# Purification of kraft lignin from black liquor by ultrafiltration for its valorization through biological depolymerization

Florian Teuffo, Clément Dumont, Tiphaine Richard, Rénato Froidevaux, Loubna Firdaous

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## ► To cite this version:

Florian Teuffo, Clément Dumont, Tiphaine Richard, Rénato Froidevaux, Loubna Firdaous. Purification of kraft lignin from black liquor by ultrafiltration for its valorization through biological depolymerization. 17th European Workshop on Lignocellulosics and Pulp (EWLP), Aug 2024, Turku (FI), Finland. hal-05420290

HAL Id: hal-05420290

https://hal.science/hal-05420290v1

Submitted on 19 Jan 2026

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# Purification of kraft lignin from black liquor by ultrafiltration for its valorization through biological depolymerization

Florian TEUFFO<fnref n="1" />, Clément DUMONT<fnref n="2" />, Tiphaine RICHARD<fnref n="2" />, Gerard MORTHA<fnref n="3" />, Muriel BIGAN<fnref n="1" />, Rénato FROIDEVAUX<fnref n="1" /> and Loubna FIRDAOUS<fnref n="1" />

## ABSTRACT

This study compared, two types of membrane materials, polyether sulfone (PES) and regenerated cellulose (RC), and examined three cutoff thresholds (30 kDa, 10 kDa, and 5 kDa) for the purification of lignin in an industrial black liquor. The results showed that all membranes used exhibited lignin retention rates exceeding 95%, regardless of the membrane type. The high rejection rates of lignin cannot be explained solely by the size of the lignin derived from the kraft process, which ranges in size from from 1-3 kDa. Therefore, we hypothesized that lignin may still contain sugars grafted onto its structure, which could account for the significant rejection rates obtained. To investigate this, structural characterization of lignin using NMR was performed. This analysis confirmed that the lignin contained in black liquor actually contains polysaccharides grafted onto its structure in the form of a lignin-carbohydrate complex. The lignin resulting from this membrane treatment was depolymerized with *Trametes versicolor* laccase using a method developed in the laboratory. Lignin depolymerization showed two phenomena: repolymerization and depolymerization. Our focus has been on the depolymerization products, which are currently being characterized by methods such as 1H NMR, FTIR and SEC.

**Keywords:** Black liquor, lignin, depolymerization, enzyme, lignin carbohydrate complex, NMR, FTIR, cut-off, ultrafiltration and SEC.

## INTRODUCTION

Lignin is produced as a by-product in the paper industry with an annual production of around 70 million tons (1). This lignin is initially present in an aqueous solution called black liquor, which still contains residues of cellulose, hemicelluloses, as well as products such as sugars, phenolic monomers, and dimers, etc. This lignin, initially contained in black liquor, can be recycled to produce both high and low added value compounds(2). The production of high value-added products by enzymatic depolymerization requires a preliminary step to separate the lignin from any impurities present in the black liquor that may have a negative influence on depolymerization. In this work, we carry out membrane separation of lignin followed by enzymatic depolymerization.

## EXPERIMENTAL

<footnote n="1">¹ UMRT BioEcoAgro, Bioprocessing/Biocatalysis and Enzymes Team, University of Lille, France.</footnote>

<footnote n="2">² ICAM School of Engineering, Lille campus, France.</footnote>

<footnote n="3">³ LGP2, Grenoble Technology Institute, France
florian.teuffo@univ-lille.fr</footnote>
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✓ Membrane separation and Enzymatic depolymerization of lignin

For lignin membrane separation using an Amicon™ 400 mL cell, we used two types of material. Regenerated cellulose (RC) and polyethersulone (PES) membranes. For each type of material, three molecular weight cut-offs (MWCO) were used: 30, 10 and 5 kDa. The pressure was 2 bar, agitation 300 rpm. To limit membrane clogging, the black liquor was diluted by two to a total volume of 400 mL. After separation, the fractions were characterized by measuring polyphenol, sugar and lignin levels, which were then used to determine rejection rates and assess membrane efficiency.

Membrane-treated lignin was depolymerized using enzymes. As the lignin structure is highly recalcitrant to enzymatic depolymerization, a sonication step was carried out beforehand to improve the response of the lignin to the depolymerizing enzymes. Lignin was sonicated using an ultrasons homogenizer (SinapTec®) at 400 W for two hours. After the sonication step, lignin was depolymerized using Trametes versicolor laccase in a 500 mL reactor. Reaction conditions were as follows: Lignin 5 mg / mL, mediator 2 mM and laccase, temperature 40°C, pH 4.5, stirring 400 rpm, all in 300 mL water. The reaction was carried out for 24h. At the end of the reaction, the reaction medium was treated by membrane ultrafiltration with 5 kDa PES membrane to separate the depolymerization products. The products were characterized by exclusion chromatography and infrared characterization.

RESULTS AND DISCUSSION

Membrane separation of lignin showed that all MWCOs used retained 95% lignin. This could be explained by the potential presence of polysaccharides on the lignin, which increase its size and membrane clogging. Structural characterization of lignin showed that lignin contained a polysaccharide fraction on its structure in the form of lignin carbohydrates complex which would be responsible for the 95% rejection rate. Acid treatment of the lignin, followed by ultrafiltration and molecular weight determination, confirmed this result. The lignin treated here does indeed contain polysaccharides.

Lignin depolymerization after separation by membrane ultrafiltration showed two types of products. The depolymerization products have been separated by membrane ultrafiltration and are currently being characterized. The aim is to determine their structure and show that they are indeed derived from lignin.

CONCLUSIONS

In conclusion, we have developed a process from lignin separation to enzymatic depolymerization. Analytical results show good lignin separation. Depolymerization, on the other hand, shows two pheomens. The next logical step is to characterize the depolymerization products obtained in order to demonstrate the effectiveness of the method developed.

ACKNOWLEDGMENTS

French National Research Agency, Fibre excellence, ZymOptiq, IEMN and all the authors who
contributed to this work

REFERENCES

1. Kumar A, Chandra R. Ligninolytic enzymes and its mechanisms for degradation of lignocellulosic waste in environment. Heliyon. 1 févr 2020;6(2):e03170.

2. O'Donohue M. La biomasse, simple source d'énergie ou source de matières premières renouvelables? 2013