Recovery and Enrichment of Organic Acids from Kraft Black Liquor by Simulated Moving Bed Adsorption

Abstract

The C1-C6 organic acid fraction of kraft black liquor has potential as a valuable and high-volume biomass-derived molecular feedstock for the production of chemicals and materials. However, large-scale recovery and purification of the multicomponent acid fraction are challenging. This paper presents the design and demonstration of a continuous simulated moving bed (SMB) adsorption process for the recovery and production of organic acids from kraft black liquor (BL). A combination of experimental multicomponent adsorption measurements, SMB operation, and model-guided process design was applied, using a granulated activated carbon adsorbent. The SMB modeling parameters, including adsorption isotherms and mass transfer parameters, were obtained experimentally through batch-mode and column breakthrough measurements using synthetic multicomponent acid streams. The preliminary SMB operating conditions were then determined by detailed SMB process modeling and optimization and fine-tuned experimentally with the aid of internal concentration profile measurements and heuristic principles of SMB operation. The adjusted operation condition was then validated by continuous production of acids with an actual pretreated BL stream. A high-quality organic acid mixture with 98% purity and 95% water rejection was obtained, with >85% acid recovery from the pretreated BL feed and a 4-fold increase in acid productivity per unit mass of adsorbent relative to a cyclic fixed-bed process. Approaches for managing the effects of residual lignin content in the pretreated feed are discussed.