Modified Pd / Y type zeolite catalyst as well as preparation method and application thereof

Abstract

The invention discloses a modified Pd / Y type zeolite catalyst and a preparation method and application thereof, and relates to the technical field of catalytic materials.The preparation method comprises the following steps that S1, Y type zeolite is subjected to magnesium element modification treatment to obtain magnesium modified Y type zeolite; s2, adding the magnesium-modified Y-type zeolite into a palladium dichloride solution, stirring at room temperature, adjusting the pH value of the system to 8-9, adding sodium borohydride, and carrying out a reduction reaction at 20-60 DEG C; s3, adding a zinc nitrate solution into the system reduced in the step S2, stirring at room temperature, filtering to obtain a filter cake I, and removing chloride ions in the filter cake I; and S4, drying the filter cake I without chloride ions, placing the dried filter cake I in a hydrogen atmosphere, and roasting the dried filter cake I at 300-500 DEG C to obtain the modified Pd / Y type zeolite catalyst. The modified Pd / Y type zeolite catalyst prepared by the preparation method disclosed by the invention has both hydrogenation activity and trans-selectivity.

Description

Technical Field

[0001] This invention relates to the field of catalytic materials technology, and more specifically to a modified Pd / Y type zeolite catalyst, its preparation method, and its application. Background Technology

[0002] Trans-cyclohexanedicarboxylic acid (TCODI) is a key intermediate in the preparation of high-performance polyesters, polyurethanes, epoxy resins, and other materials, and its demand is particularly urgent in the field of high-end engineering plastics. The synthesis of TCODI via aqueous-phase hydrogenation using purified terephthalic acid as a raw material has become the mainstream technical route for TCODI synthesis due to its significant advantages such as wide availability of raw materials and environmentally friendly process. The core breakthrough in this process lies in the research and innovation of high-performance hydrogenation catalysts.

[0003] Existing catalysts for the hydrogenation of purified terephthalic acid to prepare transcyclohexanedicarboxylic acid use Pd / Y type zeolite catalysts as the core system, such as the Pd / Pt modified Y type zeolite catalyst disclosed in Chinese patent document "CN1362288A". These catalysts, relying on the high specific surface area and unique shape-selective catalytic properties of Y-type zeolite supports, exhibit certain catalytic activity in the hydrogenation reaction of purified terephthalic acid. However, they suffer from two major technical defects in practical applications, severely restricting their industrial application and suitability for high-end scenarios: First, insufficient trans-selectivity. The trans-cyclohexanedicarboxylic acid prepared by traditional Pd / Y-type zeolite catalysts generally has a trans-isomer content of less than 75%, which is difficult to meet the stringent requirements of high-purity trans-cyclohexanedicarboxylic acid for high-end materials. Second, poor cycle stability. During continuous hydrogenation reactions, the catalyst is prone to problems such as Pd metal particle agglomeration, loss of active components, and deterioration of the support structure, leading to a rapid decline in catalytic efficiency. In existing technologies, the activity of this type of catalyst generally decreases by more than 25% after three cycles, making it unsuitable for the stable operation requirements of continuous industrial production.

[0004] To overcome the aforementioned technical bottlenecks, existing technologies mostly employ single-metal modification strategies, such as single-component modification with alkaline earth metals or transition metals. For example, the Pd-based multi-metal modified catalyst disclosed in Chinese patent document "CN105582926A" uses a TiO2 / La2O3 composite system as its support instead of Y-type zeolite, and it fails to solve the problem of synergistic modification of multi-metal components in the Y-type zeolite support scenario, making it impossible to directly apply to the performance optimization of Pd / Y-type zeolite catalysts. More importantly, single-metal modification strategies struggle to simultaneously achieve both hydrogenation activity and trans-selectivity in catalysts, often falling into the dilemma of increased activity leading to decreased selectivity, or improved selectivity resulting in insufficient activity, thus failing to break through the inherent balance bottleneck between activity and selectivity.

[0005] Therefore, it is necessary to propose a modified Pd / Y type zeolite catalyst, its preparation method, and its application to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to address the problems mentioned in the background section by providing a modified Pd / Y zeolite catalyst, its preparation method, and its application.

