CN115058911A

CN115058911A - Method for extracting cellulose from cellulose and buckwheat straws

Info

Publication number: CN115058911A
Application number: CN202210295729.0A
Authority: CN
Inventors: 宝贵荣; 王开花; 李福全; 包苏敦
Original assignee: Hohhot Minzu College
Current assignee: Hohhot Minzu College
Priority date: 2022-03-23
Filing date: 2022-03-23
Publication date: 2022-09-16

Abstract

The application provides a method for extracting cellulose from cellulose and buckwheat straws, and belongs to the technical field of cellulose extraction. The method comprises the steps of washing, air-drying, crushing and screening the buckwheat straws to obtain buckwheat straw powder; adding a NaOH solution into buckwheat straw powder, refluxing, performing reduced pressure suction filtration after the reaction is finished, washing filter residues to be neutral by using deionized water, drying a filter cake, and grinding to obtain crude cellulose; and (3) adding a sodium chlorite solution into the crude fiber, adjusting the pH value with acetic acid, refluxing again, reducing pressure and filtering after the reaction is finished, washing the crude fiber with ethanol for a plurality of times, washing the crude fiber with distilled water to be neutral, drying and grinding a filter cake to obtain the cellulose. The method takes buckwheat straws as objects, optimizes extraction conditions of buckwheat straw cellulose, adopts sodium hydroxide-sodium chlorite solution to extract the buckwheat straw cellulose, and removes lignin and hemicellulose. The basic structure of the cellulose is not changed after the buckwheat straws are treated by sodium hydroxide and sodium chlorite, and the cellulose with higher purity is obtained. The extraction method is simple and easy to popularize, and the application value of the buckwheat straws is obviously improved.

Description

Method for extracting cellulose from cellulose and buckwheat straws

Technical Field

The application relates to the technical field of cellulose extraction, in particular to a method for extracting cellulose from cellulose and buckwheat straws.

Background

The problems of energy shortage, environmental pollution and the like faced by the human society become hot problems concerned by China and even the world nowadays. Therefore, people abandon highly polluting, energy-intensive synthetic materials and have turned to great efforts to develop environmentally friendly, renewable and sustainable materials. Cellulose is one of the most abundant materials in the world, and is widely applied to environment-friendly materials due to the advantages of nature, reproducibility, good biodegradability, good mechanical properties, light weight, modification and the like. Cellulose accounts for 35% -50% of the substance in plant cell walls and is widely present in crop straws. Crop straws are mainly composed of cellulose, hemicellulose and lignin, wherein the cellulose is a scaffold of the straws, and the lignin and the hemicellulose are fillers. Cellulose is the most abundant renewable natural polymer, and has been receiving attention from many researchers because of its biocompatibility, biodegradability and unique mechanical properties. Despite these advantages, the disadvantages of cellulose, such as high hydrophilicity, poor thermoplasticity, poor solubility and easy water absorption, are disadvantageous for its wide application. Therefore, in order to overcome these disadvantages to chemically modify cellulose, common modification means include esterification, halogenation, etherification, oxidation, grafting, organic base, acid, organic/inorganic compound, and oxidant modification.

Buckwheat (Fagopyrum esculentum) is a dicotyledonous plant of genus Triticum of family Polygonaceae, has high medicinal and nutritional values, and contains active ingredients such as starch, protein, natural inositol, flavone, mineral, dietary fiber, and anthocyanin, etc., and is beneficial for health. No waste of buckwheat stems and leaves, straws, shells, rice and flour is a treasure. Wherein, the buckwheat straws are important components of buckwheat, and the main chemical components of the buckwheat straws are cellulose, hemicellulose, lignin and the like. The buckwheat straws are not completely utilized by people, and most of the buckwheat straws are accumulated in fields or burnt, so that the environmental pollution is aggravated or the natural resources are seriously consumed and wasted. In order to make the buckwheat straws better utilized, researchers research the applications of returning the buckwheat straws to the field, adding the buckwheat straws into animal feed and the like. At present, wheat straws are mostly researched in documents, but the research on the extraction process of the buckwheat straw cellulose is not reported in documents at home and abroad. However, the buckwheat straws and the wheat straws have different components, such as different proportions of cellulose, lignin, hemicellulose and the like, and different wrapping degrees of the cellulose and the buckwheat straws and the wheat straws, so that the treatment modes for extracting the cellulose from the two straws cannot be directly referred to, and specific extraction methods suitable for different raw materials need to be explored.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide cellulose for extracting cellulose from buckwheat straws for a sewage heavy metal adsorbent. The extraction method has mild conditions and high yield, improves the utilization value of the buckwheat straws, and enriches the comprehensive utilization potential of the buckwheat straws. Buckwheat straws are taken as a research object, the extraction conditions of buckwheat straw cellulose are optimized, the buckwheat straw cellulose is extracted by adopting a sodium hydroxide-sodium chlorite solution, and lignin and hemicellulose are removed. The basic structure of the cellulose is not changed after the buckwheat straws are treated by sodium hydroxide and sodium chlorite, and the cellulose with higher purity is obtained.

