Effect of the P-factor on the prehydrolysis process of eucalyptus wood for dissolving pulp production

Prehydrolysis kraft is the industrial process most frequently used to produce dissolving pulp using continuous or batch technologies. Wood prehydrolysis is the most critical step in the dissolving pulp production stages, aiming at removing hemicelluloses before wood pulping, as hemicelluloses tend to impair cellulose reactivity during the dissolving pulp derivatization process. The performance and extent of this process can be controlled mainly through retention time and temperature conditions, with the P-factor being the severity parameter used to correlate both variables in pulp mills. This study assesses the effects of the P-factor on the prehydrolysis process of eucalyptus clone wood used for dissolving pulp production, deriving regression models to aid in the decision-making and optimization of this process. Five trees from two clones—Eucalyptus urophylla and E. urophylla × E. spp. at the ages of 3 and 5 years—grown in plantations located in Bahia State, Brazil, were evaluated. Hydrothermal pretreatments were applied to wood chips under different time and temperature conditions (P-factor), and the chemical characteristics of the treated wood (lignins and carbohydrates) were determined. The experimental design provided a comprehensive view of the severity factor's effect on each wood macro-component, showing the threshold at which the required amount of hemicelluloses was removed without affecting the cellulose fraction. Hemicelluloses solubilization and removal extended up to 90% within the experimental conditions, with the optimized point achieved at a P-factor of 873. The regression models produced showed good fit for process yield, hemicellulose, and lignin removal.