阅读说明：本技术 一种黑液中木质素高值化利用方法 (high-value utilization method for lignin in black liquor ) 是由 房桂干 严振宇 邓拥军 沈葵忠 于 2019-09-12 设计创作，主要内容包括：本发明公开了一种黑液中木质素高值化利用方法,利用硫酸等稀酸来逐级调节黑液的pH值,使木质素分级沉淀,并将获得的木质素用乙醇/水混合溶液提纯,获得的木质素纯度高,分子量分布均一。通过逐级沉淀,能有效的对木质素基于分子大小进行分类,有利于木质素样品的进一步开发利用。通过乙酰化反应对木质素样品进行疏水性改性处理,可以改变木质素在有机溶剂-水混合体系中的溶解性能,使木质素能够作为原材料制备药物控释剂或纳米吸附材料等新型材料,从而拓展木质素的应用范围。本发明提供的方法成本投资低,药品毒性低,所需设备少,操作方法简单,易于实现大规模生产应用。(the invention discloses a method for utilizing lignin in black liquor at a high value, which utilizes dilute acid such as sulfuric acid to gradually adjust the pH value of the black liquor so as to precipitate the lignin in a grading way, and the obtained lignin is purified by ethanol/water mixed solution, so that the obtained lignin has high purity and uniform molecular weight distribution. Through the step-by-step precipitation, the lignin can be effectively classified based on the molecular size, and the further development and utilization of lignin samples are facilitated. The lignin sample is subjected to hydrophobic modification treatment through acetylation reaction, so that the solubility of lignin in an organic solvent-water mixed system can be changed, and the lignin can be used as a raw material to prepare novel materials such as a drug controlled release agent or a nano adsorption material, and the application range of the lignin is expanded. The method provided by the invention has the advantages of low cost and investment, low drug toxicity, less required equipment, simple operation method and easy realization of large-scale production and application.)

1. A high-value utilization method of lignin in black liquor is characterized by comprising the following steps: the method comprises the following steps:

(1) Taking a black liquor sample, filtering to remove solid impurities in the black liquor sample, and adding distilled water to dilute the black liquor sample to obtain a diluent;

(2) Adding dilute acid into the diluent under the condition of stirring, adjusting the pH value to 6, simultaneously separating out precipitate, and separating to obtain a first-stage precipitate and a first-stage supernatant; continuously adding dilute acid into the primary supernatant under the stirring condition, adjusting the pH value to 4, simultaneously separating out precipitate, and separating to obtain secondary precipitate and secondary supernatant; continuously adding dilute acid into the second-level supernatant under the stirring condition, adjusting the pH value of the liquid to be 2, simultaneously separating out precipitate, and separating to obtain third-level precipitate and third-level supernatant;

(3) Respectively adding the first-stage precipitate, the second-stage precipitate and the third-stage precipitate into an ethanol/water mixed solution, stirring to fully dissolve the precipitates, respectively marking the obtained liquid as A1, A2 and A3, respectively adding dilute acid into A1, A2 and A3 to adjust the pH values to be 6, 4 and 2, and simultaneously separating out the precipitates; the solids obtained by separating A1, A2 and A3 are respectively marked as L1, L2 and L3, and the obtained liquids are respectively marked as B1, B2 and B3;

(4) Washing L1, L2 and L3 with water to be neutral, and drying to obtain lignin samples with sequentially reduced molecular weights;

(5) Adding L2 into an acetyl chloride/glacial acetic acid mixed solution for acetylation reaction to prepare a hydrophobic modified product AL 2.

2. the method of claim 1, wherein: in the step (1), the black liquor sample is black liquor generated in a cooking section in a pulping process.

3. The method of claim 1, wherein: in the step (1), the volume of the distilled water is 8-10 times of the volume of the black liquor.

4. The method of claim 1, wherein: in the step (2) and the step (3), the dilute acid is hydrochloric acid or sulfuric acid, and the operation temperature is 20-25 ℃.

5. The method of claim 4, wherein: the concentration of the hydrochloric acid or the sulfuric acid is 1-3 mol/L.

6. The method of claim 1, wherein: in the step (2) and the step (3), the separation is performed by a centrifuge, the rotation speed of the centrifuge is 3000-.

7. The method of claim 1, wherein: in the step (3), the volume ratio of the ethanol to the water in the ethanol/water mixed solution is 7: 3.

