A method for removing half-esters in bisphenol a bis(diphenyl phosphate)

Abstract

The application discloses a method for removing half ester in bisphenol A bis(diphenyl phosphate), relates to the technical field of organic synthesis, and has the following steps: mixing bisphenol A bis(diphenyl phosphate) material containing half ester with a methylating agent in the presence of a Lewis acid catalyst to make P-OH groups in the half ester undergo a methylation reaction, wherein the methylating agent is selected from one or more of dimethyl phosphate, dimethyl carbonate and dimethyl sulfate; and performing vacuum distillation on the reaction material after the reaction is completed to remove unreacted methylating agent and by-products, and further performing solvent dissolution, acid washing, alkali washing, water washing and desolvent treatment. The method has the beneficial effects that the half ester impurities containing acidic P-OH groups are converted into corresponding phosphate esters through the methylation reaction, and the half ester content and acid value in the BDP product are reduced.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and in particular to a method for removing half-esters from bisphenol A bis(diphenyl phosphate). Background Technology

[0002] Bisphenol A bis(diphenyl phosphate), abbreviated as BDP, is an important class of halogen-free organophosphorus flame retardants. It features good thermal stability, low volatility, and good compatibility with various polymer substrates, and is commonly used for flame retardant modification of engineering plastics, polyurethane materials, and related polymer systems. With the increasing demands for environmental friendliness, stability, and processing compatibility of flame retardants in electronics, automotive parts, and high-performance engineering plastics, the purity, acid value, and impurity control levels of BDP products have gradually become important indicators affecting their application performance. Among these, half-ester impurities are a class of impurities that require key control during BDP production and refining. Half-esters typically refer to mono- or diester phosphate compounds that still contain P-OH groups in their molecular structure. These structures have a certain degree of acidity and can easily affect the acid value and subsequent application stability of BDP products.

[0003] Currently, industrial production of BDP typically employs a process combining polycondensation and end-capping reactions. In this type of process, due to the presence of multifunctional reaction sites in the reaction system, and the influence of factors such as feed ratio, reaction temperature, reaction time, mass transfer, and the degree of end-capping, some intermediate structures may not be completely converted, leading to the formation of half-ester impurities containing P-OH groups. Existing processes typically employ methods to reduce the content of these impurities, such as extending the end-capping reaction time, increasing the reaction temperature, increasing the amount of end-capping components, and refining methods like acid washing, alkali washing, and water washing. However, these measures primarily address the issue from the perspective of promoting complete reaction or physical / chemical washing, and their ability to remove half-ester impurities already formed and present in the organic phase is limited. While extending the reaction time or increasing the temperature may improve the degree of end-capping, it also easily increases side reactions and makes color control more difficult; increasing the amount of end-capping components may lead to an increase in byproducts or residual components; multiple washings can reduce some migratable acidic substances, but it is difficult to achieve sufficient removal of half-ester impurities with P-OH groups that are highly compatible with the BDP matrix. Therefore, existing post-processing methods often suffer from insufficient reduction of half-ester content, unstable acid value control, and limited product refining effect.

[0004] Therefore, the BDP production sector still needs a treatment method that can effectively reduce half-ester impurities containing P-OH groups. This method should simultaneously reduce the half-ester content and acid value of the BDP product, avoiding the incomplete treatment problems associated with relying solely on conventional washing or simple acid value adjustment. Furthermore, this treatment method should be applicable to the refining or post-processing of crude BDP, and facilitate the removal of residual small molecules after treatment, thereby obtaining BDP products with low half-ester content and acid value, and a low risk of impurity residue. Summary of the Invention

[0005] The purpose of this invention is to provide a method for removing half-esters from bisphenol A bis(diphenyl phosphate) to solve the problems of insufficient removal of half-ester impurities containing P-OH groups, unstable acid value control, and difficulty in controlling residual small molecules in existing BDP post-treatment methods.

[0006] To achieve the aforementioned objectives and address the aforementioned technical problems, this invention provides a method for removing half-esters from bisphenol A bis(diphenyl phosphate), the specific solution of which is as follows: A method for removing half-esters from bisphenol A bis(diphenyl phosphate) includes the following steps: Bisphenol A bis(diphenyl phosphate) material containing half ester is mixed with a methylating agent in the presence of a catalyst and reacted to cause the P-OH group in the half ester to undergo a methylation reaction with the methylating agent. After the reaction is complete, the resulting reactants are subjected to vacuum distillation to remove unreacted methylating agents and byproducts.

[0007] Furthermore, the methylating agent is selected from one or more of dimethyl phosphate, dimethyl carbonate, and dimethyl sulfate.

