A method for efficiently separating lignin from straw

Abstract

The application provides a method for efficiently separating lignin in straw, which comprises the following steps: a) adding a biomass derivative into benzyl alcohol to form a uniform solution, mixing a straw raw material with the obtained solution for reaction, and performing solid-liquid separation to obtain a solid residue and a liquid phase component; b) adding water into the liquid phase component and standing for layering to obtain an aqueous phase and an organic phase; and c) adding an anti-solvent into the organic phase, and performing centrifugal separation to obtain supernatant and precipitate, and the precipitate is lignin. The application uses a biomass derivative to compound benzyl alcohol to pretreat a straw raw material, and can efficiently separate lignin in the straw under mild conditions, and the separated lignin and xylose generated by hydrolysis of hemicellulose can be recovered in a simple manner, and the method has potential for suitable application and promotion.

Description

Technical Field

[0001] This invention belongs to the field of lignin separation technology and relates to a method for efficiently separating lignin from straw. Background Technology

[0002] Biomass resources are an abundant carbon-containing renewable resource and can serve as an ideal substitute for fossil fuels. The high-value utilization of biomass resources is an effective way to alleviate current energy and environmental pressures. Straw is a typical lignocellulosic biomass, and its efficient conversion into chemical raw materials is of great significance for improving rural development and agricultural construction. Straw is mainly composed of three components: cellulose, hemicellulose, and lignin. These components are intertwined and cross-linked to form a dense network structure. The conversion and utilization of any one component will inevitably be affected by the other two, resulting in low efficiency in the direct conversion and utilization of straw. Lignin acts as a "binding agent" among the three components; its efficient separation can break down the dense network of biomass and is one of the necessary steps for the high-value utilization of straw. Therefore, it is necessary to find a mild and simple pretreatment method to efficiently separate lignin from straw, thereby achieving the separation and utilization of the three major components of straw.

[0003] In recent years, methods for separating lignin from straw through pretreatment have been extensively studied, and various lignin separation methods have been developed, mainly categorized into three types: physical pretreatment, chemical pretreatment, and biological pretreatment. Physical pretreatment methods primarily include mechanical crushing, microwave radiation, and steam explosion. These methods typically require high energy consumption and generate high temperatures and pressures during the pretreatment process. Chemical pretreatment methods mainly rely on alkali and alkali-oxygen methods, which require sophisticated equipment, and the alkaline substances produced after pretreatment are difficult to remove, easily causing environmental pollution. Biological pretreatment methods offer milder reaction conditions and are environmentally friendly, but the reaction cycle often lasts for several weeks, and the pretreatment efficiency is low, hindering large-scale application.

[0004] Developing a lignin separation method that can achieve efficient separation of the three major components of straw under mild conditions is a problem that needs to be solved. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a method for the efficient separation of lignin from straw based on a combination of salicylic acid derivatives and benzyl alcohol. The salicylic acid derivatives have a structure similar to lignin, allowing them to orient themselves towards the lignin in straw and selectively polarize and break the linkages at the LCC sites. Simultaneously, the abundant hydroxyl and carboxyl groups in the salicylic acid derivatives can form a hydrogen bond network with benzyl alcohol, weakening the hydrogen bonds between lignin and carbohydrates, and synergistically promoting the release and dissolution of lignin in the solvent. By pretreating straw using this method, lignin can be efficiently separated from straw raw materials under mild conditions and in a relatively short time.

[0006] The purpose of this invention is to provide a method for efficiently separating lignin from straw.

[0007] This invention provides a method for efficiently separating lignin from straw based on a salicylic acid derivative compounded with benzyl alcohol, comprising the following steps:

[0008] Step A: Add the salicylic acid derivative to benzyl alcohol to form a homogeneous solution. Mix the straw raw material with the solution and react. Separate the solid and liquid phases to obtain solid residue and liquid phase components.

[0009] Step B: Add water to the liquid phase component and allow it to stand to separate into layers, obtaining an aqueous phase and an organic phase;

[0010] Step C: Add an antisolvent to the organic phase, centrifuge to obtain a supernatant and a precipitate, the precipitate being lignin.

[0011] Step A:

[0012] Preferably, the salicylic acid derivative is 5-sulfosalicylic acid or 5-nitrosalicylic acid.

