Ideal Adsorbed Solution Theory Calculations Research Articles

Improving separation of CH4 and N2 by adsorption on zeolite Y Ion–Exchanged with ammonium Cations: An experimental and Grand–Canonical Monte Carlo (GCMC) simulation investigation

The separation of methane (CH4) from industrially–important nitrogen (N2)-rich vent streams such as those in liquefied natural gas processing plants is challenging. Pressure swing adsorption (PSA) is a promising, cost–effective solution in gas separation, especially for small–scale units. Further development and commercialisation of PSA–based technologies require access to low–cost, selective adsorbent materials. The current work investigates the improved separation of CH4 from N2 by TMA–Y zeolite which is obtained from the ion exchange treatment of Na–Y zeolite with the ammonium salt tetramethylammonium chloride (TMACl). TMA–Y is commercially called Ionic Liquidic Zeolite (ILZ), patented at The University of Western Australia, and has now been demonstrated on tonne–scale. In particular, we use a combination of experimental and molecular simulation techniques to provide insights into the high CH4–over–N2 selectivity of TMA–Y. For this, we obtain equilibrium isotherms of CH4 and N2 on Na–Y at different temperatures and pressures before and after ion exchange. The true selectivities of the zeolite samples are determined using the Ideal Adsorbed Solution Theory (IAST) and binary–gas grand–canonical Monte Carlo (GCMC) molecular simulations. From experiments and IAST calculations, we report an increase of >110% in the CH4/N2 selectivity of Na–Y after treatment with TMACl (from 2.2 to 4.7 at 5.0 MPa and 303.15 K for a mixture of 0.1 CH4+0.9 N2 mol.mol−1). GCMC molecular simulations provide a detailed picture of the molecular origins of this effect. Specifically, the introduction of TMA+ ions into the structure of Na–Y zeolite leads to a reduction of the available adsorption volume by more than 40% (from 0.30 to 0.17 cm3.g−1 with N2 as the probe molecule) for both adsorbing gas species (i.e. CH4 and N2). However, at the same time, this leads to stronger CH4–cation interactions due to the much higher affinity of TMA+ cations (5 kJ.mol−1) than extra–framework Na+ cations (1 kJ.mol−1) towards CH4. The overall effect of these two trends combined is the higher selectivity of the resulting TMA–Y zeolite for CH4. These molecular insights are useful in the systematic engineering of new materials with improved separation performance.

Ideal Adsorbed Solution Theory (IAST) of Carbon Dioxide and Methane Adsorption Using Magnesium Gallate Metal-Organic Framework (Mg-gallate)

Ideal Adsorbed Solution Theory (IAST) is a predictive model that does not require any mixture data. In gas purification and separation processes, IAST is used to predict multicomponent adsorption equilibrium and selectivity based solely on experimental single-component adsorption isotherms. In this work, the mixed gas adsorption isotherms were predicted using IAST calculations with the Python package (pyIAST). The experimental CO2 and CH4 single-component adsorption isotherms of Mg-gallate were first fitted to isotherm models in which the experimental data best fit the Langmuir model. The presence of CH4 in the gas mixture contributed to a lower predicted amount of adsorbed CO2 due to the competitive adsorption among the different components. Nevertheless, CO2 adsorption was more favorable and resulted in a higher predicted adsorbed amount than CH4. Mg-gallate showed a stronger affinity for CO2 molecules and hence contributed to a higher CO2 adsorption capacity even with the coexistence of a CO2/CH4 mixture. Very high IAST selectivity values for CO2/CH4 were obtained which increased as the gas phase mole fraction of CO2 approached unity. Therefore, IAST calculations suggest that Mg-gallate can act as a potential adsorbent for the separation of CO2/CH4 mixed gas.

Partial Linker Substitution Strategy to Construct a Quaternary HKUST-like MOF for Efficient Acetylene Storage and Separation.

