Ideal Adsorbed Solution Theory Model Research Articles

High-Pressure Gravimetric Measurements for Binary Gas Adsorption Equilibria and Comparisons with Ideal Adsorbed Solution Theory (IAST).

Measurements of gas mixture adsorption equilibria at high pressures are important for assessing actual adsorbent selectivities but are often out of reach, given the challenging nature of the required experiments. Here, we report a high-pressure gravimetric binary gas adsorption equilibrium measurement system based on simultaneous gas density and mixture adsorption measurements in a single gas cell coupled to a magnetic-suspension balance. Compared to traditional techniques which rely on analytical measurements of gas composition, this approach does not require any sampling. Adsorption measurements of two gas mixtures (0.500 N2 + 0.500 CH4 and 0.400 N2 + 0.600 CO2, mole fraction) on a commercially available molecular sieve (NaY, sodium molecular sieve type Y) were carried out in the temperature range 282 to 325 K with a pressure up to 10 MPa. A prediction method for the gas mixture adsorption equilibria in a closed system using the ideal adsorbed solution theory (IAST) model was used to compare the experimental results. For binary mixtures of components with similar adsorption capacities (here N2 and CH4), the system can measure the adsorption equilibria at pressures higher than 1.0 MPa and the result agrees well with the IAST model prediction. For two gases with very different adsorption capacities, the uncertainty in the adsorption equilibrium measurement is much larger. The dominant uncertainty source is the gas density measurement, whose uncertainty could potentially be cut to half if the current titanium sinker is replaced with a sinker made of single-crystal silicon and with a larger volume.

Optimization performance of viscose rayon derived flexible porous carbon cloths in relation to their CO2 capture, CO2/CH4 separation and methanol adsorption

From the practical perspective, innovative porous carbon material is needed for gas adsorption and separation. Here, flexible porous carbon cloths are successfully prepared from viscose rayon cloth via controllable adjusted KOH activation. In order to optimize such flexible porous carbon cloths, the relationship between KOH activation condition and the porous carbon cloths property have been systematically studied. The effect factors on CO2 capture, CO2/CH4 separation and methanol adsorption have been analyzed in depth. Due to the largest narrow micropore volume (PV1 nm), ACC-240–800 exhibits the best CO2 uptake capacity of 4.11 mmol g−1 under ambient condition. Based on the ideal adsorbed solution theory model, the ACC-240–700 exhibits the highest selectivity of 3.73, 3.13 and 2.65 for CO2/CH4 mixing proportion of 30/70, 46/60 and 50/50, respectively, at 25 °C and 1 bar, owing to the synergetic result of O&N content and PV1 nm. The CO2/CH4 separation performance on ACC-240–700 is analyzed and confirmed by Qst calculation for CO2 and CH4, and dynamic breakthrough experiments with equimolar binary CO2/CH4 (50/50) mixture. The determining factors on methanol adsorption is mainly the porosity structure. The best methanol adsorption uptake of 12.87 mmol g−1 is observed on ACC-240–800 at 25 °C and 95 mbar, because of the largest values of SBET, Vmicro and PV1mn. The flexible porous carbon cloths provided in this work can act as effective adsorbent for carbon capture, low-quality nature gas upgrading and methanol adsorption in the industrial processes.

Experimental Measurement of Pure and Mixed-Gas Kinetics of Ethylene and Ethane Adsorption onto Mordenite, Zeolite 13X, and ZJU-74a: Insights into the Value of Single- vs Mixed-Gas Kinetics, Validity of IAST and Sips Isotherm Models, and Temperature/Pressure Relationships for Process Modeling

