Loss of volatile organics from kraft bleaching filtrates in the evaporation/drying phase of the analysis for dissolved total solids (DTS) and dissolved volatile solids (DVS)

Abstract

Measurement for describing dissolved organic matter (DOM) was needed to calibrate bleached kraft process model. Volatile solids (VS) measurement from filtered sample (DVS) was chosen as closest possible, especially because it is readily available and easy to perform. The extreme conditions of kraft chlorine dioxide bleaching filtrates (e.g. pH 2–11), however, prerequisite evaluation of the analyzing method in these circumstances. Measurements before and after evaporation/drying (SFS 3008) and redissolution showed that considerable amounts of dissolved organic carbon (DOC) escaped from acid filtrates. When identified, particularly alcohols, carboxylic acids but also aldehydes and ketons covered the majority of the disappeared quantity. According to DOC the escaped share was from 17 to 37% in the acid filtrates depending on stage (D0(/D1/D2) and conditions in production process. In alkaline bleaching stage filtrates the share was 4 to 9%. The major identified volatilized compounds in D0-filtrate were methanol and formic acid. They represented 94% of the identified compounds. Identified volatilized quantity from D0-filtrate in DVS measurement represents about 4–5 kg per metric air dry ton of pulp as discharge. The carbon of the identified volatilized compounds covered 63% of the loss measured as DOC. Knowledge of volatiles and process conditions is required when DVS is used for DOM description in kraft bleaching filtrates.