A method for performing lignocellulose fractionation at room temperature

Abstract

The application provides a method for grading lignocellulose at normal temperature, and belongs to the technical field of comprehensive utilization of agricultural wastes.The method comprises the following steps: (1) naturally air-drying a biomass raw material, crushing and sieving; (2) uniformly mixing the crushed biomass raw material with a treatment liquid, and then stirring and reacting at normal temperature; the treatment liquid is a mixed solution composed of peroxide urea and tetramethylammonium hydroxide at a molar ratio of 1:2; (3) filtering the solid-liquid mixture obtained in the reaction, and separating the obtained solid material, which is cellulose; (4) uniformly mixing the filtrate with anhydrous ethanol, separating after sedimentation, and centrifuging the obtained solid material, which is hemicellulose; (5) after separating ethanol from the supernatant obtained in the centrifugation in step (4), adding HCl to adjust the acidity and then sedimenting, and then separating the obtained solid material, which is lignin.The method can be used for grading treatment at normal temperature, has simple requirements for equipment, is convenient to operate, and is more energy-saving and environment-friendly.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive utilization technology of agricultural waste, specifically relating to a method for grading lignocellulose at room temperature. Background Technology

[0002] The overuse of non-renewable fossil fuels has led to severe environmental pollution and rapid energy depletion, threatening human survival and development. Lignocellulose, the most abundant renewable biological resource on Earth, is widely found in agricultural and forestry waste, such as corn stalks, sorghum stalks, rice husks, bark, sawdust, and leaves. Solar energy is stored in lignocellulose by plants through photosynthesis as chemical energy. After component separation and hydrolysis, it can generate cellobiose and various monosaccharides. Further catalytic conversion can produce a wealth of high-value-added chemicals, fuels, and polymer materials. It has significant research value in areas such as replacing traditional non-renewable fossil resources, improving the ecological environment, and promoting rural economic development.

[0003] Lignocellulose is mainly composed of cellulose, hemicellulose, and lignin, with an outer layer of wax and silica. The heterogeneous lignin is linked to hemicellulose through aryl ether bonds, ester bonds, and hydrogen bonds, filling the gaps in the polysaccharide components and coating the surface of cellulose. This complex structure of lignocellulose not only affects the separation of its components but also hinders the subsequent conversion and utilization of its components.

[0004] For the separation of various components in lignocellulose, the first step is to efficiently dissolve the lignocellulose to prepare a high-content lignocellulose solution, and then further separate the various components in the lignocellulose solution to achieve a graded processing process.

[0005] Existing methods typically involve pre-treating the raw materials to disrupt the compact structure of lignocellulose, increasing the contact area of ​​the cellulose, hemicellulose polymers, and lignin network, thereby improving the efficiency of subsequent hydrolysis and conversion. Simultaneously, the pre-treatment process can also break some of the bonds between the three components of lignocellulose, allowing for the separation of cellulose, hemicellulose, and lignin.

[0006] Lignocellulose pretreatment methods include mechanical crushing, ultrasonic radiation, acid treatment, alkali treatment, and biological treatment. Among these, alkali pretreatment can effectively break down the dense, stubborn structure of lignocellulose and is considered one of the most commonly used methods due to its advantages such as high efficiency, low cost, high lignin removal rate, and high cellulose recovery rate. However, simple alkali pretreatment cannot meet the high requirements for cellulose and hemicellulose recovery and cannot achieve efficient recycling of cellulose and hemicellulose from lignocellulose.

[0007] For example, patent document CN 112876693 B provides a method for dissolving lignocellulose. This method involves first cooking agricultural waste biomass raw materials using an alkaline, acidic, or solvent method to obtain lignocellulose containing lignin. Then, a treatment agent is added, and the mixture is allowed to stand at -10 to -30°C until the dispersion is completely frozen. It is then thawed at room temperature, and this freeze-thaw cycle is repeated 1-3 times to obtain a lignocellulose solution. This method suffers from high equipment requirements, high processing costs, and is not suitable for industrial production. It is evident that existing processes use repeated freeze-thaw cycles to obtain high-content lignocellulose solutions, which cannot achieve efficient dissolution of lignocellulose at room temperature. Furthermore, this patent document cannot separate cellulose and lignin, thus preventing subsequent fractionation processing.

