Cellulosic biomass is the most abundant potential source for 1G ethanol. Cellulose is a polysaccharide present in the lignocellulosic cell wall structures of plants compris­ing also hemicellulose and lignin (Fig. 4, 5, and 6). Cellulose needs to be extracted from the lignocellulosic structure by chemical digestion, to decrease its recalcitrance

Fig. 5 Chemical structure of cellulose; the glucose units are linked by 1,4-|3-D bond. Author Silvio Vaz Jr

due to the presence of lignin, followed by a hydrolysis to release glucose. The glucose can then be fermented by S. cerevisiae yeast to produce 2G ethanol (Oh et al. 2012).

Examples of lignocellulosic biomass are sugarcane bagasse and wood. Table 5 presents the chemical composition of some different lignocellulosic biomasses.

Eucalyptus, barley straw, and corn cobs are good feedstocks for 2G ethanol production because of their high cellulose content (52.7 %). Nevertheless, euca­lyptus has a high lignin content (31.9 %), which is a barrier for cellulose recovery; this is less of an issue for corn cobs (14.7 %). Other factors that also determine the best feedstock are economic factors, such as distance from the biomass to the industry, feedstock costs, and processing costs. Sugarcane bagasse is one of the most widely used feedstock to produce 2G ethanol, particularly in Brazil, where integration with 1G ethanol production from sugarcane via a biorefinery concept, can increase the profitability of the operation.

2 Analytical Techniques Applied to Biomass Chains

Biomass chains and industry typically require the use of chemical analyses that can process a large number of samples at a low cost. Such assays are not restricted only to manufacturing, but are also required in research and development (R&D). Figure 7 shows the common steps in a bioenergy chain from harvest of the bio­mass to formation of the desired products, chemical analyses may be necessary at all steps within this chain.

The quality of the biomass used determines the product quality. Therefore, reliable information is required about the chemical composition of the biomass to establish the best use (e. g., most suitable conversion process and its condi­tions), which will influence harvest and preparation steps. Conversion processes should be monitored for their yield, integrity, safety, and environmental impact. Effluent or residues should be monitored and analyzed for environmental control. Coproducts need to be monitored to avoid interference with the product yield and product purity; however, coproducts are also a good opportunity to add value to the biomass chain. Finally, products need to be monitored and analyzed to deter­mine their yields and purity and to ensure their quality relative to a recognized quality standard.

The execution of a chemical analysis follows a generic process that consists of (Atkinson 1982): (1) sampling; (2) separation; (3) detection (or measure); and (4) interpretation of results. Thus, before discussing the application of techniques, it is appropriate to consider these operations according to their status or involvement in the analysis. The location of analyte on the matrix (or inner surface) and the physical status of the sample (analyte plus matrix) defines the extraction technique used (partition, ion exchange, affinity, size exclusion filtration, etc.). The amount of sample, its purity, the type of information sought (atomic or molecular level) and its use (quantitative or qualitative) defines the detection technique. The analyte concentration has a direct influence on the techniques of extraction and detection.