**2. Experimental methods**

## **2.1. Chemicals**

Green solvents like 1-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl) imide {[BIMIM] [NtF<sup>2</sup> ]}, 1-ethyl-3-methylimidazolium ethyl sulfate {[EMIM][ESO<sup>4</sup> ]}, 1-ethyl-3-methylimidazolium hydrogen sulfate {[EMIM][HSO<sup>4</sup> ]} and 1-butyl-3-methylimidazolium acetate {[BMIM] [OAc]} were supplied by Aldrich Chemistry, Germany with purity greater than 98%. All the green solvents (i.e., ionic liquids) were used without further purifications.

#### **2.2. Sample preparation**

**1. Introduction**

Ionic liquid is a green solvent. It is composed of organic cations and inorganic or organic anions; they can have liquid state near ambient temperature. Since this green solvent has unique properties when compared to conventional solvents such as larger temperature range of liquid state [1], high thermal stability, high ionic conductivity negligible vapor pressures, nonflammability and high solvating capacity (i.e., solubility), for polar or nonpolar organic, inorganic and organometallic compounds [2, 3]. It is well known that the solvation capacity of green solvent is influenced by the hydrogen bonded structure and interaction between the individual ions (cation or anion) with other substances. On the other hand, the green solvent is an organic salt and its microscopic structure is usually composed of a large cation with low order of molecular symmetry. Hence, the unstable lattice structure lowers the melting point to well below the room temperature [4]. Therefore, the green solvent has the capabilities as environmental-friendly solvent in many green chemical processes [5] such as, biocatalytical transformation, isomerization, used in multiphase homogeneous catalysis [6], synthesis, catalysis, liquid-liquid extraction and supercritical extraction, and also used as thermal fluids, lubricants, and working fluids in elec-

But there is no systematic study on application of green solvent at different temperature and compositions. On the other hand, the solution thermodynamic properties of pure ionic liquids and its mixtures are of interest from the point of both basic and applied research [7]. Also, a detailed knowledge of the solution thermodynamic properties of mixed green solvents are important in relating the microscopic and macroscopic behavior. In this context, There is no data generated by experimental or theoretical approach. Moreover, the complete design of new green chemical processes and new green products based on green solvents and mixed green solvents can only be achieved when their solution thermodynamic properties such as molar volume, excess molar volume, partial molar volume, excess partial molar volume, and apparent molar volume are adequately characterized. But there is no data on solution thermodynamic properties of mixed green solvents at different temperature for an entire mole fractions range. Therefore, it is very important to accumulate a sufficiently large data bank not only for green processes and product design but also for the development of correlation for these properties. In addition, a better understanding of the behavior of mixed green solvent demands the knowledge of density and its temperature and composition dependence. Obtaining knowledge on the solution thermody-

namic properties is extremely important to improve their selection and performance.

]}, 1-ethyl-3-methylimidazolium ethyl sulfate {[EMIM][ESO<sup>4</sup>

green solvents (i.e., ionic liquids) were used without further purifications.

Green solvents like 1-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl) imide {[BIMIM]

[OAc]} were supplied by Aldrich Chemistry, Germany with purity greater than 98%. All the

]}, 1-ethyl-3-methylimidazo-

]} and 1-butyl-3-methylimidazolium acetate {[BMIM]

**2. Experimental methods**

lium hydrogen sulfate {[EMIM][HSO<sup>4</sup>

**2.1. Chemicals**

[NtF<sup>2</sup>

trochemical devices such as batteries, capacitors and solar cells [7].

124 Laboratory Unit Operations and Experimental Methods in Chemical Engineering

The binary mixture was prepared by transferring a known amount of the pure liquids via syringe into stoppered bottles and was properly sealed with parafilm tape to prevent evaporation and addition of moisture to the mixtures, using a Mettler AX-205 Delta Range balance with a precision of ±10−5 g. The estimated uncertainty on the composition measurement was ±10−4 g mole fraction. The stoppered bottles were placed inside a water-shaker bath set at atmospheric pressure, and allowed to shake for more than 6 h at 300 rpm in thermostatic shaker bath. Spring clamps were used to hold the flasks on the tray. The binary mixture was then allowed to settle for minimum of 12 h so that equilibrium is attained. The sample is taken from vial with a syringe to measure the density at temperature from 293.15 to 343.15 K with 5 K interval.

#### **2.3. Density measurement**

Density was measured using an Anton Paar DMA 4100 M with the oscillating U-tube method. In this method, the sample is introduced into a U-shaped borosilicate glass tube that is being excited to vibrate at its characteristic frequency. The characteristic frequency changes depending on the density of the sample. Through a precise determination of the characteristic frequency a mathematical conversion, the density of the sample can be measured. The density is calculated from the quotient of the period of oscillations of the U-tube and the reference oscillator [8]:

$$
\rho = \mathbf{K}\_{\mathsf{A}}^\* \mathbf{Q}^{2\*} f\_1 - \mathbf{K}\_{\mathsf{B}}^\* f\_2 \tag{1}
$$

where; KA and KB are apparatus constants, respectively, Q is the oscillation period of the reference oscillator. f1 and f2 are correction factors for temperature, viscosity, and nonlinearity.
