Preparation method of modified molecular sieve for norbornene adsorption dehydration, modified molecular sieve and norbornene by-product recovery process

Abstract

This invention relates to a method for preparing a modified molecular sieve for the adsorption and dehydration of norbornene, the modified molecular sieve itself, and a process for recovering norbornene byproducts. The preparation method includes a hydrothermal reaction of a 4A molecular sieve with cyclodextrin in a hydrothermal reactor; the reaction product is washed, vacuum dried, and then calcined in a tube furnace under a nitrogen atmosphere to obtain a C-modified 4A molecular sieve with a small amount of hydroxyl groups on its surface. The method of this invention avoids isomerization and polymerization of norbornene under the strong acidity of the molecular sieve surface when using the 4A molecular sieve for adsorption and dehydration; simultaneously, the surface hydroxyl groups combine with a small amount of water to quickly form a water film on the molecular sieve surface, reducing the adsorption of norbornene on the molecular sieve surface, thus reducing the mass transfer resistance of norbornene on the molecular sieve surface and increasing the dehydration rate.

Description

Technical Field

[0001] This invention belongs to the field of adsorbent materials, specifically relating to a method for preparing modified molecular sieves for the adsorption and dehydration of norbornene, the modified molecular sieve, and a process for recovering norbornene by-products. Background Technology

[0002] Norbornene is a monomer used in the preparation of COP / COC thermoplastic engineering plastics. The COP / COC polymerization process has high requirements for the moisture content and purity of raw materials. Excessive moisture content will affect the activity of the polymerization catalyst, and impurities will be introduced into the polymer, affecting the performance and quality of the polymer product. The required moisture content is below 10 ppm, but the moisture content of norbornene purified by distillation is about 200 ppm, which is difficult to meet the downstream polymerization requirements.

[0003] Before entering the polymerization process, norbornene undergoes dehydration treatment using molecular sieves. Commonly used molecular sieves include 3A, 4A, and 5A. These sieves have small pore sizes, allowing water to enter and be adsorbed. However, due to the presence of certain L- and Brønsted acids on the surface of the molecular sieves, norbornene undergoes isomerization and polymerization reactions, ultimately leading to a decrease in its purity and affecting the quality of downstream polymer products. When using immersion dehydration, the prolonged residence time results in an even greater decrease in norbornene purity, and the material becomes very viscous, resembling a paste, making accurate sampling for purity analysis and polymerization evaluation difficult.

[0004] Traditional methods involve dealumination of molecular sieves to obtain those with a high silica-to-alumina ratio, which reduces their acidity. However, acid treatment typically removes aluminum from both the inner and outer surfaces, failing to selectively modify the acidity of the outer surface and potentially damaging the pore structure, crystal structure, and framework of the molecular sieve. Currently, the main method for modifying the acidity of the outer surface of zeolite molecular sieves is chemical deposition, such as using silane reagents. However, excessive silanization often causes severe pore blockage, making it difficult for water molecules to enter the molecular sieve channels.

[0005] Patent CN10829581B provides a method for preparing ionic liquid adsorbents immobilized on cyclodextrin-modified molecular sieves. The hydroxyl groups on the outer side of the cyclodextrin are used to crosslink with the hydroxyl groups on the surface of the molecular sieve under the action of a crosslinking agent, improving the adhesion and modification of the cyclodextrin on the molecular sieve surface. The interior of the cyclodextrin cavity is relatively hydrophobic, allowing the cyclodextrin to bind with specific ionic liquids through the hydrophobic binding sites within the molecular cavity. This immobilizes the ionic liquid within the cyclodextrin molecule cavity of the modified molecular sieve, improving upon the traditional physical impregnation loading method and solving the problems of weak ionic liquid binding and easy loss in the physical impregnation loading method. However, its adsorption and dehydration performance is limited. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, the present invention aims to provide a method for preparing a modified molecular sieve for the adsorption and dehydration of norbornene. A C-modified 4A molecular sieve with a small amount of hydroxyl groups on its surface is obtained by hydrothermal calcination of 4A molecular sieve and cyclodextrin. When using this modified 4A molecular sieve for the adsorption and dehydration of norbornene, isomerization and polymerization of norbornene under the strong acidity of the molecular sieve surface are avoided.

