PEROXYMONOSULFATE AND DIMETHYLDIOXIRANE AS INTERSTAGE TREATMENTS IN 2-STAGE OXYGEN DELIGNIFICATION

Dimethyldioxirane (DMD) a selective bleaching agent is most convenient ly formed in situ by adding peroxymonosulfate (Ps) to pulp impregnated with acetone. This study investigated whether DMD formed in situ is m ore effective than Ps alone as an interstage treatment for two-stage o xygen delignification. Kraft-oxygen pulp from radiata pine was treated with a range of peroxymonosulfate in the presence or absence of aceto ne then oxygen delignified. Addition of acetone improved the overall s electivity when peroxymonosulfate (2.5% HSO5-) or greater was applied. At 5 Kappa number pulp treated with 5% HSO5- and acetone had a viscos ity 1.2 mPa.s higher than that of corresponding pulp treated with only peroxymonosulfate. Brightness after final oxygen delignification impr oved by up to two ISO units with acetone in the interstage treatment ( 5% HSO5-). Final bleaching fo the 5% Ps-acetone interstage treated pul p with 1.6% chlorine dioxide improved brightness by further 17% ISO. T hese improvements in selectivity and brightness, however, were relativ ely small compared with the increased costs and additional process com plexity required for acetone addition.