Method for co-production of porous carbon and furfural compounds from biomass, products and applications thereof

Abstract

The application provides a method for co-producing porous carbon and furfural compounds from biomass, products and applications, and belongs to the field of biomass resource utilization.The method is as follows: biomass containing pentose and / or hexose, phosphorous acid, water, an organic solvent and an iodine-containing reagent are mixed and subjected to a hydrothermal reaction to obtain a hydrothermal product; an organic layer in the hydrothermal product is separated and recovered to obtain furfural compounds, air is introduced into the remaining solid-liquid mixture and heated to obtain a hydrothermal solid residue containing phosphoric acid; and the hydrothermal solid residue is subjected to pyrolysis activation under an inert atmosphere to obtain porous carbon.The application realizes co-production of porous carbon and furfural compounds from biomass containing pentose and / or hexose by combining hydrothermal reaction and pyrolysis, can realize full utilization of biomass, improve the comprehensive value of products, and has a pore-expanding effect on the pentose and / or hexose components stripped by hydrothermal reaction, so that the porosity of the obtained porous carbon can be further improved.

Description

Technical Field

[0001] This invention belongs to the field of biomass resource utilization, and more specifically, relates to methods, products and applications of biomass co-production of porous carbon and furfural compounds. Background Technology

[0002] Lithium-sulfur batteries are a type of lithium battery that uses sulfur as the positive electrode and lithium metal as the negative electrode, offering advantages such as high energy density, high safety, and environmental friendliness. The potential and possibility of lithium-sulfur batteries as secondary batteries for next-generation energy storage systems has been widely recognized in the energy field. However, due to the poor conductivity of sulfur and its reaction products, and the significant shuttle effect during charge and discharge, high-performance lithium-sulfur batteries still face significant challenges. Porous carbon, with its good conductivity, structural stability, and high cycle stability, has become one of the most studied materials for suppressing the shuttle effect in lithium-sulfur batteries. For example, Wu et al. prepared porous carbon with interconnected micropores and mesopores using pitch for lithium-sulfur batteries (ACS Sustainable Chemistry & Engineering, 2022), and invention patent (CN114975957A) discloses a sulfur / glucose mesoporous carbon sphere lithium-sulfur battery positive electrode material and its preparation method. However, due to the high carbon emission attributes of fossil resources such as pitch and the cost limitations of high-grade biomass-based carbon materials such as glucose, these methods have not been widely applied.

[0003] Biomass, as the only renewable carbon-containing resource, boasts numerous advantages such as large reserves and carbon neutrality, making it a high-quality raw material for producing high-value functional chemicals and high-carbon products. While existing research has utilized biomass such as peanut shells, rice husks, tree bark, and corn cobs to obtain porous carbon materials for lithium-sulfur battery cathode materials, achieving considerable battery capacity, high capacity retention, and coulombic efficiency (Li et al., Ionics, 2020), and a patent (CN105417540A) has disclosed a method for preparing biomass porous carbon and its application in lithium-sulfur batteries, current research on biomass-based porous carbon for lithium-sulfur battery cathodes primarily focuses on direct pyrolysis activation and pore expansion. It does not fully consider the compositional characteristics of biomass or its graded conversion to simultaneously produce high-value chemicals or fuels while obtaining high-performance porous carbon for lithium-sulfur battery cathodes. However, a single porous carbon product is insufficient to stimulate capital investment, severely hindering the industrialization of biomass-derived porous carbon for lithium-sulfur battery cathodes.

[0004] Furfural and 5-methylfurfural are important furfural compounds that can be used to prepare liquid fuels, pharmaceutical intermediates, etc. The hydrothermal conversion of palm cellulose (hemicellulose and cellulose) from lignocellulosic biomass to prepare furfural and 5-methylfurfural shows considerable commercial potential. CN108250165A discloses a method for preparing N-(5-methylfurfural)aniline and its derivatives from biomass carbohydrates, which uses phosphorous acid-assisted hydroiodic acid-mediated fructose and other biomass to prepare 5-methylfurfural. However, the hydroiodic acid feedstock is very unstable, easily oxidized, and difficult to control, and still faces the bottleneck of needing to utilize the remaining residue in a high-value manner. These problems restrict the development and industrial application of porous carbon technology for preparing lithium-sulfur battery cathodes from biomass resources with huge reserves. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method, product and application for the co-production of porous carbon and furfural compounds from biomass, aiming to solve the problems of poor economic efficiency, inability to achieve co-production of multiple products and high-value utilization of raw materials in existing porous carbon preparation methods.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for co-producing porous char and furfural compounds from biomass is provided, the method comprising the following steps:

[0007] S1 involves mixing biomass containing pentose and / or hexose, phosphorous acid, water, organic solvent, and iodine-containing reagent, and then carrying out a hydrothermal reaction to obtain a hydrothermal product.