8. The method of claim 1, wherein: in the step (4), the drying temperature is 60-80 ℃.

9. the method of claim 1, wherein: in the step (3), the B1, B2 and B3 can be used for recovering ethanol through evaporation by a rotary evaporator.

10. The method of claim 1, wherein: in the step (5), the volume ratio of acetyl chloride to glacial acetic acid in the acetyl chloride/glacial acetic acid mixed solution is 1: 4; the acetylation reaction is carried out under the condition of stirring, the temperature of the acetylation reaction is 30-40 ℃, and the time is 1-3 h.

Technical Field

The invention belongs to the technical field of lignin recycling, and particularly relates to a high-value utilization method of lignin in black liquor.

Background

Lignin is an amorphous high molecular polymer with a relatively high molecular weight and a reticular structure, which is difficult to hydrolyze under the action of acid, and has a complex structure and non-uniform relative molecular weight, the chemical structure of the lignin is a complex compound consisting of phenylpropane structural units, and 3 basic structures (non-condensed structures) are provided, namely a guaiacyl structure, a syringyl structure and a p-hydroxyphenyl structure. In the pulping and papermaking industry, black liquor generated in a cooking section contains nearly 90% of pollutants in the pulping and papermaking process, including a large amount of degradation products such as lignin, hemicellulose and the like, and is degradation wastewater with high alkalinity, high COD (chemical oxygen demand) and high lignin content. The black liquor contains a large amount of lignin which accounts for 1-2% of the total amount of the waste liquor and 30% of the total solid content, the lignin is an important industrial raw material, the lignin has wide application range, good polydispersity, flame retardance, solvent resistance and thermal stability, and a molecular structure of the lignin contains various active functional groups and is non-toxic and cheap, so that the lignin is widely applied to the fields of high polymer plastics, surfactants, viscosity reducers, crop fertilizers, cement, soil conditioners and the like. However, at present, more than 95% of lignin waste is directly discharged with waste water, buried or treated in a concentration incineration manner, which not only pollutes the environment, but also causes huge waste of resources. About 5000 ten thousand tons of lignin byproducts are produced every year in the pulping and papermaking industry, but the utilization rate is not high, and China is less than 10 percent. Therefore, a good method for separating and extracting lignin is found, waste resources are recycled, the method has an important effect on treating pollution caused by papermaking black liquor, and the method has great research significance from the economic perspective and the environmental protection perspective.

The existing utilization method of lignin is directly utilized and degraded to be used as a chemical raw material and modified to be used. Due to the complex chemical structural units, functional groups and bonds and modes of lignin, the properties of lignin structures, relative molecular masses and the like prepared by different separation methods are greatly different. The uniformity of the molecular structure of the lignin is beneficial to the application of the lignin in the fields of polymer synthesis and materials, so that the lignin in the black liquor is separated step by step according to the molecular weight distribution range, and the lignin has important significance for high-value utilization of the lignin. And the lignin obtained by extraction is subjected to hydrophobic modification treatment, so that the solubility of the lignin in an organic solvent-water mixed system can be changed, and the lignin can be used as a raw material to prepare novel materials such as a drug controlled release agent or a nano adsorption material, and the application range of the lignin is expanded.

Disclosure of Invention

aiming at the problems of complex structure and low recovery utilization rate of the existing lignin, the invention aims to provide a high-value utilization method of lignin in black liquor, which is characterized in that the pH value of a system is adjusted step by adding acid, so that lignin is subjected to fractional precipitation to obtain a lignin sample with uniform molecular weight distribution; and the lignin sample is subjected to hydrophobic modification to expand the application range of the lignin sample.

in order to achieve the purpose, the invention provides the following technical scheme:

a high-value utilization method of lignin in black liquor comprises the following steps:

(1) Taking a black liquor sample, filtering to remove solid impurities in the black liquor sample, and adding distilled water to dilute the black liquor sample to obtain a diluent;

(2) adding dilute acid into the diluent under the condition of stirring, adjusting the pH value to 6, simultaneously separating out precipitate, and separating to obtain a first-stage precipitate and a first-stage supernatant; continuously adding dilute acid into the primary supernatant under the stirring condition, adjusting the pH value to 4, simultaneously separating out precipitate, and separating to obtain secondary precipitate and secondary supernatant; continuously adding dilute acid into the second-level supernatant under the stirring condition, adjusting the pH value of the liquid to be 2, simultaneously separating out precipitate, and separating to obtain third-level precipitate and third-level supernatant;

