Method for safely preparing gamma-valerolactone using formic acid as hydrogen source

Abstract

The application discloses a method for safely preparing gamma-valerolactone by taking formic acid as a hydrogen source. The method takes levulinic acid and formic acid as raw materials, prepares a high-efficiency homogeneous organic metal ruthenium catalyst Ru-TsDPEN, adjusts the acid-base degree of a catalytic system, and realizes one-pot efficient and safe preparation of gamma-valerolactone under solvent-free and inert atmosphere protection conditions, and the yield is as high as 94.5%. In the method, the organic metal ruthenium catalyst is simple in preparation method and high in catalytic activity. The solvent-free system is adopted and inert atmosphere protection is not needed. In-situ hydrogenation of formic acid and acid-base system catalysis are adopted, so that the hydrogen source is effectively avoided to be obtained from the outside of the system, and the reaction condition is more moderate compared with a traditional process, the yield of gamma-valerolactone is high, the economy and safety of the preparation process are significantly improved, and the method is easy for fine chemical production.

Description

Technical Field

[0001] This invention relates to the field of γ-valerol preparation technology, specifically to a safe preparation method of γ-valerol based on in-situ hydrogenation of formic acid and acid-base synergistic catalysis. Background Technology

[0002] The efficient use of energy is closely related to human survival and development. Currently, fossil fuels are increasingly depleted, and supply issues are prominently affected by geopolitical factors, hindering national sustainable development. Therefore, the development and efficient utilization of new energy sources have become particularly urgent. Biomass energy is considered a renewable, green, and clean energy source that can replace fossil fuels. Biomass can be converted into various alternative fuels and high-value-added chemicals, possessing enormous potential to replace fossil fuels such as oil and coal. Among these, γ-valerolactone has been extensively studied and can be used as a green biofuel, advanced solvent, herbicide, food additive, or platform product for synthesizing high-value-added compounds.

[0003] Currently, the main method for preparing γ-valerol uses levulinic acid and its esters as raw materials, directly hydrogenating them with hydrogen gas. This process often involves high pressure and high temperature, and requires the addition of excess hydrogen, posing significant safety risks such as leakage, fire, and explosion, and placing high demands on equipment. Meanwhile, the preparation method of γ-valerol using formic acid as a hydrogen source is gradually gaining attention. US Patents 5859263, 5608105, and 6054511 detail the generation of equimolar amounts of levulinic acid and formic acid during cellulose hydrolysis, thus allowing for the in-situ hydrogenation of formic acid to prepare γ-valerol. This hydrogenation route is atom-economical and does not require an external hydrogen source. Furthermore, formic acid has low toxicity and flammability, high energy density, and good stability, which is beneficial for industrial applications. However, to date, the performance of catalysts and the safety control technology for process conditions in hydrogenation processes using formic acid as a hydrogen source are not yet mature, hindering the practical production application of this process. Therefore, improving the catalytic performance of in-situ hydrogenation of formic acid and enhancing process safety have become critical challenges that urgently need to be addressed. Summary of the Invention

[0004] This invention addresses the aforementioned shortcomings of existing technologies by proposing a safe method for preparing γ-valerolactone using formic acid as a hydrogen source. This method is based on in-situ hydrogenation of formic acid and acid-base synergistic catalysis. The invention employs a highly efficient homogeneous catalyst, Ru-TsDPEN, and utilizes multiple safe and advantageous process conditions, including formic acid as the hydrogen source, solvent-free operation, absence of an inert atmosphere, and acid-base synergistic catalysis, to achieve the safe preparation of γ-valerolactone from the reaction source.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is: a method for safely preparing γ-valerolactone using formic acid as a hydrogen source, comprising the following steps:

[0006] (1) The organic amine ligand and the metal ruthenium salt dimer were dissolved in an organic solvent and magnetically stirred and refluxed at 50°C for 12 h. After the reaction, the mixture was cooled to room temperature to obtain a solution containing Ru-TsDPEN organometallic ruthenium catalyst. The organic amine ligand was (1R,2R)-N-p-toluenesulfonyl-1,2-diphenylethylenediamine (TsDPEN), and the metal ruthenium salt dimer was dichloro(p-methylisopropylbenzene)ruthenium(II) dimer ([RuCl2(p-cymene)]2), with a molar ratio of 1:1.

