Method for gradient dissociation of castor straws by using hydrated DES
Through the hydrated DES gradient dissociation technology, the problem of incomplete separation of castor straw components and lignin condensation in traditional methods is solved, and efficient separation of xylosol, nano-origin and high-purity cellulose slurry is achieved and multi-product development is achieved, which has enhanced the nanomaterial conversion potential of the product.
Patent Information
- Application Number
- CN202510376146.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-27
- Publication Date
- 2025-06-17
Smart Images
Figure BDA0005332759020000091 
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of separation of agricultural and forestry biomass components, and particularly to a method for dissociating castor straw by using hydrated DES gradient. Background Art
[0002] The information disclosed in the background art of the present invention is only intended to increase the understanding of the overall background of the present invention, and is not necessarily regarded as an admission or an indication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.
[0003] As a green alternative to fossil energy, the efficient conversion technology of biomass resources has become an important research direction for global sustainable development. Among non-grain biomass resources, the annual output of castor straw exceeds ten million tons, but it has not been fully developed. Castor straw is rich in cellulose (38 - 43%), hemicellulose (25 - 28%) and lignin (18 - 22%). Its cell wall structure is similar to that of broad-leaved poplar, but the methoxy content in lignin (14.5 - 16.2%) is significantly higher than that of typical broad-leaved wood (10 - 14%), forming a denser lignocellulose network structure.
[0004] At present, the research on castor straw mainly focuses on traditional low-value-added fields, such as the preparation of artificial boards and activated carbon, etc., and there is no report on high-value refining. For castor straw, the lignin-carbohydrate complex (LCC) is its key structural unit. The three-dimensional network formed by the cross-linking of lignin and carbohydrates (cellulose, hemicellulose) through covalent bonds (phenyl glycosidic bonds, ester bonds, ether bonds, etc.) constitutes a natural anti-degradation barrier, resulting in problems such as incomplete component separation and low cellulase hydrolysis efficiency in traditional acid-base treatment methods, and it is also easy to cause lignin condensation (increase in molecular weight), reducing the potential of product nanomaterial conversion. Therefore, developing a green refining method for castor straw with both high-efficiency depolymerization and product diversification is an urgent problem to be solved. Summary of the Invention
[0005] In view of this, the present invention provides a method for dissociating castor straw by using hydrated DES gradient. The present invention promotes the reaction of castor straw through two-step separation technology of DES with different degrees of hydration, and realizes the development of multiple products such as xylooligosaccharide, highly cellulase-hydrolyzable cellulose products and nano-native lignin.
[0006] In the first aspect, the present invention provides a method for dissociating castor straw by using hydrated DES gradient, including the following steps:
[0007] S1. Mix the castor straw with hydrated DES with a water content of 85-99.5% to carry out the DES-catalyzed hydrolysis reaction. After the reaction is completed, wash the hydrolysis residue with water, collect the washing liquid, which is the liquid rich in xylo-oligosaccharides; continue to wash the hydrolysis residue with the first solvent, and obtain the solid hydrolysis residue after drying;
[0008] S2. Mix the hydrated DES with a water content of 10-50% with the solid hydrolysis residue to carry out the dissociation reaction. After the reaction is completed, add the second solvent for solid-liquid separation, and dry the obtained solid product to obtain the cellulose pulp; concentrate the obtained liquid product, then carry out dialysis and freeze-drying to obtain the nano-native lignin.
[0009] Preferably, the castor straw is in powder form with a particle size of 20-60 mesh.
[0010] Preferably, in step S1, the mass ratio of the castor straw to the water in the hydrated DES is 1:(5-15).
[0011] Preferably, in step S1, the DES-catalyzed hydrolysis reaction is carried out at 150-175 °C for 10-80 min.
[0012] Preferably, the first solvent is an aqueous solution of ethanol or acetone.
