Molecular Sieving of Propyne/Propylene by a Scalable Nanoporous Crystal with Confined Rotational Shutters

Soft porous coordination polymers (PCPs) have the remarkable ability to recognize similar molecules as a result of their structural dynamics. However, their guest-induced gate-opening behaviors often lead to issues with selectivity and separation efficiency, as co-adsorption is nearly unavoidable. Herein, we report a strategy of a confined-rotational shutter, in which the rotation of pyridyl rings within the confined nanospace of a halogen-bonded coordination framework ( NTU-88 ) creates a maximum aperture of 4.4 Å, which is very close to the molecular size of propyne (C₃H₄: 4.4 Å), but smaller than that of propylene (C₃H₆: 5.4 Å). This has been evidenced by crystallographic analyses and modelling calculations. The NTU-88o (open phase of activated NTU-88 ) demonstrates dedicated C₃H₄ adsorption, and thereby leads to a sieving separation of C₃H₄/C₃H₆ under ambient conditions. The integrated nature of high uptake ratio, considerable capacity, scalable synthesis, and good stability make NTU-88 a promising candidate for the feasible removal of C₃H₄ from C₃H₄/C₃H₆ mixtures. In principle, this strategy holds high potential for extension to soft families, making it a powerful tool for optimizing materials that can tackle challenging separations with no co-adsorption, while retaining the crucial aspect of high capacity.     

Tuning Gate-Opening of a Flexible Metal–Organic Framework for Ternary Gas Sieving Separation

In comparison with the fast development of binary mixture separations, ternary mixture separations are significantly more difficult and have rarely been realized by a single material. Herein, a new strategy of tuning the gate-opening pressure of flexible MOFs is developed to tackle such a challenge. As demonstrated by a flexible framework NTU-65, the gate-opening pressure of ethylene (C₂H₄), acetylene (C₂H₂), and carbon dioxide (CO₂) can be regulated by temperature. Therefore, efficient sieving separation of this ternary mixture was realized. Under optimized temperature, NTU-65 adsorbed a large amount of C₂H₂ and CO₂ through gate-opening and only negligible amount of C₂H₄. Breakthrough experiments demonstrated that this material can simultaneously capture C₂H₂ and CO₂, yielding polymer-grade (>99.99 %) C₂H₄ from single breakthrough separation.     

Dynamic Entangled Porous Framework for Hydrocarbon (C2–C3) Storage,CO2 Capture,and Separation

Storage and separation of small (C1–C3) hydrocarbons are of great significance as these are alternative energy resources and also can be used as raw materials for many industrially important materials. Selective capture of greenhouse gas, CO₂ from CH₄ is important to improve the quality of natural gas. Among the available porous materials, MOFs with permanent porosity are the most suitable to serve these purposes. Herein, a two‐fold entangled dynamic framework {[Zn₂(bdc)₂(bpNDI)]?4DMF}_n with pore surface carved with polar functional groups and aromatic π clouds is exploited for selective capture of CO₂, C2, and C3 hydrocarbons at ambient condition. The framework shows stepwise CO₂ and C₂H₂ uptake at 195 K but type I profiles are observed at 298 K. The IAST selectivity of CO₂ over CH₄ is the highest (598 at 298 K) among the MOFs without open metal sites reported till date. It also shows high selectivity for C₂H₂, C₂H₄, C₂H₆, and C₃H₈ over CH₄ at 298 K. DFT calculations reveal that aromatic π surface and the polar imide (RNC=O) functional groups are the primary adsorption sites for adsorption. Furthermore, breakthrough column experiments showed CO₂/CH₄ C₂H₆/CH₄ and CO₂/N₂ separation capability at ambient condition.     