Multicomponent metal-organic frameworks (MOFs) have received much attention as emerging materials capable of precisely programing exquisite structures and specific functions. Here, we applied a partial linker substitution strategy to compile an HKUST-1-like quaternary MOF by introducing a bifunctional ligand into the well-known HKUST-1 structure. FUT-1, a new HKUST-like tbo topology MOF, was assembled with paddlewheel [Cu2(COO)4], triangular metallocycle pyrazole cluster Cu3(μ3-OH) (NN)3 building blocks, and two distinct linkers. FUT-1 exhibited good mechanical stability, water stability, and chemical stability (pH = 3-12) in aqueous solutions. Moreover, the porous environments created by this multicomponent primitive endow FUT-1 with high C2H2 storage and significantly selective separation performance of C2H2/CO2. Dynamic breakthrough experiments and ideal adsorbed solution theory calculations further demonstrate that FUT-1 can selectively capture C2H2 from C2H2/CO2 mixtures under ambient conditions. Based on grand canonical Monte Carlo simulations, the high C2H2 separation performance of FUT-1 is attributed to the π-complex formed between the C2H2 molecule and the trinuclear metallocycle clusters on the wall, which provides stronger affinity for C2H2 recognition than the CO2 molecule.

A Microporous Potassium‐Organic Framework for Efficient C2H2/CO2 Separation

AbstractA novel potassium‐based metal organic framework (TCBPA‐K) was prepared by using a C3‐symmetric organic building block tris(4′‐carboxybiphenyl)amine (TCBPA). The compound has a rectangular like channel along the b axis and exhibits good selective adsorption performance. The single component gas adsorption isotherms indicated that the adsorption capacity of C2H2 is much higher than that of CO2 at 298 K and 1 bar. The isosteric adsorption enthalpies of TCBPA‐K for C2H2 and CO2 are 30.6 kJ/mol and 9.1 kJ/mol respectively. Ideal adsorbed solution theory calculation recorded the separation selectivity of C2H2/CO2 (50/50, v/v) as 3.5.

Separation of ethane/ethylene gas mixture by ethane-selective CAU-3-NDCA adsorbent

Ethane-selective adsorbents for separating ethane (C2H6)/ethylene (C2H4) gas mixtures have attracted considerable interest as promising alternatives to conventional cryogenic distillation because of the possibility of directly producing high-purity C2H4 (>99.95%). Herein, CAU-3-NDCA built by the coordination bond between [Al12(OCH3)24]12+ and 2,6-naphthalenedicarboxylic acid (NDCA) was evaluated for use as a C2H6-selective adsorbent for separating a C2H6/C2H4 gas mixture. The separation performance of the adsorbents was investigated using single-component gas isotherms, ideal adsorbed solution theory calculations, dynamic breakthrough experiments for gas mixture, and molecular simulations, such as Monte Carlo simulation and density functional theory calculation. CAU-3-NDCA displayed exceptional adsorption capacity (9.2–10.2 mmol g−1 at 15 bar) and good C2H6/C2H4 selectivity (1.44–1.56) in the temperature range 293–313 K. In the breakthrough experiments, the C2H6/C2H4 separation performance of CAU-3-NDCA exhibited high-purity C2H4 productivity of 6.6 and 25.7 LSTP kg−1 under a 50/50 (v/v) and 10/90 (v/v) C2H6/C2H4 gas mixture, respectively, at 298 K and 7 bar. Recyclability was evaluated by a multi-cyclic breakthrough test for five cycles with a 10/90 (v/v) C2H6/C2H4 gas mixture. Molecular simulations indicated that the preferential adsorption of C2H6 originates from the higher affinity strength of multiple C–H···π interactions of C2H6 with NDCA linkers, in addition to the stronger methyl group–gas interaction of the methanolate group than those of C2H4. Moreover, it is characterised by thermal and moisture stability. Therefore, CAU-3-NDCA is a promising candidate for pressure swing adsorption operation as a C2H6-selective adsorbent.

