Remoção de hemiceluloses da madeira por tratamento de lixiviação alcalina com NaOH

Abstract

ABSTRACT:The aim of this work was to assess the impact of hemicellulose extraction in eucalyptus wood, through alkaline leaching (NaOH) of wood chips, on the subsequent kraft process (with varying sulphidity) and the quality of the pulp. The chips were initially saturated with water and treated with a NaOH solution in a liquor to wood ratio of 6:1 m 3 /t. The reaction times (3, 8, 14 and 16 hours), temperatures (70, 84 and 90°C) and NaOH concentrations (60, 80, 90, 120 and 156g/L) were assessed in atmospheric conditions. In the pressurized treatments (300 kPa), the reaction times, temperature and NaOH concentrations assessed were, respectively: 30, 60 and 120 minutes, 100°C and 100, 150 and 200g/L. The optimal alkaline leaching condition was determined taking into account the hemicellulose concentrations remaining in the chips and the gravimetrical yield. Chips not subjected to alkaline treatment (control) and leached with NaOH in optimum conditions were kraft cooked until kappa number 17 -18. The results indicate that alkaline leaching of chips is not efficient in extracting hemicelluloses in the wood studied. The highest extraction of 4-Omethyl-glucuronoxylan acetate reached 42% in very severe conditions (100°C, 60 minutes, 200g/L of NaOH and 300 kPa pressure). The pulp yield of the leached chips was approximately 7% lower than that of the non-leached chips (control).

Contribution of extractives to the bark color of Caesalpinia sappan

“…The residue of the bark sample from the first extraction (n-hexane) was subjected to the next extraction using fresh solvents (ethyl acetate, methanol, and hot water 100 ℃) with the same procedure, successively. Lastly, 1 % sodium hydroxide (NaOH) was used to remove all the remaining secondary metabolites as well as low-molecular-weight carbohydrates (Júnior et al 2010, ASTM D1109-84 2001.…”

“…In addition, 1 % NaOH was used to remove extractives which still bound tightly to the cell wall i.e. hemicellulose, sugars, and polymeric condensed tannins with high degree of polymeration (Júnior et al 2010, Sakai 2001). The extractive content by each solvent after successive extraction are shown in Table 1.…”

“…Polymeric cell walls components and some extractives which form matrix with cellulose, hemicellulose, or lignin could not be extracted with natural solvents. However, extraction with 1 % NaOH has the capacity of breaking some of these matrices, especially hemicellulose, thereby removing its components (Júnior et al 2010). Then, the 1 % NaOH extraction reduced the higher value of a* and b* compared with the natural solvents used in previous extractions.…”

Ultrasound-Assisted Cold Alkaline Extraction: Increasing Hemicellulose Extraction and Energy Production from Populus Wood

“…However, CAE has its disadvantages, and the most significant one is likely its efficiency, which strongly depends on the specific raw material. This pretreatment has been extensively studied for various applications, and it has been observed that the extraction of hemicelluloses is more efficient in herbaceous lignocellulosic materials than in wood [21][22][23][24].…”