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A semi-theoretical model based on the Eyring equation for viscosity and the use of activity coefficient expression according to the Regular Solution and Flory-Huggins theory were used to correlate experimental data on the viscosity of protic ionic liquids (2-hydroxyethylammoniumpropionate or 2-hydroxyethylammoniumButanoate or N-methyl-2-hydroxyethylammonium Acetate or N-methyl-2-hydroxyethylammoniumButanoate or Bis (2-hydroxyethyl) ammonium Propionate or Bis (2-hydroxyethyl) ammonium Butanoate) with water in the temperature range 293.15-333.15 K. This work compared the results with the experimental data and calculated viscosity values for performance analysis of the proposed models.
The models have a relatively simple mathematical form and can be easily incorporated into the process simulation software. It was observed that an increase in the molar volume of the ionic liquid resulted in lower interactions in the mixture.
Ionic liquids are usually liquid at room temperature and are formed by cations and anions; they are also called molten salt because of their enthalpy of vaporization and low vapor pressure.
The toxicity and hazardousness of industrial solvents, especially chlorinated hydrocarbons, is responsible not only for accidents but also harmful to human health.
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The search for cleaner technologies in industrial and even academic activities has been well deserved in recent years . The development of environmentally benign technologies and alternative processes that minimize the amount of waste at the end of the process has been thoroughly studied by researchers and this new approach has been called 'green chemistry' or green chemistry or even clean chemistry.
Ionic liquids can be used in a variety of industrial applications involving catalytic reactions [4], synthesis [5] and phase separations [6.7]; more detailed applications can be found in references [1-3].
On the other hand, direct application in industrial processes is still limited due to the scarcity of available experimental data, transport properties, for example.However, the modeling of the transport properties of mixtures containing ionic liquids is still recent.
The literature review has presented many models that were developed for the blend viscosity. Many of these models can be applied at atmospheric pressure, near the melting point. The model of Eyring (Giro etal., 2003; Mácia-Salinas etal., 2003; Habibietal., 2016) and friction-based theory (Monsalvoetal., 2006, Quiñones-Cisnerosetal. ., 2005, 2012) are models with good performance when the pressure and temperature ranges that are involved are moderate.
While these approaches are suitable for the viscosity model, density and many adjustable parameters are sometimes required to calculate viscosity; for example, the friction theory (Wang etal., 2007) has 18 fitting parameters for each pure fluid. Therefore, such models require a large number of inputs when applied to blends. In addition, the experimental method is necessary for density characterization, since it is not common to use density data of a model as input.
In this work, we have synthesized, purified and characterized five PILs and extend the model of the theory of viscosity Eyring by using excess functions hither to reported in the literature as the Regular Solution theory and Flory-Huggins theory in addition to providing new experimental data with the following ionic liquids: (2-HEAPr) 2-hydroxyethylammoniumpropionate, (2-HEAB) 2-hydroxyethylammoniumButanoate,(m-2HEAA)N-methyl-2-hydroxyethylammonium acetate , (m-2HEAB) N-methyl-2-hydroxyethylammoniumButanoate , (BHEAPr) Bis(2-hydroxyethyl)ammonium Propionate, (BHEAB) Bis(2-hydroxyethyl)ammonium butanoate in mixtures with water at the temperature range 293.15–333.15 K with the purpose of contributing andinterpreted in terms of interactions and structural factors of the ionic liquid and water.
All ionic liquids were synthesized in our laboratories by the reaction of equimolar amounts of amine and organic acid. The amine was added in a three-necked glass vial, mounted in a 283.15 K thermal bath equipped with a reflux condenser, a temperature probe PT-100 to measure the temperature and a dropping funnel. Stirring the mixture at about 450 rpm was applied to improve the contact between the reactants, allowing the reaction to be completed.
The organic acid was added dropwise to the flask under stirring along with a magnetic bar. Stirring was continued for 24 hours at laboratory temperature in order to obtain a final viscous liquid. Then, stirring, light heating and moderate vacuum (20 kPa) for the vaporization of the starting reagents and water residues, the rotavaporation occurred for at least 48 h. During the purification and storage step, the ionic liquid was protected against light in order to avoid any degradation. More details on the synthesis can be found in Alvarez etal.
For determining the viscosity of different types of ionic liquids in presence of water was used a brand Brookfieldviscometer (LVDV Model-III +). The instrument is equipped with cylinders of different diameters (spindles, in which the appropriate cylinder is used as the viscosity of the fluid.
For the ILS used in this work was used a cylinder outside diameter of 100 mm (Spindle of reference CP52. The viscometer was coupled to a thermostatic bath, thus allowing to measure the viscosity of a PILS in different temperatures, with precision in temperature of 0.1 K. Once the software of viscometer provides the values of viscosity, it was possible to make the diagram viscosity composition.
