Purification and catalytic oxidation of enzymatic hydrolysates of pretreated sugarcane bagasse for gluconic acid production

Lignocellulosic Lignocellulosic wastes from agroindustry are sources of available carbohydrates to produce second-generation ethanol (E2G) and other high added values substances (as organic acids). Among these residues, sugarcane bagasse, which is obtained from grinding of sugarcane through the extraction of the juice and which is already applied for E2G production, emerges as one of the main wastes. In this work, enzymatic hydrolysates of samples of pretreated sugarcane bagasse were processed to purification with active charcoal and subjected to catalytic oxidation in a three-phase reactor (slurry), using Pd /Al2O3 as a catalyst, aiming production of gluconic acid (GA), a product with a high added value, used in the textile and food industries. The catalytic oxidation of the hydrolysates which were purified under these conditions yielded a conversion of 70% of glucose and produced GA in a yield close to 80% in 4 hours. A mathematical model (Langmuir-Hinshelwood) studied for the catalytic oxidation of glucose from enzymatic hydrolysates proved to be reasonably adequate with the experimental data and reveals that the presence of acetic acid from the buffer solution of enzymes did not change the reaction mechanism pathway. Also, it was made a brief economic discussion of the feasibility of the process steps studied in this work based on the raw material and final product. These results point out sugarcane bagasse as a very profitable raw material for gluconic acid.