Adsorption Processes for Recovery and Enrichment of Organic Acids from Kraft Black Liquor

Kraft black liquor (Kraft BL) is a complex multicomponent byproduct from wood pulping processes. Conventionally, it is first dewatered by evaporators and then combusted to recover the inorganic pulping chemicals and produce energy from the organic components. After lignin, carbohydrate-derived organic acids are the second abundant class of organics in kraft BL (3-5 wt%) and comprise a potential biomass-derived feedstock of 30-50 million tons/yr globally. The organic acids are C₁-C₆ molecules with 1-2 COOH groups and 0-4 hydroxyl groups, thus comprising both hydroxy acids and conventional carboxylic acids. These acids could be valorized either as a bioderived feedstock for biofuels and biobased chemicals production, or further fractionated to produce specific high-value carboxylic acids from the mixture. However, both these routes require a viable process to separate carboxylic acids from BL.

In this talk we will discuss the adsorption properties of activated carbon adsorbents for separation of organic acids from the other constituents (inorganics, water) of kraft black liquor, and the development of an adsorption-based process for recovery and enrichment of organic acids. We present comprehensive packed-bed column adsorption measurements and analysis to thoroughly characterize the multicomponent adsorption phenomena and develop a cyclic operation scheme for the adsorption process. Methanol is used as a desorbent in this process. We have successfully obtained enriched organic acid mixtures (12-15 wt% on desorbent-free basis) in a single-stage operation with extended cyclic experiments. The productivity and selectivity of the adsorption process will be discussed in detail.