The starting point of the basic science program that will be developed at CTBE is within the challenges already pointed out by the Pilot Plant for Process Development (PPDP), beginning with sugarcane lignocellulosic biomass. This is mainly composed of cellulose, hemicellulose and lignin. The first two are formed by molecules which can be broken down into simple sugars. The function of lignin is to provide rigidity to the cellular wall and resistance to chemical and biological attacks. Overcoming the structural rigidity (recalcitrance) of lignocellulose and converting these polysaccharides at a low cost, into smaller sugars represent considerable scientific challenges.
Among the sugars in sugarcane, those composed of six carbon atoms (hexoses) are easily converted into ethanol through the action of yeasts of the Saccharomyces cerevisiae species. Those structured by five carbons (pentoses) are not fermentable sugars. There are a number of research fronts to solve this problem. A significant scientific effort has been directed to the genetic development of microorganisms that ferment both hexoses and pentoses in a satisfactory way. The utilization of pentoses in processes that do not include fermentation is another alternative. Xylose (a type of pentose), for example, can be a carbon source for bacteria which synthesize natural plastics known as polyhydroxyalcanoates (PHA). Another task for CTBE researchers is to study more efficient ways of utilizing pentoses in the ethanol production process.
However, the challenge for those who work with lignocellulosic biomass goes further. Due to its heterogeneous nature, different treatments have to be given to the preparation of the raw material, to the enzymes, and to the microorganisms used in the hydrolysis process. Some of these treatments are still not sufficiently known. One of the questions still without an answer is whether the separation of fiber and pith in different phases will or will not be advantageous to the processing of bagasse that will be hydrolyzed.
What one knows beforehand, however, is that it is necessary to define a physical pre-treatment that provides a more homogeneous and stable material to be hydrolyzed. From then onwards, the scientific research on the remaining process can count on a bagasse with well defined characteristics, independently of its origin. This guarantees that the experiments will be reproducible.
It is necessary to produce competent enzymes on a large scale once the sugarcane bagasse is treated. Cellulases and hemicellulases in reality form a mixture of enzymes that work in synergy to deconstruct vegetable biomass. The development of these enzymatic systems is still another technological obstacle for the second generation ethanol technology. In spite of the recent progress, there is still a long way to go before efficient enzymatic complexes can be used at a low cost by industry. It is possible to improve this development if there is a deep knowledge of the structure and composition of the pre-treated biomass and of the action of the enzymes on the material. The development of analytical methodologies for the study of the deconstruction of lignocellulosic material is one of the CTBE’s basic science program concerns. As one knows, it is possible to foresee the beginning of a study in basic science; its conclusion however, is far more unforeseeable.