SalenCrX immobilized catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of catalyst materials, in particular to a SalenCrX immobilized catalyst and a preparation method and application thereof, and the preparation method comprises the following steps: S1, preparing a Salen ligand; s2, in a protective atmosphere, mixing the Salen ligand obtained in S1, a mesoporous molecular sieve and a solvent for reaction, then adding a solution containing a Cr compound for reaction, and oxidizing a reactant to obtain a mesoporous molecular sieve packaged SalenCrX catalyst; and S3, grafting the SalenCrX catalyst packaged by the mesoporous molecular sieve obtained in the step S2 with a cocatalyst through a silanol bond. A mesoporous molecular sieve is adopted to package a SalenCrX catalyst, then a silanol bond is utilized to graft a cocatalyst, and the immobilized bifunctional catalyst is synthesized. The immobilized bifunctional catalyst facilitates separation of the catalyst and a product and is easy to form, the formed catalyst can be conveniently used in a continuous flow reactor, and the operation simplicity and economic benefits of the process are improved.

Description

Technical Field

[0001] The invention relates to the technical field of catalyst materials, and in particular to a SalenCrX solid-supported catalyst and a preparation method and application thereof. Background Art

[0002] Polypropylene carbonate is a type of polymer compound that is alternately copolymerized with CO2 and propylene oxide or CO2, propylene oxide, anhydride, etc. under the action of a catalyst. This polymer is a biodegradable polymer material with a flexible molecular chain, good gas barrier properties, and good biocompatibility. It has a broad market in the fields of film materials, biomedical materials, barrier materials, etc. The synthetic production of this material can not only solve the difficulties faced by "carbon neutrality and carbon peak", but also solve the environmental pollution caused by "white garbage". It has two-way advantages and has received great attention from the theoretical and industrial circles.

[0003] Since the Japanese scientist Inoue discovered the copolymerization of CO2 and propylene oxide into polypropylene carbonate in 1969, heterogeneous catalysts such as diethylzinc and zinc carboxylates have been widely studied. Due to the poor reaction activity and large dosage of heterogeneous catalysts, they have been replaced by homogeneous catalysts; among homogeneous catalysts, metal porphyrins, β-diimine zinc, and Salen metal complexes have been widely studied. Among them, SalenCrX catalyst has attracted great attention from researchers due to its unique catalytic activity and good thermal properties of the catalytic product.

[0004] However, in the current process of terpolymerizing propylene oxide, CO2, anhydride or glycidyl ether to synthesize polypropylene carbonate using the homogeneous catalyst SalenCrX, there is a problem that it is difficult to separate the catalyst from the product and it can only be used in an intermittent reactor but not a continuous flow reactor. Summary of the invention

[0005] In order to solve the defects in the prior art, the present invention provides a SalenCrX solid-supported catalyst and a preparation method and application thereof. The present invention uses a mesoporous molecular sieve to encapsulate the SalenCrX catalyst, and then uses a silanol bond to graft a co-catalyst to synthesize a solid-supported bifunctional catalyst. The solid-supported bifunctional catalyst is convenient for separating the catalyst from the product and is easy to shape. The formed catalyst is convenient for use in a continuous flow reactor, thereby improving the simplicity and economic benefits of the process operation.

[0006] To achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a method for preparing a SalenCrX immobilized catalyst, comprising the following steps: S1. Preparation of Salen ligand; S2. Under a protective atmosphere, the Salen ligand, mesoporous molecular sieve and solvent obtained in S1 are mixed and reacted, and then a solution containing a Cr compound is added to react, and the obtained reactant is oxidized to obtain a SalenCrX catalyst encapsulated by a mesoporous molecular sieve; S3, grafting the SalenCrX catalyst encapsulated by the mesoporous molecular sieve obtained in S2 with a co-catalyst via a silanol bond.

