A process for preparing sugar by enzymatic hydrolysis of biomass

Abstract

The present invention belongs to the field of biomass conversion, and in particular to a process for preparing sugar by enzymolysis of biomass, wherein the biomass is pretreated; an enzymolysis aid is prepared, and in the presence of the enzymolysis aid, the pretreated biomass is subjected to enzymatic hydrolysis; after the hydrolysis is completed, the supernatant is taken, the temperature is increased, the enzymolysis aid is precipitated, and an enzymolysis solution is obtained; the enzymolysis aid is cleaned and recycled; the enzymolysis solution is purified and the sugar therein is extracted. The method of the present invention has a wide scope of application, high enzymolysis efficiency, low enzyme input cost, and the enzymolysis aid is easily separated, does not pollute downstream production, and is easily recyclable, with low production cost.

Description

Technical Field

[0001] The present invention belongs to the field of biomass conversion, and in particular relates to a process for preparing sugars by enzymatic hydrolysis of biomass. Background Art

[0002] Biomass such as straw is primarily composed of cellulose, hemicellulose, and lignin. After decomposition, it can produce a variety of high-value-added biological and chemical products, making it an important renewable resource. However, the complex structure of lignocellulose requires pretreatment to increase the porosity of the cellulose, disrupt the crystalline regions of the cellulose, and remove the lignin, thereby improving enzyme accessibility. Not only do the structural characteristics of lignocellulose affect the efficiency of enzymatic hydrolysis, but lignin also adsorbs to cellulases through electrostatic and hydrogen bonding interactions. Furthermore, the hydrophobic groups on lignin can bind to those on cellulases, resulting in ineffective adsorption and affecting the efficiency of cellulase hydrolysis. Enzymes account for 40-60% of the process cost in biomass conversion. Reducing enzymatic hydrolysis costs and improving enzymatic efficiency are key to promoting the industrialization of biomass enzymatic hydrolysis. Summary of the Invention

[0003] In order to solve the problems of high enzymatic hydrolysis cost and low efficiency in the prior art, the present invention mainly provides a method for preparing glucose using biomass with high efficiency and low cost, and the technical solution is as follows:

[0004] A process for preparing sugars by enzymatic hydrolysis of biomass comprises the following steps: pre-treating the biomass; preparing an enzymatic hydrolysis aid, and enzymatically hydrolyzing the pre-treated biomass with the aid of the enzymatic hydrolysis aid; after the hydrolysis is completed, taking the supernatant, raising the temperature, and precipitating the enzymatic hydrolysis aid to obtain an enzymatic hydrolysis solution; washing and recovering the enzymatic hydrolysis aid; and purifying the enzymatic hydrolysis solution to extract the sugars therein.

[0005] Furthermore, the pretreatment includes one or more of mechanical crushing, steam explosion, concentrated acid pretreatment, dilute acid pretreatment, alkali pretreatment, solvent treatment, and ionic liquid delignification.

[0006] Furthermore, the preparation of the enzymatic hydrolysis aid includes the following steps: modifying aluminum oxide hydroxide using an olefin-containing coupling agent to obtain modified aluminum oxide; copolymerizing the modified aluminum oxide with methacryloyloxyethyltrimethylammonium chloride, acrylamide, and N-isopropylacrylamide to obtain the enzymatic hydrolysis aid.

[0007] Furthermore, the olefin-containing coupling agent includes one or more of methacryloxypropyltrimethoxysilane, allyltrimethoxysilane, vinyltri(2-methoxyethoxy)silane, vinyltrimethoxysilane, vinyltriethoxysilane or octenyltrimethoxysilane.

[0008] Furthermore, the mass ratio of the aluminum oxide hydroxide to the olefin-containing coupling agent is 1:0.8-1.5; the mass ratio of the modified aluminum oxide to N-isopropylacrylamide is 1:20-40; the mass ratio of N-isopropylacrylamide to methacryloyloxyethyltrimethylammonium chloride is 1:0.2-0.5; and the mass ratio of N-isopropylacrylamide to acrylamide is 1:0.3-0.6.