[0007] Another object of the present invention is to provide such a modified molecular sieve for the adsorption and dehydration of norbornene.

[0008] Another object of the present invention is to provide a process for recovering norbornene byproducts using this modified molecular sieve for norbornene adsorption and dehydration.

[0009] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing a modified molecular sieve for the adsorption and dehydration of norbornene includes the following steps:

[0011] 1) Mix 4A molecular sieve with cyclodextrin into a reactor and carry out a high-temperature hydrothermal reaction;

[0012] 2) After the reaction solution in step 1) is cooled, take out the substance from the reaction vessel, wash it by centrifugation with deionized water and methanol or ethanol, and then dry it under vacuum.

[0013] 3) The dried material from step 2) was placed in a tubular atmosphere furnace and calcined under a nitrogen atmosphere to obtain C-modified 4A molecular sieve with a small amount of hydroxyl groups on the surface.

[0014] In one specific implementation, the 4A molecular sieve mentioned in step 1) is a commercially available spherical molecular sieve with a diameter of 1.7-2.5 mm and a bulk density greater than 0.7 g / ml.

[0015] In one specific implementation, the cyclodextrin mentioned in step 1) is any one of α, β, γ cyclodextrin. Preferably, the amount of cyclodextrin added is 0.002 to 0.02 mol of cyclodextrin per 100g of 4A molecular sieve, more preferably 0.01 mol.

[0016] In one specific implementation, the high-temperature hydrothermal reaction described in step 1) is carried out in solvent water, and the amount of deionized water added is 100-400 mL of deionized water per 100 g of 4A molecular sieve.

[0017] In one specific implementation, the temperature of the high-temperature hydrothermal reaction in step 1) is 140-190℃, preferably 160℃, and the hydrothermal reaction time is 12-18h, preferably 15h.

[0018] In one specific implementation, the centrifugal washing method described in step 2) first washes the solid material with deionized water at a volume of 4 times for 3-5 times, preferably 4 times, and then washes it with methanol or ethanol at a volume of 4 times for 3-5 times, preferably 4 times.

[0019] In one specific implementation, the vacuum drying temperature in step 2) is 60-120°C, preferably 95°C, and the drying time is 12-48h, preferably 24h.

[0020] In one specific implementation, the heating rate of the calcination treatment in step 3) is 2-10℃ / min, preferably 5℃ / min, the temperature is 500-700℃, preferably 600℃, and the holding time is 3-8h, preferably 5h.

[0021] On the other hand, a modified molecular sieve for adsorption and dehydration of norbornene was prepared by the aforementioned preparation method.

[0022] On the other hand, a process for recovering norbornene by-product includes the step of dehydrating the by-product norbornene to a water content of less than 10 ppm using the modified molecular sieve prepared by the aforementioned preparation method or the aforementioned method for adsorption and dehydration of norbornene, and then recycling it.

[0023] Compared with the prior art, the positive effects of the present invention are as follows:

[0024] The present invention discloses a method for preparing a modified molecular sieve for the adsorption and dehydration of norbornene. This method involves hydrothermally calcining a 4A molecular sieve with cyclodextrin to obtain a C-modified 4A molecular sieve containing a small number of hydroxyl groups on its surface. This method avoids isomerization and polymerization of norbornene under the strong acidity of the molecular sieve surface when using the 4A molecular sieve for adsorption and dehydration.

[0025] Another benefit of the present invention is that after the above-mentioned modification process, the hydroxyl groups on the surface of the molecular sieve combine with a small amount of water to quickly form a water film on the surface of the molecular sieve, which reduces the adsorption of norbornene on the surface of the molecular sieve, thereby reducing the mass transfer resistance of norbornene on the surface of the molecular sieve, increasing the dehydration rate, reducing the residence time, and further reducing the degree of side reactions.

[0026] Compared with traditional acid-treated dealumination modification processes, this invention does not use acidic substances, avoiding equipment corrosion and the generation of acidic wastewater. Furthermore, it selectively modifies the acidity of the molecular sieve surface without damaging the sieve's pore structure. This reduces the surface acidity of the molecular sieve while maintaining its shape selectivity for water.

