Activity coefficient models for accurate prediction of adsorption azeotropes

In this study seven adsorption azeotropes involving binary systems and zeolite-based adsorbents were systematically investigated. Pure component isotherms and mixed-gas adsorption data were taken from published literature except for the benzene–propene system on silicalite, which is newly presented in this work using molecular simulations. Experimental adsorbed phase composition and total amount adsorbed of the azeotropic systems were compared with the predictions of several models including: the ideal adsorbed solution theory (IAST), the heterogeneous ideal adsorbed solution theory (HIAST) and the real adsorbed solution theory (RAST) coupled with the 1-parameter Margules (1-Margules) and the van Laar equations. In the latter two models an additional loading parameter was incorporated in the expression of the excess Gibbs energy to account for the reduced grand potential dependency of the activity coefficients in the adsorbed phase. It was found that the HIAST and RAST–1-Margules models were able to predict the azeotropic behaviour of some systems with good accuracy. However, only the RAST–van Laar model consistently showed an average relative deviation below 3% compared to experimental data for both the adsorbed phase composition and the total amount adsorbed across the systems. This modified van Laar equation is therefore preferable in those engineering applications when the location of adsorption azeotropes is required with great accuracy and when there is lack of detailed characterization of the adsorbent that is needed to carry out molecular simulations.

Gas Adsorption Selectivity in Topologically Disordered Metal–Organic Frameworks

<div><p>Disordered metal–organic frameworks are emerging as an attractive class of functional materials, however their applications in gas storage and separation have yet to be fully explored. Here, we investigate gas adsorption in the topologically disordered Fe-BTC framework and its crystalline counterpart, MIL‑100. Despite their similar chemistry and local structure, they exhibit very different sorption behaviour towards a range of industrial gases, noble gases and hydrocarbons. Virial analysis reveals that Fe-BTC has enhanced interaction strength with guest molecules compared to MIL‑100. Most notably, we observe striking discrimination between the adsorption of C₃H₆ and C₃H₈ in Fe‑BTC, with over a twofold increase in the amount of C₃H₆ being adsorbed than C₃H₈. Thermodynamic selectivity towards a range of industrially relevant binary mixtures is probed using ideal adsorbed solution theory (IAST). Together, this suggests the disordered material may possess powerful separation capabilities that are rare even amongst crystalline frameworks.</p></div>

Gas Adsorption Selectivity in Topologically Disordered Metal–Organic Frameworks

<div><p>Disordered metal–organic frameworks are emerging as an attractive class of functional materials, however their applications in gas storage and separation have yet to be fully explored. Here, we investigate gas adsorption in the topologically disordered Fe-BTC framework and its crystalline counterpart, MIL‑100. Despite their similar chemistry and local structure, they exhibit very different sorption behaviour towards a range of industrial gases, noble gases and hydrocarbons. Virial analysis reveals that Fe-BTC has enhanced interaction strength with guest molecules compared to MIL‑100. Most notably, we observe striking discrimination between the adsorption of C₃H₆ and C₃H₈ in Fe‑BTC, with over a twofold increase in the amount of C₃H₆ being adsorbed than C₃H₈. Thermodynamic selectivity towards a range of industrially relevant binary mixtures is probed using ideal adsorbed solution theory (IAST). Together, this suggests the disordered material may possess powerful separation capabilities that are rare even amongst crystalline frameworks.</p></div>

Effective Separation of Prime Olefins from Gas Stream Using Anion Pillared Metal Organic Frameworks: Ideal Adsorbed Solution Theory Studies, Cyclic Application and Stability

The separation of C3H4/C3H6 is one of the most energy intensive and challenging operations, requiring up to 100 theoretical stages, in traditional cryogenic distillation. In this investigation, the potential application of two MOFs (SIFSIX-3-Ni and NbOFFIVE-1-Ni) was tested by studying the adsorption–desorption behaviors at a range of operational temperatures (300–360 K) and pressures (1–100 kPa). Dynamic adsorption breakthrough tests were conducted and the stability and regeneration ability of the MOFs were established after eight consecutive cycles. In order to establish the engineering key parameters, the experimental data were fitted to four isotherm models (Langmuir, Freundlich, Sips and Toth) in addition to the estimation of the thermodynamic properties such as the isosteric heats of adsorption. The selectivity of the separation was tested by applying ideal adsorbed solution theory (IAST). The results revealed that SIFSIX-3-Ni is an effective adsorbent for the separation of 10/90 v/v C3H4/C3H6 under the range of experimental conditions used in this study. The maximum adsorption reported for the same combination was 3.2 mmolg−1. Breakthrough curves confirmed the suitability of this material for the separation with a 10-min gab before the lighter C3H4 is eluted from the column. The separated C3H6 was obtained with a 99.98% purity.

