A fundamental advantage for integration of cellulosic ethanol into current first generation ethanol production from sugarcane in Brazil is the availability of lignocellulosic material (bagasse) at the plant site and the feasible alternative to also use sugarcane crop residues (straw). Regarding this, it is fundamental to consider optimization strategies for first gener­ation ethanol production, aiming at energy savings and, thus, more surplus lignocellulosic material for second generation ethanol production. Cellulosic ethanol production in Brazil may also benefit from sharing part of the infrastructure where first generation ethanol pro­duction takes place (for instance juice concentration, fermentation, distillation, storage and cogeneration facilities). In addition, potential fermentation inhibitors generated in the lig — nocellulosic material pretreatment may have a minor effect on fermentation yields, since the hydrolyzed liquor may be fermented mixed with sugarcane juice, diluting these inhibitors.

Due to the high potential of biomass for the production of fuels and chemicals, research in Brazil has focused on the hydrolysis of sugarcane bagasse and/or straw for cellulosic ethanol production. Furthermore, the production of liquid fuels through the use of pyrolysis/ gasification has also been seen as a promising alternative.

Second generation ethanol production involves basically four steps: pretreatment, enzy­matic hydrolysis, fermentation and ethanol recovery. In recent years, pilot and demonstrat — tion scale plants have been built in Brazil and worldwide. However, enzymatic technology still faces numerous obstacles and is not yet mature enough for full commercialization. Some major challenges faced are the high cost of the pretreatment step and the low effi­ciency of the enzymatic saccharification of polysaccharides to sugars, as well as the high cost of enzymes.

Owing to the large impact of the pretreatment step on all the other operations in the process, research efforts have been made to find efficient, fast and affordable pretreatment methods which primarily aim at making biomass accessible to enzymatic attack. Several pretreatment methods have been studied in Brazil, usually involving high temperature and pressure, such as in hydrothermal and steam explosion pretreatments. These processes may be performed at different pH (acidic, basic or neutral), depending on the addition or absence of catalysts; also, the use of organic solvents in these processes is quite usual. Common to all of them is the need to integrate the process, including energy and water consumption and reagent recovery, in order to obtain high cellulosic ethanol yields at reasonable costs and low environmental impacts.

These pretreatment methods need to be further improved in combination with enzy­matic hydrolysis and fermentation, as improved enzyme mixtures may lead to less severe pretreatment conditions and, thereby, to lower enzyme costs and reduced formation of inhibitory compounds, while more robust fermentation organisms can tolerate more toxic hydrolysates.

Regarding enzymatic hydrolysis, studies have shown that reducing the cost of cellulase enzyme production is an essential step to make enzymatic hydrolysis more economically feasible. In-house enzyme production, using part of the pretreated bagasse as substrate, emerges as a potentially attractive alternative technology. Another important factor to be considered is the increase of enzyme effectiveness that can be achieved through the development of more efficient enzymes and enzymatic complexes with higher activity.