[0007] In some embodiments of the present invention, the preparation process of the Salen ligand is: firstly, a solvent and a diamine are mixed, dissolved under a protective atmosphere, and then a salicylaldehyde solution is added and reacted under a protective atmosphere to obtain the Salen ligand.

[0008] Preferably, the diamine is selected from any one of ethylenediamine, cyclohexylenediamine and o-phenylenediamine.

[0009] Preferably, the salicylaldehyde is selected from any one of salicylaldehyde and 3-tert-butyl salicylaldehyde.

[0010] Preferably, the molar ratio of the diamine to salicylaldehyde is 1:2.

[0011] Preferably, the mesoporous molecular sieve is selected from any one of MCM-22 and MCM-41.

[0012] Preferably, the Cr compound is selected from any one of CrCl2 and Cr(NO3)2.

[0013] Preferably, in S2, the ratio of the amount of the Salen ligand obtained in S1 to the mass of the mesoporous molecular sieve is 1:50-1:150 mmol / g.

[0014] Preferably, in S2, the molar ratio of the Salen ligand obtained in S1 to the Cr compound is 1:(1-1.5).

[0015] Preferably, in S2, the Salen ligand, mesoporous molecular sieve and solvent obtained in S1 are mixed and reacted at room temperature for 5 hours.

[0016] Preferably, in S2, the solution containing the Cr compound is added within 10 min to carry out the reaction, and the reaction time is 24 h.

[0017] Preferably, the oxidation step in S2 is specifically: placing the reactants in a dry oxygen atmosphere and reacting for 24 hours.

[0018] Preferably, the silanol bond in S3 is from any one of γ-chloropropyltrimethoxysilane, 11-chloroundecyltrimethoxysilane, 4-bromobutyltrimethoxysilane, 6-bromohexyltrimethoxysilane and 11-bromoundecyltrimethoxysilane.

[0019] Preferably, the co-catalyst is a tertiary amine satisfying the general formula [CH3(CH2) n ]3N, n=1 to 6. More preferably, n=1, which is triethylamine.

[0020] Preferably, S3 is specifically: mixing the SalenCrX catalyst encapsulated by the mesoporous molecular sieve obtained in S2 with the silanol bond raw material, adding a solvent for reaction, adding a co-catalyst after the reaction is completed, continuing the reaction, and drying the obtained reactant.

[0021] Preferably, the mass ratio of Cr and silanol bond raw materials in the mesoporous molecular sieve encapsulated SalenCrX catalyst obtained in S2 is (1~2): (1~2).

[0022] Preferably, the molar ratio of the co-catalyst to the silanol bond raw material is (1-1.5):1.

[0023] Preferably, the SalenCrX catalyst encapsulated by the mesoporous molecular sieve obtained by S2 is mixed with the silanol bond raw material, and the reaction temperature of the reaction by adding the solvent is 40° C. and the reaction time is 24 h.

[0024] Preferably, the reaction temperature of the reaction of adding the co-catalyst is 80° C. and the reaction time is 12 h.

[0025] In a second aspect, the present invention provides a SalenCrX supported catalyst prepared by the above method.

[0026] In a third aspect, the present invention provides use of the SalenCrX immobilized catalyst in the preparation of polypropylene carbonate.

[0027] The beneficial effects of the present invention are: The present invention first uses a mesoporous molecular sieve to encapsulate the SalenCrX catalyst, and then uses a silanol bond to graft a co-catalyst to synthesize a solid-supported bifunctional catalyst. The solid-supported bifunctional catalyst has high activity, is easy to separate from the product, and is easy to shape. The formed catalyst is convenient to use in a continuous flow reactor, thereby improving the simplicity and economic benefits of the process operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the surface morphology of the SalenCrNO3 catalyst encapsulated in MCM-22 of Example 4.

[0029] Figure 2 This is the surface morphology of the SalenCrNO3 catalyst encapsulated in MCM-22 after grafting the promoter in Example 4. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the technical solution of the invention, the present invention is further described in detail below in conjunction with specific implementation methods.

