Method for semi-continuous saccharification and three-element separation of lignocellulose
By employing a two-step hydrolysis process in which an acidic molten salt solution flows through a fixed-bed reactor under normal pressure, the problems of excessive degradation and incomplete separation of the three components in the pretreatment of lignocellulose are solved. This process achieves effective separation of pentose and hexose sugars and recovery of lignin, thereby reducing production costs.
Patent Information
- Application Number
- CN202510743799.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-05
- Publication Date
- 2025-11-07
AI Technical Summary
Existing lignocellulose pretreatment methods suffer from excessive degradation and incomplete separation of the three components under high temperature and high pressure conditions, and traditional methods also have problems with environmental pollution and high costs.
An acidic molten salt solution is passed through a fixed-bed reactor at atmospheric pressure. Hemicellulose and cellulose are hydrolyzed separately in two steps, and the separation of pentose and hexose sugars is achieved by antisolvent precipitation, and the lignin component is recovered.
The efficient separation of pentose and hexose sugars was achieved under mild conditions, reducing the degradation of cellulose and hemicellulose, decreasing the production of inhibitors, lowering production costs, and preserving the activity of lignin.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the field of utilization of agricultural and forestry waste biomass resources, and particularly relates to a method for semi-continuous saccharification of lignocellulose under mild conditions by a non-enzyme system and separation. BACKGROUND
[0002] At present, lignocellulosic biomass has become one of the most potential fossil resource substitutes due to its environmental friendliness and renewable characteristics. China is rich in biomass resources, most of which come from forestry and agricultural wastes. Lignocellulose is the main component of plant cell walls and is a dense complex formed by cellulose, hemicellulose and lignin, which has high mechanical strength and biological resistance. Before the utilization of the above three main components, pretreatment is needed to break the dense structure. Traditional pretreatment methods are mainly carried out under high temperature and high pressure conditions by using strong acid or strong alkali solution, but most of these processes only focus on the application of one component, resulting in a large loss of other components during the pretreatment process. Therefore, the development of a process for separating cellulose, hemicellulose and lignin components in lignocellulose under mild conditions will greatly improve the application value of lignocellulosic biomass resources.
[0003] The lignocellulose component separation process is a special pretreatment method, which can not only effectively improve the enzymatic hydrolysis effect of cellulose, but also can separate the main components of lignocellulose (cellulose, hemicellulose and lignin) and use them for the production of other high value-added products. At present, the main lignocellulose separation processes include: cellulose solvent and organic solvent combination method, ionic liquid method, γ-valerolactone method and organic acid-organic solvent combination method, etc. The method of separating lignocellulose by cellulose solvent and organic solvent is to combine concentrated phosphoric acid as a cellulose solvent with an organic solvent (acetone or ethanol) to separate the components of lignocellulose under mild reaction conditions. This process can recover hemicellulose and lignin under mild reaction conditions and destroy the crystal structure of cellulose, but it needs a large amount of concentrated phosphoric acid and organic solvent, causing environmental pollution (Bioresource Technology, 2012, 117: 228-233; Biotechnology and Bioengineering, 2007, 97(2): 214-223). The ionic liquid method refers to the separation of lignocellulose by using ionic liquids such as 1-ethyl-3-methylimidazolium chloride (EMIMCl), 1-allyl-3-methylimidazolium chloride (AMIMCl) and 1-allyl-3-methylimidazolium acetate (AMIMAc) (Bioresource Technology, 2012, 117: 228-233; Bioresource Technology, 2012, 117: 228-233; Bioresource Technology, 2012, 117: 228-233). The γ-valerolactone method is to use γ-valerolactone as a solvent to separate lignocellulose (Bioresource Technology, 2012, 117: 228-233). The organic acid-organic solvent combination method is to use formic acid as a solvent to separate lignocellulose (Bioresource Technology, 2012, 117: 228-233). - 3- 2- 2- - - Anion pairing forms ionic liquid which can effectively dissolve lignocellulose by breaking hydrogen bonds in it (Green Chemistry, 2014, 16(3): 1617-1627; Sustainable Chemical Processes, 2013, 1(1): 1-31). However, a large amount of ionic liquid is required in the separation process, which is expensive and difficult to recycle. The organic acid-organic solvent combination method is to hydrolyze hemicellulose with organic acid, while lignin is dissolved in organic solvent, leaving solid cellulose (Green Chemistry, 2015, 17, 3533-3539; Green Chemistry, 2017, 19, 93-97). However, the long reaction time of high temperature and acid solution leads to the further degradation of monosaccharides produced by the hydrolysis of cellulose and hemicellulose into substances that inhibit the growth and fermentation of microorganisms, affecting the subsequent biological conversion of lignocellulose components.
