The electro-oxidation of lignin in Sappi Saiccor dissolving pulp mill effluent

Abstract

Electro-oxidation reactions using a nickel anode were carried out on the calcium-spent liquor effluent obtained from Sappi Saiccor (formerly South African Industrial Cellulose Corporation) dissolving pulp mill as well as on lignin-and lignan-type compounds previously identified in the effluent. Voltammograms were obtained for each solution in order to identify the oxidation potentials of the compounds to be electro-oxidised. Value-added products such as vanillin and syringaldehyde were identified in the electro-oxidised reaction mixtures using gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC). Profiles of the changes in concentration of these compounds were determined as a function of time with maximum concentrations reached within the first half hour. These findings are significant in that few electro-oxidation reactions have been carried out on the effluent of a pulp mill which uses the acid bisulphite pulping process and no results have previously been reported on the electro-oxidation of syringaldehyde. This study contributes to a further understanding of the electro-oxidation of lignin and is of value to the paper and pulp industry at large. Reduction of the organic content of the effluent by electro-oxidation was shown to be possible.

Wastewater Treatment and Reclamation: A Review of Pulp and Paper Industry Practices and Opportunities

“…Eskelinen et al (2010) aimed the treatment of some wood extractives and achieving 51%, 76%, and 83% concentration removals of 12 mg/L abietic acid, 11.8 mg/L oleic acid, and 0.6 mg/L β-sitosterol, respectively. Particular value-added products, such as vanillin and syringaldehyde, were identified in the electro-oxidized reaction media of acid bisulfite pulping effluents (Moodley et al 2011). Dominguez-Ramos et al (2008 obtained positive results for the treatment of lignosulfonate, which may be regarded as a component of effluent from sulfite pulping.…”

Electrochemical Lignin Conversion

“…Electrooxidation of the lignin monomer syringaldehyde has been shown to produce its corresponding acid and dimers as byproducts. [37] The polymerization of lignin monomers can occur via radical coupling reactions, [10,38,39] or through intermolecular condensation reactions at lower temperatures and in less alkaline conditions. [40] The addition of lignin to anode aqueous solutions not only results in lignin oxidation but also lowers the potential needed for electrolytic hydrogen production at the cathode.…”

“…Nickel (Ni 0 ) is a widely used electrode material because of its stability, low cost and known catalytic activity for lignin depolymerization. [8,33,37] In practical applications, the architecture of the electrode is crucial because it greatly affects the electrochemical active area, mass transport and flow distribution. [45][46][47] The morphology of the Ni electrode ( Figure 4) has significant influence on lignin depolymerization, with higher for the lignin model compound (1G) in the trifluoroacetic anhydride (TFA) system.…”

“…However, the complex structure of lignin makes it very difficult to dissolve in common organic solvents. [82] Alkaline solutions (e. g., NaOH, KOH) have been widely used as the electrolyte in many lignin electrooxidation studies [10,31,44,48,59,[83][84][85][86][87][32][33][34]37,[40][41][42][43] due to increased solubility for lignin and high electron/ion conductivity. However, electrolysis in aqueous solution is limited by the water splitting reaction at 1.23 V, severely restricting the potential window for electrochemical reactions.…”

The application of advanced oxidation technologies to the treatment of effluents from the pulp and paper industry: a review

“…For example, the electrochemical oxidation of lignosulfonate achieved an 80% TOC removal (Domínguez-Ramos et al 2008). Moreover, the treatment of lignin obtained from Saiccor's acid bisulphite-based pulping process resulted in the production of vanillin, which would be a byproduct of interesting commercial value (Moodley et al 2011).…”