Macroalgal biomass hydrolysis using dicationic acidic ionic liquids

BACKGROUND Macroalgae has high potential as a bio‐fuel feedstock due to its high carbohydrate content. Conventional aqueous systems require a huge amount of energy to catalyze depolymerization and hydrolysis of macroalgae. Recently various task‐specific ionic liquids ( ILs ) successfully depolymerized different biomasses, but were thermally unstable. A variety of dicationic acidic ILs ( DAILs ) connected by oligo‐ethylene glycol ( EG ) chains bearing hydrogen sulfate ( HSO 4 − ) anions were synthesized with better thermal stability and utilized in hydrolysis of macroalgal biomass, Gelidium amansii . RESULTS The structures of DAILs were confirmed by 1 H and 13 C NMR as well as FT‐IR . EG ‐linker chain lengths and dicationic structure increased the thermal stability of DAILs and influenced their catalytic performance for G. amansii hydrolysis. DAILs linked with short oligo‐ EG chains afforded higher sugar yields and exhibited faster hydrolysis rates compared with those linked by long oligo‐ EG chains (i.e. PEG400 and PEG600 ). A maximum sugar yield of 67.45 wt% was recovered from G. amansii using [Tri‐ EG ‐( MIm ) 2 ] 2HSO 4 DAIL , after 3 min at 120 °C. CONCLUSION The synthesized DAILs showed dual properties as catalyst and reaction medium for hydrolysis of macroalgae in solvent‐less conditions. Shorter oligo‐ EG chain linked DAILs exhibited faster reaction rates with higher sugar yields. © 2016 Society of Chemical Industry