Dicyandiamide-formaldehyde-oxadiazine ternary copolymerized efficient decolorizing flocculant and preparation method thereof

Abstract

The preparation method comprises the following steps: putting an oxadiazine mother solution, paraformaldehyde and dicyandiamide into a reaction kettle, fully and uniformly mixing, controlling the temperature of the reaction kettle to be increased to 80-90 DEG C, and carrying out a condensation polymerization reaction; cooling the temperature of the reaction system to 50-60 DEG C, adding an acidic catalyst into the reaction kettle, and continuously reacting for 0.5-4 hours to obtain a polymer with the pH value of 4.0-6.5; adding aluminum chloride into the reaction kettle, and continuously reacting for 0.5-3 hours to obtain a modified polymer; the modified polymer is subjected to aging treatment, and the dicyandiamide-formaldehyde-oxadiazine ternary polymerization efficient decolorizing flocculant product is obtained. According to the dicyandiamide-formaldehyde-oxadiazine ternary copolymerized efficient decolorizing flocculant and the preparation method thereof disclosed by the invention, more efficient decolorizing, flocculation and turbidity removal of printing and dyeing wastewater are realized, the production cost is reduced, and the process stability is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wastewater treatment, and particularly relates to a dicyandiamide-formaldehyde-oxadiazine ternary copolymer high-efficiency decoloring flocculant and a preparation method thereof. BACKGROUND

[0002] Printing and dyeing wastewater is generally characterized by deep color, high content of organic pollutants, complex chemical structure, poor biodegradability, etc. The printing and dyeing industry often uses flocculation and sedimentation technology for wastewater treatment, which has a relatively simple process flow, is convenient to operate and maintain, has a remarkable decoloring effect, and has a relatively low treatment cost.

[0003] Dicyandiamide-formaldehyde polymer (DCD-FA) is an important polymer flocculant, which has a molecular main chain rich in active groups such as quaternary ammonium salt with positive charge, can strongly adsorb dye molecules with negative charge through electrostatic neutralization, can form hydrogen bonds with dye molecules through polar groups on the molecular chain, and can play a bridging adsorption effect through a long molecular chain structure. In the flocculation process, the dye molecules are aggregated into large-size flocs to be separated by the roll-sweeping and net-catching effect, and exhibit excellent performance in the field of industrial wastewater treatment, especially dye wastewater decolorization. However, the DCD-FA polymer prepared by the traditional method has a relatively low degree of polymerization and a small molecular weight, which results in a limited number of active functional groups on the molecular chain. This directly causes the flocculation process to generate small and loose floc particles with slow settling velocity, and the final effluent clarity is difficult to achieve the desired effect.

[0004] In order to overcome the above shortcomings of the traditional DCD-FA polymer, domestic and foreign researchers have devoted themselves to improving the flocculation performance through molecular structure modification. For example, urea is used to partially replace dicyandiamide or ethylenediamine is introduced as a modifier. However, these modification methods not only increase the production cost, but also have poor effect in the treatment of specific types of printing and dyeing wastewater. Moreover, most of the modification researches are still at the laboratory or pilot stage, and the stability and long-term effect in actual large-scale industrial application are relatively insufficient, and the stability and sustainability of industrial application are questionable. SUMMARY

[0005] The technical effect to be achieved by the present application is to provide a dicyandiamide-formaldehyde-oxadiazine ternary copolymer high-efficiency decoloring flocculant and a preparation method thereof, which realizes more efficient decolorization, flocculation and turbidity removal of printing and dyeing wastewater, and reduces the production cost and improves the process stability.

[0006] In order to achieve the above technical effect, the present application provides a dicyandiamide-formaldehyde-oxadiazine ternary copolymer high-efficiency decoloring flocculant, the raw materials of which include, by molar ratio: Dicyandiamide: Oxadiazine mother liquor: Paraformaldehyde: Ammonium chloride: Aluminum chloride = 1 : 2~4 : 1~2 : 0.5~1 : 0.05~0.2, wherein the effective components in the oxadiazine mother liquor include 10% oxadiazine, 9% formaldehyde, 1.33% ammonia nitrogen, and 8.72% ammonium sulfate.

[0007] As a preferred option, the acidic catalyst includes one or more inorganic ammonium salts such as ammonium chloride and ammonium sulfate.

