EXTRACTING HEMICELLULOSE PRIOR TO POPLAR KRAFT PULPING:EFFECT OF ALKALINE CONDITION ON PULP PROPERTIES

摘要

Facing with the limited oil supply,increased greenhouse gas emission,and decreasing competitiveness of traditional pulp mill,the concept of transformation of a chemical pulp mill into an integrated forest biorefinery was considered as an important technology.Under this concept,the hemicelluloses are either partially or completely extracted for bio-based material production,the remained substrate(mainly cellulose and lignin)can be further delignified for pulp.Extracting hemicelluloses prior to pulping can not only saving the energy consumption from black liquor recovery unit,but also provides additional revenues to traditional pulp mill.In the present study,the extracting hemicellulose prior to poplar kraft pulping was investigated.In order to minimize the acidification on the pulping equipment,the hot-water extraction and alkaline extraction were carried out.It was found that the mass removal increased with increase of extraction time.On the other hand,the mass removal reached 15.20％at 170 ℃ for 120min with NaOH dosage of 3％.The concentrations of sugar and furfural in the extraction liquor were measured,which were found to increase with increasing extraction time and temperature.The residual woodchips were subjected to kraft pulping at 165 ℃ for 1 h with 20％effective alkali,25％sulfidity and a liquor-to-wood ratio of 4∶1.Compared with the control sample,the overall pulp yield,Kappa number and viscosity of the pulps were all decreased with increase of extraction time and temperature.