A method for catalyzing cellulose to produce levulinic acid based on a bifunctional heteropoly acid two-phase system

Abstract

The application discloses a method for producing levulinic acid from cellulose based on a bifunctional heteropoly acid in a two-phase system, and belongs to the technical field of biomass conversion. The method uses a Keggin-type heteropoly acid with Cu, Fe, Al, Zn or Co as a heteroatom as a bifunctional catalyst, and efficiently converts cellulose into levulinic acid in a two-phase system composed of water and an organic solvent at 130-150 DEG C for 1-5 hours. After the reaction, the organic phase containing levulinic acid can be separated by simple liquid separation, and the organic solvent can be recovered by reduced pressure distillation, and the catalytic system can be recycled. The application uses a heteropoly acid catalyst with Brønsted and Lewis dual acidity, and combines a water-organic two-phase system, realizes directional conversion of cellulose and real-time extraction of products, and has the advantages of recyclable catalyst, easy separation of products, high yield of levulinic acid and the like.

Description

Technical Field

[0001] This invention belongs to the field of biomass conversion technology, specifically relating to a method for catalyzing the production of levulinic acid from cellulose using a biphasic system based on bifunctional heteropolyacids. Background Technology

[0002] Leucylpropionic acid (LA) is a platform chemical obtained through acid-catalyzed biomass conversion. Containing carbonyl and carboxyl functional groups, it is widely used as an intermediate in the preparation of fine chemicals and pharmaceuticals. Compared to edible sugar biomass such as glucose and fructose, cellulose, as a renewable non-grain biomass, is abundant and inexpensive in nature, making it an ideal raw material for LA conversion. However, the conversion of cellulose to LA is a continuous acid-catalyzed process with a long reaction pathway, requiring both Brønsted acid catalysis and Lewis acid synergistic catalysis. Furthermore, the water insolubility of cellulose makes its targeted conversion to LA difficult. Therefore, how to efficiently catalyze the conversion of cellulose to LA is of great significance for achieving the high-value utilization of cellulose.

[0003] Heteropoly acids are inorganic metal oxide clusters formed by the dehydration condensation of two or more oxoacid salts, and are widely used in acid-catalyzed reactions such as esterification and dehydration. Heteropoly acids exhibit various configurations, among which Keggin-type heteropoly acids are a class of polyoxoacid salts with a classic cage-like structure, possessing both strong acidity and good structural stability; their general chemical formula is HnXM. 12 O 40 (X represents a heteroatom, M represents a polyatom). Furthermore, Keggin-type heteropolyacids possess atomic-level acidity tunability. Introducing a Lewis acidic metal as a heteroatom into its structure yields bifunctional heteropolyacids with both Brønsted and Lewis acids, which is beneficial for the conversion of cellulose to LA. However, the strong polarity of Keggin-type heteropolyacids, while making them readily soluble in water and allowing for effective contact with cellulose to promote conversion, also leads to difficulties in the separation / recovery of these heteropolyacids.

[0004] Therefore, developing a method for the continuous production of LA from cellulose using bifunctional heteropolyacid catalysis is of great application potential and economic value. Summary of the Invention

[0005] In view of this, the present invention aims to provide a method for catalyzing the production of levulinic acid from cellulose using a biphasic system based on bifunctional heteropolyacids.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for catalyzing the production of levulinic acid from cellulose using a biphasic system based on bifunctional heteropolyacids, comprising the following steps: Cellulose, sodium chloride, mixed solvent, and heteropolyacid catalyst are mixed and catalytically reacted to obtain levulinic acid.

[0007] Preferably, the heteropolyacid catalyst is HnXW. 12 O 40 , where X is Cu, Fe, Al, Zn or Co.

[0008] Preferably, the HnXW 12 O 40 The preparation method is as follows: 100.0g Na2WO4 Dissolve H₂O in 400 mL of deionized water. Add concentrated hydrochloric acid dropwise with continuous stirring until the pH reaches 7.7. Then add 55 mmol of metal salt X and reflux for 1 hour. After cooling and filtration, add concentrated sulfuric acid dropwise to the filtrate until the pH reaches 0. Add concentrated H₂SO₄ (5 mL) again and continue reflux for 7 days. After the reaction is complete, add 147 mL of concentrated H₂SO₄ to the solution, and then extract the solution with 500 mL of diethyl ether. Dry the bottom oily layer in a vacuum oven to obtain the obtained H₅XW. 12 O 40 .

