Preparation method and application of zirconium-based catalyst for preparing cinnamyl alcohol through selective hydrogenation of cinnamyl aldehyde

Abstract

The invention belongs to the field of catalyst preparation and catalytic hydrogenation, and discloses a preparation method and application of a zirconium-based catalyst for preparing cinnamyl alcohol through selective hydrogenation of cinnamyl aldehyde. The zirconium-based catalyst is prepared by adopting an impregnation method, and the catalyst is prepared by introducing an organic ligand and carrying out high-temperature carbonization, so that the conversion rate of the catalyst to cinnamyl aldehyde is improved, and the selectivity of the catalyst to cinnamyl alcohol is improved. The preparation method adopted by the invention enables the catalyst preparation conditions to be milder and more efficient. In the aspect of application, the catalyst is prepared by using an impregnation method, so that the catalytic efficiency of ZrO2 is improved, the stability of a reaction system is improved, the catalyst is tried in a continuous reactor, the stability of 300 hours is kept, and a new thought is provided for application of cinnamyl aldehyde hydrogenation in the continuous reactor.

Description

Technical Field

[0001] The present invention belongs to the fields of catalyst preparation and catalytic hydrogenation, and relates to a preparation method and application of a zirconium-based catalyst with high stability and high selectivity for cinnamyl alcohol in a continuous flow reactor. Background Art

[0002] As a typical biomass-derived aromatic aldehyde compound, the molecular skeleton of cinnamaldehyde is derived from renewable resources such as natural cinnamon bark, and it is an important platform molecule for the high-value utilization of biomass. The selective catalytic conversion of cinnamaldehyde has become a model reaction for the development of green biomass synthesis processes, reflecting the technical potential and ecological value of biomass resources in replacing traditional fossil fuels for the production of fine chemicals. Cinnamaldehyde is not only an important by-product of biomass, but also the product after hydrogenation, cinnamyl alcohol, as a key intermediate of fine chemicals, has important application values in the fields of fragrance synthesis, preparation of pharmaceutical intermediates, and development of functional materials. The selective hydrogenation of cinnamaldehyde has attracted much attention because it is not easy to control. The challenge lies in precisely controlling the selective activation of the C=O bond to synthesize cinnamyl alcohol with high selectivity. Given that the activation energy of the C=C bond is relatively low and there are electronic structure differences within the molecule, the conjugated double bond is prone to over-hydrogenation during the reaction process. This inherent contradiction between the thermodynamic advantage and the selectivity of the target product, combined with the adsorption competition effect of the bifunctional groups on the catalyst surface, makes the carbonyl-directed hydrogenation technology have certain technical bottlenecks, and there is little record of the development of technologies for the hydrogenation of cinnamaldehyde in a continuous reactor.

[0003] Traditional methods for synthesizing cinnamyl alcohol include: the reduction method with aluminum benzylate. Aluminum chips are added to benzyl alcohol to react to form an aluminum benzylate solution. After cooling and filtering, it is added to a mixture of benzyl alcohol and cinnamaldehyde. It is heated to boiling under reduced pressure, and the generated benzaldehyde is distilled off. At the same time, benzyl alcohol is replenished until the theoretical amount of benzaldehyde is distilled off, then the feeding is stopped, and the remaining benzyl alcohol is distilled off to obtain crude cinnamyl alcohol, which is then obtained as cinnamyl alcohol through vacuum rectification. The selectivity of cinnamyl alcohol obtained by this method is relatively low, and the separation is difficult. The reduction method with potassium borohydride uses ethanol or methanol as a solvent. Potassium borohydride is added in an alkaline medium (pH = 12 - 14). After complete dissolution, cinnamaldehyde is added dropwise. After the addition is complete, the reaction continues until completion. Acetone is added to decompose the excess potassium borohydride. The pH value is adjusted to 7 with hydrochloric acid or dilute sulfuric acid. Ethanol or methanol is recovered at normal pressure by heating, and the temperature is lowered and left to stand for stratification. The crude cinnamyl alcohol in the lower layer of wastewater is separated, and then the cinnamyl alcohol finished product is obtained through vacuum distillation. However, this method has the disadvantages of complex process, difficult separation, and inability to operate in a continuous reactor.

