Room temperature ionic liquids (RTILs) are the environment-friendly alternatives for organic volatile solvents in a host of synthetic, catalytic, and electrochemical applications. These are also being used for various R&D works in nuclear fuel cycle research such as the recovery and purification of nuclides of interest from spent nuclear fuel matrices. In this work, density, refractive index (
Room temperature ionic liquids are considered as young chemicals having variety a of applications in all types of areas in chemical industry due to their unique properties. They are referred to as designer solvents as we can design them for different reactions by changing the cation and anion. They can act as both polar and nonpolar solvents which minimizes the use of lot of chemicals making our environment neat and clean and thus referred to as “green solvent” [
ASTM Grade-1 water as per ASTM D-1193 [
Structure of [HMIm]Br.
IR data of aqueous solutions of pure [HMIm]Br.
For density and refractive index measurement, a precise vibrating-tube densitometer (Anton Paar DMA-5000), coupled with Anton Paar ABBEMAT RXA-156 refractometer and a 30-station autosampler SP-3 m, was used. The densitometer and refractometer had Peltier thermostats for maintaining the desired sample temperature. Density measurements were made in complete confirmation of ASTM-D4052 [
Water activity was measured by a thermodynamic water activity meter (NOVASINA AW-Master) with a built-in thermoelectric Peltier element module for maintaining temperature of sample. Samples were loaded in polystyrene cups and placed into the activity meter. The activity meter was standardized using a two-step procedure. In the first step, purified and degassed Millipore water was used as a standard (
The aqueous solutions of [HMIm]Br were made (~0.0005 m to 0.04 m) by the authors. The density, refractive index, water activity, and other derived properties for 1-hexyl-3-methyl imidazolium bromide solutions were determined and reported.
Partial molar volume is an extensive property and can be expressed by
For electrolytes, this partial molar quantity is composition dependent. In such cases apparent molal volume of component 2 in a solution (solvent is defined as component 1) is given by
The apparent molar volume of a solute (designated as 2) in a solvent in a solution may be written as
There are several empirical correlations to correlate the apparent molar volume of a solute in the solution with the solute concentration. The following equation lists the correlation proposed by Masson [
On equating (
Similarly, the experimentally determined refractive index values of aqueous solutions of ionic liquid were correlated to the following equation:
Excess molar volume of solution is a thermodynamic property and is defined as the amount of volume which is in excess to that of an ideal solution at the same conditions of composition, temperature, and pressure and is given as
The excess molar volumes were correlated with a Redlich-Kister-type equation by least-squares fittings given by
Excess refractive index was also calculated in the same manner using the Redlich-Kister polynomial.
The experimental data (listed in Table
Density values of aqueous solution of [HMIm]Br at 298.15 K.
Conc. (m) | Expt. density (g/cm3) | Pred. density (g/cm3) | Residuals* (g/cm3) | Deviations**% |
---|---|---|---|---|
0 | 0.9970 | 0.9970 | 0 | 0 |
0.00158 | 0.9971 | 0.9971 | −0.0000 | −0.0023 |
0.0028 | 0.9971 | 0.9971 | −0.0000 | −0.0009 |
0.0034 | 0.9971 | 0.9971 | −0.0000 | −0.0009 |
0.0043 | 0.9973 | 0.9973 | −0.0000 | −0.0014 |
0.0054 | 0.9973 | 0.9973 | −0.0000 | −0.0008 |
0.0079 | 0.9974 | 0.9974 | −0.0000 | −0.0001 |
0.0082 | 0.9974 | 0.9974 | 0.0000 | 0.0006 |
0.0101 | 0.9975 | 0.9975 | 0.0000 | 0.0003 |
0.0155 | 0.9978 | 0.9978 | 0.0000 | 0.0008 |
0.0231 | 0.9987 | 0.9987 | 0.0000 | 0.0004 |
0.0351 | 0.9991 | 0.9991 | −0.0000 | −0.0004 |
**Calculated as 100*(
The average deviation for the data of Table
The standard deviation for the data of Table
Plot of deviations for density of aqueous solutions of [HMIm]Br in water at 298.15 K and 0.1 MPa.