In a first aspect, the application provides a method for extracting cellulose from buckwheat straws, which comprises the following steps:

washing, air-drying, crushing and screening the buckwheat straws to obtain buckwheat straw powder;

adding a NaOH solution into buckwheat straw powder, refluxing, performing reduced pressure suction filtration after the reaction is finished, washing filter residues to be neutral by using deionized water, drying a filter cake, and grinding to obtain crude cellulose;

and (3) adding a sodium chlorite solution into the crude fiber, adjusting the pH value with acetic acid, refluxing again, reducing pressure and filtering after the reaction is finished, washing the crude fiber with ethanol for a plurality of times, washing the crude fiber with distilled water to be neutral, drying and grinding a filter cake to obtain the cellulose.

In one possible embodiment, the buckwheat straw is washed, air-dried, pulverized and sieved to obtain buckwheat straw powder, which specifically comprises

Washing: washing buckwheat straws with water, and soaking for 2 hours to fully remove water-soluble impurities on the surfaces of the buckwheat straws;

air drying: drying the washed buckwheat straws by air;

and (3) drying: drying the air-dried buckwheat straws in a drying box;

crushing: cutting the dried buckwheat straws into small sections with the length of 4-5cm, and then crushing;

screening: sieving with 40 mesh sieve, and placing the buckwheat stalk powder in a sealed bag for use.

In one possible embodiment, the buckwheat straw powder is 2g, the mass concentration of the NaOH solution is 2-6%, and the volume of the NaOH solution is 100 mL.

In one possible embodiment, the NaOH solution has a mass concentration of 4%.

In a possible embodiment, the reflux temperature is 70-90 ℃ and the reflux duration is 60-90 min.

In one possible embodiment, the reflux temperature is 80 ℃.

In one possible embodiment, the reflux duration is 80 min.

In one possible embodiment, the crude fiber is 0.5g, and the sodium chlorite solution has a mass concentration of 3.5% and a volume of 25 mL.

In one possible embodiment, the acetic acid is adjusted to pH 2.

In a second aspect, the application provides a cellulose prepared by the method for extracting cellulose from buckwheat straws.

The application provides a cellulose and a method for extracting cellulose from buckwheat straws, which has the beneficial effects that:

according to the extraction method of the cellulose and the cellulose in the buckwheat straws, the buckwheat straws are taken as objects, the extraction conditions of the buckwheat straw cellulose are optimized, the sodium hydroxide-sodium chlorite solution is adopted to extract the buckwheat straw cellulose, and lignin and hemicellulose are removed. The basic structure of the cellulose is not changed after the buckwheat straws are treated by sodium hydroxide and sodium chlorite, and the cellulose with higher purity is obtained.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments are briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained from the drawings without inventive efforts and also belong to the protection scope of the present application.

FIG. 1 is a graph showing the effect of the mass concentration of NaOH on the cellulose content of buckwheat straw provided in the present application;

FIG. 2 is a graph showing the effect of extraction temperature on the cellulose content of buckwheat stalks provided in the present application;

FIG. 3 is a graph showing the effect of extraction time on the cellulose content of buckwheat straw provided herein;

FIG. 4 is a diagram of a sample of buckwheat straw and cellulose extracted by different methods;

FIG. 5 is a scanning electron microscope image of extracting cellulose from buckwheat straw and its different methods provided by the present application;

FIG. 6 is an infrared spectrum of the buckwheat straw and its cellulose extracted by different methods;

FIG. 7 is an XRD pattern of the buckwheat straw and its cellulose extracted by different methods.

