Adsorbent for separating mixed xylene and preparation method thereof

Abstract

The invention is suitable for the technical field of xylene adsorption separation, and provides an adsorbent for separating mixed xylene and a preparation method thereof. The preparation method comprises the following steps: firstly preparing an EtFLP6 intermediate with the purity of more than 90%, then preparing solvent-free EtFLP6 with the purity of more than 99% by using the EtFLP6 intermediate, and finally preparing solvent-free EtFLP6alpha, namely the NAC material, by using the EtFLP6. The synthesized EtFLP6alpha shows excellent selective adsorption capacity for xylene isomers at normal temperature and normal pressure, energy consumption is remarkably reduced due to the characteristic of selective adsorption of PX at normal temperature and normal pressure, meanwhile, the EtFLP6alpha has high chemical and thermal stability, and can stably run in a complex industrial environment for a long time. Besides, the EtFLP6alpha has good recoverability, the adsorption performance of the EtFLP6alpha is not obviously reduced after the EtFLP6alpha is recycled for 5 times, and the EtFLP6alpha shows outstanding recoverability and application potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of xylene adsorption separation, and particularly relates to an adsorbent for separating mixed xylene and a preparation method thereof. Background Art

[0002] Xylene isomers (including para-xylene PX, ortho-xylene OX, and meta-xylene MX) are extremely important organic chemical raw materials and are closely related to the development of the national economy. Among them, PX, as one of the most important aromatic hydrocarbon products, can be converted into key raw materials such as terephthalic acid, which is further used in the synthesis of polyesters. After a series of processing steps such as slicing, spinning, and film forming, polyesters are widely used in multiple industrial fields such as textiles and plastics. OX, as the starting material for various resin plasticizers, is used to synthesize important chemical intermediates such as phthalonitrile or participates in various organic reactions as a solvent. MX can be used to prepare chemical raw materials such as isophthalic acid and isophthalonitrile.

[0003] However, xylene isomers usually exist in the form of mixtures, and their separation has been a major challenge faced by the chemical industry in the past few decades, and is even regarded as one of the "seven major chemical separations that change the world". Through naphtha catalytic reforming or gasoline cracking processes, mixed xylene containing approximately 20%-25% PX, 20%-25% OX, and 40%-60% MX can be produced. Industrially, the separation of xylene isomers mainly relies on distillation and crystallization technologies, but these methods are energy-intensive and account for a relatively large proportion of global energy consumption. The production of PX mainly relies on an adsorption separation process centered on simulated moving bed technology, which has extremely high requirements for the performance of the adsorbent, requiring the adsorbent to have high capacity, high selectivity, high diffusion rate, and high stability under operating conditions.

[0004] Developing adsorbent separation materials with excellent performance can not only improve the product quality and production efficiency of existing processes, but also contribute to the long-term stable, safe and low-energy consumption operation of industrial production devices. In the past few decades, researchers have explored various porous adsorbent materials for hydrocarbon separation, such as zeolites, organic cages and metal-organic frameworks (MOFs). A particular advantage of porous adsorbent materials is the diversity of their structures, which endows them with excellent adsorption capabilities. However, porous adsorbent materials also have some inherent disadvantages that limit their practical applications. For example, zeolites have a weak adsorption capacity for hydrocarbons, making it difficult to achieve precise separation of hydrocarbons; the chemical stability of MOFs is relatively weak, and their structures are easily damaged under high-temperature or acidic conditions. Therefore, it is of great significance to explore new materials for separating xylene isomers. In recent years, non-porous adaptable crystals (NACs) have shown significant potential as absorption and separation materials. Different from traditional porous materials, NACs are non-porous in their original state. However, when appropriate guest molecules are introduced, NACs can form special pores, thereby exhibiting excellent absorption properties. For this reason, the present invention proposes an adsorbent for separating mixed xylenes and a preparation method thereof. Summary of the Invention

[0005] The purpose of the present invention is to provide an adsorbent for separating mixed xylenes and a preparation method thereof, aiming to solve the problems raised in the above background technology.

