Thermodynamic analysis for hydrogen production from the reaction of subcritical and supercritical gasification of the C. Vulgaris microalgae

Abstract

New technologies are essential for the efficient generation of biofuels. This work focuses on finding the best thermodynamic conditions, inhibition effects, and system conformations for the conversion of the microalgae Chlorella Vulgaris into hydrogen (H2). The conversion reaction was conducted in subcritical and supercritical water and modeling was developed as optimization problems in GAMS software. Chemical and phase equilibrium calculations were performed using Gibbs global energy minimization and entropy maximization methodologies. Thermal effects, microalgae feed composition, CH4 inhibition, and recycling of part of the produced H2 were evaluated. In supercritical gasification, a system with a temperature around 900 K, a microalgae composition between 10 and 15% (wt./wt.), and a high H/C ratio offers optimized conditions for H2 production. The inhibitory effect of CH4 is positive, increasing the mass composition of H2 by about 49% under the aforementioned conditions of temperature and composition. At lower temperatures, the inhibitory effect is more pronounced. The recycling of H2 for feed favored an increase in its mass fraction of 12.5%, in addition to increasing the endothermicity of the system without greater energy expenditure. Subcritical gasification reactions remain a challenge. A more in-depth study of the reactional paths is necessary to make its implementation feasible.