Ideal Adsorbed Solution Theory Research Articles

Evaluation of separation effect for CH4 enrichment from coalbed methane (CBM) under the synergistic action of temperature and pressure based on IAST theory

AbstractThe synergistic pressure and temperature swing adsorption (SPTSA) technology is designed for purifying coalbed methane (CBM) are proposed in this work. Cyclic processes including four steps: cooling, pressurization, heating, and depressurization. Ideal adsorption solution theory (IAST) was used to evaluate the separation effect. Super activated carbons (SACs) with specific surface area exceeds 3000 m2 g−1 were prepared and used as adsorbents. From 273 to 373 K, the adsorption selectivity (S) changes more than 4, while the S changes less than 2 with the pressure changes from 0.1 to 9 MPa, indicating that temperature change is more conducive to improve the CH4 purity compared to the pressure change. However, more CH4 purification capacity can be obtained by pressure change. In cyclic SPTSA process, the CH4 purification capacity is generally increased by more than 30% compared with the pressure swing adsorption technology, which indicated that CH4 separation and purification under the synergistic action of temperature and pressure is theoretically feasible and has a broad prospect in the CBM purification. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.

Adsorption of CO2, N2 and CH4 on a Fe-based metal organic framework, MIL-101(Fe)-NH2

MIL-101(Fe)-NH2 was synthesized using solvothermal method to assess the selective adsorption of CO2 over N2 and CH4. The BET surface area of adsorbent sample was 915 m2.g-1. The adsorption capacities of CO2, N2 and CH4 on MIL-101(Fe)-NH2 at 4 MP and 298 K were achieved equal to 13, 3.8 and 5 mmol.g-1 respectively. Khan adsorption equilibrium model was applied to correlate the adsorption isotherms of pure gases. In addition to Khan model, the adsorption isotherm of CO2, which showed type II behavior, was also obtained by BET model as well as a newly presented hybrid model, which resulted in excellent agreement with the experimental data. Moreover, the selectivity of CO2 over N2 and CH4 was estimated by Ideal Adsorbed Solution Theory (IAST). Comparison of the achieved results from IAST method with experimental data verified the accuracy of this method in the lower pressure. The selectivity coefficient was about 2.2 for CO2 over N2 and CH4 at 16 bar. The achieved results from a classical micropore diffusion model showed that the diffusion coefficient of the pure gases was approximately constant with pressure. Moreover, the estimated values for diffusion time constants (DC/rC2 × 103) for CO2, N2 and CH4 were obtained equal to 1.178, 1.118, and 0.802 respectively. The adsorption kinetic data were also correlated with empirical models. Ultimately, the results showed that pseudo-nth order empirical model achieved the best agreement with the experimental data, and it can be successfully applied for kinetic modeling of gas adsorption by MIL-101(Fe)-NH2 MOF.

Selective CO2 adsorption using N-rich porous carbon derived from KOH-activated polyaniline

The adsorption of pure gases of carbon dioxide, methane and nitrogen was examined on nitrogen-doped porous carbon (NDC) prepared from polyaniline (PANI) as precursor by chemical activation with KOH (T=650o, IR=2, t=1 h) to determine the potential for the separation of CO2 gas from flue gas or natural gas. Adsorption equilibrium of all gases was determined in a temperature range of 298–318 K and pressure up to 14 bar. Results demonstrated an excellent CO2 adsorption capacity of 3.09 mmol·g−1 owing to high CO2 interaction affinity with NDC surface compared to CH4 (1.43 mmol·g−1) and N2 (0.64 mmol·g−1) under ambient condition (298 K and 1 bar). The ideal adsorbed solution theory (IAST) was used to determine the adsorption selectivity of NDC for CO2/CH4 and CO2/N2 mixtures at different compositions. The NDC had CO2/CH4 (4.42 and 4.08 for CO2/CH4=10/90 and 50/50, respectively) and CO2/N2 (12.81 and 12.08 for CO2/N2=15/85 and 50/50, respectively) IAST selectivity at temperature of 298 K and pressure of 1bar. The moderate CO2 adsorption enthalpy indicates that N-doped activated carbon is a promising material in gas separation such as natural gas and flue gas processing.

High-Throughput Discovery of Ni(IN)2 for Ethane/Ethylene Separation.