[0006] The purpose of the present invention is achieved through the following technical solutions: A preparation method of an adsorbent for separating mixed xylenes, comprising the following steps: Step 1: Preparation of the EtFLP6 material, the specific steps are as follows: Step 11: Dissolve 2,3,5,6-tetrafluoroterephthalic alcohol and p-diethoxybenzene in hexafluoroisopropanol, stir at room temperature until completely dissolved, add trifluoromethanesulfonic acid as a catalyst, heat the reaction, quench the reaction with water, adjust the pH to neutral, perform liquid-liquid extraction, take the lower organic phase, add anhydrous sodium sulfate to the organic phase to remove residual moisture, add silica gel powder and disperse evenly by ultrasonic treatment, then remove the solvent by rotary evaporation, and separate by column chromatography to obtain an EtFLP6 intermediate with a purity greater than 90%; Step 12: Dissolve the EtFLP6 intermediate obtained in Step 11 and paraformaldehyde in dichloromethane, stir at room temperature until the EtFLP6 intermediate is completely dissolved, add boron trifluoride diethyl etherate, react at room temperature until dark green, quench the reaction with water, adjust the pH to neutral, perform liquid-liquid extraction, take the lower organic phase, add anhydrous sodium sulfate to the organic phase to remove residual moisture, add silica gel powder and disperse evenly by ultrasonic treatment, then remove the solvent by rotary evaporation, and separate by column chromatography to obtain solvent-free EtFLP6 with a purity greater than 99%; Step 2: Preparation of the NAC material; Place the EtFLP6 obtained in Step 12 in a glass bottle, add dichloromethane, heat until completely dissolved, add methylcyclohexane, and slowly evaporate at 60 °C for one day to obtain blocky crystals. Wash the liquid adhering to the crystal surface with methanol and dry it under vacuum to obtain solvent-free EtFLP6α, which is the NAC material.

[0007] Further, the specific process of Step 11 is as follows: Dissolve 4 g of 2,3,5,6-tetrafluoroterephthalyl alcohol and 28.18 g of p-diethoxybenzene in 100 ml of hexafluoroisopropanol, stir at room temperature until completely dissolved, add 0.6 ml of trifluoromethanesulfonic acid as a catalyst, react at 120 °C in an oil bath for 12 h. After the reaction is completed, quench the reaction with water, add 4 g of sodium bicarbonate to adjust the pH to neutral, add water for liquid-liquid extraction, take the lower organic phase, extract three times, add 6 g of anhydrous sodium sulfate to the organic phase to remove residual water, add 20 g of silica gel powder, ultrasonically disperse evenly, and then rotary evaporate at 30 °C in a water bath at a rotation speed of 100 revolutions per minute and a vacuum of -12 pascals to completely remove the solvent; pack the silica gel powder, sample, anhydrous sodium sulfate, and quartz sand into a column, select the developing agent to achieve effective separation of each component on a silica gel plate; use the eluent to elute p-diethoxybenzene and the EtFLP6 intermediate to obtain an EtFLP6 intermediate with a purity greater than 90%.

[0008] Further, in Step 11, select a developing agent with a volume ratio of petroleum ether to ethyl acetate of 8:1 to achieve effective separation of each component on a silica gel plate; use an eluent of 1500 mL of petroleum ether and dichloromethane with a volume ratio of 5:1 to elute p-diethoxybenzene, and then use an eluent of 1000 mL of petroleum ether and dichloromethane with a volume ratio of 1:1 to elute the EtFLP6 intermediate to obtain an EtFLP6 intermediate with a purity greater than 90%.

[0009] Further, the specific process of Step 12 is as follows: Dissolve 4 g of the EtFLP6 intermediate obtained in step 11 and 0.4 g of paraformaldehyde in 120 ml of dichloromethane. Stir at room temperature until the EtFLP6 intermediate is completely dissolved. Add 5 ml of boron trifluoride diethyl etherate and react at room temperature until it turns dark green. Quench the reaction with water, add 10 g of sodium bicarbonate to adjust the pH to neutral, add water for liquid-liquid extraction, and take the lower organic phase. After extraction three times, add 6 g of anhydrous sodium sulfate to the organic phase to remove residual moisture. Add 4 g of silica gel powder, disperse it evenly by ultrasonic wave, and then rotate and evaporate in a 30 °C water bath at a rotation speed of 100 revolutions per minute and a vacuum of -12 pascals to completely remove the solvent. Pack the silica gel powder, sample, anhydrous sodium sulfate, and quartz sand into a column, select the developing agent to achieve effective separation of each component on the silica gel plate; use the eluent to elute EtFLP6 to obtain EtFLP6 with a purity greater than 90%. Add 2 ml of acetone, let it stand for 2 h for purification, and heat it in a vacuum oven at 120 °C and -1 bar negative pressure for 12 h to obtain solvent-free EtFLP6 with a purity greater than 99%.

