Large-scale preparation method and application of cyclodextrin polymer adsorbent based on citric acid two-stage shearing effect

Abstract

The invention belongs to the technical field of development of water treatment adsorbents, and discloses a large-scale preparation method and application of a cyclodextrin polymer adsorbent based on a citric acid two-stage shear effect, and the preparation method comprises the following steps: adding an epichlorohydrin (EPI) cross-linking agent in two stages, inhibiting and relieving the self-polymerization process of the cross-linking agent, and preparing a cyclodextrin polymer adsorbent. The covalent binding of cyclodextrin CD and EPI is promoted to generate a cross-linked structure unit; citric acid serving as an EPI polymerization reaction shearing agent is synchronously added in the two stages, the citric acid induces EPI to be subjected to ring-opening reaction to inhibit the auto-polymerization process of the EPI, the rate and disorder of cross-linking polymerization reaction of the EPI and CD are reduced, and the cyclodextrin polymer material with regular morphology is prepared. According to the method, rapid preparation of kilogram-level cyclodextrin polymer by single feeding is realized, and the prepared novel cyclodextrin polymer adsorbent with multiple binding sites and a regular spherical structure can adsorb organic pollutants and heavy metal ions in water. The preparation method is easy to regulate and control, simple in step and wide in application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of the development of water treatment adsorbents, and particularly relates to a method for large-scale preparation and application of a cyclodextrin polymer adsorbent based on the two-stage shearing effect of citric acid. Background Art

[0002] With the development of industrialization and urbanization, the large-scale discharge of industrial and domestic wastewater has caused serious water pollution. Among them, organic pollutants (such as new pollutants like polycyclic aromatic hydrocarbons, pesticides, benzene series compounds, antibiotics, and phenolic compounds) and heavy metal ions are typical water pollution components. Currently, conventional treatment methods include adsorption, flocculation precipitation, membrane filtration, and advanced oxidation. Among them, the adsorption technology has the advantages of environmental friendliness, mature technology, low cost, and simple operation, and is one of the mainstream technologies in the field of water pollution control. The adsorbent material is the key to affecting the effect of the adsorption technology.

[0003] Cyclodextrin polymer is a water-insoluble polymer material obtained by chemically cross-linking and polymerizing cyclodextrin with cross-linking agents such as tetrafluoroterephthalonitrile and epichlorohydrin, and is widely used as an adsorbent for adsorbing and removing organic pollutants and heavy metal ions in water. The chemical cross-linking polymerization reaction of cyclodextrin is a complex exothermic reaction, including the cross-linking polymerization of cyclodextrin and cross-linking agent, and the self-polymerization of cross-linking agent. According to the structural type of the cross-linking agent, the cross-linking polymerization reaction is usually divided into two categories: the cross-linking polymerization of cyclodextrin with rigid cross-linking agents (such as tetrafluoroterephthalonitrile and hexachlorocyclotriphosphazene) and flexible cross-linking agents (such as epichlorohydrin and isocyanate).

[0004] The rigid cross-linking agent has a highly rigid benzene ring structure, the cross-linking agent molecule has a large volume, and the steric hindrance is large, which hinders the effective contact between the cross-linking agent and cyclodextrin and between cross-linking agents, and the reaction activity is low. The literature (Alsbaiee et al, "Rapid removal of organic micropollutants from water by a porous β-cyclodextrin polymer" Nature, 529(2015), 190-194) first mentioned using tetrafluoroterephthalonitrile with a rigid structure as a cross-linking agent, and mixing 0.2 g of β-CD, 0.1 g of tetrafluoroterephthalonitrile, and 0.3 g of K 2 CO 3It was mixed in anhydrous tetrahydrofuran and, after two days of one-step cross-linking polymerization reaction at 85 °C, 0.055 g of porous cyclodextrin polymer material was obtained. Patent CN108250325 B also carried out one-step cross-linking polymerization of 8.0 g of β-cyclodextrin and 4.0 g of tetrafluoroterephthalonitrile (rigid cross-linking agent) under the same reaction time and temperature conditions to obtain a porous cyclodextrin polymer with an irregular morphology. Patent CN112705169 A mixed 0.1 g of β-cyclodextrin and 0.2 g of hexachlorocyclotriphosphazene (rigid cross-linking agent) and dissolved them in 10 mL of N,N-dimethylformamide, added 0.15 g of potassium carbonate, and after one-step cross-linking polymerization reaction at 120 °C for 24 h, a spherical cyclodextrin polymer material was obtained. To sum up, limited by the low reaction rate, the polymerization effect of cyclodextrin and rigid cross-linking agent is poor and the yield is low under high temperature and long reaction time conditions. Usually, the feed amount of the reaction is low, which limits the large-scale preparation of cyclodextrin polymer.

