METAL-ORGANIC FRAMEWORK (MOF) MIL-125 AND PREPARATION METHOD AND USE THEREOF

Abstract

A metal-organic framework (MOF) MIL-125 and a preparation method and a use thereof are provided. The MOF MIL-125 is a round cake-like crystal and has an external specific surface area (SSA) of 160 m.sup.2/g to 220 m.sup.2/g. The MOF MIL-125 provided in the present application has a large number of microporous structures, a large external SSA, and a high catalytic activity in oxidation.

Claims

1. A metal-organic framework (MOF) MIL-125, wherein the MOF MIL-125 is a round cake-like crystal and the MOF MIL-125 has an external specific surface area (SSA) of 160 m.sup.2/g to 220 m.sup.2/g.

2. The MOF MIL-125 according to claim 1, wherein a mass content of particles with a particle size of 1.6 μm to 1.8 μm in the MOF MIL-125 is 85% to 95%.

3. The MOF MIL-125 according to claim 1, wherein the MOF MIL-125 comprises a micropore with an SSA of 1,000 m.sup.2/g to 1,500 m.sup.2/g.

4. The MOF MIL-125 according to claim 3, wherein the micropore has a pore size of 0.35 nm to 0.50 nm.

5. A preparation method of the MOF MIL-125 according to claim 1, comprising: preparing the MOF MIL-125 with a titanium-ester polymer, wherein the titanium-ester polymer is configured as a titanium source.

6. The preparation method according to claim 5, comprising: subjecting a mixture of the titanium-ester polymer, an organic ligand, and an organic solvent to a crystallization to obtain the MOF MIL-125, wherein the organic ligand is terephthalic acid; and the crystallization refers to a solvothermal crystallization.

7. The preparation method according to claim 6, wherein the crystallization is conducted for no more than 30 d at a temperature of 100° C. to 200° C. and an autogenous pressure under closed conditions.

8. The preparation method according to claim 6, wherein the crystallization is conducted for 1 d to 15 d at a temperature of 120° C. to 180° C. and an autogenous pressure under closed conditions.

9. The preparation method according to claim 6, wherein a molar ratio of the titanium-ester polymer to the organic ligand is (0.5-2):1; a mole number of the titanium-ester polymer is calculated based on a titanium content in the titanium-ester polymer; and the titanium content in the titanium-ester polymer is calculated based on a mole number of TiO.sub.2.

10. The preparation method according to claim 6, wherein the organic solvent is at least one selected from the group consisting of N,N-dimethylformamide (DMF) and methanol.

11. The preparation method according to claim 10, wherein the organic solvent comprises the DMF and the methanol, and a volume ratio of the DMF to the methanol is (6-15):1.

12. The preparation method according to claim 6, wherein the titanium-ester polymer is prepared through a transesterification reaction between a titanate and a polyol.

13. The preparation method according to claim 12, wherein the titanate is at least one selected from the group consisting of compounds with a chemical formula shown in formula II: ##STR00002## wherein R.sup.5, R.sup.6, R.sup.7, and R.sup.8 each are independently selected from the group consisting of C.sub.1-C.sub.10 alkyl groups; and the polyol comprises at least one selected from the group consisting of ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG), tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, polyethylene glycol (PEG) 200, PEG 400, PEG 600, PEG 800, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol (1,4-CHDM), 1,4-benzenedimethanol, glycerol, trimethylolpropane, pentaerythritol, xylitol, and sorbitol.

14. A preparation method of epoxycyclohexane, comprising: subjecting a raw material comprising a compound A and cyclohexene to a reaction in an presence of the MOF MIL-125 according to claim 1 to obtain the epoxycyclohexane, wherein the compound A is at least one selected from the group consisting of hydrogen peroxide and tert-butyl hydroperoxide; and

15. The preparation method according to claim 14, wherein the compound A, the cyclohexene, and the MOF MIL-125 are in a mass ratio of (0.3-1.0):(0.3-1.2):(0.05-0.1).

16. The preparation method according to claim 14, wherein the reaction is conducted at 35° C. to 80° C. for 2 h to 8 h.

17. The preparation method according to claim 5, wherein a mass content of particles with a particle size of 1.6 μm to 1.8 μm in the MOF MIL-125 is 85% to 95%.

18. The preparation method according to claim 5, wherein the MOF MIL-125 comprises a micropore with an SSA of 1,000 m.sup.2/g to 1,500 m.sup.2/g.

