FIELD OF THE INVENTION:
The invention relates to ultra-microporous metal organic framework or porous coordination polymer materials that are useful for the selective separation and recovery of carbon dioxide from mixed gas fluid streams, such as N2/CO2 or CH4/CO2.

BACKGROUND OF THE INVENTION:
Coal-fired power plants currently generate approximately 40% of the world’s electricity and are one of the largest sources of anthropogenic CO2 emissions worldwide. In order to mitigate the greenhouse gas emissions of power generation, post-combustion CO2 capture technologies have attracted significant attention. Gases such as carbondioxide, oxygen, nitrogen, hydrogen, acetylene, methane find application in a variety of industrial processes. Several industrial gas streams, fuel-rich gas streams (methane generated from Bio-gas or Shale gas), as well as effluent gases posses carbondioxide (CO2) as an impurity component in low partial pressures. Separation of CO2 from such gas mixtures is of extreme importance both in industrial economic standpoint and in minimizing green house gas emissions for a sustainable environment.

Gas separations may be carried out by a number of methods including distillation at cryogenic temperatures, the use of perm selective membranes, and by processes that utilize solid compositions that can reversibly and selectively adsorb a component of the gas mixture. For adsorption-based separation of CO2, current commercial technologies utilize liquid amine based scrubbing or zeolite molecular sieves as CO2-selective adsorbents and super saturated solutions of strong bases such as KOH or carbonates as adsorbents. These technologies, which are usually employed for the CO2 capture have several inherent limitations which restrict their long term application.

In these industrial processes, pressure swing adsorption (PSA) systems with solid sorbents, such as zeolite 13X or activated carbon, are used to separate the CO2 from the H2. However, the gas separation process is still too energy demanding for large scale coal gasification power plants to be commercially viable and further optimization of the purification process is required. Although process tuning will play a large role in this optimization, the largest opportunities lie in materials development of the solid sorbents. Synthetic zeolites (Zeolite-13x) reversibly adsorb CO2 in preference to N2. When used for instance in a pressure-swing adsorption (PSA) process for the separation of air, the zeolite bed selectively takes up the CO2 which is recovered by de-pressurization or evacuation of the bed. CO2 thus generated can be dumped into deep vents under the ground or under ocean (sequestration) or in special cases could be converted into value added products. The co-product, nitrogen gas, would also be treated in the project as an item of substantial commercial value. Such on-site PSA systems can separate up to 200 tons/day of CO2. Zeolite13x, a sodium aluminosilcate of the formula Na86[(AlO2)86(SiO2)106]•H2O, is a preferred adsorbent for air separation from a pre-treated dry stream of CO2-N2 mixture. The liquid amines are extremely corrosive and demand significant energy to release the captured CO2 (heating at T>150oC) due to their interaction with the CO2 being of chemical origin. Zeolite13x, serves as an effective physi-sorbing adsorbent and interacts with the CO2 via quadrapole-quadrapole interactions. For several years the PSA process has been in use and yet there has been no other adsorbent tried in place of Zeolite13x in a commercial set up. The drawback in this separation method is that the zeolites being highly polar easily adsorb water over CO2, hence the entire adsorption is effective only when carried out above 100oC. Also, the interactions of CO2 is quite strong (Heat of adsorption, HOA = ~50kJ/mol) hence the CO2 recovery process requires significant energy. Another energy penalty comes from the necessity to activate the zeolites at high temperatures (300oC) to achieve the pristine form of the adsorbent.

As mentioned earlier, Coal-fired power plants currently generate approximately 40% of the world’s electricity. However, alternatives to directly burning coal and scrubbing CO2 from the combustion gas exist that may be more efficient and ultimately less costly. Currently, over 90% of the world's hydrogen is produced from gasification. Coal gasification is expected to be a key technology for future clean coal power and involves the catalytic steam reforming of the fuel to produce a high pressure H2/CO2 gas mixture. CO2 is then separated from the mixture, resulting in a near pure H2 stream that can be burned to produce water as the only combustion product. However, the gas separation process is still too energy demanding for large scale coal gasification power plants to be commercially viable, and further optimization of the purification process is required. Although process tuning will play a large role in this optimization, the largest opportunities lie in materials development of the solid sorbents.

Metal organic frameworks (MOFs) with large surface areas have attracted attention as solid sorbents for large-scale gas separation applications. They have been intensively studied for CO2 capture from combustion flue gases where CO2/N2 gas separations at low pressure are pertinent. Despite the potential application for coal gasification, reports of MOFs for high pressure CO2/H2 separations have been limited. Recently, Long and co-workers examined a variety of well-known MOFs and identified Mg2(dobdc) and Cu-BTTri as the most promising candidates for CO2/H2 separations as they were found to have high CO2/H2 adsorption selectivities and large CO2 working capacities under PSA conditions relevant to coal gasification. Both of these MOFs possess metal sites with unsaturated coordination or so-called open metal sites. Although the open metal sites are advantageous in establishing strong and selective CO2 binding, they could be problematic in terms of long term hydrolytic stability. Unsaturated metal sites, which are strong Lewis acids tend to interact readily with even trace in quantities of water resulting in either diminished adsorption properties or irreversible degradation of the materials. This is problematic for practical gas separations as the complete removal of water following steam reforming during coal gasification is not practical. The existing metal-organic framework materials that have been investigated for CO2 adsorption have been based on redox active metals (e.g. Fe and Co), wherein the metal plays a key role as the adsorption active site (see e.g., U.S. 5,294,418). The metals in these cases have unsaturated cooridnations hence act as very strong Lewis acids and interact with the oxygen atom of the polarized CO2 molecule which serve as the Lewis base. Such interactions again are too strong (>50kJ/mol) for a smooth removal of CO2. Also, such materials can display significant or in some cases severe degradation under prolonged CO2 exposure. Alternatively, amine functionalized metal organic frameworks have been tried for CO2 adsorption and they seem to clearly demonstrate superiority when the pores are ultra-microporous facilitating strong CO2-amine interactions and other co-operative interactions. Problem with these adsorbents is again the high interaction strength (HOA= 40kJ/mol). Recently it has been estimated from calculations that for a smooth CO2 adsorption-desorption process an optimal HOA is of the order of 25-30 kJ/mol.

Recently, ultra-microporous MOFs (pores in the range of 4-6 Å) with exceptional post-combustion CO2 capture capabilities have been demonstrated. Ultra-microporous MOFs have some structural advantages that make them excellent gas separation sorbents. For example, the small pores can facilitate strong framework-gas interactions and can enhance the cooperative effects between the adsorbed species. They also have inherent molecular sieving capabilities. In terms of stability, the small ligands tend give rise to rigid structures and improved shelf-life when compared to the MOFs built from large organic ligands. Ultra-microporous materials typically have relatively low saturation limits at high pressure, which has made them unattractive targets for PSA applications. At high pressure, large pores can allow the guest molecules to pack densely, resulting in high uptake capacities that are important for gas separation applications. Thus obtaining high uptake capacities at high pressures from ultra-microporous MOFs is seemingly paradoxical and remains a challenge.

