Experimental (vapour + liquid) equilibrium data of (methanol + water), (water + glycerol) and (methanol + glycerol) systems at atmospheric and sub-atmospheric pressures
Introduction
Bio-diesel is a possible important substitute for fossil fuel in the near future and is a much researched topic in present times. Glycerol is a by product of biodiesel processing and binary and ternary systems containing methanol, water, and glycerol are found in the downstream of bio-diesel manufacturing process [1]. In order to recover methanol from this aqueous glycerol solution, distillation is the preferred separation technique for which (vapour + liquid) equilibrium (VLE) data are required. This investigation of the binary systems formed by methanol, water, and glycerol is a continuation of our previous studies on the phase equilibria of binary systems containing alcohols, hydrocarbons and halogenated organics [2], [3]. These binary systems and their ternary systems are found in various industrial streams, namely in the bio-diesel post-production process. {Methanol (1) + water (2)}, {water (1) + glycerol (2)} and {methanol (1) + glycerol (2)} binary systems are studied at the local atmospheric and sub-atmospheric pressures over the entire composition range. In an extensive survey of the available literature, we did not find any experimental information for these binary systems at the pressures studied in the present work.
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Materials
The chemicals used in this work were purified according to the methods suggested by Riddick et al. [4]. Analytical grade vacuum-distilled glycerol (Qualigens, India) is used in the experiments. Methanol of analytical grade (SD Fine Chemicals, India) was fractionally distilled to ensure complete removal of water. These distillations were done a few hours before the VLE experimentation. Both methanol and glycerol were stored in dessicators to prevent absorption of moisture. Double distilled water
Results and discussion
The T–x1 results for the {methanol (1) + water (2)} system at pressures (15.19, 29.38, 42.66, 56.03, 67.38, and 95.3) kPa, {water (1) + glycerol (2)} system at pressures (14.19, 29.38, 41.54, 54.72, 63.84, and 95.3 kPa) and {methanol (1) + glycerol (2)} system at pressures (32.02 and 45.3) kPa were obtained experimentally and are presented in TABLE 2, TABLE 3, TABLE 4 along with the derived phase equilibrium information. The experimental results were fitted to the Wilson model. The boiling temperatures
Conclusions
The binary mixtures, {methanol (1) + water (2)} and {water (1) + glycerol (2)} are studied at local atmospheric and sub-atmospheric pressures while the {methanol (1) + glycerol (2)} are studied at sub-atmospheric pressures, over the entire composition range in a Sweitoslawsky-type ebulliometer. The experimental results are found to be well represented by the Wilson model. It is observed that {water (1) + glycerol (2)} system exhibits negative values of excess Gibbs free energies while the systems
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