A method for separating lignocellulosic components using alcohol complexed molten salt hydrates

Abstract

The application provides a method for separating lignocellulose components by alcohol complex molten salt hydrate, and belongs to the technical field of biomass energy conversion and utilization. The method combines the use of organic acid acidified molten salt hydrate and alcohol, realizes the high-efficiency separation of lignocellulose three components into lignin, cellulose and hemicellulose, and further directional conversion of cellulose and hemicellulose to obtain oligosaccharides, including oligomeric xylose and oligomeric glucose. The separation condition of the application does not require high temperature, is relatively mild, simplifies the reaction steps, and improves the environmental friendliness of the reaction.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of biomass energy conversion and utilization, and more particularly, to a method for separating lignocellulose components by alcohol complex molten salt hydrate. BACKGROUND

[0002] The overuse of fossil resources has triggered a series of serious environmental problems, and countries have reached a consensus on developing green renewable resources to replace fossil resources. Lignocellulose is the highest carbon-containing renewable resource in nature, with the advantages of short regeneration cycle and low cost, and is one of the potential substitutes for fossil resources. Lignocellulose is mainly composed of cellulose, hemicellulose and lignin, and the composition units, connection modes and physicochemical properties of the three components are greatly different, making it difficult to be simultaneously converted and utilized. Therefore, efficient separation of the three components is the basis and prerequisite for realizing high-value utilization of lignocellulose. The separation methods of lignocellulose three components are divided into two categories: one is the "cellulose first" strategy, the core of which is to protect the original structure of cellulose, and remove the lignin component by strong alkali, high temperature and long time reaction. However, this strategy will cause the degradation of part of hemicellulose and the serious condensation of lignin structure, resulting in resource waste; the other is the "lignin first" strategy, the core of which is to protect the original structure of lignin, especially the content of β-O-4 bond. By adjusting the reaction system and reaction conditions, lignin is dissolved under mild conditions, and hemicellulose is hydrolyzed into monosaccharides dominated by xylose, and cellulose remains in solid form. However, the lignin yield of this strategy is usually below 60%, and the separation efficiency is low.

[0003] Molten salt hydrate (MSH) is a special inorganic salt solution that can selectively dissolve cellulose and hemicellulose but completely insoluble lignin. By using this property, the separation of lignocellulose components can be achieved. For example, the literature (Green Chem., 2023, 25, 9272) uses hydrochloric acid acidified molten salt to separate the lignocellulose raw material after microwave acid pretreatment, effectively realizing the separation of lignin and cellulose. However, microwave treatment increases the cost and equipment demand, and the conversion products of cellulose are numerous and have poor selectivity, which is not conducive to industrial application. By adding organic solvents to the molten salt to form an intermiscible two-phase reaction system, the structure of lignin can be protected and the separation efficiency can be improved.

[0004] The prior art discloses a method for separating lignocellulose by forming an intermiscible two-phase system of molten salt and small molecule solvents such as methanol, which disassembles lignocellulose components at a lower temperature. However, in this process, cellulose is converted into long-chain oligosaccharides, short-chain oligosaccharides, glucose, and hydroxymethylfurfural products, and hemicellulose is converted into short-chain oligoxylan, xylose, and furfural products. The conversion products of cellulose and hemicellulose have poor selectivity, and separation and subsequent conversion and utilization are difficult. The prior art also discloses a method for separating lignocellulose three components by using a hydrochloric acid-acidified molten salt and a binary / trinary alcohol intermiscible two-phase reaction system. The binary / trinary alcohol effectively protects the uncondensed structure of lignin, but cellulose and hemicellulose are simultaneously converted into oligosaccharides and monosaccharides, which have poor product selectivity and are difficult to separate.

[0005] Therefore, in order to improve the product selectivity and purity and ensure the separation effect of lignocellulose, it is of important application value to develop a method for separating lignocellulose three components into lignin, cellulose and hemicellulose, and further converting cellulose and hemicellulose into oligoxylan and oligoglucose by using an alcohol-compounded molten salt hydrate. SUMMARY

[0006] The present application aims to overcome the shortcomings of the prior art and provide a method for separating lignocellulose components by using an alcohol-compounded molten salt hydrate, which realizes efficient separation and directional conversion of lignocellulose three components to obtain lignin and oligosaccharides, wherein the oligosaccharides include oligoxylan and oligoglucose, and maintains high purity of lignin.

