WO2019183635A1

WO2019183635A1 - Metal-organic frameworks for molecular sieving and compositions and methods of use thereof

Info

Publication number: WO2019183635A1
Application number: PCT/US2019/023911
Authority: WO
Inventors: Banglin Chen; Ruibiao LIN
Original assignee: The Board Of Regents Of The University Of Texas System
Priority date: 2018-03-23
Filing date: 2019-03-25
Publication date: 2019-09-26

Abstract

Methods of using a metal-organic framework (MOF) are provided herein, including methods of using an MOF comprising a repeat unit of the formula [ML]_n, wherein M is a divalent metal ion and L is a ligand of the formula (I). The MOFs provided herein may be used in the separation of two or more molecules from each other. In some embodiments, the molecules are ethylene and ethane.

Description

METAL-ORGANIC FRAMEWORKS FOR MOLECULAR SIEVING AND

COMPOSITIONS AND METHODS OF USE THEREOF

This application claims the benefit of United States Provisional Application No. 62/647,054, filed on March 23, 2018, the entire contents of which is hereby incorporated by reference.

BACKGROUND

I. Field

The present disclosure relates generally to the fields of chemistry and materials science. More particularly, it concerns metal-organic frameworks, compositions thereof and methods of use thereof, including separating gas molecules such as ethylene and ethane.

II. Description of Related Art

Ethylene/ethane separation is an important process in the petrochemical industry, giving a worldwide ethylene production exceeding 150 million metric tons in 2016. Due to the very similar sizes and volatilities of these hydrocarbon molecules, the purification of ethylene is currently accomplished by repeated distillation-compression cycling of the mixture under harsh conditions in huge splitter column of over 100 trays. Such well- established industrial separation technology is one of the most energy-intensive processes in the chemical industry, which highly relies on thermal energy and consumes ten times energy than membrane-based separation technologies or other non-thermal ones (Sholl et al, 2016 and Chu et al. , 2017). For substituting the cryogenic distillation processes, exploration of new adsorptive separation technologies based on porous materials is dramatically driven by the potential of tremendous energy savings. As customizable porous materials, metal- organic frameworks (MOFs) are highly versatile in pore engineering, affording precise tuning and functionalization of the pore structure (Kitagawa, 2015 and Furukawa et al. , 2013), and thus have been intensively investigated as excellent adsorbents for selective gas separation (Bloch et al, 2012, Yang et al, 2014, Cadiau et al, 2016, Cui et al, 2016, Liao et al, 2017, Yoon et al, 2016, and Vaidhyanathan et al, 2010). But for ethylene/ethane separation, there is a major barrier in improving the selectivity for separating these gases because of their very similar physical properties. Various functionalized MOF adsorbents, including those feature open metal sites that help enhancing the olefin binding affinity, have been explored to overcome this challenge (He et al, 2012 and Zhai et al, 2016). However, their unavoidable co-adsorption of analogous alkanes is unfavorable for efficient olefin purification via swing adsorption or membrane-based methods, let alone other problems associated with their active metal sites, which involves the recovery of adsorbent and olefin products (high energy consumption and possible olefin polymerization) (Ji et al, 2017 and Klet et al, 2015), and water/humidity stability issues.

Ideal separation approaches like molecular sieving, allows complete separating one component from others based on molecular size or shape cut-off, which avoids the co- adsorption of impurity without sacrificing the valuable uptake capacity of porous media and gives infinite selectivity that is beneficial to membrane-based separation (Lin, 2016 and Peng et al. , 2014). Similar separation process such as potassium ions transport existing in cell- membranes of biological systems involves excluding sodium ions despite their size difference in ionic radius of sub-angstrom level (0.038 nm), giving extremely precise selectivity that can also be observed in crown ether/cryptand-ion systems. Accordingly, precise size/shape matching is vital toward specific recognition of olefin/paraffm (Pan et al. , 2006 and Ma et al. , 2009). Considering the even smaller shape difference between olefin and paraffin (only 0.028 nm in kinetic diameters for ethylene/ethane) and their identical physical properties (FIG. 1 and Table 1), it is particularly challenging to design MOFs as molecular sieves for this gas separation. Extensive research endeavors have been pursued to make tailor-made MOFs for specific molecular sieving of some important hydrocarbons (Cadiau et al. , 2016, Cui et al. , 2016, and Bao et al. , 2016), but it is yet to be shown that MOFs can sieve ethylene while completely exclude ethane.

Table 1. Comparison of physical parameters of C2H4 and C2H6 (Li et al, 2009).

Given the usefulness of materials that can effectively separate industrial feedstocks, such as ethylene from ethane, in order to obtain purer ethylene and/or purer ethane, materials that can achieve these separations are still of great importance. SUMMARY

In some aspects, the present disclosure provides MOFs which may be used to remove one type of molecules from a mixture. In one aspect, the present disclosure provides methods of separating two or more compounds using a metal organic framework comprising a repeating unit of the formula ML, wherein M is a divalent metal ion and L is a ligand of the formula:

or a hydrate thereof, wherein the method comprises:

(A) combining the metal-organic framework with a mixture comprising a first compound and a second compound; and

(B) separating the first compound from the second compound within the metal-organic framework.

In some embodiments, M is a divalent alkali earth metal such as Ca(II). In some embodiments, the metal organic framework is further defined as a metal organic framework of the formula: M(H₂0)L such as by the formula: Ca(H20)L.

In some embodiments, the first compound or the second compound is a gas molecule. Alternatively, in some embodiments, both the first and second compounds are gas molecules. In some embodiments, the first compound is an alkene(c<8) such as ethylene. In other embodiments, the first compound is an alkyne(c<8) such as ethyne. In still other embodiments, the first compound is CCh. In some embodiments, the second compound is an alkane(c<8) such as ethane or methane. In other embodiments, the second compound is N₂.

In some embodiments, the mixture comprises from about 1:999 to about 1: 1 of the first compound to the second compound. In other embodiments, the mixture comprises from about 1 :999 to about 1: 1 of the second compound to the first compound. In some embodiments, the mixture comprises about 1:99 of the first compound to the second compound. In some embodiments, the separation is carried out at a pressure from about 0.1 bar to about 10 bar such as at a pressure of about 1 bar. In some embodiments, the metal-organic framework is adhered to a fixed bed surface. In some embodiments, the separation is carried out in an absorber packed with the metal- organic framework. In some embodiments, the separation is carried out at a temperature from about 0 °C to about 75 °C such as at about room temperature.

In still another aspect, the present disclosure provides a method of separating ethylene from a mixture of ethane and ethylene comprising exposing the mixture to a metal organic framework as described herein.

