A process for the preparation of tetrahydrofuran from furfural in a one-step continuous reaction

Abstract

This invention belongs to the field of fine chemical technology and discloses a one-step continuous reaction method for preparing tetrahydrofuran from furfural. The method includes the following reaction steps: furfural is pumped to a vaporizer for vaporization; under the action of a catalyst, furfural undergoes decarbonylation to produce furan; the furan is further hydrogenated on the same catalyst to generate tetrahydrofuran; the catalyst is a Pd-M1-M2 / γ-Al2O3 catalyst. The continuous process of this invention is simple, with a furfural conversion rate of over 99%, a tetrahydrofuran yield of 75%, a 2-methyltetrahydrofuran yield of 20%, and a total yield of 95%. The catalyst has a single-pass life of over 2000 hours.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical technology, specifically relating to a method for preparing tetrahydrofuran by a one-step continuous reaction of furfural. Background Technology

[0002] Tetrahydrofuran is an excellent solvent widely used in industry, possessing advantages such as low toxicity, low boiling point (66℃), good fluidity, and excellent solubility. Currently, the industrial production of tetrahydrofuran mainly relies on the petrochemical route, specifically the propylene route to produce 1,4-butanediol, also known as the allyl alcohol route. This involves converting propylene into allyl alcohol, then reacting allyl alcohol with CO to form aldehyde allyl alcohol. The aldehyde allyl alcohol then undergoes hydrogenation to yield 1,4-butanediol. 1,4-Butanediol is then dehydrated and cyclized to obtain tetrahydrofuran. However, this process generates significant carbon emissions and leaves trace amounts of aromatic impurities in the tetrahydrofuran.

[0003] Unlike traditional petrochemical-based processes for producing tetrahydrofuran, this bio-based production route, which involves hydrolyzing corn cobs and straw to produce furfural, then decarbonylating furfural to obtain furan, and finally hydrogenating furan to obtain tetrahydrofuran, significantly reduces carbon emissions throughout the process and minimizes the impact of trace aromatic impurities remaining in the tetrahydrofuran, making it more suitable for the pharmaceutical industry. The gas-phase decarbonylation of furfural to produce furan has relatively simple process requirements, with a fixed-bed reactor as the main equipment. Using precious metals Pd and Pt as catalysts, the raw material furfural is vaporized in a vaporizer and mixed with hydrogen before entering the fixed-bed reactor. Decarbonylation occurs on the catalyst surface to obtain furan, and unconverted furfural and the product furan are condensed in a condenser. Xue Li et al. (Natural Gas Chemical Industry, 2002, 27: 9-12.) prepared 0.6% Pt-1.2% M / Al2O3-TiO2 (M as an auxiliary agent) for the gas-phase decarbonylation of furfural to furan. At a reaction space velocity of 0.3–0.4 h⁻¹ (V / V) and a reaction temperature of 290–325 °C, the furfural conversion rate was 100%, and the furan yield reached over 85% after 500 h of reaction. Patent CN1308986A discloses a highly efficient noble metal catalyst for the gas-phase decarbonylation of furfural to furan, using Al2O3-TiO2 composite oxide as a support, with a Pt loading of 0.4–0.7%, and K₂O and other auxiliary agents at a content of 0.5–2.0%. Under normal pressure, at 280℃, with a furfural volume hourly space velocity of 0.9 h⁻¹, and a furfural to hydrogen molar ratio of 0.5–2.0, the catalyst achieves a furfural conversion rate of 80–97% and a furan selectivity of 85–92%. Wang Chengxue et al. (Fine Chemicals, 2010, 35:75-78) used Pd / C as a catalyst to hydrogenate furan to tetrahydrofuran in a batch reactor, achieving a furan conversion rate of 92% and a tetrahydrofuran yield of 90.2%. Currently, the two-step process of furfural decarbonylation to furan, followed by further hydrogenation of furan to prepare tetrahydrofuran, is relatively cumbersome, and the overall yield of tetrahydrofuran is relatively low.

[0004] Therefore, it is necessary to design a method for the one-step continuous reaction of furfural to prepare tetrahydrofuran. Summary of the Invention

[0005] The purpose of this invention is to provide a one-step continuous reaction method for preparing tetrahydrofuran from furfural, in order to solve the problem in the prior art that the current two-step process of furfural decarbonylation to produce furan, and furan further hydrogenation to prepare tetrahydrofuran, has a relatively cumbersome process route and a relatively low overall yield of tetrahydrofuran.

