Otimização do cozimento kraft para produção de celulose a partir de madeiras de Eucalyptus globulus com diferentes teores de lignina

Abstract

In this research, it was optimized the kraft pulping for pulp production using Eucalyptus globulus woods with two different lignin contents. Seventy-two laboratory cooking were made with wood chips obtained from six Eucalyptus globulus trees selected from a group of 50 trees. The wood chips from three trees with the lowest lignin content, with average 20,53%, were mixed proportionally based on the tree weights, obtaining the sample of low lignin content wood. The same was made to obtain the sample for wood chips with the highest lignin content, with average 23,02%. The two lignin levels were statistically different. The two wood samples had basic densities statistically not different. Using three temperatures levels (160, 165 and 170ºC), and three active alkali (17, 18,5 and 20%), the wood chips were converted to kraft pulp. The pulp was then characterized to analyze the influence of the distinct treatments employed in the cooking on its properties. The effect of the cooking conditions was expressed by mathematical models in order to determine the optimum points for each of the evaluated properties. The optimization process indicated maximum temperature of 168ºC, and active alkali of 19%, for maximum kraft pulping yield to achieve kappa number 18; this result was for woods with low lignin content. For woods containing the high lignin content, the optimization showed cooking temperature of 169ºC and active alkali of 19% for kappa number of 18. The average reduction of 2,49% in wood lignin content promoted a gain correspondent to 2,2% in the kraft yield (o.d. basis) and a reduction on the active alkali charge of 1,2% (o.d. basis) to achieve kappa numbers from 16 to 19, preserving pulp properties in good levels of quality. If the option is to work with kappa number 19 instead of 16, the gain in kraft yield is approximately 2%. Therefore, when working with low lignin content wood and kappa number 19 instead of 16, a substantial gain of approximately 4,2% is obtained for kraft pulp yield, and additionally 2 to 2,5% reduction in the active alkali charge based on o.d. wood.