[0013] Preferably, the hydrogen bond acceptor of the DES is selected from one of choline chloride, pyrazole, ethanolamine hydrochloride or guanidine hydrochloride; the hydrogen bond donors of the DES include a first hydrogen bond donor and a second hydrogen bond donor. The first hydrogen bond donor is selected from any one of glycolic acid, oxalic acid, citric acid, malonic acid, ferric chloride or silicotungstic acid, and the second hydrogen bond donor is selected from any one of propylene glycol, cysteine, ethylene glycol or glyoxylic acid.
[0014] Further, the molar ratio of the hydrogen bond acceptor to the first hydrogen bond donor is 1:(0.02-5), and the molar ratio of the hydrogen bond acceptor to the second hydrogen bond donor is 1:(5-10).
[0015] Preferably, in step S2, the mass ratio of the solid hydrolysis residue to the hydrated DES is 1:(8-20).
[0016] Preferably, the temperature of the dissociation reaction is 100-160 °C and the reaction time is 0.5-5 h.
[0017] Preferably, the specification of the dialysis bag used for dialysis is 500-2000 Da.
[0018] In the second aspect, the present invention provides a product prepared by the above method, and the product includes xylo-oligosaccharides, nano-native lignin and cellulose pulp.
[0019] Compared with the prior art, the present invention has achieved the following beneficial effects:
[0020] (1) The present invention realizes the directional separation of components through the regulation of the hydration degree gradient: in the S1 stage, a highly hydrated DES is used to preferentially dissociate hemicellulose, and xylooligosaccharides are obtained through the selective cleavage of β-1,4 glycosidic bonds (yield > 50%), while the β-O-4 bond structure of lignin is retained (> 78%); in the S2 stage, the DES with a low hydration degree is switched to disrupt the lignin-cellulose hydrogen bond network, and nano-native lignin is precipitated in situ (yield can reach more than 70%), while the purity of the cellulose pulp can reach more than 90%, forming a stepwise separation path of "hemicellulose saccharification - lignin nanonization - cellulose purification".
[0021] (2) The present invention uses a green DES solvent to replace strong acids and bases, avoiding equipment corrosion and pollution emissions; moreover, the preparation method is simple and easy to implement, with low cost, and is easy to realize industrial production. In addition, the present invention efficiently converts the components of castor straw into three high-value-added products, namely xylooligosaccharides, nano-native lignin, and cellulose pulp, providing technical support for the utilization of castor straw resources. Detailed implementation manners
[0022] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.
[0023] The present invention provides a method for dissociating castor straw by using a hydrated DES gradient, comprising the following steps:
[0024] S1. Mix castor straw with a hydrated DES having a water content of 85 - 99.5%, carry out a DES-catalyzed hydrolysis reaction, wash the hydrolysis residue with water after the reaction is completed, collect the washing liquid, which is a liquid rich in xylooligosaccharides; continue to wash the hydrolysis residue with a first solvent, and dry it to obtain a solid hydrolysis residue;
[0025] S2. Mix a hydrated DES having a water content of 10 - 50% with the solid hydrolysis residue, carry out a dissociation reaction, after the reaction is completed, add a second solvent for solid-liquid separation, dry the obtained solid product to obtain a cellulose pulp; concentrate the obtained liquid product, carry out dialysis and freeze-drying to obtain nano-native lignin.
[0026] Although the traditional acid hydrolysis method can degrade hemicellulose, the strong acid environment causes irreversible condensation of lignin (the breakage rate of β-O-4 bonds > 50%), and the degradation products of hemicellulose are monosaccharides with low added value. In the present invention, highly hydrated deep eutectic solvents (DESs) are used. Through the Brønsted acidity of the hydrogen bond donors in the DESs, the β-1,4 glycosidic bonds of hemicellulose are selectively cleaved by the DES-catalyzed hydrolysis reaction, and xylan is directionally converted into xylo-oligosaccharides. The highly hydrated environment (close to an aqueous solution) greatly reduces the viscosity of the DES system, enhances the permeability to dense straw, and simultaneously inhibits the breakage of lignin β-O-4 ether bonds, laying a structural foundation for subsequent lignin nanosizing.