Other objects, features and advantages of the present disclosure will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present disclosure. The invention may be better understood by reference to one of these drawings in combination with the detailed description of specific embodiments presented herein.

FIGS. 1A & IB show the molecular dimensions of ethylene (FIG. 1A) and ethane (FIG. 1B). The unit of lengths is angstrom (A). The dimension of the adsorbate used to evaluate its entry into a pore is related to the shape of the pore. For cylindrical pores/channels, the size of selected molecule in two directions must be taken into account, that is the minimum cross-sectional area (Webster et al, 1998). The relevant dimensions are minimum one (MIN-l, e. g. 3.28 A for ethylene) and the next to the smallest perpendicular distance for low energy conformations or molecular orientations that enable a molecule to enter a cylinder (MIN-2, e.g. 4.18 A for ethylene). So, the minimum cross-sectional area of ethylene and ethane molecules are 13.7 (3.28 A ^c 4.18 A) and 15.5 (3.81 A ^c 4.08 A) A², respectively, which should be taken into account when evaluating their entry into a narrow cylindrical pore.

FIG. 2 shows PXRD patterns of different UTSA-280 samples.

FIG. 3 shows the TGA curve of UTSA-28O H2O.

FIGS. 4A-4F show the structure and gas sorption properties of UTSA-280. The crystal structure of guest-free UTSA-280 determined from single-crystal X-ray diffraction, showing one-dimensional channels viewed along the [001] direction. (FIG. 4A). The local coordination environments of squarate linker and calcium atom are shown in FIG. 4B. One dimensional infinite calcium oxygen chain along the [001] direction is shown in FIG. 4C. Single-component sorption isotherms of carbon dioxide at 195 K (FIG. 4D), nitrogen at 77 K and ethylene, ethane at 298 K (FIG. 4E) for UTSA-280. Qualitative comparison of IAST adsorption selectivities of different MOFs for equimolar ethylene/ethane mixture at 298 K is shown in FIG. 4F.

FIGS. 5A & 5B show the coordination model in guest-free UTSA-280 shown as ellipsoids (FIG. 5A) and related one dimensional infinite calcium oxygen chain with hydrogen bonding (FIG. 5B). In this case, 03A labeled in FIG. 5A is the oxygen atom of coordinated water.

FIG. 6 shows the calculation of BET surface area for UTSA-280 based on CO2 adsorption isotherm at 195 K. FIGS. 7A & 7B show the sorption isotherms of UTSA-280 for C2H4 and C2H6 at 273

K (FIG. 7 A) and 195 K (FIG. 7B).

FIGS. 8A & 8B show Langmuir-Freundlich fitting of the C2H4 (FIG. 8 A) and C2H6 (FIG. 8B) sorption data at 298 K for UTSA-280.

FIG. 9 shows multiple cycles of C2H4 adsorption isotherms for UTSA-280 at 273 K. FIG. 10 shows multiple cycles of C2H4 adsorption isotherms for UTSA-280 at 298 K and 0-1 bar.

FIG. 11 shows multiple cycles of C2H4 sorption isotherms for UTSA-280 at 313 K.

FIG. 12 shows multiple cycles of C2H6 adsorption isotherms for UTSA-280 at 273 K.

FIG. 13 shows multiple cycles of C2H6 adsorption isotherms for UTSA-280 at 298 K. FIGS. 14A & 14B show the sorption isotherms of UTSA-280 for C2H4 at different temperatures (FIG. 14A) as well as isosteric heats of C2H4 adsorption (GU) calculated using the Clausius-Clapeyron equation (FIG. 14B), with error bars shown in black.

FIGS. 15A-15D show single-crystal structure of UTSA-280ziC2H4 and preferential C2H4 sites. (FIG. 15A and 15B) Top and side views of packing diagram of C2H4 adsorbed structure. FIG. 15C shows preferential binding site for C2H4 molecules and their close contacts with the framework. FIG. 15D shows a schematic diagram of the size/shape sieving based on the minimum cross-sectional areas of ethylene (13.7 A2) and ethane (15.5 A2) molecules.

FIGS. 16A & 16B show electron density maps of UTSA-280 (FIG. 16A) and UTSA- 28O C2H4 (FIG. 16B).

FIGS. 17A & 17B show the coordination model in in UTSA-28O C2H4 shown as ellipsoids (FIG. 17A) as well as the Hirshfeld surface (de) displaying weak host-guest interactions in UTSA-280 (FIG. 17B).

FIG. 18 shows a schematic picture showing the DFT-D optimized C2H4 configuration in UTSA-28O C2H4. FIGS. 19A-19C show column breakthrough results and scalable synthesis of UTSA-

280. FIG. 19A shows breakthrough curves of UTSA-280 from different scales for equimolar binary mixture of C2H4/C2H6 at 298 K and 1 bar. FIG. 19B shows multi-component breakthrough curves for quaternary mixture of CH4/C2H4/C2H6/C3H8 (45/25/25/5) at 298 K and 1 bar. The breakthrough experiments were carried out in a packed column at a flow rate of 2 standard cubic centimeters per minute. Points are experimental data, and lines are drawn to guide the eye. FIG. 19C shows powder X-ray diffraction (PXRD) experiments showing the stability of UTSA-280 after immersing in water for various time.

FIG. 20 shows a schematic illustration of the apparatus for the breakthrough experiments. FIG. 21 shows the concentration curve of the desorbed C2H4 from the fixed bed during the regeneration process of UTSA-280. Desorption was carried out by purging He (50 standard cubic centimeters per minute) at 353K. Notably, all the adsorbed ethylene can be completely removed from the column in approximately 10 minutes by a helium gas purge.

FIG. 22 shows multiple cycles of breakthrough curves for equimolar binary mixture of C2H4/C2H6 at 298 K and 1 bar. The breakthrough experiments were carried out in a packed column at a flow rate of 2 standard cubic centimeters per minute. Points are experimental data, and lines are drawn to guide the eye.

FIG. 23 shows the transient breakthrough of C2H4/C2H6 mixture (50/50, v/v) in an adsorber bed packed UTSA-280. The total bulk gas phase is at 298 K and 100 kPa. The partial pressures of C2H4, and C2H6 in the inlet feed gas mixture are, respectively, p\ = 50 kPa, pi = 50 kPa.

FIG. 24 shows single-component adsorption isotherms of CH4, C2H4, C2H6 and C3H8 in UTSA-280 at 298 K. FIG. 25 shows the C2H4 adsorption isotherms for activated UTSA-280 at 298K, recorded before and after immersing in water for 11 days.

