Zeolitic imidazolate framework materials, their synthesis and use

Abstract

A novel zeolitic imidazolate framework material comprises a partially saturated benzimidazole or a partially saturated substituted benzimidazole as a linking ligand, optionally together with unsaturated benzimidazole or an unsaturated substituted benzimidazole as a further linking ligand.

Claims

1. A zeolitic imidazolate framework material comprising zinc and 4,5,6,7-tetrahydrobenzimidazole.

2. The framework material of claim 1, further comprising benzimidazole or 5-azabenzimidazole.

3. The framework material of claim 2, further comprising from 0 mol % to 99 mol % of benzimidazole or 5-azabenzimidazole, based on the total amount of benzimidazole or 5-azabenzimidazole and 4,5,6,7-tetrahydrobenzimidazole or 4,5,6,7-tetrahydro-3H-imidazo[4,5-c]pyridine in the material.

4. The framework material of claim 1, further comprising an unsaturated benzimidazole or an unsaturated substituted benzimidazole as a linking ligand.

5. The framework material of claim 1, further comprising one or more divalent transition metal ions.

6. The framework material of claim 1, further comprising one or more zinc ions or one or more cobalt ions.

7. The framework material of claim 1, further comprising a 1:1 mixture of lithium and boron ions.

8. The framework material of claim 1, wherein said framework material exhibits the SOD framework type.

9. The framework material of claim 1, wherein said framework material exhibits the RHO framework type.

10. A zeolitic imidazolate framework material comprising zinc and 4,5,6,7-tetrahydro-3H-imidazo[4,5-c]pyridine.

11. The framework material of claim 10, further comprising benzimidazole or 5-azabenzimidazole.

12. The framework material of claim 11, further comprising from 0 mol % to 99 mol % of benzimidazole or 5-azabenzimidazole, based on the total amount of benzimidazole or 5-azabenzimidazole and 4,5,6,7-tetrahydrobenzimidazole or 4,5,6,7-tetrahydro-3H-imidazo[4,5-c]pyridine in the material.

13. A method of making a zeolitic imidazolate framework material comprising the step of reacting a mixture of a source of a partially saturated benzimidazole or a source of a partially saturated substituted benzimidazole with a source of zinc in the presence of a solvent at a temperature sufficient to form the zeolitic imidazolate framework material.

14. The method of claim 13 in which the temperature is at least 20 C.

15. The method of claim 13 in which the partially saturated benzimidazole comprises 4,5,6,7-tetrahydrobenzimidazole.

16. The method of claim 13 in which the partially saturated substituted benzimidazole comprises 4,5,6,7-tetrahydro-3H-imidazo[4,5-c]pyridine.

17. The method of claim 13, wherein the source of zinc comprises zinc acetate.

18. The method of claim 13, wherein the mixture further comprises an unsaturated benzimidazole or an unsaturated substituted benzimidazole.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 compares the X-ray diffraction patterns of the EMM-36-100 material of Example 1 measured at 200 C. and 30 C. and conducted in vacuum (<10.sup.3 mbar), nitrogen (1 bar), and carbon dioxide (1 bar).

(2) FIG. 2 shows the results of CO.sub.2 adsorption isotherms conducted on the EMM-36-100 material of Example 1 at 0 C., 30 C., and 60 C.

(3) FIG. 3 shows scanning electron micrographs of EMM-36-100 synthesized at 60 C. and 20 C.

(4) FIG. 4 is a graph of the compositional analysis of EMM-36-## (## representing the mol % of 4H-BIM) performed by liquid-phase NMR against the mol % of 4,5,6,7-tetrahydrobenzimidazole added to the synthesis mixture of Example 2.

(5) FIG. 5 shows CO.sub.2 adsorption isotherms conducted at 30 C. on EMM-19 and various EMM-36-## materials produced according to Example 2.

(6) FIG. 6 shows CH.sub.4 adsorption isotherms conducted at 30 C. on ZIF-7 and various EMM-36-## materials produced according to Examples 1 and 2.

