Method for improving sugar yield of corn straw through pretreatment of alkaline eutectic solvent
By pretreating corn stalks with alkaline eutectic solvent synthesized by choline hydroxide and 1,3 propylene glycol, the problem of low sugar yield of corn stalks was solved, and the sugar yield was significantly improved and the pretreatment conditions were achieved.
Patent Information
- Application Number
- CN202411676211.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-22
- Publication Date
- 2025-02-25
AI Technical Summary
The sugar production rate of corn stalks is low, which affects the output of subsequent biofuels. The existing pretreatment methods have problems such as harsh reaction conditions, high energy consumption and strong corrosiveness.
Choline hydroxide and 1,3 propylene glycol were used to synthesize an alkaline eutectic solvent, pretreat the corn stalks, destroy their dense structure and promote cellulose enzymatic decomposition.
The sugar production rate of corn stalks has been significantly improved to reach 78.6%~91.5%, and the pretreatment steps have been simplified, with mild conditions and easy to operate.
Smart Images
Figure CN119506379A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of biomass energy, and in particular to a method for improving the sugar yield of corn stalks by pretreatment with an alkaline low eutectic solvent. Background Art
[0002] In recent years, due to the decreasing resources of oil and coal and the increasing concern for the environment worldwide, more and more research has focused on the utilization of sustainable resources. Lignocellulosic biomass is the most abundant sustainable raw material on earth, and its conversion and utilization are seen as an alternative to solve the challenge of fossil fuel shortage. Corn straw is a lignocellulosic biomass, mainly composed of cellulose, hemicellulose and lignin. Cellulose can be converted into reducing sugars by enzymatic hydrolysis, and reducing sugars can be used to further prepare biofuels such as bioethanol and hydrogen. The components of corn straw lignocellulose are intertwined and cross-linked to form a dense three-dimensional structure polymer, in which cellulose and hemicellulose are linked by hydrogen bonds, hemicellulose and lignin are linked by covalent bonds, and polysaccharides are tightly wrapped by lignin. This complex structure hinders the enzymatic hydrolysis of cellulose by cellulase, resulting in the problem of low sugar yield in corn straw, which seriously affects the yield of subsequent biofuel preparation. Therefore, in order to improve the sugar yield of corn straw sugar production, it is necessary to destroy the aggregated structure of lignocellulose and remove the lignin component through pretreatment to improve the enzymatic hydrolysis rate of lignocellulose matrix.
[0003] At present, the main pretreatment methods are physical, chemical, biological and physical and chemical methods, but they generally have problems such as harsh reaction conditions (high temperature and high pressure), high energy consumption, strong corrosiveness, long cycle, and environmental pollution. In 2022, the article "A cyclic process for enzymatic hydrolysis and fermentation of lactic acid pretreated reed" published in the international journal "Industrial Crops and Products" Volume 181 used lactic acid to pretreat reed straw, and the sugar yield of reed straw was increased to 66.43%; Patent CN115976866B disclosed the use of triethylene glycol acid solution system to pretreat sugarcane bagasse, and the enzymatic hydrolysis rate of sugarcane bagasse was increased to 80.1%. The above pretreatment methods all have a certain degree of damage to the structure of the lignocellulosic biomass matrix, which increases the accessibility of cellulase to the substrate, but the sugar yield of biomass still needs to be further improved. Therefore, finding a solvent system that is simple to synthesize, highly efficient, easy to operate, and has mild pretreatment conditions is the focus of current attention. A low eutectic solvent is a new type of green solvent that has shown great application potential in the chemical industry. It usually contains two or three components, which are composed of a hydrogen bond acceptor and a hydrogen bond donor in a certain molar ratio. The present invention proposes a method for improving the sugar yield of corn straw by pretreatment with an alkaline low eutectic solvent. A low eutectic solvent for corn straw pretreatment is synthesized using choline hydroxide and 1,3-propylene glycol. The low eutectic solvent can catalyze the selective dissolution of lignin in corn straw and destroy the aggregated structure of lignocellulose in corn straw, thereby effectively improving the sugar yield of corn straw and providing a basis for promoting the high conversion and utilization of agricultural waste. Summary of the invention
[0004] The present invention aims to solve the problem of low sugar yield of corn stalks and provide a method for improving the sugar yield of corn stalks by pretreatment with an alkaline deep eutectic solvent. The method has a good treatment effect on corn stalks, and the yield of reducing sugar after enzymatic hydrolysis of cellulose in corn stalks after pretreatment is significantly improved, and the sugar yield is increased to 78.6% to 91.5%.