[0010] Further, in step 12, select a developing agent with a volume ratio of petroleum ether to ethyl acetate of 6:1 to achieve effective separation of each component on the silica gel plate; use an eluent with a volume ratio of 1:1 of 1000 mL of petroleum ether to dichloromethane to elute EtFLP6 to obtain EtFLP6 with a purity greater than 90%.

[0011] Further, the specific process of step 2 is as follows: Place 5 g of the EtFLP6 obtained in step 12 in a 100 ml glass bottle, add 60 ml of dichloromethane, heat it to 100 °C to completely dissolve it, add 40 ml of methylcyclohexane, and slowly volatilize it at 60 °C for one day to obtain blocky crystals. Wash the liquid attached to the surface of the crystals with methanol, and heat it in a vacuum oven at 120 °C and -1 bar negative pressure for 12 h to obtain solvent-free EtFLP6α, that is, the NAC material.

[0012] An adsorbent for separating mixed xylene prepared by the preparation method described above.

[0013] Compared with the prior art, the beneficial effects of the present invention are: The synthesized EtFLP6α in the present invention exhibits excellent selective adsorption ability for xylene isomers under normal temperature and pressure: for single-component xylene isomers, it has significant adsorption ability only for PX, and hardly adsorbs OX and MX; for mixed components, the separation factor for PX is greater than 90%. The property of selectively adsorbing PX by this material at normal temperature and pressure significantly reduces energy consumption, and it also has high chemical and thermal stability, enabling it to operate stably in complex industrial environments for a long time. In addition, EtFLP6α has good recyclability. After being recycled 5 times, its adsorption performance does not show obvious decline, demonstrating outstanding recyclability and application potential. Description of the Drawings

[0014] Figure 1 The single-component adsorption capacity of EtFLP6α for xylene isomers (PX, MX, OX).

[0015] Figure 2 The change in PXRD pattern of EtFLP6α after adsorbing xylene isomers.

[0016] Figure 3 The adsorption capacity of EtFLP6α for the mixed component of PX:MX:OX = 1:1:1.

[0017] Figure 4 The PXRD pattern of EtFLP6α after adsorbing the mixed component.

[0018] Figure 5 The gas chromatography test results after adsorbing the mixed component.

[0019] Figure 6 The test results of the recycling performance of EtFLP6α. Detailed Embodiments

[0020] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention are described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0021] The following describes the specific implementation of the present invention in detail with reference to specific embodiments.

