Method for separating C8 aromatic isomer

Abstract

The invention discloses a method for separating a C8 aromatic isomer, which comprises the following steps: a mixed gas containing the C8 aromatic isomer is subjected to adsorption separation, an adsorbent adopted in the adsorption separation comprises a pillared MOF material, the pillared MOF material comprises metal ions and ligands, and the ligands comprise a main ligand and a pillared ligand. The pillared MOF material has the advantages of good stability, developed pore structure and large BET specific surface area, is used for separating C8 aromatic isomers, has high adsorption capacity and high adsorption separation selectivity, and preferentially adsorbs ethylbenzene.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of adsorption separation materials, and particularly relates to a method for separating carbon octahydroisomer. BACKGROUND

[0002] Xylene isomers and ethylbenzene are widely used in the synthesis of polyester, plasticizers, dyes, coatings and pharmaceutical chemicals, and are extremely important raw materials in basic chemical industry. Industrially, these isomers are mainly obtained by catalytic reforming, toluene disproportionation or cracked gasoline aromatization, etc., ultimately forming a carbon octahydroaromatic mixture (C8 aromatics) containing o-xylene (OX), m-xylene (MX), p-xylene (PX) and ethylbenzene (EB). Due to the similarity of these isomers in boiling point, polarity and molecular size, etc., conventional separation methods have the technical bottlenecks of poor selectivity, high energy consumption, etc.

[0003] The main separation technologies currently adopted include crystallization method, membrane method, adsorption method and simulated moving bed (SMB) process. The crystallization method (such as US5448005) can effectively enrich p-xylene, but the process is complicated and the cost is high; the membrane separation technology has shown good separation performance in the laboratory (Science, 2003, 300(5618): 456-460), but due to the short service life and high cost of the membrane, it has not been widely used in industry. The simulated moving bed technology (such as UOP's Parex process, Chem. Eng. Prog., 1970, 66: 70-75.) is the most mature adsorption separation route currently applied in industry, which uses non-acidic MFI type molecular sieve and other adsorbents for liquid phase circulation separation, but the consistency of the device is extremely high, and the operation depends on the desorbent such as diethylbenzene, which has certain limitations (CN109529764A).

[0004] Adsorption separation technology has attracted much attention in the field of aromatic hydrocarbon separation due to its low energy consumption, high efficiency, and continuous operation. In recent years, metal-organic framework materials (MOFs) have become an important direction for constructing new generation of high-efficiency adsorbents due to their flexible structure design, large specific surface area, and adjustable pore size. By designing MOFs materials with uniform nanochannels, size exclusion and shape recognition of molecules with similar structures can be achieved, significantly improving the separation performance of isomers. Although a large number of studies have focused on the preferential adsorption of PX, as the market for PX becomes saturated, the demand for ethylbenzene in high-end materials such as polystyrene continues to increase, and the technical strategy of preferentially adsorbing ethylbenzene is gradually valued by the industry. On the one hand, ethylbenzene is a core raw material for the synthesis of styrene, with high economic value-added; on the other hand, ethylbenzene can affect the selective conversion of PX during the isomerization process, and if it can be preferentially removed before entering the isomerization reactor, the reaction temperature can be reduced by 20-30℃, the hydrogen consumption can be reduced, and the processing load can be increased by 20-50%, significantly optimizing the overall process (CN114409498B). Current studies have shown that metal formate MOFs materials such as [Ni3(HCOO)6] and [Co3(HCOO)6] have good adsorption selectivity for ethylbenzene, and can effectively separate ethylbenzene from C8 aromatic hydrocarbon mixture through size exclusion and shape matching (CN114409498B). However, the adsorption selectivity of this type of material for ethylbenzene mainly depends on size sieving, the recognition mechanism is relatively single, the thermodynamic regulation ability is limited, and the pore size is small, which limits the molecular diffusion rate, resulting in slow adsorption kinetics, limited breakthrough capacity, and limiting its practical application in industrial scenarios. SUMMARY

[0005] The present application aims to provide a method for separating carbon eight aromatic isomers, which comprises performing adsorption separation on a mixed gas containing carbon eight aromatic isomers, wherein the adsorbent used in the adsorption separation comprises a pillared MOF material, and the pillared MOF material comprises metal ions and ligands, and the ligands comprise primary ligands and pillared ligands.