[0007] To achieve the above objectives, the present invention specifically adopts the following technical solution: A method for preparing a modified Pd / Y type zeolite catalyst includes the following steps: S1. Magnesium-modified Y-type zeolite was obtained by modifying Y-type zeolite with magnesium. S2. Add magnesium-modified Y-type zeolite to palladium dichloride solution and stir at room temperature. Adjust the pH of the system to 8-9, then add sodium borohydride and carry out the reduction reaction at 20-60℃. S3. Add zinc nitrate solution to the reduced system in step S2 and stir at room temperature. Filter to obtain filter cake I and remove chloride ions from filter cake I. S4. After drying the filter cake I with removed chloride ions, it is placed in a hydrogen atmosphere and calcined at 300~500℃ to obtain the modified Pd / Y type zeolite catalyst.

[0008] Preferably, the specific method for obtaining magnesium-modified Y-type zeolite by magnesium element modification treatment includes: Y-type zeolite was placed in a magnesium nitrate solution with a mass fraction of 3-10% and stirred at room temperature for 10-20 hours, then filtered to obtain filter cake II. Magnesium-modified Y-type zeolite was obtained by drying filter cake II at 120℃ for 6 hours and then calcining it in air.

[0009] Preferably, the solid-liquid ratio of the Y-type zeolite and the magnesium nitrate solution is 1:10~30.

[0010] Preferably, the calcination temperature is 500~650℃ and the calcination time is 3~6h.

[0011] Preferably, the palladium dichloride solution is 0.01~0.1 mol / L, the solid-liquid ratio of magnesium-modified Y-type zeolite and palladium dichloride solution is 1:5~20, and the stirring time in step S2 is 24 h.

[0012] Preferably, the concentration of sodium borohydride is 0.1 mol / L, and the reduction reaction time is 2 h.

[0013] Preferably, the concentration of the zinc nitrate solution is 0.01~0.1 mol / L, and the stirring time in step S3 is 6 h.

[0014] Preferably, the heating rate in step S4 is 5°C / min, and the calcination time is 1~6h.

[0015] As an inventive concept with the same technical solution described above, this invention also claims protection for a modified Pd / Y type zeolite catalyst prepared by any one of the preparation methods described above.

[0016] As an inventive concept with the same technical solution as above, this invention also claims protection for the application of modified Pd / Y type zeolite catalyst in the aqueous hydrogenation of purified terephthalic acid to prepare high trans-cyclohexanedicarboxylic acid.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By synergistically modifying Pd / Y-type zeolite with Mg-Zn, not only can the pore structure of Y-type zeolite be effectively regulated and the contact efficiency between substrate and active site be improved, but the electronic environment of palladium metal active site is also precisely optimized, providing a favorable reaction microenvironment for the formation of transcyclohexanedicarboxylic acid and significantly promoting the directional formation of target product.

[0018] 2. The co-modification with Mg-Zn effectively suppressed the agglomeration and loss of palladium metal particles, improving metal dispersion. After eight cycles of use, the modified Pd / Y zeolite catalyst maintained a hydrogenation activity retention rate of >90%, with no significant decrease in trans-selectivity, thus greatly extending the service life of the modified Pd / Y zeolite catalyst. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The materials and instruments used in the following embodiments are all commercially available.

[0020] A method for preparing a modified Pd / Y type zeolite catalyst includes steps S1 to S4.

[0021] S1. Magnesium-modified Y-type zeolite is obtained by magnesium modification treatment of Y-type zeolite. Specifically, Y-type zeolite is placed in a magnesium nitrate solution with a mass fraction of 3-10% and magnetically stirred at room temperature for 10-20 hours to allow magnesium ions to be fully adsorbed into the pores and surface of the Y-type zeolite. After stirring, the mixture is filtered to obtain filter cake II. Filter cake II is dried at 120℃ for 6 hours to remove free moisture, and then transferred to a muffle furnace for calcination in air atmosphere to obtain magnesium-modified Y-type zeolite. The solid-liquid ratio of Y-type zeolite to magnesium nitrate solution is 1:10-30, measured by mass-volume ratio. The calcination temperature is 500-650℃ and the calcination time is 3-6 hours.