Although ethylene (C2H4) is one of the most critical chemicals used as a feedstock in artificial plastic chemistry fields, it is challenging to obtain high‐purity C2H4 gas without any trace ethane (C2H6) by the oil cracking process. Adsorptive separation using C2H6‐selective adsorbents is beneficial because it directly produces high‐purity C2H4 in a single step. Herein, Ni(IN)2 (HIN = isonicotinic acid) is computationally discovered as a promising adsorbent with the assistance of the multiscale high‐throughput computational screening workflow and Computation‐Ready, Experimental (CoRE) metal–organic framework (MOF) 2019 database. Ni(IN)2 is subsequently synthesized and tested to show the ideal adsorbed solution theory (IAST) selectivity of 2.45 at 1 bar for a C2H6/C2H4 mixture (1:15), which is one of the top‐performing selectivity values reported for C2H6‐selective MOFs as well as excellent recyclability, suggesting that this material is a promising C2H6‐selective adsorbent. Process‐level simulation results based on experimental isotherms demonstrate that the material is one of the top materials reported to date for ethane/ethylene separation under the conditions considered in this work.

Adsorption of Carbon Dioxide, Water Vapor, Nitrogen, and Sulfur Dioxide on Activated Carbon for Capture from Flue Gases: Competitive Adsorption and Selectivity Aspects

There is extensive interest in postcombustion flue gas treatment for mitigating CO2 emissions and removal of acid gases. In this study we investigate the adsorption of the main flue gas components (CO2, N2, SO2, and water vapor) on Filtrasorb 400 activated carbon to understand adsorption characteristics of the main components and competitive adsorption effects. The adsorption isotherms of the pure components of flue gas, CO2 (273.15–318.15 K and 0–50 bar), N2 (298.15–313.15 K and 0–150 bar), SO2 (273.15–303.15 K and 0–3.6 bar), and water vapor (293.15–303.15 K and 0–41 mbar), were investigated. The isosteric enthalpies of adsorption were determined to be a function of surface excess. The enthalpies at zero surface coverage have the order SO2 > H2O > CO2 > N2. However, the SO2 isosteric enthalpy decreases with increasing surface excess and is lower than that of water vapor at high surface excess uptake values. The temperature range for CO2 adsorption covers the subcritical to supercritical gas transition. There was no evidence for isosteric enthalpy differences over this temperature range. The adsorption kinetics for SO2 (290.65–303.15 K) and H2O (293.15–303.15 K) adsorption were measured for each isotherm pressure increment. In both cases the adsorption kinetics followed the linear driving force model. The adsorption mechanisms for both SO2 and H2O kinetic trends are discussed in terms of the adsorption mechanisms. The water vapor adsorption kinetics showed a minimum in the region where water molecules form clusters around functional groups, which merge in the pores. The SO2 adsorption kinetics also show a minimum with increasing surface coverage, and this is attributed to dipole–dipole interactions. The activation energies for diffusion of both SO2 and H2O into F400 were very low. Both the N2 and CO2 adsorption kinetics were too fast to be measured accurately by the gravimetric method used in this study. Ideal adsorbed solution theory (IAST) was used to calculate competitive adsorption of SO2/CO2 and CO2/N2 from the isotherms of the pure components. The competitive adsorption of CO2/N2 was investigated by using the integral mass balance (IMB) experimental method, and this was used for validation of the IAST. The results provide an insight into the role of competitive adsorption in the capture of CO2 and SO2 from flue gases by adsorption from both thermodynamic and kinetic perspectives.

Rapid pressure swing adsorption for small scale ammonia separation: A proof‐of‐concept

AbstractIn a typical Haber‐Bosch process, a gas stream containing 15–20 mol% ammonia is obtained from the reactor effluent, and ammonia is then partially separated in a phase‐changing condensation unit. When operating at lower pressure for distributed manufacturing, the single‐pass conversion drops to less than 10 mol%, which makes the condensation more cost‐intensive. A small adsorber is proposed for concentrating ammonia through rapid pressure swing adsorption (RPSA) that fits the small‐scale processing. A mathematical model is developed to evaluate the feasibility of the RPSA process for ammonia separation with high recovery. The ideal adsorbed solution theory, based on the Freundlich single‐component isotherm model, is proposed to predict binary isotherms for various commercially available adsorbents. The performance of the RPSA‐assisted adsorber is then studied at different process conditions for concentrating ammonia. The effect of various operating variables such as exhaust flow rate, cycle time, and feed pressure, is investigated. The proposed numerical model shows that nearly pure ammonia can be continuously produced at optimized conditions, with more than 95% recovery. This low‐pressure RPSA‐assisted adsorber can be used to design modular ammonia devices for distributed manufacturing. Our proposed technology can be further extended to concentrate other dilute gas mixtures, such as carbon dioxide.