[0027] Although the existing alkali method or organic solvent method can separate lignin, it will break its β-O-4 bonds, and lignin forms micron-sized aggregates due to condensation, losing its nano-scale characteristics. On the basis of retaining the lignin structure in S1 of the present invention, low-hydration DESs are used. Utilizing the characteristic that the hydrogen bond interaction of DESs is enhanced after the water content is reduced, the hydrogen bond network between lignin and cellulose is preferentially disrupted, prompting lignin to be released in its native nano-scale form. At this stage, the low degree of hydration simultaneously maintains the integrity of the cellulose supramolecular structure. The obtained pulp has a purity of over 90%, and the obtained cellulose pulp product is prone to saccharification reaction.
[0028] In the present invention, the castor straw is in powder form with a particle size of 20 - 60 mesh. The present invention does not impose special restrictions on the way of making it into powder form, and common pulverization methods in the art can be used. The powdered castor straw has a large specific surface area, which promotes the progress of the DES-catalyzed hydrolysis reaction.
[0029] In step S1 of the present invention, the mass ratio of the castor straw to the water in the hydrated DES is 1:(5 - 15). A suitable solid-liquid ratio is conducive to the smooth progress of the reaction.
[0030] In step S1 of the present invention, the DES-catalyzed hydrolysis reaction is carried out at 150 - 175 °C for 10 - 80 min. The catalytic hydrolysis conditions will affect the yield of oligosaccharides and the structure of lignin in the residue. When the catalytic hydrolysis conditions are too mild, hemicellulose cannot be efficiently dissolved; when the reaction conditions are relatively severe, hemicellulose is hydrolyzed into monosaccharides in large quantities, and the lignin structure in the residue is severely damaged.
[0031] In the present invention, the first solvent is an aqueous solution of ethanol or acetone, which is used to remove water-insoluble impurities.
[0032] In the present invention, the hydrogen bond acceptor of the DES is selected from one of choline chloride, pyrazole, ethanolamine hydrochloride or guanidine hydrochloride; the hydrogen bond donors of the DES include a first hydrogen bond donor and a second hydrogen bond donor. The first hydrogen bond donor is selected from any one of glycolic acid, oxalic acid, citric acid, malonic acid, ferric chloride or silicotungstic acid, and the second hydrogen bond donor is selected from any one of propylene glycol, cysteine, ethylene glycol or glyoxylic acid. The first hydrogen bond donor provides H + to catalyze the hydrolysis of hemicellulose, and the second hydrogen bond donor adjusts the polarity of the DES to enhance the solubility of lignin and protect the lignin aryl ether bond structure. Further, the molar ratio of the hydrogen bond acceptor to the first hydrogen bond donor is 1:(0.02 - 5), and the molar ratio of the hydrogen bond acceptor to the second hydrogen bond donor is 1:(5 - 10).
[0033] In the present invention, the hydrated DES in step S1 and step S2 is preferably the same hydrated DES.
[0034] In the present invention, in step S2, the mass ratio of the solid hydrolysis residue to the hydrated DES is 1:(8 - 20). A suitable mass ratio ensures that the DES fully wraps the cellulose-lignin interface and ensures the smooth progress of the dissociation reaction. When the hydrated DES is too little, the low density of castor straw results in that the DES cannot fully infiltrate the raw materials, affecting the mass transfer during the process and making it difficult to effectively separate the components; while when the hydrated DES is too much, it causes waste of reagents and increases costs.
[0035] In the present invention, the temperature of the dissociation reaction is 100 - 160 °C, and the reaction time is 0.5 - 5 h. Too short a reaction time will result in incomplete dissociation reaction, and too long a reaction time may cause agglomeration of lignin particles.
[0036] In the present invention, the specification of the dialysis bag used for dialysis is 500 - 2000 Da, which can effectively remove small molecule impurities (such as DES residues, monosaccharides) and retain lignin nanoparticles.
