Method for improving enzymatic hydrolysis efficiency of corn straw by using potassium ferrate composite solution

Abstract

This invention provides a method for improving the enzymatic hydrolysis efficiency of corn straw using a potassium ferrate composite solution, comprising the following steps: providing a potassium ferrate composite solution, wherein Fe... 6+ The molar concentration was 40.2 mmol / L, ClO ‑ The molar concentration was 704.5 mmol / L, OH ‑ The molar concentration was 2500.1 mmol / L. Corn stalk powder was selected, and its solid-liquid ratio with the potassium ferrate composite solution was 10%. After mixing, the mixture was subjected to isothermal shaking treatment at a temperature of 4-85℃ for 3-48 hours. This invention provides a method for improving the enzymatic hydrolysis efficiency of corn stalks using a potassium ferrate composite solution. This method not only reuses the potassium ferrate composite solution but also disrupts the surface structure of the stalks, removing lignin and some hemicellulose, thus exposing more cellulose and improving the enzymatic hydrolysis efficiency.

Description

Technical Field

[0001] This invention belongs to the field of straw treatment, and in particular relates to a method for improving the enzymatic hydrolysis efficiency of corn straw using potassium ferrate compound solution. Background Technology

[0002] Utilizing lignocellulose to produce biomass energy is one of the effective ways to solve my country's energy and environmental problems. my country has abundant straw resources with enormous utilization potential, but the complex and stubborn structure of lignocellulose hinders its effective utilization. Therefore, pretreatment is necessary to break down this stubborn structure, increase the chances of contact between the internal cellulose and enzymes or microorganisms, and realize the resource utilization of straw.

[0003] Currently, the pretreatment of lignocellulose mainly includes physical, chemical, and biological methods. Among them, chemical methods have attracted much attention in practical applications due to their convenience and economy. Chemical methods refer to the pretreatment of lignocellulose using chemical reagents such as acids, alkalis, and oxidizing agents. In recent years, alkalis (NaOH, Ca(OH)2, KOH) and oxidizing agents (O3, H2O2, permanganate, ClO) have been widely used. - Various methods, including KOH pretreatment, have been successfully applied to the pretreatment of various biomass raw materials. For example, pretreatment of wheat straw with KOH (6% KOH) has shown that it can effectively break down the stubborn structure of the straw and improve its bioconversion rate; pretreatment of corn cobs with KMnO4 in an alkaline environment (pH=11.5-12) has shown that under optimal conditions, the lignin removal rate can reach 46.79%; and the use of eutectic solvents and ClO2 has also been successful. - Combined pretreatment of rice straw resulted in the removal rates of hemicellulose and lignin of 94.9% and 80.2%, respectively.

[0004] Potassium ferrate composite solution is the filtrate remaining after the preparation of potassium ferrate (K2FeO4), which contains a large amount of OH-. - Fe 6+ and ClO - These ions are either alkaline or oxidizing, possessing the potential to oxidize and destroy the stubborn structure of lignocellulose. Using potassium ferrate to prepare filtrate for treating corn stalks reduces the cost of waste alkali treatment and can be applied to the pretreatment of agricultural waste, aligning with the goal of "treating waste with waste" and providing a new approach to the resource utilization of agricultural waste. Summary of the Invention

[0005] One object of the present invention is to provide a method for improving the enzymatic hydrolysis efficiency of corn straw using potassium ferrate compound solution, and to provide at least the advantages described below.

[0006] Another objective of this invention is to provide a method for improving the enzymatic hydrolysis efficiency of corn straw using a potassium ferrate compound solution. This method not only reuses the potassium ferrate compound solution but also disrupts the surface structure of the straw, removes lignin and some hemicellulose, and exposes more cellulose, thereby improving the enzymatic hydrolysis efficiency.

[0007] The technical solution of the present invention is as follows:

[0008] A method for improving the enzymatic hydrolysis efficiency of corn straw using potassium ferrate compound solution includes the following steps:

[0009] Provide potassium ferrate compound solution, in which Fe 6+ The molar concentration was 40.2 mmol / L, ClO - The molar concentration was 704.5 mmol / L, OH - The molar concentration was 2500.1 mmol / L;

[0010] Corn stalk powder was selected, and its solid-liquid ratio with potassium ferrate compound solution was 10%. After the two were mixed, they were subjected to constant temperature oscillation treatment. The constant temperature oscillation temperature was 4-85℃, and the constant temperature oscillation time was 3-48h.

