Method for preparing dibutylene terephthalate under catalysis of ionic liquid

Abstract

The invention belongs to the technical field of organic synthesis, and particularly relates to a method for preparing dihydroxybutanediol terephthalate under catalysis of an ionic liquid. Wherein the ionic liquid takes 1-butyl-3-methylimidazole tosilate or 1-butyl sulfonic acid-3-methylimidazole trifluoromethane sulfonate as a raw material, tetrabutyl titanate and the ionic liquid are taken as catalysts, and ester exchange reaction is carried out, so that the dihydroxybutanediol terephthalate is prepared. According to the method, the ionic liquid is added as a catalyst, the ester exchange rate of the ester exchange reaction is increased and can reach 98%, generation of by-products is remarkably reduced, and the method is mild in reaction condition, low in requirement for equipment, easy to operate and suitable for industrial large-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and in particular relates to a method for preparing dihydroxybutylene terephthalate by catalysis of ionic liquid. Background Art

[0002] The PBT production technology route can be divided into ester exchange method and direct esterification method.

[0003] Direct esterification method: Direct esterification method is to directly esterify terephthalic acid (TPA) and butanediol (BG) to obtain dihydroxybutylene terephthalate, which is further polycondensed into PBT. This technical route has the advantages of low raw material consumption, less reaction equipment required, short production cycle, and high production efficiency. The obtained resin can be post-condensed and thickened in the solid phase, and can also be used to produce fibers by direct spinning process.

[0004] Ester exchange method: The ester exchange method is carried out in two steps: the first step is to synthesize dibutylene terephthalate (BHBT) through an ester exchange reaction, specifically: dimethyl terephthalate and one molecule of 1,4-butanediol undergo an ester exchange reaction to obtain monohydroxybutylene terephthalate, and then continue to undergo an ester exchange reaction with one molecule of 1,4-butanediol to obtain dibutylene terephthalate (dihydroxybutylene terephthalate); the second step is to polycondense BHBT into PBT resin under reduced pressure. During the ester exchange reaction, the activation energy of the ester exchange reaction between dimethyl terephthalate (DMT) and BG and the activation energy of the side reaction of generating tetrahydrofuran (THF) are: E 酯交换 =612×10 4 J / mol ;E 副反应 =115×10 5 J / mol According to the principle that high temperature is conducive to high activation energy reactions, in the process of industrial transesterification, under the condition that the main reaction reaches a certain speed, the formation of by-product THF can be suppressed by properly controlling the reaction temperature. In the second step of polycondensation reaction, the activation energy of BHBT polycondensation and the activation energy of thermal cracking of PBT polymer are: E 缩聚 =113×10 5 J / mol ;E 热裂解 =1167×10 5 J / mol. Similarly, in the process of industrial polycondensation, as long as the appropriate reaction temperature range is selected, it is possible to control the occurrence of thermal cracking reaction and reduce the terminal carboxyl content of PBT polymer to a lower level. The amount of THF generated is directly related to the consumption of BG. At present, the market price of BG is relatively expensive, and its consumption will directly affect the production cost of PBT resin. Therefore, the degree of THF side reaction is a key indicator reflecting whether the PBT synthesis process is reasonable, whether the technology is advanced, and the final economic benefits. How to reduce or inhibit the side reaction of THF generation has become a key topic in the research of PBT polymer synthesis process. However, the existing method uses dimethyl terephthalate and 1,4-butanediol as raw materials, tetrabutyl titanate as the catalyst, the reaction temperature is above 180°C, and a vacuum reactor is used. The ester exchange rate is not high, at about 90.0%. At the same time, 1,4-butanediol cyclization by-products THF and water are generated. It is necessary to continuously remove the water produced by the reaction in order to achieve a higher ester exchange rate. Since the catalyst tetrabutyl titanate used reacts with water at high temperature to generate titanium dioxide, thereby losing its activity, and the reaction is not smooth, the reaction continuity of the ester exchange is poor. Summary of the invention

[0005] The object of the present invention is to overcome the disadvantages of the prior art and provide a method for preparing dihydroxybutylene terephthalate by catalysis of ionic liquid.

[0006] The object of the present invention is achieved by the following technical scheme: a method for preparing dihydroxybutylene terephthalate by catalysis of ionic liquid, wherein dimethyl terephthalate and 1,4-butanediol are used as raw materials, tetrabutyl titanate and ionic liquid are used as catalysts for ester exchange reaction to prepare dihydroxybutylene terephthalate; wherein the ionic liquid is 1-butyl-3-methylimidazole p-toluenesulfonate or 1-butylsulfonic acid-3-methylimidazole trifluoromethanesulfonate.

