Coproduction of xylose, lignosulfonate and ethanol from wheat straw

• Novel process to coproduce xylose, lignosulfonate and ethanol from wheat straw.
• Recover xylose from the hydrolyzate of acid treatment with 86.4% yield.
• Directly recover sulfomethylation treatment liquor containing 5.5% lignosulfonate.
• Enzymatic hydrolysis of the treated wheat straw to fermentable sugars with 91% yield.
• Fermentation of the obtained fermentable sugars to ethanol with 87.8% yield.

A novel integrated process to coproduce xylose, lignosulfonate and ethanol from wheat straw was investigated. Firstly, wheat straw was treated by dilute sulfuric acid and xylose was recovered from its hydrolyzate. Its optimal conditions were 1.0 wt% sulfuric acid, 10% (w/v) wheat straw loading, 100 °C, and 2 h. Then the acid treated wheat straw was treated by sulfomethylation reagent and its hydrolyzate containing lignosulfonate was directly recovered. Its optimal conditions were 150 °C, 15% (w/v) acid treated wheat straw loading, and 5 h. Finally, the two-step treated wheat straw was converted to ethanol through enzymatic hydrolysis and microbial fermentation. Under optimal conditions, 1 kg wheat straw could produce 0.225 kg xylose with 95% purity, 4.16 kg hydrolyzate of sulfomethylation treatment containing 5.5% lignosulfonate, 0.183 kg ethanol and 0.05 kg lignin residue. Compared to present technology, this process is a potential economically profitable wheat straw biorefinery.