An effective method for the direct crystallization of xylonic acid from fermentation broth of agricultural residue hydrolysate

Abstract

Xylose is the second most abundant sugar in nature and conversion of xylose to xylonic acid (XA) has become a research hotspot in recent years. Xylonic acid can be applied in the equivalent market niche of gluconic acid, due to their similar physical properties. XA bioproduction and application presents certainly a promising approach for xylose valorization in lignocellulose biorefinery, while the XA crystallization is so far still an unattainable goal. In this paper, an original method was proposed and experimentally investigated for the first time to get XA crystals from fermentation broth. In the XA crystallization, methanol was introduced as buffer-cum-solvent. The H2SO4 was dropwise added into the methanol solution dissolving potassium xylonate that is beforehand produced by fermentation. During H2SO4 blending with methanol, the strong and polar H2SO4 leads to XA diffusion and aggregation. Overall, 2.21 g of xylonic acid crystals was obtained per gram of 98% H2SO4 acidification. NMR detection showed that over 99% purity of XA crystals was finally obtained at the yields of 67.2% from xylonate. The integrated process could provide a practicable and effective technology for the high-qualify XA preparation from xylose derivations and lignocellulose biomass biorefinery.