19. The preparation method according to claim 18, wherein the micropore has a pore size of 0.35 nm to 0.50 nm.

20. The preparation method according to claim 14, wherein a mass content of particles with a particle size of 1.6 μm to 1.8 μm in the MOF MIL-125 is 85% to 95%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0076] FIG. 1 is an X-ray diffractometry (XRD) pattern of the product synthesized in Example 1 of the present disclosure.

[0077] FIG. 2 is a scanning electron microscopy (SEM) image of the product synthesized in Example 1 of the present disclosure.

[0078] FIG. 3 is a physical adsorption isotherm (BET) of the product synthesized in Example 1 of the present disclosure.

[0079] FIG. 4 shows a laser particle size distribution of the product synthesized in Example 1 of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0080] The present application will be described in detail below with reference to examples, but the present application is not limited to these examples.

[0081] Unless otherwise specified, the raw materials in the examples of the present application are all purchased from commercial sources.

[0082] In the examples of the present application, XRD of a product is conducted by an X'Pert PRO X-ray diffractometer of Netherlandish PANalytical under the following conditions: Cu target, Kα radiation source (λ=0.15418 nm), voltage: 40 KV, and current: 40 mA.

[0083] In the examples of the present application, the SEM of a product is conducted by an SU8020 scanning electron microscope of Hitachi.

[0084] In the examples of the present application, the physical adsorption and pore distribution of a product are analyzed by an ASAP2020 automatic physical instrument of Micromeritics.

[0085] In the examples of the present application, a particle size distribution of a product is analyzed by a ParticleTrack G600B particle size analyzer of METTLER TOLEDO.

[0086] In the examples of the present application, a conversion rate of a transesterification reaction is calculated in the following way:

[0087] According to a mole number n of alcohol distilled during the reaction, a number of groups participating in the transesterification reaction is determined to be n, and a total mole number of the titanate in the reaction raw material is m, such that the conversion rate of the transesterification reaction is: n/4 m.

[0088] According to an embodiment of the present application, a preparation method of an MOF MIL-125 includes: [0089] a) a titanate and a polyol are thoroughly mixed in a three-necked flask, the three-necked flask is connected to a distillation device, nitrogen is introduced for protection, and a resulting mixture is subjected to a transesterification reaction for 2 h to 10 h at 80° C. to 180° C. under stirring, where a conversion rate of the transesterification reaction is 60% to 80%; [0090] b) the device obtained after the reaction in step a) is connected to a water pump or oil pump, and a resulting reaction system is subjected to vacuum distillation for 0.5 h to 5 h at a vacuum degree of 0.01 KPa to 5 KPa and a temperature of 170° C. to 230° C. to make the transesterification reaction more complete to obtain the titanium-ester polymer, where a conversion rate of the transesterification reaction is greater than 90%; [0091] c) the titanium-ester polymer obtained in step b) is mixed with the terephthalic acid and the organic solvent, and a resulting mixture is stirred or allowed to stand for 0 h to 100 h at a temperature not higher than 120° C. to obtain a gel mixture; [0092] d) the gel mixture obtained in step c) is placed in a high-pressure reactor, the high-pressure reactor is sealed, and the gel mixture is heated to 100° C. to 200° C. and then subjected to crystallization for 0 d to 30 d at an autogenous pressure; and [0093] e) after the crystallization is completed, a solid product is separated, washed with deionized water until neutral, and dried to obtain the microporous MOF MIL-125.

[0094] The titanate in step a) is one or more selected from the group consisting of tetraethyl titanate, TIPT, tetrabutyl titanate, tetrahexyl titanate, and tetraisooctyl titanate.

[0095] The polyol in step a) has a general formula of R—(OH).sub.x, where x≥2; and the polyol includes any one or a mixture of two or more selected from the group consisting of EG, DEG, TEG, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, PEG 200, PEG 400, PEG 600, PEG 800, 1,4-cyclohexanediol, 1,4-CHDM, 1,4-benzenedimethanol, glycerol, trimethylolpropane, pentaerythritol, xylitol, and sorbitol.

[0096] Preferably, a molar ratio of the titanate to the polyol in step a) is:

Ti(OR).sub.4/R—(OH).sub.x=(0.8-1.2)x/4

[0097] Preferably, the reaction in step a) is conducted for 2 h to 10 h at 80° C. to 180° C. under nitrogen protection.

[0098] Preferably, a conversion rate of the transesterification reaction in step a) is 65% to 80%.

[0099] Preferably, the step b) is conducted under vacuum distillation at a vacuum degree of 0.05 KPa to 3 KPa.

[0100] Preferably, the reaction in step b) is conducted at 170° C. to 230° C. for 0.5 h to 5 h.

