Zinc-based metal organic framework material and application thereof in one-step purification of cyclohexene and cyclohexane in C6 cyclic hydrocarbon mixture

Abstract

The invention belongs to the technical field of synthesis of metal-organic frameworks and chemical adsorption separation, and particularly relates to a zinc-based metal organic framework material and application of the zinc-based metal organic framework material in one-step purification of cyclohexene and cyclohexane in a C6 cyclic hydrocarbon mixture. The invention designs a zinc-based metal-organic framework material with a three-dimensional structure, which is formed by carrying out coordination on 2, 6-diethyl / bis (hydroxymethyl) benzobisimidazole anions and zinc ions and then assembling the 2, 6-diethyl / bis (hydroxymethyl) benzobisimidazole anions and the zinc ions. Wherein the metal-organic frameworks MAF-55 and MAF-56 show ultrahigh benzene or cyclohexane selectivity in benzene / cyclohexene / cyclohexane separation, still maintain ultrahigh performance in continuous cycle implementation, and have excellent stability and cyclicity. The two materials are loaded into a packed column and are connected in series, so that separation and purification of a C6 cyclic hydrocarbon mixture can be realized in one step, purification of cyclohexene and cyclohexane in the C6 cyclic hydrocarbon mixture can be simultaneously realized in one-step adsorption process, and a multi-stage rectification or extraction step is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of synthesis of metal-organic frameworks and chemical adsorption separation. More specifically, it relates to zinc-based metal-organic framework materials and their application in the one-step purification of cyclohexene and cyclohexane in C6 cycloalkane mixtures. Background Art

[0002] Cyclohexene and cyclohexane, as the hydrogenation products of benzene, can be oxidized to produce cyclohexanol / cyclohexanone, which are raw materials for the production of nylon 6 and nylon 66. Compared with the traditional cyclohexane oxidation route, the hydration oxidation method of cyclohexene will be more economical and environmentally friendly. Complete hydrogenation of benzene can directly obtain high-purity cyclohexane, while the cyclohexene obtained by partial hydrogenation of benzene always contains unreacted benzene and by-product cyclohexane. However, benzene (353.2K), cyclohexene (356.0K) and cyclohexane (353.9K) have very similar boiling points, and benzene / cyclohexane and benzene / cyclohexene mixtures can form azeotropes, which are extremely difficult to separate. The difficulty in separating this ternary system lies in the extremely close boiling points of the three components (benzene 353.2K, cyclohexane 353.9K, cyclohexene 356.0K), and the two components of benzene / cyclohexane and benzene / cyclohexene are prone to form azeotropes.

[0003] The extractive distillation technology commonly used in the current industry can achieve a certain degree of separation, but its high energy consumption characteristics are essentially contradictory to the environmental protection requirements. Porous coordination polymers (PCPs), also known as metal-organic frameworks (MOFs), have attracted wide attention in the field of adsorption separation due to their high specific surface area, structural diversity and designability, and unique flexibility. Research shows that most MOF materials show preferential adsorption to benzene, which results from the synergistic effect of its strong polarity and small molecular size. Although such materials can effectively separate the binary systems of benzene / cyclohexane or benzene / cyclohexene, they cannot achieve the directional purification of cyclohexene when dealing with ternary mixtures.

[0004] Recent research progress shows that by regulating the pore microenvironment and introducing specific action sites, special adsorption materials with reverse selectivity (cyclohexane > cyclohexene > benzene) can be constructed. Such materials break through the limitations of traditional polar adsorption in the molecular recognition mechanism by establishing multiple non-classical hydrogen bond networks. In theory, the series combination of forward selectivity and reverse selectivity adsorbents may achieve the efficient separation of ternary systems. However, the existing technical solutions still have significant defects: a single adsorption column can only preferentially adsorb specific components, and a simple double-column series configuration can only obtain a single purified product, and cannot simultaneously meet the separation requirements of multiple components.

[0005] The above technical bottlenecks seriously restrict the full play of the economic and environmental advantages of the cyclohexene process. Therefore, the development of new adsorption separation materials with high selectivity, fast mass transfer characteristics and process adaptability has become the key direction to break through the existing separation technology barriers. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the defects and deficiencies of high energy consumption, low efficiency in the traditional extractive distillation for separating C6 cycloalkane mixtures, and the inability of existing single adsorbents and simple tandem columns to efficiently purify cyclohexene, and to provide a zinc-based metal-organic framework material.

[0007] The object of the present invention is to provide a metal-organic framework MAF-55.

[0008] The object of the present invention is to provide a preparation method of the above-mentioned metal-organic framework MAF-55.

[0009] Another object of the present invention is to provide a metal-organic framework MAF-56.

[0010] Another object of the present invention is to provide a preparation method of the metal-organic framework MAF-56.

[0011] Another object of the present invention is to provide the application of the metal-organic framework MAF-55 or the metal-organic framework MAF-56 in the adsorption and separation of C6 cycloalkanes.

[0012] Another object of the present invention is to provide a packed column breakthrough adsorption system.

[0013] Another object of the present invention is to provide a dual adsorbent tandem system.

