Study on the catalytic degradation of sodium lignosulfonate to aromatic aldehydes over nano-CuO: Process optimization and reaction kinetics

Abstract

As one of the few renewable aromatic resources, the research of depolymerization of lignin into high-value chemicals has attracted extensive attention in recent years. Catalytic wet aerobic oxidation (CWAO) is an effective technology to convert lignin like sodium lignosulfonate (SL), a lignin derivative, into aromatic aldehydes such as vanillin and syringaldehyde. However, how to improve the yield of aromatic aldehyde and conversion efficiency is still a challenge, and many operating conditions that significantly affect the yield of these aromatic compounds have rarely been investigated systematically. In this work, we adopted the stirred tank reactor (STR) for the CWAO process with nano-CuO as catalyst to achieve the conversion of SL into vanillin and syringaldehyde. The effect of operating conditions including reaction time, oxygen partial pressure, reaction temperature, SL concentration, rotational speed, catalyst amount, and NaOH concentration on the yield of single phenolic compound was systematically investigated. The results revealed that all these operating conditions exhibit a significant effect on the aromatic aldehyde yield. Therefore, they should be regulated in an optimal value to obtain high yield of these aldehydes. More importantly, the reaction kinetics of the lignin oxidation was explored. This work could provide basic data for the optimization and design of industrial operation of lignin oxidation.