[0008] To achieve the above-mentioned technical effects, this application also provides a method for preparing a dicyandiamide-formaldehyde-oxadiazine ternary copolymer high-efficiency decolorizing flocculant, comprising the following steps: Oxadiazine mother liquor, paraformaldehyde, and dicyandiamide are added to a reaction vessel and thoroughly mixed. The temperature of the reaction vessel is controlled to rise to 80-90℃ to carry out a polycondensation reaction. The temperature of the reaction system is then lowered to 50-60℃, and an acidic catalyst is added to the reaction vessel. The reaction is continued for 0.5-4 hours to obtain a polymer with a pH value of 4.0-6.5. Aluminum chloride is added to the reaction vessel, and the reaction is continued for 0.5-3 hours to obtain a modified polymer. The modified polymer is then aged to obtain a dicyandiamide-formaldehyde-oxadiazine ternary copolymer high-efficiency decolorizing flocculant product.

[0009] In this scheme, ternary polycondensation is carried out using oxadiazine mother liquor, dicyandiamide, and paraformaldehyde as the main raw materials. Aluminum chloride is introduced in the later stage of the reaction for cationization and coordination complexation modification. Oxadiazine mother liquor is a complex industrial wastewater with high treatment difficulty and high disposal costs. During the flocculant preparation process, multiple modified monomers form long-chain polymers through polycondensation, while the oxadiazine structure is used for partial end-capping. This controls the degree of polymer crosslinking, avoiding excessive network formation that leads to floc performance degradation, while retaining sufficient active functional groups, ultimately obtaining a modified flocculant with both high polymerization degree and multiple active functional groups. This modified flocculant can achieve efficient decolorization and flocculation in water treatment through multiple synergistic effects such as charge neutralization, hydrogen bonding, bridging adsorption, and network sweeping. Furthermore, the residual unreacted paraformaldehyde component in the oxadiazine mother liquor is effectively utilized as a reaction raw material, reducing production costs and achieving resource recovery from waste.

[0010] As a preferred option, the step of adding the oxadiazine mother liquor, paraformaldehyde, and dicyandiamide into the reaction vessel and mixing them thoroughly and evenly includes: Add the oxadiazine mother liquor, paraformaldehyde, and dicyandiamide into the reaction vessel at a molar ratio of 2-4:1-2:1 and mix thoroughly and evenly.

[0011] As a preferred option, the controlled reaction vessel temperature is raised to 80-90℃ to carry out the polycondensation reaction, including: The temperature of the reactor was increased to 50-55℃ at a rate of 2℃ / min for a pre-polymerization reaction of 0.5h. The temperature of the reactor is controlled to rise to 80-90℃ at a rate of 1℃ / min for 2-5 hours to carry out the polycondensation reaction.

[0012] Furthermore, the paraformaldehyde is added in small batches multiple times.

[0013] Furthermore, the first addition of paraformaldehyde occurs before the pre-condensation reaction, and the second addition occurs after the pre-condensation reaction is completed. After the second addition, the pH value of the product of the pre-condensation reaction is 3.5-4.5.

[0014] As a preferred option, the oxadiazine mother liquor is added in small batches multiple times.

[0015] As a preferred option, the acidic catalyst includes one or more inorganic ammonium salts such as ammonium chloride and ammonium sulfate; the molar ratio of the acidic catalyst to the dicyandiamide is 0.5~1.0 : 1.

[0016] As a preferred option, the aluminum chloride is aluminum chloride containing crystal water; the molar ratio of the aluminum chloride to the dicyandiamide is 0~0.2:1.

[0017] The beneficial effects of this application are as follows: 1. The solution provided in this application significantly improves the removal efficiency of flocculants for color, chemical oxygen demand (COD), and ammonia nitrogen in dyeing and printing wastewater by using ternary condensation polymerization with oxadiazine mother liquor, dicyandiamide, and paraformaldehyde as the main raw materials. For dyeing and printing wastewater with special chemical structures and high concentrations of organic pollutants, more efficient decolorization, flocculation, and turbidity removal can be achieved by enhancing electrostatic neutralization, hydrogen bonding, bridging adsorption, and sweeping net-like trapping effects, thus solving the problem of poor treatment effects of existing technologies for specific types of dyeing and printing wastewater.

