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The study investigated the effects of two-step pretreatment on fermentable sugar production from corn stalk silage. In the first step, the corn stalk silage was extracted by tepid water and then the solid was pretreated using Fe(NO 3 ) 3 as catalyst. The results showed that 45.8 g/100 g DM total sugars was obtained and the surface of remaining solid was seriously damaged after two-step pretreatment. Compared with one-step pretreatment, the production of total sugars increased by 23.8% and the amount of the catalyst of Fe(NO 3 ) 3 decreased by 28.8%. This research provides a new effective, suitable and economical pretreatment method for biogas production from corn stalk.

Corn stover silage is an attractive raw material for the production of biofuels and chemicals due to its high content of carbohydrates and easy degradability. The effects of Fe(NO(3))(3) pretreatment conditions on sugar yields were investigated for corn stover silage. In addition, a combined severity factor was used to evaluate the effect of pretreatment conditions on the concentration of total sugars and inhibitors. Optimum pretreatment condition was obtained at 150 °C for 10 min with 0.05 M Fe(NO(3))(3), at which the yields of soluble xylose and glucose in liquid achieved 91.80% of initial xylose, 96.74% of initial arabinose and 19.09% of initial glucose, respectively, meanwhile, 91.84% of initial xylose, 98.24% of initial arabinose, and 19.91% of initial glucose were removed. In addition, a severity analysis showed that the maximum sugar concentration of 33.48 g/l was achieved at combined severity parameter value of 0.62, while the inhibitor concentration was only 0.03 g/l. Fe(NO(3))(3) is an effective catalyst to enhance hemicellulose hydrolysis in corn stover silage, the yields of monomeric xylose in the liquid fraction reached as high as 91.06% of initial xylose and 96.22% of initial arabinose, respectively.

Five inorganic salts, ZnCl 2 , FeSO 4 , Fe 2 (SO 4 ) 3 , FeCl 3 and Fe(NO 3 ) 3 were chosen as catalysts to determine their effects on hemicellulose hydrolysis in control silage (no silage additive), and the results indicated that Fe(NO 3 ) 3 was the most efficient catalyst for hemicellulose hydrolysis. The kinetics of Fe(NO 3 ) 3 catalyzed hydrolysis for control silage and acid silage (treatment with HNO 3 ) were investigated at various pretreatment conditions. The results demonstrated that Saeman model was well consistent with Fe(NO 3 ) 3 catalyzed hydrolysis reaction for corn stover silage, and kinetic parameters for this model were developed by the Arrhenius equation. Optimum pretreatment conditions were 0.05 M Fe(NO 3 ) 3 at 150 °C for 21.2 min for control silage and 12.7 min for acid silage, which obtained the maximum xylose yields 81.66% and 93.36% of initial xylan, respectively. The activation energies for hemicellulose hydrolysis in control and acid silage ranged from 44.35 to 86.14 kJ/mol and from 3.11 to 34.11 kJ/mol, respectively.

BACKGROUND: Because of its high cost, nitric acid has not been widely employed as the catalyst for hydrolysis of lignocellulosic biomass to obtain fermentable sugars. However, recently more and more research results have reported that nitric acid was more effective than other acids for the hydrolysis of lignocellulose. Therefore, it is necessary to find an optimum condition for nitric acid pretreatment and a means of reducing the cost. RESULTS: In this work, low concentrations of nitric acid and short reaction times were considered to optimize the pretreatment process. The kinetic parameters of models to predict the concentrations of xylose, glucose, arabinose, acetic acid and furfural in the hydrolysates were obtained. Applying the kinetic models, the optimum conditions were: 150 °C, 0.6% HNO3 and 1 min, which yielded a solution containing up to 22.01 g L−1 xylose, 1.91 g L−1 glucose, 2.90 g L−1 arabinose, 2.42 g L−1 acetic acid and 0.21 g L−1 furfural, which were consistent with the predicted values. The influence of temperature was also studied using the Arrhenius equation. CONCLUSIONS: A combination of experimental data and model analysis suggested that 96% xylose yield can be achieved by using low concentration nitric acid for a short reaction time, which could greatly reduce the pretreatment cost. Therefore, dilute nitric acid could be considered a good choice for the hydrolysis of corn stover. Copyright © 2010 Society of Chemical Industry