Simple preparation method of fiber Pd / PVDF hydrogenation catalyst

Abstract

The invention belongs to the technical field of hydrogenation catalyst preparation, and relates to a simple preparation method of a fiber Pd / PVDF hydrogenation catalyst. Polyvinylidene fluoride, palladium acetate and N, N-dimethylformamide are uniformly mixed and then stirred, and a spinning solution is obtained; performing electrostatic spinning on the spinning solution to obtain a nanofiber sheet; and drying to obtain the Pd / PVDF catalyst. The Pd / PVDF catalyst provided by the invention is simple in process and short in synthesis time, and the active component Pd in the prepared catalyst is uniformly dispersed, high in low-temperature catalytic activity and strong in stability. The prepared catalyst is fibrous and can be directly taken out of a reaction system after the catalytic reaction is finished, recycling is achieved, after multiple times of recycling, the catalytic activity is not obviously reduced, excellent catalytic activity and good structural stability are shown, and new possibility is provided for industrial continuous catalytic reaction.

Description

Technical Field

[0001] This invention belongs to the field of hydrogenation catalyst preparation technology, and relates to a simple method for preparing a fiber Pd / PVDF hydrogenation catalyst. Background Technology

[0002] Cyclohexanone, a key intermediate in the production of chemicals such as nylon, caprolactam, and adipic acid, is widely used in the chemical industry. The liquid-phase hydrogenation of phenol to prepare cyclohexanone offers advantages such as mild reaction conditions, simple operation, and low energy consumption; however, this process currently lacks highly efficient and ideal hydrogenation catalysts.

[0003] Palladium (Pd)-based catalysts exhibit excellent catalytic performance in the hydrogenation of phenol, but existing systems often employ fine-particle supports to enhance activity, making catalyst recovery and recycling difficult. While fibrous catalysts, which have emerged in recent years, are easier to separate, they generally suffer from complex and time-consuming preparation processes.

[0004] PVDF itself possesses excellent chemical stability, mechanical strength, and corrosion resistance. PVDF has crystalline phases such as α, β, γ, and δ, but it mostly exists as the α phase in its natural state. Its β phase, due to its all-inverse planar zigzag conformation, exhibits excellent ferroelectric and piezoelectric activity, making it an ideal matrix for functional materials. Traditional methods for obtaining the β phase of PVDF materials (such as stretching, additive induction, and annealing) often require complex post-processing. Furthermore, current methods for loading active components onto PVDF supports are mostly impregnation methods, which easily lead to uneven distribution of active components, resulting in lower catalytic activity of the catalyst. Summary of the Invention

[0005] This invention addresses the problem of uneven distribution of active components during the preparation of Pd metal supported on PVDF β-phase catalysts, which leads to low catalytic activity. It proposes a simple method for preparing fiber Pd / PVDF hydrogenation catalysts.

[0006] To achieve the above objectives, the present invention is implemented using the following technical solution: A simple method for preparing a fiber Pd / PVDF hydrogenation catalyst, comprising the following steps: (1) Polyvinylidene fluoride, palladium acetate and N,N-dimethylformamide are mixed evenly and stirred to obtain a spinning solution; (2) Electrospinning the spinning solution to obtain nanofiber sheets; drying to obtain Pd / PVDF catalyst.

[0007] Preferably, in step (1), the mass fraction of polyvinylidene fluoride is 16-22%, and the mass ratio of polyvinylidene fluoride to palladium acetate is (10-30):1.

[0008] As a preferred option, the electrospinning conditions in step (2) are: spinning voltage 12-15kV, feed rate 0.1-0.3mm / min, translation distance 50-65mm, receiver distance 12-14cm, receiver rate 70-90rpm, receiving time 1.9-2.1h, and humidity 20-70%.

[0009] This invention proposes the application of the fiber Pd / PVDF hydrogenation catalyst prepared by the above method in the hydrogenation reaction process.

