CN114292185B - Method for preparing p-coumaric acid ester by catalyzing lignin depolymerization through ionic liquid - Google Patents

Abstract

The invention discloses a method for preparing p-coumaric acid ester by catalyzing lignin depolymerization by ionic liquid. The method takes herbaceous lignin as a raw material, acidic functionalized ionic liquid as a catalyst and low-carbon alcohol as a reaction medium, and obtains coumarate by ester exchange technology under the conditions of 0.5-2.0 MPa pressure, 110-180 ℃ temperature and inert atmosphere; a p-coumarate yield of 11.8wt.% and a p-coumarate selectivity of 72.5% were highly obtainable. After the ionic liquid is repeatedly used for 10 times, the catalytic activity is not obviously reduced. The method has the advantages of relatively mild reaction conditions, high selectivity of single high value-added chemicals, renewable raw materials, reusable catalyst and the like, and the method is simple in process operation and can realize intermittent and continuous production.

Description

A kind of method that ionic liquid catalyzes depolymerization of lignin to prepare p-coumaric acid ester

technical field

The invention relates to a high value-added chemical p-coumarate, in particular to a method for preparing p-coumarate through directional conversion of herbal lignin catalyzed by an ionic liquid, and belongs to the field of efficient resource utilization of renewable agricultural and forestry waste.

Background technique

P-coumaric acid and its esters are important raw materials for the synthesis of spices, cosmetics, food and health products. They can also be used as pharmaceutical intermediates to prepare anti-adrenaline drugs such as esmolol, which play a role in immune regulation and cardiovascular protection. , prevent and improve diabetes, neuroprotection, inhibit melanin formation and delay skin aging. Because its molecular side chain has double bonds, p-coumaric acid and its esters can also be used as polymer precursors to prepare functional polymer materials, and have broad application prospects in the field of optical fiber communication with great application potential.

Currently, p-coumaric acid and its esters are mainly prepared from petroleum-based chemicals through chemical synthesis or biosynthesis. For example, p-hydroxybenzaldehyde and acetic anhydride are used as raw materials, and potassium carbonate is used as a catalyst to realize the "one-pot" synthesis of p-coumaric acid through Perkin reaction under microwave-assisted conditions. However, the above-mentioned processes generally have technical bottlenecks such as complex reaction process, high energy consumption, and many by-products. A green preparation method of p-coumaric acid ester that replaces the petroleum-based route is particularly important.

Lignin is one of the important components of biomass and is the most abundant natural aromatic polymer in nature, especially some herbal lignin contains p-coumaric acid (ester) structure. Compared with other structural units of lignin, which are mainly connected by CO bonds or CC bonds, the p-coumaric acid structure in herbaceous lignin is mainly connected by ester groups and other structural units, which also means that through the design of the catalytic system, It can realize the selective conversion of lignin to prepare p-coumaric acid ester with high added value. In recent years, Li et al. (Selective catalytic tailoring of the H unit in herbaceous lignin for methyl p-hydroxycinnamate production over metal-based ionic liquids, GreenChem., 2018, 20, 3743-3752) used bagasse lignin as raw material and utilized metal-based The ionic liquid [Bmim][FeCl ₄ ] was used as the catalyst, and the yield of methyl p-coumarate was 7.1wt.% at 145°C for 6 hours. Chinese invention patent CN201911410781.0 and Chinese invention patent application CN202011305496.5 use copper salts such as copper chloride and molybdenum oxide supported by molecular sieves as catalysts to realize the process of converting bagasse lignin to obtain p-coumaric acid ester. However, no matter the above-mentioned homogeneous or heterogeneous catalysts need to involve heavy metal ions, and the loss of metal ions is inevitable during the reaction process, resulting in increased side reactions, increasing the difficulty of product separation and purification, and the use of heavy metal ions It is also not conducive to the environment and violates the original intention of green preparation of high value-added chemicals.

Contents of the invention

The purpose of the present invention is to provide a new technology for the green preparation of p-coumarate, a high value-added fine chemical that replaces the petroleum-based route. Using ionic liquid as a catalyst, through the regulation of the catalytic process, an organic solvent-based The selective cleavage of the ester group in the herbaceous lignin molecule yields p-coumarate-based products, and high-purity p-coumarate chemicals are obtained by means of column separation. The technology has simple process and mild conditions, and is suitable for both batch and continuous production purposes.