[0008] S2 separates and recovers the organic layer in the hydrothermal product to obtain furfural compounds, while air is introduced into the remaining solid-liquid mixture and heated until the water is completely evaporated to recover iodine and water, and excess phosphorous acid is oxidized to phosphoric acid to obtain a hydrothermal solid residue containing phosphoric acid.

[0009] S3 uses phosphoric acid as a pore-expanding agent to pyrolyze and activate the hydrothermal solid residue under an inert atmosphere to produce porous carbon, thereby realizing the co-production of porous carbon and furfural compounds from biomass.

[0010] As a further preferred embodiment, in step S1, the biomass containing pentose and / or hexose includes one or more of straw, bark, sawdust, algae, and kitchen waste; the organic solvent is one or more of benzene, toluene, and methyl isobutyl ketone; and the iodine-containing reagent is one or two of elemental iodine and hydroiodic acid.

[0011] As a further preferred embodiment, in step S1, the mass ratio of biomass to water is 1:(10-50), the volume ratio of water to organic solvent is 1:(0.1-10), the ratio of biomass to iodine in the iodine-containing reagent is 1g:(2-40)mmol, and the molar ratio of iodine to phosphorous acid in the iodine-containing reagent is 1:(1-5).

[0012] As a further preferred embodiment, in step S1, the temperature of the hydrothermal reaction is 80℃~200℃, and the time of the hydrothermal reaction is 0.2h~5h.

[0013] As a further preferred embodiment, in step S3, an activator is added to the hydrothermal solid residue before pyrolysis activation. The activator is one or more of potassium phosphate, potassium hydroxide, potassium carbonate, potassium bicarbonate, and potassium chloride.

[0014] As a further preferred embodiment, in step S3, the reaction conditions for pyrolysis activation are: heating to 600℃~900℃ at a heating rate of 5℃ / min~10℃ / min and holding for 0.5h~5h, followed by cooling to room temperature.

[0015] According to another aspect of the present invention, porous carbon and furfural compounds prepared by the above method are provided.

[0016] According to another aspect of the present invention, a method for preparing lithium-sulfur battery cathode material using the above-mentioned porous carbon is provided. The method specifically involves mixing the porous carbon with sulfur and heating it to obtain the lithium-sulfur battery cathode material.

[0017] As a further preferred embodiment, the mass ratio of porous carbon to sulfur is 3:2 to 3:7.

[0018] As a further preferred embodiment, the heating temperature is 120℃~140℃, and the heating time is 1h~3h.

[0019] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0020] 1. This invention utilizes a combination of hydrothermal and pyrolysis methods to co-produce porous char and furfural compounds from biomass containing pentose and / or hexose sugars. This enables full utilization of biomass and improves the overall value of the products. Specifically, phosphorous acid is used to reduce elemental iodine to maintain the hydroiodic acid content in the solution, thereby producing furfural compounds and porous biomass hydrothermal residue during the hydrothermal stage. Phosphoric acid, a byproduct of phosphorous acid reduction of elemental iodine, is then used as a pore-expanding agent, and the biomass hydrothermal residue serves as the carbon source. Without separating phosphorous acid and phosphate, porous char is directly produced through pyrolysis activation. This method offers advantages such as low production input, diversified products, high added value, and low carbon footprint, further promoting the resource utilization of biomass. More importantly, the hydrothermal stripping of pentose and / or hexose sugar components has a pore-expanding effect, enriching the pores of the biomass hydrothermal residue and further increasing the porosity of the produced porous char, facilitating subsequent applications.