[0037] The present invention also provides a product prepared by the above method. The product includes xylo-oligosaccharides, native lignin nanoparticles and cellulose pulp. The average size of the native lignin nanoparticles obtained in the present invention is 120 - 200 nm, and its β-O-4 content is higher than 70%.
[0038] The technical solution of the present invention will be further elaborated below in conjunction with specific embodiments. The present invention has no special restrictions on the sources of the reagents used in the following embodiments, and commercially available products well-known to those skilled in the art can be used.
[0039] Example 1
[0040] This example provides a method for dissociating castor straw using hydrated DES in a gradient manner. In this example, DES is choline chloride / ethylene glycol / iron chloride (molar ratio 1:5:0.08), and the DES used in step (1) and step (2) is the same.
[0041] (1) DES-catalyzed hydrolysis reaction: Take 5 g of 20-40 mesh castor straw powder and mix it with 50 g of hydrated DES (mass ratio of DES to water is 2:98), add it to a reaction kettle for DES-catalyzed hydrolysis reaction. Hydrolyze at 150 °C for 60 minutes. After hydrolysis, filter through a glass funnel. First, wash the hydrolysis residue 2 times with 50 ml of deionized water, and collect the solution containing xylooligosaccharides. Then wash the hydrolysis residue 2 times with 50 ml of ethanol aqueous solution (ethanol content 70%), and dry the hydrolysis residue.
[0042] (2) Hydrated DES dissociation reaction: Mix the hydrolysis residue in step (1) with hydrated DES (mass ratio of DES to water is 80:20) at a mass ratio of 1:10 and react under magnetic stirring at 600 rpm, and react at 140 °C for 3 hours. After the reaction is completed, add ethanol aqueous solution (90%) and mix, then filter through a glass crucible until the filtrate is colorless. The filtrate is a solution containing lignin, and the cellulose slurry collected by the glass crucible is dried in an oven at 105 °C until constant weight. The solution is first concentrated by rotary evaporation, add three volumes of deionized water dropwise to the above lignin concentrate, dialyze for three days, and freeze-dry to obtain nano-native lignin. The yield of xylooligosaccharides can reach 58%; the yield of nano-native lignin is 70%, the β-O-4 content is 83%, and the average particle size is 160 nm; the cellulose content in the cellulose slurry is 90%.
[0043] Example 2
[0044] This example provides a method for dissociating castor straw using hydrated DES in a gradient manner. In this example, DES is choline chloride / glyoxylic acid / glycolic acid (molar ratio 1:5:2), and the DES used in step (1) and step (2) is the same.
[0045] (1) DES-catalyzed hydrolysis reaction: Take 5 g of 20-40 mesh castor straw powder and mix it with 50 g of hydrated DES (mass ratio of DES to water is 1:99), add it to a reaction kettle for DES-catalyzed hydrolysis reaction. Hydrolyze at 160 °C for 60 minutes. After hydrolysis, filter through a glass funnel. First, wash the hydrolysis residue 2 times with 50 ml of deionized water, and collect the solution containing xylooligosaccharides. Then wash the hydrolysis residue 2 times with 50 ml of ethanol aqueous solution (ethanol content 70%), and dry the hydrolysis residue.
[0046] (2) Hydrated DES dissociation reaction: Mix the hydrolysis residue in step (1) with hydrated DES (mass ratio of DES to water is 90:10) at a mass ratio of 1:15 and react under magnetic stirring at 700 rpm. React at 130 °C for 2 hours. After the reaction is completed, add an ethanol aqueous solution (90%) and mix, then filter through a glass crucible until the filtrate is colorless. The filtrate is a solution containing lignin, and the cellulose slurry collected by the glass crucible is dried in an oven at 105 °C until constant weight. The solution is first concentrated by rotary evaporation, add three volumes of deionized water dropwise to the above lignin concentrate, dialyze for three days, and freeze-dry to obtain nano-native lignin. The yield of xylo-oligosaccharides can be obtained as 61%; the yield of nano-native lignin is 73%, the β-O-4 content is 78%, and the average particle size is 185 nm; the cellulose content in the cellulose slurry is 92%.
