On the formation of oxalic acid in bleaching.
1996 (English)Conference paper (Refereed)
In modern pulp mills with prodn. of bleached chem. pulp the increased closure of the bleach plant effluent water system will lead to increased concns. of a variety of dissolved org. substances. Among these oxalic acid is one of the most detrimental due to the facile formation of insol. calcium oxalate once the pH-value is low enough to liberate calcium ions from the pulp. The ppt. may cause severe prodn. problems. Therefore, the formation of oxalic acid from the bleaching of kraft pulps with a variety of bleaching agents have been analyzed. Two methods of anal. have been employed, viz. ion chromatog. and enzymic oxidn. to hydrogen peroxide. The former is a std. method requiring a certain sample treatment whereas the latter may be used on line. Anal. of the aq. phase after each bleaching stage in a O D EO D sequence reveals that oxalic acid can be formed in all stages with the oxygen stage being the predominant contributor. A comparison between different bleaching agents applied to the same pulp again reveals oxygen as a major producer of oxalic acid. The oxalic acid can be formed from both lignin and polysaccharides but expts. with isolated lignin indicates that the predominant part of the oxalic acid is formed from carbohydrates.
Place, publisher, year, edition, pages
IdentifiersURN: urn:nbn:se:kth:diva-79847OAI: oai:DiVA.org:kth-79847DiVA: diva2:497962
211th ACS National Meeting, New Orleans, LA, March 24-28 (1996),
NR 201408052012-02-112012-02-092012-02-11Bibliographically approved