[0021] 2. Meanwhile, the porous carbon prepared by this invention has a higher porosity than the porous carbon prepared by pyrolysis in the prior art due to the dual pore-expanding effect of the hydrothermal stage and the pyrolysis stage. When it is mixed with sulfur and heated to prepare lithium-sulfur battery cathode material, it can effectively improve the cycle stability of lithium-sulfur batteries. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of biomass co-production of porous carbon and furfural compounds and its application in porous carbon lithium-sulfur batteries, provided in the embodiments of the present invention.

[0023] Figure 2 This is a schematic diagram of the steam (vapor) cooling and separation device for elemental iodine and water after hydrothermal treatment of biomass provided in this embodiment of the invention;

[0024] Figure 3 This is a comparative analysis of the electrochemical cycle performance of porous carbon prepared in Examples 1-3 and the comparative example of the present invention when applied to lithium-sulfur batteries.

[0025] Figure 4 The discharge curve is obtained by applying the porous carbon prepared in Example 1 of this invention to a lithium-sulfur battery. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] like Figure 1 As shown, the present invention provides a method for co-producing porous carbon and furfural compounds from biomass, the method comprising the following steps:

[0028] S1 involves mixing biomass, phosphorous acid, water, organic solvent, and iodine-containing reagent, followed by a hydrothermal reaction to obtain hydrothermal products. The iodine-containing reagent is one or both of elemental iodine and hydroiodic acid. During the reaction, phosphorous acid is used to reduce elemental iodine to hydroiodic acid to maintain a stable hydroiodic acid content in the reaction system. Then, hydroiodic acid is used to strip the pentose and / or hexose components from the biomass to obtain furfural compounds. Simultaneously, the stripping of the pentose and / or hexose components yields a biomass hydrothermal residue with abundant pores, thus providing a carbon source for subsequent porous carbon preparation. The use of a water-oil two-phase solvent system is beneficial to improving the yield of furfural compounds. The upper organic layer can be separated by simple centrifugation, facilitating the separation of furfural compounds and allowing for the recovery of the organic solvent.

[0029] S2 separates and recovers the organic layer in the hydrothermal product to obtain furfural compounds. At the same time, air is introduced into the remaining solid-liquid mixture and heated until the water is completely evaporated to obtain a hydrothermal solid residue containing phosphoric acid. During the heating process, hydroiodic acid is oxidized to elemental iodine and discharged with water vapor, realizing the recovery and utilization of water and iodine. Simultaneously, phosphorous acid is also oxidized to phosphoric acid, thus providing a pore-expanding agent for the subsequent preparation of porous carbon.

[0030] S3 uses phosphoric acid, a byproduct of the reduction of iodine by phosphorous acid, as a pore-expanding agent. It does not require the separation of phosphoric acid and biomass hydrothermal residue from the hydrothermal products. Instead, it directly utilizes the pyrolysis activation of the hydrothermal solid residue under an inert atmosphere to produce porous carbon, thereby achieving the co-production of porous carbon and furfural compounds from biomass.

[0031] Furthermore, in step S1, the biomass containing pentose and / or hexose can be any single or complex biomass containing one or more pentose and / or hexose, including but not limited to one or more of straw, bark, sawdust, algae, and kitchen waste. These types of biomass are rich in fructose, xylose, glucose, starch, cellulose, or hemicellulose. The organic solvent is immiscible with water and has a lower density than water; preferably, it is one or more of benzene, toluene, and methyl isobutyl ketone. The iodine-containing reagent is preferably elemental iodine, which avoids the use of unstable hydroiodic acid, is easier to control, and since hydroiodic acid is prepared from elemental iodine, the hydrothermal conversion directly uses elemental iodine, which can shorten the long process and effectively reduce the carbon footprint of the product.

[0032] Furthermore, in step S1, the mass ratio of biomass to water is 1:(10-50), the volume ratio of water to organic solvent is 1:(0.1-10), the ratio of biomass to iodine in the iodine-containing reagent is 1g:(2-40)mmol, and the molar ratio of iodine to phosphorous acid in the iodine-containing reagent is 1:(1-5). There are complex interactions between the amounts of biomass, water, iodine-containing reagents, and phosphorous acid added. The specific ratio depends on the characteristics of the biomass raw materials. When the content of pentose and / or hexose components in the biomass is low, the amount of iodine-containing reagent can be reduced. This also means that there are more non-convertible components, so the amount of water should be increased appropriately to ensure the accessibility of pentose and / or hexose components. At the same time, the amount of phosphorous acid can also be increased appropriately because non-convertible components require sufficient activators during the pyrolysis stage in the hydrothermal phase, and more phosphorous acid is also conducive to the rapid reduction of elemental iodine during the hydrothermal process. In addition, it also means that the theoretical yield of furfural compounds is low, so the amount of organic solvent can be reduced appropriately because excessive organic solvent is not very meaningful for the extraction of furfural compounds in the aqueous phase, but instead increases the energy consumption of solvent evaporation and recovery.