[0008] Patent document CN 108473522 A discloses a method for classifying lignocellulose biomass. The biomass treatment liquid used in this method contains formic acid, alcohol, water, and alkyl acetate. However, this method requires a temperature of 140°C to 180°C and a pressure of 5 to 20 Pa to separate cellulose and hemicellulose. It still has problems such as strict equipment requirements, high processing costs, and difficulty in large-scale processing. It cannot achieve efficient classification of lignocellulose with low energy consumption.

[0009] On the other hand, some researchers have reported that urea can remove some lignin from straw; however, the removal rate of lignin by urea is very low, less than 20%. In industrial production, to obtain high-quality cellulose and hemicellulose, a high lignin removal rate is often necessary to ensure its suitability as a value-added product. Therefore, how to significantly improve the lignin removal rate has become another major technical challenge in the lignin cellulose grading process.

[0010] In summary, how to effectively process lignocellulose at room temperature, efficiently grade it to obtain high-recovery cellulose and hemicellulose products, improve the removal rate of lignocellulose, and increase the added value of these products has become a pressing technical problem to be solved in the development of green resources. Summary of the Invention

[0011] The present invention aims to solve the aforementioned technical problems by providing a method for classifying lignocellulose at room temperature. The technical objective of this invention is twofold: firstly, to simplify existing lignocellulose processing techniques and reduce processing costs by providing a method for processing lignocellulose at room temperature; and secondly, to provide a high-value-added graded cellulose product that achieves efficient lignocellulose classification, resulting in high cellulose and hemicellulose recovery rates and high lignin removal rates.

[0012] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0013] A method for grading lignocellulose at room temperature includes the following steps:

[0014] (1) The biomass containing lignocellulose is air-dried, crushed and sieved.

[0015] (2) After the biomass raw material crushed in step (1) is mixed evenly with the treatment liquid, the mixture is stirred and reacted at room temperature; the treatment liquid is a mixed solution of urea peroxide and tetramethylammonium hydroxide in a molar ratio of 1:2.

[0016] (3) Filter the solid-liquid mixture obtained in step (2) and separate the solid substance, which is cellulose;

[0017] (4) Mix the filtrate from step (3) with anhydrous ethanol until homogeneous, separate after sedimentation, and the solid substance obtained by centrifugation is hemicellulose.

[0018] (5) After separating the ethanol from the supernatant obtained by centrifugation in step (4), add HCl to adjust the acidity and precipitate, and then separate the solid substance obtained, which is lignin.

[0019] (6) The filtrate obtained from centrifugation in step (5) is retained for recycling.

[0020] The method provided by this invention uses a combination of tetramethylammonium hydroxide solution (TMAH) and urea peroxide (UHP) to treat lignocellulose. The inventors unexpectedly discovered that by using this mixture, the energy required for efficient dissociation of lignocellulose can be significantly reduced, thereby achieving efficient acquisition of the three components of lignocellulose at room temperature and achieving a high recovery rate of cellulose and hemicellulose, as well as a high lignin removal rate.

[0021] The inventors initially attempted to treat the cells with urea and tetramethylammonium hydroxide solution. However, they found that while the two solutions, whether used alone or in combination, could recover cellulose and hemicellulose to some extent, the recovery rates were generally low. Furthermore, the removal rate of lignin was also low, failing to achieve the superior treatment effect of this invention.

[0022] Furthermore, the mixed solution in step (2) is an aqueous solution of urea peroxide and tetramethylammonium hydroxide, and the total mass concentration of urea peroxide and tetramethylammonium hydroxide in the mixed solution is 20%.

[0023] Furthermore, the weight ratio of biomass raw material to treatment liquid in step (2) is 1:10.

[0024] Furthermore, the temperature of the stirring reaction in step (2) is 15-35℃, and the reaction time is 2h.

[0025] Furthermore, the sieving in step (1) is sieving through a 40-mesh sieve.

[0026] Furthermore, the biomass raw materials mentioned in step (1) are pulverized using a high-speed pulverizer.

[0027] Furthermore, the biomass raw materials mentioned in step (1) include corn stalks, sorghum stalks, rice husks, bark, sawdust, leaves, or mixtures thereof.

[0028] Furthermore, in step (4), the volume ratio of the filtrate to anhydrous ethanol is 1:1.

[0029] The beneficial effects of this invention are as follows:

[0030] (1) Biomass raw materials such as straw treated by this method also have a high cellulose and hemicellulose recovery rate and lignin removal rate under normal temperature conditions, which solves the problem that existing treatment methods either use high temperature and high pressure or require repeated freeze-thaw cycles, resulting in complex processing technology.