[0004] There are studies that use γ-valerolactone aqueous solution containing dilute acid to flow through a fixed bed reactor filled with lignocellulosic biomass, and by adjusting the ratio of γ-valerolactone to water in two hydrolysis reaction stages, respectively hydrolyzing hemicellulose and cellulose components. This method can quickly take out monosaccharides produced by the hydrolysis reaction process from the reactor, shorten the reaction residence time, and avoid the further degradation of inhibitors. On the other hand, hemicellulose and cellulose are respectively saccharified and separated. However, this method cannot completely separate five-carbon and six-carbon sugars in the two-stage collected solution (Science, 2014, 243, 277-280). In addition, molten salt hydrates can exhibit Lewis and Br nsted acid catalytic properties at low concentrations, and have salting-out and salting-in effects on lignocellulose at high concentrations. Studies have shown that molten salt hydrates can effectively dissolve hemicellulose and cellulose in lignocellulose at 100℃ and normal pressure, but there are still problems that five-carbon sugars and six-carbon sugars cannot be separated, and molten salt hydrates cannot be separated from sugar products, recycled and reused. Acid catalytic properties at low concentrations, and have salting-out and salting-in effects on lignocellulose at high concentrations. Studies have shown that molten salt hydrates can effectively dissolve hemicellulose and cellulose in lignocellulose at 100℃ and normal pressure, but there are still problems that five-carbon sugars and six-carbon sugars cannot be separated, and molten salt hydrates cannot be separated from sugar products, recycled and reused.
[0005] In view of this, the present application is proposed. SUMMARY
[0006] The purpose of the present application is to provide a lignocellulose mild condition semi-continuous saccharification and three-element separation method, which solves the problems of excessive degradation of lignocellulose three elements caused by high temperature and high pressure pretreatment conditions of agricultural and forestry waste biomass, and ineffective separation.
[0007] In order to achieve the above purpose, the present application provides the specific operation steps of the method:
[0008] (1) The lignocellulosic raw material is mixed with the solid support and added into the reactor with inlet and outlet at both ends.
[0009] Preferably, the lignocellulosic raw material is agricultural and forestry waste biomass, including one or a mixture of corn stalks, rice stalks, wheat stalks, sorghum stalks, corn cobs, bamboo, birch, pine, spruce, Douglas fir, poplar, birch, sugar cane residue, sugar beet residue, chicory residue, apricot shells, and coconut shells.
[0010] Preferably, the reactor includes a fixed bed reactor or a reaction kettle; the reactor is one or more in parallel.
[0011] (2) The first acidic molten salt hydrate solution is passed through the reactor at a liquid-solid ratio of 10:1 to 30:1 with the lignocellulosic raw material, the residence time in the reactor is 10-120 minutes, the reactor temperature is 60-100°C, and the effluent rich in five-carbon sugars generated by hemicellulose hydrolysis is collected from the reactor outlet.
[0012] Preferably, the first acidic molten salt hydrate solution is composed of an acid, a molten salt, and water, wherein the acid includes one or a mixture of hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, nitric acid, formic acid, acetic acid, and oxalic acid, and the proton concentration of the acid is 0-100 mM; the molten salt is ZnBr2, LiBr, CaBr2, MgBr2, AlBr3, ZnCl2, LiCl, CaCl2, and AlCl3.