Detailed Description

The method for extracting the cellulose from the buckwheat straws comprises the following steps:

s10, washing, air-drying, crushing and screening the buckwheat straws to obtain the buckwheat straw powder.

Here, straw treatment: washing buckwheat straws with water twice, soaking for 2 hours, fully removing water-soluble impurities such as dust on the surfaces of the buckwheat straws, air-drying the buckwheat straws, and drying the buckwheat straws in a drying oven. Cutting dried buckwheat straws into small segments with the length of 4-5cm, crushing, sieving with a 40-mesh sieve, and placing the buckwheat straw powder in a sealed bag for later use.

S20, adding NaOH solution into buckwheat straw powder, refluxing, after the reaction is finished, carrying out vacuum filtration, washing filter residues to be neutral by using deionized water, drying filter cakes and grinding to obtain crude cellulose.

The buckwheat straw powder is 2g, the mass concentration of the NaOH solution is 2-6%, and the volume of the solution is 100 mL.

The reflux temperature is 70-90 ℃, and the reflux duration is 60-90 min.

S30, adding sodium chlorite solution into the crude fiber, adjusting the pH value with acetic acid, refluxing again, decompressing and filtering after the reaction is finished, washing with ethanol for a plurality of times, washing with distilled water to be neutral, drying and grinding the filter cake to obtain the cellulose.

Here, cellulose extraction: 0.5g of crude fiber is taken, 25mL of sodium chlorite (mass concentration is 3.5%) solution is added, acetic acid is used for adjusting the pH value to be 2, the mixture is refluxed for 80min at 80 ℃, the reaction is finished, the pressure reduction and suction filtration are carried out, the mixture is washed by ethanol for a plurality of times and then is washed to be neutral by distilled water, and a filter cake is dried and ground to obtain the cellulose.

Determination of the preferred NaOH mass concentration:

the concentration of sodium hydroxide is examined by single factor, the sodium hydroxide solution with the mass concentration of 2%, 4%, 6%, 8% and 10% is screened at the extraction temperature of 70 ℃ and the extraction time of 100min, and the experimental result is shown in figure 1. As seen from the figure, as the mass concentration of the NaOH solution increases, the cellulose content of the buckwheat straws increases firstly and then decreases. With the increase of the concentration of the sodium hydroxide solution, the solubility of the hemicellulose is increased, the content of the hemicellulose in the solution is high, and the viscosity of the solution is increased, so that the transfer resistance is increased, and the purity of the cellulose is reduced. Therefore, the mass concentration of the NaOH solution is preferably 4 percent.

Determination of the preferred extraction temperature:

the extraction temperature was examined for single factor, and at a sodium hydroxide mass concentration of 4% and an extraction time of 100min, the extraction temperatures of 50 ℃, 60 ℃, 70 ℃, 80 ℃ and 90 ℃ were examined for screening, and the experimental results are shown in fig. 2. The experimental results show that the optimal extraction temperature is 80 ℃.

Determination of the preferred extraction time:

and (3) carrying out single-factor investigation on the extraction time, wherein the mass concentration of the sodium hydroxide solution is 4%, and the extraction temperature is 80 ℃, and the extraction time is 60 min, 80min, 100min, 120 min and 140min for screening. It can be seen from fig. 3 that the cellulose content is highest at 80min, and decreases with the increase of extraction time after 80min, so the optimal extraction time is 80min in this experiment.

Comparing the appearance forms of the buckwheat straw cellulose obtained by different methods:

samples of buckwheat straw, crude cellulose and cellulose are shown in figure 4. Therefore, the buckwheat straws are tawny powder, and the colors of crude cellulose and cellulose sample extracted from the buckwheat straws by sodium hydroxide and sodium hydroxide-sodium chlorite are respectively yellow powder and white powder.

Comparing the cellulose content of the buckwheat straws obtained by different methods:

the method for measuring the cellulose content comprises the following steps: weighing a certain amount of sample, pouring the sample into a round-bottom flask, adding 25mL of nitric acid-ethanol mixed solution with the volume ratio of 1:4, heating and refluxing for 1h, cooling, performing suction filtration by using a G3 glass sand core funnel, washing residues by using the nitric acid-ethanol mixed solution, washing the residues to be neutral by using warm water, and finally continuously washing the residues by using absolute ethyl alcohol for a plurality of times. Dried at 105 ℃ and weighed, then calcined at 500 ℃ for 2h and weighed.

