Otimização do estágio de branqueamento de polpa kraft de eucalipto com dióxido de cloro em alta temperatura

• Ano de defesa: 2002
• Autor(a) principal: Eiras, Kátia Maria Morais
• Orientador(a): Colodette, Jorge Luiz
• Banca de defesa: Gomide, José Lívio , Oliveira, Rubens Chaves de , Silva, Cláudio Mudado , Maia, Elenice Pereira
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Mestrado em Ciência Florestal
• Departamento: Manejo Florestal; Meio Ambiente e Conservação da Natureza; Silvicultura; Tecnologia e Utilização de
• País: BR
• Palavras-chave em Português: Polpa de madeira; Branqueamento; Otimização; Dióxido de cloro; Hemiceluloses; Xilana; Ácidos hexenurônicos
• Palavras-chave em Inglês: Wood pulp; Bleaching; Optimisation; Chlorine dioxide; Hemicellulose
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::RECURSOS FLORESTAIS E ENGENHARIA FLORESTAL::TECNOLOGIA E UTILIZACAO DE PRODUTOS FLORESTAIS::TECNOLOGIA DE CELULOSE E PAPEL
• Link de acesso: http://locus.ufv.br/handle/123456789/3197

The objective of this study was to optimise the operational conditions (pH, kappa factor, time and temperature) of the first chlorine dioxide bleaching stage operated with a long period of time and a high temperature (DHT), using a 3-stage (DEopD) bleaching sequence as a reference. It was also the objective of the study to compare the performance of four different pre-bleaching treatments for eucalyptus kraft-O2 pulp, namely: (1) hot acid stage followed by conventional chlorine dioxide stage with inter-stage washing (AD); (2) hot acid stage followed by hot chlorine dioxide stage without inter-stage washing (A/D); (3) chlorine dioxide stage at long time and high temperature (DHT); and (4) conventional chlorine dioxide stage (D) - reference. The various treatment performances were assessed at 90% ISO brightness by comparing the sequences ADEop(DnD), A/DEop(DnD), DHTEop (DnD) and DEop(DnD). The most suitable conditions to operate the DHT stage include kappa factor between 0.18 and 0.26, 3-4 pH, 95°C, and 90-120 min. When operated under these conditions the DHT stage shows higher delignification efficiency and lower selectivity and brightening action in relation to a conventional D stage (30 min, 60 °C) for similar kappa factor and pH values. The DHT stage time and temperature does not significantly affect the optimum pH of this stage which seems to be in the range of 3-4. The high temperature and time used in the DHT stage decreases the metals content and OX formation in the pulp. It also decreases the oxalate and AOX contents in the filtrates. The DHT stage results in improved pulp brightness stability and decreased chlorine dioxide requirement by 10-12%, thus decreasing bleaching costs by about 7%. On the other hand, it decreases overall bleaching yield (~1%), viscosity (~14%), pulp xylan (~2%) and HexA´s (~18%) contents. It also increases effluent organic load. Furthermore, the DHT stage increases refining energy requirement although it has no significant impact on pulp strength properties. In general, the DHT stage is more attractive than the conventional one because it decreases overall bleaching costs and the generation of chlorinated organics, without penalising pulp quality. The comparison among the technologies AD, A/D, DHT and D showed the following order of efficiency: AD>A/D=DHT>D. Although the A/D and DHT efficiencies are similar, A/D technology is more selective. The AD stages shows to be the most attractive technology to bleach eucalyptus pulp because it saves three times as much chlorine dioxide as the A/D and DHT. Moreover, it producing pulps with higher viscosities. It should be noted that the A/D and DHT technologies save one bleaching stage in relation to the AD one and still allow for the achievement of 90% ISO brightness pulp in a less capital intensive three bleaching stage sequence.