[0005] The method for pretreating corn stalks with a deep eutectic solvent provided by the present invention has the following technical scheme: 1. The corn stalks are dried and crushed, and passed through a 80-100 mesh sieve. The sieved stalk powder is subjected to Soxhlet extraction with anhydrous ethanol, and then dried to obtain a solid residue; 2. Mix 10-15 g of choline hydroxide with a mass fraction of 50% and 250 ml of 1,3-propylene glycol with a mass fraction of 50%-70%, and heat and stir in a magnetic stirring heater until a uniform solution is formed to obtain a choline hydroxide-1,3-propylene glycol low eutectic solvent; 3. The solid residue collected in step 1 and the low eutectic solvent obtained in step 2 are placed in a microreactor, reacted at 90-130° C. for 60-90 min, and the reactor is taken out after the reaction is completed. After cooling to room temperature, the vacuum filtration is performed, and the filtered material residue is washed with an appropriate amount of distilled water until the pH value is neutral. The washed material residue is collected and transferred to a blast drying oven for drying to obtain corn stalk residue pretreated with the low eutectic solvent; Furthermore, in step 1, the drying temperature is 105°C, and the drying is performed until the moisture content in the solid is less than 1.5%; Furthermore, in step 2, the speed of heating and stirring is 650 rpm, and the heating temperature is 65° C.; Furthermore, in step 3, the solid-liquid ratio of the solid residue and the deep eutectic solvent in the reaction kettle is 1 g: (30-50 mL); Furthermore, in step three, the temperature in the drying oven is 55° C., and the solid is dried until the moisture content in the solid is less than 1.5%.
[0006] The advantages of the present invention are as follows: the present invention has a high removal rate of corn stalk lignin and hemicellulose, a good pretreatment effect, and the sugar yield of corn stalk is increased to 78.6% to 91.5%; the steps of synthesizing the choline hydroxide-1,3-propylene glycol low eutectic solvent are relatively simple. The present invention can be used in the field of biomass energy technology. BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Figure 1 Infrared spectra of corn straw before and after pretreatment. DETAILED DESCRIPTION
[0008] The present invention is described in detail below in conjunction with specific implementations and the effects are verified.
[0009] Embodiment 1: The corn stalk pretreatment method of this embodiment is carried out according to the following steps: 1. Place 2-3 cm long air-dried corn stalks in a Tester FW-100 grinder and grind for 30 seconds, then sieve and collect 80-100 mesh stalk powder, dry the stalk powder in a forced air drying oven at 105°C until its moisture content is less than 1.5%, then transfer the dried stalk powder to a Soxhlet extractor, add an appropriate amount of anhydrous ethanol, and extract by Soxhlet method. When the liquid in the Soxhlet extractor is colorless and clear, collect the stalk sample, then place the sample in a forced air drying oven, and dry it at 105°C until the moisture content is less than 1.5%, thereby obtaining a solid residue extracted by anhydrous ethanol; 2. Place a round-bottom flask containing 250 mL of 60% 1,3-propylene glycol on a magnetic stirring heater, slowly add 12.5 g of 50% choline hydroxide into the round-bottom flask under stirring, and react for 0.5 hour at a speed of 650 rpm and a heating temperature of 65°C to obtain a choline hydroxide-1,3-propylene glycol low eutectic solvent after the solution becomes uniform; 3. Take out 5 g of the solid residue collected in step 1 and 200 mL of the low eutectic solvent obtained in step 2, mix them evenly in a microreactor, and react at a heating temperature and heating time of 110°C and 75 minutes. After the reaction is completed, cool the mixture to room temperature, take out the material and filter it under reduced pressure, and use 1 L of distilled water to wash the material until the pH value is neutral. Collect the washed material residue and put it in a forced air drying oven, and dry it at 105°C until the moisture content is less than 1.5%, thereby obtaining corn straw residue pretreated with a low eutectic solvent.
