CN114085189B - Preparation method and application of metal biimidazole salt ionic liquid catalyst - Google Patents

Abstract

The invention relates to a preparation method and application of a metal biimidazole salt ionic liquid catalyst, wherein the catalyst is formed by reacting biimidazole containing two imidazole rings with an alkali metal compound for dehydration and combination, and the alkali metal compound provides metal cations, and the biimidazole is taken as anions to form an ionic liquid catalytic system; the preparation method comprises the steps of adding a molar ratio of 1:1.5-3, adding a proper amount of DMF as a solvent, condensing and refluxing under the protection of nitrogen at 100-130 ℃ for magnetic stirring reaction for 18-24 hours, removing the solvent by vacuum rotary evaporation at 90-120 ℃ after the reaction is finished, adding a proper amount of distilled water for washing and filtering, and vacuum drying at 100-130 ℃ for 24 hours to obtain a final product, namely yellow solid. The invention solves the problems that the traditional catalyst affects the color difference and the color of the PC product, reactions such as branching, coking, degradation and the like can occur in the subsequent reactions, and the conversion rate of bisphenol A needs to be further improved.

Description

A kind of preparation method and application of metal biimidazolium salt ionic liquid catalyst

technical field

The invention relates to the technical field of catalysts, in particular to a preparation method of a metal biimidazolium salt alkaline ionic liquid catalyst and the application of catalyzing diphenyl carbonate (DPC) and bisphenol A (BPA) to synthesize polycarbonate (PC).

Background technique

Polycarbonate (PC) is usually odorless, non-toxic, transparent, has good thermal properties and excellent mechanical properties, and is one of the five major engineering plastics. According to their different functional characteristics, they are applicable to different fields such as mechanical equipment, optical materials, building materials, and electrical and electronic. Polycarbonate on the market is divided into aliphatic, alicyclic, and aromatic according to the raw materials. At present, bisphenol A polycarbonate (PC) is the most widely used. Bisphenol A polycarbonate is synthesized using diphenyl carbonate (DPC) and bisphenol A as raw materials (reaction formula shown in Figure 3). The catalyst commonly used in this process is a basic catalyst, which can be divided into basic metal salt catalysts, quaternary Ammonium salts, quaternary phosphorus salt catalysts and heterocyclic N-containing catalysts. At present, in the PC market, most of them adopt direct phosgene method or indirect phosgene method, use basic metal catalyst as the main catalyst, and use a large amount of solvent for industrial production. Basic metal catalyst has good catalytic performance and is cheap and easy to obtain. However, it will affect the color difference and luster of the product PC, and reactions such as branching, coking, and degradation will also occur in subsequent reactions, and the conversion rate of bisphenol A needs to be further improved.

Contents of the invention

Purpose of the invention:

The present invention proposes a method for preparing a metal biimidazolium salt alkaline ionic liquid catalyst and its application, and its purpose is to provide a kind of ionic liquid catalytic system with synergistic catalytic effect composed of active component metal cations and biimidazole anions, It solves the problem that the traditional catalyst affects the color difference and luster of the product PC, and branching, coking, degradation and other reactions will occur in the subsequent reaction, and the conversion rate of bisphenol A needs to be further improved.

Technical solutions:

A metal biimidazole salt alkaline ionic liquid catalyst, the catalyst is to combine the biimidazole containing two imidazole rings with an alkali metal compound for dehydration reaction, the metal cation is provided by the alkali metal compound, and the biimidazole acts as an anion to form an ionic liquid catalytic system, Its structure is as follows:

M = Li, Na, K.

A preparation method of a metal biimidazole salt alkaline ionic liquid catalyst, adding biimidazole and an alkali metal compound with a molar ratio of 1:1.5-3 into a reaction kettle, and then adding an appropriate amount of N,N-dimethylformamide (DMF) As a solvent, condense and reflux under the protection of nitrogen at 100-130°C for 18-24 hours with magnetic stirring. After the reaction, the liquid product is 90-120°C for vacuum rotary evaporation to remove the solvent, then add an appropriate amount of distilled water to wash and filter, and vacuum dry at 100-130°C for 24 hours. The final product was obtained as a yellow solid.

The alkali metal compound is one of lithium hydroxide, sodium hydroxide or potassium hydroxide. Lithium hydroxide, sodium hydroxide, potassium hydroxide are used to provide lithium, sodium, potassium active sites.

