Green activated covalent organic framework material and benzoic acid recovery method

Abstract

The invention discloses a method for efficiently activating a prepared covalent organic framework material and recovering benzoic acid, and particularly relates to a method for efficiently activating the prepared covalent organic framework material and recovering benzoic acid by utilizing an acid-base neutralization reaction between an alkaline substance and benzoic anhydride or benzoic acid to generate corresponding salt and activating the prepared covalent organic framework material. Therefore, the covalent organic framework material with high crystallinity, high specific surface area and uniform pore channels is obtained. The invention also provides a method for recovering benzoic acid, which comprises the following steps: by utilizing the property that benzoic acid is slightly soluble in cold water, adding an acidic material and corresponding benzoate into the activated solution to generate benzoic acid, thereby separating out and obtaining benzoic acid with higher purity from the solution.

Description

Technical Field

[0001] The invention belongs to the field of processing prepared covalent organic framework materials and relates to a method for efficiently activating prepared covalent organic framework materials, which is used to improve the crystallinity and specific surface area of ​​the covalent organic framework materials and can recover high-purity benzoic acid from the activated solution. Background Art

[0002] Benzoic acid is an aromatic acid organic compound and the simplest aromatic acid. It is white needle-like or flaky crystals and widely exists in nature in the form of free acid, ester or its derivatives. It is mainly used to prepare sodium benzoate preservatives, and is used in the synthesis of drugs and dyes; it is also used to make plasticizers, mordants, fungicides and fragrances. Therefore, the commercial value of benzoic acid is huge. Therefore, if low-content benzoic acid can be recovered, it is of great value to obtain high-purity products.

[0003] Benzoic acid and benzoic anhydride are often used in some organic synthesis reactions and polymer polymerization reactions. They can also be used to prepare some crystalline materials. For example, in the synthesis of vinyl covalent organic framework materials (COFs) by melt polymerization, benzoic anhydride is needed as a template and catalyst to obtain materials with excellent performance. However, benzoic anhydride, which functions as a catalyst and template, needs to be removed after the reaction to obtain vinyl COF materials with high crystallinity, high specific surface area and orderly pores. The traditional method of removing benzoic anhydride and benzoic acid is to dissolve the reacted benzoic anhydride with organic solvents such as N,N-dimethylformamide and methanol, and then remove it. This method uses a large amount of organic solvents, and it is difficult to regenerate benzoic acid from the recovered solution, which requires a lot of energy and does not meet the requirements of green chemistry. Before this, COF activation used organic solvents, and it was very rare to activate COF materials with aqueous solutions. Summary of the invention

[0004] In view of the above problems, the present invention provides a method of activating a prepared covalent organic framework material using an alkaline solution to obtain a covalent organic framework material with higher crystallinity, and adding an acidic solution to the alkaline solution recovered after activation can obtain benzoic acid. The process flow is convenient, fast, and easy to implement large-scale industrial applications. The method specifically comprises soaking the prepared COF material in an alkaline solution to obtain a COF with higher crystallinity. The alkaline solution recovered after activation is then added with an acidic solution to recover benzoic acid. The method is simple and effective, the activation conditions are mild and green, the versatility is strong, and the processing capacity of the prepared COF is greatly improved.

[0005] On the one hand, the present invention provides a method for activating a prepared COF material using an alkaline solution under mild conditions, adding an alkaline solution, and according to the reaction principle of acid-base neutralization, using an alkaline substance and benzoic anhydride or benzoic acid to undergo an acid-base neutralization reaction to generate a corresponding salt, and removing the benzoic anhydride, thereby activating the prepared covalent organic framework to obtain a covalent organic framework material with high crystallinity and high specific surface area. It is characterized in that all COF materials generated using benzoic acid and benzoic anhydride described in the present invention are activated by an alkaline solution and then treated in a one-step process, and the process is simple and efficient to obtain a COF with high crystallinity and high specific surface area.

[0006] Further, in the present invention, the COF material generated by benzoic acid and benzoic anhydride includes but is not limited to melt-polymerized COF, such as NKCOF-41, NKCOF-42-Br - 、NKCOF-43、NKCOF-44-Br - 、NKCOF-45、NKCOF-46-Br - 、NKCOF-12、NKCOF-28、NKCOF-29、NKCOF-112-M、NKCOF-113-M、NKCOF-114-M, etc. The structure diagram is as follows Figure 1 .

