium phenomenon and is driven by particular aggregation patterns that occur in some systems and not in others. Although the successful application of the Gibbs and Butler equations indicates that strong polyelectrolyte-surfactant systems can be described in terms of an average equilibrium over wide ranges of concentration, we have identified two concentration ranges where polydispersity in either polyelectrolyte molecular weight or composition results in significant time dependence of the surface behavior.

Adsorption behavior of helium in quartz slit by molecular simulation

Due to the multiple influences of unique physicochemical properties of helium, petrographic characteristics and temperature and pressure conditions, little is known about the helium adsorption behaviors in minerals and rocks at geological conditions. Based on the grand canonical Monte Carlo simulations, this study revealed the adsorption characteristics of pure helium and the competitive adsorption of binary mixtures with different proportions of methane and helium under geological temperature and pressure conditions in quartz slit model. Molecular simulation of pure helium shows that physical adsorption of helium exists in mineral surfaces, which indicates a preservation mechanism of helium in helium source rocks. Binary mixtures simulations indicate that the adsorption capacity of methane in quartz is stronger than that of helium, and the competitive adsorption of methane increases with decreasing burial depth. This means that during the upwards migration processes of natural gas, the adsorbed helium that distributed in the migration pathway will be gradually displaced by methane, then concentrate in the hydrocarbon gases and subsequently accumulate together in favorable traps to form helium-rich natural gas reservoirs. Our results provide a molecular-scale insight into the preservation and accumulation of helium in helium source rocks and are significant for assessing the helium resource potential.

Unveiling the Preparation and Characterization of Lercanidipine Hydrochloride in an Oral Solid Self-Nanoemulsion for Enhancing Oral Delivery.

Chronic kidney disease (CKD) is becoming increasingly prevalent worldwide, particularly among the elderly, along with an increase in the incidence of hypertension and cardiovascular disorders. Developing lipid-based oral dosage forms with a higher expected bioavailability of antihypertensive drugs with nephroprotective effects poses a challenge. Lercanidipine hydrochloride (LRCH) is a newer type of third-generation dihydropyridine calcium channel blocker that functions as an antihypertensive and has significant nephroprotective effects. Due to its extensive first-pass metabolism, its bioavailability is about 10% and increases to 3-4 times when taken with a high-fat meal. Targeting this drug to the lymphatic system using the solid self-nano-emulsifying drug delivery system (SSNEDDS) is a promising approach for improving LRCH's bioavailability and dispersion rate. SSNEDDS combines the benefits of both liquid self-emulsifying and solid dosage forms, improving drug stability and extending storage time. In this study, liquid SNEDDS composed of 10% peppermint oil, 67% Tween 20, and 22.5% propylene glycolwas solidified using two adsorbent agent mixtures (SSNEDDS1: Avicel PH 101 and Aerosil 200) and (SSNEDDS2: Avicel PH 102 and Aerosil 200) separately. The prepared formulations were evaluated for powder flow, drug content, and an in-vitro dispersion test in comparison to the brand-marketed tablet as a standard or pure drug. DSC and X-ray diffraction analysis were also used. The SSNEDDS2 shows excellent flowability, a higher drug content (99.761%), and a significantly higher and faster dispersion rate of 100% within 10 minutes compared to 92% of the marketed LRCH tablet and 18.1% of the pure drug for 60 minutes. The solid-state characterization of the formulation composed of SSNEDDS2 confirmed that the LRCH was in an amorphous form inside the solidified nano system without interacting with the excipient. This study successfully prepared LRCH using the promising strategy of SSNEDDS as a hard gelatin capsule with a higher dispersion rate. It improved its stability and expected bioavailability compared to the brand-marketed tablet as the standard.

