Eucalyptus autocatalysis hydrothermal pretreatment dissolved matter model construction method and enzymolysis method

Abstract

The invention discloses a eucalyptus autocatalysis hydrothermal pretreatment dissolved matter model construction method and an enzymolysis method, and the method comprises the following steps: carrying out autocatalysis hydrothermal pretreatment on eucalyptus chips under different process conditions, after the reaction is finished, measuring the content of monosaccharide, inhibitor and lignin in a pretreatment solution, and calculating the content of the monosaccharide, the inhibitor and the lignin in the pretreatment solution according to the content of the monosaccharide, the inhibitor and the lignin. The method comprises the following steps: establishing an autocatalytic hydrothermal pretreatment lignin dissolution statistical regression equation, carrying out analysis operation by adopting a least square method, obtaining a minimum value point on an error curved surface by minimizing an error sum of squares, determining an optimal coefficient parameter, obtaining a model function, and fitting the lignin content in a pretreatment solution. The enzymolysis efficiency of the eucalyptus xylan can be improved by 70.67 times to the maximum extent through autocatalytic hydrothermal pretreatment. And a powerful tool is provided for evaluating the pretreatment effect and optimizing process parameters.

Description

Technical Field

[0001] The present invention belongs to the technical field of pulp and paper making, and particularly relates to a method for constructing a model of the self-catalytic hydrothermal pretreatment extractives of eucalyptus wood and an enzymatic hydrolysis method. Background Art

[0002] The statements herein only provide background art related to the present invention and do not necessarily constitute prior art.

[0003] Eucalyptus wood belongs to hardwood and is one of the main raw materials for pulp and paper making. It has the advantages of fast growth, high yield, good resistance and tolerance to infertility, and is known as one of the three major fast-growing tree species in China together with poplar and pine. Eucalyptus wood has a relatively high density and fiber content, and the high-grade products produced in the field of pulp and paper making have performance advantages. The main components of eucalyptus wood include cellulose, hemicellulose and lignin. In hemicellulose, polymannose is wrapped on the surface of cellulose microfibrils, while xylan is connected to lignin through ester bonds and ether bonds to form a framework structure between cellulose microfibrils. This complex and relatively stable structure directly reduces the utilization efficiency of biomass raw materials in pulping and the accessibility of chemical reagents in the reaction process. The pretreatment of lignocellulose can, to a certain extent, destroy its surface and internal complex structure, improve the reaction efficiency and reduce the use of subsequent cooking chemical reagents. In the process of pulp and paper making, pretreatment and enzymatic hydrolysis are the key steps determining the conversion efficiency and cost. The pretreatment of lignocellulose mainly includes physical pretreatment, chemical pretreatment, physicochemical pretreatment and biological pretreatment.

[0004] Hydrothermal pretreatment is one of the most mature pretreatment methods for lignocellulosic raw materials, and the hydrolysis of hemicellulose is a key aspect. Generally speaking, hydrothermal pretreatment also includes adding a small amount of acid or base to the reaction mixture to enhance the pretreatment effect through acid catalysis or base catalysis. Typical hydrothermal pretreatment does not require the addition of chemical reagents. It is the co-blending of water and biomass under high temperature and high pressure to make water autoionize, forming hydronium ions to catalyze the deacetylation of xylan, and the acetic acid obtained provides protons to promote the hydrolysis and saccharification of hemicellulose. Since the reaction system is acidified due to self-catalysis and the formation of carboxylic acids, it can be called self-catalytic hydrothermal pretreatment or autohydrolysis. Eucalyptus wood has a relatively high density and fiber content, and the high-grade products produced in the field of pulp and paper making have performance advantages. However, in the traditional pulp and paper making process, a large amount of hemicellulose and lignin are degraded in the black liquor, and the dissolution of the main components cannot be accurately predicted under different treatment conditions, thus affecting the efficient and accurate separation and regulation of each component of lignocellulose. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a method for constructing a model of the self-catalytic hydrothermal pretreatment extractives of eucalyptus wood and an enzymatic hydrolysis method.