[0009] Preferably, the mass-to-volume ratio of cellulose, sodium chloride, and mixed solvent is 0.1 g : (0.05-0.25) g : 10 mL.

[0010] Preferably, the cellulose is microcrystalline cellulose or natural lignocellulose.

[0011] Preferably, the mixed solvent is obtained by mixing water and an organic solvent in a volume ratio of (1-3):(7-9); The organic solvent is n-butanol, tetrahydrofuran, methyl isobutyl ketone, N-methylpyrrolidone, or γ-valerolactone.

[0012] Preferably, the concentration of the heteropolyacid in the reaction system is 0.04-0.16 mmol / mL, based on the volume of water.

[0013] Preferably, the catalytic reaction is carried out at a temperature of 130-160°C for 1-5 hours.

[0014] Preferably, after the catalytic reaction is completed, the organic phase is obtained by separation, and the organic phase is subjected to vacuum distillation to obtain levulinic acid; and the organic solvent is recovered and recycled.

[0015] It contains at least the following beneficial technical effects: The catalyst used in this invention is a dodecatungsten Keggin-type heteropolyacid with Cu, Fe, Al, Zn or Co as heteroatoms. It has both Brønsted acidity and Lewis acidity, and can synergistically catalyze a series of reactions such as cellulose hydrolysis, isomerization and dehydration, which is more conducive to the directional conversion of cellulose into levulinic acid.

[0016] This invention employs a two-phase reaction system composed of sodium chloride aqueous solution and organic solvent, which enables real-time extraction and separation of levulinic acid, effectively preventing further degradation of levulinic acid at high temperatures, thereby obtaining a higher yield of levulinic acid.

[0017] This invention further improves the yield of levulinic acid by optimizing the composition of the two-phase system, the amount of catalyst, and the reaction conditions. This invention overcomes the problems of difficult recovery of homogeneous acid catalysts and difficulty in separating them from the product levulinic acid. After the reaction, only simple liquid-liquid separation is required to separate the organic phase containing levulinic acid from the aqueous phase, making the operation simple.

[0018] The catalytic system of this invention has the potential for continuous production. It can separate levulinic acid from the organic phase and recover the organic solvent by vacuum distillation. The recovered organic solvent and the aqueous phase containing the catalyst can be reused in production, realizing the recycling of the catalytic system, reducing production costs, and meeting the requirements of green chemistry. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of the catalytic conversion of cellulose to prepare LA in Example 1 of the present invention.

[0020] Figure 2 H5AlW in Embodiment 1 of the present invention 12 O 40 The infrared spectrum.

[0021] Figure 3 H5AlW in Embodiment 1 of the present invention 12 O 40 Thermogravimetric diagram.

[0022] Figure 4 This illustrates the effect of the solvent system on the LA yield in Example 1 of the present invention. Detailed Implementation

[0023] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0024] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0025] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0026] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0027] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0028] Unless otherwise specified, "room temperature" and "normal temperature" in this invention refer to 25±2℃.

[0029] Unless otherwise specified, all raw materials or instruments used in the following embodiments of the present invention are commercially available.

[0030] To prepare Keggin heteropolyacids with X being Al, Na2WO4 was used. 100.0 g of 2H₂O and 400 mL of deionized water are mixed in a beaker and stirred until completely dissolved. Concentrated hydrochloric acid is added dropwise with continuous stirring until the pH reaches 7.7 and a precipitate forms during the dissolution process. AlCl₃ is then added. Add 13.32 g (55 mmol) of H₂O and reflux for 1 hour. After cooling and filtration, add concentrated H₂SO₄ dropwise to the filtrate until pH = 0. Then, add concentrated H₂SO₄ (5 mL) and continue reflux for 7 days. After the reaction, add concentrated H₂SO₄ (147 mL) to the solution and then extract the solution with diethyl ether (500 mL). Dry the bottom oily layer in a vacuum oven (70 °C, 12 h) to obtain the resulting H₅AlW. 12 O 40 .

[0031] To prepare X, which is Cu, Fe, Zn, or Co, the same molar mass of CuCl2 is used. 2H2O, FeCl3 6H2O, ZnCl2, CoCl2 6H2O replaces AlCl3 6H2O.