(7) FIG. 7 shows C.sub.2H.sub.4 adsorption isotherms conducted at 30 C. on ZIF-7 and various EMM-36-## materials produced according to Examples 1 and 2.

(8) FIG. 8 shows a scanning electron micrograph (SEM) of the EMM-38-100 material of Example 3.

(9) FIG. 9 shows a scanning electron micrograph (SEM) of the EMM-38-25 material of Example 3.

(10) FIG. 10 shows powder X-ray diffraction patterns of EMM-38-## materials of Example 3 with varying loadings of 4,5,6,7-tetrahydrobenzimidazole.

(11) FIG. 11 shows N.sub.2 adsorption isotherms conducted at 77 K on various EMM-38-## materials produced according to Example 3.

(12) FIG. 12 shows ethane adsorption isotherms conducted at 30 C. on various EMM-38-## materials produced according to Example 3.

(13) FIG. 13 shows a scanning electron micrograph (SEM) of the EMM-38-100-N material of Example 4.

(14) FIG. 14 shows a powder X-ray diffraction pattern of the EMM-38-100-N material of Example 4.

(15) FIG. 15 shows CO.sub.2 adsorption and desorption isotherms conducted at 30 C. on the EMM-38-100-N material of Example 4.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(16) Disclosed herein are certain novel zeolitic imidazolate framework (ZIF) compositions comprising a partially saturated benzimidazole or a partially saturated substituted benzimidazole as a linking ligand, optionally in combination with unsaturated benzimidazole or an unsaturated substituted benzimidazole as a further linking ligand. Also disclosed are methods of producing these novel ZIF materials with different controlled levels of partially saturated benzimidazole or partially saturated substituted benzimidazole in the structure and methods of using the resultant ZIF materials in adsorption of gases, such as methane.

(17) As used herein, the terms unsaturated benzimidazole, benzimidazole or simply BIM are used interchangeably to mean the heterocyclic aromatic compound, C.sub.7H.sub.6N.sub.2, (see formula I) which has unsaturation and a single hydrogen atom at each of the 4, 5, 6 and 7 positions of the benzene ring.

(18) ##STR00001##

(19) As used herein, the term partially saturated benzimidazole means a heterocyclic compound comprising benzimidazole, in which the unsaturation at some or all of the 4, 5, 6 and 7 positions on the benzene ring is replaced with additional hydrogen atoms. One example of a partially saturated benzimidazole comprises 4,5,6,7-tetrahydrobenzimidazole or, in some cases, abbreviated herein to 4H-BIM (see formula II).

(20) ##STR00002##

(21) As used herein, the term unsaturated substituted benzimidazole means a heterocyclic compound comprising benzimidazole which has unsaturation and at each of the 4, 5, 6 and 7 positions on the benzene ring and one or more of the carbon atoms at the 4, 5, 6, and 7 positions has been replaced with a heteroatom including, but not limited to, nitrogen, oxygen or sulfur. One example of an unsaturated substituted benzimidazole comprises 5-azabenzimidazole (see formula III).

(22) ##STR00003##

(23) As used herein, the term partially saturated substituted benzimidazole means a heterocyclic compound comprising benzimidazole, in which the unsaturation at some or all of the 4, 5, 6 and 7 positions on the benzene ring is replaced with additional hydrogen atoms and one or more of the carbon atoms at the 4, 5, 6, and 7 positions has been replaced with a heteroatom including, but not limited to, nitrogen, oxygen or sulfur. One example of a partially saturated substituted benzimidazole comprises 4,5,6,7-tetrahydro-3H-imidazo[4,5-c]pyridine, abbreviated herein to 4H-IMP (see formula IV).

