Method for preparing carbodiimide by recovering polyester film vacuum extract
The preparation of carbodiimide through a step-by-step separation process and urea decomposition method solves the problem of carbodiimide volatilization in PET film production, achieves high-purity recovery and regeneration, reduces waste disposal costs and carbon emissions, and has environmental benefits and economic value.
Patent Information
- Application Number
- CN202510722818.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-30
- Publication Date
- 2025-09-26
AI Technical Summary
In the prior art, carbodiimide added during the production of PET film volatilizes and decomposes in a vacuum environment, forming a complex mixture that is difficult to separate, resulting in material waste and environmental pollution, and high incineration costs.
A step-by-step separation process is adopted to first purify the carbodiimide in the vacuum extract, treat it with petroleum ether solvent and isocyanate protective agent, and then prepare the carbodiimide by urealysis method. The condensation reaction is carried out using methanol and an organophosphorus compound catalyst to obtain high-purity regenerated carbodiimide.
The purity and recovery rate of carbodiimide are significantly improved, waste treatment costs are reduced, carbon emissions are reduced, and resource recycling and environmental benefits are achieved.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of fine chemical synthesis, in particular to a method for preparing carbodiimide by recycling vacuum extraction of polyester film. Background Art
[0002] Polyethylene terephthalate (PET), a class of high-performance engineering plastics developed in the 1950s, is a polymer formed through the esterification reaction of terephthalic acid and ethylene glycol. Polyester resin can typically be processed into films through biaxial stretching. These films offer advantages such as high mechanical strength, excellent transparency, low cost, good dimensional stability, and excellent insulation properties, making them widely used in photovoltaic backsheet materials. Currently, backsheet materials all use PET film as the base material, providing insulation, protection, and barrier properties, ensuring the long-term reliability of solar cells.
[0003] Ordinary PET film contains ester bonds and is unstable to water. It is prone to hydrolysis under high temperature and high humidity conditions. Water molecules react with the ester bonds in the PET structure, causing the PET film to crack and fail as an insulation. Therefore, to ensure the long-term use of photovoltaic modules, an anti-hydrolysis agent is typically added to the PET backsheet base film during production to inhibit the hydrolysis reaction and thus extend the life of the PET film. The most common anti-hydrolysis agent is N,N'-bis(2,6-diisopropylphenyl)carbodiimide (hereinafter referred to as carbodiimide). However, this substance has a low melting point, a low boiling point, and poor thermal stability. It is highly volatile, reactive, and decomposes easily under high temperature and vacuum conditions, resulting in significant material waste and environmental pollution. PET film production primarily utilizes melt vacuum drying, which removes moisture through vacuum pumping. This causes the added carbodiimide to volatilize. Furthermore, carbodiimide reacts with water or alcohols at high temperatures to form urea compounds. This results in a complex extractable mixture of carbodiimide, urea compounds, alcohols, esters, water, and ethers. This mixture, which resembles lard and is difficult to separate, is currently typically disposed of by incineration, increasing waste disposal costs and carbon emissions. Summary of the Invention
[0004] The present invention aims to provide a method for recovering carbodiimide from vacuum extracts of polyester films. The method first purifies the carbodiimide in the vacuum extracts and then prepares the carbodiimide from urea compounds in the vacuum extracts via a urea decomposition process. Two types of carbodiimides, both of high purity and high yield, can be obtained. Furthermore, the entire method is simple, highly feasible, and produces minimal wastewater, effectively reducing waste disposal costs and carbon emissions.
[0005] The object of the present invention is achieved through the following technical solutions:
[0006] The method for recovering the vacuum extraction material of polyester film to prepare carbodiimide comprises the following steps:
[0007] S1. Separation and purification:
[0008] The vacuum extract was added to a petroleum ether solvent, stirred sufficiently to remove water, and then nitrogen was introduced and an isocyanate protective agent was added. After sufficient reaction, the mixture was filtered, and methanol was added. After sufficient stirring, the mixture was separated and separated to obtain a lower layer of methanol solution and an upper layer of petroleum ether solution.
