Effect of Hot-Water Pre-Extraction on Alkaline Pulping Properties of Wheat Straw

The alkaline pulping properties of wheat straw, which had been hemicelluloses pre-extracted with hot water, were studied. In this work, the process of hot-water extraction at various temperatures, reaction time and other conditions were investigated. The straws pre-extracted or not were made into pulp with NaOH-AQ at same conditions. Then the effects of pre-extraction on properties of straw pulp were studied. The results show that the yield, Kappa number and viscosity of the pulp are affected significantly by hemicelluloses pre-extraction process. The chemicals charge of the extracted straw in the pulping process is lower and shorter cooking time needed, the maximum pulping temperature reduced. These effects indicate that the action of hot-water pre-extraction before alkaline pulping is able to reduce effluent discharge and chemical demand to pulp, and it would be energy-saving. In this experiment, the optimum conditions of hot-water pre-extraction were: maximum temperature 140°C, heat-up time 30min, 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.