CN111118087B - Lignocellulose pretreatment system based on FeOCl and application thereof - Google Patents
Lignocellulose pretreatment system based on FeOCl and application thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of lignocellulose pretreatment, and particularly relates to a lignocellulose pretreatment system based on FeOCl and application thereof. The effective components of the pretreatment system consist of the following components: 0.2 to 3.5g/L of FeOCl and 0.09 to 1.55mol/L of peroxide; wherein the peroxide is any one of hydrogen peroxide or sodium peroxide or a mixture of two of the hydrogen peroxide and the sodium peroxide in any proportion; the pH value of the pretreatment system is 3 to 8. The pretreatment system can carry out Fenton-like catalytic reaction within the range of pH value of 3 to 8, has short treatment time, and effectively improves the degradation efficiency of lignin and cellulose in the lignocellulose raw material.
Description
Technical Field
The invention belongs to the technical field of lignocellulose pretreatment, and particularly relates to a lignocellulose pretreatment system based on FeOCl and application thereof.
Background
Lignocellulose is a renewable resource with extremely rich yield, is widely distributed around the world, and the reasonable utilization of biomass resources is especially important for solving the increasingly prominent global energy crisis at present. Lignocellulose existing in nature brings great challenges to the conversion and utilization of biomass resources due to the complex and compact structure of the lignocellulose, and lignocellulose pretreated by chemical, physicochemical or biological methods can overcome the recalcitrant structure of the lignocellulose and improve the enzymolysis conversion efficiency of carbohydrates. The existing physical and chemical pretreatment method usually involves severe conditions such as high temperature, high pressure, strong acid and strong base, and a great amount of loss of effective components in raw materials is often caused in the treatment process, and the structure of lignin is seriously damaged, so that the further conversion and utilization of the lignin are influenced. In addition, the existing pretreatment process also has the problems of high energy consumption, environmental pollution and the like.
The fenton reaction is widely used for degrading organic pollutants in the environment. Inspired by the fact that white rot fungi digest lignocellulose through fenton reaction in nature, fenton reaction has also been recently used to pretreat lignocellulose to improve its cellulase hydrolysis efficiency. Kato et al (Kato D M, elia N, flythe M, et al, pretreatment of lignocellustic biological using Fenton chemistry [ J]Bioresource Technology, 2014, 162, 273 to 278) of these four naturally occurring lignocellulosic biomass materials, under the conditions of: 10 Adding 200mL of lignocellulose raw material containing 12.5 mmol of Fe 2+ And 176 mmol H 2 O 2 The solution is treated at room temperature for 120 hours, the materials before and after pretreatment are subjected to enzymolysis after the treatment is finished, and the enzymolysis result shows that the enzymolysis yield of the four biomass raw materials is increased after the solution phase Fenton pretreatment, and the enzymolysis yield of the four biomass raw materials is averagely improved by 212 percent. The homogeneous Fenton reaction based on ferrous ions and peroxide is shown to be an effective biomass pretreatment process. However, the Fenton catalytic reaction has some problems in practical application, such as a large amount of water-soluble Fe 2+ Or Fe 3+ The sludge can not be recycled after the pretreatment, and finally the sludge is formed by precipitation; the utilization rate of the hydrogen peroxide is low, so that the hydrogen peroxide is seriously wasted, and the cost is increased; the reaction is generally carried out under acidic conditions of pH 3, which adversely affect the pretreatment equipment and the structure of the lignocellulose. Therefore, some researches on improving the application of the traditional fenton reaction system in lignocellulose degradation are disclosed in the prior art, for example, patent CN107029791B discloses a fenton-like pretreatment system with nano-diamond supporting noble metal silver, which improves the generation, pH acidity and excessive pH value of iron sludge in the traditional fenton pretreatmentThe utilization rate of hydrogen oxide is low, but the preparation procedure of the Fenton-like catalyst is complex, the use of a noble metal catalyst is involved, and the operation complexity and the pretreatment cost are increased; moreover, the method involves problems of catalyst deactivation, difficult recovery and the like, which limit the practical application effect.
The iron oxychloride (FeOCl) is an orthogonal crystal with a two-dimensional nano-layered structure, is easy to synthesize, and is a good Fenton-like catalytic material. CN107720928A discloses a method for removing organic pollutants in water by using FeOCl as a fenton catalyst, which can rapidly degrade and mineralize organic pollutants in water. At present, feOCl is not applied to lignocellulose pretreatment.