[0009] S2. Recovery and regeneration of carbodiimide:
[0010] The lower methanol solution is heated to remove methanol, and then cooled to form white crystals, which are filtered to obtain recovered carbodiimide;
[0011] The upper petroleum ether solution is heated to reflux and filtered while hot, and then a catalyst is added to carry out a condensation reaction. After the reaction is completed, the solution is cooled, and then methanol is added. The solution is extracted, distilled under reduced pressure, cooled, and filtered to obtain regenerated carbodiimide.
[0012] Conventional photovoltaic backsheet base film production lines often use vacuum extraction, which can cause the added anti-hydrolysis agent to be extracted and form a semi-solid substance. The present invention addresses the drawback that this semi-solid substance cannot be reused and must be disposed of by incineration. The present invention first purifies the carbodiimide in the vacuum-extracted material, and then subjecting the urea compound in the vacuum-extracted material to urea decomposition to produce carbodiimide, thereby recovering and regenerating the carbodiimide. This method has high separation efficiency, and the recovered and regenerated carbodiimide are high in purity, light in color, and have high light transmittance, making them suitable for use as new additives.
[0013] Preferably, in step S1, the isocyanate protecting agent is one or more of sodium bisulfite, sodium thiosulfate, sodium pyrosulfate and potassium bisulfite.
[0014] Preferably, in step S1, during the process of adding the isocyanate protective agent and fully reacting, the reaction temperature is 30-50° C., and ultrasonic treatment is carried out for 2-4 hours under stirring.
[0015] Preferably, in step S1, the mass volume ratio (g:ml:g) of the vacuum extract, petroleum ether solvent, and isocyanate protective agent is 100:(90-160):(8-20).
[0016] Preferably, in step S1, a bagged molecular sieve is used to remove the water.
[0017] Preferably, in step S2, the temperature for removing methanol is 50-70°C.
[0018] Preferably, in step S2, the catalyst is one or more of P-[N,N-bis(β-chloroethyl)]-1-oxo-3-nitrogen-2-phosphacyclohexane-P-oxide, 5,5-dimethyl-2-phenoxy-1,3,2-dioxaphosphacyclohexane, 2-chloro-4H-1,3,2-benzodioxaphospha-4-one, 1-oxaphosphacyclopentene, 1-thiophosphacyclopentene, and 1-methyl-1-oxo-2-phosphacyclopentene.
[0019] Preferably, in step S2, the mass ratio of the vacuum extract to the catalyst is 100:(0.07-0.18).
[0020] Preferably, in step S2, the heating reflux temperature is 70-90° C. and the time is 5-10 h.
[0021] Preferably, in step S2, the condensation reaction temperature is 80-120°C.
[0022] Compared with the prior art, the present invention has the following beneficial effects:
[0023] 1. This invention utilizes a groundbreaking step-by-step separation process to first separate impurities from the vacuum-extracted N,N'-bis(2,6-diisopropylphenyl)carbodiimide mixture, followed by purification with methanol. This method significantly improves the quality of the recovered carbodiimide, achieving high purity and whiteness while maintaining a stable overall mass recovery rate between 10.2% and 16.6%.
[0024] 2. During the separation and purification process, the present invention uses methanol as the extraction agent. To prevent methanol from reacting with 2,6-diisopropylphenyl isocyanate, the 2,6-diisopropylphenyl isocyanate is pre-blocked and protected. After separation, the blockage is removed by high temperature, effectively preventing the rapid reaction of 2,6-diisopropylphenyl isocyanate and ensuring the efficiency and stability of the extraction and separation process.
[0025] 3. In the preparation of regenerated carbodiimide, an organophosphorus compound is used as a catalyst to induce a condensation reaction of 2,6-diisopropylphenyl isocyanate to produce N,N'-bis(2,6-diisopropylphenyl)carbodiimide, resulting in a total mass regeneration rate of 48.7-60.3%. Simultaneously, the impurity content of the regenerated product is significantly reduced, the purity is significantly improved, and the color is lighter.
[0026] 4. This invention has created a new model for waste recycling, which can not only significantly reduce the factory's waste treatment costs, realize resource recycling, and effectively reduce the waste of raw materials, but also achieve remarkable results in energy conservation and emission reduction, making a positive contribution to reducing carbon emissions.
