Intensification of wheat straw autohydrolysis at minimal water input: Advancing a novel hemicellulose-first approach

Abstract

The autohydrolysis of wheat straw, as a key step in a hemicellulose-first concept, was investigated with a focus on separating xylose-based oligomers and water-soluble polymers. The feedstock preparation and the autohydrolysis with saturated steam (avoiding explosion and additional auxiliaries) are aligned to produce a hemicellulose hydrolysate rich in non-monomeric xylose at low liquid-to-solid ratios and mild reaction temperatures. For the first time, highly significant regression models for biomass solubility, yield of non-monomeric xylose, share of non-monomeric xylose and inorganics content of the hydrolysate were derived in conjunction. The findings emphasize the critical impact of dry mass content, particularly under conditions of low water input, with an optimal performance identified below 50%. High arabinoxylan solubilization (77%) and xylose recovery as non-monomers (85%) were achieved at a liquid-to-solid ratio of 1.5, without the need for extensive biomass size reduction. Wheat straw pieces larger than 1 cm with a dry mass content of 40% treated in the custom reactor at a severity factor of 3.7 (170 °C, 40 min) resulted in a hydrolysate dry mass containing 67% arabinoxylan, 8.6% glucan and only 6.8% phenolic and 2.5% inorganic compounds. Under optimized conditions, autohydrolysis with saturated steam enables controlled hemicellulose separation and the recovery of oligomers and polymers corresponding to approximately 16.4% of the biomass. The results offer valuable insights into systematic autohydrolysis interactions and provide a framework for minimizing water and energy demands – key challenges in terms of green chemistry and industrial applications.