[0005] The chemical cross-linking polymerization reaction between cyclodextrin and flexible cross-linking agents such as epichlorohydrin and isocyanate is intense, and the excessive self-polymerization of the cross-linking agent is likely to occur, resulting in a low cyclodextrin content in the material, a disordered material composition, and poor repeatability and reproducibility. Therefore, it is difficult to scale up the preparation of polymer materials. Patent 110694598B discloses a porous adsorbent resin of β-cyclodextrin polymer and its preparation method. 2 g of β-cyclodextrin and 30 mL of dry N,N-dimethylformamide are added to a three-necked flask, and then 2 g of 4,4'-diphenylmethane diisocyanate is added under mechanical stirring for a one-step cross-linking polymerization reaction. After reacting at 70 °C for 4 h, a porous cyclodextrin cross-linked polymer with an irregular morphology is rapidly formed, and the single yield is only 3.4 g. Patent CN110577609B dissolves 3 g of β-cyclodextrin in an NaOH solution, and then drops 2.5 ml of epichlorohydrin into the mixed solution at 60 °C. After a one-step cross-linking polymerization reaction for 1 h, a non-porous cyclodextrin polymer material is obtained. Patent CN106832388B adds 2 g of β-cyclodextrin to an NaOH solution containing polyethylene glycol, and then undergoes a one-step cross-linking polymerization with the added epichlorohydrin at 55-60 °C to form a porous cyclodextrin polymer material with an irregular morphology. The literature (Alsbaiee et al, "Rapid removal of organic micropollutants from water by a porous β-cyclodextrin polymer" Nature, 529 (2015), 190-194) reports that 0.3 g of β-CD is dissolved in an NaOH solution at 60 °C, and then 2.5 mL of epichlorohydrin is added dropwise to this solution for a one-step rapid cross-linking polymerization. After reacting for 1 h, a yellow gel is formed, and 3.11 g of non-porous cyclodextrin polymer material is obtained after washing and drying. In summary, the cross-linking polymerization reaction between cyclodextrin and flexible cross-linking agents is intense and the process is complex. An irregularly shaped cyclodextrin polymer is rapidly formed under low-temperature and short-time conditions, and the repeatability of the prepared material is poor, making it difficult to scale up the preparation of cyclodextrin polymer materials.

[0006] In addition, research has reported a method for preparing cyclodextrin polymer materials through the mixed cross-linking reaction of cyclodextrin with flexible and rigid cross-linking agents, and materials with irregular morphological structures have been rapidly prepared. Patent CN109021149 A discloses a method for the mixed cross-linking polymerization of cyclodextrin with flexible and rigid cross-linking agents. 3.08 g of β-cyclodextrin and 0.81 g of tetrafluoroterephthalonitrile are dissolved in a sodium hydroxide solution, and then 7.5 mL of epichlorohydrin is added dropwise at 80 °C for a one-step mixed cross-linking reaction for 1.5 h to obtain a cyclodextrin polymer material with an irregular morphology. Patent CN110577609 B also discloses a mixed cross-linking method. Approximately 3 g of β-cyclodextrin is dissolved in a sodium hydroxide solution, and then an appropriate amount of tetrafluoroterephthalonitrile and epichlorohydrin are added for a one-step mixed cross-linking polymerization reaction for 3 h to obtain a cyclodextrin polymer with an irregular morphology.