FIGS. 26A & 26B show comparison of the simulated and experimental PXRD patterns to confirm the purity of the bulk products (FIG. 26A). Breakthrough curves of kilogram-scale UTSA-280 for equimolar binary mixture of C2H4/C2H6 at 298 K and 1 bar (FIG. 26B). The breakthrough experiments were carried out in a packed column at a flow rate of 2 standard cubic centimeters per minute.

FIGS. 27A & 27B show gas sorption isotherms of UTSA-280 for CO2, N2 and CFB at 298 K (FIG. 27 A) and 273 K (FIG. 27B). FIG. 28 shows calculated IAST selectivity of UTSA-280 for 15/85 CO2/N2 and 50/50

CO2/CH4 mixtures at 298 K.

FIG. 29 shows gas sorption isotherm of UTSA-280 for C2H2 at 298 K.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Provided herein are methods for separating a first compound from a mixture of compounds using metal-organic frameworks of the formula: ML wherein L is squaric acid and which exhibits pore sizes sufficient to host guest gas molecules. In some embodiments, these metal-organic frameworks may be used to separate one gas molecule from a mixture of two or more gas molecules such as ethylene and ethane. In some embodiments, the metal- organic framework is [Ca(C404)(H20)] (termed as UTSA-280) that feature one dimensional specific ethylene channels, exhibiting exclusion of ethane from ethylene under ambient condition. In some embodiments, the material used herein exhibit channel spaces that enable recognition of ethylene molecules of high packing intensity and selectivity with ethylene productivity of 1.7 mol/kg at ambient condition. Additionally, the material may in some embodiments be easily regenerated under mild conditions because of its low adsorption heat. In some embodiments, the materials used herein may be prepared via straightforward synthesis at a large scale under environmentally friendly conditions and are water-stable.

For example, UTSA-280 may also be used for CO2 capture in various applications, including natural gas processing, trace CO2 removal in confined spaces, and air capture. For example, CO2 is an impurity in natural gas upgrading and biogas sweetening, which can cause pipeline corrosion problems.

I. Methods of Chemical Separation Using MOFs

or a hydrate thereof, wherein the method comprises:

(B) separating the first compound from the second compound within the metal-organic framework. In some embodiments, M is a divalent alkali earth metal such as Ca(II). In some embodiments, the metal organic framework is further defined as a metal organic framework of the formula: M(H₂0)L such as by the formula: Ca(H20)L.

In some embodiments, the first compound or the second compound is a gas molecule. In some of these embodiments, both the first and second compounds are gas molecules. In some embodiments, the first compound is an alkene(c<8) such as ethylene. In other embodiments, the first compound is an alkyne(c<8) such as ethyne. In some of these embodiments, the C2H4/C2H6 selectivity of UTSA-280 is infinite. Therefore, the methods of the present disclosure may facilitate almost complete removal of ethane from ethylene. In still other embodiments, the first compound is CO2. In some embodiments, the second compound is an alkane(c<8) such as ethane or methane. In other embodiments, the second compound is N₂.

In some embodiments, the mixture comprises from about 1:999 to about 1: 1 of the first compound to the second compound. In other embodiments, the mixture comprises from about 1 :999 to about 1: 1 of the second compound to the first compound. In some embodiments, the mixture comprises about 1:99 of the first compound to the second compound. In some embodiments, the separation is carried out at a pressure from about 0.1 bar to about 10 bar such as at a pressure of about 1 bar.

In some embodiments, the metal-organic framework is adhered to a fixed bed surface. In some embodiments, the separation is carried out in an absorber packed with the metal- organic framework. In some embodiments, the separation is carried out at a temperature from about 0 °C to about 75 °C such as at about room temperature.

II. Definitions

“Metal-organic frameworks” (MOFs) are framework materials, typically three- dimensional, self-assembled by the coordination of metal ions with organic linkers exhibiting porosity, typically established by gas adsorption. The MOFs discussed and disclosed herein are at times simply identified by their repeat unit as defined below without brackets or the subscript n. A mixed-metal-organic frameworks (MMOF) is a subset of MOFs having two of more types of metal ions. The term“unit cell” is basic and least volume consuming repeating structure of a solid. The unit cell is described by its angles between the edges (a, b, g) and the length of these edges (a, b, c). As a result, the unit cell is the simplest way to describe a single crystal X-ray diffraction pattern.

A“repeat unit” is the simplest structural entity of certain materials, for example, frameworks and/or polymers, whether organic, inorganic or metal-organic. In the case of a polymer chain, repeat units are linked together successively along the chain, like the beads of a necklace. For example, in polyethylene, -[-CFkCFk-ln-, the repeat unit is -CH2CH2-. The subscript“n” denotes the degree of polymerization, that is, the number of repeat units linked together. When the value for“n” is left undefined, it simply designates repetition of the formula within the brackets as well as the polymeric and/or framework nature of the material. The concept of a repeat unit applies equally to where the connectivity between the repeat units extends into three dimensions, such as in metal organic frameworks, cross-linked polymers, thermosetting polymers, etc. Note that for MOFs the repeat unit may also be shown without the subscript n.

“Pores” or“micropores” in the context of metal-organic frameworks are defined as open space within the MOFs; pores become available, when the MOF is activated for the storage of gas molecules. Activation can be achieved by heating, e.g., to remove solvent molecules.

“Multimodal size distribution” is defined as pore size distribution in three dimensions.

“Multidentate organic linker” is defined as ligand having several binding sites for the coordination to one or more metal ions.

In addition, atoms making up the compounds of the present invention are intended to include all isotopic forms of such atoms. Isotopes, as used herein, include those atoms having the same atomic number but different mass numbers. By way of general example and without limitation, isotopes of hydrogen include tritium and deuterium, and isotopes of carbon include ¹³C and ¹⁴C. Additionally, it is contemplated that one or more of the metal atoms may be replaced by another isotope of that metal. In some embodiments, the calcium atoms can be ⁴⁰Ca, ⁴²Ca, ⁴³Ca, ⁴⁴Ca, ⁴⁶Ca, or ⁴⁸Ca. Similarly, it is contemplated that one or more carbon atom(s) of a compound of the present invention may be replaced by a silicon atom(s). Furthermore, it is contemplated that one or more oxygen atom(s) of a compound of the present invention may be replaced by a sulfur or selenium atom(s).

Any undefined valency on a carbon atom of a structure shown in this application implicitly represents a hydrogen atom bonded to the atom. The use of the word “a” or “an,” when used in conjunction with the term “comprising” in the claims and/or the specification may mean“one,” but it is also consistent with the meaning of“one or more,”“at least one,” and“one or more than one.”

Throughout this application, the term“about” is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.

The terms“comprise,”“have” and“include” are open-ended linking verbs. Any forms or tenses of one or more of these verbs, such as“comprises,”“comprising,”“has,” “having,”“includes” and“including,” are also open-ended. For example, any method that “comprises,”“has” or“includes” one or more steps is not limited to possessing only those one or more steps and also covers other unlisted steps.