A molecular simulation study on pore-scale behaviour of nitrogen-based fracking fluids for potential geo-energy applications

Molecular simulations are efficient tools in differentiating individual effects of fluid-fluid interactions and pore-fluid interactions on thermophysical properties of confined fluids; e.g. the molecular packing, adsorption mechanics and availability of accessible pore volume for confined fluids and therefore, indicate the rock fracturing phenomena as a function of geological conditions, fracking fluids nature, its composition and rock mineralogy. Presently, we have deployed the classical GCMC molecular simulations to quantify the adsorption of pure nitrogen and N2–H2O mixture (50%–50% and 30%–70%) inside porous silica rocks. While we found that adsorption and molecular packing of pure nitrogen inside silica slit pores are only a function of pore height, which quantifies the pore-fluid interactions; however, for N2–H2O mixture adsorption and molecular packing of N2 inside silica slit pores has been additionally affected by the water content in the equilibrium bulk mixture that as well describes fluid-fluid interactions inside pores. It is interestingly noted that water in N2–H2O mixture results in water-assisted nitrogen adsorption inside hydrophilic silica slit pores, which has been further proven through the radial distribution function data calculations inside each slit pore. Also, the hydrophilic nature of silica increases water adsorption and hence reduces N2 adsorption inside the smallest pore of H = 20 Å. Such a reduction in N2 adsorption density below its bulk density without layering effect, inside 20 Å pore, further initiates the possibility of negative excess adsorption density.

Molecular Dynamics Study of Adsorption and Wetting of Mixtures of Simple Fluids on Planar Walls

Molecular Dynamics Study of Adsorption and Wetting of Mixtures of Simple Fluids on Planar Walls

Исследование адсорбционного разделения газовых смесей в условиях нестационарности

The influence of the initial concentration, rate and temperature of adsorption on the adsorption separation of gas mixtures (CO2, CH4, N2, H2S) is investigated. Components: N2 – 5%, H2S – 5%, CO2 – 5% and CH4 – 85%. And as an adsorbent granule of clinoptilolite of irregular shape were used. Isothermal adsorption of CO2 was obtained at different temperatures (293, 313, and 323 K). The obtained isotherms of CO2 adsorption showed that with an increase in temperature, the adsorption of CO2 decreased. The type of isotherms corresponds to Langmuir. The output curves of gas mixture adsorption depending on the gas flow rate and various main components of CO2 were also experimentally studied. The output curves of the adsorption of the CO2 component were studied at various gas flow rates of 20, 50, and 80 mL/min. Equilibrium time increases with a decrease in the gas flow rate. Output curves were also obtained depending on the initial CO2 concentrations of 5%, 10% and 20%. It was determined that with a decrease in the initial concentration of CO2, the equilibrium time also increases. Gas mixture components sorbed downwards: H2S→CO2→CH4→N2. The resulting system of model equations describing the adsorption separation of gas mixtures in a fixed adsorbent layer represents a complete mathematical model of the process under unsteady conditions. The obtained regularities of the process of adsorption of gas mixtures testify to the fact that the process takes place under non-stationary conditions. The proposed models for the optimal design of industrial absorbers can be used for adsorption separation of gas mixtures in the conditions of their unsteady flow.

Statistical mechanic and machine learning approach for competitive adsorption of CO2/CH4 on coals and shales for CO2-enhanced methane recovery

Understanding the adsorption behavior of CO2, CH4, and their mixture on coal at high pressures is necessary to achieve enhanced CH4 recovery and the simultaneous sequestration of CO2. The adsorption of CO2 and CH4 on dry coal is known to exhibit complex behavior as a function of temperature, pressure, and composition. In this study, a model for CO2 adsorption under supercritical conditions was proposed based on a combination of surface adsorption and dissolution in the coal matrix. However, the corresponding CH4 adsorption can only be presented by a surface mechanism. Although the theoretical model provides an idealized description of the heterogeneous nature of coal, it retains the ability to capture the qualitative features of the experimental isotherms. The results indicate reasonable adsorption on the coal surface and dissolution into the coal matrix in the model mechanisms. The model also provides binding energies, surface areas, absolute adsorption isotherms, and isotherms in terms of the fractional occupancy. Considering the complex behavior of mixture adsorption, a machine learning (ML) approach was applied to the adsorption data of various coals. The ML model was reliable for predicting the competitive adsorption of CO2 and CH4 regardless of the coal type (R2 = 0.9950 and 0.9923 for CO2 and CH4, respectively). According to the analytical results obtained from the theoretical model and the ML approach, the volatile matter content, fixed carbon content, and vitrinite reflectance of coal were determined to be important properties for predicting the competitive adsorption of CO2 and CH4 on coal.