This work evaluated the impact of brownstock pulp kappa number variations on modified pulping process, oxygen delignification, bleaching, and the physical characteristics on bleached pulp. Wood chips of 6-yearold Eucalyptus grandis x Eucalyptus urophylla from Brazil were used. A modified pulping process was performed with the purpose of achieving two delignification levels on brownstock pulp: kappa 18 and kappa 15. Pulps were submitted to oxygen delignification and elemental chlorine-free (ECF) bleaching to achieve 89.5 ± 0.5% of ISO brightness. Subsequently, pulps were refined in four levels (0, 750, 1500, and 3000 rotations) for physical mechanical tests. Delignification increased after increasing the cooking H factor and alkali charge. As a result, delignification negatively impacted the pulping yields (from 56.1% to 55.0%) and the pulp viscosity (from 1,317 cm³/g to 1,227 cm³/g). Pulps with an initial kappa of 15 presented more efficient oxygen delignification and lower consumption of bleaching reagents. The final viscosity of these pulps were lower (899 cm³/g against 963 cm³/g), however, than that of the pulps with an initial kappa of 18. Furthermore, the pulps with a higher unbleached kappa demanded less refining energy and had lower capillarity. The other physical properties were not influenced by the brownstock delignification level.
RESUMO.O trabalho teve por objetivo estudar a cinética da remoção dos extrativos da madeira de Eucalyptus grandis durante polpação Kraft. As polpações foram efetuadas em reatores tubulares de aço, usando-se madeira na forma de serragem nas seguintes condições: álcali ativo = 14%, sulfidez = 25%, relação licor / madeira = 10 L kg -1 de madeira seca e temperaturas de 130, 150, 160 e 180ºC durante tempos de 30, 60, 90, 120, 150 e 180 min. Após as polpações foram realizadas análises do rendimento bruto e de extrativos totais no resíduo (polpa + rejeitos). Foram determinados extrativos totais (álcool etílico-tolueno (1:2), álcool etílico e água quente, respectivamente) e extrativos solúveis em acetona. Os resultados mostraram que a maioria dos extrativos é degradada nos primeiros 30 min. do processo de polpação. Observou-se que a remoção ocorre em duas fases bem distintas: a primeira, rápida, quando a maioria dos extrativos é removida e a última, lenta, quando pequena fração dos extrativos é removida. Palavras-chave:Eucalyptus grandis, extrativos, polpação Kraft. ABSTRACT. Kinetics of the removal of Eucalyptus grandis wood extractives duringKraft pulping. The objective of this work was to study the kinetics of the removal of Eucalyptus grandis wood extractives during Kraft pulping. The pulping was done in steel tubular reactors using wood saw under the following conditions: active alkali = 14%, sulfidity = 25%; liquor-to-wood ratio = 10 L kg -1 of dry wood; and temperatures of 130, 150, 160 and 180°C during 30, 60, 90, 120, 150 and 180 minutes. After pulping, analyses were conducted of the yield and extractives in residue (pulp and reject).Total extractives (ethyl alcohol-toluene (1:2), ethyl alcohol and hot water, respectively) and soluble extractives in acetone were analyzed. The results showed that most extractives are degraded in the first 30 minutes of the pulping process. It was observed that the removal occurs in two different stages: the first is rapid, where the majority of the extractives are removed, and the last is slow, where few extractives are removed. Key words: Eucalyptus grandis, extractives, Kraft pulping process.Introdução A produção brasileira de pasta celulósica está fundamentalmente baseada na madeira, sendo o eucalipto a principal matéria-prima. O Eucalyptus grandis é uma das espécies que mais se destaca como matéria-prima para produção de polpa no Brasil, pois oferece excelentes resultados da deslignificação, branqueamento e fabricação de papel. No decorrer da década de 1990, especificamente na região Sudeste do Brasil, iniciou-se a duplicação da capacidade produtiva das indústrias de polpa e papel. Os principais componentes da madeira são: celulose, lignina, hemiceluloses, extrativos e não-extrativos (pectinas e compostos inorgânicos).A madeira de folhosas, utilizadas em larga escala, contêm a resina natural confinada nas células de parênquima radial e em pequenas quantidades no parênquima axial e nas coníferas existem canais de resina e bolsas resiníferas. Em folhosas, as células radiais ...
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