[0022] Example 1: This example provides a preparation method for an adsorbent for separating mixed xylene, including the following steps: Step 1: Preparation of the EtFLP6 material, the specific steps are as follows: Step 11: Dissolve 4 g of 2,3,5,6-tetrafluoroterephthalyl alcohol and 28.18 g of p-diethoxybenzene in 100 ml of hexafluoroisopropanol, stir at room temperature until completely dissolved, add 0.6 ml of trifluoromethanesulfonic acid as a catalyst, react at 120 °C in an oil bath for 12 h. After the reaction, quench the reaction with water, add 4 g of sodium bicarbonate to adjust the pH to neutral, add water for liquid-liquid extraction, take the lower organic phase, extract three times, add 6 g of anhydrous sodium sulfate to the organic phase to remove residual water, add 20 g of silica gel powder, ultrasonically disperse evenly, and rotary evaporate in a 30 °C water bath at a rotation speed of 100 r / min and a vacuum of -12 Pa to completely remove the solvent; load the silica gel powder, sample, anhydrous sodium sulfate, and quartz sand onto a column, select a developing agent with a volume ratio of petroleum ether to ethyl acetate of 8:1, and effectively separate each component on a silica gel plate; use an eluent of 1500 mL of petroleum ether and dichloromethane with a volume ratio of 5:1 to elute p-diethoxybenzene, and then change to an eluent of 1000 mL of petroleum ether and dichloromethane with a volume ratio of 1:1 to elute the EtFLP6 intermediate, to obtain an EtFLP6 intermediate with a purity greater than 90%; Step 12: Dissolve 4 g of the EtFLP6 intermediate obtained in Step 11 and 0.4 g of paraformaldehyde in 120 ml of dichloromethane, stir at room temperature until the EtFLP6 intermediate is completely dissolved, add 5 ml of boron trifluoride diethyl etherate, react at room temperature until dark green, quench the reaction with water, add 10 g of sodium bicarbonate to adjust the pH to neutral, add water for liquid-liquid extraction, take the lower organic phase, extract three times, add 6 g of anhydrous sodium sulfate to the organic phase to remove residual water, add 4 g of silica gel powder, ultrasonically disperse evenly, and rotary evaporate in a 30 °C water bath at a rotation speed of 100 r / min and a vacuum of -12 Pa to completely remove the solvent; load the silica gel powder, sample, anhydrous sodium sulfate, and quartz sand onto a column, select a developing agent with a volume ratio of petroleum ether to ethyl acetate of 6:1, and effectively separate each component on a silica gel plate; use an eluent of 1000 mL of petroleum ether and dichloromethane with a volume ratio of 1:1 to elute EtFLP6, to obtain an EtFLP6 with a purity greater than 90%, add 2 ml of acetone, let stand for 2 h for purification treatment, and heat in a vacuum oven at 120 °C and -1 bar negative pressure for 12 h to obtain solvent-free EtFLP6 with a purity greater than 99%; Step 2: Preparation of NAC material; Place 5 g of the EtFLP6 obtained in Step 12 in a 100 ml glass bottle, add 60 ml of dichloromethane, heat to 100 °C to completely dissolve it, add 40 ml of methylcyclohexane, slowly volatilize at 60 °C for one day to obtain a block crystal, wash the liquid attached to the crystal surface with methanol, and heat in a vacuum oven at 120 °C and -1 bar negative pressure for 12 h to obtain solvent-free EtFLP6α, that is, the NAC material. Grind EtFLP6α into a powdery NAC with uniform particle size using a mortar for subsequent performance testing.

[0023] Example 2: Performance Test The prepared EtFLP6α in Example 1 was tested for 1H NMR spectrum, single-component adsorption performance, mixed-component adsorption performance, powder XRD (PXRD) after adsorption, and cycle performance. The results are as Figure 1-6 shown. The specific operations for each test are as follows: (1) Test of single-component adsorption performance: Take EtFLP6α and place it in a 2-ml glass bottle. Add an equal amount of PX, MX, and OX to each glass bottle so that the liquid completely submerges the sample, and conduct a single-component solid-liquid adsorption experiment. Sample at the same interval time, dry the residual liquid on the surface of the sample, and test the 1H NMR spectrum to determine the adsorption amount. Finally, obtain the adsorption curve graph. Take a small amount of the sample saturated with adsorption and conduct thermogravimetric analysis to test the adsorption of each component.

[0024] (2) Test of mixed-component adsorption performance: Take EtFLP6α and place it in a 2-ml glass bottle. Add an equal amount of mixed solutions with volume ratios of PX:MX = 1:1, PX:OX = 1:1, and PX:MX:OX = 1:1:1 to each glass bottle so that the liquid completely submerges the sample, and conduct a mixed-component solid-liquid adsorption experiment. Sample at the same interval time, dry the residual liquid on the surface of the sample, and test the 1H NMR spectrum to determine the adsorption amount of each component. Finally, obtain the mixed-component adsorption curve graph. Take a small amount of the sample saturated with adsorption and conduct gas chromatography test to test the resolution of the mixed components.

[0025] (3) Crystal structure analysis: Take EtFLP6α in a 2-ml glass bottle, add PX to make it completely dissolve, and let it slowly volatilize at room temperature. Finally, obtain a smooth and crack-free block crystal. Conduct single-crystal XRD analysis on the crystal to obtain the crystal structure diagram of EtFLP6α@PX. Analyze the crystal structure. PX is encapsulated in the cavity formed by EtFLP6α and binds to EtFLP6α through multiple weak interactions.

[0026] (4) Cycle performance test: After adsorbing 30 mg of EtFLP6α in a mixed solution of PX:MX:OX = 1:1:1 for 28 h, take 5 mg to test the 1H NMR spectrum to determine the adsorption amount, and activate the remaining sample in a vacuum oven at 120 °C and a negative pressure of -1 bar for 12 h. Repeat the above process 5 times to test the cycle performance.

