2. Biochemical route: cellulosic ethanol

The biochemical route refers to the conversion of lignocellulosic biomass by hydrolysis followed by fermentation. The main end product is so-called "cellulosic" ethanol, in reference to the fraction of biomass that is mostly valorized. It is similar in nature to first-generation bioethanol produced from sugar or cereal plants such as corn and wheat. However, while first-generation bioethanol is at an advanced stage of technological maturity, second-generation bioethanol still faces technical and economic difficulties linked to the material to be recovered [33] :

• lignin cannot be fermented into ethanol. Only the cellulose and hemicellulose fractions are potential sources of fermentable sugars (see Box 1), hexoses (glucose) and pentoses respectively;

• the three polymers making up lignocellulosic material form...