[0032] Example 1 Dodecyltungsten Keggin-type heteropolyacids (H5AlW) using Al as a heteroatom 12 O 40 ) as a catalyst. Add 0.1 g cellulose and 0.2 g NaCl to a 10 mL mixed solution consisting of 1 mL water and 9 mL MIBK, H5AlW 12 O 40 The concentration was 0.12 mmol / mL (based on water volume). The reaction was heated to 140 °C and allowed to proceed for 2 h. After the reaction was complete, the mixture was immediately cooled in an ice bath to stop the reaction. The upper organic phase was separated for product analysis.

[0033] The calculated cellulose conversion rate was 86.3%, the yield of levulinic acid (LA) was 39.2%, the yield of 5-HMF was 5.1%, and the LA selectivity was 45.4%.

[0034] Comparative Example 1 Dodecyltungsten Keggin-type heteropolyacids (H5AlW) using Al as a heteroatom 12 O 40 ) as a catalyst. Add 0.1 g of cellulose to a 10 mL mixed solution consisting of 3 mL of water and 7 mL of MIBK, H5AlW 12 O 40 The concentration was 0.12 mmol / mL (based on water volume). The reaction was heated to 140 °C and allowed to proceed for 2 h. After the reaction was complete, the mixture was immediately cooled in an ice bath to stop the reaction. The upper organic phase was separated for product analysis.

[0035] Comparative Example 2 Dodecyltungsten Keggin-type heteropolyacids (H5AlW) using Al as a heteroatom 12 O 40 ) as a catalyst. Add 0.1 g of cellulose to a 10 mL mixed solution consisting of 2 mL of water and 8 mL of MIBK, H5AlW 12 O 40 The concentration was 0.12 mmol / mL (based on water volume). The reaction was heated to 140 °C and allowed to proceed for 2 h. After the reaction was complete, the mixture was immediately cooled in an ice bath to stop the reaction. The upper organic phase was separated for product analysis.

[0036] Comparative Example 3 Dodecyltungsten Keggin-type heteropolyacids (H5AlW) using Al as a heteroatom 12 O 40 ) as a catalyst. Add 0.1 g of cellulose to a 10 mL mixed solution consisting of 1 mL of water and 9 mL of MIBK, H5AlW 12 O 40 The concentration was 0.12 mmol / mL (based on water volume). The reaction was heated to 140 °C and allowed to proceed for 2 h. After the reaction was complete, the mixture was immediately cooled in an ice bath to stop the reaction. The upper organic phase was separated for product analysis.

[0037] Example 2 The only difference between this embodiment and Embodiment 1 is that the catalyst used is H5FeW. 12 O 40 .

[0038] Example 3 The only difference between this embodiment and Embodiment 1 is that the catalyst used is H6CuW. 12 O 40 .

[0039] Example 4 The only difference between this embodiment and Embodiment 1 is that the catalyst used is H6ZnW. 12 O 40 .

[0040] Example 5 The only difference between this embodiment and Embodiment 1 is that the catalyst used is H6CoW. 12 O 40 .

[0041] Example 6 Dodecyltungsten Keggin-type heteropolyacids (H5AlW) using Al as a heteroatom 12 O 40) as a catalyst. Add 0.1 g cellulose and 0.05 g NaCl to a 10 mL mixed solution consisting of 1 mL water and 9 mL MIBK, H5AlW 12 O 40 The concentration was 0.12 mmol / mL (based on water volume). The reaction was heated to 140 °C and carried out for 5 h. After the reaction was completed, the mixture was immediately cooled in an ice bath to stop the reaction. The upper organic phase was obtained by separation for product analysis.

[0042] The calculated cellulose conversion rate was 87.4%, the yield of levulinic acid (LA) was 48.6%, the yield of 5-HMF was 0%, and the LA selectivity was 55.6%.

[0043] Example 7 Dodecyltungsten Keggin-type heteropolyacids (H5AlW) using Al as a heteroatom 12 O 40 ) as a catalyst. Add 0.1 g cellulose and 0.20 g NaCl to a 10 mL mixed solution consisting of 1 mL water and 9 mL MIBK, H5AlW 12 O 40 The concentration was 0.12 mmol / mL (based on water volume). The reaction was heated to 150 °C and carried out for 4 h. After the reaction was completed, the mixture was immediately cooled in an ice bath to stop the reaction. The upper organic phase was obtained by separation for product analysis.

