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Sugarcane straw, consisting of green tops and dry leaves, can be maintained on fields to improve soil quality, or harvested for bioenergy production. The optimum option between these two uses is still uncertain and requires further study. This study, conducted across three crop cycles, provides an assessment of the moisture, nutrients, ash, extractives, cellulose, hemicelluloses, and lignin contents of four sugarcane varieties across seven regions of south‐central Brazil. Suitability of the straw fractions for nutrient recycling, bioelectricity, and second‐generation ethanol production were also evaluated. Results showed that the sugarcane straw yield (dry mass) was 14.0 Mg ha−1, and the ratio of dry straw/fresh stalk was 12%. The composition of green tops and dry leaves differed consistently across varieties, sites, and crop cycles. Dry leaves represented 60% of the straw, but green tops contained about 70% of the total N, P, and K content. Therefore, green tops recycled up to four times more nutrients than dry leaves. Green tops also had six times higher moisture and greater chlorine content which decreased the mill process efficiency. In turn, dry leaves had higher lignin, cellulose, and hemicelluloses content, greater heating value (higher: 17.3 MJ kg−1; lower: 15.6 MJ kg−1) and tended to be a better second‐generation ethanol production feedstock. Overall, the results show that it is preferable to use dry leaves for bioenergy production while leaving green tops on the field for nutrient recycling. This study pointed out that more efficient methods for separating these fractions in the field need to be developed. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd

Due to new possibilities for using sugarcane (Saccharum spp.) trash for electricity generation, and the production of 2 nd generation ethanol and others chemicals, the interest for its recovery has increased. However, the question of how much trash can be removed from sugarcane field still needs to be clarified. This study evaluated the amount of dry matter, nutrients content, structural compounds and efficiency of the enzymatic hydrolysis of the hydrothermal pretreated materials for tops and dry leaves in samples from sugarcane varieties. Tops and dry leaves present differences in nutrients content and moisture. Therefore, the amount of trash to be collected should not be simply based on percentages, but also should take into account the different fractions of the crop residues. For instance, around 80 % of N, P and K were derived from tops. Therein, the environmental indicators of the entire chain of sugarcane could be benefited because more nutrients would be recycled and less mineral fertilizers might be used for sugarcane production if tops are left on the field. Further, the tops have seven times more moisture than dry leaves and higher amounts of extractives (organic compounds of low molecular weight). Moreover, as the result of yield obtained in the pretreatment steps for dry leaves were superior to the tops and the glucose yields obtained in the enzymatic hydrolysis step were similar, it can be predicted that for second generation ethanol production, it is more viable to recover parts of the dry leaves fraction, leaving the tops on the field.

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This work investigates the evolution of cellulose crystals from sugarcane lignocellulose (bagasse and leaves) submitted to prehydrolysis (hydrothermal, dilute acid, or steam explosion) and soda delignifications. Raw and treated materials are characterized by X-ray diffraction with modeling of area-detector patterns. Three treatment effects are correlated: increase in cellulose content, quantified by strong acid hydrolysis; increase in average cellulose crystallite width, inferred from sharper 200 diffraction peaks; and decrease in crystallite distortion, evidenced by d 200 -spacing approaching reference values. Crystal contents measured according to recent developments (in Driemeier and Calligaris, J Appl Cryst 44:184-192, 2011) are compared to cellulose contents. Limitations for this comparison are discussed. Results are consistent with minimum non-crystalline cellulose in raw lignocellulose, and with partial cellulose decrystallization or more defective crystallites in treated materials.

A laboratory (2 L) scale alkaline pretreatment with and without anthraquinone addition was performed to evaluate the influence of temperature, alkaline loading, residence time, heating and stirring system on mass yield and solubilization rates of the main components. The best conditions were scaled up to pilot scale (350 L), and enzymatic conversion of structural carbohydrates into sugars for cellulosic ethanol production was analyzed. The tested conditions were 130–170 °C, 0.5–1.5% NaOH, 30–90 min with and without 0.15% w/w of anthraquinone (AQ). The AQ addition did not lead to substantial cellulose preservation in the laboratory scale; however, in the pilot scale the AQ addition resulted in 67.4% and 28.5% of cellulose preservation for reactions at 130 °C, 1.5% NaOH, 30 min (5Pil) and 170 °C 1.5% NaOH, 30 min (7Pil) respectively in relation to those studies without addition. The most efficient heating and agitation system of pilot reactor was probably the determining factor for effective performance. Temperature also seems to have a maximal effect on pilot AQ pretreatments, where lower temperature (5 Pil-130 °C) favored the cellulose preservation in relation to experiments at 170 °C. The scale-up was successfully made and the condition 5Pil with AQ was chosen as the best one in order to produce 293 kg of glucose from 1 ton of raw sugarcane bagasse.

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