[0007] In order to achieve the large-scale preparation of cyclodextrin polymer adsorbents, the present invention provides a method for preparing cyclodextrin polymer adsorbents based on the two-stage shear effect of citric acid. The epichlorohydrin (EPI) cross-linking agent is added in two stages to inhibit the self-polymerization process of the cross-linking agent and promote the covalent binding of cyclodextrin (CD) and EPI to form cross-linked structural units; the EPI polymerization reaction shear agent citric acid is added synchronously in the two stages. Citric acid induces the ring-opening reaction of EPI to inhibit the self-polymerization process of EPI, reduces the rate and disorder of the cross-linking polymerization reaction of EPI and CD, and prepares cyclodextrin polymer materials with regular morphologies. This method realizes the rapid preparation of kilogram-scale cyclodextrin polymers with a single feed, prepares a new type of cyclodextrin polymer adsorbent with multiple binding sites and regular spherical structures, which can adsorb organic pollutants and heavy metal ions in water, and has broad application prospects. Summary of the Invention

[0008] The present invention provides a method for large-scale preparation of cyclodextrin polymer adsorbents based on the two-stage shear effect of citric acid. The epichlorohydrin (EPI) cross-linking agent is added in two stages to inhibit the self-polymerization process of the cross-linking agent and promote the covalent binding of cyclodextrin (CD) and EPI to form cross-linked structural units; the EPI polymerization reaction shear agent citric acid is added synchronously in the two stages. Citric acid induces the ring-opening reaction of EPI to inhibit the self-polymerization process of EPI, reduces the rate and disorder of the cross-linking polymerization reaction of EPI and CD, and prepares cyclodextrin polymer materials with regular morphologies. This method realizes the rapid preparation of kilogram-scale cyclodextrin polymers with a single feed, prepares a new type of cyclodextrin polymer adsorbent with multiple binding sites and regular spherical structures, which can adsorb organic pollutants and heavy metal ions in water. This preparation method has simple steps, is easy to control, and has practical application significance.

[0009] The technical solution of the present invention:

[0010] A large-scale preparation method of a cyclodextrin polymer adsorbent based on the two-stage shearing effect of citric acid, the steps are as follows:

[0011] (1) The first stage: Dissolve cyclodextrin in the NaOH solution, and ultrasonicate for more than half an hour to ensure complete dissolution of cyclodextrin; among them, the mass ratio of cyclodextrin to NaOH is controlled to be 2:1 to 4:1, and the mass concentration of the NaOH solution is 10 to 20%; at 30 °C, successively drop epichlorohydrin and citric acid solution into the above-mentioned mixed solution, where the mass ratio of cyclodextrin to epichlorohydrin is controlled to be 1.5:1 to 2.5:1, the mass ratio of cyclodextrin to citric acid is controlled to be 10:1 to 50:1, the mass concentration of the citric acid solution is 40 to 50%, the dropping rate is 1 to 2 mL / min, use mechanical stirring, and the stirring speed is 200 to 300 rpm, and react for more than 1 hour to achieve covalent cross-linking between cyclodextrin and epichlorohydrin;

[0012] (2) The second stage: Add the saturated sodium hydroxide solution to the reaction solution in step (1), heat up to 50 °C, and quickly add n-decane containing a dispersant; adjust the rotation speed of mechanical stirring to 500 to 600 rpm to fully emulsify the reaction solution; after stirring for 30 min, quickly pour in epichlorohydrin and citric acid solution successively, adjust the rotation speed to 300 to 600 rpm, heat up to 60 to 80 °C, and react for more than 3 hours; among them, the mass ratio of cyclodextrin to NaOH is controlled to be 5:1, the mass ratio of cyclodextrin to epichlorohydrin is controlled to be 0.5:1 to 1.25:1, the mass ratio of cyclodextrin to citric acid is controlled to be 10:1 to 50:1, and the mass concentration of the citric acid solution is 40 to 50%; the dispersant is Span 80 and Tween 20, and their mass ratio is 3:1 to 5:1, and the dispersant is dissolved in n-decane, accounting for 0.5 to 1% of the total mass of n-decane, and the dosage of n-decane is 2 to 3 times the total reaction volume of the system;

[0013] (3) Material drying: Pour out the supernatant of the reaction in step (2), collect the precipitate, wash the material 3 to 5 times with deionized water with a volume 10 times the total reaction volume until the washing liquid is neutral, and then place it in a freeze dryer to dry for more than 48 hours to obtain a cyclodextrin polymer adsorbent based on the two-stage shearing effect of citric acid;

[0014] The cyclodextrin is one of α-CD, β-CD, γ-CD, and HPCD.

