Production of Ethanol from Lignocellulosic Materials

Bioethanol has been introduced in large scale in Brazil, the US and some European countries and is projected to be one of the dominating renewable biofuels in the transportation sector within the coming 20 years. At present bioethanol is produced almost solely from either sugar – or starch-based raw materials (e.g, cane sugar, corn, wheat etc) often called first generation (1G) bioethanol. However, it is a general opinion that future expansion has to be based on bioethanol from lignocellulosic materials, i.e. second-generation (2G) bioethanol such as agricultural residues (e.g. wheat straw, sugarcane bagasse, corn stover) and forest residues (e.g. sawdust, thinning rests), as well as from dedicated crops (salix, switch grass). These raw materials are sufficiently abundant and also available world-wide. They generate very low net greenhouse gas emissions, thus reducing environmental impacts. To achieve systems that are economic and sustainable it is necessary to efficiently utilize all parts of the raw materials, mainly cellulose, hemicellulose and lignin. This requires a high overall yield of ethanol produced by hydrolysis and fermentation of the carbohydrate fraction (hemicellulose and cellulose), as well as a high yield of the main co-product (lignin). Another option is to utilize the hemicellulose for other products like biogas. However, producing monomer sugars from cellulose and hemicellulose at high yields is far more difficult than deriving sugars from sugar – or starch-containing crops, e.g. sugarcane or corn. Therefore, the conversion PRODUCTION OF ETHANOL FROM LIGNOCELLULOSIC MATERIALS