[0013] Preferably, the mass fraction of the molten salt in the first acidic molten salt hydrate solution is 30%-55%.
[0014] (3) The second acidic molten salt hydrate solution is passed through the reactor at a speed of 1.3 ml / min for 5 min, the first acidic molten salt hydrate solution remaining in the reactor from step (2) is discharged from the outlet, and the discharge liquid is collected to obtain separation liquid A by mixing with the effluent from step (2).
[0015] Preferably, the second acidic molten salt hydrate solution is composed of an acid, a molten salt, and water, wherein the acid includes one or a mixture of hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, nitric acid, formic acid, acetic acid, and oxalic acid, and the proton concentration of the acid is 0-100 mM; the molten salt is ZnBr2, LiBr, CaBr2, MgBr2, AlBr3, ZnCl2, LiCl, CaCl2, and AlCl3.
[0016] Preferably, the mass fraction of the molten salt in the second acidic molten salt hydrate solution is 56%-72%.
[0017] (4) according to the second acid molten salt hydrate solution and lignocellulosic raw material liquid solid ratio 10:1~30:1 ratio, the second molten salt hydrate solution from the inlet through the reactor, the time through the reactor is 10-120 minutes, the reactor temperature is 80-110 DEG C, from the reactor outlet collection cellulose hydrolysis produces rich six carbon sugar separation liquid B.
[0018] (5) the raw material in the reactor after step (3) and (4) saccharification reaction after the lignin solid residue is taken out, washed repeatedly with deionized water to neutral, then solid-liquid separation, drying, collection and obtain lignin component.
[0019] Preferably, the solid-liquid separation includes high speed centrifugation and suction filtration.
[0020] Preferably, the drying is freeze drying or low temperature vacuum drying; wherein, freeze drying temperature-80 DEG C to-45 DEG C, freeze drying 12-36 hours; low temperature vacuum drying temperature is not higher than 60 DEG C, time 12-24 hours.
[0021] (6) step (3) collected separation liquid A is subjected to sugar and acid molten salt hydrate separation, and five carbon sugar oligomer is obtained; step (4) collected separation liquid B is subjected to sugar and acid molten salt hydrate separation, and six carbon sugar oligomer is obtained;
[0022] Preferably, the sugar and acid molten salt hydrate separation uses anti-solvent precipitation method, and the separation liquid A or the separation liquid B is mixed with the anti-solvent at a volume ratio of 1:5~1:35, stirred at a rotation speed of not less than 50 revolutions per minute for 1-5 hours, and the temperature is 0-25 DEG C, then white solid is precipitated, and then solid-liquid separation is carried out by centrifugation;
[0023] The solid obtained from the separation liquid A is five carbon sugar oligomer, and the solid obtained from the separation liquid B is six carbon sugar oligomer;
[0024] The liquid obtained from the separation liquid A is subjected to rotary evaporation to recover the anti-solvent and the first acid molten salt hydrate solution, respectively;
[0025] The liquid obtained from the separation liquid B is subjected to rotary evaporation to recover the anti-solvent and the second acid molten salt hydrate solution, respectively.
[0026] Preferably, the anti-solvent is one or a mixture of several of methanol, ethanol, butanol, isopropanol, acetone, hexane, tetrahydrofuran and gamma-valerolactone.
[0027] The method provided by the application has the following beneficial effects:
[0028] (1) The method of the present application can obtain five-carbon sugars and six-carbon sugars respectively and retain lignin solids under mild reaction conditions of low temperature (60-100℃), normal pressure and no enzyme, and realizes effective separation of "three elements" of lignocellulose.
[0029] (2) The method of the present application uses an acidic molten salt hydrate solution as a mobile phase to flow through a semi-continuous process of a fixed bed reactor filled with lignocellulose raw materials, which effectively reduces the inhibitors produced by high-temperature degradation of hemicellulose and cellulose under mild conditions.
[0030] (3) The acidic molten salt hydrate system of the method of the present application can selectively break the aromatic ether ester bonds of lignin and remove methoxyl groups, and further form a structure rich in uncondensed units, thereby reducing lignin condensation and maintaining the activity of lignin in subsequent applications.