It is noteworthy that in the Brookfieldviscometer readings are made automatically each viscosity temperature, varying the speed of rotation of the cylinder, point viscosity at a particular fixed temperature can be varied due to the rotation speed and the torque applied to the spindles until the maximum limit established, and upon reaching the top value of this variable, measurements are made with the decrease of this. In other words, the viscosity values reported in this paper refer in fact to average values obtained by triplicate reading equipment in each specified rotational speed value.
The dynamic viscosity can be regarded as a process enabled by a certain activation energy in accordance with the approach of Eyring theory [10]. The viscosity of binary mixtures containing ILs + water can be defined as: where η is dynamic viscosity of the mixture, h is the Planck constant, NA is Avogadro's number, (V) the molar volume of the mixture, g molar Gibbs energy of activation for the process of fluxo, R is the gas constant and T the absolute temperature. In principle, EQ.(1) can be used to describe the ideal mixture viscosity, as well as of non-ideal systems.
For a liquid mixture, ideal viscosity, EQ. (1) can be written as: where is the molar volume of Videal ideal mix, molar Gibbs energy of activation of a viscous flow can be considered as the sum of an ideal contribution and a correction or term in excess. That is, where is the ideal mixing contribution, under the same conditions of temperature, pressure and composition to the actual system per Mole, and is the molar excess Gibbs energy of activation. Combining the Eq (1)-(3) leads to the following expression:
The EQ. clearly shows that the model considers the dynamic viscosity of real solutions, as a result of the contribution of the ideal term and a term in excess. considering the following relation to the ideal mix, where xi, ηi and Vi are the mole fraction, viscosity and molar volume of component i, respectively. For the classical thermodynamics according to the behavior of mixtures of liquids we can assume the equivalence between free energy of activation and the Gibbs free energy of mixing. Thus the free energy according to the regular solution theory EQ (7)-(9). and Flory-Huggins EQ 10.
The regular solution model assumes that: the brewing process takes place without change of volume, all the configurational entropy is the internal energy of the solution comes from the interaction between atoms and their earliest neighbors, the coordination of atoms is the same before and after mixing, the interaction between the atoms does not affect its distribution (random as in ideal solution). Following this criterion, the variation of entropy in the formation of a regular solution will be the same as an ideal solution.
Mean Field Flory Huggins Lattice TheoryMean field: the interactions between molecules are assumed to be due to the interaction of a given molecule and an average field due to all the other molecules in the system. To aid in modeling, the solution is imagined to be divided into a set of cells within which molecules or parts of molecules can be placed (lattice theory). The total volume, V, is divided into a lattice of N cells, each cell of volume V. The molecules occupy the sites randomly according to a probability based on their respective volume fractions. To model a polymer chain, one occupies xiadjacent cells.
The general approach to model adjustment is to select an objective function that is a relationship between the experimental data and the data of the proposed model, and that is directly or indirectly related to the setting of desired parameters.
The best-fit parameters are obtained by minimizing (or maximizing, depending on how the function is defined) this objective function. If there are no errors in the experimental measurement and the existing model, this minimum value would be zero. However, even if the model is perfect, experimental errors in general creates a non-zero minimum value for the objective function.
The Regular Solution and Flory-Huggins model adjustable parameters (Table 4 and 5).We obtained the optimal solution by minimization of the function:
The optimization involves simultaneous solution of this system of non-linear equations and the methods we usedan excellent discussion on data modeling and optimization can be found in Press etal. (1992). The models were implemented in language VBA using the package XSEOS [14] Excess Gibbs Free Energy Models and Equations of State - a freely available Excel add-in to compute thermodynamic properties using many traditional and modern thermodynamic models.
It should be mentioned that the objective function through the trial and error method was average absolute relative deviation (AARD%) combined with other statistical error analysis parameters including average relative deviation (ARD) for better investigation on the correlative capability of the proposed network (see Eqs. 12-13) and results are presented in Table 6.
For viscosity measurements, the experimental viscosities from 293 to 333 K are listed in Tables 3. for the binary Mixture of water + 2HEAPr, water + 2HEAB, water +m-2HEAA, water+ m-2HEAB, water +BHEAPr, water +BHEAB respectively. Figures shows the trends of measured viscosities of these six binary mixtures at various temperatures and compositions. AccordingtoTables3andFig. 6, the viscose higher for water and the viscosities of binary mixtures decrease with increasing water content and temperature. In addition, the observed decrease of viscosity with na increase of water content is particularly strong at low temperatures. At higher temperatures, the differences between the viscosities of pure IL and water are much lower.
In addition, Fig. 1 to 6 plots the viscosities of binary mixtures against the mole fractionof ionic liquid at a given temperature. It Is found that all the water studied in this study appear to have a surprisingly similar effect on the viscosity of the ionic liquid. A dramatic decrease of the viscosity is observed with the addition of water. It is reduced by a factor two for a water mole fraction of ~0.2 . This was already observed in literature on other ionic liquids.