Adsorption processes can be applied to the separation of alkane/alkene mixtures. Process modeling is a key tool used to assess if the operating and capital cost of these processes can compete with the industry standard (e.g., cryogenic distillation for ethylene/ethane). These process models rely on experimental adsorbent data, which, due to simplicity, is typically gathered using only pure gases at equilibrium conditions. Gas separations are fundamentally mixed-gas processes, raising the following question: is equilibrium pure gas adsorption data suitable to predict mixed-gas separation performance? To answer this, our work provides process modeling data sets for ethylene and ethane on Mordenite, Zeolite 13X, and ZJU-74a and illustrates that pure gas kinetic measurements are sufficient to predict mixed-gas behavior and provides caution on relying on equilibrium conditions predicted by the ideal adsorbed solution theory (IAST) and extended-Sips methods. Using a modification of the volumetric method for measuring adsorption, we report pure gas kinetics as a function of temperature (20–80 °C) and pressure (<100 kPa) for the adsorption of ethylene and ethane onto Mordenite, Zeolite 13X, and ZJU-74a to supplement isotherms and aid in process modeling. At 293 K, the pseudo-second-order adsorption rate constants of ethylene and ethane, respectively, on Mordenite (4.2 and 2.0 kg·mol–1·s–1) and Zeolite 13X (6.4 and 10 kg·mol–1·s–1) increase with increasing pore size, whereas ZJU-74a (4.9 and 6.6 kg·mol–1·s–1) does not. Only Mordenite exhibited kinetic selectivity (3.2), with the ratio of rate constants for Zeolite 13X and ZJU-74a near unity, suggesting that process models of Zeolite 13X and ZJU-74a will not benefit from considering kinetics. Rate constants of all materials follow an Arrhenius trend with temperature, and the effect of pressure was within measurement error and considered negligible, allowing for simple implementation of these results into process models. Additionally, we show that the extended-Sips isotherm and IAST methods for predicting binary equilibria from pure isotherms perform poorly at predicting the equilibrium condition observed in mixed-gas kinetic experiments.

Competitive adsorption of methane and ethane on organic-rich shale at pressure up to 30 MPa: Experimental results and geological implications

Methane and ethane are the two most abundant hydrocarbon species in shale gas, while the adsorption behavior of their binary mixture in shale is still ambiguous. In this study, the adsorptions of methane, ethane, and their binary mixture on twelve dried mature lacustrine organic-rich shale samples were measured at 60 °C and variable pressures ranging from 0.001 to 30 MPa. The Langmuir and supercritical Dubinin–Radushkevich (SDR) models combined with the ideal adsorbed solution theory (IAST) and Extended Langmuir (EL) model were used to describe the raw adsorption isotherms. By contrast, the Langmuir model with consistent adsorbed phase volume can better describe the ethane excess adsorption. The IAST and EL models matched binary gas excess adsorption equally well. The adsorption capacity of pure ethane was about 1.6 times as large as pure methane, while the Langmuir pressure for ethane was lower. For the adsorption of pure and binary gas, organic matter was the primary contributor, followed by clay minerals. The adsorption selectivity of ethane over methane ranged from 3.49 to 8.85, which strongly depended on total organic carbon (TOC), and weakly negatively correlated with clay mineral content. The estimated gas-in-place (GIP) of binary gas ranged from 4.57 cm3/g to 8.08 cm3/g, which was about 30% larger than that of pure methane. A two-stage trend, first falling and then rising, was observed in relationship between binary gas GIP and TOC. This phenomenon could be attributed to the opposite effects of residual bitumen on shale porosity and gas adsorption. This study provides better insight in the storage mechanisms of shale gas and a basis for the reliable estimation of shale gas potential.

Carbon dioxide/methane mixed-gas adsorption, permeation and diffusion in a carbon molecular sieve film: Experimental observation and modeling

The CO 2 –CH 4 pure- and mixed-gas transport properties (at 35 °C) of a carbon molecular sieve (CMS) film obtained by pyrolysis of a 6FDA-mPDA polyimide precursor at 900 °C are reported. The competitive mixed-gas adsorption of CO 2 and CH 4 was predicted by the Ideal Adsorbed Solution Theory (IAST) model. The CO 2 /CH 4 mixed-gas solubility selectivity of the CMS film was lower than that of relevant glassy polymer films of various nature and increased with pressure. Mixed-gas adsorption data were coupled with gas permeation tests on the same film sample batch used for barometric adsorption measurements to derive concentration-averaged effective diffusion coefficients. Because of its large fraction of ultramicroporous bottlenecks, the diffusion coefficients of the CMS were of the same order of magnitude as those of glassy polymer films of low free volume (e.g., 6FDA-mPDA and CTA). In the range of pressures explored, the pure-gas and multicomponent CO 2 diffusion coefficients overlapped; most importantly, the methane diffusion coefficient was enhanced by the presence of CO 2 . This result suggests that carbon dioxide dilated the sieving domains of the CMS matrix under mixed-gas environment containing highly sorbing gases such as CO 2 . Consequently, the CMS film lost some of its size-sieving properties as indicated by a drop in mixed-gas CO 2 /CH 4 permselectivity relative to the values obtained under pure-gas conditions. • The first case of CO 2 –CH 4 pure- and mixed-gas adsorption in a CMS film. • Competitive effects are more deleterious for CH 4 than for CO 2 . • Competitive effects are beneficial for the CO 2 /CH 4 adsorption selectivity. • The IAST (Toth) model satisfactory predicts the CMS gas adsorption behavior. • CO 2 -induced alteration of the diffusion domains of the CMS film.