[0011] Preferably, in the method for improving the enzymatic hydrolysis efficiency of corn straw using potassium ferrate composite solution, the potassium ferrate composite solution is the residual filtrate after preparing potassium ferrate, and is prepared using the following steps:

[0012] Excess KOH solid was gradually added to the NaClO solution and stirred continuously in ice water. The effective chlorine concentration in the NaClO solution was 10%.

[0013] Remove solid KCl and excess KOH from the solution to obtain a sodium hypochlorite solution saturated with KOH.

[0014] Pour out the filtrate, heat it, and add Fe(NO3)3ˑ9H2O solid in batches with vigorous stirring. After reacting for 1-2 h, add KOH until a large amount of purplish-black solid precipitates out. Place it in an ice bath, filter it, and collect the filtrate. The purplish-black solid obtained is potassium ferrate, and the collected purplish-red filtrate is the potassium ferrate composite solution.

[0015] Preferably, in the method of improving the enzymatic hydrolysis efficiency of corn stalks using potassium ferrate compound solution, fresh corn stalks are selected, cut into 1-2 cm lengths, air-dried, dried in an oven at 60°C, pulverized, and passed through a 60-mesh sieve to obtain the corn stalk powder.

[0016] Preferably, in the method for improving the enzymatic hydrolysis efficiency of corn straw using potassium ferrate composite solution, the filtrate after constant temperature oscillation treatment can be recycled 0-6 times.

[0017] Preferably, in the method for improving the enzymatic hydrolysis efficiency of corn straw using potassium ferrate composite solution, the potassium ferrate composite solution is stored for 0-96 hours before being mixed with corn straw powder.

[0018] Preferably, in the method for improving the enzymatic hydrolysis efficiency of corn straw using potassium ferrate composite solution,

[0019] The storage time of the potassium ferrate composite solution is 0, 6, 12, 24, 48 or 96 hours;

[0020] The isothermal oscillation treatment temperature is 4, 25, 45, 65 or 85℃;

[0021] The isothermal oscillation treatment time is 3, 6, 12, 24 or 48 hours;

[0022] The filtrate after isothermal oscillation treatment is recycled 0, 1, 2, 3, 4, 5 or 6 times.

[0023] Preferably, the method for improving the enzymatic hydrolysis efficiency of corn straw using potassium ferrate compound solution further includes the following steps:

[0024] The corn stalk powder that has been treated with constant temperature oscillation was sampled, soaked in dilute hydrochloric acid for 30 minutes, then rinsed several times with deionized water, and dried to obtain the enzymatically hydrolyzed saccharified sample at a drying temperature of 60℃.

[0025] The enzymatically hydrolyzed saccharified sample was mixed with a citrate-sodium citrate buffer at a solid-liquid ratio of 2%, pH 4.8, and molar concentration of 0.1 mol / L. Then, cellulase and glucosidase were added for enzymatic hydrolysis and saccharification treatment for 48 h at 50℃. The cellulase content was 50 U / mg, and the glucosidase content was 100 U / g.

[0026] After centrifugation, the supernatant was collected, filtered, and the concentration of reducing sugar in the filtrate was measured. Changes on the surface of the straw were also observed.

[0027] The present invention has the following beneficial effects:

[0028] Potassium ferrate composite solution is the filtrate remaining after the preparation of potassium ferrate, which contains a large amount of Fe. 6+ ,ClO - OH - Ions have the potential to disrupt the stubborn structure of lignocellulose and enhance enzymatic hydrolysis and saccharification.

[0029] Using corn stalks as raw material, and applying them to the pretreatment of compound liquid and subsequent enzymatic hydrolysis and saccharification experiments, the enzymatic hydrolysis and saccharification effect of the fresh compound liquid was the best when the straw was pretreated at 45℃ for 24 h, with a reducing sugar yield as high as 362.92 mg / g, which was 308.88% higher than the control.

[0030] The compound solution disrupts the surface structure of straw, removing lignin and some hemicellulose, thus exposing more cellulose and improving enzymatic hydrolysis efficiency. The main ion involved in the compound solution is OH-. - and ClO - The two have a mutually promoting effect, but no synergistic effect; after 6 cycles, the pretreatment efficiency of the composite liquid decreased by about 55.48%.

[0031] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0032] Figure 1 The graph shows the changing trends of three ions in potassium ferrate compound solution over storage time.

[0033] Figure 2 The effect of different storage times (0-96 h) of potassium ferrate compound solution on the enzymatic hydrolysis and saccharification of corn straw is shown in the figure.

[0034] Figure 3 Figure 1 shows the effect of potassium ferrate compound solution treatment time on the 48-hour enzymatic hydrolysis and saccharification of corn straw.