The object of the present invention is achieved through the following technical solutions:

A method for preparing p-coumaric acid ester by catalyzing depolymerization of lignin by ionic liquid: using herbal lignin as raw material, acidic functionalized ionic liquid as catalyst, and low-carbon alcohol as reaction medium, under the pressure of 0.5-2.0MPa, 110-180 Under the condition of ℃ temperature and inert atmosphere, the coumaric acid ester is obtained by transesterification; the acidic functionalized ionic liquid is alkyl imidazole hydrogen sulfate, sulfoalkyl imidazole hydrogen sulfate, alkylpyridine hydrogen sulfate, sulfoalkyl One of pyridine hydrogen sulfate, alkyl quaternary ammonium hydrogen sulfate and sulfoalkyl quaternary ammonium hydrogen sulfate.

To further realize the purpose of the present invention, preferably, the acidic functionalized ionic liquid is one of the following structural formulas:

Preferably, the lignin is organic solvent herbal lignin.

Preferably, the organic solvent-type herbal lignin biomass is derived from one of corncobs, rice straw, wheat straw, corn straw, sorghum straw, bagasse, miscanthus, pennisetum and switchgrass.

Preferably, the low-carbon alcohol is one or more of methanol, ethanol, propanol and isopropanol.

Preferably, the gas in the inert atmosphere is one of nitrogen, argon or helium.

Preferably, the reaction time of the transesterification is 1-6 hours; the reaction of the transesterification is carried out in a rotating reactor, and the rotational speed of the reactor is 400-700 r/min.

Preferably, the amount of the acidic functionalized ionic liquid is 0.05-2.5mol/kg lignin; the volume-to-mass ratio of the reaction medium to lignin is 5:1-25:1, the volume unit is milliliters, and the mass unit is grams .

Preferably, after the coumaric acid ester is obtained through transesterification, a purification process is also included. The purification process is column separation, and the eluent of column separation is petroleum ether and ethyl acetate with a volume ratio of 1:1-3. Esters mixed solution.

Preferably, the acidic functionalized ionic liquid is reused; the reused acidic functionalized ionic liquid is obtained by extracting with dichloromethane, removing the extractant by rotary evaporation, and drying in a vacuum drying oven for 6-12 hours.

According to the feature that the herbaceous lignin structure is rich in p-coumaric acid structure, the acidic functionalized ionic liquid is used as a catalyst, methanol and other low-carbon alcohols are used as a reaction medium, and the reaction is carried out at 110-180°C for 1-6 hours. Through the reaction of transesterification technology, the selective conversion of renewable herbal lignin to prepare high-value-added chemical p-coumaric acid esters is obtained, and a new green preparation technology for high-value-added fine chemicals p-coumaric acid esters that replaces petroleum-based routes is obtained. .

The present invention has following advantage and effect relative to prior art:

1) The present invention builds a functional ionic liquid catalytic system based on the intrinsic characteristics that the herbaceous lignin molecule is rich in p-coumaric acid structure and is mainly connected to other structural units through ester groups, and uses the principle of transesterification to achieve mild conditions Under the selective cleavage of the p-coumaric acid structural unit in the herbaceous lignin structure, a high-value-added fine chemical p-coumaric acid ester with a wide range of uses is obtained. Realize the goal of obtaining green preparation of bulk chemicals that replace petroleum-based routes starting from renewable raw materials.

2) Compared with the existing p-coumaric acid ester preparation technology, the inventive method has the greatest advantage in that what the present invention provides is a method for preparing p-coumaric acid ester with renewable agricultural and forestry waste component lignin as raw material The green method, whose raw materials are renewable and the catalyst can be reused, meets the requirements of the current "double carbon" strategy. Compared with the preparation methods of lignin-based p-coumarate reported in a few existing literatures, the catalyst used in the present invention is a functionalized ionic liquid, which does not involve metal ions and halide ions, and can avoid its impact on the environment.

3) Compared with the existing lignin depolymerization technology, the method of the present invention has milder reaction conditions, and the constructed catalytic system is based on the characteristics of lignin structural differences. Therefore, the selectivity of the product obtained by the method of the present invention is obvious Higher than the current lignin depolymerization technology.