The term“effective,” as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

The term“hydrate” when used as a modifier to a compound means that the compound has less than one (e.g., hemihydrate), one (e.g., monohydrate), or more than one (e.g., dihydrate) water molecules associated with each compound molecule, such as in solid forms of the compound.

The term“saturated” when referring to an atom means that the atom is connected to other atoms only by means of single bonds.

The above definitions supersede any conflicting definition in any of the reference that is incorporated herein by reference. The fact that certain terms are defined, however, should not be considered as indicative that any term that is undefined is indefinite. Rather, all terms used are believed to describe the invention in terms such that one of ordinary skill can appreciate the scope and practice the present invention.

III. Examples

The following examples are included to demonstrate preferred embodiments of the disclosure. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventor to function well in the practice of the disclosure, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the disclosure.

Example 1: Results

Using common chemical raw materials calcium nitrate and squaric acid, [Ca(C404)(H20)]-l.5H20 (Robl el al, 1987) was synthesized under mild condition in water

(FIG. 2 and FIG. 3). In the as-synthesized UTSA-28O H2O, the pentagonal bipyramidal Ca atom is coordinated by seven O atoms from five different C4O4² linkers and one water molecule, bridged by organic linker to from one dimensional infinite chain, resulting in one dimensional channel occupied by guest water molecules (FIG. 4). Without being bound by theory, the hydrogen bonding between coordinated H2O molecules and O atom of C4O4² linkers further stabilize the framework (FIG. 5). After removing the guest water molecules, the framework of activated UTSA-280 is fully maintained, as determined by single-crystal X- ray diffraction (SCXRD) experiments (FIG. 4, Table 2). The coordinated H2O molecule is retained in the structure. One dimensional open cylindrical channel is obtained after guest removal (FIG. 4A), showing aperture sizes with slightly different shape of 3.2 ^c 4.5 and 3.8 ^c 3.8 A². These apertures display similar cross-sectional areas of about 14.4 A², which is larger than the minimum cross-sectional area of C2H4 (13.7 A²) but smaller than that of C2H6 (15.5 A²) (Webster et al. , 1998). The total solvent-accessible volume was estimated to be 27.8% of the unit cell volume. While UTSA-280 is remarkably stable in water (FIG. 2), the existence of the coordinated water molecules may be used in some emobodiments for guest-free UTSA-280 to display permanent porosity. The activation of UTSA-28O H2O may be performed under relatively mild condition to retain the coordinated water. The Brunauer- Emmett-Teller surface area of activated UTSA-280 was measured to be -331 m²/g (Langmuir surface area: -455 m²/g) by CO2 sorption experiment at 195 K (FIG. 4D and FIG. 6). The experimental total pore volume is -0.18 cm³/g, in full agreement with the theoretical pore volume from the crystal structure (0.18 cm³/g).

Table 2. Crystal data and structure refinements of UTSA-280 and UTSA-28O3C₂H

To investigate the feasibility of employing UTSA-280 to separate C2H4/C2H6 mixture, pure component equilibrium adsorption isotherms for C2H4 and C2H6 were collected at ambient conditions. FIG. 4E shows the data obtained at 298 K. The C2H4 uptake in UTSA- 280 reaches 88.1 cm³/cm³ (2.5 mmol/g) at 298 K and 1 bar, higher than those of benchmark zeolites that widely studied for ethylene/ethane separation, such as zeolite 5 A, cation exchanged ETS-10 (Engelhard Titanosilicate-lO) (1.0-2.3 mmol/g) (Mofarahi et al, 2013 and Anson et al. , 2008). In contrast, ethane adsorption does not occur in UTSA-280 under the same conditions, which means ethane molecule is completely excluded by the pore apertures, consistent with the structural pore size analysis. At lower temperature (273 K), while a larger C2H4 uptake can be observed, there is still no uptake increasing for C2H6 (FIG. 7). This remains true even at 195 K. According to the amount of adsorbed C2H4 and the pore volume, the density of C2H4 in the pore channel at room temperature is up to 389 g/liter, which is about 342 times as gaseous C2H4 density of 1.138 g/liter (298 K, 1 bar) and close to the liquid C2H4 density of 568 g/liter (169.4 K, 1 bar), implying the highly efficient packing of ethylene molecules in UTSA-280. Due to the complete size exclusion of C2H6, record-high apparent C2H4/C2H6 selectivity, exceeding 10000, can be calculated from the measured isotherms (FIG. 4F, FIG. 8, and Table 3), which are orders of magnitude larger than those of FeMOF-74 (13.6) (Bloch et al, 2012), NOTT-300 (48.7) (Yang et al, 2014), and p-complexation sorbents (Yang, 2003), such as PAF-l-SChAg (27) (Li et al, 2014), and the recently reported silica zeolite ITQ-55 (-100) (Bereciartua et al , 2017) (Table 4). It should be noted that such calculated selectivity is often subject to uncertainties due to the large error from the ultra-low apparent C2H6 uptake. Multiple sorption measurements were subsequently conducted carefully to test the material cyclability, showing no C2H6 adsorption and no loss of C2H4 uptake capacity in UTSA-280 (FIGS. 9-13). Table 3. Langmuir-Freundlich parameter fits for C2H4 and C2H6 at 298 K in UTSA-280.

Adsorbates

C2H4 3.10 0.0753 0.84387

C2H6 0.55 4.0792E-4 1.3631

Table 4. Summary of the adsorption uptakes, selectivities and heat of adsorption data for C2H4 and C2H6 in various ethylene sorbents.