Disclosure of Invention
In order to solve the problems in the prior art, the invention aims to provide a pretreatment system for promoting the degradation of lignocellulose based on FeOCl, the system can perform Fenton-like catalytic reaction within the pH value range of 3-8, the pretreatment time is short, and the degradation efficiency of cellulose in a lignocellulose raw material is effectively improved.
In order to achieve the technical purpose, the invention adopts the following technical scheme:
the lignocellulose degradation pretreatment system based on FeOCl comprises the following effective components:
0.2 to 3.5g/L of FeOCl and 0.09 to 1.55mol/L of peroxide;
wherein the peroxide is one or a mixture of two of hydrogen peroxide and sodium peroxide in any proportion;
the pH value of the pretreatment system is 3 to 8.
Preferably, the effective components of the pretreatment system consist of the following components:
0.8-1.6 g/L FeOCl and 0.78-1.55mol/L hydrogen peroxide.
Based on a general inventive concept, the invention also provides the application of the pretreatment system in the pretreatment of the lignocellulose raw material.
The method for pretreating the lignocellulose raw material by using the pretreatment system comprises the following steps:
weighing a proper amount of lignocellulose raw material, and adding the lignocellulose raw material into a pretreatment system prepared according to the prepared amount; the treatment time is 1 to 12h; the addition amount of the lignocellulose raw material is 1g: 5 to 30mL.
Preferably, the lignocellulose raw material is wood raw material or crop straw; more specifically, the wood material is eucalyptus, beech, pine, birch or poplar; the crop straw is corn straw, wheat straw, sorghum straw, cotton straw or bagasse.
Based on one general inventive concept, the invention also proposes the use of the pretreatment system in the degradation of lignocellulose.
The method for promoting the biodegradation of the lignocellulose raw material by using the pretreatment system specifically comprises the following steps:
(1) Weighing a proper amount of lignocellulose raw material, and adding the lignocellulose raw material into a pretreatment system prepared according to the prepared amount; the treatment time is 1 to 12h;
the addition amount of the lignocellulose raw material is 1g: 5 to 30mL; the lignocellulose raw material is a wood raw material or crop straws;
(2) And (3) treating the treated lignocellulose raw material according to the solid-liquid ratio of 1g: adding 8 to 50mL of the solution into a buffer solution;
the buffer solution is one of citrate buffer solution or phosphate buffer solution or a mixture of the citrate buffer solution and the phosphate buffer solution in any proportion, and the pH range of the buffer solution is 4-6;
(3) Adding lignocellulose degrading enzyme, and carrying out enzymolysis for 12 to 72h at the temperature of 30 to 50 ℃; the addition amount of the lignocellulose degrading enzyme is 5 to 100FPU/g.
Preferably, the pretreatment time of the lignocellulosic feedstock in step (1) above is 6h.
Preferably, the lignocellulose degrading enzyme in the step (3) is a complex enzyme composed of any one or more than two of cellulase, hemicellulase or lignin peroxidase in any proportion; more specifically, the lignocellulose degrading enzyme in step (3) is cellulase.
FeOCl and hydrogen peroxide form a Fenton-like catalytic reaction system, and the Fenton-like catalytic reaction system is applied to pretreatment of lignocellulose degradation; the lignocellulose raw material treated by the pretreatment system is used for biological enzymolysis conversion, and research results show that the pretreatment system can obviously improve the enzymolysis efficiency of the lignocellulose raw material: compared with the treatment time of 72-120h of the traditional Fenton catalytic reaction, the pretreatment system can achieve the optimal treatment effect within 12h, greatly shortens the pretreatment time and improves the treatment efficiency.
The lignocellulose raw material treated by the pretreatment system is applied to separation and extraction of lignin, and research results show that the extraction rate of the lignin in the pretreated raw material is higher than that under the condition of no pretreatment; and the pretreatment system is combined with milder extraction conditions (including an alkaline method and a wood grinding method), so that the molecular structure and functional groups of the obtained lignin are more complete, and the molecular weight distribution is more concentrated.
In addition, the research of the invention also proves that the pretreatment system can exert the catalytic effect within the range of pH value of 3-8, overcomes the defect that the traditional Fenton catalytic reaction can only be carried out under the acidic condition, and is a mild, efficient and high-practicability lignocellulose pretreatment system.
