Pd-loaded PAN catalyst and preparation method thereof, and method for preparing carboxylic ester by using Pd-loaded PAN catalyst

Abstract

The invention belongs to the technical field of olefin hydroesterification reaction and catalysts thereof, and particularly relates to a Pd-loaded PAN catalyst, a preparation method thereof and a method for preparing carboxylic ester by adopting the Pd-loaded PAN catalyst. The preparation method of the Pd-loaded PAN catalyst comprises the following steps: performing vacuum drying on PAN, and then pre-oxidizing to obtain pre-oxidized PAN; adding the pre-oxidized PAN into a sulfonating reagent solution, stirring for reaction, taking out, washing and drying to obtain sulfonated PAN; and putting the sulfonated PAN into a Pd compound solution in a dark N2 atmosphere, and filtering, washing and drying after dipping to obtain the Pd-loaded PAN catalyst. According to the preparation method of the Pd-loaded PAN catalyst provided by the invention, the prepared catalyst has many active sites and is applied to preparation of carboxylic ester, so that the catalyst is recycled, and the stability of the catalyst is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of olefin hydroesterification reaction and catalysts thereof, and specifically relates to a Pd-loaded PAN catalyst and a preparation method thereof, and a method for preparing carboxylic acid esters by using the same. Background Art

[0002] Since the alkoxycarbonylation reaction of olefins occupies an important position in the production of chemicals, the alkoxycarbonylation reaction of olefins has attracted widespread attention. Based on this, Lucite International has developed a two-step process for the production of methyl methacrylate (MMA), in which the first step of carbonylation of ethylene is catalyzed by a palladium / bisphosphine / 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 the production of MMA. However, there are many problems with the catalytic system currently used for the preparation of methyl acrylate by methoxycarbonylation. For example, homogeneous palladium catalysts have high separation energy consumption, ionic liquid catalysts are cumbersome to prepare, and are expensive. In addition, most of the existing catalytic systems require additional acid additives, etc. Therefore, it is of great significance to develop a high-efficiency and low-cost multiphase catalytic system to achieve the recovery of precious metal Pd and the efficient preparation of methyl acrylate.

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

[0004] CN102671704A discloses a Pd complex catalyst and a preparation method and application thereof. The structural formula of the Pd complex catalyst is R is methyl, ethyl, propyl, or diphenylmethyl, and the Pd complex catalyst has good stability. When a small amount of catalyst is used, the Heck reaction can be promoted and a high catalytic activity is exhibited to achieve catalysis of the Heck reaction. However, the complex catalyst is still not homogeneous during the reaction, 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 adopts amine-functionalized polyacrylonitrile fiber as a carrier, utilizes the coordination reaction between the amine groups on the surface of the carrier and the metal ions Ni and Pd, and simultaneously supports the two metal ions on the surface of the fiber carrier. The coordination effect firmly combines the metal and the carrier together. The electron-donating effect of the amine groups reduces the electron binding energy of the metal, further improving its catalytic activity. The metal ions are reduced to small-sized and highly active metal elements using a reducing agent, and a fiber-supported metal nickel / palladium catalyst with good stability and high catalytic activity is prepared. However, the acrylonitrile fiber carrier obtained by simple amine 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 acid esters to achieve catalyst recycling and improve catalyst stability.

[0007] The method for preparing 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 out, washing, and drying to obtain the sulfonated PAN;

[0010] (3) In a light-proof and N2 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 1-20wt.%.

[0014] Preferably, the reaction temperature of step (2) is -10°C-60°C, and the reaction time is 3-12h; the drying temperature of step (2) is 50-120°C, and the time is 4-12h. 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 allyl palladium chloride; the solvent used for the Pd compound solution is one of methanol, toluene, ethanol, and deionized water; and the concentration of Pd in ​​the Pd compound solution is 0.1-1wt.%.

[0017] Preferably, the immersion time of step (3) is 6h-72h. 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, heating and reacting to obtain carboxylic acid ester.

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

[0021] The alcohol is one of methanol, ethanol, ethylene glycol and propylene glycol, 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 mass purity of the terminal olefin is 90-100%.

