A catalyst for synthesizing polypropylene carbonate and application thereof

Abstract

This invention provides a catalyst for the synthesis of polypropylene carbonate and its application. The catalyst is a zinc-manganese dicarboxylic acid bimetallic catalyst, wherein the molar ratio of zinc to manganese is in the range of (10:1)–(1:1), preferably 5:1, and the particle size of the catalyst is 10–50 nm. The beneficial effects of this invention are: the zinc-manganese dicarboxylic acid bimetallic catalyst of this invention has a simple preparation step, mild preparation conditions, low cost, and is easy to industrialize. When used to catalyze the production of polypropylene carbonate in a polymerization reactor, the catalyst exhibits high activity, resulting in a polymer with a high molecular weight and low ether content.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation, and in particular relates to a catalyst for the synthesis of polypropylene carbonate and its application. Background Technology

[0002] Since the advent of industrial production, carbon dioxide emissions have been rising continuously, leading not only to increased greenhouse effects but also to a waste of carbon resources. How to strengthen the development and utilization of carbon dioxide and turn waste into treasure is a major challenge for human society. Current research has found that carbon dioxide can copolymerize with epoxy compounds to produce biodegradable polycarbonates. Polypropylene carbonate (PPC), obtained through copolymerization of carbon dioxide and propylene oxide, possesses excellent biodegradability, mechanical properties, oxygen barrier properties, and transparency. It can be widely used in the plastics industry and can be processed into various plastic products, such as packaging films, agricultural films, and disposable products, using traditional processes like extrusion, calendering, blow molding, and injection molding. Its applications span the food, pharmaceutical, agricultural, plastics, and polymer chemical industries, demonstrating promising prospects.

[0003] Catalysts are crucial for the polymerization of polypropylene carbonate (PPC), as they directly influence the chain segment structure and molecular weight of the polymer, thus affecting its mechanical properties. Currently, PPC polymerization catalysts mainly include zinc dicarboxylate, zinc complexes, rare earth complexes, DMC, SalenMX, zinc phenoxylate (cadmium), porphyrin metal complexes, β-diimine metal complexes, polynuclear metal complexes, and other metal complexes containing MO or MN bonds. These catalysts are complex to synthesize and have high raw material costs, making industrial application difficult. Patent CN105418907B proposes a method for preparing a zinc dicarboxylate catalyst and a modified zinc dicarboxylate catalyst, which can yield up to 150g of polymer per gram of catalyst. However, its preparation process is difficult to replicate, requires strict pH control, and necessitates the addition of the chain extender ADR, further increasing preparation costs. Patent CN1116332C proposes a combined catalyst composed of rare earth complexes, alkyl metal compounds and organic compounds, which can achieve a number average molecular weight of 90,000. However, using rare earth elements as catalysts is costly and the preparation process is complex. Summary of the Invention

[0004] In view of this, the present invention aims to propose a catalyst for the synthesis of polypropylene carbonate and its application, so as to solve the problems of complex preparation process and high cost of existing catalysts.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0006] A method for preparing a catalyst for the synthesis of polypropylene carbonate, wherein the catalyst is a zinc-manganese dicarboxylic acid bimetallic catalyst, wherein the molar ratio of zinc to manganese is in the range of (10:1)-(1:1), preferably, the molar ratio of zinc to manganese is 5:1, and the particle size of the catalyst is 10-50 nm.

[0007] Furthermore, the method for preparing the catalyst includes the following steps:

[0008] S1. Add zinc salt and manganese salt to methylcyclohexane, mix well, and prepare solution A;

[0009] S2. Dissolve the dicarboxylic acid in methylcyclohexane, mix well, and prepare solution B;

[0010] S3. Add solution B to solution A, heat at temperature 1 and stir thoroughly, then heat at temperature 2 and stir thoroughly.