The coverage-dependent isosteric heat of adsorption (6)_st) for ethylene was estimated based upon the Clausius-Clapeyron equation using pure component isotherms collected at 273, 298 and 313 K (FIG. 14). The experimental Q_s t value for C2H4 (ranging from 20.5 to 35.0 kJ/mol) in UTSA-280 was found to be markedly lower than those of many efficient C2H4 sorbents (Table 3), such as MOFs functionalized with open metal sites (40-85 kJ/mol) (Bloch et al, 2012 and Yoon et al, 2010) and p-complexation sorbents (60-120 kJ/mol) (Li et al. , 2014 and Aguado et al. , 2012). Such a low apparent adsorption enthalpy, associated with the absence of strong binding sites in guest-free UTSA-280, enable its regeneration to perform under mild conditions, thus avoid C2H4 oligomerization/polymerization that often happens under catalysis of open metal sites (Ji et al. , 2017 and Klet et al. , 2015). Therefore, the exceptionally selective C2H4 adsorption realized by UTSA-280 at ambient conditions is unprecedented and favorable, which can be attributed to size and shape cut-off from the optimal pore sizes rather than strong binding affinity. Presumably, the main host-guest interactions between C2H4 and UTSA-280 are C- H· · p and C-H· 0 interactions, which usually play an important role in protein folding and molecular recognition. To determine the nature of the interactions of C2H4 molecules within UTSA-280 structurally, SCXRD experiments were carried out. Data of UTSA-28O C2H4 were collected at room temperature on a C2H4-loaded sample (FIG. 15, Table 2). Non hydrogen atoms of the adsorbate can be located by employing this technique. Upon the C2H4 loading, the framework of [Ca(C4O4)(H2O)]-0.4C2H4 retains the same as the synthesized and activated structures, while an remarkable increasing in residual electron density peaks (F₀ ^~Fc contoured at 1.9 e/A³ in UTSA-28O C2H4) were clearly observed within the cylindrical channel, demonstrating the presence of C2H4 molecules (FIG. 16). A single crystallographic type of adsorbed C2H4 molecule can be successfully located in the middle of the channel from dispersed electron density peaks (FIG. 15 A, 15B, and FIG. 17). The refined C2H4 shows two-fold disordering over two sites with partial occupancy, which oriented linearly with its C=C axis along the channel and tilted with its minimum cross section along the diagonal of pore aperture. The orientation of C2H4 molecules inside the channels can minimize any possible steric hindrance and electrostatic repulsion from the framework. Weak C-H O hydrogen bonding (3.32-3.44 A), p · p stacking (3.31 A) and van der Waals (vdW) interactions (shortest C-H· · p distance of 3.32 A) are found between discrete C2H4 molecules and the aromatic rings of the C4O4² ligand or coordinated water molecules (FIG. 15C), in which the H O (2.65-2.85 A) and H C_K (2.89-3.02 A) distance are comparable with the sum of vdW radii of hydrogen (1.20 A) and oxygen (1.52 A) or carbon (1.70 A) atoms. Clearly, these gas-framework distances are significantly larger than those observed in MOFs with strong binding sites (e.g. 2.42 A for C2H4 with the open Fe site in Fe-MOF-74) (Bloch el al, 2012, being consistent with its lower adsorption enthalpy. Considering the vdW radii of atoms, tilted C2H4 molecule well fits the narrow pore channel (FIG. 15D). In contrast, significant steric hindrance is unavoidable when C2H6 molecule of staggered conformation is put inside the channels with whichever orientations, owing to its larger cross section (15.5 A²) than the pore aperture (14.4 A²). Thus, the specific C2H4 adsorption is because C2H4 molecule can diffuse into the confined channel utilizing its optimal orientation and weak interaction, while C2H6 molecule is totally excluded from the pore channel.

Based on the gas-loaded structure, we performed first-principles dispersion-corrected density functional theory (DFT-D) calculations to further confirm the C2H4 adsorption nature in UTSA-280. We found that the calculated C2H4 adsorption location and orientation are consistent with the experimental results from the diffraction data (FIG. 18). In UTSA-280, C2H4 molecules are preferentially located at the center of the pore channel, with C=C bond parallel to the channel axis. The adsorbed molecule interacts with the surrounding channel surface through p· · ·p stacking (3.31 A) and vdW interactions with the aromatic rings of the C4O4² linkers. Overall, the adsorption interaction is of weak dispersive interaction in nature.

The DFT-D calculated static binding energy is quite modest, -37.8 kJ/mol, consistent with the relatively low isosteric heat at zero coverage (34.1 kJ/mol) observed experimentally in UTSA-280. In general, employing adsorbents of low adsorption heat can reduce the regeneration energy and requirement for heat transformation during gas adsorption. Clearly, the restricted cylindrical channel enables the efficient packing of C2H4 molecules along the channels, while showing its inaccessibility to slightly large C2H6 molecules of similar physical property. Such completely molecular exclusion of ethane from ethylene associated with low binding affinity indicates UTSA-280 can serve as promising molecular sieve for ethane removal. In common process for ethylene production based on the cracking of heavier hydrocarbons fractions, followed by dehydrogenation reactions, the conversion yield of the later step is only around 50-60% (Faiz el al, 2012). Other processes such as catalytic dehydrogenation also give an equimolar mixture of olefins and paraffins. So the upgrading of ethylene based on ethane removal from the C2H4/C2H6 mixture is a very important process before further utilization. Although certain molecular exclusion can also be achieved on few flexible porous materials (Sen et al. , 2017 and Kishida el al. , 2016), the co-adsorption of other impurities during the opening of the pore structure makes their column breakthrough separation very tough, giving low-purity ethylene. In contrast, the pore system in rigid UTSA-280 is only accessible to ethylene, which also maximizes the working C2H4 capacity up to 100% of uptake capacity. Consequently, to evaluate the performance of UTSA-280 in a practical adsorptive separation process, breakthrough experiments were performed, in which an equimolar C2H4/C2H6 mixture was flowed over a packed column of the activated solid with a rate of 2 standard cubic centimeters per minute at 298 K (FIG. 19A and FIG. 20). As expected, clean separation of challenging C2H4/C2H6 mixture was realized with UTSA-280. C2H6 was first to elute through the bed, then the outlet gas quickly reached pure grade with no detectable C2H4 (below the detection limit of the experimental setup), whereas the solid adsorbent retained C2H4 for a remarkable time before the breaking through of C2H4. Hence, C2H6 can be completely removed from C2H4 with no loss of valuable C2H4, which is in line with the sorption experiments. The amount of C2H4 enriched from equimolar C2H4/C2H6 mixture was up to 1.7 mol/kg. Concentrated ethylene can be then recovered with high purity during the regeneration step, which could be alternatively carried out by applying a vacuum or temperature control in an actual process (FIG. 21). Regeneration of UTSA-280 under a He flows at 353 K revealed that the adsorbed gas can be completely recovered within ten minutes, which is significantly faster than those of Ag-doped adsorbent (up to thousands of minutes) (Li et al, 2014). These results demonstrate that the challenging C2H6 removal can be easily addressed under ambient condition (lbar, 298 K), which is superior to benchmark zeolite ITQ-55 (operated at 8.5 bar and 323 K) of smaller pore aperture (Bereciartua et al. , 2017). Multiple breakthrough experiments under aforementioned operating condition show the same retention time as the initial, which revealed that UTSA-280 maintained its ethylene uptake capacity and molecular exclusion of ethane (FIG. 22). For comparison with breakthrough experiments of UTSA-280, transient breakthrough simulation was also carried out (FIG. 23), which was found to be consistent with the experimental results.

