(584h) Production of Carboxylic Acids from Lignite with Two-Stage Alkali-O2 Oxidation

Alkali-O₂ oxidation of lignite can yield carboxylic acids (CAs). But the species with different reactivities in lignite are oxidized under identical conditions, resulting in a low CA yield. In this work, we proposed a two-stage oxidation process of lignite to increase the CA yield. First, lignite was extracted using a NaOH aqueous solution to divide the lignite into two parts: extract (Ex, 25.4 %) and residue (Re), which have different reactivities. Then, Ex and Re were oxidized separately with alkali-O₂ oxidation under different conditions. The extraction conditions and the alkali-oxygen oxidation conditions of Ex and Re were investigated. The results indicated that the carbon yield of CAs from Ex was 35.32 %, including 5.60 % formic acid, 6.15 % acetic acid, 11.95 % oxalic acid, 0.85 % succinic acid, and 11.13 % benzene carboxylic acids (BCAs) at 230 °C, an initial O₂ pressure of 4.5 MPa and a NaOH content of 1M for 40 min. The yield of carboxylic acids from Re was 36.69 %, including 0.35 % formic acid, 5.05 % acetic acid, 11.81 % oxalic acid, and 19.48 % BCAs at 260 °C, an initial O₂ pressure of 5.5 MPa and a NaOH content of 3 M for 70 min. The total CAs yield was 36.28 %, which is much higher than 26.7% with the traditional one-stage alkali-O₂ oxidation. The structural properties of Ex, Re and lignite were studied in detail with ¹³C NMR and FT-IR to reveal the different reactivities and yields.

The project is financially supported by the National Natural Science Foundation of China (No. 21676019 and 21076138).