[0007] Furthermore, the alkaline solution for activating the COF material is any one or a combination of aqueous solutions (pH>7) of sodium hydroxide, potassium hydroxide, barium hydroxide, sodium carbonate, sodium bicarbonate, ammonia water, sodium monohydrogen phosphate, sodium hydrogen phosphate, etc., which are treated at a suitable temperature for a period of time. According to the reaction principle of acid-base neutralization, alkaline substances are used to react with benzoic anhydride or benzoic acid to generate corresponding salts, activate the prepared covalent organic framework, and remove excess benzoic acid.

[0008] Preferably, NaHCO3 solution.

[0009] Preferably, the alkaline concentration of the NaHCO3 solution is 0.001-2 mol / mL. Preferably, 1 mol / mL.

[0010] Preferably, the soaking time is 1 min-120 h. Preferably, 12 h.

[0011] Preferably, the reaction temperature is 20°C-37°C.

[0012] The traditional method of activating melt polymerization COF requires the use of a large amount of organic solvent, which is highly polluting to the environment, and it is difficult to recover benzoic acid and benzoic anhydride from the activated organic solvent. In the present invention, an alkaline solution is used to react with anhydride to generate a corresponding salt, which can be quickly activated as a catalyst and porogen to participate in the preparation of benzoic anhydride in COF. The method is simple and effective, the activation conditions are mild and green, the principle is highly versatile, and the ability to process the prepared COF is greatly improved.

[0013] On the other hand, the present invention provides a method for recovering benzoic acid by dropping an activated alkaline solution with an acidic solution. An acidic solution is added dropwise to the activated alkaline solution, and benzoic acid is generated by an acidic substance and a benzoate, and benzoic acid is slightly soluble in cold water and then precipitated, thereby obtaining high-purity benzoic acid. It is characterized in that all alkaline activated recovery liquids described in the present invention are produced by dropping an acidic solution until a white precipitate is formed, and high-purity benzoic acid is obtained, and the process is simple, efficient, and has a high recovery rate.

[0014] Furthermore, the acidic substance described in the present invention refers to a substance that can provide a hydrogen proton or accept an electron pair, such as any one or a combination of aqueous solutions of hydrochloric acid, sulfuric acid, nitric acid, carbonic acid, acetic acid, formic acid, sodium bisulfite, sodium bisulfate, etc.

[0015] Preferably, a hydrochloric acid solution.

[0016] Preferably, the concentration of the acidic solution is preferably 0.1-3 mol / mL.

[0017] Preferably, the reaction temperature is 20°C-37°C.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The present invention does not require the use of organic solvents and high temperature and high pressure treatment. The entire process can be completed at room temperature and pressure using water as a solvent. The entire preparation process does not involve the use of organic solvents and high temperature and high pressure equipment, which has significant advantages in environmental protection and energy consumption reduction.

[0020] (2) The present invention can significantly improve the crystallinity of COF materials prepared by melt polymerization without using organic solvents, increase their specific surface area, and make their pores more uniform and orderly.

[0021] (3) The present invention can simply, efficiently and quickly recover the benzoic acid in the activated solution, thereby achieving the reuse of benzoic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above-described aspects and other aspects of the present invention will be clearly described below by detailed description of the present invention and accompanying drawings. For the purpose of illustrating the present invention, the embodiments in the accompanying drawings are currently preferred, however, it is to be understood that the present invention is not limited to the specific embodiments disclosed.

[0023] Figure 1 NKCOF-41、NKCOF-42-Br - 、NKCOF-43、NKCOF-44-Br - 、NKCOF-45、NKCOF-46-Br - , NKCOF-12, NKCOF-28, NKCOF-29, NKCOF-112-M, NKCOF-113-M, NKCOF-114-M structure diagram.

[0024] Figure 2 (a) PXRD and (b) N2-adsorption / desorption curves of unactivated NKCOF-41.

[0025] Figure 3 (a) PXRD and (b) N2-adsorption / desorption curves of NKCOF-41 activated by DMF and methanol.

[0026] Figure 4 (a) PXRD and (b) N2- adsorption-desorption curves of NKCOF-41 activated by sodium carbonate solution.

[0027] Figure 5 (a) PXRD and (b) N2- adsorption-desorption curves of NKCOF-41 activated by sodium hydroxide solution.

[0028] Figure 6 (a) pH of the solution when activating the covalent organic framework material, (b) pH of the solution when recovering benzoic acid.

[0029] Figure 7 (a) PXRD and (b) N2- adsorption-desorption curves of NKCOF-41 activated by sodium bicarbonate solution.