The application of a metal biimidazolium salt basic ionic liquid catalyst in the synthesis of polycarbonate (PC) from diphenyl carbonate (DPC) and bisphenol A (BPA).

Beneficial effect:

(1) Compared with simple heterocyclic nitrogen-containing catalysts and quaternary ammonium salts and quaternary phosphorus salt catalysts, the catalytic system of the present invention has stronger coordination and nucleophilic ability, and the biimidazole anion and metal cation produce a synergistic effect, which can improve the reaction conversion rate, enhanced catalytic activity and reaction selectivity.

(2) The catalyst system of the present invention is based on the physical properties of ionic liquids. It is paste or solid at normal temperature, not easy to burn, explode, and oxidize, and has good thermal and chemical stability.

(3) The conversion rate of bisphenol A in the present invention is increased from about 70% to more than 90%, and the molecular weight of PC can be controlled through process adjustment.

(4) In addition to playing a catalytic role in the process of synthesizing PC, the catalyst of the present invention also has a certain plasticizing and toughening effect, and provides a new technology for synthesizing high-performance PC with controllable molecular weight.

Description of drawings

Fig. 1 is a schematic diagram of catalyst synthesis;

Fig. 2 is reaction device figure;

Fig. 3 is diphenyl carbonate and bisphenol A synthetic polycarbonate (PC) reaction mechanism figure;

Fig. 4 is the infrared spectrum analysis figure of prepared catalyst;

Figure 5 is a thermogravimetric analysis diagram of the prepared catalyst.

Detailed ways

The present invention will be further described in detail below by way of examples.

As shown in Figure 1, the catalyst of the present invention combines biimidazole containing two imidazole rings with an alkali metal compound for dehydration reaction, metal cations are provided by the alkali metal compound, and biimidazole is used as an anion to form an ionic liquid catalytic system. In this paper, biimidazole is used to design ionic liquid catalysts for catalysis. Biimidazole (2,2'-Biimidazole) contains imidazole-like structures and is white granular crystals at room temperature. The unshared electron pair of the 1-position nitrogen atom in the imidazole ring participates in the ring Like conjugation, the hydrogen on this nitrogen atom is easy to leave in the form of hydrogen ions, and has specific proton accepting and donating properties. In this reaction, the free imidazole ring is negative, and metal lithium, sodium, and potassium are positive.

Catalyst structure of the present invention is as follows:

M = Li, Na, K.

The catalyst based on the ionic liquid is stable in nature, easy to store, green and pollution-free, and the biimidazolium anion has higher selectivity for the transesterification reaction, and can produce a synergistic effect with the metal cation, enhance the catalytic activity, and increase the reaction conversion rate. The present invention utilizes infrared spectrometer (FT-IR), thermogravimetric analyzer (TG) etc. to characterize the structure and thermal stability of catalyst, with DPC and BPA as raw material, the metal imidazole basic ionic liquid of above-mentioned preparation is used as catalyst to investigate its catalytic performance.

Example 1:

Add 0.1 mol of biimidazole and 0.2 mol of lithium hydroxide in a three-necked flask, then add 50 mL of DMF as a solvent, condense and reflux under the protection of nitrogen at 100°C for 16 hours with magnetic stirring, and after the reaction, the liquid product is evaporated in vacuo at 120°C to remove the solvent, and then add 60 mL of Wash with distilled water, filter, and dry under vacuum at 120°C for 24 hours to obtain the final product, lithium biimidazole, as a yellow solid. The infrared spectrum analysis diagram is shown in Figure 4, and the thermogravimetric analysis diagram is shown in Figure 5.

The curve A3 corresponding to biimidazole lithium in Figure 4 has the NH bond characteristic peak in the range of 2600cm ^-1 to 2800cm ^-1 . Compared with biimidazole A1, the peak shape of A3 at 2780cm ^-1 becomes smaller, which is due to biimidazole After connecting with metal lithium, the NH bond energy will decrease. The wave number near 1500cm ^-1 is the characteristic peak of C=N on the imidazole ring, 1600cm ^-1 is the characteristic peak of C=C double bond, and the bending vibration peak of the imidazole ring is at 750cm ^-1 , so it can be known that the sample lithium biimidazole is the target product.

