Ethanol production from the red seaweed Eucheuma denticulatum and recovery of 5-hydroxymethylfurfural

Abstract

In this study, ethanol was produced via thermal-acid hydrolysis, enzymatic saccharification, and fermentation from the red seaweed Eucheuma denticulatum as a biomass. Also, the removal and further recovery of 5-hydroxymethylfurfural (5-HMF) from hydrolysates were investigated. The thermal-acid hydrolysis produced 38.37 g/L monosaccharides and 6.55 g/L 5-HMF under the optimized condition of 13.7% (w/v) seaweed slurry and 479 mM H2SO4 at 121 °C for 54 min. More monosaccharide (6.43 g/L) was obtained from subsequent enzymatic saccharification using 8 U/mL of commercial enzyme C-Tec2 at 45 °C for 36 h. By detoxification, 88.0% of 5-HMF was removed from seaweed hydrolysates using a 1:1 ratio of polyethylenimine (PEI) to 5-HMF (g/g) at a pH of 11.0 for 15 min. Ethanol fermentation of E. denticulatum hydrolysate was performed using wild-type and galactose-adapted Saccharomyces cerevisiae. The ethanol concentration was maximized to 19.56 g/L (YEtOH = 0.43 g/g) by fermenting detoxified E. denticulatum hydrolysate with galactose-adapted S. cerevisiae Furthermore, for the valuation of 5-HMF (removed from hydrolysate) as a platform chemical, 85.6% of 5-HMF was recovered from the PEI-5-HMF solution by H2SO4 at pH 1.0.