Photoinduced reactions of lignin and lignin degradation products: Photo-oxidation of chlorinated organics in bleach plant effluents; photoinduced reactions of lignin in high-yield pulps.

摘要

Photo-oxidation of chlorinated organics in bleach plant effuents. Preliminary studies were undertaken to explore the response of chlorinated phenolics in the E-1 stage effluents from conventional chlorination of softwood kraft pulp towards photo-oxidation. The experiments were conducted in a photo-chemical reactor (RPR-100 Rayonet) by irradiating the effluent with medium pressure mercury lamps in presence of oxidants such as oxygen and hydrogen peroxide. Chlorinated organics--high molecular materials as well as simple polychlorinated phenols--were degraded resulting in substantial color removal and conversion of organically bound chlorine to inorganic chloride.;The photo-oxidative processes could be markedly accelerated by addition of photosensitizer (benzophenone), and by hydrogen peroxide indicating the importance of photoinduced autoxidation reactions.;Conducting the reactions in a thin film reactor (Ace Glass Laboratories, NJ) in the presence of oxygen resulted in an acceleration of the decolorization and dechlorination rates.;Photo-induced reactions of lignin in high yield pulps. In a series of experiments, attempts were made to understand the phenomenon of photobleaching. Handsheets were irradiated in a Atlas C i 35 weather-O-meter using a xenon lamp which simulates sunlight. It was found that the photobleached sheets undergo reversion on storage in dark, in the presence of oxygen. Pre-extraction of the pulp with n-hexane and acetone had some effect on slowing down the yellowing process implying that extractives contribute to yellowing. Treatment of pulps with sodium borohydride prior to irradiation with light (;In another series of experiments it was demonstrated that increase in the peroxide levels during bleaching results in increased brightness instability of groundwood pulps as observed from accelerated aging tests in a Weather-O-meter.