[0006] The pillared MOF material used in the present application is constructed from two types of ligands, one type being primary ligands (or called base ligands) that coordinate with metal ions to form a layered structure, and the other type being pillared ligands that play a connecting role between layers.

[0007] According to some embodiments of the present application, the primary ligand is selected from C2-C10 heteroaromatic dicarboxylic acids with or without substituents, and the substituents are selected from one or more of C1-C5 alkyl, halogen, C1-C5 halogenated alkyl, amino, hydroxyl, cyano, and C1-C5 alkoxy.

[0008] According to some embodiments of the present application, the C2-C10 heteroaromatic ring dicarboxylic acid with or without substituents is selected from furan dicarboxylic acid with or without substituents, thiophene dicarboxylic acid with or without substituents, imidazole dicarboxylic acid with or without substituents.

[0009] According to some embodiments of the present application, the substituents are selected from one or more of methyl, ethyl, fluorine, chlorine, bromine, iodine, trifluoromethyl, amino, hydroxyl, cyano, methoxy.

[0010] According to some embodiments of the present application, the main ligand is selected from 2,5-furan dicarboxylic acid or 2,5-thiophene dicarboxylic acid.

[0011] According to some embodiments of the present application, the pillared ligand is as shown in Formula I:

[0012]

[0013] In Formula I, each R is independently selected from hydrogen, C1-C5 alkyl, halogen, C1-C5 haloalkyl, amino, hydroxyl, cyano, C1-C5 alkoxy.

[0014] According to some embodiments of the present application, each R is independently selected from hydrogen, methyl, ethyl, fluorine, chlorine, bromine, iodine, trifluoromethyl, amino, hydroxyl, cyano, methoxy. According to some embodiments of the present application, each R is hydrogen.

[0015] According to some embodiments of the present application, the pillared ligand is meso-α,β-di(4-pyridyl)ethanediol.

[0016] According to some embodiments of the present application, the metal ion is selected from cobalt ion and nickel ion. According to some embodiments of the present application, the metal ion is cobalt ion.

[0017] According to some embodiments of the present application, the pillared MOF material has a pore size of

[0018] According to some embodiments of the present application, the pillared MOF material has a BET specific surface area of 400-580 m 2 / g.

[0019] According to some embodiments of the present application, the pillared MOF material has a pore volume of 0.1-0.2 cm 3 / g.

[0020] According to some embodiments of the present application, the method for preparing the pillared MOF material comprises: dissolving a metal inorganic salt, a pillaring ligand and a host ligand in a solvent, and performing a hydrothermal reaction. The temperature of the hydrothermal reaction affects the generation of crystals, and too high or too low temperature can result in failure to generate crystals. Therefore, the temperature of the hydrothermal reaction is 60-150°C, and the reaction time is 12-72 hours. Further preferably, the temperature is 70-100°C, and the reaction time is 24-48 hours.

[0021] According to some embodiments of the present application, in the above preparation method, after the hydrothermal reaction is completed, the generated solid is washed and dried. According to some embodiments of the present application, after the hydrothermal reaction is completed, the product is sequentially washed with N,N-dimethylformamide and anhydrous methanol, and then naturally dried in air to obtain the product; the drying time is 6-24 hours. According to some embodiments of the present application, the product after the hydrothermal reaction is washed and centrifuged with N,N-dimethylformamide for several times to replace the residual alkali solution and inorganic salt in the pores, and then washed and centrifuged with anhydrous methanol for several times to replace the residual organic ligand and water in the pores, thereby completing the purification of the adsorbent.

[0022] According to some embodiments of the present application, in the above preparation method, the solvent is a mixture of N-dimethylformamide and methanol.

