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

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 <FONT FACE=Symbol>&raquo;</FONT> 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

Study of the effect of contact force model on the dynamic response of mechanical systems with dry clearance joints : computational and experimental approaches

The main objective of this work is to present a computational and experimental study on the contact forces developed in revolute clearance joints. For this purpose, a well-known slider-crank mechanism with a revolute clearance joint between the connecting rod and slider is utilized. The intra-joint contact forces that generated at this clearance joints are computed by considered several different elastic and dissipative approaches, namely those based on the Hertz contact theory and the ESDU tribology-based for cylindrical contacts, along with a hysteresis-type dissipative damping. The normal contact force is augmented with the dry Coulomb’s friction force. In addition, an experimental apparatus is use to obtained some experimental data in order to verify and validate the computational models. From the outcomes reported in this paper, it is concluded that the selection of the appropriate contact force model with proper dissipative damping plays a significant role in the dynamic response of mechanical systems involving contact events at low or moderate impact velocities.Fundação para a Ciência e a Tecnologia (FCT

Paper mill wastewater detoxification by solar photocatalysis

In the WATER project the German Aerospace Center, and the Universidade Federal de Uberlndia, analyse the possibilities of treating paper mill effluents by solar photocatalysis for the paper mill of the Brazilian paper producer Votorantim Celulose e Papel, VCP, at Luiz Ant(tm)nio, SP, Brazil. The degradation of the bio-polymer lignin is a vast problem in paper production. The tests have shown that treatment by the photocatalyst TiO2 and solar radiation is an ecological future oriented approach to solve this problem. The treatment of lignin containing process water by solar photocatalysis was optimised and the economics for solar treatment plants of different sizes was estimated to check the possibilities for implementing the technology in industrial processes

Theoretical and experimental studies on the adsorption of aromatic compounds onto cellulose

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