Accordingly, there exists a need in the art for alternative CO2-adsorbent materials that display decreased degradation under conditions relevant for separation of CO2 from fluid streams and favours facile CO2 removal. If such materials can be made with cheap and readily available chemical components, that could be advantageous and will remain great contribution to the art. A relatively low temperature activation and desorption character is critical for the development of CO2-adsorbent materials. Gas separation is to a large extent dictated by functionalized pores in the range of 3 to 6 Å. Single small ligand MOFs has many advantages: synthesis is often simple and can be scaled up easily, they typically are rigid and have high stability. Additionally, such systems could favour ultra-micropores (3-6 Å) which are well suited for maximal interactions between host and guest and such materials possess very high stability.

ABBREVIATIONS:
IISERP-MOF1-(Ni(4-PyC)2)(THF)
IISERP-MOF2-[Ni-(4Pyc)2.DMF]
PSA- Pressure swing adsorption
TSA - Temperature swing adsorption

SUMMARY OF THE INVENTION:
To address the above issues, this invention discloses a new polymeric metal organic frameworks represented by formula MX(B)Y.(solvent)Z , (herein after referred as IISERP-MOF) material developed in the Indian Institute of Science Education and Research, Pune. These are suitably stable and efficiently and selectively adsorb carbon dioxide and are functionalized with specific functional groups that are moderate bases to ensure facile adsorption-desorption.

Accordingly, in one aspect, the invention provides polymeric metal-organic frameworks (MOFs) of formula MX(B)Y.(solvent)Z , wherein M is a metal selected from the group consisting of Ni, Cu, Co, Mg, Zn, Cd and B is a ligand selected from 4-pyridylcarboxylic acid (isonicotinic acid) or 4-pyridylcarboxylic acid optionally substituted with NH2 or OH or its derivatives; and
X and Y are each integers greater than zero and selected to provide a neutral compound; and wherein, Z may be zero or greater than zero.

In another aspect, the invention provides methods for removing CO2 from a fluid stream consisting of CO2 and at least one other component. Particularly for CO2:N2 gas mixtures containing CO2 at low partial pressures representing the flue gas compositions and CO2:H2 gas mixtures containing CO2 at partial pressures representing the pre-combustion gas mixtures. This comprising contacting the fluid stream with a Polymeric Metal Organic Framework, of formula MX(B)Y.(solvent)Z wherein M is a metal selected from the group consisting of Ni, Cu, Co, Mg, Zn, Cd and B is 4-pyridylcarboxylic acid also known as isonicotinic acid or optionally substituted with NH2 or OH. The IISERP-MOF is capable of selectively and reversibly binding CO2 under conditions suitable to yield CO2-reduced fluid stream.

In another aspect, the invention provides a method for preparing MX(B)Y.(solvent)Z , which comprises heating a reaction mixture comprising M2+ salts, B and solvents under solvothermal conditions suitable for formation of the MX(B)Y.(solvent)Z , (IISERP-MOF) wherein M and B are defined above.

In a preferred aspect, the invention provides NiMOF1, with a composition, Ni9(H2O)4(H2O)2(C6NH4O2)18.(H2O)17(CH3OH)4(C4H8O)4, which is simultaneously referred as IISERP-MOF1 and hence, both NiMOF1 and IISERP-MOF1 are used interchangeably throughout the specification and the same may be appreciated as such by the person skilled in the art.
In another preferred aspect, the invention provides NiMOF2, with a composition, Ni(C6NH4O2)2.(C3H7NO), which is simultaneously referred as IISERP-MOF2 and hence, both NiMOF2 and IISERP-MOF2 are used interchangeably throughout the specification and the same may be appreciated as such by the person skilled in the art.

Importantly, in the case of NiMOF1 as well as NiMOF2, the milligram scale solvothermal reaction has been carried out in 25gram scale with a facile scale-up procedure.

“Optionally substituted” means the referenced group is functionalized, as is familiar to those skilled in the art, at one or more functionalizable positions with groups that do not interfere with the intended function of the overall material in fact would bring in more functional groups into the monomer which is not supplied by the pyridyl core (e.g., the IISERP-MOF formed with an optionally substituted ligand). Suitable functional groups include, for example, one or more (e.g., one to four, or one to three, or one to two, or one) groups that are each independently selected from the group consisting of R-OH, where R = pyridyl or phenyl ring, or any other monoprotic nucleophile such as -SH.

BRIEF DESCRIPTION OF THE DRAWINGS:
Figure 1 shows the comparison of the pxrd patterns of the as synthesized phase of NiMOF1 with its corresponding simulated PXRD patterns generated from their single crystal data.

Figure 2 shows TGA of the as made sample and the completely activated sample. TGA carried out on the methanol exchanged sample of NiMOF1. The weight loss have been calculated using formula Ni9(H2O)4(H2O)2(C6NH4O2)18(H2O)17(CH3OH)4(C4H8O)4 (M. Wt. 3557.2). All the volatile solvent molecules are removed by 100oC (4 THF + 4 MeOH + 2 H2O(surface adsorbed) loss, calc:12.71%, obsd: 12.7), while most of the free solvent water and the coordinated water come off at 180oC (calc: 9.61%; obsd: 10.21).

Figure 3 illustrates the Thermal ellipsoid representation of NiMOF1, with the ellipsoids placed at 50% probability. Note the disorder on the isonicotinate units have been modeled satisfactorily. The model involves two isonicotinate units with 50% occupancies positioned close to each other. They are rotated by 180C with respect to each other. This renders the Ni(1) and Ni(2) coordinating simultaneously to a 50% occupied pyridyl group and a 50% occupied carboxylate group.

Figure 4 shows Connolly representation of the three-dimensional structure of NiMOF1, showing the bimodal distribution of the pores.

Figure 5 shows a) CO2 and N2 adsorption isotherms carried out on NiMOF1 at different temperatures.

Figure 6 shows Pore size distribution in NiMOF1 modeled through DFT calculations using the 195K CO2 adsorption branch showing a bimodal distribution, which is in agreement with the single crystal structure. The smaller ultra-micropores are ~3.5 Å, while the larger ones are ~4.8 Å.

Figure 7 shows the comparison of the HOA trend obtained from the virial and DFT modeling done using the CO2 isotherms carried out at -10C, 0C, +10C and +25oC on NiMOF1.

Figure 8 shows the CO2 selectivity over N2 calculated using the 195K, 248K and 273K isotherms employing a IAST model with a nominal composition of 15CO2:85N2.

Figure 9 shows PSA working capacity of NiMOF1 for a swing from 10bar to 1bar at 298K for flue gas mix (15CO2:85N2). Working capacity 3.7 mmol/g for a PSA (10bar to 1bar) at 298K for flue gas mixture, 15%CO2 and 85% N2.

Figure 10 shows the comparison of the 195K CO2 and 77K N2 adsorption isotherms of the mg and gm scale syntheses, showing the laboratory scale scalability.

Figure 11 Isotherms simulated from a hydrogen purification (80H2:20CO2) and pre-combustion mixture (60H2:40CO2).

Figure 12 (A) and (B) The working capacity of NiMOF1 determined from simulation compared to that of several industrial sorbents and MOFs determined from (i) 80H2:20CO2 and (ii) 60H2:40CO2 gas mixtures at 313 K. The working capacities have been evaluated using a desorption pressure of 1 bar. (C) and (D) Comparison of the H2/CO2 selectivity of 1 vs other known MOFs and industrial sorbents determined from (i) 80H2:20CO2 and (ii) 60H2:40CO2 gas mixtures at 313 K. Data for activated carbon JX101, zeolite 13X, Mg-MOF-74 and Cu-BTTri are taken from the published literature.