[0023] According to some embodiments of the present application, in the above preparation method, the metal inorganic salt is selected from the chloride salt, nitrate salt, acetate salt, carbonate salt, sulfate salt or perchlorate salt of a metal ion.

[0024] According to some embodiments of the present application, in the above preparation method, the molar ratio of the metal inorganic salt to the pillaring ligand is 1:(1-3).

[0025] According to some embodiments of the present application, in the above preparation method, the molar ratio of the inorganic salt, pillaring ligand and host ligand is 1:(1.5-2):1, and most preferably 1:1.5:1.

[0026] According to some embodiments of the present application, the temperature for the adsorption separation is -5-300°C, such as -5°C, 0°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 150°C, 160°C, 170°C, 200°C, etc. According to some embodiments of the present application, the temperature for the adsorption separation is 20-120°C. According to some embodiments of the present application, the temperature for the adsorption separation is 20-90°C.

[0027] According to some embodiments of the present application, the total pressure of the mixed gas is 100-1000 kPa, such as 100 kPa, 200 kPa, 300 kPa, 400 kPa, 500 kPa, 600 kPa, 700 kPa, 800 kPa, 900 kPa, etc. According to some embodiments of the present application, the total pressure of the mixed gas is 100-400 kPa.

[0028] According to some embodiments of the present application, the temperature of the adsorption separation is 50-70℃, and the total pressure of the mixed gas is 100 kPa.

[0029] According to some embodiments of the present application, the temperature of the adsorption separation is 60℃, and the total pressure of the mixed gas is 100 kPa.

[0030] According to some embodiments of the present application, the carbon eight aromatic hydrocarbon isomers include at least two of p-xylene, o-xylene, m-xylene and ethylbenzene.

[0031] According to some embodiments of the present application, the carbon eight aromatic hydrocarbon isomers include ethylbenzene and one, two or three selected from p-xylene, o-xylene and m-xylene. When the mixed gas contains ethylbenzene, the adsorbent preferentially adsorbs ethylbenzene.

[0032] The preparation process of the metal organic framework material is to use cheap and easily available symmetric carboxylic acid as a pillar supporting ligand or a main ligand, and to perform a hydrothermal reaction with a series of metal inorganic salts, so that the raw material price of the material is low, the synthesis condition is mild, the operation is simple, the post-treatment is easy, and the material synthesis cost is low. In the method of the present application, the metal organic framework material has high adsorption separation selectivity for ethylbenzene in xylene isomers, and the material structure and adsorption performance are stable, the stability is good, and the material has good industrial application prospect.

[0033] The metal organic framework material used in the present application as an adsorbent only needs to be heated to 50-150℃ under vacuum or inert atmosphere conditions such as nitrogen after adsorption saturation, and maintained for 2-10 hours to realize regeneration. Too high temperature or too long time will cause the structure of the adsorbent to be destroyed; too low temperature or too short time, the adsorbate remaining in the adsorbent will not be completely removed.

[0034] The adsorbent prepared by the above preferred method in the present application has stable structure and performance, and has high selectivity and adsorption capacity for ethylbenzene in xylene isomers.

[0035] Preferably, the flow rate of the mixed gas through the adsorbent is 1-50 mL / min.

[0036] Preferably, the mixed gas comprises two or more of p-xylene, m-xylene, o-xylene and ethylbenzene. The feed gas composition of the present application is very wide, and various concentrations can be applied, from 50 ppm to 95%.

[0037] The metal organic framework material used in the present application can be prepared into spherical, columnar, particulate or other adsorption separation materials by different processing techniques, or into membrane materials according to existing conventional techniques for the preferential adsorption of ethylbenzene by xylene isomers.