[0006] To achieve the above purpose, the present invention is realized through the following technical solutions:

[0007] In a first aspect, the present invention provides a method for constructing a self-catalytic hydrothermal pretreatment dissolution model of eucalyptus wood, comprising the following steps:

[0008] Subject the eucalyptus wood chips to self-catalytic hydrothermal pretreatment under different process conditions. After the reaction ends, measure the contents of monosaccharides, inhibitors, and lignin in the pretreatment solution, establish a statistical regression equation for lignin dissolution in self-catalytic hydrothermal pretreatment, perform analysis and calculation using the least squares method, obtain the minimum value point on the error surface by minimizing the sum of squared errors, determine the optimal coefficient parameters, obtain the model function, and fit the lignin content in the pretreatment solution to achieve simulation calculation and on-line control of the dissolution of the hydrolysis solution; improve the enzymatic hydrolysis efficiency to improve the high-value utilization efficiency of lignocellulose.

[0009] In some embodiments, the eucalyptus wood chips are 20 - 30 mm in length, 15 - 20 mm in width, and 2 - 5 mm in thickness.

[0010] In some embodiments, the temperature of the self-catalytic hydrothermal pretreatment is 105 - 175 °C, the heat preservation time is 30 - 150 min, and the solid-liquid ratio is 1:3 - 6, and a cross experiment is carried out.

[0011] In some embodiments, the model function is:

[0012]

[0013] X T ∈[105, 175], X t ∈[30, 150], where Y L is the lignin dissolution amount, X T is the reaction time, and X t is the heat preservation time.

[0014] Preferably, when obtaining the model function, the Gauss-Newton method is used to solve the vector parameters.

[0015] Preferably, it further includes the steps of analyzing the fitting degree of the obtained model function and performing a significance test on the overall model.

[0016] In a second aspect, the present invention provides a method for enzymatic hydrolysis of eucalyptus wood, comprising the following steps: subject the eucalyptus wood chips to self-catalytic hydrothermal pretreatment using the optimal self-catalytic hydrothermal pretreatment process parameters obtained by the method for constructing a self-catalytic hydrothermal pretreatment dissolution model of eucalyptus wood;

[0017] Air-dry the pretreated eucalyptus wood and then perform xylanase treatment. The enzyme dosage is 20 - 40 u / g, and the enzymatic hydrolysis time is 40 - 50 h. After the enzymatic hydrolysis is completed, terminate the reaction to obtain the treated eucalyptus wood chips.

[0018] In some embodiments, during autocatalytic hydrothermal pretreatment, the eucalyptus chips have a length of 20 - 30 mm, a width of 15 - 20 mm, and a thickness of 2 - 5 mm.

[0019] Preferably, during xylanase treatment, to make the reaction as complete as possible, the eucalyptus chips subjected to autocatalytic hydrothermal pretreatment are cut so that the eucalyptus chips have a length of 10 - 15 mm, a width of 5 - 8 mm, and a thickness of 2 - 5 mm.

[0020] In some embodiments, the termination of the reaction is to heat and inactivate the reaction mixture in a water bath.

[0021] In some embodiments, during enzymatic hydrolysis reaction, the pH value of the system is adjusted to 4.8 - 5 using a citric acid - sodium citrate buffer solution.

[0022] Preferably, the temperature of the enzymatic hydrolysis reaction is 45 - 55 °C.

[0023] The beneficial effects obtained from one or more of the above embodiments of the present invention are as follows:

[0024] The present invention uses autocatalytic hydrothermal pretreatment of eucalyptus, with the lignin dissolution amount as the response value, and processes the experimental parameter data through the Gauss - Newton method in least squares. This method utilizes the structural information of the model (through the Jacobian matrix). Compared with the simple least - squares gradient descent method, it has a faster convergence speed in some cases and does not require manual selection of the learning rate. The determination coefficient R of the statistical model is obtained 2 = 0.9843, Adjusted R 2 = 0.9817, and the goodness of fit of the model is relatively reliable; the F - distribution and P - value hypothesis test are used to test whether the overall model is significant, F = 377.0577 > F α＝0.01 , and the P - value under this distribution is 0.0000. It is considered that the model is highly significant at the 0.01 level, and the independent variables in the model jointly have a significant explanatory ability for the dependent variable. The enzymatic hydrolysis effect of the eucalyptus chips after autocatalytic hydrothermal pretreatment is analyzed. The dissolution amount of sugar components in the chips with a hydrothermal temperature of 105 - 135 °C is very small and changes little. When the hydrothermal pretreatment temperature is 135 - 165 °C, the dissolution of xylose accelerates and reaches the maximum dissolution amount of 6.35 g / L at 165 °C.