Adsorption for efficient low carbon hydrogen production: part 2\u2014Cyclic 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.

Selective Gas Uptake and Rotational Dynamics in a (3,24)-Connected Metal-Organic Framework Material.

The desolvated (3,24)-connected metal-organic framework (MOF) material, MFM-160a, [Cu3(L)(H2O)3] [H6L = 1,3,5-triazine-2,4,6-tris(aminophenyl-4-isophthalic acid)], exhibits excellent high-pressure uptake of CO2 (110 wt% at 20 bar, 298 K) and highly selective separation of C2 hydrocarbons from CH4 at 1 bar pressure. Henry's law selectivities of 79:1 for C2H2:CH4 and 70:1 for C2H4:CH4 at 298 K are observed, consistent with ideal adsorption solution theory (IAST) predictions. Significantly, MFM-160a shows a selectivity of 16:1 for C2H2:CO2. Solid-state 2H NMR spectroscopic studies on partially deuterated MFM-160-d12 confirm an ultra-low barrier (∼2 kJ mol-1) to rotation of the phenyl group in the activated MOF and a rotation rate 5 orders of magnitude slower than usually observed for solid-state materials (1.4 × 106 Hz cf. 1011-1013 Hz). Upon introduction of CO2 or C2H2 into desolvated MFM-160a, this rate of rotation was found to increase with increasing gas pressure, a phenomenon attributed to the weakening of an intramolecular hydrogen bond in the triazine-containing linker upon gas binding. DFT calculations of binding energies and interactions of CO2 and C2H2 around the triazine core are entirely consistent with the 2H NMR spectroscopic observations.

Ion-exchanged ETS-10 adsorbents for CO2/CH4 separation: IAST assisted comparison of performance with other zeolites

ETS-10, the well-known member of titanosilicates, was synthesized, characterized, and then employed to study CO2 and CH4 adsorption on its cation exchanged forms. Equilibrium isotherms of as-synthesized, K-, Mg-, and Sr-ETS-10 were analyzed at 298 K and pressures up to 100 kPa. High selectivities of CO2/CH4 were observed for all the adsorbents. By a closer look at equilibrium isotherms, adsorption selectivity was found to be in the order of K- > as-synthesized- > Sr- > Mg-ETS-10. Analyses of the data revealed that ETS-10 adsorbents containing monovalent cations have more rectangular isotherms and higher CO2/CH4 selectivity. On the other hand, ETS-10 adsorbents exchanged by divalent cations showed lower selectivity but more curvature isotherms which makes the regeneration easier in the pressure swing adsorption process (PSA). High-pressure adsorption experiments at different temperatures up to 348 K were also studied for the most selective adsorbent, i.e., K-ETS-10. Finally, the ETS-10 adsorbents performance in different binary mixtures of CO2/CH4 was investigated by Ideal Adsorption Solution Theory (IAST), and the results were evaluated and compared with the performance of other aluminosilicates and high silica zeolites in CO2/CH4 separation. The comparison led to a new trade-off plot, i.e., adsorption capacity versus CO2/CH4 selectivity, which can be helpful for adsorbent selection.

Isomeric Scandium-Organic Frameworks with High Hydrolytic Stability and Selective Adsorption of Acetylene.

Two solvent-controlled topological isomers of scandium-organic frameworks [Sc(Hpzc)(pzc)]·DMF·2H2O (1·DMF·2H2O) and [Sc(Hpzc)(pzc)]·DMA·4H2O (2·DMA·4H2O) were synthesized using 2,5-pyrazinedicarboxylate (pzc2-) (DMF = dimethylformamide; DMA = dimethylacetamide). Despite the isomeric nature of the obtained metal-organic frameworks (MOFs), they possess different structural features and unique adsorption properties toward gases and iodine. The compound 1 has widely spread among MOF structures a dia topology with ultranarrow channels, which together with inner surface functionalization leads to enhanced CO2 adsorption and high selectivity factors in CO2/CH4 and CO2/N2 gas mixtures (25.9 and 35.6, respectively, 1/1 v/v). Moreover, a rare preferable adsorption of CO2 over C2H2 was demonstrated. The biporous isomeric framework 2 has a crb topology inherent in zeolites. A remarkable adsorption affinity to C2H2 with the ideal adsorbed solution theory selectivity factor of 127.1 for a C2H2/C2H4 mixture (1/99 v/v) was achieved for 2. Both compounds have exceptional chemical stability in a wide range of pH from acidic to basic media.

