Influence of inorganic species on the formation of polysaccharide and lignin degradation products in the analytical pyrolysis of pulps

摘要

The catalytic effect of inorganic species on the analytical pyrolysis of pulps has been evaluated by removing the natural inorganic species with mild acid washing. In order to evaluate the influence of a specific cation, individual metal ions were introduced to the acid-washed pulps by ion-exchange. In addition, the effect of some anions on pyrolysis mechanisms was studied by treating the acid-washed pulps with salts beyond their ion-exchange capacity. The presence and type of cations in pulps has a major effect on the distribution pattern of the pyrolysis products. During pyrolysis of pulps, hydrogen and calcium ions were found to be beneficial in terms of anhydrosugar yields from polysaccharides. The absolute yields of anhydrosugars obtained from protonated and calcium-exchanged pulps were of the same order of magnitude. In contrast, sodium strongly suppressed transglycosylation reactions and the formation of the anhydrosugars from both cellulose and hemicelluloses. Sodium also facilitated the demethoxylation, demethylation and dehydration of lignins, and significantly changed the lignin pyrolysis pattern, whereas the absolute amount of lignin pyrolysis products was less influenced. In order to increase the pyrolytic yield of anhydrosugars, it is preferable to have pulps in the hydrogen or calcium form. It was found that the pulps could easily be converted to their calcium form by washing the original pulp with calcium-rich water. It is further suggested that the reduction in pyrolytic yields of anhydrosugars in the presence of sodium is more due to the catalytic effect of sodium on the pyrolysis mechanisms than physical changes (swelling) in the fiber structure.