CN114011459B - Titanium double-acid ionic liquid catalyst and preparation method and application thereof - Google Patents

Abstract

The invention relates to a titanium double-acid ionic liquid catalyst for synthesizing diphenyl carbonate by an ester exchange method, a preparation method and application thereof, wherein the catalyst combines Lewis acidic titanium metal salt and functional ionic liquid; the preparation method comprises the steps of mixing equimolar amount of alkyl imidazole with raw materials with functional groups, reacting for 24 hours at the temperature of 60-90 ℃, washing for 3-4 times with ethyl acetate, performing rotary evaporation, and drying for 6 hours at the temperature of 80 ℃ to obtain an intermediate I; n (N) ₂ Under protection, tiCl is introduced into a reactor containing intermediate I ₄ And (3) heating, stirring and dissolving the aqueous solution of hydrochloric acid, condensing and refluxing, controlling the reaction temperature at 50-60 ℃ and the reaction time at 12h, washing 3-4 times by acetonitrile after the reaction is finished, and drying at 80 ℃ for 6h to obtain different types of titanium double-acid ionic liquid catalysts respectively. The invention solves the problems of unsatisfactory activity, stability and selectivity of the traditional catalyst used for synthesizing diphenyl carbonate by the transesterification method.

Description

A titanium-based double acid ionic liquid catalyst and its preparation method and application

Technical field

The invention relates to the technical field of catalysts, and specifically relates to a titanium-based bis-acid ionic liquid catalyst for synthesizing diphenyl carbonate by transesterification method and its preparation method and application.

technical background

Polycarbonate (PC) is the only plastic with excellent transparency among the five major engineering plastics. It has high transparency, strong toughness, excellent mechanical properties, and has certain flame retardant properties. It has huge demand in the infrastructure area. The traditional preparation method of polycarbonate is the phosgene method, but phosgene is highly toxic. The three wastes produced not only corrode equipment, but also pollute the environment, and the atom utilization rate is low. The existing phosgene method to synthesize polycarbonate also requires its gradual upgrading.

Diphenyl carbonate (DPC) is an important organic reaction intermediate, serving as a key raw material to replace the highly toxic phosgene and bisphenol A in the synthesis of polycarbonate. The transesterification method for synthesizing diphenyl carbonate does not produce three wastes, and the atom utilization rate is as high as 100%. The source of its industrial chain is the petrochemical industry, which generates propylene oxide, a derivative of propylene, and the greenhouse gas CO ₂ , and its final product is polycarbonate. and H ₂ O, which does not produce three wastes at all. Its broad prospects can be imagined, and it fully meets the requirements of green economic development. However, the catalytic effects of traditional catalysts used to synthesize diphenyl carbonate by transesterification, such as Lewis metal salts, tetrabutyl titanate, and dibutyl tin oxide, are not ideal. Therefore, the development of high activity, high stability, and high selectivity catalysts Catalysts are key.

Contents of the invention

Purpose of invention:

The present invention proposes a titanium-based bis-acid ionic liquid catalyst and its preparation method and application. Its purpose is to solve the problems of unsatisfactory activity, stability and selectivity of traditional catalysts used in the synthesis of diphenyl carbonate by transesterification.

Technical solutions:

A titanium-based double acid ionic liquid catalyst. This catalyst combines Lewis acidic titanium metal salt with functionalized ionic liquid. Its structure is as follows:

R ₁ =C _n H _2n +1;

R ₂ =(CH ₂ ) ₃ SO ₃ H, CH ₂ COO, (CH ₂ ) ₂ OH;

X=TiCl ₅ .

Further, the functional group of the functionalized ionic liquid is one of sulfonic acid group, acetic acid group or hydroxyl group.

Furthermore, the anion X is a coordination chelate-TiCl ₅ formed by coordination with the cation.

A method for preparing a titanium-based double acid ionic liquid catalyst,

Step 1. Mix an equimolar amount of alkyl imidazole and raw materials with functional groups at a reaction temperature of 60-90°C for 24 hours. Wash with ethyl acetate 3-4 times, rotary evaporate, and dry at 80°C for 6 hours. Obtain intermediate I;

Step 2. Under _N2 protection, add TiCl ₄ hydrochloric acid aqueous solution to the reactor equipped with Intermediate I, heat, stir, dissolve and condense to reflux. The reaction temperature is controlled at 50-60°C and the reaction time is controlled at 12h. After the reaction is completed, use After washing with acetonitrile 3-4 times and drying at 80°C for 6 hours, different types of titanium-based double acid ionic liquid catalysts were obtained.

Further, the molar ratio of intermediate I to TiCl ₄ in step (2) is 1:0.5-1.25.

Further, the molar ratio of intermediate I to TiCl ₄ in step (2) is 1:1.