[0038] Compared with the prior art, the present application has the following advantages:

[0039] The metal organic framework adsorbent prepared in the present application is a metal organic framework material with uniform pore structure, and the pore size is The pore size of the adsorbent is close to the kinetic diameter range of xylene isomers (ethylbenzene: p-xylene: m-xylene: o-xylene: ), which is suitable for the separation of xylene isomers. The xylene molecules with larger kinetic size (such as m-xylene and o-xylene) diffuse into the pores slowly, while the p-xylene and ethylbenzene molecules with smaller kinetic size diffuse into the pores faster, so that the material can separate xylene isomers based on the difference in kinetic diffusion rate. In addition, the aromatic carboxylic acid ligand endows the pore with aromatic characteristics, which can produce effective π-π stacking with the benzene ring of xylene isomers, and the smaller molecules can produce more effective π-π stacking with the benzene ring of the pore. Notably, the smaller five-membered ring in the main ligand makes the pore in the vertical direction have a secondary space similar to a "pocket", which makes the ethyl group of the EB molecule more suitable, so that the material can also realize effective separation of xylene isomers and preferential adsorption of ethylbenzene based on the difference in thermodynamic affinity.

[0040] The ligand and metal salt used for the preparation of the metal organic framework material involved in the present application are inexpensive and easy to obtain, the synthesis conditions are mild, the purification steps are simple, and the operation and scale-up are easy. The metal organic framework material involved in the present application is structurally stable and has stable performance, has a high adsorption capacity for p-xylene isomers, can realize high-efficiency separation of xylene isomers and preferential adsorption of ethylbenzene at very low concentrations, and the adsorption performance remains the same as the original effect after repeated adsorption-regeneration. In terms of preferential adsorption of ethylbenzene in xylene isomers, the adsorbent prepared in the present application is far superior to most solid adsorbents. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 The isotherm of xylene isomer single-component vapor adsorption in Example 1.

[0042] Figure 2 Figure for breakthrough experiment of xylene isomer mixed gas (equal proportion) in Example 1.

[0043] Figure 3 Figure for breakthrough experiment of xylene isomer mixed gas (actual industrial proportion) in Example 1. DETAILED DESCRIPTION

[0044] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely used to explain the present application, and do not limit the protection scope of the present application.

[0045] In the present application, the terms "carbon eight aromatic hydrocarbon isomer" and "xylene isomer" can be used interchangeably, representing aromatic hydrocarbons with molecular formula C8H10, examples including p-xylene, m-xylene, o-xylene, ethylbenzene.

[0046] Measurement method

[0047] 1. Measurement method of pore size:

[0048] The pore size of the adsorbent material described in the present application is obtained based on the CIF file of single crystal structure test, and analyzed by the structure measurement tool in the Material Studio software. The specific method is as follows: the distance between the closest two atomic centers on both sides of the pore opening in the corresponding crystal direction is measured. If the closest atomic center distance measured in the x (or a) direction and the y (or b) direction of the material is both , then the pore size of the pore is defined as

[0049] 2. Measurement method of specific surface area:

[0050] The specific surface area of the material described in the present application is determined by nitrogen adsorption-desorption isotherm test at 77K. The test sample is pretreated by degassing under vacuum or inert atmosphere to remove surface impurities. Then, based on the nitrogen adsorption data in the relative pressure P / P0=0.05 to 0.30 range, the specific surface area of the material is calculated according to the BET (Brunauer-Emmett-Teller) model, and the unit is m 2 / g.

[0051] 3. Measurement method of pore volume:

[0052] The pore volume of the material in the present application is determined by nitrogen adsorption-desorption isotherm test at 77K. The total pore volume of the material is calculated based on the adsorption amount at relative pressure P / P0≈0.99, assuming that the pores are completely filled with liquid nitrogen at this condition. The adsorption amount is converted according to the density of liquid nitrogen (about 0.808 g / cm 3 ), and finally the pore volume per unit mass of the material is obtained, with the unit of cm 3 / g.