[0101] Preferably, a conversion rate of the transesterification reaction in step b) is greater than 90%.

[0102] Preferably, a molar ratio of the titanium-ester polymer to the terephthalic acid in step c) is: titanium-ester polymer:terephthalic acid=(0.5-2):1, [0103] where a mole number of the titanium-ester polymer is calculated based on a titanium content in the titanium-ester polymer; and [0104] the titanium content in the titanium-ester polymer is calculated based on a mole number of TiO.sub.2.

[0105] Preferably, the organic solvent in step c) is a mixture of D1VIF and methanol, and a volume ratio of DMF to methanol meets the following condition: [0106] DMF:methanol=(6-15):1.

[0107] Preferably, the stirring in step c) may be omitted, or the stirring may be conducted at 20° C. to 100° C. for 1 h to 50 h.

[0108] Preferably, the crystallization in step d) is conducted at 120° C. to 180° C. for 1 d to 15 d.

[0109] Preferably, the crystallization in step d) is conducted in a dynamic or static state.

[0110] Preferably, the MOF MIL-125 obtained in step e) has microporous structures with a narrow pore size distribution and less non-skeleton titanium.

EXAMPLE 1

[0111] A specific preparation process was as follows: 5 g of tetraethyl titanate and 10 g of PEG 200 were added to a three-necked flask and thoroughly mixed, the three-necked flask was connected to a distillation device, nitrogen was introduced for protection, and a resulting mixture was subjected to a transesterification reaction for 5 h at 175° C. under stirring, where a conversion rate of the transesterification reaction was 75%; a water pump was connected to the device, and a resulting reaction system was subjected to vacuum distillation for 1 h at a vacuum degree of 3 KPa and a temperature of 200° C. to make the transesterification reaction more complete to obtain a titanium-PEG ester polymer, where a conversion rate of the transesterification reaction was 92%; 5 g of the titanium-PEG ester polymer, 5 g of terephthalic acid, 18 mL of DMF, and 2 mL of methanol were mixed and stirred for 2 h at room temperature, and a resulting mixture was then transferred to a stainless steel high-pressure reactor; the high-pressure reactor was sealed and placed in an oven that had been heated to 120° C., and crystallization was conducted for 2 d at an autogenous pressure; and after the crystallization was completed, a solid product was separated through centrifugation, washed with deionized water until neutral, and dried at 110° C. in air to obtain the microporous MOF MIL-125, which was denoted as A1.

EXAMPLE 2

[0112] A specific preparation process was as follows: 5 g of tetraethyl titanate and 3.13 g of EG were added to a three-necked flask and thoroughly mixed, the three-necked flask was connected to a distillation device, nitrogen was introduced for protection, and a resulting mixture was subjected to a transesterification reaction for 5 h at 100° C. under stirring, where a conversion rate of the transesterification reaction was 70%; a water pump was connected to the device, and a resulting reaction system was subjected to vacuum distillation for 1 h at a vacuum degree of 3 KPa and a temperature of 170° C. to make the transesterification reaction more complete to obtain a titanium-EG ester polymer, where a conversion rate of the transesterification reaction was 90%; 3 g of the titanium-EG ester polymer, 2 g of terephthalic acid, 9 mL of DMF, and 1.2 mL of methanol were mixed and stirred for 2 h at room temperature, and a resulting mixture was then transferred to a stainless steel high-pressure reactor; the high-pressure reactor was sealed and placed in an oven that had been heated to 150° C., and crystallization was conducted for 15 d at an autogenous pressure; and after the crystallization was completed, a solid product was separated through centrifugation, washed with deionized water until neutral, and dried at 110° C. in air to obtain the MOF MIL-125, which was denoted as A2.

EXAMPLE 3

[0113] A specific preparation process was as follows: 5 g of tetrabutyl titanate and 11.35 g of 1,4-benzenedimethanol were added to a three-necked flask and thoroughly mixed, the three-necked flask was connected to a distillation device, nitrogen was introduced for protection, and a resulting mixture was subjected to a transesterification reaction for 5 h at 160° C. under stirring, where a conversion rate of the transesterification reaction was 80%; a water pump was connected to the device, and a resulting reaction system was subjected to vacuum distillation for 1 h at a vacuum degree of 3 KPa and a temperature of 230° C. to make the transesterification reaction more complete to obtain a titanium-1,4-benzenedimethanol ester polymer, where a conversion rate of the transesterification reaction was 95%; 4 g of the titanium-1,4-benzenedimethanol ester polymer, 6.2 g of terephthalic acid, 20 mL of DMF, and 2.3 mL of methanol were mixed and stirred for 2 h at room temperature, and a resulting mixture was then transferred to a stainless steel high-pressure reactor; the high-pressure reactor was sealed and placed in an oven that had been heated to 170° C., and crystallization was conducted for 1 d at an autogenous pressure; and after the crystallization was completed, a solid product was separated through centrifugation, washed with deionized water until neutral, and dried at 110° C. in air to obtain the MOF MIL-125, which was denoted as A3.