[0025] The present invention provides a powerful tool for evaluating the pretreatment effect and precisely controlling process parameters, and provides a theoretical basis and technical support for the high - value utilization of all components of eucalyptus.

[0026] The use of the autocatalytic hydrothermal pretreatment technology can effectively improve the enzymatic hydrolysis efficiency. Directly performing hydrothermal pretreatment and xylanase treatment on eucalyptus chips before pulping can disrupt the intact structure of lignin, enable more enzymes to participate in the hydrolysis process of hemicellulose, reduce ineffective adsorption, swell the fibers, provide a larger acting area for the enzymes, shorten the enzymatic hydrolysis time, and improve the enzymatic hydrolysis efficiency. It can reduce the energy consumption and chemical usage in subsequent pulping, improve the strength properties of the pulp, and enhance the purity and whiteness of the pulp, which is beneficial for the production of high-quality special papers. Since a large amount of hemicellulose and lignin will degrade in the hydrolysis solution during the pretreatment process, in order to accurately control the dissolution of the main components and abstract and simplify the complex reaction phenomena, a simple and easy-to-implement regression model is selected to predict the dissolution of xylose and lignin under different reaction conditions.

[0027] Through a large number of experiments on the autocatalytic hydrothermal pretreatment of eucalyptus in this invention, it is found that there is a significant correlation between the reaction temperature, holding time and the lignin dissolution amount. By using the Gauss-Newton method to solve the model parameters, the obtained statistical regression equation can achieve more accurate fitting, so as to better understand the relationship between variables and make predictions.

[0028] (2) In this invention, the eucalyptus chips are first subjected to autocatalytic hydrothermal pretreatment and then xylanase treatment, which significantly improves the accessibility of the enzymatic reaction, promotes the further dissolution of glucose and xylose, and improves the hydrolysis efficiency.

[0029] (3) A large amount of experimental data obtained in this invention provides theoretical support for the high-value utilization of all components of eucalyptus. Description of the Drawings

[0030] The specification drawings forming a part of this invention are used to provide a further understanding of this invention. The schematic embodiments of this invention and their descriptions are used to explain this invention and do not constitute an improper limitation to this invention.

[0031] Figure 1 It is the error surface and contour plot of the coefficient parameter a2 of the independent variable reaction temperature and the coefficient parameter a3 of the independent variable holding time of the fitting equation for the embodiments of this invention;

[0032] Figure 2 It is the fitting effect diagram and residual diagram of the reaction temperature and holding time on the lignin dissolution amount under the prediction model of the eucalyptus autocatalytic hydrothermal pretreatment system for the embodiments of this invention;

[0033] Figure 3SEM images of eucalyptus chips before and after enzymatic hydrolysis under different hydrothermal pretreatment conditions of the embodiments of the present invention. Among them, (a-1) is the SEM image of the surface of the original eucalyptus chips, and (b-1), (c-1), and (d-1) are the SEM images of the surface of eucalyptus after autohydrothermal pretreatment at 105°C, 145°C, and 165°C respectively; (a-2) is the SEM image of the surface of the original eucalyptus chips after being treated with xylanase, and (b-2), (c-2), and (d-2) are the SEM images of the surface of eucalyptus under the treatment of xylanase in combination with hydrothermal pretreatment at 105°C, 145°C, and 165°C respectively;

[0034] Figure 4 XRD patterns of eucalyptus before and after being treated with autohydrothermal pretreatment in combination with xylanase in the embodiments of the present invention;

[0035] Figure 5 Dissolution rules of arabinose, galactose, glucose, and mannose under different conditions of autohydrothermal pretreatment of eucalyptus in the embodiments of the present invention;

[0036] Figure 6 Dissolution effects of arabinose, galactose, glucose, mannose, and xylose in the xylanase hydrolysis solution of eucalyptus under different hydrothermal pretreatment conditions in the embodiments of the present invention. Detailed implementation manners

[0037] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0038] The following combines specific embodiments to make a further detailed description of the present invention. It should be noted that the specific embodiments are explanations rather than limitations of the present invention.

