Method for preparing polycarbonate diol by using titanate catalyst

Abstract

The invention is suitable for the technical field of chemical industry, and provides a method for preparing polycarbonate diol by using a titanate catalyst, which comprises the following steps: step 1, transesterification: mixing dimethyl carbonate and 1, 6-hexanediol according to a molar ratio of 1.1-1.5: 1, adding isopropyl titanate which accounts for 0.01-2% of the total raw material amount as a catalyst, and reacting at the temperature of 50-60 DEG C for 1-3 hours; carrying out transesterification on the mixture; step 2, carrying out condensation polymerization to obtain a polycarbonate diol crude product; and step 3, carrying out reduced pressure purification, and removing the small molecular polymer and the residual titanium isopropoxide catalyst to obtain the high-purity polycarbonate diol. According to the present invention, the efficient titanium isopropoxide catalyst is used under the normal pressure, such that the preparation of the high-purity and narrow-molecular-weight-distribution polycarbonate diol is achieved, the operation condition is mild, the production efficiency is high, the cost is low, and the catalyst has characteristics of low boiling point, easy removal and environmental protection.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical engineering, and in particular relates to a method for preparing polycarbonate diol by utilizing a titanate catalyst. Background Art

[0002] As a key chemical raw material, polycarbonate diol plays an important role in the manufacture of polyurethane elastomers, polyester polyols and polycarbonate materials. Traditionally, this raw material is mainly synthesized by phosgene method or ring-opening polymerization of cyclic carbonates. However, these two methods have significant defects, such as severe equipment corrosion and harsh reaction conditions.

[0003] In recent years, a new method combining transesterification and polycondensation has gradually attracted attention. This method can not only avoid many disadvantages of traditional methods, but also effectively improve the molecular weight and yield of the product by adjusting the reaction conditions.

[0004] At present, the main technical route for preparing polycarbonate diols is to first use an ester exchange reaction to convert dimethyl carbonate (DMC) and 1,6-hexanediol (HDO) into low molecular weight polycarbonate diols, and then further increase their molecular weight through a polycondensation reaction. In this process, the application of catalysts is crucial to accelerate the reaction rate and improve efficiency. Isopropyl titanate has become a common catalyst choice due to its high activity and stability.

[0005] Although existing technologies have been able to successfully prepare polycarbonate diols, they still face several challenges in practical applications: 1) High energy consumption: Current methods usually require operation under high temperature and high pressure conditions, which not only increases equipment investment but also increases energy consumption. 2) Impact of byproducts: Byproducts that may be produced during the reaction have an adverse effect on the quality and yield of the final product. 3) Process complexity: In order to ensure product quality, reaction conditions (such as temperature, pressure and time) must be precisely controlled, which increases the complexity and technical requirements of production.

[0006] Therefore, in view of the above situation, there is an urgent need to develop a method for preparing polycarbonate diol using titanate catalysts that can operate under mild conditions, reduce the generation of by-products, and simplify the production process, so as to overcome the shortcomings in current practical applications. Summary of the invention

[0007] The object of the present invention is to provide a method for preparing polycarbonate diol using a titanate catalyst, aiming to solve the problems mentioned in the above background technology.

[0008] The present invention is achieved by a method for preparing polycarbonate diol using a titanate catalyst, comprising the following steps: Step 1: Transesterification reaction Dimethyl carbonate and 1,6-hexanediol are mixed in a molar ratio of 1.1 to 1.5:1, and 0.01% to 2% of isopropyl titanate is added as a catalyst; Under normal pressure, the mixture is heated to 150-220° C. to carry out an ester exchange reaction; initially, the reaction is carried out in a full reflux mode for 1-9 hours, and then the temperature is raised within the same temperature range for 1-5 hours to gradually extract the azeotrope formed by dimethyl carbonate and methanol; Step 2: Polycondensation Under normal pressure and high-purity nitrogen protection, the reaction temperature is maintained at 150-220° C., and the polycondensation reaction is continued for 3-8 hours to obtain a crude polycarbonate diol; Step 3: Purification under reduced pressure Under the conditions of reduced pressure of 3 to 20 kPa and temperature of 150 to 220° C., the reaction is carried out for 1 to 5 hours to remove the small molecular polymer and the residual isopropyl titanate catalyst to obtain polycarbonate diol.

