ALKALINE DELIGNIFICATION OF HARDWOODS IN A FLOW-THROUGH REACTOR WORKING AT A LOW RESIDENCE TIME .1. PROCESS ANALYSIS AND PARAMETERS OPTIMIZATION

This work dealt with the delignification of poplar chips by means of a flow-through reactor. Three processes were analysed: "sodium hydroxide", "sodium hydroxide in the presence of anthraquinone" and "kraft". The results clearly showed the important influence of sodium hydroxide concentration. Addition of anthraquinone and/or sodium sulphur improved considerably both kinetics and selectivity of the delignification reactions. Moreover, the process analysis showed that the recondensation reactions of the dissolved lignin fragments on the fibres were not pronounced. In the three cases, the resulting pulps were fast delignified and less degraded as compared with those obtained under similar conditions with batch reactors. Preliminary analysis showed that the lignin fractions recovered during the treatments were contaminated by sugars (mainly xylose). On the other hand, the hydrolysis of hemicelluloses was not very important, because of their short residence time in the reactor after extraction from wood.