Comparison of three fermentation strategies for alleviating the negative effect of the ionic liquid 1-ethyl-3-methylimidazolium acetate on lignocellulosic ethanol production

The conversion of lignocellulosic materials provides a sustainable pathway towards the production of renewable fuels. Ethanol is now one of the most widely used transport bio-fuels and the use of ionic liquids has provided a promising technical tool to convert the carbohydrates in lignocellulosic materials to fermentable sugars for ethanol production. However, some ionic liquids will be remained in the obtained sugars which inhibit the yeast growth and have a negative effect on the subsequent ethanol fermentation process. In this paper, three fermentation strategies, viz the increase of the inoculum size, the two step fermentation and the fed batch fermentation were investigated to alleviate the negative effect of the ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIMAc) on lignocellulosic ethanol production. When the EMIMAc concentration was 10 g l−1, all these three fermentation strategies could effectively increase the ethanol productivity and keep a relatively high ethanol yield for the glucose ethanol fermentation process (42.7-43.6%). For the conventional ethanol fermentation process, its ethanol productivity increased from 1.80 to 2.20 g l−1 h−1 by increasing its inoculum size from 0.01 to 0.10 (v/v). For the two step ethanol fermentation process, its ethanol productivity arrived at 2.32 g l−1 h−1 when the feeding number was 3. For the fed batch ethanol fermentation process, its ethanol productivity reached 2.43 g l−1 h−1 when the feeding interval time was 3 h. These three fermentation strategies could also greatly improve the ethanol production of the ionic liquid EMIMAc treated wheat straw by increasing its ethanol productivity and keeping a relatively high ethanol yield. These results provide useful information for improving the lignocellulosic ethanol production via the ionic liquid technology.