Isolation of Carboxylic Acids and NaOH from Kraft Black Liquor with a Membrane-Based Process Sequence

Silvia Margareta Maitz, Lukas Wernsperger, Marlene Kienberger*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


In kraft pulping, large quantities of biomass degradation products dissolved in the black liquor are incinerated for power generation and chemical recovery. The black liquor is, however, a promising feedstock for carboxylic acids and lignin. Efficient fractionation of black liquor can be used to isolate these compounds and recycle the pulping chemicals. The present work discusses the fractionation of industrial black liquor by a sequence of nanofiltration and bipolar membrane electrodialysis units. Nanofiltration led to retention of the majority of lignin in the retentate and to a significant concentration increase in low-molecular-weight carboxylic acids, such as formic, acetic, glycolic and lactic acids, in the permeate. Subsequent treatment with bipolar membrane electrodialysis showed the potential for simultaneous recovery of acids in the acid compartment and the pulping chemical NaOH in the base compartment. The residual lignin was completely retained by the used membranes. Diffusion of acids to the base compartment and the low current density, however, limited the yield of acids and the current efficiency. In experiments with a black liquor model solution under optimized conditions, NaOH and acid recoveries of 68–72% were achieved.

Original languageEnglish
Article number92
Issue number1
Publication statusPublished - 10 Jan 2023


  • biorefinery
  • bipolar membrane electrodialysis
  • black liquor
  • carboxylic acids
  • lignin
  • nanofiltration

ASJC Scopus subject areas

  • Chemical Engineering (miscellaneous)
  • Process Chemistry and Technology
  • Filtration and Separation


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