Application of a titanium-based double acid ionic liquid catalyst in the preparation of diphenyl carbonate.

The invention has the following characteristics:

(1) The titanium-based double acid ionic liquid catalyst prepared by the present invention has high activity and good stability. The catalyst prepared by the invention has good catalytic activity for the transesterification reaction of dimethyl carbonate and phenol, and the total yield of diphenyl carbonate and methylphenyl carbonate can reach more than 40%, and the selection of transesterification is The performance can reach 70.01%-99.91%.

(2) The double-acid ionic liquid catalysis has no saturated vapor pressure, so it can be used for reactions under vacuum and high-pressure conditions. It is not easy to burn, explode, or oxidize, and has good thermal stability and chemical stability.

(3) The titanium-based double acid ionic liquid catalyst of the present invention combines the high activity of the TiCl ₄ metal anion with the high stability of the ionic liquid cation, so that it forms a more stable transition state with DMC when participating in the catalytic reaction. This is more conducive to the reaction.

(4) During the transesterification reaction, TiCl ₄ significantly enhances the electron absorption capacity of the titanium atoms in TiCl ₄ under the action of the macromolecular imidazole cationic group, and the positron cloud of the macromolecular ionic liquid cationic group will also move toward The carbonyl carbon in DMC is shifted. Under the synergistic effect of anions and cations, the carbonyl carbon of DMC is more electron deficient, which is more conducive to the attack of phenolic oxygen anions, shortens the reaction time, and improves the catalytic efficiency.

Description of drawings

Figure 1 is a schematic diagram of catalyst synthesis;

Figure 2 is a mechanism diagram for the synthesis of diphenyl carbonate by titanium-based di-acid ionic liquid catalyzed transesterification method;

Figure 3 is the infrared spectrum of the titanium-based double acid ionic liquid catalyst.

Detailed ways

The present invention will be further described in detail below through examples. Through these descriptions, the features and advantages of the present invention will become more apparent.

Ionic liquids have the characteristics of designable structure and adjustable performance and are used in the field of catalysis. Research on catalytic synthesis of ethylene carbonate and propylene carbonate is common, but research on their catalytic transesterification reaction to synthesize diphenyl carbonate is not. Common. Therefore, starting from the reaction mechanism of the transesterification method to synthesize diphenyl carbonate, and based on the research on traditional catalysts, a titanium-based bis-acid ionic liquid was designed to have different acidities and specific functions for catalyzing dimethyl carbonate and phenol. Diphenyl carbonate is synthesized to overcome the problems of low conversion rate and poor selectivity of traditional catalysts.

The present invention combines poor stability TiCl ₄ with a functional ionic liquid catalyst through a coordination method to prepare a titanium-based double acid ionic liquid catalyst. On the one hand, it overcomes the shortcomings of poor stability of highly active TiCl ₄ , and on the other hand, it further improves Catalytic activity of ionic liquids. This ionic liquid catalyst is an acid site modification of the traditional ionic liquid structure, and then introduces highly active Lewis metal titanium to increase acidic sites to achieve mutual synergistic catalysis of double acid sites and further improve the activity of the catalyst.

As shown in Figure 1, the titanium-based bis-acid ionic liquid catalyst of the present invention combines Lewis metal titanium with a functionalized ionic liquid. The functional groups of the functionalized ionic liquid include: sulfonic acid group, acetate group, hydroxyl group, etc., anion X is a coordination chelate-TiCl ₅ formed by coordination with cations. The modified functional cationic group can provide a variety of acidic states from strong acid to weak acid, giving the catalyst the characteristics of adjustable acidity. The structure of the titanium-based double acid ionic liquid catalyst is as follows:

R ₁ =C _n H _2n+1 ;

R ₂ =(CH ₂ ) ₃ SO ₃ H, CH ₂ COO, (CH ₂ ) ₂ OH;

X=TiCl ₅ .

A method for preparing a titanium-based bis-acid ionic liquid catalyst for synthesizing diphenyl carbonate,

Step 1. Add alkyl imidazole into the reactor, and then add an equal molar amount of raw materials with functional groups, such as chloroethanol, chloroacetic acid, 1,3-propane sultone and hydrochloric acid, etc., 30-40°C Stir to dissolve and condense under reflux. After the dissolution is complete, control the reaction temperature to 60-90°C, react for 24 hours, wash 3-4 times with ethyl acetate, and dry at 80°C for 6 hours to obtain intermediate I respectively.

Step ₂ : Under N2 protection, add TiCl ₄ hydrochloric acid aqueous solution to the reactor equipped with intermediate I. The molar ratio of intermediate I to TiCl ₄ is 1:0.5-1.25. Heat, stir, condense and reflux. The reaction temperature is controlled at 50-60°C and the reaction time is controlled at 12h. After the reaction is completed, wash with acetonitrile 3-4 times and dry at 80°C for 6h to obtain different types of titanium-based double acid ionic liquid catalysts. A, B and C.