[0031] (4) The method of the present application has low reaction temperature, and does not need enzyme preparation for cellulose and hemicellulose saccharification, and the acidic molten salt hydrate system can be recycled and reused, which can greatly reduce the production cost compared with the traditional biological refining process. BRIEF DESCRIPTION OF DRAWINGS
[0032] Figure 1 It is a flowchart of the present application.
[0033] Figure 2 It is a sugar concentration change over time in the acidic molten salt hydrate reaction solution of Example 1.
[0034] Figure 3 It is an inhibitor concentration change over time in the acidic molten salt hydrate reaction solution of Example 1.
[0035] Figure 4 It is a nuclear magnetic resonance spectrum of the separated lignin of Example 1. DETAILED DESCRIPTION
[0036] In order to enable those skilled in the art to better understand the present application, the present application will be further described in detail below in combination with specific embodiments.
[0037] Example 1
[0038] 1 g (dry weight) of bamboo chips was mixed with solid support glass beads and uniformly added to a glass chromatographic column with an inlet and an outlet at both ends.
[0039] The first acidic molten salt hydrate solution in the molten salt hydrate storage tank 1 is an acidic lithium bromide hydrate solution, in which the concentration of hydrochloric acid is 40 mmol / L, and the mass fraction of lithium bromide is 50%.
[0040] The second acidic molten salt hydrate solution is an acidic lithium bromide hydrate solution, in which the concentration of hydrochloric acid is 40 mmol / L and the mass fraction of lithium bromide is 65%.
[0041] (1) Pentose extraction and separation: The first acidic molten salt hydrate solution is introduced into the reactor at a flow rate of 0.45 mL / min for 30 min, and the temperature of the reactor is 100°C. The effluent is collected from the outlet to the sugar solution dilution tank.
[0042] Then, the second acidic molten salt hydrate solution is introduced into the reactor at a flow rate of 1.3 mL / min for 5 min, and the temperature of the reactor is 100°C. The effluent is collected from the outlet to the sugar solution dilution tank, and the mixture of the two effluents is labeled as separation liquid A.
[0043] Then, the volume of methanol, which is the anti-solvent, is added to the sugar solution dilution tank, and the volume of methanol is 20 times the volume of separation liquid A. The dilution liquid is obtained. The dilution liquid is introduced into the saccharide crystallization tank, which contains acetone, which is the anti-solvent, and the volume of acetone is 15 times the volume of separation liquid A. The crystallization and sedimentation are carried out at 0°C and 200 rpm for 1 h, and then the solid-liquid separation is carried out by centrifugation. The solid is the crude xylose extract, and the liquid is distilled to recover methanol, acetone and the first acidic molten salt hydrate solution, which are returned to the corresponding containers for reuse.
[0044] (2) Hexose extraction and separation: The second acidic molten salt hydrate solution is introduced into the fixed bed reactor at a flow rate of 0.45 mL / min for 35 min, and the temperature of the reactor is 100°C. The effluent is collected from the outlet to the sugar solution dilution tank, and the mixture is labeled as separation liquid B.
[0045] Then, the volume of methanol, which is the anti-solvent, is added to the sugar solution dilution tank, and the volume of methanol is 20 times the volume of separation liquid B. The dilution liquid is introduced into the saccharide crystallization tank, which contains acetone, which is the anti-solvent, and the volume of acetone is 15 times the volume of separation liquid B. The crystallization and sedimentation are carried out at 0°C and 200 rpm for 1 h, and then the solid-liquid separation is carried out by centrifugation. The solid is the crude xylose extract, and the liquid is distilled to recover methanol, acetone and the first acidic molten salt hydrate solution, which are returned to the corresponding containers for reuse.
[0046] (3) Lignin component separation: The lignin solid residue in the reactor is taken out, washed repeatedly with deionized water until neutral, and freeze-dried at -50°C for 12 h to obtain the lignin solid.