[0015] The cyclodextrin polymer adsorbent obtained by the above preparation method is used for the adsorption and removal of organic pollutants and heavy metal ions in water.

[0016] Advantages of the present invention: The large-scale preparation method of cyclodextrin polymer materials based on the two-stage shearing effect of citric acid realizes the kilogram-scale large-scale preparation of cyclodextrin polymer adsorbents with multiple binding sites and regular spherical structures. This method has simple steps, provides new ideas for the design and large-scale preparation of cyclodextrin polymer adsorbents, and has good application prospects. Brief Description of the Drawings

[0017] Figure 1 is the SEM image of the cyclodextrin polymer adsorbent based on the two-stage shearing effect of citric acid.

[0018] Figure 2 is the infrared spectrum of the cyclodextrin polymer adsorbent based on the two-stage shearing effect of citric acid.

[0019] Figure 3 is the adsorption and removal effect diagram of the cyclodextrin polymer adsorbent based on the two-stage shearing effect of citric acid on organic pollutants in water.

[0020] Figure 4 is the adsorption and removal effect diagram of the cyclodextrin polymer adsorbent based on the two-stage shearing effect of citric acid on heavy metal ions in water. Detailed Embodiments

[0021] The following further describes the specific embodiments of the present invention in combination with the drawings and technical solutions.

[0022] Example 1 Large-scale preparation process of β-cyclodextrin polymer adsorbent based on the two-stage shearing effect of citric acid

[0023] Add 1.0 kg of β-CD to 2.0 kg of 15% NaOH solution, sonicate for 30 minutes, then transfer it to a 10 L reactor and stir at a speed of 300 rpm at 30 °C. Subsequently, add 0.4 kg of epichlorohydrin to the reactor and immediately add 0.1 L of 2.5 mol / L citric acid solution to promote preliminary cross-linking polymerization. After 1 hour, add 0.5 kg of 40% NaOH solution and raise the temperature to 50 °C. Dissolve Span80 (45 g) and Tween20 (15 g) as dispersants in 3 L of n-decane (emulsifier), pour it into the reactor, and stir vigorously at a speed of 550 rpm for 30 minutes. Then immediately add epichlorohydrin (1.0 kg) and citric acid solution (2.5 mol / L, 0.1 L) to initiate highly cross-linked polymerization, while raising the temperature to 70 °C and adjusting the speed to 500 rpm. After reacting for 3 hours, collect the precipitate, wash it with deionized water and freeze-dry it to obtain a β-cyclodextrin polymer adsorbent based on the two-stage shearing effect of citric acid, with a yield of 1.105 kg.

[0024] Comparative Example 1: A two-stage β-cyclodextrin polymer was prepared according to the method of Example 1, but without adding the citric acid solution. There were a large number of hard light yellow lumps in the material prepared by this method, showing significant heterogeneity.

[0025] Figure 1 SEM image of the cyclodextrin polymer adsorbent based on the two-stage shear effect of citric acid. The material is regular spherical particles. Figure 2 FTIR image of the cyclodextrin polymer adsorbent based on the two-stage shear effect of citric acid. The material shows an O-H stretching vibration centered at 3445 cm -1 a C-H asymmetric stretching vibration centered at 2926 cm -1 a C-O-C stretching vibration centered at 1165 cm -1 a C-OH stretching vibration centered at 1035 cm -1 These are the characteristics of the CD unit of the crosslinked cyclodextrin polymer. In addition, the material shows a carboxyl C=O stretching vibration peak centered at 1730 cm -1 indicating that citric acid is incorporated into the polymer structure.

