Pd supported pan catalysts, methods of making the same, and methods of making carboxylate esters using the same

Abstract

The application belongs to the technical field of olefin hydroesterification and its catalyst, and particularly relates to a Pd supported PAN catalyst, a preparation method thereof, and a method for preparing carboxylic acid ester by using the same. The preparation method of the Pd supported PAN catalyst comprises the following steps: vacuum drying PAN, then pre-oxidizing to obtain pre-oxidized PAN; adding the pre-oxidized PAN into a sulfonating reagent solution, stirring and reacting, taking out, washing, drying to obtain sulfonated PAN; placing the sulfonated PAN in a Pd compound solution under light shielding and N2 atmosphere, filtering after completing the impregnation, washing and drying to obtain the Pd supported PAN catalyst. The preparation method of the Pd supported PAN catalyst provided by the application has many active sites of the catalyst, and the catalyst is applied in the preparation of carboxylic acid ester, so that the catalyst can be recycled and reused, and the stability of the catalyst is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of olefin hydroesterification reaction and its catalyst, and particularly relates to a Pd supported PAN catalyst and a preparation method thereof, and a method for preparing carboxylic acid ester by using the same. BACKGROUND

[0002] Due to the important position of the alkoxy carbonylation of olefins in the production of chemicals, the alkoxy carbonylation of olefins has attracted widespread attention. Accordingly, the Lucaite International Company developed a two-step process for producing methyl methacrylate (MMA), in which the first step of the carbonylation of ethylene is catalyzed by a palladium / biphosphine / acid system. The reaction has the advantages of mild reaction conditions, high atom economy, and high product yield, and is a very promising green route for producing MMA. However, there are many problems in the catalytic system used for the preparation of methyl methacrylate by methoxycarbonylation. For example, the homogeneous palladium catalyst has high separation energy consumption, the ionic liquid catalyst is complicated to prepare and expensive, and in addition, most of the existing catalytic systems need to add additional acid additives, etc. Therefore, it is of great significance to develop a high-efficiency and low-cost heterogeneous catalytic system, realize the recovery of noble metal Pd, and efficiently prepare methyl methacrylate.

[0003] At present, the types of heterogeneous hydroesterification reaction catalysts mainly include supported transition metal complexes, biphasic systems and metal oxides, etc. Among them, the supported transition metal complexes have higher reaction activity and adjustable selectivity under mild conditions, and thus have better application potential.

[0004] CN102671704A discloses a Pd complex catalyst and a preparation method and application thereof, and the structure formula of the Pd complex catalyst is R is methyl, ethyl, propyl, benzhydryl, the Pd complex catalyst has good stability; in the case of using a small amount of catalyst, the Heck reaction can be promoted, and high catalytic activity is shown, realizing the catalysis of the Heck reaction, but the complex catalyst is still homogeneous in the reaction process, which is not conducive to the separation of the catalyst.

[0005] CN103586074A discloses a method for preparing a fiber-supported metal nickel / palladium catalyst. The method uses amino-functionalized polyacrylonitrile fiber as a carrier, and utilizes the coordination reaction between the amino groups on the surface of the carrier and the metal ions Ni and Pd to simultaneously load the two metal ions on the surface of the fiber carrier. The coordination effect firmly combines the metal and the carrier, and the electron-donating effect of the amino group reduces the electron binding energy of the metal, further improving its catalytic activity. The metal ions are reduced to a small, highly active metal element using a reducing agent, thereby preparing a fiber-supported metal nickel / palladium catalyst with good stability and high catalytic activity. However, the acrylonitrile fiber carrier obtained by simple amino modification has poor thermal stability. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for preparing a Pd-loaded PAN catalyst. The prepared catalyst has multiple active sites and is applied in the preparation of carboxylic esters, thereby realizing catalyst recycling and reuse and improving catalyst stability.

[0007] The preparation method of the Pd-loaded PAN catalyst of the present invention comprises the following steps:

[0008] (1) vacuum drying PAN and then pre-oxidizing it to obtain pre-oxidized PAN;

[0009] (2) adding the pre-oxidized PAN to the sulfonation reagent solution, stirring the reaction, taking it out, washing it, and drying it to obtain the sulfonated PAN;

[0010] (3) In a dark environment and under a nitrogen atmosphere, the sulfonated PAN is placed in a Pd compound solution. After impregnation, the solution is filtered, washed, and dried to obtain a Pd-loaded PAN catalyst.