[0007] Therefore, the purpose of the present application is to provide a method for separating lignocellulose components by using an alcohol-compounded molten salt hydrate.

[0008] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0009] The present application protects a method for separating lignocellulose components by using an alcohol-compounded molten salt hydrate, which comprises the following steps:

[0010] S1. Acidizing the molten salt hydrate solution;

[0011] S2. Mixing and reacting the lignocellulose raw material, the acidized molten salt hydrate solution and the alcohol at 150 DEG C or below;

[0012] S3. After the reaction is completed, collecting the upper organic phase and the lower aqueous phase, respectively;

[0013] The alcohol is an alcohol with 6-12 carbon atoms.

[0014] The acid used in the acidizing treatment is an organic acid.

[0015] The application discloses a method for separating lignocellulose components by alcohol complex molten salt hydrate, deconstructing lignocellulose three components and converting them into saccharide compounds and uncondensed lignin. The method constructs an immiscible two-phase system of organic acid molten salt / alcohol, and treats the molten salt hydrate with organic acid to prevent condensation in the subsequent lignin extraction process, peel off the connection between components, extract the amphiphilic lignin component into the amphiphilic alcohol system in situ, block the contact with the molten salt system and inhibit the structure condensation. On the other hand, the cellulose and hemicellulose can be degraded into oligosaccharides, the molten salt hydrate degrades the cellulose into oligoglucose with a polymerization degree of 4-11, and degrades the hemicellulose into oligoxylan with a polymerization degree of 4-15. If inorganic acid such as hydrochloric acid and sulfuric acid is used, the lignin structure is more strongly destroyed, the internal connection of the cellulose and hemicellulose is broken, and monosaccharides are released. The organic acid used in the application is not enough to completely destroy these connections, and can maintain a longer fragment, which is helpful to generate polysaccharides.

[0016] The molten salt hydrate (MSH) can effectively destroy the hydrogen bond network in the cellulose and hemicellulose due to its strong polarity. The destruction leads to the swelling of the cellulose structure, and further promotes the dissolution of the cellulose in the molten salt hydrate. Under acidic conditions, the molten salt hydrate can catalyze the selective breaking of part of the glycosidic bonds in the cellulose and hemicellulose, and convert these polysaccharides into oligosaccharides with a specific polymerization degree.

[0017] The lignin, as an aromatic polymer with high molecular weight and complex structure, remains relatively stable in the process, and is finally separated as a solid residue with high purity and structural integrity.

[0018] At the same time, the alcohol with carbon atoms 6-12 can effectively prevent the condensation reaction of lignin by undergoing alkoxylation reaction with the Cα-OH group in the lignin phenylpropane structural unit. In addition, the weak polarity and amphiphilic nature of the alcohol with carbon atoms 6-12 make it have good affinity with lignin. This affinity makes lignin separate from the acidic aqueous phase and transfer to the organic phase system dominated by the alcohol with carbon atoms 6-12. In the process of transferring lignin to the alcohol phase, the purity of lignin is improved due to the reduction of its contact and reaction with other components in the reaction system.

[0019] The lignocellulose is composed of three components of cellulose, hemicellulose and lignin. Preferably, the organic acid in step S1 is selected from at least one of citric acid, acetic acid, salicylic acid, p-toluenesulfonic acid or succinic acid.

[0020] Preferably, the concentration of the acid used in the acidification treatment in step S1 is 20-500 mM.

[0021] Preferably, the acid used in the acidification process in step S1 is added in an amount of 0.01 to 0.05 times the mass of the molten salt hydrate.

[0022] Specifically, the pH of the solution after acidification is 3 to 3.5.

[0023] Specifically, the enriched saccharide compound is an oligosaccharide, including oligomeric xylose with a degree of polymerization of 4 to 15 and oligomeric glucose with a degree of polymerization of 4 to 11.

[0024] Preferably, the molten salt hydrate solution in step S1 is formed by dissolving a molten salt hydrate in water.

[0025] Preferably, the molten salt hydrate in step S1 is at least one selected from LiBr, LiCl, ZnBr2, or ZnCl2.

[0026] More preferably, the molten salt hydrate in step S1 is at least one selected from LiBr and LiCl.

