A thesis submitted in partial fulfillment of the requirements for the degree of

84 Figure 3.9: Distribution coefficient and comparison with existing solvents 90 Figure 3.10: Selectivity and comparison with existing solvents 90 Figure 3.11: Experimental and NRTL tie lines for DES1(1)+ Toluene(2)+. 138 Figure 5.1: Atomically Annotated Structures of Different Molecular Types 147 Figure 5.2: Binding Data Points Correlated with Experimental and MD Simulation for .

Figure 2.12: RDF plots within functional entities/groups of DES (Nomenclature as per Table 2.2 and Fig

Introduction and Review of Literature

Introduction

Some typical polyaromatic structures of sulfur and nitrogen compounds present in fuel oil are shown below in Figure 1.1. Therefore, it is important to reduce the nitrogen level of the diesel oil due to both the potential pollution threat and storage requirements. It is essential to reduce the nitrogen and sulfur content of diesel oil with the ultimate goal of zero emissions.

Therefore, the extraction solvents must be sufficiently selective for the extraction of PAH species at high capacity. Most commercial solvents commonly used in the extraction process are acetonitrile, n-methylpyrrolidone (NMP), sulfolane and ethylene glycol.

Figure 1.1: Nitrogen and sulphur containing polyaromatic compounds

Deep Eutectic Solvent (DES) and its Properties

DESs are currently attracting widespread scientific and technological interest as low-cost alternatives to conventional and unconventional solvents, such as ionic liquids (ILs). DESs are now widely recognized as a new class of ionic liquid (IL) analogues because they share many features and properties with ILs. The preparation of DESs can be considered as a strategy to overcome some of the disadvantages of ILs, such as high melting temperature, high price and toxicity, because they share many of the ILs attractive solvent properties, such as low volatility, high thermal stability and conductivity, wide liquid range and high solubility.

They are easier to synthesize and only require the stirring of the two components under gentle heating because the components are easily mixed without any further purification. They are chemically inert and most of the synthesized DESs are biodegradable, biocompatible and non-toxic.

Figure 1.2: Typical structures of the halide salts and hydrogen bond donors used for DES syntheses

Environmental Aspect of DES

The raw materials of most DES are usually easily available on a large scale, such as urea and common halide salt. To reduce the risk to humans and nature, most DES exhibit negligible toxicity. Once the properties of green solvents such as DESs have been discussed, we will now turn to their use as an extractive solvent.

Before that, we will briefly discuss about LLE or Liquid Liquid Equilibrium process in general for extraction of aromatics.

Liquid Liquid Equilibrium Extraction (LLE) of Aromatics

Ionic Liquids as Solvents
DES as Solvents

38] investigated three different DES, all based on choline chloride, for liquid-liquid separation of an azeotropic mixture of heptane + ethanol at 25 °C. Equilibrium data for the ternary system consisting of BTEX aromatics, n-octane and DES were measured at 25 °C. In addn., the performance of COSMO-RS in predicting the ternary bond lines of the investigated systems was evaluated and.

Equilibrium data for the ternary system consisting of ethylbenzene and n-octane with all DES were measured at 25°C and atmospheric pressure. 45] investigated four different glycerol-based deep eutectic solvents (DES) as extraction agents for the separation of the azeotropic mixture {methyl ethyl ketone + ethanol} via liquid–liquid extraction.

Objectives of the Thesis

46] reported a new method of denitrogenation of fuels using DES as extractants and demonstrated the essential role of rational control of the physicochemical character of DES in achieving superior denitrogenation efficiency. Among the investigated DESs, a 1 : 2 molar mixture of choline chloride and phenylacetic acid presented the best denitrogenation efficiency, showing the simultaneous efficient removal of both basic and non-basic N-compounds.

Thesis Organization

Alnashef, Phase equilibria of toluene/heptane with deep eutectic solvents based on ethyltriphenylphosphonium iodide for the potential use in the separation of aromatics from naphtha, J. Qiu, Deep eutectic solvents as new extraction media for phenolic compounds from model oil, Chem. Wu, Separation of toluene from toluene/alkane mixtures with phosphonium salt-based deep eutectic solvents, Fuel Process.

Žuteg, Separation of hydrocarbons by liquid-liquid extraction with deep eutectic solvents, Solvent Extr. Kroon, Glycerol-based deep eutectic solvents as extractants for the separation of MEK and ethanol via liquid-liquid extraction, Journal of Chemical & Engineering Data.

Figure 1.5: Schematic outline of the current thesis

Preparation and Prediction of Thermophysical Properties of DES

Introduction

Mixing a high melting point salt such as a hydrogen bond acceptor (HBA) (halogenated quaternary salt) and a hydrogen bond donor (HBD) such as ethylene glycol creates a DES [2,3]. Effective applications of DES include technologies such as metal processing, solvent extraction, CO2 capture, and biomass dissolution [6,7]. DESs have been considered better substitutes for ionic liquids (ILs) due to their cost advantage and some toxicological problems compared to ionic liquids [10].