[0009] Furthermore, the preparation of the enzymatic hydrolysis aid includes the following steps: placing an olefin-containing coupling agent in ethanol to obtain a coupling agent solution; taking aluminum oxide hydroxide and dispersing it in water, then mixing it with the coupling agent solution, after mixing evenly, reacting it at 70-80° C. for 1-2 hours, separating and collecting the precipitate, washing it thoroughly, and then drying it to obtain modified aluminum oxide;

[0010] Methacryloxyethyltrimethylammonium chloride, acrylamide, and N-isopropylacrylamide are placed in deoxygenated water to obtain a mixed monomer solution; the modified alumina is fully dispersed in ethanol and then mixed with the mixed monomer solution; after uniform mixing, an initiator is added, and the mixture is reacted at 50-75° C. for 5-10 hours under a nitrogen atmosphere; after cooling to room temperature, the product is fully washed to obtain the product.

[0011] Furthermore, the initiator accounts for 1.5-4% of the mass of N-isopropylacrylamide.

[0012] Furthermore, the initiator includes one or more of azobisisobutyronitrile, ammonium persulfate, potassium persulfate or azobisisobutyramidine hydrochloride.

[0013] Furthermore, the preparation of aluminum oxyhydroxide includes the following steps: hydrothermally reacting aluminum nitrate and sodium phosphate at 170-200° C. for 20-28 hours; separating and collecting the precipitate, washing it thoroughly, and then drying it.

[0014] Furthermore, after the hydrolysis is completed, the filtrate is collected by filtration; the temperature is raised to 55-70° C. to precipitate the enzymatic hydrolysis aid, and the enzymatic hydrolysis aid and the enzymatic hydrolysis solution are separated; and the enzymatic hydrolysis aid is cleaned and recovered.

[0015] By adopting the above scheme, the method of the present invention has the following advantages:

[0016] 1. The enzymatic hydrolysis aid of the present invention can weaken the hydrophobic interaction between lignin and cellulase, reduce the charge exposed on the lignin surface, occupy the binding sites on the lignin surface, increase the steric hindrance between lignin and cellulase, and prevent the irreversible adsorption of cellulase on lignin.

[0017] 2. The enzymatic hydrolysis aid of the present invention is temperature-responsive, fully dispersed in the enzymatic hydrolysis system, promoting enzymatic hydrolysis, and capable of phase separation and recovery at high temperatures, making it environmentally friendly and sustainable. Furthermore, N-isopropylacrylamide copolymerizes with the other monomers, increasing their phase separation temperature, allowing them to maintain good dispersibility and working conditions even at the optimal temperature for the enzymatic hydrolysis reaction.

[0018] 3. The enzymatic hydrolysis aid of the present invention contains aluminum oxide, which can form electrostatic adsorption on lignin, occupy the active sites on lignin, change the surface charge, and thus weaken the hydrogen bonds and electrostatic interactions between lignin and cellulase. In addition, the aluminum oxide is fixed by the polymer and can be separated after the enzymatic hydrolysis is completed, which solves the problem that metal ions are difficult to separate and will cause additional impact on subsequent fermentation, product separation, and waste liquid treatment.

[0019] 4. The enzymatic hydrolysis aid of the present invention contains both hydrophilic and hydrophobic groups, which can adsorb to lignin, forming a competitive adsorption with the enzyme, reducing the amount of enzyme adsorbed on lignin. Furthermore, the amphiphilic nature of the enzymatic hydrolysis aid acts as a surfactant, which can promote the desorption of xylanase adsorbed on the lignin surface.

[0020] 5. The present invention combines alumina and polymer through a coupling agent. The coupling agent can not only form a coupling, but also form a hydrogen bond with lignin through ether. The ether bond and hydrocarbon group it carries are similar to the ether structure on the benzene ring, and the compatibility further improves the adsorption performance of the enzymatic hydrolysis aid and lignin.