[0027] Preferably, the concentration of the molten salt hydrate solution in step S1 is 20 to 85 wt.%.

[0028] More preferably, the concentration of the molten salt hydrate solution in step S1 is 40 to 65 wt.%.

[0029] Preferably, the alcohol in step S2 is an alcohol with 6 to 8 carbon atoms.

[0030] Preferably, the amount of the molten salt hydrate solution after acidification in step S2 is added is 40 to 60 times the mass of the lignocellulosic raw material.

[0031] Preferably, the lignocellulosic raw material in step S2 is at least one selected from pine, poplar, eucalyptus, or corn straw.

[0032] Preferably, the amount of the lignocellulosic raw material in step S2 is added is 0.1 to 1 g.

[0033] Preferably, the alcohol in step S2 is at least one selected from hexanol, octanol, or 2-ethylbutanol.

[0034] Preferably, the amount of the alcohol in step S2 is added is 10 to 40 times the mass of the lignocellulosic raw material.

[0035] Preferably, the temperature of the reaction in step S2 is 70 to 150°C. A temperature higher than 150°C will cause severe condensation of lignin and the color becomes darker.

[0036] More preferably, the temperature of the reaction in step S2 is 90 to 130°C.

[0037] Preferably, the reaction time of step S2 is 0.5-5h.

[0038] More preferably, the reaction time of step S2 is 1-4h.

[0039] Preferably, the method further comprises the step of post-treating the upper organic phase to obtain a lignin-containing filter residue.

[0040] Preferably, the method further comprises the step of using an anti-solvent to separate oligosaccharides from the lower aqueous phase, and then dissolving the oligoxylan in water to separate it from oligoglucose.

[0041] Specifically, the method for separating lignocellulose components by using alcohol-compounded molten salt hydrate further comprises the following steps:

[0042] The upper organic phase rich in lignin is subjected to rotary evaporation to remove alcohol, and the solid is freeze-dried to constant weight to obtain a dried filter residue containing lignin; the lower aqueous phase rich in saccharide compounds is subjected to anti-solvent precipitation to separate oligosaccharides, and the anti-solvent has a polarity difference from the molten salt hydrate, so that the interaction between the oligosaccharides and the molten salt hydrate is weakened, thereby promoting the precipitation of the oligosaccharides, and then the oligoxylan is dissolved in water to separate it from oligoglucose.

[0043] The lignin in the alcohol phase can be obtained by rotary evaporation. The oligoglucose and oligoxylan in the molten salt phase can be separated by adding a small-molecule anti-solvent such as a low-carbon alcohol or ketone, and then the oligoxylan can be further separated from the oligoglucose by dissolving it in water, thereby efficiently realizing the separation of the three components of lignocellulose and the conversion into specific products.

[0044] Preferably, the anti-solvent is one of methanol, ethanol, isopropanol, acetone or acetonitrile.

[0045] Anti-solvent precipitation is a process in which the hydrolysis product rich in oligosaccharides is added to 10 times the volume of anti-solvent. After uniform stirring at room temperature, white solids precipitate from the mixture, and oligosaccharides are obtained by centrifugal separation.

[0046] Compared with the prior art, the method of the present application has the following advantages:

[0047] The present application provides a method for separating lignocellulose components by using alcohol-compounded molten salt hydrate, which combines organic acid-acidified molten salt hydrate and alcohol to realize efficient separation and directional conversion of the three components of lignocellulose. The yield of uncondensed lignin obtained by separation is more than 87.6%, the purity of lignin is more than 80%, the yield of oligoglucose is more than 75%, and the yield of oligoxylan is more than 60%, which shows the high efficiency and high selectivity of the method in the separation of biomass components. The separation conditions of the present application are relatively mild, without high temperature, thereby simplifying the reaction steps and improving the environmental friendliness of the reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 Flow chart for the separation of various components of lignocellulose;

[0049] Figure 2 Graph showing the effect of different citric acid concentrations on the yields of oligosaccharides and monosaccharides in Examples 1 and 3;

[0050] Figure 3 Graph showing the effect of different citric acid concentrations on the yield of xylan and xylose products. Other reaction conditions were the same as in Example 1. DETAILED DESCRIPTION

[0051] In order to more clearly and completely describe the technical solution of the present invention, the present invention is further described in detail through specific embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Various changes can be made within the scope of the rights of the present invention.

