Adsorption最新文献

Abstract

Emissions of carbon dioxide (CO₂) from fossil fuel usage continue to be an incredibly challenging problem to the attainment of CO₂ free global economy; carbon Capture and Storage (CCS) and the substitution of fossil fuel with clean hydrogen have been identified as significant primary techniques of achieving net zero carbon emissions. However, predicting the number of gases trapped in the geological storage media effectively and safely is essential in attaining decarbonization objectives and the hydrogen economy. Successful underground storage of carbon dioxide and hydrogen depends on the wettability of the storage/cap rocks as well as the interfacial interaction between subsurface rocks, the injected gas, and the formation of brine. A key challenge in determining these factors through experimental studies is the presence of conflicting contact angle data and the difficulty of accurately replicating subsurface conditions in the laboratory. To address this issue, molecular dynamics simulations offer a microscopic approach to recreating subsurface conditions and resolving experimentally inconsistent results. Herein, we report the molecular dynamics simulation results for hydrogen (H₂) and cushion gas (e.g., CO₂ and N₂) on quartz surfaces to understand the capillary and trapping of these gases in sandstone formations. The results of these three gasses were compared to one another. The simulation predictions showed that the intermolecular interactions at the CO₂-quartz surface area are more substantial than at the N₂ and H₂-quartz interface, suggesting that the quartz surface is more CO₂-wet than N₂ and H₂-wet under the same circumstances. In addition, it was found that CO₂ has a substantially higher adsorption rate (∼ 65 Kcal/mol) than N₂ (∼ 5 Kcal/mol) and H₂ (∼ 0.5 Kcal/mol). This phenomenon can be explained by the fact that CO₂ density is substantially larger than N₂/H₂ density at the same geo-storage conditions. As a result, CO₂ could be the most favorable cushion gas during underground hydrogen storage (UHS) because a higher CO₂ residual is expected compared to H₂. However, due to the Van der Waal Interaction force with quartz, only a small amount of H₂ can be withdrawn.

Abstract

Dynamic adsorption is important for evaluating the Volatile Organic Compounds (VOCs) adsorption performance. During adsorption process, the exothermal characteristic could lead to an increase of the column temperature, which might cause bed combustion and is negative to the adsorption efficiency. In present study, we chose graphene oxide(GO) as adsorbent, comparing with hypercrosslinked polymeric adsorbent(HPA), and conducted the dynamic adsorption experiment of ethanol, n-hexane and cyclohexane at 308 K, 318 and 328 K with different adsorbent column height. The results showed that the temperature had linear and negative influence on breakthrough capacity for three VOCs on two adsorbents. And the breakthrough adsorption capacity of ethanol, n-hexane and cyclohexane on two adsorbents were as follows: ethanol > cyclohexane > n-hexane, closely related with physical parameters of VOCs. But the physical properties of ethanol, n-hexane and cyclohexane have little influence on dynamic adsorption rate in this paper. In addition, for n-hexane and cyclohexane, the breakthrough adsorption capacity on HPA were higher than that on GO, but their k values were similarity on HPA and GO. While for ethanol, the breakthrough capacity and k value on GO were higher than HPA. Most important of all, the negative effect of temperature on VOCs adsorption on GO was lower than HPA. Therefore, GO is a good alternative adsorbent for VOCs recovery. Furthermore, with higher column height, the dynamic adsorption capacity was higher but the adsorption rate was lower. While the influence of temperature on dynamic adsorption capacity and rate were relative independent with column height of adsorbent.

Density functional theory (DFT) calculations were utilized to evaluate the adsorption of cyano radical (^.C≡N) on H-capped (5, 0), (6, 0), and (8, 0) zigzag aluminum nitride nanotubes (AlNNTs) and the results were compared to the adsorption on a (6, 0) zigzag aluminum phosphide nanotube (AlPNT). The most stable configuration (C-side) involves the attachment of CN to the outer surfaces of pure AlPNT and AlNNT via a covalent bond. The adsorption energy of^.CN on the (5, 0) AlNNT surface, with a tube diameter of 4.82 Å and length of 16.4 Å, was found to be -253.17 kJ mol⁻¹ through N-side (IV) and -259.12 kJ mol⁻¹ through C-side (V), indicating a chemisorption process. The adsorption of^.CN through the C-side on (5, 0) AlNNT is more stable than through the C-side on (6, 0) and (8, 0) AlNNTs. Natural bond orbital (NBO) revealed that in these configurations, there was a charge about 0.254 (C-side) and 0.357 (N-side) |e| transferred from the (5, 0) AlNNT to the^.CN as an electron acceptor, demonstrated by a strong orbital hybridization during the adsorption process. The decrease in softness, energy gap, and electrophilicity of^.CN-adsorbed AlNNT can indicate a shift toward enhanced stability and reduced reactivity. Increasing the diameter and length of AlNNTs leads to significant alterations in the structural and electronic features of the nanotubes, as suggested by our findings. The analysis of the total density of states (DOS) illustrated the interaction between^.CN and the nanotube surfaces resulted in alterations in the electronic structure of the nanotubes.

