PERACID DELIGNIFICATION AND BLEACHING OF CHEMICAL PULPS .1. DELIGNIFICATION

Peracids may prove viable for use in elemental chlorine-free and in to tally chlorine-free bleaching sequences. Not only are the quality para meters as good or better th nn iol ozone, but the low capital and oper ating costs are attractive particularly as mills assess the viability of ozone. Peracids have been used as delignification agents for wood a nd pulp, as activating agents for lignin before oxygen of a peroxide s tage. In laboratory work, peroxy acid has been tested as a replacement for chlorine and ozone with excellent results in Kappa number decreas e and strength retention. In the first stage replacing a chlorination stage comparative results using equilibrium mixtures of peracetic acid or distilled peracetic acid, or permonosulphuric acid or mixed acid s olution or dimethyldioxirane as alternatives to ozone are discussed. T he use of pressurized oxygen together with acid peroxide, peracetic ac id, permonosulphuric or mixed acid solution treatment produces deligni fication of up to 67%.