Study of the anions profile throughout the sulphite pulp line

Abstract

In this study, the sulphur oxide anions profile at all stages of the Mg acid sulphite pulping process was evaluated by Ion Chromatography (IC). The concentration of bisulphite anions decreased almost two-third along the cooking, while the sulphate concentration increased progressively. Of the bisulphite consumed, only a third was converted to sulfates. Unexpectedly, the maximum thiosulphate concentration was found in the pulping acid filling step, being further decreased along the cooking. The chloride ions rise progressively during the cooking being extracted essentially from the wood, although a noticeable part of the phosphate anions belongs to pulping reagents and inlet water. The low molecular weight fraction of lignosulphonates (LS) appeared in the cooking liquor in the residual delignification step and, together with xylonic acid, contributed to an overestimation of the fluoride concentration determined by the IC due to the same retention time in the chromatographic column during the analysis.

Keywords:

• Anions analysis
• dissolving pulp
• ion chromatography
•  pulping

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supporting information

Supporting information includes the figures on the schematic representation of a sulphite process (Figure S1), the sampling points for the anions analysis (Figure S2) and the tandem ESI-MS spectra for the most abundant monomeric LS (Figure S3). Table S1 includes the data on thin (SSL) and thick (THSL) Ca-based sulphite liquors from E. globulus cooking reported by Rueda et al.^[12]

Additional information

Funding

This work was financially supported by Caima – Indústria de Celulose S.A. within the scope of the PhD project of Inês S. F. Mendes and by CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the Portuguese Foundation for Science and Technology/MCTES.