[0114] The crystallization in Examples 1 to 3 was static crystallization.

EXAMPLE 4

[0115] An MOF MIL-125 was prepared by the same method as in Example 1, and specific preparation conditions were different from Example 1 as in Table 1 and Table 2.

TABLE-US-00001 TABLE 1 Condition parameters for the preparation of a titanium-ester polymer Temperature Time Vacuum degree Titanate, polyol, and a molar Reaction Reaction for vacuum for vacuum for vacuum No. ratio thereof temperature time distillation distillation distillation 1# TIPT:glycerol = 2.4:0.6  80° C. 10 h  180° C. 3 h 0.01 KPa 2# Tetrahexyl titanate:pentaerythritol =  90° C. 8 h 210° C. 2.5 h 0.05 KPa 0.75:0.25 3# Tetraisooctyl titanate:1,2- 120° C. 4 h 170° C. 5 h 5 KPa propanediol = 0.8:0.2 4# Tetrahexyl titanate:1,4- 180° C. 2 h 230° C. 0.5 h 1.5 KPa cyclohexanediol = 0.7:0.3

TABLE-US-00002 TABLE 2 Conditions for synthesis of the MOF MIL-125 Titanium-ester polymer, terephthalic acid, and a molar ratio thereof; and organic Temperature and time No. solvents, and a volume ratio thereof for crystallization A4 Terephthalic acid:1# = 1:1; 100° C., and DMF:methanol = 10:1 30 d A5 Terephthalic acid:2# = 1:0.9; 120° C., and DMF:methanol = 12:1 10 d A6 Terephthalic acid:3# = 1:0.7; 200° C., and DMF:methanol = 13:1 5 d A7 Terephthalic acid:4# = 1:0.5; 180° C., and DMF:methanol = 9:1 8 d

[0116] The crystallization involved in Example 4 was dynamic crystallization conducted in a rotary oven. The temperature and time for crystallization were shown in Table 2, and a rotational speed of the rotary oven was 35 rpm.

EXAMPLE 5

[0117] A specific preparation process was as follows: 5 g of tetraethyl titanate and 10 g of PEG 200 were added to a three-necked flask and thoroughly mixed, the three-necked flask was connected to a distillation device, nitrogen was introduced for protection, and a resulting mixture was subjected to a transesterification reaction for 5 h at 175° C. under stirring, where a conversion rate of the transesterification reaction was 75%; a water pump was connected to the device, and a resulting reaction system was subjected to vacuum distillation for 1 h at a vacuum degree of 3 KPa and a temperature of 200° C. to make the transesterification reaction more complete to obtain a titanium-PEG ester polymer, where a conversion rate of the transesterification reaction was 92%; in order to verify that the titanium-ester polymer obtained in the present application was resistant to hydrolysis and insoluble in water, 5 g of the titanium-PEG ester polymer, 5 g of terephthalic acid, 18 mL of DMF, 2 mL of methanol, and 0.5 g of water were mixed and stirred for 2 h at room temperature, and a resulting mixture was then transferred to a stainless steel high-pressure reactor; the high-pressure reactor was sealed and placed in an oven that had been heated to 120° C., and crystallization was conducted for 2 d at an autogenous pressure; and after the crystallization was completed, a solid product was separated through centrifugation, washed with deionized water until neutral, and dried at 110° C. in air to obtain the microporous MOF MIL-125, which was denoted as A8. The crystallization in this example was static crystallization.

EXAMPLE 6

Phase Structure Analysis

[0118] The samples A1 to A8 in Examples 1 to 5 each were subjected to XRD analysis, with Example 1 as a typical representative. FIG. 1 shows an XRD pattern of the sample A1 prepared in Example 1, and it can be seen from the figure that the sample A1 is a microporous MOF MIL-125. Compared with an XRD pattern of a product synthesized by the existing technique, the XRD pattern of the microporous MOF MIL-125 synthesized by the present application has clear peaks with sharp peak shapes and without tailing, and has a flat baseline, indicating that the microporous MOF MIL-125 synthesized by the present application has a regular structure, no heterocrystals, and no amorphous products.