[0031] Example 1 This embodiment provides a method for preparing a SalenCrX immobilized catalyst, comprising the following steps: (1) Preparation of Salen ligand In a 500 mL three-necked round-bottom flask equipped with a condenser, add 200 mL of anhydrous ethanol and then add 0.02 mol of ethylenediamine; transfer 100 mL of anhydrous ethanol solution containing 0.04 mol of 3-tert-butyl salicylaldehyde to a constant pressure dropping funnel and place it on the other mouth of the round-bottom flask. After N2 is introduced to replace the air in the round-bottom flask, stir and reflux under magnetic stirring under the protection of N2 until the ethylenediamine is completely dissolved, open the constant pressure dropping funnel, add the ethanol solution of 3-tert-butyl salicylaldehyde dropwise within 10 minutes, and continue to stir and reflux under magnetic stirring under the protection of N2 for 12 hours. After the reaction is completed, stop heating, continue stirring, cool to room temperature, transfer the reaction solution to a large beaker, let it stand, filter, and wash with anhydrous ethanol 3 times, and vacuum dry at 60°C to constant weight to synthesize the Salen ligand for later use.

[0032] (2) MCM-22 encapsulated SalenCrCl catalyst Under nitrogen protection, 0.2 mol of the Salen ligand obtained in step (1) was placed in a 500 mL three-necked round-bottom flask, and then 30 g of MCM-22 and 200 mL of dry tetrahydrofuran were added (the mass ratio of the amount of Salen ligand to MCM-22 was 1:150 mmol / g); 0.2 mol of CrCl2 was dissolved in 100 mL of dry tetrahydrofuran, transferred to a constant pressure dropping funnel, and placed on the three-necked flask. At room temperature, the Salen ligand in the three-necked flask reacted with MCM-22 for 5 hours, then the constant pressure dropping funnel was opened, and the CrCl2 solution was added dropwise. The addition was completed within 10 minutes, and the reaction was continued for 24 hours at room temperature. After the reaction was completed, the reaction system was placed in a dry air atmosphere and the reaction was continued for 24 hours. The reaction mixture was washed three times with saturated ammonium chloride and brine respectively, and the solid mixture was separated and dried under reduced pressure to constant weight to obtain the MCM-22 encapsulated SalenCrCl catalyst.

[0033] (3) Grafting of co-catalyst onto MCM-22 The MCM-22 encapsulated SalenCrCl catalyst obtained in (2) and γ-chloropropyltrimethoxysilane were added in a ratio of Cr to γ-chloropropyltrimethoxysilane of 2:1, and dioxane was used as a solvent. The reaction was stirred at 40°C for 24 hours. After the reaction was completed, a slightly excess amount of triethylamine (the ratio of triethylamine to γ-chloropropyltrimethoxysilane was 1.2:1) was added, and the reaction was continued at 80°C for 12 hours. The solid was separated, and the solid was freeze-dried to remove the solvent, and the desired immobilized catalyst was obtained, which was recorded as MCM-22@Salen(E)CrCl.

[0034] Example 2 The preparation method is the same as that of Example 1, except that in the preparation process of (1) Salen ligand, ethylenediamine is replaced by cyclohexanediamine.

[0035] The obtained catalyst was recorded as MCM-22@Salen(cyclo)CrCl.

[0036] Example 3 The preparation method is the same as that of Example 1, except that in the preparation process of (1) Salen ligand, ethylenediamine is replaced by o-phenylenediamine.

[0037] The obtained catalyst was recorded as MCM-22@Salen(benzene)CrCl.

[0038] Example 4 The preparation method is the same as that of Example 1, except that, in the process of (2) MCM-22 encapsulating the SalenCrCl catalyst, CrCl2 is replaced by Cr(NO3)2.

[0039] The obtained catalyst was recorded as MCM-22@Salen(II)CrNO3.

