1.1.1.1 directly extracted from the straw holocellulose with alkali to extract raw materials from straw hemicellulose method has been widely acceptable, and different methods of hemicellulose prepared lye has been established. Holocellulose with alkaline extraction of hemicellulose from pale brown, which contains a small amount of lignin (l% to 2%), this method can be used not only to identify the structure of hemicellulose, cellulose can be used as semi- In recent years, preparation methods, different alkali on straw hemicellulose yield and chemical composition have been extensively studied [4-6]. The study found that the lignin structure as herbs simpler than wood, so the annual herb of hemicellulose extracted easier than wood hemicellulose, while the difficulty of extraction and separation conditions are also related [#]. Different alkali straw hemicellulose fraction of wheat straw effects shown in Table 1. Generally accepted that potassium hydroxide, sodium hydroxide and hydroxide Keng best straw hemicellulose extraction, which Cellulose Science and Technology Vol 18 three kinds of alkaline extraction of hemicellulose was higher. Potassium hydroxide is generally more suitable for extraction of straw hemicellulose, and this is because in the course of the resulting solution of potassium acetate in ethanol is greater than the solubility of sodium acetate [#]. In addition, 10% KOH and 2% H3B03 hemicellulose extraction at 20 ℃ the best time is 21-26 h, and at 20 ℃ for 2h under optimal KOH extraction mass fraction is 20% ^ '30%, yield 34.21% ^ '34 .93%. With 24% KOH at 20 ℃ 2h extraction time, H3B03 the optimum amount of 2% or 5%. In KOH mass fraction of 24%, H3B03 amount of 2%, 20 ℃ under the conditions of extraction of wheat straw straw holocellulose 2h, the isolated hemicellulose xylose, arabinose, galactose, glucose molar ratio of 58: 5.6: 0.7: 2.0, uronic acid mass fraction of 3.1%, mass fraction of phenolic acids and 0.8%, hemicellulose weight-average molecular weight of 120,000 g/mo11410
1.1.1 alkali extraction method
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Keywords: straw; hemicellulose; separation; purification
1 hemicellulose separation
fractionation three components of biomass is cellulose, hemicellulose and lignin separation, and component composition of biomass conversion is based on structural characteristics, through physical, chemical and biological methods to transform for the significant fuel and materials. However, the traditional separation methods and technologies can not clean the dissociation of biomass components, components into the process of low efficiency, product type less pollution (such as cellulose industry). Therefore, the components of agricultural biomass separation and purification, chemical conversion of each component, for agricultural biomass into renewable and efficient use of resources to provide a theoretical basis. Over the past decade, the world of hemicellulose research has become one of the hotspots. Hemicellulose is a variety of plant fiber raw materials in a complex composition, the structure of hemicellulose in the study and hemicellulose on the basis of the theory, they often need to hemicellulose separated from the raw material in the separation process should try to complete separation, and to minimize changes in hemicellulose. In plant cell walls, hemicellulose and lignin bond between the connection (usually twenty-one benzene, ether), and acetyl cinnamic acid-based and light-based formation of vinegar key, cellulose and hemicellulose, although not between bond of connection, but the combination between them more closely [[2], these factors lead to the separation of hemicellulose is more difficult and complicated. So far there is no way to get high purity without the other components of the hemicellulose and hemicellulose in the separation process is also accompanied by varying degrees of degradation. Nevertheless, people are still actively exploring high yield and high purity separation of hemicellulose. In this paper, straw hemicellulose in recent years, the separation and purification methods are reviewed.
Abstract: China is a large agricultural country, every year a large number of agricultural straw is not fully utilized. Agricultural straw hemicellulose content is generally between 28% -35%. In the straw cell wall, hemicellulose and lignin, the connection between the chemical bond, and hydrogen bonding between cellulose connection, thus limiting the hemicellulose from the cell wall of separation. Separation of hemicellulose technology chemical, mechanical and chemical Combination, heat treatment, membrane separation, but so far no single technology can be more complete separation of hemicellulose from plant cell walls will separate. This paper summarizes recent years, agricultural straw hemicellulose separation technology, and made the main problems.
