Recovery of sodium organic salts from partially wet oxidized black liquor

Partial wet oxidation is a recently proposed biorefinery concept for black liquor, generating carboxylic acids and their sodium salts. The aim of this study is to investigate the recovery of sodium organic salts and carboxylic acids from partial wet oxidation downstream by using a preliminary thermodynamic model. The paper illustrates the speciation of sodium formate-sodium acetate-water system together with formic and acetic acids in aqueous solution with respect to pH and temperature. The speciation results indicate that salt recovery requires water evaporation and high pH, whereas acid recovery requires low pH. Temperature slightly influences the salt recovery but has no major impact on acid recovery. Hence, the alternatives for the recovery process can be evaporator-crystallizer-pH reduction with acid or evaporative crystallizer-cooling crystallizer-pH reduction with acid addition.