[0011] Preferably, the vacuum drying temperature in step (1) is 50-100° C., and the drying time is 4-24 h.

[0012] Further preferably, the pre-oxidation in step (1) adopts an atmosphere of air, 1% O2 / N2, or O2, the pre-oxidation temperature is 150-250°C, and the pre-oxidation time is 5-200 min.

[0013] Preferably, the sulfonating agent in step (2) is one of concentrated sulfuric acid, chlorosulfonic acid, sulfur trioxide, aminosulfonic acid, and sulfite; the solvent used in the sulfonating agent solution is one of toluene, dichloroethane, dichloromethane, and deionized water; and the concentration of the sulfonating agent in the sulfonating agent solution is 1-20 wt.%.

[0014] Preferably, the reaction temperature of step (2) is -10°C-60°C, and the reaction time is 3-12 hours; the drying temperature of step (2) is 50-120°C, and the drying time is 4-12 hours. The washing liquid used in step (2) is deionized water, toluene or dichloromethane.

[0015] Preferably, the mass ratio of the pre-oxidized PAN to the sulfonation reagent in step (2) is (1-5):(5-10).

[0016] Preferably, the Pd compound in step (3) is one of palladium acetate, palladium chloride, palladium acetylacetonate, and allylpalladium chloride; the solvent used in the Pd compound solution is one of methanol, toluene, ethanol, and deionized water; and the concentration of Pd in ​​the Pd compound solution is 0.1-1 wt.%.

[0017] Preferably, the immersion time in step (3) is 6 hours to 72 hours. The washing in step (3) is performed by alternating washing with methanol and water.

[0018] A Pd-loaded PAN catalyst is prepared by the preparation method of the Pd-loaded PAN catalyst.

[0019] The method for preparing carboxylic acid ester by using the Pd-loaded PAN catalyst comprises the following steps: mixing alcohol and the Pd-loaded PAN catalyst, adding terminal olefin, pressurizing, and heating to react to obtain carboxylic acid ester.

[0020] The temperature is raised to 50-180° C., preferably 80-120° C., the reaction pressure is controlled at 1-10 MPa, preferably 1-4 MPa; and the reaction time is controlled at 2-10 h.

[0021] The alcohol is one of methanol, ethanol, ethylene glycol and glycerol, and is also used as the solvent of the reaction system.

[0022] The terminal olefin is one of ethylene, propylene, butylene, butadiene and styrene, and the purity of the terminal olefin is 90-100%.

[0023] The gas used for pressurization is CO or a mixture of CO and N2, and the purity of the gas used is 90-100%.

[0024] Specifically, the method for preparing carboxylic acid ester using Pd-supported PAN catalyst comprises the following steps:

[0025] (1) PAN is dried at 50-100° C. under vacuum conditions for 4-24 h, and then pre-oxidized at 150-250° C. for 5-200 min in an atmosphere of air, 1% O 2 / N 2 , or O 2 to obtain pre-oxidized PAN.

[0026] (2) Add the pre-oxidized PAN to the sulfonation reagent solution, stir and react at -10°C-60°C for 3-12 hours, remove, wash, and dry at 50-120°C for 4-12 hours to obtain sulfonated PAN.

[0027] (3) In a dark, N2 atmosphere, sulfonated PAN was placed in a Pd compound solution and stored for 1-2 days before filtering to obtain brown-red fibers. The fibers were washed alternately with methanol and water until the solution was colorless and dried at 60°C for 12 h to obtain a Pd-loaded PAN catalyst. The reaction formula is:

[0028]

[0029] (4) In a 250 mL autoclave, alcohol and Pd-loaded PAN catalyst were added in sequence, followed by the addition of terminal olefins. The autoclave was sealed and replaced three times with CO or a mixture of CO and N2. CO or a mixture of CO and N2 was then added to the autoclave until the pressure reached 1-4 MPa. The temperature was slowly raised to 80-120°C using a temperature controller and the reaction was continued for 2-10 h. The reaction was then cooled to room temperature, the autoclave was unloaded, and the resulting carboxylate was quantitatively analyzed using an Agilent 6890.

