VISCOSITY REDUCTION OF BLACK LIQUOR FROM WHEAT STRAW SODA PULPING BY HEAT TREATMENT WITH OXYGEN

摘要

A three-factor and three-level orthogonal experiment design was employed to study the effects of alkali charge, maximum temperature and holding time at the maximum temperature on the viscosity of black liquor from wheat straw soda pulping by a simple heat treatment. While a four-factor and three-level orthogonal experiment was designed to study the effects of alkali charge, maximum temperature, holding time, and oxygen pressure on the viscosity reduction of black liquor from wheat straw soda pulping by an oxygen enhanced heat treatment. The results showed that the viscosity reduction of wheat straw black liquor by heat treatment with oxygen was much efficient than that treated by simple heat treatment due to the heat treatment with oxygen can decompose hemicelluloses and lignin macromolecules in black liquor. The critical concentration of black liquor treated by heat with oxygen, if compared with the similar heat treatment condition but without oxygen enhanced, increased by around 5%. In addition, the optimal condition of heat treatment with oxygen was determined as follows: alkali charge on total solids content was 1.0% (as NaOH), with maximum temperature of 170 °C, holding time at the maximum temperature of 45 min and oxygen pressure of 0.5 MPa.