[0035] Figure 4 The effect of different temperatures (4-85℃) on the enzymatic hydrolysis and saccharification of corn stalks over 48 h is shown in the figure.

[0036] Figure 5 The effect of different ions in potassium ferrate compound solution on the enzymatic hydrolysis and saccharification of corn straw over 48 h is shown in the figure.

[0037] Figure 6 The graph shows the effect of different ions in potassium ferrate compound solution on the content of various components in corn straw.

[0038] Figure 7 SEM images showing the changes in surface morphology of corn stalks before and after treatment;

[0039] Figure 8 Amplitude and 3D height diagrams of corn stalks before and after treatment;

[0040] Figure 9 A diagram showing the changes in surface functional groups of corn stalks before and after treatment;

[0041] Figure 10XRD analysis images of corn stalks before and after treatment;

[0042] Figure 11 The graph shows the effect of the number of times the potassium ferrate compound solution is recycled on the 48-hour enzymatic hydrolysis and saccharification of corn straw. Detailed Implementation

[0043] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0044] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not imply the presence or addition of one or more other elements or combinations thereof.

[0045] Enzymatic hydrolysis yield is a key indicator for evaluating pretreatment efficiency.

[21] Therefore, this invention uses corn stalks as raw material. First, the pretreatment effect of potassium ferrate composite solution is evaluated through enzymatic hydrolysis and saccharification experiments. Second, the mechanism of pretreatment is elucidated by analyzing the changes in chemical composition, microstructure, surface functional groups, crystallinity, and other indicators before and after pretreatment. Finally, the filtrate is recovered to determine the number of times the composite solution can be recycled.

[0046] Materials and Methods

[0047] 1. Experimental Materials

[0048] Corn stalks were sourced from Taigu District, Shanxi Province. Fresh stalks were cut to 1-2 cm, air-dried, and then dried in an oven at 60℃. After pulverization, the stalks were passed through a 60-mesh sieve and stored for later use. The hydrolytic enzymes used were cellulase (50 U / mg) and glucosidase (100 U / g). The reagents used in the experiment, including Fe(NO3)3ˑ9H2O (AR), KOH (AR), NaClO (AR), and 3,5-dinitrosalicylic acid (AR), were all purchased from Tianjin Chemical Reagent Co., Ltd.

[0049] 2 Experimental Design

[0050] 2.1 Preparation of potassium ferrate composite solution

[0051] Excess KOH solid was gradually added to a NaClO solution (10% available chlorine) and stirred continuously in an ice bath. KCl solid and excess KOH were removed from the solution using a G4 sintered glass funnel, yielding a KOH-saturated sodium hypochlorite solution. The filtrate was poured off and heated to a certain temperature in a water bath. Fe(NO3)3ˑ9H2O solid was added in batches with vigorous stirring. After reacting for 1-2 hours, KOH was added until a large amount of purplish-black solid precipitated. The solution was then placed in an ice bath, filtered using a G4 sintered glass funnel, and the filtrate was collected. The purplish-black solid obtained was potassium ferrate, and the collected purplish-red filtrate was the potassium ferrate composite solution.

[0052] 2.2 Preprocessing

[0053] The pretreatment experiment was conducted in a 250 mL Erlenmeyer flask with a solid-liquid ratio of 10% (m / v). The reagent was a potassium ferrate composite solution diluted 1-fold (Fe... 6+ = 40.2 mmol / L; ClO - = 704.5 mmol / L; OH - = 2500.1 mmol / L). The specific operating steps were as follows: First, place the straw powder in an Erlenmeyer flask, add the compound solution, and place the flask in a constant temperature shaker (SHZ-82A, Changzhou, Huaguan). Simultaneously, set different parameters (compound solution storage time: 6, 12, 24, 48, 96 h; pretreatment time: 3, 6, 12, 24, 48 h; pretreatment temperature: 4, 25, 45, 65, 85℃). Samples were taken within the specified time. The obtained samples were soaked in dilute hydrochloric acid for 30 min to remove iron-containing solid residues, then rinsed multiple times with deionized water, dried in a 60℃ oven, weighed, bagged, and stored for later use. All experiments were performed in triplicate.

[0054] Fe alone 6+ ,ClO - OH - The chemical reagents used in the pretreatment experiment were K2FeO4, NaClO and KOH, with concentrations equivalent to the concentrations of each ion in the composite solution. The remaining operating steps were the same as above.

[0055] Collect the pretreated filtrate and cycle it 0, 1, 2, 3, 4, 5, and 6 times (pretreatment) before performing enzymatic hydrolysis and saccharification experiments. The optimal pretreatment conditions determined in the above experiments are used for pretreatment, and the remaining operating steps are the same as above. Add OH- alone... - The treatment served as a control, with a concentration equivalent to the OH in the composite solution at -0 h. - concentration.