[0009] According to a further technical solution, in step one, the conversion rate of 1,6-hexanediol in the raw material reaches more than 95%.

[0010] According to a further technical solution, in step 2, a polycarbonate diol having a hydroxyl value of 51 to 61 and a molecular weight of 1840 to 2200 is finally obtained.

[0011] According to a further technical solution, in step three, the purified polycarbonate diol product has a hydroxyl value of 51 to 61, a molecular weight of 1840 to 2200, a molecular weight distribution of 1.9 to 2.1, and does not contain a catalyst.

[0012] The present invention provides a method for preparing polycarbonate diol using a titanate catalyst, which has the following beneficial effects: 1) Under normal pressure conditions, polycarbonate diol with a molecular weight of 2000 was prepared using isopropyl titanate as a catalyst. Compared with traditional high temperature and high pressure operations, this method not only greatly reduces equipment investment and operation difficulty, but also improves production safety and efficiency.

[0013] 2) The present invention uses isopropyl titanate as a catalyst, which has excellent catalytic activity and stability. In the transesterification reaction, it can significantly promote the efficient conversion of 1,6-hexanediol (HDO); and in the polycondensation reaction stage, by maintaining a constant reaction temperature, the molecular weight of polycarbonate diol can be further increased. This efficient catalytic mechanism not only speeds up the production process, but also effectively reduces costs, ensuring that the final product yield exceeds 90%.

[0014] 3) The present invention adopts a reduced pressure treatment in the purification step, specifically, the reaction is carried out at a pressure of 3kPa to 20kPa and a temperature range of 150°C to 220°C for 1 to 5 hours. This process effectively removes small molecular polymers and residual isopropyl titanate catalyst, thereby obtaining a polycarbonate diol with a narrow molecular weight distribution. Such product characteristics are particularly important for ensuring the stability and reliability of material performance.

[0015] 4) The present invention adopts the transesterification method to prepare polycarbonate diol, and the main raw materials are dimethyl carbonate (DMC) and 1,6-hexanediol (HDO), which are in sufficient supply in the market. More importantly, the entire preparation process does not involve any toxic or harmful substances, such as phosgene, and therefore has obvious environmental advantages.

[0016] In summary, the present invention achieves the preparation of narrow molecular weight distribution polycarbonate diol by using an efficient isopropyl titanate catalyst under normal pressure. The method not only has mild operating conditions, high production efficiency, and low cost, but also has a low boiling point and is easy to remove, and is environmentally friendly, showing significant advantages over the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of a simple device for preparing polycarbonate diol using a titanate catalyst provided in an embodiment of the present invention.

[0018] In the figure: 1-oil bath, 2-magnet, 3-four-necked flask, 4-air inlet, 5-thermometer A, 6-glass stopper, 7-thorn-shaped fractionation column, 8-distillation head, 9-thermometer B, 10-serpentine condenser, 11-tail pipe, 12-receiving bottle. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0020] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0021] The purpose of the present invention is to prepare polycarbonate diol (PCDL) with a molecular weight of 2000±150 and excellent performance by transesterification and polycondensation reaction of dimethyl carbonate (DMC) and 1,6-hexanediol (HDO) using isopropyl titanate as a catalyst under normal pressure.

[0022] like Figure 1 As shown, a method for preparing polycarbonate diol using a titanate catalyst provided by one embodiment of the present invention comprises the following steps: Step 1: Transesterification reaction DMC (dimethyl carbonate) and HDO (1,6-hexanediol) are mixed in a molar ratio of 1.1 to 1.5:1, and 0.01% to 2% of isopropyl titanate is added as a catalyst; Under normal pressure, the mixture is heated to 150-220°C for transesterification reaction; the reaction is initially carried out in full reflux mode for 1-9 hours, and then the temperature is raised within the same temperature range for 1-5 hours to gradually extract the azeotrope formed by DMC and ME. This process can achieve a conversion rate of HDO in the raw material of more than 95%.

[0023] Step 2: Polycondensation Under normal pressure and high-purity nitrogen protection, the reaction temperature is maintained at 150-220°C, and the polycondensation reaction is continued for 3-8 hours; Finally, a crude polycarbonate diol (PCDL) having a hydroxyl value of 51 to 61 and a molecular weight of 1840 to 2200 can be obtained; Step 3: Purification under reduced pressure Under the conditions of reduced pressure of 3 to 20 kPa and temperature of 150 to 220° C., react for 1 to 5 hours to remove small molecular polymers and residual isopropyl titanate catalyst; The purified PCDL product has the characteristics of hydroxyl value of 51-61, molecular weight of 1840-2200, molecular weight distribution of 1.9-2.1, and is completely free of catalyst, ensuring the excellent performance of the product.