In addition to the separation of binary C2H4/C2H6 mixture, there is tremendous current interest in the recovery of valuable ethylene from refinery gas streams (a typical consisting of 51% methane, 21.4% ethylene, 21.1% ethane and 6.5% propane) (Yang, 2003 and Zhang et al. , 2008), which usually is used as fuel gas. An adsorptive separation process that uses this molecular sieve for the recovery of C2H4 from similar mixture could potentially result in substantial economic benefits. It should be noted that separation on multi-components gas mixture may also happen during actual process since ethylene is often contaminated with similar hydrocarbons in current ethylene plants. To evaluate the feasibility of using UTSA- 280 for this task, we carried out breakthrough experiments for a quaternary CH4/C2H4/C2H6/C3H8 mixture (45/25/25/5). Based on the sieving effect, specific C2H4 enrichment from above quaternary gas mixture was realized with UTSA-280 (FIG. 19B and FIG. 24). The presence of CH4, C2H6 and C3H8 showed no effects on separating C2H4 as these three gases were completely excluded at the beginning of the experiment.

Among reported MOFs for C2H4/C2H6 separation, MOFs with open metal sites are indeed efficient to capture C2H4 via strong coordination interactions, which can produce very high C2H4 uptake at ambient conditions. However, MOFs with open metal sites are highly sensitivity to moisture due to their preferred coordination with water, resulting in a significantly reduced C2H4 uptake capacity and/or binding affinity. In contrast, UTSA-280 is stable in water (FIG. 19C) as demonstrated by PXRD patterns of the sample after immersing in water for days. Furthermore, gas sorption experiments of the re-activated UTSA-280 from the water-treated sample revealed that this material still maintains the same sorption capacities for C2H4 (FIG. 25), further indicating that UTSA-280 is water-stable. Actually, UTSA-280 can exhibit reversible water adsorption and desorption at 298 K (Horike et al, 2013). Such properties are apparently important for its potential industrial application. Furthermore, UTSA-280 is easily synthesized from very common chemical commodity via green and scalable method at room temperature, in which the only solvent is water. For example, 0.22 kilograms of UTSA-28O H2O was quickly obtained by easily mixing a saturated aqueous solution of sodium squarate (Na2C₄04) with an aqueous solution of Ca(N03)2-4H20 (FIG. 26). Overall, by virtue of the optimal pore channel of an old, water- stable, ultramicroporous MOF made by environmentally friendly method, molecular exclusion of ethane from ethylene was realized for promising energy-efficient separation technologies.

Optimal pore size and suitable functionality are essential features for porous materials to address key challenging gas separations. The foregoing results illustrate that the ideal molecular exclusion of ethane from ethylene can be readily achieved by simply size/shape matching, dramatically facilitating the very challenging membrane-based separation of such essential hydrocarbons. In principle, pore engineering in MOF chemistry is generally applicable to other types of porous material including porous organic polymers, covalent organic framework and hydrogen-bonded organic frameworks. Detailed examination of the pore features in various porous materials may be needed for the discovery of other molecular sieves in the future, and thus broaden the exploration of separations technologies with energy efficient prospects, affording tremendous opportunity for valuable gas separations.

Example 2: Methods and Materials

A. General Materials

Calcium nitrate tetrahydrate (Ca(N03)2-4H20, 99%, Fisher Chemical), sodium hydroxide (NaOH, 98%, Alfa Aesar), glacial acetic acid (C2H4O2, 99.7%, Fisher Chemical), squaric acid (or 3,4-dihydroxycyclobut-3-ene-l,2-dione, C4H2O4, 99.0%, Oakwood Chemicals), were purchased and used without further purification. N₂ (99.999%), CO2 (99.999%), C2H4 (99.5%), C₂H₆ (99.5%), He (99.999%) and mixed gases of C2H4/C2H6 = 50/50 (v/v) and CH4/C2H4/C2H6/C3H8 = 45/25/25/5 (v/v/v/v) were purchased form Airgas.

B. Methods

i. Single component gas sorption measurement

The gas sorption isotherms were collected on an automatic volumetric adsorption apparatus (Micromeritics ASAP 2020 surface area analyzer). Prior to the sorption measurements, the as-synthesized sample was washed with methanol for three times and placed in a quartz tube and dried under high vacuum for 36-72 hours at 110 °C to remove the guest water molecules, giving the activated UTSA-280 for gas sorption analyses.

ii. Breakthrough separation experiments

The breakthrough experiments were carried out in dynamic gas breakthrough set-up (FIG. 20). A stainless steel column with inner dimensions of 9 mm and length of 150 mm was used for sample packing. Pelleted microcrystalline sample (3.2 g) with particle size of 220-320 mm was then packed into the column. The column was placed in a temperature controlled environment (maintained at 298 K). The mixed gas flow and pressure were controlled by using a pressure controller valve and a mass flow controller. Outlet effluent from the column was continuously monitored using gas chromatography (GC-2014, SHIMADZU) with a thermal conductivity detector (TCD). The column packed with sample was firstly purged with helium gas flow for two hours at 373 K. The mixed gas flow rate during breakthrough process is 2 standard cubic centimeters per minute using 50/50 (v/v) C2H4/C2H6 at 1 bar. After the breakthrough experiment, the sample was regenerated with helium gas flow (50 standard cubic centimeters per minute) for about 15 minutes at 353 K.

iii. X-ray diffraction analysis of powder samples

Powder X-ray diffraction patterns were collected using a Rigaku Ultima IV diffractometer (Cu Ka□ = 1.540598 A) with an operating power of 40 kV, 44 mA and a scan rate of 8.0°/min. The data were collected in the range of 2Q = 5-40°.

iv. Single-crystal X-ray diffraction experiments

The single crystal of UTSA-280 loaded with ethylene molecules was obtained by loading ethylene gas at about 600 mmHg and ambient temperature. Diffraction data were collected on a Bruker D8 Venture CCD diffractometer with Cu Ka radiation (l = 1.54178 A) at 298 K. Multi-scan absorption corrections were performed with Bruker APEX III. The structures were solved by the direct method and refined with the full-matrix least-squares technique using the SHELXTL program package. For the framework, anisotropic thermal parameters were applied to all non-hydrogen atoms. Hydrogen atoms were generated geometrically. For gas molecules, ethylene were located from the strong electron density peaks and refined with isotropic displacement parameters. The C-C distances were restrained to 1.30(1) for ethylene. Hydrogen atoms on ethylene molecules were added with geometrical constraints. In Crystal data for the compounds were summarized in Table 2. Cambridge Crystallographic Data Centre 1582383-1582384 contain the supplementary crystallographic data of UTSA-280 and UTSA-280=>C2H4, respectively.

