Chemical and Microstructural Changes in Eucalyptus Globulus Fibers Subjected to Four Different Pretreatments and Their Influence on the Enzymatic Hydrolysis

Abstract

In order to understand the relation between chemical composition, microscopic structure and enzymatic digestibility, different Eucalyptus globulus wood pretreated samples were examined. Pretreated materials obtained by steam explosion and autohydrolysis were compared with those obtained by organosolv and kraft processes. Chemical analyses of pretreated materials showed a decrease in the content of xylans, except in the kraft pulp. FT-IR spectra showed that the residual lignin in autohydrolysis pulp had experienced greater changes compared to those in steam explosion and organosolv pulps, whereas minor changes in lignin kraft pulp were observed. The fiber morphology indicated that autohydrolysis pretreatment was the most aggressive treatment. Reduction in the content of lignin and its redistribution on the fiber wall were confirmed through confocal laser microscopy. The formation of discrete lignin droplets deposited on the surface of the fibers was observed in all pretreatments, with a higher frequency in organosolv followed by steam explosion. A significant increase in enzymatic accessibility was achieved in organosolv, autohydrolysis and steam explosion pulps, due to xylans removal combined with lignin redistribution. Homogeneous lignin distribution and higher xylan content may be related to the low enzymatic hydrolysis efficiency in kraft pulp.

Ethanol Production from Hydrolyzed Kraft Pulp by Mono- and Co-Cultures of Yeasts: The Challenge of C6 and C5 Sugars Consumption

“…In the assay with S. cerevisiae ( Figure 1A), after a very short lag phase, glucose started to be consumed for biomass growth and also for ethanol production. The maximum ethanol concentration of Energies 2020, 13, 744 6 of 15 19.81 ± 0.15 g·L −1 was reached at 8.9 h simultaneously with glucose exhaustion. Biomass concentration increased while glucose was being consumed and remained constant until 24.0 h, when ethanol started to be assimilated, resulting in a little increase in biomass concentration.…”

“…Kraft pulping also leads to hemicelluloses and some cellulose loss and decreases the degree of polymerization of cellulose [14]. The utilization of Kraft pulping as a pretreatment method for LCB has many advantages such as low sugar degradation, pulps free of inhibitors such as furfural and hydroxymethylfurfural (HMF), the recovery of chemicals used, and finally energy production in the recovery boiler [15,16].The enzymatic hydrolysis of Kraft pulp of sweet sorghum bagasse [17], pine, poplar, birch, beech, and wheat straw [16,18], hemp [18], eucalyptus [19], moso bamboo [20], spruce, and birch-aspen mixture [21] has been studied. Hydrolysates with sugar profiles adequate for fermentation have been obtained, proving the viability of Kraft pulping as a LCB pretreatment.…”

“…The enzymatic hydrolysis of Kraft pulp of sweet sorghum bagasse [17], pine, poplar, birch, beech, and wheat straw [16,18], hemp [18], eucalyptus [19], moso bamboo [20], spruce, and birch-aspen mixture [21] has been studied. Hydrolysates with sugar profiles adequate for fermentation have been obtained, proving the viability of Kraft pulping as a LCB pretreatment.…”

Bioethanol Potential From High Density Short Rotation Woody Crops on Marginal Lands in Central Chile

“…The pretreatment conditions used in this work were determined in a previous optimization work developed in the Bioenercel Consortium framework (TRONCOSO et al, 2017).…”

“…The reactor was heated at 3ºC . min -1 , and the cooking was conducted at 194ºC and residence time of 1 min, according to previous work (TRONCOSO et al, 2017).…”