Figure 13 shows hydrolytic stability tests on NiMOF1 from PXRD. PXRD comparisons of the as made sample with the simulated. Presented is also the PXRDs indicating the hydrolytic stability of NiMOF1.

Figure 14 shows hydrostatic stability tests on NiMOF1 from PXRD. Pressure induced amorphization test for NiMOF1. Note there is hardly any loss in crystallinity or gas uptake. Pressure of 70bar is twice what is industrially used.

Figure15 Top: The secondary building units in NiMOF2, showing the effective tetrahedral coordinations around Ni center. Connectivtiy of these tetrahedral Ni nodes to form an adamantane type unit. Bottom: Three dimensional structure of IISER-MOF2 formed by the periodic extension of the adamantane units by the linkings provided by carboxylate and pyridyl groups of the isonicotinate units. A view along a axis (left) showing porous square channel, along b axis (top right) and along c axis (bottom right). H atoms are not shown for clarity.

Figure 16 shows the Pxrd pattern of NiMOF2 showing the bulk purity as well as steam stability (top) and bulk purity of mg scale vs 25g scale sample (bottom)

Figure 17 shows the TGA (top) and DSC (bottom) of NiMOF2 shows the thermal stability of the material.

Figure 18 shows the N2 adsorption of NiMOF2 at 77K (top). BET (bottom left) and Langmuir (bottom right) surface area analysis of IISER-MOF2 using adsorption branch of 77K N2 isotherm.
Figure 19 shows the experimental CO2 sorption isotherms of NiMOF2 at different temperature. Filled circles are adsorption and open circles are desorption branch.

Figure 20 shows the pore size distribution determined from NLDFT model using 273K CO2 isotherm. The stability of the material also was further studied by gas adsorption measurement. The steam treated sample (60%RH, 7 Day) was subjected for pre-treatment at 180ºC for 24 hrs followed by a CO2 adsorption measurement at 273K. It was observed from the isotherms that there was hardly any loss in CO2 uptake (~ 2%) even after 7days of stream treatment.

Figure 21 shows the CO2 sorption isotherms of NiMOF2 at 273K for g scale and mg scale sample.

Figure 22 Presents the heat of adsorption for CO2 of NiMOF2 calculated from virial model using 303K 273K and 263 K CO2 isotherm.

Figure 23 shows the CO2: N2 selectivity of NiMOF2 predicted from pure component CO2 isotherms using IAST model for typical flue gas composition (15 CO2: 58 N2).

Figure 24 shows the CO2 sorption isotherms of NiMOF2 at 273K before and after steam treatment showing hydrolytic stability of it.

Figure 25 shows the comparison of experimental and simulated CO2 Isotherms (top) and simulated (from GCMC) binary component isotherm at 313K for flue gas composition (15 CO2:85 N2).

DETAILED DESCRIPTION OF THE INVENTION:
The invention will now be described with reference to certain preferred and optional embodiments, so that the various aspects therein will be more clearly understood and appreciated.

Definitions
The term "alkyl" means a straight or branched chain saturated hydrocarbon containing from 1 to 4 carbon atoms. Representative examples of alkyl include, but are not limited to, methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, iso-butyl, and tert-butyl. When an "alkyl" group is a linking group between two other moieties, then it may also be a straight or branched chain; examples include, but are not limited to -CH2-, -CH2CH2-, and -CH2CH2CH(CH3).

The term "alkynyl" means a straight or branched chain hydrocarbon containing from 2 to 4 carbons and containing at least one carbon-carbon triple bond. Representative examples of alkynyl include, but are not limited to ethynyl, 2-propynyl, and 3-butynyl.

The term "aryl" means a phenyl (i.e., monocyclic aryl), or a bicyclic ring system containing at least one phenyl ring or an aromatic bicyclic ring containing only carbon atoms in the aromatic portion of the bicyclic ring system.

The term "halo" or "halogen" means -CI, -Br, -I or -F.

The term "heteroaryl" means a monocyclic heteroaryl or a bicyclic ring system containing at least one heteroaromatic ring. The monocyclic heteroaryl can be a 5 or 6 membered ring. The 5 membered ring consists of two double bonds and one, two, three or four nitrogen atoms and/or one oxygen or sulfur atom. The 6 membered ring consists of three double bonds and one, two, three or four nitrogen atoms. The 5 or 6 membered heteroaryl is connected to the parent molecular moiety through any carbon atom or any nitrogen atom contained within the heteroaryl. Representative examples of monocyclic heteroaryl include, but are not limited to, furyl, imidazolyl, isoxazolyl, isothiazolyl, oxadiazolyl, oxazolyl, pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, pyrazolyl, pyrrolyl, tetrazolyl, thiadiazolyl, thiazolyl, thienyl, triazolyl, and triazinyl.

The instant inventors have found that certain solid state compositions comprising polymeric metal-organic frameworks developed in IISER, Pune, (IISERP-MOF) can selectively adsorb CO2 for its separation and recovery from fluid mixtures, such as N2-CO2 or O2-CO2 or CH4-CO2 or H2-CO2.
According to preferred embodiment, the invention provides (IISERP-MOF) ultra-microporous metal organic frameworks of formula MX(B)Y.(solvent)z,
wherein, M is selected from the group consisting of Ni, Cu, Co, Mg, Zn, Cd;
B is a ligand selected from 4-pyridylcarboxylic acid or optionally substituted 4-pyridylcarboxylic acid (isonicotinic acid) or its derivatives; and
X and Y are each integers greater than zero and selected to provide a neutral compound; and wherein, Z may be zero or greater than zero.

In certain embodiments, the substituted 4-pyridylcarboxylic acid (isonicotinic acid) comprise -NH2 or -OH as substitutions. According to the invention, the term “IISERP-MOF” means a porous metal-organic framework comprising metal cation in +2 oxidation state and 4-pyridylcarboxylate or optionally substituted form of 4-pyridylcarboxylate or its substituted derivatives as the sole ligand, which is prepared by solvothermal reaction. The solvothermal reaction is carried out in such a manner that the inclusion of specific components is vital to the successful formation of the particular and active form of this composition as a pure phase.

The IISERP-MOFs according to the invention may be optionally solvated (e.g., hydrated) or may be anhydrous. Thus the IISERP-MOF may be crystalline, amorphous, a combination of crystalline forms, or any mixture thereof.

According to the ultra-microporous metal organic frameworks of formula MX(B)Y.(solvent)z of the invention, wherein, if Z is greater than zero, then the MOF is said to be solvated or solvate. “Solvated” and “solvate” means and includes that the referenced composition (i.e., IISERP-MOF) contains a stoichiometric or non-stoichiometric amount of solvent molecules that are non-covalently associated with the crystalline or amorphous framework of the composition (i.e., the solvent is held within the framework of the composition by intermolecular forces). According to this embodiment, where the solvent is water, the solvate is a “hydrate.” Examples of other solvents include, but are not limited to, water, methanol, ethanol, isopropanol, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, tetrahydrofuran, acetonitrile, toluene, benzene, chloroform, dichloromethane, and mixtures thereof.

