EFFECT OF HOT-WATER PRE-EXTRACTION OF WHEAT STRAW ON ALKALINE PULPING

摘要

The pre-extraction of hemicellulose from wheat straw before pulping was studied in this paper. The process of hot-water extraction at different temperatures, reaction time and other conditions were investigated. The straws pre-extracted or not were made into pulp with NaOH-AQ at same conditions. The effects of preextraction on pulping were studied. The results show that the yield, Kappa number, viscosity and residual alkali in the black liquor are affected obviously by hemicellulose pre-extraction process. The alkaline pulping of pre-extracted wheat straw needs lower alkaline charge and shorter cooking time compared with the traditional pulping. These results indicate that hot-water pre-extraction before alkaline pulping can reduce effluent discharge and reduce chemical demand. Results of pulping showed that pulp from preextracted wheat straw had lower Kappa number compared with that without pre-extraction, while the yield and viscosity were decreased to some extent. In this experiment, the optimized conditions of hot-water pre-extraction were: maximum temperature 140°C, heat-up time 30min, holding time at maximum temperature 60min and liquor ratio 1:10. The optimal pulping conditions were: alkali charge 12%, maximum temperature 155°C, heat-up time 90min, and holding time at maximum temperature 60min and liquor ratio 1:5.