CN110551295A - Method for separating chemical components of gramineous plants and purifying lignin - Google Patents

Abstract

The invention provides a method for separating chemical components of gramineous plants and purifying lignin. The method uses gramineous plant straws as raw materials, uses an acidic solubilizer to dissolve lignin, and filters, washes, dilutes and sets aside. After the centrifugation step, a cellulose solid product and a lignin precipitate are obtained, and the precipitate is dialyzed to obtain pure lignin. The invention utilizes an easily recovered acidic solubilizer to effectively separate the plant components, and is an environment-friendly green process. The chemical components of the gramineous straw can be separated under the condition of low temperature and short time, and no high temperature is required. High-pressure pressure vessels can save production costs, improve production efficiency and reduce energy consumption.

Description

A method for separating chemical components of Poaceae and purifying lignin

technical field

The invention relates to the technical field of biomass energy, in particular to a method for separating chemical components of gramineous plant straw and purifying lignin.

Background technique

Excessive consumption of fossil fuels such as oil and coal mines has led to the continuous deterioration of the ecological environment, and fossil fuels are difficult to regenerate. Lignocellulose comes from natural and renewable plants. Cellulose is the most widely distributed and most abundant polysaccharide in nature, accounting for more than 50% of the carbon content in the plant kingdom. It is the most abundant renewable organic energy on earth. The solid fiber components obtained after separation can be further developed and utilized by means of component separation, such as papermaking, monosaccharide production, methylcellulose, cellulose ether, polymeric cellulose, etc.; the obtained lignin can be further developed and utilized. By means of grafting or modification, it can be made into a reinforcing agent, an anti-scaling agent, a binder, etc. Therefore, the development of lignocellulose to replace fossil fuels and make greater use of its value has received increasing attention.

Lignocellulose is the most abundant biomass resource in nature, which is mainly composed of cellulose, hemicellulose and lignin. Cellulose is a linear polymer compound composed of β-D-glucose units connected by 1-4-glycosidic bonds. Hemicellulose is a general term for non-cellulosic polysaccharides in the cell wall, consisting of two or more sugar groups, usually with a branched structure. Lignin is an aromatic high polymer with three-dimensional spatial structure, which is composed of phenylpropane units connected by ether bonds and carbon-carbon bonds. Together, lignin and hemicellulose form so-called lignin-hemicellulose complexes, which fill between the microfibrils of the cell wall and are also present in the intercellular layer.

Poaceae straw has a short growth cycle and large yield. As agricultural by-products, straw, bean straw, wheat straw, etc. are an inexhaustible renewable natural resource. Poaceae straw is not only renewable, but also has good biocompatibility and biodegradability. At present, straw, bean straw, wheat straw, etc. are mostly used for power generation, incineration, ethanol production, etc., with low added value and a certain destructive effect on the environment.

The patent (CN104404803B) discloses a method for the separation of straw components and the utilization of straw components. The inventive method first separates the hemicellulose through steam explosion treatment of the straw, and then steams the remaining material after extracting the hemicellulose again. Blasting treatment to achieve separation of cellulose and lignin. Although this process can effectively avoid the problem of secondary pollution caused by chemical treatment, this method has high requirements on the accuracy of parameters, and the process parameters actually applied to production must be consistent with laboratory equipment to ensure the availability of parameters. It can only stay in the laboratory stage, therefore, this method may restrict the realization of industrial application.

Patent (CN104987429B) discloses a kind of extraction method of Antrodia camphorata compound component separation, takes Antrodia camphorata fruit body powder or mycelium as raw material, adopts enzymolysis, supercritical CO ₂ extraction, ion exchange chromatography, membrane separation ultrafiltration and chromatography The separation and extraction of Antrodia camphorata compound components can be realized by the technology combined with the purification method. Although this method can obtain a higher purity of the isolate, the method adopted requires a lot of cost, and may not be a suitable method for the separation of common plant components.

