18504: Aqueous Ammonia Pretreatment of Sugar Cane Bagasse followed by Consecutive Hydrolysis and Alcoholic Fermentation

Brazil is the largest producer of sugarcane. The reduction of costs due to economy in logistics makes sugar cane bagasse (SCB) a natural candidate for producing low cost 2^nd generation bioethanol.

This work focuses on the alkaline pretreatment employing ammonium hydroxide for removing lignin and hemicellulose from sugar cane bagasse (SCB). In natura and steam exploded bagasse (17 kgf and 205^oC, 20 min), both donated by CTC, Piracicaba, Brazil, were used.

SCB was treated with 4, 10 and 15 wt.% of ammonium hydroxide solution at 1:5 solid-liquid ratio (by weight) at 100°C for 1 hour. The pretreatment was carried out in a stainless steel cylindrical reactor. Consecutive saccharification and fermentation of SCB was performed in shake flasks of 250 mL. The solid samples, which included treated and untreated SCB, were subject to compositional analysis according to NREL standard method. SEM of the samples allowed observation of structural modifications of the lignocellulosic matrix.

Saccharification experiments were carried out at 250 rpm and 50^oC, 3-5 % of solid loading for in natura bagasse, and 7-10% for exploded bagasse (30 FPU/cellulose, Accellerase, 1500, Genencor).

The results showed that for exploded bagasse, 15% (w/w) NH₄OH provide the higher cellulose contents in the pretreated material (79.2% cellulose, 3.4% hemicellulose, 15.5% lignin). For in natura bagasse the best result was for 10% w/w of NH₄OH (72.0% cellulose, 15.5% hemicellulose, 10.5% lignin).

The hydrolyzed biomass was used in fermentation assays employing commercial Saccharomyces cerevisiae, 30^oC. All experiments reached ca. 90% of the theoretical fermentation yield.