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pm | Research progress on the separation and extraction (14th Nov 22 at 12:48am UTC) | | Original Title: Research Progress on Separation and Extraction of Lignin Lignin is a natural macromolecular material with phenolic structure, which widely exists in woody plants, herbaceous plants and vascular plants. It is the second largest natural macromolecular material in nature after cellulose in quantity and the only aromatic compound that can be obtained from renewable resources in industry. Lignin is widely used in building materials industry, petroleum industry, light industry and agriculture. Lignin is also an important component of human Dietary fibres (DF), which can change the activity of microorganisms in the intestinal system, reduce the content of cholesterol and blood sugar in the blood, and prevent cardiovascular diseases [2]; lignin also has antioxidant activity [3] and cancer cell inhibition activity [4]. As a natural antioxidant active substance, the anti-free radical activity of lignin in wood and crop straw has been extensively studied [5], while the research on lignin in dietary fibers such as vegetables and fruits is rare [6]. Lignin was extracted from carrot and its structure and antioxidant activity were studied. It is expected to get a natural, non-toxic side effects of antioxidant active substances, which has a wide range of applications in food industry, cosmetics, health products and so on. The extraction and separation methods of lignin generally include acid, alkali, supercritical, aqueous two-phase, ionic liquid, organic solvent and other means, among which the organic solvent method has become the most popular extraction and separation method in recent years because of its environmental protection, economy and easy separation. However, most of them require high temperature and high pressure conditions, and there are still many technical difficulties in its complete industrialization, which greatly limits its application. Therefore, this paper also introduces several improved methods by using organic solvents, and focuses on the experimental process of extracting and separating carrot lignin by using high boiling solvent. The individual unifies the reading material the elaboration, hoped has the help to everybody. Method for extracting and separating lignin Expand the full text Acid precipitation method Klason [7] used 64% ~ 72% concentrated sulfuric acid to hydrolyze carbohydrates to separate lignin, which was called Klason lignin. Due to Klason wood The simplicity of lignin measurement makes it widely used in many measurements, but this method is not suitable for the study of lignin structure. Willstatter [8] first used 40% ~ 42% fuming concentrated hydrochloric acid to dissolve cellulose at 0 ℃ to separate hydrochloric acid lignin or Willstatter lignin. Compared with Klason lignin, it can be applied to structural studies. Although acid solution can hydrolyze cellulose into aqueous solution and precipitate lignin, this separation method itself has great disadvantages. Because under the action of temperature rise and protons, lignin produces positive carbon ions under acidic conditions. Alkali precipitation method Wang Sanfan et al. Used alkali precipitation method to treat papermaking black liquor from different cooking processes, which proved that it was effective to extract lignin by alkali precipitation method [9]. The mechanism of alkali precipitation is that the lignin in the black liquor of papermaking contains phenolic hydroxyl group, phenolic alcohol group, carboxylic acid group, carbonyl group and other easily chelated groups, which is a typical multi-group ligand and can form a lignin chelate with "chelation" with the added metal ions. The main factors affecting the precipitation rate of lignin were pH value and the dosage of metal ions. Lignin chelate could be formed only by adding high valence metal cations under alkaline conditions, and the precipitation rate of lignin increased with the increase of pH value; the higher the valence state of metal ions and the smaller the radius, the easier the chelation, and the greater the dosage, the greater the precipitation rate of lignin. Ultrafiltration Lignin is a kind of macromolecular compound, which can be extracted from black liquor of papermaking by ultrafiltration in principle. Li Zhongmin et al discussed the feasibility of recovering lignin by ultrafiltration. The experiment proved that the ultrafiltration method could effectively recover lignin from papermaking black liquor, and the recovery rate was 95.5%. The permeation flux of high concentration solution was smaller than that of low concentration solution, and the time needed to achieve constant permeation flux was shorter; Treatment of ultrafiltration membrane with 5 G/L polyoxyethylene sorbitan monolaurate surfactant can reduce the deposition or adsorption of solute on the membrane surface and improve the anti-fouling performance of ultrafiltration membrane [10]. Supercritical extraction of lignin Cellulose and lignin are selectively separated by utilizing the different distribution of cellulose and lignin in the solvent under the supercritical condition. With the increase of CO2 pressure, the conditions of supercritical extraction become more and more similar to those of organic solvent extraction due to the use of organic solvents as additives. However,hemp extraction centrifuge, with the continuous optimization of the selection of additives, the operating pressure of CO2 will continue to decrease, and