[0027] The adsorption ability of EtFLP6α for xylene isomers was investigated through a single-component solid-liquid adsorption experiment, and the adsorption results were confirmed by 1H NMR spectrum. As Figure 1As shown, the adsorption amount of EtFLP6α for PX vapor increases with time and reaches saturation at 50 min. The adsorption amount of PX is 1 mol / EtFLP6α, while the adsorption amounts for OX and MX vapors are always very low. The results indicate that EtFLP6α has the potential for selective adsorption of PX.

[0028] To investigate the structural changes of EtFLP6α after adsorbing xylene isomers, the results are as Figure 2 shown. The PXRD pattern of EtFLP6α adsorbed with PX is different from that of the original EtFLP6α, indicating the formation of a new crystal structure. However, when EtFLP6α is placed in OX or MX solutions, there is no obvious change in the PXRD pattern of EtFLP6α. And long crystals are obtained for the crystal structure diagram. The simulated PXRD pattern of EtFLP6α and PX (Simulated EtFLP6α+PX) exported by Mercury software is consistent with that of the adsorbed single-component PX Figure 1 . The results show that EtFLP6α only has the adsorption ability for PX among the xylene isomers.

[0029] Figure 3 , Figure 4 , Figure 5 The results are for the adsorption performance test of the mixed component with PX:MX:OX = 1:1:1 (OMP). The adsorption amount of EtFLP6α for PX vapor increases with time and reaches saturation at 28 h. The adsorption amount of PX is 0.9 mol / EtFLP6α, while the adsorption amounts for OX and MX vapors are always very low, less than 0.1 mol / EtFLP6α ( Figure 3 ). The PXRD results of the mixed component are consistent with those of the single-component PX and the single-crystal simulation results, indicating that EtFLP6α can selectively adsorb PX from the xylene isomers ( Figure 4 ). The gas chromatography test results show ( Figure 5 ) that PX, MX, and OX peak at 7.468, 7.617, and 8.632 minutes respectively. The peak areas are determined by integration and are the relative areas of 28877, 1365, and 1460 respectively. The separation degree for PX can be obtained as 91.09% from the ratio between the peak areas, further confirming the high selectivity of EtFLP6α for PX.

[0030] Figure 6 The results show that after being recycled 5 times, the adsorption performance of EtFLP6α does not decline, indicating its excellent recyclability. Its excellent recyclability is attributed to the reversible structural changes between the guest-free and guest-containing states.

[0031] The above are only the preferred embodiments of the present invention. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicability of the patent.

Claims

1. A preparation method of an adsorbent for separating mixed xylene, characterized in that, It includes the following steps: Step 1: Preparation of the EtFLP6 material, and the specific steps are as follows: Step 11: Dissolve 2,3,5,6-tetrafluoroterephthalic alcohol and p-diethoxybenzene in hexafluoroisopropanol, stir at room temperature until completely dissolved, add trifluoromethanesulfonic acid as a catalyst, heat for reaction, then quench the reaction with water, adjust the pH to neutral, perform liquid-liquid extraction, take the lower organic phase, add anhydrous sodium sulfate to the organic phase to remove residual moisture, add silica gel powder and disperse it evenly by ultrasonic treatment, then remove the solvent by rotary evaporation, and separate by column chromatography to obtain an EtFLP6 intermediate with a purity greater than 90%; Step 12: Dissolve the EtFLP6 intermediate obtained in Step 11 and paraformaldehyde in dichloromethane, stir at room temperature until the EtFLP6 intermediate is completely dissolved, add boron trifluoride diethyl etherate, react at room temperature until it turns dark green, quench the reaction with water, adjust the pH to neutral, perform liquid-liquid extraction, take the lower organic phase, add anhydrous sodium sulfate to the organic phase to remove residual moisture, add silica gel powder and disperse it evenly by ultrasonic treatment, then remove the solvent by rotary evaporation, and separate by column chromatography to obtain solvent-free EtFLP6 with a purity greater than 99%; Step 2: Preparation of the NAC material; Place the EtFLP6 obtained in Step 12 in a glass bottle, add dichloromethane, heat until completely dissolved, add methylcyclohexane, slowly evaporate at 60 °C for one day to obtain a block crystal, wash the liquid attached to the crystal surface with methanol, and dry it under vacuum to obtain solvent-free EtFLP6α, that is, the NAC material.

