Energy-Related Assessment of a Hemicellulose-First Concept – Debottlenecking of a Hydrothermal Wheat Straw Biorefinery

A hemicellulose-first approach can offer advantages for biorefineries utilizing wheat straw as it combines lignocellulose fractionation and potentially higher added value from pentose-based hemicellulose. Therefore, a tailored hydrothermal concept for the production of xylooligosaccharides and xylan is investigated. The focus is on assessing energy requirements and potential improvements based on experimental results. The wheat straw pretreatment and the downstream processing of the hemicellulose hydrolysate are modeled at a scale of 30,000 tons wheat straw dry mass per year. The results confirm that the hydrothermal concept can be implemented in an energy-efficient manner without the need for additional auxiliaries, due to targeted process design, heat integration and high solids loading during hydrolysis. The resulting specific energy requirements for pretreatment and hydrolysate processing are 0.28 kWh/kg and 0.13 kWh/kg of wheat straw dry mass, respectively. Compared to thermal hydrolysate processing alone, the combination of a multi-effect evaporator and a pressure-driven ultrafiltration can reduce heating and cooling energy by 29 % and 44 %, respectively. However, the ultrafiltration requirements (e.g., electrical energy, membrane area, costs) depend heavily on the properties of the hydrolysate and its interactions with the membrane. This work can contribute to the commercially viable ramp-up of wheat straw multi-product biorefineries.