Bleaching of low kappa AQ pulps: Laboratory and mill trials

Anthraquinone can be used to lower the brownstock kappa number of kraft pulps. In this paper, laboratory and mill trial results demonstrate the magnitude of the kappa number reduction achievable for both softwoods and hardwoods. The low kappa number kraft-AQ pulps have been bleached using conventional and ECF sequences. Both laboratory and mill trial results demonstrate that the reduction in kappa number obtained with AQ translates directly into a reduction in WC required in the first bleaching stage as well as a reduction in the caustic charge required in the subsequent extraction stage.