Synthesis of polyphenol monomer and preparation method of loose nanofiltration membrane

Abstract

The invention provides a synthesis method of a polyphenol monomer and a preparation method of a novel loose nanofiltration membrane. The preparation method comprises the following steps: firstly, reacting benzaldehyde with 1, 3-diaminoguanidine hydrochloride under a certain condition to synthesize a polyphenol monomer (HCTT); then respectively dissolving HCTT and anhydrous piperazine (PIP) in a PBS (Phosphate Buffer Solution) to serve as a composite aqueous phase solution; the preparation method comprises the following steps: dissolving 1, 3, 5-trimesoyl chloride (TMC) in n-hexane to serve as an oil phase solution; and carrying out interfacial polymerization on the composite aqueous phase solution and the oil phase solution on one side of the dense surface of the hydrolyzed polyacrylonitrile membrane (HPAN) to obtain the loose nanofiltration membrane. The method has the advantages that the reaction activity of the polyphenol monomer is reduced, the polyphenol monomer has a lower migration rate in a water phase solution, and the loose nanofiltration membrane prepared by using the polyphenol monomer as one of the reaction monomers has high pure water flux, good dye / salt separation selectivity, high flux recovery rate after multiple cycles and low irreversible pollution rate.

Description

Technical Field

[0001] The patent of the present invention belongs to the technical field of separation membrane materials, and relates to a method for synthesizing a polyphenol monomer and preparing a loose nanofiltration membrane, and in particular to a method for preparing a nanofiltration membrane for efficiently separating dyes from salts in dye wastewater. Background Art

[0002] Dye wastewater usually contains organic dyes and inorganic salts, of which dyes and salts can be further separated and recycled. If they are discharged directly without treatment, it will not only cause serious environmental pollution, but also waste resources. However, commercially available nanofiltration membranes (NF) usually have difficulty separating dyes and inorganic salts (divalent salts).

[0003] Therefore, the development of loose nanofiltration membranes (LNMs) that can separate dyes / salts has become one of the hot topics of research at home and abroad in recent years. Unlike traditional NF membranes, the network structure of the selective layer of LNMs membranes is looser, which can simultaneously achieve high retention of dyes and high penetration of inorganic salts. At present, the preparation of loose nanofiltration membranes generally adopts the preparation of loose nanofiltration functional layers on base membranes. The monomers used are usually piperazine (PIP) and 1,3,5-trimethylbenzenecarboxylic acid chloride (TMC). These two monomers are loaded onto the base membrane by interfacial polymerization to form a functional layer. However, the reaction rates of these two monomers are extremely fast, making the interfacial polymerization reaction difficult to control, making it difficult to accurately control the pore size, thickness and other indicators of the functional layer. Therefore, preparing a new type of reaction monomer to achieve controllable interfacial polymerization reaction is the key to preparing loose nanofiltration membranes. The present invention provides a method for preparing a polyphenol monomer. Compared with PIP, the prepared polyphenol monomer (HCTT) has the characteristics of large molecular weight and low migration rate in the aqueous phase, which reduces the reaction activity in interfacial polymerization, making the performance regulation of the loose nanofiltration functional layer simple and controllable. The loose nanofiltration membrane prepared by interfacial polymerization of HCTT and TMC on the base membrane has excellent comprehensive properties. Summary of the invention

[0004] The present invention aims at the resource recovery problem of dyes in dye wastewater, and aims to provide a membrane material capable of separating organic dyes from inorganic salts. Meanwhile, the process is also beneficial to the harmless treatment of dye wastewater.

[0005] To solve the above problems, the present invention adopts the following technical solutions: (1) First, prepare a polyphenol monomer, (E)-N,2-bis((E)-2,3,4-trihydroxybenzylidene)-N'-(Z)-2,3,4-trihydroxybenzylidene)hydrazine-1-carbonyl nitrogen amide (abbreviated as HCTT). Specifically, first weigh the raw materials benzaldehyde and 1,3-diaminoguanidine hydrochloride, and the molar ratio thereof is (3-3.5):1. Benzaldehyde is dissolved in ethanol and stirred evenly; then 1,3-diaminoguanidine hydrochloride is dissolved in a 50°C ethanol and water miscible solvent (volume ratio, ethanol: water = 2:1), and stirred evenly; the above two solutions are poured into a three-necked flask together, reacted and refluxed, the reaction temperature is 70-90°C, the reaction reflux time is 4-8 hours, the obtained product is washed with acetone, dried under negative pressure, and finally recrystallized with ethanol.