[0023] The gas used for the pressurization is CO or a mixture of CO and N2, and the mass 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. for 4-24 h under vacuum conditions, and then pre-oxidized at 150-250° C. for 5-200 min in an atmosphere of air, 1% O2 / N2, or O2 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 environment and N2 atmosphere, sulfonated PAN was placed in a Pd compound solution and filtered after storage for 1-2 days 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, and terminal olefins were charged. The autoclave was sealed, and the autoclave was replaced with CO or a mixture of CO and N2 for three times. CO or a mixture of CO and N2 was then charged until the pressure of the autoclave was 1-4 MPa. The temperature was slowly raised to 80-120°C by a temperature controller to react for 2-10 h, and then cooled to room temperature. The autoclave was unloaded, and the obtained carboxylate was quantitatively analyzed using Agilent 6890.

[0030] The present invention introduces sulfonate ions after pre-oxidation and sulfonation of polyacrylonitrile, and then uses it as a solid acid catalyst for catalytic reaction. In addition, PAN after pre-oxidation undergoes cyclization, and the structure is full of unsaturated N atoms, which is conducive to the fixation of Pd complexes. The present invention prepares PAN-loaded Pd-based complexes through the techniques of pre-oxidation, sulfonation, impregnation, etc. of PAN, and uses the complexes for carbonylation reaction of olefins, which can solve the problem of difficulty in recycling homogeneous hydroesterification catalysts and obtain 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 multiphase 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 the structure and properties are flexibly 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 in conjunction with specific embodiments.

[0036] In the following examples and comparative examples, the mass purity of the alcohol is 90%-100%, the mass purity of CO or the mixed gas of CO and N2 is 90%-100%, and the other chemical reagents used are all commercially available products, and the equipment used is all existing equipment. The conditions not specified in the comparative examples are 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 with air at 150°C for 200 min 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 3 times, and dried at 50° C. for 12 h to obtain sulfonated PAN.

[0041] (3) In a dark environment and 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 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.

[0042] (4) In a 250 mL autoclave, 100 mL of methanol and 1 g of Pd-supported PAN catalyst were added in sequence, and 0.08 mol of ethylene was charged. The autoclave was sealed, and the autoclave was replaced with CO for 3 times. CO was then charged until the pressure of the autoclave reached 4 MPa. The temperature was slowly raised to 80° C. by a temperature controller to react for 10 h, and then cooled to room temperature. The autoclave was unloaded, and the obtained carboxylic acid ester was quantitatively analyzed by Agilent 6890. The ethylene conversion rate was 99%, and the selectivity of 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 3 times, and dried at 120° C. for 4 h to obtain sulfonated PAN.

[0047] (3) In a dark environment and 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 in sequence, and 0.08 mol of styrene was charged. The autoclave was sealed, and the autoclave was replaced with a mixed gas of CO and N2 for 3 times. The mixed gas of CO and N2 was then charged until the pressure of the autoclave was 2 MPa. The temperature was slowly raised to 120° C. by a temperature controller to react for 2 h, and then cooled to room temperature. The autoclave was unloaded, and the obtained carboxylic acid ester was quantitatively analyzed by Agilent 6890. The styrene conversion rate was 96%, and the selectivity of the product methyl phenylpropionate was 98%.

[0049] Repeatability: After the reaction, the catalyst was taken out, washed with methanol several times, dried at 80°C for 6 hours, and the above reaction was repeated. After 10 reactions, the conversion rates were 96%, 96%, 95%, 95%, 95%, 94%, 94%, 95%, and 94%, respectively; 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 an aminosulfonic acid / deionized water solution (20 mL, aminosulfonic 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 environment and N2 atmosphere, sulfonated PAN was immersed in a toluene solution of acetylacetone palladium with a Pd concentration of 0.1 wt.%, stored for 72 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.