[0013] Preferably, the concentration of the salicylic acid derivative in the solution is 1wt% to 20wt%, specifically 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 8wt%, 10wt%, 12wt%, 15wt%, 16wt%, 18wt%, and 20wt%.

[0014] Preferably, the straw raw material is crushed crop straw, and more preferably, it is crushed crop straw with a particle size ≤20 mesh.

[0015] Preferably, the solid-liquid ratio of the straw raw material to the solution is 1g:(5-20)ml, specifically 1g:5ml, 1g:10ml, 1g:15ml or 1g:20ml.

[0016] Preferably, the reaction temperature is 80–120°C and the reaction time is 40–120 min.

[0017] Benzyl alcohol is a common biodegradable organic solvent. Its structure contains both a benzene ring and a hydroxyl group, exhibiting a high degree of similarity to the structural units of lignin. This allows it to interact strongly with lignin, resulting in superior lignin-dissolving ability compared to other organic solvents. Furthermore, benzyl alcohol is chemically stable, exhibiting low toxicity and corrosiveness, making it suitable as a solvent for separating lignin from straw. Additionally, benzyl alcohol is poorly soluble in water, allowing for the separation of soluble sugars from the pretreated reaction solution by forming a two-phase system through the addition of water.

[0018] The biomass derivative used in this invention is a salicylic acid derivative, such as 5-sulfosalicylic acid and 5-nitrosalicylic acid, preferably 5-sulfosalicylic acid. The salicylic acid derivative is characterized by having a hydrophobic benzene ring structure and a hydrophilic hydroxyl structure similar to lignin, which can be directionally adsorbed with lignin in straw and selectively polarize and break the linkages at the LCC sites. At the same time, the abundant hydroxyl and carboxyl groups in 5-sulfosalicylic acid can form a hydrogen bond network with benzyl alcohol, weakening the hydrogen bonds between lignin and carbohydrates, and synergistically promoting the release and dissolution of lignin in solvents.

[0019] In this invention, straw raw material is first mixed and reacted with a salicylic acid derivative benzyl alcohol solution. The straw raw material is pulverized crop straw, mainly composed of cellulose, hemicellulose, and lignin. To ensure sufficient contact and reaction between the straw raw material and the solution, it is preferable to first pulverize the straw raw material into powder, with the particle size of the pulverized straw powder preferably ≤20 mesh. The reaction temperature is preferably 80–120℃, specifically 80℃, 90℃, 100℃, 110℃, or 120℃; the reaction time is preferably 40–120 min, specifically 40 min, 60 min, 80 min, 100 min, or 120 min.

[0020] After the reaction is complete, the reaction system is cooled to room temperature. The solid residue and liquid phase components are then separated, and the separated solid residue is washed with ethanol and water, respectively, to remove residual solvent from the solid surface. This invention does not impose any particular limitation on the method of solid-liquid separation, including but not limited to solid-liquid separation methods well known to those skilled in the art, such as filtration, vacuum filtration, and centrifugation.

[0021] Step B:

[0022] Preferably, the volume ratio of the liquid phase component to the added water is 1:(1-5). After standing and separating, the upper layer is the aqueous phase and the lower layer is the organic phase. Preferably, a separatory funnel is used to separate the aqueous phase and the organic phase. The aqueous phase contains xylose generated from the hydrolysis of hemicellulose in the straw raw material, which can be used for the recovery and further conversion of xylose; the organic phase contains lignin separated from the straw raw material, which is recovered by adding an antisolvent to precipitate the lignin.

[0023] Step C:

[0024] Preferably, the antisolvent is one or more of ethyl acetate, isopropyl ether, dimethyl carbonate, and diethyl ether, with dimethyl carbonate being the most preferred.

[0025] Preferably, the volume ratio of the antisolvent to the organic phase is 1:(8-50).

[0026] Allow the lignin to precipitate by standing. Separate the precipitated lignin by centrifugation. Recover the antisolvent by negative pressure rotary evaporation of the supernatant. The remaining benzyl alcohol can be recycled without further purification.