[0010] Example 2: This example differs from Example 1 in that in step 2, 10 g of choline hydroxide with a mass fraction of 50% is added, and the other steps and parameters are the same as those in Example 1.
[0011] Example 3: This example differs from Example 1 in that in step 2, 15 g of choline hydroxide with a mass fraction of 50% is added, and the other steps and parameters are the same as those in Example 1.
[0012] Example 4: This example differs from Example 1 in that in step 3, 150 mL of a low eutectic solvent is added to the reaction kettle, and the other steps and parameters are the same as those in Example 1.
[0013] Example 5: This example differs from Example 1 in that in step 3, 250 mL of a low eutectic solvent is added to the reaction kettle, and the other steps and parameters are the same as those in Example 1.
[0014] Example 6: This example differs from Example 1 in that in step 3, the heating condition of the reactor is 90°C, and the other steps and parameters are the same as those in Example 1.
[0015] Example 7: This example differs from Example 1 in that in step 3, the heating condition of the reactor is 130°C, and the other steps and parameters are the same as those in Example 1.
[0016] Example 8: This example differs from Example 1 in that in step 3, the heating time of the reactor is 60 minutes, and the other steps and parameters are the same as those in Example 1.
[0017] Example 9: This example differs from Example 1 in that in step 3, the heating time of the reactor is 90 minutes, and the other steps and parameters are the same as those in Example 1.
[0018] Example 10: This example differs from Example 1 in that in step 3, the concentration of ethylene glycol added to the reactor is 50%, and the other steps and parameters are the same as those in Example 1.
[0019] Example 11: This example differs from Example 1 in that in step 3, the concentration of ethylene glycol added to the reactor is 70%, and the other steps and parameters are the same as those in Example 1.
[0020] Example 12: This example differs from Example 1 in that the solid residue obtained in step 1 is not pretreated with a subsequent low eutectic solvent, thereby obtaining unpretreated corn straw residue.
[0021] The contents of cellulose, hemicellulose, lignin and ash in the solid residue collected after Soxhlet extraction in step 1 were 41.23%, 21.43%, 14.87% and 22.47%, respectively.
[0022] The reducing sugar yield after enzymatic hydrolysis of the corn straw residue obtained in Examples 1 to 12 was measured. The enzymatic hydrolysis method was based on the method described in the article "Deconstructing sugarcanebagasse lignocellulose by acid-based deep eutectic solvents to enhance enzymatic digestibility" published in Carbohydrate Polymers 2022, No. 298. Cellic CTec2 cellulose complex enzyme was used for enzymatic hydrolysis according to the enzyme load of 30FPU / g TS. 1g of corn straw residue obtained in Examples 1 to 12 was taken out and 0.25 mL of cellulase and 50 mL of citric acid-sodium citrate buffer (0.1mol / L) were added to a blue cap bottle and mixed evenly and placed in a constant temperature shaker at 50°C, and continuously shaken at 150rpm for 72 hours. After the enzymatic hydrolysis experiment was completed, centrifuged at 4000rpm in a centrifuge for 5 minutes. The mixture with the enzymatic hydrolysis residue was filtered through a 0.45μm microporous filter membrane to obtain the enzymatic hydrolyzed sugar solution of the corn straw residue in Examples 1 to 12.
[0023] The total reducing sugar was determined by Agilent 1100 high performance liquid chromatograph, the chromatographic column was C18 (250 mm × 4.6 m, Agilent Technologies, USA), the mobile phases were 100 M sodium phosphate buffer (PH = 6.7) and acetonitrile, the detection wavelength was 250 nm, the column temperature was 30 ° C, the flow rate was 1 mL per minute, and the injection volume was 5 μL. The mass of reducing sugar in the enzymatic hydrolyzate after pretreatment was divided by the mass of cellulose in the corn stalk before pretreatment, then divided by 1.1, and then multiplied by 100% to obtain the sugar yield, and the result was expressed as a percentage.