(24) ##STR00004##

(25) In some embodiments, where the linking ligand comprises 4,5,6,7-tetrahydrobenzimidazole (4H-BIM) or 4,5,6,7-tetrahydro-3H-imidazo[4,5-c]pyridine, optionally in a mixed ligand system also comprising benzimidazole or 5-azabenzimidazole, the ZIF synthesis is conducted in the presence of a solvent. In this case, a novel ZIF material is produced which is designated herein as EMM-36, or more specifically as EMM-36-##, where ## refers to the mol % of 4H-BIM or 4H-IMP of the total organic linkers in the final material. EMM-36-## has the SOD framework type and is closely structurally related to ZIF-7. EMM-36-100 (where 4H-BIM or 4H-IMP is the only organic linker in the structure) is isostructural with the large pore phase of ZIF-7 and is found to exhibit the unique propertyfor a porous materialof having essentially no nitrogen adsorption at 77 K while adsorbing CO.sub.2 at room temperature. Surprisingly and unlike the nearly isostructural ZIF-7 (formed from benzimidazole as the only organic linker), EMM-36-100 does not exhibit phase change behavior at room temperature. This property and the adsorption behavior of other EMM-36-## materials are examined further in the Examples.

(26) EMM-36 has an X-ray diffraction pattern similar to that of ZIF-7 and includes the characteristic lines listed in Table 1 below:

(27) TABLE-US-00001 TABLE 1 Interplanar Relative Intensity d-Spacing () Two-theta (100 I/Io) 12.313 7.173 88.3 11.8097 7.480 100 8.4946 10.406 33.1 7.2150 12.257 21.3 6.7984 13.012 20.3 6.1556 14.377 24.9 5.8850 15.042 63 5.4460 16.263 44.8 4.8362 18.330 17 4.6996 18.868 9.1 4.5617 19.443 23.3 4.2544 20.863 10.8 4.0936 21.692 2.3 3.9243 22.640 6.0

(28) In other embodiments, where the linking ligand comprises 4,5,6,7-tetrahydrobenzimidazole (4H-BIM) or 4,5,6,7-tetrahydro-3H-imidazo[4,5-c]pyridine (4H-IMP), optionally in a mixed ligand system also comprising benzimidazole or 5-azabenzimidazole, the ZIF synthesis is conducted in the presence of toluene as a structure directing agent. In this case, a further novel ZIF material is produced which is designated herein as EMM-38-##, where ## refers to the mol % of 4H-BIM or 4H-IMP of the total organic linkers in the final material. EMM-38-## has the RHO framework type and is closely structurally related to ZIF-11.

(29) EMM-38 has an X-ray diffraction pattern similar to that of ZIF-11 and includes the characteristic lines listed in Table 2 below:

(30) TABLE-US-00002 TABLE 2 Interplanar Relative Intensity d-Spacing () Two-theta (100 I/Io) 20.7068 4.264 100 14.5293 6.078 11.3 11.9230 7.408 18.3 10.3385 8.546 1.3 9.1399 9.669 2.7 8.0393 10.997 0.9 7.3000 12.114 5.3 6.9025 12.815 4.4 6.4519 13.714 4.5 5.9164 14.962 3.7 5.6570 15.652 10.4 5.2891 16.748 7.9 5.0890 17.412 3.6 4.8038 18.455 7.6

(31) All X-ray diffraction data reported herein were collected with a Panalytical XPert Pro diffraction system with an Xcelerator multichannel detector, equipped with a germanium solid state detector, using copper K-alpha radiation. The diffraction data were recorded by step-scanning at 0.02 degrees of two-theta, where theta is the Bragg angle, and using an effective counting time of 2 seconds for each step. The interplanar spacings, d-spacings, were calculated in Angstrom units, and the relative intensities of the lines, I/I.sub.0 is the ratio of the peak intensity to that of the intensity of the strongest line, above background. The intensities are uncorrected for Lorentz and polarization effects. The relative intensities are given in terms of the symbols vs=very strong (75-100), s=strong 50-74), m=medium (25-49) and w=weak (0-24).