[0007] As a preferred technical solution, it includes the following steps: S1. Discharging: Add dimethyl terephthalate, 1,4-butanediol, tetrabutyl titanate and ionic liquid to the reaction device, seal the reaction device, and replace the air in the reaction device with nitrogen; S2. Transesterification: Place the reaction device in an oil bath at 90-160°C, and after the reactants are fully melted, raise the temperature to 130-220°C and react for 4-6 hours.

[0008] As a preferred technical solution, the mass volume ratio of dimethyl terephthalate to 1,4-butanediol is 70-85g, the volume ratio of butyl phthalate to 1,4-butanediol is 1:340-360, and the mass ratio of dimethyl terephthalate to ionic liquid is 70-85:1.

[0009] As a preferred technical solution, the sealing in step S1 is performed by applying vacuum silicone grease and wrapping with raw tape. The ground part of the glass bottle is coated with vacuum grease, and the outside of the glass bottle interface is wrapped with raw tape to prevent leakage.

[0010] As a preferred technical solution, the reaction device in step S1 adopts vacuum-nitrogen cycle for gas replacement, the vacuum degree during replacement is ≤100Pa, and the vacuum nitrogen cycle is performed 3 times.

[0011] As a preferred technical solution, the heating rate in step S2 is 5 to 12°C / min.

[0012] As a preferred technical solution, when the ionic liquid is 1-butyl-3-methylimidazole toluenesulfonate, the reaction device is placed in an oil bath at 150°C, and after the reactants are fully melted, the temperature is raised to 210°C and heated for 4 hours, and then raised to 220°C and heated for 1 hour.

[0013] As a preferred technical solution, when the ionic liquid is 1-butylsulfonic acid-3-methylimidazolium trifluoromethanesulfonate, the reaction device is placed in an oil bath at 100°C, and after the reactants are fully melted, the temperature is raised to 140°C and heated for 4 hours, and then raised to 150°C and heated for 1 hour.

[0014] Transesterification reaction is the reaction of ester with alcohol / acid / ester (different esters) under the catalysis of acid or base to generate a new ester and a new alcohol / acid / ester. Bis(hydroxybutylene) terephthalate is prepared by transesterification of dimethyl terephthalate with 1,4-butanediol. The reaction equation is as follows: dimethyl terephthalate first reacts with 1,4-butanediol to generate monobutylene terephthalate and methanol, and then continues to react to generate bi(hydroxybutylene) terephthalate and methanol.

[0015] The reaction mechanism of ionic liquid catalyzed transesterification: the sulfonic acid group on 1-butylsulfonic acid-3-methylimidazolium trifluoromethanesulfonate is very acidic and can easily lose the H atom on the sulfonic acid to form a proton. The proton attacks the ester group on dimethyl terephthalate and combines with the carbonyl group to form a carbon cation. The protonic 1,4-butanediol combines with the carbon cation to form a tetrahedral intermediate. This intermediate then decomposes into monobutylene terephthalate and methanol (due to the boiling point of methanol at 64.5°C, it directly escapes from the reactor at the reaction temperature), and produces protons to catalyze the next round of reaction to generate dihydroxybutylene terephthalate from monobutylene terephthalate. The principle of transesterification catalyzed by ionic liquid 1-butyl-3-methylimidazolium p-toluenesulfonate is the same as that of 1-butylsulfonic acid-3-methylimidazolium trifluoromethanesulfonate.

[0016] The present invention has the following advantages: the present invention discloses a method for preparing dihydroxybutylene terephthalate by catalysis of ionic liquid, wherein dimethyl terephthalate and 1,4-butanediol are used as raw materials, tetrabutyl titanate and ionic liquid are used as catalysts for transesterification reaction, wherein the ionic liquid is 1-butyl-3-methylimidazole p-toluenesulfonate or 1-butylsulfonic acid-3-methylimidazole trifluoromethanesulfonate. The method of the present invention adds ionic liquid as a catalyst, improves the transesterification rate of the transesterification reaction (can reach 98%), significantly reduces the generation of by-products, and has mild reaction conditions, low requirements on equipment, simple operation, and is suitable for industrial large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the infrared analysis spectrum of the product prepared in Experimental Example 1. In the figure, BHBT is dihydroxybutylene terephthalate and DMT is dimethyl terephthalate. DETAILED DESCRIPTION

