Isolation and purification of technical lignins

Natural lignin, as contained in plants, is fundamentally altered with regard to its chemical structure and properties upon pulping of wood or other biomass processing (Berlin and Balakshin, 2014). The products of these conversions, technical lignins, have only rather limited resemblance to native lignins – this is why the distinction between technical and native lignins is made. Technical lignins need to be retrieved from complex products mixtures, so-called “black liquors”, which also contain other components, such as process chemicals, salts and other inorganics, degradation products from lignin and carbohydrates (Niemelä and Alén, 1999).

Lignin isolation from their production matrices reduces or eliminates interference from non-lignin constituents and thus plays a crucial role in lignin characterization. ALICE offers several approaches for the isolation and purification of lignin from spent pulping liquors generated in the kraft and sulfite pulping processes as well as from other biorefinery streams: precipitation, ultrafiltration and accelerated solvent extraction.

References

Berlin, A. & Balakshin, M. (2014)
Industrial Lignins: Analysis, Properties, and Applications.
In: Bioenergy Research: Advances and Applications, Chapter 18, pp. 315-336. doi: 10.1016/B978-0-444-59561-4.00018-8

Niemelä, K. & Alén, R. (1999)
Characterization of Pulping Liquors. In: Analytical Methods in Wood Chemistry, Pulping, and Papermaking.
Sjöström, E. & Alen, R. (eds.). Berlin, Heidelberg: Springer Berlin Heidelberg, pp. 193-231. doi: 10.1007/978-3-662-03898-7_7

Kraft lignin is usually recovered from black liquor in the laboratory and on an industrial scale by acid precipitation and heat coagulation (Zhu and Theliander, 2015, Sewring et al., 2019). The isolation procedure consists of three steps: acidification, filtration, and washing. Acidification of black liquor is done with a mineral acid, such as sulfuric or hydrochloric acid, under intensive mixing. The filter cake generated upon filtration is exhaustively washed with deionized water until the residual ash content of the isolated kraft lignin is reduced to less than 2%.

References

Sewring, T., Durruty, J., Schneider, L., Schneider, H., Mattsson, T. & Theliander, H. (2019)
Acid Precipitation of Kraft Lignin from Aqueous Solutions: The Influence of pH, Temperature, and Xylan.
J. Wood Chem. Tech., 39, 1-13. doi: 10.1080/02773813.2018.1488870

Zhu, W. & Theliander, H. (2015)
Precipitation of Lignin from Softwood Black Liquor: An Investigation of the Equilibrium and Molecular Properties of Lignin.
BioResources, 10. doi: 10.15376/biores.10.1.1696-1715

The development of semipermeable membranes has led to a wide use of ultrafiltration (UF) in many fields, including, the isolation and fractionation of technical lignins (Zinovyev et al., 2017, Sulaeva et al., 2019, Sevastyanova et al., 2014). UF also allows for the quantitative isolation of lignosulfonates with high purity (Sumerskii et al., 2015).

The application of membranes with different molecular weight cut-offs provides selected lignin fractions with low dispersity, which are of interest both for analytical purposes and in development of lignin applications.

ALICE core facility offers analytical and preparative scale lignin purification by means of UF with molecular-weight cut-off of 1, 3, 5, 10, 30 and 100 kDa.

Additionally, ALICE offers a novel approach for isolation of lignosulfonates from spent sulphite liquor by an adsorption method (Sumerskii et al., 2015). We offer this method in three variants: small analytical scale, preparative scale, and large preparative scale, allowing to isolate up to 1 gram, 10 grams, and 100 grams of purified lignosulfonate, respectively.

References

Sevastyanova, O., Helander, M., Chowdhury, S., Lange, H., Wedin, H., Zhang, L., Ek, M., Kadla, J. F., Crestini, C. & Lindström, M. E. (2014)
Tailoring the molecular and thermo–mechanical properties of kraft lignin by ultrafiltration.
Journal of Applied Polymer Science, 131, 40799. doi: 10.1002/app.40799

Sulaeva, I., Vejdovszky, P., Henniges, U., Mahler, A. K., Rosenau, T., & Potthast, A. (2019).
Molar Mass Characterization of Crude Lignosulfonates by Asymmetric Flow Field-Flow Fractionation.
ACS Sustainable Chemistry & Engineering, 7(1), 216-223. doi: 10.1021/acssuschemeng.8b02856

Sumerskii, I., Korntner, P., Zinovyev, G., Rosenau, T., & Potthast, A. (2015).
Fast track for quantitative isolation of lignosulfonates from spent sulfite liquors.
Rsc Advances, 5(112), 92732-92742. doi:10.1039/c5ra14080c

Zinovyev, G., Sumerskii, I., Korntner, P., Sulaeva, I., Rosenau, T., & Potthast, A. (2017).
Molar mass-dependent profiles of functional groups and carbohydrates in kraft lignin.
Journal of Wood Chemistry and Technology, 37(3), 171-183. doi: 10.1080/02773813.2016.1253103

Lignin isolation by means of precipitation, ultrafiltration or adsorption methods may not guarantee absolute purity of the final sample. Quite often lignins are still contaminated with non-lignin impurities, such as extractives, carbohydrates, tannins, or lignin degradation products (Brunow et al., 1999), which may interfere with further analysis. Therefore, crude isolated lignin can additionally be purified by means of solvent extractions prior to lignin characterization for accurate quantitative data.

Conventional lignin purification is based on solvent extraction in a Soxhlet apparatus with different solvent systems. Beside this technique, ALICE provides a more efficient and flexible purification approach – in terms of process conditions and high throughput – by means of a Dionex™ ASE™ 350 Accelerated Solvent Extractor (Thurbide et al., 2000).

Required sample amount: 1-2 g

References

Brunow, G., Lundquist, K., & Gellerstedt, G. (1999).
Lignin.
In E. Sjöström & R. Alén (Eds.), Analytical Methods in Wood Chemistry, Pulping, and Papermaking (pp. 77-124). Berlin, Heidelberg: Springer Berlin Heidelberg.

Thurbide, K. B., & Hughes, D. M. (2000).
A rapid method for determining the extractives content of wood pulp.
Industrial & Engineering Chemistry Research, 39(8), 3112-3115. doi: 10.1021/ie0003178