4) The catalytic system constructed by the method of the present invention has significant advantages such as high activity, simple operation, easy product separation, environmental friendliness, and reusable catalyst.

5) The medium used in the method of the present invention can be reused through simple distillation.

6) The present invention has mild reaction conditions, simple process operation, and can realize discontinuous or continuous reaction.

Description of drawings

Fig. 1 is the gas chromatography (GC-FID) spectrum of the depolymerization product of bagasse lignin in the [bSmim][HSO ₄ ] catalytic system obtained in Example 1.

Fig. 2 is the mass spectrogram of the product methyl p-coumarate obtained in Example 1.

Fig. 3 is the Fourier transform infrared spectrum (FT-IR) spectrogram of the product methyl p-coumarate obtained in Example 1.

Fig. 4 is a hydrogen nuclear magnetic resonance ( ¹ H NMR) spectrum of the product methyl p-coumarate obtained in Example 1.

Fig. 5 is a carbon nuclear magnetic resonance spectrum ( ¹³ C NMR) spectrum of the product methyl p-coumarate obtained in Example 1.

Figure 6 is a diagram of the reusability performance of ionic liquids.

detailed description

In order to better understand the present invention, the present invention will be further described below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

Example 1: Preparation of methyl p-coumarate by selective depolymerization of bagasse lignin catalyzed by ionic liquid 1-butanesulfonate-3-methylimidazolium bisulfate ([bSmim]HSO ₄ )

A method for preparing p-coumaric acid esters by ionic liquid catalyzed depolymerization of lignin: 2 mmol ionic liquid 1-butanesulfonic acid-3-methylimidazolium bisulfate ([bSmim]HSO ₄ ), 2 g organic solvent-based bagasse Lignin and 20 mL of methanol were added into a 50 mL autoclave (maximum operating pressure 20 MPa, maximum operating temperature 300° C.). Seal the reactor, and replace the reactor with high-purity argon (purity greater than 99.9%) for 3 times to discharge the air in the reactor, and then pressurize to 0.5 MPa. The reaction mixture was heated to 140° C., and reacted for 4 h under the stirring condition of 600 r/min. Rotary evaporation is used to realize the recovery and reuse of reaction medium methanol, and ethyl acetate extraction is used to extract small molecule chemicals obtained from lignin depolymerization, water is added to precipitate incompletely reacted lignin, and 0.22um organic membrane is used to filter The method separates it from the solution, and recovers the ionic liquid catalyst by means of dichloromethane extraction. After the reaction, the remaining liquid was transferred to a beaker, and 50 mL of deionized water was added thereto. Using ethyl acetate:petroleum ether with a volume ratio of 2:1 as the eluent, methyl p-coumarate was obtained by means of column separation. The results showed that the depolymerization rate of bagasse lignin was 56.2%, the mass yield of methyl p-coumarate was 11.8wt.%, and the selectivity was 72.5%.

The depolymerization rate of lignin obtained in this embodiment is calculated by formula 1:

Formula 1: Lignin depolymerization rate=(1-mass of incompletely reacted lignin/mass of lignin raw material)×100%

The yield of methyl p-coumarate obtained in the present embodiment is calculated by formula 2

Formula 2: yield of methyl p-coumarate = mass of methyl p-coumarate/mass of lignin raw material × 100%

The selectivity of methyl p-coumarate obtained in this embodiment is calculated by formula 3

Formula 3: Selectivity of methyl p-coumarate = mass of methyl p-coumarate/mass of volatile small molecule product × 100%

The small molecule products obtained in this example refer to products that can be directly detected by gas chromatography. These compounds are qualitatively analyzed by gas chromatography and quantitatively analyzed by gas chromatography. The results of GC-MS analysis (Fig. 1) showed that the compound was mainly composed of methyl p-coumarate and other phenolic compounds such as 4-ethylphenol.

The structure of methyl p-coumarate obtained in this example was identified by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance ( ¹ H-NMR, ¹³ C-NMR) and mass spectrometry, and the results are shown in Figures 2-5.

Fig. 2 is the mass spectrogram of the product methyl p-coumarate obtained in Example 1. The characteristic mass spectrum fragments of m/z=178, 147, 119, 91, 65 and 45 attributed to methyl p-coumarate are clearly visible.