Comparative Evaluation of Different MOF and Non‐MOF Porous Materials for SO2 Adsorption and Separation Showing the Importance of Small Pore Diameters for Low‐Pressure Uptake

AbstractThe search for adsorbents for flue gas desulfurization processes is a current interest. For the first time, a comparative experimental study of SO2 adsorption by porous materials including the prototypical metal–organic frameworks NH2‐MIL‐101(Cr), Basolite F300 (Fe‐1,3,5‐BTC), HKUST‐1 (Cu‐BTC), the zeolitic imidazolate frameworks (ZIF)‐8, ZIF‐67, the alumosilicate Zeolite Y, the silicoaluminumphosphate (SAPO)‐34, Silica gel 60, the covalent triazine framework (CTF)‐1, and the active carbon Ketjenblack is carried out. Microporous materials with pore sizes in the range of 4–8 Å or with nitrogen heterocycles are found to be optimal for SO2 uptake in the low‐pressure range. The SO2 uptake capacity at 1 bar correlates with the Brunauer‐Emmett‐Teller‐surface area and pore volume rather independently of the surface microstructure. Zeolite Y and SAPO‐34 are stable toward humid SO2. The materials Zeolite Y and CTF‐1(600) show the most promising SO2/CO2 selectivity results with an ideal adsorbed solution theory selectivity in the range of 265–149 and 63–43 with a mole fraction of 0.01–0.5 SO2, respectively, at 293 K and 1 bar.

Robust Heterometallic CoIILaIII2-Organic Framework for the Highly Efficient Separation of Acetylene from Light Hydrocarbon Mixtures.

A highly robust heterometallic CoIILaIII2-organic framework (NUC-19) is synthesized and features 1D rectangle-like channels with a window size of 3.4 × 6.3 Å2 and a carboxyl-group-modified inner surface. NUC-19 exhibits significantly differential uptake for C2H2, C2H4, and CH4, and the ideal adsorbed solution theory selectivities of C2H2/C2H4 (1:99, v/v) and C2H2/CH4 (50:50, v/v) at room temperature can reach up to 4.0 and 79.7, respectively. Fixed-bed dynamic breakthrough experiments under simulated industrial conditions indicate that NUC-19 could efficiently trap C2H2 from mixed gases of C2H2/CH4 and C2H2/C2H4.

Hierarchical porous N-doped carbon xerogels for high performance CO2 capture and supercapacitor

Novel microporous carbon xerogels (CX-HMTAs) with different morphologies and well-developed porosity were successfully fabricated. The hierarchical pore, surface structure, and nitrogen content could be easily controlled by adjusting the amount of hexamethylenetetramine (HMTA). The samples as-obtained exhibited high micropore volume and large specific surface area, which were applied as supercapacitor electrodes and CO2 capture materials. The CX-HMTA4 with a moderate concentration of HMTA (0.72 %) afforded the highest CO2 adsorption capability with 4.21 mmol g−1 at 273 K and 1 bar, and excellent ideal adsorption solution theory (IAST) selectivity with 70 for CO2/N2 capture at 298 K. Moreover, the CX-HMTA4 were simultaneously conducted as a supercapacitor electrode, and gave a maximum specific capacitance of 161 F g-1 and high stability (retained 99.4 % capacity after 1000 cycles) in 6 M KOH electrolyte at 1 A g-1, showed a great advance when compared with most reported benchmark carbon materials. The multifunctional porous carbon materials presented herein were facilely prepared without any activation, exhibiting considerable potentials for large-scale gas adsorption/separation and electrochemical energy storage.

Efficient synthetic approach for nanoporous adsorbents capable of pre- and post-combustion CO2 capture and selective gas separation

