Characterisation Of The Wet Oxidation Of Black Liquor For Its Integration In Kraft Paper Mills

As a mandatory first step to assess the implementation of wet oxidation in the current approach of paper mills as biorefineries, this paper discusses for the first time ever the effect of this treatment on the chemical composition of intermediates and final products, as well as the evolution of sulphur, nitrogen, ions, Gross Calorific Value and the properties related to the subsequent handling and downstream processing of Kraft black liquor. It was found that around 50% of the initial carbon was transformed into carboxylic acids, mainly acetic and lactic; thus showing the high potential of black liquor as a renewable resource for the production of these compounds. The oxidation of organic sulphur into sulphates and the no formation of SOx involve odourless and low-polluting emissions during the wet oxidation. The wet oxidised black liquor is also less viscous (30% lower pumping costs) and easier to purify than the raw material. The treatment did not have a significant effect on evaporation rates, but decreased the Gross Calorific Value, although the heat generated per unit of total organic carbon remained constant.