Fig. 3 is the FT-IR spectrogram of the product methyl p-coumarate obtained in Example 1. Among them, 3380cm ^-1 is attributed to the stretching vibration of phenolic hydroxyl group, and the strong transmission peak at 1687cm ^-1 is attributed to the stretching vibration of carbonyl group. Combined with the characteristic infrared peaks of symmetric CO chemical bonds appearing at 1198cm ^-1 and 1170cm ^-1 , it indicates that the compound has It contains an ester group; the infrared peaks at 1614cm ^-1 , 1542cm ^-1 , 1431cm ^-1 , 1281cm ^-1 and 833cm ^-1 indicate that there is a para-group benzene ring in this compound.

Fig. 4 is the ¹ H NMR spectrum of the product methyl p-coumarate obtained in Example 1. The characteristic peak at 10.04ppm belongs to the hydrogen atom in the phenolic hydroxyl group; the multiple peaks at 7.57ppm, 6.81ppm and 6.42ppm belong to the hydrogen atom of the benzene ring and the conjugated olefin; the multiplet at 3.46ppm belongs to the hydrogen atom in the methoxyl group .

Fig. 5 is the ¹³ C NMR spectrum of the product methyl p-coumarate obtained in Example 1. The characteristic peak at 167ppm is attributed to the carbonyl carbon in the ester group; the characteristic peaks at 160ppm, 130ppm, 125ppm and 116ppm indicate that there is a para-substituted phenolic structure in the compound, and the characteristic peaks at 145ppm and 114ppm are respectively assigned to the carbon atoms in the alkene structure ; The characteristic peak at 52ppm belongs to the methyl carbon atom in the methoxyl group.

Therefore, based on the structural characterization data obtained in Figures 2-5, it can be seen that the obtained product is a high-purity methyl p-coumarate chemical.

This example provides a method for the preparation of important petroleum-based fine chemical methyl p-coumarate through the selective depolymerization of lignin catalyzed by ionic liquid. The method uses lignin in renewable agricultural and forestry waste as raw material, providing A green strategy for the preparation of important chemical products that replaces petroleum-based routes is proposed. Compared with the current petroleum-based route, the method has simple process and renewable raw materials; compared with the current production technology of lignin-based methyl p-coumarate (Green Chem., 2018, 20, 3743-3752, CN201911410781.0) , the catalyst adopted in the present invention does not contain heavy metal ions and halide ions, is more friendly to the environment, and the efficiency of the present invention (the yield of methyl p-coumarate) is significantly higher than the metal halide ionic liquid ( 7.1wt.%) and copper salt (4wt.% ~ 10wt.%) catalytic system.

Example 2: Preparation of methyl p-coumarate by selective depolymerization of corncob lignin catalyzed by ionic liquid butanesulfonate pyridinium bisulfate ([bSPy]HSO ₄ )

The difference between this embodiment and embodiment 1 is:

The catalyst used was butanesulfonate pyridinium bisulfate ionic liquid ([bSPy]HSO ₄ ); the catalyst dosage was 5 mmol; the lignin used was organic solvent lignin derived from corn cob, and the dosage was 5 g; The reaction temperature is 150°C; the reaction time is 3h; the stirring speed of the reactor is 500r/min; the eluent used for the separation and purification of p-coumarate column is ethyl acetate and petroleum ether with a volume ratio of 1:1. The test method and product characterization method are the same as in Example 1.

The depolymerization rate of obtained corn cob lignin was 56.8%, the yield of methyl p-coumarate was 10.5wt.%, and the selectivity was 73.2%.

Example 3: Preparation of ethyl p-coumarate by selective depolymerization of corn straw lignin catalyzed by ionic liquid butanesulfonate tributylamine hydrogen sulfate ([bSb ₃ N]HSO ₄ )

The difference between this embodiment and embodiment 1 is:

The catalyst used is butanesulfonate tributylamine bisulfate ionic liquid ([bSb ₃ N]HSO ₄ ); the catalyst dosage is 1 mmol; The dosage is 2.5g; the reaction temperature is 180°C; the reaction time is 6h; the stirring speed of the reactor is 500r/min; the eluent used for separation and purification of p-coumarate column is ethyl acetate with a volume ratio of 1:1 and petroleum ether. The test method and product characterization method are the same as in Example 1.