[0011] S4. Filter the product obtained in S3 and wash it with acetone;

[0012] S5. Dry the product obtained in S4 in air atmosphere and grind it into powder;

[0013] S6. The powder obtained in S5 is ball-milled in a ball mill to obtain the catalyst.

[0014] Further, in step S1, the zinc salt is zinc oxide; the manganese salt is manganese oxide; the mass fraction of methylcyclohexane is 1000; the mass fraction of zinc salt is 16.2-162, preferably 120-150; the mass fraction of manganese salt is 1.42-142, preferably 10.5-131.5.

[0015] Further, in step S2, the dicarboxylic acid is one of maleic acid, glutaric acid, adipic acid, octanoic acid, lauryl acid, 2,3-dimethyl-succinic acid, brassic acid, and 2,2'-biphenylcarboxylic acid, the mass fraction of the dicarboxylic acid is 20, and the mass fraction of the methylcyclohexane is 200.

[0016] Furthermore, in step S3, the heating temperature 1 is 65 ℃ and the stirring time is 2 hours, and the heating temperature 2 is 110 ℃ and the stirring time is 4 hours.

[0017] Furthermore, in step S5, the drying temperature is 120 ℃ and the drying time is 12 hours.

[0018] Furthermore, in step S6, the ball mill rotation speed is 1000-2000 rpm.

[0019] A catalyst prepared by any one of claims 1-7.

[0020] A method for polymerizing polypropylene carbonate, characterized in that: a catalyst prepared by the preparation method according to any one of claims 1-7 is used.

[0021] Furthermore, the polypropylene carbonate is obtained by copolymerization of carbon dioxide and propylene oxide in a polymerization reactor; the amount of catalyst is 0.2-2% of the mass of propylene oxide, the pressure of carbon dioxide is 1-3.5 MPa, the polymerization temperature is 50-100 ℃, and the reaction time is 3-20 h.

[0022] The prepared zinc-manganese dicarboxylic acid bimetallic catalyst exhibits high activity, and the polymerized product has a high molecular weight and low ether segment content, which is related to the catalyst's preparation and structure. The copolymerization mechanism is considered to involve the insertion of small monomer segments into the monomer's metal-heteroatom bond during the polymerization reaction. The epoxide first coordinates to the metal center of the catalyst, and then the epoxide undergoes ring-opening and insertion through the attack of the low electronegativity carbon atom in the epoxide by the anion. The zinc-manganese dicarboxylic acid bimetallic catalyst has two metal active centers, enabling it to catalyze ring-opening polymerization more quickly, thereby obtaining a higher molecular weight. Since carbon dioxide cannot homopolymerize while propylene oxide can, when the growth chain end is propylene oxide, the next ligand can be either propylene oxide or carbon dioxide; when the growth chain end is carbon dioxide, the next ligand can only be an epoxide. The diacid ligand and bimetallic center of this catalyst increase the polarization of the active bonds, resulting in a stronger ability to capture carbon dioxide. This leads to a higher carbon dioxide insertion rate when the growth chain end is propylene oxide, thereby reducing the number of propylene oxide-propylene oxide segments, i.e., reducing the formation of ether segments. Simultaneously, the bimetallic-X coordination bond of this catalyst effectively prevents monomeric propylene oxide bite-back, inhibits the formation of propylene carbonate, prevents the termination of polymer backbone growth, and thus improves the yield and molecular weight of the resulting polymer.

[0023] Compared with existing technologies, the zinc-manganese dicarboxylic acid bimetallic catalyst of the present invention has the following advantages:

[0024] The zinc-manganese bimetallic catalyst of the dicarboxylic acid described in this invention has a simple preparation process, mild preparation conditions, low cost, and is easy to industrialize.

[0025] The zinc-manganese bimetallic catalyst of the dicarboxylic acid described in this invention is used to catalyze the production of polypropylene carbonate. The reaction is carried out in a polymerization reactor. The catalyst has high activity, and the resulting polymer has a high molecular weight and a low ether content. Detailed Implementation

[0026] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0027] The present invention will now be described in detail with reference to embodiments.

