Green and efficient pretreatment of biomass and its use for the selective preparation of 2,3-dihydrobenzofuran

Abstract

This invention discloses a green and efficient pretreatment method for biomass and its application in the selective preparation of 2,3-dihydrobenzofuran. The pretreatment includes: uniformly mixing biomass raw materials with a ternary eutectic solvent, reacting the mixture in a microwave synthesizer, and then washing, filtering, and drying the reactants to collect the solid residue, thus obtaining the pretreated biomass. The ternary eutectic solvent used in this invention is a mixed solution of zinc chloride, ethylene glycol, and water. It is simple to prepare, uses readily available and harmless raw materials, and is recyclable. Zinc has the dual functions of solvent and catalyst, increasing the total number of hydrogen bonds, promoting the breaking of β-O-4 bonds, and increasing the acidity of the solvent. It also forms metal ion complexes with water ligands, promoting biomass pyrolysis. The pretreatment method of this invention can achieve a lignin removal rate of over 80% at low temperatures, requires a short reaction time, uses readily available and harmless solvents, and exhibits a selectivity for 2,3-dihydrobenzofuran exceeding 40% after pyrolysis, providing technical support for advancing industrialization.

Description

Technical Field

[0001] This invention belongs to the field of biomass energy utilization technology, specifically relating to a green and efficient pretreatment of biomass and its application in the selective preparation of 2,3-dihydrobenzofuran. Background Technology

[0002] Pyrolysis is one of the main methods for converting and utilizing biomass energy. It is a clean, environmentally friendly, and easy-to-operate conversion method, yielding bio-oils containing various high-value-added chemicals. Among these, 2,3-dihydrobenzofuran has high medicinal value and can be used for traumatic and ischemic central nervous system injuries. Since 2,3-dihydrobenzofuran is mainly obtained from cellulose and hemicellulose in lignocellulosic biomass, separating lignin from biomass is a major challenge for the high-value utilization of biomass. Appropriate pretreatment can selectively remove lignin, making subsequent pyrolysis reactions more selective.

[0003] Currently, commonly used pretreatment methods mainly include physical pretreatment, chemical pretreatment, physicochemical pretreatment, and biological pretreatment. Physical pretreatment is simple to operate, but its treatment effect is more focused on the crystallinity and size of the substance, and it is difficult to break the active bonds inside the substance. Chemical pretreatment is relatively mature, but the treatment cost of acid and alkali waste liquid is high, and improper treatment can cause significant environmental damage. Physicochemical pretreatment equipment such as steam explosion or ammonia fiber explosion is complex to operate and has a high cost. Biological methods have harsh working conditions and a long cycle, and the enzyme activity is also relatively low.

[0004] Patent CN115772273A provides a pretreatment method using organic solvents including glycerol formaldehyde, acids, and alkalis. The reaction process involves low pressure and the solvent can be recycled. However, the preparation process is complex, and the waste liquid generated by acids and alkalis is expensive to treat and environmentally harmful. Patent CN115976116A provides a pretreatment method using steam explosion and a eutectic solvent to treat biomass, achieving a high lignin removal rate. However, this method has drawbacks such as affecting the cellulose structure and unstable treatment results. Patent CN115873136A provides a eutectic solvent pretreatment method using choline chloride-ethylene glycol-p-toluenesulfonic acid as the solvent. The pretreatment time is short, but p-toluenesulfonic acid is toxic and highly corrosive, harming the environment and easily corroding equipment and pipelines. Therefore, developing environmentally friendly, efficient, low-cost, and high-lignin-removal-rate eutectic solvents is crucial for biomass pretreatment and applications. Summary of the Invention

[0005] To address the aforementioned technical problems in existing technologies, the present invention aims to provide a green and efficient pretreatment method for biomass and its application in the selective preparation of 2,3-dihydrobenzofuran. The present invention provides a green and efficient biomass pretreatment method that can achieve a delignification efficiency of over 80% at low temperatures, and the selectivity for 2,3-dihydrobenzofuran can be higher than 40%.

