The Study Of Saccharides Hydrolysis To Levulinic Acid

Levulinic acid,which has good reactive activity,is an important green platform chemical. Levulinic acid is always prepared by acid hydrolysis under the condition of high temperature and high pressure, so the problem exists in the corrosion for the equipment. The paper aim at keeping the preparation of levulinic acid under normal temperature and pressure conditions. The reaction kinetic of glucose hydrolysis, and use ketones to restrain the humus material which is generated in the glucose hydrolysis process were studied.The preparation of levulinic acid from saccharides was compared by using ultrasound-microwave assisted method. The results showed: The generation rate of levulinic acid by monosaccharides hydrolysis was related to the their conformations. The generation rate of levulinic acid by oligosaccharides or polysaccharides hydrolysis was related to their monosaccharides hydrolysis rate, and the yield of levulinic acid was related to their own structures and monosaccharide compositions. Using the corn starch as raw material for the parparation of levulinic acid. Optimization of the preparation of levulinic acid from corn starch using central composite design, the optimum conditions were: the microwave power 100 W, the reaction time 90 min, the concentration of the hydrochloric acid 4.5 mol/L, the ratio of liquid to solid 15:1(mL/g), with the levulinic acid yield 23.17%.The ratio of liquid to solid (mL/g), the concentration of hydrochloric acid, the reaction temperature that impact on the reaction kinetic of glucose hydrolysis were studied. The reaction kinetics orders could be controlled by the ratio of liquid to solid, while the ratio of liquid to solid was greater than 30:1 for the first order reaction, less than 30:1 for the second order reaction. The realationship between initial reaction rate and the hydrochloric acid was in a linear. The conversion rate of glucose and the generation rate of levulinic acid increased significantly when the reaction temperature increased. The decomposition activation energy of glucose is 110.63 kJ/mol, the generation activation energy of levulinic acid is 161.41 kJ/mol.Ketones were used to restrain the humus material which was generated in the glucose hydrolysis process, and their impact on the inhibition rate for the humus material and the yield of levulinic acid were studied. Adding 5%(L:L) of acetone and 5%(L:L) of 2-butanone simultaneously had a good inhibition on restraining the humus material. The maximum inhibition rate was 27.52% when the reaction time was in 24 h, the largest yield of levulinic acid was 28.93% when the reaction time was in 21 h. In addition, adding acetone and 2-butanone simultaneously made the generation activation energy of levulicic acid reduce by 16.28 kJ/mol, which was beneficial to the generation of levulinic acid. Sodium chloride was added for the activation of hydrochloric acid, it could accelerate the decomposition of glucose and the generation of levulinic acid. The addition of sodium chloride made the decomposition activation energy of levulicic acid reduce by 13.413 kJ/mol, and made the generation activation energy of levulicic acid reduce by 23.896 kJ/mol.