Adsorption and separation of propane/propylene on various ZIF-8 polymorphs: Insights from GCMC simulations and the ideal adsorbed solution theory (IAST)

Olefin/paraffin separation is critical for modern chemical industry, yet consumes huge amount of energy as these molecules are very similar. ZIF-8 polymorphs brought very promising opportunities to solve such problem by showing unprecedented propane/propylene separation performance in our recent work (S. Zhou, Y. Wei, L. Li, Y. Duan, et al., Sci. Adv., 2018, 4, eaau1393), whereas some relevant scientific questions remain poorly understood: 1. How the geometrical difference among these polymorphs lead to the superior gas separation performance? 2. How to develop polymorphs with even better adsorption/separation performance? Herein, Grand Canonical Monte Carlo (GCMC) simulations and the IAST model were employed to study the adsorption of propane/propylene on several ZIF-8 polymorphs with a large variety of topology, which is critical for understanding and implementing ZIF-based adsorption or membrane separation process. Our simulation results well agree with the experimental data, revealing the adsorption and separation mechanism of olefin/paraffin on the ZIF-8 polymorphs. The ZIFs’ interactions with gas and their porosity were found to well correlate with the gas uptake, and the density distribution contours further revealed the adsorption competition between propane and propylene. The adsorption of propane + propylene mixtures on ZIF-8 polymorphs was further studied via multi-component GCMC and IAST, both yielding similar results, such as propane selectivities and uptakes. This work not only provided with in-depth insights to understand the adsorption and separation of olefin/paraffin on ZIFs, but also validated combining GCMC with IAST as an efficient methodology to study this subject.

Nitrogen-doped asphaltene-based porous carbon nanosheet for carbon dioxide capture

Abstract A series of porous carbon nanosheets having abundant micropore, nanoscale thickness and doped nitrogen were synthesized using asphaltene by three different facile routes. The three carbon nanosheets exhibited high CO 2 adsorption capacity of 4.0, 4.3, 3.6 mmol/g (25 °C, 1 bar) and 5.3, 6.3, 5.1 mmol/g (0 °C, 1 bar), which should be ascribed to their developed microporous structures and surface nitrogen-containing groups. In order to evaluate their practical application, the separation performance of CO 2 from CO 2 /N 2 and CO 2 /CH 4 was investigated according to breakthrough curves under simulate post-combustion flue gas and coalbed methane, it showed CO 2 adsorption quantities at 25 °C from CO 2 /N 2 (15/85, v/v) and CO 2 /CH 4 (10/90, v/v) reached up to 1.22 mmol/g and 1.18 mmol/g. Furthermore, the selectivity factors for CO 2 compared with N 2 and CH 4 were demonstrated as 15.3 and 7.3 by both ideal adsorbed solution theory model and initial slope method. Moreover, these porous carbon nanosheets could be easily regenerated and showed good stability in >10 times adsorption-desorption cycle, suggesting it promising adsorbents for CO 2 capture.

Simulation of CO2/CH4 high pressure separation on microporous activated carbon

Pure component adsorption equilibrium of CH4 and CO2 on activated carbon have been studied at three different temperatures, 298, 323, and 348 K within a pressure range of 10–2000 kPa. Binary adsorption equilibrium isotherm was described using extended Sips equation and ideal adsorbed solution theory (IAST) model. Experimental breakthrough curves of CO2/CH4 (40:60 in a molar basis) were performed at four different pressures (300, 600, 1200, and 1800 kPa). The experimental results of binary isotherms and breakthrough curves have been compared to the predicted simulation data in order to evaluate the best isotherm model for this scenario. The IAST and Sips models described significantly different results for each adsorbed component when higher pressures are set. These different results cause a significant discrepancy in the estimation of the equilibrium selectivity. Simulated and experimental equilibrium selectivity data provided by IAST presented values of around 4, for CO2/CH4, and extended Sips presented values of around 2. Also, simulated breakthrough curves showed that IAST fits better to the experimental data at higher pressures. According to the simulations, in a binary mixture at total pressure over 800 kPa, extended Sips model underestimated significantly the CO2 adsorbed amount and overestimated the CH4 adsorbed amount.