The apparent molal volumes for [HMIm]Br in aqueous solution at 298.15 were calculated with (
Apparent molal volume values of [HMIm]Br as a function of concentration.
Molality (mol · kg−1) |
|
---|---|
0.0016 | 193.7778 |
0.0043 | 196.1672 |
0.0054 | 197.9337 |
0.0079 | 199.5758 |
0.0082 | 200.3581 |
0.0101 | 200.008 |
0.0155 | 200.5182 |
0.0351 | 200.6666 |
0.0434 | 200.6378 |
Apparent molal volume of [HMIm]Br in water at 298.15 K.
Experimental refractive index values have been shown in Table
Experimental data for refractive index, water activity, and vapour pressure of aqueous solution of [HMIm]Br.
Conc. | Refractive index | Water activity | Vapour pressure |
---|---|---|---|
|
|
|
kPa |
0 | 1.332428 | 1.000 | 3.1686 |
0.0005 | 1.332456 | 0.999 | 3.1654 |
0.0015 | 1.332483 | 0.998 | 3.1623 |
0.00158 | 1.332487 | 0.998 | 3.1623 |
0.0028 | 1.332528 | 0.997 | 3.1591 |
0.0034 | 1.332553 | 0.996 | 3.1559 |
0.0043 | 1.332593 | 0.996 | 3.1559 |
0.0054 | 1.332638 | 0.995 | 3.1528 |
0.0079 | 1.332737 | 0.994 | 3.1496 |
0.0082 | 1.332752 | 0.994 | 3.1496 |
0.0101 | 1.332832 | 0.993 | 3.1464 |
0.0155 | 1.333033 | 0.991 | 3.1401 |
0.0231 | 1.333308 | 0.990 | 3.1369 |
0.0351 | 1.333775 | 0.987 | 3.1274 |
0.0434 | 1.334107 | 0.986 | 3.1242 |
Variation in the refractive index of aqueous solutions of [HMIm]Br with concentration at 298.15 K and 0.1 MPa.
Experimental water activity values have been shown in Table
Variation of water activity with the concentration in the aqueous solutions of [HMIm]Br at 298.15 K at 0.1 MPa.
Vapour pressure of aqueous solutions of [HMIm]Br at 298.15 K.
At infinity dilution there will be no solute-solute interaction. Here the positive values of
Excess volume is a resultant contribution of physical, chemical, and structural effects. The physical contribution involving nonspecific interactions between the real species of mixture contribute a positive value to
Excess volume and excess refractive index values of aqueous solution of [HMIm]Br.
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Plot of excess molar volume versus mole fraction concentration of aqueous solution of [HMIm]Br solutions at 298.15 K and 0.1 MPa.
Plot of excess refractive index versus mole fraction concentration of aqueous solution of [HMIm]Br solutions at 298.15 K and 0.1 MPa.
In the present work density, refractive index, and water activity of [HMIm]Br in aqueous solutions at 298.15 K and 0.1 MPa were determined experimentally at Reprocessing R&D Division. Based on the experimental results, apparent molal volume, vapour pressure, and excess properties have been estimated and reported. At infinity dilution there will be no solute-solute interaction. Therefore
Density of water
Density of aqueous solution
Density of pure [HMIm]Br
Molality
Total volume of the solution
Number of moles of water
Number of moles of the solute
Partial molal volume of pure component
Apparent molal volume
The limiting apparent molal volume
Empirical constant
Predicted refractive index of solution
Refractive index of water at sodium d-line
Coefficient of refractive index correlation
Coefficient of refractive index correlation
Cubic expansion coefficient (thermal isobaric expansibility)
Excess molar volume
Molar volume of solution
Molar volume of pure components
Molar mass of water
Molar masses of [HMIm]Br
Mole fraction of water
Mole fraction of [HMIm]Br
Adjusted coefficients for excess molar volume
Solute
Solvent.