[0047] During the above process of introducing the lithium bromide hydrate solution, samples are taken every 3 minutes, and the concentrations of pentoses (xylose monosaccharides, xylose oligosaccharides) and hexoses (glucose monosaccharides, glucose oligosaccharides) produced by the hydrolysis of hemicellulose and cellulose in the reaction solution change with time as follows: Figure 2The process (1) and (2) above achieve the hydrolysis and separation of hemicellulose and cellulose, respectively. The final yield of soluble five-carbon sugars can reach 77.2%, and the yield of soluble six-carbon sugars can reach 92.5%, among which the yields of xylo-oligosaccharides and gluco-oligosaccharides are 28.4% and 68.1%, respectively. The common inhibitors produced by traditional pretreatment methods of lignocellulose, such as formic acid, acetic acid, levulinic acid, 5-hydroxymethylfurfural, and furfural, have only acetic acid concentration exceeding 1 g / L, and the rest are less than 0.2 g / L Figure 3 ) in this process. Figure 4 The yield of lignin is 92.8% due to the less separation of lignin condensation and the retention of more active β-aryl ether bonds.
[0048] Example 2
[0049] 2 g (dry weight) of corn straw was mixed with solid support glass beads and evenly added into two parallel glass chromatography columns.
[0050] The first acid molten salt hydrate solution was prepared by mixing sulfuric acid with a concentration of 40 mmol / L and zinc chloride with a mass fraction of 30% in the molten salt hydrate storage tank 1.
[0051] The second acid molten salt hydrate solution was prepared by mixing sulfuric acid with a concentration of 40 mmol / L and zinc chloride with a mass fraction of 72% in the molten salt hydrate storage tank 2.
[0052] (1) Five-carbon sugar extraction and separation: The first acid molten salt hydrate solution was introduced into the parallel reactors at a flow rate of 1.3 mL / min for 10 min, and then the second acid molten salt hydrate solution was introduced into the reactors at a flow rate of 1.3 mL / min for 5 min. The reactor temperature was 80°C. The effluent was collected and mixed in the sugar solution dilution tank, and labeled as separation liquid A.
[0053] Then, the anti-solvent ethanol was added for dilution, and the volume of ethanol was 10 times the volume of separation liquid A. The diluted solution was introduced into the sugar crystallization tank, and crystallization and sedimentation were carried out at 25°C and 150 rpm for 5 h, and then solid-liquid separation was carried out by centrifugation. The solid was xylo-oligosaccharide crude extract, and the liquid was distilled to recover ethanol and acid molten salt hydrate solution, which was returned to the corresponding container for repeated use.
[0054] (2) Six-carbon sugar extraction and separation: The second acid molten salt hydrate solution was introduced into the parallel reactors at a flow rate of 1.3 mL / min for 10 min. The reactor temperature was 110°C. The effluent was collected and mixed in the sugar solution dilution tank, and labeled as separation liquid B.
[0055] Then, anti-solvent tetrahydrofuran is added to dilute it, the volume of which is 15 times the volume of separation liquid B, the above dilution is introduced into the saccharide crystallization tank, and crystallization and sedimentation are carried out at 20°C and 150 rpm for 3 h, and then solid-liquid separation is carried out by centrifugation. The solid is a crude oligomeric glucose extract, and the liquid is subjected to distillation to recover tetrahydrofuran and the acidic molten salt hydrate solution respectively, and is returned to the corresponding container for repeated use.
[0056] (3) Lignin component separation: the lignin solid residue in the reactor is taken out, washed repeatedly with deionized water until neutral, and freeze-dried at -45°C for 36 h to obtain a lignin solid.
[0057] The above processes (1) and (2) realize the separate hydrolysis and separation of hemicellulose and cellulose. The final yield of soluble five-carbon sugars can reach 63.2%, and the yield of soluble six-carbon sugars can reach 81.2%, of which the yield of oligomeric xylose and oligomeric glucose is 36.4% and 45.2% respectively. The common inhibitors generated by traditional pretreatment methods of lignocellulose, such as formic acid, acetic acid, levulinic acid, 5-hydroxymethylfurfural and furfural, only have acetic acid with a concentration of more than 1 g / L, and the rest are less than 1 g / L. The separated lignin solid retains more functional groups and linkages, and the yield is 85%.