[0040] Example 5 The preparation method is the same as that of Example 2, except that, in the process of (2) MCM-22 encapsulating the SalenCrCl catalyst, CrCl2 is replaced by Cr(NO3)2.

[0041] The obtained catalyst was recorded as MCM-22@Salen(cyclo)CrNO3.

[0042] Example 6 The preparation method is the same as that of Example 3, except that, in the process of (2) MCM-22 encapsulating the SalenCrCl catalyst, CrCl2 is replaced by Cr(NO3)2.

[0043] The obtained catalyst was recorded as MCM-22@Salen(benzene)CrNO3.

[0044] Example 7 The preparation method is the same as that of Example 1, except that in step (2), the mass ratio of the amount of the Salen ligand to MCM-22 is 1:50 mmol / g.

[0045] Example 8 The preparation method is the same as that of Example 1, except that in step (2), the molar ratio of CrCl2 to Salen ligand is 1.5:1.

[0046] Example 9 The preparation method is the same as that of Example 1, except that the MCM-22 encapsulated SalenCrCl catalyst obtained in (2) and γ-chloropropyltrimethoxysilane are added in a molar ratio of Cr to γ-chloropropyltrimethoxysilane of 1:2, and the molar ratio of triethylamine to γ-chloropropyltrimethoxysilane is 1:1. Example 10 The preparation method is the same as that of Example 1, except that the MCM-22 encapsulated SalenCrCl catalyst obtained in (2) and γ-chloropropyltrimethoxysilane are added in a molar ratio of Cr to γ-chloropropyltrimethoxysilane of 1:1, and the molar ratio of triethylamine to γ-chloropropyltrimethoxysilane is 1.5:1.

[0047] Comparative Example 1 The preparation method is the same as in Example 1, except that: In step (2), 30 g of MCM-22 solid powder was not added, and the amount of dry tetrahydrofuran was replaced from 200 mL to 300 mL; There is no step (3) of grafting the co-catalyst onto MCM-22.

[0048] The obtained catalyst was recorded as Salen(II)CrCl.

[0049] Comparative Example 2 The preparation method is the same as in Example 2, except that: In step (2), 30 g of MCM-22 solid powder was not added, and the amount of dry tetrahydrofuran was replaced from 200 mL to 300 mL; There is no step (3) of grafting the co-catalyst onto MCM-22.

[0050] The obtained catalyst was recorded as Salen(cyclo)CrCl.

[0051] Comparative Example 3 The preparation method is the same as that of Example 3, except that: In step (2), 30 g of MCM-22 solid powder was not added, and the amount of dry tetrahydrofuran was replaced from 200 mL to 300 mL; There is no step (3) of grafting the co-catalyst onto MCM-22.

[0052] The obtained catalyst was recorded as Salen(benzene)CrCl.

[0053] Comparative Example 4 The preparation method is the same as that of Example 4, except that: In step (2), 30 g of MCM-22 solid powder was not added, and the amount of dry tetrahydrofuran was replaced from 200 mL to 300 mL; There is no step (3) of grafting the co-catalyst onto MCM-22.

[0054] The obtained catalyst was recorded as Salen(II)CrNO3.

[0055] Comparative Example 5 The preparation method is the same as that of Example 5, except that: In step (2), 30 g of MCM-22 solid powder was not added, and the amount of dry tetrahydrofuran was replaced from 200 mL to 300 mL; There is no step (3) of grafting the co-catalyst onto MCM-22.

[0056] The obtained catalyst was recorded as Salen(cyclo)CrNO3.

[0057] Comparative Example 6 The preparation method is the same as that of Example 6, except that: In step (2), 30 g of MCM-22 solid powder was not added, and the amount of dry tetrahydrofuran was replaced from 200 mL to 300 mL; There is no step (3) of grafting the co-catalyst onto MCM-22.

[0058] The obtained catalyst was recorded as Salen(benzene)CrNO3.