Gas sorption and selectivity study of N,N,N′,N′-tetraphenyl-1,4-phenylenediamine based microporous hyper-crosslinked polymers

One of the most important parameters to design porous polymeric materials for gas storage and separation is to discover appropriate linker. Determining the effect of linker, in fixed core, over the selectivity and adsorption has been great challenge. Here, three different N,N,N′,N′-tetraphenyl-1,4-phenylenediamines (TPPA) based microporous hyper-crosslinked polymers synthesized by the Friedel-Craft reactions. Hypercrosslinked polymer, TPPA-DMM, was obtained from dimethoxymethane (DMM) and hypercrosslinked-covalent polymer, TPPA-DMB, from dimethoxybenzene (DMB) in presence of FeCl3. TPPA-CC, covalent triazine polymer was synthesized from cyanuric chloride (CC) via AlCl3 as the catalyst. After the careful characterization of these microporous structures with different analytical and spectral analyses, the gas uptake (for CO2, CH4, O2, CO, and H2) and selectivity properties (for CO2/N2, CO2/O2, for CO2/CO and CO2/CH4) were comparatively investigated at pipe gas temperatures and up to 1 bar. The high BET specific surface areas ranging from 742 to 883 m2/g with ultramicropore characters (0.53–0.58 nm), high chemical stability in different solvents even in concentrated acid and thermal stability (up to 450 °C) promised that these materials can be used in pipe gas processes. By changing the linkers on the core, materials have high gas uptake properties reaching 12.98 wt% for CO2 uptake, 1.57 wt% for CH4 uptake, 1.06 wt% for CO uptake at 1 bar/273 K and also reaching 1.28 wt% for H2 uptake at 1 bar/77 K. In addition, the unusual N2 phobic character down to 0.2 wt% and O2 phobic character down to 0.3 wt% were observed. The selectivity was calculated by using the ideal adsorbed solution theory (IAST). The selectivities were found reaching 80.4 for CO2/N2, 8.5 for CO2/CH4, 30.1 for CO2/CO and 39.1 for CO2/O2. These calculations show that the obtained polymers can be used in post combustion processes which needs high pressures and temperatures. The selectivities of the synthesized materials for the gas sorptions changed drastically by switching the linkers in all three materials. Interestingly, IAST calculations from single to dual gas, in the different ratios, showed that selectivities were almost the same for each polymer within itself at same temperature. To date, these are the first reported discoveries for the porous organic polymers in the literature.

Capture and Separation of SO2 Traces in Metal-Organic Frameworks via Pre-Synthetic Pore Environment Tailoring by Methyl Groups.

Herein, we report a pre‐synthetic pore environment design strategy to achieve stable methyl‐functionalized metal–organic frameworks (MOFs) for preferential SO2 binding and thus enhanced low (partial) pressure SO2 adsorption and SO2/CO2 separation. The enhanced sorption performance is for the first time attributed to an optimal pore size by increasing methyl group densities at the benzenedicarboxylate linker in [Ni2(BDC‐X)2DABCO] (BDC‐X=mono‐, di‐, and tetramethyl‐1,4‐benzenedicarboxylate/terephthalate; DABCO=1,4‐diazabicyclo[2,2,2]octane). Monte Carlo simulations and first‐principles density functional theory (DFT) calculations demonstrate the key role of methyl groups within the pore surface on the preferential SO2 affinity over the parent MOF. The SO2 separation potential by methyl‐functionalized MOFs has been validated by gas sorption isotherms, ideal adsorbed solution theory calculations, simulated and experimental breakthrough curves, and DFT calculations.

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.

7-Connected FeIII3-Based Bio-MOF: Pore Space Partition and Gas Separations.

We reported herein a new 3D bio-MOF (NbU-12) using a pore space partition strategy: MIL-88D was selected as a primary framework, and adenine connected two independent MIL-88D to form a self-interpenetrated structure. Because of this, the hexagonal channel in MIL-88D split into two small rectangular channels. Different from the reported series CPM-35 materials, NbU-12 simultaneously maximized the retention of open metal sites from MIL-88D and introduced a Watson-Crick face to the pore surface of NbU-12. Remarkably, NbU-12 exhibits an excellent selectivity performance toward C2H6/C2H4 and C2H6/CH4, which was proven by ideal adsorbed solution theory calculation and breakthrough experiments.