[0053] Example 1

[0054] 0.37 mmol of meso-α,β-di(4-pyridyl)ethyleneglycol (DPG), 0.56 mmol of cobalt nitrate hexahydrate were dissolved in a mixed solution of DMF / anhydrous methanol (15 mL each), followed by the addition of 0.37 mmol of 2,5-furandicarboxylic acid (FDCA), and then placed in an 80°C oven for 24 h after complete dissolution. After the reaction was completed, the sample was cooled to room temperature, and the solid product was collected by suction filtration, washed with DMF and methanol three times respectively, and then naturally dried in air to obtain the sample. The pore size of the material is , the BET specific surface area is 542 m 2 / g, and the pore volume is 0.17 cm 3 / g. The purified adsorbent was degassed at 150°C under vacuum for 24 hours to obtain a desolvated adsorbent, followed by gas adsorption.

[0055] In order to test the adsorption separation performance of the metal organic framework material prepared in this example, a single-component vapor adsorption experiment of xylene isomers was carried out using the above adsorbent. 100 mg of the adsorbent was taken, and the adsorption temperature was set to 60°C. The test results show that the adsorption amounts of xylene, ethylbenzene, m-xylene and o-xylene are 181.5 mg / g, 152.9 mg / g, 116.1 mg / g and 67.5 mg / g respectively at 60°C and 1 kPa, and the adsorption isotherm is shown in Figure 1 .

[0056] In order to verify the actual separation effect of the above metal organic framework material on xylene isomers, a breakthrough experiment of xylene isomer mixed gas was carried out using the above synthesized adsorbent. Specifically, the components of PX, EB, MX and OX were prepared into a mixed solution with a volume ratio of 1:1:1:1, and then nitrogen was used as the bubbling gas to generate xylene isomer mixed gas through the above mixed solution to carry out the breakthrough experiment, with the breakthrough temperature being 60°C, the pressure being 0.1 MPa, and the nitrogen flow rate being 20 mL / min. The test results show that OX breaks through at 60 min / g, MX breaks through at 844 min / g, PX breaks through at 1028 min / g, and EB breaks through at 1120 min / g, and the breakthrough curve is shown in Figure 2 .

[0057] To verify the actual separation effect of the above-mentioned metal-organic framework material industrial actual component on the mixture of para-xylene isomers, a breakthrough experiment of xylene isomer mixed gas was carried out using the above-synthesized adsorbent. The specific method is to prepare a mixed solution by mixing PX, EB, MX, OX and other components in a volume ratio of 22:6:50:22, and then use nitrogen as the bubbling gas to generate xylene isomer mixed gas through the above mixed solution to carry out the breakthrough experiment. The breakthrough temperature is 60°C, the pressure is 0.1 MPa, and the nitrogen flow rate is 20 mL / min. After testing, OX is broken through at 89 min / g, MX is broken through at 765 min / g, PX is broken through at 1318 min / g, and EB is broken through at 1856 min / g. The breakthrough curve is shown in Figure 2. Figure 3 .

[0058] Example 2

[0059] The metal-organic framework synthesized in Example 1 was degassed at 150°C under vacuum for 24 hours to obtain a desolvated adsorbent, and then gas adsorption was carried out.

[0060] A single-component vapor adsorption experiment of xylene isomers was carried out using the above adsorbent. 100 mg of adsorbent was taken and the adsorption temperature was set to 30°C. After testing, the adsorption amounts of para-xylene, ethylbenzene, m-xylene and o-xylene were 224.8 mg / g, 184.6 mg / g, 157.8 mg / g and 131.0 mg / g, respectively, at 30°C and 1 kPa.

[0061] A breakthrough experiment of xylene isomer mixed gas was carried out using the above-synthesized adsorbent. The specific method is to prepare a mixed solution by mixing PX, EB, MX, OX and other components in a volume ratio of 1:1:1:1, and then use nitrogen as the bubbling gas to generate xylene isomer mixed gas through the above mixed solution to carry out the breakthrough experiment. The breakthrough temperature is 30°C, the pressure is 0.1 MPa, and the nitrogen flow rate is 20 mL / min. After testing, OX is broken through at 92 min / g, MX is broken through at 712 min / g, PX is broken through at 1032 min / g, and EB is broken through at 1101 min / g.

