Dechlorination of pulp bleaching plant E-1 effluent by ArF* and KrF* excimer laser photolysis: Part 2. Dechlorination of polychlorinated oxylignins

The E-1 effluent from bleaching of pine kraft pulp was fractionated by ultrafiltration to obtain polychlorinated oxylignin fractions, PCOL-1, PCOL-2, PCOL-3 and POCL-4 with relative molecular mass (Mr) of 6500, 6000, 5500 and 3500, respectively. These PCOLs were characterized by elemental and functional group analyses, and gel permeation chromatography. The PCOLs were decolorized and dechlorinated in the presence of H2O2 in O2-saturated solution at 20 °C by ArF* (193 nm) excimer photolysis. The results showed that both the decolorization and dechlorination were dependent on both the initial pH and concentration of H2O2 per substrate in the reaction mixture. In general, the decolorization increases with increasing pH and concentration of added H2O2. At pH 10.5 with 8% H2O2 per substrate to the initial reaction mixture, approximately 70% of chromophoric structures were degraded within the initial 60 min irradiation of ArF* (193 nm) laser radiation, then leveled off. The dechlorination reactions followed first order reaction law; first order with respect to total organically bound chlorine; first order overall. The dechlorination rates increase with increasing both pH and concentration of H2O2 per substrate. The quantum yields (Φ) for the generation of chloride ions from PCOLs in the presence of 2% H2O2 were appreciably lower than the values observed for the monomeric chlorophenols, in the range of approximately 0.03 versus 0.9. The ArF* excimer laser photolysis of PCOLs were also monitored by gel permeation chromatography. PCOL-2 was degraded into fragments with relative molecular mass (Mr) of approximately 1500. Similarly, PCOL-3 and PCOL-4 were degraded into fragments with Mr of approximately 4000 and 3000, respectively. In contrast, the Mr of PCOL-1 was increased to approximately 6500, indicating the occurrence of condensation among the degraded fragments.