[0024] Example 1

[0025] The specific steps are as follows: 1. Prepare raw materials: weigh the raw materials according to the molar ratio of DMC:HDO=1.2:1, and add 0.02% of isopropyl titanate as a catalyst.

[0026] 2. Transesterification reaction: Heat the mixture to 150°C under normal pressure to carry out transesterification reaction, and reflux for 5 hours without extracting any fractions.

[0027] 3. Polycondensation reaction: Under normal pressure and high-purity nitrogen protection, the reaction temperature was maintained at 170°C and the polycondensation reaction was continued for 5 hours.

[0028] 4. Removal of catalyst: After the polycondensation reaction is completed, the reaction is carried out under a reduced pressure of 10 kPa and a temperature of 170° C. for 3 hours to remove the isopropyl titanate catalyst and purify the product.

[0029] Through the above steps, a catalyst-free polycarbonate diol with a hydroxyl value of 56, a molecular weight of 2020, a molecular weight distribution of 1.9 is finally obtained, and the product yield is 95%.

[0030] Example 2

[0031] The specific steps are as follows: 1. Prepare raw materials: weigh the raw materials according to the molar ratio of DMC:HDO=1.3:1, and add 0.5% of isopropyl titanate as a catalyst.

[0032] 2. Transesterification reaction: Heat the mixture to 160°C under normal pressure to carry out transesterification reaction, and reflux for 4 hours without extracting any fractions.

[0033] 3. Polycondensation reaction: Under normal pressure and high-purity nitrogen protection, the reaction temperature was maintained at 170°C and the polycondensation reaction was continued for 4 hours.

[0034] 4. Removal of catalyst: After the polycondensation reaction is completed, the reaction is carried out under a reduced pressure of 10 kPa and a temperature of 170° C. for 3 hours to remove the isopropyl titanate catalyst and purify the product.

[0035] Through the above steps, a catalyst-free polycarbonate diol with a hydroxyl value of 54, a molecular weight of 2077, a molecular weight distribution of 1.95 is finally obtained, and the product yield is 92%.

[0036] Example 3

[0037] The specific steps are as follows: 1. Prepare raw materials: weigh the raw materials according to the molar ratio of DMC:HDO=1.4:1, and add 1% of isopropyl titanate as a catalyst.

[0038] 2. Transesterification reaction: Heat the mixture to 170°C under normal pressure to carry out transesterification reaction, and reflux for 3 hours without extracting any fractions.

[0039] 3. Polycondensation reaction: Under normal pressure and high-purity nitrogen protection, the reaction temperature was maintained at 190°C and the polycondensation reaction was continued for 4 hours.

[0040] 4. Removal of catalyst: After the polycondensation reaction is completed, the reaction is carried out under a reduced pressure of 10 kPa and a temperature of 190° C. for 3 hours to remove the isopropyl titanate catalyst and purify the product.

[0041] Through the above steps, a catalyst-free polycarbonate diol with a hydroxyl value of 55, a molecular weight of 2040, a molecular weight distribution of 1.91 is finally obtained, and the product yield is 94%.

[0042] Experimental data analysis Can be used Figure 1The device shown is used for a simple experiment. A four-necked flask 3 is arranged on the upper side of an oil bath pot 1. A magnet 2 is arranged in the four-necked flask 3. An air inlet 4, a thermometer A5 and a glass stopper 6 are arranged on the upper part of the four-necked flask 3. A thorn-shaped distillation column 7 is also connected to the top of the four-necked flask 3. A distillation head 8 is arranged on the upper part of the thorn-shaped distillation column 7. A thermometer B9 is arranged on the upper part of the distillation head 8. A serpentine condenser 10 is connected to the side of the distillation head 8. The other end of the serpentine condenser 10 is connected to a receiving bottle 12 through a tail pipe 11.