[0008] Furthermore, the half-ester is a phosphate monoester or phosphate diester compound containing a P-OH group in its molecule.

[0009] Furthermore, the catalyst is a Lewis acid catalyst, which is selected from one or more of anhydrous aluminum chloride, anhydrous magnesium chloride, and titanium tetrachloride.

[0010] Preferably, the catalyst is selected from anhydrous magnesium chloride.

[0011] Furthermore, the amount of catalyst used is 0.1 to 1.0 wt% of the mass of bisphenol A bis(diphenyl phosphate) material.

[0012] Preferably, the amount of catalyst used is 0.2 to 0.6 wt% of the mass of bisphenol A bis(diphenyl phosphate) material.

[0013] Furthermore, the molar ratio of the methylating agent to the half-ester of the bisphenol A bis(diphenyl phosphate) material is (1-10):1.

[0014] Furthermore, the reaction temperature for the methylation reaction is 80°C to 180°C.

[0015] Furthermore, the reaction time for the methylation reaction is 1 to 8 hours.

[0016] Preferably, the molar ratio of the methylating agent to the half-ester of the bisphenol A bis(diphenyl phosphate) material is (2-5):1.

[0017] Preferably, the reaction temperature of the methylation reaction is 120°C to 150°C.

[0018] Preferably, the methylation reaction takes 2 to 4 hours.

[0019] Furthermore, after vacuum distillation, the resulting material is subjected to solvent dissolution, acid washing, alkali washing, water washing, and solvent removal treatment in sequence.

[0020] Furthermore, the method is implemented in the crude product refining stage of the bisphenol A bis(diphenyl phosphate) preparation process, or in the post-processing stage of the bisphenol A bis(diphenyl phosphate) finished product.

[0021] Furthermore, the method can be performed intermittently or continuously.

[0022] Preferably, when the method is carried out in the crude product refining stage of the bisphenol A bis(diphenyl phosphate) preparation process, the methylation reaction is set after the end-capping reaction and before acid washing.

[0023] Preferably, when the method is carried out continuously, a continuous methylation reactor is set up after the end-capping reaction step, so that the crude bisphenol A bis(diphenyl phosphate) containing half ester is mixed with preheated dimethyl carbonate and then fed into a tubular reactor for methylation reaction, and the reaction product is fed into a thin film evaporator to remove unreacted dimethyl carbonate, methanol and carbon dioxide.

[0024] The beneficial effects of the technical solution provided by this invention are as follows: This invention utilizes a methylating agent to react with the P-OH groups in the half-ester in the presence of a Lewis acid catalyst, converting the half-ester impurities containing acidic P-OH groups into corresponding phosphate esters, thereby achieving reactive removal of half-ester impurities from bisphenol A bis(diphenyl phosphate). Test results show that after treatment using this method, the half-ester content in BDP products can be reduced to a low level, and the product's acid value decreases simultaneously. This indicates that this invention does not simply rely on washing or acid-base neutralization to reduce the acid value, but rather achieves impurity removal through half-ester structural transformation.

[0025] In this invention, the methylating agent and the Lewis acid catalyst work together in the half-ester conversion process. Conventional washing alone, adding only the catalyst, or not adding the catalyst all fail to achieve the same half-ester removal effect, indicating that the combination of the methylating agent and the Lewis acid catalyst is crucial for effective half-ester conversion. Furthermore, when the amount of methylating agent used is too low, the half-ester removal effect decreases, indicating that the amount of methylating agent needs to be controlled within an appropriate range based on the half-ester content in the material to ensure both the half-ester conversion effect and product quality.

[0026] This invention employs vacuum distillation after the methylation reaction to remove unreacted methylating agents and byproducts, reducing their residual risk in BDP products. Especially when using dimethyl carbonate as the methylating agent, the main reaction byproducts are methanol and carbon dioxide. Combined with vacuum distillation, this method helps obtain BDP products with low half-ester content, low acid value, and controllable residues.

[0027] Compared to conventional washing and acid removal methods, this invention has a different mechanism of action. Conventional washing is difficult to effectively remove half-ester impurities, and acid removal mainly reduces the acid value by neutralizing or capturing acidic components. However, this invention targets the P-OH groups in the half-ester for methylation conversion, thus more directly reducing the half-ester content and solving the problem that half-ester impurities in BDP are difficult to remove effectively through conventional post-treatment.

[0028] The methylating reagent used in this invention (such as dimethyl carbonate) is an environmentally friendly reagent, and its byproducts are methanol and carbon dioxide, which are non-toxic and harmless. They can be easily removed by vacuum distillation, which helps to reduce the risk of residue.

