High solids alkaline oxidation and biomethane conversion of residual lignin

Abstract

Residual lignin recovered from biological conversion processes and pulp and paper industry wastes can be converted to water-soluble products by alkaline oxidation under oxygen pressure at high solids loading within the temperature range 130-180° C. No problems associated with repolymerization reactions are encountered at solids loading between 10-30% where the initial molar ratio of hydroxide base to lignin residual is at last 0.4, possibly because of enhanced reactivity in the oxidation reaction of aromatic groups in self-associate structures. The water-soluble oxidation products can be fractionated to recover a low molecular weight fraction in which pH can be adjusted using CO2 without forming precipitates. Sodium carbonate byproduct can be recovered from the pH adjusted reaction mixture using acetone precipitation. The low molecular weight fraction of the pH adjusted oxidation products can be used as feed for anaerobic digestion to biomethane.

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