[0004] To overcome the above-mentioned drawbacks, the current catalyst used for the selective hydrogenation of cinnamaldehyde is noble metal Pt. For example, Xiao Qiang et al. from Zhejiang Normal University (CN 103230804B) invented a catalyst with Fe3O4 and MCNT composite support loaded with Pt and its application in the selective hydrogenation of α,β-unsaturated aldehydes. Although this method has achieved good results, the selectivity does not exceed 95%. It will increase the process flow during separation, resulting in an increase in energy consumption. At the same time, Pt belongs to noble metals, further increasing the production cost. There is also a method using ZrO2 as a catalyst for transfer hydrogenation. For example, (A facile synthesis of in-situ formed amorphous zirconia catalysts for efficient transfer hydrogenation of unsaturated aldehydes[J].Fuel,2022,317:123551) uses amorphous zirconia as the active center. Although the conversion rate is very high, there are certain defects in the stability of the catalyst.

[0005] At the same time, few studies have applied the cinnamaldehyde hydrogenation to prepare cinnamyl alcohol system in a continuous reactor. Based on the hydrophobicity of carbon materials, it is more conducive to enriching substances with less polarity, while for substances with greater polarity, they are more likely to desorb. The polarity of cinnamyl alcohol is higher than that of cinnamaldehyde. Relative to cinnamyl alcohol, carbon materials have a stronger adsorption ability for cinnamaldehyde, and at the same time, it may also make cinnamyl alcohol more likely to desorb. This characteristic may enhance the stability of the catalyst.

[0006] To solve the problem of low selectivity of the catalyst for cinnamyl alcohol and at the same time solve the problem of the stability of the catalyst in the fixed bed, taking advantage of the advantages of carbon materials, a new catalyst is designed for use in a continuous flow fixed bed reactor. The prepared catalyst not only has a selectivity for cinnamyl alcohol reaching more than 99%, but also the reaction stability exceeds 300 h. Summary of the Invention

[0007] The present invention provides a preparation method and application of a zirconium-based catalyst for the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol. The synthesis scheme of the catalyst is relatively simple. The prepared catalyst is used in a continuous flow fixed bed reactor. The prepared catalyst not only has a selectivity for cinnamyl alcohol reaching more than 99%, but also the reaction stability exceeds 300 h. At the same time, the influence of different carbon sources on the activity of the catalyst is verified.

[0008] The technical solution of the present invention:

[0009] A preparation method of a zirconium-based catalyst for the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol, the steps are as follows:

[0010] S1. Dissolve ZrOCl2·8H2O and the organic ligand in deionized water to prepare solution A; drop solution A into the SiO2 support by the method of equal-volume impregnation;

[0011] S2. Place the impregnated SiO2 support in a normal-temperature environment and let it stand for aging;

[0012] S3. Dry the aged SiO2 support to obtain the catalyst precursor;

[0013] S4. Place the catalyst precursor in a quartz tube reactor and introduce an inert gas for pretreatment; heat the catalyst precursor from room temperature to 400 - 600 °C and treat for 4 h, then cool to room temperature to obtain the zirconium-based catalyst.

[0014] In step S1, the organic ligand includes glucose, fructose or dopamine hydrochloride.

[0015] In step S1, the mass ratio of ZrOCl2·8H2O to dopamine hydrochloride is 1 / 0.01 - 1 / 0.1.

[0016] In step S3, the drying temperature is 60 - 140 °C.

[0017] In step S4, the heating rate is 3 - 10 °C / min.

