Fractional recovery of lignin from black liquor using acid-assisted flocculation with lignin-based flocculants
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Supporting information
Accepted version
Author(s)
Type
Journal Article
Abstract
Black liquor (BL), the alkaline effluent from straw pulping, is rich in lignin with diverse molecular weights but poses serious environmental challenges. Here, a stepwise acid-assisted flocculation (AAF) strategy was developed for fractional lignin recovery and water treatment, in which a quaternary-ammonium-modified lignin flocculant (L-CTA) was employed following the “using-waste-to-treat-waste” principle. Through sequential AAF, high- (>5000 Da), medium- (1000–5000 Da), and low-MW (800–1000 Da) lignin fractions were selectively recovered (recovery rates of 91.7, 88.0, and 89.5%, respectively) under mild conditions. Structural analyses revealed a molecular transition from β-O-4-rich, syringyl-dominated, and compact product of high-MW fraction, to more oxidized and guaiacyl-enriched low-MW lignin fractions with lower thermal stability. Mechanistic studies, by a combination of instrumental analyses (zeta potential, quartz crystal microbalance, and isothermal titration calorimetry) and theoretical computations (density functional theory and molecular dynamics), demonstrated that the AAF process followed enthalpy–entropy compensation: high-MW lignin separation relied on both an enthalpy reduction of electrostatic attraction and entropy increases of bound-water release during π–π stacking, whereas low-MW lignin favored an enthalpy-dominated process. This study provides a mechanistic-guided and environmental-benign route for simultaneous primary treatment of BL and fractional recovery of lignin, thereby contributing to sustainable development within the pulping industry.
Date Issued
2026-05-25
Date Acceptance
2026-04-29
Citation
ACS Sustainable Chemistry and Engineering, 2026, 14 (20), pp.9529-9540
ISSN
2168-0485
Publisher
American Chemical Society
Start Page
9529
End Page
9540
Journal / Book Title
ACS Sustainable Chemistry and Engineering
Volume
14
Issue
20
Copyright Statement
Copyright © 2026 American Chemical Society. This is the author’s accepted manuscript made available under a CC-BY licence in accordance with Imperial’s Research Publications Open Access policy (www.imperial.ac.uk/oa-policy)
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Publication Status
Published
Article Number
acssuschemeng.6c01587
Date Publish Online
2026-05-12