Vapour-liquid partition of volatile organic compounds in kraft black liquors

The vapour-liquid partition of various VOC (Volatile Organic Compounds) in a number of industrial black liquors was investigated. The information can be used to determine the distribution of VOC in different condensate and ga s streams in a kraft mill. Batchwise evaporation of weak black liquors was performed on a lab scale. T he evaporation was carried out at atmospheric pressure up to over 90% dry s olids content. During evaporation, condensate samples were collected and an alysed with respect to 15 compounds, total organic carbon (TOC), chemical o xygen demand (COD) and pH. The study resulted in concentration profiles of various VOC in the vapour ( condensate) during evaporation. An increase in concentrations of total redu ced sulphur compounds (TRS), ammonia, methanol and guaiacol at high dry sol ids content indicated a chemical degradation of the liquor. The condensates with the lowest TOC and COD levels were obtained for a dry solid content of 30-40 wt-% regardless of the original dry solids content i n the black liquor.