Catalyst for synthesizing furan by decarbonylation of furfural as well as preparation method and application of catalyst

Abstract

The invention belongs to the technical field of furan synthesis, and particularly relates to a catalyst for synthesizing furan through furfural decarbonylation and a preparation method and application thereof.The catalyst comprises a carrier and active components loaded on the carrier, and the active components comprise a main active component and an auxiliary active component; the main active component is located on the outer layer of the carrier, and the main active component is metal palladium; the auxiliary active component is embedded into the carrier, and the auxiliary active component is alkali metal oxide. According to the preparation method of the catalyst, the loading capacity of Pd is reduced, the problem that the catalyst is rapidly inactivated due to the fact that the raw material furfural is easy to coke is solved through the special structure of Pd, and the activity, selectivity and stability of the catalyst are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of furan synthesis, and particularly relates to a catalyst for synthesizing furan by decarbonylating furfural, and a preparation method and application thereof. Background Art

[0002] Furan is an important intermediate compound, widely used in many important organic syntheses and drug production, and can be used to prepare pyrrole, tetrahydrofuran, 2-acetylpyrazine, etc. Among them, tetrahydrofuran is an important derivative of furan, which can be used as a solvent and can also be used to prepare polytetramethyleneimine acetal.

[0003] At present, the domestic production methods of furan include furoic acid decarboxylation, furfural oxidation and furfural decarbonylation. Among them, furfural decarboxylation and furfural oxidation have been gradually eliminated due to their low reaction activity and high toxicity to catalysts. The raw materials of furfural decarbonylation come from renewable plant energy, which is a cheap organic chemical raw material. The furan is prepared by furfural decarbonylation, and the selectivity of furfural and the yield of furan are both high.

[0004] Furfural decarbonylation can be divided into gas phase method and liquid phase method. The gas phase method has the characteristics of simple operation, continuous operation, large processing capacity, low catalyst dosage, and regeneration. However, furfural vaporization is relatively difficult, and it is easy to polymerize and coke during the vaporization process, blocking the preheating pipeline, and also causing waste of furfural. Liquid phase decarbonylation generally does not require the introduction of other gases, but requires a special automatic sampling device and condensation reflux device to control the amount of furfural in the reactor and condense and reflux unreacted furfural. The catalysts used in the two methods are similar, and both are precious metal palladium catalysts at present, and the yield of furan is also relatively close. However, compared with the gas phase decarbonylation method, the biggest disadvantage of the liquid phase decarbonylation method is that the catalyst has poor stability and is easy to deactivate, resulting in high catalyst unit consumption and increased production costs. Therefore, the furfural gas phase decarbonylation method production technology route is adopted in industry.

[0005] Patent CN103084168A discloses a furfural gas phase reduction decarbonylation catalyst, wherein the carrier is at least one of activated carbon, alumina, silicon dioxide, titanium dioxide, vanadium pentoxide, and tin dioxide, the main active component is Pd, and the co-catalyst active component is at least one of Ni, Co, Mg, Ca, Ba, Ge, Cr rare earth elements and alkali metals. A large amount of organic solvents need to be used in the preparation process of the catalyst, which may cause safety hazards and increase production costs. At the same time, the preparation process of the catalyst is also complicated, and batch production is difficult and costly. Patent CN117816191A prepares a catalyst with platinum as the active component, and ZrO2 and CeO2 are used to modify alumina, while Co is used as the active component, and the amount of platinum used is reduced under the premise of ensuring the catalytic effect of the catalyst. However, the catalyst has a large number of component types and uses precious metal platinum, so the production cost of the catalyst is limited.

[0006] In recent years, the rising price of palladium and the poor stability of Pd catalysts have limited the use of palladium catalysts in furfural gas phase decarbonylation. Therefore, it is urgent to develop a new furfural decarbonylation catalyst to improve the activity and stability of the catalyst and reduce the cost of the catalyst. Summary of the invention

[0007] The purpose of the present invention is to provide a catalyst for synthesizing furan by decarbonylation of furfural, and a preparation method and application thereof, so as to overcome the shortcomings of the prior art and provide a preparation method for the catalyst for synthesizing furan by decarbonylation of furfural, which not only reduces the loading amount of the noble metal Pd, but also improves the stability of the catalyst.

[0008] In order to achieve the above object, the technical solution of the present invention is: In a first aspect, the present invention provides a catalyst for decarbonylating furfural to synthesize furan, comprising a carrier and an active component supported on the carrier, wherein the active component comprises a main active component and an auxiliary active component; The main active component is located in the outer layer of the carrier, and the main active component is metal palladium; The auxiliary active component is embedded in the carrier, and the auxiliary active component is an alkali metal oxide.

