Comparison between liquid and solid acids catalysts on reducing sugars conversion from furfural residues via pretreatments

Liquid sulphuric acid is adopted and compared with carbon-based sulfonated solid acids (coal tar-based and active carbon-based) for furfural residues conversion into reducing sugars. The optimum hydrolysis conditions of liquid acid are at 4% of sulphuric acid, 25:1 of liquid and solid ratio, 175 °C of reaction temperature and 120 min of reaction time. The reducing sugar yields are reached over 60% on liquid acid via NaOH/H2O2, NaOH/microwave and NaOH/ultrasonic pretreatments, whereas only over 30% on solid acids. The TOFs (turnover number frequency) via NaOH/H2O2 pretreatments are 0.093, 0.020 and 0.023 h−1 for liquid sulphuric acid, coal tar-based and active carbon-based solid acids catalysts, respectively. Considering the efficiency, cost and environment factors, the liquid and solid acids have their own advantages of potential commercial application values.