The depolymerization rate of the obtained organic solvent-type corn stalk lignin was 62.7%, the yield of methyl p-coumarate was 8.6wt.%, and the selectivity was 65.2%.

Example 4: Preparation of isopropyl p-coumarate by selective depolymerization of straw lignin catalyzed by ionic liquid 1-propanesulfonate-3-methylimidazolium hydrogensulfate ([pSmim]HSO ₄ )

The difference between this embodiment and embodiment 1 is:

The ionic liquid catalyst adopted is 1-propanesulfonic acid group-3-methylimidazolium bisulfate ([pSmim]HSO ₄ ); the catalyst dosage is 5 mmol; the lignin used is organic solvent lignin derived from rice straw , the dosage is 2.5g; the reaction medium is isopropanol; the reaction temperature is 180°C; the reaction time is 6h; the stirring speed of the reactor is 700r/min. The test method and product characterization method are the same as in Example 1.

The depolymerization rate of obtained corn cob lignin was 73.2%, the yield of isopropyl p-coumarate was 6.7wt.%, and the selectivity was 45.8%.

Example 5: Preparation of propyl p-coumarate by selective depolymerization of sorghum straw lignin catalyzed by ionic liquid 1-propanesulfonate-3-methylimidazolium bisulfate ([pSmim]HSO ₄ )

The difference between this embodiment and embodiment 1 is:

The ionic liquid catalyst used is 1-propanesulfonate-3-methylimidazolium bisulfate ([pSmim]HSO ₄ ); the catalyst dosage is 5 mmol; the lignin used is organic solvent-based lignin derived from sorghum straw The dosage is 5g; the reaction medium is n-propanol; the inert gas is helium; the reaction temperature is 170°C; the reaction time is 1h; the stirring speed of the reactor is 400r/min. The test method and product characterization method are the same as in Example 1.

The depolymerization rate of the obtained sorghum straw lignin was 67.5%, the yield of propyl p-coumarate was 5.9wt.%, and the selectivity was 55.2%.

Example 6: Ionic liquid 1-butanesulfonate-3-methylimidazolium bisulfate ([bSmim]HSO ₄ ) catalyzed the selective depolymerization of Miscanthus lignin to prepare ethyl p-coumarate

The difference between this embodiment and embodiment 1 is:

The ionic liquid catalyst adopted is 1-butanesulfonic acid group-3-methylimidazolium bisulfate ([bSmim]HSO ₄ ); the catalyst dosage is 5 mmol; the lignin used is organic solvent-type lignin derived from Miscanthus , the dosage is 5g; the reaction medium is ethanol; the inert gas is divided into helium, the reaction temperature is 150°C; the reaction time is 6h; the stirring speed of the reactor is 600r/min. The test method and product characterization method are the same as in Example 1.

The depolymerization rate of obtained Miscanthus lignin was 58.9%, the yield of propyl p-coumarate was 9.8wt.%, and the selectivity was 66.7%.

Example 7: Ionic liquid 1-butanesulfonate-3-methylimidazolium bisulfate ([bSmim]HSO ₄ ) catalyzes the selective depolymerization of pennisetum lignin to prepare ethyl p-coumarate

The difference between this embodiment and embodiment 1 is:

The ionic liquid catalyst used is 1-butanesulfonic acid-3-methylimidazolium bisulfate ([bSmim]HSO ₄ ); the catalyst dosage is 5 mmol; the lignin used is the organic solvent type derived from Pennisetum The amount of lignin is 5g; the reaction medium is ethanol; the inert gas is helium; the reaction temperature is 150°C; the reaction time is 6h; the stirring speed of the reactor is 600r/min. The test method and product characterization method are the same as in Example 1.

The depolymerization rate of the obtained pennisetum lignin was 62.1%, the yield of propyl p-coumarate was 10.2wt.%, and the selectivity was 68.3%.

Example 8: Preparation of ethyl p-coumarate by selective depolymerization of switchgrass lignin catalyzed by ionic liquid 1-butanesulfonate-3-methylimidazolium bisulfate ([bSmim]HSO ₄ )

The difference between this embodiment and embodiment 1 is:

The ionic liquid catalyst adopted is 1-butanesulfonic acid group-3-methylimidazolium bisulfate ([bSmim]HSO ₄ ); the catalyst dosage is 5 mmol; the lignin adopted is organic solvent-type lignin derived from switchgrass , the dosage is 5g; the reaction medium is ethanol; the inert gas is nitrogen, the pressure is 2.0MPa; the reaction temperature is 150°C; the reaction time is 6h; the stirring speed of the reactor is 600r/min. The test method and product characterization method are the same as in Example 1.