[0056] 2.3 Enzymatic hydrolysis and saccharification

[0057] Weigh 0.8 g of the pretreated sample into a 100 mL Erlenmeyer flask, add 0.1 mol / L citrate-sodium citrate buffer solution (pH 4.8, autoclaved) to make the total volume of the enzymatic hydrolysate 40 mL. Then add cellulase (50 U / mg) and glucosidase (100 U / g), respectively, and incubate at 50 °C for 48 h for enzymatic hydrolysis and saccharification. After centrifugation, collect the supernatant, filter, and determine the reducing sugar concentration in the filtrate.

[0058] The formula for calculating reducing sugar content (mg / g) is:

[0059]

[0060] in, C This represents the glucose content (mg) in the sample test tube calculated based on the standard curve. Vt Represents the total volume of the sample extract (mL); W Represents the dry weight of the sample (g); Vs This represents the sample volume (mL) taken during the measurement.

[0061] 3. Measurement Items and Methods

[0062] Spectrophotometry

[22] Fe was measured at a wavelength of 515 nm. 6+ The concentration was determined by adding Ba(NO3)2 to the purplish-red potassium ferrate composite solution. The color of the filtrate was removed by generating the sparingly soluble compound BaFeO4, resulting in a colorless filtrate. Then, iodometric titration was performed on the filtrate.

[23] Determination of ClO in filtrate by titration (phenolphthalein indicator) - and OH - Using DNS method

[24] The concentration of reducing sugars in the solution was determined using the Van Soest method.

[25] The contents of cellulose, hemicellulose, and lignin in straw were determined. After gold sputtering, the surface morphology of straw samples before and after pretreatment was observed using a scanning electron microscope (Regulus 8100, Hitachi, Japan). The straw samples were analyzed using an XRD instrument (Bruker D8 Advance, Germany), and the crystallinity of cellulose was calculated.

[26] After being pressed into KBr pellets, the straw samples were scanned in a PerkinElmer Fourier Transform Infrared Spectrometer (Tensor 27, Bruker, Germany) to determine the changes in surface functional group structure. Atomic force microscopy (AFM) (Bruker Dimension lcon, Bruker, Germany) was used to acquire amplitude maps and three-dimensional height maps of the corn straw samples before and after pretreatment.

[0063] 4. Data Analysis

[0064] Experimental data were organized using Microsoft Excel 2016; graphs were created using Origin Pro 2018; and SPSS was used. P Significance analysis was performed on values ​​<0.05.

[0065] Results and Analysis

[0066] 1. Effect of storage time on the change of ion concentration in the composite solution

[0067] Figure 1 The figure shows the changing trends of three ions in the composite solution over storage time. As can be seen from the figure, at room temperature (25℃), the initial color of the composite solution was purplish-red. With increasing storage time, the Fe content in the solution... 6+ ,ClO - OH - The concentration gradually decreased and gradually stabilized after 48 h, at which point the composite solution contained almost no Fe. 6+ The color of the filtrate also changed from purplish-red to colorless, accompanied by the formation of a reddish-brown precipitate. Figure 1 The above phenomena indicate that the purplish-red Fe in the composite solution... 6+ Unstable, it was completely converted to Fe after 48 hours. 3+ Its relationship with OH - This reaction combines to form a reddish-brown precipitate, Fe(OH)3. The above reaction consumes some OH groups. - (Equation 1), thus leading to OH in the composite solution - Slightly lower. Additionally, the ClO content in the composite solution at room temperature... - It is relatively stable under alkaline conditions; the partial decrease in stability may be due to a small amount of ClO. - Under light, it undergoes a self-decomposition reaction (Equation 2). The possible reaction equations involved above are:

[0068]

[0069] It has been reported that both strong oxidants and alkalis can disrupt the complex and stubborn structure of lignocellulose, improving the efficiency of subsequent enzymatic hydrolysis and saccharification. After 48 hours of storage, the contents of oxidants and alkalis in the composite solution changed, suggesting that storage time affects the pretreatment effect of the composite solution.