[0018] The present invention is further described below in conjunction with the accompanying drawings and embodiments, and the protection scope of the present invention is not limited to the following: Embodiment 1: A method for preparing dihydroxybutylene terephthalate catalyzed by ionic liquid, comprising the following steps: S1. Discharging: Add dimethyl terephthalate, 1,4-butanediol, tetrabutyl titanate and 1-butyl-3-methylimidazole toluenesulfonate to the reaction device, seal the reaction device by applying vacuum silicone grease and wrapping raw tape, and replace the gas in the reaction device by vacuum-nitrogen cycle. The vacuum degree during replacement is 100Pa, and the vacuum nitrogen is circulated 3 times to replace the air in the device with nitrogen; wherein the mass volume ratio of dimethyl terephthalate and 1,4-butanediol is 70g, the volume ratio of tetrabutyl titanate and 1,4-butanediol is 1:340, and the mass ratio of dimethyl terephthalate and 1-butyl-3-methylimidazole toluenesulfonate is 70:1; S2. Transesterification: Place the reaction device in an oil bath at 150°C, and after the reactants are fully melted, heat to 210°C for 4 h, and then heat to 220°C for 1 h, with the heating rate being 5°C / min.

[0019] Embodiment 2: A method for preparing dihydroxybutylene terephthalate catalyzed by ionic liquid, comprising the following steps: S1. Discharging: Add dimethyl terephthalate, 1,4-butanediol, tetrabutyl titanate and 1-butylsulfonic acid-3-methylimidazole trifluoromethane sulfonate to the reaction device, seal the reaction device by applying vacuum silicone grease and wrapping raw tape, and replace the gas in the reaction device by vacuum-nitrogen cycle. The vacuum degree during replacement is 90Pa, and the vacuum nitrogen is circulated 3 times to replace the air in the device with nitrogen; wherein the mass volume ratio of dimethyl terephthalate to 1,4-butanediol is 85g, the volume ratio of tetrabutyl titanate to 1,4-butanediol is 1:360, and the mass ratio of dimethyl terephthalate to 1-butylsulfonic acid-3-methylimidazole trifluoromethane sulfonate is 85:1; S2. Transesterification: The reaction device was placed in an oil bath at 160°C, and after the reactants were fully melted, the temperature was raised to 220°C for reaction for 6 hours, wherein the heating rate was 12°C / min.

[0020] Embodiment 3: A method for preparing dihydroxybutylene terephthalate catalyzed by ionic liquid, comprising the following steps: S1. Discharging: Add dimethyl terephthalate, 1,4-butanediol, tetrabutyl titanate and 1-butylsulfonic acid-3-methylimidazole trifluoromethane sulfonate to the reaction device, seal the reaction device by applying vacuum silicone grease and wrapping raw tape, and replace the gas in the reaction device by vacuum-nitrogen cycle. The vacuum degree during replacement is 80Pa, and the vacuum nitrogen is circulated 3 times to replace the air in the device with nitrogen; wherein the mass volume ratio of dimethyl terephthalate to 1,4-butanediol is 78g, the volume ratio of tetrabutyl titanate to 1,4-butanediol is 1:350, and the mass ratio of dimethyl terephthalate to 1-butylsulfonic acid-3-methylimidazole trifluoromethane sulfonate is 78:1; S2. Transesterification: The reaction device was placed in an oil bath at 120°C, and after the reactants were fully melted, the temperature was raised to 170°C for reaction for 5 hours, wherein the heating rate was 10°C / min.

[0021] The beneficial effects of the present invention are described below by experiments: Experimental Example 1: A method for preparing dihydroxybutylene terephthalate catalyzed by ionic liquid, comprising the following steps: S1. Discharging: Add 78.22g of dimethyl terephthalate, 53mL of 1,4-butanediol, 150μL of tetrabutyl titanate and 1.3065g of 1-butyl-3-methylimidazole p-toluenesulfonate to the reaction device, connect the reaction device to a condenser for recovering and observing methanol, seal the device by applying vacuum silicone grease and wrapping with raw tape, and use vacuum-nitrogen cycle for gas replacement. The vacuum degree during replacement is 80Pa, and the vacuum nitrogen cycle is repeated 3 times to replace the air in the device with nitrogen. S2. Transesterification: The reaction device was placed in an oil bath at 120°C, and after the reactants were fully melted, the temperature was raised to 210°C for reaction for 4 hours, and then the temperature was raised to 220°C for reaction for 1 hour, wherein the heating rate was 10°C / min.

[0022] When the temperature rises to 192℃, the first drop of methanol appears. When heated at 210℃ for 4 h, 63% of methanol is precipitated. When the temperature rises to 220℃ and heated for 1 h, the methanol mass is 95% and the ester exchange rate is 95.0%.