[0022] S2. Magnesium-modified Y-type zeolite was added to a palladium dichloride solution and stirred at room temperature for 24 hours to achieve Pd 2+ Uniform impregnation; after adjusting the pH of the system to 8-9 with dilute sodium hydroxide solution, 0.1 mol / L sodium borohydride is slowly added dropwise as a reducing agent, and the reduction reaction is carried out at 20-60℃ for 2 hours to achieve Pd uniform impregnation. 2+ The solution is reduced to palladium; wherein the palladium dichloride solution is 0.01~0.1mol / L, and the solid-liquid ratio of magnesium-modified Y-type zeolite to palladium dichloride solution is 1:5~20, and the mass-volume ratio is used for measurement.

[0023] S3. Add 0.01~0.1mol / L zinc nitrate solution to the reduced system from step S2 and stir at room temperature for 6 hours to allow Zn to... 2+ The catalyst surface and pores were further modified; after stirring, the filter cake I was obtained by filtration, and the chloride ions in the filter cake I were removed; the removal method included: repeatedly washing the filter cake I with deionized water until no white precipitate was detected by silver nitrate solution, indicating that the chloride ions were completely removed.

[0024] S4. After drying the chloride-removed filter cake I in an oven at 120℃ for 8 hours, it was placed in a tube furnace and calcined at 300~500℃ in a hydrogen atmosphere to activate the catalyst. After cooling, the modified Pd / Y type zeolite catalyst was obtained. The calcination heating rate was 5℃ / min, and the calcination time was 1~6 hours. The modified Pd / Y type zeolite catalyst had a palladium loading of 1~5%, magnesium in the form of magnesium oxide with a content of 1~5%, and zinc in the form of zinc oxide with a content of 0.3~1.5%.

[0025] Steps S1 to S4 prepare modified Pd / Y type zeolite catalysts using impregnation and reduction methods. The steps are clear and the operation is simple, requiring no complex equipment. The raw materials are readily available, and the process parameters are easy to control, making it suitable for industrial-scale production. The reaction conditions for catalyst application are mild, and it can be directly adapted to existing purified terephthalic acid hydrogenation production units without equipment modification, thus reducing the cost and barriers to industrial application.

[0026] This invention utilizes the synergistic modification effect of alkaline earth metals and transition metals to regulate the pore structure and metal dispersion of modified Pd / Y type zeolite catalysts. It also provides a method for preparing modified Pd / Y type zeolite catalysts and their application in the aqueous hydrogenation of purified terephthalic acid to prepare high-trans-cyclohexanedicarboxylic acid, achieving efficient conversion of purified terephthalic acid and directional synthesis of high-trans-cyclohexanedicarboxylic acid to meet the needs of industrial production.

[0027] The preparation method of the present invention will be further described in detail below with reference to specific embodiments.

[0028] Example 1 S1. Weigh 100g of Y-type zeolite and add it to 2000mL of 5% magnesium nitrate solution. Stir magnetically at room temperature for 12h, then filter to obtain filter cake II. Dry filter cake II in an oven at 120℃ for 6h, then transfer it to a muffle furnace at 550℃ for calcination for 4h. After cooling, obtain 98g of magnesium-modified Y-type zeolite. The solid-liquid ratio of Y-type zeolite to magnesium nitrate solution is 1:20.

[0029] S2. Add 98g of magnesium-modified Y-type zeolite to 1470mL of 0.05mol / L palladium dichloride solution and stir at room temperature for 24h. Adjust the pH of the system to 8.5 with 1mol / L sodium hydroxide solution, and then slowly add 300mL of 0.1mol / L sodium borohydride to carry out a reduction reaction at 20~60℃ for 2h. The solid-liquid ratio of magnesium-modified Y-type zeolite to palladium dichloride solution is 1:15.

[0030] S3. Add 500 mL of 0.02 mol / L zinc nitrate solution to the reduced system in step S2 and stir at room temperature for 6 h. After stirring, filter to obtain filter cake I. Remove chloride ions from filter cake I and take 5 mL of the final washing solution.

[0031] S4. After drying the chloride-removed filter cake I in an oven at 120℃ for 8 hours, it was placed in a tube furnace and calcined at 300℃ in a hydrogen atmosphere at a flow rate of 50 mL / min to activate the catalyst. After cooling, 102 g of modified Pd / Y zeolite catalyst was obtained. The calcination heating rate was 5℃ / min, and the calcination time was 3 hours.