Drawings
FIG. 1 is an XRD analysis pattern of FeOCl prepared;
FIG. 2 is an XPS analysis of FeOOL;
FIG. 3 is an SEM electron micrograph of FeOOL prepared in FIG. 3;
FIG. 4 shows the effect of pretreatment system on the enzymatic hydrolysis of lignocellulose at different pH values;
FIG. 5 shows the effect of different FeOCl additions on the pretreatment effect;
FIG. 6 different H 2 O 2 Influence of the addition amount on the pretreatment effect;
FIG. 7 the effect of different pretreatment times on the pretreatment effect;
FIG. 8 is a Fourier infrared spectrum analysis spectrum of lignin obtained under different extraction conditions;
FIG. 9 is a schematic diagram of aNuclear magnetic resonance spectrum of lignin obtained before and after treatment 1 H-NMR spectrum.
Detailed Description
The present invention will be described in further detail with reference to specific examples.
Relevant experiments of the inventor show that the pretreatment system can obviously improve the degradation efficiency of lignocellulose in the wood raw materials such as eucalyptus, beech, pine, birch and poplar, and crop straws such as corn, wheat, sorghum, cotton and bagasse after pretreatment; in the following examples, the inventor only takes corn stalks as an example to explain the effect, and the used corn stalks are produced in the consolidation city of Henan province; crushing the corn straws, sieving the crushed corn straws with a 60-mesh sieve, and drying the crushed corn straws for later use;
the lignocellulose degrading enzyme used by the invention is a cellulose complex enzyme (CTec 2) which is purchased from Novoxil (China) biotechnology limited company; the embodiment of the invention takes cellulose as an example for specific description; if other components in the lignocellulose raw material, such as hemicellulose, lignin and the like, are used as substrates, other degrading enzymes, such as hemicellulase and lignin peroxidase, can also be selected;
the other various starting materials are all common commercial products or are obtained by methods known to the person skilled in the art or disclosed in the prior art.
Example 1
The FeOCl used in the invention is prepared by the following steps:
putting a proper amount of ferric trichloride hexahydrate into a mortar, fully grinding, and then transferring into a crucible; covering a crucible cover, putting the crucible cover into a muffle furnace, and heating for 60 min at 220 ℃ in an air atmosphere; and taking out the sample, cleaning the sample by using anhydrous acetone, and removing unreacted ferric trichloride to obtain mauve FeOCl.
In order to verify the purity of the FeOCl, the FeOCl is characterized and analyzed by X-ray diffraction, X-ray photoelectron spectroscopy and a Scanning Electron Microscope (SEM);
FIG. 1 is an XRD (X-ray diffraction) spectrum of the prepared FeOCl, and can be seen that the sample prepared by the invention completely corresponds to the standard peak position of the FeOCl, and the diffraction peak has a sharp shape, which indicates that the prepared FeOCl has high purity and complete crystal form;
FIG. 2 is an XPS spectrum of FeOCl, which shows that the valence structure of each element in the obtained FeOCl conforms to the valence and energy level distribution of the element in the FeOCl;
FIG. 3 is an SEM electron micrograph of the prepared FeOCl sample, and it can be seen from the SEM images under different magnifications that the microstructure of the prepared FeOCl is in an obvious layered structure and conforms to the characteristics of the typical layered structure of the FeOCl;
in summary, the FeOCl prepared in this embodiment has a complete structure, and the valence, energy level distribution and microstructure of each element in the compound all conform to the characteristics of typical FeOCl, and the FeOCl is used for subsequent tests.
Example 2
In order to investigate the pretreatment effect of a Fenton-like catalytic reaction system in which FeOOL participates on a lignocellulose raw material, the invention utilizes the FeOOL and hydrogen peroxide to form the Fenton-like reaction system to pretreat corn straws, and then inspects the degradation effect of cellulose in the pretreated corn straws, wherein the specific test process is as follows:
1. test method
(1) Fenton-like pretreatment
Weighing 5g of crushed corn straws, adding the crushed corn straws into a 100mL pretreatment system, treating the corn straws at room temperature for a period of time, and washing and drying a sample for subsequent enzymolysis;
(2) Enzymolysis treatment
Weighing 0.5 g of the treated corn straw sample, placing the corn straw sample into a 50mL triangular flask, adding 20mL of 0.05M citric acid-sodium citrate buffer solution, wherein the pH value of the buffer solution is 4.8; adding cellulose complex enzyme according to the amount of 20 FPU/g dry material, stirring, and performing shake enzymolysis in a shaking table at 50 deg.C and 180 r/min for 48 h; adding an amount of antibiotic (ampicillin) to prevent the growth of microorganisms; after enzymolysis, a proper amount of saccharification liquid is diluted by 10 times with water to determine the sugar concentration.