[0014] The above objects of the present invention are achieved by the following technical solutions:

[0015] The present invention protects a zinc-based metal-organic framework material, which is formed by coordinating 2,6-diethyl / dihydroxymethylbenzimidazole anion with zinc ions to assemble a zinc-based metal-organic framework material with a three-dimensional structure.

[0016] Further, the 2,6-diethyl / dihydroxymethylbenzimidazole is represented as 2,6-diethylbenzimidazole or 2,6-dihydroxymethylbenzimidazole, and the structural formulas of the two are as follows:

[0017]

[0018] 2,6-Diethylbenzimidazole 2,6-Dihydroxymethylbenzimidazole

[0019] The present invention protects a metal-organic framework MAF-55, which is constructed by zinc ions, fluoride ions and 2,6-diethylbenzimidazole anion, and its chemical formula is [Zn2F2(ebdim)];

[0020] Among them, ebdim 2- Represents the organic ligand 2,6-bisethylbenzbisimidazole anion.

[0021] This paper designs and synthesizes a novel zinc-based metal-organic framework (MOF) material, codenamed MAF-55, using zinc salt, fluoride ion, and 2,6-bisethylbenzimidazole as raw materials. The activated MAF-55 material exhibits benzene / cyclohexene / cyclohexane selectivity in the adsorption of C6 cyclic hydrocarbon mixtures, and exhibits high stability and recyclability.

[0022] Furthermore, the metal-organic framework MAF-55 is a trigonal system with a space group of The unit cell parameters are Unit cell volume

[0023] The present invention provides a method for preparing the metal-organic framework MAF-55, comprising the following steps: mixing zinc salt, fluoride ions, and 2,6-diethylbenzbisimidazole in ethylene glycol or a mixed solvent containing ethylene glycol, and preparing the metal-organic framework MAF-55 by a solvothermal method.

[0024] Furthermore, the zinc salt is zinc acetate, zinc nitrate, zinc chloride or a hydrate of the above zinc salts.

[0025] Furthermore, the fluoride ions are derived from fluoride salts, and the fluoride salts are selected from ammonium fluoride, zinc fluoride or hydrates of the above fluoride salts.

[0026] Furthermore, the solvent thermal temperature is 140-180°C, preferably 160°C.

[0027] Furthermore, the solvent thermal time is 1 to 3 days, preferably 3 days.

[0028] Furthermore, the molar ratio of the zinc salt, the fluoride ion and the 2,6-bisethylbenzimidazole is 1:(0.5-2.0):(0.5-1.0), preferably 1:(1-1.5):(0.5-0.6).

[0029] Furthermore, the mixing ratio of the volume of the ethylene glycol or the mixed solvent containing ethylene glycol to the mass of 2,6-bisethylbenzimidazole is 1 mL: (7-15) mg, preferably 1 mL: (7-12) mg.

[0030] Furthermore, in the mixed solvent containing ethylene glycol, the volume proportion of ethylene glycol is ≥50%.

[0031] Preferably, the mixed solvent containing ethylene glycol is a mixture of isopropyl alcohol and ethylene glycol.

[0032] Furthermore, the volume ratio of isopropanol to ethylene glycol is 1:(1 - 3), more preferably 1:(1 - 2).

[0033] Furthermore, the solvothermal method includes a solvothermal reaction and post-treatment.

[0034] Furthermore, the conditions (reaction temperature, time, etc.) of the solvothermal reaction are as described above.

[0035] Furthermore, the post-treatment includes at least cooling. When the post-treatment is only cooling, the product obtained after cooling is a single crystal of metal-organic framework MAF-55; when the post-treatment includes cooling, washing, drying, and activation, the product obtained after activation is a metal-organic framework MAF-55 powder.

[0036] Furthermore, the cooling is to cool to room temperature, and the cooling rate is 5 - 10 °C·h -1 , preferably 5 °C·h -1 .

[0037] Furthermore, as an alternative implementation, the activation method is vacuum heating.

[0038] Furthermore, the temperature of the vacuum heating is 220 - 280 °C, preferably 250 °C.

[0039] Furthermore, the time of the vacuum heating is 2 - 6 hours, preferably 4 hours.

[0040] Furthermore, the washing is performed using methanol.

[0041] The present invention protects a metal-organic framework MAF-56, which is constructed by zinc ions and 2,6-bis(hydroxymethyl)benzimidazole anions, and its chemical formula is [Zn(dobdim)];

[0042] wherein, dobdim 2- represents the organic ligand 2,6-bis(hydroxymethyl)benzimidazole anion.

[0043] The present invention uses zinc salt, nitrate, and 2,6-bis(hydroxymethyl)benzimidazole as raw materials to design and synthesize a novel zinc-based metal-organic framework material. The activated material (code named MAF-56) can exhibit cyclohexane / cyclohexene / benzene selectivity in the adsorption of C6 cycloalkane mixtures, and shows high stability and recyclability.