[0033] Furthermore, in step S1, the hydrothermal reaction temperature is 80℃~200℃, the hydrothermal reaction time is 0.2h~5h, and the stirring speed is 150 rpm~550 rpm during the hydrothermal reaction. The specific reaction conditions are selected based on two factors: firstly, the molecular weight of the pentose and / or hexose components in the biomass and the amount of high molecular weight components. When the molecular weight is large and there are many high molecular weight components, the reaction temperature can be appropriately increased, the reaction time extended, and the stirring speed increased; secondly, the market value of furfural compounds and the pore structure requirements and corresponding market value of porous carbon can be taken into account. By adjusting the reaction parameters, the conversion rate of pentose and / or hexose components can be controlled, thereby obtaining the yield of furfural compounds with the greatest comprehensive value and high-performance porous carbon.

[0034] Further, in step S2, based on the selected organic solvent and the boiling point differences of furfural compounds, existing distillation technology is used to recover the organic solvent in the organic layer and separate furfural compounds such as furfural and 5-methylfurfural. The remaining solid-liquid mixture is placed in an evaporation vessel equipped with at least a stirring, heating, and air bubbling device. Hydroiodic acid and phosphorous acid are oxidized to elemental iodine and phosphoric acid, respectively, under the action of hot air. The elemental iodine and water are discharged from the outlet of the evaporation vessel in the form of hot steam and enter a cooling separation device through a heated pipe to recover elemental iodine and water, respectively.

[0035] Furthermore, in step S2, the principle of the vapor (steam) cooling separation device for elemental iodine and water is as follows: Figure 2Specifically, iodine vapor and water vapor begin to condense as soon as they enter the cooling separation device with hot air. Under positive pressure in the upper space, an aqueous solution containing trace amounts of iodine and air pass through a filter plate into the lower space. The air is discharged from the side port under the filter plate, and the low-concentration iodine aqueous solution is discharged from the water inlet at the bottom of the device. Undissolved elemental iodine remains in the upper space. After a certain amount has been retained, the low-concentration iodine aqueous solution in the lower space is emptied, and the outlet valve at the bottom of the device is switched. The elemental iodine in the upper space is dissolved and rinsed with the same organic solvent as in the hydrothermal reaction. The organic solvent containing high concentrations of iodine is discharged from the iodine inlet at the bottom of the device. The concentrations of elemental iodine in the recovered low-concentration iodine aqueous solution and the organic solvent containing high concentrations of iodine can be determined by chemical analysis and then used quantitatively according to the needs of the hydrothermal reaction.

[0036] Furthermore, in step S3, an activator is added to the hydrothermal solid residue and then pyrolyzed for activation. The activator is one or more of phosphoric acid, potassium phosphate, potassium hydroxide, potassium carbonate, potassium bicarbonate, and potassium chloride. By adding an activator, the porosity of the prepared porous carbon can be further improved, making the prepared porous carbon more suitable for use in lithium-sulfur batteries and achieving better battery cycle stability.

[0037] Furthermore, in step S3, as the temperature increases, the yield of porous carbon decreases. Porous carbon has a large number of pores, and the number of pores increases. When the carbonization temperature exceeds a suitable temperature, the pore size of the porous carbon decreases, and local collapse occurs on the product surface. Therefore, the reaction conditions for pyrolysis activation are: heating at a rate of 5℃ / min to 10℃ / min to 600℃ to 900℃ and holding for 0.5h to 5h, followed by cooling to room temperature.

[0038] According to another aspect of the present invention, porous carbon and furfural compounds prepared by the above method are provided.

