Flocculation Separation Of Lignin In The Rice Straw Pretreatment Lye And Process Optimization

Lignin as a renewable natural organic polymer has widely application in the fields of industry, agriculture, medicine and other fields. Agricultural waste straw, one of the main sources of lignin, the biomass of rice straw containing about 20% of the lignin which is an abundant biomass resources and have the potential use value. However it also contains 35% to 40% cellulose and 25% of hemicellulose, they are built up a dense network structure so that lignin must be wiped out before each component of lignocellulose be utilized. Lignin can be effectively pretreated by SO3 micro-thermal explosion combined with alkali treatment. However, in order to realize the resource utilization of lignin while avoiding environmental pollution, an effective separation technology is needed, which can not only separate lignin from lignin lye with high efficiency, but also allow lye to be recycled. Therefore, the main contents of this paper include:selection of the optimum lye lignin separation method, process optimization of flocculation separation conditions and exploration separation mechanism of different separation methods, and the following results are obtained:(1)Firstly, screen flocculation from metal ions, organic solvents and macromolecular compounds which can efficiently separated lignin from lignin lye. CaCl2 and glyoxal showed high ability to separate lignin lye.1.2g flocculation product was obtained by adding 1g of CaCl2 into 100mL lye, and its lignin content reached about 17%; Adding lOmL 30% aqueous solution of glyoxal into 100mL lye obtained about 1.7g of flocculation product, and 35% lignin content was gained.(2)Then using lignin product yield and lignin content of flocculation as indicators, optimized the process of CaCl2 separation method, and a best process route was obtained:addition amount of CaCl2 was 1% of the amount of alkali liquor, flocculation temperature was 50.39℃,and the flocculation time was 6 h. Under the condition of alkaline pH of 11, lignin yield reached about 1.0 g, lignin content in the separation product was about 40%. Using Design Expert software for typical experimental model analysis, obtained the conditions gaining biggest flocculation product yield and the lignin content:CaCl2 addition amount of 1.09g, flocculation temperature was 50.39℃, alkaline pH of 10.91. Under this condition, determine lignin of CaCl2 flocculation separation lye:the actual flocculation isolated product yield achieved 0.8347g and the actual lignin content in the flocculation product reached 44.32% after 6h, which shows that optimal flocculation conditions indicate an obvious effect.(3) Using FT-IR, XPS detection methods to determine lignin of separated lye acted on combination of amines and glyoxal. The infrared spectrum showed that an distinct characteristic absorption band was presented corresponding to the method that using combination of glyoxal and ethylenediamine to separate lignin, elemental analysis showed that N element content of the separated product has been significantly increased. At the same time, by optimizing the lignin separation process with combination of glyoxal and ethylenediamine, obtained the best process route: addition amount of 30% glyoxal solution was 10% of the amount of total alkali liquor, addition amount of ethylenediamine was 1% of total alkali and flocculation temperature was 90 ℃with flocculation time 6 h, and maintaining pH to the original alkaline environment (around 13), the yield of the separated lignin was about 2.0 g, and lignin content in flocculation was about 39%.