Patent (CN105484083B) discloses a process for the separation of lignocellulose components. The process pretreats biomass by irradiation, couples low-boiling tetrahydrofuran or high-boiling γ-lactate reaction, and obtains cellulose components by one-time filtration. After recovering tetrahydrofuran, or adding saturated NaCl solution, the lignin is phase-separated and precipitated, and filtered for a second time. The residue is a lignin component, and the secondary filtrate is dried to obtain a hemicellulose component. The irradiation pretreatment used in this method has certain radioactivity, which poses certain safety hazards to the human body, and the tetrahydrofuran used in the method also has a certain carcinogenic risk to the human body. Very friendly crafting method.

The patent (CN106061891B) discloses a process for removing lignin from plants by using mixed acid. The process involves a system for delignifying plant matter impregnated with a solution of an organic acid selected from acetic acid, formic acid, propionic acid, butyric acid or a mixture of these acids, preferably a mixture of acetic acid and formic acid, containing said plant matter and comprising Hydrogen peroxide composition with at least one phosphorus additive for impregnation with a solution of an organic acid selected from acetic acid, formic acid, propionic acid, butyric acid or mixtures of these acids, preferably a mixture of acetic acid and formic acid delignification of plant matter. This method requires many types of mixed acids, and uses phosphorus as an additive, which is likely to cause secondary pollution of chemical reagents, and may not be an environmentally friendly process method.

Patent (CN105861592B) discloses a method for pretreating lignocellulosic biomass. The method uses lignocellulosic biomass with a particle size of 0.5 to 2 mm as raw material, and uses solid alkali as catalyst to treat lignocellulosic biomass in a hydrothermal environment. The lignocellulosic biomass is pretreated to break the dense structure of lignocellulose and catalyze the stripping and degradation of lignin in lignocellulose and the dissolution and separation of hemicellulose. The preparation method of the solid base used in this method is relatively complicated, and the requirements for raw materials are also high. The raw materials need to be pretreated to make the particle size smaller, which may lead to increased production costs.

Patent (CN105854907B) discloses a method for separating and preparing ultra-low viscosity carboxymethyl cellulose from straw components. The method first adopts acid method to hydrolyze straw hemicellulose to obtain fermentable monosaccharide, and then adopts organic solvent method to extract straw lignin High activity lignin is obtained, cellulose is purified by alkaline oxidation method, and finally carboxymethyl cellulose is prepared by etherification modification of straw cellulose. The process is divided into four stages, which are relatively cumbersome, and chemicals are used in each stage, which may cause secondary pollution of chemicals.

The existing gramineous plant chemical component separation technology is relatively complex, the experimental conditions are relatively high, and it is easy to cause secondary pollution. Therefore, how to realize the separation of plant components with maximum efficiency under optimal conditions is an important research direction in the application range of biomass energy.

SUMMARY OF THE INVENTION

The main purpose of the present invention is to provide a method for separating chemical components of gramineous plant straws. The method uses an acidic solubilizer, which can efficiently separate the chemical components of gramineous plant straws cell wall, and the acidic solubilizer can be reused and operated. The process is simple, the time cost is reduced, the energy consumption is reduced, and the cost is saved, which can reduce the pollution of chemicals to the environment and the phenomenon of cost increase caused by long reaction time and high reaction temperature.

Another object of the present invention is to provide a method for purifying the lignin obtained by the above method. This method uses conventional experimental methods such as dilution, standing, centrifugation, and dialysis to obtain pure lignin, so as to achieve efficient utilization of biomass resources. the goal of.

A method for separating chemical components of gramineous plant straw and purifying lignin, comprising the following steps:

(1) Pulverization: Select sun-dried grass stalks and pulverize them with a pulverizer to obtain slag of grass stalks for use.

(2) Acid hydrolysis: Weigh the gramineous plant straw scraps prepared in step (1), the acidic solubilizer and deionized water, put the gramineous plant straw scraps into a porous round-bottomed flask, and the acidic solubilizer and deionized water Put the ionized water into the conical flask and stir it evenly. Put the porous round-bottomed flask and the conical flask into the water bath at the same time, and fix it with a test tube holder. After heating to the set temperature in the water bath, the acid in the conical The solubilizer solution was added to the porous round-bottomed flask, continued stirring, and the reaction time was set. At the end of the reaction, deionized water equal to the total weight of the reaction raw materials was added to the porous round-bottomed flask to prepare a fiber suspension for use.

