Composite titanium-based catalyst, method for synthesizing the same, and use thereof

Abstract

The application discloses a composite titanium catalyst and a synthesis method and application thereof. The composite titanium catalyst is prepared by mixing and reacting a polyvinylpyrrolidone aqueous solution and a hydrochloric acid solution of butyl titanate. The high molecular weight polylactic acid is prepared by mixing lactic acid and the composite titanium catalyst solution, performing pre-polymerization, and then adding tin dichloride in a polycondensation stage. The composite catalyst system is composed of the composite titanium catalyst and the tin dichloride, the synthesis method has the advantages of simple preparation, easy operation and short catalytic polycondensation time, the prepared polylactic acid has high yield and large relative molecular mass, and is suitable for large-scale industrialized production of polylactic acid.

Description

Technical Field

[0001] This invention belongs to the field of polymer synthesis technology, and relates to a composite titanium catalyst, its synthesis method and application. Background Technology

[0002] Polylactic acid (PLA), as a biodegradable material, holds promise as a replacement for traditional plastics, thus addressing the problem of white pollution. Currently, there are two main methods for synthesizing PLA: direct lactic acid polymerization and lactide polymerization. Melt polymerization, a type of direct lactic acid polymerization, is characterized by simple equipment, low cost, and short polymerization time. During melt polycondensation, transition metal compounds play a crucial role as catalysts. Due to the complex equilibrium of free lactic acid, water, polymer, and lactide in the system, polymerization often becomes excessively long without a catalyst or with an inappropriate catalyst, and high molecular weight PLA cannot be easily obtained. Therefore, selecting a suitable catalyst system is key to preparing high molecular weight PLA in melt polycondensation.

[0003] Currently, tin-based catalysts are commonly used in the melt condensation polymerization of polylactic acid (PLA), such as stannous dichloride and composite catalysts formed with alkoxyaluminum, alkoxysilane, and alkoxyyttrium. These catalysts can effectively catalyze lactic acid polymerization, but the relative molecular mass of the resulting PLA is generally in the range of 7 × 10⁻⁶. 4 The following are examples of catalysts with relatively low molecular weights. Researchers such as Kouyu Tomita have demonstrated that metal compounds with moderate electronegativity exhibit high catalytic activity in polyester polycondensation (K. Tomita. Studies on the formation of poly(ethylene terephthalate): 6. Catalytic activity of metal compounds in polycondensation of bis(2-hydroxyethyl)terephthalate. Polymer, 1976, 17, 221-224.). Titanium-based catalysts, with their moderate electronegativity, exhibit outstanding activity in polyester production and low toxicity, making them a focus of attention and successfully applied in the preparation of polyesters such as PBT. However, the excessively high catalytic activity of traditional titanium catalysts accelerates polycondensation but also catalyzes polymer thermal and oxidative degradation, leading to increased side reactions and ultimately resulting in low relative molecular weights and yellowing products. Furthermore, the excessively high catalytic activity of traditional titanium catalysts causes the viscosity of the molten system to rise too rapidly, posing a danger to industrial production. Therefore, there is an urgent need to find a catalyst that maintains high catalytic activity while suppressing various degradation side reactions. Summary of the Invention

[0004] The purpose of this invention is to provide a composite titanium catalyst, its synthesis method, and its application.

[0005] The technical solution for achieving the objective of this invention is as follows:

[0006] The specific steps for synthesizing the composite titanium catalyst are as follows: dissolving polyvinylpyrrolidone in water to prepare a polyvinylpyrrolidone solution, dissolving tetrabutyl titanate in 0.1 mol / L hydrochloric acid to prepare a tetrabutyl titanate solution, adding the tetrabutyl titanate solution dropwise to the polyvinylpyrrolidone solution, and reacting to obtain a composite titanium catalyst solution, wherein the ratio of polyvinylpyrrolidone, water, tetrabutyl titanate and hydrochloric acid is 0.5:150:(0.4~6):20, g:g:g:mL.

[0007] Preferably, the ratio of polyvinylpyrrolidone, water, tetrabutyl titanate, and hydrochloric acid is 0.5:150:2:20 (g:g:g:mL). The catalyst synthesized using this ratio has the highest yield and the highest molecular weight of polylactic acid.

[0008] This invention provides a composite titanium catalyst synthesized by the above-described synthesis method.

[0009] The method for synthesizing high molecular weight polylactic acid using the above-mentioned composite titanium catalyst is as follows: lactic acid is mixed with a composite titanium catalyst solution, a prepolymerization reaction is carried out first, and then a tin-based catalyst, tin dichloride, is added during the polycondensation stage to obtain high molecular weight polylactic acid. The ratio of the composite titanium catalyst solution to lactic acid is 0.005:1, mL:g.