Binary and ternary adsorption equilibria for CO2/CH4/N2 mixtures on Zeolite 13X beads from 273 to 333 K and pressures to 900 kPa

Reliable adsorption equilibrium data and theoretical models for their accurate representation are crucial to the design of any adsorption based separation. The adsorption equilibria of carbon dioxide, methane and nitrogen are particularly important to the development of industrial pressure swing adsorption processes intended to separate CO2 and N2 from a variety of conventional as well as unconventional natural gas sources. The adsorption equilibrium capacities of gas mixtures needed for process design and simulation are often predicted from pure component adsorption data using various models including the ideal adsorbed solution theory (IAST). In this work, we present the adsorption equilibrium capacity data for a ternary gas mixture of CO2, CH4 and N2 as well as pure and binary gas mixtures of the same components on a commercial zeolite 13X, measured at temperatures of (273, 303 and 333 K) and pressures from (25 to 900 kPa) using a dynamic column breakthrough (DCB) apparatus. Although previous adsorption studies have reported the adsorption equilibria of pure and to a lesser degree binary gas mixtures on zeolite 13X, no experimental data are available in the literature for a ternary gas mixture of CO2, CH4 and N2 on zeolite 13X APG-III, a promising adsorbent for carbon capture and natural gas separation. The measured pure component adsorption capacities were regressed to a Toth isotherm model and the obtained Toth parameters were used to implement an IAST model for binary and ternary adsorption predictions. The IAST predictions of mixture gas adsorption represented the binary and ternary adsorption equilibria well with their corresponding maximum deviations being 0.055 and 0.3 mmol/g, respectively. This indicates the IAST can be applied successfully to these adsorption systems even though they involve molecules with different adsorption affinity and adsorbents with heterogeneous surfaces.

Pure and Binary Adsorption of Carbon Dioxide and Nitrogen on AQSOA FAM Z02

Adsorption equilibria of CO2, N2, and the CO2/N2 binary system on AQSOA FAM Z02 grains were measured over a temperature range of 295 to 348 K and over a wide range in pressure from 0.2 to 20 bar using a gravimetric method. CO2 and N2 single-component experimental equilibrium measurements were regressed using the Toth equation. CO2 adsorption on AQSOA FAM Z02 reported higher loadings compared to N2 adsorption at all measured temperatures, with an adsorption capacity of 6.1 mmol g–1. The adsorption of the CO2/N2 binary mixture at different gas-phase compositions (0.15/0.85, 0.50/0.50, and 0.80/0.20 mole fractions) was studied. The experimental data were compared with the prediction of ideal adsorbed solution theory (IAST), which also included the nonidealities in the bulk gas phase. The IAST model has shown agreement with the experimental data with <4% average relative error in the absolute adsorbed amount.

Pure and Binary Gas Adsorption Equilibrium for CO2–N2 on Oxygen Enriched Nanostructured Carbon Adsorbents

Pure component (CO2 and N2) adsorption isotherms of oxygen enriched nanostructured carbon (RF-700) were evaluated using a static volumetric analyzer at four different adsorption temperatures ranging from 30 to 100 °C. Langmuir, Sips, and dual-site Langmuir (DSL) models were used to correlate pure component adsorption isotherms and it was found that Sips and DSL isotherm model fitted well with the experimental data, indicating the heterogeneous nature of the adsorbent surface. Fixed-bed column was used to obtain dynamic breakthrough data for binary system CO2–N2 at different adsorption temperatures (30–100 °C) and CO2 feed concentrations (5–12.5% by volume). Extended Sips, extended DSL, and IAST (ideal adsorbed solution theory) models using pure component adsorption isotherm data were used for the prediction of adsorption of binary system (CO2–N2). Predicted equilibria data was compared with experimental breakthrough curve data, and it was found that extended forms of the isotherm models (Sips and DSL) und...