2. The preparation method according to claim 1, characterized in that The specific process of Step 11 is as follows: Dissolve 4 g of 2,3,5,6-tetrafluoroterephthalic alcohol and 28.18 g of p-diethoxybenzene in 100 ml of hexafluoroisopropanol, stir at room temperature until completely dissolved, add 0.6 ml of trifluoromethanesulfonic acid as a catalyst, react in an oil bath at 120 °C for 12 h, after the reaction is completed, quench the reaction with water, add 4 g of sodium bicarbonate to adjust the pH to neutral, add water for liquid-liquid extraction, take the lower organic phase, after extracting three times, add 6 g of anhydrous sodium sulfate to the organic phase to remove residual moisture, add 20 g of silica gel powder, disperse it evenly by ultrasonic treatment, and then perform rotary evaporation in a 30 °C water bath at a rotation speed of 100 revolutions per minute and a vacuum degree of -12 pascals to completely remove the solvent; Pack the silica gel powder, sample, anhydrous sodium sulfate, and quartz sand into a column, select the developing agent to effectively separate each component on the silica gel plate; Use the eluent to elute p-diethoxybenzene and the EtFLP6 intermediate to obtain an EtFLP6 intermediate with a purity greater than 90%.

3. The preparation method according to claim 2, characterized in that, In Step 11, select a developing agent with a volume ratio of petroleum ether to ethyl acetate of 8:1 to effectively separate each component on the silica gel plate; Use an eluent of 1500 mL of petroleum ether and dichloromethane with a volume ratio of 5:1 to elute p-diethoxybenzene, and then use an eluent of 1000 mL of petroleum ether and dichloromethane with a volume ratio of 1:1 to elute the EtFLP6 intermediate to obtain an EtFLP6 intermediate with a purity greater than 90%.

4. The preparation method according to claim 1, characterized in that, The specific process of Step 12 is as follows: Dissolve 0.4 g of paraformaldehyde and the EtFLP6 intermediate obtained in step 11 of 4 g in 120 ml of dichloromethane, stir at room temperature until the EtFLP6 intermediate is completely dissolved, add 5 ml of boron trifluoride diethyl ether, react at room temperature until it turns dark green, quench the reaction with water, add 10 g of sodium bicarbonate to adjust the pH to neutral, add water for liquid-liquid extraction, take the lower organic phase, after extracting three times, add 6 g of anhydrous sodium sulfate to the organic phase to remove residual water, add 4 g of silica gel powder, disperse evenly by ultrasonic wave, and then rotate and evaporate in a 30 °C water bath at a rotation speed of 100 revolutions per minute and a vacuum degree of -12 pascals to completely remove the solvent; pack the silica gel powder, sample, anhydrous sodium sulfate, and quartz sand into a column, select the developing agent to effectively separate each component on the silica gel plate; use the eluent to elute EtFLP6 to obtain EtFLP6 with a purity greater than 90%, add 2 ml of acetone, let it stand for 2 h for purification treatment, and heat in a vacuum oven at 120 °C and -1 bar negative pressure for 12 h to obtain solvent-free EtFLP6 with a purity greater than 99%.

5. The preparation method according to claim 4, characterized in that, In step 12, select a developing agent with a volume ratio of petroleum ether to ethyl acetate of 6:1 to effectively separate each component on the silica gel plate; use an eluent with a volume ratio of 1:1 of 1000 mL of petroleum ether to dichloromethane to elute EtFLP6 to obtain EtFLP6 with a purity greater than 90%.

6. The preparation method according to claim 1, characterized in that, The specific process of step 2 is as follows: Place 5 g of the EtFLP6 obtained in step 12 in a 100 ml glass bottle, add 60 ml of dichloromethane, heat to 100 °C to completely dissolve it, add 40 ml of methylcyclohexane, slowly volatilize at 60 °C for one day to obtain massive crystals, wash the liquid attached to the crystal surface with methanol, and heat in a vacuum oven at 120 °C and -1 bar negative pressure for 12 h to obtain solvent-free EtFLP6α, that is, the NAC material.

7. An adsorbent for separating mixed xylene prepared by the preparation method according to any one of claims 1-6.

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