[0006] The technical solution adopted in this invention is as follows:

[0007] A green and efficient pretreatment method for biomass includes the following steps:

[0008] 1) Crush and dry the biomass raw materials to obtain biomass powder;

[0009] 2) Preparation of ternary eutectic solvent: Mix hydrogen bond acceptor and water evenly, then add hydrogen bond donor ethylene glycol to a beaker, heat and stir until a transparent homogeneous solution is obtained, thus obtaining ternary eutectic solvent;

[0010] 3) Microwave reaction: The ternary eutectic solvent in step 2) is uniformly mixed with the biomass powder in step 1) and then added to the microwave synthesis tube. The microwave synthesis tube is then placed under the microwave radiation of the microwave synthesizer for microwave pretreatment. After that, the mixture is centrifuged, and the lower solid mixture is collected and washed with ammonium chloride aqueous solution. After washing, the mixture is centrifuged again, washed with deionized water until neutral, and dried to obtain the pretreated biomass.

[0011] Furthermore, in step 1), the particle size of the biomass powder is between 20 and 200 mesh, preferably between 40 and 60 mesh.

[0012] Furthermore, the biomass is bagasse, sawdust, straw, or pine leaves, preferably bagasse.

[0013] Furthermore, the hydrogen bond acceptor includes zinc chloride, choline chloride, or betaine, with zinc chloride being the preferred hydrogen bond acceptor.

[0014] Furthermore, the mass ratio of hydrogen bond acceptor to ethylene glycol is 1:2 to 15, preferably 1:8 to 10; the mass ratio of water to ethylene glycol is 1:0.2 to 1.0, preferably 1:0.25 to 0.5.

[0015] Furthermore, in step 2), the heating and stirring temperature is 70-90℃, the stirring time is 10-80 min, and the stirring speed is 200-600 r / min.

[0016] Furthermore, in step 3), the mass ratio of biomass to ternary eutectic solvent is 1:5-30, preferably 1:10-20.

[0017] Further, the reaction conditions for microwave pretreatment in step 3) are: microwave power of 100-400W, processing temperature of 50-70℃, and processing time of 10-60min. The preferred microwave power is 250-300W, the preferred processing temperature is 60-65℃, and the preferred processing time is 25-30min.

[0018] Further, in step 3), the concentration of the ammonium chloride aqueous solution is 0.5-3 mol / L, preferably 1 mol / L to 2 mol / L.

[0019] This invention also provides an application of the aforementioned green and efficient pretreated biomass for the selective preparation of 2,3-dihydrobenzofuran. The application method is as follows: a pyrolysis reaction is carried out in a pyrolysis furnace. The pretreated biomass is loaded into the isothermal zone of the pyrolysis furnace, and N2 is introduced to purge the air. Then, the reaction is carried out under an N2 atmosphere, and the temperature is increased from room temperature to the reaction temperature of 500-550°C at a rate of 30-60°C / min. The temperature is then maintained at 500-550°C for 1-30 min, preferably 5-10 min. The gaseous products generated by pyrolysis are discharged and condensed and collected to obtain a liquid phase product containing the pyrolysis target product 2,3-dihydrobenzofuran.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1) This invention provides a green and efficient pretreatment method that uses a zinc chloride-ethylene glycol-water ternary eutectic solvent for treatment. The method is simple to prepare, can effectively reduce the viscosity of the eutectic solvent, uses readily available and harmless raw materials that can be recycled, and reduces production costs.

[0022] 2) In the zinc chloride-ethylene glycol-water ternary eutectic solvent provided by the present invention, zinc has the dual functions of solvent and catalyst, increasing the total number of hydrogen bonds and promoting the breaking of β-O-4 bond energy. Heating zinc can increase the acidity sites of the solvent, form metal ion complexes with water ligands, and promote biomass pyrolysis.