Highly Robust Tetranuclear Cobalt-Based 3D Framework for Efficient C2H2/CO2 and C2H2/C2H4Separations

A novel noninterpenetrated tetranuclear cobalt(II)-based metal-organic framework, (NH4)2·[Co4(μ3-OH)2(ina)2(pip)3]·4EtOH·H2O (simplified as NbU-10·S), constructed by mix linkers was synthesized by a hydrothermal method. Interestingly, the presence of a hydrophobic benzene ring in the organic linker makes NbU-10·S exhibit high stability in high temperature and even in aqueous solution over a wide pH range of about 4-13. Magnetic studies showed that the tetranuclear cobalt(II) units in NbU-10·S show dominant antiferromangetic properties. However, in the absence of Lewis basic functional sites and open metal sites in the material, NbU-10 still displays high C2H2/CO2 and C2H2/C2H4 selectivity in ideal adsorbed solution theory calculations and dynamic breakthrough experiments. Moreover, density functional theory calculations were performed to identify the adsorption characteristics of different gas molecules.

Facile synthesis of anionic porous organic polymer for ethylene purification

The removal of acetylene from ethylene is of vital significance in the petroleum and chemical industry, the presence of trace acetylene impurities in ethylene polymerization process could lead to the interruption of ethylene polymerization. Herein, we construct a new anionic porous organic polymer using potassium tetraphenylborate via Friedel–Crafts alkylation reaction under mild conditions. The resulting material, APOP, possesses good thermal stability and a decent BET surface area, as exemplified by thermogravimetric analysis measurement and nitrogen gas sorption experiment. Acetylene and ethylene adsorption isotherms reveal that APOP has a higher adsorption capacity of acetylene than that of ethylene under same conditions. Ideal adsorbed solution theory calculations and breakthrough experiments both demonstrate that APOP is capable of selective adsorption of acetylene over ethylene. To the best of our knowledge, APOP represents the first anionic porous organic polymer material capable of selective adsorption of acetylene over ethylene, and the exploration of APOP may provide a new way for these key gas separations using ionic porous organic polymer materials.

Guest-Responsive Reversal in Structural Transformation after a [2 + 2] Topochemical Reaction in a 3D Pillared Layer MOF: Uncovering the Role of C-H···O Interaction.

Here, we report the influences of the C-H···O interaction, weaker than other conventional noncovalent interactions, on the guest-responsive structural modification of a photoactive metal-organic framework (MOF) and the impact on gas sorption properties. A photoactive pillared-layer three-dimensional MOF {[Cd(pzdc)(bpee)]2·3H2O}n (1) (where bpee = 1,2-bis(4-pyridyl)ethylene and pzdc = 2,3-pyrazinedicarboxylate) was synthesized and characterized. Compound 1 shows guest-responsive structural contraction by the movement of two-dimensional layers supported by the C-H···O interaction between the pillar (bpee) and layer (pzdc) linkers. Further, 1 was postsynthetically modified using light by exploiting the parallel arrangement of the olefinic double bondsof the bpee pillars based on a [2 + 2] cycloaddition reaction to produce {[Cd2(pzdc)2(rctt-tpcb)]·3H2O}n, (1IR) (rctt-tpcb = regio cis,trans,trans-tetrakis(4-pyridyl)cyclobutane) in a single-crystal-to-single-crystal transformation (SCSC) manner. The C-H···O interaction between the two linkers is not possible in the photomodified framework, and thus guest-responsive structural expansion is realized. Such a reversal of the structural transformation facilitates the enhanced CO2 uptake in 1IR with respect to 1 at their dehydrated states. Further, the photomodified compound 1IR does not uptake N2 and CH4 at 273 K and shows high selectivity as realized by an ideal adsorbed solution theory calculation. The facile diffusion of CO2 in the irradiated framework is also supported by the kinetic measurements based on MeOH adsorption isotherms at 293 K. Here, postsynthetic modification by a [2 + 2] photochemical reaction is the key to control the structural change for enhanced CO2 uptake capacity.