[0010] Preferably, the hydrogenation reaction is the hydrogenation of phenol to produce cyclohexanone.

[0011] Electrospinning technology can obtain fiber carriers with high specific surface area and three-dimensional porous structure, which not only significantly improves the mass transfer efficiency of reactants and reduces mass transfer resistance, but also effectively enhances the efficiency of catalytic reactions. Furthermore, the preparation process is simple and the parameters are easy to control. In the process proposed in this invention, the synergistic effect of high-voltage electric field and shear force induced by solvent evaporation during electrospinning effectively induces the formation of the β phase in PVDF. Furthermore, by using electrospinning technology to load the active component Pd, the resulting catalyst metal component is uniformly dispersed and exhibits high catalyst activity. After the active component and polymer are co-dispersed in a homogeneous and stable spinning solution, the spinning solution is placed under a high-voltage electric field for stretching and refining. During this process, the solvent rapidly evaporates, and the polymer chains solidify, thereby fixing the dispersion state of the components and avoiding phase separation or sedimentation due to time delay. This invention directly introduces the palladium active component into the PVDF fiber matrix through electrospinning, simultaneously achieving active component loading and phase change processes, obtaining stable β-phase PVDF without complex subsequent processing steps. This catalyst can be directly applied to the liquid-phase hydrogenation of phenol to prepare cyclohexanone, and exhibits high low-temperature catalytic activity and cycle stability.

[0012] Compared with the prior art, the advantages and positive effects of the present invention are as follows: 1. The Pd / PVDF catalyst prepared according to the present invention has a simple process, short synthesis time, and the active component Pd in ​​the prepared catalyst is uniformly dispersed, with high catalytic activity at low temperature and strong stability.

[0013] 2. The catalyst prepared by this invention is fibrous and can be directly removed from the reaction system after the catalytic reaction is completed, so as to achieve recycling without the need for a special catalyst activation step.

[0014] 3. After repeated use, the catalyst of this invention does not show a significant decrease in catalytic activity, exhibiting excellent catalytic activity and good structural stability, providing new possibilities for continuous industrial catalytic reactions. Attached Figure Description

[0015] Figure 1 a is a SEM image of the catalyst prepared in Example 1. Figure 1 b is a SEM image of the catalyst after the hydrogenation of phenol to prepare cyclohexanone.

[0016] Figure 2 The XRD characterization results are for the catalyst prepared in Example 1.

[0017] Figure 3 The catalyst prepared in Example 1 ( Figure 1 a) EDS characterization results. Detailed Implementation

[0018] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described below with reference to specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0019] Numerous specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways than those described herein, and therefore the invention is not limited to the specific embodiments disclosed in the following specification.

[0020] In the following embodiments, some of the devices and materials are manufactured or have the following specifications. Unless otherwise specified, all other materials are conventional reagents used in chemical and chemical engineering experiments.

[0021] N,N-Dimethylformamide: Content (≥99.5%), Shanghai Lingfeng Chemical Reagent Co., Ltd.

[0022] Palladium acetate: Pd content 45.8%-47%, Shaanxi Ruike New Materials Co., Ltd.

[0023] Polyvinylidene fluoride: CAS No.: 24937-79-9, KYNAR®761 powder, Arkema (China) Investment Co., Ltd.

[0024] Electrospinning device: ET-2535X, Beijing Yongkang Leyue Technology Development Co., Ltd.