[0029] The present invention utilizes the characteristic that the amount of methylating agent can be flexibly adjusted according to the half-ester content, thus ensuring the high quality of the product. Attached Figure Description

[0030] Figure 1 This is the HPLC chromatogram of the product in Example 1 of the present invention.

[0031] Figure 2 This is an appearance diagram of the bisphenol A bis(diphenyl phosphate) product of the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Of course, the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] Example 1 This embodiment provides a method for removing half-esters of bisphenol A bis(diphenyl phosphate) using dimethyl carbonate.

[0034] Specifically, the steps include the following: S1, Add raw materials.

[0035] Add 500g of crude bisphenol A bis(diphenyl phosphate) containing 0.5% half ester to the reaction vessel.

[0036] S2, methylation reaction.

[0037] Dimethyl carbonate and 2g of anhydrous magnesium chloride were added to the crude bisphenol A bis(diphenyl phosphate). The molar ratio of the half ester to dimethyl carbonate was 1:5. The mixture was heated to 140°C under stirring and reacted for 3 hours to induce methylation of the P-OH groups in the half ester with dimethyl carbonate.

[0038] S3, vacuum distillation.

[0039] After the reaction is complete, the resulting reactants are subjected to vacuum distillation at 0.05 MPa and 145 °C to remove unreacted dimethyl carbonate and methanol.

[0040] S4, post-processing.

[0041] After vacuum distillation, the resulting material is subjected to solvent dissolution, acid washing, alkali washing, water washing, and solvent removal treatment in sequence to obtain the treated bisphenol A bis(diphenyl phosphate) product.

[0042] Example 2 The treated bisphenol A bis(diphenyl phosphate) product was prepared using the same method as in Example 1, except that: In Example 1, dimethyl carbonate was replaced with dimethyl phosphate, and the molar ratio of the half-ester to dimethyl phosphate was 1:3; unreacted dimethyl phosphate and byproducts were removed by vacuum distillation.

[0043] Example 3 The treated bisphenol A bis(diphenyl phosphate) product was prepared using the same method as in Example 1, except that: In Example 1, dimethyl carbonate was replaced with dimethyl sulfate, and the molar ratio of the half-ester to dimethyl sulfate was 1:2.5; unreacted dimethyl sulfate and byproducts were removed by vacuum distillation.

[0044] Example 4 The treated bisphenol A bis(diphenyl phosphate) product was prepared according to the same methylation principle as in Example 1, with the difference being: This embodiment employs a continuous processing method. A primary continuous methylation reactor is set up after the end-capping reaction of bisphenol A bis(diphenyl phosphate). Crude bisphenol A bis(diphenyl phosphate) containing 0.5% half-ester is mixed with dimethyl carbonate preheated to 100°C at a flow rate of 4500 kg / h. The flow rate of dimethyl carbonate is 75 kg / h. Anhydrous magnesium chloride is added as a catalyst, and the mixed material enters a tubular reactor for the methylation reaction.

[0045] The temperature of the tubular reactor was controlled at 140℃ and the residence time was 30 minutes. The reaction product entered the thin film evaporator, where unreacted dimethyl carbonate, methanol and carbon dioxide were removed under a vacuum of 50 Pa and a temperature of 140℃ to obtain the treated bisphenol A bis(diphenyl phosphate) product.

[0046] Example 5 The treated bisphenol A bis(diphenyl phosphate) product was prepared using the same method as in Example 1, except that: The molar ratio of the half-ester to dimethyl carbonate is 1:2, the reaction temperature is 120℃, and the reaction time is 4 hours.

[0047] Example 6 The treated bisphenol A bis(diphenyl phosphate) product was prepared using the same method as in Example 1, except that: The molar ratio of the half-ester to dimethyl carbonate is 1:10, the reaction temperature is 180℃, and the reaction time is 1 hour.

[0048] Comparative Example 1 The crude product containing half-ester bisphenol A bis(diphenyl phosphate) from the same source as in Example 1 was processed, except that: This comparative example does not add dimethyl carbonate or anhydrous magnesium chloride for methylation. Instead, 500g of crude bisphenol A bis(diphenyl phosphate) containing 0.5% half ester is subjected to toluene dissolution, acid washing, alkali washing, water washing and solvent removal treatment in a conventional process to obtain the treated bisphenol A bis(diphenyl phosphate) product.

