Influence of different pretreatment methods on bioethanol production from wheat straw

Article investigates the influence of different pretreatment methods on sugar conversion and bioethanol production. Different dilute acid and alkaline pretreatment methods are compared to determine the best pretreatment method to give the highest glucose and ethanol yields under the mild operating conditions. Wheat straw is used as a raw material as it is the most widely grown cereal in Europe. Dilute sulfuric acid, hydrochloric acid, nitric acid and potassium hydroxide solutions are used for pretreatment in combination with enzymatic hydrolysis. Results indicate that the highest cellulose-to-glucose conversion rate of 316.7 g kg of biomass is achieved by the pretreatment with nitric acid. The lowest glucose concentration of 221.3 g kg is achieved by hydrochloric acid. In the wheat straw samples pretreated with sulfuric acid and KOH, two different approaches are used. Solid phase of half the samples is rinsed with water before adding enzymes, and the rest of the samples are not. The rinsed samples pretreated with KOH solution give the highest ethanol yield of 104.3 g kg, while the lowest ethanol yield is 67.7 g kg from samples pretreated with HCl solution. Unrinsed samples and rinsed samples pretreated with sulfuric acid give an ethanol yield of 78.7 g kg and 92.0 g kg, respectively. These results indicate that rinsing the solid phase of the samples with distilled water before hydrolysis removes most of the inhibitory compounds formed during the pretreatment with dilute acid and increases fermentation efficiency by approximately 12%.