A sulfuric acid-activated palladium-carbon catalyst, its preparation method and use

Abstract

The application discloses a sulfuric acid acidified palladium carbon catalyst and a preparation method and application thereof, and the preparation process of the catalyst comprises the following steps: sulfuric acid acidification of activated carbon, washing, preparation of a palladium chloride hydrochloride solution as a precursor, preparation of a suspension of the sulfuric acid acidified activated carbon in deionized water, dropwise addition of the palladium chloride hydrochloride solution into the suspension of the sulfuric acid acidified activated carbon, vigorous stirring, filtration, vacuum drying, and obtaining of the sulfuric acid acidified palladium carbon catalyst, and application of the catalyst to preparation of 2,5-dimethyltetrahydrofuran. The application self-prepares a high-efficiency sulfuric acid acidified palladium carbon catalyst to catalyze a reaction, the catalyst has good circulation stability, and has the advantages of simple reaction, low reaction temperature, easy separation of a product, high yield and the like.

Description

Technical Field

[0001] This invention belongs to the field of 2,5-dimethyltetrahydrofuran preparation technology, specifically relating to a sulfuric acid-acidified palladium-on-carbon catalyst, its preparation method, and its application. Background Technology

[0002] 2,5-Dimethyltetrahydrofuran (DMTHF) is a valuable organic solvent with excellent flammability (RON=82), high energy density (31MJ / L), good volatility, and low miscibility with water, making it an excellent candidate for gasoline alternatives. It can also be converted into other high-value-added chemicals, such as 2,4-hexadiene and 2,5-hexanediol.

[0003] Currently, there are only a few reports in the literature on the preparation process of 2,5-dimethyltetrahydrofuran, most of which have problems such as harsh reaction conditions, complex preparation process, difficulty in catalyst recovery, high cost, and low production efficiency. Summary of the Invention

[0004] To address the above problems, the present invention aims to provide a sulfuric acid-acidified palladium-on-carbon catalyst, its preparation method, and its application.

[0005] To achieve the above objectives, the following technical solution is proposed:

[0006] A method for preparing a sulfuric acid-acidified palladium-on-carbon catalyst includes the following steps:

[0007] 1) Pour a 50% sulfuric acid solution into a container containing activated carbon, stir for 1 hour, then soak for 48 hours, and then drain the sulfuric acid solution.

[0008] 2) Wash the activated carbon after sulfuric acid treatment with distilled water, filter and rinse until the filtrate is neutral, and dry it in an oven to constant weight;

[0009] 3) Prepare a palladium chloride hydrochloride solution as a precursor. Place sulfuric acid-acidified activated carbon in deionized water to prepare a suspension of sulfuric acid-acidified activated carbon. Add the palladium chloride hydrochloride solution dropwise to the suspension of sulfuric acid-acidified activated carbon. After stirring vigorously for 24 hours, filter and vacuum dry to obtain the sulfuric acid-acidified palladium carbon catalyst.

[0010] Furthermore, the process of preparing the palladium chloride hydrochloride solution involves dissolving 5g of PdCl2 in 250mL of 0.226mol / L HCl, and the process of preparing the suspension of sulfuric acid-acidified activated carbon involves placing 1g of sulfuric acid-acidified activated carbon in 30mL of deionized water.

[0011] Furthermore, in step 3), the vacuum drying temperature is 120°C and the drying time is 8 hours.

[0012] A sulfuric acidified palladium-on-carbon catalyst prepared by the above preparation method.

[0013] The application of a sulfuric acid-acidified palladium-on-carbon catalyst in the preparation of 2,5-dimethyltetrahydrofuran includes the following steps: 5-hydroxymethylfurfural raw material, solvent, and sulfuric acid-acidified palladium-on-carbon catalyst are placed in a polytetrafluoroethylene liner. The polytetrafluoroethylene liner is then transferred to a high-pressure reactor. After the air is replaced with nitrogen three times, hydrogen is introduced to bring the reaction pressure to 3-5 MPa, preferably 4 MPa. The rotation speed is adjusted to carry out the reaction. After the reaction is completed, samples are taken for GC and GC-MS analysis.

