Obtenção de insumos quimicos a partir do aproveitamento integral do bagaço de cana

AUTOR(ES)
DATA DE PUBLICAÇÃO

1995

RESUMO

Sugar cane bagasse was pre-treated by steam explosion in a 0.65 L stainless-steel reactor. The experiments were carried out at temperatures ranging from 165 to 210°C and for 5 to 60 min, using 11 g of water-free bagasse. At 190°C ca. 36% of the sugar cane bagasse was dissolved after 15 min. Under these conditions, 86% of glucans was recovered in the form of cellulose, 3.2% was hydrolysed to glucose, 0.12% was decomposed into hydroxymethylfurfural and 11 % into unidentified compounds. 73% of the xylans was hydrolysed to arabinose (2.5%), arabinose bonded to xylans (1%), xylose (7.4%), furfural (2.8%), xylose oligomers (51%) and unidentified componds (8.3%). The acetyl groups were hydrolysed to acetic acid (39%) and acetyl groups bonded to xylans (36%); 12% remained in the pre-treated bagasse and 13% were not identified 20% of the lignin was hydrolysed to soluble products. Pre-treatment under milder conditons proved to be insuficient for obtaining high yields of hydrolysed polyoses. More severe conditions led to condensation reactions between lignin, hydroxymethylfurfural and furfural. The results obtained for the pre-treatment at 190°C, for 15 min in a 240 L reactor with 10 kg of water-free bagasse were comparable to those carried out at laboratory scale. With the pilot plant conditions the amount of celulose in the pre-treated bagasse was higher than that found in the benchtop experiments. The quantities of xylan and of acetyl groups recovered from the tiquor as known componds were lower, which shows that the polyoses were decomposed to a higher degree in the pilot plant. On the other hand, the composition of hydrolysed compounds was unchanged. Delignification of pre-treated bagasse in the bench experiments was examined by varying the solid/liquid ratio (1:10/1:40 - w/v), the temperature (25-100°C), the reaction time (0.5-8.0 h) and the NaOH concentration (0.25-10%). The reactions were carried out with mechanical stirring (200 rpm), in a constant temperature bath, using 10 g of water-free bagasse. The best results were obtained under the following conditions: 1% (w/v) NaOH solution, 1:20 (w/v) solid-liquid ratio, 100°C, and 1 h reaction time. The delignification yield was 90%, and 80% of the lignin was recovered after precipitation at pH 2. Cellulose recovery reached 97.0% and the amount of lignin found in the pulp equaled 5.0%. After 2 h, the delignification yield increased to 95%, but the amount of lignin recovered from the solid phase remained the same and the cellulose yield dropped to 91.5%. The lignin residue found in this pulp was equal to 2.8%. Lowering the NaOH concentrarion from 1 to 0.5% did not affect the cellulose yield, but delignification dropped to 83.1% and the lignin residue increased to 7.1%. Delignifications carried out in a pilot plant, i.e., 10 kg water-free bagasse in a 300 L stainless steel reactor, solid/liquid ratio equal to 1:20 (w/v), showed yields similar to those obtained on the laboratory scale. However, the lignin recovered after precipitation at pH 2 was 4% lower than that obtained in the laboratory, due the losses during filtering. 10% less cellulose (87%) was recovered when compared to laboratory scale. On the other hand, the lignin in the pulp remained unchanged (5.1%), giving a Kappa number of 21. The viscosity of the unbleached pulp was 16.6 cP. The lignin precipitated with acid (pH 2) was found to have the following composition: C9H7.10(O)1.00(O)0.16(OCH3)0.83(O)(OH)1.10S0.03. The apparent average molecular mass was equal to 4000 g/mol, with a polydispersity index of 9.3. FTIR spectroscopy indicates that this is a HGS type lignin. Proton NMR of an acetylated sample shows 1.9 aromatic protons per C9, which is an indication of a highly condensed macromolecule.

ASSUNTO(S)

bioquimica vegetal quimica organica bagaço de cana

ACESSO AO ARTIGO

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