(3) Respectively adding the first-stage precipitate, the second-stage precipitate and the third-stage precipitate into an ethanol/water mixed solution, stirring to fully dissolve the precipitates, respectively marking the obtained liquid as A1, A2 and A3, respectively adding dilute acid into A1, A2 and A3 to adjust the pH values to be 6, 4 and 2, and simultaneously separating out the precipitates; the solids obtained by separating A1, A2 and A3 are respectively marked as L1, L2 and L3, and the obtained liquids are respectively marked as B1, B2 and B3;

(4) washing L1, L2 and L3 with water to be neutral, and drying to obtain lignin samples with sequentially reduced molecular weights;

(5) Adding L2 into an acetyl chloride/glacial acetic acid mixed solution for acetylation reaction to prepare a hydrophobic modified product AL 2.

In the further scheme, in the step (1), the black liquor sample is black liquor generated in a cooking section in a pulping process. The volume of the distilled water is 8-10 times of the volume of the black liquor; it is further preferred that the volume of distilled water is 9 times the volume of black liquor.

In the further scheme, in the step (2) and the step (3), the operation temperature is 20-25 ℃; the dilute acid is hydrochloric acid or sulfuric acid, and the concentration of the hydrochloric acid or the sulfuric acid is 1-3 mol/L; the separation is carried out by adopting a centrifugal machine, the rotating speed of the centrifugal machine is 3000-4000r/min, and the centrifugal time is 10-20 min.

Further, in the step (3), the volume ratio of ethanol to water in the ethanol/water mixed solution is 7: 3.

in the step (4), the drying temperature is 60-80 ℃.

further, in the step (3), the B1, B2 and B3 can be used for recovering ethanol through evaporation by a rotary evaporator.

in the step (5), the volume ratio of acetyl chloride to glacial acetic acid in the acetyl chloride/glacial acetic acid mixed solution is 1: 4; the acetylation reaction is carried out under the condition of stirring, the temperature of the acetylation reaction is 30-40 ℃, and the time is 1-3 h.

compared with the prior art, the invention has the beneficial effects that:

(1) the invention utilizes dilute acid such as sulfuric acid to gradually adjust the pH value of the papermaking black liquor, so that lignin is precipitated in a grading way, and the obtained lignin is purified by using ethanol/water mixed solution, and the obtained lignin has high purity and uniform molecular weight distribution. Through the step-by-step precipitation, lignin can be effectively classified based on molecular size, wherein the molecular weight distribution ranges of lignin samples L1, L2 and L3 are 3000-3500 Da, 2500-3000 Da and 2000-2500 Da respectively. Wherein the polydispersity index of L2 is 1.29, the molecular weight distribution is relatively uniform, and the further development and utilization of the lignin sample are facilitated.

(2) According to the invention, acetyl is introduced at the position of phenolic hydroxyl through acetylation reaction, and the lignin sample is subjected to hydrophobic modification, so that the solubility of lignin in an organic solvent can be increased; by introducing hydrophobic acetyl, the acetylated lignin can form nano colloidal spheres in an organic solvent-water mixed system by a self-assembly method, so that the application range of the lignin is expanded, the lignin can be used as a raw material to prepare novel materials such as a drug controlled release agent or a nano adsorption material, and the application value of the lignin is improved.

(3) the high-value utilization method of lignin in black liquor provided by the invention has the advantages of low cost and investment, low drug toxicity, less required equipment, simple operation method and easy realization of large-scale production and application.

drawings

FIG. 1 is a gel permeation chromatogram of lignin sample L1;

FIG. 2 is a gel permeation chromatogram of lignin sample L2;

FIG. 3 is a gel permeation chromatogram of lignin sample L3;

FIG. 4 is an infrared spectrum of a lignin sample L2 and a hydrophobically modified product AL 2.

Detailed Description

The present invention will be further described with reference to the following examples. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. 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 invention.

The black liquor sample used in this example was black liquor produced in the cooking stage of the pulping process. The pulping process comprises the following specific steps: 2000g of oven-dried eucalyptus is put into a 10L vertical cooking pot, the vulcanization degree is 25%, the solid-to-liquid ratio is 1:4, the dosage of Na2O is 17.5%, the H factor is calculated from 100 ℃, the temperature is raised to 170 ℃, and then the temperature is preserved until the H factor is accumulated to 2100. And collecting the discharged black liquor for later use after the reaction is finished.