Study Of Mechanism Of Cooking Of Corn Stalk With A Solid Alkali And Active Oxygen And Characteirstic Of The Surface Of Its Pulp

With the development of society, oil is fast consumed due to the increased demand.Mankind is facing a difficult situation to look for a substitute for the future because the oilwill be used up for decades afterward according to the present rate of consumption. The plantbiomass will be the only carbon resources on the earth when the oil is used up in future,meaning that every country needs more investigation on the utilization of biomass, whichrelates to the development and safety of the country. The research in this dissertation wasperformed based on this situation and some meaningful results were obtained. In China, agreat amount of agricultural wastes was produced every year, especially for corn stalk.Therefore, corn stalk selected as a research object has the great significance for thesustainable development of agriculture.A novel method of cooking of corn stalk with active oxygen and a solid alkali wasstudied in this dissertation. Lignin can be removed by this method, and it can be used in theprocess of separation of lignocellulose. The active oxygen comes from O₂and H₂O₂, and thesolid alkali is MgO. This method is considered as a clean process for using the green chemicaland the solid alkali can be recycled. Otherwise, this method is different from the traditionaloxygen delignification, that is, a new medium system is built by the novel cooking methodthrough the substitute for the soluble alkali with the insoluble solid alkali.The process condition of the novel cooking was studied, and the optimum condition wasobtained: cooking temperature of165°C, solid alkali of15.4%, initial oxygen pressure of1.0MPa, H₂O₂of3.0%, solid-to-liquor ratio of1:6and keeping time of2h. Under the optimumcondition, the rate of delignification was82.1%, and the yield of pulp was50.7%. The resultsshowed that the solid alkali is an indispensable factor because it can protect the carbohydrateand increase the rate of delignification; the main factor of delignification was O₂, but thecombination of O₂and H₂O₂can obviously increase the rate of delignification.The results showed that the corn stalk became fibration after cooking and the ratio of O/Con the pulp surface increased. In the XPS after cooking, the intensity of C1decreased, but thatof C2, C3, C4increased showing that cellulose and hemicellulose are the main componentson the surface of pulp, and small amounts of carbohydrate are oxidized. In the pictures ofAFM, the pitting corrosion was observed on the surface of pulp cooked by active oxygen andthe solid alkali, but the surface of pulp cooked by alkaline cooking was glossy, meaning thatthe damage on the surface of pulp cooked by active oxygen and a solid alkali is more seriousthan that of alkaline cooking. TEM showed that the middle layer (ML) of fibrocyte was destroyed completely by active oxygen and the solid alkali cooking, but the alkaline cookingwas less efficient.The results showed that the protection of solid alkali resulted from Mg²⁺or its ionicgroup that must be put into the alkaline condition. The reason of the increase ofdelignification rate by solid alkali was possibly from its capacity that could provide duplet.The results from the cooking of absorbent cotton and microcrystalline cellulose showed thatthe solid alkali could protect cellulose from carbonization, but its crystal structure changedand the degree of polymerization (DP) decreased, especially for the low DP cellulose. Thepossible protective pathways of Mg were discussed in the dissertation.The results showed that a great amount of lignin was removed in the temperature riseperiod, and the rate of delignification increased with the increase of keeping time. The part ofdelignification was in the ML, and the reactive center was the benzene ring of lignin. Thebenzene ring of lignin was largely removed after the cooking with active oxygen and a solidalkali, especially for the benzene rings that contain conjugate double bond.The results indicate that the cooking with active oxygen and a solid alkali can be apretreatment of biorefinery because it can improve the rate of enzymolysis of cellulose.