A phenol-formaldehyde resin-containing sewage treatment agent and a method for producing the same

Abstract

The application discloses a phenolic resin-containing sewage treatment agent and a preparation method thereof, and belongs to the field of water pollution treatment. The preparation method comprises the following steps: catalytically reacting phenolic resin and amino silane in a solvent A to obtain amino-modified phenolic resin; then, Schiff base reaction is carried out between the amino-modified phenolic resin and an aldehyde group reagent under acidic conditions to obtain modified phenolic resin containing a Schiff base structure; finally, crosslinking is carried out between the modified phenolic resin and a crosslinking agent under alkaline conditions to obtain the sewage treatment agent. The application introduces amino groups, Schiff base structures and a crosslinking network into the phenolic resin skeleton through three-step continuous chemical modification, forms a synergistic adsorption system with heavy metal ion chelating sites and organic pollutant adsorption sites, and the prepared agent has high adsorption capacity for Cu2+ and methylene blue, is good in selectivity, is stable in structure, can effectively prevent secondary pollution, and is particularly suitable for the treatment of electroplating and printing and dyeing mixed wastewater.

Description

Technical Field

[0001] This invention relates to the field of water pollution control, specifically to a wastewater treatment agent containing phenolic resin and its preparation method. Background Technology

[0002] With rapid industrial development, wastewater discharged from industries such as electroplating, metallurgy, and dyeing contains large amounts of heavy metal ions (such as Cu²⁺ and Pb²⁺) and organic pollutants (such as dyes and phenolic compounds), posing a serious threat to the aquatic environment. Currently used water treatment agents include activated carbon, ion exchange resins, and inorganic adsorbents, but these have significant limitations: activated carbon has a limited adsorption capacity for heavy metal ions and is difficult to regenerate; ion exchange resins are expensive and have poor selectivity for organic pollutants; and inorganic adsorbents such as zeolite and clay are easily saturated and may cause secondary pollution.

[0003] Phenolic resin, as a polymer material with a three-dimensional network structure, shows great potential in water treatment due to its large specific surface area, good chemical stability, and readily available raw materials. However, ordinary phenolic resins have a single surface functional group, resulting in insufficient adsorption selectivity and capacity for specific pollutants. Furthermore, unreacted monomers may leach out during use, leading to secondary pollution problems. For example, the phenolic resin adsorbent disclosed in Chinese patent CN112125234A, while possessing certain adsorption performance, lacks targeted chemical modification, resulting in poor synergistic removal of heavy metals and organic pollutants in complex wastewater systems.

[0004] While some studies have explored ways to improve adsorption performance through amino modification or Schiff base reactions, these approaches often employ a single modification strategy, making it difficult to simultaneously address the synergistic removal of heavy metals and organic pollutants. Furthermore, traditional crosslinking agents such as formaldehyde may pose environmental risks, and conventional preparation processes suffer from low efficiency in introducing functional groups and poor structural stability, limiting their practical application.

[0005] Therefore, developing a phenolic resin-based water treatment agent with high adsorption capacity, excellent selectivity and good stability, capable of effectively removing heavy metal ions and organic pollutants simultaneously and avoiding secondary pollution, has become a pressing technical challenge in this field. Summary of the Invention

[0006] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a wastewater treatment agent containing phenolic resin and its preparation method, which can effectively prevent secondary pollution and is particularly suitable for the treatment of mixed wastewater from electroplating and dyeing.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] In a first aspect, this application provides a method for preparing a modified phenolic resin, characterized by comprising the following steps:

[0009] (1) Phenolic resin and aminosilane are reacted in solvent A in the presence of a catalyst to obtain amino-modified phenolic resin.

[0010] (2) The amino-modified phenolic resin and the aldehyde reagent were subjected to a Schiff base reaction in solvent B. The reaction system was adjusted to acidic conditions with an acidic pH adjuster to obtain a modified phenolic resin containing a Schiff base structure.

[0011] (3) The modified phenolic resin containing Schiff base structure is subjected to a crosslinking reaction with a crosslinking agent under alkaline conditions. The reaction system is adjusted to alkaline conditions with an alkaline pH adjuster to obtain a wastewater treatment agent containing phenolic resin.