[0009] In some embodiments, the alkali metal oxide is one of potassium oxide and sodium oxide, and the content of the alkali metal oxide is 1-10 wt % based on the total amount of the catalyst.

[0010] In some embodiments, based on the total amount of the catalyst, the content of the metal palladium is 0.05-0.5 wt %, and the particle size of the metal palladium is 2.5-4.5 nm.

[0011] In some embodiments, the carrier is one of TiO2, Al2O3, SiO2, activated carbon and ZSM-5, and the carrier size is 3-5 mm.

[0012] In a second aspect, the present invention provides a method for preparing the catalyst for decarbonylation of furfural to furan as described in the first aspect, comprising the following steps: adding a carrier to a palladium salt solution, then adding a precipitant to react, and obtaining a catalyst intermediate through aging, drying and calcining; and impregnating the catalyst intermediate into an alkali metal salt solution, and obtaining a catalyst for decarbonylation of furan after drying.

[0013] In some embodiments, the palladium salt is one of tetraaminopalladium nitrate, palladium acetate, palladium nitrate and palladium sulfate, and the concentration of the palladium salt is 0.01-2 mol / L.

[0014] In some embodiments, the precipitant is one of sodium carbonate, potassium carbonate, sodium hydroxide and potassium hydroxide, the reaction temperature is 25-90° C., and the pH is 8-12.

[0015] In some embodiments, the aging time is 1-4 h, the drying temperature is 70-80° C., and the drying time is 10-12 h; the calcination temperature is 400-500° C., and the calcination time is 1-5 h.

[0016] In some embodiments, the alkali metal salt is one of potassium hydroxide, sodium hydroxide, potassium nitrate and sodium nitrate, and the concentration of the alkali metal salt solution is 0.1-2 mol / L; Alternatively, the immersion temperature is 25-60° C. and the immersion time is 0.5-12 h.

[0017] In a third aspect, the present invention provides use of the catalyst for furfural decarbonylation to furan described in the first aspect in furfural decarbonylation to furan.

[0018] Beneficial effects of the present invention: Compared with conventional Pd-containing catalysts (with a Pd loading of about 1-3 wt%), the catalyst for furfural decarbonylation to furan prepared by the present invention not only reduces the Pd loading, thereby reducing costs, but also solves the problem of rapid catalyst deactivation caused by easy coking of the raw material furfural, thereby improving the activity, selectivity and stability of the catalyst. DETAILED DESCRIPTION

[0019] In the following examples, the catalyst activity test method is: the prepared catalyst is ground and sieved to obtain catalyst particles of 10-20 mesh. 3.5g of the catalyst is weighed and loaded into the reactor, and then placed in a heating furnace for furfural decarbonylation to furan reaction. The reaction conditions are: the volume concentration of hydrogen in the reaction gas is 100%, the reaction temperature is 310°C, and the volume space velocity of the furfural feed is 0.4h -1 . Conversion rate and selectivity are used as indicators of catalyst activity.

[0020] Example 1 Weigh palladium tetraamine nitrate (concentration of 0.5 mol / L) and potassium hydroxide (concentration of 1 mol / L) and dissolve them in deionized water respectively, stir and dissolve at room temperature, and ensure that the loading amount of metal palladium is 0.15wt%. Weigh Al2O3 (mass of 7g) and place it in a three-necked flask, add palladium tetraamine nitrate solution to the three-necked flask, raise the temperature to 60℃ and stir and dissolve. Slowly add potassium hydroxide aqueous solution to the above solution and stir continuously. After the solution is dripped, the solution is maintained at a certain pH (pH 8-12). After aging for 2h, filter and remove the excess solution. After drying at 80℃ overnight, calcine at 450℃ for 3h to obtain a catalyst intermediate. Weigh potassium hydroxide (concentration of 1 mol / L) and dissolve it in deionized water and stir and dissolve it, wherein the potassium oxide loading amount is 3%. Add the above-prepared catalyst intermediate, soak for 8h, filter and remove the excess solution, and dry at 80℃ overnight to obtain a catalyst for furan decarbonylation. The catalytic performance of the catalysts prepared at different pH values ​​is shown in Table 1 below.

