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- Effect of unbleached pulp kappa number on the kinetics of chlorine dioxide delignificationPublication . Simões, Rogério; Barroca, Maria J. M. C.; Castro, José Almiro A. M.Chlorine dioxide delignification of different unbleached kraft pulps from Eucalyptus globulus, having Kappa numbers of 12 to 18, was studied in the temperature range of 285 K to 358 K. The effect of the unbleached pulp Kappa number on the initial fast phase of delignification was investigated with respect to the depletion factors for Kappa number and chlorine dioxide concentration, as proposed by Barroca et al. Furthermore, the behaviour of the floor lignin content of the pulp, or the floor Kappa number, was analysed within this range. The results show that all pulps exhibit a similar pattern, with respect to temperature, in depletion factors for Kappa number and chlorine dioxide concentration. The degree of normalised delignification and chlorine dioxide consumption is very similar and independent of the Kappa number of the unbleached pulps. Moreover, the results reveal that there is a strong correlation between the floor lignin content and the temperature, and that this correlation is applicable to a wide range of unbleached pulp Kappa numbers, since the residual Kappa number is independent of its initial value. The results enable the general application of a kinetic model to kraft pulps with different unbleached Kappa numbers.
- Effect of carry-over on the kinetics of chlorine dioxide delignification of an unbleached hardwood kraft pulpPublication . Simões, Rogério; Barroca, Maria J. M. C.; Castro, José Almiro A. M.This work is concerned with the kinetics of the prebleaching stage of a kraft pulp of Eucalyptus globulus with chlorine dioxide. Its main purpose is to discuss the influence of the degree of washing, expressed as the COD of the pulp, on the kinetics and stoichiometry of chlorine dioxide delignification. The effect of the carry-over on the rate of delignification of a Do stage was studied over time for pulps with different initial organic charges (COD). A set of experiments was specially designed to discriminate the individual role of lignin and of COD upon the initial consumption of chlorine dioxide. A modified mathematical model, taking into account the reactions of chlorine dioxide with both lignin and the carry-over, has been developed. In this model, the initial chlorine dioxide consumption (in the fast phase of reaction) is dependent on two factors: the carry-over of the pulp and the temperature of operation. However, the carry-over does not affect the corresponding initial depletion factor for the Kappa number. The role of the dissolved organic material, carried with the pulp, upon the rate of reaction in the slow period is better described in the stoichiometry. The fit of the experimental results obtained for pulps with different COD reveals good prediction capabilities for both Kappa number and chlorine dioxide concentration in a conventional D0 stage.
- Determination of sugar content in Pinus pinaster and its corresponding hollocellulose, cellulose and kraft pulpsPublication . Duarte, Ana Paula; Gaiolas, Carla Sofia Cardona Jorge; Belgacem, Mohamed Naceur; Simões, RogérioThis paper deals with the study of the polysaccharide complex from Portuguese Pinus pinaster, as well as from its main components, i.e., holocellulose, cellulose and pulps obtained using different cooking conditions. Nordic Pinus sylvestris was also studied in order to compare it with Portuguese pine. Two methods were used: one consisted of the hydrolysis of polysaccharides with trifluoroacetic acid (TFA) and quantification of the amount of each sugar using High Performance Liquid Chromatography (HPLC). The latter approach used here consisted of the hydrolysis of the samples under scrutiny by sulphuric acid and converting it into alditols, which were then esterified before injecting to Gas Chromatography coupled with Mass Spectrometry. Myo-inositol was used as an internal standard. The results obtained by the two methods showed that the TFA procedure prevents monosaccharide degradation, comparatively with the sulphuric acid one. In fact, the overall sugar yield was found systematically higher than 93% for TFA hydrolysis, whereas that corresponding to H2SO4 treatment never exceeded 77%. The sugar composition of both pines was found very similar and the sulfidity level (from 10 to 55%) did not affect the pulp sugar composition. The glucose/mannose and xylose/arabinose ratios were found to be around 3.5 for both Portuguese and Nordic pines. Finally, kraft pulping of Pinus pinaster was found to affect drastically galactose, mannose and arabinose.
- Papermaking potential of Acacia dealbata and Acacia melanoxylonPublication . Santos, António J. A.; Anjos, Ofélia M. S.; Simões, RogérioThe pulping and papermaking potential of Acacia dealbata and Acacia melanoxylon were studied using Eucalyptus globulus as a reference. Pulp yield, alkali consumption and delignification in the kraft process, of both species, compare very well with the reference. Pulp yield can be higher than that of E globulus and the residual lignin content lower after cooking, which is in good agreement with the lower lignin and extractives content of the wood samples used. Pulps produced from Acacia have slightly lower fibre length and coarseness and higher fibre width and wet fibre flexibility than E globulus pulps. As a consequence of fibre characteristics, the paper produced from Acacia is denser and exhibits higher tensile and burst strength, and lower tear resistance than that from E globulus, at a given PFI revolution. For the same sheet density E globulus displays higher strength properties, but the consequence of achieving this is a lower drainage rate and higher energy consumption in refining.