King Grass: A very promising material for the production of second generation ethanol in tropical countries

King Grass is a fast growing, high yield, hybrid grass that grows in a variety of soil conditions and does not compete with food crops. King Grass is perennial and can be harvested several times per year. Therefore it has a high potential for ethanol production in tropical countries. The pretreatments alkaline delignification (66.6-133 °C, 30-180 min, solid to liquid ratio 1:13.3-1:20 wt and NaOH concentration 0.7-2% wt), diluted acid hydrolysis (2% wt sulfuric acid, solid to liquid ratio of 1.0 g biomass/mL solution, stirring at 90 °C for 90 min), steam explosion (at 180 °C for 5 min, i.e., severity 3.05), alkaline peroxide (2% vol. H2O2, liquid to solid ratio of 20:1 wt, pH 11.5, stirring at 35 °C for 3 h) and aqueous ammonia soaking (15% wt ammonia solution, 8 mL of ammonia solution per gram of material, at 60 °C for 6 h) were studied. The alkaline pretreatment with NaOH led to the highest concentration of reducing sugars, i.e., 58.6 g/L, and to the highest ethanol concentration, i.e., 17.9 g/L. A more detailed study of the effect of the alkaline pretreatment conditions (temperature, solid to liquid ratio, NaOH concentration and residence time) on the production of ethanol from King Grass was carried out. Under pretreatment conditions of 120 °C for 1 h with 2% wt NaOH and a solid to liquid ratio of 1:20 the highest ethanol yield reported so far was obtained, i.e., 27.7 g/L (165.9 mg ethanol/g dry biomass, 92% of theoretical yield). Furthermore, this pretreatment allowed the removal of most of lignin present in King Grass, i.e., 94%, and allowed a high recovery of the cellulosic fraction in the solid (93-99%). Under typical growing conditions of King Grass in Colombia this maximum ethanol yield corresponds to 12,616 L/ha/year which is higher than that obtained from sugar cane bagasse (4602 L/ha/year).