The sorption of Zr(IV) and Y(III) was examined using an iron-tin silicate (FeSnSi) composite prepared by the co-precipitation technique. The analytical tools that characterize prepared composite are FT-IR, SEM, EDX, XRD, and XRF. The effects of temperature, pH, ion concentrations, and shaking time are all considered in the sorption studies conducted on Zr(IV) and Y(III). The sorption of studied metal ions depends on pH, and the pseudo-2nd-order model governs the kinetics of reactions. Negative Gibbs energy values confirmed the excellent feasibility and spontaneity of the sorption process. Positive enthalpy values indicate that this process was endothermic. Positive entropy values demonstrated that the disorder between the solid and liquid phases was enhanced during adsorption. Freundlich and Langmuir models are used to study isotherms. The results of the binary system verify that Zr(IV) may be separated from the Zr-Y system at various pHs. According to the findings, the produced composite may effectively remove Zr(IV) and Y(III) from aqueous solutions. It may also be viable for purifying wastewater contaminated with these metal ions.

Adsorption is the most efficient technique for the removal of toxic organic dyes and metal ions from wastewater and it demands efficient, low-cost, environment friendly and collectable adsorbents. In this study, a one-pot strategy has been developed for the crosslinking of chitosan and carboxymethyl cellulose with citric acid to form the cross-linked hydrogel. The synthesized biosorbent hydrogel was characterized by FTIR, XRD and SEM that have confirmed the successful crosslinking. The batch adsorption experiments were performed to examine the capacity of hydrogel for the adsorption of Cu(II). The optimization of the adsorption process was carried out on the basis of various factors including; metal ion concentration, time, temperature, pH, agitation speed and adsorbent dose. Different isothermal and kinetic models were applied to interpret the data. The thermodynamic studies revealed that Langmuir model was the best fit with > 90% Cu(II) removal at pH 6. The kinetic studies confirmed the suitability of pseudo-second-order kinetics with correlation coefficient (R²) value 1. Several adsorption–desorption cycles were performed to check the recovery and reusability of hydrogel without the loss of maximum adsorption capacity.

Fluoride ions have been detected in the surface or groundwater in excess amounts due to industrial effluent and various geochemical reactions. The removal of fluoride is indispensable to make water fit for drinking purposes. Various techniques such as membrane filtration, reverse osmosis, precipitation, ion exchange, electrodialysis, and adsorption have been used for the removal of fluoride in past decades but adsorption has shown great potential due to the low cost and availability of raw materials for the synthesis of adsorbents. In this present study, a mixture of coconut fiber ash and bentonite clay was doped with potash alum (PCBB) for the synthesis of biochar. PCBB biochar was pyrolyzed at 300 °C and showed a high surface area and adsorption capacity towards fluoride ions. The as-synthesized PCBB was characterized by FESEM, FTIR, BET, XRD, and XPS techniques. The kinetics study showed that within 120 min of reaction time, the adsorption equilibrium was reached, and the adsorption of fluoride proceeds through the pseudo-second-order reaction. Sorption was evaluated using the adsorption isotherm models. From the results, it was found that PCBB follows the Langmuir isotherm model. The adsorption experiments for fluoride removal were performed at different pH, catalyst dosage, time, and initial concentration to check the removal efficiency of the PCBB. The optimized reaction conditions were obtained for 10 ppm fluoride concentration, 1.0 g of catalyst dosage, at 5.0 pH, and 120 min of reaction time with 92% removal efficiency. The role of PCBB towards sustainable management has been discussed in accordance with the circular economy.