supercritical extraction becomes a competitive separation process [11]. Separation of Lignin by Aqueous Phase Extraction Two-phase aqueous extraction is widely used in the extraction of bioactive substances because of its mild extraction conditions. ABS process can solve the problem of high consumption of chemicals and energy in traditional pulping process, and the operation of temperature and pressure is relatively easier than that of organic solvent extraction. Lignin and cellulose were separated from each other by adding different concentrations of K2CO3, (NH4) 2SO4 and NaOH into Stock solution PEG-6000 according to the different partition coefficients in the two aqueous phases of lignin and cellulose. The use of two aqueous phases for lignin extraction will likely be a powerful adjunct to the delignification process in pulping [12]. Organic solvent method At present, with the widespread recognition and acceptance of the concept of sustainable development, green chemistry process has become a hot research topic. This requires the components to be separated. The process should not only achieve the multi-level effective utilization of the separation products, but also take into account the more effective recycling of the separation reagents. In this context, organic solvents have attracted much attention. Compared with the existing alkaline or acid pulping method, the method for separating the cellulose, the hemicellulose and the lignin by using the organic solvent has the following advantages: (1) vacuum drying is used, so that the extract and the solvent can be quickly and effectively separated; (2) the extract can be recycled by condensation, so that the emission of pollutants to the environment is reduced; And (3) the organic solvent is used, so that the extraction environment is relatively mild, the denaturation degree of the lignin is less, and the implementation of subsequent chemical modification is facilitated. However,wiped film distillation, organic solvent pulping still requires high temperature and high pressure, and there are still many technical difficulties in complete industrialization, which greatly limits its application. Several methods of improvement using organic solvents are described below. Inorganic alkaline aqueous solution method and organic solvent-water mixed solvent method The inorganic alkaline aqueous solution method and the organic solvent-water mixed solvent method adopted by Fuzhou University can effectively separate the residue of straw fermentation Xtracting the enzymolysis lignin. The separation and extraction process of the lignin does not go through chemical processes such as high temperature, high pressure, strong acid, strong alkali and the like, The structure is kept well, and the chemical reaction activity is high. Inorganic Alkaline Aqueous Solution Method and Organic Solvent-Water Mixed Solvent Method Adopted by Fuzhou University It can effectively separate and extract enzymolysis lignin from the residue of straw fermentation. The lignin is separated and extracted without high temperature and high pressure, The chemical structure of natural lignin is well maintained and has high chemical reactivity in chemical processes such as strong acid and strong alkali. 2.6.2 High-boiling solvent method (HBS) with microwave radiation as heating source From the point of view of energy saving and emission reduction, energy saving and environmental protection, and in line with the current reality and green needs, microwave radiation is used as the heating source. Lignin was extracted from carrot by using ethylene glycol as extractant, and the results were satisfactory. The microwave radiation is used as a heating source, so that the method has the advantages of rapidness, energy conservation, high efficiency and cleanness; and the extracting agent, namely the aqueous solution of ethylene glycol, has the characteristics of low toxicity and difficult volatilization, can be recycled through distillation after extraction, basically has no pollutant discharge, and has the advantages of zero emission and no pollution. In this method, water-insoluble lignin is dissolved in a high-boiling alcohol solvent under heating conditions to separate from cellulose, and then lignin is obtained by water precipitation, which can better maintain the original structure and activity of lignin and has broad application prospects [13, 14]. The following is a specific experiment: Extraction and Separation Process of Carrot Lignin by High Boiling Solvent Rinse fresh carrots and dry at room temperature. Cut the carrot into 0.5 mm thick slices with a clean stainless steel blade. Stored at room temperature and ventilated for different periods of time. The above carrot slices were quickly de-enzymed in a blast drying oven at 120 ℃, then dried to constant weight at 60 ℃, ground into powder, sieved with a sieve with an aperture of 0. 