New Supercage Metal–Organic Framework Based on Allopurinol Ligands Showing Acetylene Storage and Separation

To develop efficient adsorbent materials for storage and separation of C₂H₂, an unprecedented supercage MOF, [Me₂NH₂]⋅[Zn₃(ALP)(TDC)_2.5]⋅3.5DMF⋅2 H₂O ( 1 ) was constructed through medicinal molecule allopurinol (ALP) and S-containing 2,5-thiophenedicarboxylic acid (H₂TDC). 1 contains a novel linear trinuclear cluster that is composed by ALP and carboxylates and forms a final uncommon 5-connected yfy topological framework. The framework possesses three types of interlinked cages decorated by rich functional sites, and reveals not only high adsorption capacity for C₂H₂ but also excellent selective separation for C₂H₂/CO₂ and C₂H₂/CH₄ at 298 K. Dynamic breakthrough experiments on C₂H₂/CO₂ (1:1) mixture and C₂H₂/CH₄ (1:1) mixture also demonstrated the potential of the material to separate C₂H₂ from CO₂ or CH₄ mixtures. Molecular simulations were also studied to identify the different CO₂- and C₂H₂- binding sites in 1 , such as carboxylate groups, S atoms and carbonyl groups.     

Adsorption of natural gas and its whole components on adsorbents

Adsorption of each component of natural gas on adsorbent prepared from petroleum coke was studied. At 25 °C and 3.5 MPa, adsorption capacity of the components of natural gas are as follows: C₃H₈, H₂S(0.980) > CO₂(0.691) > C₂H₆(0.160) > CH₄(0.136) > N₂(0.096) (g/g). For natural gas, adsorption capacity is 145.2 (mL/mL) and delivery capacity is 105.7 (mL/mL). One equation between adsorption capacity and boiling point of adsorbed gas was firstly generalized. The adsorption capacity of different component like O₂, N₂, CH₄, C₂H₆, CO₂, H₂S on adsorbents were predicted using the equation. The results fit well with the experimental data. The equation has significance in predicting the adsorption capacity for any component of natural gas. Charge-discharge tests were conducted 10 times, the result indicates that natural gas has significantly worse reversibility in adsorption and desorption in the adsorbent than that of CH₄. The contents of the components after 10 charge-discharge show that the adsorption capacity drop of natural gas is due to the irreversible adsorption of heavy or polar components like C₃H₈, H₂S.     

New hyperbranched carbosiloxane–carbosilane polymers with aromatic units in the backbone

New hyperbranched polymers based on a carbosiloxane–carbosilane skeleton with aromatic units in the backbone have been prepared via one-pot hydrosilylation reaction using HSi(Me)₂–O–CH₂–C₆H₄–OSiMe–(CH₂)₄(C₃H₅)₂ as a novel AB₂ monomer. These polymers are easy to prepare, have narrow polydispersity values and present allyl groups on the surface which can be used as synthetic platforms for the introduction of different terminal groups like amine groups through hydrosilylation reactions, opening the door to functionalized polymers. The polymerization process was monitored using real-time ¹H NMR spectroscopy and the resulting hyperbranched polymers were characterized using ¹H NMR, ¹³C NMR, ²⁹Si NMR and SEC/MALLS. The degree of branching in these polymers was determined by quantitative ²⁹Si NMR spectroscopy and found to be very close to the theoretical value of 0.50 for AB₂ systems. The hydrolytic degradation of these polymers in protic solvents has been studied by ²⁹Si NMR.     

Multifunctional coupling agents for living cationic polymerization. IV. Synthesis of end-functionalized multiarmed poly(vinyl ethers) with multifunctional silyl enol ethers