[0018] 2. The solution provided in this application uses oxadiazine mother liquor containing formaldehyde residue, ammonia nitrogen and ammonium sulfate as the main raw material, which not only reduces production costs, but also realizes the resource utilization of waste, avoiding the cost increase problem caused by the use of expensive modifiers in the prior art.

[0019] 3. The flocculant of this application has a higher degree of polymerization and molecular weight, which can form larger and denser flocs, accelerate the settling speed, and thus improve the clarity of the effluent, solving the problems of small floc particles, loose structure and slow settling of traditional DCD-FA flocs.

[0020] 4. The solution provided in this application has a stable process, is easy to control, and reduces the generation of by-products. It has better stability and long-term effects in actual large-scale industrial applications, and reduces secondary impacts on the environment. Attached Figure Description

[0021] Figure 1 The relevant data spectrum of the compound dicyandiamide provided in Example 1 of this invention; Figure 2 The relevant data spectrum of oxadiazine provided in Example 1 of the present invention; Figure 3 The data spectrum related to the flocculant provided in Example 1 of this invention; Figure 4 A verification diagram of the decolorization effect of the flocculant is provided for Example 1 of the present invention. Detailed Implementation

[0022] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0023] Exemplary embodiments of this application are described below.

[0024] This application provides a highly efficient decolorizing flocculant based on a dicyandiamide-formaldehyde-oxadiazine ternary copolymer, wherein the raw materials comprise, by molar ratio: Dicyandiamide: Oxadiazine mother liquor: Paraformaldehyde: Ammonium chloride: Aluminum chloride = 1 : 2~4 : 1~2 : 0.5~1 : 0.05~0.2; Specifically, the oxadiazine mother liquor selected in this application is the mother liquor generated during the production process of oxadiazine. It has a complex composition, with effective components including 10% oxadiazine, 9% formaldehyde, 1.33% ammonia nitrogen, and 8.72% ammonium sulfate. These components can serve as reactants or auxiliary agents in the polymerization reaction, effectively utilizing waste materials and reducing production costs. Preferably, the acidic catalyst includes one or more inorganic ammonium salts such as ammonium chloride and ammonium sulfate.

[0025] This application also provides a method for preparing the above-mentioned dicyandiamide-formaldehyde-oxadiazine ternary copolymer high-efficiency decolorizing flocculant, including the following steps: S1: Add the oxadiazine mother liquor, paraformaldehyde and dicyandiamide into the reactor and mix them thoroughly and evenly. Control the temperature of the reactor to 80-90℃ to carry out the polycondensation reaction. Specifically, after adding the oxadiazine mother liquor, paraformaldehyde, and dicyandiamide to the reactor, thorough stirring is first performed to ensure a homogeneous mixture. Subsequently, the temperature is gradually increased to 80-90°C, at which point a polycondensation reaction occurs, promoting the formation of preliminary polymer chains between dicyandiamide and formaldehyde in the oxadiazine mother liquor medium. The reaction mechanism can be divided into two steps: The first step is an addition reaction to generate a hydroxymethyl derivative. One dicyandiamide molecule contains four active hydrogen atoms. Each formaldehyde molecule undergoes a nucleic acid electrophilic addition reaction with the -NH2 group of dicyandiamide, potentially generating a tetrahydroxymethyldicyandiamide derivative. The reaction equation is as follows: Figure 1 As shown.

[0026] Figure 1 The second step is a condensation polymerization reaction, which mainly occurs between the hydroxymethyl groups of two molecules or between the hydroxymethyl group and an active hydrogen atom on the amino group of another dicyandiamide molecule. The former reaction generates -CH2O- and -CH2- bonds, while the latter reaction generates -CH2- bonds, thus linking the two dicyandiamide molecules together. In neutral or weakly alkaline media, dicyandiamide first undergoes addition with formaldehyde to form hydroxymethyldicyandiamide, which then undergoes further condensation polymerization under weakly acidic conditions to generate a long-chain polymer linked by ether bonds or methylene groups.