[0044] Furthermore, the metal-organic framework MAF-55 is of trigonal system, space group The unit cell parameters are The unit cell volume

[0045] The present invention protects a method for preparing the metal-organic framework MAF-56, which comprises the following steps: mixing a zinc salt, a nitrate, and 2,6-bis(hydroxymethyl)benzimidazole in N,N-dimethylacetamide or a mixed solvent containing N,N-dimethylacetamide, and obtaining the metal-organic framework MAF-56 through a solvothermal method.

[0046] Further, the zinc salt is zinc acetate, zinc nitrate, zinc chloride, or a hydrate of the above zinc salts.

[0047] Further, the nitrate is selected from potassium nitrate, sodium nitrate, or a hydrate of the above nitrates.

[0048] Further, the temperature of the solvothermal process is 120 - 160 °C, preferably 140 °C.

[0049] Further, the time of the solvothermal process is 12 - 72 hours.

[0050] Further, the molar ratio of the zinc salt, the nitrate, and 2,6-bis(hydroxymethyl)benzimidazole is 1:(0.5 - 1.5):(0.5 - 1), preferably 1:(0.5 - 0.6):(0.5 - 0.6).

[0051] Further, the mixing ratio of the volume of the N,N-dimethylacetamide or the mixed solvent containing N,N-dimethylacetamide to the mass of 2,6-bis(hydroxymethyl)benzimidazole is 1 mL:(5 - 12) mg, preferably 1 mL:(5.5 - 11) mg.

[0052] Further, the volume ratio of the N,N-dimethylacetamide to ethanol is 1:(0.5 - 2), preferably 1:(0.8 - 1.5).

[0053] Further, the solvothermal method includes a solvothermal reaction and post-treatment.

[0054] Further, the conditions of the solvothermal reaction (reaction temperature, time, etc.) are as described above.

[0055] Further, the post-treatment includes at least cooling. When the post-treatment is only cooling, the product obtained after cooling is a single crystal of the metal-organic framework MAF-56; when the post-treatment includes cooling, washing, drying, and activation, the product obtained after activation is a powder of the metal-organic framework MAF-56.

[0056] Further, the cooling is to cool to room temperature, and the cooling rate is 5 - 10 °C·h -1 , preferably 5 °C·h -1 .

[0057] Further, as an alternative embodiment, the activation method is vacuum heating.

[0058] Further, the temperature of the vacuum heating is 220 - 280 °C, preferably 250 °C.

[0059] Further, the time of the vacuum heating is 2 - 6 hours, preferably 4 hours.

[0060] Further, the washing is performed using methanol.

[0061] The present invention protects the application of the zinc-based metal-organic framework material, or the metal-organic framework MAF-55, or the metal-organic framework MAF-56 in the adsorption and separation of C6 cycloalkanes.

[0062] Preferably, the C6 cycloalkanes include one or more of benzene, cyclohexene, and cyclohexane.

[0063] The present invention protects a packed column adsorption system, and the adsorbent of the adsorption system comprises one or more of the zinc-based metal-organic framework material, the metal-organic framework MAF-55, and the metal-organic framework MAF-56.

[0064] The present invention also protects a dual adsorbent series system, which includes a first adsorbent, a second adsorbent, at least two packed columns, and valves. The first adsorbent and the second adsorbent are respectively loaded into different packed columns, and the packed columns are connected through the valves;

[0065] wherein, the first adsorbent is the metal-organic framework MAF-55; the second adsorbent is the metal-organic framework MAF-56.

[0066] Further, the adsorbent is dispersed and used with an organic solvent.

[0067] Preferably, the organic solvent is mesitylene.

[0068] Further, the dual adsorbent series system further includes a collector.

[0069] Further, the series connection mode of the dual adsorbent series system includes direct series connection or bypass series connection.

[0070] Further, the valve is a three-way valve, and the series connection and bypass switching are realized through the three-way valve.

[0071] Further, the specific manner of the direct series connection is as follows: when the three-way valve connects two packed columns, the tail end of the packed column where the first adsorbent is located is directly connected to the front end of the packed column where the second adsorbent is located, and at this time, the two packed columns are directly connected in series.

[0072] Furthermore, the specific manner of bypass series connection is as follows: on the basis of direct series connection, when the three-way valve first connects the packed column where the first adsorbent is located and the collector, the liquid flowing out of the packed column where the first adsorbent is located is collected separately first. After a certain period of time, the collection is stopped. At this time, the three-way valve connects the two packed columns, and the remaining components enter the packed column where the second adsorbent is located.

[0073] When the mixture to be processed is a C6 cycloalkane mixture, the C6 cycloalkane mixture first passes through the first adsorbent (mainly capturing benzene), and high-purity cyclohexane first flows out and is collected through the bypass. The remaining components then pass through the second adsorbent (mainly capturing cyclohexane). At this time, high-purity cyclohexene first flows out. That is, the purification of cyclohexene and cyclohexane is completed in one-step adsorption process.

[0074] Compared with the prior art, the present invention has the following beneficial effects:

[0075] The present invention designs a class of metal-organic frameworks with a three-dimensional structure assembled after the coordination of 2,6-bis(ethyl / hydroxymethyl)benzimidazole anions and zinc ions, and uses a bypass series strategy to achieve the purification of cyclohexene and cyclohexane in one step.

