Towards closed chemical cycles: Recycling sulphuric acid

Project Description

Metsä Group’s next-generation bioproduct mill in Äänekoski, Finland uses several state-of-the-art technologies to contribute to the circular economy.

Metsä Group is the first forestry company in the world to introduce a large-scale sulphuric acid plant as an integrated part of the Äänekoski site’s pulp production. The plant captures and converts the mill’s odorous gases into sulphuric acid, a chemical needed to produce tall oil, another of the mill’s bioproducts. As a result, the bioproduct mill is self-sufficient with respect to this chemical, while its sulphate emissions to water and air are minimised. This investment is an important step towards a closed chemical cycle. The approximately €20 million investment is the first large-scale sulphuric acid plant in the world to be integrated into the pulp production process. With a value of €1.2 billion, the bioproduct mill is the largest investment in the history of the Finnish forest industry. Äänekoski is the most energy-efficient pulp mill in the world, and the centre of an industrial ecosystem in which other companies also participate.

This unique plant produces approximately 35 tonnes – one truckload – of sulphuric acid a day, equal to the amount required for the mill’s daily tall oil production. Due to internal circulation, the chemical does not need to be purchased externally, reducing transport needs by 360 truckloads a year.

Project Purpose

While sulphuric acid is a common and relatively inexpensive chemical, converting sulphuric gases into sulphuric acid in an integrated manner close to the mill has considerable environmental benefits. Based on this experience, sulphuric acid plants may become more common in conjunction with pulp mills.

Project Evaluation

Looking forward, sulphuric acid could also be used in the production of chlorine dioxide and in separating lignin from black liquor. There is thus the potential to develop an industrial ecosystem based on sulphuric acid production.

Ilkka Poikolainen

VP, Mill Manager of Äänekoski bioproduct mill

A plant that makes a process chemical, sulphuric acid, out of the sulphuric compounds in odorous gases i.e. a side stream of pulp production, is a significant step towards a closed chemical cycle, says Ilkka Poikolainen, VP, Mill Manager of the Metsä Group’s bioproduct mill. This improves our bioproduct mill’s environmental performance and resource efficiency even further. Sulphuric acid is needed to make things including the important bioproduct tall oil, which is also produced in Äänekoski. A leading principle behind the bioproduct mill is to expand the product portfolio. The sulphuric acid plant complements the bioproduct concept.

Main features:

CO2 Emissions saved (tCO2)

about 360 truckloads a year


€20 million


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