Peracid delignification and bleaching of chemical pulps .1. Delignification

Peracids may prove viable for use in elemental chlorine-free and in totally chlorine-free bleaching sequences. Not only are the quality parameters as good or better th nn iol ozone, but the low capital and operating costs are attractive particularly as mills assess the viability of ozone. Peracids have been used as delignification agents for wood and pulp, as activating agents for lignin before oxygen of a peroxide stage. In laboratory work, peroxy acid has been tested as a replacement for chlorine and ozone with excellent results in Kappa number decrease 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 solution or dimethyldioxirane as alternatives to ozone are discussed. The use of pressurized oxygen together with acid peroxide, peracetic acid, permonosulphuric or mixed acid solution treatment produces delignification of up to 67%.