Telechelic ( 8 ) and end-functionalized four-arm star polymers ( 9 ) were synthesized through the coupling reactions of end-functionalized living poly(isobutyl vinyl ether) ( 5; DP _n ～ 10) with the bi-and tetrafunctional silyl enol ethers, H_4-nC? [CH₂OC₆H₄C(OSiMe₃) = CH₂]_n ( 3: n = 2; 4: n = 4). The precursor polymers 5 were prepared by living cationic polymerization with functionalized initiators, CH₃CH(Cl)OCH₂CH₂X(6), in conjunction with zinc chloride in methylene chloride at ?15°C. The initiators 6 were obtained by the addition of hydrogen chloride gas to vinyl ethers bearing pendant functional groups X , including acetoxy [? OC(O)CH₃], styryl (? OCH₂C₆H₄-p-CH = CH₂), and methacryloyl [? OC(O)C(CH₃) = CH₂]. The coupling reactions with 3 and 4 in methylene chloride at ?15°C for 24 h afforded the end-functionalized multiarmed polymers ( 8 and 9 ) in high yield (>91%), where those with styryl or methacryloyl groups are new multifunctional macromonomers. © 1994 John Wiley & Sons, Inc.     

The adsorption of H<Subscript>2</Subscript>O and D<Subscript>2</Subscript>O on porous polystyrene adsorbents

The adsorption of H₂O and D₂O on porous polymers, Chromosorb-102 (styrene-divinylbenzene copolymer) and MN-200 (supercross-linked polystyrene), was studied by gas chromatography. Test adsorbates used to study the properties of the surface of these polymers were n-alkanes (C₆-C₉), C₆H₆, and the polar compounds CHCl₃, CH₃NO₂, CH₃CN, (CH₃)₂CO, C₂H₅COOCH₃, and (C₂H₅)₂O. The experimental data on the retention of the sorbates were used to determine the contributions of dispersion and specific intermolecular interactions to the total energy of adsorption for the systems studied. The electron donor K _D and electron acceptor K _A characteristics of the surfaces of Chromosorb-102 and MN-200 were determined. The K _D and K _A values obtained allow these polymers to be classified as weakly specific adsorbents with the predominance of electron acceptor properties. The adsorption isotherms of H₂O and D₂O were measured at 55, 67, and 80°C. The dependences of the isosteric heats of adsorption Q _st on adsorption values were determined. The conclusion was drawn that H₂O interacted with the surface of the polymers by the adsorption mechanism, whereas absorption likely made a noticeable contribution to the retention of D₂O.     

Gram-Scale Synthesis of an Ultrastable Microporous Metal-Organic Framework for Efficient Adsorptive Separation of C2H2/CO2 and C2H2/CH4

A highly water and thermally stable metal-organic framework (MOF) Zn₂(Pydc)(Ata)₂ (1, H₂Pydc = 3,5-pyridinedicarboxylic acid; HAta = 3-amino-1,2,4-triazole) was synthesized on a large scale using inexpensive commercially available ligands for efficient separation of C₂H₂ from CH₄ and CO₂. Compound 1 could take up 47.2 mL/g of C₂H₂ under ambient conditions but only 33.0 mL/g of CO₂ and 19.1 mL/g of CH₄. The calculated ideal absorbed solution theory (IAST) selectivities for equimolar C₂H₂/CO₂ and C₂H₂/CH₄ were 5.1 and 21.5, respectively, comparable to those many popular MOFs. The Q_st values for C₂H₂, CO₂, and CH₄ at a near-zero loading in 1 were 43.1, 32.1, and 22.5 kJ mol⁻¹, respectively. The practical separation performance for C₂H₂/CO₂ mixtures was further confirmed by column breakthrough experiments.     

Tuning the Adsorption Selectivity of ZIF-8 by Amorphization

Amorphous metal–organic frameworks (a_mMOFs) with a partially collapsed structure are a new category of porous hybrid materials. Here, solid-state amorphization of ZIF-8 was achieved by mechanical compression at 0.75 GPa. The compression-induced amorphous ZIF-8 (a_mZIF-8) had a collapsed structure, but retained partial porosity. Benefiting from the deformed channel, the resultant a_mZIF-8 exhibited preferable adsorption of C₃H₆, resulting in higher thermodynamic adsorption selectivity of C₃H₆/C₃H₈ (6.72) than the crystalline counterparts (1.06). Further, a_mZIF-8 achieved complete separation of an equimolar C₃H₆/C₃H₈ mixture with the first breakthrough of C₃H₈. a_mZIF-8 also displayed an enhancement in CO₂/N₂ and CO₂/CH₄ adsorption selectivities. More importantly, a self-standing a_mZIF-8 membrane with boundary-free microstructure was constructed for the first time, and exhibited separation potential for H₂/CH₄, CO₂/N₂, CO₂/CH₄, and C₃H₆/C₃H₈ with ideal selectivities of 14.79, 12.83, 16.23, and 2.67, respectively.     

