Anti-solvent precipitation of saturated steam autohydrolyzed wheat straw xylan - Regression model-based...

The precipitation of water-soluble carbohydrates using organic solvents offers considerable potential, as separation and purification can be achieved in a single step. Therefore, ethanol precipitation of potential high-value xylan - the main component of wheat straw hemicellulose - is investigated and optimized. Pelletized wheat straw, prepared without chemical or biotechnological auxiliaries, is autohydrolyzed using saturated steam. The pretreatment is designed to effectively solubilize hemicellulose, resulting in a hydrolysate low in impurities that is concentrated and precipitated without further purification. An optimal custom design based on I-optimality is used to systematically investigate the influence of feed concentrate dry mass content (20 to 40 %), ethanol (anti-solvent) fraction (30 to 70 %) and precipitation temperature (4 to 52 °C). Interactions and the effects of selected process parameters on the response parameters "precipitation yield" and "precipitate purity" are qualitatively and quantitatively analyzed using regression models. Highly significant and robust models are derived and validated. The precipitation yield for wheat straw xylan can be well over 70 % (up to 86 %) of the hydrolysate dry mass if a proper hemicellulose-first process design is used. Without intensive downstream processing, wheat straw xylan achieves 82 to 93 % of the carbohydrate content relative to xylan laboratory standards, albeit with differences in composition. The regression models reveal correlations with considerable potential for the valorization of hemicellulose using a relatively simple but optimized hemicellulose-first process. This study provides insights regarding carbohydrate precipitation parameters in a robust, transferable framework, demonstrating their applicability in lignocellulosic biorefineries.