[0032] Testing revealed that the modified Pd / Y zeolite catalyst contained 2.01% palladium, 1.48% magnesium oxide, and 0.79% zinc oxide, meeting the design requirements.

[0033] The following detailed description, in conjunction with specific embodiments, further illustrates the application of the modified Pd / Y type zeolite catalyst of the present invention in the aqueous hydrogenation of purified terephthalic acid to prepare high trans-cyclohexanedicarboxylic acid.

[0034] Example 2 Example 2 demonstrates the performance of the modified Pd / Y zeolite catalyst in the hydrogenation reaction of purified terephthalic acid. The modified Pd / Y zeolite catalyst prepared in Example 1 was used in the aqueous phase hydrogenation reaction of purified terephthalic acid under the following specific reaction conditions: 166g of purified terephthalic acid and 2490g of deionized water were added to the reactor to prepare a 6.7% purified terephthalic acid aqueous solution; 3.32g of catalyst, which is 2% of the mass of purified terephthalic acid, was added; the reactor was sealed, nitrogen was purged three times, hydrogen was introduced, the pressure was increased to 4MPa, the temperature was increased to 140℃, the stirring speed was adjusted to 1000rpm, and the reaction was carried out for 4h.

[0035] After the reaction was completed, the pressure was released by cooling, and samples were taken for detection by high performance liquid chromatography. The results showed that the conversion rate of purified terephthalic acid was 100%, the total yield of cyclohexanedicarboxylic acid was 98.5%, and the content of trans-cyclohexanedicarboxylic acid was 91.2%.

[0036] Example 3 Example 3 is a test of the cyclic stability of the modified Pd / Y zeolite catalyst. The reaction conditions of Example 2 were repeated, and the catalyst after the reaction was recovered by filtration, washed three times with deionized water, dried at 120°C for 4 hours, and then used again for the hydrogenation reaction of purified terephthalic acid. This cycle was repeated 8 times.

[0037] Test results show that in the 8th cycle reaction, the conversion rate of purified terephthalic acid was still 100%, the total yield of cyclohexanedicarboxylic acid was 98.1%, the content of trans-cyclohexanedicarboxylic acid was 90.8%, the catalyst activity retention rate was 99.6%, and there was no significant decrease in trans selectivity, indicating that the modified Pd / Y type zeolite catalyst has excellent cycle stability.

[0038] The modified Pd / Y zeolite catalyst of this invention utilizes Mg-Zn synergistic modification of Pd / Y zeolite. This not only effectively regulates the pore structure of Y zeolite and improves the contact efficiency between the substrate and active sites, but also precisely optimizes the electronic environment of the palladium metal active sites, providing a favorable reaction microenvironment for the formation of trans-cyclohexanedicarboxylic acid and significantly promoting the directional formation of the target product. The trans-cyclohexanedicarboxylic acid content is ≥90%, which is more than 15% higher than that of the unmodified Pd / Y zeolite catalyst, meeting the demand for high trans-cyclohexanedicarboxylic acid in the synthesis of high-end materials. The co-modification of Mg-Zn effectively suppressed the agglomeration and loss of palladium metal particles and improved the metal dispersion. After the modified Pd / Y zeolite catalyst was recycled 8 times, the hydrogenation activity retention rate was still >90%, the trans selectivity did not decrease significantly, and the catalyst life was greatly extended.

[0039] Under optimized reaction conditions, the conversion rate of purified terephthalic acid can reach 100%, and the total yield of cyclohexanedicarboxylic acid is ≥98%, which balances high activity and high selectivity, thereby improving the economic benefits of production.

[0040] The following is a summary of Examples 1, 2 and 3.

[0041] First, the preparation method disclosed in Example 1 controls the modification of magnesium and Pd. 2+ Modified Pd / Y zeolite catalysts with palladium loading, magnesium oxide, and zinc oxide content meeting design requirements were prepared under conditions including supported reduction, zinc modification, and calcination in a hydrogen atmosphere. The synergistic effect of various process parameters during preparation ensured that the active components were uniformly dispersed on the support surface, laying the foundation for subsequent catalytic performance.