The depolymerization rate of the obtained switchgrass lignin was 55.6%, the yield of propyl p-coumarate was 7.5wt.%, and the selectivity was 68.1%.

Example 9: Preparation of ethyl p-coumarate by selective depolymerization of bagasse lignin catalyzed by ionic liquid propanesulfonate pyridinium bisulfate ([pSPy]HSO ₄ )

The difference between this embodiment and embodiment 1 is:

The ionic liquid catalyst adopted is propanesulfonate pyridinium bisulfate ([pSPy]HSO ₄ ); the catalyst consumption is 5mmol; the lignin adopted is the organic solvent type lignin derived from bagasse, and its consumption is 5g; The medium is ethanol; the inert gas is divided into nitrogen, and the pressure is 0.5MPa; the reaction temperature is 150°C; the reaction time is 6h; the stirring speed of the reactor is 600r/min. The test method and product characterization method are the same as in Example 1.

The depolymerization rate of obtained bagasse lignin was 54.9%, the yield of propyl p-coumarate was 11.0wt.%, and the selectivity was 72.8%.

Example 10: Preparation of ethyl p-coumarate by selective depolymerization of bagasse lignin catalyzed by ionic liquid ethylpyridine bisulfate ([ePy]HSO ₄ )

The difference between this embodiment and embodiment 1 is:

The ionic liquid catalyst adopted is ethyl pyridinium bisulfate ([ePy]HSO ₄ ); the catalyst consumption is 5mmol; the lignin adopted is the organic solvent type lignin derived from bagasse, and its consumption is 5g; the reaction medium is Ethanol; the inert gas is divided into nitrogen, and the pressure is 0.5MPa; the reaction temperature is 150°C; the reaction time is 6h; the stirring speed of the reactor is 600r/min. The test method and product characterization method are the same as in Example 1.

The depolymerization rate of obtained bagasse lignin was 48.3%, the yield of propyl p-coumarate was 7.6wt.%, and the selectivity was 70.9%.

Example 11: Preparation of methyl p-coumarate by selective depolymerization of bagasse lignin catalyzed by ionic liquid 1-propyl-3-methylimidazolium bisulfate ([pmim]HSO ₄ )

The difference between this embodiment and embodiment 1 is:

The ionic liquid catalyst adopted is 1-propyl-3-methylimidazolium bisulfate ([pmim]HSO ₄ ); the amount of catalyst used is 8 mmol; the lignin used is organic solvent-type lignin derived from bagasse, which The dosage is 5g; the reaction medium is methanol; the inert gas is argon, and the pressure is 0.5MPa; the reaction temperature is 150°C; the reaction time is 6h; the stirring speed of the reactor is 600r/min. The test method and product characterization method are the same as in Example 1.

The depolymerization rate of obtained bagasse lignin was 49.8%, the yield of methyl p-coumarate was 6.9wt.%, and the selectivity was 70.4%.

Example 12: Preparation of methyl p-coumarate by selective depolymerization of bagasse lignin catalyzed by ionic liquid tetrabutylammonium bisulfate ([b ₄ N]HSO ₄ )

The difference between this embodiment and embodiment 1 is:

The ionic liquid catalyst adopted is tetrabutylammonium bisulfate ([b ₄ N]HSO ₄ ); the catalyst consumption is 10mmol; the lignin adopted is the organic solvent type lignin derived from bagasse, and its consumption is 5g; The medium is methanol; the inert gas is divided into argon, and the pressure is 2.0MPa; the reaction temperature is 150°C; the reaction time is 6h; the stirring speed of the reactor is 600r/min. The test method and product characterization method are the same as in Example 1.

The depolymerization rate of the obtained bagasse lignin was 50.6%, the yield of methyl p-coumarate was 7.3wt.%, and the selectivity was 69.8%.