[0012] Optionally, in step (1), the phenolic resin is a thermoplastic phenolic resin; the aminosilane is selected from at least one of 3-aminopropyltriethoxysilane, N-phenylaminomethyltriethoxysilane, N-(n-butyl)-3-aminopropyltrimethoxysilane, aminosilane oligomers, α-aminomethyltriethoxysilane, and 4-aminobutyltriethoxysilane.

[0013] Optionally, in step (1), the mass ratio of the phenolic resin to the aminosilane is 1:0.25 to 0.35; the amount of the catalyst is 0.6% to 0.8% of the mass of the phenolic resin; the reaction temperature is 70℃ to 75℃; and the reaction time is 3h to 3.5h.

[0014] Optionally, in step (2), the aldehyde reagent is selected from at least one of salicylaldehyde, vanillin, 2-hydroxy-1-naphthaldehyde, pyridine-2-carboxaldehyde, and furan-2-carboxaldehyde; the molar ratio of the amino-modified phenolic resin to the aldehyde reagent is 1:1.2 to 1.4.

[0015] Optionally, in step (2), the acidic pH adjuster adjusts the pH of the reaction system to 4.5 to 5.0; the Schiff base reaction temperature is 55℃ to 60℃, and the reaction time is 5h to 6h.

[0016] Optionally, in step (3), the crosslinking agent is selected from at least one of epichlorohydrin, glycidyl sulfonate, γ-glycidyl etheroxypropyltrimethoxysilane, epoxy resin type crosslinking agent, isocyanate, and vinyl sulfone; the mass ratio of the modified phenolic resin containing Schiff base structure to the crosslinking agent is 1:0.08 to 0.12.

[0017] Optionally, in step (3), the alkaline pH adjuster adjusts the pH of the reaction system to 9-10; the temperature of the crosslinking reaction is 75℃-80℃, and the reaction time is 2h-2.5h.

[0018] Secondly, this application provides a wastewater treatment agent containing phenolic resin, which is prepared by the method for preparing a modified phenolic resin as described in the first aspect.

[0019] Compared with the prior art, the beneficial effects of this invention are as follows:

[0020] This invention successfully prepared a high-performance phenolic resin-containing wastewater treatment agent through a three-step continuous chemical modification process, effectively solving the technical defects of existing water treatment materials, such as low adsorption capacity, poor selectivity, and susceptibility to secondary pollution for heavy metals and organic pollutants. The method introduces heavy metal chelating sites through aminosilane modification, constructs organic pollutant adsorption sites through Schiff base reactions, and forms a stable three-dimensional network through cross-linking reactions, achieving synergistic effects of multiple adsorption functions and structural stabilization.

[0021] The reagent exhibits excellent comprehensive performance, with an adsorption capacity of ≥45mg / g for Cu²⁺ and ≥60mg / g for methylene blue, significantly higher than that of unmodified phenolic resin. The cross-linked network structure effectively prevents the leaching of functional components, avoiding secondary pollution. At the same time, the synergistic effect of its functional groups enables it to have good selective adsorption capacity in complex wastewater systems and remains stable over a wide pH range, making it particularly suitable for the treatment of mixed wastewater from electroplating and dyeing.

[0022] The preparation process of this invention uses readily available raw materials, mild reaction conditions, and closely linked steps, making it easy to scale up production. The resulting reagent combines high-efficiency adsorption with long-term stability, reducing the dosage per unit treatment and replacement frequency. It effectively controls the overall application cost while improving the wastewater treatment effect. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0024] Figure 1 The adsorption of Cu²⁺ by water treatment reagents prepared with different aldehyde groups in the embodiments of the present invention;

[0025] Figure 2 The adsorption of methylene blue by water treatment reagents prepared with different aldehyde groups in the embodiments of the present invention;

[0026] Figure 3 This is a scan of the water treatment reagent prepared by salicylaldehyde in an embodiment of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] Example 1: This invention discloses a method for preparing a wastewater treatment agent containing phenolic resin, comprising the following steps:

[0029] First, in a reaction vessel, 10 parts by weight of thermoplastic phenolic resin and 2.5 parts by weight of 3-aminopropyltriethoxysilane were co-dispersed in 20 parts by weight of ethanol and stirred until homogeneous. 0.06 parts by weight of hydrochloric acid were added as a catalyst, and the reaction was carried out at 72°C with stirring for 3.2 hours to obtain an amino-modified phenolic resin mixture. After the reaction was complete, some of the solvent was removed by vacuum distillation to obtain a viscous amino-modified phenolic resin.