[0018] In step S4, the inert gas includes but is not limited to N2 and Ar;

[0019] Load the zirconium-based catalyst into a continuous flow reactor, the mass concentration of cinnamaldehyde in isopropanol is 0.5 - 3%, the reaction temperature is 60 - 160 °C, and the flow rate is 0.05 - 0.3 mL / min under the condition of 0.1 MPa.

[0020] Advantages of the present invention:

[0021] (1) By introducing a carbon source into the catalyst in the present invention, not only can the dispersion degree of ZrO2 be increased, but also the carbonized organic ligand can increase the adsorption rate of the catalyst to cinnamaldehyde, further increasing the conversion rate of cinnamaldehyde. The carbon layer can also promote the desorption of the product, thereby improving the stability of the catalyst.

[0022] (2) The selection of the organic ligand is also important in the present invention. Ligands with too strong complexing ability will increase the difficulty of the raw materials contacting the active sites, which is not conducive to improving the activity of the catalyst.

[0023] (3) It is found during the pretreatment of the catalyst precursor that only under an inert atmosphere can the best effect of the catalyst be maintained. This is because the ligand is prone to decomposition and loss under a hydrogen atmosphere at high temperature, which will reduce the introduced carbon amount. Description of the Drawings

[0024] Figure 1 Catalyst reaction stability diagram for Example 8.

[0025] Figure 2 Catalyst reaction stability diagram for Comparative Example 3.

[0026] Figure 3 XRD diagram of the catalysts in Example 1 and Comparative Example 1.

[0027] Figure 4 TEM diagram of the catalyst in Example 1. Detailed implementation manners

[0028] The following further illustrates the detailed implementation manners of the present invention in conjunction with the accompanying drawings and technical solutions.

[0029] Example 1

[0030] Using the basic principle of the equal-volume impregnation method, a ZrO2-based composite catalyst was constructed. First, 1.20 g of ZrOCl2·8H2O and 0.05 g of dopamine hydrochloride were accurately weighed and dissolved together in 2 mL of deionized water to form a solution. Subsequently, the prepared solution was dropped into 1.0 g of fumed silica drop by drop to ensure that the solution fully infiltrated the pores of the carrier. The obtained sample was aged by standing at room temperature for 12 h and then transferred to a drying oven at 100 °C for overnight drying. The dried sample was placed in an N2 atmosphere and heated from room temperature to 500 °C at a rate of 5 °C / min and held at a constant temperature for 4 h, and the target catalyst ZrO2@C / SiO2 was obtained after natural cooling. The obtained catalyst was loaded into a continuous flow reactor with an inner diameter of 10 mm. The mass concentration of cinnamaldehyde in isopropanol was 1%, the reaction temperature was 100 °C, and the flow rate was 0.07 mL / min under the condition of 0.1 MPa. After the reaction system was stabilized, the effluent was collected and the reaction products were analyzed and detected by gas chromatography.

[0031] Example 2

[0032] The dopamine hydrochloride in Example 1 was replaced with glucose. The remaining reaction conditions were the same as those in Example 1.

[0033] Example 3

[0034] The dopamine hydrochloride in Example 1 was replaced with fructose. The remaining reaction conditions were the same as those in Example 1.

[0035] Example 4

[0036] In Example 1, accurately weighing 1.20 g of ZrOCl2·8H2O and 0.05 g of dopamine hydrochloride was replaced by accurately weighing 1.20 g of ZrOCl2·8H2O and 0.08 g of dopamine hydrochloride. The remaining reaction conditions were the same as those in Example 1.

[0037] Example 5

[0038] In Example 1, first accurately weigh 1.20 g of ZrOCl₂·8H₂O and replace 0.01 g of dopamine hydrochloride with 0.05 g of dopamine hydrochloride. The remaining reaction conditions are the same as those in Example 1.

[0039] Example 6

[0040] In Example 1, replace heating from room temperature to 450 °C at a rate of 5 °C / min and holding for 4 h with heating from room temperature to 500 °C at a rate of 5 °C / min and holding for 4 h. The remaining reaction conditions are the same as those in Example 1.

