Study On Ethanol Ammonia Pretreatment To Improve Saccharification Of Wheat Straw And Preparation Of Submicron Lignin Spheres

With the rapid development of industrial civilization,the global demand for energy is increasing.However,the excessive use of fossil fuels has caused serious energy and environmental crises worldwide.Therefore,the use of lignocellulosic raw materials to produce energy,chemicals,or materials has attracted more and more attention,because lignocellulosic raw materials,especially waste biomass from agriculture and forestry,are readily available and renewable.However,due to the strong natural anti-degradation structure of wood fiber raw materials,the carbohydrates in the wood fiber raw materials cannot be efficiently converted and utilized.Therefore,the pretreatment technology of wood fiber raw materials has become a very important part in the process of conversion and utilization of wood fiber raw materials.However,the commonly used pretreatment technologies have problems such as high energy consumption,unclean processes,large water consumption,and difficulty in high-value utilization of lignin.Therefore,according to the characteristics of straw-based lignin fiber raw materials,the development of clean and efficient pretreatment technology is extremely important to improve the conversion and utilization efficiency of wood fiber raw materials(especially to improve the downstream saccharification efficiency).In this paper,wheat straw is treated with a less-researched ethanol ammonia pretreatment method.The effects of key pretreatment process parameters on hydrolysis and saccharification of wheat straw enzymes and the physical and chemical structure of wheat straw after pretreatment are systematically studied.The separated lignin is processed to prepare submicron lignin spherical particles,which provides a solution for the high value utilization of lignin.It is found through research that the pretreatment conditions for ethanol ammonia water pretreatment are better: the reaction temperature is 170 °C,the reaction time is 2 hours,the ethanol concentration in the pretreatment system is 55%(v / v),and the amount of ammonia water is 60%(based on the dry wheat straw raw material Mass),the liquid-solid ratio of the system is 8.Under this pretreatment condition,77% of the lignin and 90% of the extract can be efficiently removed,and the enzymatic hydrolysis conversion of cellulose and hemicellulose in wheat straw can exceed 90% after pretreatment.The total sugar yield was 81.7%,which was 2.25 times the pretreatment effect of conventional ethanol organic solvents.This is because,based on the characterization of the substrate properties after pretreatment,it was found that pretreatment with ethanol and ammonia can make the substrate fibers swell,remove lignin and extract efficiently,and significantly increase the void ratio and specific surface area of the substrate,and partially reduce the fiber.The crystallinity of the protein significantly increases the substrate’s accessibility to the enzyme and greatly increases the saccharification efficiency.And it was found through experiments that the substrate after ethanol ammonia water pretreatment was not washed with water,and its saccharification efficiency was not significantly reduced,which was beneficial to saving water consumption.On the other hand,both pretreated ethanol and ammonia are easy to recycle and reuse.According to the experimental results,the recovery rate of ethanol can reach 93.7%,while the recovery rate of ammonia water is 85.7%.The recovery and reuse of ethanol and ammonia can ensure the cleanliness of the entire pretreatment process and reduce the cost of pretreatment.In addition,since no metal salt is introduced in the pretreatment process of ethanol and ammonia water,the purity of the separated lignin is high.In this work,sub-micron lignin particles with an average diameter of 161.2 nm were prepared by acetylation of the separated lignin.The particle surface has a smooth and uniform distribution and has a hollow structure,which is expected to be used for slow release of drugs / active substances.The use of high added value of lignin can also significantly increase the economic feasibility of the entire pretreatment process.In summary,ethanol ammonia pretreatment is a clean and efficient pretreatment method,which can significantly improve downstream saccharification and achieve high value-added utilization of lignin.Therefore,ethanol ammonia water pretreatment has good potential for future scale-up production and practical application..