[0028] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0029] The present invention will be described in detail below with reference to embodiments.

[0030] In the following embodiments, the catalyst was evaluated using the following method: The prepared zinc-manganese dicarboxylic acid bimetallic catalyst and propylene oxide were added to a polymerization reactor. The mass fraction of the zinc-manganese dicarboxylic acid bimetallic catalyst was 0.25% of the mass of propylene oxide. After purging with nitrogen and carbon dioxide, carbon dioxide was introduced into the polymerization reactor. The reaction temperature was controlled at 85 °C, the carbon dioxide pressure in the polymerization reactor was maintained at 2 MPa, and the reaction time was 5 hours. The obtained polymer was tested: the number-average molecular weight of the polymer was determined using gel permeation chromatography (GPC), and the structure and ether segment ratio of the polymer were determined using nuclear magnetic resonance spectroscopy. Catalyst activity = mass of polymer obtained (g) / amount of catalyst used (g).

[0031] In the following embodiments, the preparation steps of the zinc-manganese dicarboxylic acid bimetallic catalyst are as follows:

[0032] S1. A certain mass of zinc salt and a certain mass of tin salt are added to 1000 parts by mass of methylcyclohexane, mixed evenly, and prepared into solution A; wherein the zinc salt is 16.2-162 parts by mass; and the manganese salt is 1.42-142 parts by mass.

[0033] S2. Dissolve 20 parts of the dicarboxylic acid in 200 parts of the same methylcyclohexane described in S1, and mix thoroughly. Prepare solution B.

[0034] S3. Add solution B to solution A, heat to 65 ℃, stir for 2 hours, then raise the temperature to 110 ℃ and stir for 4 hours;

[0035] S4. Filter the product obtained in S2 and wash it with acetone;

[0036] S5. Dry the product from S3 in air at 120 °C for 12 hours, and then grind it into powder.

[0037] S6. The powder obtained in S4 is ball-milled in a ball mill to prepare a zinc-manganese dicarboxylic acid bimetallic catalyst; the ball milling speed is 1000-2000 rpm.

[0038] Example 1

[0039] 130 parts by mass of zinc salt and 22.8 parts by mass of manganese salt were added to 1000 parts by mass of methylcyclohexane and mixed thoroughly. 20 parts by mass of lauryl diacid were dissolved in 200 parts by mass of methylcyclohexane and mixed thoroughly. This mixture was then added to the solution obtained in step S1. The mixture was heated to 65 °C and stirred for 2 hours, then heated to 110 °C and stirred for 4 hours. After the reaction was complete, the product was filtered and washed with acetone. The resulting solid was dried in air at 120 °C for 12 hours and ground into powder. The powder was ball-milled at 1500 rpm to prepare the dicarboxylic acid zinc-manganese bimetallic catalyst. The catalyst evaluation results are shown in Table 1.

[0040] Example 2

[0041] 130 parts by mass of zinc salt and 113.9 parts by mass of manganese salt were added to 1000 parts by mass of methylcyclohexane and mixed thoroughly. 20 parts by mass of lauryl diacid were dissolved in 200 parts by mass of methylcyclohexane and mixed thoroughly. This mixture was then added to the solution obtained in step S1. The mixture was heated to 65 °C and stirred for 2 hours, then heated to 110 °C and stirred for 4 hours. After the reaction was complete, the product was filtered and washed with acetone. The resulting solid was dried in air at 120 °C for 12 hours and ground into powder. The powder was ball-milled at 1500 rpm to prepare the dicarboxylic acid zinc-manganese bimetallic catalyst. The catalyst evaluation results are shown in Table 1.

