Preparation of Peracids for Bleaching, 1994 Pulping Conference Proceedings

S. Wang, H-m. Chang, H. Jameel, B. Amini

Peracids, such as peroxymonosulfuric acid (Px) and peracetic acid (Pa), have been proposed as a replacement for chlorine compounds in delignifying and bleaching wood pulps. In the manufacture Px, hydrogen peroxide is reacted with sulfuric acid to form peracids. High molar ration of sulfuric acid and 70% hydrogen peroxide are necessary to achieve high conversion of the peroxide to peracids. Mixed peracids (Pxa) containing both Px and Pa, can be manufactured using hydrogen peroxide, sulfuric acid and acetic acid. High conversion ratios are possible at low molar ratios of acetic acid and sulfuric acid with 50% hydrogen peroxide. These high conversions can be achieved using various combinations of hydrogen peroxide, sulfuric acid and acetic acid. As a result, one of the big benefits of Pxa is the flexibility that can be achieved in the production of the peracid to suit the individual requirements of the mill. If the bleach plant effluents are to be recycled and the sulfur balance is an issue, low molar ratios of sulfuric acid can be used. If the effluents are to be discharged and the BOD is a problem, low molar ratios of acetic acid can be used. In addition the cost of peracid manufacture can be optimized for the cost of the various chemicals used.