[0062] To verify the actual separation effect of the above-mentioned metal organic framework material industrial actual component on the mixture of para-xylene isomers, a breakthrough experiment of xylene isomer mixed gas was carried out using the above-synthesized adsorbent. The specific method is to prepare a mixed solution by mixing PX, EB, MX, OX and other components in a volume ratio of 22:6:50:22, and then use nitrogen as the bubbling gas to generate xylene isomer mixed gas through the above-mentioned mixed solution to carry out the breakthrough experiment, the breakthrough temperature is 30°C, the pressure is 0.1 MPa, and the nitrogen flow rate is 20 mL / min. The test shows that OX breaks through at 114 min / g, MX breaks through at 688 min / g, PX breaks through at 1059 min / g, and EB breaks through at 1798 min / g.

[0063] Example 3

[0064] The metal organic framework synthesized in Example 1 was degassed under vacuum at 150°C for 24 hours to obtain a desolvated adsorbent, and then gas adsorption was carried out.

[0065] A single-component vapor adsorption experiment of xylene isomers was carried out using the above-mentioned adsorbent. 100 mg of adsorbent was taken and the adsorption temperature was set to 90°C. The test shows that the adsorption amounts of para-xylene, ethylbenzene, m-xylene and o-xylene are 127.2 mg / g, 120.7 mg / g, 93.4 mg / g and 34.5 mg / g respectively at 90°C and 1 kPa.

[0066] A breakthrough experiment of xylene isomer mixed gas was carried out using the above-synthesized adsorbent. The specific method is to prepare a mixed solution by mixing PX, EB, MX, OX and other components in a volume ratio of 1:1:1:1, and then use nitrogen as the bubbling gas to generate xylene isomer mixed gas through the above-mentioned mixed solution to carry out the breakthrough experiment, the breakthrough temperature is 90°C, the pressure is 0.1 MPa, and the nitrogen flow rate is 20 mL / min. The test shows that OX breaks through at 43 min / g, MX breaks through at 635 min / g, PX breaks through at 874 min / g, and EB breaks through at 961 min / g.

[0067] To verify the actual separation effect of the above-mentioned metal organic framework material industrial actual component on the mixture of para-xylene isomers, a breakthrough experiment of xylene isomer mixed gas was carried out using the above-synthesized adsorbent. The specific method is to prepare a mixed solution by mixing PX, EB, MX, OX and other components in a volume ratio of 22:6:50:22, and then use nitrogen as the bubbling gas to generate xylene isomer mixed gas through the above-mentioned mixed solution to carry out the breakthrough experiment, the breakthrough temperature is 90°C, the pressure is 0.1 MPa, and the nitrogen flow rate is 20 mL / min. The test shows that OX breaks through at 62 min / g, MX breaks through at 571 min / g, EB breaks through at 906 min / g, and PX breaks through at 1219 min / g.

[0068] Example 4

[0069] Dissolve 0.37 mmol meso-a, b-bis(4-pyridyl)ethyleneglycol (DPG), 0.56 mmol cobalt nitrate hexahydrate into a mixed solution of DMF / anhydrous methanol (15 mL each), then add 0.37 mmol 2, 5-thiophenedicarboxylic acid (TDCA), and place in an 80 °C oven for 24 h after complete dissolution. Cool to room temperature after the reaction is completed, collect the solid product by suction filtration, wash three times with DMF and methanol respectively, and dry naturally in air to obtain the sample. The pore size of this material is The BET specific surface area is 414 m 2 / g, and the pore volume is 0.13 cm 3 / g. The purified adsorbent is degassed at 150 °C under vacuum for 24 h to obtain the desolvated adsorbent, followed by gas adsorption.