[0006] The preparation formula of polyphenol monomer HTCC is as follows: (2) Preparation of loose nanofiltration membrane. HCTT and anhydrous piperazine (PIP) with a molar ratio of 1: (0.3-3) were dissolved in PBS buffer to obtain solutions of the two monomers. After ultrasonic stirring until uniform dispersion, the two monomer solutions were mixed to obtain a fresh composite aqueous phase solution ①, and the total concentration of HCTT and PIP was 2 g / L. 1,3,5-Trimethylol chloride (TMC) was dissolved in n-hexane as the oil phase solution ②, and its solution concentration was 1.2 g / L. A commercially available hydrolyzed polyacrylonitrile membrane (HPAN, water flux 200 LMHbar⁻¹) was fixed on the interfacial polymerization reaction bracket, and the interfacial polymerization reaction was carried out on the dense side of the membrane. First, the composite aqueous phase solution ① was poured in and allowed to stand for 2 minutes. After the aqueous phase was poured out, the excess solution was sucked out with filter paper, and then a certain amount of oil phase solution ② was poured in and allowed to stand for 1 minute. Then the bracket was placed in a fume hood at room temperature for a few seconds to dry, and then placed in an oven for post-treatment for a certain period of time. Finally, the membrane is removed from the reaction support to obtain a loose nanofiltration membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 The infrared spectrum of HCTT synthesized in the present invention; in the figure: at 1607 cm -1 A new peak appears at , which is attributed to the stretching vibration of C=N generated by the amine-aldehyde condensation reaction of the two raw materials.

[0008] Figure 2 This is a scanning electron microscope image of the cross section of the loose nanofiltration membrane in Example 1; in the image: the overall thickness of the composite membrane is about 150 microns, wherein the thickness of the loose layer is about 79 nanometers.

Claims

1. A polyphenol monomer, (E)-N,2-bis((E)-2,3,4-trihydroxybenzylidene)-N'-(Z)-2,3,4-trihydroxybenzylidene)hydrazine-1-carbonyl nitrogen amide (abbreviated as HCTT), characterized by: The structural formula of the monomer is as follows: 。 2. The method for preparing polyphenol monomer HTCC according to claim 1, characterized in that: The preparation formula is as follows: 。 3. The method for preparing the polyphenol monomer HCTT according to claim 2, characterized in that: The steps include: (1) Dissolve benzaldehyde in ethanol and stir evenly; (2) Dissolve 1,3-diaminoguanidine hydrochloride in a 50°C hot mixture of ethanol and water (volume ratio, ethanol: water = 2:1) and stir evenly; (3) The solutions obtained in the above two steps are poured into a three-necked flask, reacted and refluxed, and the product is washed with acetone, dried under negative pressure, and finally recrystallized with ethanol.

4. The method for preparing polyphenol monomers according to claim 3, characterized in that: The molar ratio of the raw materials is: benzaldehyde:1,3-diaminoguanidine hydrochloride=(3-3.5):

1.

5. The method for preparing polyphenol monomers according to claim 3, characterized in that: The reaction temperature is 70-90°C, and the reaction reflux time is 4-8 hours.

6. A method for preparing a loose nanofiltration membrane, characterized in that: HCTT and anhydrous piperazine (PIP) were dissolved in PBS buffer to prepare two monomer solutions, and the two monomer solutions were mixed after ultrasonic stirring until they were uniformly dispersed to obtain a fresh composite aqueous phase solution ①, and the total concentration of HCTT and PIP was 2 g / L; 1,3,5-benzene trimesoyl chloride (TMC) was dissolved in n-hexane as an oil phase solution ②, and its solution concentration was 1.2 g / L; a commercially available hydrolyzed polyacrylonitrile membrane (HPAN, water flux 200LMH bar⁻¹) was fixed on an interfacial polymerization reaction bracket, and an interfacial polymerization reaction was carried out on the dense side of the membrane; first, the composite aqueous phase solution ① was poured on the membrane surface and allowed to stand for 2 minutes; after the aqueous phase was poured out, the excess solution was sucked out with filter paper, and then a certain amount of oil phase solution ② was poured in and allowed to stand for 1 minute; then the bracket was placed in a fume hood to dry at room temperature for several seconds, and then placed in an oven for post-treatment for a certain period of time to obtain an HPAN-based composite membrane; finally, the composite membrane was removed from the reaction bracket to obtain a loose nanofiltration membrane.

7. The method for preparing a loose nanofiltration membrane according to claim 6, characterized in that: The composite aqueous phase solution ① has a raw material molar ratio of HCTT:PIP=1:(0.3~3).

8. The method for preparing a loose nanofiltration membrane according to claim 6, characterized in that: The drying time at room temperature in a fume hood is 20 to 40 seconds.

9. The method for preparing a loose nanofiltration membrane according to claim 6, characterized in that: The oven post-treatment temperature is 40~80℃ and the time is 5~30 minutes.

Images