[0021] 6. The enzymatic hydrolysis aid of the present invention is copolymerized with a cationic monomer and can be adsorbed to lignin via electrostatic attraction. This competitive adsorption reduces unproductive enzyme adsorption on lignin, thereby enhancing enzymatic hydrolysis. Furthermore, the aluminum oxide is located at the outer end of the side chain of the enzymatic hydrolysis aid, providing less steric hindrance than the main chain, making it easier to move freely in the enzymatic hydrolysis system and capture free lignin.

[0022] 7. The preparation process of the present invention is simple, has a wide range of applications, high enzymatic hydrolysis efficiency, low enzyme input cost, and the enzymatic hydrolysis auxiliary agent is easy to separate and will not cause pollution to downstream production. It is easy to recycle and has low production cost, thus achieving sustainable resources. DETAILED DESCRIPTION

[0023] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0024] Example 1: (1) Aluminum nitrate and sodium phosphate were hydrothermally reacted at 180°C for 24 hours; the precipitate was separated and collected, washed thoroughly, and then dried to obtain aluminum oxyhydroxide; 5 g of methacryloxypropyltrimethoxysilane was placed in ethanol to obtain a coupling agent solution;

[0025] (2) 4 g of aluminum hydroxide was dispersed in water and then mixed with the coupling agent solution. After mixing evenly, the mixture was reacted at 70-80 ° C for 1-2 h, and the precipitate was separated and collected. The precipitate was washed three times and dried at 60 ° C to obtain modified aluminum oxide.

[0026] (3) 10 parts by mass of methacryloyloxyethyl trimethylammonium chloride, 15 parts by mass of acrylamide, and 30 parts by mass of N-isopropylacrylamide were placed in water to obtain a mixed monomer solution; 1.2 parts by mass of modified alumina were placed in ethanol and fully dispersed, and then mixed with the mixed monomer solution; after mixing evenly, 0.6 parts by mass of azobisisobutyronitrile was added, and the mixture was reacted at 60°C for 7 hours under a nitrogen atmosphere; after cooling to room temperature, the product was washed 3 times to obtain an enzymatic hydrolysis aid.

[0027] Example 2: The difference from Example 1 is that:

[0028] (1) Aluminum nitrate and sodium phosphate were hydrothermally reacted at 180°C for 24 hours; the precipitate was separated and collected, washed thoroughly, and then dried to obtain aluminum oxide hydroxide; 3 g of methacryloxypropyltrimethoxysilane was placed in ethanol to obtain a coupling agent solution.

[0029] Example 3: The difference from Example 1 is that:

[0030] (1) Aluminum nitrate and sodium phosphate were hydrothermally reacted at 180°C for 24 hours; the precipitate was separated and collected, washed thoroughly, and then dried to obtain aluminum oxide hydroxide; 4 g of vinyltriethoxysilane was placed in ethanol to obtain a coupling agent solution.

[0031] Example 4: The difference from Example 1 is that:

[0032] (3) 6 parts by mass of methacryloyloxyethyl trimethylammonium chloride, 15 parts of acrylamide, and 30 parts of N-isopropylacrylamide were placed in water to obtain a mixed monomer solution; 1.2 parts of modified alumina were fully dispersed in ethanol and then mixed with the mixed monomer solution; after mixing evenly, 0.6 parts of azobisisobutyronitrile was added and the mixture was reacted at 60°C for 7 hours under a nitrogen atmosphere; after cooling to room temperature, the product was fully washed to obtain an enzymatic hydrolysis aid.

[0033] Example 5: The difference from Example 1 is that:

[0034] (3) 15 parts of methacryloyloxyethyl trimethylammonium chloride, 15 parts of acrylamide and 30 parts of N-isopropylacrylamide were placed in water to obtain a mixed monomer solution; 1.2 parts of modified alumina were fully dispersed in ethanol and then mixed with the mixed monomer solution; after mixing evenly, 0.6 parts of azobisisobutyronitrile were added and reacted at 60°C for 7 hours under a nitrogen atmosphere; after cooling to room temperature, the product was fully washed with water to obtain an enzymatic hydrolysis aid.