[0039] Example 1

[0040] 1. Weigh 50 g of eucalyptus chips with qualified selected size, based on oven-dry weight, and put them into the small tank of a Japanese vertical cooking pot, and add deionized water with a liquid-to-solid ratio of 1:4.

[0041] 2. Set the heating program of the cooking pot. The initial temperature is 20°C, the heating-up time is 90 min, and the reaction temperatures are set to 105°C, 115°C, 125°C, 135°C, 145°C, 155°C, 165°C, and 175°C respectively, and the holding times are set to 30 min, 60 min, 90 min, 120 min, and 150 min respectively.

[0042] 3. After the reaction is completed, release the gas from the cooking pot, cool it, and separate the solid and liquid. Put the liquid into a 4°C refrigerator for testing, and wash the solid and air-dry it in a fume hood.

[0043] 4. Measure the monosaccharides and lignin in the pre-hydrolysate obtained in Step 3. First, perform two-step acid hydrolysis to hydrolyze the polysaccharides into monosaccharides, while forming acid-soluble lignin and Klason lignin. Use 72 wt% H 2 SO 4 Adjust the pH to 3.5 ± 0.2. After centrifugation, wash the precipitate with water until neutral, and obtain Klason lignin after freeze-drying. After centrifugation, dilute the supernatant by an appropriate multiple and measure its absorbance at a wavelength of 205 nm using a UV-visible spectrophotometer. Calculate the acid-soluble lignin using the formula.

[0044] Lignin content = acid-soluble lignin content + Klason lignin content.

[0045] Table 1. Lignin dissolution amounts under different treatment conditions

[0046]

[0047]

[0048] 5. Take a certain amount of the supernatant obtained in Step 4, and digest it at 121 °C for 1 h in a 4 wt% H 2 SO 4 system. After diluting by an appropriate multiple, measure the change in monosaccharide content using an ICS-5000+ ion chromatograph.

[0049] 6. Filter the pre-hydrolysate obtained in Step 3 through a 0.22 μm needle filter into a sample bottle, and measure the content of inhibitors generated by the pre-hydrolysis using an HPLC high-performance liquid chromatograph.

[0050] 7. Through the above, 40 sets of experimental values of lignin dissolution at different reaction temperatures and holding times are obtained. Use 36 sets of data as the training set and 4 sets of data as the validation set to establish a statistical model for lignin dissolution in autocatalytic hydrothermal pretreatment. Assume the model function:

[0051]

[0052] X T ∈[115, 175], X t ∈[30, 150]. When using the least squares method to solve the model parameters, it is necessary to minimize the sum of the squares of the errors between the observed values and the model function, that is, to find the minimum point on the error hypersurface.

[0053]

[0054] In the formula, the vector a is the parameter to be optimized.

[0055] 8. To solve for the vector parameter a, the Gauss-Newton method is introduced. This method is a way to find the minimum point in one-dimensional or multi-dimensional parameter space. To determine the correct iteration direction, this method is sometimes replaced by the Levenberg-Marquardt method. The Levenberg-Marquardt method combines the advantages of the Gauss-Newton method and the gradient descent method and introduces a damping factor. Both the Levenberg-Marquardt method and the Gauss-Newton method can be implemented using the second-order Taylor series expansion to find the minimum point of X 2 (a). Assume that f(x) has infinitely many continuous derivatives near x 0 , and the following function can be obtained:

[0056]

[0057] If x is equal to the sum of x 0 and an offset h, and the offset h is small enough, then the first three terms of the above formula can give a good approximation. The first three terms include the first derivative and the second derivative of f(x) at x 0 , that is:

[0058]

[0059] The parameter vector a = (a 1 a 2 ...a j ...a M ) T determines the dimension of the minimization problem. Substituting the variables in the above formula, we have: x 0 →a; the corresponding step size is h→Δa; substituting the function f(x 0 )→X 2 (a) for Taylor series expansion, the approximate value of the error surface at the new position a + Δa is:

[0060]

[0061] After converting the above formula into matrix form and performing a series of transformations, finally, by solving the normal equation (J T J)Δa = J T r, the parameter adjustment amount Δa is obtained, where J is the Jacobian matrix of the function f(x i |a) with respect to the parameter a, and r is the residual vector.