[0039] According to another aspect of the present invention, the application of the above-mentioned porous carbon in lithium-sulfur batteries is provided, specifically: the porous carbon and sulfur are mixed in a mass ratio of 3:2 to 3:7 and heated at a temperature of 120°C to 140°C for a time of 1 hour to 3 hours to obtain a lithium-sulfur battery cathode material.

[0040] The technical solution provided by the present invention will be further described below with reference to specific embodiments.

[0041] Example 1

[0042] (1) In a 500mL reactor equipped with a stirrer, add 5g poplar powder, 45mmol phosphorous acid, 50mL distilled water, 7.5mmol elemental iodine and 150mL toluene. Close the reactor and heat to 130℃ for 1h. After cooling completely, open the reactor and centrifuge to separate the upper organic phase containing furfural compounds. Gas chromatography results showed that the mass yields of 5-methylfurfural and furfural were 16% and 12%, respectively.

[0043] (2) Transfer the solid-liquid mixture after centrifugation to a 100mL round-bottom flask equipped with a venting tube. Introduce air at a flow rate of 10mL / min. While heating the material to 80°C, stir the material magnetically at a speed of 300 rpm. When the unreacted phosphorous acid in the material is completely oxidized to phosphoric acid, the iodine element is discharged in the form of elemental iodine along with water vapor with the flowing air. The remaining solid mixture in the round-bottom flask is the hydrothermal solid residue containing phosphoric acid.

[0044] (3) Add 2g of hydrothermal solid residue and 20g of potassium bicarbonate to a 100mL zirconia ball milling jar containing 8 zirconia grinding balls with a diameter of 10mm. Set the ball milling speed to 400 rpm and ball mill for 1 hour.

[0045] (4) Transfer the mixed powder obtained by ball milling to a corundum crucible, set the gas flow rate and heating program (after venting the N2 gas at room temperature for 30 min, the temperature is raised from room temperature to 900℃ at 10℃ / min under the N2 gas flow, held for 1 h, and then cooled to 300℃ at 10℃ / min under the N2 gas flow, and then cooled naturally to room temperature) to carry out one-step pyrolysis activation. After the process is completed, take it out and wash it with water, and dry the solid to obtain porous carbon.

[0046] (5) Example 2

[0047] Except for adding 2g of potassium bicarbonate during ball milling in step (3), the other operating parameters are the same as in Example 1.

[0048] Example 3

[0049] Except for step (3) when potassium bicarbonate was not added during ball milling, the other operating parameters are the same as in Example 1.

[0050] Example 4

[0051] (1) In a 500 mL reactor equipped with a stirrer, add 2.5 g cellulose, 100 mmol phosphorous acid, 125 mL distilled water, 10 mmol elemental iodine and 15 mL toluene, close the reactor, heat to 180 °C and react for 5 h. After cooling completely, open the reactor and centrifuge to separate the upper organic phase containing furfural compounds. Gas chromatography results showed that the mass yield of 5-methylfurfural was 37%.

[0052] (2) Transfer the solid-liquid mixture after centrifugation to a 100mL round-bottom flask equipped with a venting tube. Introduce air at a flow rate of 10mL / min. While heating the material to 100℃, stir the material magnetically at a speed of 200 rpm. When the unreacted phosphorous acid in the material is completely oxidized to phosphoric acid, the iodine element is discharged in the form of elemental iodine along with water vapor with the flowing air. The remaining solid mixture in the round-bottom flask is the hydrothermal solid residue containing phosphoric acid.

[0053] (3) Add 2g of hydrothermal solid residue and 15g of potassium chloride to a 100mL zirconia ball milling jar containing 8 zirconia grinding balls with a diameter of 10mm. Set the ball milling speed to 400 rpm and ball mill for 1 hour.

[0054] (4) Transfer the mixed powder obtained by ball milling to a corundum crucible, set the gas flow rate and heating program (after venting the N2 gas at room temperature for 30 min, the temperature is raised from room temperature to 700℃ at 5℃ / min under the N2 gas flow, held for 5 h, and then cooled to 300℃ at 5℃ / min under the N2 gas flow, and then cooled naturally to room temperature) to carry out one-step pyrolysis activation. After the process is completed, take it out and wash it with water, and dry the solid to obtain porous carbon.

