Chloroform Formation in Bleaching, 1990 Pulping Conference Proceedings

The formation of chloroform in pulp bleaching has been investigated with mill and laboratory studies. These studies found that chloroform production increased with hypochlorite use in either the hypochlorite or extraction stages. In addition to chloroform, compounds generated in the chlorination stage (intermediates) decomposed to form more chloroform upon an increase of pH. This occurred when filtrates were discharged to the sewers or carried into the extraction stage with the pulp. In hypochlorite-free mills, the intermediates were often the major source of chloroform. Production of these materials and chloroform observed in the mills studied ranged between 0.025 and 0.29 kg/air dried tonne bleached pulp. Lower chlorine factors reduced both chloroform and intermediate production in the chlorination stage. An increase in substitution of chlorine dioxide for chlorine could lower chloroform generation by reducing the chlorine factor. Chloroform generation at a mill practicing oxygen delignification was within the range of those using conventional bleaching processes.