Post-treatment method of polycarbonate diol

Abstract

The invention discloses a polycarbonate diol post-treatment method which comprises the following steps: S1, mixing polycarbonate diol with dilute acid to fully hydrolyze a titanium catalyst; s2, mixing the polycarbonate diol mixed with dilute acid with water, and feeding the mixture into a coalescer for oil-water separation; s3, the Ti content of polycarbonate diol prepared after the oil phase is dehydrated and dried is 1t; the total amount of free alcohol is 1t; in addition, the odor is obviously reduced. The polycarbonate diol prepared by the treatment method has the advantages of low catalyst residue, low free alcohol residue, low odor and the like, and has industrial feasibility.

Description

Technical Field

[0001] This invention belongs to the field of polycarbonate diols, specifically relating to a continuous post-processing method for polycarbonate diols to obtain products with low Ti residue, low free alcohol residue and low odor. Background Technology

[0002] Compared to polyether polyols and polyester polyols, polycarbonate diols possess excellent flexibility, heat resistance, water resistance, and chemical stability, making them essential raw materials for the preparation of high-end polyurethane products such as coatings, adhesives, and leather.

[0003] Polycarbonate diols can be prepared using two main methods: the phosgene method (including the cyclic carbonate method and the dichloroformate method) and the transesterification method. The former, due to the unique properties of phosgene, has virtually no industrial applications, while the transesterification method is the mainstream industrial approach. The transesterification method typically uses a titanium-based catalyst to catalyze the transesterification reaction between carbonates and alcohols, involving two steps: atmospheric pressure transesterification and vacuum polycondensation. After the reaction, the catalyst remains in the material. However, the titanium-based catalyst can catalyze the subsequent reaction between polycarbonate diol and isocyanate, leading to difficulties in reaction control and a high risk of forming polymeric gels or even explosive polymerization. Therefore, post-processing to remove residual catalyst from polycarbonate diols is essential. Residual free alcohols in the finished polycarbonate diol, such as hexanediol and pentanediol, can also affect the subsequent reaction with isocyanate. Free alcohols can consume isocyanate, affecting main chain growth and impacting product performance. Furthermore, free alcohols can migrate and precipitate in polyurethane products, causing performance defects. Therefore, reducing the free alcohol content is also an effective way to improve the quality of polycarbonate diols. Furthermore, the production of polycarbonate diol involves high-temperature conditions, which can easily lead to side reactions in the raw material alcohols. For example, when using 1,4-butanediol, tetrahydrofuran is produced as a side reaction, and when using 1,5-pentanediol, tetrahydropyran and other cyclic ether-like odorous substances are produced as side reactions. This results in a strong odor in polycarbonate diol, which is an important factor affecting product quality.

[0004] Asahi Kasei, a manufacturer of polycarbonate diol, often uses the addition of phosphate esters to polycarbonate diol to deactivate titanium-based catalysts. For example, patent CN115197409A discloses a process involving mixing and heating monophosphate, diephosphate, and triphosphate. The molar ratio of phosphorus to the transesterification catalyst is 0.1–5, and the mass ratio of monophosphate to diephosphate to triphosphate satisfies a relationship of 50–90:3–25:0.01–5 (monophosphate:diephosphate:triphosphate), thus inhibiting the activity of the titanium-based catalyst. However, this patented method leaves Ti still in the polycarbonate diol, failing to achieve effective separation and posing a potential risk.

[0005] Patent CN119912671B provides a method for purifying crude polycarbonate diol containing titanate catalysts, comprising the following steps: dissolving the crude product (PCDL): organic solvent: pure water in a mass ratio of 1:1 to 10:1 to 10 using dichloromethane, trichloromethane, tetrahydrofuran, or ethyl acetate solvent under jacketed hot water heating. The filtrate and residue are separated by high-purity nitrogen pressure filtration, and the organic and aqueous phases are collected separately after the filtrate has settled and separated. Next, the organic phase is transferred to a concentration vessel, the temperature and vacuum are adjusted, and the organic solvent is recovered and recycled to obtain a qualified polycarbonate diol product. This invention effectively removes residual titanate catalysts from polycarbonate diol through an innovative purification process, achieving the production of high-purity products. While this patent introduces solvents in the post-processing, and a removal step is included, it inevitably leads to a deterioration in the odor of the polycarbonate diol, an increase in VOCs, and the process is intermittent.

[0006] Furthermore, both of the aforementioned patents only involve post-treatment methods for residual Ti catalysts in polycarbonate diol, without systematically improving the quality of free alcohol and odor. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, such as incomplete removal of Ti element, ineffective improvement of free alcohol and odor, the present invention provides a post-treatment method for polycarbonate diols, which simultaneously achieves catalyst and free alcohol removal and odor reduction, thereby comprehensively improving the quality of polycarbonate diols.