2. Measurement method
Determination of cellulose, hemicellulose and lignin the determination was carried out according to the biomass trix determination procedure established by the us renewable energy laboratory (NREL);
the sugar concentration is measured by a Dionex P680 high performance liquid chromatograph, and the detector is an RI101 refractive index detector; a hydrogen ion exchange chromatographic column A Minex HPX-87H, the column temperature is 55 ℃, and the used mobile phase is 5 mmol/L H 2 SO 4 (pH 2.0) and a flow rate of 0.6 mL/min.
3. Formula for calculation
The following formula for calculating the retention of cellulose, hemicellulose and lignin is shown in formula 1:
4. Results and analysis
4.1 Effect of pretreatment on the major constituents in corn stover
In order to investigate the influence of the pretreatment system consisting of FeOOCl on the components of the corn stalks, 5g of the corn stalks were placed in a 100mL pretreatment system for treatment for 12h, wherein the addition amount of FeOOCl was 0.16g 2 O 2 0.78mol/L; after treatment, determining the content of lignin, cellulose and hemicellulose in the corn straws, and calculating the retention rate;
through determination, the retention rate of lignin, cellulose and hemicellulose in the pretreated corn straws is 94.34%, 93.56% and 93.79%; the pretreatment process can cause the loss of partial components in the raw materials, which is inevitable, but after the pretreatment system is used for pretreating the corn straws, the retention rate of the three elements in the sample exceeds 93 percent, which indicates that the pretreatment system is a mild pretreatment system and has little influence on the content of the three elements in the corn straws.
4.2 Effect of the pH value of the pretreatment System on the treatment Effect
Next, we investigated the degradation effect of pretreatment systems on cellulose in corn stalks under different pH conditions: respectively adjusting the pH value of the pretreatment system to 3, 4, 5, 6, 7 and 8, treating for 24 hours, and then washing and drying a sample; adding the pretreated corn straws into a biological enzymolysis reaction system for enzymolysis, determining the sugar concentration in an enzymolysis solution, and converting the sugar concentration and the amount of the added corn straws into sugar content (the unit is g/100g, and the sugar content is expressed by the amount of sugar generated by 100g of straws); three groups of parallels are arranged in the test, and the test results are averaged;
the sugar content of the enzymolysis liquid obtained after 48h enzymolysis of corn stalks under different pH values is shown in figure 4;
it can be seen that after the corn straws are treated by the pretreatment systems under different pH values, the sugar content in the enzymolysis liquid has no obvious difference; the Fenton-like catalytic pretreatment system with participation of FeOCl can perform Fenton-like catalytic reaction within the range of pH value of 3-8, and overcomes the defect that the traditional Fenton catalytic reaction can only be performed under acidic condition.
4.3 Influence of FeOCl content in pretreatment system on treatment effect
In order to investigate the influence of different component contents of a pretreatment system on the enzymolysis efficiency of the corn straws, the corn straws are respectively placed in the pretreatment system with the addition amounts of FeOCl of 0.02g, 0.04g, 0.08g, 0.16g and 0.32g for treatment for 12 hours; then carrying out enzymolysis treatment on the pretreated corn straws, and determining the sugar content of an enzymolysis solution; taking corn straws without pretreatment as a blank control group (CK); three groups of parallel tests are set in the tests, and the test results are averaged; the sugar content of the corn stalk enzymatic hydrolysate is shown in figure 5;
it can be seen that the sugar content in the pretreated corn stalk enzymatic hydrolysate is higher than that in the blank control group which is not pretreated; with the increase of the addition amount of FeOCl, the sugar content in the pretreated corn straw enzymatic hydrolysate is gradually increased, and when the addition amount is 0.16g, the sugar content in the corn straw enzymatic hydrolysate reaches 19.18g/100g at most; then, with further increase of the addition amount, the sugar content in the enzymolysis liquid is not greatly increased, and the enzymolysis liquid basically presents a steady state.