[0030] Figure 8 1H NMR of recovered benzoic acid. Example

[0031] The preparation method of the present invention will be described in further detail below in conjunction with specific examples. It should be understood that the following examples are only exemplary illustrations and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0032] The reagents, materials, etc. used in the following examples, unless otherwise specified, can be obtained from commercial sources. All chemicals were purchased from commercial sources and were not further purified unless otherwise specified. Unless otherwise specified in the context of this application, the technical terms and abbreviations used in this application have the conventional meanings known to those skilled in the art.

[0033] Example 1

[0034] Activate NKCOF-41 with DMF and methanol. The specific steps are as follows: Take 1 kg of unactivated NKCOF-41 material and put it into a 2L beaker. Pour excess DMF at room temperature until the liquid level is higher than NKCOF-41. Replace DMF every 3 hours until the DMF supernatant becomes colorless and clear. Then wash it with excess methanol three times, each time for 3 hours. The obtained product is vacuum dried at 120 °C for 12 hours to obtain 0.51 kg of NKCOF-41.

[0035] The unactivated NKCOF-41 was characterized by X-ray powder diffraction (PXRD) and N2 adsorption-desorption. Figure 2 5° is the characteristic peak of NKCOF-41, and PXRD shows that there is a characteristic peak of NKCOF-41 at 5°, proving its successful synthesis, but the peak intensity is only 17000, indicating that the unactivated NKCOF-41 has poor crystallinity. N2 adsorption and desorption characterization shows that the specific surface area of ​​unactivated NKCOF-41 is 50 m 2 / g, the pore distribution is uneven.

[0036] The NKCOF-41 activated with DMF and methanol was characterized by X-ray powder diffraction (PXRD) and N2 adsorption-desorption. Figure 3 The PXRD data showed that the characteristic peak intensity of NKCOF-41 at 5° was 410,000 after activation, and the crystallinity was significantly enhanced compared with that of unactivated NKCOF-41. The N2 adsorption-desorption characterization showed that the specific surface area of ​​NKCOF-41 after activation was 1200 m 2 / g, compared with the unactivated NKCOF-41, the specific surface area is significantly increased, the pore distribution is uniform, and the pore size is 1.8nm.

[0037] Example 2

[0038] Activate NKCOF-41 with sodium carbonate solution. The specific steps are as follows: Take 1 kg of unactivated NKCOF-41 material, put it into a 2L beaker, pour in excess 1 mol / mL Na2CO3 aqueous solution at room temperature, and the liquid level is higher than NKCOF-41. Filter the system every 3 hours and collect the filtrate. Continue to soak the solid in excess new 1 mol / mL Na2CO3 aqueous solution. Repeat 3 times, and the obtained product is vacuum dried at 120 °C for 12 hours to obtain 0.49 kg NKCOF-41.

[0039] The NKCOF-41 activated by sodium carbonate solution was characterized by X-ray powder diffraction (PXRD) and N2 adsorption-desorption. Figure 4 .like Figure 4 (a) shows that after activation, the characteristic peak intensity of NKCOF-41 at 5° is 140,000, and the crystallinity is significantly enhanced compared with that of unactivated NKCOF-41. Figure 4 (b) N2 adsorption-desorption characterization shows that the specific surface area of ​​activated NKCOF-41 is 1050 m 2 / g, compared with the unactivated NKCOF-41, the specific surface area is significantly increased, the pore distribution is uniform, and the pore size is 1.8nm.

[0040] Example 3

[0041] Activate NKCOF-41 with sodium hydroxide solution. The specific steps are as follows: Take 1 kg of unactivated NKCOF-41 material, put it into a 2L beaker, pour in excess 1 mol / mL NaOH aqueous solution at room temperature, and the liquid level is higher than NKCOF-41. Filter the system every 3 hours and collect the filtrate. Continue to soak the solid in excess new 1 mol / mL NaOH aqueous solution. Repeat 3 times, and the obtained product is vacuum dried at 120 ° C for 12 hours to obtain 0.49 kg NKCOF-41.

[0042] The NKCOF-41 activated by NaOH solution was characterized by X-ray powder diffraction (PXRD) and N2 adsorption-desorption. Figure 5 .like Figure 5 (a) shows that after activation, the characteristic peak intensity of NKCOF-41 at 5° is 420,000, and the crystallinity is significantly enhanced compared with that of unactivated NKCOF-41. Figure 5 (b) N2 adsorption-desorption characterization shows that the specific surface area of ​​activated NKCOF-41 is 1250 m 2 / g, compared with the unactivated NKCOF-41, the specific surface area is significantly increased, the pore distribution is uniform, and the pore size is 1.8nm.

