Optimization of Glycerol Gasification Process in Supercritical Water Using Thermodynamic Approach

Abstract

Glycerol is a byproduct of biodiesel production. An alternative to use of this byproduct is the gasification with supercritical water (SCWG) for hydrogen generation. This work aims to analyze the conditions that enhance the formation of hydrogen using the response surface methodology in combination with optimization techniques. The results of the reaction in the equilibrium condition were obtained using Gibbs energy minimization method for isothermic systems and entropy maximization method for adiabatic systems. The proposed thermodynamic models were solved using GAMS 23.9.5 software in combination with CONOPT3 solver. As a result of the simulations, the final compositions of the gaseous phase and the thermal behavior for the operational conditions of the reaction are presented. The reaction was characterized by the formation of hydrogen, evaluating the temperature between 586.64 and 1259 K, pressures in the range of 216.36 to 283.64 bar and the glycerol / water molar ratio varying from 0.032 to 0.368 in the feeding according to the planning experimental. Higher hydrogen formation was observed for isothermic reaction conditions, indicating that glycerol SCWG was an endothermic reaction, this fact is justified by the results of adiabatic reactors. Hydrogen formation is mainly influenced by the effects of temperature and glycerol composition, reaching the maximum hydrogen formation (2.29 moles) operating in an isothermal manner for high temperatures (1123 K) and high glycerol/water ratios in the feed (0.368). For both results, the pressure pressure on the amount of internal hydrogen was not statistically significant at 95%.