4.4 H in pretreatment system 2 O 2 Influence of the content on the treatment Effect
Next, different H's were examined 2 O 2 Influence of the addition amount on the enzymolysis efficiency of the corn straws; wherein H 2 O 2 The addition amounts are respectively 0.09mol/L, 0.19mol/L, 0.38mol/L, 0.78mol/L and 1.55mol/L; after 12h of treatment, the determination result of the sugar content in the corn straw enzymatic hydrolysate is shown in figure 6;
it can be seen that when H is 2 O 2 When the addition amount is 0.09 to 0.38mol/L, the sugar content in the pretreated corn straw enzymatic hydrolysate is slowly increased from 7.56g/100g to 10.21g/100g; when H is present 2 O 2 When the addition amount is 0.78mol/L, the sugar content in the pretreated corn straw enzymatic hydrolysate is rapidly increased to about 2 times under the condition of 0.38mol/L, and the sugar content reaches 21.13g/100g; when H is present 2 O 2 The addition amount is continuously increased to 1.55mol/L, the sugar content in the corn straw enzymolysis liquid finally reaches 21.73g/100g, and is only increased by 2.84% compared with 21.13g/100g when the addition amount is 0.78mol/L;
as can be seen from the above test results, feOCl is associated with H 2 O 2 The Fenton-like pretreatment system can improve the enzymolysis efficiency of cellulose in the corn straws, but the more the FeOCl is added in the system, the better the FeOCl is, so 0.08 to 0.16g is the better addition range of the FeOCl, and 0.78 to 1.55mol/L is H 2 O 2 The preferred addition range of (3).
4.5 Effect of pretreatment time on treatment Effect
In order to investigate the influence of the pretreatment time on the enzymolysis efficiency of the corn straws, 5g of straws are added with a mixture containing 0.16g of FeOCl and 0.78mol/L of H 2 O 2 Setting pretreatment time gradients of 1h, 2h, 3h, 6h, 9h and 12h in a 100mL pretreatment system, carrying out enzymolysis treatment on the pretreated corn straw sample, and determining the sugar content in an enzymolysis solution; taking corn straws which are not pretreated as a control group, setting three groups of parallel tests, and taking an average value of test results; the change curve of sugar content in the corn straw enzymatic hydrolysate pretreated at different times is shown in figure 7;
as can be seen from the figure, when the pretreatment time is 6 hours, the sugar content in the corn straw enzymatic hydrolysate reaches the maximum value of 21.68g/100g; then, the sugar content in the enzymolysis liquid of the treated corn straws is not increased continuously but is reduced to a certain extent along with the continuous increase of the pretreatment time to 9h and 12h, but the sugar content in the enzymolysis liquid of the pretreated corn straws is closer to and higher than the sugar content in the enzymolysis liquid of the pretreated corn straws after the pretreatment time of 9h and 12h; the optimum treatment effect can be achieved after the Fenton-like catalytic system composed of FeOOL is treated for 6 hours, and compared with the treatment time of 120 hours of the existing Fenton catalytic system in the background art, the Fenton-like catalytic system composed of FeOOL can obviously shorten the pretreatment time of the corn straws, so that the degradation efficiency of cellulose in the corn straws is effectively improved.
Example 3
The test result of the embodiment 2 shows that the Fenton-like pretreatment system composed of FeOCl can improve the enzymolysis efficiency of the cellulose in the corn straw within the range of pH 3 to 8, that is, the Fenton-like pretreatment system can promote the degradation of the cellulose in the corn straw, and effectively shorten the pretreatment time. Whereas in natural lignocellulosic feedstocks cellulose, hemicellulose and lignin are present in some covalently bound manner, the degradation of cellulose is theoretically accompanied by degradation of lignin and hemicellulose; therefore, the inventor next inspects the influence of the pretreatment system on the degradation and extraction of lignin in the corn straws, and the specific test process is as follows:
1. test method
(1) Degreasing treatment
When the corn straw is used for extracting lignin, firstly carrying out hydroalcoholic treatment to remove pigments and lipids of the straw, and specifically comprising the following steps: taking a certain amount of corn straw raw material, and mixing the raw material according to a solid-liquid ratio of 1g: adding 10mL of distilled water, and treating for 2h at 60 ℃; filtering to remove filtrate by vacuum pump, drying the raw materials, wrapping with filter paper, and performing Soxhlet extraction with ethanol; putting the degreased raw materials in a fume hood for airing, and then drying for later use;
(2) Fenton-like pretreatment
5g of corn stover feedstock subjected to hydroalcoholic treatment was placed in 100ml of FEOCl and H 2 O 2 The pretreatment system is used for 6 hours, the addition amount of FeOCl in the pretreatment system is 1.6g/L, and H 2 O 2 0.78mol/L; after pretreatment, cleaning and drying the raw materials for subsequent use;
(3) Separating and extracting lignin
Taking 20g of corn straws before and after Fenton-like pretreatment, respectively placing the corn straws in 200mL of NaOH solutions with different concentrations, and reacting for 2h at different temperatures; filtering to remove precipitate, adjusting pH to 2 with 3% hydrochloric acid solution, centrifuging after precipitation is complete, and lyophilizing to obtain lignin;
(4) Acetylation of lignin
50mg of lignin was dissolved in 3ml of a mixed solution of DMSO: NMS (2, v/v), and reacted for 24 hours at room temperature in the dark; adding 1mL of acetic anhydride to react for 1.5h, and then adding a small amount of ethanol into the reaction system to remove the redundant acetic anhydride; slowly adding the solution into a hydrochloric acid solution with 10 times of volume and pH value of 2 until a precipitate is separated out; washing the precipitate with ethanol until no acetic anhydride smell is generated, centrifuging, and freeze-drying to obtain the acetylated lignin for molecular weight determination.