The level of CO2 in the atmosphere has increased rapidly due to vast quantities of fossil fuel combustion emissions, and it is accelerating global warming. Hence, pre- and post-combustion CO2 capture and storage (CCS) has become a vital necessity. Cost-effective and efficient nanoporous adsorbents for pre- and post-combustion CO2 capture were developed in this study. The highly porous and oxygen-rich carbon adsorbents were prepared in a facile one-pot process via the direct chemical activation of a molecularly imprinted polymer (MIP) and a MIP composite with activated carbon. The porous carbon adsorbent prepared from the MIP composite had a large specific surface area and specific pore volume of 3010 m2 g−1 and 1.506 cm3 g−1, respectively. Its bimodal pore structure contained micropores and mesopores. This nanoporous carbon adsorbent was rich in electron-dense oxygen presented in a variety of oxygen surface functional groups, which was also advantageous for CCS. These merits afforded selective CO2 adsorption and a high storage capacity under pre- and post-combustion conditions. The efficient carbon adsorbent can be stored 22.1 mmol g−1 and 3 mmol g−1 of CO2 at 25 bar and 1 bar, respectably, which was in the upper range of values reported for porous carbon. Selective CO2 capture by the carbon adsorbents was confirmed by evaluating their selectivity in CO2/CH4, CO2/N2, and CO2/H2 binary gas mixtures at 298 K based on the ideal adsorbed solution theory (IAST). The most effective adsorbent had CO2/H2 (40:60) and CO2/N2 (50:50) selectivity of 534 and 22.6, respectively. The isosteric heat of CO2 adsorption on the porous carbon adsorbents further corroborated the selective CO2 capture.

Adsorption–Desorption Behaviors of Methanol and Ethyl Acetate on Silica Gel: Modeling and Experimental Tests

Methanol and ethyl acetate are typical oxygen-containing volatile organic compounds which are widely used in industry, often leading to serious pollution. Herein, the adsorption–desorption hybrid process has been applied to recover and recycle the methanol and ethyl acetate waste gases using micro–mesoporous silica gel. Results show that compared with commercial activated carbons, the silica gels perform better (85%) in adsorbing the methanol and ethyl acetate due to their stronger affinity. Further tests show that competitive adsorption happens between them. The silica gel shows stronger affinity to ethyl acetate than to methanol. It is also found that an increase in the flow rate and concentration could facilitate the mass transfer of the substances in the pores of the silica gels. Based on the tests, an adsorption process simulation method with ideal adsorption solution theory and the linear driving force model has been applied to simulate the overshoot behaviors of breakthrough curves for the dynamic adsorption of this binary mixture on silica gels (error in ±7%). In this way, the concentration distribution of each adsorbed component on the solid phase in the adsorption bed has also been visualized and analyzed, which was validated by experimental tests. A dynamic adsorption model has been proposed to describe the adsorbed multicomponents on the solid phase for the adsorption of mixture. Finally, according to the adsorption and desorption profiles, a temperature swing–pressure swing combined process is proposed to desorb the adsorbed methanol–ethyl acetate mixture.

Effective CO2 adsorption at low pressure over nitrogen-enriched porous carbons, derived from melamine-loaded polyaniline

Polyaniline (PANI)-derived carbon has been applied in various adsorptions because of the presence of nitrogen and relatively high porosity. In this study, melamine/PANI mixture was pyrolyzed at low temperatures (500–650 °C) to derive porous carbons with high nitrogen content because of added melamine. Obtained carbons (Melamine/PANI-derived Carbons, MPCs) were characterized and applied in CO2 adsorption under low pressure, and MPC-550 (prepared at 550 °C) showed much better performance than PC-550, derived from pure PANI, because of high N content (since N leads to polarity and basicity, which are helpful for CO2 adsorption) and narrow pores (even with low porosity). For example, MPC-550 and PC-550 (prepared at 550 °C) had adsorption capacity of 1.2 and 1.0 mmol/g (at 0.15 atm); and isosteric heat of adsorption (IHA) at zero coverage of 46 and 32 kJ/mol, respectively. On the other hand, N2 adsorption relied mainly on porosity; therefore, MPC-550 had lower N2 adsorption than PC-550. Accordingly, MPC-550 and PC-550 showed ideal adsorbed solution theory selectivity (CO2/N2) of 75 and 61, respectively, under 1 atm. MPC-550 had competitive selectivity compared with other carbon-based adsorbents. MPC-500, prepared at 500 °C, showed very high selectivity (110) and IHA (48 kJ/mol); however, had relatively low CO2 adsorption because of low porosity. Based on the advantages of MPC-550, compared with those of PC-550, adding nitrogenous compounds (like melamine) to PANI, before pyrolysis, is one of the recommendable methods for porous carbons, especially with high N content. Finally, MPC-550 was recyclable in CO2 adsorption and can be suggested as a promising adsorbent for CO2 capture from offgas.