[0076] (1) High-efficiency separation: The purification of cyclohexene and cyclohexane is completed in one-step adsorption process, avoiding multi-stage distillation or extraction steps.

[0077] (2) The metal-organic frameworks MAF-55 and MAF-56 structures of the present invention show ultra-high selectivity for benzene or cyclohexane in the separation of benzene / cyclohexene / cyclohexane, and still maintain ultra-high performance in the continuous cycle implementation, with good stability and recyclability. Description of the Drawings

[0078] Figure 1 Schematic diagram of the device for one-step purification of cyclohexene by direct series connection of double adsorbents (upper figure), and one-step purification of cyclohexene and cyclohexane by bypass series connection (lower figure).

[0079] Figure 2 Structural (a) and pore (b) diagrams of MAF-55.

[0080] Figure 3 Structural (a) and pore (b) diagrams of MAF-56.

[0081] Figure 4 PXRD spectra of MAF-55 after being soaked in different solvents for one week.

[0082] Figure 5 PXRD spectra of MAF-56 after being soaked in different solvents for one week.

[0083] Figure 6This is the thermogravimetric analysis diagram of MAF-55.

[0084] Figure 7 This is the thermogravimetric analysis diagram of MAF-56.

[0085] Figure 8 This is the adsorption-desorption isotherm (298K) of MAF-55 single-component benzene / cyclohexene / cyclohexane.

[0086] Figure 9 This is the adsorption-desorption isotherm (298K) of single-component benzene / cyclohexene / cyclohexane on MAF-56.

[0087] Figure 10 This is a gas chromatogram of the n-hexane extract of MAF-55 after acid hydrolysis after the sample was soaked in equimolar mixtures of benzene / cyclohexane, benzene / cyclohexene, cyclohexene / cyclohexane and benzene / cyclohexene / cyclohexane.

[0088] Figure 11 This is a gas chromatogram of the n-hexane extract of MAF-56 after acid hydrolysis after the sample was soaked in equimolar mixtures of benzene / cyclohexane, benzene / cyclohexene, cyclohexene / cyclohexane and benzene / cyclohexene / cyclohexane.

[0089] Figure 12 Statistical diagram of the cyclic stability of MAF-55 in an equimolar mixture of benzene / cyclohexene / cyclohexane.

[0090] Figure 13 Statistical diagram of the cyclic stability of MAF-56 in an equimolar mixture of benzene / cyclohexene / cyclohexane.

[0091] Figure 14 The liquid phase penetration curve of an equimolar benzene / cyclohexene / cyclohexane mixture on a MAF-55 column

[0092] Figure 15 This is the liquid phase breakthrough curve of an equimolar benzene / cyclohexene / cyclohexane mixture on a MAF-56 column.

[0093] Figure 16 This is the liquid phase breakthrough curve of an equimolar benzene / cyclohexene / cyclohexane mixture directly connected in series with a MAF-55 adsorption column and a MAF-56 adsorption column.

[0094] Figure 17 This is the liquid phase breakthrough curve of an equimolar benzene / cyclohexene / cyclohexane mixture of a MAF-55 adsorption column and a MAF-56 adsorption column connected in series. DETAILED DESCRIPTION

[0095] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field.

[0096] Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0097] Example 1 Preparation of MAF-55 Single Crystal

[0098] A mixture of Zn(OAc)2·2H2O (40 mg, 0.18 mmol), 2,6-diethylbenzimidazole (22 mg, 0.10 mmol), ammonium fluoride (8 mg, 0.22 mmol), isobutanol (1 mL), and ethylene glycol (1 mL) was sealed in a polytetrafluoroethylene reactor and maintained at 160 °C for 3 days, and then cooled to room temperature at a rate of 5 °C h –1 to form a small amount of light yellow block crystals, namely MAF-55 single crystal.

[0099] Example 2 Preparation of MAF-55 Powder

[0100] A mixture of Zn(OAc)2·2H2O (440 mg, 2.0 mmol), 2,6-diethylbenzimidazole (220 mg, 1.02 mmol), ammonium fluoride (80 mg, 2.16 mmol), isobutanol (10 mL), and ethylene glycol (20 mL) was sealed in a 100 mL pressure-resistant glass tube, maintained at 160 °C for 3 days, and then cooled to room temperature. After filtration, light yellow MAF-55 powder was obtained, washed with methanol, then dried in air, heated under vacuum to 250 °C, and then kept at a constant temperature for 4 hours to obtain MAF-55 powder (0.37 g, yield: ~92%).

[0101] Example 3 Preparation of MAF-56 Single Crystal

[0102] A mixture of Zn(NO3)2·6H2O (59.5 mg, 0.20 mmol), 2,6-bis(hydroxymethyl)benzimidazole (22 mg, 0.10 mmol), potassium nitrate (10 mg, 0.10 mmol), N,N-dimethylacetamide (1 mL), and ethanol (1 mL) was sealed in a polytetrafluoroethylene reactor, maintained at 140 °C for 3 days, and then cooled to room temperature at a rate of 5 °C h –1 to form a small amount of light yellow block crystals, namely MAF-56 single crystal.