[0027] 5. The method involved in the present invention is characterized by simple operation and strong feasibility. The amount of wastewater discharged during operation is small. It has both good environmental benefits and significant economic value, and has broad application prospects and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Figure 1 It is the appearance of polyester film production extract;
[0029] Figure 2 This is a gas chromatogram of an extract from polyester film production. DETAILED DESCRIPTION
[0030] Example 1
[0031] S1. Weigh 100 g of the vacuum extract and add it to 120 ml of petroleum ether. Stir to form a suspension. Add bagged molecular sieves to remove moisture from the suspension. Then, introduce nitrogen gas and add 9 g of sodium bisulfite at 30°C. Ultrasonicate the mixture for 4 hours while stirring. After filtering to remove excess isocyanate protective agent and impurities, add 80 ml of methanol to the petroleum ether solution and stir. After separation, the upper layer of petroleum ether solution and the lower layer of methanol solution are obtained.
[0032] S2. The methanol solution was heated to 70°C to remove methanol. Heating was stopped when the methanol recovery reached 90%. White crystals were formed after cooling. Carbodiimide was recovered by filtration. A second recrystallization was performed using 70 ml of methanol. The mass recovery ratio of the recovered carbodiimide was 16.6%.
[0033] The upper petroleum ether solution was heated to reflux at 90°C for 8 hours, filtered while hot, and then 0.07g of catalyst (2-chloro-4H-1,3,2-benzodioxophosphin-4-one) was added to the petroleum ether solution. A condensation reaction was carried out at 100°C. The isocyanate content in the system was detected using the di-n-butylamine back titration method (GB / T12009.4-2016). The reaction was terminated when the isocyanate content was less than 0.2%. After cooling, 100ml of methanol was added for extraction. The methanol was distilled off under reduced pressure at 60°C. Distillation was stopped when the methanol distillation volume reached 85%. After cooling, the regenerated carbodiimide was filtered to obtain the regenerated carbodiimide. A second recrystallization was performed using 70ml of methanol. The mass regeneration rate of the regenerated carbodiimide was 48.7%.
[0034] The appearance of the vacuum extracted product is as follows: Figure 1 As shown in the gas chromatogram Figure 2 As shown. By comparing with the standard, Figure 2As can be seen, the peak at 6.7 min is the solvent; the peak at 16.152 min, compared with relevant standard substances, is 2,6-diisopropylphenyl isocyanate, accounting for approximately 71.4%; the peak at 22.186 min, compared with relevant standard substances, is the anti-hydrolysis agent itself, N,N'-bis(2,6-diisopropylphenyl)carbodiimide, accounting for approximately 22.8%. Small amounts of other substances are also present, such as 2,6-diisopropylaniline at 16.304 min, accounting for approximately 2.1%; methyl 2,6-diisopropylphenyl isocyanate at 17.689 min, accounting for approximately 0.4%; and 1,3-bis(3,5-diisopropyl)phenylurea at 17.689 min, accounting for approximately 2.6%.
[0035] Example 2
[0036] S1. Weigh 100 g of the vacuum extract into 160 ml of petroleum ether solvent, stir to form a suspension, and add bagged molecular sieves to remove moisture. Then, introduce nitrogen gas, add 15 g of sodium pyrosulfate at 45°C, and sonicate for 2 hours with stirring. After filtering to remove excess isocyanate protective agent and impurities, add 100 ml of methanol to the petroleum ether solution for extraction. After separation, the upper layer of petroleum ether solution and the lower layer of methanol solution are obtained.
[0037] S2. Heat the lower methanol solution to 80°C to remove methanol. Stop heating when the methanol recovery reaches 90%. Cool the solution to form white crystals, which are filtered to recover the carbodiimide compound. Recrystallize the solution a second time using 70 ml of methanol, achieving a mass recovery of 10.2% of the carbodiimide.