[0023] Experimental Example 2: A method for preparing dihydroxybutylene terephthalate catalyzed by ionic liquid, comprising the following steps: S1. Discharging: Add 78.22g of dimethyl terephthalate, 53mL of 1,4-butanediol, 150μL of tetrabutyl titanate and 1.3065g of 1-butylsulfonic acid-3-methylimidazole trifluoromethanesulfonate to the reaction device, connect the reaction device to a condenser for recovering and observing methanol, seal the device by applying vacuum silicone grease and wrapping with raw tape, and use vacuum-nitrogen cycle for gas replacement. The vacuum degree during replacement is 80Pa, and the vacuum nitrogen cycle is repeated 3 times to replace the air in the device with nitrogen. S2. Transesterification: The reaction device was placed in an oil bath at 100°C. After the reactants were fully melted, the temperature was raised to 140°C for 4 hours, and then raised to 150°C for 1 hour. The rate of heating was 10°C / min.

[0024] When the temperature rises to 130℃, the first drop of methanol appears. After heating at 140℃ for 4h, 88.0% of methanol is precipitated. After heating to 150℃ for 1h, the quality of methanol is 98% and the ester exchange rate is 98.0%.

[0025] The ionic liquids 1-butyl-3-methylimidazolium p-toluenesulfonate and 1-butylsulfonic acid-3-methylimidazolium trifluoromethanesulfonate in the above reaction are both commercially available. The CAS number of 1-butyl-3-methylimidazolium p-toluenesulfonate is 410522-18-8, MW is 310.41, and the molecular formula is: C 15 H 22 N2O3S. CAS of 1-butylsulfonic acid-3-methylimidazolium trifluoromethanesulfonate: 657414-80-7, MW: 368.35, molecular formula: C9H 15 F3N2O6S2.

[0026] The product prepared in Experimental Example 1 and the experimental principle dimethyl terephthalate were subjected to infrared spectrum analysis, and the results were as follows Figure 1 As shown, from Figure 1 It can be seen that the experimental example 1 of the present invention successfully prepared dihydroxybutylene terephthalate.

[0027] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which are all covered by the protection scope of the present invention.

Claims

1. A method for preparing dihydroxybutylene terephthalate by ionic liquid catalysis, characterized in that: Dimethyl terephthalate and 1,4-butanediol are used as raw materials, tetrabutyl titanate and ionic liquid are used as catalysts for ester exchange reaction to prepare dihydroxybutylene terephthalate; wherein the ionic liquid is 1-butyl-3-methylimidazole p-toluenesulfonate or 1-butylsulfonic acid-3-methylimidazole trifluoromethanesulfonate.

2. The method for preparing dihydroxybutylene terephthalate catalyzed by ionic liquid according to claim 1, characterized in that: It includes the following steps: S1. Discharging: Add dimethyl terephthalate, 1,4-butanediol, tetrabutyl titanate and ionic liquid to the reaction device, seal the reaction device, and replace the air in the reaction device with nitrogen; S2. Transesterification: Place the reaction device in an oil bath at 90-160°C, and after the reactants are fully melted, raise the temperature to 130-220°C and react for 4-6 hours to generate dihydroxybutylene terephthalate.

3. The method for preparing dihydroxybutylene terephthalate catalyzed by ionic liquid according to claim 1 or 2, characterized in that: The mass volume ratio of dimethyl terephthalate to 1,4-butanediol is 70-85 g, the volume ratio of dimethyl terephthalate to 1,4-butanediol is 1:340-360, and the mass ratio of dimethyl terephthalate to ionic liquid is 70-85:

1.

4. The method for preparing dihydroxybutylene terephthalate catalyzed by ionic liquid according to claim 2, characterized in that: The sealing in step S1 is performed by applying vacuum silicone grease and wrapping raw tape to seal the device.

5. The method for preparing dihydroxybutylene terephthalate catalyzed by ionic liquid according to claim 2, characterized in that: The reaction device in step S1 adopts vacuum-nitrogen cycle to carry out gas replacement, the vacuum degree during replacement is ≤100Pa, and the vacuum nitrogen cycle is performed 3 times.

6. The method for preparing dihydroxybutylene terephthalate catalyzed by ionic liquid according to claim 2, characterized in that: The heating rate in step S2 is 5-12°C / min.

7. The method for preparing dihydroxybutylene terephthalate catalyzed by ionic liquid according to claim 2, characterized in that: When the ionic liquid is 1-butyl-3-methylimidazole p-toluenesulfonate, the reaction device is placed in an oil bath at 150° C., and after the reactants are fully melted, the temperature is raised to 210° C. and heated for 4 h, and then raised to 220° C. and heated for 1 h.

8. The method for preparing dihydroxybutylene terephthalate catalyzed by ionic liquid according to claim 2, characterized in that: When the ionic liquid is 1-butylsulfonic acid-3-methylimidazolium trifluoromethanesulfonate, the reaction device is placed in an oil bath at 100° C., and after the reactants are fully melted, the temperature is raised to 140° C. and heated for 4 h, and then raised to 150° C. and heated for 1 h.

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