[0031] (2) The processing method of the present invention has simple equipment requirements and is easy to operate. Since it is carried out at room temperature, no other energy consumption is required, so it is more green and environmentally friendly and will not cause secondary pollution to the environment.

[0032] (3) The waste liquid generated by this invention contains a large amount of urea, so it can be directly recycled and used as agricultural fertilizer, achieving zero emissions in the whole process. Attached Figure Description

[0033] Figure 1 The image shows actual cellulose products treated at room temperature with TMAH, UHP, or a mixture of TMAH and UHP (TMAH-UHP). Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described in detail below with reference to embodiments. It should be noted that the following embodiments are for explanation and illustration only and are not intended to limit the invention. Non-essential improvements and adjustments made by those skilled in the art based on the above description are still within the scope of protection of this invention.

[0035] Example 1

[0036] A method for grading lignocellulose at room temperature includes the following steps:

[0037] (1) Air dry the sweet sorghum stalks naturally, then crush them using a high-speed pulverizer and pass them through a 40-mesh sieve for later use.

[0038] (2) Take 10g of straw from step (1), mix it evenly with the mixture of tetramethylammonium hydroxide solution (TMAH) and urea peroxide (UHP) in a blue-capped bottle. The solid mass concentration in the mixture is 20%, and the molar ratio of UHP to TMAH is 1:2. Mix the straw and the mixture evenly at a mass ratio of 1:10, and react in a shaker in a constant temperature water bath at 15℃ for 2 hours.

[0039] (3) After the solid-liquid mixture obtained in step (2) is mixed evenly, it is filtered and the solid substance obtained is cellulose.

[0040] (4) Mix the filtrate from step (3) with anhydrous ethanol at a ratio of 1:1 (V / V), let it settle for a short time, and then separate it with a high-speed centrifuge. The solid substance obtained by centrifugation is hemicellulose.

[0041] (5) After separating the ethanol from the supernatant obtained by centrifugation in step (4) using a rotary evaporator, concentrated HCl is added to adjust the acidity and allow it to settle. The solid substance obtained by separating it with a high-speed centrifuge is lignin.

[0042] (6) The filtrate (containing urea) obtained from centrifugation in (5) is retained and recycled as agricultural fertilizer.

[0043] Example 2

[0044] A method for grading lignocellulose at room temperature includes the following steps:

[0045] (1) Wash the corn stalks, dry them, crush them using a high-speed pulverizer, and then pass them through a 40-mesh sieve for later use.

[0046] (2) Take 20g of corn stalks from step (1), mix them evenly with a mixture of tetramethylammonium hydroxide solution (TMAH) and urea peroxide (UHP) in a blue-capped bottle. The solid mass concentration in the mixture is 20%, and the molar ratio of UHP to TMAH is 1:2. Mix the stalks and the mixture evenly at a mass ratio of 1:10, and react them in a shaker in a constant temperature water bath at 25°C for 2 hours.

[0047] (3) After the solid-liquid mixture obtained in step (2) is mixed evenly, it is filtered and the solid substance obtained is cellulose.

[0048] (4) Mix the filtrate from step (3) with anhydrous ethanol at a ratio of 1:1 (V / V), let it settle for a short time, and then separate it with a high-speed centrifuge. The solid substance obtained by centrifugation is hemicellulose.

[0049] (5) After separating the ethanol from the supernatant obtained by centrifugation in step (4) using a rotary evaporator, concentrated HCl is added to adjust the acidity and allow it to settle. The solid substance obtained by separating it with a high-speed centrifuge is lignin.

[0050] (6) The filtrate (containing urea) obtained from centrifugation in (5) is retained and recycled as agricultural fertilizer.

[0051] Example 3

[0052] A method for grading lignocellulose at room temperature includes the following steps:

[0053] (1) Wash the rice husks, dry them, crush them using a high-speed pulverizer, and then pass them through a 40-mesh sieve for later use.

[0054] (2) Take 15g of rice husk from step (1), mix it evenly with the mixture of tetramethylammonium hydroxide solution (TMAH) and urea peroxide (UHP) in a blue-capped bottle. The solid mass concentration in the mixture is 20%, and the molar ratio of UHP to TMAH is 1:2. Mix the straw and the mixture evenly at a mass ratio of 1:10, and react in a shaker in a constant temperature water bath at 35℃ for 2 hours.

[0055] (3) After the solid-liquid mixture obtained in step (2) is mixed evenly, it is filtered and the solid substance obtained is cellulose.

