Chemical pretreatment of sugarcane bagasse with liquid fraction recycling

Abstract

Pre-treating lignocellulosic biomass is a major technological challenge. Recycling the liquid fraction may reduce chemical inputs and water use but may have lower efficiency. Seven chemical pre-treatments of sugarcane bagasse were compared: four acids (sulfuric, citric, phosphoric, and oxalic), two alkaline (sodium and calcium hydroxides) and an oxidative (alkaline hydrogen peroxide). The liquid fractions resulting from these pre-treatments were reused up to five times. After each pre-treatment cycle, the solid fraction was hydrolyzed with Celluclast 1.5L enzyme in a 1:10 solid-liquid ratio. Sulfuric and oxalic acids solubilized 80% of the hemicellulose over the cycles. Sodium and calcium hydroxides and hydrogen peroxide removed lignin until the fourth cycle. About 70% of lignin were removed with alkaline hydrogen peroxide. This pre-treatment lead to the highest glucose release after the enzymatic hydrolysis, above 50% in the three cycles analyzed. The best efficiency in enzymatic hydrolysis followed the order H2O2-alkaline > NaOH > oxalic acid > phosphoric acid > H2SO4 > citric acid > Ca (OH)2. With the recycling, more than 62% in reagents used in the pre-treatment of sugarcane bagasse were saved, enabling an economy in the costs at this stage of the process.