[0010] Furthermore, the amount of tin-based catalyst tin dichloride added is 0.1 to 0.5 wt% of the mass of lactic acid, more preferably 0.5 wt%. At this catalyst dosage, the synthesized polylactic acid has the highest molecular weight, a high yield, and a good color.

[0011] Furthermore, the prepolymerization temperature is 150–160°C, preferably 160°C. At this temperature, the dehydration reaction can be fully carried out under reduced pressure, while side reactions can be avoided, resulting in the highest molecular weight of the prepolymer.

[0012] Furthermore, the polycondensation temperature is 160–180°C, preferably 180°C. At this temperature, the polylactic acid produced has the highest molecular weight, better yield and color, and the problem of decreased optical purity of the product caused by higher temperatures can be avoided.

[0013] Furthermore, the polycondensation time is 6 to 10 hours, preferably 10 hours. At this polycondensation time, the polylactic acid with the highest molecular weight is obtained, and the production of the side reaction lactide is reduced.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] In the composite titanium catalyst of this invention, metallic titanium coordinates with nitrogen (N) in nitrogen-containing compounds, effectively catalyzing the condensation polymerization of lactic acid. This process maintains high catalytic activity while suppressing various side reactions. Using this composite titanium catalyst for melt condensation polymerization of lactic acid, a weight-average molecular weight of 3 × 10⁻⁶ can be obtained in a relatively short time (8–10 h). 5 The polylactic acid produced by this invention has a short catalytic polycondensation time, high yield, and a large relative molecular mass, which is beneficial for large-scale industrial production. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to specific embodiments.

[0017] Example 1

[0018] Synthesis of composite titanium catalysts:

[0019] 0.5 g of polyvinylpyrrolidone was dissolved in 150 g of water to obtain an aqueous solution of polyvinylpyrrolidone. 2 g of tetrabutyl titanate was dissolved in 20 mL of 0.1 mol / L hydrochloric acid to obtain a tetrabutyl titanate solution. The tetrabutyl titanate solution was added dropwise to the aqueous solution of polyvinylpyrrolidone to react and obtain a composite titanium catalyst solution.

[0020] Example 2

[0021] 1. The synthesis of the composite titanium catalyst is basically the same as in Example 1, except that the amount of tetrabutyl titanate used is changed. The amount of tetrabutyl titanate used is shown in Table 1.

[0022] 2. Synthesis of polylactic acid:

[0023] (1) Add 200g of lactic acid to a 250ml three-necked flask, and insert a stirring rod into the middle of the flask. Seal the connection between the stirring rod and the flask neck with a rubber stopper, and apply silicone oil to the joint. Fix the other end of the stirring rod to a mechanical stirrer. Connect one end of each side port to a high-pressure argon cylinder and the other end to a vacuum pump. Repeat the vacuuming and gas exchange process 3-4 times. Connect a condenser to one side of the three-necked flask and circulate cooling water. Connect one end of the condenser to the flask and the other end to a single-necked flask, and seal the joints of the glassware with tape.

[0024] (2) Prepolymerization stage: Under the protection of nitrogen at normal pressure, a composite titanium catalyst with different amounts of tetrabutyl titanate and 0.005 ml / g lactic acid was added and prepolymerized at 160 °C for 4 h to obtain oligomers.

[0025] (3) Polycondensation stage: 0.5 wt% tin dichloride catalyst was added at a polycondensation temperature of 180℃, and the polycondensation reaction was mechanically stirred for 4 h to obtain polylactic acid with different molecular weights. The yield and molecular weight of polylactic acid were determined, and the results are shown in Table 1.

[0026] Table 1 Comparison of the effects of tetrabutyl titanate dosage test

[0027]

[0028] The above results indicate that the highest yield was obtained when the amount of tetrabutyl titanate was 2g.

[0029] Example 3

[0030] Synthesis of polylactic acid:

[0031] (1) Add 200g of lactic acid to a 250ml three-necked flask, and insert a stirring rod into the middle of the flask. Seal the connection between the stirring rod and the flask neck with a rubber stopper, and apply silicone oil to the joint. Fix the other end of the stirring rod to a mechanical stirrer. Connect one end of each side port to a high-pressure argon cylinder and the other end to a vacuum pump. Repeat the vacuuming and gas exchange process 3-4 times. Connect a condenser to one side of the three-necked flask and circulate cooling water. Connect one end of the condenser to the flask and the other end to a single-necked flask, and seal the joints of the glassware with tape.

[0032] (2) Prepolymerization stage: Under the protection of nitrogen at normal pressure, the composite titanium catalyst prepared in Example 1 with 0.005 ml / g lactic acid was added and prepolymerized at 160 °C for 4 h to obtain oligomers.