[0027] Meanwhile, this patent utilizes the characteristic that cyclodextrin macromolecules have difficulty entering the molecular sieve channels. By leveraging the hydrogen bonds formed between the molecular sieve and cyclodextrin, and employing high-temperature hydration, the cyclodextrin is uniformly dispersed on the molecular sieve surface. Subsequently, it is further calcined to form a surface carbon hybrid molecular sieve loading material containing a small amount of hydroxyl groups. Cyclodextrin serves only as a precursor, and since water molecules need to enter the molecular sieve channels for adsorption, calcining the cyclodextrin into carbon not only covers the acidity of the molecular sieve surface but also avoids the phenomenon of decreased water absorption rate of the molecular sieve due to the hydrophobicity of the cyclodextrin's interior. Detailed Implementation

[0028] To better understand the technical solution of the present invention, the following embodiments will further illustrate the method provided by the present invention. However, the present invention is not limited to the listed embodiments, but should also include any other known modifications within the scope of the claims of the present invention.

[0029] Unless otherwise specified, all raw materials used in this invention are commercially available. The cyclodextrin was purchased from Beijing Innocare Technology Co., Ltd., with a purity of 99% β-cyclodextrin, and the 4A molecular sieve was purchased from Alfaesa (China) Chemical Co., Ltd. Unless otherwise specified, the equipment is conventionally used in the field.

[0030] The norbornene in this invention is obtained by distillation and purification after the AD addition reaction of DCPD and ethylene. The main components are 99.9% norbornene, water content of 250-600 ppm, cyclopentadiene of 5-20 ppm, and toluene of 10-100 ppm.

[0031] The gas chromatography analysis method used in this invention was as follows: a Shimadzu Angilent 7820A+ gas chromatograph, a DB-5 capillary column (5% Phenyl Methyl Siloxan, 30m × 0.32mm × 0.25μm), and a flame ionization detector (FID). The injector and detector temperatures were both 290℃; the column temperature was initially set at 100℃ and held for 1 minute, then increased to 250℃ at a rate of 15℃ / min and held for 5 minutes. The column pressure was 8.59 psi, and the flow rate was 1.5 mL / min. The injection volume was 0.2 μL. Quantification was performed using the area normalization method.

[0032] Example 1

[0033] 1) 100g of 4A molecular sieve was mixed with 0.01mol β-cyclodextrin in a hydrothermal reactor containing 150ml of deionized water. After tightening the reactor, the mixture was hydrothermally heated at 160℃ for 15h. After cooling the reaction solution from the above step, the material in the reactor was removed and washed four times each with four times the volume of deionized water and ethanol. Then, it was vacuum dried at 100℃ for 24h. The dried material was placed in a tubular atmosphere furnace and heated from room temperature to 600℃ at a rate of 5℃ / min under a nitrogen atmosphere, and held at that temperature for 5h. After cooling, C-modified 4A molecular sieve with a small amount of hydroxyl groups on the surface was obtained. 100ml of the above molecular sieve was packed into a glass column in a glove box, and 500g of 99.9% purity norbornene containing 200ppm water was continuously circulated for dehydration at a rate of 100g / h. After 5h, samples were taken for gas chromatography analysis and water content analysis. The results are shown in Table 1.

[0034] Other embodiments are the same as in Example 1, except for the molecular sieve preparation conditions described below, and the results are shown in Table 1.

[0035] Table 1. Specific reaction conditions and results for Examples 1-9

[0036]

[0037] Comparative Example 1

[0038] The 4A molecular sieve was calcined at 600°C for 6 hours without any treatment, and then the dehydration effect of norbornene was evaluated under the same conditions as in Example 1. The results showed that the purity of norbornene was 99.57% and the water content was 103 ppm.

[0039] Comparative Example 2

[0040] 30g of 4A molecular sieve was added to 300g of 1.0mol / L HCl, transferred to a hydrothermal reactor, and treated at 90℃ for 12h. After treatment, the sieve was filtered, washed until neutral, dried overnight at 120℃, and calcined at 550℃ for 8h to obtain the acid-treated molecular sieve. The dehydration effect of norbornene was evaluated under the same conditions as in Example 1. The results showed that the purity of norbornene was 99.82%, and the water content was 127ppm.