The acidic solubilizer solution and the gramineous plant straw residue were separated and heated to a set temperature and then mixed together. The effect of the acidic solubilizer on the separation of plant components at this temperature can be accurately explored. In order to avoid the influence of rotation speed on the reaction, all reactions were carried out at the same rotation speed.

The addition of deionized water can quickly reduce the temperature to the temperature required for the reaction, which ensures the accuracy of the reaction time.

(3) Filtration: Filtration of the fiber suspension obtained in step (2), separation to obtain a cellulose-containing solid product and a filtrate in which lignin is dissolved, for subsequent use.

(4) Washing: the solid product obtained in step (3) is washed with deionized water, and the washed waste liquid is collected.

(5) Dilution: the filtrate obtained in step (3) and the waste liquid obtained in step (4) are mixed to obtain a mixed solution, and the mixed solution is diluted with deionized water until the acid solubilizer concentration is lower than its critical micelle concentration.

Lignin is soluble in acid, and when the acid concentration is as low as its critical micelle concentration, lignin will precipitate out of the acid solution to form a precipitate.

(6) Standing: the mixed solution obtained in step (5) is left standing until the supernatant of the upper layer and the sediment of the lower layer are separated.

(7) Centrifugation: the supernatant liquid obtained in step (6) was sucked off, and the lower sediment was centrifuged to remove excess water.

Centrifugation mainly separates lignin from water. While removing water, acidic solubilizers and monosaccharide small molecules dissolved in water are also removed together.

(8) Dialysis: transfer the sediment after centrifugation in step (7) into a semipermeable membrane bag, and put the semipermeable membrane bag into deionized water for dialysis.

The acidic solubilizers and small monosaccharide molecules attached to the lignin are transferred to deionized water through the semipermeable membrane, and the lignin macromolecules are retained in the semipermeable membrane.

(9) Drying: after the dialysis in step (8) is completed, the precipitate is centrifuged to remove moisture, and freeze-dried to obtain pure lignin.

Centrifuging again to remove water can reduce the drying time of the lignin later.

Preferably, the grass plant described in step (1) is any one of wheat, corn, soybean, rice, barley, sorghum, oat, and sugarcane.

Preferably, the acidic solubilizer component in step (2) is p-toluenesulfonic acid, and the mass percent concentration of the p-toluenesulfonic acid in the total experimental weight is 30%-60%.

Preferably, the set temperature in step (2) is 60-80° C., and the reaction time is 15-60 min.

Preferably, the filtration described in the step (3) adopts vacuum filtration, and the vacuum filtration adopts a Buchner funnel to be connected to a suction bottle and a vacuum pump in sequence.

Among them, the Buchner funnel is connected with the suction bottle and the vacuum pump in turn, which can speed up the filtration speed.

Preferably, the washing described in step (4) uses deionized water to wash the solid product to neutrality.

Washing the solid product to neutrality can ensure that no acidic solubilizer is attached to the solid product. During the washing process, the small monosaccharide substances on the solid product will be dissolved in water and removed, so a pure solid product can be obtained. .

Preferably, the critical micelle concentration in step (5) is 1%.

Preferably, the mixture standing time described in step (6) is 24h.

Preferably, the dialysis in deionized water described in the step (8) is to measure the conductivity of the deionized water every 12 hours, and replace the deionized water until the conductivity is less than 0.1.

Acidic solubilizers and monosaccharide small molecules dissolved in water will generate electrical conductivity. By comparing the electrical conductivity of pure water with the electrical conductivity of dialysis water, the speed of dialysis and the end point of the reaction can be effectively known.

Preferably, the centrifugation conditions described in step (7) and step (9) are at 20° C., the rotation speed is 8000 r/min, and the centrifugation is performed for 10 min.

beneficial effect

1. The method of the present invention realizes that only a kind of acid solubilizer for convenient recovery can be used to effectively separate plant components, which is a kind of environmentally friendly green technology, which effectively avoids the recovery of chemical reagents in traditional technology. It has the disadvantage of too much cost investment, and gets rid of the problem of dependence on the joint action of multiple chemical reagents in the component separation process.

2. The method of the present invention separates the grass components under low temperature and short time conditions, does not require high temperature and high pressure pressure vessels, can save production costs, improve production efficiency, reduce energy consumption, and low temperature operating conditions can also be effectively avoided. The occurrence of safety accidents such as burns.

