Adsorption Of Binary Mixtures Research Articles

Vacancy solution model using the aNRTL activity coefficient for prediction of binary adsorption equilibria

Based on the Vacancy Solution Model (VSM) and the Adsorption Non-Random Two-Liquid (aNRTL) model of the activity coefficient, a novel model called VSM-aNRTL for gas adsorption equilibria is introduced. In this study, an innovative isotherm equation was applied to experimental monocomponent adsorption equilibrium data from the NIST/ARPA-E Database. The parameters derived from this application were subsequently utilized to predict the equilibrium data for 12 binary adsorption systems across three distinct temperatures, employing the extended model. The proposed model proved effective in correlating the adsorption isotherms of pure components, achieving a reduction in the number of adjustable parameters compared to the original VSM that employs the Wilson activity coefficient. It also outperformed the Ideal Adsorbed Solution Theory (IAST) model by incorporating only one additional parameter. Furthermore, the new model was employed to predict the equilibrium data of binary mixture adsorption, demonstrating results with lower deviations compared to both the IAST and the traditional VSM-Wilson models.

Competitive random sequential adsorption of binary mixtures of disks and discorectangles

The two-dimensional (2D) packings of binary mixtures of disks with diameter d and discorectangles with aspect ratio ɛ (length-to-width ratio ε=l/d ) were studied numerically. The competitive random sequential adsorption (RSA) with simultaneous deposition of particles was considered. The aspect ratio was changed within the range ε=1−10 . In the competitive model, the particle was selected with probability pd (disks) and pε=1−pd (discorectangles), and then they were placed sequentially on a solid surface without overlapping with previously placed particles. Behavior of the total coverage in jamming state ϕ T at different values of pd and ɛ was analyzed. For core–shell structure of the particles the percolation connectivity of films was also discussed.

Bridging adsorption behavior of confined CH[formula omitted]-CO[formula omitted] binary mixtures across scales

An accurate understanding of the competitive adsorption of CH4-CO2 binary mixtures in nano-confined systems is critical for engineering CO2 storage in shale gas reservoirs. Due to difficulties in making reliable experimental observations in nano-scale, atomistic simulations (ASs), such as the Grand Canonical Monte Carlo (GCMC) method, provide a viable approach to studying the adsorption behavior of confined fluids. ASs are, however, limited in the size of the compositional domain due to the high computational cost. This work proposes a framework that combines AS and the lattice Boltzmann (LB) method to bridge the physics of confined fluids across scales. The Peng–Robinson equation of state (PR-EoS) produces fugacity coefficients, which serve as input for conducting multi-component GCMC simulations. These GCMC simulations explore the competitive adsorption behavior of CH4-CO2 in nano-slits at various composition, pressure, and channel-width conditions. Both components generate adsorption layers with high densities near the walls with CO2 preferentially adsorbing compared to CH4 on the organic walls of carbon sheets. At the mesoscale, a pseudopotential model represents the intermolecular forces in multi-component, multiple-relaxation-time LB simulations. The LB simulations are in good agreement with the GCMC results, allowing us to obtain values for tunable LB parameters. We then extend the use of LB to simulate adsorption behavior in complex networks with nano-sized channels. The phase behavior and fluid properties in the complex geometries of nano-channels differ from nano-slits and bulk systems. The bridging of physics from GCMC (microscale) to LB (mesoscale) via the macroscale PR-EoS connects the adsorption behavior of binary systems across scales.

Influence of uniaxial strain loading on the adsorption-diffusion properties of binary components of CH4/CO2 in micropores of bituminous coal by macromolecular simulation

Heterogeneous and anisotropic coal tends to deform under strong mining disturbances, affecting the microscopic adsorption and diffusion of binary CH4-CO2 mixtures in micropores. Therefore, the grand canonical Monte Carlo and molecular dynamics methods were used to study the influence of the uniaxial strain loading on the adsorption-diffusion properties of binary components of CH4/CO2 in coal micropores. The results show that compression strain has significant effects on adsorption selectivity and thermodynamic factor compared to tension strain, and CH4 displacement efficiency is greater when the strain is less than −0.12. Both compression and tension strains have dual effects on promotion and inhibition of volumetric swelling of the gas-containing coal matrix, micropore development and gas diffusion. Furthermore, the diffusivity of CH4 is significantly larger than that of CO2, and Einstein diffusion is dominated by low-velocity motion. Results provide an important basis for the optimal coalbed methane recovery design in deformed coal reservoirs.