[0027] This invention provides a method for efficiently separating lignin from straw based on a salicylic acid derivative compounded with benzyl alcohol. This method can efficiently separate lignin from straw raw materials under relatively mild conditions while preserving a relatively intact cellulose component. The separated lignin and xylose generated from the hydrolysis of hemicellulose can both be easily recovered. Furthermore, the solvents involved in each reaction step can be recycled, preventing environmental pollution. Compared with existing straw lignin separation methods, the method employed in this invention is economical, environmentally friendly, and has higher processing efficiency, making it suitable for further widespread application.

[0028] Using this invention to pretreat corn stalks, the lignin separation rate can reach over 85%, and the cellulose retention rate is over 85%.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] This invention utilizes a benzyl alcohol solution formulated with salicylic acid derivatives to pretreat straw raw materials, efficiently separating lignin from the raw materials under relatively mild conditions while preserving a relatively complete cellulose component. Furthermore, the separated lignin and xylose generated from the hydrolysis of hemicellulose can be easily recovered. Moreover, this method is relatively environmentally friendly, as the solvents involved in each reaction step can be recycled, causing no environmental pollution. It achieves a lignin separation efficiency of over 85% at relatively low temperatures and short reaction times, demonstrating significant advantages over existing lignin separation methods and making it suitable for further widespread application.

[0031] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments.

[0032] Unless otherwise expressly stated, numerical ranges throughout the application include any subranges therein and any numerical values ​​incremented by the smallest subunit of a given value. Unless otherwise expressly stated, numerical values ​​throughout the application represent approximate measures or limitations on the range of embodiments including minor deviations from a given value and having approximately the mentioned value as well as having the mentioned precise value. Except in the detailed description of the working embodiments provided at the end, all numerical values ​​of parameters (e.g., quantities or conditions) in this application (including the appended claims) should in all cases be understood to be modified by the term “approximately,” regardless of whether “approximately” actually precedes the numerical value. “Approximately” indicates that the stated numerical value allows for slight inaccuracies (some close to precision at that value; approximately or reasonably close to the value; approximate). If the inaccuracy provided by “approximately” is not understood in this common sense in the art, then “approximately” as used herein at least indicates a variation that can be produced by common methods of measuring and using these parameters. For example, “approximately” can include variations less than or equal to 10%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or less than or equal to 0.5%. Attached Figure Description

[0033] Figure 1 This is a scanning electron microscope (SEM) image of corn stalks before pretreatment.

[0034] Figure 2 This is a scanning electron microscope (SEM) image of corn stalks after pretreatment.

[0035] Figure 3 Fourier transform infrared (FTIR) spectra of corn stalks before and after pretreatment. Detailed Implementation

[0036] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0037] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0038] raw material:

[0039] The corn stalks came from Mengcheng area, Anhui Province;

[0040] 5-Sulfosalicylic acid was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0041] Calculation method:

[0042] To determine the structural and compositional changes of corn stalks during pretreatment, component analysis of samples before and after pretreatment is necessary. Based on the two-step acid hydrolysis method developed by the National Renewable Energy Laboratory (NERL), the content of sugars and lignin in biomass components can be determined. To ensure the universality of the experimental results, each experiment was conducted three times, and the average value was taken. The specific procedure is as follows:

[0043] (1) Measurement of carbohydrate compounds

[0044] Take an appropriate amount of the sample to be tested (m1) and place it in a beaker. Add 72% concentrated sulfuric acid until the sample is submerged. Stir the mixture at room temperature for 1 hour, then transfer it to a pressure-resistant glass bottle. Add a certain amount of deionized water to dilute the acid concentration to 4%, and record the solution volume V0 at this point. Autoclave the solution for 1 hour at 121℃. After autoclaving, allow it to cool naturally to room temperature, filter and wash with deionized water, and dry it to constant weight (m2) in a 105℃ oven. Filter the filtrate through a 0.45µm filter and analyze it using high-performance liquid chromatography (HPLC). To accurately measure the monosaccharide content in the filtrate, first, weigh the required monosaccharide standard and prepare a standard stock solution with a concentration of 10 mg / mL. Then, take an appropriate amount of the standard stock solution and prepare mixed standard solutions with concentrations of 60 μg / mL, 50 μg / mL, and 40 μg / mL.

