LigniOx Process Concept to Produce Lignin Dispersants at a Kraft Pulp Mill and an Organosolv Biorefinery

The LigniOx oxidation process uses O2 under alkaline conditions to solubilise water-insoluble lignins. The oxidized lignins with increased anionic charge have been demonstrated to work as a concrete plasticiser and versatile dispersants.

Recently, a concept of LigniOx process for producing lignin dispersants at a kraft pulp mill has been developed. In the concept, unwashed kraft lignin (primary cake from CO2 precipitation stage) is O2 oxidised partly using oxidised white liquor, available in the mill, as a source of alkali. Thereafter, the oxidised lignin solution is post-treated by membrane filtration to recycle the chemicals (Na, S) and to produce high-performance dispersants. Based on a simulation study, recovering 20% of the lignin in black liquor, and oxidising this unwashed lignin does not increase the need to purge fly ash in a kraft pulp mill, unlike the conventional lignin recovery process alone.

Most lignin precursors carry methoxy groups, which are released as methanol in the course of lignin oxidation. Therefore, in addition to the lignin dispersants produced by the integrated LigniOx process, high quantities of methanol (MeOH) is formed as a by-product. This MeOH is transferred to the evaporation plant at the kraft pulp mill within the permeate fraction from the membrane filtration. The crude MeOH from the evaporation can be purified using an already existing technology. The high quality bioMeOH is a valuable raw material for the chemical industry. Production of bioMeOH would increase the economic viability of the LigniOx process concept for the sustainable lignin dispersants.

Besides kraft pulp mills, the LigniOx process has been demonstrated to apply to organosolv biorefineries. Integration benefits of this technology also exist for the production of organosolv lignin based dispersants with MeOH as a by-product.