[0041] Comparative Example 3

[0042] 100g of 4A molecular sieve was mixed with 0.01mol β-cyclodextrin in a hydrothermal reactor containing 150ml of deionized water. The reactor was tightened and hydrothermally heated at 160℃ for 15h. After the reaction was completed and cooled, the material in the reactor was removed and washed four times each with four times the volume of deionized water and ethanol. The mixture was then vacuum dried at 100℃ for 24h. 100ml of the molecular sieve was packed into a glass column in a glove box, and 500g of 99.9% purity norbornene containing 200ppm water was continuously circulated at a rate of 100g / h for dehydration. After 5h, samples were taken for gas chromatography and water content analysis. The results showed that the purity of norbornene was 99.9% and the water content was 212ppm.

[0043] Although the present invention has been described in detail through the preferred embodiments described above, it should be understood that the above description should not be considered as a limitation of the present invention. Those skilled in the art will understand that modifications or adjustments can be made to the present invention based on the teachings of this specification. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for preparing a modified molecular sieve for the adsorption and dehydration of norbornene, characterized in that, Includes the following steps: 1) Mix 4A molecular sieve and cyclodextrin together in a reactor and carry out a high-temperature hydrothermal reaction; the temperature of the high-temperature hydrothermal reaction is 140-190℃, and the hydrothermal reaction time is 12-18h; the amount of cyclodextrin added is 0.002-0.02mol of cyclodextrin per 100g of 4A molecular sieve. 2) After the reaction solution in step 1) is cooled, take out the substance from the reaction vessel, wash it by centrifugation with deionized water, then wash it by centrifugation with methanol or ethanol, and then dry it under vacuum. 3) The dried material from step 2) is placed in a tubular atmosphere furnace and calcined under a nitrogen atmosphere to obtain carbon-modified 4A molecular sieve with a small amount of hydroxyl groups on the surface; the calcination temperature is 500-700℃ and the holding time is 3-8h.

2. The preparation method according to claim 1, characterized in that, The 4A molecular sieve mentioned in step 1) is a spherical molecular sieve with a diameter of 1.7-2.5 mm and a bulk density greater than 0.7 g / ml.

3. The preparation method according to claim 1, characterized in that, The cyclodextrin mentioned in step 1) is any one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin.

4. The preparation method according to claim 1, characterized in that, The amount of cyclodextrin added is 0.01 mol of cyclodextrin per 100g of 4A molecular sieve.

5. The preparation method according to claim 1, characterized in that, The high-temperature hydrothermal reaction described in step 1) is carried out in deionized water as a solvent. The amount of deionized water added is 100-400 mL of deionized water per 100 g of 4A molecular sieve.

6. The preparation method according to claim 1, characterized in that, The temperature of the high-temperature hydrothermal reaction in step 1) is 160℃, and the hydrothermal reaction time is 15h.

7. The preparation method according to claim 1, characterized in that, Step 2) Centrifugal washing method: First wash with 4 times the volume of deionized water for 3-5 times, then wash with 4 times the volume of methanol or ethanol for 3-5 times.

8. The preparation method according to claim 7, characterized in that, Step 2) Centrifugal washing method: First wash with 4 times the volume of deionized water (4 times the volume of solid material) 4 times, then wash with 4 times the volume of methanol or ethanol (4 times the volume of solid material) 4 times.

9. The preparation method according to claim 1, characterized in that, The vacuum drying temperature in step 2) is 60-120℃, and the drying time is 12-48h.

10. The preparation method according to claim 9, characterized in that, The vacuum drying temperature in step 2) is 95℃, and the drying time is 24h.

11. The preparation method according to claim 1, characterized in that, Step 3) The heating rate of the calcination treatment is 2-10℃ / min, the temperature is 600℃, and the holding time is 5h.

12. The preparation method according to claim 11, characterized in that, The heating rate of the calcination treatment in step 3) is 5℃ / min.

13. A modified molecular sieve for adsorption and dehydration of norbornene prepared by the preparation method according to any one of claims 1 to 12.

14. A process for recovering norbornene by-product, characterized in that, The method includes the step of using a modified molecular sieve for adsorption and dehydration of norbornene prepared by any one of claims 1 to 12 or the modified molecular sieve for adsorption and dehydration of norbornene as described in claim 13 to dehydrate the by-product norbornene to a water content of less than 10 ppm, and then recycling it.

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