[0026] Scale-up preparation process of the hydroxypropyl-β-cyclodextrin polymer adsorbent based on the two-stage shear effect of citric acid in Example 2

[0027] 1.0 kg of hydroxypropyl-β-CD was added to 2.2 kg of 16% NaOH solution, sonicated for 30 minutes, and then transferred to a 10 L reactor and stirred at 30 °C at a speed of 300 rpm. Subsequently, 0.6 kg of epichlorohydrin was added dropwise to the reactor, and immediately 0.1 L of 1.5 mol / L citric acid solution was added to promote preliminary crosslinking polymerization. After 1 hour, 0.6 kg of 40% NaOH solution was added, and the temperature was raised to 50 °C. Span80 (50 g) and Tween20 (20 g) were dissolved in 2.5 L of n-decane (emulsifier) as dispersants and poured into the reactor, and vigorously stirred at a speed of 500 rpm for 30 minutes. Subsequently, epichlorohydrin (1.2 kg) and citric acid solution (1.5 mol / L, 0.1 L) were immediately added to initiate highly crosslinked polymerization, while the temperature was raised to 80 °C and the speed was adjusted to 600 rpm. After reacting for 3 hours, the precipitate was collected. After the reaction, the precipitate was collected, washed with deionized water and freeze-dried to obtain the hydroxypropyl-β-cyclodextrin polymer adsorbent based on the two-stage shear effect of citric acid, with a yield of 1.485 kg.

[0028] Scale-up preparation process of the γ-cyclodextrin polymer adsorbent based on the two-stage shear effect of citric acid in Example 3

[0029] 1.0 kg of γ-CD was added to 2.5 kg of 20% NaOH solution, ultrasonicated for 30 minutes, and then transferred to a 10 L reactor and stirred at 200 rpm at 30 °C. Subsequently, 0.5 kg of epichlorohydrin was dropped into the reactor, and immediately 0.1 L of 3.0 mol / L citric acid solution was added to promote preliminary cross-linking polymerization. After 1 hour, 0.5 kg of 40% NaOH solution was added, and the temperature was raised to 50 °C. Span80 (40 g) and Tween20 (10 g) were dissolved in 3.5 L of n-decane (emulsifier) as dispersants, poured into the reactor, and vigorously stirred at 550 rpm for 30 minutes. Subsequently, epichlorohydrin (1.5 kg) and citric acid solution (3.0 mol / L, 0.1 L) were immediately added to initiate highly cross-linked polymerization, while the temperature was raised to 60 °C and the rotation speed was adjusted to 450 rpm. After reacting for 3 hours, the precipitate was collected. After the reaction ended, the precipitate was collected, washed with deionized water, and freeze-dried to obtain a γ-cyclodextrin polymer adsorbent based on the two-stage shear effect of citric acid, with a yield of 1.074 kg.

[0030] Example 4 Adsorption and Removal of Organic Pollutants in Water by β-Cyclodextrin Polymer Adsorbent Based on the Two-Stage Shear Effect of Citric Acid

[0031] The adsorption reaction was carried out in a 100 mL glass bottle to ensure that the total volume of the reaction solution was 50 mL. First, 0.25 g of the material was weighed into a glass centrifuge tube, and then 50 mL of naphthalene, 4-chlorophenol, 4-bromophenol, sulfamethoxazole, toluene, imidacloprid, and butachlor with a concentration of 5 mg / L were poured in to initiate the adsorption test. The glass bottle was placed on an oscillator and reacted at 180 rpm and 25 °C. After reacting for 24 hours, the sample was drawn with a 1 mL syringe and filtered through a PTFE membrane filter (0.22 μm), and then transferred to an autosampler vial (2 mL) for HPLC analysis. As Figure 3 shown, the removal rates of naphthalene, 4-chlorophenol, 4-bromophenol, sulfamethoxazole, toluene, imidacloprid, and butachlor in water by the material were 92%, 83%, 85%, 89%, 87%, 93%, and 91% respectively. Example 5 Adsorption and Removal of Heavy Metal Ions in Water by β-Cyclodextrin Polymer Adsorbent Based on the Two-Stage Shear Effect of Citric Acid