[0055] Example 5

[0056] (1) In a 500mL reactor equipped with a stirrer, add 5g xylose, 25mmol phosphorous acid, 150mL distilled water, 5mmol elemental iodine and 150mL toluene, close the reactor, heat to 110℃ and react for 1h. After cooling completely, open the reactor and centrifuge to separate the upper organic phase containing furfural compounds. The gas chromatography results showed that the furfural yield was 70%.

[0057] (2) Transfer the solid-liquid mixture after centrifugation to a 100mL round-bottom flask equipped with a venting tube. Introduce air at a flow rate of 10mL / min. While heating the material to 95°C, stir the material magnetically at a speed of 400 rpm. When the unreacted phosphoric acid in the material is completely oxidized to phosphoric acid, the iodine element is discharged in the form of elemental iodine along with water vapor with the flowing air. The remaining solid mixture in the round-bottom flask is the hydrothermal solid residue containing phosphoric acid.

[0058] (3) Add 2g of hydrothermal solid residue and 2g of potassium carbonate to a 100mL zirconia ball milling jar containing 8 zirconia grinding balls with a diameter of 10mm. Set the ball milling speed to 400 rpm and ball mill for 1 hour.

[0059] (4) Transfer the mixed powder obtained by ball milling to a corundum crucible, set the gas flow rate and heating program (after venting the N2 gas at room temperature for 30 min, the temperature is raised from room temperature to 900℃ at 10℃ / min under the N2 gas flow, held for 0.5 h, and then cooled to 300℃ at 10℃ / min under the N2 gas flow, and then cooled naturally to room temperature) to carry out one-step pyrolysis activation. After the process is completed, take it out and wash it with water, and dry the solid to obtain porous carbon.

[0060] Example 6

[0061] (1) In a 500 mL reactor equipped with a stirrer, add 5 g of Scenedesmus, 45 mmol of phosphorous acid, 100 mL of distilled water, 7.5 mmol of elemental iodine and 150 mL of toluene. Close the reactor and heat to 200 °C for 2 h. After cooling completely, open the reactor and centrifuge to separate the upper organic phase containing furfural compounds. Gas chromatography results showed that the mass yield of 5-methylfurfural was 13%.

[0062] (2) Transfer the solid-liquid mixture after centrifugation to a 100mL round-bottom flask equipped with a venting tube. Introduce air at a flow rate of 10mL / min. While heating the material to 100℃, stir the material magnetically at a speed of 350 rpm. When the unreacted phosphorous acid in the material is completely oxidized to phosphoric acid, the iodine element is discharged in the form of elemental iodine along with water vapor with the flowing air. The remaining solid mixture in the round-bottom flask is the hydrothermal solid residue containing phosphoric acid.

[0063] (3) Add 2g of hydrothermal solid residue and 5g of potassium hydroxide to a 100mL zirconia ball milling jar containing 8 zirconia grinding balls with a diameter of 10mm. Set the ball milling speed to 400 rpm and ball mill for 1 hour.

[0064] (4) Transfer the mixed powder obtained by ball milling to a corundum crucible, set the gas flow rate and heating program (after venting the N2 gas at room temperature for 30 min, raise the temperature from room temperature to 850°C at 5°C / min under the N2 gas flow, hold for 1 h, continue to cool down to 300°C at 10°C / min under the N2 gas flow, and then cool down naturally to room temperature) to carry out one-step pyrolysis activation. After the end, take it out and wash it with water, and dry the solid to obtain porous carbon.

[0065] Example 7

[0066] (1) In a 500mL reactor equipped with a stirrer, add 5g of Chinese cabbage leaf tail (dried powder), 45mmol of phosphorous acid, 50mL of distilled water, 7.5mmol of elemental iodine and 150mL of toluene, close the reactor, heat to 120℃ and react for 1h. After cooling completely, open the reactor and centrifuge to separate the upper organic phase containing furfural compounds. The gas chromatography results showed that the mass yields of 5-methylfurfural and furfural were 11% and 36%, respectively.

[0067] (2) Transfer the solid-liquid mixture after centrifugation to a 100mL round-bottom flask equipped with a venting tube. Introduce air at a flow rate of 10mL / min. While heating the material to 85°C, stir the material magnetically at a speed of 400 rpm. When the unreacted phosphorous acid in the material is completely oxidized to phosphoric acid, the iodine element is discharged in the form of elemental iodine along with water vapor with the flowing air. The remaining solid mixture in the round-bottom flask is the hydrothermal solid residue containing phosphoric acid.