[0119] Test results of the other samples are only slightly different from the pattern of the sample Al in Example 1 in the intensity of the diffraction peak, and all of these samples are microporous MOF MIL-125.

EXAMPLE 7

Morphology Analysis

[0120] The samples A1 to A8 in Examples 1 to 5 each were subjected to SEM analysis, with Example 1 as a typical representative. FIG. 2 is an SEM image of the sample A1 prepared in Example 1, and it can be seen from the SEM image that the synthesized product has a regular morphology of a round cake shape and a uniform size distribution, and does not include other heterocrystals and amorphous products.

EXAMPLE 8

Low-Temperature Nitrogen Physical Adsorption Analysis

[0121] The samples A1 to A8 in Examples 1 to 5 each were subjected to low-temperature nitrogen physical adsorption analysis, with Example 1 as a typical representative. FIG. 3 shows a physical adsorption isotherm of the sample A1 prepared in Example 1, and it can be seen from the figure that the isotherm is a typical type I adsorption isotherm, indicating a typical microporous structure.

[0122] Test results of the other samples are similar to the test results of the sample 1 in Example 1, and the samples each have a typical type I adsorption isotherm and a typical microporous structure.

EXAMPLE 9

Pore Distribution Analysis

[0123] The samples A1 to A8 in Examples 1 to 5 each were subjected to physical adsorption and pore distribution analysis. Table 3 shows the physical adsorption and pore distribution results of the samples A1 to A6 prepared in Examples 1 to 4, and these samples each have an SSA of 1,200 m.sup.2/g to 1,350 m.sup.2/g and a micropore size of 0.37 nm to 0.48 nm.

TABLE-US-00003 TABLE 3 SSA and pore distribution of samples BET SSA/ t-Plot external Pore Sample m.sup.2g−.sup.1 SSA/m.sup.2g−.sup.1 distribution/nm A1 1350 167 0.40 A2 1268 170 0.37 A3 1212 181 0.40 A4 1304 165 0.41 A5 1312 214 0.45 A6 1289 200 0.48

[0124] Test results of the other samples are similar to the test results of the sample A1 in Example 1, and these samples each have an SSA of 1,000 m.sup.2/g to 1,500 m.sup.2/g.

[0125] The external SSA of each of the samples was calculated by the t-Plot method. The samples A1 to A6 prepared in Examples 1 to 4 each have an external SSA of 160 m.sup.2/g to 214 m.sup.2/g.

[0126] Test results of the other samples are similar to the test results of the sample A1 in Example 1, and these samples each have an external SSA of 160 m.sup.2/g to 220 m.sup.2/g.

EXAMPLE 10

Particle Size Distribution Analysis

[0127] The samples A1 to A8 in Examples 1 to 5 each were subjected to laser particle size analysis, with Example 1 as a typical representative. FIG. 4 shows a particle size distribution of the sample Al prepared in Example 1, and it can be seen from the figure that the particle size distribution of the synthesized sample is relatively concentrated and uniform and the particle size is 1 μm to 2 μm.

[0128] Test results of the other samples are similar to the test results of the sample 1 in Example 1, and these samples each have a relatively concentrated and uniform particle size distribution and a particle size of 1 μm to 2 μm.

EXAMPLE 11

Determination of Oxidation Reaction Performance

[0129] Hydrogen peroxide was used as oxidizing agent to determine the performance of oxidizing cyclohexene.

[0130] With the sample A1 as a typical representative, the performance was specifically tested as follows: [0131] 0.1 g of the sample A1 (as a catalyst), 10 mL of acetonitrile, 0.36 g of cyclohexene, and 0.5 g of hydrogen peroxide (mass fraction: 30%) were added to a round-bottom flask, and heated in a 60° C. water bath for reflux condensation to allow a reaction for 4 h.

[0132] Reaction results of the sample A1 are as follows: cyclohexene conversion: 38%, selectivity for epoxidation products in the product: 78.5%, hydrogen peroxide conversion rate: 73.2%, and selectivity of the oxidizing agent for epoxidation products: 72.2%. In the prior art, the cyclohexene conversion rate is 26%, and the selectivity for epoxidation products in the product is only 25%.

[0133] The samples A2 to A8 each were subjected to performance analysis according to the above steps. Reaction results of these samples are similar to the reaction results of the sample A1.

[0134] The above examples are merely few examples of the present application, and do not limit the present application in any form. Although the present application is disclosed as above with preferred examples, the present application is not limited thereto. Some changes or modifications made by any technical personnel familiar with the profession using the technical content disclosed above without departing from the scope of the technical solutions of the present application are equivalent to equivalent implementation cases and fall within the scope of the technical solutions.