Improved microfiltration of prehydrolysis liquor of wood from dissolving pulp mill by flocculation treatments for hemicellulose recovery

Prehydrolysis liquor (PHL) of wood is a byproduct of dissolving pulp from prehydrolysis kraft process, but contains a great amount of soluble hemicelluloses. Membrane filtration of PHL is a promising method for hemicelluloses recovery but extremely difficult mostly due to high fouling tendency. In this study, flocculation was employed to reduce fouling of regenerated cellulose (RC) membranes. The results showed that flocculation by polyaluminium chloride (PAC) at 500 mg/L prior to microfiltration improved the flux over 102 folds for a volume reduction factor of 10. The flux was further increased by 81.2% by addition of anionic polyacrylamide (APAM) at 50 mg/L. However, combination of PAC and cationic polyacrylamide (CPAM) aggravated membrane fouling due to the adhesion of CPAM on membranes. Variation of chemical compositions revealed that lipophilic substances and lignin were key foulants for RC membranes.