[0070] 2. Effect of compound liquid storage time on the enzymatic hydrolysis and saccharification of corn straw

[0071] The sugar production rate from enzymatic hydrolysis is a key indicator for evaluating pretreatment efficiency. Figure 2The effect of storage time (0-96 h) of the compound solution on the enzymatic hydrolysis and saccharification of corn straw was investigated. As shown in the figure, under the conditions of pretreatment time and temperature set at 24 h and 25℃ respectively, the reducing sugar yield of the pretreated sample with fresh compound solution (0 h storage) was the highest, at 312.75 mg / g. With increasing storage time, the reducing sugar yield decreased slightly, but the difference was not significant. P >0.05), while the reducing sugar content of the composite solution stored for 48 h decreased significantly to 287.95 mg / g ( P <0.05%, a decrease of 7.93% compared to the fresh compound solution; in addition, the reducing sugar yield of the compound solution stored for 48 h and 96 h did not differ significantly ( P >0.05). The above phenomena indicate that storage time affects the pretreatment effect of the composite solution; when the storage time is greater than 48 h, the pretreatment efficiency decreases significantly, which may be related to the reduction of the three ions in the composite solution. Figure 1 Therefore, subsequent experiments used fresh compound liquid for straw pretreatment.

[0072] 3. Effect of pretreatment time on enzymatic hydrolysis and saccharification of corn straw

[0073] Figure 3 The effect of pretreatment time on the enzymatic hydrolysis and saccharification of corn straw was investigated. The pretreatment temperature was set at 25℃, and fresh compound solution (stored for 0 h) was used as the reagent. As shown in the figure, after 48 h of enzymatic hydrolysis and saccharification, the yield of reducing sugar in the pretreated sample significantly increased from 183.90 mg / g to 312.75 mg / g as the pretreatment time increased from 3 h to 24 h. P <0.05). When the pretreatment time reached 48 h, the reducing sugar yield of straw was 315.28 mg / g, which was not significantly different from the reducing sugar yield after 24 h of pretreatment. P The value >0.05 indicates that 24 h is the optimal pretreatment time for the composite solution, therefore the pretreatment time for subsequent experiments was set to 24 h.

[0074] 4 Effect of pretreatment temperature on enzymatic hydrolysis and saccharification of corn straw

[0075] Under optimal pretreatment conditions, the effects of different pretreatment temperatures (4-85℃) on the enzymatic hydrolysis and saccharification of corn straw over 48 h were investigated. Figure 4 As shown in the figure, the yield of reducing sugar gradually increases with the increase of pretreatment temperature, indicating that increasing the temperature is beneficial for the compound liquid to break down the stubborn structure of corn straw and promote enzymatic hydrolysis and saccharification; the reasons for the above phenomenon may be: (1) At room temperature, ClO - Under alkaline conditions, Fe 6+ More stable Figure 1 Heating will promote ClO -Decomposition forms highly oxidizing reactive oxygen species [O] (Formula 2), which oxidize and degrade the straw. [35-36] And Fe 6+ Unstable, heating will cause Fe 6+ It reacts rapidly with H2O to form a precipitate, thus losing its oxidizing ability; (2) OH - It can break the hydrogen bonds and ester bonds within lignocellulose; heating can increase the OH groups. - Lignin degradation ability

[37] This disrupts the stubborn structure of the straw.

[0076] However, when the temperature increased from 45℃ to 65℃, the increase in reducing sugar production was not significant. P >0.05), which may be due to the heating temperature of 45℃ causing ClO in the composite solution to increase. - Slow decomposition produces [O], which reacts with OH- - They work together to degrade straw; and when the temperature rises to 65℃, ClO - The rapid decomposition of the straw generates a large amount of [O] in a short period of time. This [O] readily combines with each other to form O2, which is then lost (Formula 3), thus reducing its effect on the straw. Lin Yi et al.

[38] The results show that when the temperature is ≤33℃, the effect of temperature on the decay of available chlorine in sodium hypochlorite is relatively small, while when the temperature is ≥40℃, the effect on the decay of available chlorine increases, which is similar to the conclusions of this study. To fully utilize the ClO in the composite solution... - In order to minimize the energy consumption of pretreatment, subsequent experiments all used a heating temperature of 45℃.

