The term second generation means that, contrary to biofuels of the first generation (bioethanol from sugar or starch containing plants or biodiesel from rape seed or palm oil), raw materials are used which are not used for the production of food products. These include mainly lignocellulosic raw materials such as energy plants where the whole plant is processed, straw, wood and various agricultural and wood processing waste products, such as organic waste.
Bioethanol from Lignocellulose
Biofuel yields can be clearly increased should lignocellulose be processed to bioethanol. In comparison to the use of sugar and starch containing raw materials this process is, however, due to the conversion of lignocellulose to sugar, more sophisticated. A challenge is the hemicellulose, as the resulting pentose (xylose and arabinose) can normally not be fermented. Nevertheless, yeasts can be gene technologically modified so that the glucose as well as arabinose and xylose can be fermented to ethanol.
Biobutanol from Lignocellulose
Meanwhile, there are some companies focusing on biobutanol as second generation biofuel. BUTALCO develops new production processes for biofuels and biochemicals based on genetically optimised yeasts and, together with partners, in downstream processing technologies. Yeasts as production organisms for bio- butanol have decisive advantages compared to bacteria: yeasts have GRAS (Generally Recognized as Safe) status and are easy to genetically modify. They are well established with a high robustness and the production process is easier to control. As ethanol producers are used to working with yeast, it is much more probable that the ethanol production plants in Brazil, Europe or North America will use yeasts rather than bacteria should they switch from ethanol to butanol. |
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