[0027] The reaction conditions at this stage need to be strictly controlled. The initial pH of the reaction system is preferably controlled within the range of 3.5-4.5, as such condensation polymerization is difficult to occur in alkaline media. Furthermore, due to the large number of active groups in the system, excessively extending the reaction time or further heating will promote intermolecular cross-linking reactions, thereby forming a network structure of polymers and leading to a deterioration in floc performance.

[0028] Preferably, this step includes: adding the oxadiazine mother liquor, paraformaldehyde, and dicyandiamide into the reaction vessel at a molar ratio of 2-4:1-2:1 and mixing thoroughly and evenly. During the feeding process, the stirrer should be continuously running at a speed of 150 rpm to ensure that the components are evenly dispersed.

[0029] Optionally, the oxadiazine mother liquor is added in small batches multiple times. Adding the oxadiazine mother liquor in batches facilitates the control of the reaction system to form a homogeneous suspension, thereby better controlling the reaction rate and heat of reaction, and avoiding excessively vigorous reactions that could lead to side reactions or non-uniform polymer structures.

[0030] In one implementation, the temperature of the controlled reaction vessel is raised to 80-90°C to carry out the polycondensation reaction, including: The temperature of the reactor was increased to 50-55℃ at a rate of 2℃ / min for a pre-polymerization reaction of 0.5h. The temperature of the reactor is controlled to rise to 80-90℃ at a rate of 1℃ / min for 2-5 hours to carry out the polycondensation reaction.

[0031] Specifically, the pre-condensation reaction is carried out at a lower temperature to initiate a partial addition reaction, generating a hydroxymethyl derivative. The temperature is then gradually increased to 80-90°C at a slower rate and held at this temperature for 2-5 hours to promote the main condensation reaction, forming the polymer. This step, through staged temperature control, effectively controls the progress of the condensation reaction, avoiding over-crosslinking or under-polymerization. The entire process requires stirring, for example at a stirring rate of 150-250 rpm, to ensure the homogeneity of the reaction system and efficient heat transfer.

[0032] Preferably, the paraformaldehyde is added in small, multiple batches. Further, the first addition of paraformaldehyde occurs before the pre-polymerization reaction, and the second addition occurs after the pre-polymerization reaction is completed. After the second addition, the pH value of the product of the pre-polymerization reaction is 3.5-4.5.

[0033] Specifically, the first part of paraformaldehyde is added to the homogeneous suspension system formed by the oxadiazine mother liquor and dicyandiamide. After the feeding is completed, the temperature is increased at a rate of 2°C / min and the reaction is stirred continuously for 30 minutes. Then, the second part of paraformaldehyde is added. At this time, the pH value of the reaction system should be controlled at 3.5-4.5, which helps the further polycondensation reaction to proceed under suitable acidic conditions, ensuring the full polymerization reaction and the optimization of product performance.

[0034] S2: Reduce the temperature of the polycondensation product to 50-60℃, add an acidic catalyst to the reaction vessel, and continue the reaction for 0.5-4h to obtain a high molecular polymer; Specifically, the pH value of the polymer is 4.0-6.5. Preferably, the acidic catalyst includes one or more inorganic ammonium salts such as ammonium chloride and ammonium sulfate; the molar ratio of the acidic catalyst to the dicyandiamide is 0.5-1.0:1. When ammonium chloride is used as the acidic catalyst, ammonium chloride reacts with hydroxymethyldicyandiamide, and partial end-capping with oxadiazine yields the target product. The reaction process is described below. Figure 2 .

[0035] Figure 2 S3: Add aluminum chloride to the reaction vessel and continue the reaction for 0.5-3 hours to obtain the modified polymer; Specifically, the addition of aluminum chloride introduces Al 3+ Ions, Al 3+Ions can undergo coordination complexation or cross-linking reactions with specific groups on the polymer chain, further modifying the polymer and improving its flocculation performance, for example, by forming a more stable floc structure or increasing the adsorption capacity for negatively charged dyes. Preferably, the aluminum chloride is aluminum chloride containing crystal water, such as aluminum chloride hexahydrate (AlCl3·6H2O); the molar ratio of the aluminum chloride to the dicyandiamide is 0~0.2:1.

[0036] S4: The modified polymer is aged to obtain a dicyandiamide-formaldehyde-oxadiazine ternary copolymer high-efficiency decolorizing flocculant product.