Combining TiCl ₄ with functionalized ionic liquids, the high activity of TiCl ₄ is combined with the high stability of functionalized ionic liquids to achieve high activity, high selectivity and high stability of the catalyst, and the acidic groups are in contact with metallic titanium It has synergistic catalytic effect and achieves better catalytic effect.

The application of a titanium-based di-acid ionic liquid catalyst for the preparation of diphenyl carbonate. The reaction mechanism of using the titanium-based di-acid ionic liquid catalyst of the present invention to synthesize diphenyl carbonate is shown in Figure 2. First, it is weakly acidic. Phenol will remove hydrogen ions in the solvent to form phenol oxygen anions. At the same time, the macromolecular ionic liquid cationic group, under the interaction with Lewis acidic titanium metal anions, significantly enhances the electron-attracting ability of the titanium atom, and the macromolecular ionic liquid cations The positron cloud of the group will also shift towards the DMC carbonyl carbon. Under the synergistic effect of anions and cations, the DMC carbonyl carbon is more electron deficient and is more conducive to the attack of phenolic oxygen anions. At this time, an unstable transition state is formed ( 1), under the action of a catalyst, the transition state (1) is converted into a stable intermediate (2); at this time, under the action of phenol oxygen anions, the carbonyl carbon C—O bond is broken to form methylphenyl carbonate and methanol, Methylphenyl carbonate will react with phenol to form diphenyl carbonate, or two molecules of methylphenyl carbonate will undergo a disproportionation reaction to form diphenyl carbonate. The catalyst will enter the next reaction step. Theoretically, the more positive charges the cationic group has, the more The larger, the better the reaction effect, which should be reflected in the reaction rate and selectivity.

A titanium-based bis-acid ionic liquid catalyst (infrared spectrum is shown in Figure 3) is used to catalyze the transesterification reaction of dimethyl carbonate and phenol to synthesize diphenyl carbonate as follows.

Weigh 18.84g (0.2mol) of phenol and 36.03g (0.4mol) of dimethyl carbonate, mix and add them to a three-necked flask with a reflux condensation device. Add 0.5 titanium-based bis-acid ionic liquid catalyst under _N2 protection. g, its mass is approximately 1% of the total mass of the reactants; stir and heat the reaction system to 160-180°C, adjust the reflux ratio to 3:1, and after 7-9 hours of reaction, cool the reaction system to room temperature (25°C) , then distill the reaction solution under reduced pressure, use a gas chromatograph to detect the purity of the product, and calculate the conversion rate, selectivity and yield.

Example 1

(1) Preparation of Catalyst A, Intermediate I

Weigh a certain amount of N-methylimidazole into the reactor, slowly add 1,3-propane sultone in an equimolar amount to N-methylimidazole at a rate of 10-100ml/s under reflux, and control the reaction temperature. After reacting for 24 hours at 60°C, the reaction solution was washed and filtered three times with ethyl acetate, rotary evaporated, and dried at 80°C for 6 hours to obtain white intermediate I.

(2) Preparation of Catalyst A

Under the protection of _N2 , heat 0.1 mol of intermediate I to 50°C to completely dissolve it, then add 0.1 mol of TiCl ₄ hydrochloric acid aqueous solution, reflux and condense at constant temperature and start stirring. After 12 hours of reaction, the imidazole sulfonic acid series bis-acid ionic liquid is obtained Catalyst A-[(CH ₂ ) ₃ SO ₃ H-mim]-TiCl ₅ .

Example 2

(1) Preparation of Catalyst B, Intermediate I

Weigh a certain amount of N-methylimidazole into the reactor, and slowly add chloroacetic acid in an equimolar amount to N-methylimidazole at a rate of 10-100ml/s under reflux. The reaction temperature is controlled at 90°C. After 24 hours of reaction , the reaction solution was washed and filtered 4 times with diethyl ether, followed by rotary evaporation and drying at 80°C for 6 hours to obtain white intermediate I.

(2) Preparation of Catalyst B

Under the protection of _N2 , heat 0.1 mol of Intermediate I to 55°C to completely dissolve it, then add 0.1 mol of TiCl ₄ hydrochloric acid aqueous solution, reflux and condense at constant temperature and start stirring. After 12 hours of reaction, the imidazole acetic acid series bis-acid ionic liquid catalyst is obtained B-[CH ₂ COO-mim]-TiCl ₅ .

Example 3

(1) Preparation of Catalyst C, Intermediate I

Under the protection of _N2 , weigh a certain amount of N-methylimidazole into the reactor, slowly add an equal molar amount of chloroethanol to N-methylimidazole at a rate of 10-100ml/s under reflux, and control the reaction temperature at 80 ℃, after reacting for 24 hours, the reaction solution was washed and filtered three times with acetonitrile, rotary evaporated, and dried at 80℃ for 6 hours to obtain light yellow intermediate I.