[0025] Unless otherwise specified, the reaction process is as follows: The selective hydrogenation of phenol was carried out in a high-pressure reactor to evaluate the catalytic performance of the catalyst. A fiber catalyst sheet (approximately 7 cm²) was used. 2A phenol-cyclohexane solution (1 wt%, 5 mL) and cyclohexane were sequentially added to a 50 mL high-pressure reactor. After sealing, a leak test was performed. The reactor was purged five times with 0.2 MPa H2 to remove air. After purging, hydrogen gas was introduced until the pressure reached 0.1 MPa. The heating mantle and stirring switches on the reactor were turned on, and the temperature was raised to 80 °C and maintained. The stirring speed was kept at 100 rpm during the reaction. After the reaction was completed, the heating switch was turned off, and the heating mantle on the outside of the reactor was removed. The reactor was allowed to cool naturally to room temperature. The venting switch was turned on to release excess hydrogen gas. Then, the reactor was opened, and the sheet-like fiber catalyst was removed and recovered with tweezers. At the same time, 1 mL of the reaction solution was taken and analyzed by gas chromatography to calculate the conversion rate of phenol and the selectivity of cyclohexanone.

[0026] Example 1 This embodiment provides a specific preparation process for the Pd / PVDF catalyst. A 20 mL mixed solution of 18% PVDF and palladium acetate in a 15:1 mass ratio was prepared and stirred at 60°C for 4 hours at a stirring rate of 500 rpm to obtain an electrospinning solution. Nanofiber sheets of 10*30 cm were obtained using an electrospinning apparatus. The electrospinning operating conditions were set as follows: operating voltage 14 kV, syringe advance rate 0.2 mm / min, translation distance 60 mm, receiver receiving distance 13 cm, receiving speed 80 rpm, receiving time 2 hours, and humidity 30%. The spun nanofiber sheets were cut into 6*6 cm pieces and dried in a 70°C oven for 16 hours. They were then pressed and sheared into 3 cm diameter fiber discs using a 3 cm diameter stainless steel cylinder to obtain monolayer Pd / PVDF catalyst. The SEM characterization image of the catalyst is shown below. Figure 1 As shown in Figure a, the EDS characterization of the catalyst is as follows: Figure 3 As shown (original image is) Figure 1 a) Figure 3 The white portion shown is composed of Pd metallic particles. Figure 3 As can be seen, the active component Pd can be uniformly dispersed on the catalyst surface.

[0027] Testing showed that the catalyst prepared in this embodiment achieved a phenol conversion of 80% and a cyclohexanone selectivity of 99% after a reaction at 80℃ and 100 rpm for 30 min; and a phenol conversion of 95% and a cyclohexanone selectivity of 98% after a reaction at 100℃ and 100 rpm for 30 min. After the reaction, the sheet-like catalyst was removed and dried in a 70℃ oven for 1 h, followed by SEM characterization. The results are as follows. Figure 1 As shown in b, from Figure 1 a and Figure 1 As can be seen from b, the microstructure of the catalyst did not change significantly before and after the reaction.

[0028] Example 2 Unless otherwise specified, this embodiment and the following embodiments are consistent with Embodiment 1. An electrospinning solution with a PVDF mass fraction of 16% and a PVDF to palladium acetate mass ratio of 20:1 was prepared. Nanofiber sheets of 10*30cm were obtained by electrospinning using an electrospinning apparatus. The electrospinning operating conditions were set as follows: operating voltage 12kV, syringe advance rate 0.1mm / min, translation distance 65mm, receiver receiving distance 12cm, receiving speed 70rpm, receiving time 2h, and humidity 25%. The spun nanofiber sheets were cut into 6*6cm specifications, dried in a 70℃ oven for 16h, and then pressed and sheared into 3cm diameter fiber discs using a 3cm diameter stainless steel cylinder to obtain single-piece Pd / PVDF catalyst.

[0029] According to the test results, the catalyst prepared in this example has a phenol conversion rate of 78% and a cyclohexanone selectivity of 98% after a reaction at 80°C, 100 rpm and 30 min.