[0024] Infrared spectra of corn stalks before and after pretreatment Figure 1 As shown in the figure, it can be seen that after being treated with choline hydroxide-1,3-propylene glycol low eutectic solvent, 1508cm -1 The characteristic absorption peak of the aromatic ring skeleton of lignin and the absorption peak of the methoxyl stretching vibration in lignin are 1252 cm -1 The 1728 cm-1 carbonyl stretching vibration of hemicellulose is significantly reduced, indicating that lignin has been effectively removed. -1 The absorption peak at 1634cm disappeared, indicating that the content of hemicellulose decreased. -1 The decrease in the intensity of the absorption peak at also proves the removal of hemicellulose.
[0025] The sugar yield of each embodiment is shown in Table 1. From the information in Table 1, it can be seen that the sugar yield of corn stalks pretreated with the alkaline low eutectic solvent synthesized by choline hydroxide and 1,3-propylene glycol is significantly improved compared with the sugar yield of corn stalks not pretreated, reaching 78.6% to 91.5%.
[0026] Table 1 Sugar yield of corn stover in Examples 1 to 12.
[0027] Example Pre-treatment sample name Sugar yield (%) 1 Deep eutectic solvent pretreatment of corn stover-1 91.5 2 Deep eutectic solvent pretreatment of corn stover-2 85.8 3 Deep eutectic solvent pretreatment of corn stover-3 86.6 4 Deep eutectic solvent pretreatment of corn stover-4 83.9 5 Deep eutectic solvent pretreatment of corn stover-5 90.2 6 Deep eutectic solvent pretreatment of corn stover-6 82.1 7 Deep eutectic solvent pretreatment of corn stover-7 81.5 8 Deep eutectic solvent pretreatment of corn stover-8 78.6 9 Deep eutectic solvent pretreatment of corn stover-9 80.1 10 Deep eutectic solvent pretreatment of corn stover-10 88.2 11 Deep eutectic solvent pretreatment of corn stover-11 84.4 12 Untreated corn stover 23.6
[0028] In summary, the low eutectic solvent of the present invention destroys the dense structure of corn straw, increases the contact area between cellulose and cellulase, and significantly improves the saccharification rate of corn straw, which is of great significance for the high-value utilization of corn straw lignocellulose resources.
Claims
1. A method for improving the sugar yield of corn stalks by pretreatment with an alkaline deep eutectic solvent, characterized in that: The steps include:
1. After crushing the air-dried corn stalks, pass through a 80-100 mesh sieve and dry, perform Soxhlet extraction on the sieved stalk powder with anhydrous ethanol, and obtain a solid residue after drying; 2. Evenly mix a certain amount of choline hydroxide with a mass fraction of 50% and 1,3-propylene glycol, and stir and heat them continuously in a magnetic stirring heater at 650 rpm and 65° C. for 0.5 hour to obtain a choline hydroxide-1,3-propylene glycol low eutectic solvent; 3. The solid residue collected in step 1 and the low eutectic solvent prepared in step 2 are uniformly mixed in a microreactor, and the mixture is heated to react for a certain period of time. After the reaction is completed, the mixture is cooled to room temperature, the material is taken out and filtered under reduced pressure, and the solid residue and the filtrate are collected separately. The solid residue is dried in a forced air drying oven at 105° C. until the moisture content is less than 1.5%, and the corn straw residue treated with the low eutectic solvent is obtained.
2. The method for improving the sugar yield of corn stalks by pretreatment with an alkaline deep eutectic solvent according to claim 1, characterized in that In step 2, the mass fraction of 1,3-propylene glycol is 50% to 70%, and the solid-liquid ratio of choline hydroxide to 1,3-propylene glycol is (10 g to 15 g): 250 mL.
3. The method for improving the sugar yield of corn stalks by pretreatment with an alkaline deep eutectic solvent according to claim 1 or 2, characterized in that In step 3, the ratio of the mass of the solid residue extracted with anhydrous ethanol added to the microreactor to the volume of the low eutectic solvent is 5g: (150mL~250mL), the heating time is 60 minutes~90 minutes, and the heating temperature is 90℃~130℃.