[0047] Example 3
[0048] This example provides a method for dissociating castor straw using hydrated DES gradient. In this example, DES is guanidine hydrochloride / cysteine / silicotungstic acid (molar ratio is 1:5:0.2), and the DES used in step (1) and step (2) is the same.
[0049] (1) DES-catalyzed hydrolysis reaction: Take 5 grams of 20-40 mesh castor straw powder and mix it with 50 g of hydrated DES (mass ratio of DES to water is 0.5:99.5), add it to the reaction kettle for DES-catalyzed hydrolysis reaction. Hydrolyze at 170 °C for 60 minutes. After hydrolysis, filter through a glass funnel. First, wash the hydrolysis residue with 50 ml of deionized water twice to collect the solution containing xylo-oligosaccharides. Then wash the hydrolysis residue with 50 ml of ethanol aqueous solution (ethanol content 70%) twice and dry the hydrolysis residue.
[0050] (2) Hydrated DES dissociation reaction: Mix the hydrolysis residue in step (1) with hydrated DES (mass ratio of DES to water is 60:40) at a mass ratio of 1:10 and react under magnetic stirring at 600 rpm. React at 140 °C for 2 hours. After the reaction is completed, add an ethanol aqueous solution (90%) and mix, then filter through a glass crucible until the filtrate is colorless. The filtrate is a solution containing lignin, and the cellulose slurry collected by the glass crucible is dried in an oven at 105 °C until constant weight. The solution is first concentrated by rotary evaporation, add three volumes of deionized water dropwise to the above lignin concentrate, dialyze for three days, and freeze-dry to obtain nano-native lignin. The yield of xylo-oligosaccharides can be obtained as 62%; the yield of nano-native lignin is 75%, the β-O-4 content is 86%, and the average particle size is 143 nm; the cellulose content in the cellulose slurry is 91%.
[0051] Comparative Example 1
[0052] This comparative example is different from Example 1 in that step (1) is not carried out. The specific steps are as follows:
[0053] Mix 5 g of castor straw powder with a particle size of 20 - 40 mesh and hydrated DES (the mass ratio of DES to water is 80:20) at a mass ratio of 1:10 and react under magnetic stirring at 600 rpm for 3 hours at 140 °C. After the reaction is completed, add an ethanol aqueous solution (90%) and mix, then filter through a glass crucible until the filtrate is colorless. The filtrate is a lignin-containing solution, and the cellulose slurry collected by the glass crucible is dried in an oven at 105 °C until a constant weight is achieved. The solution is first concentrated by rotary evaporation, then three volumes of deionized water are added dropwise to the above lignin concentrate, dialyzed for three days, and freeze-dried to obtain nano-native lignin. The yield of xylo-oligosaccharides is 0%; the yield of nano-native lignin is approximately 58%, the β-O-4 content is 75%, and the average particle size is 230 nm; the cellulose content in the cellulose slurry is 82%.
[0054] Comparative Example 2
[0055] This comparative example is different from Comparative Example 1 in that the mass ratio of DES to water in this comparative example is 20:80.
[0056] The yield of xylo-oligosaccharides obtained in this comparative example is 0%; the yield of nano-native lignin is approximately 32%, the β-O-4 content is 65%, and the average particle size is 350 nm; the cellulose content in the cellulose slurry is 65%.
[0057] Comparative Example 3
[0058] This comparative example provides a traditional sulfuric acid-alkali stepwise treatment method.
[0059] (1) Sulfuric acid pretreatment: React 5 g of castor straw powder with 50 mL of 2 wt% dilute sulfuric acid (pH = 1.5) at 150 °C for 60 min, filter and wash with water to obtain a hemicellulose hydrolysis solution;
[0060] (2) Alkali extraction: React the residue with 50 mL of 10 wt% NaOH solution at 140 °C for 3 h, filter and precipitate lignin with acid.
