Lignin is one of the most abundant polymers in plant biomass, after cellulose and hemicellulose. Due to its abundance and the current environmental issues, lignin valorization to chemicals is a well-researched topic. Three main types of lignin with various readiness level emerge today to replace petroleum-based components, and in particular phenol. If the evolution of the chemical valorization of these lignins is still difficult to anticipate from a quantitative point of view, its future seems promising.
A huge potential
Lignin (from the Latin lignum which means wood) is a family of polyphenolic macromolecules, one of the main components of wood with cellulose and hemicellulose. Quantitatively, lignin forms the third family of compounds in order of abundance in plants and terrestrial ecosystems dominated by dead or living plant biomass (15 to 25%), after cellulose (constituting 35 to 50% of the biomass terrestrial plant) and hemicellulose (30 to 45%). Lignin is currently used in lumber and fuel. Due to its abundance and the current environmental issues, lignin valorization to chemicals is a well-researched topic. The large lignin producers remain today the chemical pulp manufacturers (Borregaard, Stora Enso, UPM, etc.). Globally, no less than 50 million tons of lignins are produced each year.[i]
But the chemical valorization remains low
The preferred route is highly dependent on energy prices (advantage of lignin combustion compared to external energy supply) and the added value of applications. The lignin valorization to chemicals remains very low (< 3%) compared to its valorization as a fuel. The main current application is the synthesis of phenolic resins. To fully replace a substance in the final product, a “ready-to-use” lignin is attractive when its price is close to phenol price that it replaces to avoid more costly investments. However, the price of lignin must be lower than phenol price to replace part of a substance by lignin, to justify the additional steps and costs required. In both situations, an extra cost can be tolerated to enhance the biobased origin of the final product.
Lignosulfonates dominate, Kraft lignins settle, Organosolv lignins still in the dark
Lignosulfonates are the most represented type of lignin on the market, with 1.3 million tonnes of production capacity worldwide. Dominated by the Norwegian Borregaard LignoTech, this market is the most mature.
Far behind with current production capacities of around 123,000 tonnes per year, Kraft lignins are the second source, dominated by the major Scandinavian (Stora Enso, UPM) and North American (West Fraser, Domtar) papermakers. Demand is growing, and new entrants are positioning themselves on this market, making its evolution difficult to anticipate.
Still shy, the Organosolv processes (using different mixtures of solvents for lignin extraction) are struggling to industrialize. Although they have been well researched for many years, this type of lignin is currently only at a pilot scale, hampered by the heavy investments required for its industrialization. European and American players have a total capacity of only a few dozen tonnes per year. Due to the high quality of this type of lignin, the projects are intensifying but there will not be an established industrial production before a couple of years.
What future for lignin?
Phenolic resins will remain the priority application, but many others are under study, at stages that are sometimes already well advanced. First example: the synthesis of carbon fibers. Providing greater mechanical performance than glass fibers, there is a high interest in applications such as wind turbine blades[ii] manufacturing or in the automobile industry to lighten structures and thus reduce fuel consumption.
In stark contrast now, Stora Enso (world leader in Kraft lignin) plans in the short term to enhance its range with a bitumen replacer in the asphalt. H4A, a company working in the construction of buildings and roads, has already successfully used Stora Enzo’s products by replacing half of the bitumen with lignin.[iii] In addition, the production of bio-asphalt with lignin requires less energy since the mixing temperature of the asphalt can be considerably reduced, doubly reducing the carbon footprint.
Let’s continue with Stora Enso, who is multiplying the projects. The group announced in August 2019 that it will invest € 10 million in the production of bio-based carbon materials for energy storage at Sunila Mill (Finland), its Kraft lignin production site. The group even has its own pilot plant in Sunila.[iv]
In Belgium, the Derbigum[v] project aims to develop a Walloon industry for the collection, extraction, and use of lignin. The Belgian LignoValue[vi] project should lead at the start of 2021 to an operational pilot line in Flanders to produce bio aromatics from lignin. The European LigniOx[vii] project aims to demonstrate the technical and economic viability of the technology for converting lignin into dispersants, targeting plasticizers for concrete and paints.
Therefore, Lignin is approaching a turning point in its chemical recovery: increasing demand, multiplication of applications, diversity of lignins produced. Industrial projects are finally developing. There is no doubt that the lignin valorization to chemicals looks promising, pending a favorable regulatory framework that can make this future even more ambitious.
[i] ADEME, « Etat de l’art sur la production de molécules chimiques issues du bois en France », Final report, September 2015
[ii] Valbiom, « Molécules issues de la valorisation de la lignine », Jean-Luc Wertz, March 2015