[0042] Example 3

[0043] 130 parts by mass of zinc salt and 11.4 parts by mass of manganese salt were added to 1000 parts by mass of methylcyclohexane and mixed thoroughly. 20 parts by mass of lauryl diacid were dissolved in 200 parts by mass of methylcyclohexane and mixed thoroughly. This mixture was then added to the solution obtained in step S1. The mixture was heated to 65 °C and stirred for 2 hours, then heated to 110 °C and stirred for 4 hours. After the reaction was complete, the product was filtered and washed with acetone. The resulting solid was dried in air at 120 °C for 12 hours and ground into powder. The powder was ball-milled at 1500 rpm to prepare the dicarboxylic acid zinc-manganese bimetallic catalyst. The catalyst evaluation results are shown in Table 1.

[0044] Example 4

[0045] 130 parts by mass of zinc salt and 22.8 parts by mass of manganese salt were added to 1000 parts by mass of methylcyclohexane and mixed thoroughly. 20 parts by mass of maleic acid were dissolved in 200 parts by mass of methylcyclohexane and mixed thoroughly. This solution was then added to the mixture obtained in step S1. The mixture was heated to 65 °C and stirred for 2 hours, then heated to 110 °C and stirred for 4 hours. After the reaction was complete, the product was filtered and washed with acetone. The resulting solid was dried in air at 120 °C for 12 hours and ground into powder. The powder was ball-milled at 1500 rpm to prepare the dicarboxylic acid zinc-manganese bimetallic catalyst. The catalyst evaluation results are shown in Table 1.

[0046] Example 5

[0047] 130 parts by mass of zinc salt and 22.8 parts by mass of manganese salt were added to 1000 parts by mass of methylcyclohexane and mixed thoroughly. 20 parts by mass of glutaric acid were dissolved in 200 parts by mass of methylcyclohexane and mixed thoroughly. This solution was then added to the mixture obtained in step S1. The mixture was heated to 65 °C and stirred for 2 hours, then heated to 110 °C and stirred for 4 hours. After the reaction was complete, the product was filtered and washed with acetone. The resulting solid was dried in air at 120 °C for 12 hours and ground into powder. The powder was ball-milled at 1500 rpm to prepare the dicarboxylic acid zinc-manganese bimetallic catalyst. The catalyst evaluation results are shown in Table 1.

[0048] Example 6

[0049] 130 parts by mass of zinc salt and 22.8 parts by mass of manganese salt were added to 1000 parts by mass of methylcyclohexane and mixed thoroughly. 20 parts by mass of brassic acid were dissolved in 200 parts by mass of methylcyclohexane and mixed thoroughly. This mixture was then added to the solution obtained in step S1. The mixture was heated to 65 °C and stirred for 2 hours, then heated to 110 °C and stirred for 4 hours. After the reaction was complete, the product was filtered and washed with acetone. The resulting solid was dried in air at 120 °C for 12 hours and ground into powder. The powder was ball-milled at 1500 rpm to prepare the dicarboxylic acid zinc-manganese bimetallic catalyst. The catalyst evaluation results are shown in Table 1.

[0050] Example 7

[0051] 130 parts by mass of zinc salt and 22.8 parts by mass of manganese salt were added to 1000 parts by mass of methylcyclohexane and mixed thoroughly. 20 parts by mass of 2,2'-biphenyl dicarboxylic acid were dissolved in 200 parts by mass of methylcyclohexane and mixed thoroughly. This solution was then added to the mixture obtained in step S1. The mixture was heated to 65 °C and stirred for 2 hours, then heated to 110 °C and stirred for 4 hours. After the reaction was complete, the product was filtered and washed with acetone. The resulting solid was dried in air at 120 °C for 12 hours and ground into powder. The powder was ball-milled at 1500 rpm to prepare the dicarboxylic acid zinc-manganese bimetallic catalyst. The catalyst evaluation results are shown in Table 1.