Effect of framework rigidity in metal-organic frameworks for adsorptive separation of ethane/ethylene

Ethane-selective adsorbents having high adsorption capacities along with high selectivity toward C 2 H 6 are required to develop a cost-effective adsorption process for the facile separation of ethane (C 2 H 6 ) from the ethane and ethylene (C 2 H 4 ) mixture. Understanding the roles of physicochemical properties of the C 2 H 6 -selective adsorbent in terms of its C 2 H 6 /C 2 H 4 separation performance is especially essential for the design of novel advanced materials. Herein, we selected the known metal-organic framework structure, namely, the pillared three-dimensional framework DUT-8, which is synthesized by incorporation of 2,6-naphthalenedicarboxylic acid as a linker. We compared physicochemical properties of DUT-8 according to the framework flexibility and the type of metal ion. Even though the framework stability of DUT-8 is very low in the presence of water vapor, we further evaluated the C 2 H 6 /C 2 H 4 separation performance of isomorphous DUT-8(M) adsorbents with different metal ions (M = Co, Ni, Cu, and Zn) by means of single-gas isotherm measurements, ideal adsorbed solution theory calculations, grand canonical Monte Carlo simulations, and density functional theory calculations. Separation results showed that preferential uptakes of C 2 H 6 were observed from the C 2 H 6 /C 2 H 4 mixture particularly over the rigid framework of DUT-8 (Cu and Ni) through the C–H‧‧‧π interaction close to the metal node. Thus, high selectivity of C 2 H 6 was achieved over DUT-8(Cu and Ni) along with high uptakes of C 2 H 6 (up to 11.2 mmol/g) at a temperature range of 283–303 K and pressure of 10 bar. The breakthrough separation results on DUT-8(Cu) showed that the binary mixture of C 2 H 6 /C 2 H 4 (1 : 9 v/v) can be effectively separated at pressures of 1 and 5 bar with high productivity of high purity ethylene (20.8 L/kg at 1 bar and 45.0 L/kg at 5 bar). The facile regeneration possibility over DUT-8 is confirmed by the dynamic desorption studies, expecting continuous production of high purity ethylene. • Rigid and flexible DUT-8 MOFs were investigated for separation of ethane/ethylene. • Flexible DUT-8 MOFs with Ni, Zn, and Co exhibited low uptakes for both two gases. • Rigid DUT-8 MOFs with Cu and Ni showed exceptional uptakes particularly for ethane. • Rigid DUT-8 frameworks have good selectivity by CH···π interaction with ethane. • High purity ethane over 99.95% could be efficiently separated over DUT-8(Cu).

Tailoring the Pore Environment of a Robust Ga-MOF by Deformed [Ga3O(COO)6] Cluster for Boosting C2H2 Uptake and Separation.

The construction of superstable metal-organic frameworks (MOFs) for selective gas uptake is urgently demanded but remains a great challenge. Herein, a unique bifunctional deformed [Ga3O(COO)6] inorganic secondary building unit (SBU) generated from the desymmetrical evolution of typical triangular prismatic trinuclear cluster was first introduced, which was extended by an isosceles triangular organic linker to produce a robust Ga-MOF (SNNU-63). Remarkably, SNNU-63 can stabilize in water at 25 °C for 96 h and at 80 °C for more than 24 h, which surpasses nearly all other Ga-MOFs. The combined effects of open metal sites and hydrophobic pore environment provided by deformed [Ga3O] SBUs render SNNU-63 with high C2H2 storage capacity and efficient C2H2 and natural gas purification performance. The ideal adsorbed solution theory calculation, column breakthrough tests, and grand canonical Monte Carlo simulations demonstrate that SNNU-63 is a potential material for addressing the challenge of C2H2/CO2 and C2H2/CH4 mixture separation under ambient conditions.

