Study On Aox Reduction Techonlogy In The Process Of Chlirine Bledching For Bagasse Pulp

With the improvement of environmental requirements, the national AOX emission limit is being improved. The existing non-wood pulp ECF bleaching process has not meet the requirements of the new standard for AOX emission. Therefore, how to reduce the content of AOX in wastewater has become an important research field of China’s pulp and paper industry.The unbleached bagasse kraft pulp is as raw material in this thesis. Through the three stages bleaching of D0EpD1, adding the various additives (such as sodium sulfide, sulfamic acid, dimethyl sulfoxide etc), explore technology and the principle of AOX reduction in bleach effluent. Results are as follows:After adjustment and optimization of D0EpD1bleaching process for bagasse pulp, the optimum conditions shows below. Pulp dense is10%,ClO2total volume (active chlorine) is2%, Do:ClO2is1.6%(active chlorine),60min,60℃.Ep:NaOH is2.5%, H2O2is1%,65℃,90min. D,:ClO2is0.4%(active chlorine),70℃,75min.Don’t wash pulp after Do stage, and add1%sodium sulfide in alkaline extraction. Comparing to not add, the content of AOX in bleaching effluent is lower15%, but brightness drops2%ISO. In Do stage,0.1%sulfamic acid can make the content of AOX in the effluent fall10%, but the brightness reduces1.2%ISO. Add1%dimethyl sulfoxide in Do stage can make the content of AOX in the effluent decrease11.2%, the brightness reduces1.6%ISO at the same time. In D1stage,0.05%sulfamic acid can make the content of AOX in the effluent fall11.8%. And0.5%of dimethyl sulfoxide can make the content of AOX decrease19.2%. The experiment also found that, with the increase of D stage bleaching temperature, content of AOX in wastewater also increased.Changes of lignin degradation products in the bleaching effluent and main functional groups of bleached pulp were analyzed respectively by ultraviolet-visible spectrum, GC-MS and infrared spectrum. Through the ultraviolet spectrum detecting bleaching effluent before and after adding additive (sodium sulfide, sulfamic acid,dimethyl sulfoxide) found:there is a absorption peak in280nm place, which is caused mainly by the phenolic substances of lignin. According to the absorbance size was informed that absorbance of bleaching effluent was smaller after adding the additive. Through analyzing IR spectrum of pulp before and after adding the additive was found that Na2S and sulfamic acid could reduce the content of phenol-type lignin in pulp, but maked part of lilac-type lignin structure undegraded. Na2S and dimethyl sulfoxide make C-O-C, C=O structure in the cellulose and hemicellulose be retained. The content of beta-glycosidic bond and C-O-C structure in the cellulose and hemicellulose can be reduced after adding sulfamic acid. Composition of lignin degradation products in bleaching effluent was analyzed by GC-MS. It could be concluded that the content of organic chlorine, such as chlorobenzene and chlorine phenol, was significantly less after adding the additive. But Na2S and sulfamic acid inhibited poorly production of some phenol substances. Dimethyl sulfoxide was better than them on inhibiting production of phenol substances.