3. Due to the separation of chemical components in a low temperature environment, the degradation degree of cellulose and hemicellulose is low, so the yield of solid fiber components obtained is high, and the obtained lignin has a low degree of polycondensation and better retention. The original macromolecular structure of lignin.

4. The solid fiber product obtained by the method of the present invention can better preserve its original form, and can be further used to manufacture paper, which provides a new type of pulping idea for the pulp and paper industry, and can also be used for biomass energy. In the industry, the solid fiber products are enzymatically hydrolyzed into monosaccharides, and then fermented into bioethanol or biomass diesel.

The above content is only an overview of the technical solutions of the present invention. In order to understand the technical means of the present invention more clearly, the present invention will be further described below with reference to the accompanying drawings.

Description of drawings

Fig. 1 is the process flow diagram of the present invention;

Fig. 2 is the morphology of the solid product prepared by the present invention under a 40-fold microscope;

Fig. 3 is the molecular weight distribution curve diagram of lignin obtained by the present invention.

Detailed ways

The invention discloses a method for separating chemical components of a gramineous plant cell wall and purifying lignin. Under the condition of low temperature and short time, an acidic solubilizer is used to dissolve the lignin, so that the lignin is separated from the solid product together with the acidic solubilizer. According to the property of lignin soluble in acid but not soluble in water, by diluting the filtrate containing acid solubilizer and lignin, when the acid solubilizer concentration is lower than the critical micelle concentration, the lignin will be separated from the acid solubilizer and form a precipitate . The obtained lignin can remove the acidic solubilizer and monosaccharide small molecular substances attached to the lignin by simple dialysis, thereby obtaining pure lignin. The solid product can retain a good fiber form, and can not only be used to make paper, but also be used for hydrolysis to obtain fermentable monosaccharides.

In order to understand the present invention, the present invention will be further described below with reference to the examples.

Wherein, the grasses are any one of wheat, corn, soybean, rice, barley, sorghum, oat, and sugarcane. In the specific embodiment, we use rice straw as an example to illustrate.

In order to investigate the influence of different process conditions on the solid product yield and lignin removal rate, we set up different investigation conditions, including different concentrations of acidic solubilizers, different reaction temperatures, and different reaction times. Specific examples are as follows. Show:

Example 1:

The total weight of the experiment is 200g, and the ratio of raw material weight to total weight is 1:10.

(1) pulverization: select sun-dried grass stalks, and pulverize with a pulverizer to obtain slag of grass stalks, for subsequent use;

(2) acidolysis: take by weighing 20g of gramineous plant straw scraps, 60g p-toluenesulfonic acid and 120g deionized water, wherein p-toluenesulfonic acid accounts for 30% of the total weight, and the gramineous plant straw scraps are put into a porous circle In the bottom flask, put p-toluenesulfonic acid and deionized water into the conical flask and stir evenly, put the porous round bottom flask and the conical flask into the water bath at the same time, fix it with a test tube holder, and heat it to 80 in the water bath. ℃, the p-toluenesulfonic acid solution in the conical flask was added to the porous round-bottom flask, and the stirring was continued for 30 min. After the reaction was completed, 200 g of deionized water was added to the porous round-bottom flask to prepare a fiber suspension for use;

(3) filter: adopt cloth funnel to filter the fiber suspension of step (2) gained, separate and obtain the filtrate containing cellulose-containing solid product and dissolving lignin, for subsequent use;

(4) washing: the solid product obtained in step (3) is washed with deionized water, the solid product is washed to neutrality, and the washed waste liquid is collected;

(5) dilution: the filtrate obtained in step (3) and the waste liquid obtained in step (4) are mixed to obtain a mixed solution, and the mixed solution is diluted with deionized water, and diluted to a p-toluenesulfonic acid concentration lower than 1%;

(6) leave standstill: stand the mixed solution gained in the standstill step (5) for 24h, to separate the supernatant of the upper layer and the sediment of the lower layer;

(7) Centrifugation: suction off the supernatant liquid obtained in step (6), and centrifuge the lower sediment at 20° C. for 10 min to remove excess water;

(8) Dialysis: transfer the sediment after centrifugation in step (7) into a semi-permeable membrane bag, put the semi-permeable membrane bag into pure water for dialysis, measure the conductivity of deionized water every 12 hours, and replace Deionized water until the conductivity is less than 0.1;

(9) Drying: After the dialysis in step (8) is completed, the precipitate is centrifuged for 10 min at 20° C. at a rotational speed of 8000 r/min to remove moisture, and freeze-dried to obtain pure lignin.