[0059] Effect Example 1 Morphology Characterization of Catalyst Figure 1 This is the surface morphology of the MCM-22 encapsulated SalenCrNO3 catalyst obtained in step (2) of Example 4. Figure 2 This is the surface morphology of the grafted catalyst obtained in step (3) of this embodiment. Figure 1 and Figure 2The SEM photos of the catalysts did not show the presence of SalenCrNO3 on the outer surface of MCM-22, indicating that SalenCrNO3 was encapsulated in the pores of the MCM-22 molecular sieve, and the encapsulation and grafting process did not destroy the morphology and crystal structure of MCM-22. On the one hand, this encapsulation effect allowed SalenCrX to interact with the pores of MCM-22 to form a "zeolite enzyme"-like structure, which improved the activity and stability of the catalyst; on the other hand, because the molecules of SalenCrX were larger than the pores of the MCM-22 molecular sieve, it was difficult for SalenCrX to leave the pores of the molecules, resulting in a loss of activity.

[0060] After SalenCrX is encapsulated with MCM-22 molecular sieve, a quaternary ammonium base co-catalyst is grafted on the surface of the MCM-22 molecular sieve, which can effectively prevent the grafted co-catalyst from occupying the molecular sieve pores and pores, which causes a significant reduction in the amount of SalenCrX encapsulation. It also prevents the co-catalyst grafted on the surface from forming a local confined structure that pseudo-encapsulates SalenCrX. This pseudo-encapsulation structure is easy to fall off during the use and washing of the catalyst, resulting in a loss of catalyst activity. At the same time, the detached SalenCrX catalyst remains in the product polypropylene carbonate, which will cause a decrease in product stability.

[0061] Effect Example 2 Catalyst Activity Detection (1) Catalytic terpolymerization of CO2, propylene oxide and phthalic anhydride The catalyst prepared in the examples and comparative examples was mixed with pretreated propylene oxide and phthalic anhydride (n 催化剂 :n 环氧丙烷 :n 邻苯二甲酸酐 =15000:1:1) was added to a 500 mL autoclave that had been vacuum dried. At room temperature, the air in the autoclave was replaced with CO2 2-3 times. Subsequently, 2 MPa of CO2 gas was charged, and the reaction temperature was set to 25°C and the reaction time was set to 40 h. After the reaction was completed, it was cooled to room temperature, depressurized to normal pressure, the autoclave was opened, the solid catalyst was separated by filtration, the crude product was dissolved in dichloromethane, and the unreacted reactants and residual solvent dichloromethane were removed by vacuum distillation, weighed, and recorded. The activity of the catalyst was calculated, and its activity data is shown in Table 1.

[0062] Table 1

[0063] (2) Catalytic terpolymerization of CO2, propylene oxide and maleic anhydride The catalytic process and data analysis were the same as (1). The results are shown in Table 2.

[0064] Table 2

[0065] It can be seen from Table 1 and Table 2 that under the same conditions, the present invention uses a mesoporous molecular sieve to first encapsulate the SalenCrX catalyst, and then uses a silanol bond to graft the catalyst to obtain a solid-supported catalyst to catalyze the terpolymerization of CO2, propylene oxide and acid anhydride, and its catalytic activity is greatly improved.

[0066] Effect Example 3 Application of Catalyst in Polymerization Reaction (1) Preparation of polypropylene carbonate using CO2, propylene oxide and phthalic anhydride as raw materials Polymerization process: The catalyst prepared in the examples and comparative examples was mixed with pretreated propylene oxide and phthalic anhydride (n 催化剂 :n 环氧丙烷 :n 邻苯二甲酸酐 =15000:1:1) was added to a 500 mL autoclave that had been vacuum dried. At room temperature, the air in the autoclave was replaced with CO2 for 2 to 3 times. Subsequently, 2 MPa of CO2 gas was filled, and the reaction temperature was set to 25°C and the reaction time was 40 h. After the reaction was completed, it was cooled to room temperature, depressurized to normal pressure, the autoclave was opened, the solid catalyst was separated by filtration, the crude product was dissolved in dichloromethane, and the unreacted reactants and residual solvent dichloromethane were removed by vacuum distillation, weighed, and recorded. After the distillation was completed, the remaining polymer was dissolved in tetrahydrofuran, 5% HCl anhydrous ethanol solution was slowly added, and it was allowed to stand for precipitation to obtain a large amount of white polymer precipitate. It was filtered and repeated 2 to 3 times. The copolymer was vacuum dried at 50°C for 6 hours, weighed, and recorded to obtain the target compound. The separated solid catalyst was continued to be used in the reaction and reused 6 times.