[0030] Next, 10 parts by weight of the amino-modified phenolic resin (based on solid content) obtained in step (1) were redispersed in 15 parts by weight of methanol to form a homogeneous solution. 12 parts by weight of salicylaldehyde were added dropwise, while the pH of the reaction system was adjusted to 4.8 using acetic acid. The Schiff base reaction was carried out for 5.5 hours at 58°C and a stirring rate of 250 rpm under nitrogen protection. After the reaction was completed, the solvent was removed by vacuum distillation to obtain the modified phenolic resin solid containing the Schiff base structure.

[0031] Finally, 15 parts by weight of the modified phenolic resin containing the Schiff base structure obtained in step (2) were dissolved in an appropriate amount of water. Under stirring, 1.8 parts by weight of epichlorohydrin were added, and the pH of the reaction system was adjusted to 9.5 using a 5% sodium hydroxide aqueous solution. The temperature was raised to 78°C, and the crosslinking reaction was carried out under these conditions for 2.2 hours. After the reaction was completed, the product was cooled and repeatedly washed with deionized water until the washings were neutral. The solid product was vacuum dried at 65°C to constant weight, ground, and the wastewater treatment agent powder was obtained.

[0032] Furthermore, the performance of the prepared wastewater treatment agent was tested:

[0033] First, the adsorption capacity of Cu²⁺ was tested, including: preparing a copper nitrate solution with pH=5.0 and an initial concentration of 100 mg / L. Accurately weigh 0.0500 g of the reagent and add it to 100 mL of the above copper ion solution. The mixture was shaken at 25°C and 150 rpm for 4 hours for adsorption. The concentration of Cu²⁺ in the solution after equilibrium was determined using atomic absorption spectrometry. Figure 1As shown, the equilibrium adsorption capacity of this agent for Cu²⁺ is calculated to be 46.3 mg / g.

[0034] In detail, the adsorption capacity of Cu²⁺ is calculated according to the following formula ( (Unit: mg / g)

[0035]

[0036] in: and The initial and equilibrium concentrations of Cu²⁺ (mg / L) are given; V is the solution volume (L); and m is the mass of the added reagent (g). Each sample was tested in triplicate, and the average value was taken.

[0037] Next, the adsorption capacity of methylene blue was tested, including: preparing a methylene blue solution with pH=7.0 and an initial concentration of 100 mg / L. Accurately weigh 0.0500 g of the reagent and add it to 100 mL of the above dye solution. The solution was shaken at 25°C and 150 rpm for 6 hours for adsorption. The absorbance was measured at 664 nm using a UV-Vis spectrophotometer, and the equilibrium concentration was calculated. Figure 2 As shown, the equilibrium adsorption capacity of this agent for methylene blue is calculated to be 61.8 mg / g.

[0038] In detail, the adsorption capacity of methylene blue is calculated according to the following formula ( (Unit: mg / g)

[0039]

[0040] in: and The initial and equilibrium concentrations of methylene blue are represented by (mg / L); V is the solution volume (L); and m is the mass of the added reagent (g). Each sample was tested in triplicate, and the average value was taken. Implementation Scheme 1 achieved an adsorption capacity of 62 mg / g for methylene blue.

[0041] Example 2

[0042] This invention discloses a method for preparing a wastewater treatment agent containing phenolic resin, comprising the following steps:

[0043] First, in a reaction vessel, 10 parts by weight of thermoplastic phenolic resin and 3.5 parts by weight of N-phenylaminomethyltriethoxysilane were co-dispersed in 18 parts by weight of isopropanol and stirred until homogeneous. 0.08 parts by weight of p-toluenesulfonic acid were added as a catalyst, and the mixture was stirred at 75°C for 3 hours to obtain an amino-modified phenolic resin mixture. Post-treatment was performed as in step (1) of Example 1.

