Pretreatment of rice straw for ethanol production by a two-step process using dilute sulfuric acid and sulfomethylation reagent

Ethanol is now one of the most widely used transport bio-fuels and production of ethanol from rice straw (RS) is an effective RS utilization way. This work investigated a novel two-step RS pretreatment process with the goal of decreasing the ethanol production cost through complete utilization of its components. In the process, RS was first treated with dilute sulfuric acid to remove the hemicellulose and recover the xylose from its hydrolyzate as a feedstock for xylitol production, and then the residue was treated with the standard sulfomethylation reagent to remove the lignin and recover its hydrolyzate containing the lignosulfonate as a cement water reducer. Among tested conditions, the best acid treatment (AT) conditions were 100 °C, 1.0 wt% sulfuric acid, 10% (w/v) RS and 2 h, and the hydrolyzate recycled 5 times. After AT, the xylose was recovered from its hydrolyzate with 83.2% yield. The best sulfomethylation treatment (ST) conditions were 160 °C, 15% (w/v) acid treated RS, and 5 h using the standard sulfomethylation reagent. After ST, its hydrolyzate containing 5.0% lignosulfonate was directly recovered as a cement water reducer. Under the above best two-step treatment conditions, 94% hemicellulose and 92% lignin in the origin RS were removed, but cellulose had almost no loss. After the simultaneous saccharification and fermentation of the two-step treated RS (100 g L−1) for 72 h, the ethanol concentration and its yield reached 40.6 g L−1 and 86.4% respectively. It suggests the two-step pretreatment process was an efficient RS pretreatment method for its ethanol production. This process can be an example of RS bio-refinery for bio-fuel production.