The Improvement of the Bleaching of Peroxyformic Sugar Cane Bagasse Pulp by Photocatalysis and Photosensitization

Abstract

Presented here is a new process in two stages for bleaching peroxyformic sugar cane bagasse pulp combining photosensitization and photocatalysis. The first stage consists of an irradiation (1h), with tungsten or mercury lamps, of the pulp under alkaline pH in aqueous suspension at a consistency of 5% with TiO2 and methylene blue (MB) or 3,4,9,10-perylenetetracarboxylic acid (PTCA) or Fe (II) 4,4?,4??,4???-tetrasulfophthalocyanine (TSPC) (concentration " 10-5 mol L-1) in the presence of bubbling oxygen and hydrogen peroxide (2% pulp basis). The second photobleaching stage performed with hydrogen peroxide (3%) efficiently completed the delignification and the brightness gain, removing completely the sensitizer from the pulp. Under those conditions, efficient bleaching of the pulp was obtained, using uv/vis light and PTCA or MB (unbleached pulp: kappa number: 13, brightness: 44, viscosity: 900 dm³ kg-1; bleached pulp: kappa number: 1.2-1.3, brightness: 86, viscosity: 510-550 dm³ kg-1) or visible light with MB (kappa number: 1.7, brightness: 80, viscosity: 625 dm³ kg-1). The mechanisms of photobleaching to increase the selectivity and the efficiency of the process remain to be established.

Keywords

• cellulosic pulp
• bleaching
• photocatalysis
• titanium dioxide
• lignin
• photobleaching
• oxygen
• hydrogen peroxide
• photosensitization
• singlet oxygen