Nanoporous activated carbon cloth as a versatile material for hydrogen adsorption, selective gas separation and electrochemical energy storage

The efficient storage of energy combined with a minimum carbon footprint is still considered one of the major challenges towards the transition to a progressive, sustainable and environmental friendly society on a global scale. The energy storage in pure chemical form using gas carriers with high heating values, including H2 and CH4, as well as via electrochemical means using state-of-the-art devices, such as batteries or supercapacitors, are two of the most attractive alternatives for the combustion of finite, carbon-rich and environmentally harmful fossil fuels, such as diesel and gasoline. A few-step, reproducible and scalable method is presented in this study for the preparation of an ultra-microporous (average pore size around 0.6nm) activated carbon cloth (ACC) with large specific area (> 1200m2/g) and pore volume (~ 0.5cm3/g) upon combining chemical impregnation, carbonization and CO2 activation of a low-cost cellulose-based polymeric fabric. The ACC material shows a versatile character towards three different applications, including H2 storage via cryo-adsorption, separation of energy-dense CO2/CH4 mixtures via selective adsorption and electrochemical energy storage using supercapacitor technology. Fully reversible H2 uptake capacities in excess of 3.1wt% at 77K and ~ 72bar along with a significant heat of adsorption value of up to 8.4kJ/mol for low surface coverage have been found. Upon incorporation of low-pressure sorption data in the ideal adsorbed solution theory model, the ACC is predicted to selectively adsorb about 4.5 times more CO2 than CH4 in ambient conditions and thus represents an appealing adsorbent for the purification of such gaseous mixtures. Finally, an electric double-layer capacitor device was assembled and tested for its electrochemical performance, constructed of binder-free and flexible ACC electrodes and aqueous CsCl electrolyte. The full-cell exhibits a gravimetric capacitance of ~ 121F/g for a specific current of 0.02A/g, which relative to the ACC's specific area, is superior to commercially available activated carbons. A capacitance retention of more than 97% was observed after 10,000 charging/discharging cycles, thus indicating the ACC's suitability for demanding and high-performance energy storage on a commercial scale. The enhanced performance in all tested applications seems to be attributed to the mean ultra-micropore size of the ACC material instead of the available specific area and/or pore volume.

Thermodynamic analysis of single and binary adsorption of Food Yellow 4 and Food Blue 2 on CC-chitosan: Application of statistical physics and IAST models

The paper is a complementary study of Food Yellow 4 and Food Blue 2 adsorption in single-compound and binary systems on modified chitosan (CC-chitosan), using statistical physics and Ideal Adsorbed Solution Theory (IAST) models. In order to provide new macroscopic interpretations of adsorption mechanisms, three thermodynamic functions were determined, such as configurationally entropy, free enthalpy and internal energy. The configurationally entropy trend showed that the dye molecules have plenty possibilities/positions to be docked on empty receptor sites at low concentrations, but limited possibilities at high equilibrium concentrations. The study of the free enthalpy and internal energy confirmed that the adsorption process in single-compound and binary systems is spontaneous. The second theoretical approach is based on the IAST model to predict the multicomponent adsorption isotherms using single-compound isotherm data. The IAST model provides a very good prediction of binary adsorption data, for both the adsorbates. Best results were obtained for Food Yellow 4 adsorption data; while for Food Blue 2 an increasing deviation between experimental and modeling binary adsorption data can be observed along with increasing concentration. Finally, the IAST model correctly described the decrease in adsorption capacity of both the dyes from single-compound to binary system, due to competition effects.

Study of synthesis parameters of MIL-53(Al) using experimental design methodology for CO2/CH4 separation

In this study hydrothermal method was used to synthesize MIL-53(Al) (MIL stands for Materials Institute of Lavoisier). Plackett–Burman (P–B) as an experimental design method was applied to investigate the effect of synthesis and activation conditions on specific surface area, relative crystallinity, and production yield of MIL-53(Al) synthesis. Some parameters such as ligand-to-metal molar ratio, synthesis time, synthesis temperature, calcination temperature, and calcination time were selected as the variables. The Brunauer–Emmett–Teller (BET) technique was used in order to estimate the specific surface area of samples while the relative crystallinity of the samples was estimated by comparing their X-Ray Diffraction (XRD) pattern. The morphology of the samples was investigated by field emission scanning electron microscopy. The yield of final products was determined based on organic ligands. The results revealed the significant effect of synthesis temperature on BET surface area, particle size, yield, and crystallinity. The calcination temperature has significant positive effect on BET and crystallinity. Also, the negative significant effect of molar ratio on yield was concluded from the results. However, negligible effect of synthesis and calcination time on the properties of prepared materials were observed. Furthermore, separation capability of a selected sample for carbon dioxide (CO2) and methane (CH4) was measured. Pure gas adsorption data were successfully fitted to Langmuir, Sips, and Toth models. The selected sample provided high adsorption capacity for both gases. The binary adsorption of gases was also investigated based on extended Langmuir equations and the ideal adsorbed solution theory (IAST) models. Comparing the experimental and models data indicated good agreement between the IAST model and experiments. Finally, high CO2/CH4 selectivity of 7.6 was obtained experimentally for the CO2/CH4 molar ratio of 0.2/0.8.