[0008] In a first aspect, one embodiment of the present invention provides a continuous post-processing method for polycarbonate diol, comprising the following steps:

[0009] S1: Mix polycarbonate diol with dilute acid to fully hydrolyze the titanium catalyst;

[0010] S2: Polycarbonate diol mixed with dilute acid is mixed with water and then fed into a coalescer for oil-water separation.

[0011] S3: High-quality polycarbonate diol is prepared by dehydration and drying of the oil phase, with Ti content as low as <3ppm, free alcohol content as low as <500ppm, and odor significantly reduced.

[0012] The polycarbonate diol has a molecular weight of 500-4000, and the catalyst content in the polycarbonate diol, calculated as Ti element, is 5-30 ppm, and the free alcohol content is 800-2500 ppm.

[0013] The polycarbonate diol described in this invention is prepared by transesterification of carbonate and alcohol under the action of a titanium-based catalyst, as can be found in existing technologies such as CN 109957101 B.

[0014] Among them, titanium-based catalysts include one or two of tetrabutyl titanate and isopropyl titanate;

[0015] Carbonates include one or more of the following: dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, and ethylene carbonate;

[0016] Alcohols are mainly diols, such as diethylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentanediol, and 1,4-cyclohexanediol. They also include polyfunctional alcohols such as glycerol, trimethylolpropane, and pentaerythritol. In addition, polymers with a molecular weight of less than 1000, such as polyoxyethylene ether, polyoxypropylene ether, polytetrahydrofuran, and polycaprolactone, as well as caprolactone and valerate, are also classified as alcohols.

[0017] In one embodiment of the present invention, the dilute acid in step S1 is obtained by diluting one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid with water, with a mass concentration of <20%, preferably 5-15%, and more preferably dilute phosphoric acid with a mass concentration of <20%.

[0018] The amount of pure acid used in dilute acid is 8-20 times the mass of Ti in polycarbonate diol, and can be further 10-15 times.

[0019] The mixing temperature of dilute acid and polycarbonate diol is 60-150℃, preferably 80-120℃; the mixing time is 10-120 min, preferably 30-60 min. The dilute acid is used to promote the complete hydrolysis of the titanium-based catalyst to ensure the subsequent removal effect.

[0020] In one embodiment of the present invention, the mixing of water with the dilute acid and polycarbonate glycol mixture in step S2 can be carried out in the reactor of step S1, or online. The amount of water used is 20-150% of the mass of polycarbonate glycol, preferably 30-50%; the mixing temperature is 80-150°C, preferably 80-130°C. If mixing is carried out in the reactor of step S1, the mixing time is 30-120 min, preferably 45-60 min.

[0021] In one embodiment of the present invention, the coalescer in step S2 is a packing type. To avoid clogging, a large-sized packing with a diameter of 5-10 mm is used. The packing can be one or a combination of glass beads, ceramic particles, and quartz sand.

[0022] The coalescence separation temperature is 10-50°C higher than the incoming material temperature (the temperature of the mixture of acid, water, and polycarbonate).

[0023] The linear velocity of the material in the agglomerator is 2-6 m / min, preferably 3-5 m / min;

[0024] Depending on the separation effect, the coalescer can be set up in single or multi-stage series; after coalescence separation, the Ti content in polycarbonate diol is <3ppm and the total amount of free alcohol is <500ppm.

[0025] In one embodiment of the present invention, in step S3, the oil phase dehydration is carried out by a scraped film evaporator or a dehydration tower to achieve a water content of <200ppm in polycarbonate diol; in addition, this step can further remove odor substances such as cyclic ethers generated during the preparation of polycarbonate diol to obtain a low-odor product.

[0026] This invention provides a method for continuous post-processing of polycarbonate diol, which can obtain high-quality polycarbonate diol products with Ti content <3ppm, total free alcohol content <500ppm, and significantly reduced odor.

[0027] Compared with the prior art, the advantages of this invention are as follows:

[0028] (1) This method can simultaneously achieve catalyst, free alcohol removal and odor reduction, which is a comprehensive improvement in the quality of polycarbonate diol.

[0029] (2) This method is a continuous production process, and it is simple to operate and has a stable production process. It is an efficient production process. Detailed Implementation

[0030] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0031] Main raw material sources

[0032] Polycarbonate diol was prepared according to the method described in patent CN 109957101 B.

[0033] Main testing methods

[0034] 1. Ti content in polycarbonate diol:

[0035] Testing using inductively coupled plasma atomic emission spectrometry (ICP): Polycarbonate diol is added to digestion reagents such as nitric acid and hydrogen peroxide, and the organic matrix is ​​completely destroyed by microwave digestion or heating with a hot plate before the process is tested.