In yet another embodiment, the invention provides a method for preparing MX(B)Y.(solvent)z, which method comprises heating a reaction mixture comprising
M2+ salts, 4-pyridylcarboxylic acid (isonicotinic acid) or optionally substituted 4-pyridylcarboxylic acid or its derivatives and solvents under solvothermal conditions suitable for formation of the Mx(B)y.(solvent)z, wherein, M is selected from the group consisting of Ni, Cu, Co, Mg, Zn, Cd; B is a ligand selected from 4-pyridylcarboxylic acid or optionally substituted 4-pyridylcarboxylic acid (isonicotinic acid) or its derivatives; X and Y are each integers greater than zero and selected to provide a neutral compound; and wherein, Z may be zero or greater than zero.

In certain embodiments, the IISERP-MOFs has an average pore size (e.g., average pore diameter) along its largest axis between about 4 Å and about 6 Å. In certain embodiments, the average pore size is between about 4 Å and about 6 Å as estimated from their DFT models carried out using their CO2 adsorption data.

Thus in a further embodiment, the invention provides a method for removing CO2 from a fluid stream consisting of CO2 and at least one other component particularly at low partial pressures, which method comprises contacting the fluid stream with a Polymeric Metal Organic Framework, of formula MX(B)Y.(solvent)z, wherein, M is selected from the group consisting of Ni, Cu, Co, Mg, Zn, Cd; B is a ligand selected from 4-pyridylcarboxylic acid (isonicotinic acid) or optionally substituted 4-pyridylcarboxylic acid with NH2 or OH as substituents or its derivatives;
X and Y are each integers greater than zero and selected to provide a neutral compound; and wherein, Z may be zero or greater than zero.

The IISERP-MOF shows “selective binding to carbondioxide” or “selectively binds carbondioxide” i.e., the IISERP-MOF1 preferentially binds to carbondioxide (CO2) with respect to nitrogen as measured by gas adsorption isotherms at 298 K according to methods familiar to those skilled in the art. In certain embodiments, the molar ratio of CO2 to nitrogen adsorbed is greater than 1, or greater than 2, or greater than 5 or greater than 10 or even greater than 20. For example, the ratio of carbon dioxide to nitrogen adsorbed can be between greater than 1 and 20, or between about 2 and 20, or between about 5 and 20, or between about 10 and 20. The IISERP-MOF shows “reversible binding to carbon dioxide” or “reversibly binds carbon dioxide” i.e., at least 50 wt%, or at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 99% of any adsorbed carbon dioxide is desorbed from the material when exposed to a vacuum, and also retains the ability to re-adsorb carbon dioxide after the desorption process (e.g., the IISERP-MOF can be regenerated).

In particular, the IISERP-MOFs are polymeric metal-organic frameworks that include at least one M2+ cation coordinated by 'carboxylate' and 'pyridyl' groups from the '4-pyridylcarboxylate ligand' or ‘optionally NH2 or OH substituted form of 4-pyridylcarboxylate'.

In one embodiment, the CO2-selective IISERP-MOF adsorbents can be, a IISERP-MOF, IISERP-MOF solvate, IISERP-MOF hydrate that comprises or consists essentially of, one or more M2+ cations and 4-pyridylcarboxylate unit or optionally substituted 4-pyridylcarboxylate. In particular, CO2-selective IISERP-MOF sorbents can be according to the formula, MX(B)Y.(solvent)Z, wherein M is selected from the group consisting of Ni, Cu, Co, Mg, Zn, Cd and B is a ligand selected from 4-pyridylcarboxylic acid (isonicotinic acid) or optionally substituted 4-pyridylcarboxylic acid, wherein X and Y are each integers greater than 0; and X and Y are selected to provide a neutral compound and wherein, Z may be zero or greater than zero.

In another embodiment, the invention provides MX(B)Y.(solvent)Z, that could be grown as single crystal using the solvothermal preparation procedure mentioned above. The structure of IISERP-MOFs according to the invention has been determined to molecular level precision using single crystal x-ray diffraction. The bulk purity has been ascertained by comparing the experimental powder x-ray diffraction (pxrd) with the one simulated from the single crystal x-ray diffraction, Elemental analysis, SEM etc. Further, the stabilities have been assessed from Thermogravimetric analyses, gas adsorption studies and pxrds done on sample subjected to conditions relevant to the operation conditions of the industrial gas separation processes.

Accordingly in an embodiment, the invention encompasses IISERP-MOFs which include all possible combinations of the M2+ cation with isonicotinic acid (INA) or optionally substituted isonicotinic acid that would generate ultra-microporous (4 - 6Å) pores within the framework. All these IISERP-MOFs would be synthesized via solvothermal conditions. The adsorption site has been identified as the isonicotinate ring unit acting as a moderate base, while the metal does not seem to have much role in interacting with the CO2. This has been determined via advanced GCMC computational simulations.

In a particular embodiment, the IISERP-MOFs are selected from Ni(INA)2H2O.Solvent; Zn(INA)2.DMF; Mg(INA)2.DMF/DMA and Cu(INA)Cl.DMF as shown in below table 1.

Table 1
Compound code a(Å) b(Å) c(Å) a(o) ß(o) ?(o) V(Å3) Formula
IISERP MOF-1 30.64 25.16 12.68 90 112.74 90 9021.4 Ni(INA)2H2O.THF
IISERP-MOF2 6.25 12.52 10.28 90 91.27 90 804.5 Ni(INA)2H2O.DMF

IISERP MOF-3 19.62 18.57 14.65 90 128.72 90 4161.7 Zn(INA)2.DMF
IISERP MOF-4 9.88 13.01 10.68 90 100.87 90 1348.3 Mg(INA)2.DMF/DMA
IISERP MOF-5 24.28 17.76 12.06 90 109.56 90 4901.0 Cu(INA)Cl.DMF
or a solvate or hydrate thereof, where INA is isonicotinate.

Any of the preceding IISERP-MOF can be prepared by heating a reaction mixture comprising a metal cation in 2+ oxidation state in the form of carbonate salt, M and isonicotinic acid or optionally substituted isonicotinic acid, B, and a solvent under conditions suitable for formation of a MOF, wherein M and B are defined in any of the preceding formulae or embodiments.

Suitable solvents include Methanol, Water, Ethanol and Tetrahydrofuran a combination of any of these. Solvents of the commercial grade in hydrous form (comprising significant amount of water as impurity) could be used. This could make the synthesis cost come down massively.

Suitable reaction conditions include heating the reaction mixture at a temperature between about 25°C and about 120°C for a period of time suitable to form the IISERP-MOF. For example, the reaction mixture can be heated at a temperature between about 110 °C and about 150°C, or between about 50°C and about 150°C, or between about 50 °C and about 100°C, or between about 75°C and about 100°C. As would be clear to one skilled in the art, where the reaction is heated to a temperature about the boiling point/decomposition point of the selected solvent (at standard atmospheric pressure), the reaction mixture can be placed in a sealed vessel for the duration of the heating step.