Experimental studies on the measurement of their thermodynamic properties have recently been reported in literature [11-13]. It is precisely this part that the present work considered both structural properties and dynamics of the DES components together as a single unit in liquid phases. Considering this fact, we report a comprehensive study on both experimental analysis and classical MD simulations to explain their fluid behavior.

The application of ammonium- and phosphonium-based DES has been recently studied regarding their physiochemical properties together with their aromatic extraction [21-23]. The halide-based quaternary ammonium and phosphonium salt were reported to readily mix with HBD to form DESs that were found to be highly selective for aromatic compounds. For example, it has been used for the purification of fuel by LLE process where Hizaddin et al.

The HBA namely methyltriphenylphosphonium bromide (MTPB) and tetrabutylammonium bromide (TBAB) were used in this work together with HBD such as ethylene glycol and glycerol. This paved the way for the creation of four new DES consisting of the combination of the HBA (phosphonium or ammonium salt) and HBD (ethylene glycol and glycerol). Then MD simulations were performed to study the non-bonded interaction between the HBD and HBA which are the key factors for the formation of DES.

Experimental Section

Chemicals Used
Analysis of Water Content in Chemicals
Preparation of DES
Analysis Methods

It can be seen that there are no significant changes in the regions of the spectrum upon formation of the DES. This is also evident from the extent of the electrostatic interactions as discussed in the previous section. The first solvation shell of the RDF was considered and integrated for the calculation of the coordination number.

Thus, the primary focus is the recovery of the nitrogen-containing PAH, such as quinoline, from fuel oil. The spectra for the third system (DES1+ Quinoline+ Heptane) are shown in Figure 3.5 and Figure 3.6. A sample calculation for calculating the mole fraction from NMR spectra is also given in Appendix-A (Figure A.1).

To study the effect of the phosphonium salt, we performed the LLE experiments using ethylene glycol as a solvent for the extraction of both toluene and quinoline. Both values appeared to be higher at a low concentration of the aromatic feed. Furthermore, the slope of the connecting lines was found to be opposite for toluene and quinoline.

The conventional solvents such as sulfolane and n-methylpyrrolidone (NMP) have some limitations for the removal of sulfur and nitrogen contents [3-6]. The new generation of green solvents such as Ionic Liquid (IL) and Deep Eutectic Solvents (DES) have been used for the extraction of PAH and have therefore gained enormous importance [7]. From the NMR spectra (Figures 4.2-4.5), the hydrogen atom (which was bonded to the nitrogen atom) of quinoline, present at ~8.89 ppm, was used to quantify its concentration. Here the two ends of the connecting lines represent the composition in the extract and raffinate phases.

As shown in Figure 5.2, the binary system namely DES-quinoline shows miscibility, while the other binaries, DES-heptane and heptane-quinoline are completely immiscible. From Figure 5.2, it can be observed that the data of the refinement stage occupies the extreme corner point of the ternary diagram. It should be noted that the selectivity of DES is much higher compared to that of ionic liquids (ILs) used in previous work [32-34].

From the observation of Figure 5.4 ((a)-(c)) it is seen that the quinoline molecule reaches within the bromide group at 3 Å, indicating that the formation of a weak bond takes place, while in the case of MTP and EG quinoline within 3 Å and 1.5 reaches. Å, respectively.

Figure 2.1: Formation of DESs with HBA and HBD ratio of 1:4

Computational Details for Molecular Dynamic Simulation

Results and Discussion

Eutectic Behavior
Physical Properties

FTIR Analysis
TGA Analysis

The –OH stretching vibration of DES shifts to a lower wave number, indicating that –OH of ethylene glycol or glycerol participates in the hydrogen bond formation with the anion of HBA [11,52]. However, in all cases, the Bra anion of the HBA (MTP) has a twentyfold higher electrostatic interaction energy with the HBD group (ETH or GLC) compared to its vdW interaction. On the other hand, no significant peaks are observed for the RDFs of MTP-ETH and MTP-Br, indicating that each of the hydrogen atoms in the.

The simulations reported here show that a large number of HBD molecules interact with the anion compared to the HBA cation. The results of MD simulations showed that hydrogen bond interactions between HBA and HBD anions are the main contributor to the formation of the eutectic mixture. RDF revealed the fact that the bromide ion interacts more strongly with the hydroxyl group of the ethylene glycol or glycerol molecule.

It is also very clear that the slopes of the bond lines for toluene and quinoline are of opposite nature. Where Hi is the peak area of the single 'H' atom and xi is the mole fraction of the ith component in the sample. This is in contrast to toluene, where the interaction decreases due to the unavailability of the lone pair.

The first step of the COSMO calculation is the generation of the sigma profiles of the investigated compounds and are shown in Figure 4.12.