[0062] After obtaining the parameter vector a, the model function is:

[0063]

[0064] Among them, X T ∈[115, 175], Xt ∈[30, 150], X T is the reaction temperature, and Xt is the heat preservation time.

[0065] 9. A two-sided t-test is performed on the coefficient parameters. At the 0.05 significance level, the critical value t α / 2 = 2.045 can be obtained by looking up the t-distribution table. It is calculated that |t| > t α / 2 , and the P-value is less than 0.05. Then it is considered that this independent variable has a significant effect on the lignin dissolution amount. Among them, a 1 , a 2 and a 4 meet this situation; |t| ≤ t α / 2 , and the P-value is greater than 0.05. The null hypothesis cannot be rejected, and it is considered that the influence of this independent variable on the lignin dissolution amount is not significant. a 3 , a 5 and a 6 belong to this category. Taking the parameters a 2 and a 3 as an example, as Figure 1 , the error surface diagrams of the parameters a 2 and a 3 more intuitively verify that the error of this model is the smallest under this parameter estimation value.

[0066] 10. Perform goodness-of-fit analysis and overall model significance test on the obtained model function. The coefficient of determination R 2 = 0.9843, Adjusted R 2 = 0.9817, and their values are still relatively high, indicating that the model is not overfitted due to excessive addition of parameters, and the goodness-of-fit of the model is relatively reliable; the mean square error MSE is 1.1803. Combining the high R 2 and Adjusted R 2 , it shows that the prediction accuracy of this model is relatively high; use the F-distribution and P-value hypothesis test to test whether the overall model is significant. F = 377.0577 > F α＝0.01 , and the P-value under this distribution is 0.0000. This means that it is almost impossible to obtain such a large F statistic under the condition that the null hypothesis holds. Therefore, we have strong evidence to reject the null hypothesis and consider that the model is highly significant at the 0.01 level, and the independent variables in the model jointly have significant explanatory ability for the dependent variable. According to the regression equation, the influence of the reaction temperature and heat preservation time on the lignin dissolution amount in the autocatalytic hydrothermal pretreatment system can be obtained. As Figure 2 shown in a, with the increase of temperature and the extension of heat preservation time, the lignin dissolution amount shows an increasing trend. From Figure 2 the residual plot in b, the residual points are randomly distributed above and below the zero value, without obvious regular aggregation and systematic deviation, which is a positive signal for the reliability of the model.

[0067] Example 2

[0068] 1. By exploring the optimal conditions of autothermal hydrothermal pretreatment on the hydrolysis effect of xylanase from eucalyptus through the optimal condition group of hydrothermal pretreatment in Example 1, the hydrothermal pretreatment conditions were determined as follows: liquid-to-solid ratio of 1:4, heating-up time of 90 min, heat preservation time of 90 min, and reaction temperature of 105°C - 175°C.

[0069] 2. After the eucalyptus chips obtained through steps 1, 2, and 3 of Example 1 under the experimental conditions of step 1 in Example 3 were washed, dried, and air-dried, 10 g of oven-dry wood chips were weighed and placed in a 50-ml conical flask.

[0070] 3. 0.1 mol / L citric acid solution and sodium citrate solution were prepared and mixed to form a buffer solution with a pH of 4.8 - 5 to dilute xylanase. The dosage of xylanase was 30 u / g, which was added to the conical flask containing 50 g of buffer solution and mixed evenly with the eucalyptus wood chips, and the reaction was carried out on a constant-temperature shaker at 50°C for 48 h.

[0071] 4. After the reaction in step 3 ended, the enzyme reaction was terminated. The conical flask was placed in a water bath preheated to 98°C for inactivation for 20 min, and solid-liquid separation was carried out.