[0023] 3) The present invention provides a green and efficient pretreatment method that uses a ternary eutectic solvent and microwave synergy. Through dipole rotation and ion conduction, the reaction time of the pretreatment can be significantly reduced, and more uniform heat transfer can be achieved with lower energy consumption. This can achieve a high lignin removal rate at low temperature. The eutectic solvent and microwave synergy can improve the polarity of the solution and improve the stability of active protons.

[0024] 4) The low eutectic solvent obtained by this invention is used to pretreat biomass and then applied to the catalytic cracking of biomass. Compared with direct cracking of biomass, the reaction activation energy is reduced, the types of products are greatly reduced, and the difficulty of subsequent purification steps is reduced. The total types of products obtained are reduced to less than ten, and the selectivity of 2,3-dihydrobenzofuran can reach 42.718%. Attached Figure Description

[0025] Figure 1 This is an SEM image of sugarcane bagasse after preprocessing in Example 1.

[0026] Figure 2 Infrared images of sugarcane bagasse after different pretreatments. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0028] In the embodiments and comparative examples of the present invention, the bagasse was dried in an oven at 110°C for 24 hours before use, and the particle size of the dried bagasse after sieving was 40-60 mesh.

[0029] Example 1

[0030] 1g of zinc chloride was dissolved in 20ml of deionized water and mixed thoroughly. Then, 10g of ethylene glycol was added to the zinc chloride and deionized water mixture. The mixture was stirred at 80℃ and 500r / min for 1h to obtain a transparent homogeneous solution, which is the ternary eutectic solvent. 1.5g of sieved and dried sugarcane bagasse was mixed thoroughly with the above ternary eutectic solvent and placed in a microwave synthesis tube. The microwave synthesis tube was then placed under microwave radiation in a microwave synthesizer and microwave pretreated at 300W and 60℃ for 0.5h. The solid-liquid product in the microwave synthesis tube was centrifuged, and the lower solid mixture was collected and washed with an ammonium chloride aqueous solution (2.1397g of ammonium chloride dissolved in 20ml of deionized water). The mixture was stirred at 90℃ and 600r / min for 1.5h. After stirring, the product was filtered and washed with deionized water until neutral. The pretreated sugarcane bagasse was dried at 110℃ for 24h to obtain the pretreated sugarcane bagasse.

[0031] The solid bagasse obtained after pretreatment has a mass of 1.35g and a lignin removal rate of 83.04%.

[0032] SEM images of sugarcane bagasse after pretreatment in Example 1 are shown below. Figure 1 As shown.

[0033] Example 2

[0034] 1g of zinc chloride was dissolved in 20ml of deionized water and mixed thoroughly. Then, 5g of ethylene glycol was added to the zinc chloride and deionized water mixture. The mixture was stirred at 80℃ and 500r / min for 1h to obtain a transparent homogeneous solution, which is the ternary eutectic solvent. 1.50g of sieved and dried sugarcane bagasse was mixed thoroughly with the above ternary eutectic solvent and placed in a microwave synthesis tube. The microwave synthesis tube was then placed under microwave radiation in a microwave synthesizer and microwave pretreated at 300W and 60℃ for 0.5h. The solid-liquid product in the microwave synthesis tube was centrifuged, and the lower solid mixture was collected and washed with an ammonium chloride aqueous solution (2.1397g of ammonium chloride dissolved in 20ml of deionized water). The mixture was stirred at 90℃ and 600r / min for 1.5h. After stirring, the product was filtered with deionized water until neutral. The pretreated sugarcane bagasse was dried at 110℃ for 24h to obtain the pretreated sugarcane bagasse.

[0035] The solid bagasse obtained after pretreatment has a mass of 1.36g and a lignin removal rate of 75.43%.