[0014] Furthermore, the amount of palladium-carbon catalyst acidified with sulfuric acid is 4%-8% wt of the amount of 5-hydroxymethylfurfural feedstock, preferably 4% wt.

[0015] Further, the solvent is one or more of water, methanol, ethanol, isopropanol, and 1,4-dioxane, preferably isopropanol, and the concentration of 5-hydroxymethylfurfural in the solvent is 0.077 g / mL to 0.155 g / mL, preferably 0.155 g / mL.

[0016] Furthermore, the rotation speed is 600 rpm, the reaction temperature is 110-140℃, preferably 130℃, and the reaction time is 4-8h, preferably 6h.

[0017] The beneficial effects of this invention are as follows:

[0018] This invention provides a self-made, highly efficient sulfuric acid-acidified palladium-carbon catalyst for catalytic reactions. The catalyst exhibits good cycle stability and has advantages such as simple reaction, low reaction temperature, easy product separation, and high yield. Attached Figure Description

[0019] Figure 1 Reaction pathway diagram for the preparation of 2,5-dimethyltetrahydrofuran by catalytic hydrogenolysis of 5-hydroxymethylfurfural;

[0020] Figure 2 The gas phase mass spectrum of 2,5-dimethyltetrahydrofuran (trans) prepared in Example 16;

[0021] Figure 3 The gas phase mass spectrum of 2,5-dimethyltetrahydrofuran (cis) prepared in Example 16;

[0022] Figure 4 The gas chromatogram of 2,5-dimethyltetrahydrofuran prepared in Example 16 is shown. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited thereto.

[0024] Example 1

[0025] Preparation of sulfuric acidified palladium on carbon catalyst

[0026] Take about 50g of activated carbon and put it into a 500mL beaker. Pour 250mL of 50% sulfuric acid solution into the beaker containing the activated carbon, stir for 1 hour and then soak for 48 hours. After that, pour out as much sulfuric acid solution as possible from the beaker, wash the activated carbon after sulfuric acid acidification with distilled water, filter and rinse until the filtrate is neutral, and put it in an oven to dry to constant weight.

[0027] Pd / AC was prepared by chemisorption. A palladium chloride hydrochloride solution (5g PdCl2 dissolved in 250mL 0.226mol / L HCl) was prepared as a precursor, and water was used as a solvent. The loading of Pd on activated carbon was fixed at 5% by mass. The palladium chloride hydrochloride solution was added dropwise to a suspension of sulfuric acid-acidified activated carbon (1g sulfuric acid-acidified activated carbon was placed in 30mL deionized water). After stirring vigorously for 24h, the mixture was filtered, dried under vacuum at 120℃ for 8h, and then stored for use.

[0028] Example 2

[0029] like Figure 1 The diagram shows the reaction pathway for the preparation of 2,5-dimethyltetrahydrofuran via catalytic hydrogenolysis of 5-hydroxymethylfurfural.

[0030] 2.5 g of 5-hydroxymethylfurfural and 30 mL of ethanol were added to a polytetrafluoroethylene (PTFE) liner, followed by 0.2 g of a commercial 5% palladium-on-carbon catalyst. The PTFE liner was then transferred to a high-pressure reactor. After three nitrogen purgings, hydrogen was introduced to bring the reaction pressure to 3 MPa. The reaction temperature was set to 120 °C, the rotation speed to 600 rpm, and the reaction time to 4 h. The reactor was then started. After the reaction, samples were taken for GC and GC-MS analysis. The results are shown in Table 1.

[0031] The formulas for calculating the yield (Y) of 2,5-dimethyltetrahydrofuran, the conversion (X) of 5-hydroxymethylfurfural, and the selectivity (S) are as follows:

[0032] X = (mass of 5-hydroxymethylfurfural actually participating in the reaction / mass of 5-hydroxymethylfurfural in the raw materials) × 100%;

[0033] Y = (mass of 2,5-dimethyltetrahydrofuran in the reaction products / theoretical mass of 2,5-dimethyltetrahydrofuran) × 100%;

[0034] S = (Y / X) × 100%.

