Investigation into the use of gas hydrate technology for the treatment of vinasse

Abstract

One of the challenges associated with vinasse, the by-product of bioethanol production, is the high concentration of dissolved solids, largely in the form of K+, SO42−, Mg2+, Ca2+, and Cl−. While traditional desalination technologies such as evaporation and distillation are employed in the concentration of salts to recover purified or potable water, these methods are energy intensive. The application of a novel technology known as gas hydrate technology can make the process of desalination less energy intensive, since the latent heat of fusion is much less compared to the heat of vaporisation for water. Reliable gas hydrate equilibrium experimental data plays a crucial role in the design of a hydrate-based process to treat vinasse. The systems measured in this study were based on the results of an extensive literature review conducted on the characterisation of vinasse. The isochoric pressure search method was used to measure the dissociation points for carbon dioxide hydrate in the presence of mixed salt solutions and synthesized vinasse mixtures containing (5 wt % KCl + 1 wt % Na2SO4 + 0.5 wt % MgCl2 + 0.5 wt % CaCl2 + 2.2 wt % ethanol + 0.5 wt % propionic acid + 0.3 wt % acetic acid). A thermodynamic model based on the solid solution theory of van der Waals and Platteeuw, UNIQUAC model along with Debye-Hückel term were used to calculate the hydrate dissociation conditions in the presence of mixed salts and synthetic vinasse mixtures. New UNIQUAC interaction parameters were optimized. Good agreement between the experimental data and model results were achieved.