[0032] The adsorption reaction was carried out in a 100 mL glass bottle to ensure that the total volume of the reaction solution was 50 mL. First, 0.5 g of the material was weighed into a glass centrifuge tube, and then 50 mL of a mixed heavy metal aqueous solution (Cu 2+ 、Cd 2+ 、Zn 2+ 、Pb 2+The concentrations of all were 10 mg / L) to initiate the adsorption test. The glass bottle was placed on an oscillator and reacted at 180 rpm and 25 °C. After reacting for 30 min, the supernatant of the sample was extracted with a 5 mL syringe and filtered through a PTFE membrane filter (0.22 μm), and then the concentration of heavy metal ions in the solution was determined by ICP-AES. As Figure 4 shown, the material's removal rates for Cu 2+ , Cd 2+ , Zn 2+ and Pb 2+ in water were 95%, 93%, 92% and 96% respectively.

Claims

1. A large-scale preparation method of cyclodextrin polymer adsorbent based on the dual-stage shear effect of citric acid, characterized in that: Here are the steps: (1) The first stage: dissolving cyclodextrin in a NaOH solution and ultrasonicating for more than half an hour to ensure that the cyclodextrin is completely dissolved; at 30° C., epichlorohydrin and citric acid solution are added dropwise to the above mixture, and the mixture is stirred for more than 1 hour to achieve covalent crosslinking between cyclodextrin and epichlorohydrin; (2) The second stage: adding a saturated sodium hydroxide solution to the reaction solution in step (1), heating the mixture to 50° C., and quickly adding n-decane containing a dispersant; stirring the mixture to fully emulsify the reaction solution; after stirring for 30 min, quickly pouring in epichlorohydrin and citric acid solution, adjusting the stirring speed to 300-600 rpm, heating the mixture to 60-80° C., and reacting the mixture for more than 3 hours; (3) Material drying: The reaction supernatant of step (2) was discarded, and the precipitate was collected and washed with deionized water 10 times the total reaction volume for 3 to 5 times until the washing liquid was neutral, and then placed in a freeze dryer for more than 48 hours to obtain a cyclodextrin polymer adsorbent based on the dual-stage shear effect of citric acid.

2. The method for large-scale preparation of cyclodextrin polymer adsorbent according to claim 1, characterized in that: In step (1), the mass ratio of cyclodextrin to NaOH is controlled to be 2:1 to 4:1, and the mass concentration of the NaOH solution is 10 to 20%.

3. The large-scale preparation method of cyclodextrin polymer adsorbent according to claim 1, characterized in that: In step (1), the mass ratio of cyclodextrin to epichlorohydrin is controlled to be 1.5:1-2.5:1, the mass ratio of cyclodextrin to citric acid is controlled to be 10:1-50:1, the mass concentration of the citric acid solution is 40-50%, the dropping speed is 1-2 mL / min, and the stirring speed is 200-300 rpm.

4. The method for large-scale preparation of cyclodextrin polymer adsorbent according to claim 1, characterized in that: In step (2), the stirring speed is 500-600 rpm.

5. The method for large-scale preparation of cyclodextrin polymer adsorbent according to claim 1, characterized in that: In step (2), the mass ratio of cyclodextrin to NaOH is controlled to be 5:1, the mass ratio of cyclodextrin to epichlorohydrin is controlled to be 0.5:1-1.25:1, the mass ratio of cyclodextrin to citric acid is controlled to be 10:1-50:1, and the mass concentration of the citric acid solution is 40-50%.

6. The method for large-scale preparation of cyclodextrin polymer adsorbent according to claim 1, characterized in that: In step (2), the dispersants are Span 80 and Tween 20, the mass ratio of which is 3:1 to 5:1, and the dispersants are dissolved in n-decane, accounting for 0.5 to 1% of the total mass of n-decane. The amount of n-decane added is 2 to 3 times the total reaction volume of the system.

7. The method for large-scale preparation of cyclodextrin polymer adsorbent according to claim 1, characterized in that: The cyclodextrin is one of α-CD, β-CD, γ-CD and HPCD.

8. The cyclodextrin polymer adsorbent obtained by the preparation method according to claim 1 is used for adsorption and removal of organic pollutants and heavy metal ions in water.

Images