[0103] Example 4 Preparation of MAF-56 Powder

[0104] A mixture of Zn(NO)3·6H2O (298 mg, 1.0 mmol), 2,6-bis(hydroxymethyl)benzimidazole (110 mg, 0.51 mmol), potassium nitrate (50 mg, 0.50 mmol), N,N-dimethylacetamide (10 mL) and ethanol (10 mL) was sealed in a 50 mL pressure-resistant glass tube, maintained at 140 °C for 12 hours, and then cooled to room temperature at a rate of 5 °C h –1 -1, and a pale yellow powder was obtained after filtration, washed with methanol, then dried in air, heated under vacuum to 250 °C, and then kept at a constant temperature for 4 hours to obtain MAF-56 powder (0.28 g, yield: ~85%).

[0105] Example 5 Adsorption Separation and Purification of Single Adsorbent

[0106] (1) The MAF-55 adsorption column was filled with an activated MAF-55 sample (1.60 g, prepared according to the method of Example 2) dispersed in mesitylene, and the tail end was directly connected to a collector.

[0107] (2) The MAF-56 adsorption column was filled with an activated MAF-56 sample (1.80 g, prepared according to the method of Example 4) dispersed in mesitylene, and the tail end was directly connected to a collector.

[0108] Example 6 Composition and Process of Double Adsorbent Series System

[0109] Composition of double adsorbent in series: The first adsorption column was filled with an activated MAF-55 sample (1.60 g) dispersed in mesitylene; the second adsorption column was filled with an activated MAF-56 sample (1.80 g) dispersed in mesitylene. The two adsorption columns were connected by a three-way valve.

[0110] The C6 cycloalkane mixture first passed through the first adsorbent (MAF-55, mainly capturing benzene), and the composition was analyzed by gas chromatography-mass spectrometry in real-time sampling. Initially, high-purity cyclohexane first flowed out from the first packed column and was collected from the bypass until the purity of cyclohexane was detected to be lower than a specific requirement. Subsequently, the three-way valve between the two packed columns was connected, and the remaining mixture then passed through the second adsorbent (MAF-56, mainly capturing cyclohexane). At this time, high-purity cyclohexene first flowed out and was collected. Finally, high-purity cyclohexene and cyclohexane were obtained.

[0111] (1) Direct series connection (as shown in Figure 1 the above figure): When the three-way valve connected the two adsorption columns, that is, the tail end of the MAF-55 adsorption column was directly connected to the front end of the MAF-56 adsorption column, at this time, the MAF-55 adsorption column and the MAF-56 adsorption column were directly connected in series.

[0112] (2) Bypass series connection (as shown in Figure 1(The following figure): When the three-way valve first connects the first adsorption column and the collector, the liquid flowing out of the MAF-55 adsorption column is collected separately first. After a certain period of time, the collection stops. At this time, the three-way valve connects the two adsorption columns, and the remaining components enter the MAF-56 adsorption column.

[0113] Experimental Example Performance Test

[0114] 1. Test Method

[0115] (1) Single crystal structure parameters: Single crystal diffraction data were collected on a Rigaku XtaLAB P300DS or Synergy R, DWsystem, HyPix single-crystal diffractometer (Cu Kα).

[0116] (2) Thermal stability characterization: Obtained by thermogravimetric analysis, heated to 700 °C at 5 °C min –1 on a TAQ55 thermogravimetric analyzer to obtain a thermogravimetric curve.

[0117] (3) Solvent stability characterization: By immersing the activated sample in different solvents (such as water, methanol, acetone, acid, base, etc.) for one week, X-ray diffraction (PXRD) data were collected on a SmartLab X-ray powder diffractometer (Cu Kα).

[0118] (4) Different vapor adsorption property characterization: MAF-55 and MAF-56 were placed in a glass sample tube. After vacuum heating treatment, their different vapor adsorption isotherms were measured on a BELSORP max II adsorption instrument at 298 K (controlled temperature by circulating water bath).

[0119] (5) Mixture adsorption and continuous adsorption-desorption cycle experiment: The activated sample (about 200 mg) was placed in a glass tube (60 mL), and then a 1:1:1 (molar ratio) benzene / cyclohexene / cyclohexane mixture (20 mL) was immediately injected into the glass tube, then sealed and stored at 298 K. After 12 hours, the sample was filtered and purged with N2 (20 mL min –1 ) for 30 minutes at room temperature to remove the surface solvent. A part of the sample (about 10 mg) was digested with nitric acid (0.2 mL, 6 M) and extracted three times with n-hexane (0.5 mL), and then the n-hexane extracts were combined (1.5 mL) for GC-MS analysis. At the same time, the remaining sample (non-acidified) was heated at 120 °C under vacuum for 2 hours and then used for the next adsorption process, and the above operations of adsorption in the mixture and desorption by heating were repeated for ten consecutive adsorption-desorption cycle experiments.

[0120] (6) Gas chromatography - mass spectrometry analysis: Analyze the ratio of benzene / cyclohexene / cyclohexane in the digestion solution on an Agilent 7890A gas chromatography (GC) system equipped with an Agilent 5975C mass spectrometer (MS) and an Agilent CP Sil5CB column. For each GC injection, manually inject 1 μL aliquots of the analyte. Data acquisition and processing are controlled by the Agilent 5975C data analysis software.