[0072] 5. The hydrolyzate after the xylanase reaction was hydrolyzed into monosaccharides by two-step acidolysis, and acid-soluble lignin was formed simultaneously. 72 wt% H 2 SO 4 was used to adjust the pH to 3.5 ± 0.2. After centrifugation, the supernatant was diluted by an appropriate multiple, and then the absorbance was measured at a wavelength of 205 nm using a UV-visible spectrophotometer, and the acid-soluble lignin was calculated using the formula.

[0073] 1 ml of the centrifuged supernatant was taken, 70 μL of H 2 SO 4 and 930 μL of distilled water were added, and digestion was carried out at 121°C for 1 h under a 4 wt% H 2 SO 4 system. After dilution by an appropriate multiple, it was filtered through a 0.22-μm needle filter into a sample bottle, and the monosaccharide content of different enzyme hydrolysates was measured using an ICS-5000+ ion chromatograph.

[0074] As Figure 5 shown, for the eucalyptus wood pretreated by autothermal hydrothermal pretreatment at 105°C - 135°C, the arabinose, galactose, glucose, xylose, and mannose in the enzyme hydrolysate all increased slowly. When the temperature was further increased to 165°C, the anti-degradation barrier of the wood chips was severely damaged, the structure became loose and porous, which was beneficial for the penetration of xylanase, and the five monosaccharides were violently dissolved, and the xylose dissolution amount was as high as 6.35 g / L.

[0075] When the pretreatment temperature reaches 175 °C, the high-density lignin microspheres formed on the surface of the wood chips block areas such as pits and cell corners, thus forming a barrier that hinders the entry of enzymes into the biomass. Echoing the SEM results, this leads to a decrease in the monosaccharide content in the enzyme reaction solution.

[0076] As can be seen from the data in Table 2, compared with the eucalyptus chips without hydrothermal pretreatment, the enzymatic hydrolysis efficiency of the eucalyptus chips after hydrothermal pretreatment can be increased by up to 70.67 times when treated with xylanase.

[0077] Table 2. Contents of sugars in the xylanase-treated liquids of untreated eucalyptus and eucalyptus pretreated by autocatalytic hydrothermal treatment

[0078]

[0079] 6. The air-dried eucalyptus chips after hydrothermal pretreatment and hydrothermal combined with xylanase treatment were cut into small pieces and then freeze-dried. The dried wood chips were placed on a specimen stage with conductive adhesive, and then sputter-coated with gold to increase their conductivity. After sputter-coating, scanning electron microscopy observations were carried out. Figure 6 SEM images of the eucalyptus surface under different treatment conditions. The surface structure of the original eucalyptus chips ( Figure 3 , a-1) is flat and compact. As the reaction temperature increases, a large amount of lignin and carbohydrates dissolve out, and the surface of the wood chips exfoliates in layers, and the pit membranes gradually rupture ( Figure 3 , b-1, c-1). After further treatment with xylanase, the microfibril fragments on the surface of the wood chips are further removed, and the surface is smoother than that of the wood chips only treated by hydrothermal pretreatment, indicating that xylanase cuts the LCC linkage and a large amount of hemicellulose dissolves out ( Figure 3 , a-2, b-2, c-2).

[0080] When the hydrothermal treatment temperature reaches 165 °C ( Figure 3 , d-1), a large number of microspheres are formed on the surface of the wood chips. The high-density microspheres are formed by the migration of lignin from the cell wall to the wood chips and redeposition or repolycondensation with carbohydrates. A large number of lignin microspheres block areas such as pits and cell corners, which are crucial for the pretreatment liquid and enzymes to pass through the biomass. Therefore, a barrier that hinders the entry of enzymes into the biomass is formed. Therefore, the difference in the surface damage degree between the wood chips treated with xylanase after hydrothermal treatment at 165 °C and those only treated by hydrothermal treatment is not obvious. ( Figure 3 , d-2).

[0081] Select the untreated eucalyptus chips, the hydrothermally pretreated eucalyptus chips and the eucalyptus chips treated by hydrothermal combined with xylanase for crystallinity (XRD) analysis. The crystallinities are 50.87%, 64.31% and 67.87% respectively as Figure 4 shown. First, the three kinds of eucalyptus chips were ground and passed through a 100-mesh sieve, with a scanning step size of 0.0500°, a scanning speed of 20.0° / min, and a scanning range of 5-50°.