Comparative study of adsorbents performance in ethylene/ethane separation

Some potential adsorbents for ethylene/ethane separation are ethylene selective while the others are ethane selective. Among different adsorbents, i.e., zeolites and metal organic frameworks (MOFs), a comparative study is critical to find the more suitable adsorbent for the separation. In this paper, binary ethylene/ethane adsorption performances of zeolites and MOFs, i.e., equilibrium selectivities and adsorption capacities are investigated utilizing ideal adsorbed solution theory (IAST). IAST model is applied at different gas compositions (0.1–0.9 ethylene mole fractions) and pressures up to 100 kPa. The results revealed that the most selective adsorbent toward ethylene is 5A zeolite while MOFs have higher equilibrium adsorption capacities. Among zeolites and MOFs, 5A and Fe2(dobdc) have the highest selectivity (27.4 and 13.6) and capacity (≈2.8 and 5.8 mmol ethylene/g) at 100 kPa and 298 K for a 50/50 mixture. Among ethane selective adsorbents, Silicalite-1 zeolite and UTSA-33a (MOF) have the highest selectivity and capacity (≈2.9 and ≈1.5 mmol ethane/g) at 100 kPa and 298 K for a 50/50 mixture, respectively. Investigation showed that adsorption capacity of ethylene selective adsorbents is higher than that of ethane selective ones.

Evaluating adsorbed-phase activity coefficient models using a 2D-lattice model

Despite the wide use of the real adsorbed solution theory to predict multicomponent adsorption equilibrium, the models used for the adsorbed phase activity coefficients are usually borrowed from the gas–liquid phase equilibria. In this work, the accuracy of the Wilson and NRTL models for evaluating adsorbed phase activity coefficients is tested using a 2D-lattice model. An accurate model for adsorbed-phase activity coefficients should have no problem in fitting adsorption data obtained using this simple lattice model. The results, however, show that the commonly used Wilson and NRTL models cannot describe the adsorbed phase activity coefficients for slightly non-ideal to strong non-ideal mixtures. Therefore, until new models for adsorbed phase activity coefficients are developed, we should use existing models for liquids with care. In the second part of this work, the use of Monte Carlo simulations on a segregated 2D-lattice model, for predicting adsorption of mixtures is investigated. The segregated model assumes that the competition for adsorption occurs at isolated adsorption sites, and that the molecules from each adsorption site interact with the bulk phase independently. Two binary mixtures in two adsorbent materials were used as case studies for testing the predictions of the segregated 2D-lattice model: the binary system CO2–N2 in the hypothetical pure silica zeolite PCOD8200029, with isolated adsorption sites and normal preference for adsorption, and the binary system CO2–C3H8 in pure silica mordenite (MOR), with isolated adsorption sites and inverse site preference. The segregated 2D-lattice model provides accurate predictions for the system CO2–N2 in PCOD8200029 but fails in predicting the adsorption behaviour of CO2–C3H8 in pure silica MOR. The predictions of the segregated ideal adsorbed solution theory model are superior to those of the 2D-lattice model.

Prediction of molecular separation of polar-apolar mixtures on heterogeneous metal-organic frameworks: HKUST-1.

Due to the combination of metal ions and organic linkers and the presence of different types of cages and channels, metal-organic frameworks often possess a large structural and chemical heterogeneity, complicating their adsorption behavior, especially for polar-apolar adsorbate mixtures. By allocating isotherms to individual subunits in the structure, the ideal adsorbed solution theory (IAST) can be adjusted to cope with this heterogeneity. The binary adsorption of methanol and n-hexane on HKUST-1 is analyzed using this segregated IAST (SIAST) approach and offers a significant improvement over the standard IAST model predictions. It identifies the various HKUST-1 cages to have a pronounced polar or apolar adsorptive behavior.