[0077] 5. Mechanistic Analysis

[0078] 5.1 Effects of different ions in the composite solution

[0079] To investigate the mechanism of action of compound liquid pretreatment on corn straw, comparisons were made between untreated (blank) and Fe... 6+ ,ClO - OH - The enzymatic hydrolysis and saccharification effects of straw treated with fresh compound liquor (compound liquor-0 h) and compound liquor stored for 48 h (compound liquor-48 h) were compared. Figure 5 It can be seen that the effects of each treatment are as follows: composite solution - 0 h > composite solution - 48 h > OH - ClO - >Fe 6+ Untreated corn stalks have low enzymatic hydrolysis efficiency because lignin and hemicellulose are encapsulated within natural lignin-cellulose, making it difficult for cellulase to directly contact cellulose during enzymatic hydrolysis. The compound solution-0 h treatment yielded the highest reducing sugar production at 362.92 mg / g, significantly lower than the blank and Fe... 6+ ,ClO- OH - The combined solution treatment at 48 h improved the concentrations by 308.88%, 286.17%, 170.90%, 21.60%, and 9.98%, respectively. The combined solution pretreatment at 0 h was significantly better than the three individual ion treatments (OH-). - ,ClO - Fe 6+ The value is less than the sum of the three, suggesting a promoting effect between ions in the composite solution, but no synergistic effect. (Blank and Fe) 6+ The difference in treatment effects was not significant. P >0.05), the reason may be Fe 6+ It is unstable and readily forms precipitates, thus having little chance of reacting with straw. The pretreatment effect of the compound solution at 48 h was significantly lower than that at 0 h, but still higher than that of OH alone. - The analysis indicates that storage time affects the pretreatment effect of the composite solution; a large amount of OH- will remain in the composite solution after 48 hours of storage. - and ClO - ( Figure 1 There is still a mutually reinforcing effect between them.

[0080] 5.2 Chemical Composition Analysis

[0081] Chemical composition analysis was performed on the pretreated straw. Figure 6 As shown in the figure, Fe alone 6+ The chemical composition of treated and untreated straw is similar, indicating that Fe... 6+ It has no significant effect on any component of straw. However, ClO alone... - The treatment resulted in a decrease in lignin content and an increase in cellulose content, indicating that ClO - It can oxidize and degrade some lignin, thus increasing the relative content of cellulose. OH - The treatments significantly reduced the lignin and hemicellulose content in straw while increasing the relative cellulose content, and the combined liquid-0h and combined liquid-48h treatments further enhanced this effect. The oxidant can oxidize and cleave lignin while preserving cellulose.

[13] Alkali can weaken the hydrogen bonds between cellulose and hemicellulose, as well as the ester bonds between hemicellulose and other components, thereby disrupting the lignin structure and dissolving some of the hemicellulose.

[39] Therefore, this experiment fully demonstrates that ClO - and OH - Both methods can remove lignin and disrupt the dense physical structure of straw, with the effect being even better when the two are mixed. Furthermore, the disruption of the lignin structure increases the enzyme's accessibility to the embedded fibers, promoting subsequent enzymatic hydrolysis. This research result is consistent with... Figure 5 The analysis results are similar.

[0082] 5.3 SEM Analysis

[0083] The surface morphology of straw before and after pretreatment was observed using SEM. Figure 7 af). As shown in the figure, the surface of untreated corn stalks is smooth, flat, and has a compact structure ( Figure 7 a); Fe 6+ The treatment has some effect on the surface morphology of the straw, but it is not significant. Figure 7 b) ClO - After treatment, numerous cracks and fragments began to appear on the surface of the straw. Figure 7 c); and OH - The straw surfaces treated with the compound solution at 0 h and 48 h showed severe damage, becoming very rough and irregular, with numerous pores. Figure 7 (df), among which, the straw treated with the composite liquid-0 h and composite liquid-48 h had a looser structure and more surface pores. The reason for the changes in the straw surface may be ClO - OH - Pretreatment with compound solution can dissolve lignin or part of hemicellulose in corn straw. Figure 5 This process roughens the surface of the straw and causes extensive damage, increasing the surface area of ​​the straw and facilitating the interaction of cellulose hydrolytic enzymes with the interior of the straw.

[0084] 5.4 AFM Analysis

[0085] Amplitude diagrams and 3D height diagrams of corn stalks before and after pretreatment are shown below. Figure 8 As shown, the light and dark features of the AFM image represent the hydrophilicity and hydrophobicity of the corn stalk, with cellulose being hydrophilic (the sugar rings contain hydrophilic hydroxyl groups) and lignin being hydrophobic.

[40] The amplitude diagram of untreated corn stalks was darker, while the amplitude diagram of corn stalks pretreated with the compound solution was brighter, indicating that some lignin was removed and more hydrophilic cellulose was exposed.

[40] Additionally, the roughness parameter R a and R max Table 1 shows the average surface roughness and the maximum vertical distance between the highest and lowest data points, respectively. Higher values ​​indicate a rougher straw surface. The amplitude map of untreated corn straw shows a smooth and even surface, with minimal undulation in the three-dimensional height map. After pretreatment with the composite liquid, the amplitude map of corn straw becomes rough, uneven, and grooved, with significant undulation in the three-dimensional height map. The roughness parameter R for each treatment is... a With R max The values ​​are ranked as follows: Composite solution -0 h > Composite solution -48 h > OH - ClO - >Fe 6+ The blank result further validates the conclusions of the previous sections.