[0037] Specifically, the obtained modified polymer is aged at room temperature, for example, for 24 hours. The aging process helps to further stabilize and improve the polymer molecular chains, bringing the product performance to its optimal state.

[0038] For specific implementation examples, please refer to the following examples and comparative examples.

[0039] Example 1 S10: Add 130 g of oxadiazine mother liquor to a four-necked round-bottom flask and start the stirrer, setting the speed to 150 rpm; slowly add 68 g of industrial-grade dicyandiamide powder to the reaction system, and while stirring, slowly add another 100 g of oxadiazine mother liquor to form a homogeneous suspension system; add 25 g of paraformaldehyde in batches, and after the addition is complete, program the temperature at a rate of 2 °C / min. After stirring the reaction continuously for 30 minutes, add 13.8 g of paraformaldehyde. Once a stable ternary mixture system has formed in the reactor, slowly raise the temperature to 80-90 °C and react for 4 hours; S20: After the polycondensation reaction is complete, stop heating and circulate cooling water into the reactor jacket to lower the temperature to 50-60℃. At this temperature, add 12 g of analytical grade ammonium chloride at once and maintain the temperature at 50-60℃ for 60 minutes. During this stage, the pH value should be stable between 4.0 and 6.5, and the viscosity of the system will rise to 500-600 mPa·s. S30: Control the temperature of the reaction system within the range of 50-60℃, slowly add 17.0 g AlCl3·6H2O to the reactor, strictly control the feeding rate to prevent local overheating, react for 2 hours, and obtain a light yellow to colorless transparent viscous liquid modified polymer. S40: The reaction system was aged at room temperature for 14 hours to obtain a dicyandiamide-formaldehyde-oxadiazine ternary copolymer high-efficiency decolorizing flocculant product.

[0040] Example 2-3 The difference between Examples 2 and 3 and Example 1 lies in the amount of substances added in each step and the process control; otherwise, they are the same as Example 1.

[0041] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the oxadiazine mother liquor in the raw materials was replaced with water, and the amount of added substances and process control in the remaining steps were adjusted accordingly.

[0042] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that, in addition to adding oxadiazine mother liquor, oxadiazine raw material was added, and the amount of added substances and process control in the remaining steps were adjusted accordingly.

[0043] The control parameters for each step in Examples 1-3 and Comparative Examples 1-2 are detailed in Table 1.

[0044] Table 1 Control parameters for each step in Examples 1-3 and Comparative Examples 1-2 The physical properties and decolorization performance of the flocculants prepared in Examples 1-3 and Comparative Examples 1 and 2 were tested. Specific test items and methods were as follows: dicyandiamide residue was quantitatively analyzed using high-performance liquid chromatography (HPLC); by-product filter cake yield was calculated by collecting the filter cake through vacuum filtration, drying the cake, and then weighing it; viscosity was measured using a digital viscometer; solid content was determined by the loss on drying method; COD removal rate was calculated using the potassium dichromate oxidation method; ammonia nitrogen removal rate was calculated using Nessler's reagent colorimetric method; color removal rate was determined using standard physicochemical analysis methods; and melamine impurity content was determined using high-performance liquid chromatography (HPLC). The test data are shown in Table 2 below. Table 2. Test results of each embodiment and comparative example. As can be seen from the test results in Table 2, the flocculants prepared in Examples 1, 2 and 3 of this application show significant advantages in all performance indicators.

[0045] Examples 1 and 2 both achieved a COD removal rate of 85%, an ammonia nitrogen removal rate of 80%, and a color removal rate exceeding 90%. Example 3 also maintained a high removal efficiency. This is far superior to the removal effects of Comparative Examples 1 and 2, especially in terms of COD and ammonia nitrogen removal, where the performance of Comparative Examples 1 and 2 is significantly insufficient. The COD removal rate of Comparative Example 2 is even as low as 50%, and the ammonia nitrogen residue of Comparative Examples 1 and 2 is high.

[0046] The flocculant in this embodiment has higher viscosity and solids content, indicating a high degree of polymerization and large molecular weight, enabling it to form larger and denser flocs, which is beneficial for rapid sedimentation and efficient solid-liquid separation. In contrast, Comparative Example 1 has a viscosity of only 7 cp and a solids content of 27.5%, with small floc particles and poor filtration performance. Although Comparative Example 2 has a high dicyandiamide conversion rate, excessive cross-linking leads to a whitish appearance after dilution and poor water solubility, resulting in a large amount of filter cake.

