Abstract
Steam explosion is a well-known process to pretreat lignocellulosic biomass in order to enhance sugar yields in enzymatic hydrolysis, but pretreatment conditions have to be optimized individually for each material. In this study, we investigated how the results of a pretreatment optimization procedure are influenced by the chosen reaction conditions in the enzymatic hydrolysis. Beechwood was pretreated by steam explosion and the resulting biomass was subjected to enzymatic hydrolysis at glucan loadings of 1% and 5% employing either washed solids or the whole pretreatment slurry. For enzymatic hydrolysis in both reaction modes at a glucan loading of 1%, the glucose yields markedly increased with increasing severity and with increasing pretreatment temperature at identical severities and maximal values were reached at a pretreatment temperature of 230 °C. However, the optimal severity was 5.0 for washed solids enzymatic hydrolysis, but only 4.75 for whole slurry enzymatic hydrolysis. When the glucan loading was increased to 5%, glucose yields hardly increased for pretreatment temperatures between 210 and 230 °C at a given severity, and a pretreatment temperature of 220 °C was sufficient under these conditions. Consequently, it is important to precisely choose the desired conditions of the enzymatic hydrolysis reaction, when aiming to optimize the pretreatment conditions for a certain biomass.
Highlights
Lignocellulosic biomass plays a major role as a sustainable feedstock for biofuel and biochemical production due to its great abundance and relatively low cost [1,2,3]
We showed in this study that the results of a pretreatment optimization for beechwood depend on the chosen enzymatic hydrolysis conditions
For enzymatic hydrolysis at a glucan loading of 1%, the glucose yields increased with increasing pretreatment temperature, even at identical severities, and maximal values were reached at a pretreatment temperature of 230 ◦ C
Summary
Lignocellulosic biomass (e.g., wood, agricultural residues or wastepaper products) plays a major role as a sustainable feedstock for biofuel and biochemical production due to its great abundance and relatively low cost [1,2,3]. Cellulose, hemicelluloses and lignin are the main components of structural plant material, whereas the latter provides natural protection towards degradation of (hemi-)celluloses and thereby contributes to the recalcitrance towards biochemical conversion [5,6]. To overcome this recalcitrance and to enhance sugar release by enzymatic hydrolysis, a range of physicochemical. The biomass is heated to the target temperature by injection of saturated steam, followed by an explosive pressure release after the desired incubation time This leads to a disruption of the matrix of the plant material and a reduction of the particle size in an energy efficient way [12,13]. Steam explosion pretreatment has been shown to yield highly reactive substrates across various feedstocks such as hardwoods [14,15,16,17] or herbaceous biomass [18,19,20] and belongs to the most economical methods [21,22,23]
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