Improving saccharide concentration by mixing octyl acetate during semi-flow, hot-compressed water treatment of woody biomass

Biomass-based ethanol or acetic acid can be produced by fermentation of saccharides following wood hydrolysis. Both high saccharide yield and concentration are essential for achieving an efficient hydrolysis process. However, there can be a trade-off between yield and concentration during semi-flow, hot-compressed water treatment, a candidate for wood hydrolysis. This trade-off is because the fast water flow rate is necessary for high saccharide yields, but the large amount of water dilutes the produced hydrolysate. In this study, we mixed octyl acetate, which is a water-immiscible solvent, during hot-compressed water treatment of beech wood. By adding octyl acetate, a high flow rate was achieved without increasing the water flow rate, and the saccharide concentration was thus improved, while suppressing the decrease in saccharide yield. Furthermore, lignin-derived oligomers, which have inhibitory effects on fermentation, were removed from hydrolysate because they can dissolve in octyl acetate. We performed acetic acid fermentation using the obtained hydrolysate and found that the fermentability was markedly improved compared with the hydrolysate obtained without octyl acetate.