[0035] Example 3

[0036] The operation process was the same as in Example 2, except that the commercially available 5% palladium-on-carbon catalyst was replaced with the sulfuric acid-acidified palladium-on-carbon catalyst prepared in Example 1. The results are shown in Table 1.

[0037] Table 1 Summary of catalytic performance of different palladium-on-carbon catalysts

[0038] Example catalyst Conversion rate Selective Yield 2 Commercial Palladium Carbon 96.72％ 1.21％ 1.17％ 3 Homemade palladium carbon 90.94％ 89.27％ 81.18％

[0039] Compared with Examples 1-2, the commercial palladium on carbon showed poor selective production of 2,5-dimethyltetrahydrofuran from HMF; the self-made sulfuric acid-acidified palladium on carbon catalyst showed considerable catalytic effect. Further adjustments to other reaction conditions were made to observe the reaction effect.

[0040] Examples 4-6

[0041] The reaction temperature was changed, and other conditions were the same as in Example 3. The results are shown in Table 2.

[0042] Table 2 Summary of catalytic performance of palladium-on-carbon catalysts acidified with sulfuric acid at different temperatures

[0043] Example reaction temperature Conversion rate Selective Yield 4 110℃ 85.23％ 87.55％ 74.62％ 5 130℃ 92.47％ 90.91％ 84.06％ 6 140℃ 92.98％ 91.26％ 84.85％

[0044] Comparing Examples 3-6, it can be found that when the reaction temperature is increased from 110℃ to 130℃, the conversion rate, selectivity and yield of HMF to DMTHF are significantly improved. When the temperature is further increased to 140℃, there is no significant improvement compared with 130℃.

[0045] Examples 7-8

[0046] The reaction pressure was changed, and other conditions were the same as in Example 5. The results are shown in Table 3.

[0047] Table 3. Summary of catalytic performance of palladium-on-carbon catalysts for sulfuric acid oxidation under different reaction pressures.

[0048] Example Reaction pressure Conversion rate Selective Yield 7 4MPa 96.25％ 91.68％ 88.24％ 8 5MPa 98.12％ 89.99％ 88.30％

[0049] Comparing Examples 5, 7 and 8, when the reaction pressure was increased from 3 MPa to 4 MPa, the conversion rate, selectivity and yield all showed an upward trend. When the pressure was increased from 4 MPa to 5 MPa, the conversion rate improved, the selectivity decreased slightly, and the yield remained basically unchanged.

[0050] Example 9

[0051] The reaction time in Example 7 was set to 8 hours, and samples were taken and analyzed at reaction times of 5 hours, 6 hours, 7 hours, and 8 hours. The results are shown in Table 4.

[0052] Table 4 Product yield at different reaction times

[0053]

[0054] Comparing Examples 7 and 8, the HMF conversion rate gradually increased with the extension of reaction time. When the reaction time was extended from 4h to 6h, the selectivity and yield of DMTHF gradually increased. When the reaction time was extended from 6h to 8h, the selectivity began to decrease, while the yield remained basically unchanged.

[0055] Example 10

[0056] 4g of 5-hydroxymethylfurfural and 30mL of ethanol were added to a polytetrafluoroethylene (PTFE) liner, followed by 0.2g of the sulfuric acid-acidified palladium-on-carbon catalyst prepared in Example 1. The PTFE liner was transferred to a high-pressure reactor. After three purgings with inert gas, hydrogen was introduced to a reaction pressure of 4MPa. The reaction temperature was set to 130℃, the rotation speed to 600rpm, and the reaction time to 6h. The reactor was then started. After the reaction, samples were taken for GC and GC-MS analysis. The results are shown in Table 5.

[0057] Examples 11-14

[0058] The amounts of 5-hydroxymethylfurfural feedstock and catalyst were varied, while other operating conditions remained the same as in 10. The results are shown in Table 5.

[0059] Table 5. Summary of product yields under different catalyst dosages and 5-hydroxymethylfurfural feedstock.