The Adsorption and Simulated Separation of Light Hydrocarbons in Isoreticular Metal–Organic Frameworks Based on Dendritic Ligands with Different Aliphatic Side Chains

Three isoreticular metal–organic frameworks, JUC‐100, JUC‐103 and JUC‐106, were synthesized by connecting six‐node dendritic ligands to a [Zn₄O(CO₂)₆] cluster. JUC‐103 and JUC‐106 have additional methyl and ethyl groups, respectively, in the pores with respect to JUC‐100. The uptake measurements of the three MOFs for CH₄, C₂H₄, C₂H₆ and C₃H₈ were carried out. At 298 K, 1 atm, JUC‐103 has relatively high CH₄ uptake, but JUC‐100 is the best at 273 K, 1 atm. JUC‐100 and JUC‐103 have similar C₂H₄ absorption ability. In addition, JUC‐100 has the best absorption capacity for C₂H₆ and C₃H₈. These results suggest that high surface area and appropriate pore size are important factors for gas uptake. Furthermore, ideal adsorbed solution theory (IAST) analyses show that all three MOFs have good C₃H₈/CH₄ and C₂H₆/CH₄ selectivities for an equimolar quaternary CH₄/C₂H₄/C₂H₆/C₃H₈ gas mixture maintained at isothermal conditions at 298 K, and JUC‐106 has the best C₂H₆/CH₄ selectivity. The breakthrough simulations indicate that all three MOFs have good capability for separating C2 hydrocarbons from C3 hydrocarbons. The pulse chromatographic simulations also indicate that all three MOFs are able to separate CH₄/C₂H₄/C₂H₆/C₃H₈ mixture into three different fractions of C1, C2 and C3 hydrocarbons.     

A Microporous Metal‐Organic Framework Supramolecularly Assembled from a CuII Dodecaborate Cluster Complex for Selective Gas Separation

A novel 3D metal‐organic framework BSF‐1 based on the closo‐dodecaborate cluster [B₁₂H₁₂]^2? was readily prepared at room temperature by supramolecular assembly of CuB₁₂H₁₂ and 1,2‐bis(4‐pyridyl)acetylene. The permanent microporous structure was studied by X‐ray crystallography, powder X‐ray diffraction, IR spectroscopy, thermogravimetric analysis, and gas sorption. The experimental and theoretical study of the gas sorption behavior of BSF‐1 for N₂, C₂H₂, C₂H₄, CO₂, C₃H₈, C₂H₆, and CH₄ indicated excellent separation selectivities for C₃H₈/CH₄, C₂H₆/CH₄, and C₂H₂/CH₄ as well as moderately high separation selectivities for C₂H₂/C₂H₄, C₂H₂/CO₂, and CO₂/CH₄. Moreover, the practical separation performance of C₃H₈/CH₄ and C₂H₆/CH₄ was confirmed by dynamic breakthrough experiments. The good cyclability and high water/thermal stability render it suitable for real industrial applications.     