[0030] Example 3 An electrospinning solution with a PVDF mass fraction of 22% and a PVDF to palladium acetate mass ratio of 10:1 was prepared. Nanofiber sheets of 10*30cm were obtained by electrospinning using an electrospinning apparatus. The electrospinning operating conditions were set as follows: operating voltage 15kV, syringe advance rate 0.3mm / min, translation distance 50mm, receiver distance 14cm, receiving speed 90rpm, receiving time 2h, and humidity 70%. The spun nanofiber sheets were cut into 6*6cm pieces and dried in a 70℃ oven for 16h. They were then pressed and sheared into 3cm diameter fiber discs using a 3cm diameter stainless steel cylinder to obtain single-piece Pd / PVDF catalysts.

[0031] According to the test results, the catalyst prepared in this example has a phenol conversion rate of 75% and a cyclohexanone selectivity of 98% after a reaction at 80°C, 100 rpm and 30 min.

[0032] Example 4 This embodiment uses the catalyst recovered in Example 1 for a cyclic experiment. The catalyst recovery method is as follows: after the hydrogenation reaction is completed, the fiber catalyst is removed with tweezers without any treatment. Fresh reactants of the same composition are added to the reactor, followed by the fiber catalyst, and the same operating steps are repeated for a cyclic reaction. Testing showed that after four cycles at 80°C, 100 rpm, and 30 min, the catalyst activity did not significantly decrease. Furthermore, the morphology of the fiber catalyst remained unchanged after four cycles, indicating good catalytic stability. Mechanical stirring had no significant impact on the catalyst's catalytic performance, and the catalyst can be reused without additional recovery processes.

[0033] Comparative Example 1 The difference between this comparative example and Example 1 is that the spinning voltage was adjusted to 11kV, while the other preparation conditions remained the same as in Example 1. After testing, the catalyst prepared in this comparative example showed a phenol conversion rate of 40% and a cyclohexanone selectivity of 98% after a reaction at 80°C, 100 rpm, and 30 min. However, the catalyst agglomerated and its morphology changed after the reaction.

[0034] Comparative Example 2 The difference between this comparative example and Example 1 is that the concentration of PVDF in Example 1 was changed to 14%, while the other conditions remained the same. After testing, the catalyst prepared in this comparative example showed that the phenol conversion rate was 28% and the cyclohexanone selectivity was 99% after a reaction at 80°C, 100 rpm and 30 min.

[0035] Comparative Example 3 The difference between this comparative example and Example 1 is that electrospinning was not used. Instead, the mixture of PVDF, palladium acetate, and DMF was directly placed in a 70°C oven and dried for 16 hours to obtain the catalyst. Testing showed that, for the same mass, the catalyst prepared in this comparative example exhibited a phenol conversion of 5% and a cyclohexanone selectivity of 98% after a reaction at 80°C, 100 rpm, and 30 minutes.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A simple method for preparing a fiber Pd / PVDF hydrogenation catalyst, characterized in that, The steps are as follows: (1) Polyvinylidene fluoride, palladium acetate and N,N-dimethylformamide are mixed evenly and stirred to obtain a spinning solution; (2) Electrospinning the spinning solution to obtain nanofiber sheets; drying to obtain Pd / PVDF catalyst.

2. The simple method for preparing the fiber Pd / PVDF hydrogenation catalyst according to claim 1, characterized in that, In step (1), the mass fraction of polyvinylidene fluoride is 16-22%, and the mass ratio of polyvinylidene fluoride to palladium acetate is (10-30):

1.

3. The simple method for preparing the fiber Pd / PVDF hydrogenation catalyst according to claim 1, characterized in that, In step (2), the electrospinning conditions are: spinning voltage 12-15kV, feed rate 0.1-0.3mm / min, translation distance 50-65mm, receiver distance 12-14cm, receiver rate 70-90rpm, receiving time 1.9-2.1h, and humidity 20-70%.

4. The application of the fiber Pd / PVDF hydrogenation catalyst prepared by any one of claims 1-3 in the hydrogenation reaction process.

5. The application according to claim 4, characterized in that, The hydrogenation reaction is the hydrogenation of phenol to produce cyclohexanone.

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