[0070] In order to test the adsorption separation performance of the metal organic framework material prepared in this example, a single-component vapor adsorption experiment of xylene isomers was carried out using the above adsorbent. Take 100 mg of adsorbent, and set the adsorption temperature to 60 °C. The test results show that the adsorption amounts of xylene, ethylbenzene, m-xylene and o-xylene are 151.9 mg / g, 142.1 mg / g, 96.1 mg / g and 61.5 mg / g respectively at 60 °C and 1 kPa.

[0071] In order to verify the actual separation effect of the above metal organic framework material on xylene isomers, a breakthrough experiment of xylene isomer mixed gas was carried out using the above synthesized adsorbent. The specific method is to prepare a mixed solution of PX, EB, MX, OX and other components in a volume ratio of 1:1:1:1, then use nitrogen as the bubbling gas, and generate xylene isomer mixed gas through the above mixed solution to carry out the breakthrough experiment, with a breakthrough temperature of 60 °C, a pressure of 0.1 MPa, and a nitrogen flow rate of 20 mL / min. The test results show that OX breaks through at 55 min / g, MX breaks through at 784 min / g, PX breaks through at 998 min / g, and EB breaks through at 1010 min / g.

[0072] In order to verify the actual separation effect of the above-mentioned metal organic framework material industrial actual component on the mixture of para-xylene isomers, a breakthrough experiment of xylene isomer mixed gas was carried out using the above-synthesized adsorbent. The specific method is to prepare a mixed solution by mixing PX, EB, MX, OX and other components according to the volume ratio of 22:6:50:22, and then using nitrogen as the bubbling gas, the breakthrough experiment is carried out by generating xylene isomer mixed gas through the above mixed solution, the breakthrough temperature is 60℃, the pressure is 0.1 MPa, and the nitrogen flow rate is 20 mL / min. After testing, OX is penetrated in 71 min / g, MX is penetrated in 665 min / g, PX is penetrated in 1212 min / g, and EB is penetrated in 1316 min / g.

[0073] Example 5

[0074] Dissolve 0.37 mmol of meso-α,β-di(4-pyridyl)ethyleneglycol (DPG), 0.56 mmol of nickel nitrate hexahydrate into a mixed solution of DMF / anhydrous methanol (15 mL each), then add 0.37 mmol of 2,5-furandicarboxylic acid (FDCA), and after complete dissolution, place it in an 80℃ oven for 24 h. After the reaction is completed, cool it to room temperature, collect the solid product by suction filtration, wash it with DMF and methanol three times respectively, and then dry it naturally in air to obtain the sample. The pore size of this material is The BET specific surface area is 577 m 2 / g, and the pore volume is 0.18 cm 3 / g. After purification, the adsorbent is degassed at 150℃ under vacuum for 24 h to obtain a desolvated adsorbent, and then gas adsorption is carried out.

[0075] In order to test the adsorption separation performance of the metal organic framework material prepared in this embodiment, a single-component vapor adsorption experiment of xylene isomers was carried out using the above adsorbent. Take 100 mg of adsorbent, and set the adsorption temperature to 60℃. After testing, the adsorption amounts of para-xylene, ethylbenzene, m-xylene and o-xylene are 185.1 mg / g, 160.9 mg / g, 118.1 mg / g and 72.5 mg / g respectively at 60℃ and 1 kPa.

[0076] In order to verify the actual separation effect of the above metal organic framework material on the xylene isomers, a breakthrough experiment of xylene isomer mixed gas was carried out using the above synthesized adsorbent. The specific method is to prepare a mixed solution of PX, EB, MX, OX and other components in a volume ratio of 1:1:1:1, then use nitrogen as the bubbling gas, and generate xylene isomer mixed gas through the above mixed solution to carry out the breakthrough experiment, the breakthrough temperature is 60℃, the pressure is 0.1MPa, and the nitrogen flow rate is 20mL / min. After testing, OX breaks through at 68min / g, MX breaks through at 854min / g, PX breaks through at 1078min / g, and EB breaks through at 1140min / g.