After the separation, solid fiber and pure lignin were obtained, wherein the yield of solid fiber product was 64.46%, and the lignin removal rate was 33%.

Example 2:

The total weight of the experiment is 200g, and the ratio of raw material weight to total weight is 1:10.

(1) pulverizing: the method is the same as in Example 1;

(2) acidolysis: take by weighing 20g of gramineous plant straw scraps, 90g p-toluenesulfonic acid and 90g deionized water, wherein p-toluenesulfonic acid accounts for 45% of the total weight, and the gramineous plant straw scraps are put into a porous circle In the bottom flask, put p-toluenesulfonic acid and deionized water into the conical flask and stir evenly, put the porous round bottom flask and the conical flask into the water bath at the same time, fix it with a test tube rack, and heat it to 80 in the water bath. ℃, the p-toluenesulfonic acid solution in the conical flask was added to the porous round-bottom flask, and the stirring was continued for 15 min. After the reaction was completed, 200 g of deionized water was added to the porous round-bottom flask to prepare a fiber suspension for use;

(3) filtering: the method is the same as in Example 1;

(4) washing: the method is the same as in Example 1;

(5) dilution: method is with embodiment 1;

(6) leave standstill: method is with embodiment 1;

(7) Centrifugation: the method is the same as in Example 1;

(8) Dialysis: the method is the same as in Example 1;

(9) Drying: the method is the same as that of Example 1.

After the separation, solid fiber and pure lignin were obtained, wherein the yield of solid fiber product was 62.55%, and the lignin removal rate was 37%.

Example 3:

The total weight of the experiment is 200g, and the ratio of raw material weight to total weight is 1:10.

(1) pulverizing: the method is the same as in Example 1;

(2) acidolysis: take by weighing 20g of gramineous plant straw scraps, 120g p-toluenesulfonic acid and 60g deionized water, wherein p-toluenesulfonic acid accounts for 60% of the total weight, and the gramineous plant straw scraps are put into the porous circle In the bottom flask, put p-toluenesulfonic acid and deionized water into the conical flask and stir evenly, put the porous round bottom flask and the conical flask into the water bath at the same time, fix it with a test tube rack, and heat it to 60 in the water bath. ℃, the p-toluenesulfonic acid solution in the conical flask was added to the porous round-bottom flask, and the stirring was continued for 30 min. After the reaction was completed, 200 g of deionized water was added to the porous round-bottom flask to prepare a fiber suspension for use;

(3) filtering: the method is the same as in Example 1;

(4) washing: the method is the same as in Example 1;

(5) dilution: method is with embodiment 1;

(6) leave standstill: method is with embodiment 1;

(7) Centrifugation: the method is the same as in Example 1;

(8) Dialysis: the method is the same as in Example 1;

(9) Drying: the method is the same as that of Example 1.

After the separation, solid fiber and pure lignin were obtained, wherein the yield of solid fiber product was 65.04%, and the removal rate of lignin reached 30%.

Example 4:

The total weight of the experiment is 200g, and the ratio of raw material weight to total weight is 1:10.

(1) pulverizing: the method is the same as in Example 1;

(2) acidolysis: take by weighing 20g of gramineous plant straw scraps, 120g p-toluenesulfonic acid and 60g deionized water, wherein p-toluenesulfonic acid accounts for 60% of the total weight, and the gramineous plant straw scraps are put into the porous circle In the bottom flask, put p-toluenesulfonic acid and deionized water into the conical flask and stir evenly, put the porous round bottom flask and the conical flask into the water bath at the same time, fix it with a test tube holder, and heat it to 80 in the water bath. ℃, add the p-toluenesulfonic acid solution in the conical flask to the porous round-bottomed flask, continue to stir for 45 min, the reaction is over, add 200 g of deionized water to the porous round-bottomed flask to prepare a fiber suspension for use;

(3) filtering: the method is the same as in Example 1;

(4) washing: the method is the same as in Example 1;

(5) dilution: method is with embodiment 1;

(6) leave standstill: method is with embodiment 1;

(7) Centrifugation: the method is the same as in Example 1;

(8) Dialysis: the method is the same as in Example 1;

(9) Drying: the method is the same as that of Example 1.