Gel formation in cationic polymerization of divinyl ethers. II. 2,2-Bis{4-[(2-vinyloxy)ethoxy]phenyl}propane

Cationic polymerization of 2,2-bis{4-[(2-vinyloxy)ethoxy]phenyl}propane [CH₂CH O CH₂CH₂O C₆H₄ C(CH₃)₂ C₆H₄ OCH₂CH₂ O CHCH₂; 2], a divinyl ether with oxyethylene units adjacent to the polymerizable vinyl ether groups and a bulky central spacer, was investigated in CH₂Cl₂ at 0°C with the diphenyl phosphate [(C₆H₅O)₂P(O)OH]/zinc chloride (ZnCl₂) initiating system. The polymerization proceeded quantitatively and gave soluble polymers up to 85% monomer conversion. In the same fashion as the polymerization of 1,4-bis[2-vinyloxy(ethoxy)]benzene (CH₂CH O CH₂CH₂O C₆H₄ OCH₂CH₂ O CHCH₂; 1) that we already studied, the content of the unreacted pendant vinyl ether groups of the produced soluble polymers decreased with monomer conversion, and almost all the pendant vinyl ether groups were consumed in the soluble products prior to gelation. Alternatively, endo-type double bonds were gradually formed in the polymer main chains by chain transfer reactions and other side reactions as the polymerization proceeded. The polymerization behavior of isobutyl vinyl ether (3), a monofunctional vinyl ether, under the same conditions, showed that the endo-type olefins in the polymer backbones are of no polymerization ability with the growing active species involved in the present polymerization systems. These results indicate that the intermolecular crosslinking reactions occurred primarily by the pendant vinyl ether groups, and the final stage of crosslinking process leading to gelation also may occur by the small amount of the residual pendant vinyl ether groups (supposedly less than 2%). The formation of the soluble polymers that almost lack the unreacted pendant vinyl ether groups is most likely due to the frequent occurrence of intramolecular crosslinking reactions. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1931–1941, 1999     

Transport of C1–C3 hydrocarbons in poly(phenylene oxides) membranes

Transport of CH₄, C₂H₄ and C₂H₆ in poly(phenylene oxides) membranes at low pressures has been studied. The relation between the free volume and permeability of the polymers was analyzed in terms of the `dual-sorption' model. The accessible free volume of the polymers was estimated assuming the density of a sorbed fluid is equal to the density of the corresponding liquid. Transient separation of the three-component mixture CH₄/C₂H₄/C₂H₆ was studied.     

Tests of a “free-volume” model of gas permeation through polymer membranes. I. Pure CO2, CH4, C2H4, and C3H8 in polyethylene

Permeability coefficients have been measured for CO₂, CH₄, C₂H₄, and C₃H₈ in polyethylene membranes at temperatures of 5, 20, and 35°C and at applied gas pressures of up to 30 atm. The temperature and pressure dependence of the permeability coefficients was represented satisfactorily by an extension of Fujita's free-volume model of diffusion of small molecules in polymers. The results of the present steady-state permeability measurements provide further support for the conclusion reached from previous unsteady-state diffusivity measurements that Fujita's model is applicable to the transport of small molecules, such as CO₂, CH₄, C₂H₄, and C₃H₈, in polyethylene. It was previously thought that this model is applicable only to the transport of larger molecules, such as of organic vapors, in polymers.     

Highly Robust Microporous Metal-Organic Frameworks for Efficient Ethylene Purification under Dry and Humid Conditions

Two C₂H₆-selective metal-organic framework (MOF) adsorbents with ultrahigh stability, high surface areas, and suitable pore size have been designed and synthesized for one-step separation of ethane/ethylene (C₂H₆/C₂H₄) under humid conditions to produce polymer-grade pure C₂H₄. Experimental results reveal that these two MOFs not only adsorb a high amount of C₂H₆ but also display good C₂H₆/C₂H₄ selectivity verified by fixed bed column breakthrough experiments. Most importantly, the good water stability and hydrophobic pore environments make these two MOFs capable of efficiently separating C₂H₆/C₂H₄ under humid conditions, exhibiting the benchmark performance among all reported adsorbents for separation of C₂H₆/C₂H₄ under humid conditions. Moreover, the affinity sites and their static adsorption energies were successfully revealed by single crystal data and computation studies. Adsorbents described in this work can be used to address major chemical industrial challenges.     