[0045] Cellulose % = 0.9 * V0 * C glucose * 100% / ml;

[0046] (2) Measurement of acid-insoluble lignin

[0047] The solid obtained after the two-step acid hydrolysis was ground and added to a ceramic boat, which was then placed in a muffle furnace and calcined at 550°C for 2 hours, with the heating rate controlled at 5°C / min. After calcination, the muffle furnace was allowed to cool naturally to room temperature, and the mass of the solid was weighed and recorded as (m3).

[0048] Acid-insoluble lignin % = (m2-m3)*100% / m1;

[0049] (3) Determination of acid-soluble lignin content

[0050] First, take a certain volume of the filtrate obtained from the sulfuric acid hydrolysis and dilute it to the target concentration according to the set ratio. Then, measure the absorbance of ultraviolet light at a wavelength of 205 nm using a UV-Vis spectrophotometer, with a 4% sulfuric acid solution as a blank control group. It should be noted that the absorbance values ​​measured in the experiment are valid in the range of 0.7 to 1. The formula for calculating the acid-soluble lignin content is as follows:

[0051] The content of acid-soluble lignin in the filtrate (g / L) = A*D / 110,

[0052] The percentage of acid-soluble lignin in the sample to be tested (%) = D * d * A * V0 * 100% / (110 * m1)

[0053] in:

[0054] D represents the dilution factor of the filtrate.

[0055] A represents the ultraviolet absorbance value.

[0056] The optical path width (mL) of the quartz cuvette.

[0057] V0 represents the total volume (mL) of the hydrolysate.

[0058] 110 represents the molar absorptivity (L / g·cm)m 2 ,

[0059] This indicates the dry weight (g) of the sample to be tested.

[0060] The lignin content in the sample is the sum of the contents of acid-insoluble lignin and acid-soluble lignin.

[0061]

[0062] Example 1

[0063] 1) After crushing the corn stalks, pass them through a 20-mesh sieve, weigh 4.0g, measure 60ml of 5-sulfosalicylic acid compound benzyl alcohol solution with a concentration of 4%, and place it in a 100ml mechanically stirred reactor.

[0064] 2) Adjust the reactor speed to 500 rpm, raise the temperature to 100℃ and maintain it for 1 hour.

[0065] 3) After the reaction is complete, turn off the power to the reactor and place the reactor in circulating water to cool it to room temperature.

[0066] 4) Pour the reactants out of the reaction vessel, filter under vacuum to obtain the reaction liquid and solid residue, and wash the solid residue with ethanol and water respectively.

[0067] 5) Add twice the volume of water to the reaction solution, let it stand to separate the phases, and use a separatory funnel to separate the aqueous phase and the organic phase.

[0068] 6) Add 10 times the volume of dimethyl carbonate to the organic phase to precipitate lignin, centrifuge to recover the precipitate, wash and dry to obtain solid lignin.

[0069] 7) The solid residue obtained from filtration in step 4) was subjected to a two-step acid hydrolysis method to determine the lignin separation rate and cellulose retention rate;

[0070] The results showed that, under the above conditions, the lignin separation rate was 86.5% and the cellulose retention rate was 88.5%.

[0071] Figure 1 This is a scanning electron microscope (SEM) image of the corn stalks before pretreatment in this embodiment; Figure 2 This is a scanning electron microscope (SEM) image of corn stalks after pretreatment in this embodiment; Figure 3 These are the Fourier transform infrared (FTIR) spectra of corn straw before and after pretreatment in this embodiment; through... Figure 1 and Figure 2 The comparison shows that the original corn stalks have a smooth and dense surface structure. Hemicellulose and lignin in the corn stalks are entangled and combined with cellulose fibers, forming a dense three-dimensional network structure. This compact and highly ordered structure hinders the further development and utilization of corn stalks. In contrast, the solid residue after pretreatment with 5-sulfosalicylic acid and benzyl alcohol has a rough and uneven surface with many cracks and pores, which is related to the shedding of hemicellulose and lignin.

[0072] pass Figure 3 Comparison of FTIR spectra of straw before and after pretreatment, 1514 cm⁻¹ after pretreatment 1 The tensile vibration peaks of the lignin aromatic ring structure at the corresponding positions and the 1256 cm⁻¹ 1 The vibrational peak of the C=O bond in hemicellulose at the corresponding position was significantly weakened compared to before pretreatment, confirming the large-scale removal of lignin and hemicellulose from corn stalks after pretreatment with 5-sulfosalicylic acid and benzyl alcohol.

