Recycling of pre-hydrolysis liquor to improve the concentrations of hemicellulosic saccharides during water pre-hydrolysis of aspen woodchips

In this study, the pre-hydrolysis liquor (PHL) was recycled during aspen chip water pre-hydrolysis, and the effects of PHL recycling on the extraction and accumulation of the hemicellulosic saccharides especially that with high molecular weight in the PHL were studied. The results showed that the concentration of hemicellulose saccharides in PHL depended on the pre-hydrolysis temperature and PHL recycling times. Compared to the unrecycled PHL, the concentration of hemicellulosic saccharides in PHL increased significantly when recycling PHL once or twice at 170 °C. Furthermore, the amount of high-molecular-weight hemicelluloses (HMHs) in PHL recycled once at 170 °C increased from 2.58 g/L (unrecycled) to 6.18 g/L, but the corresponding average molecular weight of HMHs decreased from 9.2 kDa to 7.6 kDa. The concentration of hemicellulosic saccharides in PHL decreased with PHL recycling time at 180 °C, accompanied by the formation of a significant amount of furfural.