Sulfonation of kraft lignon to water soluble value added products

Abstract

Kraft lignin is water insoluble and has limited end-use applications. The main objective of this MSc studies was to rend kraft lignin water soluble, and various value-added products including dispersants and flocculants. In this work, softwood kraft lignin was supplied from FPInnovations from its pilot facilities in Thunder Bay, ON. It was then modified using BURL lab facilities of Lakehead University. In one alternative, phenolation and hydroxymethylation of kraft lignin were followed as pre-treatment processes to improve the reactivity of lignin. Unmodified kraft lignin, phenolated lignin and hydroxymethylated lignin were then sulfonated through 1) concentrated sulfuric acid and 2) sodium sulfite treatments. All lignin samples treated with sodium sulfite exhibited increased in charge density and solubility. Additionally, sulfuric acid treatment of phenolated lignin yielded soluble product (SAP) with a high charge density (e.g. 3 meq/g). However, sulfuric acid treatment of phenolated lignin was unsuccessful in producing lignin with desired charge density and solubility. The synthesized soluble sulfonated lignin samples (SS, SSH, SSP, and SAP) demonstrated a greater solubility than kraft lignin, but weaker solubility than commercial and industrial lignosulfonates. The application of sulfonated lignin samples were evaluated as dispersants in cement and kaolinite; adsorbent on kaolinite and calcium carbonate to produce modified fillers for composites and papermaking as well as flocculants for textile industry. The addition of the sulfonated lignin to cement did not increase the fluidity of the cement, but improved the fluidity of kaolinite to some extent. The adsorption of sulfonated lignins on calcium carbonate and kaolinite were greater than that of kraft lignin, which shows that modified lignin can have a high adsorption capacity to produce modified fillers. The samples, which were phenolated, exhibited a greater adsorption affinity than other samples on calcium carbonate. In this study, ethyl violet and basic blue solutions were used as model wastewater samples of textile industry. The results showed that, the sulfonated lignin samples were generally able to remove ethyl violet, but were unsuccessful in removing basic blue from solution.