[0038] The upper petroleum ether solution was heated to reflux at 70°C for 10 hours, filtered while hot, and then 0.15g of catalyst (5,5-dimethyl-2-phenoxy-1,3,2-dioxaphosphorinane) was added to the petroleum ether solution. A condensation reaction was carried out at 120°C. The isocyanate content in the system was detected by the dibutylamine back titration method. The reaction was terminated when the isocyanate content was less than 0.2%. After cooling, 110ml of methanol was added for extraction. The methanol was distilled off under reduced pressure at 60°C. Distillation was stopped when the methanol distillation volume reached 85%. After cooling, the solution was filtered to obtain the regenerated carbodiimide, which was then recrystallized a second time using 70ml of methanol. The mass regeneration rate of the regenerated carbodiimide was 59.4%.
[0039] Example 3
[0040] S1. Weigh 100 g of the vacuum extract and add it to 90 ml of petroleum ether. Stir to form a suspension. Add bagged molecular sieves to remove moisture. Purge with nitrogen. Add 20 g of potassium bisulfite at 50°C and sonicate for 2 h. After filtering to remove excess isocyanate protective agent and impurities, add 120 ml of methanol to the petroleum ether solution and stir. After separation, obtain an upper petroleum ether solution and a lower methanol solution.
[0041] S2. Heat the lower methanol solution to 70°C to remove methanol. Heating is stopped when the methanol recovery reaches 90%. After cooling, white crystals are formed, which are filtered to recover the carbodiimide compound. A second recrystallization is performed using 70 ml of methanol, yielding a mass recovery ratio of 13.4% for the recovered carbodiimide.
[0042] The upper petroleum ether solution was heated to reflux at 90°C for 5 hours, filtered while hot, and then 0.2g of catalyst (a mixture of 1-oxaphosphole and 1-thiophosphole, mass ratio 1:1) was added to the petroleum ether solution. A condensation reaction was carried out at 80°C. The isocyanate content in the system was detected by the di-n-butylamine back titration method. The reaction was terminated when the isocyanate content was less than 0.2%. After cooling, 70ml of methanol was added for extraction. The methanol was distilled off under reduced pressure at 60°C. Distillation was stopped when the methanol distillation volume reached 85%. After cooling, the solution was filtered to obtain the regenerated carbodiimide, which was then recrystallized a second time using 70ml of methanol. The mass regeneration rate of the regenerated carbodiimide was 60.3%.
[0043] Example 4
[0044] S1. Weigh 100 g of the vacuum extract and add it to 90 ml of petroleum ether. Stir to form a suspension. Add bagged molecular sieves to remove moisture. Purge with nitrogen. Add 8 g of sodium thiosulfate at 50°C and sonicate for 4 h while stirring. After filtering to remove excess isocyanate protective agent and impurities, add 90 ml of methanol to the petroleum ether solution and stir. After separation, obtain an upper petroleum ether solution and a lower methanol solution.
[0045] S2. Heat the lower methanol solution to 70°C to remove methanol. Heating is stopped when the methanol recovery reaches 90%. After cooling, white crystals are formed, which are filtered to recover the carbodiimide compound. A second recrystallization is performed using 70 ml of methanol, resulting in a mass recovery ratio of 14.5% for the recovered carbodiimide.
[0046] The upper petroleum ether solution was heated to reflux at 90°C for 5 hours, filtered while hot, and then 0.1g of catalyst (2-chloro-4H-1,3,2-benzodioxophosphin-4-one) was added to the petroleum ether solution. A condensation reaction was carried out at 90°C. The isocyanate content in the system was detected by the di-n-butylamine back titration method. The reaction was terminated when the isocyanate content was less than 0.2%. After cooling, 90ml of methanol was added for extraction. The methanol was distilled off under reduced pressure at 60°C. Distillation was stopped when the methanol distillation volume reached 85%. After cooling, the solution was filtered to obtain the regenerated carbodiimide, which was then recrystallized a second time using 70ml of methanol. The mass regeneration rate of the regenerated carbodiimide was 50.6%.
[0047] The performance indicators of the recovered carbodiimide and the regenerated carbodiimide obtained in Examples 1 to 4 are shown in Table 1.