v. Density-functional theory calculations

First-principles density functional theory (DFT) calculations were performed using the Quantum-Espresso package (Giannozzi el al, 2009). A semi-empirical addition of dispersive forces to conventional DFT was included in the calculation to account for van der Waals interactions (Barone el al. , 2009). Vanderbilt-type ultrasoft pseudopotentials and generalized gradient approximation (GGA) with a Perdew-Burke-Emzerhof (PBE) exchange correlation was used. A cutoff energy of 544 eV and a 2 ^c 2 ^c 4 k-point mesh (generated using the Monkhosrt-Pack scheme) were found to be enough for the total energy to converge within 0.01 meV/atom. The structure of UTSA-280 was first optimized. C2H4 gas molecule was then introduced to the optimized host structure at the experimentally identified adsorption site, followed by a full structural relaxation. To obtain the gas binding energy, an isolated gas molecule placed in a supercell (with the same cell dimensions as the MOF crystal) was also relaxed as a reference. The static binding energy (at T = 0 K) was then calculated using EB = E(MOF) + E(C₂H₄) - E(MOF + C2H4).

vi. Fitting of pure component isotherms

The pure component isotherm data for C2H4 and C2H6 in UTSA-280 were fitted with the single-site Langmuir-Freundlich model:

where p (unit: kPa) is the pressure of the bulk gas at equilibrium with the adsorbed phase, N (unit: mmol/g) is the adsorbed amount per mass of adsorbent, N^max (unit: mmol/g) is the saturation capacities, b (unit: l/kPa) is the affinity coefficient and n represent the deviation from an ideal homogeneous surface. The fitted parameter values are presented in Table 3.

vii. Isosteric heat of adsorption

The binding energy of C2H2 is reflected in the isosteric heat of adsorption, Q_{s t}. The Clausius-Clapeyron equation was employed to calculate the enthalpies of C2H4 adsorption:

where P is the pressure, T is the temperature, R is the universal gas constant. Adsorption heats (gst) of UTSA-280 for ethylene reported here are estimated using pure component isotherms collected at 273, 298 and 313 K.

viii. IAST calculations of adsorption selectivities

The adsorption selectivity for C2H2/C2H4 separation is defined by s a. qjq₂

Pit Pl (3),

where q 1 and qi are the molar loadings in the adsorbed phase in equilibrium with the bulk gas phase with partial pressures pi and pi.

ix. Transient breakthrough of C₂H₂/C₂H₄ mixtures in fixed bed adsorbers

For comparison with breakthrough experiments with UTSA-280, transient breakthrough simulations were undertaken using the same methodology as discussed in earlier publications (Krishna et al, 2014). The dimensions of the breakthrough tube, sample mass, and flow rates were chosen to precisely match the experimental conditions. The simulated breakthrough is shown FIG. 11. The breakthrough times of C2H6 and C2H4 are captured reasonably accurately. The simulated breakthroughs are somewhat sharper than those observed experimentally. The reason for this is that in the simulations, intra-crystalline diffusional influences are ignored. The distended characteristics of the experimental breakthroughs with UTSA-280 are because of finite diffusional resistances.

The separation performance of UTSA-280 for separation of 50/50 C2H2/C2H4 feed mixture was investigated. The total bulk gas phase is at 298 K and 100 kPa.

Example 3: Synthetic Procedures

A. Synthesis of [Ca(C₄0₄)(H₂0)] · 1.5H₂0

The synthesis of single-crystal sample was followed by a reported method with minor modifications. A solution of squaric acid (182 mg, 1.6 mmol) and NaOH (3.2 mmol, 128 mg) in 16 mL water was carefully layered on a solution of Ca(N03)2-4H₂0 (8.0 mmol, 1.888 g), CH3COOH (2.75 mL, 2.882 g) and NaOH (32 mmol, 1.280 g) in 40 mL water. Colorless single crystals of [Ca(C404)(H20)]-l.5H₂0 were obtained in a few days. The resultant crystals was filtered, washed thoroughly with water, and dried under air, with yields of 61% based on squaric acid. Microcrystalline powder sample was obtained by mixing a saturated aqueous solution (10 mL) of sodium squarate (Na2C₄0₄, 1 mmol, 0.158 g) with an aqueous solution (10 mL) of Ca(N03)2-4H20 (5 mmol, 1.180 g). Microcrystalline powders came out immediately and the reaction completely finished within few minutes, then after 10 minutes at room temperature, the sample was filtered, washed thoroughly with water, and dried under air, with yields of 0.146 g (74% based on sodium squarate).

B. Large-scale synthesis of [Ca(C₄0₄)(H₂0)] 1.5H₂0

Synthesis of 1000-times scale was carried out as followed. Microcrystalline powder sample was obtained by mixing a saturated aqueous solution (3.29 L) of sodium squarate (Na2C₄0₄, 1190 mmol, 188 g) with an aqueous solution (0.6 L) of Ca(N03)2-4H20 (5950 mmol, 1404 g). Microcrystalline powders came out immediately and the reaction completely finished within few minutes, then after 10 minutes at room temperature, the sample was filtered, washed thoroughly with water, and dried under air, with yields of 219 g (93% based on sodium squarate).

C. Preparation of [Ca(C₄0₄)(H₂0)] (UTSA-280)

A single crystal of as-synthesized [Ca(C₄0₄)(H20)]-l.5H20 was sealed in a glass capillary, activated in situ under high vacuum for 48 hours at 100 °C followed at 110 °C for 24 hours. The obtained [Ca(C₄0₄)(H20)] crystal was sealed for X-ray diffraction experiment. Activation at higher temperature leads to loss of the coordination water and collapse of the crystalline framework structure.

Example 4: Selective Sorption of CO2 and Ethyne

In some embodiments, UTSA-280 may be employed for CCh/CFL and/or CO2/N2 separation. Single component adsorption isotherms of UTSA-280 for CO2, CH₄, and N2 were collected at ambient conditions, which show selective uptake of CO2 over N2 and CH₄ (FIGS. 27A & 27B). For CO2, the uptake capacity of UTSA-280 is 67.3 cm³/g (3.0 mmol/g) at 1 bar and 298 K. In contrast, for CFL and N2 sorption at 1 bar and 298 K, the sorption capacities of UTSA-280 are only 0.20 and 0.24 mmol/g, respectively. The CO2 sorption isotherm is steep, with an uptake capacity at low-pressure region of about 38 cm³/g (1.69 mmol/g, at 0.15 bar and 298 K), therefore CO2 removal at low concentration may be achieved. The IAST selectivity of UTSA-280 for separating 15/85 (v/v) CO2/N2 and 50/50 (v/v) CCh/CFL mixtures at 298 K was also calculated (FIG. 28), giving a high selectivity of 72 and 60, respectively. Notably, the selectivity of UTSA-280 for 50/50 (v/v) CCh/CFL mixture is higher than that of the benchmark SIFSIX-2-Cu-i (33; Nugent et al, 2013). Furthermore, the sorption for ethyne was also evaluated (FIG. 29). At 298 K and 1 bar, UTSA-280 can take up C2H2 of 67.3 cm³/g (3.0 mmol/g), thus UTSA-280 may be used in ethyne storage and/or separation applications. All of the compounds, compositions, and methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the disclosure may have focused on several embodiments or may have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations and modifications may be applied to the compounds, compositions, and methods without departing from the spirit, scope, and concept of the invention. All variations and modifications apparent to those skilled in the art are deemed to be within the spirit, scope, and concept of the invention as defined by the appended claims.