[0021] Table 1 Catalytic performance of catalysts prepared at different pH

[0022] As can be seen from Table 1, after the precipitation agent potassium hydroxide is added dropwise, at pH 9, the Pd-containing catalyst prepared by aging catalyzes the decarbonylation of furfural to synthesize furan, and the furfural conversion rate and furan are the highest, that is, the furfural conversion rate is 99.8%, and the furan selection is 96.1%. This is because pH affects the specific surface area of ​​the catalyst and the dispersion of the effective active components. If the pH is too low, the effective active components cannot be loaded on the catalyst surface, and if the pH is too high, the effective active components will agglomerate and the dispersion will decrease. Therefore, pH 9 is selected as the optimal pH value.

[0023] Example 2 After the precipitation agent potassium hydroxide in Example 1 was added dropwise, the pH was controlled to 9, the type of carrier (TiO2, Al2O3, SiO2, C (columnar), ZSM-5) was used as a variable, the carrier size was 4 mm, and the specific surface area, porosity and pore size of different types of carriers were similar. The remaining preparation steps were exactly the same as in Example 1. The catalytic performance of the catalysts prepared with different carriers is shown in Table 2 below.

[0024] Table 2 Catalytic performance of catalysts prepared with different supports

[0025] As can be seen from Table 2, the furfural conversion rate of the Pd-containing eggshell catalyst prepared with Al2O3 as the carrier is 99.8%, and the furan conversion rate is 96.1%. This is because Al2O3 has suitable acid strength and high mechanical strength.

[0026] Example 3 After the precipitation agent potassium hydroxide in Example 1 was added dropwise, the pH was controlled to 9, the reaction temperature (30-90° C.) was a variable, and the remaining preparation steps were exactly the same as in Example 1. The catalytic properties of the catalysts prepared at different reaction temperatures are shown in Table 3 below.

[0027] Table 3 Catalytic performance of catalysts prepared at different reaction temperatures

[0028] As can be seen from Table 3, when the reaction temperature is 50°C, the furfural conversion rate and furan selection of the prepared catalyst are the highest, that is, the furfural conversion rate is 99.8%, and the furan selection is 96.1%. This is because the reaction temperature directly affects the particle size of the active component. Too low or too high a reaction temperature is not conducive to the formation of a suitable particle size of Pd. Therefore, 50°C is selected as the optimal reaction temperature.

[0029] Example 4 The pH after the addition of potassium hydroxide as the precipitant in Example 1 was controlled to be 9, the potassium oxide loading (1-9 wt%) was a variable, and the remaining preparation steps were exactly the same as in Example 1. The catalytic performance of the catalysts prepared with different potassium oxide loadings is shown in Table 4 below.

[0030] Table 4 Catalytic performance of catalysts prepared with different potassium oxide loadings

[0031] It can be seen from Table 4 that when the potassium oxide loading is 3wt%, the furfural conversion rate and furan selectivity of the prepared catalyst are the highest, that is, the furfural conversion rate is 99.8%, and the furan selectivity is 96.1%. This is because the potassium oxide loading directly affects the acidity and alkalinity of the carrier. If the potassium oxide loading is too low, the effect of inhibiting the coking of the raw materials on the catalyst surface is low. If the potassium oxide loading is too high, on the one hand, it will cover up the effective active components and reduce the activity of the catalyst, and on the other hand, it will also reduce the selectivity of the catalyst.

[0032] Example 5 Based on Example 4, the potassium oxide loading was further optimized on the basis of 3 wt %, thereby selecting the optimal potassium oxide loading. The potassium oxide loading (0.05-0.45 wt %) was used as a variable, and the remaining preparation steps were exactly the same as Example 4. The catalytic performance of the catalysts prepared with different potassium oxide loadings is shown in Table 5 below.

[0033] Table 5 Catalytic performance of catalysts prepared with different potassium oxide loadings

[0034] It can be seen from Table 5 that when the potassium oxide loading is 0.15wt%, the furfural conversion rate and furan selection of the prepared catalyst are the highest, that is, the furfural conversion rate is 99.9% and the furan selection is 97.7%. Therefore, the potassium oxide loading of 0.15wt% is the best potassium oxide loading.

[0035] Example 6 The catalytic activity of the catalyst prepared in Example 1 and the commercial Pd catalyst were tested, and the results are shown in Table 6 below.

[0036] Table 6 Catalytic performance of Example 1 and commercial catalysts

[0037] As can be seen from Table 6, the catalyst prepared in Example 1 of the present invention is significantly better than the Pd catalyst in terms of furfural conversion, furan selection and single operation time. This is because the raw material furfural is easy to coke, resulting in blockage of the pores of the conventional Pd catalyst, which in turn leads to a reduction in the active components of the catalyst. The catalyst prepared by the present invention has effective active components on the surface of the carrier, which can effectively reduce the negative impact of raw material coking on the catalyst. At the same time, the addition of K can reduce the coking of the raw material on the catalyst surface and extend the life of the catalyst.

