Hydrolysis of wheat straw by dilute sulfuric acid in a continuous mode

• Effective saccharification approach of wheat straw is established in a continuous dilute sulfuric acid medium.
• The maximum reducing sugar yield ratio is as high as 60.80%.
• The material balance and reaction mechanism are analyzed in the whole process.
• Hemicellulose and cellulose are converted to reducing sugar fully and the change of lignin is negligible.

Wheat straw is an abundant agricultural residue with low commercial value worldwide which has great potential in bioethanol conversion. However, high production costs and low yield rate of fermentable sugar restrict its commercialization. A continuous dilute sulfuric acid hydrolysis process was established in which dilute acid (0–1.00%) was taken as flow phase. This process aims to reach high saccharification efficiency and low toxicity of reducing sugar (RS). The hydrolysis of wheat straw was carried out in dilute sulfuric acid with temperature gradient elevating. Each sample of 250 mL was taken when temperature elevates from 60 °C to 230 °C (temperature interval 20–30 °C). The optimized saccharification conditions were achieved at the flow rate of 25 mL/min and sulfuric acid concentration of 1.00%. The maximum RS yield ratio is as high as 60.80%. Furfural is detected by GC–MS with a low content which is the only kind of by-product in the hydrolysate. The hydrolysis mechanism is clarified by analyzing the change of three main compositions in wheat straw under optimized conditions. Besides, SEM, FT-IR analysis techniques are used and the results show that the hemicellulose and cellulose in the wheat straw can be fully converted to RS, while the change in lignin is negligible. This approach is a novel and promising technique for utilizing real straw resource for high yield of RS.

Hydrolysis of wheat straw by dilute sulfuric acid in a continuous mode. The world is desperate need of renewable energy to solve vital strategic, economic and environment problems with the depletion of global fossil fuel. Wheat straw is an abundant agricultural residue worldwide which has great potential in bioethanol conversion. However, high production costs and low yield rate of fermentable sugar restrict its commercialization. We focus on developing more effective saccharification process with little inhibitors of wheat straw. Consequently, a continuous dilute sulfuric acid hydrolysis approach is established in which dilute acid is taken as flow phase. The hydrolysis of wheat straw was carried out in dilute sulfuric acid with temperature gradient elevating. Each sample of 250 mL was taken when temperature elevates from 60 to 230 °C (temperature interval 20–30 °C). The optimized saccharification conditions were achieved at the flow rate of 25 mL/min and sulfuric acid concentration of 1.00%. The maximum reducing sugar (RS) yield ratio is as high as 60.80% in the whole continuous hydrolysis reaction. Furfural is detected by GC–MS with a low content which is the only kind of by-product in the hydrolysate. The hydrolysis mechanism is clarified by analyzing the change of three main compositions in wheat straw under optimized conditions. Besides, SEM, FT-IR analysis techniques are used and the results show that the hemicellulose and cellulose in the wheat straw can be fully converted to RS, while the change in lignin is negligible. This approach is a novel and promising technique for utilizing real straw resource for high yield of RS.Figure optionsDownload as PowerPoint slide