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

The effect of liquid and solid acids catalysts on reducing sugar yields via different pretreatments of furfural residues. •Furfural residues conversion into reducing sugars was researched.•Yields of liquid and solid acids are over 60% and 30%, respectively.•TOF for liquid acid is about 4–5 times of that for solid acids.•Liquid acid is extremely efficient.•Solid acids are green and reusable. 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 120min 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 0.023h−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.