Selective Conversion of Hemicellulose in Macroalgae Enteromorpha prolifera to Rhamnose

Direct hydrothermal conversion (HC) of macroalgae Enteromorpha prolifera was conducted over the temperature range of 140-240 degrees C. At 160 degrees C, monosaccharides and small molecular acids began to generate. A high yield (18.8%) of monosaccharides was obtained at 180 degrees C, whereas 29.6% of small molecular organic acids was attained at 200 degrees C. Formic acid (FA) was then employed as a catalyst, which could selectively catalyze the conversion of hemicellulose at low temperature (94.1%, 140 degrees C). Rhamnose (45.2%) based on the mass of carbohydrates in E. prolifera was produced by the catalysis of 0.7 mL of FA (160 degrees C, 60 min, 1 g of biomass loading). A low ratio of biomass amount to water was beneficial to the solution of water-soluble components of hemicellulose in E. prolifera to get high yields to monosaccharides. HC showed promise to be an applicable and efficient method in the treatment of E. prolifera with high conversion of carbohydrates.