Dynamic modelling, simulation and theoretical performance analysis of Volatile Organic Compound (VOC) abatement systems in the pharma industry

Volatile Organic Compound (VOC) use is extremely widespread in the pharmaceutical industry, posing great risks, as potential organic gas releases are harmful to both environment and human health. Fixed-bed columns containing Activated Carbon (AC) or other adsorbents selectively remove VOCs from gas effluent streams. Nevertheless, adsorbing beds can be quickly and/or irregularly saturated, due to simultaneous and significant variations of flowrates and mixture compositions. This paper presents the development and implementation of a dynamic, non-isothermal adsorption model used for studying binary VOC mixture adsorption on industrial AC beds for a wide variety of structural and operating conditions. A scenario-based investigation of binary mixture behaviour examines (via multiple dynamic simulations, experimental corroboration and predictive formulas) the effect of key parameter changes on bed performance. Theoretical bed performance analysis (employing Glueckauf hodographs) has been employed to provide valuable insight into nonisothermal VOC capture bed operation, for both clean and used beds.

Optimization of a Binary Dye Mixture Adsorption by Moroccan Clay Using the Box-Behnken Experimental Design

Optimization of a Binary Dye Mixture Adsorption by Moroccan Clay Using the Box-Behnken Experimental Design

Protein association on multimodal chromatography media

The phenomenon of protein-protein association on multimodal chromatography resins was described for two different case study examples. The adsorption pattern of single-component solutions of calcium-rich alpha-lactalbumin (aLaCa) and calcium-depleted alpha-lactalbumin (aLa) and their mixtures with bovine serum albumin was determined on a multimodal anion-exchange chromatography medium. In single-component solutions, both aLaCa and aLa exhibited identical adsorption behavior at low resin loadings, whereas at high loadings the adsorption strength of aLa markedly exceeded that of alaCa. In binary mixtures, the adsorption of BSA enhanced at high concentrations of aLa or aLaCa in the adsorbed phase. The unusual adsorption patterns observed were attributed to the tendency of the proteins for molecular association in the adsorbed phase in single and binary solutions. The phenomena was examined for different pH of the solution: pH 6, 7, 8, and different solvent environments: phosphate buffer (PB), bis tris buffer (BT), 100 mM NaCl in BT and bis tris propane buffer (BTP). The strongest effect was observed for PB and for 100 mM NaCl in BT.Its occurrence was also evidenced for other case study example, i.e., adsorption of single-component solutions and binary mixtures of a monoclonal antibody (mAb) and lysozyme (LYZ) on a multimodal cation-exchange chromatography medium. The enhancement of adsorption of mAb was observed at high concentrations of LYZ in the adsorbed phase. To quantify the underlying effects, a mechanistic model was used, which accounted for both protein association and exclusion resulting from attractive and repulsive protein-protein iterations in the adsorbed phase.

Microcanonical-ensemble perturbation theory for thermodynamic and diffusion properties of square-well fluids

We present results for thermodynamic and diffusion properties of a square-well fluid (SW) using the Microcanonical-Ensemble perturbation theory (MEPT) [Mol. Phys. 116, 351 (2018)]. The aim of this work is to assess the accuracy of MEPT that is required in order to model real substances properties. We consider the extension of MEPT for binary mixtures of SW fluids, using the Lorentz-Berthelot combining rules. The phase behavior of binary square-well mixtures are studied, exploring in detail the influence of the hard-core size ratios, dispersion energy ratios, and variable attractive range potential. Excellent agreement between the MEPT approach and Gibbs Ensemble Monte Carlo (GEMC) simulation is found, for a wide range of temperatures and compositions. The relevance of perturbation terms of order higher than two is also considered, comparing with SAFT-VR results. This approach is a first step in modeling inhomogeneous systems, such as adsorption and interfacial properties of binary mixtures based on discrete potential systems as reference fluids.

Molecular Simulation on Competitive Adsorption Differences of Gas with Different Pore Sizes in Coal.

