Isolation of lignin

The transfer from a fossil based to a biobased economy opens the way to utilize process streams from biobased industries like the pulp and paper industry, where wood as a renewable material is processed in high quantities and volumes. In the last years, the product portfolio of a traditional pulp and paper mill has broadened by not only producing cellulose-based products but also other materials such as turpentine, tall oil, carboxylic acids and lignin, hence, a modern pulp and paper mill can be considered as a biorefinery.

Lignin is the largest renewable resource of aromatic compounds and makes up 30-40% of wood. In most of the mills, the lignin is burned as energy source for the pulping and paper making processes. The isolation of Kraft lignin by precipitation is already commercially available and is carried out with CO₂ from the bomb. In order to increase the economic and ecologic attractiveness for the mills for plant derived off gas may be used as acidifying agent. The aim of the doctoral thesis is the development of a precipitation reactor for using plant derived CO₂ for Kraft lignin precipitation. To make the lignin available in specified qualities for certain applications, the combination of the precipitation with conditioning steps like heat treatment of the lignin containing liquor and the downstream processing using filtration and washing of lignin are part of research.