RESUMEN
Lignin, the second most abundant biopolymer on earth and with a predominantly aromatic structure, has the potential to be a raw material for valuable chemicals and other bio-based chemicals. In industry, lignin is underutilized by being used mostly as a fuel for producing thermal energy. Valorization of lignin requires knowledge of the structure and different linkages in the isolated lignin, making the study of structure of lignin important. In this article, lignin samples isolated from two types of reactors (autoclave reactor and displacement reactor) were analyzed by FT-IR, size exclusion chromatography, thermogravimetric analysis (TGA), and Py-GC-MS. The average molecular mass of the organosolv lignins isolated from the autoclave reactor decreased at higher severities, and FT-IR showed an increase in free phenolic content with increasing severity. Except for molecular mass and molecular mass dispersity, there were only minor differences between lignins isolated from the autoclave reactor and lignins isolated from the displacement reactor. Carbohydrate analysis, Py-GC-MS and TGA showed that the lignin isolated using either of the reactor systems is of high purity, suggesting that organosolv lignin is a good candidate for valorization.
Asunto(s)
Lignina , Polímeros , Lignina/química , Espectroscopía Infrarroja por Transformada de Fourier , Peso Molecular , CalorRESUMEN
During autocatalyzed steam explosion of lignocellulose, polysaccharides in the cell wall are hydrolyzed and dehydrated to form various furaldehydes. In addition to furfural, 5-methylfurfural and 2-acetylfuran were identified in condensates from autocatalyzed steam explosion of Scandinavian softwood (Norway spruce, Picea abies). The presence of 5-methylfurfural can be explained by an acid-catalyzed dehydration of 6-deoxyaldohexoses, which are known to be present in lignocellulosic biomass. However, the presence of 2-acetylfuran cannot be explained by previously published reaction mechanisms since the required substrate (a 1-deoxyhexose or a 1-deoxyhexosan) is not known to be present in lignocellulosic biomass. In model experiments, it was shown that 2-acetylfuran is formed from rhamnose and fucose upon heating in the presence of the Lewis acid Cr3+. Possible reaction pathways for the formation of 2-acetylfuran from 6-deoxyaldohexoses are suggested. This reaction can potentially enable the targeted production of 2-acetylfuran from renewable biomass feedstocks.
Asunto(s)
Furaldehído , Vapor , Humanos , Biomasa , Deshidratación , Lignina/metabolismo , Catálisis , HidrólisisRESUMEN
The redeposition of lignin to the fiber surface after organosolv pretreatment was studied using two different reactor types. Results from the conventional autoclave reactor suggest that redeposition occurs during the cooling down stage. Redeposited particles appeared to be spherical in shape. The size and population density of the particles depends on the concentration of organosolv lignin in the cooking liquor, which is consistent with the hypothesis that reprecipitation of lignin occurs when the system is cooled down. The use of a displacement reactor showed that displacing the spent cooking liquor with fresh cooking liquor helps in reducing the redeposition and the inclusion of a washing stage with fresh cooking liquor reduced the reprecipitation of lignin, particularly on the outer fiber surfaces. Redeposition of lignin was still observed on regions that were less accessible to washing liquid, such as fiber lumens, suggesting that complete prevention of redeposition was not achieved.