[0052] Unless otherwise specified, the reagents and materials used in the following examples were commercially available.

[0053] Test indicators:

[0054] (1) Lignin yield (%): The upper organic phase enriched in lignin is subjected to rotary evaporation to remove alcohol, and the solid is freeze-dried to a constant weight to obtain a dry filter residue containing lignin. The ratio of the obtained dry filter residue to the lignin content measured in the raw material components is the lignin yield;

[0055] (2) Purity of lignin (%): determined by cysteine ​​method:

[0056] 1. Solution Preparation: First, dissolve 10 g of L-cysteine ​​in 100 mL of 72% sulfuric acid to prepare a cysteine ​​solution containing 72% sulfuric acid.

[0057] 2. Sample treatment: 5 mg of lignin sample was placed in a glass vial, and then 1.0 mL of the cysteine ​​solution prepared above was added;

[0058] 3. Mixing: Use a magnetic stirrer to stir the mixture at 400 rpm for 60 min to ensure complete dissolution of the sample;

[0059] 4. Dilution: The solution was further diluted to 50 mL with deionized water to form a diluted solution with a concentration less than 1 g / L for UV detection;

[0060] 5. Ultraviolet absorption measurement: Measure the ultraviolet absorption of the diluted solution at λ = 283 nm;

[0061] 6. Calculate the purity of lignin using the following formula:

[0062] Lignin purity (%) = (A 283 x V) / (ε x m)

[0063] A 283 is the UV absorbance of the diluted solution at 283 nm; V is the total volume of the diluted solution (L); m is the mass of the lignin sample (g); ε is the absorption coefficient of UV absorbance of lignin at λ = 283 nm

[0064] (3) Yield of oligomeric glucose (%): The yield was calculated by analyzing the aqueous solution of the lower layer enriched with saccharide compounds using high performance liquid chromatography.

[0065] (4) Yield of oligomeric xylose (%): The yield was calculated by analyzing the aqueous solution of the lower layer enriched with saccharide compounds using high performance liquid chromatography.

[0066] Example 1: A method for separating lignocellulose components by alcohol complex molten salt hydrate

[0067] S1: 4 g of ultrapure water, 0.089 g of citric acid, and 6 g of LiBr were weighed and mixed to obtain a 60 wt.% LiBr solution containing 240 mM citric acid.

[0068] S2: 0.2 g of pine wood, 10 g of 60 wt.% LiBr solution containing 240 mM citric acid, and 5 g of hexanol solution were added to a 100 mL thick-walled glass reaction tube, the pH was 3, and the reaction tube was placed in an oil bath at 110°C. After 1 h of reaction at normal pressure, the reaction tube was removed and cooled to room temperature.

[0069] S3: The reaction solution was separated using a separatory funnel. The upper layer was an organic phase enriched with lignin, and the lower layer was an aqueous phase containing saccharide compounds.

[0070] S4: The upper layer of the organic phase enriched with lignin was subjected to rotary evaporation. The solid insoluble material was freeze-dried to a constant weight to obtain a dry filter residue containing lignin. The purity of the lignin is shown in Table 1.

[0071] S5: The lower layer of the aqueous phase enriched with saccharide compounds was collected, and methanol was used to perform anti-solvent precipitation to separate oligosaccharides. Subsequently, oligomeric xylose was further separated by dissolving with water, and oligomeric glucose was further separated.

[0072] (2) Take 1 g of the liquid separated by anti-solvent and mix with 5 g of 4 wt.% H2SO4 in a 15 mL thick-walled glass reactor. Stir at 300 rpm with magnetic stirring in an oil bath at 130 °C for 1 h. After the reaction is completed, cool to room temperature. After the reaction is completed, cool to room temperature, and the oligomeric glucose, oligomeric xylose in the hydrolysis product is fully hydrolyzed into glucose, xylose, respectively. Analyze the solution by high performance liquid chromatography, and use the additional amount of glucose, xylose formed by dilute acid hydrolysis to calculate the amount of oligomeric glucose, oligomeric xylose. The product yield is shown in Table 1.

