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Caracterização do efeito da explosão a vapor sobre as propriedades fisico-quimicas da lignina de Eucalyptus grandis
| Content Provider | Semantic Scholar |
|---|---|
| Author | Emmel, Alexandre |
| Copyright Year | 2012 |
| Abstract | Pretreatment of lignocellulosic materials is essential for their efficient conversion because of the various physical and chemical barriers which greatly inhibit the accessibility of the substrate to chemical and biological catalysts. One pretreatment method that several workers have used to enhance the conversion of lignocellulosics is high pressure steaming, with or without rapid decompression (explosion). Acid-impregnated chips of E. grandis were steam-treated over a range of temperatures and residence times into the steam gun to evaluate the effect of pretreatment on the recovery yield of wood components (carbohydrates and lignin) and the chemical properties of the lignin component found within the wood chips. Steam explosion of Eucalyptus grandis has been carried out under various pretreatment conditions (200-210°C, 2-5 min) after impregnation of the wood chips with 0.25 and 0.5% (m/m) dilute H2SO4. Acid-catalysed steam treatment allowed good yields of hemicellulose recovery (mostly as xylose) in the water-soluble fraction, as well as a relatively high susceptibility to hydrolysis of the water-insoluble fraction. Formation of dehydration byproducts (furfural and hydroxymethylfurfural) and water-soluble chromophores (lignincarbohydrate complexes) was monitored in the water soluble fraction by UV spectroscopy and their concentration increased with pretreatment severity. Klason lignin of steam-treated substrates also varied according to pretreatment severity. Longer residence times into the steam gun seemed to impair more drastic pretreatment conditions (greater severities) to the wood chips. This was apparent from the greater amount of glucose released in the water-solubles, lower hemicellulose recovery and lignin yields beyond 100% when pretreatment was carried out for longer residence times of 5 min. The best possible xylose recovery yield (nearly 70%) was obtained after pretreating 0,5% H2SO4impregnated wood chips for 2 min at 210°C. The effect of alkali washing on the chemical composition of steam-treated substrates and the physical characterization of the alkali-soluble lignin obtained at each pretreatment condition were also assessed in this study. FTIR spectroscopy allowed a direct observation of the pretreatment effect on the chemical composition of the wood chips, particularly after the alkali washing step. Klason lignin of steam-treated and alkali-washed substrates varied accordingly to pretreatment severity. Higher pretreatment temperatures and residence times resulted in a more extensive depolymerization of Iignin. This was apparent from their analysis by differential scanning calorimetry, were a gradual decrease in the temperature required for lignin fragmentation was observed. On the other hand, lignin condensation also occurred at higher residence times in the steam gun and this was shown to be greater than the effect derived from increasing the pretreatment temperature. A considerable increase in the susceptibility of the water-insoluble fraction to alkali extraction was observed towards higher pretreatment severities, with the best lignin yield obtained after alkali-washing of 0.5% H2S04-impregnated wood chips that had been steamtreated for 2 min at 210°C. Therefore, alkali-washing resulted in steam-treated substrates with higher cellulose content, thus increasing their theoretical yield to fermentable sugars through saccharification and/or fermentation. On the other hand, the lignin component obtained after steam explosion and mild alkali-washing is still suitable for conversion to chemical products. Therefore, aside from maximum hydrolysis yield and xylan recovery, pretreatment optimization should include lignin recovery in an active form to evaluate its probable use as a raw material for industrial applications. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://acervodigital.ufpr.br/bitstream/handle/1884/28218/D%20-%20ALEXANDRE%20EMMEL.pdf?isAllowed=y&sequence=1 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