[0052] Example 8

[0053] 130 parts by mass of zinc salt and 22.8 parts by mass of manganese salt were added to 1000 parts by mass of methylcyclohexane and mixed thoroughly. 20 parts by mass of lauryl diacid were dissolved in 200 parts by mass of methylcyclohexane and mixed thoroughly. This mixture was then added to the solution obtained in step S1. The mixture was heated to 65 °C and stirred for 2 hours, then heated to 110 °C and stirred for 4 hours. After the reaction was complete, the product was filtered and washed with acetone. The resulting solid was dried in air at 120 °C for 12 hours and ground into powder. The powder was ball-milled at 1000 rpm to prepare the dicarboxylic acid zinc-manganese bimetallic catalyst. The catalyst evaluation results are shown in Table 1.

[0054] Example 9

[0055] 130 parts by mass of zinc salt and 22.8 parts by mass of manganese salt were added to 1000 parts by mass of methylcyclohexane and mixed thoroughly. 20 parts by mass of lauryl diacid were dissolved in 200 parts by mass of methylcyclohexane and mixed thoroughly. This mixture was then added to the solution obtained in step S1. The mixture was heated to 65 °C and stirred for 2 hours, then heated to 110 °C and stirred for 4 hours. After the reaction was complete, the product was filtered and washed with acetone. The resulting solid was dried in air at 120 °C for 12 hours and ground into powder. The powder was ball-milled at 2000 rpm to prepare the dicarboxylic acid zinc-manganese bimetallic catalyst. The catalyst evaluation results are shown in Table 1.

[0056] Comparative Example 1

[0057] 130 parts by mass of zinc salt and 15.2 parts by mass of manganese salt were added to 1000 parts by mass of methylcyclohexane and mixed thoroughly. 20 parts by mass of lauryl diacid were dissolved in 200 parts by mass of methylcyclohexane and mixed thoroughly. This mixture was then added to the solution obtained in step S1. The mixture was heated to 65 °C and stirred for 2 hours, then heated to 110 °C and stirred for 4 hours. After the reaction was complete, the product was filtered and washed with acetone. The resulting solid was dried in air at 120 °C for 12 hours and ground into powder. The powder was ball-milled at 1500 rpm to obtain the catalyst. The catalyst evaluation results are shown in Table 1.

[0058] Comparative Example 2

[0059] 195 parts by mass of zinc salt and 228 parts by mass of manganese salt were added to 1000 parts by mass of methylcyclohexane and mixed thoroughly. 20 parts by mass of lauryl iodide were dissolved in 200 parts by mass of methylcyclohexane and mixed thoroughly. This mixture was then added to the solution obtained in step S1. The mixture was heated to 65 °C and stirred for 2 hours, then heated to 110 °C and stirred for 4 hours. After the reaction was complete, the product was filtered and washed with acetone. The resulting solid was dried in air at 120 °C for 12 hours and ground into powder. The powder was ball-milled at 1500 rpm to obtain the catalyst. The catalyst evaluation results are shown in Table 1.

[0060] Comparative Example 3

[0061] 130 parts by weight of zinc salt were added to 1000 parts by weight of methylcyclohexane and mixed thoroughly. 20 parts by weight of lauryl diacid were dissolved in 200 parts by weight of methylcyclohexane and mixed thoroughly. This mixture was then added to the solution obtained in step S1. The mixture was heated to 65 °C and stirred for 2 hours, then heated to 110 °C and stirred for 4 hours. After the reaction was complete, the product was filtered and washed with acetone. The resulting solid was dried in air at 120 °C for 12 hours and ground into powder. The powder was ball-milled at 1500 rpm to obtain the catalyst. The catalyst evaluation results are shown in Table 1.

[0062] Comparative Example 4

[0063] 22.8 parts by weight of manganese salt were added to 1000 parts by weight of methylcyclohexane and mixed thoroughly. 20 parts by weight of lauryl diacid were dissolved in 200 parts by weight of methylcyclohexane and mixed thoroughly. This mixture was then added to the solution obtained in step S1. The mixture was heated to 65 °C and stirred for 2 hours, then heated to 110 °C and stirred for 4 hours. After the reaction was complete, the product was filtered and washed with acetone. The resulting solid was dried in air at 120 °C for 12 hours and ground into powder. The powder was ball-milled at 1500 rpm to obtain the catalyst. The catalyst evaluation results are shown in Table 1.