[0121] The purity of component i is calculated by the following formula:

[0122]

[0123] where A i is the peak area of component i.

[0124] The selectivity is calculated by the following formula: [[ID=I6]]

[0125]

[0126] where A' i are the peak areas of component i in the blank sample, respectively.

[0127] (7) Column breakthrough experiment: Disperse the activated MAF - 55 / MAF - 56 sample (1.60 / 1.80 g) with mesitylene (30 mL), transfer it to a glass column (length: 15 cm; diameter: 0.6 cm), and place a small cotton ball at the bottom. Then, slowly add a 50:50 (molar ratio) benzene / cyclohexene / cyclohexane mixture (10 mL) diluted with mesitylene (30 mL) to the top of the column, and collect the effluent at the bottom every 2 minutes. Finally, analyze the content of the effluent with a gas chromatography - mass spectrometry instrument.

[0128] The benzene / cyclohexene / cyclohexane production (Q i ) is defined by the amount of the cumulative outlet effluent with a purity of 99.9 / 99.5%+:

[0129]

[0130] where m is the mass of the adsorbent (g).

[0131] 2. Measurement results

[0132] Figure 2 Figure shows the structure and pore diagram of MAF - 55. This metal - organic framework crystallizes in the trigonal system, space group R3m, and the unit cell parameters are Unit cell volume In the structure of this metal - organic framework MAF - 55, each F -Two Zn(II) ions are bridged to form a {Zn(μ-F)} chain with a 31 helix along the c-axis. The organic ligand is completely deprotonated and coordinates with four Zn(II) atoms through four N atoms on two adjacent 31 helix {Zn(μ-F)} chains, forming a three-dimensional honeycomb framework with one-dimensional sugar-loaf-shaped pores along the c-axis (porosity: 22.7%). The pore window diameter is ( Figure 2 a, and the pore cavity size is ( Figure 2 b).

[0133] Figure 3 Figure of the structure and pores of MAF-56. This metal-organic framework MAF-56 is constructed from zinc ions and 2,6-bis(hydroxymethyl)benzimidazole anions, with the chemical formula [Zn(dobdim)], where dobdim 2- represents the organic ligand 2,6-bis(hydroxymethyl)benzimidazole anion. This metal-organic framework also crystallizes in the trigonal system, space group The unit cell parameters are The unit cell volume In the structure of this metal-organic framework, each Zn(II) coordinates / chelates with N / O atoms from the dobdim 2- ligand. The dobdim 2- ligand has hydroxyl groups and completely deprotonated imidazole groups, and coordinates with four Zn(II) through four N atoms and two O atoms, while the non-deprotonated H2dobdim coordinates with two Zn(II) through two N atoms and two O atoms, finally forming a three-dimensional framework with one-dimensional pores (porosity: 31.8%). The pore window diameter is ( Figure 3 a, and the pore cavity size is ( Figure 3 b).

[0134] Figure 4 Figure shows the PXRD patterns of MAF-55 after being soaked in different solvents for one week. It can be seen that the original synthesized powder diffraction peaks of MAF-55 can completely correspond to those of the simulated powder, proving that the synthesized sample is a pure phase. After being placed for one week under different conditions, the powder diffraction peaks completely correspond to those of the simulated powder, proving its good stability.

[0135] Figure 5 Figure shows the PXRD patterns of MAF-56 after being soaked in different solvents for one week. It can be seen that the original synthesized powder diffraction peaks of MAF-56 can completely correspond to those of the simulated powder, proving that the synthesized sample is a pure phase. After being placed for one week under different conditions, the powder diffraction peaks completely correspond to those of the simulated powder, proving its good stability.

[0136] Figure 6This is the thermogravimetric analysis diagram of MAF-55. It can be seen that MAF-55 loses its guest at 100 °C and can be stable up to 550 °C, indicating relatively high thermal stability.

[0137] Figure 7 This is the thermogravimetric analysis diagram of MAF-56. It can be seen that MAF-56 can be stable up to 300 °C, indicating relatively high thermal stability.

[0138] Figure 8 This is the adsorption-desorption isotherm (298K) of MAF-55 for single-component benzene / cyclohexene / cyclohexane. It can be seen that the adsorption amount of benzene is the largest, followed by cyclohexene, and the adsorption amount of cyclohexane is the smallest, further indicating the possibility of MAF-55 for separating benzene / cyclohexene / cyclohexane.

[0139] Figure 9 This is the adsorption-desorption isotherm (298K) of MAF-56 for single-component benzene / cyclohexene / cyclohexane. It can be seen that the adsorption amounts of benzene, cyclohexene, and cyclohexane are not very different, but the adsorption amount of cyclohexane in the low-pressure part is greater than that of cyclohexene and benzene.

[0140] Figure 10 This is the gas chromatogram of the n-hexane extract after acidolysis of the sample of MAF-55 soaked in equimolar benzene / cyclohexane, benzene / cyclohexene, cyclohexene / cyclohexane, and benzene / cyclohexene / cyclohexane mixtures. It can be seen that in the binary and ternary benzene / cyclohexene / cyclohexane mixtures, MAF-55 still maintains ultra-high selectivity for benzene.

