Concentrating Biomass-Derived Hydrolyzates for Production of Fuels and Chemicals Using Thermal Evaporation – Impact on Sugar Quality and Loss

Concentration of intermediate sugar streams in the biorefinery has become a hot topic of interest as new intensified processing routes are envisioned to convert lignocellulosic biomass to fuels and chemicals.  Fed-batch fermentation and inorganic catalysis benefit from consuming concentrated sugar syrups since specific productivity is dramatically increased and equipment size is condensed.  Likewise, upstream solid-liquid separations that utilize a large quantity of water to achieve high sugar recovery inherently dilute the clarified sugar stream and require subsequent re-concentration.  Thermal evaporation is a well-characterized industrial process used to concentrate cane and beet sugars in addition to fruit juices.  This method provides a straightforward approach to concentrate hemicellulosic and cellulosic sugars and also offers removal of undesirable furfural produced during upstream pretreatment.  Unfortunately, significant losses of sugars can occur when evaporating mixed biomass sugar solutions containing hexoses and more thermally labile pentoses, and any sugar loss is detrimental to the product yield and process economics of the biochemical conversion platform.  In this work, we characterize the sugar degradation kinetics during evaporative concentration of biomass-derived hydrolyzates as a function of various parameters including temperature, pH, and water activity, and identify optimal conditions that preserve sugar yields and quality.