[0044] Next, 10 parts by weight of the amino-modified phenolic resin (based on solids content) obtained in step (1) were redispersed in 18 parts by weight of acetone. 13 parts by weight of 2-hydroxy-1-naphthal were added dropwise, and the pH of the reaction system was adjusted to 4.5 using phosphoric acid. The Schiff base reaction was carried out for 5 hours at 60°C and a stirring rate of 300 rpm under nitrogen protection. The post-treatment was the same as step (2) in Example 1.

[0045] Finally, 15 parts by weight of the modified phenolic resin containing the Schiff base structure obtained in step (2) were dissolved in an appropriate amount of water. While stirring, 1.2 parts by weight of γ-glycidoxypropyltrimethoxysilane were added, and the pH of the reaction system was adjusted to 10 using an 8% potassium hydroxide aqueous solution. The temperature was raised to 80°C, and the crosslinking reaction was carried out under these conditions for 2 hours. The post-treatment was the same as step (3) in Example 1, yielding a wastewater treatment agent powder.

[0046] Furthermore, the prepared wastewater treatment agent was subjected to performance tests (using the same methods as in Example 1), including: the adsorption capacity test result for Cu²⁺ was 43.5 mg / g; and the adsorption capacity test result for methylene blue was 60.2 mg / g.

[0047] Example 3

[0048] This invention discloses a method for preparing a wastewater treatment agent containing phenolic resin, comprising the following steps:

[0049] First, in a reaction vessel, 10 parts by weight of thermoplastic phenolic resin and 2.8 parts by weight of 4-aminobutyltriethoxysilane were co-dispersed in 22 parts by weight of 1,2-propanediol and stirred until homogeneous. 0.07 parts by weight of supported heteropolyacid was added as a catalyst, and the mixture was stirred at 70°C for 3.5 hours to obtain an amino-modified phenolic resin mixture. Post-treatment was performed as in step (1) of Example 1.

[0050] Next, 10 parts by weight of the amino-modified phenolic resin (based on solids content) obtained in step (1) were redispersed in 20 parts by weight of ethylene glycol methyl ether. 11 parts by weight of vanillin were added dropwise, and the pH of the reaction system was adjusted to 5.0 using citric acid. The Schiff base reaction was carried out for 6 hours at 55°C and a stirring rate of 200 rpm under nitrogen protection. The post-treatment was the same as step (2) in Example 1.

[0051] Finally, 15 parts by weight of the modified phenolic resin containing the Schiff base structure obtained in step (2) were dissolved in an appropriate amount of water. While stirring, 1.5 parts by weight of glycidyl sulfonate were added, and the pH of the reaction system was adjusted to 9.0 using ammonia. The temperature was raised to 75°C, and the crosslinking reaction was carried out under these conditions for 2.5 hours. The post-treatment was the same as step (3) in Example 1, yielding a wastewater treatment agent powder.

[0052] The prepared wastewater treatment agent was subjected to performance tests (using the same method as in Example 1), including: the adsorption capacity test result for Cu²⁺ was 41.7 mg / g; and the adsorption capacity test result for methylene blue was 56.5 mg / g.

[0053] Example 4

[0054] This invention discloses a method for preparing a wastewater treatment agent containing phenolic resin, comprising the following steps:

[0055] First, in a reaction vessel, 10 parts by weight of thermoplastic phenolic resin and 3.0 parts by weight of N-(n-butyl)-3-aminopropyltrimethoxysilane were co-dispersed in 18 parts by weight of dimethylformamide (DMF) and stirred until homogeneous. Then, 0.075 parts by weight of acidic ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) was added as a catalyst, and the reaction was stirred at 73°C for 3.3 hours. After the reaction, the mixture was poured into a large amount of deionized water to precipitate, filtered, and the solid was washed with ethanol and dried under vacuum at 60°C to obtain amino-modified phenolic resin.

[0056] Next, 10 parts by weight of the amino-modified phenolic resin obtained in step (1) were redispersed in 20 parts by weight of ethanol. 14 parts by weight of pyridine-2-carboxaldehyde were added dropwise, while the pH of the reaction system was adjusted to 4.6 using formic acid. Under nitrogen protection, the Schiff base reaction was carried out at 56°C and a stirring rate of 280 rpm for 5.8 hours. After the reaction was completed, the solvent was removed by vacuum distillation using a rotary evaporator to obtain a yellow solid, which is the modified phenolic resin containing the Schiff base structure.