[0030] The present invention pre-oxidizes and sulfonates polyacrylonitrile, introducing sulfonate ions and subsequently using it as a solid acid catalyst for catalytic reactions. Furthermore, the pre-oxidized PAN undergoes cyclization, resulting in a structure filled with unsaturated nitrogen atoms, which facilitates the fixation of the Pd complex. The present invention prepares a PAN-supported Pd-based complex through pre-oxidation, sulfonation, and impregnation of PAN. This complex is then used in the carbonylation of olefins, addressing the difficulty in recovering homogeneous hydroesterification catalysts while achieving higher reaction efficiency.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The preparation method of the Pd-loaded PAN catalyst of the present invention modifies and fixes Pd and sulfonate groups on a polyacrylonitrile carrier, which is beneficial to the synergistic effect between Pd and H ions and N on polyacrylonitrile, thereby improving the reaction activity of the Pd site.

[0033] (2) The Pd-loaded PAN catalyst prepared by the present invention is a heterogeneous catalyst with polyacrylonitrile as a carrier. In the preparation of carboxylic acid esters, it is beneficial to separate the catalyst system from the reaction raw materials and products, reduce separation energy consumption, and realize the recovery and reuse of the catalyst.

[0034] (3) The Pd-loaded PAN catalyst prepared by the present invention has a variety of functional groups on the polyacrylonitrile carrier, and its structure and properties are flexible and adjustable, which is beneficial to improving the reaction activity and stability of the catalyst. DETAILED DESCRIPTION

[0035] The present invention will be further described below with reference to specific embodiments.

[0036] In the following Examples and Comparative Examples, the alcohols were all of 90%-100% purity by mass, the CO or CO and N₂ mixtures were all of 90%-100% purity by mass, all other chemical reagents used were commercially available, and all equipment used was existing. Any conditions not specified in the Comparative Examples were the same as those in Example 1.

[0037] Example 1

[0038] The method for preparing carboxylic acid ester using Pd-supported PAN catalyst comprises the following steps:

[0039] (1) PAN was dried at 100°C for 4 h under vacuum conditions and then pre-oxidized at 150°C for 200 min using air to obtain pre-oxidized PAN.

[0040] (2) 0.2 g of pre-oxidized PAN was added to a chlorosulfonic acid / dichloromethane solution (20 mL, chlorosulfonic acid concentration 1 wt.%), stirred at 0°C for 6 h, taken out, washed with dichloromethane three times, and dried at 50°C for 12 h to obtain sulfonated PAN.

[0041] (3) In a dark, N2 atmosphere, sulfonated PAN was immersed in a palladium acetate methanol solution with a Pd concentration of 1 wt.%, stored for 6 h, and then filtered to obtain a brown-red fiber. The fiber was washed alternately with methanol and water until the solution was colorless, and dried at 60°C for 12 h to obtain a Pd-loaded PAN catalyst.

[0042] (4) In a 250 mL autoclave, 100 mL of methanol and 1 g of Pd-supported PAN catalyst were added in sequence, followed by the introduction of 0.08 mol of ethylene. The autoclave was sealed, and the reactor was replaced with CO three times. CO was then refilled until the reactor pressure reached 4 MPa. The temperature was slowly raised to 80°C using a temperature controller and the reaction was continued for 10 h. The reaction was then cooled to room temperature, the autoclave was unloaded, and the resulting carboxylate was quantitatively analyzed using an Agilent 6890. The ethylene conversion was 99%, and the selectivity for the product methyl propionate was 99%.

[0043] Example 2

[0044] The method for preparing carboxylic acid ester using Pd-supported PAN catalyst comprises the following steps:

[0045] (1) PAN was dried at 50°C for 12 h under vacuum conditions, and then pre-oxidized at 250°C for 5 min using 1% O2 / N2 to obtain pre-oxidized PAN.

[0046] (2) 0.2 g of pre-oxidized PAN was added to a concentrated sulfuric acid / toluene solution (20 mL, concentrated sulfuric acid concentration 10 wt.%), stirred at 60° C. for 3 h, taken out, washed with toluene three times, and dried at 120° C. for 4 h to obtain sulfonated PAN.

[0047] (3) In a dark, N2 atmosphere, sulfonated PAN was immersed in an ethanol solution of palladium chloride with a Pd concentration of 0.6 wt.%, stored for 24 h, and then filtered to obtain brown-red fibers. The fibers were washed alternately with methanol and water until the solution was colorless, and dried at 60°C for 12 h to obtain a Pd-loaded PAN catalyst.