[0035] Example 6: The difference from Example 1 is that:

[0036] (3) 10 parts by mass of methacryloyloxyethyl trimethylammonium chloride, 15 parts of acrylamide, and 30 parts of N-isopropylacrylamide were placed in water to obtain a mixed monomer solution; 0.75 parts of modified alumina were fully dispersed in ethanol and then mixed with the mixed monomer solution; after mixing evenly, 0.6 parts of azobisisobutyronitrile were added and reacted at 60°C for 7 hours under a nitrogen atmosphere; after cooling to room temperature, the product was fully washed to obtain an enzymatic hydrolysis aid.

[0037] Example 7: The difference from Example 1 is that:

[0038] (3) 10 parts by mass of methacryloyloxyethyl trimethylammonium chloride, 15 parts of acrylamide, and 30 parts of N-isopropylacrylamide were placed in water to obtain a mixed monomer solution; 1.5 parts of modified alumina were fully dispersed in ethanol and then mixed with the mixed monomer solution; after mixing evenly, 0.6 parts of azobisisobutyronitrile was added and reacted at 60°C for 7 hours under a nitrogen atmosphere; after cooling to room temperature, the product was fully washed to obtain an enzymatic hydrolysis aid.

[0039] Example 8: The difference from Example 1 is that:

[0040] (3) 10 parts by mass of methacryloyloxyethyl trimethylammonium chloride, 15 parts of acrylamide, and 30 parts of N-isopropylacrylamide were placed in water to obtain a mixed monomer solution; 1.2 parts of modified alumina were fully dispersed in ethanol and then mixed with the mixed monomer solution; after mixing evenly, 0.6 parts of azobisisobutyronitrile was added and the mixture was reacted at 75°C for 8 hours under a nitrogen atmosphere; after cooling to room temperature, the product was fully washed to obtain an enzymatic hydrolysis aid.

[0041] Example 9: The difference from Example 1 is that:

[0042] (3) 10 parts by mass of methacryloyloxyethyl trimethylammonium chloride, 15 parts of acrylamide, and 30 parts of N-isopropylacrylamide were placed in water to obtain a mixed monomer solution; 1.2 parts of modified alumina were fully dispersed in ethanol and then mixed with the mixed monomer solution; after mixing evenly, 0.6 parts of azobisisobutyronitrile was added and the mixture was reacted at 60°C under a nitrogen atmosphere for 10 hours; after cooling to room temperature, the product was fully washed to obtain an enzymatic hydrolysis aid.

[0043] Comparative Example 1: The difference from Example 1 is:

[0044] 10 parts by mass of methacryloyloxyethyltrimethylammonium chloride, 15 parts of acrylamide, and 30 parts of N-isopropylacrylamide were placed in water to obtain a mixed monomer solution; 0.6 parts of azobisisobutyronitrile was added, and the mixture was reacted at 6°C for 8 hours under a nitrogen atmosphere; after cooling to room temperature, the product was thoroughly washed to obtain an enzymatic hydrolysis aid.

[0045] Comparative Example 2: The difference from Example 1 is:

[0046] 18 parts of acrylamide and 36 parts of N-isopropylacrylamide were placed in water to obtain a mixed monomer solution; 1.2 parts of modified alumina were fully dispersed in ethanol and then mixed with the mixed monomer solution; after uniform mixing, 0.6 parts of azobisisobutyronitrile was added, and the mixture was reacted at 60°C for 7 hours under a nitrogen atmosphere; after cooling to room temperature, the product was fully washed to obtain an enzymatic hydrolysis aid.