[0067] Data analysis: The yield of polypropylene carbonate was the average data of 6 consecutive reuses of the catalyst, and the median was taken for the remaining data. The results are shown in Table 3.

[0068] Table 3

[0069] (2) Preparation of polypropylene carbonate using CO2, propylene oxide and maleic anhydride as raw materials The aggregation process and data analysis are the same as (1). The results are shown in Table 4.

[0070] Table 4

[0071] It can be seen from Table 3 and Table 4 that under the same conditions, the present invention adopts mesoporous molecular sieve to first encapsulate SalenCrX catalyst, and then uses silanol bond to graft the catalyst to obtain the solid-supported catalyst. When applied to the polymerization reaction of polypropylene carbonate, the yield of polypropylene carbonate can be improved, the glass transition temperature of the polymer can be improved, the carbonate chain content and the thermal decomposition temperature can be improved, and the separation degree between the catalyst and the polymer can be improved. The recovery rate of the catalyst is significantly improved compared with the recovery rate of the catalyst without solid support.

[0072] The above are only preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limiting the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a SalenCrX immobilized catalyst, It is characterized in that The following steps are involved: S1. Preparation of Salen ligand; S2. Under a protective atmosphere, the Salen ligand, mesoporous molecular sieve and solvent obtained in S1 are mixed and reacted, and then a solution containing a Cr compound is added to react, and the reactants are oxidized to obtain a SalenCrX catalyst encapsulated by a mesoporous molecular sieve; S3, grafting the SalenCrX catalyst encapsulated by the mesoporous molecular sieve obtained in S2 with a co-catalyst via a silanol bond.

2. The preparation method according to claim 1, It is characterized in that The ratio of the amount of the Salen ligand obtained in S1 to the mass of the mesoporous molecular sieve is 1:50~1:150 mmol / g.

3. The preparation method according to claim 1, It is characterized in that In S2, the molar ratio of the Salen ligand obtained in S1 to the Cr compound is 1:(1-1.5).

4. The preparation method according to any one of claims 1 to 3, It is characterized in that The mesoporous molecules are selected from any one of MCM-22 and MCM-41.

5. The preparation method according to any one of claims 1 to 3, It is characterized in that The Cr compound is selected from CrCl 2 、Cr(NO 3 ) 2 Any one of .

6. The preparation method according to claim 1, It is characterized in that The co-catalyst is a tertiary amine satisfying the general formula [CH 3 (CH 2 ) n ] 3 N, n=1~6.

7. The preparation method according to claim 1, It is characterized in that The silane bond in S3 is from any one of γ-chloropropyltrimethoxysilane, 11-chloroundecyltrimethoxysilane, 4-bromobutyltrimethoxysilane, 6-bromohexyltrimethoxysilane and 11-bromoundecyltrimethoxysilane.

8. The preparation method according to claim 1 or any one of claims 6 to 7, It is characterized in that The S3 is specifically: mixing the SalenCrX catalyst encapsulated by the mesoporous molecular sieve obtained in S2 with the silanol bond raw material, adding a solvent for reaction, adding a co-catalyst after the reaction is completed, continuing the reaction, and drying the obtained reactant.

9. A SalenCrX immobilized catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the SalenCrX immobilized catalyst according to claim 9 in the preparation of polypropylene carbonate.

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