[0141] Figure 11 This is the gas chromatogram of the n-hexane extract after acidolysis of the sample of MAF-56 soaked in equimolar benzene / cyclohexane, benzene / cyclohexene, cyclohexene / cyclohexane, and benzene / cyclohexene / cyclohexane mixtures. It can be seen that in the binary and ternary benzene / cyclohexene / cyclohexane mixtures, MAF-56 still maintains high selectivity for cyclohexane.

[0142] Figure 12 This is the statistical chart of the cyclic stability data of MAF-55 in an equimolar benzene / cyclohexene / cyclohexane mixture. It can be seen that after ten consecutive rounds of adsorption / desorption, the purity of benzene adsorbed by MAF-55 remains almost unchanged, indicating good cyclic performance of MAF-55.

[0143] Figure 13 This is the statistical chart of the cyclic stability data of MAF-56 in an equimolar benzene / cyclohexene / cyclohexane mixture. It can be seen that after ten consecutive rounds of adsorption / desorption, the purity of cyclohexane adsorbed by MAF-56 remains almost unchanged, indicating good cyclic performance of MAF-56.

[0144] Figure 14It is the liquid-phase breakthrough curve of an equimolar benzene / cyclohexene / cyclohexane mixture for the MAF-55 column. Since MAF-55 has the strongest interaction with benzene and the weakest interaction with cyclohexane, it can be seen that cyclohexane flows out first. Therefore, a high-purity cyclohexane can be obtained after a single adsorption of the C6 cycloalkane mixture through the MAF-55 adsorption column.

[0145] Figure 15 It is the liquid-phase breakthrough curve of an equimolar benzene / cyclohexene / cyclohexane mixture for the MAF-56 column. Cyclohexane has the strongest interaction with the adsorbent MAF-56 and the weakest interaction with benzene, and it can be seen that benzene flows out first. Therefore, a high-purity benzene can be obtained after a single adsorption of the C6 cycloalkane mixture through the MAF-56 adsorption column.

[0146] Figure 16 It is the liquid-phase breakthrough curve of an equimolar benzene / cyclohexene / cyclohexane mixture for the directly series-connected MAF-55 adsorption column and MAF-56 adsorption column. It can be seen that the ortho-benzene / cyclohexene / cyclohexane-selective adsorbent MAF-55 will adsorb most of the benzene; the anti-benzene / cyclohexene / cyclohexane-selective adsorbent MAF-56 will adsorb most of the cyclohexane, and cyclohexene flows out of the outlet first. Therefore, after a single adsorption of the C6 cycloalkane mixture through the directly series-connected ( Figure 1 the above figure) MAF-55 adsorption column and MAF-56 adsorption column, a high-purity cyclohexene can be obtained.

[0147] Figure 17 It is the liquid-phase breakthrough curve of an equimolar benzene / cyclohexene / cyclohexane mixture for the bypass series-connected MAF-55 adsorption column and MAF-56 adsorption column. It can be seen that the adsorbent MAF-55 has the strongest interaction with benzene and the weakest interaction with cyclohexane, and cyclohexane flows out first. Therefore, high-purity cyclohexane can be collected first through the bypass at the end of the first adsorption column. At the same time, the composition of the outflowing liquid is analyzed in real time by a gas chromatography-mass spectrometry (GC-MS) analyzer. When the purity of cyclohexane is less than the target purity, the collection is stopped in time, and the remaining mixture (mainly cyclohexene, remaining cyclohexane, and a small amount of benzene) is allowed to enter the second anti-selective adsorption column. Cyclohexane has the strongest interaction with the adsorbent MAF-56, resulting in cyclohexene flowing out first. At this time, high-purity cyclohexene is collected. Since the pressure of the second adsorption column for adsorbing cyclohexane is reduced, the amount of high-purity cyclohexene flowing out is more than that of the cyclohexene purification by direct series connection. The one-step adsorption process can not only obtain high-purity cyclohexene but also high-purity cyclohexane. Therefore, after a single adsorption of the C6 cycloalkane mixture through the bypass series-connected ( Figure 1 the following figure) MAF-55 adsorption column and MAF-56 adsorption column, high-purity cyclohexane can be collected in the bypass, and high-purity cyclohexene can be obtained at the series-connected end.

[0148] As can be seen from the above, the two adsorbents MAF-55 and MAF-56 have opposite benzene / cyclohexene / cyclohexane selectivities. For benzene, cyclohexene, and cyclohexane compounds, since the molecular polarity order is benzene > cyclohexene > cyclohexane, and the molecular size order is benzene < cyclohexene < cyclohexane, most porous materials are benzene / cyclohexene / cyclohexane selective, such as MAF-55. A few porous materials with abundant polar sites and appropriate pore sizes / shapes can utilize multiple non-classical hydrogen bonds to achieve special cyclohexane / benzene selectivity. MAF-56 achieves reverse selectivity by forming host-guest C-H…O / N interactions between the abundant N / O sites in the pores and the guest. Among them, adsorbents that achieve cyclohexane / cyclohexene / benzene selectivity for the three components are unprecedented.