[0047] Process example: corn straw is fully dried and then crushed into powder with a D90 of 0.5-0.8 mm; the powder is hydrothermally treated at 200°C for 2 hours to obtain pretreated corn straw; cellulose complex enzyme C2730 is placed in a buffer solution, added to the pretreated corn straw to an enzyme concentration of 5 FPU / g corn straw, and enzymolysis is carried out at 50°C at a speed of 150 r / min for 48 hours; after the hydrolysis is completed, the filtrate is filtered and collected; the temperature is increased to 60°C to precipitate an enzymatic hydrolysis aid, and the enzymatic hydrolysis aid and an enzymatic hydrolysis solution are separated; the enzymatic hydrolysis aid is cleaned and recovered, and the glucose content in the enzymatic hydrolysis solution is determined.

[0048] Example sample test:

[0049] No enzymatic hydrolysis aid was used as a control example. The cellulose content in corn straw was determined using the concentrated sulfuric acid method, and the glucose yield was calculated. The recovered enzymatic hydrolysis aid was washed three times with water and ethanol, and then applied to a new enzymatic hydrolysis experiment according to the method of the process example. The application was repeated 10 times, and the glucose yield of the 10th time was recorded. The results are as follows:

[0050]

[0051] In Example 2, when aluminum oxyhydroxide is modified, the coupling agent added is less than that in Example 1, and the glucose yield is also less than that in Example 1, indicating that the coupling agent is beneficial to improving the adsorption of the enzymolysis aid and xylan and promoting enzymolysis. However, after the enzymolysis aid of Example 2 is recycled 10 times, the glucose yield decreases slightly. This may be because the hydrophobic coupling agent has a certain effect on the phase transition temperature of the enzymolysis aid. The reduction of the hydrophobic group can increase the phase transition temperature, which is beneficial to the recovery of the enzymolysis aid. The coupling agent of Example 3 adopts vinyltriethoxysilane, and the enzymolysis glucose yield decreases. This may be because the chain length of vinyltriethoxysilane is shorter, the degree of freedom of the aluminum oxide at the outer end decreases, and the binding efficiency with lignin also decreases.

[0052] In Example 4, the content of methacryloyloxyethyl trimethylammonium chloride was low, while in Example 5, the content was high. The initial glucose yield in Example 4 decreased significantly, but the glucose yield after the cycle in Example 5 also decreased significantly, indicating that while methacryloyloxyethyl trimethylammonium chloride promotes enzymatic hydrolysis, excessive methacryloyloxyethyl trimethylammonium chloride can affect the recovery of the enzymatic hydrolysis aid. Meanwhile, the higher content of methacryloyloxyethyl trimethylammonium chloride in Example 5 compared to Example 1 did not increase the glucose yield; instead, it decreased slightly, indicating that the content of methacryloyloxyethyl trimethylammonium chloride needs to be controlled within an appropriate range. In Comparative Example 2, no methacryloyloxyethyl trimethylammonium chloride was added to the copolymer, resulting in a significant decrease in glucose yield. In Example 7, the content of modified alumina was increased compared to Example 6, and the initial glucose yield in Example 7 increased significantly, indicating that the content of modified alumina is highly correlated with enzymatic hydrolysis efficiency. The glucose yield after the cycle in Example 7 was not as well maintained as in Example 6, but was similar to that in Example 1, indicating that, unlike the coupling agent alone, the modified alumina after compounding has little impact on the recovery of the enzymatic hydrolysis aid. In Comparative Example 1, no modified alumina was added, and the glucose yield decreased significantly.

[0053] The polymerization reaction temperature of Example 9 is high, and the polymerization time of Example 10 is long. The initial glucose yield of the two examples decreases, and the glucose yield after the cycle decreases significantly, indicating that the enzymatic hydrolysis aid prepared at a higher temperature and for a longer time has a reduced effect on the enzymatic hydrolysis effect and will also have a greater impact on the recovery of the enzymatic hydrolysis aid. It may be that excessive polymerization affects the phase transition temperature of the enzymatic hydrolysis aid.