[0048] (4) In a 250 mL autoclave, 100 mL of methanol and 1 g of Pd-supported PAN catalyst were added, followed by the addition of 0.08 mol of styrene. The autoclave was sealed and replaced three times with a mixture of CO and N₂. The mixture of CO and N₂ was then added until the pressure reached 2 MPa. The temperature was slowly raised to 120°C using a temperature controller and the reaction was continued for 2 h. The reaction was then cooled to room temperature and the autoclave was unloaded. The resulting carboxylate was quantitatively analyzed using an Agilent 6890. The styrene conversion was 96%, and the selectivity for the product, methyl phenylpropionate, was 98%.

[0049] Repeatability: After the reaction, the catalyst was removed, washed several times with methanol, dried at 80°C for 6 h, and the above reaction was repeated. After 10 reactions, the conversions were 96%, 96%, 95%, 95%, 94%, 94%, 95%, and 94%, respectively; and the selectivities were 98%, 98%, 98%, 98%, 97%, 97%, 98%, 97%, and 97%, respectively.

[0050] Example 3

[0051] The method for preparing carboxylic acid ester using Pd-supported PAN catalyst comprises the following steps:

[0052] (1) PAN was dried at 80°C for 12 h under vacuum conditions and then pre-oxidized at 200°C for 180 min in an O2 atmosphere to obtain pre-oxidized PAN.

[0053] (2) 1 g of pre-oxidized PAN was added to a sulfamic acid / deionized water solution (20 mL, sulfamic acid concentration 20 wt.%), stirred at -10°C for 12 h, taken out, washed with deionized water three times, and dried at 60°C for 8 h to obtain sulfonated PAN.

[0054] (3) In a dark, N2 atmosphere, sulfonated PAN was immersed in a toluene solution of acetylacetonate palladium with a Pd concentration of 0.1 wt.%, stored for 72 h, and then filtered to obtain a brown-red fiber. The fiber was washed alternately with methanol and water until the solution was colorless, and dried at 60°C for 12 h to obtain a Pd-loaded PAN catalyst.

[0055] (4) In a 250 mL autoclave, 100 mL of methanol and 1 g of Pd-supported PAN catalyst were added, followed by the introduction of 0.2 mol of ethylene. The autoclave was sealed and replaced with CO three times. CO was then introduced to a pressure of 2 MPa. The temperature was slowly raised to 120°C using a temperature controller and the reaction was continued for 2 h. The reaction was then cooled to room temperature and the autoclave was unloaded. The resulting carboxylate was quantitatively analyzed using an Agilent 6890. The ethylene conversion was 98%, and the selectivity for the product methyl propionate was 96%.

[0056] Example 4

[0057] The method for preparing carboxylic acid ester using Pd-supported PAN catalyst comprises the following steps:

[0058] (1) PAN was dried at 60°C for 18 h under vacuum conditions, and then pre-oxidized at 180°C for 60 min in an O2 atmosphere to obtain pre-oxidized PAN.

[0059] (2) 0.8 g of pre-oxidized PAN was added to a SO3 / dichloroethane solution (20 mL, SO3 concentration 10 wt.%), stirred at 25°C for 8 h, taken out, washed three times with deionized water, and dried at 80°C for 6 h to obtain sulfonated PAN.

[0060] (3) In a dark, N2 atmosphere, sulfonated PAN was immersed in a deionized aqueous solution of allylpalladium chloride with a Pd concentration of 0.5 wt.%, stored for 36 h, and then filtered to obtain brown-red fibers. The fibers were washed alternately with methanol and water until the solution was colorless, and dried at 60°C for 12 h to obtain a Pd-loaded PAN catalyst.

[0061] (4) In a 250 mL autoclave, 100 mL of ethanol and 1 g of Pd-supported PAN catalyst were added in sequence, followed by the introduction of 0.1 mol of ethylene. The autoclave was sealed and replaced with CO three times. CO was then refilled until the pressure reached 3 MPa. The temperature was slowly raised to 110°C using a temperature controller and the reaction was continued for 4 h. The reaction was then cooled to room temperature and the autoclave was unloaded. The resulting carboxylate was quantitatively analyzed using an Agilent 6890. The ethylene conversion was 98%, and the selectivity for the product methyl propionate was 99%.

[0062] Comparative Example 1

[0063] In a 250 mL high-pressure reactor, 0.05 mmol PdCl2(PPh3)2, 100 mL methanol were added in turn, the reactor was replaced with CO for 3 times, 0.6 mol ethylene was injected, and then CO was filled into the reactor until the pressure reached 4 MPa. The temperature was slowly increased to 80°C by a temperature controller, and the reaction was carried out for 10 h. After cooling to room temperature, the reactor was opened, and the reaction liquid was analyzed quantitatively by Agilent 6890. No product methyl propionate was detected.