[0043] Example 4

[0044] Sodium bicarbonate solution is used to activate NKCOF-41. The specific steps are as follows: Take 1 kg of unactivated NKCOF-41 material and put it into a 2L beaker. Pour an excess of 0.1 mol / mL NaHCO3 aqueous solution at room temperature. The liquid level is higher than NKCOF-41. At this time, the solution is alkaline. Figure 6 As shown in (a), the pH meter reading is 8.02. The system is filtered every 3 hours and the filtrate is collected. The solid is continuously immersed in an excess of new 0.1 mol / mL NaHCO3 aqueous solution.

[0045] Add 1 mol / mL hydrochloric acid solution to the filtrate until the formation of white precipitate stops. At this time, the solution is acidic. Figure 6 As shown in (b), the pH meter showed 1.82. The system was filtered, the white precipitate was washed with water, and 0.31 kg of white powder was obtained after dehydration and drying.

[0046] After hydrochloric acid was added dropwise to the obtained filtrate and no white precipitate was produced, NKCOF-41 was washed with a large amount of clean water. The product was vacuum dried at 120°C for 12 hours to obtain 0.50 kg of NKCOF-41.

[0047] The NKCOF-41 activated by NaHCO3 solution was characterized by X-ray powder diffraction (PXRD) and N2 adsorption-desorption. Figure 7 .like Figure 7 (a) shows that after activation, the characteristic peak intensity of NKCOF-41 at 5° is 280,000, and the crystallinity is significantly enhanced compared with that of unactivated NKCOF-41. Figure 7 (b) N2 adsorption-desorption characterization shows that the specific surface area of ​​activated NKCOF-41 is 1150 m 2 / g, compared with the unactivated NKCOF-41, the specific surface area is significantly increased, the pore distribution is uniform, and the pore size is 1.8nm.

[0048] The white powder obtained after dehydration and drying was 1 HNMR analysis, such as Figure 8 , proving that the recovered white powder is benzoic acid.

[0049] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Activating the prepared melt-polymerized covalent organic framework material using an alkaline substance, characterized in that: The melt-polymerized covalent organic framework material is a covalent organic framework material prepared by melt polymerization using benzoic acid and benzoic anhydride as catalysts.

2. Activate the above-mentioned melt-polymerized covalent organic framework material with alkaline substances, so as to obtain a covalent organic framework material with higher crystallinity, higher specific surface area and more uniform pores.

3. The covalent organic framework material using alkaline substances to activate melt polymerization as claimed in claim 2, characterized in that the alkaline substance refers to a substance with the ability to provide electrons or the ability to accept protons. Preferably, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate. At room temperature, the synthesized covalent organic framework material is immersed in an alkaline solution of 0.1-1 mol / mL for 12 hours, and then a covalent organic framework material with better properties is obtained.

4. The method of claim 2 wherein the prepared covalent organic framework material is activated by an alkaline substance comprises the following steps: 1) Soaking the prepared covalent organic framework material in a 0.1-1 mol / mL alkaline solution at room temperature and stirring for 12 hours; 2) After the stirring is completed, filtering and separating the covalent organic framework material and the alkaline solution, and collecting the alkaline solution; 3) Washing the separated covalent organic framework material with water at room temperature for 2 hours, and drying to obtain the material.

5. Recover benzoic acid from the activated alkaline solution, characterized in that: The principle that an acidic substance reacts with the corresponding benzoate to generate benzoic acid, and benzoic acid is slightly soluble in cold water and then precipitates, is used to obtain benzoic acid.

6. The acidic solution according to claim 5, characterized in that The acidic solution is a solution of an acidic substance in water. An acidic substance refers to a substance that can provide a hydrogen proton or accept an electron pair. Preferably, the acidic substance is hydrochloric acid, sulfuric acid, acetic acid, or formic acid.

7. The method of claim 5 for recovering benzoic acid from an activated alkaline solution, characterized in that: The operation steps are as follows: 1) adding 0.1-1 mol / mL acidic solution to the alkaline solution collected in claim 4 at room temperature, and stirring continuously until a white precipitate is generated; 2) When the generation of white precipitate stops, stop adding the acid solution; 3) Filter, wash the white precipitate with water, and dry to obtain benzoic acid.

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