Using transient breakthrough experiments for screening of adsorbents for separation of C2H4/CO2 mixtures

The recovery of C2H4 from gaseous reactor effluents from processes such as oxidative coupling of methane (OCM), and biomass gasification (at relatively low temperatures (770–880 °C) is becoming of increasing industrial and economic importance. The reactor effluents are N2/H2/CO/CO2/CH4/C2H6/C2H4 mixtures, typically containing less than 15% C2H4. For recovery of C2H4, pressure swing adsorption (PSA) technology using a selective adsorbent offers an energy-efficient alternative to the more conventional separation schemes such as amine absorption and cryogenic distillation The major objective of this investigation is to screen commercially available cation exchanged zeolites (13X, CaX, NaY, 5A, 4A) and activated carbon (AC) to determine the most suitable adsorbent. For all these materials, the adsorption strengths of CO2, and C2H4 are significantly higher than that of other gaseous constituents; consequently, the C2H4/CO2 separation selectivity is the key to the efficacy of any adsorbent. The variety of adsorbents were screened using transient breakthrough experiments with feed mixtures using different C2H4/CO2 ratios. On the basis of the breakthroughs, the adsorbents could be distinguished in three different categories: (i) 13X and 4A are selective to CO2, (ii) CaX, NaY, and 5A are virtually non-selective, and (iii) AC is selective to C2H4 over the entire range of feed compositions and is therefore the adsorbent of choice.The experimental breakthrough results are also compared with simulations using published unary isotherm data, along with the Ideal Adsorbed Solution Theory (IAST) for determination of mixture adsorption equilibrium. This comparison demonstrates that screening adsorbents solely on the basis of IAST calculations is likely to be misleading. This article underscores the need for performing transient breakthrough experiments with realistic feed gas mixtures for process modelling and development purposes.

Selective Ethane/Ethylene Separation in a Robust Microporous Hydrogen-Bonded Organic Framework.

The separation of ethane (C2H6) from ethylene (C2H4) is of prime importance in the production of polymer-grade C2H4 for industrial manufacturing. It is very challenging and still remains unexploited to fully realize efficient C2H6/C2H4 separation in the emerging hydrogen-bonded organic frameworks (HOFs) due to the weak nature of hydrogen bonds. We herein report the benchmark example of a novel ultrarobust HOF adsorbent (termed as HOF-76a) with a Brunauer-Emmett-Teller surface area exceeding 1100 m2 g-1, exhibiting the preferential binding of C2H6 over C2H4 and thus highly selective separation of C2H6/C2H4. Theoretical calculations indicate the key role of the nonpolar surface and the suitable triangular channel-like pores in HOF-76a to sterically "match" better with the nonplanar C2H6 molecule than the planar C2H4, thus affording overall stronger multipoint van der Waals interactions with C2H6. The exceptional separation performance of HOF-76a for C2H6/C2H4 separation was clearly demonstrated by gas adsorption isotherms, ideal adsorbed solution theory calculations, and simulated and experimental breakthrough curves. Breakthrough experiments on HOF-76a reveal that polymer-grade ethylene gas can be straightforwardly produced from 50/50 (v/v) C2H6/C2H4 mixtures during the first adsorption cycle with a high productivity of 7.2 L/kg at 298 K and 1.01 bar and 18.8 L/kg at 298 K and 5.0 bar, respectively.