Example 13: Reusable performance of ionic liquid 1-butanesulfonic acid-3-methylimidazolium bisulfate ([bSmim]HSO ₄ )

The ionic liquid catalyst [bSmim]HSO used in Example ₁ was separated and obtained from the mixed liquid after the reaction by means of dichloromethane extraction, and then the extraction agent dichloromethane was removed by rotary evaporation at 50° C., and then in Dry at constant temperature in a vacuum oven at 100°C for 24 hours. Gained ionic liquid catalyst carries out circulation experiment according to the step described in embodiment 1. Tests show that the catalyst still exhibits good catalytic activity after repeated experiments for 10 times, the conversion rate of bagasse lignin can still reach more than 55%, and the mass yield and selectivity of methyl p-coumarate can still reach 10.9 wt.% and 69.8% (Figure 6).

As can be seen from the above examples, the method for the preparation of high value-added methyl p-coumarate by ionic liquid catalytic lignin selective conversion based on the principle of transesterification in the present invention has high catalyst activity, reusability, no need to add heavy metal ions and Halogen ion; lignin conversion process is simple, the conditions are mild, and batch and continuous reactions can be realized.

The implementation of the present invention is not limited by the above examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods, including Within the protection scope of the present invention.

Claims (10)

1. A method for preparing p-coumarate by catalyzing lignin depolymerization through ionic liquid is characterized by comprising the following steps: taking herbal lignin as a raw material, taking acidic functionalized ionic liquid as a catalyst, taking low-carbon alcohol as a reaction medium, and carrying out ester exchange under the conditions of 0.5-2.0 MPa pressure, 110-180 ℃ and inert atmosphere to obtain coumarate; the acidic functionalized ionic liquid is one of alkyl imidazole hydrogen sulfate, sulfoalkyl imidazole hydrogen sulfate, alkyl pyridine hydrogen sulfate, sulfoalkyl pyridine hydrogen sulfate, alkyl quaternary ammonium hydrogen sulfate and sulfoalkyl quaternary ammonium hydrogen sulfate.

2. The method for preparing p-coumarate by ionic liquid catalyzed lignin depolymerization according to claim 1, wherein: the acidic functionalized ionic liquid is one of the following structural formulas:

3. the method for preparing p-coumarate by depolymerizing lignin catalyzed by ionic liquid according to claim 1, wherein: the lignin is organic solvent type herbaceous lignin.

4. The method for preparing p-coumarate by depolymerizing lignin catalyzed by ionic liquid according to claim 3, wherein: the biomass of the organic solvent type herbaceous lignin is derived from one of corncobs, straws, wheat straws, corn straws, sorghum straws, bagasse, miscanthus, pennisetum and switchgrass.

5. The method for preparing p-coumarate by ionic liquid catalyzed lignin depolymerization according to claim 1, wherein: the lower alcohol is one or more of methanol, ethanol, propanol and isopropanol.

6. The method for preparing p-coumarate by depolymerizing lignin catalyzed by ionic liquid according to claim 1, wherein: the gas of the inert atmosphere is one of nitrogen, argon and helium.

7. The method for preparing p-coumarate by depolymerizing lignin catalyzed by ionic liquid according to claim 1, wherein: the reaction time of the ester exchange is 1 to 6 hours; the transesterification reaction is carried out in a rotating reactor, the rotating speed of which is 400-700 r/min.

8. The method for preparing p-coumarate by depolymerizing lignin catalyzed by ionic liquid according to claim 1, wherein: the dosage of the acidic functionalized ionic liquid is 0.05-2.5 mol/kg lignin; the volume-mass ratio of the reaction medium to the lignin is 5-25, wherein the volume unit is milliliter and the mass unit is gram.

9. The method for preparing p-coumarate by depolymerizing lignin catalyzed by ionic liquid according to claim 1, wherein: the method is characterized in that the method also comprises a purification process after the coumarate is obtained through ester exchange, wherein the purification process is column separation, and eluent obtained through the column separation is a mixture of 1:1 to 3 of mixed solution of petroleum ether and ethyl acetate.

10. The method for preparing p-coumarate by ionic liquid catalyzed lignin depolymerization according to claim 1, wherein: the acidic functionalized ionic liquid is repeatedly used; the repeatedly used acidic functionalized ionic liquid is extracted by dichloromethane, the extractant is removed by rotary evaporation, and then the acidic functionalized ionic liquid is dried in a vacuum drying oven for 6 to 12 hours to obtain the ionic liquid.

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