Adsorção da γ-Valerolactona utilizada na conversão de compostos lignocelulósicos em batelada e coluna de leito fixo

Abstract

Given today's high energy consumption, biofuels are an alternative to traditional fossil fuels, mainly because they are renewable. Lignocellulosic biomass is a low cost and high availability product, with ethanol production capacity. The conversion to fermentable sugars uses the biodegradable organic solvent, γ-valerolactone (GVL), to accelerate the conversion rates for sugars, but the presence of this compound in the fermentation stage is harmful to the microorganisms, so its removal is necessary. The adsorption separation process has shown to be promising in the removal of GVL. This process intends to remove the GVL from the solution, maintaining the same concentration of glucose (GL) and water. The goal of this work is to evaluate the adsorption separation process for GVL, consequently improving the process of obtaining lignocellulosic ethanol. A preliminary batch adsorption study with six different adsorbents, namely: four synthetic resins (Amberlite XAD16, Dowex Optipore L-493, Sepabeads SP850, Sepabeads SP825L), activated carbon and clay bofe, and determined that Dowex Optipore L-493 resin was the most efficient in removing GVL in an aqueous solution of GL, with an average adsorption capacity of 359,24 mgGVL/gadsorvente. The resin was characterized with helium gas pycnometry (apparent density of 1,14 g/cm³), zero point charge (pH 4) and humidity (4.3%). Regarding the kinetics, the models of Pseudo-first order (PPO), Pseudo-second order (PSO), and intraparticle diffusivity were tested, and the latest was the best fit to the experimental data, as well as, showed fast kinetics, reaching equilibrium in 30 min. The mathematic models tested for the adsorption equilibrium were Langmuir, Freundlich, SIPS, Redlich-Peterson and Toth. All the isothermal models well represented the equilibrium experimental data, so the Langmuir isotherm was applied in the column system which obtained a maximum adsorption capacity of de 414,75 mg/g at pH 4 at 25 °C. In the fixed bed column experiments the effect of GVL concentration, bed height and solution flow was evaluated and the Linear Driving Force model was tested in the experimental data. The effect of the concentration is verified in the rupture curve, that the more perpendicular, the greater the concentration of the solution. The breakthrough time is directly proportional to the bed height, and inversely proportional to the flow rate. In general, the work was able to identify a high GVL removal capacity using the L-493 resin, presenting satisfactory results in the fixed bed column application, as well as determined to be a monocomponent adsorption. Thus, it is possible to apply the method on a large scale to improve the production of lignocellulosic ethanol.