REFERENCES

The following references, to the extent that they provide exemplary procedural or other details supplementary to those set forth herein, are specifically incorporated herein by reference.

Aguado et al., J. Am. Chem. Soc., 134: 14635-14637, 2012.

Anson et al., Chem. Eng. Sci., 63:4171-4175, 2008.

Bachman et al. J. Am. Chem. Soc., 139:15363-15370, 2017.

Bao et al. , Energy Environ. Sci., 9:3612-3641, 2016.

Barone et al. , J. Comput. Chem. 30, 934-939, 2009.

Bereciartua et al. , Science, 358: 1068-1071, 2017.

Bloch et al, Science, 335: 1606-1610, 2012.

Cadiau et al, Science, 353: 137-140, 2016.

Chang e/ al, Chem. Commun. 51 :2859-2862, 2015.

Chu et al. , Nat. Mater., 16: 16-22, 2017.

Cui et al, Science, 353: 141-144, 2016.

Faiz et al, Chem. Eng. Sci., 73:261-284, 2012.

Furukawa et al, Science, 341 : 1230444, 2013.

Geier et al, Chem. Sci. 4:2054-2061, 2013.

Giannozzi et al., J. Phys.: Condens. Matter 21 :395502, 2009.

He et al, Energy Environ. Sci. 5:9107-9120, 2012.

Horike et al., J. Am. Chem. Soc., 135:4612-4615, 2013.

Ji et al. , J. Am. Chem. Soc., 139: 11325-11328, 2017.

Kishida et al., Angew. Chem. Int. Ed. 55: 13784-13788, 2016).

Kitagawa, Angew. Chem. Int. Ed., 54: 10686-10687, 2015.

Klet et al. , J. Am. Chem. Soc. 137: 15680-15683, 2015.

Krishna et al. Microporous Mesoporous Mater. 185:30-50, 2014.

Li et al. Chem. Soc. Rev. 38: 1477-1504, 2009.

Li et al. , J. Am. Chem. Soc., 136:8654-8660, 2014.

Liao et al, Science, 356: 1193-1196, 2017.

Lin, Science, 353: 121-122, 2016.

Ma et al, J. Am. Chem. Soc., 131:6445-6451, 2009. Mofarahi et al, Adsorption, 19: 101-110, 2013.

Nugent et al., Nature, 495:80-84, 2013.

Pan et al., Angew. Chem. Int. Ed., 45:616-619, 2006.

Peng et al, Science, 346: 1356-1359, 2014.

Robl et al, Mater. Res. Bull., 22:373-380, 1987.

Sen et al., J. Am. Chem. Soc., 139: 18313-18321, 2017.

Sholl et al, Nature, 532:435-437, 2016.

Vaidhyanathan et al, Science, 330:650-653, 2010.

Webster et al, J. Am. Chem. Soc., 120:5509-5516, 1998.

Yang et al, Nat. Chem. 7: 121-129, 2014.

Yang, in Adsorbents: Fundamentals and Applications. (John Wiley & Sons, Inc.), pp. 280- 381, 2003.

Yoon et al, Angew. Chem. Int. Ed., 49:5949-5952, 2010.

Yoon et al, Nat. Mater., 16:526-531, 2016.

Zhai et al., Nat. Commun., 7: 13645, 2016.

Zhang et al, Chem. Commun. 51 :2714-2717, 2015.

Zhang, et al, Energy & Fuels, 22: 1142-1147, 2008.

Claims

CLAIMS What Is Claimed Is:

1. A method of separating two or more compounds using a metal organic framework comprising a repeating unit of the formula ML, wherein M is a divalent metal ion and L is a ligand of the formula:

or a hydrate thereof, wherein the method comprises:

(B) separating the first compound from the second compound within the metal- organic framework.

2. The method of claim 1, wherein M is a divalent alkali earth metal.

3. The method of claim 2, wherein M is Ca(II).

4. The method according to any one of claims 1-3, wherein the metal organic framework is further defined as a metal organic framework of the formula: M(H20)L.

5. The method of claim 4, wherein the metal organic framework is further defined as by the formula: Ca(H20)L.

6. The method according to any one of claims 1-5, wherein the first compound or the second compound is a gas molecule.

7. The method of claim 6, wherein both the first and second compounds are gas molecules.

8. The method of according to any one of claims 1-7, wherein the first compound is an alkene(c<8).

9. The method of claim 8, wherein the first compound is ethylene.

10. The method according to any one of claims 1-7, wherein the first compound is an alkyne(c<8).

11. The method of claim 10, wherein the first compound is ethyne.

12. The method according to any one of claims 1-7, wherein the first compound is CO2.

13. The method according to any one of claims 1-12, wherein the second compound is an alkane(c<8).

14. The method of claim 13, wherein the second compound is ethane.

15. The method of claim 13, wherein the second compound is methane.

16. The method according to any one of claims 1-12, wherein the second compound is N₂.

17. The method according to any one of claims 1-16, wherein the ratio of the first compound to the second compound in the mixture is from about 1:999 to about 1 : 1.

18. The method of claim 17, wherein the ratio of the first compound to the second compound in the mixture is from about 1 : 99 to about 1: 1.

19. The method according to any one of claims 1-16, wherein the ratio of the second compound to the first compound in the mixture is from about 1 : 999 to about 1 : 1.

20. The method according to any one of claims 1-19, wherein the separation is carried out at a pressure from about 0.1 bar to about 10 bar.

21. The method of claim 20, wherein the separation is carried out at a pressure of about 1 bar.

22. The method according to any one of claims 1-21, wherein the metal-organic framework is adhered to a fixed bed surface.

23. The method according to any one of claims 1-22, wherein the separation is carried out in an absorber packed with the metal-organic framework.

24. The method of claim 1, wherein the separation is carried out at a temperature from about 0 °C to about 75 °C.

25. The method of claim 24, wherein the separation is carried out at about room temperature.