[0007] (2) The cooled solution was rotary evaporated under reduced pressure at 40°C to obtain a dark red solid;

[0008] (3) Pour the dark red solid into a centrifuge tube and wash it three times with a weak polar solvent. Then centrifuge and filter to obtain the eluted solid.

[0009] (4) The eluted solid was placed in an oven to dry and obtain a dark red solid powder, which is the Ru-TsDPEN catalyst, and stored in a drying oven.

[0010] (5) Mix levulinic acid, formic acid, Ru-TsDPEN catalyst with acidic or basic additives evenly, add to a reaction vessel and stir and heat to react to obtain γ-valerol.

[0011] Preferably, the organic solvent used in step (1) is methanol; and the weakly polar solvent used in step (3) is diethyl ether.

[0012] Preferably, in step (3), the centrifugation conditions are 1500 r / min for 15 min; in step (4), the drying conditions are 60°C at normal pressure for 30 min.

[0013] Preferably, the molar ratio of levulinic acid, formic acid, catalyst, and acid-base additive in step (5) is 1:1:0.01:0~2.

[0014] Preferably, the alkaline additive used in step (5) is triethylamine, and the acidic additive used is acetic acid.

[0015] Preferably, the reaction temperature in step (5) is 50-170℃ and the reaction time is 1-24h; the initial reaction pressure in step (5) is atmospheric pressure and no inert gas atmosphere protection is required.

[0016] Preferably, the levulinic acid and formic acid raw materials can be: A) a mixed solution of levulinic acid and formic acid obtained from biomass under acid catalysis, or B) a mixed solution of levulinic acid and formic acid obtained from biomass with added excess formic acid under acid catalysis, or C) a solution obtained by directly mixing levulinic acid and formic acid.

[0017] Preferably, the reaction temperature in step (5) is 150℃ and the reaction time is 12h; the molar ratio of levulinic acid, formic acid, Ru-TsDPEN catalyst and triethylamine in step (5) is 1:1:0.01:2.

[0018] Preferably, it includes the following steps:

[0019] (1) 0.9162 g TsDPEN ((1R,2R)-N-p-toluenesulfonyl-1,2-2-phenylethylenediamine) and 1.531 g [RuCl2(p-cymene)]2 (dichloro(p-methylisopropylbenzene)ruthenium(II) dimer) were dissolved in methanol and magnetically stirred and refluxed at 50 °C for 12 h. After the reaction was completed, the solution was cooled to room temperature and poured into a rotary evaporator. The solution was then evaporated under reduced pressure at 40 °C to remove the methanol and peel off the solid to obtain a dark red solid. The solid was poured into a centrifuge tube, washed three times with ether, and centrifuged at 1500 rpm for 15 min. The solid was then poured out and placed in an oven to dry at 60 °C for 30 min. The resulting dark red solid powder Ru-TsDPEN was then stored in a drying oven.

[0020] (2) Add 36 mmol formic acid and 36 mmol levulinic acid, 0.36 mmol Ru-TsDPEN catalyst, and 72 mmol triethylamine to a 50 mL high-pressure reactor. Seal the reactor, stir evenly, and heat to 150 °C for 12 hours. After the reaction is completed, cool to room temperature. The yield of γ-valerol reached 94.5%.

[0021] Beneficial effects:

[0022] 1. Formic acid is one of the main products in the acid hydrolysis of biomass. Using formic acid as a hydrogen source can reduce dependence on external hydrogen sources and improve the atom economy of the reaction.

[0023] 2. Formic acid is an economical, safe, and easy-to-operate renewable energy liquid hydrogen storage carrier. Using formic acid as a hydrogen source to reduce levulinic acid to prepare γ-valerol can improve the safety of the reaction process.

[0024] 3. The homogeneous organometallic ruthenium catalyst Ru-TsDPEN is easy to prepare and still has high catalytic activity under solvent-free and inert atmosphere protection conditions.

[0025] 4. Solvent-free systems can avoid the risk of fire and explosion that may be caused by solvent separation in the later stage, and the absence of inert atmosphere protection can avoid the risk of asphyxiation caused by inert gas leakage.