[0041] Example 7

[0042] In Example 1, replace heating from room temperature to 450 °C at a rate of 5 °C / min and holding for 4 h with heating from room temperature to 550 °C at a rate of 5 °C / min and holding for 4 h. The remaining reaction conditions are the same as those in Example 1.

[0043] Example 8

[0044] In Example 1, replace the flow rate of 0.07 mL / min under the condition of 0.1 MPa with a flow rate of 0.1 mL / min under the condition of 0.1 MPa. The reaction time is extended by 300 h, and samples are taken every 2 h for detection. The remaining reaction conditions are the same as those in Example 1.

[0045] Comparative Example 1

[0046] Using the basic principle of the equal-volume impregnation method, a ZrO₂ catalyst was constructed. First, accurately weigh 1.20 g of ZrOCl₂·8H₂O, dissolve it in 2 mL of deionized water to form a solution. Subsequently, the prepared solution was gradually dropped into 1.0 g of fumed silica to ensure that the solution fully infiltrated the pores of the carrier. The obtained mixture was aged by standing at room temperature for 12 h and then transferred to a 100 °C drying oven for overnight drying. The dried sample was placed in an N₂ atmosphere, heated from room temperature to 450 °C at a rate of 5 °C / min and held for 4 h, and then naturally cooled to obtain the target catalyst ZrO₂ / SiO₂. The obtained catalyst was loaded into a continuous flow reactor with an inner diameter of 10 mm. The mass concentration of cinnamaldehyde in isopropanol was 1%, the reaction temperature was 100 °C, and the flow rate was 0.07 mL / min under the condition of 0.1 MPa. After waiting for the reaction system to stabilize, the effluent was collected, and the reaction products were analyzed and detected by gas chromatography.

[0047] Comparative Example 2

[0048] The catalyst prepared in Example 1 was calcined in air for 4 h to obtain the catalyst ZrO2 / SiO2-A. The obtained catalyst was loaded into a continuous flow reactor with an inner diameter of 10 mm. The mass concentration of cinnamaldehyde in isopropanol was 1%, the reaction temperature was 100 °C, and the flow rate was 0.1 mL / min under the condition of 0.1 MPa. After the reaction system was stabilized, the effluent was collected every two hours, and the reaction products were analyzed and detected by gas chromatography.

[0049] Comparative Example 3

[0050] 0.05 g of citric acid was used to replace 0.05 g of dopamine hydrochloride in Example 1. The other reaction conditions were the same as those in Example 1.

[0051] Comparative Example 4

[0052] The dried sample in Example 1 was placed in an H2 atmosphere instead of a N2 atmosphere. The other reaction conditions were the same as those in Example 1.

[0053] Comparative Example 5

[0054] The reaction time in Comparative Example 1 was extended by 50 h, and samples were taken and detected every 2 h. The other reaction conditions were the same as those in Comparative Example 1.

[0055] The gas chromatography data in Examples 1-7 and Comparative Examples 1-4 were analyzed, and the results are shown in Table 1:

[0056] Table 1. Comparison of the performance of selective hydrogenation of cinnamaldehyde in Examples and Comparative Examples

[0057]

[0058]

[0059] As can be seen from Table 1, the addition of the organic ligand not only increased the conversion rate of the catalyst to cinnamaldehyde, but also increased the selectivity of the catalyst to cinnamyl alcohol. After changing the organic ligand, the activity of the catalyst was still higher than that of ZrO2 / SiO2 without the ligand. Figure 1 and Figure 2The stability of two catalysts was compared. Experiments have shown that the introduction of ligands significantly increases the stability of the catalyst. As documented in the literature, this is because the active centers are encapsulated by carbon, which not only increases the adsorption capacity of raw materials but also further prevents the loss of active centers (Carbon encapsulated bimetallic FeCo nanoalloys for one-step hydroxylation of benzene to phenol[J].Applied Catalysis A:General,2022,633:118499.).