Micropores are the primary sites for methane occurrence in coal. Studying the regularity of methane occurrence in micropores is significant for targeted displacement and other yield-increasing measures in the future. This study used simplified graphene sheets as pore walls to construct coal-structural models with pore sizes of 1 nm, 2 nm, and 4 nm. Based on the Grand Canonical Monte Carlo (GCMC) and molecular dynamics theory, we simulated the adsorption characteristics of methane in pores of different sizes. The results showed that the adsorption capacity was positively correlated with the pore size for pure gas adsorption. The adsorption capacity increased with pressure and pore size for competitive adsorption of binary mixtures in pores. As the average isosteric heat decreased, the interaction between the gas and the pore wall weakened, and the desorption amount of CH4 decreased. In ultramicropores, the high concentration of CO2 (50–70%) is more conducive to CH4 desorption; however, when the CO2 concentration is greater than 70%, the corresponding CH4 adsorption amount is meager, and the selected adsorption coefficient SCO2/CH4 is small. Therefore, to achieve effective desorption of methane in coal micropores, relatively low pressure (4–6 MPa) and a relatively low CO2 concentration (50–70%) should be selected in the process of increasing methane production by CO2 injection in later stages. These research results provide theoretical support for gas injection to promote CH4 desorption in coal pores and to increase yield.

Adsorption of Binary Mixture of Highly Positively Charged PTMA5M and Partially Negatively Charged PAA onto PSL Particles Studied by Means of Brownian Motion Particle Tracking and Electrophoresis

Effects of ionic strength on the adsorption of highly charged polycationic ((2-dimethylamino)ethyl methacrylate) methyl chloride quaternary salt (PTMA5M) individually as well as in a binary mixture with polyanionic acrylic acid (PAA) onto polystyrene sulfate latex (PSL) particles with negative charges were investigated by means of Brownian movement particle tracking and measurement of electrophoretic mobility. In addition, the adsorption mechanism was confirmed by Fourier transform infrared (FT-IR) and energy-dispersive X-ray (EDX) spectroscopic methods. The hydrodynamic thickness of the adsorbed polyelectrolyte layer (δH) and electrophoretic mobility (EPM) of particles as a function of concentration ratios of the two polyelectrolytes were measured to clarify the effect of negatively charged molecules on the structure of the positively charged adsorbed layer at various ionic strengths. Extremely thick δH was confirmed for the case of excess dosage of polycations. The δH decreased more significantly with the addition of PAA than increasing ionic strength. Interestingly, in the presence of PAA, the adsorbed layer thickness increased more at lower ionic strength than at higher ionic strength. In addition, the initial δH decreases remarkably after a time lapse of 1 h. Contrary to the decrease of the δH, almost all EPM either remained unchanged or increased over time depending on the concentration ratio of the two polyelectrolytes. Constant charge density, desorption of polyanions, and then reconformation of the adsorbed polycationic layer are proposed model components.

Evaluation of thermal effects on carbon dioxide breakthrough curve for biogas upgrading using pressure swing adsorption

Selective carbon dioxide capture using pressure swing adsorption can transform raw biogas into high energy content biomethane and subsequently sequestration of CO2. In this work, the PSA technology for biogas upgrading is modelled and evaluated using one-dimensional binary mixture adsorption, heat and mass transfer model using Aspen Adsorption™ version 10. This model is validated using experimental data reported previously on zeolite NaUSY, since the CO2 breakthrough curve depicts reasonable agreement. This work considers two heat transfer conditions (gas and gas/solid conductions) to compare their effects on CO2 breakthrough and temperature responses at different positions along the adsorption bed. Three different biogas mixtures are charged over zeolite NaUSY bed to evaluate CO2 concentration on breakthrough curve and bed temperature profile. The influence of axial mass dispersion coefficient on breakthrough characteristics and temperature distribution along adsorption bed is examined. In addition, the effects of cooling outside column wall on CO2 breakthrough curve and bed temperature distribution is also explored. The findings indicate that the heat generated during adsorption possesses influences the adsorption performance rather significantly. Reducing this heat restrains the thermal effects on the breakthrough curves, thereby improving the methane purity and recovery.

Adsorption of Binary Mixtures of the Lennard-Jones Truncated and Shifted Fluid on Planar Walls

Gas phase adsorption of binary mixtures on planar walls in dispersive systems was studied by molecular dynamics simulations, extending a previous study on the adsorption of pure components. The interactions between all particles, fluid as well as solid, were described by the Lennard-Jones truncated and shifted potential with a cutoff radius of 2.5 σ. Two classes of fluid mixtures were studied: (a) symmetric mixtures, in which the pure components and also their interactions with the wall particles are the same but the unlike fluid–fluid interaction parameter is varied; (b) an asymmetric mixture, in which the dispersive energy of one fluid component was lowered, such that it becomes light-boiling. For the asymmetric mixture, both nonselective walls as well as walls with different selectivity for the two fluid components were investigated. Data on the surface excess, the thickness, and the structure of the adsorbate layer as well as on the selectivity were measured. The results give insight into how adsorption of binary mixtures is influenced by the different dispersive interactions between the fluids and between the fluids and the wall.