[0033] (3) Polycondensation stage: 0.5 wt% tin dichloride catalyst was added at a polycondensation temperature of 180℃, and the polycondensation reaction was mechanically stirred for 10 h to obtain a product with a molecular weight of 3×10⁻⁶. 5 Polylactic acid.

[0034] Example 4

[0035] Synthesis of polylactic acid:

[0036] (1) Add 200g of lactic acid to a 250ml three-necked flask, and insert a stirring rod into the middle of the flask. Seal the connection between the stirring rod and the flask neck with a rubber stopper, and apply silicone oil to the joint. Fix the other end of the stirring rod to a mechanical stirrer. Connect one end of each side port to a high-pressure argon cylinder and the other end to a vacuum pump. Repeat the vacuuming and gas exchange process 3-4 times. Connect a condenser to one side of the three-necked flask and circulate cooling water. Connect one end of the condenser to the flask and the other end to a single-necked flask, and seal the joints of the glassware with tape.

[0037] (2) Prepolymerization stage: Under the protection of nitrogen at normal pressure, different amounts of the composite titanium catalyst prepared in Example 1 were added, and the oligomers were obtained by prepolymerization at 160°C for 4 hours.

[0038] (3) Polycondensation stage: 0.5 wt% tin dichloride catalyst was added at a polycondensation temperature of 180℃, and the polycondensation reaction was mechanically stirred for 6 h to obtain polylactic acid with different molecular weights. The optical purity, yield and molecular weight of polylactic acid were determined, and the results are shown in Table 2.

[0039] Table 2 Comparison of the Effect of Composite Titanium Catalyst Usage Amount

[0040]

[0041] The above results indicate that the amount of composite titanium catalyst has a certain impact on the product molecular weight, yield, and optical purity, with the best results achieved at a dosage of 0.005 ml / g of titanium catalyst. Further increasing the dosage does not improve these three results; instead, it shows a decreasing trend.

[0042] Example 5

[0043] Synthesis of polylactic acid:

[0044] (1) Add 200g of lactic acid to a 250ml three-necked flask, and insert a stirring rod into the middle of the flask. Seal the connection between the stirring rod and the flask neck with a rubber stopper, and apply silicone oil to the joint. Fix the other end of the stirring rod to a mechanical stirrer. Connect one end of each side port to a high-pressure argon cylinder and the other end to a vacuum pump. Repeat the vacuuming and gas exchange process 3-4 times. Connect a condenser to one side of the three-necked flask and circulate cooling water. Connect one end of the condenser to the flask and the other end to a single-necked flask, and seal the joints of the glassware with tape.

[0045] (2) Prepolymerization stage: Under the protection of nitrogen at normal pressure, the composite titanium catalyst prepared in Example 1 with 0.005 ml / g lactic acid was added and prepolymerized at 160 °C for 4 h to obtain oligomers.

[0046] (3) Polycondensation stage: Different amounts of tin dichloride catalyst were added at a polycondensation temperature of 180℃, and the polycondensation reaction was mechanically stirred for 10 h to obtain polylactic acid with different molecular weights. The optical purity, yield and molecular weight distribution index (PDI) of polylactic acid were determined, and the results are shown in Table 3.

[0047] Table 3 Comparison of the effects of tin dichloride dosage on the test results

[0048]

[0049] The above results indicate that the dosage of tin dichloride has a certain impact on the molecular weight, yield, and molecular weight distribution index of the product. When the dosage of tin dichloride reaches 0.5 wt%, the molecular weight, yield, and distribution index all reach their optimal levels. Further increasing the dosage leads to a decrease in both molecular weight and yield, and the distribution index widens, which is detrimental to industrial processing.

[0050] Example 6

[0051] Synthesis of polylactic acid:

[0052] (1) Add 200g of lactic acid to a 250ml three-necked flask, and insert a stirring rod into the middle of the flask. Seal the connection between the stirring rod and the flask neck with a rubber stopper, and apply silicone oil to the joint. Fix the other end of the stirring rod to a mechanical stirrer. Connect one end of each side port to a high-pressure argon cylinder and the other end to a vacuum pump. Repeat the vacuuming and gas exchange process 3-4 times. Connect a condenser to one side of the three-necked flask and circulate cooling water. Connect one end of the condenser to the flask and the other end to a single-necked flask, and seal the joints of the glassware with tape.

[0053] (2) Prepolymerization stage: Under the protection of nitrogen at atmospheric pressure, 0.005 ml / g of the composite titanium catalyst prepared in Example 1 was added, and the oligomers were obtained by prepolymerization at different temperatures for 4 h. The molecular weight, yield and molecular weight distribution index of the oligomers were determined, and the results are shown in Table 4.

[0054] Table 4 Comparison of Effects of Different Prepolymerization Temperatures

[0055]

[0056]

[0057] The above results indicate that the product yield and molecular weight are optimal when the prepolymerization temperature is 160℃, and the molecular weight distribution index is the lowest.