[0026] 5. Acid-base synergistic catalysis can control the reaction process while ensuring high yield, making the reaction milder and improving the inherent safety of the process.

[0027] 6. This invention uses the highly efficient homogeneous catalyst Ru-TsDPEN to achieve the safe preparation of γ-valerol from the reaction source under multiple safe and advantageous process conditions, including formic acid as the hydrogen source, solvent-free and inert atmosphere-free protection, and acid-base synergistic catalysis.

[0028] 7. Example 12 is the best example. 36 mmol formic acid and 36 mmol levulinic acid, 0.36 mmol Ru-TsDPEN catalyst, and 72 mmol triethylamine were added to a 50 mL high-pressure reactor and sealed. The mixture was stirred evenly and heated to 150 °C for 12 hours. After the reaction was completed and cooled to room temperature, the yield of γ-valerol reached 94.5%, the conversion rate of levulinic acid was ≥99%, and the conversion rate of formic acid was ≥99%, which had unexpected effects. Attached Figure Description

[0029] The present invention will be further described below with reference to the accompanying drawings.

[0030] Figure 1 Ru-TsDPEN catalyst synthesis reaction

[0031] Figure 2 Ru-TsDPEN catalyst

[0032] Figure 3 Example 11: High-performance liquid chromatography analysis of the post-reaction solution Detailed Implementation

[0033] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited thereto:

[0034] Examples 1-7

[0035] Preparation of the catalyst Ru-TsDPEN:

[0036]

[0037] 0.9162 g of TsDPEN ((1R,2R)-N-p-toluenesulfonyl-1,2-2-phenylethylenediamine) and 1.531 g of [RuCl2(p-cymene)]2 (dichloro(p-methylisopropylbenzene)ruthenium(II) dimer) were dissolved in methanol. The solution was magnetically stirred and refluxed at 50 °C for 12 h. After the reflux was completed, the solution was cooled to room temperature and poured into a rotary evaporator flask. The solution was then evaporated under reduced pressure at 40 °C to remove the methanol. The solid was then peeled off to obtain a dark red solid. The solid was poured into a centrifuge tube, washed three times with ether, and centrifuged at 1500 rpm for 15 min. The washed solid was then placed in an oven and dried at 60 °C for 30 min. The resulting dark red solid powder, Ru-TsDPEN, was then stored in a desiccator.

[0038] The reaction formula for preparing γ-valerol using formic acid as a hydrogen source is as follows:

[0039]

[0040] Add 36 mmol formic acid, 36 mmol levulinic acid, and 0.36 mmol Ru-TsDPEN catalyst to a 50 mL high-pressure reactor, and seal the reactor. Stir uniformly and heat to 50℃, 70℃, 90℃, 110℃, 130℃, 150℃, and 170℃ for 12 hours. After the reaction is completed and cooled to room temperature, open the high-pressure reactor, take a sample, dilute it, and perform high-performance liquid chromatography analysis. The results are listed in Table 1.

[0041] Table 1. Detection results of Examples 1-7

[0042]

[0043]

[0044] In the initial stage, even with increasing temperature, the yield of γ-valerolactone and the conversion of levulinic acid showed a relatively slow increase. When the temperature reached 90℃, the reaction rate accelerated significantly, peaking at 150℃, where the yield of γ-valerolactone and the conversion of levulinic acid reached 68.7% and 74.4%, respectively. This is because, under high temperature conditions, formic acid is almost completely decomposed, and high temperature promotes the hydrogenation reduction of levulinic acid to prepare γ-valerolactone. However, when the temperature increased to 170℃, the yield of γ-valerolactone decreased to 61.9%. This may be due to the increased side reactions leading to a decrease in the selectivity of levulinic acid with increasing temperature. Therefore, 150℃ was ultimately selected as the optimal temperature condition.

[0045] Examples 8-14

[0046] Add 36 mmol formic acid, 36 mmol levulinic acid, and 0.36 mmol Ru-TsDPEN catalyst to a 50 mL high-pressure reactor, and seal the reactor. Stir uniformly and heat to 150 °C for 1 h, 3 h, 6 h, 9 h, 12 h, 18 h, and 24 h. After the reaction is completed and cooled to room temperature, open the high-pressure reactor, take samples, dilute them, and perform high-performance liquid chromatography analysis. The results are listed in Table 2. Figure 3 The solution after the reaction in Example 11 was analyzed by high performance liquid chromatography.