[0068] (3) Add 2g of hydrothermal solid residue and 10g of potassium carbonate to a 100mL zirconia ball milling jar containing 8 zirconia grinding balls with a diameter of 10mm. Set the ball milling speed to 400 rpm and ball mill for 1 hour.

[0069] (4) Transfer the mixed powder obtained by ball milling to a corundum crucible, set the gas flow rate and heating program (after venting the N2 gas at room temperature for 30 min, the temperature is raised from room temperature to 750°C at 10°C / min under the N2 gas flow, held for 4 h, and then cooled to 300°C at 10°C / min under the N2 gas flow, and then cooled naturally to room temperature) to carry out one-step pyrolysis activation. After the process is completed, take it out and wash it with water, and dry the solid to obtain porous carbon.

[0070] Example 8

[0071] (1) In a 500mL reactor equipped with a stirring device, add 5g corn stalks, 45mmol phosphorous acid, 50mL distilled water, 15mmol hydroiodic acid, and 150mL toluene. Close the reactor and heat to 130℃ for 2h. After cooling completely, open the reactor and centrifuge to separate the upper organic phase containing furfural compounds. Gas chromatography results showed that the mass yields of 5-methylfurfural and furfural were 13% and 12%, respectively.

[0072] (2) Transfer the solid-liquid mixture after centrifugation to a 100mL round-bottom flask equipped with a venting tube. Introduce air at a flow rate of 10mL / min. While heating the material to 100℃, stir the material magnetically at a speed of 250 rpm. When the unreacted phosphorous acid in the material is completely oxidized to phosphoric acid, the iodine element is discharged in the form of elemental iodine along with water vapor with the flowing air. The remaining solid mixture in the round-bottom flask is the hydrothermal solid residue containing phosphoric acid.

[0073] (3) Add 2g of hydrothermal solid residue and 2g of potassium phosphate to a 100mL zirconia ball milling jar containing 8 zirconia grinding balls with a diameter of 10mm. Set the ball milling speed to 400 rpm and ball mill for 1 hour.

[0074] (4) Transfer the mixed powder obtained by ball milling to a corundum crucible, set the gas flow rate and heating program (after venting the N2 gas at room temperature for 30 min, raise the temperature from room temperature to 800°C at 5°C / min under the N2 gas flow, hold for 1.5 h, continue to cool down to 300°C at 10°C / min under the N2 gas flow, and then cool down naturally to room temperature) to carry out one-step pyrolysis activation. After the end, take it out and wash it with water, and dry the solid to obtain porous carbon.

[0075] To further illustrate the technical advantages of the present invention, comparative experiments were conducted using Examples 1-3 as comparative examples, specifically as follows:

[0076] Comparative Example

[0077] Compared with Example 1, the poplar powder was not subjected to the hydrothermal treatment in steps (1) and (2). Instead, 2g of poplar powder was directly ball-milled with 45mmol of phosphoric acid and 2g of potassium bicarbonate. The other operating parameters were the same as in Example 1.

[0078] The porous carbon prepared in Examples 1-3 and the comparative example was applied to lithium-sulfur batteries. The porous carbon and elemental sulfur were thoroughly ground and mixed at a mass ratio of 2:3, placed in a polytetrafluoroethylene liner of a reaction vessel, and treated in a 155°C oven for 12 hours under argon gas in a glove box to obtain a porous carbon / sulfur composite material. This composite material was then mixed with conductive carbon black and PVDF binder at a mass ratio of 7:2:1 in a solder paste mixer. The resulting paste was evenly coated onto aluminum foil, dried in a 60°C vacuum drying oven, and pressed into discs to obtain the positive electrode sheet for the lithium-sulfur battery. In an argon-filled glove box, a coin cell was assembled using a lithium sheet as the negative electrode, a Celgard 2400 separator, and an LIR2025 battery casing. The specific capacity and efficiency curves of this battery after 100 charge-discharge cycles at a 0.5C discharge rate are shown below. Figure 3 The charge-discharge curves of Example 1 at 0.1C and 0.5C are shown below. Figure 4 .