[0058] Example 7

[0059] Synthesis of polylactic acid:

[0060] (1) Add 200g of lactic acid to a 250ml three-necked flask, and insert a stirring rod into the middle of the flask. Seal the connection between the stirring rod and the flask neck with a rubber stopper, and apply silicone oil to the joint. Fix the other end of the stirring rod to a mechanical stirrer. Connect one end of each side port to a high-pressure argon cylinder and the other end to a vacuum pump. Repeat the vacuuming and gas exchange process 3-4 times. Connect a condenser to one side of the three-necked flask and circulate cooling water. Connect one end of the condenser to the flask and the other end to a single-necked flask, and seal the joints of the glassware with tape.

[0061] (2) Prepolymerization stage: Under the protection of nitrogen at normal pressure, 0.005 ml / g of the composite titanium catalyst prepared in Example 1 was added, and the oligomer was obtained by prepolymerization at 160°C for 4 h.

[0062] (3) Polycondensation stage: 0.5 wt% tin dichloride catalyst was added at different polycondensation temperatures, and the polycondensation reaction was mechanically stirred for 6 h to obtain polylactic acid with different molecular weights. The optical purity, yield and molecular weight distribution index of polylactic acid were determined, and the results are shown in Table 5.

[0063] Table 5 Comparison of Polycondensation Temperature Effects

[0064]

[0065] The above results indicate that when the polycondensation temperature is lower, the molecular weight of the synthesized polylactic acid is not high; when the polycondensation temperature is too high, the side reactions are aggravated, the yield of polylactic acid decreases, and depolymerization occurs at the same time, which leads to a decrease in the molecular weight of polylactic acid and a decrease in yield; the optimal polycondensation temperature is 180℃.

[0066] Example 8

[0067] Synthesis of polylactic acid:

[0068] (1) Add 200g of lactic acid to a 250ml three-necked flask, and insert a stirring rod into the middle of the flask. Seal the connection between the stirring rod and the flask neck with a rubber stopper, and apply silicone oil to the joint. Fix the other end of the stirring rod to a mechanical stirrer. Connect one end of each side port to a high-pressure argon cylinder and the other end to a vacuum pump. Repeat the vacuuming and gas exchange process 3-4 times. Connect a condenser to one side of the three-necked flask and circulate cooling water. Connect one end of the condenser to the flask and the other end to a single-necked flask, and seal the joints of the glassware with tape.

[0069] (2) Prepolymerization stage: 0.005 ml of the composite titanium catalyst prepared in Example 1 was added under the protection of nitrogen at normal pressure, and the oligomer was obtained by prepolymerization at 160°C for 4 h.

[0070] (3) Polycondensation stage: 0.5 wt% tin dichloride catalyst was added at a polycondensation temperature of 180℃, and the polycondensation reaction was mechanically stirred for different times to obtain polylactic acid with different molecular weights. The optical purity, yield and molecular weight of polylactic acid were determined, and the results are shown in Table 6.

[0071] Table 6 Comparison of the effects of different polycondensation times

[0072]

[0073] The above results indicate that the product exhibits the highest molecular weight and best optical purity when the polycondensation time is 10 hours. As the reaction time increases, the molecular weight of polylactic acid decreases sharply, and the optical purity also declines. Considering all factors, a polycondensation reaction time of 10 hours yields the best polymerization effect.

Claims

1. A method for synthesizing composite titanium-based catalysts, characterized in that, The specific steps are as follows: dissolve polyvinylpyrrolidone in water to prepare a polyvinylpyrrolidone solution, dissolve tetrabutyl titanate in 0.1 mol / L hydrochloric acid to prepare a tetrabutyl titanate solution, add the tetrabutyl titanate solution dropwise to the polyvinylpyrrolidone solution, and react to obtain a composite titanium catalyst solution, wherein the ratio of polyvinylpyrrolidone, water, tetrabutyl titanate and hydrochloric acid is 0.5:150:2:20, g:g:g:mL.

2. The composite titanium catalyst synthesized by the synthesis method according to claim 1.

3. A method for synthesizing high molecular weight polylactic acid using a composite titanium-based catalyst, characterized in that, Specifically, lactic acid is mixed with the composite titanium catalyst solution described in claim 1, and a prepolymerization reaction is carried out first. Then, tin-based catalyst tin dichloride is added during the polycondensation stage to obtain high molecular weight polylactic acid. The ratio of the composite titanium catalyst solution to lactic acid is 0.005:1 (mL:g), the amount of tin-based catalyst tin dichloride added is 0.5wt% of the mass of lactic acid, the prepolymerization temperature is 160℃, the polycondensation temperature is 180℃, and the polycondensation time is 10h.

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