[0047] Table 2 Detection results of Examples 8-14

[0048]

[0049] As shown in Table 2, in the initial stage, the yield of γ-valerolactone and the conversion rate of levulinic acid were both very low. Due to the short reaction time, the decomposition of formic acid to produce hydrogen was insufficient, resulting in inadequate hydrogen supply, which limited the conversion of levulinic acid and the formation of γ-valerolactone. With the extension of time, the conversion rate of levulinic acid increased, accompanied by a higher selectivity for γ-valerolactone. However, from 12h to 24h, although the yield of γ-valerolactone increased slowly, the yield only increased by 3.4%. From the perspective of efficiency and energy consumption, we finally selected 12h as the optimal reaction time.

[0050] Examples 15-21

[0051] 36 mmol formic acid, 36 mmol levulinic acid, and 0.36 mmol Ru-TsDPEN catalyst were added to a 50 mL high-pressure reactor. Then, 3.6, 18, 36, 54, 72, and 90 mmol triethylamine or 3.6 mmol acetic acid were added (Example 16), and the reactor was sealed. The mixture was stirred uniformly and heated to 150 °C for 12 hours. After the reaction was completed and cooled to room temperature, the high-pressure reactor was opened, a sample was taken, diluted, and analyzed by high-performance liquid chromatography. The results are listed in Table 3.

[0052] Table 3 Detection results of Examples 15-21

[0053]

[0054] The addition of acid-base additives (Example 16) showed that acetic acid (acetic acid) had a certain inhibitory effect on the reaction, which is also a way to slow down the reaction process in the later safe preparation of γ-valerolactone. When 3.6 mmol of acetic acid was added, the yield of γ-valerolactone decreased to 53.1%. Meanwhile, without the addition of triethylamine, the conversion rate of levulinic acid and the yield of γ-valerolactone were relatively low, at 68.7% and 74.4%, respectively. However, the increase of triethylamine can promote the activity of the ruthenium-based catalyst and prevent the side reactions of γ-valerolactone. Therefore, with the increase of triethylamine, the conversion rate of levulinic acid increased rapidly, and in this process, levulinic acid was essentially converted. When the amount of triethylamine reached 72 mmol, the yield of γ-valerolactone reached 94.5% as seen in Example 20. Subsequently, despite increasing the amount of triethylamine, the yield of γ-valerolactone decreased. This was because the ethylenediamine and triethylamine contained in TsDPEN resulted in an excess of alkalinity in the reaction system, inhibiting catalyst activity and preventing further conversion of levulinic acid to γ-valerolactone. Therefore, we determined the optimal amount of triethylamine to be 72 mmol.

[0055] The present invention is not limited to the specific technical solutions described in the above embodiments. All technical solutions formed by equivalent substitutions are within the scope of protection claimed by the present invention.

Claims

1. A method for safely preparing γ-valerolactone using formic acid as a hydrogen source, characterized in that: Includes the following steps: (1) 0.9162 g of (1R,2R)-N-p-toluenesulfonyl-1,2-diphenylethylenediamine and 1.531 g of [RuCl2(p-cymene)]2 (dichloro(p-methylisopropylbenzene)ruthenium(II) dimer) were dissolved in methanol. The mixture was magnetically stirred and refluxed at 50 °C for 12 h. After the reaction, the mixture was cooled to room temperature. The cooled solution was poured into a rotary evaporator and rotary evaporated under reduced pressure at 40 °C to remove the methanol. The solid was then peeled off to obtain a dark red solid. The solid was poured into a centrifuge tube and washed three times with ether. After centrifugation, the solid was centrifuged at 1500 rpm for 15 min and then poured out. The washed solid was placed in an oven and dried at 60 °C for 30 min. The resulting dark red solid powder Ru-TsDPEN was then stored in a drying oven. (2) Add 36 mmol formic acid, 36 mmol levulinic acid, and 0.36 mmol Ru-TsDPEN catalyst to a 50 mL high-pressure reactor, add 72 mmol triethylamine, seal, stir evenly and heat to 150 °C for 12 hours, end the reaction and cool to room temperature, and the yield of γ-valerol reaches 94.5%.

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