088 mm to obtain carrot fine powder, and placed in a drying vessel for later use. Weigh 16.3 G of carrot powder and place it in an autoclave. After being added into the ethylene glycol solution with the mass fraction of 80% according to a certain feed liquid mass ratio, the mixture is heated to a certain temperature and is cooled to 60 deg C after reacting for a certain time. The reaction mixture was filtered under reduced pressure, and the filter cake was washed with warm water at 70 ° C to obtain lignin solution. At room temperature, decarboxylation after extraction ,wiped film evaporator, 3 volumes of water were added and stirred for 15 min, and the lignin was precipitated. Filtering under reduced pressure, and washing the filter cake with warm water at about 60 deg C to obtain brown powdery coarse lignin. Wrap 0.5 G of crude lignin with filter paper and put it in a fat extractor, and extract it with a mixed solvent of V (benzene): V (ethanol) = 1:1 for 8 H until the extract from the upper part of the fat extractor to the lower part is colorless. The lignin was removed and vacuum dried to give 0.46 G of purified lignin [15]. After a series of experiments, the optimum conditions of extracting carrot lignin with HBS were as follows: fresh carrot slices as raw material, mass ratio of raw material 1:6, reaction temperature 210 ℃, reaction time 2 H. Under these conditions, the yield of lignin was the highest. Application of lignin Lignin is a renewable natural macromolecular organic compound. Its development and comprehensive utilization are of great significance to the rational use of resources, economic development and environmental protection. In agriculture, it is used as a slow-release pesticide. Lignin can be used as a carrier to prepare lignin slow-release pesticides by physical adsorption and chemical reaction with pesticides, fungicides, herbicides and plant growth regulators under specific conditions. On the one hand, because lignin has a variety of active groups, it has a strong combination with pesticide molecules, which reduces the release rate of pesticides. On the other hand, the slow degradation of lignin by microorganisms in nature also slows down the release of pesticides. Therefore, lignin slow-release pesticides can prolong the efficacy, reduce toxicity, improve the utilization rate of pesticides, reduce environmental pollution, and have great application potential in modern agriculture. It can also be used to make fertilizer. Because of the difficulty of alkali recovery, the black liquor of non-wood pulping is often discharged directly into the natural environment, resulting in serious pollution of the soil and rivers where the sewage is discharged. The main method to solve the problem is the ammoniation reaction of lignin. At present, the production of "ammonia-nitrogen lignin" by oxidative ammonolysis is mostly studied: under oxidative conditions, lignin can undergo ammoniation reaction to produce nitrogen-modified lignin, which can be used as a potential agricultural nitrogen fertilizer or humus. Generally, nitrogen fertilizer will be released rapidly after application, which will seep into the groundwater system and cause secondary pollution, while nitrogen-modified lignin has long-term and slow effects, and to a certain extent, it can reduce environmental pollution. In addition, lignin can also be used to produce functional fertilizers, such as chelated fertilizer, activated phosphate fertilizer, soil improvement fertilizer and so on. Lignin can be used as a coating material. Therefore, lignin-coated urea can be prepared, which has better slow-release effect and yield-increasing effect than common urea, and its slow-release characteristic has stronger after-effect than common urea. It can maintain the continuous and balanced supply of nutrients, improve the utilization rate of nitrogen fertilizer, and reduce the environmental pollution caused by nitrogen fertilizer [16]. In addition to agriculture, lignin is widely used in industry and construction. Conclusion The above materials show that the separation, extraction and purification of lignin has been widely concerned, and the method has reached the level of a hundred schools of thought contending and a hundred flowers blooming. The technology of extracting lignin by organic solvent has obvious advantages. Because of the good volatility of organic solvent, organic solvent can be recovered and lignin can be purified by distillation. The recovered organic solvent can be recycled repeatedly, a closed circulation system is formed in the whole process, and no waste water or a small amount of waste water is discharged, so that the method is an effective technical approach for realizing pollution-free or low-pollution 'green environmental protection', is also an effective way for extracting and purifying the lignin, and provides a new approach for large-scale development and utilization of lignin resources in industry. The extraction and purification technology of lignin needs to be improved, and the lignin with high purity as raw material can be used to produce lignin products with good performance. Our country has done some work in the utilization of lignin. However, it is far from keeping up with the needs of the development of the national economy. Organize the research work of lignin in a planned way It will be an urgent task to develop China's lignin industry and catch up with the international advanced level. In addition, the anti-free radical activity of lignin in wood and crop straw has been extensively studied, while the research on lignin in dietary fibers such as vegetables and fruits is rare. Lignin in dietary fiber is of great significance in food, cosmetics and health care products, which is in line with people's urgent need for high-quality life. Therefore, the study of lignin in dietary fiber will be a very promising work, and we should increase this research. References: [1] Jiang Tingda. Lignin. Beijing: Chemical Industry Press, 2001. [2] WiUiarns R L. Elliot M S. Antioxidants in Grapes and Wine:Chemistry and Health Effects. In Natural antioxidants:Chemistry,Health Effects and Aapplications[M]. Shaihidi F,Ed. 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