[0058] Example 3
[0059] 1 g (dry weight) of pine powder is uniformly mixed with solid support glass beads and added to a glass chromatography column.
[0060] The first acidic molten salt hydrate solution is stored in molten salt hydrate storage tank 1, in which the concentration of oxalic acid is 30 mmol / L, and the mass fraction of calcium bromide is 50%.
[0061] The second acidic molten salt hydrate solution is stored in molten salt hydrate storage tank 2, in which the concentration of oxalic acid is 30 mmol / L, and the mass fraction of calcium bromide is 65%.
[0062] (1) Five-carbon sugar extraction and separation: the first acidic molten salt hydrate solution is introduced into the reactor at a flow rate of 0.22 mL / min for 60 min, and then the second acidic molten salt hydrate solution is introduced into the reactor at a flow rate of 1.3 mL / min for 5 min, and the temperature of the reactor is 90°C. The above outflow is collected and mixed in a saccharide dilution tank, and is marked as separation liquid A.
[0063] Then, anti-solvent isopropyl alcohol is added to dilute it, the volume of which is 15 times the volume of separation liquid A, the above dilution is introduced into the saccharide crystallization tank, and crystallization and sedimentation are carried out at 22°C and 250 rpm for 4 h, and then solid-liquid separation is carried out by centrifugation. The solid is a crude oligomeric xylose extract, and the liquid is subjected to distillation to recover isopropyl alcohol and the acidic molten salt hydrate solution respectively, and is returned to the corresponding container for repeated use.
[0064] (2) Separation of six-carbon sugars: The second acidic molten salt hydrate solution was fed into the reactor at a flow rate of 0.22 mL / min for 60 min, and the reactor temperature was 98 °C. The effluent was collected in a sugar dilution tank and labeled as separation liquid B.
[0065] Then, anti-solvent butanol was added to dilute it, and the amount of butanol was 5 times the volume of separation liquid B. The dilution liquid was fed into a sugar crystallization tank, and the crystallization was carried out at 10 °C with stirring at 250 rpm for 2 h, and then the solid-liquid separation was carried out by centrifugation. The solid was the crude oligomeric glucose extract, and the liquid was distilled to recover butanol and acidic molten salt hydrate solution, which was returned to the corresponding container for repeated use.
[0066] (3) Separation of lignin components: The lignin solid residue in the reactor was taken out, washed repeatedly with deionized water until neutral, and freeze-dried at -80 °C for 18 h to obtain lignin solid.
[0067] The above processes (1) and (2) realize the hydrolysis and separation of hemicellulose and cellulose, respectively. The final yield of soluble five-carbon sugars can reach 83.5%, and the yield of soluble six-carbon sugars can reach 89.3%, of which the yields of oligomeric xylose and oligomeric glucose are 47.3% and 67.2%, respectively. The common inhibitors produced by traditional pretreatment of lignocellulose, such as formic acid, acetic acid, levulinic acid, 5-hydroxymethylfurfural, and furfural, have only acetic acid concentration exceeding 1 g / L, and the rest are less than 0.3 g / L. The separated lignin solid retains more functional groups and linkages, and the yield is 65%.
[0068] In this paper, specific examples are used to elaborate the inventive concept in detail. The above examples are only used to help understand the core idea of the invention. It should be noted that any obvious modification, equivalent replacement or other improvement made by those skilled in the art without departing from the inventive concept should be included in the protection scope of the invention.