[0006] To achieve the above objectives, the present invention provides a method for preparing tetrahydrofuran from furfural via a one-step continuous reaction, comprising the following reaction steps:

[0007] Furfural is fed to the vaporizer via a feed pump and vaporized. Under the action of a catalyst, furfural undergoes decarbonylation to produce furan, and furan is further hydrogenated on the same catalyst to produce tetrahydrofuran. The catalyst is a Pd-M1-M2 / γ-Al2O3 catalyst.

[0008] The chemical formula for the one-step continuous reaction of furfural to prepare tetrahydrofuran is as follows:

[0009]

[0010] In one specific embodiment, the Pd-M1-M2 / γ-Al2O3 catalyst uses metallic Pd as the active component, and the mass fraction of Pd in ​​the Pd-M1-M2 / γ-Al2O3 catalyst is 0.05-5.0 wt%, preferably 0.05-0.5 wt%.

[0011] In one specific embodiment, the Pd-M1-M2 / γ-Al2O3 catalyst contains a γ-Al2O3 support loaded with a metal oxide promoter M1 and a metal promoter M2. The metal oxide promoter M1 is one of MgO, BaO, CaO, SrO, La2O3, and ZrO2, and the mass fraction of M1 in the Pd-M1-M2 / γ-Al2O3 catalyst is 3.0–20.0 wt%, preferably 5.0–15.0%. The metal promoter M2 is one of Pt, Ni, and Ru, and the mass fraction of M2 in the Pd-M1-M2 / γ-Al2O3 catalyst is 0.01–0.50 wt%.

[0012] In one specific embodiment, the Pd-M1-M2 / γ-Al2O3 catalyst is prepared by: firstly, preparing an M1 / γ-Al2O3 intermediate by impregnation, and then using the M1 / γ-Al2O3 intermediate by impregnation to obtain the Pd-M1-M2 / γ-Al2O3 catalyst.

[0013] In one specific embodiment, the specific steps for preparing the Pd-M1-M2 / γ-Al2O3 catalyst include: first, preparing a solution of the precursor of metal oxide promoter M1, immersing a certain amount of γ-Al2O3 support in the precursor solution of metal oxide promoter M1 for impregnation, and then drying and calcining to obtain the M1 / γ-Al2O3 intermediate.

[0014] The precursors of active metal Pd and auxiliary metal M2 are then prepared into a solution. The resulting M1 / γ-Al2O3 intermediate is immersed in the precursor solution of active metal Pd and auxiliary metal M2 for impregnation. After drying, calcination, washing and reduction, Pd-M1-M2 / γ-Al2O3 catalyst is obtained.

[0015] In one specific embodiment, the drying temperature for preparing the M1 / γ-Al2O3 intermediate is 100–120°C, the drying time is 1–8 h, the calcination temperature is 400–800°C, and the calcination time is 1–8 h.

[0016] In one specific embodiment, the calcination temperature for preparing the Pd-M1-M2 / γ-Al2O3 catalyst from the M1 / γ-Al2O3 intermediate is 300–500 °C, and the calcination time is 1–8 h.

[0017] In one specific embodiment, the reducing agent used in the reduction process is one of formaldehyde, NaBH4, hydrazine hydrate, and hydrogen, preferably hydrogen, and the reduction space velocity is 100–600 h⁻¹. -1 The reduction temperature is 150–400℃, and the reduction time is 3–10 h.

[0018] In one specific embodiment, the hydrogenation pressure for preparing tetrahydrofuran is 0.1–3.0 MPa, the reaction temperature is 200–300 °C, and the furfural feed mass hourly space velocity is 0.1–1.0 h⁻¹. -1 The molar ratio of hydrogen to furfural is 1.0 to 20.0.

[0019] In one specific embodiment, the Pd-M1-M2 / γ-Al2O3 catalyst is used for no more than 2000 hours.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention adds alkaline metal oxide additives such as CaO to provide alkalinity to the catalyst surface, which on the one hand is beneficial to improve metal dispersion, and on the other hand promotes the decarbonylation reaction of furfural. In addition, it also inhibits the ring-opening side reaction of furan and improves the yield of tetrahydrofuran.

[0022] This invention uses the addition of metal additives Pt, Ni, and Ru to form an alloy with metal Pd, which improves the metal dispersion and inhibits metal agglomeration, thereby increasing the catalyst lifetime.

[0023] The continuous process adopted in this invention is simple, with a furfural conversion rate of over 99%, a tetrahydrofuran yield of 75%, a 2-methyltetrahydrofuran yield of 20%, and a total yield of 95%. The catalyst has a single-pass life of over 2000 hours.

