Xylo-oligomers recovery from autohydrolyzed Miscanthus

Xylo-oligomers (XOs) can be produced during autohydrolysis of lignocellulosic biomass, through the hydronium-catalyzed degradation of xylan. The sugar oligomer enriched hydrolysate is washed off to recover XOs and the pretreated solid residue is further processed to ethanol industry. XOs can be a value-added co-product for ethanol industry as XOs exhibit prebiotic effect and inhibit the growth of pathogens in human intestines. However, direct separation of XOs from the hydrolysate is a complex problem, because in addition to XOs, there are other monomeric and oligomeric sugars, sugar degradation products and acid solubilized lignin. Process simulation was performed to integrate mass and energy balance using parameters identified from the lab-scale experiments.  The amount of monomeric and oligomeric sugars in hydrolyzate from pretreated Miscanthus were characterized and the degree of polymerization of XOs is found ~5 based on HPEAC characterization.  Impurities in the hydrolysate (dissolved lignin, organic acids, and monomeric sugars) were removed using resin adsorption (Amberlite XAD, for example). The XOs crystals were obtained by a series of evaporations followed by crystallization. Previous results on simulation showed the water flow during the biomass washing directly affected the XOs production and the energy required removing water on further purification steps, but presented no effect to ethanol production. Simulation showed that 0.114 OD kg biomass /1 kg water that could achieve an optimal condition during washing. Relationship among hydrolyzate washing, impurity removal efficiency, and total energy consumption will be discussed in details from the process simulation.