Study on soda-oxygen pulping of bagasse with alkali pretreatment and black liquor back-cycling

The save-energy and clean soda-oxygen pulping of bagasse were studied in this paper. Soda pretreatment with or without supersonic were tried and compared during the pretreatment stage of soda-oxygen pulping. Consequently, the process of soda-oxygen pulping with the back-cycling of black liquor was carried out at low cooking temperature in consideration of saving energy, environmentally friendly production, etc. The pulp with good properties was obtained under the pulping at 105 degrees C for 120 min with 15% NaOH charge, 0.5% MgSO4, AOA-1 as a pulping additive self-regulated, 12% pulp consistency, and 0.6 MPa initial oxygen pressure, when the soda pretreatment conditions were as follows: 90 degrees C for 10 min with 15% NaOH charge and 10% bagasse consistency. The resultant pulps had yield above 60%, Kappa number ranging from 15.37 to 17.16, viscosity above 758 dm(3)/kg, brightness above 55.9%, and handsheets with burst index above 3.03 KPa.m(2)/g, tear index above 5.47 mN.m(2)/g, and tensile index above 34.4 N.m/g. The results showed that alkali pretreatment can reduce the maximum pulping temperature effectively, while the supersonic pretreatment seemed not to be helpful to the pulping. The pulping with black liquor back-cycling can enhance black liquor concentration above two times and keep the properties of pulps steady.