2. Analytical method
(1) Lignin molecular weight determination
The weight average molecular weight (Mw) and the number average molecular weight (Mn) of the lignin sample are measured by an Agilent PL-GPC 220 type gel permeation chromatograph under the following specific analysis conditions:
weighing 4mg of acetylated lignin sample, dissolving the acetylated lignin sample in 2 mL of chromatographic grade tetrahydrofuran, taking a polystyrene standard sample as a reference molecular mass, taking tetrahydrofuran as an eluent, and detecting an ultraviolet absorption value at 254nm, wherein the sample amount is 10 mu L;
(2) Infrared spectroscopic analysis of lignin
Uniformly mixing KBr powder and a small amount of lignin sample according to the proportion of 1 ~1 The number of sample scans was 32, and the resolution was 2cm ~1 ；
(3) Lignin proton nuclear magnetic resonance spectrum 1 H-NMR analysis
Dissolving a 50mg lignin sample in 0.5mL DMSO-d 6, transferring the solution into a 5mm sample tube, and placing the sample tube into a probe of a nuclear magnetic resonance spectrometer 1 H-NMR measurement was carried out by means of a reverse probe, and the working frequency of the measurement was 500M Hz based on DMSO-d 6 (2.5 ppm).
3. Results and discussion
3.1 Influence of Fenton-like pretreatment on lignin extraction rate in corn straw
In order to investigate the influence of Fenton-like pretreatment on the extraction rate of lignin in the corn straws, the corn straws subjected to Fenton-like pretreatment are respectively placed in 0.025mol/L, 0.05mol/L and 0.1mol/L NaOH solutions, and are respectively reacted for 2 hours at the conditions of 25 ℃, 50 ℃ and 75 ℃, and then the lignin in the corn straws is extracted; the ratio of the total content of the lignin in the obtained lignin and the corn straw is the extraction rate of the lignin; in the test, untreated corn straws are used as a control group, three groups of parallel tests are set in each group, and the test results are averaged; the extraction rate of lignin in the corn stalks under different pretreatment times and extraction conditions is shown in tables 1 to 3;
TABLE 1 amount of lignin extracted at different NaOH concentrations at 25 deg.C
TABLE 2 amount of lignin extracted at different NaOH concentrations at 50 deg.C
TABLE 3 amount of lignin extracted at different NaOH concentrations at 75 deg.C
From the aspect of NaOH extraction concentration, the extraction rate of lignin obtained from the corn straws is gradually increased before and after pretreatment along with the increase of the concentration of the used NaOH; under the conditions of different reaction temperatures, the extraction rate of lignin in the corn straws subjected to Fenton-like pretreatment is higher than that under the conditions without pretreatment; the lignin extraction rate of the pretreatment for 6 hours is higher than that of the pretreatment for 3 hours;
when the lignin is extracted by an alkaline method, the connecting bonds of the lignin, cellulose and hemicellulose in the corn straws are dissociated under the action of strong alkali, so that the higher the concentration of the alkali used is, the higher the extraction rate of the lignin is; the results show that the Fenton-like catalytic reaction system can promote the dissociation of lignin in the pretreatment stage, so that the extraction rate of the lignin extracted by a subsequent alkaline method is improved.
