Measurements and Correlation of the (Solid + Liquid) Equilibria of [1-Decyl-3-methylimidazolium Chloride + Alcohols (C 2 -C 12 )] † Urszula Doman ´ ska* and Ewa Bogel-Lukasik Physical Chemistry Division, Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland This work presents the solid + liquid equilibria in binary systems consisting of 1-decyl-3- methylimidazolium chloride, [C 10 mim][Cl], and alcohols [ethanol, 1-butanol, 1-hexanol, 1-octanol, 1-decanol, 1-dodecanol, 2-butanol, 2-methyl-2-propanol (tert-butyl alcohol)]. The measurements were carried out by using a dynamic method from 270 K to the melting point of the ionic liquid, 1-decyl-3-methylimidazolium chloride. The solubility of 1-decyl-3-methylimidazolium chloride, [C 10 mim][Cl], in primary alcohols decreases with increasing of the length of the alcohol’s alkyl chain. The difference between the primary, secondary, and tertiary alcohol is not significant. The differential scanning calorimetry (DSC) was used to determine the melting point, the enthalpy of fusion, and the enthalpy of the solid + solid phase transition of [C 10 mim][Cl]. Therefore, the solid-liquid equilibria were correlated by means of the Wilson, UNIQUAC ASM, and NRTL 1 equations. Hence, the root-mean-square deviations of the solubility temperatures were from 0.70 to 4.77 K and depended on the particular equation used. Introduction This paper is a part of our research, and it is a continuation of the systematic study of the ionic liquid (IL) solubility measurements in alcohols (C 2 -C 12 ). 1-4 The study of ILs has become the subject of the increas- ing number of scientific investigations including phase equilibria and physicochemical properties. 5-13 Over the past few years, room-temperature ILs have generated much excitement among some sections of the chemistry community for their potential as green “de- signer solvents”. But to what extent can these liquids be used in industrial processes and in particular in the development of clean technologies? 14 For that reason, clean technology concerns the reduc- tion of waste from an industrial chemical process to a minimum: it requires the rethinking and redesign of many current chemical processes. 15 Accordingly, it is most important to explore, develop, and understand the role of ionic liquids as media for industrially relevant chemistry, and to provide all the physical and chemical engineering data necessary in order to facilitate the design and operation of a pilot plant. In brief, ionic liquids are characterized by the following: (1) They have a liquid range of 300 °C, allowing tremendous kinetic control. (2) They are outstandingly good solvents for a wide range of inorganic, organic, and polymeric materi- als; high solubility implies small reactor volumes. (3) They exhibit Bro ¨nsted, Lewis, and Franklin acidity, as well as superacidity. (4) They have no effective vapor pressure. (5) They range from hydrophobic to hydro- philic, from water-sensitive to air-stable. (6) They exhibit electrochemical window and good conductivity. (7) They are a replacement for conventional volatile organic solvents, which is very important because of the Montreal Protocol’s settlements. 15-17 Thermodynamic properties of mixtures containing halide ionic liquids have already been described in the literature. 18-20 Moreover, the synthesis methods of chloride ionic liquids were reported elsewhere. 21-25 Applications of the ionic liquids were reported in the literature as well. 15,20,23,26-31 This work presents the solid + liquid equilibria of binary mixtures of {1-decyl-3-methylimidazolium chlo- ride, [C 10 mim][Cl], + an alcohol (ethanol, 1-butanol, 1-hexanol, 1-octanol, 1-decanol, 1-dodecanol, 2-butanol, 2-methyl-2-propanol (tert-butyl alcohol)}. Experimental Section 1. Materials. The 1-decyl-3-methylimidazolium chlo- ride, [C 10 mim][Cl], sample was obtained from Solvent Innovation GmbH, Ko ¨ln, Germany. The sample purity was g98 mass %, and it was used without any purifica- tion. The substance was packed under nitrogen. All alcohols were delivered from Sigma-Aldrich Che- mie GmbH, Stenheim, Germany. Before direct use, they were fractionally distilled over different drying reagents to the mass fraction purity g99.8 mass %. The solvents were stored over freshly activated molecular sieves of type 4 Å (Union Carbide). Analysis for the water contamination using the Karl-Fischer technique for the alcohols showed that the impurity in each of the solvents was <0.02 mol %. As a final point, it was found that the solution-crystallization procedure was quite slow and difficult; thus, the solubility measurements were very time-consuming. The crystallization process after the dissolution of the sample was as long as a few hours until 24 h. Very often, it was necessary to prepare a new sample to observe the new experimental point. 2. Apparatus and Procedure. The methods applied were as follows: differential scanning calorimetry (DSC) and modified dynamic method. Differential Scanning Microcalorimetry (DSC). The melting point, the enthalpy of fusion, and the enthalpy of the solid-solid phase transition measure- ments of 1-decyl-3-methylimidazolium chloride, [C 10 - * To whom correspondence should be addressed. Tel: 00- 48-22-6213115. Fax: 00-48-22-6282741. E-mail: Ula@ ch.pw.edu.pl. † Presented at Thermodynamics 2003, Cambridge, U.K., April 9-11, 2003. 6986 Ind. Eng. Chem. Res. 2003, 42, 6986-6992 10.1021/ie030464g CCC: $25.00 © 2003 American Chemical Society Published on Web 11/14/2003