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. 2025 Mar 29;17(7):926.
doi: 10.3390/polym17070926.

Efficient Lignin Precipitation from Softwood Black Liquor Using Organic Acids for Sustainable Valorization

Elsa Duret  1 , Luanna C R de Moura  1 , Amaia Morales  2 , Jalel Labidi  2 , Eduardo Robles  1 , Fatima Charrier-El Bouhtoury  1
Affiliations

Efficient Lignin Precipitation from Softwood Black Liquor Using Organic Acids for Sustainable Valorization

Elsa Duret et al. Polymers (Basel). .

Abstract

The chemical industry's transition towards sustainability necessitates the development of eco-friendly processes that can replace petrochemical derivatives. Lignin, the second most abundant plant polymer, has potential as a renewable alternative to phenolic compounds. This study investigates lignin precipitation from softwood black liquor using five organic acids (acetic, citric, lactic, malic, and oxalic) as a sustainable alternative to sulfuric acid. The precipitated lignins were subjected to comprehensive chemical and thermal characterization, revealing higher total phenolic content and enhanced reactivity when organic acids were employed. Notably, organic acid-precipitated lignins demonstrated comparable or superior purity, with ash contents below 0.50%, compared to 3.28% observed for sulfuric acid-precipitated lignin. These findings suggest that organic acids are a viable and greener alternative for lignin precipitation, promoting higher purity and yield, thus supporting lignin valorization efforts.

Keywords: black liquor; lignin; organic acids; precipitation; softwood.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Lignins precipitated with different acids presenting different colors (AL: acetic acid, CL: citric acid, LL: lactic acid, ML: malic acid, OL: oxalic acid, HL: hydrochloric acid, and SL: sulfuric acid).
Figure 2
Figure 2
Lignin precipitation yields and amount of acid used.
Figure 3
Figure 3
FTIR spectra of lignins and black liquor.
Figure 4
Figure 4
Thermogravimetric (TGA) (A) and derived thermogravimetric curves (DTG) (B) of lignins.
See this image and copyright information in PMC

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