[0086]

[0087] 5.5 FTIR Analysis

[0088] FTIR can be used to measure changes in the functional groups on the surface of corn stalks before and after pretreatment, thereby qualitatively inferring changes in the chemical composition of the stalks. The results are as follows: Figure 9 As shown. Fe alone 6+ The FTIR curves of the treated and untreated samples showed no significant difference, indicating that Fe... 6+ The treatment did not alter the chemical composition of the straw. Wavenumber 3350 cm⁻¹ -1 This represents the stretching vibration of -OH in cellulose, wavenumber 2917 cm⁻¹. -1 The position represents the stretching vibration of cellulose -CH2.

[40] Pretreatment (excluding Fe) 6+ (External processing) can broaden or intensify both peaks; wavenumber 890cm -1 It is a characteristic peak of the β-glycosidic bond between glucose units in cellulose.

[13] Pretreatment (excluding Fe) 6+ The pretreatment (excluding Fe) significantly enhanced the peak intensity at this location, with the highest peak intensities observed in the composite solution-0h and composite solution-48h treatments, indicating that the pretreatment (excluding Fe) significantly enhanced the peak intensity at this location. 6+ (External treatment) can effectively retain cellulose, increasing its relative content, and the composite solution pretreatment has the best effect. At a wavenumber of 1735 cm⁻¹ -1 The absorption peak at that location is a characteristic peak of the uronic acid ester groups of the lignin-hemicellulose complex.

[11] ClO - OH - After pretreatment with the composite solution at 0 h and 48 h, the characteristic peaks at this location essentially disappeared, indicating that the four pretreatment methods can degrade lignin or hemicellulose. Wavenumber 1235 cm⁻¹ -1 The absorption peak at that point corresponds to the stretching vibration of C=O in lignin (guaiacyl).

[11] wavenumber 1605 cm -1 1515 cm -1 and 834 cm -1 The location represents the out-of-plane bending vibration of CH in the syringyl group of lignin.

[41] Pretreatment (excluding Fe) 6+ (External treatment) can weaken the intensity of the above four peaks. After pretreatment with the composite solution at -0 h and -48 h, the above peaks even disappeared completely, indicating that a large amount of lignin in the straw was dissolved after pretreatment, and the composite solution pretreatment had the best effect on removing lignin. In summary, based on the changes in the characteristic peaks after pretreatment, reflecting the changes in chemical composition, and... Figure 6 The trends in chemical composition changes shown are basically consistent.

[0089] 5.6 XRD Analysis

[0090] Figure 10 The images show the XRD patterns of corn stalks before and after pretreatment. The saccharification efficiency of biomass enzymatic hydrolysis is significantly affected by the crystallinity of the cellulose structure; therefore, studying the crystallinity of biomass is crucial for enzymatic hydrolysis and saccharification.

[42] As shown in the figure, the diffraction peaks at 15.94° and 22.16° represent the diffraction intensities in the amorphous and crystalline regions, respectively. The positions of the pretreated corn stalks in both regions remained unchanged, while the diffraction peak intensity in the crystalline region significantly increased, and the peaks became sharper. According to the Segal formula, the crystallinity of the untreated corn stalk raw material was 43.12%. After Fe... 6+ ,ClO - OH - After pretreatment with the composite solution for 0 h and 48 h, the crystallinity increased by 2.99%, 8.21%, 14.94%, 25.26%, and 16.74%, respectively. These results indicate that some amorphous regions, such as soluble polysaccharides, lignin, hemicellulose, and amorphous cellulose, were dissolved, leading to an increase in the relative content of crystalline cellulose.

[43] This is similar to the results of other studies, such as pretreatment with dilute acid, steam explosion, and alkaline H2O2 pretreatment of straw. [41,43-44] As shown in the figure, the crystallinity was highest after pretreatment with the composite solution at 0 h, indicating the highest relative content of crystalline cellulose. This provides more contact opportunities for cellulase, further demonstrating that the composite solution at 0 h pretreatment has the highest cellulose content. Figure 6 In addition, Fe alone 6+ The chemical composition remains essentially unchanged between the treated and untreated samples. Figure 6 However, the crystallinity increased slightly. Figure 10 This may be because of Fe 6+ The treatment process dissolved more readily soluble polysaccharides (amorphous regions).