[0036] 2. Free alcohol content in polycarbonate diol:

[0037] Using BSTFA as the derivatizing agent, the temperature was raised to 60-80℃ under pyridine catalysis, heated for 30 minutes, and then subjected to gas chromatography for testing.

[0038] 3. Odor rating of polycarbonate diol:

[0039] According to the subjective odor evaluation method, namely the artificial smelling method, 50g of sample was placed in a 100ml glass bottle and sealed. After being kept at a constant temperature of 50℃ for 24 hours, the grade was determined by artificial smelling (5 parallel samples were prepared for each sample, and 5 people smelled and scored them from 10cm away from the bottle mouth (if the grade is not clear, a decimal point can be used to distinguish it). The highest and lowest scores were removed and the average value was taken).

[0040] Rating Odor intensity description Specific features Level 0 Water, odorless After repeated sniffing, no detectable odor was found. Level 1 Very slight odor The faint odor can only be detected by careful sniffing, but it is not pleasant. Level 2 Slight odor It is easily detectable, has a mild smell, and causes no obvious discomfort. Level 3 Distinct odor The odor is distinct and identifiable as that of alcohols or esters. Level 4 Strong / irritating odor The odor is strong and persistent, causing noticeable discomfort.

[0041] Example

[0042] Example 1

[0043] 30g of 15% phosphoric acid solution (15 times the mass of Ti) was added to 20kg of PCDL (HDO, PDO copolymer) with a molecular weight of 2000, Ti content of 15ppm, and free alcohol content of 1230ppm. The mixture was heated to 120℃ and maintained at that temperature, then stirred for 30min to complete hydrolysis. 6kg of water (30% of the PCDL mass) was added, the mixture was heated to 130℃ and stirred for 60min, then heated to 140℃ and fed into a coalescing separator filled with 10mm quartz sand. Separation was completed by controlling the material linear velocity at 3m / min. The oil phase was dehydrated by a scraped-film evaporator to obtain the final product with a water content of 153ppm. The Ti content was tested to be 1.5ppm, the total free alcohol content was 256ppm, and the odor level decreased from level 3 to level 2.

[0044] Example 2

[0045] 48 g of 15% hydrochloric acid (18 times the mass of Ti) was added to 20 kg of PCDL (HDO homopolymer) with a molecular weight of 3000, Ti content of 20 ppm, and free alcohol content of 923 ppm. The mixture was heated to 130°C and maintained at that temperature, then stirred for 45 min to complete hydrolysis. 14 kg of water (70% of the PCDL mass) was added, the mixture was heated to 140°C, stirred for 100 min, and then heated to 150°C before entering a coalescing separator filled with 10 mm glass beads. Separation was completed by controlling the material linear velocity at 4 m / min. The oil phase was dehydrated by a scraped-film evaporator to obtain the final product with a water content of 156 ppm. The Ti content was tested to be 2.2 ppm, the total free alcohol content was 356 ppm, and the odor level decreased from level 3 to level 1.5.

[0046] Example 3

[0047] 120g of 10% sulfuric acid (20 times the mass of Ti) was added to 20kg of PCDL (HDO homopolymer) with a molecular weight of 4000, Ti content of 30ppm, and free alcohol content of 867ppm. The mixture was heated to 150℃ and maintained at that temperature, then stirred for 120min to complete hydrolysis. 30kg of water (150% of the mass of PCDL) was added, the mixture was heated to 150℃ and stirred for 120min, then heated to 160℃ and fed into a coalescing separator filled with 10mm ceramic particles. Separation was completed by controlling the material linear velocity at 2m / min. The oil phase was dehydrated in a dehydration tower to obtain the final product with a water content of 179ppm. The Ti content was tested to be 2.4ppm, the total free alcohol content was 387ppm, and the odor level decreased from 3.5 to 2.

[0048] Example 4

[0049] 20 kg of PCDL (HDO, PDO copolymer) with a molecular weight of 1000, a Ti content of 12 ppm, and a free alcohol content of 1867 ppm was added with 24 g of 10% hydrochloric acid (10 times the mass of Ti). The mixture was heated to 60°C and maintained at that temperature, then stirred for 60 min to complete hydrolysis. 10 kg of water (50% of the PCDL mass) was added, the mixture was heated to 80°C, stirred for 45 min, and then heated to 120°C before entering a coalescing separator filled with 8 mm glass beads. Separation was completed by controlling the material linear velocity at 5 m / min. The oil phase was dehydrated in a dehydration tower to obtain the final product with a water content of 157 ppm. The Ti content was tested to be 1.9 ppm, the total free alcohol content was 289 ppm, and the odor level decreased from 3.5 to 1.5.