[0049] Comparative Example 2 The crude bisphenol A bis(diphenyl phosphate) containing half-ester was treated in the same manner as in Example 1, except that: This comparative example does not contain dimethyl carbonate, but only anhydrous magnesium chloride, and is subjected to stirring under the same temperature and time conditions as in Example 1.

[0050] Comparative Example 3 The crude bisphenol A bis(diphenyl phosphate) containing half-ester was treated in the same manner as in Example 1, except that: This comparative example includes dimethyl carbonate, but not anhydrous magnesium chloride.

[0051] Comparative Example 4 The crude bisphenol A bis(diphenyl phosphate) containing half-ester was treated in the same manner as in Example 1, except that: In this comparative example, instead of vacuum distillation after the methylation reaction, the resulting reactants were directly subjected to solvent dissolution, acid washing, alkali washing, water washing, and solvent removal treatment in sequence.

[0052] Comparative Example 5 The crude product containing half-ester bisphenol A bis(diphenyl phosphate) from the same source as in Example 1 was processed, except that: This comparative example does not use dimethyl carbonate for methylation. Instead, an acid scavenger is added to the crude bisphenol A bis(diphenyl phosphate) product, and acid scavenging is performed under treatment conditions comparable to those in Example 1.

[0053] The acid scavenger is 3,4-epoxycyclohexanecarboxylic acid 3,4-epoxycyclohexylmethyl ester, the amount of acid scavenger added is 13.9g, the treatment temperature is 65℃, and the treatment time is 4 hours.

[0054] Comparative Example 6 The crude bisphenol A bis(diphenyl phosphate) containing half-ester was treated in the same manner as in Example 1, except that: In this comparative example, the molar ratio of the half-ester to dimethyl carbonate is 1:0.5.

[0055] Experimental test: 1. Half-ester content test method: determined by liquid chromatography area normalization method.

[0056] (a) Instruments and reagents used: (1) Liquid chromatograph.

[0057] (2) Chromatographic column: C18 column (250mm×4.6mm, 5um) (3) Flat-headed sampler: 50 μl.

[0058] (4) Methanol (chromatographic grade).

[0059] (5) Distilled water.

[0060] (6) Acetic acid (analytical grade).

[0061] (II) Inspection conditions: (1) Mobile phase and gradient conditions. Mobile phase A: Water (100 mL water with 200 μl acetic acid) Mobile phase B: Methanol

[0062] (2) Detection wavelength: 254nm.

[0063] (3) Flow rate: 1.0 mL / min.

[0064] (III) Sample Preparation Weigh approximately 50 mg of sample, dissolve it in chromatographic methanol, dilute to 10 mL, shake well, and set aside.

[0065] (iv) Analysis and Operation When the instrument is in a stable state, inject 50 μl of sample. After the analysis is completed, the area-normalized content is directly calculated by the workstation.

[0066] 2. Acid value test method (a) Reagents and Instruments (1) Potassium hydroxide (KOH) standard titration solution: 0.01 mol / L.

[0067] (2) Phenolphthalein: 10g / L.

[0068] (3) Isopropanol reagent.

[0069] (4) Graduated cylinder: 50mL.

[0070] (5) Alkaline burette: 10 mL (accuracy 0.05 mL).

[0071] (6) Iodine flask: 250mL.

[0072] (7) Electronic balance.

[0073] (II) Analysis Operation Measure 30 mL of isopropanol, add 3-5 drops of phenolphthalein, and neutralize with standard potassium hydroxide (KOH) solution until a faint pink color appears. Accurately weigh 10 g of the sample into a ground-glass conical flask, add the neutralized isopropanol solution, and after the sample is completely dissolved, add 3-5 drops of phenolphthalein indicator. Titrate with 0.01 mol / L standard potassium hydroxide (KOH) solution until a pink color appears and remains for 5 seconds.

[0074] (III) Calculation Acid value X=

[0075] Where: X—sample acid value, in milligrams of potassium hydroxide per gram, mgKOH / g; C —The accurate value of the concentration of the potassium hydroxide (KOH) standard titration solution, in mol / L; V —The volume of the standard potassium hydroxide (KOH) titration solution, in mL; M —Weigh the test mass, in grams; 56.1 — Molar mass of KOH, conversion factor.

