Studies On Delignification Mechanism And Kinetics Of Formic Acid Based Wheat Straw Cooking Processes

As a kind of fiber material, wheat straw plays an important role in China. It is of great importance to study delignification mechanism and kinetics. The application of the theory in the process control is promising.This study is focused on the delignification mechanism and kinetics of wheat straw formic acid based pulping process. It is shown in the result after the analysis of lignin remained in the pulp in different time and at varied temperature that the lignin in the pulp reduced instantly, which means that the delignification is quite easy, especially at high temperature. The temperature is the key element to affect the cooking process. The rate constant and the order of reaction are determined through the establishment of kinetic equation in delignification reaction. Under the temperature of 70 ℃ , 80 ℃ , 90 ℃ , 100℃, the rate constants are 8.42×10-4, 1.75×10-3, 3.55×10-3, 9.85×10-3 and the order of reactions are 1.32, 1.23, 0.99, 0.79 respectively. In the range of temperature and time under which the experiment is carried out, the average active energy is Ea=87.05 kJ/mol, the frequency constant is K0 =1.32 × 1011L/mol · min, and the kinetic equation in delignification reaction is -dL/dt = 1.32 × 1011exp(-10470/T)L. The delignification apparently belongs to the first-order reaction. It is indicated through the test of the lignin distribution in the cell wall with the aid of SEM-EDXA that the sequence of lignin removing is the S> ML> CC. It is shown from the IR test results that the ether linkage is inclined to be broken in the FA cooking process. In addition, the possibility of the application of H-factor in the control of pulp quality is discussed in this paper.