There is an urgent need to address sulfur dioxide (SO₂) from the burning of fossil fuels, which poses a serious hazard to the surrounding environment due to its emission. In this work, UiO-66-type metal–organic framework materials (MOFs) were prepared by hydrothermal method and applied to flue gas desulfurization. Through characterization analysis, it was found that UiO-66 sample had high crystallinity and good thermal stability. Besides, UiO-66 sample had a large specific surface area (1423 m²/g) and a large pore volume (0.69 cm³/g). In the desulfurization experiments of SO₂/CO₂/O₂/N₂ gas mixture (0.3/10.0/5.5/84.2 vol.%), UiO-66 had a breakthrough time of 137.6 min/g for SO₂, the high selectivity of SO₂/CO₂ (36.0), and strong acid resistance. Besides, the adsorption thermodynamic analysis can confirm that the adsorption process of UiO-66 for SO₂ was a combination of physical adsorption and chemical adsorption. At 1.0 bar and 298 K, the adsorption capacity of SO₂ on UiO-66 reached 8.12 mmol/g.

The extended Langmuir (EL) model remains a popular tool within the adsorption community to describe mixture adsorption. Nevertheless, its thermodynamic consistency breaks down when the saturation capacities of the species differ. This effect also triggers large differences with other fundamental and popular models, the ideal adsorbed solution theory (IAST) and Nitta model, requiring an implicit calculation. A loading-explicit multicomponent model (dsEL) was proposed more recently and attracted attention by its implementation in open-source software. The thermodynamic consistency of dsEL is established here. Furthermore, to aid general model selection including this new model, predictive properties are presented in comparison to various other models, especially the popular EL and (Langmuir based) IAST. While the low loading predictions are similar for all models, the high pressure limit for EL varies from the preferential uptake of the smallest component (dsEL, IAST, Nitta). By presenting analytic equations for the infinite dilution behaviour and by introducing iso-selectivity lines, remaining differences with dsEL and IAST are easily demonstrated. In a model toolbox, dsEL models present themselves as relatively simple and robust, thermodynamically consistent, explicit modifications of the EL model, capturing various features of IAST.

Knowledge of adsorption isotherms is essential for the design and optimization of chromatographic separation processes. Since the experimental determination of these thermodynamic functions is a complicated and time consuming task, there is a need to develop methods which are fast and easy to apply. An attractive group of methods is based on neglecting in the analysis of measured dynamic elution profiles all kinetic effects. These methods assume the validity of an isotherm model equation and exploit the possibility to solve analytically the column mass balance equations of the equilibrium model. If just the dispersive part of an elution profile is, the method is known as “elution by characteristic point” (ECP). The ECP method has been applied successfully to analyse column effluent profiles of single component dissolved in a mobile phase. This work extends the ECP method to analyse just the shapes of elution profiles recorded after injecting samples that contain two key components to be separated. The extended ECP method requires recording only one overloaded elution profile for the two-component mixture and offers a fast and efficient way to estimate isotherm model parameters. The method is in particular attractive if there is limited access to the pure components, as for example in cases of enantiomers. The underlying theory is presented and applied for the case that the adsorption equilibria can be described satisfactorily by the classical competitive Langmuir model. Core of the theory are the available analytical equations describing the outlet concentration profiles of the two solutes for the equilibrium controlled case the. Considering a case study, it is shown that the extended ECP method can be applied successfully for columns characterized by 2500 or more theoretical plates. However, the method can be useful also for columns with lower efficiency. It provides then a rough estimation regarding the isotherm courses.

The removal of the main impurity CO₂ is a crucial step in biogas upgrading. In this work, the separation of CO₂ from CH₄ on electrospun polyacrylonitrile-based carbon nanofibers (CNFs) is investigated using breakthrough experiments. The CNFs are prepared at various carbonization temperatures ranging from 600 to 900 °C and feature a tailorable pore size that decreases at higher carbonization temperatures. The adsorption properties of the different CNFs are studied measuring pure component isotherms as well as column breakthrough experiments. Adsorption kinetics are discussed using a linear driving force approach to model the breakthrough experiment and obtain the adsorption rate constant. Moreover, different approaches to determine the selectivity of the competitive CO₂/CH₄ adsorption are applied and discussed in detail. The results clearly prove that a size exclusion effect governs the adsorption selectivity on the CNFs. While CH₄ cannot adsorb in the pores of CNFs prepared at 800 °C or above, the smaller CO₂ is only excluded from the pores of CNFs prepared at 900 °C. For CNFs carbonized in the range from 600 to 750 °C, values of the CO₂/CH₄ selectivity of 11–14 are obtained. On the CNFs prepared at 800 °C the CH₄ adsorption is severely hindered, leading to a reduced adsorbed amount of CH₄ and consequently to an improved CO₂/CH₄ selectivity of 40. Furthermore, owing to the shrinking pores, the adsorption rates of CH₄ and CO₂ decrease with higher carbonization temperature.