After the separation, solid fibers and pure lignin were obtained, wherein the yield of solid fibers was 55.65%, and the removal rate of lignin reached 45%.

Example 5:

The total weight of the experiment is 200g, and the ratio of raw material weight to total weight is 1:10.

(1) pulverizing: the method is the same as in Example 1;

(2) acidolysis: take by weighing 20g of gramineous plant straw scraps, 90g p-toluenesulfonic acid and 90g deionized water, wherein p-toluenesulfonic acid accounts for 45% of the total weight, and the gramineous plant straw scraps are put into a porous circle In the bottom flask, put p-toluenesulfonic acid and deionized water into the conical flask and stir evenly, put the porous round bottom flask and the conical flask into the water bath at the same time, fix it with a test tube holder, and heat it to 70 in the water bath. ℃, add the p-toluenesulfonic acid solution in the conical flask to the porous round-bottomed flask, continue to stir for 60 min, the reaction is over, add 200 g of deionized water to the porous round-bottomed flask, and prepare a fiber suspension for use;

(3) filtering: the method is the same as in Example 1;

(4) washing: the method is the same as in Example 1;

(5) dilution: method is with embodiment 1;

(6) leave standstill: method is with embodiment 1;

(7) Centrifugation: the method is the same as in Example 1;

(8) Dialysis: the method is the same as in Example 1;

(9) Drying: the method is the same as that of Example 1.

After the separation, solid fiber and pure lignin were obtained, wherein the yield of solid fiber product was 59.98%, and the removal rate of lignin reached 40%.

Example 6:

The total weight of the experiment is 200g, and the ratio of raw material weight to total weight is 1:10.

(1) pulverizing: the method is the same as in Example 1;

(2) acidolysis: take 20g of gramineous plant straw scraps, 90g p-toluenesulfonic acid and 90g deionized water, wherein p-toluenesulfonic acid accounts for 45% of the total weight, and the gramineous plant straw scraps are put into the porous circle In the bottom flask, put p-toluenesulfonic acid and deionized water into the conical flask and stir evenly, put the porous round bottom flask and the conical flask into the water bath at the same time, fix it with a test tube holder, and heat it to 80 in the water bath. ℃, add the p-toluenesulfonic acid solution in the conical flask to the porous round-bottomed flask, continue to stir for 60min, the reaction is over, add 200 g of deionized water to the porous round-bottomed flask, and prepare a fiber suspension for use;

(3) filtering: the method is the same as in Example 1;

(4) washing: the method is the same as in Example 1;

(5) dilution: method is with embodiment 1;

(6) leave standstill: method is with embodiment 1;

(7) Centrifugation: the method is the same as in Example 1;

(8) Dialysis: the method is the same as in Example 1;

(9) Drying: the method is the same as that of Example 1.

After the separation, solid fiber and pure lignin were obtained, wherein the yield of solid fiber product was 51.28%, and the lignin removal rate was 42%.

The results obtained under different experimental conditions are shown in Table 1, and the results of the solid fiber product yield and lignin removal rate obtained in different embodiments.

Table 1

Through the analysis of the experimental results, we can find that with the increase of p-toluenesulfonic acid concentration, the reaction time increases, the reaction temperature increases, and the removal rate of lignin also increases.

As shown in Figure 2, the morphology of the solid product was observed through a microscope, and it was found that the solid product could well retain its fiber morphology and could be used to further manufacture paper or other chemicals.

Figure 3 shows the molecular weight distribution curve of lignin obtained by GPC analysis. From the curve in the figure, it can be seen that the molecular weight distribution of lignin is wide, and no polycondensation of macromolecular lignin occurs, and lignin of various molecular weights is well preserved.

The above are only preferred embodiments of the present invention, and do not limit the present invention in any form. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Technical personnel, within the scope of the technical solution of the present invention, can make some changes or modifications to equivalent examples of equivalent changes by using the technical content disclosed above, but any content that does not depart from the technical solution of the present invention, according to the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments by the technical essence of the invention still fall within the scope of the technical solutions of the present invention.

