ACTIVATOR FOR PEROXIDE BLEACHING OF MECHANICAL PULP

In situ activation of peroxide tetraacetylethylenediamine (TAED) to pr oduce a strong oxidant is a safe and low cost (capital intensive) alte rnative to pre-formed peracids or other strong oxidizing agents. Unlik e pre-formed peracids, the combination of TAED and peroxide can provid e effective bleaching. In alkaline medium, one mole of TAED reacts wit h two moles of perhydroxyl ion (hydrogen peroxide) to produce two mole s of peracetic anion. Generally peracids are considered to be better a nd more active bleaching agents than peroxide. Various aspects of pero xide reaction with a commercial thermomechanical softwood pulp have be en investigated namely temperature, time, charge, peroxide/TAED ratio, alkalinity, and buffering to maximize brightness gain. Considering th at bleaching processes vary from mill to mill, experiments were conduc ted to evaluate the impact of the sequence of addition of an activator in one- and two-stages using peroxide and TAED. The use of TAED in pe roxide bleaching liquor offers a mean to significantly improve pulp br ightness. Enhanced bleaching efficiency is achieved using a short time cycle implying lower energy requirement and reduction in production c osts.