Black Liquor Electrolysis for Hydrogen and Lignin Extraction

Abstract

Black liquor is a pulp mill effluent from wood cooking with a solid content of 15-18 wt.%, which is mostly lignin. The present study focuses the electrolysis of black liquor for energy recovery. The process has several economic and environmental advantages, as it simultaneously generates a clean fuel (hydrogen) at the cathode and a precipitated material with economic value (lignin) at the anode surface. Platinum, nickel, and AISI 304 stainless steel bulk electrodes are tested for black liquor electrolysis, both as anodes and as cathodes. Voltammetric methods are used to study the lignin oxidation in the black liquor at room temperature, allowing the calculation of kinetic parameters such as the charge transfer coefficient and the number of exchanged electrons. The hydrogen evolution reaction in the black liquor is also evaluated. A small-scale laboratory black liquor electrolyzer using Ni plates is assembled and its operation parameters are evaluated.