Steam explosion (SE) is a promising hydrothermal pretreatment technology for future biorefineries. In this study, the three steps of the steam explosion process, (1) the steam treatment (2) the explosion, and (3) the impact step were separately considered and their effects on structural changes of wood were studied. The SE experiments were performed on single wood pieces in different experimental set-ups at 7 and 14 bar pressure with 5 and 10 min treatment times. Mercury porosimetry and environmental scanning electron microscopy analyses were conducted to characterise both internal and external changes in the wood. It was found that the explosion step is not responsible for the disintegration of the wood material into small pieces; instead, the disintegration occurs due to impact of softened wood chips. However, the porosity profiles of the tracheids change during the explosion step. Altogether, all three steps of the SE process contribute in a synergistic way to an increase in pore size and total intrusion volume.
Steam explosion pretreatment modifies both the chemical and physical structures of a biomass. Chemical modifications are generated during the treatment of biomass with steam at high temperature. Physical modifications are created during the explosion step, which produces disintegrated and defibrillated biomass. In this study, the contribution of each modification to an increase in enzymatic hydrolysis has been studied. It was found that both physical and chemical modifications contributed to an increase in enzymatic hydrolysability. Additionally, high resolution Xray tomography was performed to identify the structural modification created during the steam explosion process. Comparison of the 3-D microstructure of a steam-exploded wood sample with an untreated wood sample revealed that several kinds of cracks were created during the explosion step, and the micro-structure of the wood sample was vigorously destroyed.
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