The T2 curve corresponding to lithium biimidazole in Figure 5, the rapid decline at around 100°C is caused by dehydration, and the temperature at which the sample actually begins to thermally decompose is at 290°C, and its catalytic temperature reaches a maximum of 260°C, so the thermal stability of the catalyst meet the requirements of catalytic reaction. When the temperature reaches 500°C, the thermal decomposition basically ends, and the corresponding residual amount is greater than 20%. Therefore, the thermal stability of lithium biimidazole meets the temperature requirements of the catalytic reaction, and no thermal decomposition occurs during the catalytic process.

Example 2:

Add 0.1 mol of biimidazole and 0.2 mol of sodium hydroxide in a three-necked flask, then add 50 mL of DMF as a solvent, condense and reflux under the protection of nitrogen at 110°C for 24 hours with magnetic stirring, and remove the solvent by rotary evaporation of the liquid product at 120°C after the reaction, and then add 60 mL of Wash with distilled water, filter, and vacuum-dry at 120°C for 24 hours to obtain the final product, sodium biimidazole, as a light yellow solid. The infrared spectrum analysis diagram is shown in Figure 4, and the thermogravimetric analysis diagram is shown in Figure 5.

The curve A2 corresponding to biimidazole sodium in Figure 4, compared with biimidazole A1, the peak shape of A2 becomes smaller at 2750cm ^-1 , which is also due to the decrease of NH bond energy after biimidazole is connected with metal sodium. Other analyzes are the same as above, and Fig. 4 illustrates that the sample biimidazole sodium is the target product.

In the T3 curve corresponding to biimidazole sodium in Figure 5, the rapid decline within 100 °C is caused by dehydration, and the temperature at which the sample actually begins to thermally decompose is at 290 °C, and its catalytic temperature reaches a maximum of 260 °C, so the catalyst biimidazole sodium The thermal stability meets the requirements of catalytic reaction.

Example 3:

Add 0.1 mol of biimidazole and 0.2 mol of potassium hydroxide in a three-necked flask, then add 50 mL of DMF as a solvent, condense and reflux under nitrogen protection at 120°C for 22 hours with magnetic stirring, and remove the solvent by rotary evaporation of the liquid product at 120°C after the reaction is complete, and then add 60 mL of Wash with distilled water, filter, and dry under vacuum at 120°C for 24 hours to obtain the final yellow solid biimidazole potassium. The infrared spectrum analysis diagram is shown in Figure 4, and the thermogravimetric analysis diagram is shown in Figure 5.

The curve A4 corresponding to biimidazole potassium in Fig. 4, compared with biimidazole A1, the peak shape of A4 becomes smaller at 2700cm ^-1 , which is also due to the decrease of NH bond energy after biimidazole is connected with metal potassium. Other analyzes are the same as above, and Fig. 4 illustrates that the sample biimidazole potassium is the target product.

The T4 curve corresponding to biimidazole potassium in Figure 5, the rapid decline within 100 °C is caused by dehydration, and the temperature at which the sample actually begins to thermally decompose is at 285 °C, and its catalytic temperature is up to 260 °C, so the catalyst biimidazole potassium The thermal stability meets the requirements of catalytic reaction.

Example 4

The procedure for synthesizing polycarbonate catalyzed by lithium biimidazole is the same as in Example 1, except that the molar ratio of biimidazole and lithium hydroxide is changed to 1:1.5, and the experimental results are shown in Table 2.

Example 5

The procedure for synthesizing polycarbonate catalyzed by lithium biimidazole is the same as in Example 1, and the molar ratio of biimidazole and lithium hydroxide is changed to 1:2.5. The experimental results are shown in Table 2.

Example 6

The procedure for synthesizing polycarbonate catalyzed by lithium biimidazole is the same as in Example 1, and the molar ratio of biimidazole and lithium hydroxide is changed to 1:3. The experimental results are shown in Table 2.