[0043] By comparing and analyzing the polycarbonate diol (PCDL) products obtained by the above examples and the traditional method, the results show that the present technology can stably prepare a polycarbonate diol product with a molecular weight of about 2000 and excellent performance. As shown in Table 1, the method not only has mild operating conditions and high production efficiency, but also has high product purity and narrow molecular weight distribution, and has significant advantages.

[0044] Table 1 PCDL product test data of the embodiment Project Name Hydroxyl value (mgKOH / g) Molecular weight (Mn) Molecular weight distribution (D) Product yield% Example 1 56 2020 1.90 95 Example 2 54 2077 1.95 92 Example 3 55 2040 1.91 94 The above embodiment of the present invention provides a method for preparing polycarbonate diol using a titanate catalyst, and the main advantages are as follows: 1) Under normal pressure conditions, polycarbonate diol with a molecular weight of 2000 was prepared using isopropyl titanate as a catalyst. Compared with traditional high temperature and high pressure operations, this method not only greatly reduces equipment investment and operation difficulty, but also improves production safety and efficiency.

[0045] 2) The present invention uses isopropyl titanate as a catalyst, which has excellent catalytic activity and stability. In the transesterification reaction, it can significantly promote the efficient conversion of 1,6-hexanediol (HDO); and in the polycondensation reaction stage, by maintaining a constant reaction temperature, the molecular weight of polycarbonate diol can be further increased. This efficient catalytic mechanism not only speeds up the production process, but also effectively reduces costs, ensuring that the final product yield exceeds 90%.

[0046] 3) The present invention adopts a reduced pressure treatment in the purification step, specifically, the reaction is carried out at a pressure of 3kPa to 20kPa and a temperature range of 150°C to 220°C for 1 to 5 hours. This process effectively removes small molecular polymers and residual isopropyl titanate catalyst, thereby obtaining a polycarbonate diol with a narrow molecular weight distribution. Such product characteristics are particularly important for ensuring the stability and reliability of material performance.

[0047] 4) The present invention adopts the transesterification method to prepare polycarbonate diol, and the main raw materials are dimethyl carbonate (DMC) and 1,6-hexanediol (HDO), which are in sufficient supply in the market. More importantly, the entire preparation process does not involve any toxic or harmful substances, such as phosgene, and therefore has obvious environmental advantages.

[0048] In summary, the present invention achieves the preparation of narrow molecular weight distribution polycarbonate diol by using an efficient isopropyl titanate catalyst under normal pressure. The method not only has mild operating conditions, high production efficiency, and low cost, but also has a low boiling point and is easy to remove, and is environmentally friendly, showing significant advantages over the prior art.

[0049] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0050] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing polycarbonate diol using a titanate catalyst, characterized in that: The following steps are involved: Step 1: Transesterification reaction Dimethyl carbonate and 1,6-hexanediol are mixed in a molar ratio of 1.1 to 1.5:1, and 0.01% to 2% of isopropyl titanate is added as a catalyst; Under normal pressure, the mixture is heated to 150-220° C. to carry out an ester exchange reaction; initially, the reaction is carried out in a full reflux mode for 1-9 hours, and then the temperature is raised within the same temperature range for 1-5 hours to gradually extract the azeotrope formed by dimethyl carbonate and methanol; Step 2: Polycondensation Under normal pressure and high-purity nitrogen protection, the reaction temperature is maintained at 150-220° C., and the polycondensation reaction is continued for 3-8 hours to obtain a crude polycarbonate diol; Step 3: Purification under reduced pressure Under the conditions of reduced pressure of 3 to 20 kPa and temperature of 150 to 220° C., the reaction is carried out for 1 to 5 hours to remove the small molecular polymer and the residual isopropyl titanate catalyst to obtain polycarbonate diol.

2. The method for preparing polycarbonate diol using a titanate catalyst according to claim 1, characterized in that: In step 1, the conversion rate of 1,6-hexanediol in the raw material reaches more than 95%.

3. The method for preparing polycarbonate diol using a titanate catalyst according to claim 2, characterized in that: In step 2, a polycarbonate diol having a hydroxyl value of 51 to 61 and a molecular weight of 1840 to 2200 is finally obtained.

4. The method for preparing polycarbonate diol using a titanate catalyst according to claim 3, characterized in that: In step three, the purified polycarbonate diol product has a hydroxyl value of 51 to 61, a molecular weight of 1840 to 2200, a molecular weight distribution of 1.9 to 2.1, and does not contain a catalyst.

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