[0079] Compare Figure 3The results of Examples 1-3 and the comparative examples show that the average coulombic efficiency of the batteries corresponding to each sample is as high as 98%, indicating good reversibility. After hydrothermal treatment, the cycle stability of Example 1 battery with 20g potassium bicarbonate is better than that of Example 2 battery with 2g potassium bicarbonate, and the cycle stability of Example 2 battery with 2g potassium bicarbonate is better than that of Comparative Example 2 battery without potassium bicarbonate. This indicates that appropriately increasing the amount of activator can effectively improve the porous structure of porous carbon and improve its application performance as a cathode material for lithium-sulfur batteries. Example 2 battery with 2g potassium bicarbonate The battery cycle stability of Example 3 was better than that of Comparative Example 1 battery, which did not undergo hydrothermal treatment but had 2g of potassium bicarbonate added for pyrolysis. This indicates that hydrothermal treatment can not only obtain valuable 5-methylfurfural and furfural, increasing yield, but also remove cellulose and hemicellulose components, which helps to better form the porous structure of porous carbon, thereby improving the cycle stability of lithium-sulfur batteries. The cycle stability of Example 3 battery, which did not have potassium bicarbonate added after hydrothermal treatment, was comparable to that of the Comparative Example battery, which did not undergo hydrothermal treatment but had 2g of potassium bicarbonate added for pyrolysis. This indicates that hydrothermal removal of cellulose and hemicellulose and potassium bicarbonate have similar effects on pore expansion.

[0080] In addition, the present invention also compares the performance of other lithium-sulfur batteries that also use biomass as raw material with that of Example 1. The relevant comparison results are shown in Table 1, which shows that the present invention has obvious technical advantages.

[0081] Table 1. Performance comparison results of Example 1 with other lithium-sulfur batteries using biomass as raw material.

[0082]

[0083] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for co-production of porous char and furanic compounds from biomass, characterized in that, The method includes the following steps: S1 involves mixing biomass containing pentose and / or hexose, phosphorous acid, water, organic solvent, and iodine-containing reagent, and then carrying out a hydrothermal reaction to obtain a hydrothermal product. S2 separates and recovers the organic layer in the hydrothermal product to obtain furfural compounds, while air is introduced into the remaining solid-liquid mixture and heated until the water is completely evaporated to recover iodine and water, and excess phosphorous acid is oxidized to phosphoric acid to obtain a hydrothermal solid residue containing phosphoric acid. S3 uses phosphoric acid as a pore-expanding agent to pyrolyze and activate the hydrothermal solid residue under an inert atmosphere to produce porous carbon, thereby realizing the co-production of porous carbon and furfural compounds from biomass.

2. The method for co-producing porous char and furfural compounds from biomass as described in claim 1, characterized in that, In step S1, the biomass containing pentose and / or hexose includes one or more of straw, bark, sawdust, algae, and kitchen waste; the organic solvent is one or more of benzene, toluene, and methyl isobutyl ketone; and the iodine-containing reagent is one or two of elemental iodine and hydroiodic acid.

3. The method for co-producing porous char and furfural compounds from biomass as described in claim 1, characterized in that, In step S1, the mass ratio of biomass to water is 1:(10~50), the volume ratio of water to organic solvent is 1:(0.1~10), the ratio of biomass to iodine in the iodine-containing reagent is 1g:(2~40)mmol, and the molar ratio of iodine to phosphorous acid in the iodine-containing reagent is 1:(1~5).

4. The method for co-producing porous char and furfural compounds from biomass as described in claim 1, characterized in that, In step S1, the temperature of the hydrothermal reaction is 80℃~200℃, and the time of the hydrothermal reaction is 0.2h~5h.

5. The method for co-producing porous char and furfural compounds from biomass as described in claim 1, characterized in that, In step S3, an activator is added to the hydrothermal solid residue and then pyrolysis activation is performed. The activator is one or more of potassium phosphate, potassium hydroxide, potassium carbonate, potassium bicarbonate, and potassium chloride.

6. The method for co-producing porous char and furfural compounds from biomass as described in any one of claims 1 to 5, characterized in that, In step S3, the reaction conditions for pyrolysis activation are as follows: the temperature is increased to 600°C to 900°C at a heating rate of 5°C / min to 10°C / min and held for 0.5h to 5h, and then cooled to room temperature.

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