[0042] Secondly, the performance verification experiment in Example 2 shows that the modified Pd / Y zeolite catalyst prepared in this invention exhibits excellent catalytic activity and selectivity in the aqueous hydrogenation of purified terephthalic acid to prepare high-trans-cyclohexanedicarboxylic acid. Under the given reaction conditions, the conversion rate of purified terephthalic acid reaches 100%, the total yield of cyclohexanedicarboxylic acid is 98.5%, and the trans-isomer content is as high as 91.2%, which is superior to the trans-selectivity of existing single modified Pd-based catalysts and can efficiently meet the needs of preparing high-value-added trans-cyclohexanedicarboxylic acid.

[0043] Finally, the cyclic stability test in Example 3 further confirmed the performance of the modified Pd / Y zeolite catalyst of the present invention. After 8 cycles, the modified Pd / Y zeolite catalyst still maintained 100% substrate conversion, with no significant decrease in total yield and trans-selectivity, and an activity retention rate of 99.6%. This indicates that the synergistic effect of Mg-Zn co-modification not only optimizes the catalytic active sites but also significantly improves the anti-sintering ability and structural stability of the Pd active component, effectively reducing catalyst loss costs in industrial applications and demonstrating feasibility for long-term industrial application.

[0044] In summary, the preparation method of this modified Pd / Y zeolite catalyst is controllable, and the modified Pd / Y zeolite catalyst has excellent catalytic activity, high trans selectivity and excellent cycle stability, and has promising application prospects in the field of aqueous hydrogenation of purified terephthalic acid.

Claims

1. A process for the preparation of a modified Pd / Y-type zeolite catalyst, characterized in that, Includes the following steps: S1. Magnesium-modified Y-type zeolite was obtained by modifying Y-type zeolite with magnesium. S2. Add magnesium-modified Y-type zeolite to palladium dichloride solution and stir at room temperature. Adjust the pH of the system to 8-9, then add sodium borohydride and carry out the reduction reaction at 20-60℃. S3. Add zinc nitrate solution to the reduced system in step S2 and stir at room temperature. Filter to obtain filter cake I and remove chloride ions from filter cake I. S4. After drying the filter cake I with removed chloride ions, it is placed in a hydrogen atmosphere and calcined at 300~500℃ to obtain the modified Pd / Y type zeolite catalyst.

2. The method for preparing a modified Pd / Y-type zeolite catalyst according to claim 1, characterized by, Specific methods for obtaining magnesium-modified Y-type zeolite by magnesium element modification include: Y-type zeolite was placed in a magnesium nitrate solution with a mass fraction of 3-10% and stirred at room temperature for 10-20 hours, then filtered to obtain filter cake II. Magnesium-modified Y-type zeolite was obtained by drying filter cake II at 120℃ for 6 hours and then calcining it in air.

3. The method of claim 2, wherein the modified Pd / Y-zeolite catalyst is prepared by the steps of: The solid-liquid ratio of the Y-type zeolite and magnesium nitrate solution is 1:10~30.

4. The method of claim 2, wherein the modified Pd / Y-zeolite catalyst is prepared by the steps of: The roasting temperature is 500~650℃ and the roasting time is 3~6h.

5. The method for preparing a modified Pd / Y type zeolite catalyst according to claim 1, characterized in that, The palladium dichloride solution is 0.01~0.1mol / L, the solid-liquid ratio of magnesium-modified Y-type zeolite and palladium dichloride solution is 1:5~20, and the stirring time in step S2 is 24h.

6. The method for preparing a modified Pd / Y type zeolite catalyst according to claim 1, characterized in that, The concentration of sodium borohydride was 0.1 mol / L, and the reduction reaction time was 2 h.

7. The method for preparing a modified Pd / Y type zeolite catalyst according to claim 1, characterized in that, The concentration of the zinc nitrate solution is 0.01~0.1 mol / L, and the stirring time in step S3 is 6 h.

8. The method for preparing a modified Pd / Y type zeolite catalyst according to claim 1, characterized in that, In step S4, the heating rate during calcination is 5°C / min, and the calcination time is 1~6h.

9. A modified Pd / Y type zeolite catalyst, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the modified Pd / Y type zeolite catalyst as described in claim 9 in the aqueous hydrogenation of purified terephthalic acid to prepare high trans-cyclohexanedicarboxylic acid.