1.1.2 Hydrogen peroxide extraction method in recent years, studies have found that hydrogen peroxide is not only suitable for the removal of raw materials as straw and grass lignin, but also the dissolution and extraction of hemicellulose [lo]. Hydrogen peroxide in alkaline medium to form HOO one making it can be used to bleach, hydrogen peroxide, but unstable, easily under alkaline conditions, especially in the manganese,
herve leger skirts, iron, copper and other transition elements in the presence of decomposition HO-and 02 - Dilute alkali at pH 11.5, temperature of 50 ℃ under the conditions of the black straw processing dewaxing 12h, when there is no added H202, only got 7.3% of the hemicellulose, and in the same conditions, there is H20: there, they got 69.6% of hemicellulose [13]. In addition, the study also found, with 2% H202 at pH 11.512.0, 45 ℃ under the conditions of the corn stalks dewaxing process,
vibram five fingers outlet, the quality of the proceeds of the hemicellulose fraction of up to 63.3% ^ '64 .7%, molecular weight about 54,740 ^ 69,060 g / moll This approach than other organic acids such as peracetic acid extracted hemicellulose large molecular weight.
1.1 chemical present, generally from the delignification of the raw materials and defatted using chemical methods to separate the hemicellulose. Quantitative separation from the straw hemicellulose as follows: First, pretreatment of the raw material, a toluene ethanol (volume ratio 2 / 1) out of the pro-phenol insurance component; to get the raw materials and then the sum obtained after delignification cellulose, and alkali extraction. In addition, the direct extraction method from less hemicellulose and hemicellulose impurities is accompanied by the same time out, to the purification more difficult. Therefore, most of the first non-test material extract prepared holocellulose, and then extracted from holocellulose isolated hemicellulose. In the preparation of holocellulose, due to minimize the degradation of cellulose and hemicellulose, hence the preparation of holocellulose in general still remained 1% ^ '2% of the lignin, hemicellulose classification to produce difficult.
1.1.1.2 directly from the dewaxing of straw hemicellulose extracted directly with alkaline hemicellulose extraction dewaxing of raw materials is another way of preparation. After adjusting the pH value of alkaline extraction of hemicellulose and lignin available,
Beats By Dre Headphones, this method has environmentally friendly, simple and efficient and so on. In recent years, this method is used to separate 17-81 small straw, bagasse [191, a large straw [lo], corn stalks, rice straw [River hemicellulose and lignin. The result showed that at 30 ℃, extraction dewaxing corn stalks,
tods shoes outlet, black straw, rice straw stalks 18 h, respectively, to be 78.0%, 68.8%, 82.1% lignin and 72.1%, 72.6%, 84.6% of the semi-fiber Su. Alkali treatment makes the light-based acid, p-coumaric acid, ferulic acid and lignin or hemicellulose bond breakage in the vinegar, hemicellulose and lignin between twenty-one diphenyl ether bond breaking, the hemicellulose and lignin The yield is high. With 1.0 mol / L NaOH under the same conditions, respectively, from corn stalks, black straw,
Salvatore Ferragamo outlet, rice straw stalks in the removal of 89.2%, 92.6% and 88.9% of the silica (silicon dioxide are mainly concentrated in the skin part of the straw ). Experiments show that, 1.0 mol / L NaOH straw removal of silica is the preferred solvent. At the same time, 1.0 mol / L NaOH straw is also a large number of soluble proteins and low molecular weight polysaccharides. Dewaxing of raw materials directly from alkaline extraction of hemicellulose content in phenolic compounds is about half cellulose extracted holocellulose from 5-10 times the polyphenol content, which indicates that extraction of holocellulose with alkali from the dewaxing than direct extraction of hemicellulose from hemicellulose raw materials of high purity.
CLC number: 0636.1 Document code: A
world crop acreage in China The first annual yield over 700 million tons of agricultural straw, rice straw of which about 1.8 million tons, 110 million tons of wheat straw, corn stalks 200 million tons. In addition, the bagasse is a by-product of sugar industry, is one of the most important non-wood renewable resources of agricultural solid waste is one of China's output of 7 million tons of bagasse. The burning of agricultural waste is mainly used for direct heat, and partly used as feed, fertilizer and raw material for pulp and paper industry, but in the insufficient use of these areas 20% of total agricultural waste}. Therefore, the effective use of such a huge amount of agricultural waste, agricultural development in China will play a positive role in promoting. Agricultural straw renewable natural resources into chemicals or biodegradable materials are generally two ways: one is the direct conversion approach, all components of the straw directly into industrial products, as components for such a transformation does not require separation process is simple, can significantly reduce costs, but because the components are mixed together, conversion efficiency is low; the other is the indirect way of transformation, the biomass of agricultural straw after the separation of each component using the first transformation, this transformation high efficiency, availability of agricultural straw biomass maximum use of high-value, which is a component separation and conversion of two key components of the process.
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