The heating at the selected temperature can continue for a period of time suitable to form the IISERP-MOF at the temperature selected. For example, heating can be for a period of time between about 1 minute and about 168 hours, such as between 1 hour and about 144 hours, or between about 1 hour and 120 hours, or between about 1 hour and 96 hours, or between about 1 hour and 72 hours, or between about 12 hours and about 72 hours, or between about 24 hours and about 72 hours. In certain examples, the heating can be for about an hour, or about 2 hours, or about 4 hours, or about 8 hours, or about 8 hours, or about 12 hours, or about 24 hours, or about 48 hours, or about 72 hours, or about 96 hours.

The IISERP-MOF will generally precipitate from the reaction mixture during the preceding reaction conditions. Upon completion of the heating step, the reaction mixture containing precipitated IISERP-MOF may optionally be cooled prior to filtering off the formed IISERP-MOF according to methods familiar to those skilled in the art. Alternatively, the IISERP-MOF may be collected by centrifugation of the reaction mixture followed by decantation of the supernatant. The resulting solid IISERP-MOF isolated by filtration or centrifugation can be optionally washed with a suitable solvent, such as, but not limited to water, acetone, methanol, ethanol, tetrahydrofuran, and mixtures thereof.

In yet another embodiment, the invention provides Carbondioxide Separation Methods using the IISERP-MOFs of the instant invention.

The carbon dioxide (CO2) separation process can be operated by simply bringing an CO2-containing fluid stream into contact with the IISERP-MOF compositions, such as in typical temperature or pressure swing adsorption processes to generate an CO2-reduced fluid stream. The term “fluid stream” includes both gas streams that comprise CO2 or liquid streams in which CO2 has been dissolved. The amount of CO2 in the fluid stream can be at extremely low partial pressures, typically in the range of 5 to 25% by composition. In certain embodiments, the fluid stream is a gas stream that comprises CO2 and nitrogen (e.g., flue gas, CO2 lean gas compositions in chemical industries). In other embodiments, the fluid stream is a gas stream that comprises predominantly nitrogen, but also a quantity of CO2 and trace quantities of water.

An “CO2-reduced fluid stream” means that the fluid stream, after contacting with a CO2-selective adsorbent described in this application (i.e., a IISERP-MOF of the invention), contains reduced CO2-content with respect to the CO2-content of the fluid stream prior to contacting the adsorbent. In certain embodiments, the carbon dioxide-reduced fluid stream contains at least 5% or 10% or 20% or 30% or 40% or 50% or 60% or 70% or 80% or 90& or 95% or 98% or 99% less CO2 with respect to the fluid stream prior to contacting the adsorbent.

Specific applications for this type of process include the separation of CO2 from gas streams containing CO2 and nitrogen, such as flue gas, and for the separation of trace amounts of CO2 from a stream. Such a process is advantageous over prior art separation processes in that liquid amines are used which irreversibly bind CO2, thereby needing energy in the form of heat for chemically captured CO2 to be recovered, and in IISERP-MOF case, the sorbent (complex) to be regenerated by heating or by reducing the CO2 partial pressure over the adduct.

In yet another embodiment, CO2-selective sorbent compositions comprising IISERP-MOF provided in accordance with the invention that may be used in both pressure swing adsorption (PSA) and temperature swing adsorption (TSA) processes for the recovery of CO2 or nitrogen or both.

In the pressure swing method, CO2-N2 or CO2-H2 gas mixtures (preferably dry) at ambient temperature (25-35oC) and at pressures ranging from 1 atm to about 10 atm is passed through a column containing a fixed bed that is packed with the above solid absorbents. CO2 is selectively absorbed by the packed bed resulting in an effluent of nearly pure nitrogen. At the end of this adsorption step the bed can be rinsed and the resulting carbondioxide rich solid in the bed can be regenerated. In this type of cycle, since CO2 is adsorbed, the bed can be rinsed with CO2, such as by using a portion of the CO2 product produced by the cycle. This may be done by lowering the pressure of the atmosphere above the absorbent bed to about ambient conditions or by partially evacuating it to sub-ambient pressures as low as 0.05 atm (e.g., vacuum swing adsorption (VSA)).

Alternatively, carbondioxide desorption may be achieved by depressurizing the bed followed by purging it with some of the product nitrogen. The PSA methods described here may be used for the large scale production of carbondioxide or nitrogen from air, but are also useful for the removal of residual low levels of carbondioxide from nitrogen, argon and other gases that are inert to the absorbents.

In the temperature-swing method an CO2-containing gas mixture, preferably a dry mixture, at about 1 atm to 10 atm is passed through the absorbent column which results, as above, in a selective adsorption of CO2. In this case however, the regeneration of the absorbent is accomplished by heating. The desorption of CO2 may be assisted by also reducing the effective partial pressure of CO2 in the atmosphere above the absorbent by depressurization, partial evacuation to 0.1 to 0.3 atm, or a Pressure swing between 1 to 10atm or by sweeping the bed with a pre-heated stream of some of the inert gas product. The latter is essentially a combined PSA/TSA process.

Specific examples of PSA and VSA processes have been well described in the art (Ref 1. Minh T. Ho, Guy W. Allinson, and Dianne E. Wiley, Reducing the cost of CO2 capture from flue gases using pressure swing adsorption, Industrial & Engineering Chemistry Research 47 (2008), 4883; Ref 2. Zhixiong Zhang, Jianyu Guan, Zhenhua Ye, Ref 3. Separation of a Nitrogen-Carbon Dioxide Mixture by Rapid Pressure Swing Adsorption, Adsorption 1998, Volume 4, 173; Ref 4. Jan Andre Wurzbacher, Christoph Gebald and Aldo Steinfeld, Separation of CO2 from air by temperature-vacuum swing adsorption using diamine-functionalized silica gel, Energy Environ. Sci., 2011,4, 3584-3592; Ref 5. Concurrent Separation of CO2 and H2O from Air by a Temperature-Vacuum Swing Adsorption/Desorption Cycle, Ref 6. Jan Andre Wurzbacher, Christoph Gebald, Nicolas Piatkowski, and Aldo Steinfeld, Environ. Sci. Technol., 2012, 46 (16), pp 9191–9198).

In all of these processes the absorbent is in the solid state and can be used in various forms such as powders, as single crystals, as pellets, as a slurry, or any other suitable form for the particular application.

While specific embodiments have been described in detail, those with ordinary skill in the art will appreciate that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims, and any and all equivalents thereof. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. All references mentioned herein, including publications, patent applications, and patents, are incorporated by reference in their entirety. In addition, the materials, methods, and examples herein are only illustrative and not intended to be limiting.

EXAMPLES
Example 1
Synthesis of NiMOF1 (Ni(4-PyC)2)(Solvents)x, form 1, solvents = H2O, DMF, THF)
Synthesis of NiMOF1 (Ni(4-PyC)2)(THF):
In a typical synthesis, a solvothermal reaction between Nickel carbonate (0.119g; 1mmol), Pyridine -4-carboxylic acid (0.244g; 2mmol) in a solution containing 1.5ml THF+2.5ml water +2ml MeOH at 150oC for 72hrs. From this green colored polycrystalline product was isolated by filtration and was washed with plenty of water and methanol. The air dried sample gave a yield of ~85% (based on Ni). The PXRD pattern indicated this to be a pure phase of NiMOF1. We have also prepared 10gms of this sample with an easy scale-up procedure. CHN analysis (calculated values within brackets: C: 43.45 (43.2210); H: 3.62 (4.7039); N: 7.02 (7.0880)%.