[0044] The calculated cellulose conversion rate was 91.2%, the yield of levulinic acid (LA) was 51.6%, the yield of 5-HMF was 0%, and the LA selectivity was 56.6%.

[0045] Experimental Example 1 The catalyst of Example 1 was tested.

[0046] The H5AlW prepared in Example 1 12 O 40 The ICP-OES analysis results of the catalyst are shown in Table 1. The prepared H5AlW 12 O 40 The molar ratio of Al to W in H5AlW is very close to the theoretical value of 1:12, indicating that H5AlW 12 O 40 It conforms to the elemental composition of Keggin-type heteropolyacids.

[0047] Table 1 The H5AlW obtained in Example 1 12 O 40 The infrared spectrum of the catalyst is as follows Figure 2As shown, the spectrum exhibits fingerprint peaks belonging to Keggin-type heteropolyacids in the 700-1000 cm⁻¹ range, further indicating that the heteropolyacid has a distinct Keggin structure.

[0048] The H5AlW obtained in Example 1 12 O 40 Thermogravimetric diagram of the catalyst is as follows Figure 3 As shown, the slight weight loss at 150°C is due to H5AlW 12 O 40 The removal of physically adsorbed water at 150-300℃ results in a thermal weight loss of H5AlW. 12 O 40 The removal of water of crystallization, with a thermal weight loss of H5AlW at 300-600℃, results in the following: 12 O 40 The decomposition of the Keggin structure shows that H5AlW 12 O 40 The catalyst exhibits good thermal stability at the actual catalytic temperature.

[0049] Experimental Example 2 The effect of the difference in different solvent systems between Example 1 and Comparative Examples 1-3 on the LA yield is as follows: Figure 4 As shown, the effect of the solvent system on the LA yield was investigated at the same catalyst concentration (0.12 mmol / ml, calculated by water volume). It can be seen that a smaller water volume and the addition of sodium chloride significantly improve the LA yield.

[0050] Methods for calculating cellulose conversion, LA and 5-HMF yields, and selectivity: Cellulose conversion (%) = (m0-m1) / m0×100% LA yield (%) = n LA / n G ×100% 5-HMF (%) = n 5-HMF / n G ×100% LA selectivity= LA yield / Cellulose conversion×100% m0 is the mass of cellulose before conversion, m1 is the remaining mass of cellulose after conversion, and n LA n is the number of moles of LA in the product. G n is the number of glucose units in cellulose before conversion. 5-HMF It is the number of moles of 5-HMF in the product.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for catalyzing the production of levulinic acid from cellulose using a biphasic system based on a bifunctional heteropolyacid, characterized in that, Includes the following steps: Cellulose, sodium chloride, mixed solvent, and heteropolyacid catalyst are mixed and catalytically reacted to obtain levulinic acid.

2. The method according to claim 1, characterized in that, The heteropolyacid catalyst is HnXW. 12 O 40 , where X is Cu, Fe, Al, Zn or Co.

3. The method according to claim 1, characterized in that, The mass-volume ratio of the cellulose, sodium chloride, and mixed solvent is 0.1 g : (0.05-0.25) g : 10 mL.

4. The method according to claim 3, characterized in that, The cellulose is microcrystalline cellulose or natural lignocellulose.

5. The method according to claim 3, characterized in that, The mixed solvent is obtained by mixing water and organic solvent in a volume ratio of (1-3):(7-9); The organic solvent is n-butanol, tetrahydrofuran, methyl isobutyl ketone, N-methylpyrrolidone, or γ-valerolactone.

6. The method according to claim 1, characterized in that, The concentration of the heteropolyacid in the reaction system is 0.04-0.16 mmol / mL, based on the volume of water.

7. The method according to claim 1, characterized in that, The catalytic reaction is carried out at a temperature of 130-160℃ for 1-5 hours.

8. The method according to claim 1, characterized in that, After the catalytic reaction is completed, the organic phase is obtained by separation. The organic phase is then subjected to vacuum distillation to obtain levulinic acid. The organic solvent is recovered and recycled.

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