[0073] Example 2 A method for separating lignocellulose components by alcohol complexed molten salt hydrate

[0074] The experimental method is the same as Example 1, except that the acid in S1 is 240 mM hydrochloric acid concentration.

[0075] Example 3 A method for separating lignocellulose components by alcohol complexed molten salt hydrate

[0076] The experimental method is the same as Example 1, except that the acid in S1 is 30 mM citric acid solution.

[0077] Example 4 A method for separating lignocellulose components by alcohol complexed molten salt hydrate

[0078] The experimental method is the same as Example 1, except that the reaction time in S2 is 40 min.

[0079] Example 5 A method for separating lignocellulose components by alcohol complexed molten salt hydrate

[0080] The experimental method is the same as Example 1, except that the reaction time in S2 is 5 h.

[0081] Example 6 A method for separating lignocellulose components by alcohol complexed molten salt hydrate

[0082] The experimental method is the same as Example 1, except that the concentration of the molten salt hydrate solution in S1 is 20 wt.%.

[0083] Example 7 A method for separating lignocellulose components by alcohol complexed molten salt hydrate

[0084] The experimental method is the same as Example 1, except that the concentration of the molten salt hydrate solution in S1 is 85 wt.%.

[0085] Example 8 A method for separating lignocellulose components by alcohol complexed molten salt hydrate

[0086] The experimental method is the same as Example 1, except that the alcohol in S2 is dodecanol.

[0087] Example 9 A method for separating lignocellulosic components using alcohol complexed molten salt hydrates

[0088] The experimental method is the same as Example 1, except that the alcohol in S2 is octanol.

[0089] Example 10 A method for separating lignocellulosic components using alcohol complexed molten salt hydrates

[0090] The experimental method is the same as Example 1, except that the alcohol in S2 is 2-ethylbutanol.

[0091] Example 11 A method for separating lignocellulosic components using alcohol complexed molten salt hydrates

[0092] The experimental method is the same as Example 1, except that the molten salt compound in S2 is LiCl.

[0093] Example 12 A method for separating lignocellulosic components using alcohol complexed molten salt hydrates

[0094] The experimental method is the same as Example 1, except that the molten salt compound in S2 is ZnBr2.

[0095] Comparative Example 1 A method for separating lignocellulosic components using alcohol complexed molten salt hydrates

[0096] A method for separating lignocellulosic components using alcohol complexed molten salt hydrates, which is different from Example 1 in that no alcohol is added in S2, and the corresponding reaction is not followed by the step of removing alcohol by liquid separation, and the specific steps are as follows:

[0097] S1 4 g of ultrapure water, 0.089 g of citric acid and 6 g of LiBr were weighed and mixed to obtain a 60 wt.% LiBr solution containing 240 mM citric acid.

[0098] S2 0.2 g of pine wood and 10 g of 60 wt.% LiBr solution containing 240 mM citric acid were placed into a 100 mL thick-walled glass reaction tube, which was placed in an oil bath at 110°C, and reacted at normal pressure for 1 h, after which it was taken out and cooled to room temperature.

[0099] S3 The reaction solution was filtered and quantitatively analyzed by high performance liquid chromatography.

[0100] (1) 1 g of the filtered reaction solution was diluted 10 times with water, and then quantitatively analyzed by high performance liquid chromatography, and the glucose and xylose yields are shown in Table 1.

[0101] (2) Take 1 g of the filtered reaction solution and mix with 5 g of 4 wt.% H2SO4 in a 15 mL thick-walled glass reactor. Stir at 300 rpm with magnetic stirring in an oil bath at 130 °C for 1 h. After the reaction is completed, cool to room temperature. The oligomeric glucose and oligomeric xylose in the hydrolysis product are fully hydrolyzed into glucose and xylose, respectively. Analyze the solution by high performance liquid chromatography. The additional amount of glucose and xylose formed by dilute acid hydrolysis is used to calculate the amount of oligomeric glucose and oligomeric xylose. The product yield is shown in Table 1.

[0102] S4 Filter the reaction solution by suction filtration. Wash the solid insoluble matter with ultrapure water until the filtrate is transparent. Freeze-dry the solid insoluble matter to constant weight to obtain dry filter residue containing lignin. The purity of lignin is shown in Table 1.