Xu (2013) [8] investigated the densities and viscosities of {n-butylammonium acetate N4AC (1) + water (2)} and {n-butylammonium nitrate N4NO3 (1) + water (2)} systems have been measured at temperatures (293.15, 298.15, 303.15, 308.15, and 313.15) K under atmospheric pressure. Notes that the viscosity deviations of the studied binary systems also have negative deviations and become less negative when the temperature rises.
In the work of Govindaetal.[9] and collaborators investigated properties of mixtures containing TriethylammoniumILs + dimethylsulfoxide - DMSO systems showed the negative at all investigated temperatures. In fact, temperature influences strongly on the viscosity deviation. As the temperature increased, the deviations also increased toward the positive values for triethylammonium acetate TEAA or triethylammoniumdihydrogen phosphate TEAP or triethylammoniumhydrogensulfate TEAS + DMSO system.
Apparently, the viscosity of the pure ILs and their mixtures increasing the mole fraction of ILs In DMSO whereas the values decreased as the temperature increased in the three systems . These authors report that the change in the magnitude of the positive values as a function of temperature can be attributed to the decrease in hydrogen bonding.
By increasing the temperature the interactions become very weak due to weakening of the dipolar association by the IL as well as the dissociation of the IL ion-pair are weakened intramolecular ion-ion interactions, ion-solvent, solventre-solventre promoting a reduction of potential energy when the chemical bonds tends to zero, in turn contributing to an increase the degree of disorder of the constituents: cations, anions and solvent complicating the packaging as well as hydrogen bonds and van derWaals and facilitating the flow of the mixture .
According to Kauzmann and Eyring, the viscosity of a mixture depends strongly on its entropy, which is related to the liquid structure. Therefore, the viscosity deviation depends on molecular interactions as well as on the size, and shape of the molecule. It can be seen in figures 1 to 6 that for all compositions and temperature studied therein, the viscosity deviations are negative in most of the mixtures studied, but in some cases at high temperatures contain tier values positive deviations from the Raoult's law, this behaviour is characteristic of mixtures without strong specific interactions.
The change in the magnitude of the positive values as a function of temperature can be attributed to decrease the importance of hydrogen bonding, with decreasing potential energy of interactions of ions tending to zero. By intramolecular interactions of ions attributed to hydrogen bonding as well as van derWaals bond. By increasing the temperature the interactions become very weak due to weakening the dipolar association by the IL aswell as the dissociation of the ionic liquid ion pair.
The minimum of deviations are presented at 293 K , the system 2-HEAPr + Water features with minimum magnitude of ~ -1288 mPa.s em x = 0.4 molar fraction of Water, 2-HEAB + Water ~ (-1356 mPa.s, x=0.4), m-2HEAA +Water ~ (- 1100 mPa.s, x= 0.5), m-2HEAB + Water ~ (-592 mPa.s, x= 0.4),BHEAPr +Water ~ (-1033 mPa.s, x= 0.4), BHEAB + Water ~ (- 1659 mPa.s, x=0.4).Thus, we can establish following series BHEAB > 2-HEAB > 2HEAPr > m-2HEAA > BHEAPr> m-2HEAB with regard to the minimum magnitude of the deviation from ideality, i.e. the anion features greater influence than the cation in this aspect, but to evaluate the presence of substituint realize the high influence of that group making the mixture (m-2HEAB+ Water) with smaller magnitude of deviation from the Raoult's law.
The negative deviation occurs in solutions that form exothermic ('outside heating'). This means that the forces of attraction between molecules Ionic Liquid and water in solution are stronger than those that exist in the pure state of the solute and the solvent. The molecules have less ability to escape in the solution than in the pure State. As a result the partial pressure of the solution is less than the calculated by Raoult's law (has a lower vapour pressure).
The viscosity of the (water + 2HEAPr, water+2HEAB, water +m-2HEAA, water+ m-2HEAB, water +BHEAPr, water +BHEAB) binary mixture as a function of composition and of temperature from (293 to 333) K were determined. From these experimental results, deviations from ideality properties were then deduced. This investigation shows negative deviations fromthe ideal behaviour for all properties covered in this work independently of the temperature and composition studied.
From experimental values, excess Gibbs energies of activation of viscous flow were then calculated for this involved binary systemusing Regular Solution Theory Flory and Huggins Theory. Binary mixture were then analysed in terms of the structure and interactions changes in solution. Finally, reported data were compared to those published by our group previously in the case of the PLI + water. This comparison provides useful information concerning the role of H-bonds in solution for mixture containing a PIL mixed with a polar and associative (water).
Experimental Data of Viscosity Protic Ionic Liquids. (2024, Feb 06). Retrieved from https://studymoose.com/document/experimental-data-of-viscosity-protic-ionic-liquids
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