Hydrothermal Oxidation of Industrial Alkali Lignin for Producing Small Molecular Organic Acids

Abstract

To control the serious pollution caused by alkaline pulping in paper industry and utilize alkali lignin – the main organic ingredient residing in black liquor, an experimental research on hydrothermal oxidation of industrial alkali lignin for producing small molecule organic acids (mostly formic and acetic acids) was conducted using batch reactors. The results showed that the yields of acetic acid almost entirely increased and then decreased with oxygen supplies, reaction times and reaction temperatures, while the yields of formic acid fell in a narrow range of ~ 4% irrespective of all the hydrothermal conditions. A highest total yield of formic and acetic acids of 23.0% was achieved at the conditions of 300 °C, a 100% oxygen supply and a 60 s reaction time, and at the same time a highest yield of acetic acid of 20.3% was obtained. Based on the products recognized, the main pathways for producing small molecular organic acids, particularly formic and acetic acids were discussed.