[0056] (4) Mix the filtrate from step (3) with anhydrous ethanol at a ratio of 1:1 (V / V), let it settle for a short time, and then separate it with a high-speed centrifuge. The solid substance obtained by centrifugation is hemicellulose.

[0057] (5) After separating the ethanol from the supernatant obtained by centrifugation in step (4) using a rotary evaporator, concentrated HCl is added to adjust the acidity and allow it to settle. The solid substance obtained by separating it with a high-speed centrifuge is lignin.

[0058] (6) The filtrate (containing urea) obtained from centrifugation in (5) is retained and recycled as agricultural fertilizer.

[0059] Comparative Example 1

[0060] The method of Example 1 is different in that only urea peroxide (UHP) is used as the treatment solution, and the recovery rate of cellulose and hemicellulose and the removal rate of lignin after treatment are calculated.

[0061] Comparative Example 2

[0062] The method of Example 1 was followed, except that only tetramethylammonium hydroxide solution (TMAH) was used as the treatment solution, and the recovery rates of cellulose and hemicellulose and the removal rate of lignin after treatment were calculated.

[0063] Comparative Example 3

[0064] The method of Example 2 differs in that urea solution is used as the treatment liquid, and the recovery rate of cellulose and hemicellulose and the removal rate of lignin after treatment are calculated.

[0065] Comparative Example 4

[0066] The method of Example 2 is different in that: urea and tetramethylammonium hydroxide solution are mixed at a molar ratio of 1:2 as the treatment solution, and the recovery rate of cellulose and hemicellulose and the removal rate of lignin after treatment are calculated.

[0067] Comparative Example 5

[0068] The method of Example 3 is different in that: urea peroxide and tetramethylammonium hydroxide solution are mixed at a molar ratio of 1:1 as the treatment solution, and the recovery rate of cellulose and hemicellulose and the removal rate of lignin after treatment are calculated.

[0069] Comparative Example 6

[0070] The method of Example 1 is followed, except that urea and tetramethylammonium hydroxide solution are mixed at a molar ratio of 2:1 as the treatment solution, and the recovery rate of cellulose and hemicellulose and the removal rate of lignin after treatment are calculated.

[0071] Comparative Example 7

[0072] The method of Example 1 is different in that the mass ratio of straw to mixed liquid is adjusted to 1:8 in step (2).

[0073] Test case

[0074] The recovery rates of cellulose and hemicellulose and the removal rates of lignin after treatment in the examples and comparative examples were determined according to the method described in "Determination of Structural Polysaccharides and Lignin in NREL Biomass". The test results are shown in Table 1 below:

[0075] Table 1

[0076]

Claims

1. A method for fractionating lignocellulose at ambient temperature, characterized by, The method comprises the following steps: (1) naturally air-drying a biomass raw material containing lignocellulose, crushing and sieving; (2) mixing the crushed biomass raw material in step (1) with a treatment liquid uniformly, and then stirring at room temperature; the treatment liquid is a mixed solution of urea peroxide and tetramethylammonium hydroxide in a molar ratio of 1:2, and the mixed solution is an aqueous solution of urea peroxide and tetramethylammonium hydroxide, wherein the total mass concentration of urea peroxide and tetramethylammonium hydroxide in the mixed solution is 20%; (3) filtering the solid-liquid mixture obtained in step (2) to separate the obtained solid material, which is cellulose; (4) mixing the filtrate in step (3) with anhydrous ethanol uniformly, separating after sedimentation, and centrifuging the obtained solid material, which is hemicellulose; (5) adding HCl to the supernatant obtained in step (4) after separation of ethanol to adjust the pH value and then sedimenting, and separating the obtained solid material, which is lignin; (6) recycling the filtrate obtained in step (5) after centrifugation.

2. The method of claim 1, wherein, The weight ratio of the biomass raw material to the treatment liquid in step (2) is 1:

10.

3. The method of claim 1, wherein, The stirring temperature in step (2) is 15-35℃, and the reaction time is 2h.

4. The method according to claim 1, characterized in that The sieving in step (1) is sieving through a 40-mesh sieve.

5. The method of claim 1, wherein, The biomass raw material in step (1) is crushed by a high-speed crusher.

6. The method of claim 1, wherein, The biomass raw material in step (1) comprises corn stalks, sorghum stalks, rice husks, tree bark, wood chips, leaves, or a mixture thereof.

7. The method of claim 1, wherein, The volume ratio of the filtrate to anhydrous ethanol in step (4) is 1:1.

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