Abstract
Wet explosion pretreatment of hybrid poplar sawdust (PSD) for the production of fermentable sugar was carried out in the pilot-scale. The effects of pretreatment conditions, such as temperature (170–190 °C), oxygen dosage (0.5–7.5% of dry matter (DM), w/w), residence time (10–30 min), on cellulose and hemicellulose digestibility after enzymatic hydrolysis were ascertained with a central composite design of the experiment. Further, enzymatic hydrolysis was optimized in terms of temperature, pH, and a mixture of CTec2 and HTec2 enzymes (Novozymes). Predictive modeling showed that cellulose and hemicellulose digestibility of 75.1% and 83.1%, respectively, could be achieved with a pretreatment at 177 °C with 7.5% O2 and a retention time of 30 min. An increased cellulose digestibility of 87.1% ± 0.1 could be achieved by pretreating at 190 °C; however, the hemicellulose yield would be significantly reduced. It was evident that more severe conditions were required for maximal cellulose digestibility than that of hemicellulose digestibility and that an optimal sugar yield demanded a set of conditions, which overall resulted in the maximum sugar yield.
Highlights
The increasing focus on greenhouse gas emissions from fossil energy production, along with the decreasing resource of fossil fuels, has increased the global interest in finding alternative resources for the production of fuel, chemicals, and materials
In the United States, more than one billion tons of lignocellulosic biomass can be produced annually, which can be used for the production of biofuels to replace the domestic use of fossil fuels and for substituting the use of fossil fuel for producing chemicals [1]
While glucan and xylan contents in the poplar sawdust were found to be lower than that of milled biomass of whole hybrid poplar, as previously reported [33], the lignin content of the poplar sawdust residues was found to be higher. This could be due to the content of bark residues with higher lignin content in the poplar sawdust sample used in this study
Summary
The increasing focus on greenhouse gas emissions from fossil energy production, along with the decreasing resource of fossil fuels, has increased the global interest in finding alternative resources for the production of fuel, chemicals, and materials. In the United States, more than one billion tons of lignocellulosic biomass can be produced annually, which can be used for the production of biofuels to replace the domestic use of fossil fuels and for substituting the use of fossil fuel for producing chemicals [1]. Among the lignocellulosic biomass materials, hybrid poplar (Populus spp.) is considered a promising feedstock for the production of cellulosic biofuels due to its large genetic diversity, availability for harvest over the whole year, fast growth rate, as well as higher bulk density as compared to the herbaceous feedstock, which eases the transport and storage [3].
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