[0091] 5.7 Analysis of the number of times the composite liquid is recycled

[0092] To evaluate the economic efficiency of composite liquid pretreatment, it is necessary to analyze the recycling and reuse of the composite liquid. Figure 11 For composite liquid and OH - (OH in equivalent composite solution) - The effect of concentration and number of recycling cycles on the enzymatic hydrolysis and saccharification of corn straw was investigated. Results showed that the reducing sugar yield gradually decreased with increasing recycling cycles. After 6 recycling cycles, the reducing sugar yield of the compound solution decreased from the initial 362.92 mg / g to 161.59 mg / g, a reduction of 55.48%. The pretreatment effect of the 0th and 1st recycling cycles of the compound solution was significantly better than that of OH- alone. -As the number of cycles increases, the pretreatment effect of the composite solution is basically equivalent to that of OH alone. - The reason for this treatment may be that some ClO remained in the composite solution during the first recycling. - In subsequent recycling, ClO - Completely decomposed, leaving only OH groups in the end. - Therefore, the first recycling of the composite solution can jointly exert the effects of ClO. - and OH - The effect was that the reducing sugar production only decreased by 14.38% at this time.

[0093] Potassium ferrate compound solution contains Fe 6+ ,ClO - OH - Three ions have the potential to break down the stubborn structure of straw and promote enzymatic hydrolysis and saccharification. After straw pretreatment and enzymatic hydrolysis and saccharification experiments, the following conclusions were drawn: (1) The optimal conditions for pretreatment of the composite liquid were: storage time of 0 h, pretreatment time of 24 h, and pretreatment temperature of 45℃, at which time the reducing sugar yield was 362.92 mg / g; (2) Mechanism studies found that the ion that plays the main role in the pretreatment of the composite liquid is OH. - With ClO - The two promote each other, but do not have a synergistic effect; the composite liquid increases the relative content of cellulose by removing lignin and some hemicellulose, thus promoting the increase of reducing sugar production; (3) SEM, AFM, FTIR and XRD analysis further verified that the composite liquid pretreatment can effectively destroy the complex and stubborn structure of straw. (4) After 6 cycles, the pretreatment efficiency of the composite liquid decreased by about 55.48%. The above results can provide a theoretical basis for the application of waste potassium ferrate filtrate in the pretreatment process of lignocellulose.

[0094] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for improving the enzymatic hydrolysis efficiency of corn straw using potassium ferrate compound solution, characterized in that, Includes the following steps: Provide potassium ferrate compound solution, in which Fe 6+ The molar concentration was 40.2 mmol / L, ClO - The molar concentration was 704.5 mmol / L, OH - The molar concentration was 2500.1 mmol / L; Fresh corn stalks were selected, cut into 1-2 cm lengths, air-dried, dried in an oven at 60℃, pulverized, and passed through a 60-mesh sieve to obtain corn stalk powder. After the potassium ferrate composite solution was stored for 0 hours, corn stalk powder with a solid-liquid ratio of 10% was selected, mixed, and then subjected to constant temperature oscillation treatment at a temperature of 45°C for 24 hours. in; The potassium ferrate composite solution is the remaining filtrate after preparing potassium ferrate, and is prepared using the following steps: Excess KOH solid was gradually added to a NaClO solution and the mixture was kept stirred in ice water. The effective chlorine concentration in the NaClO solution was 10%. Remove solid KCl and excess KOH from the solution to obtain a sodium hypochlorite solution saturated with KOH. Pour out the filtrate, heat it and add Fe(NO3)3ˑ9H2O solid in batches under vigorous stirring. After reacting for 1-2 h, add KOH until a large amount of purplish-black solid precipitates out. Put it in an ice bath, filter it and collect the filtrate. The purplish-black solid obtained is potassium ferrate, and the collected purplish-red filtrate is potassium ferrate composite solution. The filtrate after the isothermal oscillation treatment can be recycled 0 or 1 times.

2. The method for improving the enzymatic hydrolysis efficiency of corn straw using potassium ferrate composite solution as described in claim 1, characterized in that, It also includes the following steps: The corn stalk powder that has been treated with constant temperature oscillation was sampled, soaked in dilute hydrochloric acid for 30 minutes, then rinsed several times with deionized water, and dried to obtain the enzymatically hydrolyzed saccharified sample at a drying temperature of 60℃. The enzymatically hydrolyzed saccharified sample was mixed with a citrate-sodium citrate buffer at a solid-liquid ratio of 2%, with a pH of 4.8 and a molar concentration of 0.1 mol / L. Then, cellulase and glucosidase were added for enzymatic hydrolysis and saccharification treatment for 48 h at a temperature of 50 °C. The cellulase content was 50 U / mg and the glucosidase content was 100 U / g. After centrifugation, the supernatant was collected, filtered, and the concentration of reducing sugar in the filtrate was measured. Changes on the surface of the straw were also observed.

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