[0061] The yield of xylo-oligosaccharides obtained in this comparative example is 12%; the product hardly contains nano-native lignin, the average particle size of lignin particles is 3.5 μm, the β-O-4 content is 20%; the cellulose content in the cellulose slurry is 77%.
[0062] Test Example
[0063] Using the cellulose slurries obtained in Examples 1-3 and Comparative Examples 1-3 as substrates, enzymatic hydrolysis reactions were carried out under the same conditions. The reaction conditions were as follows: 2% substrate, the enzyme hydrolysis solution was a citric acid buffer solution with a pH of 5.0, the enzyme hydrolysis temperature was 50 °C, the enzyme dosage was 20 FPU / g of cellulase, and the hydrolysis was carried out for 72 hours. The glucose yields of Examples 1-3 and Comparative Examples 1-3 are summarized in Table 1.
[0064] Table 1 Glucose Yields of Examples 1-3 and Comparative Examples 1-3
[0065]
[0066]
[0067] As can be seen from Table 1, the cellulose prepared by the gradient hydration DES method has better enzymatic hydrolysis effect.
[0068] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.
Claims
1. A method for dissociating castor straw using a hydrated DES gradient, characterized in that: The steps include: S1, mixing castor straw with hydrated DES having a water content of 85-99.5%, performing DES catalytic hydrolysis reaction, washing the hydrolysis residue with water after the reaction is completed, collecting the washing liquid, i.e., a liquid rich in xylooligosaccharides; further washing the hydrolysis residue with the first solvent, and obtaining a solid hydrolysis residue after drying; S2, mixing the hydrated DES with a water content of 10-50% with the solid hydrolysis residue to carry out a dissociation reaction. After the reaction is completed, adding a second solvent to carry out solid-liquid separation, and drying the obtained solid product to obtain a cellulose slurry; concentrating the obtained liquid product, dialyzing it, and freeze-drying it to obtain the original nano lignin.
2. The method according to claim 1, characterized in that The castor straw is in powder form, and its particle size is 20-60 meshes.
3. The method according to claim 1, characterized in that In step S1, the mass ratio of the castor straw to the water in the hydrated DES is 1:(5-15).
4. The method according to claim 1, characterized in that In step S1, the DES catalytic hydrolysis reaction is carried out at 150-175° C. and the reaction time is 10-80 min.
5. The method according to claim 1, characterized in that The first solvent is an aqueous solution of ethanol or acetone.
6. The method according to claim 1, characterized in that The hydrogen bond acceptor of the DES is selected from one of choline chloride, pyrazole, ethanolamine hydrochloride or guanidine hydrochloride; the hydrogen bond donor of the DES includes a first hydrogen bond donor and a second hydrogen bond donor, the first hydrogen bond donor is selected from any one of glycolic acid, oxalic acid, citric acid, malonic acid, ferric chloride or silicotungstic acid, and the second hydrogen bond donor is selected from any one of propylene glycol, cysteine, ethylene glycol or glyoxylic acid.
7. The method according to claim 6, characterized in that The molar ratio of the hydrogen bond acceptor to the first hydrogen bond donor is 1:(0.02-5), and the molar ratio of the hydrogen bond acceptor to the second hydrogen bond donor is 1:(5-10).
8. The method according to claim 1, characterized in that In step S2, the mass ratio of the solid hydrolysis residue to the hydrated DES is 1:(8-20).
9. The method according to claim 1, characterized in that The temperature of the dissociation reaction is 100-160° C., and the reaction time is 0.5-5 h. The specification of the dialysis bag used in the dialysis is 500-2000 Da.
10. The product prepared by the method according to any one of claims 1 to 9, characterized in that: The products include xylooligosaccharides, nano-original lignin and cellulose pulp.