Fermentable Liquid Energy Carriers by Microwave-Assisted Hydrothermal Depolymerisation of Several Biomass Carbohydrates

This work addresses the production of fermentable liquid aqueous solutions by microwave-assisted hydrothermal treatment of cellulose and hemicellulose and alginic acid. A reactivity comparison was established at different temperatures (160–210 °C), reaction times (0 and 5 min) and solid/water ratios (1/20 and 1/10 g/g). The nature of the carbohydrates and the hydrothermal conditions exerted a significant influence on the reactivity, which increased as follows: cellulose 6) and mono-/disaccharides, carboxylic acids, ketones and furans. While the chemical composition of the hydrolysates produced from hemicellulose was not affected by the microwave pre-treatment, all the liquids having a high concentration of DP > 6 oligosaccharides, the microwave conditions substantially influenced the composition of the liquids produced from cellulose and alginic acid. The former contained high proportions of oligosaccharides and saccharides, while the latter comprised water-soluble DP > 6 oligomers/oligosaccharides, saccharides, carboxylic acids and furans. The yeast Metschnikowia pulcherrima was used to assess the fermentability of the hydrolysates. All the hydrolysates were fermentable and their efficiency decreasing as follows: cellulose (high/low saccharides/inhibitors proportion) > hemicellulose (high/low oligosaccharides/inhibitors proportion) > alginic acid (low/high saccharides/inhibitors proportion).