A metal biimidazolium salt alkaline ionic liquid catalyst catalyzes the reaction of diphenyl carbonate (DPC) and bisphenol A (BPA) to synthesize polycarbonate (PC) and the specific implementation method is as follows:

Weigh 1-1.2:1 DPC and BPA respectively and pour them into a three-necked flask, pass in nitrogen gas to test the airtightness, and purge and discharge the air in the flask, turn on the mechanical stirring, turn on the heating mantle, and set the heating temperature to 150°C. Until the material is completely melted and the temperature of the still liquid reaches 140°C, add the catalyst in an amount of 0.25% of the mass of the reactant. After checking again that the airtightness is good, turn off the nitrogen, turn on the vacuum pump, and evacuate to 15-5KPa, and continue to heat up to the temperature of the still liquid. Carry out the first step of transesterification reaction at 150-180°C, continue the reaction for 30-60 minutes, then gradually raise the temperature to 220°C, and collect the phenol generated during the process through the condensing device. After the temperature of the gas phase dropped to 50°C and became stable, the second-step polycondensation reaction began. Gradually increase the temperature to 220-280°C at a rate of 5°C per minute, adjust the pressure to 10-1KPa, continue the reaction under this condition for 20-60min, stop the reaction, and cast into the corresponding mold to prepare the corresponding PC sample Or sample, the reaction device is shown in Figure 2.

After the distillate is detected by a gas chromatograph, the percentage of each component in the product is determined by the area normalization method, and the conversion rate, selectivity and yield of the reactant and the target product are calculated, and the product is obtained with an Ubbelohde viscometer The measurement is carried out, and the viscosity-average molecular weight is estimated by a one-point method to measure and evaluate the catalytic performance.

Catalyst prepared by embodiment 1-3 and traditional catalyst sodium hydroxide, heterocyclic nitrogen-containing catalyst (pyridine), quaternary ammonium salt (tetrabutyl ammonium hydroxide) and quaternary phosphonium salt (tetrabutyl ammonium hydroxide) are used to catalyze carbonic acid respectively Polycarbonate (PC) was synthesized from diphenyl ester (DPC) and bisphenol A (BPA). The catalytic evaluation results are shown in Table 1.

The catalytic performance contrast of table 1 embodiment 1-3 and traditional catalyst

As can be seen from the data in Table 1, the catalytic effect of the present invention is remarkable, and compared with traditional catalysts, reaction conversion rate and product selectivity are all greatly improved, wherein the best catalytic effect is the biimidazole lithium of embodiment 1, its conversion The rate is as high as 97.31%, and the selectivity is as high as 95.47%. In addition, the molecular weight distribution of the PC product synthesized by the present invention is narrow, and the molecular weight can be controlled. Through the test of notched impact strength, it can be seen that the notched impact strength of PC synthesized by the present invention is higher than that of traditional catalysts, which shows that the present invention not only has a good catalytic effect, but also has a certain plasticizing and toughening effect.

The catalytic effect evaluation of table 2 embodiment 1 and 4-6

As can be seen from Table 2, along with the gradual increase of lithium-containing compound addition, its reactivity increases gradually, when the mol ratio of biimidazole and lithium hydroxide is 1:2 (embodiment 1), its conversion rate and notched impact strength reached the maximum value.

Compared with traditional basic catalysts, the invention has mild and easy-to-control reaction process, and further improves reaction conversion rate and selectivity. The catalyst not only plays a catalytic role in the catalytic process, but also has a certain plasticizing and toughening effect in the process of synthesizing PC. The synthesized PC has good impact resistance and comprehensive properties.

Claims (2)

1. a kind of preparation method of metal biimidazole salt alkaline ionic liquid catalyst is characterized in that: in reactor, add the biimidazole and alkali metal compound of mol ratio 1:1.5-3, then add appropriate N, N-dimethyl Use methyl formamide as a solvent, condense and reflux under nitrogen protection at 100-130°C for 18-24 hours with magnetic stirring, and remove the solvent by rotary evaporation at 90-120°C for liquid products after the reaction, then add an appropriate amount of distilled water to wash and filter, and vacuum at 100-130°C After drying for 24 hours, the final product was obtained as a yellow solid; The structure of the metal biimidazolium salt alkaline ionic liquid catalyst is as follows:

M = Li, Na, K; The alkali metal compound is one of lithium hydroxide, sodium hydroxide or potassium hydroxide. 2. the application of a metal biimidazolium salt alkaline ionic liquid catalyst in the synthetic polycarbonate reaction of catalyzed diphenyl carbonate and bisphenol A, is characterized in that: The structure of the metal biimidazolium salt alkaline ionic liquid catalyst is as follows:

M = Li, Na, K.

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