Molecular Weight Distributions of Effluents from Chloring Dioxide Delignification, 1994 Pulping Conference Proceedings

T. A. Schwantes, T. J. McDonough

The amount of low molecular weight chlorinated organic material formed during bleaching is a concern because this material has the potential to adversely affect the environment. To study the extent of the formation of low molecular weight material during elemental chlorine free (ECF) bleaching, a method of aqueous gel permeation chromatography (GPC) was developed for the determination of bleaching effluent molecular weight distributions. It employs Sephadex gels, aqueous LiCl effluents, and total organic carbon (TOC) detection.

Softwood kraft pulp was delignified with ClO2, NaOH, and O2 and the molecular weight distributions for both the D and (EO) stage effluents were determined. Complete substitution of ClO2 for Cl2 decreased the proportion of low (<960) molecular="" weight="" material="" in="" the="" bleaching="" effluents="" by="" 14-18%.="" smaller="" effects="" resulted="" from="" changes="" in="" d="" stage="" initial="" ph="" and="" reaction="" time.="" oxygen="" delignification="" prior="" to="" 100%="" chlorine="" dioxide="" bleaching="" slightly="" decreased="" the="" proportion="" of="" low="" molecular="" weight="" material="" in="" the="" (eo)="" stage="">