[0055] (4) In a 250 mL autoclave, 100 mL of methanol and 1 g of Pd-supported PAN catalyst were added in sequence, and 0.2 mol of ethylene was charged into the autoclave. The autoclave was sealed, and the autoclave was replaced with CO for 3 times. CO was then charged into the autoclave until the pressure of the autoclave reached 2 MPa. The temperature was slowly raised to 120° C. by a temperature controller to react for 2 h, and then cooled to room temperature. The autoclave was unloaded, and the obtained carboxylic acid ester was quantitatively analyzed by Agilent 6890. The ethylene conversion rate was 98%, and the selectivity of 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 light-proof, 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, and 0.1 mol of ethylene was charged into the autoclave. The autoclave was sealed, and the autoclave was replaced with CO for 3 times. CO was then charged into the autoclave until the pressure of the autoclave reached 3 MPa. The temperature was slowly raised to 110° C. by a temperature controller to react for 4 h, and then cooled to room temperature. The autoclave was unloaded, and the obtained carboxylic acid ester was quantitatively analyzed by Agilent 6890. The ethylene conversion rate was 98%, and the selectivity of the product methyl propionate was 99%.

[0062] Comparative Example 1

[0063] In a 250mL autoclave, 0.05mmol PdCl2(PPh3)2 and 100mL methanol were added in sequence, the autoclave was sealed, the autoclave was replaced with CO for 3 times, 0.6mol ethylene was flushed in, and CO gas was then charged until the pressure of the autoclave was 4MPa. The temperature was slowly raised to 80°C by a temperature controller, the reaction was continued for 10h, cooled to room temperature, the autoclave was unloaded, and the liquid obtained by the reaction was quantitatively analyzed by Agilent 6890. The product methyl propionate was not detected.

[0064] Comparative Example 2

[0065] In a 250mL autoclave, 0.05mmol Pd(OAc)2, 0.5mmol methanesulfonic acid, 0.4mmol 1,2-bis[(di-tert-butylphosphino)methyl]benzene, and 100mL methanol were added in sequence, the autoclave was sealed, the autoclave was replaced with CO for 3 times, 0.2mol ethylene was flushed in, and CO gas was then charged until the pressure of the autoclave was 3MPa. The temperature was slowly raised to 80°C by a temperature controller, the reaction was carried out for 6h, cooled to room temperature, the autoclave was unloaded, and the liquid obtained by the reaction was quantitatively analyzed 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 without the sulfonation step (2), the product methyl propionate was not detected.

[0068] Comparative Example 4

[0069] The same as Example 1, but the pre-oxidation step (1) was eliminated, and the product methyl propionate was not detected.

[0070] Comparative Example 5

[0071] The same as Example 1, except that the sulfonation temperature was changed to 100° C., no product methyl propionate was detected.

[0072] Of course, the above contents are only preferred embodiments of the present invention and cannot be considered to limit the scope of the embodiments of the present invention. The present invention is not limited to the above examples, and equal changes and improvements made by ordinary technicians in the technical field within the essential scope of the present invention should all fall within the scope of the patent coverage of the present invention.

Claims

1. A method for preparing a Pd-loaded PAN catalyst, characterized in that: The following steps are involved: (1) vacuum drying PAN and then pre-oxidizing it to obtain pre-oxidized PAN; (2) adding the pre-oxidized PAN to the sulfonation reagent solution, stirring the reaction, taking out, washing, and drying to obtain the sulfonated PAN; (3) In a light-proof and N2 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.

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

3. The method for preparing a Pd-loaded PAN catalyst according to claim 2, characterized in that: The pre-oxidation atmosphere in step (1) is one of air, O2 / N2, and O2, the pre-oxidation temperature is 150-250°C, and the pre-oxidation time is 5-200min.

4. The method for preparing a Pd-supported PAN catalyst 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; and the concentration of the sulfonating agent in the sulfonating agent solution is 1-20wt.%.

5. The method for preparing a Pd-supported PAN catalyst according to claim 1, characterized in that: The reaction temperature of step (2) is -10°C-60°C, and the reaction time is 3-12h.

6. The method for preparing a Pd-supported PAN catalyst according to claim 1, characterized in that: 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 according to claim 1, characterized in that: The Pd compound in step (3) is one of palladium acetate, palladium chloride, palladium acetylacetonate, and allyl palladium 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 0.1-1wt.%.

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

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

10. A method for preparing carboxylic acid esters using the Pd-supported PAN catalyst according to claim 9, characterized in that: The following steps are involved: The alcohol and Pd-loaded PAN catalyst are mixed, terminal olefin is added, pressurized, and heated to react to obtain carboxylic acid ester.

Images