The calculation formula of the cellulose content is as follows:

cellulose content (mass before baking-mass after baking)/mass of product obtained x 100%

A certain amount of buckwheat straws, crude cellulose and a cellulose sample extracted by sodium chlorite are weighed, and the cellulose content is measured according to the method, wherein the cellulose content in the buckwheat straws is 61.76 percent, the cellulose content after sodium hydroxide extraction is 74.49 percent, and the cellulose content after sodium chlorite bleaching extraction is 83.21 percent. The cellulose content of the buckwheat straw sample extracted by different methods is higher than that of the buckwheat straw. The content of cellulose extracted by sodium hydroxide-sodium chlorite reaches up to 83.21%, the cellulose is white powder (figure 4) in color, and the cellulose is free of variegated color, so the sodium hydroxide-sodium chlorite is adopted for extracting the cellulose in the application.

Characterization of buckwheat straw cellulose:

analysis by scanning Electron microscope

The surface appearance of the buckwheat straw, the crude cellulose and the cellulose product was observed by a scanning electron microscope, and the result is shown in fig. 5. Fig. 5a shows the rough and irregular sheet structure of the buckwheat straw surface, which is the structure formed by wrapping the main chemical components of cellulose of the buckwheat straw with lignin and hemicellulose. The pores and reduced roughness appearing on the surface of the crude cellulose from the sodium hydroxide extraction of FIG. 5b indicate the removal of part of the lignin. The cellulose surface after the sodium chlorite extraction treatment of fig. 5d exhibited a helical structure and appeared fine pores and numerous individual fines, the cellulose surface became loose because the cellulose was completely exposed except for most of the lignin and hemicellulose that was wrapped around the cellulose.

Infrared spectroscopic analysis

The infrared spectrum is shown in FIG. 6. The characteristic peak of hemicellulose in buckwheat straws is 1732cm ^-1 Characteristic peaks of acetyl and lignin are 1592 and 1506cm ^-1 An aromatic skeleton belt is arranged at the position. According to the infrared spectrum, the characteristic peaks of the buckwheat straws after chemical treatment are weakened, the process has good effect of removing lignin and hemicellulose, and in addition, the characteristic absorption peak of cellulose is enhanced after treatment. Cellulose characteristic peak hydroxyl stretching vibration peak 3412cm ^-1 (ii) a C-H stretching vibration of alkyl 2928cm ^-1 The absorption peak at (a); 1652cm ^-1 The absorption peak is the bending vibration of the cellulose absorbing water; 1432cm ^-1 Has an absorption peak of CH ₂ Symmetric bending vibration; 1384. 1323cm ^-1 The absorption peaks are bending vibration of O-H and C-H; C-C stretching vibration, 1057cm ^-1 The absorption peak is C-O-C pyran ring framework vibration; 893cm ^-1 The absorption peak is the characteristic absorption of glucose beta-glycosidic bond in the cellulose, and the absorption peaks can be used as the characteristic peak for identifying the cellulose. The experimental result shows that the basic structure of the cellulose is not changed after the buckwheat straws are treated by the sodium hydroxide and the sodium chlorite, and the cellulose with higher purity is obtained.

XRD analysis

XRD was used to analyze the crystal structures of buckwheat straws, crude cellulose treated with sodium hydroxide, and cellulose obtained by bleaching with sodium chlorite, and the results are shown in fig. 7. As can be seen from the analysis in fig. 7, the positions of the diffraction peaks of the buckwheat straw and all the extracted cellulose are substantially consistent, and two strong diffraction peaks mainly appear at 2 θ ═ 22 ° and 2 θ ═ 16 °, wherein the 2 θ ═ 22 ° diffraction peak belongs to the type I cellulose 002 crystal plane, and the 2 θ ═ 16 ° diffraction peak belongs to the type I cellulose 110 crystal plane, which is a typical cellulose structure. The characteristic peak of the XRD pattern of the cellulose treated by buckwheat straws, sodium hydroxide extraction and sodium chlorite (figure 4) at 22 degrees is enhanced, which shows that the removal of lignin and hemicellulose in the buckwheat straws improves the crystallinity of cellulose molecules. Despite the variation in the intensity of the diffraction peaks, the internal structure of the cellulose was not destroyed after the chemical treatment. The sodium chlorite extracted cellulose had higher diffraction peaks compared to the peaks of other products, indicating that the cellulose was more crystalline.

