The mill ecosystem in Äänekoski is expanding with the construction of Metsä Fibre's lignin refinery demo plant in connection with its bioproduct mill. Technology company ANDRITZ is delivering equipment for the demo plant and Dow, a global company active in the chemical industry, is also involved in the project.

Construction has already started in the Äänekoski mill area, and the plant is planned to be ready for test use in 2025. The plant will produce two tonnes of the new kind of lignin product per day.

New lignin product could function as a bio-dispersant plasticizer

Along with pulp, lignin is one of the most common biopolymers in nature. Approximately one quarter of the softwood and hardwood chips used by Metsä Fibre's pulp and bioproduct mills is lignin.
The pulp process at the Äänekoski bioproduct mill produces approximately 1,800 tonnes of lignin per day. This makes it a significant side stream from the perspective of bioproduct modification.

"Lignin has always been an interesting material from a research perspective. Right now, we are particularly interested in it because the market has a clear need to find sustainable solutions to replace fossil raw materials," says Anna Suurnäkki, VP, Research at Metsä Fibre.

In pulp production, lignin is separated from the fibres into black liquor in the chemical cycle and used as a bioenergy source. The demo plant's modified lignin could be used as, for example, a bio-dispersant plasticiser in concrete and gypsum applications.

Concrete plasticisers are additives that improve the technical features of concrete, such as its pumpability.

Product can be utilized in liquid or dried form

The demo plant will refine the lignin using the LigniOx process, which uses black liquor from the bioproduct mill's evaporation plant as raw material. The black liquor is fed to the demo plant along a pipeline.
In the LigniOx process, lignin is precipitated from black liquor using carbon dioxide, after which it is further processed with alkali and oxygen. The end product is finalised during post-treatment.

The new lignin product is a liquid that can be utilised as such or dried. In the process, the demo plant will use bioenergy and other commodities produced by the adjacent bioproduct mill. The fractions left over from the separation of lignin are returned to the bioproduct mill's chemical cycle.

Plasticiser market is growing

Existing concrete plasticisers are mainly synthetic products. Even though the proportion of plasticiser in concrete mass is less than one per cent, the global demand for plasticisers amounts to millions of tonnes per year. Demand is expected to increase, particularly in developing countries.

"We believe that our new lignin product has potential. We are also aware of the fact that it is a new product that needs trialling. With the demo plant, we can offer test batches that help us assess the market's interest in the product," says Suurnäkki.