Example 2 Characterization of NiMOF1 (IISERP-MOF1)
Powder X-ray diffraction pattern of NiMOF1 indicated the presence of a pure phase. See Figure 1. An analysis using SQUEEZE reveals significant potential voids calculated at 45%. From the TGA of the as-made sample, the loss of the terminal water and the bridging water could not be resolved; hence a better resolved TGA was obtained by carrying out TGA on a freshly solvent exchanged sample (Figure 2). All the volatiles and free solvent molecules are removed below 100oC, while most of the coordinated water comes off at 180oC, however some of the water molecules (µ-2 bridging water molecules) (obsd: ~2.0%) do not leave the structure even at 200oC, which is quite unusual. It is highly likely that these are the bridging water molecules (calcd: 2.05%) that are crucial for holding the framework together. The loss of the µ-2 bridging water moieties triggers the collapse of the structure.
Single crystal structure of NiMOF1
The structure of NiMOF1 is built up from corner-sharing nickel dimers and isolated octahedral nickel centers. There are two such nickel dimers, one built up from Ni(2) and Ni(3) atoms and has seven 4-PyC, one µ-2 bridging water and a terminal water coordinated to them. Another cyrstallographically independent dimer made up of Ni(4) atoms has eight 4-PyC ligands, a bridging water coordinated to it. These µ-2 water bridged Ni dimers form the building unit of NiMOF1 which are markedly different from the hydroxo bridged Ni clusters reported in the literature (Figure 3) and could account for some of the hydrolytic stability of NiMOF1. If the dimers are reduced to a node and the PyC moieties to linear linkers, the structure is a six-connected cubic network. This three-dimensional framework consists of two types of channels and a cage system (Figure 4). Of the two channels, one is one-dimensionally aligned along the c-axis (~6.9 x 6.9Å, none of the dimensions factor the vander Waal radii). The other channel exhibits two-dimensional accessibility along both a- and c- axes (7.5 x 9Å), and four such channels surround the former one-dimensional channel. The access to the one-dimensional channels from the a- and b-axes is blocked by the cages in the structure which are made up of the same nickel dimers which line the one-dimensional channels. These dimers are arranged into a square and are capped by two isolated nickel octahedra on either side to generate the cage (15 x 12 x 9Å). The negative contribution of the cages to the porosity of the structure is elaborated in the Supp info. In effect, the channel system in NiMOF1 is constituted by alternating 2-D and the 1-D channels stacked along the b-axis ((Figure 4). They are lined by carboxylate groups and bridging water molecules imparting a polar character.
The N2 adsorption isotherm at 77 K is given in Figure 5 and yields a BET surface area of 945 m2/g. Despite the modest surface area, 195K uptake is notably higher than that of most other ultra-microporous MOFs. Figure 5 depicts the CO2 adsorption isotherms over a range of temperatures with a total uptake of 11mmol/g, 5.5mmol/g and 3.6mmol/g at 195K, 273K and 303K at 1bar, respectively. The DFT model of the 195K CO2 adsorption branch indicated a bimodal pore distribution in the ultra-microporous regime (3.5 and 4.8Å, Figure 6).

The CO2 heat of adsorption in NiMOF1 were determined via both virial fits and a DFT model using isotherms collected at -25oC, -10oC, 0oC, +10oC and +30oC. The virial fit presented in Figure 2C shows that NiMOF1 has the zero-loading HOA value of 34 kJ/mol and this falls down to a value of 26 at ~2 mmol/g loading and settles down at a moderate 28 kJ/mol at higher loadings. Both the models showed a similar trend (Figure 7). The material shows excellent selectivities for CO2 over N2. At 1 bar, NiMOF1 practically does not adsorb any N2, and under the PSA condition considered here (1-10bar) it has selectivity S(CO2-N2):71(Table S5). In fact, it out performs many of the other reported materials such as Mg(DOBDC), BioMOF-12, ZIF-78, bio-MOF-11, en-Cu-BTTri, Cu-TDPAT, all at 298K and 1 bar. The fit for the 195 K data shows high selectivity (170-60) at low pressure region (0.025-0.165 bar). The CO2-N2 selectivity calculated using 248K and 273K data have a different profile (Figure 8) which can be explained by considering the early filling of the ultra-micropores by CO2 in the adsorption run and at higher temperatures significantly less nitrogen is adsorbed giving a much higher selectivity of 50-63 with little change across the temperatures investigated.

The working capacity, a measure of how much CO2 can be removed from a gas mixture by a sorbent over a given pressure or temperature or vacuum swing. If a pressure swing was carried out between a total pressure of 10bar and 1bar for a mixture of composition 15CO2:85N2, it can be seen that at 298K the working capacity is predicted to be 4.1mmol/g, with a selectivity of 71 (Figure 9). This compares very favorably to other compounds that have similar heats of adsorption for CO2 for instance HKUST-1: [WC(CO2-N2)1.6; ?H: 26kJ mol-1], Zn-MOF-74 [WC: 2.7; ?H: 30kJ mol-1], PCN-11 [WC: 1.4; ?H: 3kJ mol-1] (Table S1). The working capacity is even comparable to the touted Mg-MOF-74[WC(CO2-N2): 4.1; ?H: 45kJ mol-1] that possesses a significantly higher HOA and is not moisture stable, making it less attractive for adsorption processes. To the best of our knowledge NiMOF1 has the highest reported high-pressure CO2 uptake capacity for an ultra-microporous MOF.

Example 3
In addition, IISERP-MOF1 could be scaled-up to 10gm with ease and the product showed comparable crystallinity and similar gas sorption characteristics (Figure 10).

Example 4
Hydrogen Purification by IISERP-MOF1 (NiMOF1)
To more thoroughly explore the potential of IISERP-MOF1 for pre-combustion CO2 capture, binary mixtures of CO2 and H2 were simulated at 313 from 1-40 bar at two relevant gas compositions - 80H2:20CO2 and 60H2:40CO2 (Figure 11). Figures 12A and 12B compare the simulated PSA working capacities of IISERP-MOF1 (using a desorption pressure of 1 bar) to the working capacities of the recently reported industrial benchmarks zeolite 13X and activated carbon JX101, and two of the top performing MOFs identified for this application, MgMOF-74 and CuBTTri. A similar comparison of the CO2/H2 selectivities is given in Figures 12C and 12D at the two H2/CO2 ratios. At low CO2 concentrations (80% H2, 20% CO2), IISERP-MOF1 has the largest working capacity up to an adsorption pressure of 15 bar, but remains amongst the top performers in this respect throughout the pressure range. Only the MOF CuBTTri has a significantly higher working capacity at pressures greater than 25 bar. However, CuBTTri has a very poor H2/CO2 selectivity, the lowest of all the materials compared, making it unsuitable for practical use. At higher CO2 concentrations (60% H2, 40% CO2), the working capacity of IISERP-MOF1 is less competitive. Nonetheless, when compared to zeolite 13X, which is used industrially for PSA based CO2 scrubbing of natural gas, IISERP-MOF1 has an almost identical selectivity but roughly double the working capacity throughout the pressure range. Compared to the high performance activated carbon JX101, Ni Pyridine carboxylate has a higher working capacity for the 80:20 gas mixture, and a comparable working capacity for the 60:40 gas mixture throughout the whole pressure range. However, IISERP-MOF1 has a CO2/H2 selectivity that is at least 2.5 times better than JX101 for both gas compositions. Figure 12 shows that MgMOF-74 has one of the highest working capacities at all pressures and both gas compositions. Moreover, in all cases it also has the highest CO2/H2 selectivity, outperforming IISERP-MOF1 by at least 50% in this respect. Despite the favorable adsorption properties, MgMOF-74 is not hydrolytically stable due to the presence of open metal sites, which limits its practical use.