[0036] Example 3

[0037] 5g of zinc chloride was dissolved in 20ml of deionized water and mixed thoroughly. Then, 10g of ethylene glycol was added to the zinc chloride and deionized water mixture. The mixture was stirred at 80℃ and 500r / min for 1h to obtain a transparent homogeneous solution, which is the ternary eutectic solvent. 1.50g of sieved and dried sugarcane bagasse was mixed thoroughly with the above ternary eutectic solvent and placed in a microwave synthesis tube. The microwave synthesis tube was then placed under microwave radiation in a microwave synthesizer at 300W and 60℃ for 0.5h. The solid-liquid product in the microwave synthesis tube was centrifuged, and the lower solid mixture was collected and washed with an ammonium chloride aqueous solution (2.1397g of ammonium chloride dissolved in 20ml of deionized water). The mixture was stirred at 90℃ and 600r / min for 1.5h. After stirring, the product was filtered with deionized water until neutral. The pretreated sugarcane bagasse was dried at 110℃ for 24h to obtain the pretreated sugarcane bagasse.

[0038] The solid bagasse obtained after pretreatment has a mass of 1.30g and a lignin removal rate of 78.35%.

[0039] Comparative Example 1

[0040] 1.50g of sieved and dried sugarcane bagasse was mixed evenly with 20mL of deionized water and placed in a beaker. The mixture was stirred at 90℃ for 6 hours. After stirring, the product was filtered to obtain pretreated sugarcane bagasse. The pretreated sugarcane bagasse was then dried at 110℃ for 24 hours to obtain pretreated sugarcane bagasse.

[0041] The solid bagasse obtained after pretreatment has a mass of 1.38g and a lignin removal rate of 50.39%.

[0042] Comparative Example 2

[0043] The only difference between Comparative Example 2 and Example 1 is that the microwave pretreatment temperature is replaced with 40°C, while other conditions remain unchanged, and the pretreated sugarcane bagasse is finally obtained.

[0044] The solid bagasse obtained after pretreatment has a mass of 1.34g and a lignin removal rate of 78.36%.

[0045] Comparative Example 3

[0046] The only difference between Comparative Example 3 and Example 1 is that the microwave pretreatment temperature is replaced with 80°C, while other conditions remain unchanged, and the pretreated sugarcane bagasse is finally obtained.

[0047] The solid bagasse obtained after pretreatment has a mass of 1.33g and a lignin removal rate of 79.87%.

[0048] Infrared images of the original untreated bagasse, the bagasse pretreated in Example 1, and the bagasse pretreated in Comparative Example 3 are shown below. Figure 2 As shown.

[0049] Comparative Example 4

[0050] The only difference between Comparative Example 4 and Example 1 is that "in the preparation of the ternary eutectic solvent, 1g of zinc chloride was replaced with 1g of choline chloride", while other conditions remained unchanged, and the pretreated sugarcane bagasse was finally obtained.

[0051] The solid bagasse obtained after pretreatment has a mass of 1.34 g and a lignin removal rate of 74.39%.

[0052] Comparative Example 5

[0053] The only difference between Comparative Example 5 and Example 1 is that "in the preparation of the ternary eutectic solvent, 10g of ethylene glycol was replaced with 10g of propylene glycol", while other conditions remained unchanged, and the pretreated bagasse was finally obtained.

[0054] The solid bagasse obtained after pretreatment has a mass of 1.33g and a lignin removal rate of 75.69%.

[0055] Comparative Example 6

[0056] 1 g of zinc chloride was dissolved in 20 ml of deionized water and mixed thoroughly. Then, 10 g of ethylene glycol was added to the zinc chloride and deionized water mixture. The mixture was stirred at 80°C and 500 r / min for 1 h to obtain a transparent homogeneous solution, which is the ternary eutectic solvent. 1.50 g of sieved and dried sugarcane bagasse was mixed thoroughly with the above ternary eutectic solvent and placed in a beaker. The mixture was heated in an oil bath at 90°C and stirred for 6 h. The solid-liquid product was then centrifuged. The lower solid mixture was collected and washed with an ammonium chloride aqueous solution (2.1397 g of ammonium chloride dissolved in 20 ml of deionized water). The mixture was stirred at 90°C and 600 r / min for 1.5 h. After stirring, the product was filtered with deionized water until neutral. The pretreated sugarcane bagasse was dried at 110°C for 24 h to obtain the pretreated sugarcane bagasse. The solid bagasse obtained after pretreatment has a mass of 1.35g and a lignin removal rate of 69.87%.