[0024] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The present invention will now be described in further detail. Detailed Implementation

[0025] The embodiments of the present invention will be described in detail below. The specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0026] Catalyst preparation:

[0027] Example A1

[0028] A certain mass of calcium nitrate tetrahydrate was weighed and dissolved in purified water. A certain amount of γ-Al₂O₃ support was immersed in the above solution for equal-volume impregnation. Impregnation lasted 24 h, followed by drying at 120 °C for 6 h and calcination at 500 °C for 4 h to obtain a CaO / γ-Al₂O₃ support with a CaO loading of 10.0 wt%. A certain mass of palladium chloride and chloroplatinic acid solids were weighed and dissolved in purified water with hydrochloric acid solution. The above CaO / γ-Al₂O₃ support was immersed in the prepared solution for equal-volume impregnation. Impregnation lasted 24 h, followed by drying at 120 °C for 6 h. The catalyst was transferred to a crucible and calcined in a muffle furnace at 500 °C for 4 h. The filtrate was washed with purified water until no chloride ions were present, dried at 120 °C for 6 h, and subjected to a hydrogen hourly space velocity (HHSV) of 300 h⁻¹. -1 The catalyst was reduced at 300℃ for 4 hours to obtain catalyst 1, in which the loading of metal Pd was 0.4%, the loading of metal Pt was 0.05%, and the loading of CaO was 10.0wt%.

[0029] Example A2

[0030] The auxiliary agent M1 is BaO, and the other properties are the same as in Example A1, to obtain catalyst 2.

[0031] Example A3

[0032] The auxiliary agent M1 is La2O3, and the other conditions are the same as in Example A1, thus obtaining catalyst 3.

[0033] Example A4

[0034] The CaO / γ-Al2O3 support was calcined at 600℃, and other procedures were the same as in Example A1, to obtain catalyst 4.

[0035] Example A5

[0036] The CaO / γ-Al2O3 support was calcined at 400℃, and other conditions were the same as in Example A1, to obtain catalyst 5.

[0037] Example A6

[0038] Metal additive M2 is Ru, and the rest is the same as in Example A1, to obtain catalyst 6.

[0039] Example A7

[0040] Metal additive M2 is Ni, and the rest is the same as in Example A1, to obtain catalyst 7.

[0041] Example A8

[0042] With the additive Pt loading at 0.10%, and other parameters the same as in Example A1, catalyst 8 was obtained.

[0043] Example A9

[0044] With the additive Pt loading at 0.025%, and other parameters the same as in Example A1, catalyst 9 was obtained.

[0045] Example A10

[0046] With the additive Pt loading at 0.15%, and other parameters the same as in Example A1, catalyst 10 was obtained.

[0047] Example A11

[0048] The reducing agent was formaldehyde, the reduction temperature was 60°C, the reduction time was 4 hours, and other conditions were the same as in Example A1, resulting in catalyst 11.

[0049] Example A12

[0050] The reducing agent was NaBH4, the reduction temperature was 60℃, the reduction time was 4h, and other conditions were the same as in Example A1, thus obtaining catalyst 12.

[0051] Example A13

[0052] The reducing agent was hydrazine hydrate, the reduction temperature was 60°C, the reduction time was 4 hours, and other conditions were the same as in Example A1, thus obtaining catalyst 13.

[0053] Comparative Example A1

[0054] A certain mass of palladium chloride solid was weighed and dissolved in purified water. An appropriate amount of hydrochloric acid was added to dissolve the palladium chloride solid. The γ-Al₂O₃ support was then added to the prepared solution, and the mixture was impregnated in equal volumes. Impregnation lasted 24 hours, followed by drying at 120°C for 6 hours, and calcination at 500°C for 4 hours in a muffle furnace. The filtrate was washed with purified water until no chloride ions were found, and then dried at 120°C for 6 hours. The loading of metallic Pd was 0.4%, yielding catalyst 14.

[0055] Catalyst evaluation was conducted in a fixed-bed reactor, with 3.0 g of catalyst packed into a reaction tube with an inner diameter of 13 mm and a hydrogen space velocity of 300 h⁻¹. -1 The reaction was carried out at 300℃ for 4 hours. Furfural feedstock solution was pumped into the fixed-bed catalyst bed using a feed pump. Catalyst evaluation conditions: reaction temperature 280℃, reaction pressure 1.0 MPa, furfural feed mass hourly space velocity 0.8 h⁻¹. -1 The molar ratio of hydrogen to furfural was 4.0. The evaluation results are shown in Table 1.

[0056] Table 1. Screening of catalysts for one-step furfural to tetrahydrofuran production.