N-enriched GO Adsorbent Series for Selective Adsorption of CO2: Characterization, Equilibrium, and Thermodynamic Studies

In this study a series of GO-based adsorbents were assembled via impregnation method using N-resources: 3-aminopropyl-triethoxysilane (APTS) as primary amio-silane, Piperazine (PIP) as secondary cyclic diamine, and ethanolamine (EA) as primary amine. The influence of amine type, adsorption temperature and pressure were undertaken to obtain the best CO2 adsorption performance. The characterizing techniques including FTIR, SEM, TGA, BET, BJH, and MP confirmed well impregnation of amine functionalities to the GO framework and high thermal stability of adsorbents. GO/APTS showed the maximum CO2 uptake (43.114 mmol/g) predicted by the Sips isotherm model and the highest CO2 ¬(15% V, balanced N2) selectivity (33.7 %) estimated by the ideal adsorbed solution theory. The experimental adsorption capacity of GO/APTS is 2.3 times higher than pristine GO. This behavior highlights the role of electron-donor amine and methyl groups and high molecular weight of APTS as well as high interfacial area of GO/APTS in CO2 capture.

Adsorption for efficient low carbon hydrogen production: part 2—Cyclic experiments and model predictions

Hydrogen as clean energy carrier is expected to play a key role in future low-carbon energy systems. In this paper, we demonstrate a new technology for coupling fossil-fuel based hydrogen production with carbon capture and storage (CCS): the integration of CO2 capture and H2 purification in a single vacuum pressure swing adsorption (VPSA) cycle. An eight step VPSA cycle is tested in a two-column lab-pilot for a ternary CO2–H2–CH4 stream representative of shifted steam methane reformer (SMR) syngas, while using commercial zeolite 13X as adsorbent. The cycle can co-purify CO2 and H2, thus reaching H2 purities up to 99.96%, CO2 purities up to 98.9%, CO2 recoveries up to 94.3% and H2 recoveries up to 81%. The key decision variables for adjusting the separation performance to reach the required targets are the heavy purge (HP) duration, the feed duration, the evacuation pressure and the flow rate of the light purge (LP). In contrast to that, the separation performance is rather insensitive towards small changes in feed composition and in HP inlet composition. Comparing the experimental results with simulation results shows that the model for describing multi-component adsorption is critical in determining the predictive capabilities of the column model. Here, the real adsorbed solution theory (RAST) is necessary to describe all experiments well, whereas neither extended isotherms nor the ideal adsorbed solution theory (IAST) can reproduce all effects observed experimentally.

Influence of Salinity on the Removal of Ni and Zn by Phosphate-Intercalated Nano Montmorillonite (PINM)

The salinity influence on the adsorptions of Ni and Zn onto phosphate-intercalated nano montmorillonite (PINM) were investigated. Single adsorption isotherm models fitted the single adsorption data well. The adsorption capacity of Ni was higher than that of Zn onto PINM at different salinities. The single adsorption parameters from Langmuir model (QmL and bL) were compared with the binary adsorption (QmL* and bL*). The QmL* of Zn was lower than that of Ni. The simultaneous presence of Ni and Zn decreased the adsorption capacities. The single and binary adsorptions onto PINM were affected by the salinity. The competitive Langmuir model (CLM), P-factor, Murali and Aylmore (M−A) models, and ideal adsorbed solution theory (IAST) were satisfactory in predicting the binary adsorption data; the CLM showed the best fitting results. Our results showed that the PINM can be used as an active Ni and Zn adsorbent for a permeable reactive barrier (PRB) in the remediation of saline groundwater.

Removal of Salicylic and Ibuprofen by Hexadecyltrimethylammonium-Modified Montmorillonite and Zeolite

The removal of salicylic acid (SA) and ibuprofen (IB) by sorption onto HDTMA-modified montmorillonite (HM) and zeolite (HZ) was investigated at pH 7. The single sorption data were fitted well by the Freundlich, Langmuir, Dubinin−Radushkevich (DR), and Polanyi−Dubinin−Manes (PDM) models (R2 > 0.94). The sorption affinity of Freundlich and the maximum sorption capacity of Langmuir and PDM models of pharmaceuticals onto HM were consistently higher than that of HZ mainly owing to the higher organic carbon content. In addition, the KF, qmL, and qm values were in the order of IB > SA owing to higher hydrophobicity and molar volume. Since the predominant speciation of SA and IB is anionic at pH 7 (>pKa), sorption onto HM occurs mainly by the two-dimensional surface adsorption onto the pseudo-organic medium in the HM, whereas the interaction of anionic pharmaceuticals with the positively charged “head” of HDTMA is responsible for HZ. Sorption isotherms were fitted well by the PDM model, which indicated that pore-filling was one of the dominating sorption mechanisms. The extended Langmuir model, modified Langmuir competitive model, and ideal adsorbed solution theory employed with Freundlich and Langmuir sorption models were applied to predict binary sorption. The effect of competition between the solutes was clearly evident in the characteristic curves; the maximum sorbed volume (qv.m) was reduced, and the sorbed volume (qv) had a wider distribution toward the sorption potential density.