Ethanol dehydration via azeotropic distillation with gasoline fraction mixtures as entrainers: A pilot-scale study with industrially produced bioethanol and naphta

Abstract

Various hydrocarbons (n-hexane, cyclohexane, toluene, isooctane) and mixtures of them (binary, ternary or quaternary), as well as two different types of industrially produced naphtha (one obtained by direct distillation and the other from a catalytic cracking process), have been tested as candidate entrainers to dehydrate ethanol. The tests were carried out in an azeotropic distillation column on a semi pilot plant. The results show that it is possible to dehydrate bioethanol using naphtha as entrainer, obtaining as a result a fuel blend with negligible water content and ready for immediate use in motor vehicles. 1. Introduction In order to reduce the greenhouse gas emissions produced by the transportation sector, the use of biomass as a fuel or in a mixture with fossil fuels has been promoted by government legislative and financial initiatives. Among the various biofuel technologies, bioethanol has advanced the most. However, bioethanol obtained from the fermentation of biomass, which can come from different sources, needs to undergo several steps of purification. This bioethanol is produced in an aqueous media and must thus be dehydrated before it can be used as a fuel. European legislation permits a maximum of 0.3% water by weight fraction in the bioethanol to be blended with gasoline [1]. Even though the presence of a binary azeotrope in the water + ethanol mixture makes it impossible to separate ethanol and water in a single distillation step, there exists many other techniques [2] that can be used, alone or in combination, to dehydrate ethanol. Some of them include, but are not limited to: adsorption on molecular sieves [3], azeotropic distillation [4], pressure swing distillation [5], pervaporation [6], extractive distillation with ionic liquids [7], etc. Concretely, in recent years several papers have treated bioethanol dehydration through only simulation testing different techniques such as pressure swing absorption [8], hybrid processes (distillation/adsorption/vapor permeation [9], based on liquid-liquid extraction [10], heteroazeotropic distillation using a gasoline additive as entrainer [11], extractive batch distillation [12] or a heat-pump-assisted extractive distillation in a single step [13] and comparing them to the conventional process. Though all the techniques presented in these papers seem viable alternatives and arouse improvements in bioethanol dehydration process, the results presented are almost all based on

Bioethanol from Microalgal Biomass: A Promising Approach in Biorefinery

“…The separation of a bioethanol + water mixture is not possible in a single distillation step (azeotropic mixture), but many alternative processes exist, alone or in combination, to dehydrate ethanol. Adsorption on molecular sieves, azeotropic distillation, pressure swing distillation, evaporation, extractive distillation with ionic liquids, pressure swing absorption, hybrid processes (distillation/adsorption/vapor permeation), liquid-liquid extraction, heteroazeotropic distillation using a gasoline additive as entrainer, extractive batch distillation or a heat-pump-assisted extractive distillation in a single step are cited [40].These techniques are more or less energy demanding depending on the technique and the separation requirements. A biorefinary location is defined, for the supply chain, raw material, energy and water availability, taxes, among other factors.…”

Study of Methanol Extraction from Saturated Alkanes: Solvent Screening, Liquid–Liquid Equilibrium Measurement, and Thermodynamic Simulation

“… Because the vapor part produced by boiling azeotrope at constant pressure has the same composition as the liquid part, the azeotrope formed by saturated alkanes and methanol cannot be separated by conventional distillation methods. The methods of azeotrope separation generally include azeotrope distillation, , extractive distillation, − membrane separation, , and liquid–liquid extraction, − while the last one is widely used in azeotrope separation due to its advantages of convenient operation and simple equipment. As a very mature separation means, liquid–liquid extraction has low construction cost and a simple operation process in industry, which is suitable for industrial mass production.…”

Screening of Imidazole Ionic Liquids for Separating the Acetone–n-Hexane Azeotrope by COSMO-SAC Simulations and Experimental Verification

“…The mass fraction of acetone in the azeotrope is 59%, and the azeotropic temperature is 323 K. Therefore, it is difficult to effectively separate high-purity acetone by traditional distillation methods. In this case, the commonly used methods include membrane distillation, , pressure-swing distillation, , azeotropic distillation, and extractive distillation . Pressure-swing distillation is an effective separation method that relies on the characteristics of the azeotrope components to be separated varying greatly with pressure.…”