[0038] Comparative Example 1 Different from Example 1, the impregnation treatment of the catalyst intermediate with the alkali metal salt is omitted, and the catalyst intermediate is directly used as a catalyst for furan decarbonylation of furfural, and the remaining preparation steps are exactly the same as those of Example 1 to prepare a Pd / Al2O3 catalyst. The performance test results of the catalysts prepared in Example 1 and Comparative Example 1 are shown in Table 7.

[0039] Table 7 Catalytic performance of catalysts prepared in Example 1 and Comparative Example 1

[0040] The test results in Table 7 show that the catalyst prepared in Comparative Example 1 has a furfural conversion rate of 96.1% and a furan conversion rate of 93.4%, and a short catalyst life. This is because the addition of alkali metal oxides can improve the anti-coking ability of the catalyst, thereby extending the life of the catalyst.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A catalyst for decarbonylating furfural to furan, comprising a carrier and an active component supported on the carrier, characterized in that: The active components include a main active component and a co-active component; The main active component is located in the outer layer of the carrier, and the main active component is metal palladium; The auxiliary active component is embedded in the carrier, and the auxiliary active component is an alkali metal oxide; The preparation method of the catalyst for synthesizing furan by decarbonylation of furfural comprises the following steps: adding a carrier into a palladium salt solution, then adding a precipitant to react, and obtaining a catalyst intermediate through aging, drying and calcining; The catalyst intermediate is added into an alkali metal salt solution for impregnation, and after drying, a catalyst for furfural decarbonylation to furan is obtained; The palladium salt is one of tetraaminopalladium nitrate, palladium acetate, palladium nitrate and palladium sulfate; The precipitant is one of sodium carbonate, potassium carbonate, sodium hydroxide and potassium hydroxide, the reaction temperature is 25-90° C., and the pH is 8-12; The alkali metal salt is one of potassium hydroxide, sodium hydroxide, potassium nitrate and sodium nitrate.

2. The catalyst for synthesizing furan by decarbonylation of furfural according to claim 1, characterized in that The alkali metal oxide is one of potassium oxide and sodium oxide; based on the total amount of the catalyst, the content of the alkali metal oxide is 1-10 wt%.

3. The catalyst for synthesizing furan by decarbonylation of furfural according to claim 1, characterized in that Based on the total amount of the catalyst, the content of the metal palladium is 0.05-0.5 wt %, and the particle size of the metal palladium is 2.5-4.5 nm.

4. The catalyst for synthesizing furan by decarbonylation of furfural according to claim 1, characterized in that The carrier is one of TiO2, Al2O3, SiO2, activated carbon and ZSM-5, and the size of the carrier is 3-5 mm.

5. A method for preparing a catalyst for decarbonylating furfural to furan according to any one of claims 1 to 4, characterized in that: The following steps are involved: The carrier is added into a palladium salt solution, and then a precipitant is added to react, and a catalyst intermediate is obtained through aging, drying and calcination; the catalyst intermediate is added into an alkali metal salt solution for impregnation, and after drying, a catalyst for furfural decarbonylation to furan is obtained; The palladium salt is one of tetraaminopalladium nitrate, palladium acetate, palladium nitrate and palladium sulfate; The precipitant is one of sodium carbonate, potassium carbonate, sodium hydroxide and potassium hydroxide, the reaction temperature is 25-90° C., and the pH is 8-12; The alkali metal salt is one of potassium hydroxide, sodium hydroxide, potassium nitrate and sodium nitrate.

6. The method for preparing a catalyst for synthesizing furan by decarbonylation of furfural according to claim 5, characterized in that: The concentration of the palladium salt is 0.01-2 mol / L.

7. The method for preparing a catalyst for decarbonylating furfural to furan according to claim 5, characterized in that: The aging time is 1-4 h, the drying temperature is 70-80° C., and the drying time is 10-12 h; the calcination temperature is 400-500° C., and the calcination time is 1-5 h.

8. The method for preparing a catalyst for decarbonylating furfural to furan according to claim 5, characterized in that: The concentration of the alkali metal salt solution is 0.1-2 mol / L.

9. The method for preparing a catalyst for decarbonylating furfural to furan according to claim 5, characterized in that: The immersion temperature is 25-60° C. and the immersion time is 0.5-12 h.

10. Use of the catalyst for decarbonylating furfural to furan according to any one of claims 1 to 4 in decarbonylating furfural to furan.

Images