[0057]

[0058] As can be seen from Examples A1, A2, A3 and Comparative Example A1 in Table 1, metal oxide additives have a significant impact on the one-step reaction of furfural to tetrahydrofuran. The addition of metal oxide additives promotes the reaction to a certain extent and improves the selectivity of tetrahydrofuran. The best effect is achieved with CaO additive, resulting in a furfural conversion rate of 99.9%, a tetrahydrofuran selectivity of 75.2%, and a 2-methyltetrahydrofuran selectivity of 20.5%. Comparing the data from Examples A1, A4, and A5, it is evident that the calcination temperature has a significant impact after loading the metal oxide additive. At a calcination temperature of 400℃, the catalyst is not completely calcined, resulting in low activity. The reaction data show little difference at calcination temperatures of 500 and 600℃, making a calcination temperature of 500–600℃ the preferred choice. Comparing Examples A1, A6, and A7, metal additive M2 has a significant impact on the reaction performance, with Pt additive showing the best performance. Examples A1, A8-A10 further investigated the effect of Pt additive content. When the Pt content was low, at 0.025%, the furfural conversion rate was 97.6% and the tetrahydrofuran selectivity was 73.6%. When the Pt content reached 0.05% or higher, the furfural conversion rate was >99.9%, and the tetrahydrofuran selectivity remained at ~75%. Increasing the Pt additive content would increase the catalyst usage cost; a Pt content of 0.05% was preferred. Examples A1, A11-A13 compared the effect of the reducing agent on catalytic performance. With hydrogen as the reducing agent, the furfural conversion rate and tetrahydrofuran selectivity were optimal, possibly due to the formation of a PdPt alloy during hydrogen reduction.

[0059] Optimization of the reaction process:

[0060] Example B1

[0061] Catalyst evaluation was conducted in a fixed-bed reactor, with 3.0 g of catalyst 1 loaded into a 13 mm inner diameter reaction tube. Furfural feedstock solution was pumped into the fixed-bed catalyst bed using a feed pump. Catalyst evaluation conditions: reaction temperature 280℃, reaction pressure 1.0 MPa, furfural feed mass hourly space velocity 0.8 h⁻¹. -1 The molar ratio of hydrogen to furfural was 4.0. The evaluation results are shown in Table 2.

[0062] Examples B2 to B8 show the results of changing the corresponding reaction conditions, as shown in Table 2.

[0063] Table 2 Effect of reaction conditions on the one-step production of tetrahydrofuran from furfural

[0064]

[0065] As can be seen from the comparison of Examples B1 to B3 in Table 2, the reaction effect is better at a reaction temperature of 280℃. When the reaction temperature is lower than 260℃, some furfural does not have time to participate in the reaction, resulting in incomplete reaction and poor hydrogenation effect. When the reaction temperature is increased to 300℃, the selectivity of tetrahydrofuran decreases due to the excessively high temperature. Examples B1, B4, and B5 show that the reaction effect is better when the hydrogen-aldehyde ratio is 4.0. When the hydrogen-aldehyde ratio is increased to 6.0, the selectivity of tetrahydrofuran decreases to 72.2%. When the hydrogen-aldehyde ratio decreases to 2.0, the selectivity of furan is only 52.2%, indicating a significant amount of furan. Comparing Examples B1, B6, and B7, the furfural conversion rate decreases with increasing furfural feed space velocity. A furfural feed space velocity of 0.80 h⁻¹ is also observed. -1 The furfural conversion rate was 99.9%. Comparing the data from Examples B1, B8, and B9, it can be seen that the tetrahydrofuran selectivity was highest at a hydrogen pressure of 1.0 MPa. When the hydrogen pressure was lower, furfural was not completely converted, and when the hydrogen pressure was increased to 2.0 MPa, the tetrahydrofuran selectivity showed a decreasing trend.

[0066] Life assessment test:

[0067] The lifetime evaluation test of catalyst 1 was carried out under the same reaction process conditions as in Example B1. The product after hydrogenation was analyzed, and the analysis results are shown in Table 3.

[0068] Table 3. Catalyst lifetime evaluation results for the one-step furfural to tetrahydrofuran process.

[0069]

[0070] As shown in Table 3, the furfural conversion rate remained relatively stable at over 99.7% for reaction times ranging from 10 to 1200 h, while the tetrahydrofuran selectivity remained at approximately 75%, indicating that catalyst 1 exhibited good stability. After 1200 h of reaction, the furfural conversion rate showed a decreasing trend, but it still remained above 99.3%.