[0149] Traditional (direct) tandem dual adsorbents achieve one-step purification of cyclohexene in a C6 cycloalkane mixture. By connecting two adsorbents with positive and reverse benzene / cyclohexene / cyclohexane selectivities in series, the adsorbent with positive benzene / cyclohexene / cyclohexane selectivity will adsorb a large amount of benzene; the adsorbent with reverse benzene / cyclohexene / cyclohexane selectivity will adsorb a large amount of cyclohexane, and cyclohexene will flow out of the outlet first. By controlling the collection time, high-purity cyclohexene can be obtained. Finally, one-step purification of cyclohexene in a benzene / cyclohexene / cyclohexane ternary mixture is achieved.

[0150] The bypass tandem strategy achieves simultaneous purification of two components, cyclohexene and cyclohexane. When the C6 cycloalkane mixture first passes through the first adsorption column with positive selectivity, since the adsorbent MAF-55 has the strongest interaction with benzene and the weakest interaction with cyclohexane, cyclohexane flows out first. Therefore, high-purity cyclohexane can be collected first through a bypass at the end of the first adsorption column. At the same time, the composition of the outflowing liquid is analyzed in real time by a gas chromatography-mass spectrometry (GC-MS) analyzer. When the purity of cyclohexane is less than the target purity, the collection is stopped in time, and the remaining mixture (mainly cyclohexene, remaining cyclohexane, and a small amount of benzene) is allowed to enter the second adsorption column with reverse selectivity. Cyclohexane has the strongest interaction with the adsorbent MAF-56, resulting in cyclohexene flowing out first. At this time, high-purity cyclohexene is collected. Since the pressure of the second adsorption column for adsorbing cyclohexane is reduced, the amount of high-purity cyclohexene flowing out is more than that of the cyclohexene purified by direct tandem. The one-step adsorption process can not only obtain high-purity cyclohexene but also high-purity cyclohexane.

[0151] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A zinc-based metal-organic framework material, characterized in that, The zinc-based metal-organic framework material is formed by coordinating 2,6-bis(ethyl / hydroxymethyl)benzimidazole anion with zinc ions to assemble a zinc-based metal-organic framework material with a three-dimensional structure.

2. A metal-organic framework MAF-55, characterized in that, The metal-organic framework MAF-55 is constructed from zinc ions, fluoride ions, and 2,6-bis(ethyl)benzimidazole anion, and its chemical formula is [Zn2F2(ebdim)]; Among them, ebdim 2- represents the organic ligand 2,6 - bis(ethyl)benzimidazole anion.

3. The metal-organic framework MAF-55 according to claim 2, wherein The metal-organic framework MAF-55 is trigonal with a space group of The unit cell parameters are The unit cell volume 4. The preparation method of the metal-organic framework MAF-55 according to claim 2 or 3, characterized in that, It includes the following steps: Mix zinc salt, fluoride ions, and 2,6-bis(ethyl)benzimidazole in ethylene glycol or a mixed solvent containing ethylene glycol, and obtain the metal-organic framework MAF-55 by solvothermal method.

5. A metal-organic framework MAF-56, characterized in that The metal-organic framework MAF-56 is constructed from zinc ions and 2,6-bis(hydroxymethyl)benzimidazole anion, and its chemical formula is [Zn(dobdim)]; Among them, dobdim 2- represents the organic ligand 2,6-bis(hydroxymethyl)benzimidazole anion.

6. The metal-organic framework MAF-56 according to claim 5, characterized in that The metal-organic framework MAF-56 is a trigonal system with a space group The unit cell parameters are Unit cell volume 7. The preparation method of the metal-organic framework MAF-56 according to claim 5 or 6, characterized in that, It includes the following steps: Mix zinc salt, nitrate, and 2,6-bis(hydroxymethyl)benzimidazole in N,N-dimethylacetamide or a mixed solvent containing N,N-dimethylacetamide, and obtain the metal-organic framework MAF-56 by solvothermal method.

8. Use of the zinc-based metal-organic framework material according to claim 1, or the metal-organic framework MAF-55 according to claim 2 or 3, or the metal-organic framework MAF-56 according to claim 5 or 6 in the adsorption and separation of C6 cycloalkanes.

9. A packed column breakthrough adsorption system, characterized in that, The adsorbent of the packed column breakthrough adsorption system comprises one or more of the zinc-based metal-organic framework material according to claim 1, the metal-organic framework MAF-55 according to claim 2 or 3, and the metal-organic framework MAF-56 according to claim 5 or 6.

10. A dual adsorbent series system, characterized in that, The double adsorbent series system includes a first adsorbent, a second adsorbent, at least two packed columns, and valves. The first adsorbent and the second adsorbent are respectively loaded into different packed columns, and the packed columns are connected through valves; Among them, the first adsorbent is the metal-organic framework MAF-55 according to claim 2 or 3; the second adsorbent is the metal-organic framework MAF-56 according to claim 5 or 6.

Images