[0048] Table 1:
[0049]
[0050] Note: The transmittance is tested by spectrophotometer, and the solution is 0.5% methanol solution.
[0051] As shown in Table 1, the carbodiimide recovery and regeneration method of the present invention has a relatively simple preparation process and strong operability. The recovered and regenerated carbodiimide has high purity, few impurities, and high light transmittance, which can effectively solve the problem of factory waste disposal, reduce carbon emissions, and save raw material costs. Compared with recycled carbodiimide, the regenerated carbodiimide has higher purity and lighter color, mainly because the regeneration process has more reaction steps and can effectively remove the impact of impurities on the product. The recovered and regenerated N,N'-bis(2,6-diisopropylphenyl)carbodiimide can be reused and can be used as an anti-hydrolysis agent for polymer materials such as PET, TPU, PBT, PA, and EVA. It has high application prospects and economic value, and provides a new approach to hazardous waste treatment for polyester film processing companies.
Claims
1. A method for recovering carbodiimide from a vacuum extract of polyester film, characterized in that: The steps include: S1. Separation and purification: The vacuum extract was added to a petroleum ether solvent, stirred sufficiently to remove water, and then nitrogen was introduced and an isocyanate protective agent was added. After sufficient reaction, the mixture was filtered, and methanol was added. After sufficient stirring, the mixture was separated and separated to obtain a lower layer of methanol solution and an upper layer of petroleum ether solution. S2. Recovery and regeneration of carbodiimide: The lower methanol solution is heated to remove methanol, and then cooled to form white crystals, which are filtered to obtain recovered carbodiimide; The upper petroleum ether solution is heated to reflux and filtered while hot, and then a catalyst is added to carry out a condensation reaction. After the reaction is completed, the solution is cooled, and then methanol is added. The solution is extracted, distilled under reduced pressure, cooled, and filtered to obtain regenerated carbodiimide.
2. The method for recovering carbodiimide from vacuum-extracted polyester film according to claim 1, characterized in that: In step S1, the isocyanate protecting agent is one or more of sodium bisulfite, sodium thiosulfate, sodium pyrosulfate and potassium bisulfite.
3. The method for recovering carbodiimide from vacuum-extracted polyester film according to claim 1, characterized in that: In step S1, during the process of adding an isocyanate protective agent and fully reacting, the reaction temperature is 30-50° C., and ultrasonic treatment is carried out for 2-4 hours under stirring.
4. The method for recovering carbodiimide from vacuum-extracted polyester film according to claim 1, characterized in that: In step S1 , the mass-to-volume ratio (g:ml:g) of the vacuum extract, petroleum ether solvent, and isocyanate protective agent is 100:(90-160):(8-20).
5. The method for recovering carbodiimide from vacuum-extracted polyester film according to claim 1, characterized in that: In step S1, the water is removed by using a bagged molecular sieve.
6. The method for recovering carbodiimide from vacuum-extracted polyester film according to claim 1, characterized in that: In step S2, the temperature of removing methanol is 50-70°C.
7. The method for recovering carbodiimide from vacuum-extracted polyester film according to claim 1, characterized in that: In step S2, the catalyst is one or more of P-[N,N-bis(β-chloroethyl)]-1-oxo-3-nitrogen-2-phosphacyclohexane-P-oxide, 5,5-dimethyl-2-phenoxy-1,3,2-dioxaphosphacyclohexane, 2-chloro-4H-1,3,2-benzodioxaphospha-4-one, 1-oxaphosphacyclopentene, 1-thiophosphacyclopentene, and 1-methyl-1-oxo-2-phosphacyclopentene.
8. The method for recovering carbodiimide from vacuum-extracted polyester film according to claim 1, wherein: In step S2, the mass ratio of the vacuum extract to the catalyst is 100:(0.07-0.18).
9. The method for recovering carbodiimide from vacuum-extracted polyester film according to claim 1, wherein: In step S2, the heating reflux temperature is 70-90° C. and the time is 5-10 h.
10. The method for preparing carbodiimide by recycling vacuum-extracted materials from polyester film according to claim 1, characterized in that: In step S2, the condensation reaction temperature is 80-120°C.