According to the extraction method of the cellulose in the buckwheat straws, sodium hydroxide is used for removing hemicellulose, a sodium chlorite bleaching method is used for removing lignin, and the structure is represented by an IR (infrared radiation), SEM (scanning electron microscope) method and an XRD (X-ray diffraction) method. The influence factors of the extracted cellulose are researched by a single factor method: sodium hydroxide mass concentration, extraction temperature and extraction time. The experimental result shows that the optimal conditions for extracting the cellulose are that the mass concentration of the sodium hydroxide solution is 4%, the reaction temperature is 80 ℃, the reaction time is 80min, and the product is washed and dried; and (3) adding 0.5g of the product into a sodium chlorite (mass concentration is 3.5%) solution, adjusting the pH value to be 2 by using acetic acid, refluxing at 80 ℃ for 80min, washing and drying the product to obtain the cellulose. Under the optimized conditions, the cellulose content is 83.21%.

The structure is analyzed by means of a scanning electron microscope, a Fourier infrared spectrum and an XRD characterization method, and the experimental structure shows that the basic structure of the cellulose treated by the chemical reagent is not changed. Compared with loose porous cellulose with changed surface, which is extracted from the buckwheat straws and extracted from sodium chlorite, the loose porous cellulose has stronger diffraction peaks, and the characteristic peaks of the cellulose are not changed.

The cellulose provided by the application is prepared by the method.

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be clearly and completely described below. The examples, in which specific conditions are not specified, were carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are conventional products which are not indicated by manufacturers and are commercially available.

The optional reagents and instruments are sodium hydroxide (analytically pure), Fengshan chemical reagent science and technology Limited, Tianjin; nitric acid (analytically pure) permanent chemical plant; absolute ethanol (analytical grade) tianjin, remote chemical reagents ltd; buckwheat stalks are purchased from Nemantel flag, Tongliao, inner Mongolia. The buckwheat straws are washed, dried, crushed and screened (40-mesh screen). Other chemical reagents used in this study were analytically pure.

DHG-9240A electric heating constant temperature air blast drying oven (Shanghai Qixin scientific instruments Co., Ltd.); a GX-251250 g multifunctional pulverizer (Zhejiang Gaoxin Industrial and trade Co., Ltd.); JA5003 analytical balance (shanghai balance instrument factory); SHB-B25 circulating water type multipurpose vacuum pump (Zhengzhou great wall science, industry and trade Co., Ltd.); SET B S25 electromagnetic heating stirrer; muffle furnace Baotou Yunjie electric furnace factory; SU1510 scanning electron microscope; a Bruker-VERTEX-70 infrared spectrophotometer; rigaku UItima IV x-ray diffractometer.

The embodiments described above are some, but not all embodiments of the present application. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but is merely representative of selected embodiments of the application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Claims

1. A method for extracting cellulose from buckwheat straws is characterized by comprising the following steps:

2. The extraction method according to claim 1, wherein the buckwheat straw is washed, air-dried, pulverized and sieved to obtain buckwheat straw powder, specifically comprising

air drying: drying the washed buckwheat straws by air;

and (3) drying: drying the air-dried buckwheat straws in a drying oven;

3. The extraction method according to claim 1, wherein the buckwheat straw powder is 2g, the NaOH solution has a mass concentration of 2-6% and a volume of 100 mL.

4. The extraction process according to claim 3, characterized in that the NaOH solution has a mass concentration of 4%.

5. The extraction method according to any one of claims 1 to 4, wherein the two refluxing temperatures are both 70 to 90 ℃ and the refluxing duration is both 60 to 90 min.

6. The extraction process according to claim 5, characterized in that the reflux temperature is 80 ℃.

7. The extraction process according to claim 6, characterized in that the reflux duration is 80 min.

8. The extraction process according to claim 1, wherein the crude fiber is 0.5g, and the sodium chlorite solution has a mass concentration of 3.5% and a volume of 25 mL.

9. The extraction process according to claim 1, wherein the acetic acid is adjusted to pH 2.

10. Cellulose is characterized by being prepared by the method for extracting the cellulose in the buckwheat straws as claimed in any one of claims 1 to 9.