(32) In addition to the linking ligands described above the novel ZIF materials disclosed herein comprise one or more metal ions. Suitable metal ions may include one or more divalent transition metals. Suitable metal ions may include one or more zinc ions, one or more cobalt ions and a 1:1 mixture of lithium and boron ions. Zn.sup.2+ ions are preferred. Further it is to be appreciated that, although the linking ligands are described herein as imidazole compounds, this is only for simplicity and in the final ZIF materials these compounds will be present as deprotonated, negatively-charged imidazolate species.

(33) In one embodiment, the ZIF materials disclosed herein may be prepared by dissolving a source of desired metal ion(s), such as zinc acetate, and sources of the desired linking ligands in an appropriate solvent to form a reaction mixture and then maintaining this reaction mixture under conditions sufficient to form the crystalline ZIF materials as a precipitate.

(34) In another embodiment, it will be appreciated from the preceding discussion that the selection of the solvent may dictate the structure of the ZIF produced. Thus, suitable solvents include alcohols, such as methanol and ethanol, in which case the ZIF produced may be of the SOD framework type. Alternately, where the solvent includes toluene, optionally together with methanol and/or ethanol, the ZIF produced may be of the RHO framework type.

(35) In yet a further embodiment, techniques such as liquid-assisted grinding or mechanochemical techniques could be utilized to synthesize the disclosed ZIF materials.

(36) The novel ZIF materials disclosed herein may have selectivity for adsorbing a variety of elements and compounds from fluids containing the same. Examples of such elements and compounds comprise hydrogen, nitrogen, oxygen, noble gases, carbon monoxide, carbon dioxide, sulfur dioxide, sulfur trioxide, hydrogen sulfide, ammonia, methane, higher carbon number hydrocarbons, alcohols, amines and mixtures thereof. Examples of hydrocarbons include alkanes, such as ethane, propane, butane, pentane, hexane and octane, and alkenes, such as ethene, propene, butene, hexene and octene. Examples of alcohols include methanol, ethanol, propanol and butanol (e.g., isobutanol, n-butanol, tert-butanol, 2-methyl-1-butanol, 3-methyl-2-butanol, etc.). Examples of amines include methylamine, ethylamine, propylamine and butylamines.

(37) The invention will now be more particularly described with reference to the following non-limiting Examples and the accompanying drawings.

Example 1: Synthesis of EMM-36-100

(38) 100 mg of 4,5,6,7-tetrahydrobenzimidazole was dissolved in 10 mL of ethanol and 0.1 mL of NH.sub.4OH (conc.) was added to the solution. To this solution, 0.1 g of Zn(OAc).sub.2 was added and the reaction mixture stirred at room temperature (25 C.) for 16 hours. The product was isolated by filtration, washed with ethanol and dried at 90 C. under air.

(39) FIG. 1 shows X-ray diffraction patterns of the resultant EMM-36-100 measured at 200 C. and 30 C. conducted in vacuum (<10.sup.3 mbar, bottom), nitrogen (1 bar, middle), and carbon dioxide (1 bar, top). The results are consistent with the large pore phase of the SOD framework structure under all conditions, suggesting there is no phase change over the whole range of conditions tested.

(40) FIG. 2 shows the results of CO.sub.2 adsorption isotherms conducted on the EMM-36-100 material at 0 C., 30 C., and 60 C. and demonstrates that the material has a Type I isotherm for all temperatures ranging from 20 to 60 C. FIG. 3 shows SEM micrographs of EMM-36-100 synthesized at 20 C. and 60 C. It can be seen that elevating the synthesis temperature results in larger particles with an increase in crystallite size.

Example 2: Synthesis of EMM-36-##

(41) The process of Example 1 was repeated but with a series of mixtures of benzimidazole (BIM) with varying quantities from 1 to 99 mol % of 4,5,6,7-tetrahydrobenzimidazole (4H-BIM). Compositional analyses of the resultant EMM-36-## products were performed by liquid-phase .sup.1H NMR and a comparison of those results with the content of the initial synthesis mixtures is shown in FIG. 4. The solid line in FIG. 4 represents the ideal incorporation of the 4,5,6,7-tetrahydrobenzimidazole in the ZIF structure, whereas the diamonds represent the incorporation observed by .sup.1H NMR. It is apparent from FIG. 4 that 4H-BIM and BIM incorporate into the ZIF framework structure at ratios very similar to their starting reaction mixtures. This ability allows for fine control of the composition of EMM-36.