[0057] The reaction performance of the catalyst was evaluated in a vertical pyrolysis furnace. The pyrolysis process was as follows: 0.4 g of pretreated sugarcane bagasse was weighed, placed in a quartz crucible, and loaded into the isothermal zone of the pyrolysis furnace; nitrogen gas was introduced to purge for 30 min to remove oxygen from the reactor; after purging, the temperature was increased to 500 °C at a rate of 50 °C / min, and then held at that temperature for 5 min. The gaseous products generated by pyrolysis were discharged and condensed and collected. The organic matter distribution in the collected liquid phase products was analyzed by GC-MS. The results are shown in Table 1.

[0058] Table 1 Mass distribution of liquid phase products from pretreated sugarcane bagasse pyrolysis

[0059]

[0060] In addition, the liquid products collected after catalytic cracking of the pretreated bagasse in Examples 1-3 and Comparative Examples 1-6 have very low water content, which can be ignored. This may be because the bagasse was dried in an oven at 110°C for 24 hours before use, and the bagasse itself has a very low water content, and the water produced during catalytic cracking is also very low.

[0061] As shown in Table 1, compared with the liquid phase product results of untreated bagasse, the yield of furans in the examples and comparative examples was increased, and all of them were the target product 2,3-dihydrobenzofuran (that is, the furan compounds in the liquid phase product were basically 100% in the form of 2,3-dihydrobenzofuran). In Example 1, 2,3-dihydrobenzofuran accounted for 42.72% of the liquid phase product.

[0062] As can be seen from Table 1, in Example 1 of the present invention, when the ratio of the ternary eutectic solvent is m(zinc chloride):m(ethylene glycol):m(water) = 1:10:20, the microwave power is 300W, and the reaction is carried out at a processing temperature of 60°C for 0.5h, the selectivity of the target product 2,3-dihydrobenzofuran can reach 42.72%.

[0063] Depend on Figure 1 It can be seen that the surface of the treated sample has a porous or network structure, indicating that pretreatment can disrupt the cell wall structure of bagasse to some extent. The flat structure of the bagasse is significantly disrupted after pretreatment, forming granular and fibrous entities, suggesting that the pretreated bagasse has a larger specific surface area and porosity, which can increase the adsorption of metal active sites and promote the breaking of intermolecular bonds. Figure 2 It can be seen that, compared with untreated bagasse, the absorption peaks representing cellulose hydroxyl groups and β-1,4 glycosidic bonds increased after pretreatment, indicating that more cellulose was exposed after bagasse pretreatment. The C=C aromatic skeleton representing the lignin aromatic ring was relatively flat in bagasse after DES pretreatment. This is because DES can form hydrogen bonds with lignin and other phenolic compounds, removing lignin and making it more conducive to the formation of the target product.

[0064] Appropriate modifications to this invention by those skilled in the art, such as changing the mesh size, appropriately altering the temperature, biomass dosage, or selecting the pyrolysis method, are all within the scope of this invention. The content described in this specification is merely an enumeration of implementations of the inventive concept, and the scope of protection of this invention should not be considered limited to the specific forms described in the embodiments.