Low-Concentration C2H6 Capture Enabled by Size Matching in the Ultramicropore

Low-concentration ethane capture is crucial for environmental protection and natural gas purification. The ideal physisorbent with strong C₂H₆ interaction and large C₂H₆ uptake at low-concentration level has rarely been reported, due to the large pK_a value and small quadrupole moment of C₂H₆. Herein, we demonstrate the perfectly size matching between the ultramicropore (pore size of 4.6 Å) and ethane (kinetic diameter of 4.4 Å) in a nickel pyridine-4-carboxylate metal–organic framework (IISERP-MOF 2 ), which enables the record-breaking performance for low concentration C₂H₆ capture. IISERP-MOF 2 exhibits the large C₂H₆ adsorption enthalpy of 56.7 kJ/mol, and record-high C₂H₆ uptake at low pressure of 0.01–0.1 bar and 298 K (1.8 mmol/g at 0.01 bar). Molecule simulations and C₂H₆-loading crystal structure analysis revealed that the maximized interaction sites in IISERP-MOF 2 with ethane molecule originates the strong C₂H₆ adsorption. The dynamic breakthrough experiments for gas mixtures of C₂H₆/N₂(1/999, v/v) and C₂H₆/CH₄ (5/95, v/v) proved the excellent low-concentration C₂H₆ capture performance.     

Membrane separation of multicomponent mixture of alkanes C1–C4

The membrane separation of the four-component mixture of gaseous alkanes C₁–C₄ is studied. Homogeneous films based on two high-permeable polymers, namely, addition-type poly[3-(trimethylsilyl)tricyclononene-7] and poly[3,4-bis(trimethylsilyl)tricyclononene-7], are used as membranes. Separation of the multicomponent mixture of hydrocarbons on these polymers follows the same trends as separation of binary mixtures CH₄-C₄H₁₀ on polyacetylenes. In the presence of higher hydrocarbons, the permeability coefficients of methane decrease and the permeates become enriched with higher hydrocarbons. During separation of the multicomponent mixture, permeability coefficients P(C₄H₁₀) attain high values (up to 12000 Barrers).     

Synthesis and Polymerization of the Organometallic Monomer Series Based on Cymantrenylethyl Acrylate

{η⁵ -C₅H₄[CH(CH₃)OC(O)CH = CH₂])Mn(CO)3, {η⁵—C₅[CH-(CH₃)OC(O)C(CH₃)=CH₂]]Mn(CO)₃, and {η⁵—C₅H₄[CH(CH₃)-OC(O)CH=C(CH₃)2])Mn(CO)₃ were synthesized (63, 57, and 51%, respectively) from {η⁵—C₅H₄[CH(CH₃)OH])Mn(CO)₃, toluene-sulfonic acid, and the acrylic, methacrylic, and dimethylacrylic acids, and from (η⁵-C₅H₄[CH(CH₃)OH]}Mn(CO)₃, pyridine, and the acrylic, methacrylic, and dimethylacrylic acyl chlorides [26, 48, and 25% (impure), respectively]. No product was obtained when NaH was used as the base in the latter method. The acrylate and methacrylate monomers were bulk homopolymerized at 65°C with AIBN (75% yield, M_n = 88,550 g/mol; 78% yield, M_n = 349,350 g/mol, respectively). The dimethylacrylate did not polymerize under these conditions. The polymers lost vinylcymantrene upon heating to 257 and 279°C, respectively. The polymers did not exhibit a clear T_g but were observed to soften at 85 and 160°C, respectively, and they could be pulled into fibers.     

Cumulative author index

For the compounds C₆H₅C₆H₄YC₆H₄C₆H₅ and C₆H₅C₆H₄YC₆H₄C₆H₄YC₆H₄C₆H₅ where Y is either Si(CH₃)₂ or CH₂, reduction potentials and p-band positions are reported. These data as well as the UV data for several phenyl derivatives are consistent with silicon blocking, to a large extent, conjugation (little or no through conjugation) of biphenyl moieties separated by Si(CH₃)₂groups.