3.2 Infrared characterization and analysis of lignin
In order to investigate the influence of pretreatment and different extraction conditions on the chemical structure and functional groups of the obtained lignin, infrared spectrum analysis is carried out on the structure of the lignin by using a Fourier infrared spectrum analyzer (figure 8); the extraction temperature of the obtained lignin is 75 ℃; in the figure, A, B, C and D are infrared spectra of lignin obtained under the conditions of NaOH concentration of 0.025mol/L, 0.05mol/L, 0.1mol/L and 0.2mol/L respectively;
the characteristic absorption of each functional group of lignin is mainly concentrated at 800-1800 cm -1 In the fingerprint area of (1), wherein, 1707cm -1 C = O stretching vibration absorption peak of ketone and carbonyl representing non-conjugated carbonyl, 1656cm -1 Represents a C = O stretching shock absorption peak of carbonyl conjugated aromatic ketone, 1513cm -1 Representing the absorption peak of the benzene ring skeleton in the range of 1241cm -1 Represents the C = O condensation absorption peak of the aromatic nucleus associated with the syringyl nucleus, 1126cm -1 C-C, C-O stretching shock absorption peak of the guaiacyl and syringyl, 835cm -1 Represents a C-H telescopic shock absorption peak of the violaceous essence group;
as can be seen from the figure, the lignin sample after Fenton-like pretreatment has 1513cm of lignin when NaOH is 0.025M -1 And 1126cm -1 The absorption peak-to-average vibration amplitude is larger than that of the lignin which is not pretreated, and is 835cm -1 Significant absorption peak, while 835cm in the lignin sample without pretreatment -1 The absorption peak at (a) almost disappeared; the fact shows that the Fenton-like pretreatment not only can not influence the chemical structure of the lignin, but also can promote the separation of the lignin, so that the lignin with more complete molecular structure and functional groups is obtained;
the effect of pretreatment on lignin structure gradually increased with increasing concentration of NaOH used for extracting ligninReducing the absorption peaks of two lignin samples to be closer under the condition of 0.05 to 0.1M; 1513cm in lignin sample without pretreatment under 0.2M condition -1 、1126cm -1 And 835cm -1 The absorption peak is larger than the absorption peak amplitude of lignin obtained by pretreatment; however, the infrared spectra of the lignin obtained under the conditions of different NaOH concentrations are compared together, so that the peak patterns of absorption peaks in the lignin are widened along with the increase of the NaOH concentration, and the discrimination between the absorption peaks is reduced; the reason for this may be that the high concentration of alkali can open the connection between lignin and hemicellulose and cellulose, thereby promoting the separation and extraction of lignin, but too high concentration of alkali can also cause the degradation of lignin, destroy the main structure and functional groups of lignin molecules, and the destruction increases with the increase of alkali concentration, thereby counteracting the promotion of the fenton pretreatment on the complete separation of lignin.
3.3 Determination of lignin molecular weight
The results show that the Fenton-like pretreatment system can promote the separation of lignin in the corn straws, so that the extraction rate of the lignin is improved, and the molecular structure (including a benzene ring framework and functional groups) of the obtained lignin is more complete; however, too high alkali concentration (such as NaOH concentration 0.2 mol/L) can destroy the molecular structure of lignin; in order to further reveal the promotion effect of the pretreatment system on lignin separation, the invention utilizes a milder wood grinding method to extract lignin from the corn straws before and after pretreatment, and measures the molecular weight of the obtained lignin;
the wood grinding method comprises the following specific steps:
(1) 30g of corn straws subjected to 6h Fenton-like pretreatment or non-pretreated corn straws are put into a ball mill for ball milling for 2h at 500 revolutions per minute;
(2) Extracting for 2h at 100 ℃ by using 96% dioxane after the ball milling is finished, wherein the load of the dioxane is 1g;
(3) Concentrating the extracting solution to 60mL, and then dripping into 95% ethanol with 3 times of volume; removing the precipitate, and then concentrating the filtrate to 60mL again;
(4) Slowly adding the concentrated solution into 10 times of hydrochloric acid solution with pH value of about 2, and filtering or centrifuging to obtain precipitate, i.e. lignin;
purifying the obtained lignin by a Beckmann lignin purification method, and then measuring the molecular weight of the lignin by acetylation; the number average molecular weight M of the obtained lignin n Weight average molecular weight M w And polydispersity index (M) w /M n ) Are listed in Table 4;
TABLE 4 comparison of the molecular weights of the lignins obtained under different conditions
The method has the advantages that after Fenton-like pretreatment for 6 hours, the obtained lignin has larger number average molecular weight and weight average molecular weight than the lignin obtained without pretreatment, and the dispersibility is more concentrated, so that the Fenton-like pretreatment system provided by the invention can promote the separation of the lignin in the corn straws, and the obtained lignin has a more complete molecular structure and is more concentrated in distribution.