[0073] Example 2

[0074] Following the steps in Example 1, with all other conditions unchanged, the solid-liquid ratio of the reaction between corn stalks and benzyl alcohol solution containing 5-sulfosalicylic acid was changed to 4g:20ml, 4g:40ml, and 4g:80ml. The corresponding lignin separation rates were measured to be 77.1%, 81.4%, and 87.6%, and the cellulose retention rates were 89.2%, 88.7%, and 87.8%, respectively.

[0075] Example 3

[0076] Following the steps in Example 1, with all other conditions unchanged, the concentration of 5-sulfosalicylic acid was varied to 2%, 6%, and 8%. The corresponding lignin separation rates were 76.2%, 89.4%, and 88.7%, and the cellulose retention rates were 94.2%, 81.1%, and 73.1%, respectively.

[0077] Example 4

[0078] Following the steps in Example 1, with all other conditions unchanged, the reaction temperature was varied to 80°C, 90°C, 110°C, and 120°C. The corresponding lignin separation rates were measured to be 76.4%, 82.4%, 89.9%, and 92.7%, and the cellulose retention rates were 92.20%, 90.24%, 84.20%, and 72.30%, respectively.

[0079] Example 5

[0080] Following the steps in Example 1, with all other conditions unchanged, the reaction time was varied to 40 min, 50 min, 70 min, and 80 min. The corresponding lignin separation rates were measured to be 83.23%, 84.50%, 85.72%, and 87.70%, and the cellulose retention rates were 90.61%, 89.80%, 88.20%, and 87.60%, respectively.

[0081] As can be seen from the above embodiments, the method provided by the present invention can achieve a high lignin separation rate and cellulose retention rate when separating lignin from straw.

[0082] Comparative Experiment 1

[0083] Following the steps in Example 1, with all other conditions unchanged, the solvent for the 5-sulfosalicylic acid compound was changed to water, methanol, ethanol, or benzaldehyde. The corresponding lignin separation rates were measured to be 41.23%, 49.82%, 57.12%, and 78.70%, respectively, and the cellulose retention rates were 71.36%, 92.17%, 89.20%, and 89.70%, respectively.

[0084] Comparative Experiment 2

[0085] Following the steps in Example 1, with all other conditions unchanged, the types of solutes in the benzyl alcohol mixture were changed. The solutes were salicylic acid, 2-hydroxy-5-methylbenzenesulfonic acid, and p-toluenesulfonic acid. The corresponding lignin separation rates were determined to be 39.23%, 60.72%, and 80.14%, respectively, and the cellulose retention rates were 92.34%, 88.42%, and 85.67%, respectively.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for efficiently separating lignin from straw, characterized in that, Includes the following steps: Step A: Add the salicylic acid derivative to benzyl alcohol to form a homogeneous solution. Mix the straw raw material with the solution and react. Separate the solid and liquid phases to obtain solid residue and liquid phase components. Step B: Add water to the liquid phase component and allow it to stand to separate into layers, obtaining an aqueous phase and an organic phase; Step C: Add antisolvent to the organic phase, centrifuge to obtain supernatant and precipitate, the precipitate being lignin; In step A, the salicylic acid derivative is 5-sulfosalicylic acid; In step A, the concentration of the salicylic acid derivative in the solution is 2wt%~8wt%; In step A, the solid-liquid ratio of the straw raw material to the solution is 1g:(5~20)ml; In step A, the reaction temperature is 80~120℃ and the reaction time is 40~120min; In step C, the antisolvent is one or more of ethyl acetate, isopropyl ether, dimethyl carbonate, and diethyl ether.

2. The method according to claim 1, characterized in that, In step A, the straw raw material is crop straw with a particle size ≤20 mesh after crushing.

3. The method according to claim 1, characterized in that, In step B, the volume ratio of the liquid phase component to the added water is 1:(1~5).

4. The method according to claim 1, characterized in that, In step C, the volume ratio of the antisolvent to the organic phase is 1:(8~50).

5. The method according to claim 1, characterized in that, In step C, the antisolvent in the supernatant is recovered by rotary evaporation, and the remaining benzyl alcohol is recycled.

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