Microporous mixed-ligand metal–organic framework with fluorine-decorated pores for efficient C2H2/C2H4 separation

The selective separation of C2H2 from C2H4 is a very important process for downstream industrial production, and porous metal-organic frameworks (MOFs) have shown great potential for such an application due to their tunable pore surroundings and adjustable building blocks. In this study, a new microporous MOF formulated as {(Et2NH2)[In(TBOT)(2,3-FDA)](DEF)(H2O)2}n (1, H3TBOT ​= ​4,4′,4’’-(((2,4,6-trimethylbenzene-1,3,5-triyl)tris(oxy))tris(methylene))tribenzoic acid, 2,3-HFDA ​= ​2,3-difluorobenzoic acid and DEF ​= ​N,N-diethylformamide) with 2-fold interpenetrated network and 1D fluorine-decorated pores has been prepared via using an acid-acid mixed-ligand strategy. The activated complex 1 (named as 1a) demonstrates apparently higher C2H2 uptake than C2H4 around room temperature, resulting in its relative high C2H2/C2H4 (v:v ​= ​1:99) IAST (Ideal Adsorbed Solution Theory) selectivity of 10.3 ​at 298 ​K and 1 ​bar. Furthermore, the GCMC (grand canonical Monte Carlo) simulation results indicate that the 2,3-FDA moieties serve as preferential binding sites for C2H2 via the multipoint F2⋯H–CC–H⋯F2 interactions, implying the feasibility of the mixed-ligand approach for building porous MOFs with the targeted applications.

Multiple Functions of Gas Separation and Vapor Adsorption in a New MOF with Open Tubular Channels

Separation or purification is one of the difficult problems in the petrochemical industry. To help solve the difficulty of separation or purification for C2H2/CO2 and C2Hn/CH4 in the chemical industry, we synthesized a new metal-organic framework (MOF), [Ni(dpip)]·2.5DMF·H2O (1), by a bipyridyl-substituted isophthalic acid ligand. The MOF includes two types of one-dimensional (1D) tubular channels with different sizes and porous environments. The unique tubular channels lead to not only remarkable gas sorption capacity of C2H4, C2H2, and CO2, but also good selectivity for C2H2/CH4, C2H2/CH4, CO2/CH4, and C2H2/CO2, as demonstrated by single-component sorption isotherm results, ideal adsorbed solution theory calculations, and dynamic breakthrough curves. Grand canonical Monte Carlo (GCMC) simulation reveals preferential adsorption sites in the MOF for CO2, C2H2, and C2H4. The MOF also exhibits an obvious size-selective absorption effect on vapor molecules.

Adsorption-Based Separation of Near-Azeotropic Mixtures-A Challenging Example for High-Throughput Development of Adsorbents.

Adsorption of gas mixtures is central to adsorption-based gas separations, and the number of adsorbate mixture/adsorbent systems that exist is staggering. Because examples of machine learning (ML) models predicting single-component adsorption of arbitrary molecules in large libraries of crystalline adsorbents have been developed, it is interesting to determine whether these models can accurately predict mixture adsorption. Here, we use molecular simulations to generate mixture adsorption data with a set of 12 near-azeotropic molecules in a diverse set of MOFs. These data provide a challenging example for any method to rapidly predict mixture adsorption in MOFs. We combine a previous ML single-component isotherm model with ideal adsorbed solution theory (IAST) to make predictions that can be compared directly with molecular simulation data for these adsorbed mixtures. This combination of ML and IAST illustrates the scope that is available with these methods, but the accuracy of the resulting predictions is disappointing. By examining the same examples with IAST based on minimal molecular simulation data for single-component isotherms, we show that having an accurate description of adsorption in the dilute loading limit is critical to being able to accurately predict mixture adsorption. This observation points to a useful direction for future work developing robust ML models of adsorption isotherms for diverse collections of molecules and adsorbents.

A Fluorinated Metal‐Organic Framework, FMOF‐2, for Preferential Adsorption of Ethane over Ethylene

The preferential adsorption of ethane over ethylene would significantly simplify the overall ethane‐ethylene separation scheme for ethylene purification. Ethane‐selective adsorbents are still lacking compared to ethylene‐selective adsorbents. We discovered that a fluorinated Metal‐Organic Framework, FMOF‐2, exhibits preferential adsorption of ethane over ethylene at pressures in the range of 40 kPa with ideal adsorbed solution theory selectivity of 3.3. The material was characterized by X‐ray diffraction, argon physisorption at 87 K, thermal gravimetric analysis, scanning electron microscope (SEM) image, and X‐ray photoelectron analysis. Exposed fluorine functional groups on a porous material produced via a hydrogen‐bonding type electrostatic attraction are thought to serve as ethane adsorption sites.