[0082] Compared with the untreated eucalyptus chips, the diffraction peak intensity of the eucalyptus wood treated by self-catalyzed hydrothermal pretreatment and hydrothermal combined with xylanase treatment at 22.5° increases, indicating that these two pretreatment methods act on the fiber surface and amorphous regions, removing the substances in some amorphous regions (such as hemicellulose and lignin), making the arrangement of cellulose molecular chains more regular, and the relative increase in the crystalline region, thus resulting in the enhancement of the diffraction peak intensity.

[0083] 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 changes and modifications. 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 constructing a model of eucalyptus autocatalytic hydrothermal pretreatment extract, characterized in that: The steps include: Eucalyptus chips were subjected to autocatalytic hydrothermal pretreatment under different process conditions. After the reaction, the contents of monosaccharides, inhibitors and lignin in the pretreatment liquid were measured. A statistical regression equation for the dissolution of lignin in autocatalytic hydrothermal pretreatment was established. The least squares method was used for analysis and calculation. By minimizing the sum of squared errors, the minimum point on the error surface was obtained, the optimal coefficient parameters were determined, and the model function was obtained. The lignin content in the pretreatment liquid was fitted, and the dissolution amount of lignin under different treatment conditions was accurately predicted to realize the simulation calculation and online control of the hydrolyzate dissolution.

2. The method for constructing a model of eucalyptus autocatalytic hydrothermal pretreatment extract according to claim 1, characterized in that: The eucalyptus wood chips are 20-30 mm long, 15-20 mm wide and 2-5 mm thick.

3. The method for constructing a model of extracts from the autocatalytic hydrothermal pretreatment of eucalyptus according to claim 1, characterized in that: The temperature of the autocatalytic hydrothermal pretreatment is 105-175°C, the holding time is 30-150min, the solid-liquid ratio is 1:4, and a crossover test is performed.

4. The method for constructing a model of eucalyptus autocatalytic hydrothermal pretreatment extract according to claim 1, characterized in that: The model function is: X T ∈[105, 175], X t ∈[30, 150], where Y L is the amount of lignin dissolved, X T is the reaction time, X t For the insulation time.

5. The method for constructing a model of eucalyptus autocatalytic hydrothermal pretreatment extract according to claim 1, characterized in that: When obtaining the model function, the Gauss-Newton method is used to solve the vector parameters; Preferably, the method further includes the steps of performing a fitting degree analysis on the obtained model function and a significance test on the overall model.

6. A method for enzymatic hydrolysis of eucalyptus, characterized in that: The method comprises the following steps: using the preferred autocatalytic hydrothermal pretreatment process parameter group obtained by the method for constructing the autocatalytic hydrothermal pretreatment extract model of eucalyptus according to any one of claims 1 to 5 to perform autocatalytic hydrothermal pretreatment on eucalyptus chips; The pretreated eucalyptus is air-dried and then treated with xylanase, the enzyme dosage is 20-40u / g, the enzymolysis time is 40-50h, and after the enzymolysis is completed, the reaction is terminated to obtain treated eucalyptus chips.

7. The enzymatic hydrolysis method of eucalyptus according to claim 6, characterized in that: During the autocatalytic hydrothermal pretreatment, the eucalyptus wood chips were 20-30 mm long, 15-20 mm wide, and 2-5 mm thick; Preferably, during the xylanase treatment, the eucalyptus chips pretreated by autocatalytic hydrothermal treatment are cut into pieces having a length of 10-15 mm, a width of 5-8 mm, and a thickness of 2-5 mm.

8. The enzymatic hydrolysis method of eucalyptus according to claim 6, characterized in that: The termination reaction is to place the reaction mixture in a water bath and heat it to inactivate it.

9. The enzymatic hydrolysis method of eucalyptus according to claim 6, characterized in that: During the enzymatic hydrolysis reaction, the system uses a citric acid-sodium citrate buffer solution to adjust the pH value to 4.8-5.

10. The enzymatic hydrolysis method of eucalyptus according to claim 6, characterized in that: The temperature of the enzymatic hydrolysis reaction is 45-55°C.

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