[0064] Comparative Example 5

[0065] The evaluation was conducted using zinc glutarate, a common commercial catalyst. The evaluation results are shown in Table 1.

[0066] Table 1 Catalyst evaluation results in each example

[0067]

[0068] As shown in Table 1, the zinc-manganese dicarboxylic acid bimetallic catalyst exhibits the best catalytic performance when the molar ratio of zinc to manganese is 5:1. The catalyst activity is 201.5 g / gcat, with a low ether content. It meets the needs of industrial production and has good industrial prospects. Meanwhile, lauryl diacid shows the best catalytic effect as a dicarboxylic acid coordination bimetallic catalyst.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the preparation of a catalyst for the synthesis of polypropylene carbonate, characterized in that: The catalyst is a zinc-manganese bimetallic catalyst of a dibasic acid, wherein the molar ratio of zinc to manganese ranges from (10:1) to (1:1); the particle size of the catalyst is 10-50 nm; The preparation method of the catalyst comprises the following steps: S1. zinc salt and manganese salt are added to methylcyclohexane, mixed uniformly, and prepared into A solution; S2. the dibasic acid is dissolved in methylcyclohexane, mixed uniformly, and prepared into B solution; S3. B solution is added to A solution, fully stirred at heating temperature 1, and then fully stirred at heating temperature 2; S4. the product obtained in S3 is filtered and washed with acetone; S5. the product obtained in S4 is dried in air atmosphere and ground into powder; S6. the powder obtained in S5 is ball milled in a ball mill to obtain the catalyst; In step S1, the zinc salt is zinc oxide; the manganese salt is manganese oxide; the mass fraction of methylcyclohexane is 1000; the mass fraction of the zinc salt is 16.2-162; In step S2, the dibasic acid is one of maleic acid, glutaric acid, adipic acid, suberic acid, lauric acid, 2,3-dimethyl-butane diacid, barbital acid, and 2,2'-diphenyl dicarboxylic acid; the mass fraction of the dibasic acid is 20, and the mass fraction of methylcyclohexane is 200; In step S6, the ball milling speed is 1000-2000 rpm.

2. The method for preparing a catalyst for synthesizing polypropylene carbonate according to claim 1, characterized by: The molar ratio of zinc to manganese is 5:

1.

3. The method for preparing a catalyst for synthesizing polypropylene carbonate according to claim 1, characterized by: The mass fraction of the zinc salt is 120-150; the mass fraction of the manganese salt is 1.42-142.

4. The method for preparing a catalyst for synthesizing polypropylene carbonate according to claim 1, characterized by: The mass fraction of the manganese salt is 10.5-131.

5.

5. The method for preparing a catalyst for synthesizing polypropylene carbonate according to claim 1, characterized by: In step S3, the heating temperature 1 is 65 ℃, and the stirring time is 2 hours; the heating temperature 2 is 110 ℃, and the stirring time is 4 hours.

6. The method for preparing a catalyst for synthesizing polypropylene carbonate according to claim 1, characterized by: In step S5, the drying temperature is 120 ℃, and the drying time is 12 hours.

7. A catalyst prepared by the preparation method of any one of claims 1-6.

8. A polymerization process for polypropylene carbonate characterized by: A catalyst prepared by the preparation method of any one of claims 1-6.

9. The polymerization process for polypropylene carbonate according to claim 8, characterized by: The polycyclohexane is obtained by copolymerization of carbon dioxide and propylene oxide, the copolymerization is carried out in a polymerization kettle; the catalyst is used in an amount of 0.2-2 % of the mass of propylene oxide, the carbon dioxide pressure is 1-3.5 MPa, the polymerization temperature is 50-100 ℃, and the reaction time is 3-20 h.

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