PyGAPS: a Python-based framework for adsorption isotherm processing and material characterisation

Material characterisation through adsorption is a widely-used laboratory technique. The isotherms obtained through volumetric or gravimetric experiments impart insight through their features but can also be analysed to determine material characteristics such as specific surface area, pore size distribution, surface energetics, or used for predicting mixture adsorption. The pyGAPS (Python General Adsorption Processing Suite) framework was developed to address the need for high-throughput processing of such adsorption data, independent of the data origin, while also being capable of presenting individual results in a user-friendly manner. It contains many common characterisation methods such as: Brunauer–Emmett–Teller and Langmuir surface area, t and αs plots, pore size distribution calculations (Barrett–Joyner–Halenda, Dollimore–Heal, Horvath–Kawazoe, DFT/NLDFT kernel fitting), isosteric enthalpy calculations, ideal adsorbed solution theory calculations, isotherm modelling and more, as well as the ability to import and store data from Excel, CSV, JSON and SQLite databases. In this work, a description of the capabilities of pyGAPS is presented. The code is then be used in two case studies: a routine characterisation of a UiO-66(Zr) sample and in the processing of an adsorption dataset of a commercial carbon (Takeda 5A) for applications in gas separation.

Inverse ideal adsorbed solution theory for calculation of single-component adsorption equilibria from mixture isotherms supported by adsorption equilibrium distribution

Adsorption isotherm data of methanol, ethanol, and dimethyl carbonate were determined via headspace experiments on two activated carbons (RB 4 from CABOT Norit and SC 40 from SilCarbon) at different temperatures. However, dimethyl carbonate (DMC) showed a significant decomposition to methanol and CO2 during the adsorption experiments. Hence, the measured isotherm data for DMC were always two-component isotherm data assuming CO2 as non-adsorbing component. Thus, ideal adsorbed solution theory (IAST) was inverted to determine the single-component isotherm of DMC using two-component isotherm data and the known single component isotherm of methanol. The inverse IAST was supported by the calculation of the adsorption equilibrium distribution. This calculation was done with the expectation maximization method and results were used to determine the most probable isotherm equations to initialize the inverse IAST calculation. The methodology was validated for mixtures of methanol and ethanol where both single-component isotherms were known. Finally, single-component isotherms were calculated for DMC on RB 4 and SC 40 at different temperatures.

Flexible Microporous Framework Based on Pb4 Clusters for Highly Selective Storage and Separation of Energy Gases

In this work, a microporous Pb(II)-based framework (FJI-H22) has been synthesized upon solvothermal reaction, which is constructed from two kinds of rarely seen tetranuclear Pb(II) clusters. FJI-H22 has two kinds of one-dimensional microporous channels (ca. 12.80 A × 15.08 and 6.05 A × 11.83 A) along the crystallographic b axis. Interestingly, when immersed in methanol FJI-H22 can undergo reverse single-crystal-to-single-crystal transformations to form FJI-H22-MeOH. In particular, high stability (stable up to 300 °C in atmosphere), large Brunauer–Emmett–Teller (BET) surface area (483 m2·g–1), and the nature of microporosity enable desolvated FJI-H22 to be a good candidate for purification of natural gas. As anticipated, desolvated FJI-H22 can selectively adsorb C2/C3 hydrocarbons over CH4 at 298 K and 1 bar. Furthermore, ideal adsorbed solution theory calculations reveal that FJI-H22 shows highly selective separation of higher hydrocarbons over CH4 under ambient conditions.

Molecular Simulation of Capture of Sulfur-Containing Gases by Porous Aromatic Frameworks

The adsorption of pure SO2 and H2S and their selective adsorption from various gas mixtures by porous aromatic frameworks (PAFs) are investigated using grand canonical Monte Carlo (GCMC) simulations and first-principles density functional theory calculations. The influence of functional groups including −CH3, −CN, −COOH, −COOCH3, −OH, −OCH3, −NH2, and −NO2 on the adsorption of pure SO2 and H2S as well as selective capture of SO2 and H2S from SO2/N2, SO2/CO2, H2S/CO2, and H2S/CH4 mixtures is explored. Our calculations indicate that PAFs exhibit high loadings for pure SO2 and H2S gas adsorption at 298 K up to 40 bar compare to other gases such as CH4 and CO2. Additional functional groups enhance gas uptake at low pressures because of stronger interaction with the gas molecules while reducing gas uptake at high pressures because of a decrease in pore volume. The contributions of electrostatic interactions to gas adsorption loadings are analyzed in GCMC simulations. Ideal adsorbed solution theory calculations...