Assessment of CO2 adsorption capacity in Wollastonite using atomistic simulation

The paper deals with the understanding of the CO2 capacity of adsorption through the anhydrite cement compound, i.e., CaO·SiO2 structure. The Wollastonite structure is prepared with various CaO/SiO2 ratios for the atomistic simulations. Subsequently, simulations of binary adsorption of H2O and CO2 have been performed to arrive at C–S–H structure. The CaO/SiO2 ratio is varied from 0.66 to less than 1.5 in the present study. The interlayer spacing between CaO sheets is considered as 13.5 Å. The impact of the electrostatic charges has been explored using available CLAY_FF and CSH_FF potentials. The outcomes have been successfully examined and compared with experimental results. To understand the capacity adsorption of CO2 and selectivity effect on C–S–H forming, numerical experiments have been performed using CO2 concentrations from 10 ppm up to 1,000,000 ppm at 20 °C. These numerical experiments allow understanding of the selectivity of H2O and CO2 in binary mixture adsorption, and the capacity of CO2 adsorption in the Wollastonite atomic structure. According to the physisorption simulations, the CO2 adsorption capacity depends not only on CO2 concentration but also the Wollastonite structure. The possible CaCO3 precipitation and C–S–H structure are addressed.

Molecular Dynamics Study of Wetting and Adsorption of Binary Mixtures of the Lennard-Jones Truncated and Shifted Fluid on a Planar Wall.

The wetting of surfaces is strongly influenced by adsorbate layers. Therefore, in this work, sessile drops and their interaction with adsorbate layers on surfaces were investigated by molecular dynamics simulations. Binary fluid model mixtures were considered. The two components of the fluid mixture have the same pure component parameters, but one component has a stronger and the other a weaker affinity to the surface. Furthermore, the unlike interactions between both components were varied. All interactions were described by the Lennard-Jones truncated and shifted potential with a cutoff radius of 2.5σ. The simulations were carried out at constant temperature for mixtures of different compositions. The parameters were varied systematically and chosen such that cases with partial wetting as well as cases with total wetting were obtained and the relation between the varied molecular parameters and the phenomenological behavior was elucidated. Data on the contact angle as well as on the mole fraction and thickness of the adsorbate layer were obtained, accompanied by information on liquid and gaseous bulk phases and the corresponding phase equilibrium. Also, the influence of the adsorbate layer on the wetting was studied: for a sufficiently thick adsorbate layer, the wall’s influence on the wetting vanishes, which is then only determined by the adsorbate layer.

Functional Phenylboronate Polymers for the Recovery of Diols, Sugar Alcohols, and Saccharides from Aqueous Solution.

The ongoing transition from fossil to renewable feedstocks demands new efficient processes for an economically viable production of biomass‐derived commodities and fine chemicals. Novel energy‐ and material‐efficient product purification and separation will play a crucial role due to altered product and feed composition. The present study comprises the synthesis and tests of cross‐linked p‐vinylphenylboronate polymers for the separation of 18 diols, sugar alcohols, and saccharides, which can be obtained during biomass processing. The separation was based on molecular recognition, that is, esterification of the phenylboronate with vicinal diols. A correlation of the molecular complexation constant, the polymer swelling, and the maximum adsorption capacity was found. The adsorption curves over time were recorded. Preliminary results on competitive adsorption of binary mixtures showed a high potential for the separation of substrates with significantly different complexation constants. Desorption tests implied easier desorption of substrates that only adsorb on the outer polymer shell.

Adsorption of binary mixtures on two-dimensional triangular lattices

The adsorption of interacting binary mixtures on triangular lattices is studied by combining theory and Monte Carlo (MC) simulations. Two theoretical approximations are used in the present work: (i) the cluster approximation (CA), based on exact counting of adsorption states on small lattices; and (ii) an extension of the standard quasi-chemical approximation (QCA) that includes two adsorbed species (a and b). In the case of CA, an own algorithm is developed to obtain the configurational grand partition function for small cells. Repulsive lateral couplings between adsorbate-adsorbate species are incorporated in the lattice-gas framework. Theoretical (CA and QCA) total and partial adsorption isotherms are compared with MC simulations. Quantitative and qualitative differences are shown and discussed, being CA the more accurate approach in all cases.

