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

Abstract 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 ( M r ) 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 H 2 O 2 in O 2 -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 H 2 O 2 per substrate in the reaction mixture. In general, the decolorization increases with increasing pH and concentration of added H 2 O 2 . At pH 10.5 with 8% H 2 O 2 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 H 2 O 2 per substrate. The quantum yields ( Φ ) for the generation of chloride ions from PCOLs in the presence of 2% H 2 O 2 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 ( M r ) of approximately 1500. Similarly, PCOL-3 and PCOL-4 were degraded into fragments with M r of approximately 4000 and 3000, respectively. In contrast, the M r of PCOL-1 was increased to approximately 6500, indicating the occurrence of condensation among the degraded fragments.