[0054] Those skilled in the art can make various other corresponding changes and deformations based on the technical solutions and concepts described above, and all of these changes and deformations should fall within the scope of protection of the claims of the present invention.

Claims

1. A process for preparing sugars by enzymatic hydrolysis of biomass, characterized in that: The biomass is pretreated; an enzymatic hydrolysis aid is prepared, and the pretreated biomass is subjected to enzymatic hydrolysis with the participation of the enzymatic hydrolysis aid; after the hydrolysis is completed, the supernatant is collected, the temperature is increased, and the enzymatic hydrolysis aid is precipitated to obtain an enzymatic hydrolysis solution; the enzymatic hydrolysis aid is cleaned and recovered; the enzymatic hydrolysis solution is purified to extract sugars therein; the preparation of the enzymatic hydrolysis aid comprises the following steps: The olefin-containing coupling agent is placed in ethanol to obtain a coupling agent solution; aluminum oxide hydroxide is fully dispersed in water, and then mixed with the coupling agent solution. After mixing evenly, the mixture is reacted at 70-80°C for 1-2 hours, and the precipitate is separated and collected, fully washed, and then dried to obtain modified alumina; Methacryloxyethyltrimethylammonium chloride, acrylamide, and N-isopropylacrylamide are placed in deoxygenated water to obtain a mixed monomer solution; the modified alumina is fully dispersed in ethanol and then mixed with the mixed monomer solution; after mixing evenly, an initiator is added and the mixture is reacted at 50-75°C under a nitrogen atmosphere for 5-10 hours; after cooling to room temperature, the product is fully washed to obtain the product; The mass ratio of the aluminum oxide hydroxide to the olefin-containing coupling agent is 1:0.8-1.5; the mass ratio of the modified aluminum oxide to N-isopropylacrylamide is 1:20-40; the mass ratio of N-isopropylacrylamide to methacryloyloxyethyltrimethylammonium chloride is 1:0.2-0.5; and the mass ratio of N-isopropylacrylamide to acrylamide is 1:0.3-0.

6.

2. The process for preparing sugars by enzymatic hydrolysis of biomass according to claim 1, characterized in that: The pretreatment includes one or more of mechanical crushing, steam explosion, concentrated acid pretreatment, dilute acid pretreatment, alkali pretreatment, solvent treatment, and ionic liquid delignification.

3. The process for preparing sugars by enzymatic hydrolysis of biomass according to claim 1, characterized in that: The olefin-containing coupling agent includes one or more of methacryloxypropyltrimethoxysilane, allyltrimethoxysilane, vinyltri(2-methoxyethoxy)silane, vinyltrimethoxysilane, vinyltriethoxysilane or octenyltrimethoxysilane.

4. The process for preparing sugars by enzymatic hydrolysis of biomass according to claim 1, characterized in that: The initiator accounts for 1.5-4% of the mass of N-isopropylacrylamide.

5. The process for preparing sugars by enzymatic hydrolysis of biomass according to claim 1, characterized in that: The initiator includes one or more of azobisisobutyronitrile, ammonium persulfate, potassium persulfate or azobisisobutyramidine hydrochloride.

6. The process for preparing sugars by enzymatic hydrolysis of biomass according to claim 1, characterized in that: The preparation of the aluminum oxyhydroxide comprises the following steps: Aluminum nitrate and sodium phosphate are hydrothermally reacted at 170-200°C for 20-28 hours; the precipitate is separated and collected, thoroughly washed, and then dried.

7. The process for preparing sugars by enzymatic hydrolysis of biomass according to claim 1, characterized in that: After the hydrolysis is completed, the filtrate is collected by filtration; the temperature is raised to 55-70°C to precipitate the enzymatic hydrolysis aid, and the enzymatic hydrolysis aid and the enzymatic hydrolysis solution are separated; the enzymatic hydrolysis aid is cleaned and recovered.

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