To valorize side streams into biochemicals and biomaterials

Lignin has been a good source for renewable bioenergy, but it is currently an underutilized source for biobased products and has the potential to replace many of the oil-based products. While lignosulfonates have found their use cases, there is a huge untapped potential for kraft-lignin and lignin originating from second generation (2G) biorefineries¹. With the upcoming capacity increases of the 2G biorefineries in the following decade, there is an urgent need to find new lignin-based bioproducts that will result in economic success for 2G biorefineries. Lignin should also be considered as a future source of biochemicals, especially aromatic biochemicals.

The kraft-lignin is currently primarily used for pulp mill energy production; however, the value-added potential is high. 2G biorefinery-based lignin commonly contains cellulose residues, which makes it less pure lignin-wise compared to kraft-lignin. The 2G lignin is also interesting in terms of its modifiability towards applications of interest. Lately, there have been new exciting applications of this “less pure” lignin, such as cellulose mixtures in plastics, fibers, and wood adhesives. The potential production capacity of biorefinery lignin is over 200 million tons/y, which makes it an abundant source for aromatic biochemicals, polymers, as well as fuels, and energy.

RETHINKING THE VALUE OF LIGNIN

Lignin researchers also suggest a paradigm shift in the thinking on how the lignin should be valorized.  Their thinking is, that lignin products should be engineered to fit the characteristics of the polymeric lignin without the in-between degradation. At the moment the prevalent ideology has been in degradation of lignin towards platform chemicals that are then transformed to e.g., polymers. Depolymerization of lignin continues to be an economical and technical challenge, even though the lignin value creation has been successful in the case of vanillin (from monomeric lignin) – polyurethane (from residue lignin oligomers).  A lignin from kraft process and 2G-based lignin have different qualities, thus a new way of thinking is needed.

LIGNIN IS A BUILDING BLOCK FOR BIO-BASED MATERIALS

The conventional and more mature application areas of lignin have been resins, polyurethanes, carbon fibers, and thermoplastics, but there are some new potential applications of 2G-based lignin where the synergy between the lignin and cellulose is utilized. For example, it has been noticed that spinning² (wet, dry jet-wet, or electro) of lignin becomes possible together with cellulose. This might lead to interesting new products in the area of composite fibers. 2G-lignin could serve as also a drop-in³ additive to other bio-based plastics (e.g., PLA, PHB). Manufacturing of plywood could also benefit from 2G-lignin-based resins.

Finally, some interesting application areas for lignin are likely to become extremely important for us in the near future, such as carbon fibers, 3D printing, and electrode material for batteries and fuel cells.

The success of lignin in these areas would coincide with the transformations that societies will undergo in the renewable energy transition that will majorly impact transportation sector. Today one can only dream of a car that is manufactured with 3D printing and carbon fibers based on lignin, powered by a battery with the lignin-based electrode material, but luckily today’s dreams are tomorrow’s reality.

Terminology

1. Second-generation (2G) biofuels are fuels manufactured from various types of non-food biomass, including lignocellulosic biomass, agricultural residues or waste and non-food energy crops.  First-generation  (1G) biofuels are made from sugar-starch feedstocks like sugarcane and corn and oil feedstocks for bioethanol and biodiesel.
2. Wet, dry jet-wet, or electro spinning are manufacturing processes of polymer fibers.
3. Drop in materials are biomaterials that can replace fossil-based raw materials e.g., in plastics manufacturing without the need to invest in new equipment and change of current manufacturing process.

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References
Li, H., Liang, Y., Li, P., & He, C. (2020). Conversion of biomass lignin to high-value polyurethane: A review. Journal of Bioresources and Bioproducts.
Balakshin, M., Capanema, E. A., Sulaeva, I., Schlee, P., Huang, Z., Feng, M., … & Rosenau, T. (2020). New opportunities in the valorization of technical lignins. ChemSusChem, 2021(14), 1-22.
Xu, C. C., Dessbesell, L., Zhang, Y., & Yuan, Z. (2021). Lignin valorization beyond energy use: has lignin’s time finally come? Biofuels, Bioproducts and Biorefining, 15(1), 32-36.

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