[0057] Then, 15 parts by weight of the modified phenolic resin containing the Schiff base structure obtained in step (2) were dispersed in an appropriate amount of water. While stirring, 1.65 parts by weight of isocyanate (hexamethylene diisocyanate) were added, and the pH of the reaction system was adjusted to 9.2 using a 6% sodium hydroxide aqueous solution. The temperature was raised to 77°C, and the crosslinking reaction was carried out under these conditions for 2.3 hours. After the reaction was completed, the product was filtered, repeatedly washed with deionized water until the wash solution was neutral, and vacuum dried at 70°C to constant weight to obtain the wastewater treatment agent powder.

[0058] Furthermore, the prepared wastewater treatment agent was subjected to performance tests (using the same methods as in Example 1), including: the adsorption capacity test result for Cu²⁺ was 39.2 mg / g; and the adsorption capacity test result for methylene blue was 57.1 mg / g.

[0059] Example 5

[0060] This invention discloses a method for preparing a wastewater treatment agent containing phenolic resin, comprising the following steps:

[0061] First, in a reaction vessel, 10 parts by weight of thermoplastic phenolic resin and 2.6 parts by weight of aminosilane oligomer (ammonia value 300 mg KOH / g) were co-dispersed in 16 parts by weight of 2-methyltetrahydrofuran and stirred until homogeneous. 0.065 parts by weight of hydrochloric acid were added as a catalyst, and the reaction was stirred at 71°C for 3.4 hours. The post-reaction treatment was the same as step (1) in Example 4, yielding amino-modified phenolic resin.

[0062] Next, 10 parts by weight of the amino-modified phenolic resin obtained in step (1) were redispersed in 22 parts by weight of isopropanol. 12.5 parts by weight of furan-2-carboxaldehyde were added dropwise, while the pH was adjusted to 4.9 using acetic acid. Under nitrogen protection, a Schiff base reaction was carried out at 59°C and a stirring rate of 220 rpm for 5.2 hours. The post-reaction treatment was the same as in step (2) of Example 4, yielding a modified phenolic resin containing a Schiff base structure.

[0063] Finally, 15 parts by weight of the modified phenolic resin containing the Schiff base structure obtained in step (2) were dispersed in an appropriate amount of water. While stirring, 1.35 parts by weight of vinyl sulfone (divinyl sulfone) were added, and the pH of the reaction system was adjusted to 9.8 using a 7% potassium hydroxide aqueous solution. The temperature was raised to 76°C, and the crosslinking reaction was carried out under these conditions for 2.4 hours. The post-reaction treatment was the same as step (3) in Example 4, yielding a wastewater treatment agent powder.

[0064] Furthermore, the prepared wastewater treatment agent was subjected to performance tests (using the same methods as in Example 1), including: the adsorption capacity test result for Cu²⁺ was 37.5 mg / g, and the adsorption capacity test result for methylene blue was 58.6 mg / g.

[0065] In the embodiments of this application, Figure 1The bar chart visually demonstrates the adsorption capacity (Qe, unit: mg / g) of Cu²⁺ in simulated wastewater using water treatment agents prepared according to the method of this invention using five different aldehyde reagents: salicylaldehyde, vanillin, 2-hydroxy-1-naphthal, pyridine-2-carboxaldehyde, and furan-2-carboxaldehyde. The bar chart clearly shows that among all tested aldehyde reagents, the agent prepared with salicylaldehyde exhibits the highest Cu²⁺ adsorption capacity, exceeding 46 mg / g, significantly superior to the other aldehyde reagents. This chart directly proves that the choice of aldehyde reagent has a crucial impact on the adsorption performance of heavy metal ions in the final product and verifies the preferred position of salicylaldehyde in the technical solution of this invention. Furthermore, the adsorption capacity of all products in the examples is significantly higher than that of ordinary unmodified phenolic resin, reflecting the significant effect of this invention's dual modification strategy of aminosilane and Schiff base reaction in enhancing heavy metal adsorption capacity.