[0060]

[0061] Under the condition that the reaction effect remains basically unchanged, the maximum amount of HMF used is 5.5g (i.e., the maximum concentration is 0.155g / mL), and the minimum amount of catalyst used is 0.22g (4% wt HMF).

[0062] Examples 15-17

[0063] Different solvents were selected, and other operating conditions were the same as in Example 13. The results are shown in Table 6.

[0064] Table 6 Summary of Product Yields with Different Solvents

[0065] Example solvent Conversion rate Selective Yield 15 water 58.96％ 4.90％ 2.89％ 16 Isopropanol 99.87％ 93.96％ 93.84％ 17 1,4-Dioxane 97.70％ 91.05％ 88.96％

[0066] As can be seen from the table, isopropanol is the most effective solvent. The gas chromatography-mass spectrum of 2,5-dimethyltetrahydrofuran prepared in Example 16 is shown below. Figure 2 and Figure 3 As shown, the gas chromatogram is as follows: Figure 4 As shown.

[0067] Example 18

[0068] The catalyst was separated from the material obtained after the reaction in Example 16 by filtration. The obtained catalyst was directly used in the next cycle under the reaction conditions of Example 16 without adding any fresh catalyst. The results are shown in Table 7. After five cycles, the conversion, selectivity and yield were slightly reduced within acceptable ranges.

[0069] Table 7 Catalytic performance of catalysts at different cycle numbers

[0070]

Claims

1. The application of a sulfuric acid-acidified palladium-on-carbon catalyst in the preparation of 2,5-dimethyltetrahydrofuran, characterized in that, The process includes the following steps: 5-hydroxymethylfurfural raw material, solvent, and sulfuric acid-acidified palladium-carbon catalyst are added to a polytetrafluoroethylene (PTFE) liner. The PTFE liner is then transferred to a high-pressure reactor. After the air is replaced with nitrogen three times, hydrogen is introduced until the reaction pressure is 3-5 MPa. The rotation speed is adjusted to carry out the reaction. After the reaction is completed, samples are taken for GC and GC-MS analysis. The preparation method of sulfuric acid-acidified palladium-on-carbon catalyst includes the following steps: 1) Pour a 50% sulfuric acid solution into a container containing activated carbon, stir for 1 hour, then soak for 48 hours, and then drain the sulfuric acid solution. 2) Wash the activated carbon acidified with sulfuric acid with distilled water, filter and rinse until the filtrate is neutral, and dry it in an oven to constant weight; 3) Prepare a palladium chloride hydrochloride solution as a precursor. Place sulfuric acid-acidified activated carbon in deionized water to prepare a suspension of sulfuric acid-acidified activated carbon. Add the palladium chloride hydrochloride solution dropwise to the suspension of sulfuric acid-acidified activated carbon. After stirring vigorously for 24 hours, filter and vacuum dry to obtain the sulfuric acid-acidified palladium carbon catalyst.

2. The application as described in claim 1, characterized in that, The process for preparing palladium chloride hydrochloride solution is to dissolve 5 g of PdCl2 in 250 mL of 0.226 mol / L HCl. The process for preparing sulfuric acid-acidified activated carbon suspension is to place 1 g of sulfuric acid-acidified activated carbon in 30 mL of deionized water.

3. The application as described in claim 1, characterized in that, The vacuum drying temperature in step 3) is 120℃ and the drying time is 8h.

4. The application as described in claim 1, characterized in that, The amount of palladium-carbon catalyst acidified with sulfuric acid is 4%-8% wt of the amount of 5-hydroxymethylfurfural feedstock.

5. The application as described in claim 1, characterized in that, The solvent is one or more of water, methanol, ethanol, isopropanol, and 1,4-dioxane, and the concentration of 5-hydroxymethylfurfural in the solvent is 0.077 g / mL to 0.155 g / mL.

6. The application as described in claim 1, characterized in that, The rotation speed is 600 rpm, the reaction temperature is 110-140℃, and the reaction time is 4-8 hours.

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