Analysis of aliphatic and phenolic compounds present in industrial black liquors using HPLC-DAD and IC-MS/MS methods

Carboxylic acids and aromatic compounds are essential building blocks and starting materials for the production of a wide range of fine chemicals and materials. Their recovery from kraft black liquor, an industrial effluent from pulp and paper mills, is a promising way to produce alternative bio-based chemicals. Reliable methods are needed to identify and quantify the molecules of interest in complex mixtures such as black liquors. First, an HPLC-DAD-based method was developed for the determination of aliphatic acids and phenolic compounds. It allowed the separation of 31 aliphatic and phenolic compounds. The method was applied to the identification of aliphatic and phenolic compounds in industrial black liquors. Then, an IC-MS/MS method was developed to confirm the identification and quantification of organic compounds in black liquor samples. 22 compounds were detected and identified by MS/MS detection. According to both methods, the major aliphatic acids in softwood kraft black liquor are formic acid (9.8 g/L), acetic acid (7.1 g/L), lactic acid (5.2 g/L), glycolic acid (4.7 g/L), 2-hydroxybutyric acid (2.3 g/L), and oxalic acid (1.3 g/L). Phenolic compounds were detected at very low levels (total concentration 1.4 g/L). This study demonstrates the value of a multi-technique strategy for the identification and quantification of organic compounds in complex matrices such as black liquor.