[0047] The embodiments of this application did not produce filter cake as a byproduct during the preparation process, while Comparative Example 1 produced 5-10% filter cake, and Comparative Example 2 produced as much as 30%. This not only increased the post-processing cost but also reduced the product yield and imposed an additional burden on the environment.

[0048] This application achieves resource recovery from waste by effectively utilizing oxadiazine mother liquor, which not only reduces production costs but also avoids the increased costs and environmental problems associated with traditional modification methods. Furthermore, the beneficial effects of this application are significant.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. 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 or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A highly efficient decolorizing flocculant based on a dicyandiamide-formaldehyde-oxadiazine ternary copolymer, characterized in that, The raw materials include, by molar ratio: Dicyandiamide: Oxadiazine mother liquor: Paraformaldehyde: Acidic catalyst: Aluminum chloride = 1 : 2~4 : 1~2 : 0.5~1 : 0.05~0.2, wherein the oxadiazine mother liquor is the mother liquor produced during the production of oxadiazine, and the effective components in the oxadiazine mother liquor include 10% oxadiazine, 9% formaldehyde, 1.33% ammonia nitrogen, and 8.72% ammonium sulfate.

2. The dicyandiamide-formaldehyde-oxadiazine ternary copolymer high-efficiency decolorizing flocculant as described in claim 1, characterized in that, The acidic catalyst includes one or more inorganic ammonium salts such as ammonium chloride and ammonium sulfate.

3. A method for preparing a dicyandiamide-formaldehyde-oxadiazine ternary copolymer high-efficiency decolorizing flocculant, characterized in that, Includes the following steps: Add the oxadiazine mother liquor, paraformaldehyde and dicyandiamide into the reactor and mix them thoroughly and evenly. Control the temperature of the reactor to rise to 80-90℃ to carry out the polycondensation reaction. The temperature of the polycondensation product is lowered to 50-60℃, an acidic catalyst is added to the reaction vessel, and the reaction is continued for 0.5-4 hours to obtain a polymer with a pH value of 4.0-6.

5. Aluminum chloride was added to the reaction vessel, and the reaction was continued for 0.5-3 hours to obtain the modified polymer; The modified polymer was aged to obtain a dicyandiamide-formaldehyde-oxadiazine terpolymer high-efficiency decolorizing flocculant product.

4. The preparation method according to claim 3, characterized in that, The step of adding the oxadiazine mother liquor, paraformaldehyde, and dicyandiamide into the reaction vessel and mixing them thoroughly and evenly includes: Add the oxadiazine mother liquor, paraformaldehyde, and dicyandiamide into the reaction vessel at a molar ratio of 2-4:1-2:1 and mix thoroughly and evenly.

5. The preparation method according to claim 3, characterized in that, The process of raising the temperature of the controlled reactor to 80-90℃ to carry out the polycondensation reaction includes: The temperature of the reactor was increased to 50-55℃ at a rate of 2℃ / min for a pre-polymerization reaction of 0.5h. The temperature of the reactor is controlled to rise to 80-90℃ at a rate of 1℃ / min for 2-5 hours to carry out the polycondensation reaction.

6. The preparation method according to claim 5, characterized in that, The paraformaldehyde is added in small amounts multiple times.

7. The preparation method according to claim 6, characterized in that, The first addition of paraformaldehyde occurs before the pre-polymerization reaction, and the second addition occurs after the pre-polymerization reaction is completed. After the second addition, the pH value of the product of the pre-polymerization reaction is 3.5-4.

5.

8. The preparation method according to claim 3 or 4, characterized in that, The oxadiazine mother liquor is added in small batches multiple times.

9. The preparation method according to claim 3, characterized in that, The acidic catalyst includes one or more inorganic ammonium salts such as ammonium chloride and ammonium sulfate; the molar ratio of the acidic catalyst to the dicyandiamide is 0.5~1.0 :

1.

10. The preparation method according to claim 3, characterized in that, The aluminum chloride is aluminum chloride containing water of crystallization; the molar ratio of the aluminum chloride to the dicyandiamide is 0~0.2:1.

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