(42) CO.sub.2 adsorption isotherms were conducted at 30 C. on the EMM-36-## products and the results are shown in FIG. 5. It will be seen that EMM-36-## exhibits a stepped isotherm similar to ZIF-7 at low 4H-BIM ratios. As the 4H-BIM content is increased up to 25 mol %, the isotherm step shifts to as low as 0.05 bar. At higher levels of 4H-BIM, a Type I isotherm results.

(43) CH.sub.4 adsorption isotherms were also conducted at 30 C. on EMM-36-## materials and the results are shown in FIG. 6. As the 4H-BIM content is increased beyond 15 mol %, the isotherm step occurs below 1 bar. Above about 25 mol % 4H-BIM, the materials remain in the open pore phase throughout the isotherm (above 0.01 bar).

(44) C.sub.2H.sub.4 adsorption isotherms were conducted at 30 C. on ZIF-7 as well as the EMM-36-## materials. The results shown in FIG. 7 demonstrate the potential utility of the EMM-36-## materials as C.sub.2H.sub.4 adsorbents.

Example 3: Synthesis of EMM-38-##

(45) 100 mg of a mixture of 4,5,6,7-tetrahydrobenzimidazole (4H-BIM) with varying amounts benzimidazole (BIM) was dissolved in 10 mL of methanol/toluene (1:1) and 0.1 mL of NH.sub.4OH (conc.) added to the solution. To this solution, 0.1 g of Zn(OAc).sub.2 was added and the reaction mixture stirred at room temperature (25 C.) for 16 hours. The product is filtered out, washed with ethanol and dried at 70 C. under air.

(46) The SEM of the resultant EMM-38-100 product (containing 100 mol % 4H-BIM) is shown in FIG. 8 and the SEM of the EMM-38-25 product (containing 25 mol % 4H-BIM) is shown in FIG. 9. Powder X-ray diffraction patterns of the EMM-38-25, EMM-38-50 and EMM-38-100 materials are shown in FIG. 10 exhibiting the RHO framework structure.

(47) N.sub.2 adsorption isotherms were conducted at 77 K on the EMM-38-## products and the results are shown in FIG. 11. In contrast to ZIF-11, EMM-38-## exhibits nitrogen-accessible pore volume at low temperatures.

(48) Ethane adsorption isotherms were conducted at 30 C. on the EMM-38-## products and the results are shown in FIG. 12. At modest contents of 4H-BIM, EMM-38-## exhibits isotherms very similar to that of ZIF-11. At higher 4H-BIM contents, the capacity for ethane decreases.

Example 4: Synthesis of EMM-38-100-N (N Signifies Presence of Nitrogen in the Partially Saturated Ring)

(49) 100 mg of 4,5,6,7-tetrahydro-3H-imidazo[4,5-c]pyridine and 100 mg of zinc acetate dehydrate were loaded into a 20 mL vial. To this, 0.1 mL of NH.sub.4OH (conc.) and 10 mL of ethanol was added. The reaction was stirred overnight at 60 C. The solids were then isolated via centrifugation and dried at 90 C.

(50) The SEM of the resultant EMM-38-100-N product is shown in FIG. 13. A powder X-ray diffraction pattern of the EMM-38-100-N product is shown in FIG. 14 and demonstrates the material has the RHO framework structure, closely isostructural with EMM-38-##.

(51) CO.sub.2 adsorption and desorption isotherms were conducted at 30 C. on the EMM-38-100-N product and the results are shown in FIG. 15. What was notable is the higher capacity observed for EMM-38-100-N when compared to ZIF-11 or EMM-38-##.