[0066] In the embodiments of this application, Figure 2 Showing with Figure 1 A comparison of the adsorption capacity of five products from the same series for methylene blue, a model molecule of organic pollutants. Data shows that the product prepared using salicylaldehyde also exhibits the best adsorption performance, with a capacity exceeding 62 mg / g. The graphs reveal the differences in the adsorption capacity of organic dye molecules for the Schiff base structure and its associated functional groups (such as ortho-hydroxyl groups and aromatic rings) introduced by different aldehyde reagents. These results are consistent with... Figure 1 The combined results demonstrate that the method described in this invention (especially when using salicylaldehyde) can synergistically enhance the removal capacity of heavy metal ions and organic pollutants, achieving the design objective of multiple effects with a single agent, and providing experimental evidence for solving the problem of multiple pollutant coexistence in complex wastewater systems.

[0067] In the embodiments of this application, Figure 3 Microscopic images of the water treatment agent prepared in Example 1 (using salicylaldehyde as the aldehyde reagent) at high magnification are provided. SEM images show that the modified phenolic resin agent exhibits a porous, rough surface morphology and a certain three-dimensional network structure. This structure significantly increases the specific surface area of ​​the material, providing more active sites for pollutant adsorption. More importantly, the images show a uniformly covered modified layer with a dense structure, confirming the successful construction of a stable surface structure and internal network through three-step chemical modification (aminosilane grafting, Schiff base reaction, and crosslinking). This microstructure is one of the key pieces of evidence explaining the high adsorption capacity, good stability (effectively preventing the dissolution of functional components), and excellent selectivity of the product of this invention, supporting the technical effects of this invention from a morphological perspective.

[0068] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a modified phenolic resin, characterized in that, Includes the following steps: (1) Phenolic resin and aminosilane are reacted in solvent A in the presence of a catalyst to obtain amino-modified phenolic resin, wherein the phenolic resin is a thermoplastic phenolic resin; the aminosilane is selected from at least one of 3-aminopropyltriethoxysilane, N-phenylaminomethyltriethoxysilane, N-(n-butyl)-3-aminopropyltrimethoxysilane, α-aminomethyltriethoxysilane, and 4-aminobutyltriethoxysilane; (2) The amino-modified phenolic resin and the aldehyde reagent were subjected to a Schiff base reaction in solvent B. The reaction system was adjusted to acidic conditions with an acidic pH adjuster to obtain a modified phenolic resin containing a Schiff base structure. (3) The modified phenolic resin containing Schiff base structure is subjected to a crosslinking reaction with a crosslinking agent under alkaline conditions. The reaction system is adjusted to alkaline conditions with an alkaline pH adjuster to obtain a wastewater treatment agent containing phenolic resin.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of phenolic resin to aminosilane is 1:0.25 to 0.35; the amount of catalyst is 0.6% to 0.8% of the mass of phenolic resin; the reaction temperature is 70℃ to 75℃; and the reaction time is 3h to 3.5h.

3. The preparation method according to claim 1, characterized in that, In step (2), the aldehyde reagent is selected from at least one of salicylaldehyde, vanillin, 2-hydroxy-1-naphthaldehyde, pyridine-2-carboxaldehyde, and furan-2-carboxaldehyde; the molar ratio of the amino-modified phenolic resin to the aldehyde reagent is 1:1.2 to 1.

4.

4. The preparation method according to claim 1 or 3, characterized in that, In step (2), the acidic pH adjuster adjusts the pH of the reaction system to 4.5 to 5.0; the Schiff base reaction temperature is 55℃ to 60℃, and the reaction time is 5h to 6h.

5. The preparation method according to claim 1, characterized in that, In step (3), the crosslinking agent is selected from at least one of epichlorohydrin, glycidyl sulfonate, γ-glycidyl etheroxypropyltrimethoxysilane, epoxy resin type crosslinking agent, isocyanate, and vinyl sulfone; the mass ratio of the modified phenolic resin containing Schiff base structure to the crosslinking agent is 1:0.08 to 0.

12.

6. The preparation method according to claim 1 or 5, characterized in that, In step (3), the alkaline pH adjuster adjusts the pH of the reaction system to 9-10; the temperature of the crosslinking reaction is 75℃-80℃, and the reaction time is 2h-2.5h.

7. A wastewater treatment agent containing phenolic resin, characterized in that, It is prepared by any one of the methods for preparing a modified phenolic resin according to claims 1-6.

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