Influence of caffeic acid on the adsorption of toluene onto an organophilic zeolite

Abstract Wastewaters and polluted natural water can contain a large variety of organic substances deriving from both natural and anthropogenic sources. Hydrophobic zeolites have great potential for the removal of different organic substances and among them aromatic, chlorinated, and oxygenated compounds. In this work the influence of caffeic acid - an allelochemical representing low molecular weight natural organic matter - on the adsorption of toluene in aqueous matrix has been investigated. To accomplish this task, the adsorption of caffeic acid on ZSM-5 has been studied. Differently from toluene, whose adsorption is not significantly influenced by pH, the uptake of caffeic acid onto zeolite strongly depends on pH, the maximum saturation capacity (46 mg g−1) was obtained at pH 4, corresponding to the nonionized form of caffeic acids. Additionally, caffeic acid interacts with zeolite framework and water molecule as suggested from the shift in the apparent dissociation constant evaluated from adsorption data and confirmed by structural investigation. Competitive adsorption of binary mixture of toluene and caffeic acid in a wide concentration range shows that ZSM-5 is a selective adsorbent for Toluene, and when caffeic acid is present at high concentration (100 mg L−1) the adsorbed quantity of toluene from solution is reduced of less than 15 %.

Elucidation of Selectivity Reversals for Binary Mixture Adsorption in Microporous Adsorbents.

The adsorption selectivity, Sads, is a key metric that quantifies the efficacy of any adsorbent in mixture separations. It is common practice to use ideal adsorbed solution theory (IAST) for estimating the value of Sads, using unary isotherm data inputs. In a number of experimental investigations, the phenomena of selectivity reversals and adsorption azeotropy (Sads = 1) have been reported in the published literature; such reversals may result from changes in mixture compositions, pressures, or pore loadings. In many cases, IAST is unable to anticipate such selectivity reversals. In this article, configurational-bias Monte Carlo simulations are used to gain insights into the phenomena of selectivity reversals. Two fundamentally different scenarios of selectivity reversals have been identified. In the first scenario, selectivity reversals are caused by inhomogeneous distribution of adsorbates due to preferential location and siting of a guest species in the pore space. For example, CO2 locates preferentially in the side pockets of mordenite and in window regions of DDR, CHA, and LTA zeolites. CO2 also congregates around the extra-framework cations of NaX zeolite. IAST fails to anticipate such selectivity reversals because its development relies on the assumption that the competition between guest species is uniform within the pore space. In the second scenario, selectivity reversals are caused by entropy effects that manifest near pore saturation conditions; the component that is preferentially adsorbed is the one that has the higher packing efficiency. For a homologous series of compounds, the component with the smaller chain length is favored at high pore occupancies. For adsorption of mixtures of alkane isomers within the intersecting channel network of MFI zeolite, the linear isomer is favored on the basis of entropic considerations.

Electrically heated catalyst device

The performance of the MIL-101(Cr) loaded with cuprous oxide (Cu2O) nanoparticles was evaluated in both equilibrium and kinetic conditions for adsorption of propane and propylene via volumetric method. The single-component adsorption isotherms were measured at temperatures of 303, 323, 343 and 363 K and pressures up to 400 kPa. To correlate the experimental isotherm data points, temperature-dependent Sips model was applied, which exhibited high accuracy of prediction. The synthesized samples were characterized by XRD, BET, FE-SEM, EDS mapping and TEM techniques. The binary mixture adsorption behavior and selectivity of propane/propylene were calculated by using the ideal adsorbed solution theory (IAST). Obtained results showed that by increasing the loading of Cu2O nanoparticles up to 15 wt%, the propylene selectivity of MIL-101(Cr) was enhanced from 1.5 to 12.2 at 100 kPa and 303 K. Moreover, the optimum performance in terms of both adsorption capacity and selectivity was achieved using 12%[email protected](Cr) sample. Fast diffusion of the adsorbates, obtained by accurate fitting of the isothermal micropore model to the uptake curves data, along with reusability suggest the 12%[email protected](Cr) as a promising adsorbent for effective separation of propane/propylene mixture.

Kinetic Trapping and Adsorption Equilibration of Binary Mixtures within Nanopores

We investigate the kinetics of competitive adsorption of binary gas mixtures in restrictive nano-porous materials by simulating the uptake dynamics of the mixture inside a longitudinal pore via a K...