Dilute Sulphuric Acid Extraction of Hemicelluloses from Eucalyptus Grandis and Its Effect on Kraft and Soda-aq Pulp and Handsheet Properties

The extraction of hemicelluloses prior to pulping is an attractive process to be incorporated in the pulp and paper mills to generate valuable by-products such as xylose and xylo-oligomers in addition to core products. This paper investigates the impact of xylan extraction by dilute acid on cooking conditions, pulp yield and properties during kraft and soda-AQ pulping of Eucalyptus grandis wood chips. Modified soda-AQ pulping of the wood chips from which 21.3% of xylan was extracted using a low alkali charge maintained the pulp yield, viscosity and kappa number of nonextracted wood chips. The combination of these processes resulted in chemical reduction while increasing the digester capacity by 12%. Due to extraction, the handsheet properties were reduced, especially the tear index. The degree of hemicellulose pre-extraction and pulping conditions can be optimized based on final paper application.