[0103] Comparative Example 2 A method for separating lignocellulose components by complexing alcohol with molten salt hydrate

[0104] The experimental method is the same as in Example 1, except that the alcohol in S2 is butanol.

[0105] Comparative Example 3 A method for separating lignocellulose components by complexing alcohol with molten salt hydrate

[0106] The experimental method is the same as in Example 1, except that the alcohol in S2 is tetradecanol.

[0107] Comparative Example 4 A method for separating lignocellulose components by complexing alcohol with molten salt hydrate

[0108] The experimental method is the same as in Example 1, except that no molten salt compound is added in S2.

[0109] Comparative Example 5 A method for separating lignocellulose components by complexing alcohol with molten salt hydrate

[0110] The experimental method is the same as in Example 1, except that the molten salt compound is not acidified in step S1.

[0111] Comparative Example 6 A method for separating lignocellulose components by complexing alcohol with molten salt hydrate

[0112] The experimental method is the same as in Example 1, except that the molten salt compound is acidified with sulfuric acid in step S1, so that the pH of the solution is 3, which is the same as the pH of the solution in Example 1.

[0113] Table 1 Product yield and lignin purity

[0114]

[0115]

[0116] From Table 1, the alcohol complex molten salt hydrate separation method of lignocellulose components in Examples 1-12 of the present application, the product yield, oligomeric glucose yield is more than 75%, oligomeric xylose yield is more than 60%, lignin yield is more than 87.6%, and the purity of lignin is more than 80%. Among them, the method of Example 1 has the best lignin extraction yield and purity.

[0117] In Comparative Example 1, no alcohol is added, the purity of lignin decreases, the yield of oligomeric glucose and oligomeric xylose decreases, in Comparative Example 2, butanol is used to replace hexanol, which is difficult to play a role in inhibiting the condensation of lignin, and the purity decreases significantly; in Comparative Example 3, tetradecanol is used, which cannot further improve the purity of lignin extraction, but rather decreases, and there are hidden dangers in storage and use safety; in Comparative Example 4, no molten salt compound is added, it is difficult to convert into oligosaccharides, and the yield decreases significantly; in Comparative Example 5, the molten salt compound is not acidified in step S1, the comprehensive yield and purity decrease, indicating that acidification is a necessary condition for the reaction; in Comparative Example 6, sulfuric acid is used to acidify the molten salt compound, cellulose and hemicellulose are converted into oligosaccharides and monosaccharides, and the yield of oligosaccharides decreases.

[0118] Obviously, the above examples of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and impossible to exhaust all the embodiments. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A method for separating lignocellulosic components with alcohol complexed molten salt hydrates, characterized by, The method comprises the following steps: S1. Acidifying the molten salt hydrate solution; S2. Mixing the lignocellulose raw material, the acidified molten salt hydrate solution and alcohol at 150℃ or below to react; S3. Collecting the upper organic phase and the lower aqueous phase after the reaction is completed; The alcohol is at least one of hexanol, octanol, dodecanol or 2-ethylbutanol; The acid used in the acidification is an organic acid.

2. The method of claim 1, wherein, The organic acid used in step S1 is at least one of citric acid, acetic acid, salicylic acid, p-toluenesulfonic acid or succinic acid.

3. The method of claim 1, wherein, The concentration of the acid used in step S1 is 20-500mM.

4. The method of claim 1, wherein, The molten salt hydrate used in step S1 is at least one of LiBr, LiCl, ZnBr2 or ZnCl2 hydrate.

5. The method of claim 1, wherein, The amount of alcohol added in step S2 is 10-40 times the mass of the lignocellulose raw material.

6. The method of claim 1, wherein, The reaction time in step S2 is 0.5-5h.

7. The method of claim 1, wherein, The method further comprises a step of post-treating the upper organic phase to obtain a filter residue containing lignin.

8. The method of claim 1, wherein, The method further comprises a step of separating oligosaccharides from the lower aqueous phase by using an anti-solvent to precipitate, and then dissolving the oligosaccharides in water to separate oligoxylan and oligoglucose. The method further comprises a step of post-treating the upper organic phase to obtain a filter residue containing lignin. The method further comprises a step of separating oligosaccharides from the lower aqueous phase by using an anti-solvent to precipitate, and then dissolving the oligosaccharides in water to separate oligoxylan and oligoglucose.

Images