Electrochemical Decomposition of Wheat Straw Lignin into Guaiacyl‐, Syringyl‐, and Phenol‐Type Compounds Using Pb/PbO2 Anode and Alloyed Steel Cathode in Alkaline Solution

Abstract

An electrocatalytic method was applied to decompose unit structures of wheat straw lignin (WSL) through oxidation on Pb/PbO2 and reduction on alloyed materials cathode with different catalytic activity in alkaline solution. Six of guaiacyl‐type (G) compounds were chosen as target products for evaluating their properties and efficiencies of all selected cathodes in WSL decomposition. A series of alloyed materials were examined as catalysts for the electrocatalytic decomposition, thereinto, the selected catalysts were characterized and evaluated by a systematic study for hydrogenation of WSL in NaOH solution. The effects of reaction parameters, such as pH, current density, lignin concentration and temperature, on product yields were investigated. Gas chromatography (GC) monitored maximum yields of 1.134 and 1.248 g/kg‐lignin of guaiacol and acetovanillone using FeW9Cr4V5Co3 as cathode, 0.364, 3.797, and 1.147 g/kg‐lignin of 4‐ethylguaiacol, vanillin, and vanillyl acetone using 304 alloyed steel as cathode, 1.040 g/kg‐lignin of 4‐propyl guaiacol using FeW9Cr4Mo3V as cathode, respectively. Based on the maximum yield of guaiacyl‐type compounds, 304 alloyed steel gave the best results with respect of lignin decomposition at the optimum conditions. In addition, gel permeation chromatography (GPC) demonstrated that the average molecular weights (Mw) of the lignin decreased in the process of all reactions and the unit structures cut down from lignin were electro‐catalytically hydrogenated to guaiacyl‐, syringyl‐, and phenol‐type compounds. © 2018 American Institute of Chemical Engineers Environ Prog, 38:e13117, 2019