Adsorbed solution theory based modeling of binary adsorption of nitrobenzene, aniline and phenol onto granulated activated carbon

The modeling study on simultaneous adsorption of three binary systems (nitrobenzene–aniline (NI–AN), nitrobenzene–phenol (NI–PH) and phenol–aniline (PH–AN)) onto granular activated carbon (GAC) in aqueous solution were performed at 30°C by conducting batch experiments. The single solute equilibrium adsorption data of nitrobenzene (NI), aniline (AN) and phenol (PH) were fitted with Langmuir, Freundlich and Redlich–Peterson model. The Redlich–Peterson and Freundlich model gave better fitting as compared to Langmuir model for individual adsorption. The binary adsorption data were examined and compared by using ideal adsorbed solution theory (IAST) and real adsorbed solution theory (RAST) models. IAST model didn’t provide an acceptable prediction of binary data except for low liquid concentration levels, as it undervalued AN and PH adsorption capacity and overvalued NI adsorption capacity. This is due to the non-ideality of binary mixtures at high concentration levels in the solution. The RAST model gave an excellent prediction of binary adsorption experimental data, thus it can be used as a reliable model for the design of industrial adsorption equipment.

Adsorption of Volatile Organic Compounds. Experimental and Theoretical Study

The adsorption of traces of five volatile organic compounds (VOCs) comprising butanal, 2-ethyl-2-hexenal, 2,6-dimethylcyclohexanone, 2,4,6-trimethylanisole, and 2,4,6-trimethylphenol from liquid toluene was investigated. Twenty-one commercial adsorbents of different classes were tested in batch adsorption experiments using the six-component mixture. The Na form of FAU zeolite (NaY) performed by far the best for the overall removal of these compounds from toluene, although removal of all six compounds to very low concentrations (<50 ppm) might not be feasible (in a single step). To further investigate the adsorption behavior of this zeolite, the ideal adsorbed solution theory (IAST) combined with Monte Carlo (MC) simulations was used. A force field was developed for these compounds that allows the computation of pure-component adsorption isotherms in zeolites using MC simulations. The pure-component isotherms are used as input in an IAST model to predict multicomponent adsorption behavior in zeolites. Simulations of binary and six-component mixture are compared to experimentally obtained adsorption isotherms. We show that (1) NaY zeolite performs best for the overall adsorption of the selected compounds from liquid toluene and (2) a combined molecular simulation–IAST approach can be used for this system to predict the adsorption behavior in NaY reasonably well.

A modelling analysis of PCE/TCE mixture adsorption based on Ideal Adsorbed Solution Theory

For a proper design of multicomponent adsorption systems, the availability of reliable adsorption models is paramount. In this work, an experimental and modelling analysis of PCE/TCE adsorption, aimed at investigating adsorption capacities in a binary system, is carried out. All the experimental tests are conducted at constant pH and temperature. The analyte concentration is varied over a wide range in order to cover as much as possible real cases that could lead to different adsorption behaviours and, consequently, to different modelling results. Experimental data show that the PCE adsorption capacity does not depend on TCE presence, and the equilibrium final conditions are not related to different analyte adsorption rates. The equilibrium adsorption data are analyzed by using different adsorption models, namely Langmuir multicomponent, Ideal Adsorbed Solution Theory (IAST) and Predictive Real Adsorbed Solution Theory (PRAST) models. The Langmuir model provides the worst data prediction since its basic hypotheses do not reflect the physical behaviour of the system. The IAST model does not provide a satisfactory prediction of binary data except for low liquid concentration levels, as it underestimates the PCE adsorption capacity and overestimates TCE. It follows that when the solid coverage increases, the PCE–TCE mixture behaviour is not ideal. Finally, the PRAST model, here developed for liquid systems for the first time, is considered in order to take into account a non-ideal system by including activity coefficients. The PRAST model provides a very good prediction of PCE adsorption experimental data but it is not useful to predict TCE adsorption data, its performance being even worse than IAST. The inability of the model to correctly predict both isotherms simultaneously lies in the particular type of non-ideality of the system itself, as shown by experimental data.