Improved Eucalyptus Pulp Bleachability Via High Temperature Acid Treatment Edvins Ratnieks Celso Foelkel Vera Sacon Moacir Sauer RIDCEll S A I Introduction This paper presents the key findings of the Riocell Technology Center to understand and develop the state of the art technology of acid hydrolysis to decrease the kappa number of pulps The Center has been studying specifically this phenomen since 1 994 It takes part of a major development project to understand and improve the bleachability of the eucalyptus kraft pulp produced by the mill The driving forces of this project have been the economical aspects of chemicals consumption due to poor selectivity and reactivity increasing production costs chlorine gas elimination and especially the kraft cook heterogeneity and its associated consequences Our first perception of the opportunities in the acid hydrolysis field are associated with the studies of the unbleached pulp leaching presented as a mill case in the 1994 Latin American Delignification Conference E Ratnieks V Sacon C Zimmer C Foelkel The findings were further on extended and presented in the 1995 TAPPI Pulping Conference E Ratnieks C Foelkel V Sacon C Zimmer Both alkaline and acid effects were studied We found at that time the results very promising to reduce the kappa number prior to the bleach plant The acid hydrolysis of pulps has been a known practice G Gellerstedt E L Lindfors 1987 at least on how it affects lignin An elegant explanation on how it affects the sugar polymers in the pulp has been recently given 1 Vuorinen A Teleman P Engenstr6m J Buchert M Tenkanen 1996 One concern is the pulp yielO and selectivity losses that come together with acid hydrolysis stages This practical observation points out that multiple pulp structures undergo acid cleavage and water oxidation no matter which chemical structure predominates The specific purpose of this paper is to present the results produced with the eucalyptus kraft pulp from our mill regarding its behavior to acid hydrolysis and the solutions we provided to maximize the kapPi number reduction without excessive yield loss A selection of eucalyptus pulps were also studied with respect to this behavior 2 Current Status of Development Our early studies on eucalyptus kraft pulps with respect to acid trei trnent were developed under the scope of the time and temperature variables that could alter the leaching of lignin This means some screening lab trials have indicated that temperatures above 100 oc could produce some important changeS on the kaPPi number of pulps As the trials were targeting lignin removal and the kappa number was decreasing substantially the acid hydrolysis treatment was thought to be promising The Table 1 oescribes some of the results we have got in the beginning of our work Trabalho apresentado nO 300 Congresso Anual de Celulose e Papel da i BTCP realizado em Sao Paulo SP Bri sil de 03 a 07 Oe novernbro oe1997 91