Claims
1. A method for lignocellulosic semi-continuous saccharification and xylo- and lignin separation, c h a r a c t e r i s e d in that, The method comprises the following steps: (1) uniformly mixing lignocellulose raw material with solid support and adding into a reactor with inlet and outlet at two ends; (2) according to the ratio of 10:1-30:1 of the first acidic molten salt hydrate solution to the lignocellulose raw material, the first acidic molten salt hydrate solution is passed through the reactor from the inlet, the time for passing through the reactor is 10-120 minutes, the temperature of the reactor is 60-100℃, and the effluent liquid rich in five-carbon sugars generated by hemicellulose hydrolysis is collected from the outlet of the reactor; (3) replacing and discharging the first acidic molten salt hydrate solution remaining in the reactor with the second acidic molten salt hydrate solution from the outlet, and collecting the discharge liquid to mix with the effluent liquid of step (2) to obtain separation liquid A; (4) according to the ratio of 10:1-30:1 of the second acidic molten salt hydrate solution to the lignocellulose raw material, the second molten salt hydrate solution is passed through the reactor from the inlet, the time for passing through the reactor is 10-120 minutes, the temperature of the reactor is 80-110℃, and the separation liquid B rich in six-carbon sugars generated by cellulose hydrolysis is collected from the outlet of the reactor; (5) taking out the lignin solid residue obtained after the saccharification reaction of the raw material in the reactor in steps (3) and (4), repeatedly washing with deionized water until neutral, then performing solid-liquid separation and drying to collect and obtain a lignin component; (6) performing sugar and acidic molten salt hydrate separation on the separation liquid A collected in step (3) to obtain five-carbon sugar oligomers; performing sugar and acidic molten salt hydrate separation on the separation liquid B collected in step (4) to obtain six-carbon sugar oligomers; Wherein, steps (5) and (6) are not in order.
2. The method of claim 1, wherein, In the step (1), the lignocellulose raw material is agricultural and forestry waste biomass, including one or a mixture of several of corn stalks, rice stalks, wheat stalks, sorghum stalks, corn cobs, bamboo, birch, pine, spruce, Douglas fir, poplar, birch, sugar cane residue, sugar beet residue, chicory residue, apricot shells, and coconut shells.
3. The method of claim 1, wherein, In the step (1), the reactor includes a fixed bed reactor or a reaction kettle; the reactor is one or more in parallel.
4. The method of claim 1, wherein, The first acidic molten salt hydrate solution and the second molten salt hydrate solution are both composed of acid, molten salt and water, wherein the acid includes one or a mixture of several of hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, nitric acid, formic acid, acetic acid and oxalic acid, and the proton concentration of the acid is 0-100mM; the molten salt is ZnBr2, LiBr, CaBr2, MgBr2, AlBr3, ZnCl2, LiCl, CaCl2, AlCl3.
5. The method of claim 1, wherein, The mass fraction of the molten salt in the first acidic molten salt hydrate solution is 30%-55%; the mass fraction of the molten salt in the second acidic molten salt hydrate solution is 56%-72%.
6. The method of claim 1, wherein, The solid-liquid separation in step (5) includes high-speed centrifugation and suction filtration; the drying is freeze drying or low-temperature vacuum drying; wherein the freeze drying temperature is-80℃ to-45℃, and the freeze drying time is 12-36 hours; the low-temperature vacuum drying temperature is not higher than 60℃, and the time is 12-24 hours.
7. The method of claim 1, wherein, The sugar in step (6) is separated from the acidic molten salt hydrate using anti-solvent precipitation method. Separation liquid A or separation liquid B is mixed with anti-solvent at a volume ratio of 1:5 to 1:35, stirred at a speed of not less than 50 revolutions per minute for 1-5 hours at a temperature of 0-25°C, and then white solid is precipitated and separated by centrifugation; The solid obtained from separation liquid A is an oligomer of five-carbon sugar, and the solid obtained from separation liquid B is an oligomer of six-carbon sugar; The liquid obtained from separation liquid A is subjected to rotary evaporation to recover the anti-solvent and the first acidic molten salt hydrate solution, respectively; The liquid obtained from separation liquid B is subjected to rotary evaporation to recover the anti-solvent and the second acidic molten salt hydrate solution, respectively.
8. The method of claim 7, wherein, The anti-solvent is one or a mixture of several of methanol, ethanol, butanol, isopropanol, acetone, hexane, tetrahydrofuran, and γ-valerolactone.