[0077] In order to verify the actual separation effect of the above metal organic framework material on the xylene isomers, a breakthrough experiment of xylene isomer mixed gas was carried out using the above synthesized adsorbent. The specific method is to prepare a mixed solution of PX, EB, MX, OX and other components in a volume ratio of 1:1:1:1, then use nitrogen as the bubbling gas, and generate xylene isomer mixed gas through the above mixed solution to carry out the breakthrough experiment, the breakthrough temperature is 60℃, the pressure is 0.1MPa, and the nitrogen flow rate is 20mL / min. After testing, OX breaks through at 68min / g, MX breaks through at 854min / g, PX breaks through at 1078min / g, and EB breaks through at 1140min / g.

[0078] The above specific embodiments have described the technical solutions and beneficial effects of the present application in detail. It should be understood that the above description is only the most preferred embodiment of the present application, and is not intended to limit the present application. Any modifications, supplements and equivalent replacements made within the principle range of the present application shall be included in the protection scope of the present application.

Claims

1. A method for separating carbon eight aromatic hydrocarbon isomers, comprising the step of: subjecting a mixed gas comprising carbon eight aromatic hydrocarbon isomers to an adsorptive separation, wherein, The adsorbent used in the adsorptive separation comprises a pillared MOF material, the pillared MOF material comprising metal ions and ligands, the ligands comprising primary ligands and pillaring ligands.

2. The method of claim 1, wherein, The primary ligands are selected from C2-C10 heteroaromatic ring dicarboxylic acids with or without substituents, the substituents being selected from one or more of C1-C5 alkyl, halogen, C1-C5 haloalkyl, amino, hydroxyl, cyano, C1-C5 alkoxy.

3. The method of claim 2, wherein, The C2-C10 heteroaromatic ring dicarboxylic acids with or without substituents are selected from furan dicarboxylic acids, thiophene dicarboxylic acids, imidazole dicarboxylic acids with or without substituents, preferably from 2,5-furan dicarboxylic acids or 2,5-thiophene dicarboxylic acids.

4. The method according to any one of claims 1-3, characterized in that, The pillaring ligands are as shown in Formula I: In Formula I, each R is independently selected from hydrogen, C1-C5 alkyl, halogen, C1-C5 haloalkyl, amino, hydroxyl, cyano, C1-C5 alkoxy; Preferably, the pillaring ligands are meso-α,β-di(4-pyridyl)glycol.

5. The method according to any one of claims 1-4, characterized in that, The metal ions are selected from cobalt ions and nickel ions.

6. The method according to any one of claims 1-5, characterized in that, The pore size of the pillared MOF material is The BET specific surface area is 400-580 m 2 / g, and the pore volume is 0.1-0.2 cm 3 / g.

7. The method according to any one of claims 1 to 6, characterized in that, The method for preparing the pillared MOF material comprises: dissolving a metal inorganic salt, a pillaring ligand and a primary ligand in a solvent, and performing a hydrothermal reaction at 60-150°C for 12-72h, and optionally washing and drying the generated solid.

8. The method of claim 7, wherein, The solvent is a mixture of N-dimethylformamide and methanol; The metal inorganic salt is selected from chloride salts, nitrate salts, acetate salts, carbonate salts, sulfate salts or perchlorate salts of the metal ions; The molar ratio of the metal inorganic salt to the pillaring ligand is 1:(1-3); Preferably, the molar ratio of the inorganic salt, the pillaring ligand and the primary ligand is 1:(1.5-2):1, most preferably 1:1.5:

1.

9. The method according to any one of claims 1-7, characterized in that, The temperature for the adsorptive separation is -5-300°C, and the total pressure of the mixed gas is 100-1000kPa; preferably, the temperature for the adsorptive separation is 20-120°C, and the total pressure of the mixed gas is 100-400kPa.

10. The method according to any one of claims 1-9, characterized in that, The carbon octahydroaromatic isomers comprise at least two of p-xylene, o-xylene, m-xylene and ethylbenzene, preferably the carbon octahydroaromatic isomers comprise ethylbenzene and one, two or three selected from p-xylene, o-xylene and m-xylene.

Images