[0076] Table 1 Test Data Table

[0077] The test results from the examples and comparative examples show that after treating bisphenol A bis(diphenyl phosphate) materials containing half-esters with methylating agents under anhydrous magnesium chloride catalysis, the half-ester content and acid value in the product are significantly reduced. This indicates that the P-OH groups in the half-esters can undergo methylation under the action of methylating agents, thereby converting the highly acidic and unstable half-ester impurities into the corresponding phosphate ester structures. Different methylating agents and continuous treatment methods all showed good half-ester reduction effects, indicating that this method has good process adaptability. In contrast, conventional washing processes are difficult to effectively remove half-esters. Adding only a catalyst or only a methylating agent cannot achieve the same half-ester removal effect, indicating that the joint participation of methylating agents and catalysts in the reaction is the key to achieving half-ester conversion. When the amount of methylating agent is below the limit range, the half-ester removal effect decreases significantly, indicating that the amount of methylating agent needs to be controlled within an appropriate range. While acid scavenging can lower the acid value, its effect on reducing the half-ester content is limited, indicating that its main function is to neutralize or capture acidic components, rather than to achieve the reactive conversion of the half-ester P-OH groups as described in this invention. Furthermore, residual methylating agents and byproducts were detected in samples that did not undergo vacuum distillation, demonstrating that vacuum distillation is essential for removing unreacted methylating agents and byproducts and ensuring product purity. In summary, this invention, through a combined process of "methylating agent + Lewis acid catalyst + vacuum distillation," achieves effective conversion and removal of half-ester impurities in BDP, providing a more direct and stable half-ester reduction effect compared to conventional washing and acid scavenging treatment routes.

[0078] Depend on Figure 1 As can be seen, the HPLC chromatogram of the bisphenol A bis(diphenyl phosphate) product obtained in Example 1 shows a clear main peak and relatively few impurity peaks with a low peak area ratio. This indicates that after methylation, vacuum distillation, and post-treatment, the main component of the product has a high proportion, while impurities such as half-esters are effectively reduced. Combined with the area normalization method test results, it can be seen that the half-ester content in the treated product is at a low level, and the acid value is also correspondingly reduced. This indicates that the present invention uses a methylation reagent to treat BDP materials containing half-esters in the presence of a Lewis acid catalyst, which is beneficial to the conversion of P-OH groups in the half-esters, thereby achieving effective removal of half-ester impurities. These chromatogram results corroborate the test data, demonstrating that the treatment method used in Example 1 can obtain a BDP product with low half-ester content and few impurity peaks.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for removing half-esters from bisphenol A bis(diphenyl phosphate), characterized in that, Includes the following steps: Bisphenol A bis(diphenyl phosphate) material containing half ester is mixed with a methylating agent in the presence of a catalyst and reacted to cause the P-OH group in the half ester to undergo a methylation reaction with the methylating agent. After the reaction is complete, the resulting reactants are subjected to vacuum distillation to remove unreacted methylating agents and byproducts.

2. The method according to claim 1, characterized in that, The methylating agent is selected from one or more of dimethyl phosphate, dimethyl carbonate, and dimethyl sulfate.

3. The method according to claim 1, characterized in that, The half-ester is a phosphate monoester or phosphate diester compound containing a P-OH group in its molecule.

4. The method according to claim 1, characterized in that, The catalyst is a Lewis acid catalyst, which is selected from one or more of anhydrous aluminum chloride, anhydrous magnesium chloride, and titanium tetrachloride, and the amount used is 0.1 to 1.0 wt% of the mass of bisphenol A bis(diphenyl phosphate) material.

5. The method according to claim 1, characterized in that, The molar ratio of the methylating agent to the half-ester of bisphenol A bis(diphenyl phosphate) is (1-10):

1. The methylation reaction is carried out at a temperature of 80°C to 180°C. The reaction time for the methylation reaction is 1 to 8 hours.

6. The method according to claim 1, characterized in that, After vacuum distillation, the resulting material is subjected to solvent dissolution, acid washing, alkali washing, water washing, and solvent removal treatment in sequence.

7. The method according to claim 1, characterized in that, The method is implemented in the crude product refining stage of the bisphenol A bis(diphenyl phosphate) preparation process, or in the post-processing stage of the bisphenol A bis(diphenyl phosphate) finished product.

8. The method according to claim 1, characterized in that, The method can be performed intermittently or continuously.

9. The method according to claim 7, characterized in that, When the method is implemented in the crude product refining stage of the bisphenol A bis(diphenyl phosphate) preparation process, the methylation reaction is set after the end-capping reaction and before acid washing.

10. The method according to claim 8, characterized in that, When the method is carried out continuously, a continuous methylation reactor is set up after the end-capping reaction step, so that the crude bisphenol A bis(diphenyl phosphate) containing half ester is mixed with preheated dimethyl carbonate and then fed into a tubular reactor for methylation reaction, and the reaction product is fed into a thin film evaporator to remove unreacted dimethyl carbonate, methanol and carbon dioxide.

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