[0065] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A green and efficient pre-treated biomass, characterized in that... The pretreatment method for biomass includes the following steps: 1) Crush and dry the biomass raw materials to obtain biomass powder; 2) Preparation of ternary eutectic solvent: Mix hydrogen bond acceptor and water evenly, then add hydrogen bond donor ethylene glycol to a beaker, heat and stir until a transparent homogeneous solution is obtained, thus obtaining ternary eutectic solvent; 3) Microwave reaction: The ternary eutectic solvent in step 2) is uniformly mixed with the biomass powder in step 1) and then added to a microwave synthesis tube. The microwave synthesis tube is then placed under microwave radiation in a microwave synthesizer for microwave pretreatment. After that, the mixture is centrifuged, and the lower solid mixture is collected and washed with ammonium chloride aqueous solution. After washing, the mixture is centrifuged again, washed with deionized water until neutral, and dried to obtain the pretreated biomass. The hydrogen bond acceptor includes zinc chloride; The mass ratio of hydrogen bond acceptor to ethylene glycol is 1:8~10; The reaction conditions for microwave pretreatment in step 3) are: microwave power of 100~400W, treatment temperature of 50~70℃, and treatment time of 10min~60min.

2. The green and efficient pre-treated biomass according to claim 1, characterized in that... In step 1), the particle size of the biomass powder is 20-200 mesh.

3. The green and efficient pre-treated biomass according to claim 2, characterized in that... In step 1), the particle size of the biomass powder is 40-60 mesh.

4. The green and efficient pre-treated biomass according to claim 1, characterized in that... Biomass consists of sugarcane bagasse, sawdust, straw, or pine leaves.

5. The green and efficient pretreated biomass according to claim 4, characterized in that... The biomass is sugarcane bagasse.

6. The green and efficient pre-treated biomass according to claim 1, characterized in that... The mass ratio of water to ethylene glycol is 1:0.2~1.

0.

7. The green and efficient pre-treated biomass according to claim 6, characterized in that... The mass ratio of water to ethylene glycol is 1:0.25-0.

5.

8. The green and efficient pre-treated biomass according to claim 1, characterized in that... In step 2), the heating and stirring temperature is 70-90℃, the stirring time is 10-80 min, and the stirring speed is 200-600 r / min.

9. The green and efficient pre-treated biomass according to claim 1, characterized in that... In step 3), the mass ratio of biomass to ternary eutectic solvent is 1:5-30.

10. The green and efficient pre-treated biomass according to claim 9, characterized in that... In step 3), the mass ratio of biomass to ternary eutectic solvent is 1:10-20.

11. The green and efficient pre-treated biomass according to claim 1, characterized in that... The reaction conditions for microwave pretreatment in step 3) are: microwave power of 250~300W, treatment temperature of 60~65℃, and treatment time of 25min~30min.

12. The green and efficient pre-treated biomass according to claim 1, characterized in that... In step 3), the concentration of the ammonium chloride aqueous solution is 0.5-3 mol / L.

13. The green and efficient pre-treated biomass according to claim 12, characterized in that... In step 3), the concentration of the ammonium chloride aqueous solution is 1 mol / L to 2 mol / L.

14. The application of the green and efficient pretreated biomass according to claim 1 for the selective preparation of 2,3-dihydrobenzofuran, characterized in that... The pyrolysis reaction is carried out in a pyrolysis furnace. The pretreated biomass is loaded into the isothermal zone of the vertical pyrolysis furnace, and N2 is introduced to purge the air. Then the reaction is carried out under N2 atmosphere. The temperature is increased from room temperature to the reaction temperature of 500-550℃ at a rate of 30-60℃ / min, and the reaction temperature of 500-550℃ is maintained for 1-30min. The gaseous products generated by pyrolysis are discharged and condensed and collected to obtain a liquid product containing the pyrolysis target product 2,3-dihydrobenzofuran.

15. The application of the green and efficient pretreated biomass according to claim 14 for the selective preparation of 2,3-dihydrobenzofuran, characterized in that... The pyrolysis reaction is carried out in a pyrolysis furnace and kept at a constant temperature of 500-550℃ for 5-10 minutes.

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