Optimizing Hemicelluloses Pre-extraction in Eucalyptus Kraft Pulping: A Pathway towards Enhancing Pulp Mill Biorefineries

A critical pathway towards enhancing pulp mill biorefineries is to integrate the extraction and utilization of hemicelluloses into the pulping processes. Hence, an industrial pre-extraction strategy for hemicelluloses targeting eucalyptus kraft pulping process was developed. Alkaline solution or pulping white liquor was used to pre-extract hemicelluloses before actual pulping process. The Response Surface Methodology (RSM) technique was applied to investigate the most suitable conditions to maximize the yield of these hemicelluloses while simultaneously minimizing the damage to pulp yields and properties. Temperature (°C) [105, 155], alkali concentration (%) [3, 8], sulfidity (%) [20, 30] and retention time (min) [19, 221] were combined to evaluate their effects on hemicellulose yields and chemical structures. The optimal pre-extraction conditions identified in this work (5.75% NaOH concentration, 25% sulfidity at 135 °C for 60 min) successfully allowed recovering 4.8% of hemicelluloses (based on the wood dry weight) and limited damages to pulp yields and properties. The cellulose content in pulp can even be increased by about 10%. Hemicellulose emulsification properties were also evaluated, which were comparable to synthetic emulsifiers. This study provides an industrial pathway to effectively separate and utilize wood hemicelluloses from the pulping process, which has the potential to improve the economy and material utilization of pulp and paper mills.