3.4 Lignin proton Nuclear magnetic resonance Spectroscopy 1 H-NMR analysis
1 H-NMR is a means for analyzing the hydrogen-containing structure of lignin, and the structure of lignin can be analyzed by the appearance of resonance peaks at different chemical shifts in a map; in order to reveal the mechanism of the accelerating action of the pretreatment system on the separation and extraction of lignin, the inventor carries out proton nuclear magnetic resonance spectroscopy on the lignin extracted by the wood grinding method 1 The H-NMR analysis and the specific analysis result are shown in figure 9;
as can be seen from the figure, the samples extracted from the corn straws before and after the pretreatment have characteristic peaks of lignin H, G and S belonging to a typical herbaceous lignin structure; wherein, the chemical shift is generated by protons on aromatic rings on the syringyl phenylpropane (S) and the guaiacyl (G) structural units at 6.7 to 6.79ppm, which shows that the contents of the S unit and the G unit are equivalent; 7.5ppm is hydrogen in p-hydroxyphenyl, 4.17ppm signal peak is generated by H beta and H gamma connected with carbon in aromatic ether bond, which shows existence of beta-O-4 bond in lignin, and absorption intensity of lignin sample after pretreatment is consistent with that of untreated lignin, which shows that beta-O-4 bond of lignin is not destroyed basically in Fenton treatment process, 3.72ppm is signal peak of wood methoxyl strong, 1.51ppm is proton signal peak of methyl and methylene in carbonyl, lignin side chain aliphatic proton signal peak is between 1.24 to 0.86ppm; from the figure, it can be seen that the lignin basically retains the original lignin structure after the Fenton-like pretreatment, which shows that the pretreatment has little influence on the skeleton structure of the lignin.
In conclusion, the pretreatment system can promote the separation of lignin in the corn straws, improve the extraction rate of the lignin, and after the pretreatment system is used for treatment, the framework structure of the lignin is not affected, and the original structure of the lignin is basically reserved, so that the high-quality lignin with larger molecular weight, more concentrated distribution and more complete structure is obtained, and a foundation is laid for further development and utilization of the subsequent lignin.
Claims (1)
1. A method for improving the extraction rate of lignin in a lignocellulose raw material by using a lignocellulose pretreatment system based on FeOCl is characterized by comprising the following steps:
(1) Degreasing treatment
Taking a certain amount of corn straw raw material, and mixing the raw material according to a solid-liquid ratio of 1g: adding 10mL of distilled water, and treating for 2h at 60 ℃; filtering to remove filtrate by vacuum pump, drying the raw materials, wrapping with filter paper, and performing Soxhlet extraction with ethanol; putting the degreased raw materials in a fume hood for airing, and then drying for later use;
(2) Fenton-like pretreatment
5g of corn stalk material treated with hydroalcoholic are placed in 100mL of FeOCl and H 2 O 2 The pretreatment system is used for 6 hours, the addition amount of FeOCl in the pretreatment system is 1.6g/L, and H 2 O 2 The addition amount is 0.78mol/L; after pretreatment, cleaning and drying the raw materials for subsequent use; the pH value of the pretreatment system is 3 to 8;
(3) Separating and extracting lignin
Taking 20g of the corn straw subjected to Fenton-like pretreatment, putting the corn straw into 200mL of NaOH solution with the concentration of 0.1M, and reacting for 2h at 75 ℃; filtering to remove precipitate, adjusting pH to 2 with 3% hydrochloric acid solution, centrifuging after precipitation is completed, and lyophilizing to obtain lignin;
(4) Acetylation of lignin
Dissolving 50mg of lignin in 3mL of a mixed solution, wherein the volume ratio of DMSO to NMS in the mixed solution is 2; adding 1mL of acetic anhydride to react for 1.5h; slowly adding the solution into a hydrochloric acid solution with 10 times of volume and pH value of 2 until a precipitate is separated out; washing the precipitate with ethanol until no acetic anhydride smell is generated, centrifuging, and freeze-drying to obtain the acetylated lignin for molecular weight determination.
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| CN101434976A (en) * | 2008-12-23 | 2009-05-20 | 中国石油化工股份有限公司 | Novel method for saccharification of ligno-cellulose |
| CN107519900A (en) * | 2017-08-11 | 2017-12-29 | 北京科瑞多环保科技有限公司 | A kind of fenton catalyst and its preparation method and application |
| CN108048509A (en) * | 2018-02-09 | 2018-05-18 | 河南农业大学 | A kind of preprocess method of non-three plain ingredient of efficient removal lignocellulosic |
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| CN107519900A (en) * | 2017-08-11 | 2017-12-29 | 北京科瑞多环保科技有限公司 | A kind of fenton catalyst and its preparation method and application |
| CN108048509A (en) * | 2018-02-09 | 2018-05-18 | 河南农业大学 | A kind of preprocess method of non-three plain ingredient of efficient removal lignocellulosic |
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