Example 5
Stability studies
Mentioned in this section are some of the important requirements for any MOF when it comes to its potential industrial application. These ultra and microporous MOFs are quite interesting owing to their good stability to solvent removal as compare to the large pore MOFs which in many cases require highly demanding moisture free handling and in spite of that tend to show partial to complete loss of long range order. IISER-MOF1 has excellent shelf-life and they retain complete porosity even after 6 months. Additionally, the hydrolytic stability of the material was confirmed by exposing the material to steam for over 7 days ((Figure 13). IISERP-MOF1 loses < 5% porosity after 2 days (calculated from 77K N2 and 195K CO2 isotherms) and no further loss was observed even after 7 days. Many MOFs have been reported to lose substantial amount of their porosity due to amorphization at high pressures. When IISERP-MOF1 was subjected to ~70bar (0.5 tons) for about 24hrs and they did not show any amorphization as evidenced from the PXRD and gas adsorption (Figure 14).

Example 6
Synthesis of [Ni-(4Pyc)2.DMF] ( IISER-MOF2)
In a typical synthesis, a solvothermal reaction was carried out by mixing Nickel acetate tetrahydrate (0.25g; 1mmol), Pyridine -4-carboxylic acid (0.244g; 2mmol) and triethylamine (40µl) into a solution containing 5ml DMF+4ml CH3CN at 150oC for 72hrs. From this green colored polycrystalline product was isolated by filtration and was washed with plenty of water and methanol. The air dried sample gave a yield of ~80% (based on Ni). The PXRD pattern indicated this to be a pure phase of NiMOF2. We have also prepared 10gms of this sample with an easy scale-up procedure.

Example 7
Structure of NiMOF2 (IISERP-MOF2)
The structure of the material is built-up from octahedrally coordinated Ni centres of which 4 coordinations come from two different carboxylate group and two from pyridyl nitrogen. When the carboxylates are reduced to a singly connecting linker it can be seen that the effective coordination around each Ni center is tetrahedral. These tetrahedral Ni nodes connect with each other to form an adamantane type unit. The periodic extension of this adamantane units results in the 3D framework with a highly symmetrical cubic topology (Figure 15). Thus overall structure is a three dimensional cubic net having well defined 3D channels along a-axis (7.01 X 7.01 Å , not factoring the van der Waals radii), [1 1 0], [0 1 1] and [1 0 1] directions. The channels are occupied by DMF molecules in the as-synthesized form. It is remarkable that such a porous net is still non-interpenetrated and this can totally be attributed to the small size of the linking struts, PyC or isonicotinate. The 3D ultra-microporous channel system present herein is key to the high capacity and simultaneous selectivity exhibited by this material, and this requires the presence of these tetrahedral nodes (Ni centers) and the small linker (PyC). Very few linkers could be able to satisfy all these design requirements and we identify PyC as being one of the cheap and best for this purpose.

Example 8
Characterization of NiMOF2 (IISERP-MOF2)
The purity of the bulk material was confirmed by PXRD (Figure 16). Most importantly it was found that the material can be made as a highly pure phase in 25g scale via a mere scaling up of the involved reaction components, which is very important from an industrial application point of view. Further, the thermal stability of the material was confirmed from Thermo gravimetric Analysis (TGA). It was found that material has no weight loss up to 130ºC and from 130ºC to 280ºc there is a gradual weight loss of 20% which is due to DMF molecules trapped inside the pore (Figure 17). From the TGA it is clear the material is thermally stable up to 280ºC. For gas adsorption studies material can be activated at 180ºC under vacuum for 36hrs. Otherwise the material can be activated by soaking it in mixture of low boiling solvents (e.g. DCM, MeOH, Acetone) for 4 days with replenishing the solvent in every 12 hrs, followed by evacuation at lower temperature. The formula was evaluated to be Ni(C6NH4O2)2.(C3H7NO), M. Wt. 375.99 g/mol, which is consistent with the composition evaluated from the single crystal x-ray determined structure.

The gas adsorption studies reveals that material can take up to 7.5 mmol/g of N2 at 77K temperature. The 77 K N2 Isotherm yielded a BET surface area of 467 m2/g and a Langmuir surface area of 695 m2/g.(Figure 18). Interestingly the material shows very good uptake of CO2 at ambient condition (4.17 mmol/g @ 303K and 1bar) but there was hardly any uptake of N2 at ambient condition. This makes the material an excellent CO2 sorbent with exceptional selectivity over N2. The saturation capacity of the material was confirmed by low temperature (195K) CO2 isotherm to be 7.35 mmol/g.(Figure 19)
The pore size distribution was determined from a NLDFT model using CO2 isotherm at 273K. Although there was two different pore size (4.75 and 5.6 Å) the majority of the pore size was 4.75Å. This confirms the ultra-microporous structure of the framework (Figure 20). For the large scale synthesis of the material, the bulk purity was confirmed from the PXRD analysis as well as from gas adsorption isotherm. A comparison of the 273K CO2 isotherms confirms the consistency in porosity between the preparations(Figure 21)
To evaluate the Heat of Adsorption (HOA) of the material, we have carried out variable temperature CO2 isotherm in the range of 303K to 248K. The HOA of the material (36 KJ/mol) was found to be less than 40 KJ/mol which is critical for regeneration of the adsorbed CO2.(Figure 22) Also, the CO2:N2 selectivity was calculated at 303K and 273k using the IAST model. For a typical flue gas composition (15% CO2:85% N2) the material exhibits a selectivity of 185 and 145 at 303 and 273K respectively. (Figure 23). Figure 24 shows the materials stability to steam and boiling water, which are relevant conditions when it comes to flue gas separations.

To evaluate the material’s performance in terms of selectivity for CO2 from flue gas mixture using PSA process we have simulated the Pure and Binary component isotherm using Grand Canonical Monte Carlo (GCMC) simulation. From the binary component isotherm it is clear that the material is highly selective to CO2 over N2 even at 10 bar pressure (Figure 25).

The working capacity of the material is also evaluated from binary component isotherm for a pressure swing of 2bar to 0.15 bar. The working capacity of the material was found to be 2.27 mmol/g, which is quiet high for such an ultra-micro porous material. It would be expected that such an ultra micro porous material will have restricted kinetics of CO2. Fitting the experimental rate of adsorption data to a spherical pore model we obtained an average CO2 self diffusion coefficient of 7.2141X 10-09 m2/s, which is at least 2 order higher than Zeolite-13X (current industrial standard) and is comparable to some of the high performing MOFs.