[0071] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions and substitutions can be made without departing from the inventive concept, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A process for the preparation of tetrahydrofuran from furfural in a one-step continuous reaction, characterized in that, The reaction steps include the following: Furfural is fed to the vaporizer via a feed pump and vaporized. Under the action of a catalyst, furfural undergoes decarbonylation to produce furan, and furan is further hydrogenated on the same catalyst to produce tetrahydrofuran. The catalyst is a Pd-M1-M2 / γ-Al2O3 catalyst. In the Pd-M1-M2 / γ-Al2O3 catalyst, the γ-Al2O3 support is loaded with metal oxide promoter M1 and metal promoter M2. The metal oxide promoter M1 is one of BaO, CaO, and La2O3, and the mass fraction of M1 in the Pd-M1-M2 / γ-Al2O3 catalyst is 3.0~20.0wt%. The metal promoter M2 is one of Pt, Ni, and Ru, and the mass fraction of M2 in the Pd-M1-M2 / γ-Al2O3 catalyst is 0.01~0.50wt%.

2. The process for the preparation of tetrahydrofuran from furfural in one step by continuous reaction according to claim 1, characterized in that, The Pd-M1-M2 / γ-Al2O3 catalyst uses metallic Pd as the active component, and the mass fraction of Pd in ​​the Pd-M1-M2 / γ-Al2O3 catalyst is 0.05~5.0wt%.

3. The process for the preparation of tetrahydrofuran by one-step continuous reaction of furfural according to claim 2, characterized by the fact that, The mass fraction of Pd in ​​the Pd-M1-M2 / γ-Al2O3 catalyst is 0.05~0.5wt%.

4. The method for preparing tetrahydrofuran from furfural via a one-step continuous reaction according to claim 1, characterized in that, The mass fraction of M1 in the Pd-M1-M2 / γ-Al2O3 catalyst is 5.0~15.0%.

5. The process for the preparation of tetrahydrofuran in one step from furfural by continuous reaction according to claim 1, characterized in that, The preparation method of the Pd-M1-M2 / γ-Al2O3 catalyst is as follows: first, M1 / γ-Al2O3 intermediate is prepared by impregnation method, and then Pd-M1-M2 / γ-Al2O3 catalyst is prepared by impregnation method using M1 / γ-Al2O3 intermediate.

6. The process for the preparation of tetrahydrofuran by one-step continuous reaction of furfural according to claim 5, characterized by the fact that, The specific steps for preparing the Pd-M1-M2 / γ-Al2O3 catalyst include: first, preparing a solution of the precursor of metal oxide promoter M1, then immersing a certain amount of γ-Al2O3 support in the precursor solution of metal oxide promoter M1 for impregnation, and then drying and calcining to obtain the M1 / γ-Al2O3 intermediate. The precursors of active metal Pd and auxiliary metal M2 are then prepared into a solution. The resulting M1 / γ-Al2O3 intermediate is immersed in the precursor solution of active metal Pd and auxiliary metal M2 for impregnation. After drying, calcination, washing and reduction, Pd-M1-M2 / γ-Al2O3 catalyst is obtained.

7. The process for the continuous production of tetrahydrofuran from furfural in one step according to claim 6, characterized in that, The drying temperature for preparing the M1 / γ-Al2O3 intermediate is 100~120℃, the drying time is 1~8h, the calcination temperature is 400~800℃, and the calcination time is 1~8h.

8. The method for preparing tetrahydrofuran from furfural via a one-step continuous reaction according to claim 6, characterized in that, The calcination temperature for preparing Pd-M1-M2 / γ-Al2O3 catalyst from M1 / γ-Al2O3 intermediate is 300~500℃, and the calcination time is 1~8h.

9. The process for the preparation of tetrahydrofuran by one-step continuous reaction of furfural according to claim 6, characterized by that, The reducing agent used in the reduction process is one of formaldehyde, NaBH4, hydrazine hydrate, or hydrogen, and the reduction space velocity is 100~600 h⁻¹. -1 The reduction temperature is 150~400℃, and the reduction time is 3~10h.

10. The process for the preparation of tetrahydrofuran by one-step continuous reaction of furfural according to claim 9, characterized by the fact that, The reducing agent used in the reduction process is hydrogen gas.

11. The method for preparing tetrahydrofuran from furfural via a one-step continuous reaction according to claim 1, characterized in that, The hydrogenation pressure for preparing tetrahydrofuran is 0.1–3.0 MPa, the reaction temperature is 200–300 °C, and the furfural feed mass hourly space velocity is 0.1–1.0 h⁻¹. -1 The molar ratio of hydrogen to furfural is 1.0 to 20.

0.

12. The method for preparing tetrahydrofuran from furfural via a one-step continuous reaction according to claim 1, characterized in that, The Pd-M1-M2 / γ-Al2O3 catalyst has been used for more than 2000 hours.

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