Abstract
Current fuel ethanol research deals with process engineering trends for improving the efficiency of bioethanol production. Pretreatment has been viewed as one of the most expensive and energy intensive processing steps in the lignocellulosic biomass-to-fermentable sugars conversion process. The objective of this work is to develop multiscale models of hydrothermal pretreatment methods, starting from the microscale level where chemical reaction takes place followed by the mesoscale level in which the diffusion in lignocellulosic material is the main process and finally the macroscale level where the mixing and bulk diffusion are important. At microscale level, a new mechanism for hydrolysis of hemicellulose has been proposed in which the bond breakage is function of position in the hemicellulose chain and all the bonds with same position undergo the breakage at the same time. The result of model prediction showed a high correlation with the experimental data, moreover it was found that the probability of xylooligomer breakage from the middle of the chain is higher than the probability of the breakage from the sides. At the mesoscale level a model for diffusion of water into wood and diffusion of soluble sugars out of the wood in aqueous media has been developed. Finally, a general model for considering water diffusion into the biomass, hydrolysis reaction and diffusion of soluble sugars out of the wood simultaneously has been proposed. © 2009 The Institution of Chemical Engineers.