Claims (10)

1. A method for separating chemical components of gramineous plants and purifying lignin, characterized in that: the method comprises the following steps:

(1) Crushing: selecting dried gramineous plant straw, and crushing by using a crusher to prepare gramineous plant straw slag for later use;

(2) Acid hydrolysis: weighing the grass family plant straw slag prepared in the step (1), an acid solubilizer and deionized water, putting the grass family plant straw slag into a porous round-bottom flask, putting the acid solubilizer and the deionized water into a conical flask, uniformly stirring, putting the porous round-bottom flask and the conical flask into a water bath kettle, fixing the porous round-bottom flask and the conical flask by using a test tube rack, heating the porous round-bottom flask and the conical flask in the water bath kettle to a set temperature, adding the acid solubilizer solution in the conical flask into the porous round-bottom flask, continuously stirring, setting the reaction time, and adding deionized water with the weight equal to the total weight of the reaction raw materials into the porous round-bottom flask when the reaction is finished to prepare a fiber suspension for later;

(3) and (3) filtering: filtering the fiber suspension obtained in the step (2), and separating to obtain a solid product containing cellulose and a filtrate dissolved with lignin for later use;

(4) Washing: washing the solid product prepared in the step (3) by using deionized water, and collecting the waste liquid obtained by washing;

(5) diluting: mixing the filtrate obtained in the step (3) and the waste liquid obtained in the step (4) to prepare a mixed solution, and diluting the mixed solution by using deionized water until the concentration of the acid solubilizer is lower than the critical micelle concentration of the acid solubilizer;

(6) Standing: standing the mixed solution obtained in the step (5) until the supernatant of the upper layer is separated from the precipitate of the lower layer;

(7) centrifuging: sucking off the supernatant obtained in the step (6), centrifuging the lower-layer precipitate, and removing excessive water;

(8) And (3) dialysis: transferring the precipitate obtained in the step (7) after centrifugation into a semipermeable membrane bag, and putting the semipermeable membrane bag into deionized water for dialysis;

(9) And (3) drying: and (8) after dialysis is finished, centrifuging the precipitate, removing water, and freeze-drying to obtain pure lignin.

2. the method for separating chemical components of gramineous plants and purifying lignin according to claim 1, wherein: the gramineae plant in the step (1) is any one of wheat, corn, soybean, rice, barley, sorghum, oat and sugarcane.

3. The method for separating chemical components of gramineous plants and purifying lignin according to claim 1, wherein: in the step (2), the acid solubilizer is p-toluenesulfonic acid, and the mass percentage concentration of the p-toluenesulfonic acid in the total weight of the experiment is 30-60%.

4. The method for separating chemical components of gramineous plants and purifying lignin according to claim 1, wherein: in the step (2), the set temperature is 60-80 ℃, and the reaction time is 15-60 min.

5. the method for separating chemical components of gramineous plants and purifying lignin according to claim 1, wherein: and (4) filtering in the step (3) by adopting vacuum filtration, wherein the vacuum filtration adopts a Buchner funnel to be sequentially connected with a suction bottle and a vacuum pump.

6. the method for separating chemical components of gramineous plants and purifying lignin according to claim 1, wherein: the washing described in step (4) uses deionized water to wash the solid product to neutrality.

7. the method for separating chemical components of gramineous plants and purifying lignin according to claim 1, wherein: the critical micelle concentration in step (5) is 1%.

8. the method for separating chemical components of gramineous plants and purifying lignin according to claim 1, wherein: and (4) standing the mixed solution in the step (6) for 24 hours.

9. The method for separating chemical components of gramineous plants and purifying lignin according to claim 1, wherein: and (5) putting the mixture into deionized water for dialysis, specifically measuring the conductivity of the deionized water every 12 hours, and replacing the deionized water until the conductivity is less than 0.1.

10. the method for separating chemical components of gramineous plants and purifying lignin according to claim 1, wherein: the centrifugation conditions in the step (7) and the step (9) are that the rotation speed is 8000r/min at 20 ℃, and the centrifugation is 10 min.