(2) Preparation of Catalyst C

Under the protection of _N2 , heat 0.1 mol of intermediate I to 60°C to completely dissolve it, then add 0.1 mol of TiCl ₄ hydrochloric acid aqueous solution, reflux and condense at a constant temperature and start stirring. After 12 hours of reaction, the imidazole hydroxyl-based bis-acid ionic liquid catalyst C is obtained. -[(CH ₂ )OH-mim]-TiCl ₅ .

Example 4

Catalyst C and its catalytic steps for synthesizing diphenyl carbonate are the same as Example 3. The molar ratio of intermediate I and TiCl ₄ is changed to 1:0.5. The experimental results are shown in Table 2.

Example 5

Catalyst C and its catalytic steps for synthesizing diphenyl carbonate are the same as Example 3. The molar ratio of intermediate I and TiCl ₄ is changed to 1:0.75. The experimental results are shown in Table 2.

Example 6

Catalyst C and its catalytic steps for synthesizing diphenyl carbonate are the same as Example 3. The molar ratio of intermediate I and TiCl ₄ is changed to 1:1.25. The experimental results are shown in Table 2.

The samples of Examples 1-3 were used as catalysts to respectively catalyze the transesterification reaction of dimethyl carbonate and phenol to synthesize diphenyl carbonate. The catalytic effects are as shown in Table 1, where MPC is monophenyl carbonate and DPC is diphenyl carbonate. ester.

Table 1 Performance comparison of titanium-based double acid ionic liquid catalysts

From the data in Table 1, it can be seen that the catalytic effect of the more acidic catalysts A and B is significantly higher than that of the weakly acidic catalyst C, which shows that the acidity of the catalyst is enhanced and the catalytic effect of the catalyst is better. Comparing Catalysts A and B, the acidity of the sulfonic acid group is higher than that of the acetic acid group, indicating that the strong acid has a significant inhibitory effect on side reactions, with a selectivity as high as 99.90%. However, although the selectivity of the acetic acid group is slightly worse, the final product DPC is The yield is higher. Taking the yields of MPC and DPC into account, titanium-based ionic liquids containing sulfonic acid groups have the best catalytic effect.

Table 2 Effects of different TiCl ₄ addition amounts on catalytic performance

It can be seen from Table 2 that as the amount of TiCl ₄ gradually increases, its reactivity gradually increases. When the molar ratio of intermediate I to TiCl ₄ is 1:1, its conversion rate reaches the maximum value. When the molar ratio of intermediate I to TiCl 4 When the molar ratio of ₄ is 1:1.25, the conversion rate decreases. The reason may be that excess titanium tetrachloride cannot form a stable coordination chelate with intermediate I. As the temperature increases during the reaction, excess titanium tetrachloride overflows the reaction system and affects its participation in the reaction to provide its active sites. point.

Claims (6)

1. The application of a titanium double-acid ionic liquid catalyst for preparing diphenyl carbonate is characterized in that: the catalyst combines Lewis acidic titanium metal salt with functional ionic liquid, and has the following structure:

；

R ₁ ＝C _n H _2n +1；

R ₂ ＝(CH ₂ ) ₃ SO ₃ H、CH ₂ COO、(CH ₂ ) ₂ OH；

X＝TiCl ₅ 。

2. the use according to claim 1, characterized in that: the functional group of the functional ionic liquid is one of sulfonic acid group, acetic acid group or hydroxyl group.

3. The use according to claim 1, characterized in that: the anion X is a coordination chelate-TiCl formed by coordination with the cation ₅ 。

4. The use according to claim 1, characterized in that: the preparation method of the titanium double-acid ionic liquid catalyst,

step 1, mixing equimolar amount of alkyl imidazole with a raw material with a functional group, reacting for 24 hours at the temperature of 60-90 ℃, washing for 3-4 times with ethyl acetate, performing rotary evaporation, and drying for 6 hours at the temperature of 80 ℃ to obtain an intermediate I;

step 2, N ₂ Under protection, tiCl is introduced into a reactor containing intermediate I ₄ And (3) heating, stirring and dissolving the aqueous solution of hydrochloric acid, condensing and refluxing, controlling the reaction temperature at 50-60 ℃ and the reaction time at 12h, washing 3-4 times by acetonitrile after the reaction is finished, and drying at 80 ℃ for 6h to obtain different types of titanium double-acid ionic liquid catalysts respectively.

5. The use according to claim 4, characterized in that: intermediate I and TiCl in step (2) ₄ The molar ratio is 1:0.5-1.25.

6. The use according to claim 4, characterized in that: intermediate I and TiCl in step (2) ₄ The molar ratio is 1:1.