Improving chlorine dioxide bleaching with aldehydes

Total replacement of chlorine with chlorine dioxide in the first stage of bleaching increases the overall bleaching cost to reach a target kappa number. BY adding aldehydes to the Do stage, the effectiveness of chlorine dioxide delignification is improved. The application of 1. 5%formaldehyde on pulp (o.d. basis) in the Do stage decreases the kappa number after the first extraction? stage by as much as 30% and allows a decrease in the chlorine dioxide applied in the sequence. Although formaldehyde is the cheapest of the aldehydes, glyoxal and glucose are also effective. The results are discussed in the context of the fate of the chlorite formed during chlorine dioxide delignification.