Thus the Ni Pyridine carboxylate based ultra-micro porous Metal Organic framework [Ni-(4Pyc)2.DMF], IISER-MOF2, has demonstrated its high working capacity as a solid sorbent for CO2/N2 separation from flue gas compositions (15CO2: 85N2). The material is highly stable to steam, boiling water and has very good shelf-life.

Without being limited by theory, it is further believed that the incorporated amino or hydroxyl groups in NiMOF1 or Ni MOF2 can increase the polarizing character of the pore, which may have implications in gas uptake and selectivity.

Summary
IISERP-MOF1,and IISERP-MOF2 serve as excellent prototypes for demonstrating how an ultra-microporous MOF built from a small and readily available ligand, can have highly favorable adsorption/desorption characteristics for gas separation processes, despite having pores <6Å in size and a modest surface area (945 and 470m2/g, respectively). IISERP-MOF1 has working capacities for PSA based separation from post and pre-combustion CO2 gas mixtures that are competitive with the best known MOFs for that application. Simulations of the CO2 adsorption in IISERP-MOF1, suggest that strong cooperative guest-guest interactions, in part, allow for the exceptional 8.2mmol/g CO2 uptake capacity of IISERP-MOF1 at 10bar, 298K. Meanwhile, IISERP-MOF2 also has good working capacities for CO2/N2 separation from post-combustion mixtures and in fact, poses a better performance in terms of parasitic energy compared to IISERP-MOF1 and many other compounds in the literature. In addition to possessing favorable gas adsorption properties, IISERP-MOF1 and IISERP-MOF2 also exhibits excellent stability and recyclability – properties that are critical for practical operation in gas separation processes. Following 160 hours of steam treatment and 24 hours of exposure to 70 bar pressure, IISERP-MOF1 and IISERP-MOF2 structure remains unchanged. Moreover, IISERP-MOF1 and IISERP-MOF2 retains its CO2 adsorption properties following exposure to steam. The simple, single ligand synthesis and isolation to the gram scale suggests that potential industrial-level scale ups should also be straight forward. With all these features and considering IISER-MOF1 and IISERP-MOF2 are built from inexpensive and readily available components, they form attractive candidates for a variety of gas separation and purification applications. ,CLAIMS:1. Ultra-microporous metal organic frameworks of formula MX(B)Y.(solvent)Z,
wherein, M is selected from the group consisting of Ni, Cu, Co, Mg, Zn, Cd;
B is a ligand selected from 4-pyridylcarboxylic acid or optionally substituted 4-pyridylcarboxylic acid (isonicotinic acid) or its derivatives; and
X and Y are each integers greater than zero and selected to provide a neutral compound; and wherein, Z may be zero or greater than zero.
2. The ultramicroporous metal organic frameworks according to claim1, wherein, the solvent is selected from water, methanol, ethanol, isopropanol, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, tetrahydrofuran, acetonitrile, toluene, benzene, chloroform, dichloromethane and mixtures thereof.
3. The ultramicroporous metal organic frameworks according to claim 1, wherein, the substituted form of 4-pyridylcarboxylate is substituted either with -NH2 or -OH.
4. The ultramicroporous metal organic frameworks according to claim 1, wherein, the MX(B)Y.(solvent)z comprise at least one M2+ cation coordinated by 'carboxylate' and 'pyridyl' groups from the '4-pyridylcarboxylate ligand' or optionally ‘NH2 or OH substituted form of 4-pyridylcarboxylate' and terminal bridging solvent molecules.
5. The ultramicroporous metal organic frameworks according to any one of the preceding claims 1 to 4, for use in selective adsorption of CO2 for its separation and recovery from fluid mixtures, such as N2-CO2 or O2-CO2 or CH4-CO2 or H2-CO2 etc.
6. A method for preparing MX(B)Y.(solvent)z, comprising heating a reaction mixture comprising M2+ salts, 4-pyridylcarboxylic acid or optionally substituted 4-pyridylcarboxylic acid (isonicotinic acid) or its derivatives and solvents under solvothermal conditions suitable for formation of the Mx(B)y.(solvent)z, wherein, M is selected from the group consisting of Ni, Cu, Co, Mg, Zn, Cd; B is a ligand selected from 4-pyridylcarboxylic acid or optionally substituted 4-pyridylcarboxylic acid (isonicotinic acid) or its derivatives; X and Y are each integers greater than zero and selected to provide a neutral compound; and wherein, Z may be zero or greater than zero.
7. A method for removing CO2 from a fluid stream consisting of CO2 and at least one other component particularly at low partial pressures, relevant to flue gas conditions, which method comprises bringing an CO2-containing fluid stream into contact with a composition comprising of formula MX(B)Y.(solvent)z, wherein, M is selected from the group consisting of Ni, Cu, Co, Mg, Zn, Cd; B is a ligand selected from 4-pyridylcarboxylic acid or optionally substituted 4-pyridylcarboxylic acid (isonicotinic acid) with -NH2 or -OH or its derivatives; X and Y are each integers greater than zero and selected to provide a neutral compound; and wherein, Z may be zero or greater than zero;
to obtain the sorbent complex and thereby obtaining CO2 reduced stream.
8. The method for removing CO2 from a fluid stream according to claim 7, wherein the “fluid stream” includes gas streams that comprise CO2 or liquid streams in which CO2 has been dissolved.
9. The method for removing CO2 from a fluid stream according to claim 7 further comprise recovering the CO2 from the sorbent complex by heating or by reducing the CO2 partial pressure over the sorbent complex.
10. CO2-selective sorbent compositions comprising Ultra-microporous metal organic frameworks of formula MX(B)Y.(solvent)Z, wherein, M is selected from the group consisting of Ni, Cu, Co, Mg, Zn, Cd;
B is a ligand selected from 4-pyridylcarboxylic acid or optionally substituted 4-pyridylcarboxylic acid (isonicotinic acid) or its derivatives; and
X and Y are each integers greater than zero and selected to provide a neutral compound; and wherein, Z may be zero or greater than zero.
11. A method for removing CO2 from a fluid stream consisting of CO2 and at least one other component particularly at high pressures (1-35bar), represented by a composition of 20%CO2:80%H2 and 40%CO2:60%H2, relevant to pre-combustion gas mixtures, which method comprises bringing an CO2-containing fluid stream into contact with a composition comprising of formula MX(B)Y.(solvent)z, wherein, M is selected from the group consisting of Ni, Cu, Co, Mg, Zn, Cd; B is a ligand selected from 4-pyridylcarboxylic acid or optionally substituted 4-pyridylcarboxylic acid (isonicotinic acid) with -NH2 or -OH or its derivatives; X and Y are each integers greater than zero and selected to provide a neutral compound; and wherein, Z may be zero or greater than zero;
to obtain the sorbent complex and thereby obtaining CO2 reduced stream.
12. The CO2-selective sorbent compositions according to claim 10, for use in pressure swing adsorption (PSA) and temperature swing adsorption (TSA) processes for the recovery of CO2 or nitrogen or both.
13. The CO2-selective sorbent compositions according to claim 11, for use in pressure swing adsorption (PSA) and temperature swing adsorption (TSA) processes for the recovery of CO2 or hydrogen or both.