[0050] Example 5

[0051] 5.3 g of 15% phosphoric acid (8 times the mass of Ti) was added to 20 kg of PCDL (HDO homopolymer) with a molecular weight of 500, Ti content of 5 ppm, and free alcohol content of 2350 ppm. The mixture was heated to 80°C and maintained at that temperature, then stirred for 10 min to complete hydrolysis. 4 kg of water (20% of the PCDL mass) was added, the mixture was heated to 90°C, stirred for 30 min, and then heated to 130°C before entering a coalescing separator filled with 10 mm quartz sand. Separation was completed by controlling the material linear velocity at 4 m / min. The oil phase was dehydrated in a dehydration tower to obtain the final product with a water content of 143 ppm. The Ti content was tested to be 1.2 ppm, the total free alcohol content was 376 ppm, and the odor level decreased from level 4 before treatment to level 2.

[0052] Example 6

[0053] 20 kg of PCDL (HDO, BDO copolymer) with a molecular weight of 1500, a Ti content of 10 ppm, and a free alcohol content of 1435 ppm was added with 26 g of 10% sulfuric acid (13 times the mass of Ti). The mixture was heated to 100°C and maintained at that temperature, stirred for 35 min to complete hydrolysis. 6 kg of water (30% of the PCDL mass) was then added, the mixture was heated to 110°C, stirred for 90 min, and then heated to 130°C before entering a coalescing separator filled with 10 mm ceramic particles. Separation was completed by controlling the material linear velocity at 3 m / min. The oil phase was dehydrated in a dehydration tower to obtain the final product with a water content of 165 ppm. The Ti content was tested to be 2.1 ppm, the total free alcohol content was 312 ppm, and the odor level decreased from 3.5 to 1.5.

[0054] Comparative Example

[0055] 20 kg of PCDL (HDO, PDO copolymer) with a molecular weight of 2000, Ti content of 15 ppm, and free alcohol content of 1230 ppm was heated to 120°C and maintained at that temperature. After stirring for 30 min, 6 kg of water (30% of the PCDL mass) was added, and the temperature was raised to 130°C and stirred for 60 min. The mixture was then heated to 140°C and fed into a coalescing separator filled with 10 mm quartz sand. Separation was completed by controlling the material linear velocity at 3 m / min. The oil phase was dehydrated by a scraped-film evaporator to obtain the final product, which had a water content of 149 ppm. The Ti content was tested to be 13.7 ppm, the total free alcohol content was 367 ppm, and the odor level decreased from level 3 to level 2.5.

[0056] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for post-treating a polycarbonate diol, characterized by, The method comprises the following steps: S1: mixing polycarbonate diol with dilute acid; S2: mixing polycarbonate diol with dilute acid with water, entering a coalescer, and performing oil-water separation; S3: obtaining polycarbonate diol after oil phase is dehydrated and dried. The polycarbonate diol is prepared by transesterification reaction of carbonates and alcohols under the action of a titanium catalyst.

2. The method of claim 1, wherein, The polycarbonate diol has a molecular weight of 500-4000, a catalyst content of 5-30 ppm in terms of Ti element, and a free alcohol content of 800-2500 ppm.

3. The method of claim 1 or 2, wherein, The dilute acid is one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and has a mass concentration of <20%, preferably 5-15%. Preferably, the amount of pure acid in the dilute acid is 8-20 times the mass of Ti, and further can be 10-15 times.

4. The method according to any one of claims 1 to 3, wherein, The mixing temperature of the dilute acid and the polycarbonate diol is 60-150°C, preferably 80-120°C; and the mixing time is 10-120 min, preferably 30-60 min.

5. The method of claim 1, wherein, The amount of water in step S2 is 20-150% of the mass of the polycarbonate diol, preferably 30-50%.

6. The method of claim 1 or 5, wherein, The mixing temperature in step S2 is 80-150°C, preferably 80-130°C.

7. The method according to any one of claims 1 to 6, wherein, The coalescer in step S2 is a packed type, and a packing with a diameter of 5-10 mm is used, and the preferred packing is one or a combination of glass beads, ceramic particles, and quartz sand.

8. The method of any one of claims 1-7, wherein, The coalescing separation temperature in step S2 is higher than the incoming material temperature by 10-50°C; and the linear speed of the material in the coalescer is 2-6 m / min, preferably 3-5 m / min.

9. The method of claim 8, wherein, After coalescing separation, the Ti content in the polycarbonate diol is <3 ppm, and the total free alcohol content is <500 ppm.

10. The method of any one of claims 1-9, wherein, In step S3, the oil phase is dehydrated by a wiped film evaporator or a dehydration tower to achieve a water content of <200 ppm in the polycarbonate diol.