[0064] Comparative Example 2

[0065] In a 250 mL high-pressure reactor, 0.05 mmol Pd(OAc)2, 0.5 mmol methanesulfonic acid, 0.4 mmol 1,2-bis[(di-tert-butylphosphine)methyl]benzene, 100 mL methanol were added in turn, the reactor was replaced with CO for 3 times, 0.2 mol ethylene was injected, and then CO was filled into the reactor until the pressure reached 3 MPa. The temperature was slowly increased to 80°C by a temperature controller, and the reaction was carried out for 6 h. After cooling to room temperature, the reactor was opened, and the reaction liquid was analyzed quantitatively by Agilent 6890. The ethylene conversion rate was 92%, and the selectivity of the product methyl propionate was 90%.

[0066] Comparative Example 3

[0067] The same as Example 1, but the sulfonation step (2) was removed. No product methyl propionate was detected.

[0068] Comparative Example 4

[0069] The same as Example 1, but the pre-oxidation step (1) was cancelled. No product methyl propionate was detected.

[0070] Comparative Example 5

[0071] The same as Example 1, but the sulfonation temperature was replaced by 100°C. No product methyl propionate was detected.

[0072] Of course, the above only describes the preferred embodiments of the present application, and should not be considered as limiting the scope of the embodiments of the present application. The present application is also not limited to the above examples, and equivalent changes and improvements made by those skilled in the art within the scope of the present application should be attributed to the patent coverage of the present application.

Claims

1. A method for preparing a Pd-supported PAN catalyst for olefin carbonylation, characterized in that: The following steps are involved: (1) PAN is vacuum dried and then pre-oxidized to obtain pre-oxidized PAN; (2) Add the pre-oxidized PAN to the sulfonation reagent solution, stir and react at -10℃-60℃, take out, wash and dry to obtain sulfonated PAN; (3) In a light-proof, N2 atmosphere, sulfonated PAN is placed in a Pd compound solution. After impregnation, the solution is filtered, washed, and dried to obtain a Pd-loaded PAN catalyst.

2. The method for preparing a Pd-supported PAN catalyst for olefin carbonylation according to claim 1, wherein: The vacuum drying temperature of step (1) is between 50-100°C and the drying time is 4-24h.

3. The method for preparing a Pd-supported PAN catalyst for olefin carbonylation according to claim 2, wherein: The pre-oxidation atmosphere in step (1) is one of air and O2, the pre-oxidation temperature is 150-250°C, and the pre-oxidation time is 5-200 minutes.

4. The method for preparing a Pd-supported PAN catalyst for olefin carbonylation according to claim 1, wherein: The sulfonating agent in step (2) is one of concentrated sulfuric acid, chlorosulfonic acid, sulfur trioxide, aminosulfonic acid, and sulfite. The solvent used in the sulfonating agent solution is one of toluene, dichloroethane, dichloromethane, and deionized water. The concentration of the sulfonating agent in the sulfonating agent solution is 1-20 wt.%.

5. The method for preparing a Pd-supported PAN catalyst for olefin carbonylation according to claim 1, wherein: The reaction time of step (2) is 3-12 hours.

6. The method for preparing a Pd-supported PAN catalyst for olefin carbonylation according to claim 1, wherein: The mass ratio of the pre-oxidized PAN to the sulfonation reagent in step (2) is (1-5):(5-10).

7. The method for preparing a Pd-supported PAN catalyst for olefin carbonylation according to claim 1, wherein: The Pd compound in step (3) is one of palladium acetate, palladium chloride, palladium acetylacetonate, and allylpalladium chloride. The solvent used in the Pd compound solution is one of methanol, toluene, ethanol, and deionized water. The concentration of Pd in ​​the Pd compound solution is 0.1-1 wt.%.

8. The method for preparing a Pd-supported PAN catalyst for olefin carbonylation according to claim 1, wherein: The immersion time of step (3) is 6h-72h.

9. A Pd-supported PAN catalyst for olefin carbonylation, characterized in that: The catalyst is prepared by the method for preparing the Pd-supported PAN catalyst for olefin carbonylation according to any one of claims 1 to 8.

10. A method for preparing carboxylic acid esters using the Pd-supported PAN catalyst for olefin carbonylation according to claim 9, characterized in that: The following steps are involved: Mix alcohol and Pd-loaded PAN catalyst, add terminal olefin, pressurize and heat to react to obtain carboxylic acid ester.

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