[0060] Examples 1, 2, and 3 demonstrate the promoting effect of different carbon sources on the activity of the catalyst. Although the ligand was changed, the activity of the catalyst was still higher than that of the comparative example.

[0061] As can be seen from Examples 1, 4, and 5, under the same reaction conditions after the introduction of dopamine hydrochloride, the catalytic activity of ZrO2@C / SiO2 is much higher than that of ZrO2 / SiO2, and the selectivity of the catalyst after the introduction of dopamine hydrochloride is higher than 99%. This indicates that the introduction of dopamine hydrochloride increases the adsorption capacity of the catalyst for cinnamaldehyde.

[0062] As can be seen from Examples 1, 6, and 7, under the same reaction conditions after the introduction of dopamine hydrochloride, the heat treatment temperature has an impact on the activity of the catalyst within a certain range. The best effect is achieved when the treatment temperature is 500 °C.

[0063] Comparative Example 2 shows that after removing the carbon on the catalyst surface, it basically returns to the state without the introduction of dopamine hydrochloride, further proving the promoting effect of the introduction of the carbon source on the catalyst activity.

[0064] Comparative Example 3 shows that although the introduction of citric acid also promotes the activity of the catalyst, due to the too strong complexation of citric acid, the resistance to the contact between the carbon layer and the raw materials increases, and the activity is not as good as that of dopamine hydrochloride, glucose, or fructose.

[0065] Comparative Example 4 shows that the atmosphere during the pretreatment of the catalyst precursor also affects the activity of the catalyst, and the best effect is achieved only under an inert atmosphere.

[0066] As can be seen from the comparison between Example 8 and Comparative Example 5( Figure 1 and Figure 2 ), the catalyst after adding dopamine hydrochloride in the reaction not only improves the conversion rate of cinnamaldehyde hydrogenation to cinnamyl alcohol but also maintains a stability of 300 h, while the catalyst without adding dopamine hydrochloride is in a state of slow deactivation.

[0067] The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Without departing from the essence of the present invention, any improvements or changes made by those skilled in the art to the above description shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A preparation method of a zirconium-based catalyst for the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol, characterized in that, The steps are as follows: S1. Dissolve ZrOCl2·8H2O and the organic ligand in deionized water to prepare solution A; use the equal-volume impregnation method to drop solution A into the SiO2 support; S2. Place the impregnated SiO2 support in a normal-temperature environment and let it stand for aging; S3. Dry the aged SiO2 support to obtain the catalyst precursor; S4. Place the catalyst precursor in a quartz tube reactor and introduce an inert gas for pretreatment; heat the catalyst precursor from room temperature to 400 - 600 °C and treat for 4 h, then cool to room temperature to obtain the zirconium-based catalyst.

2. The preparation method according to claim 1, wherein in step S1, the organic ligand includes glucose, fructose or dopamine hydrochloride.

3. The preparation method according to claim 1, wherein in step S1, the mass ratio of ZrOCl2·8H2O to dopamine hydrochloride is 1:0.01 - 1:0.

1.

4. The preparation method according to claim 1, wherein in step S3, the drying temperature is 60 - 140 °C.

5. The preparation method according to claim 1, wherein in step S4, the heating rate is 3 - 10 °C / min.

6. The preparation method according to claim 1, wherein in step S4, the inert gas includes but is not limited to N2 and Ar.

7. Use of the zirconium-based catalyst obtained by the preparation method according to any one of claims 1-6, characterized in that, Load the zirconium-based catalyst into a continuous flow reactor. The mass concentration of cinnamaldehyde in isopropanol is 0.5 - 3%, the reaction temperature is 60 - 160 °C, and the flow rate is 0.05 - 0.3 mL / min under the condition of 0.1 MPa.

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