NEW PULPING TECHNOLOGY OF NON-WOOD FIBER WITH FORMIC ACID

摘要

The chemical pulping of annually harvested non-wood fiber like wheat straw with organic solvent such as formic acid is a brand new pulping technology. The influence of many process parameters, such as concentration of formic acid, cooking temperature, cooking time, as well as the time of pre-treatment, on the pulp yield and Kappa number are investigated in this study. The relationship between the pulp yield and kappa number are a well fitted during cooking process. The range analysis shows that the factor that most effectively influences the change of kappa number is the cooking temperature and that of the yield is the FA concentration. Meanwhile, the analysis of lignin structure in wheat straw materials, unbleached pulp and black liquor with difference FTIR spectra shows that the S lignin units can be easily removed during cooking process. There are some more secondary alcohol OH in black liquor than in raw material, which is caused by the cleavage of β-O-4 bonds and dissolving of syringyl type and guaiacyl type lignin. The lignin condensation reaction occurred during cooking. Both the conjugated and unconjugated C=O are intensified in black liquor and in unbleached pulp, which lead to the coloration pulp after cooking. The test results shows that the cooking time can only affect the degree of delignification but not the lignin structure. The attempt of the formic acid pulping of wheat straw and analyzing of lignin structure in the cooking process is favorable for the optimization of pulping process with organic solvent and for the application of lignin by-products.