Liquid–Liquid Phase Equilibria of Systems of Palm and Soya Biodiesels: Experimental and Modeling

Abstract

Liquid−liquid phase equilibria of two systems of concern in the biodiesel production process are determined experimentally. The first system is the binary mixture of water + biodiesel within a temperature range of 297.2 to 333.2 K, in order to determine water solubilities in two biodiesels prepared from palm and soya oil. The experimental results showed that water solubilities were limited to values below 0.05 mol % and that the solubility increased with increasing temperature and biodiesel unsaturation. Next, the phase diagrams of ternary mixtures of glycerol + methanol + mentioned biodiesels were determined at three temperatures (293.2, 303.2, and 313.2 K). The reliability of the experimental data of tie lines was ascertained using the Othmer-Tobias relation. The UNIQUAC model was then used to model both the binary and ternary experimental data. Results showed the suitability of this model in correlating the phase behavior of such systems. ■ INTRODUCTIONThe production of alternative fuels from renewable sources is becoming attractive because of the high prices of fossil fuels, the decline of fuel reserves, and the concern about the environment. 1 Nowadays, biodiesel is receiving increasing attention as a renewable fuel, because of particular advantages over petrodiesel: In contrast to diesel fuel, biodiesel contains longchain alkyl esters with oxygen in their structures, which results in more complete burning. In addition, it has a higher flash point compared to petrodiesel. Therefore, this fuel is less flammable and more safe. In addition, its cetane number is higher than that of petrodiesel because the fatty acid methyl esters used as biodiesels contain long-chain compounds similar to long-chain alkanes such as hexadecane, which make for a higher-quality diesel. 2 There are four basic methods for biodiesel production from oils and fats: base-catalyzed transesterification, direct acidcatalyzed transesterification, conversion of the oil into its fatty acids and then into biodiesel, and noncatalytic transesterification of oils and fats such as the BIOX process or the supercritical alcohol process. 3 In the base-catalyzed transesterification method, biodiesel is obtained via a transesterification reaction of triglycerides from oils and fats with an excess of alcohol, and using a catalyst to accelerate the reaction. The reaction product is composed of fatty acid methyl esters and glycerol as a byproduct. After biodiesel production, some steps are carried out for the separation and purification of the desired product. This includes respectively, the separation of the biodiesel phase from the glycerol phase, recycling the unreacted alcohol, water-washing, and drying.Therefore, accurate information on the phase equilibria of the components involved in biodiesel production, and the ability to predict equilibria where information is not available, is necessary in order to determine optimum operating conditions for the separation and purification units of biodiesel production. Some studies have been carried out in this ...

Liquid–Liquid Phase Equilibria for Soybean Oil Methanolysis: Experimental, Modeling, and Data Prediction

“…The RMSD value for this overall estimation was much lower for the UNIQUAC model than for the NRTL one. Moreover, comparing the LLE calculated with experimental values (Figures –), it can also be seen that UNIQUAC was more suitable for the LLE modeling of these four compounds, as previously observed in the literature. − ,, …”

“…In all cases, glycerol solubility in oil and FAMEs was below 0.15 wt %. The values reported previously were only slightly higher (0.25 and 0.33 wt % at 25 and 45 °C, respectively) …”

“…However, only the UNIQUAC model achieved an acceptable fit for the experimental data in the soybean oil–methanol mixture. The UNIQUAC method has also shown an adequate fit of LLE data for these mixtures in previous publications. − …”

“…Six major compounds coexist until the end of the triglyceride methanolysis reaction: triglycerides, FAMEs, methanol, glycerol, diglycerides, and monoglycerides. However, previous literature has focused mainly on the FAMEs–methanol–glycerol equilibrium, which represents the end of the reaction. − The remaining binary and ternary systems formed by these six compounds have hardly been studied, ,, with the exception of the oil–methanol binary mixture, which corresponds to the initial stage of the reaction. ,− …”

Optimized Production of Fatty Acid Ethyl Esters (FAEE) from Waste Frying Oil by Response Surface Methodology

“…Considering this, the study of the transesterification reaction of waste frying oil originated in a country outside the EU, using bioethanol as the alcohol instead of methanol has still interest for the production of biofuels to be self-consumed [ 3 ], since in this way the FAEE produced will have a fully renewable origin [ 4 ]. However, the FAEE synthesis is more challenging than the FAME production at both laboratory and industrial scales, especially the FAEE purification steps, due to the fact that FAEE, ethanol and glycerol form a tri-phasic system difficult to separate [ 5 , 6 ]. Thus, reaching the mandatory 96.5 wt% of ester content in biodiesel is easily accomplished for FAME, but not so easily for FAEE.…”