Recovering Lignin in a Real-Case Industrial Kraft Pulp Mill: Pilot-Scale Experiment and Impact on the Mill Commodities

Existing industrial Kraft mills can be the basis for the deployment of lignin valorization into added-value products. Lignin can be recovered by its precipitation from black liquors. However, it is of tremendous importance to better determine the impact of lignin extraction on the overall chemical and energy balances of the mill. Therefore, we have sampled the black liquors from an industrial Kraft mill (treating softwood), which is a typical European mill. Lignin has been precipitated by CO2 at a pilot scale in order to quantify the consumption of chemical commodities. Black liquors and lignin cakes were comprehensively characterized in order to evaluate the mineral and organic balances. The experimental results were implemented in a global simulation of the industrial Kraft mill in order to assess the impact of lignin recovery from the black liquor on the chemical and energy balances. The additional consumptions of chemicals are 258-266 kg of H2SO4 and 163-195 kg of NaOH/t of produced lignin. The pulp mill capacity can be increased by 1.5 t of pulp/t of lignin to overcome the steam loss (i.e., 6.7-7.1 t of steam/t of lignin).

Automated summary

Existing industrial Kraft mills can serve as the foundation for the utilization of lignin in value-added products. Precipitation from black liquors allows for the recovery of lignin. However, it is crucial to assess the impact of lignin extraction on the overall chemical and energy balances of the mill.