Thermophysical Properties Of Aqueous Solutions Research Articles

Influence of temperature and anion type on thermophysical properties of aqueous solutions of morpholine based amino acid ionic liquids

Densities and sound velocities of aqueous solutions of N-butyl-N-methylmorpholine based amino acid ionic liquids (AAILs), including N-acetyl-L-alanine, N-acetyl-L-valinate, N-acetyl-L-leucinate, and N-acetyl-L-izoleucinate anions were measured at a temperature from 293.15 to 313.15 K at 5 K intervals and atmospheric pressure. These data were used to calculate the apparent molar volumes and the apparent molar compressibilities in the concentration range of (0.02 to 0.3) mol.kg−1. Infinite dilution values for the volumetric and acoustic properties were evaluated by an extrapolation procedure based on Redlich – Meyer type equations. The limiting apparent molar expansibility coefficients were also obtained from the slopes of the apparent molar volume at infinite dilution versus temperature. Using the Passynski method, the hydration numbers for AAILs in an aqueous medium were calculated. The results indicate that in the studied solutions, the ion–solvent interactions are determined by the hydrophobic effect, which results in the decrease of the limiting apparent molar compressibilities and an increase of limiting apparent molar expansibility coefficients in the order: [Mor1,4][N-Ac-L-Ala], [Mor1,4][N-Ac-L-Val], [Mor1,4][N-Ac-L-Leu], [Mor1,4][N-Ac-L-Izoleu]. The empirical slopes in Redlich –Rosenfeld – Meyer equations show that the hydrophobicity of amino acid anions is also responsible for the ion-ion interactions.

Процессы молекулярного переноса в жидкостных питательных средах дрожжевой и пивной отраслях промышленности. Часть 3. Исследование теплофизических свойств водных растворов мелассы и концентрата пивного сусла

Thermophysical properties of aqueous solutions of molasses and beer wort concentrate with different dry matter content in a wide range of temperature changes were investigated. Seven samples of aqueous solution of beet molasses with an initial dry matter concentration of 77.7 wt.% and seven samples of beer wort concentrate with an initial dry matter concentration of 81 wt.% were studied. The temperature variation range was 10–70℃ with a discreteness of 10℃. Thermal conductivity, specific heat capacity, and thermal diffusivity of the initial solutions were determined by unsteady plane source and differential scanning calorimetry methods. Numerical values of the above-mentioned thermal constants for aqueous solutions of beet molasses in the range of dry matter mass concentrations n of from 16 to 70% at the temperatures of from 293 to 353 K and of beer wort concentrate in the range of dry matter mass concentrations of from 10.2 to 72.4% at temperatures from 284 to 342 K have been experimentally established. Graphical dependences of heat capacity, thermal conductivity, and thermal diffusivity of these parameters on temperature are given. Design equations of the required parameters are obtained, which are of interest both from the point of view of fundamental science on the development of the theory for liquid state of matter, and from the applied point of view of engineering calculations and design of biotechnological equipment.

Phase equilibria and thermophysical properties of aqueous solutions of two bis(fluorosulfonyl)imide-based ionic liquids

Ionic liquids comprising bis(fluorosulfonyl)imide (FSI) anion have been recognized to be well suited for technological applications as solvent and electrolyte media. In this work, we thoroughly investigated the thermodynamic and transport behavior of binary aqueous systems of two hydrophobic FSI-based ionic liquids, namely [EMIM][FSI] and [BMPYR][FSI]. Systematic measurements of phase equilibria, density, viscosity, and electric conductivity were conducted, our aim being to provide truly reliable information that would substantially upgrade that existing in the literature. Employing DSC measurements on the neat ILs and dynamic measurements of freezing or cloud point temperatures as well as static solubility measurements for aqueous ILs, phase diagrams for both these systems over a 100 K window were established. Rather large solubilities of water in these ILs allow for measurements of various other properties in the homogeneous IL-rich region. Extensive data thus obtained on water activity in this region were correlated for each system simultaneously with the mutual liquid-liquid solubilities, using an extended SSF (Sum of Symmetrical Functions) equation. This global excess Gibbs energy model not only accurately captures all the VLE, LLE, and SLE data we determined experimentally, but also discloses an enthalpy-driven system energetics with hydrophobic hydration effects that are more pronounced in the case of [BMPYR][FSI]. The measurements of density, viscosity, and conductivity covering the systems from the neat ILs to those almost saturated with water gave positive excess volumes and negative viscosity deviations that rise and diminish, respectively, as T increases. The conductivity increases monotonously with increasing water content and temperature. Accurate functional representations were also established for the volumetric, viscosity, and conductivity data, capturing simultaneously their composition and temperature dependence. The linkage between conductivity and viscosity was further analyzed by means of the fractional Walden rule which provided excellent fits for both isopleths and isotherms and indicated comparatively weaker coupling for the [BMPYR][FSI] system and the direction of the isothermal composition changes. Finally, comparing the FSI ILs with their TFSI analogs, the former were found to be clearly less hydrophobic.

Physicochemical properties of dilute aqueous solutions of 1-Ethyl-3-Methylimidazolium Ethylsulfate, 1-Ethyl-3-Methylimidazolium Methylsulfate, 1-Ethyl-3-Methylimidazolium Tosylate and 1, 3-Dimethylimidazolium Methylsulfate at different temperatures and at atmospheric pressure

This work presents the experimental data on thermophysical properties of aqueous solutions of imidazolium-based ionic liquids (ILs) such as 1-Ethyl-3-Methylimidazolium Ethylsulfate [EMIM][EtSO4], 1-Ethyl-3-Methylimidazolium Methylsulfate [EMIM][MeSO4], 1-Ethyl-3-Methylimidazolium Tosylate [EMIM][Tos], and 1,3-Dimethylimidazolium Methylsulfate [MMIM][MeSO4] in water at different temperatures. Many researchers have studied imidazolium based ILs in different solvents but there is scarcity of data in dilute region. So the aim of this work is to understand the interactions between imidazolium based ILs and water in dilute region. To understand the ion-ion and ion–solvent interactions between IL and water, the thermophysical properties such as density (ρ), speed of sound (u), and viscosity (η) have been measured at temperatures T = (298.15, 303.15, 308.15 and 313.15) K and at atmospheric pressure. The properties like apparent molar volume, limiting apparent molar volume and coefficient of thermal expansion have been derived from the density data. The speeds of sound and density data were combined to evaluate isentropic and isothermal compressibilities. Using Jones-Dole equation, the viscosity A and B coefficients have been determined. The influence of IL cation chain length, different anions and temperature on the sign, magnitude of BV (the deviation parameter from Debye-Hückel theory) and on viscosity B-coefficient has been discussed.

THERMOPHYSICAL PROPERTIES OF 1-ETHYL-3-METHYLIMIDAZOLIUM CHLORIDE SOLUTION FROM 293.15 TO 323.15 K

ABSTRACT Aqueous systems composed of ionic liquid make up a new alternative for use in processes involving the separation of biomolecules. The objective of this experiment was to obtain the thermo-physical properties of density, refractive index, electrical conductivity, molar volume, thermal expansion coefficient and apparent specific volume of the ionic liquid 1-ethyl-3-methylimidazolium chloride. The thermo-physical properties of aqueous solutions of this ionic liquid were measured as a function of the mass fraction w = (0.05, 0.125, 0.2, 0.275 and 0.35), temperature T = (293.15, 303.15, 313.15 and 323.15) K and pH = (7.5, 8.0 and 8.5). Models representing the combined effects between variables were fit since they are required for industrial applications where the physical parameters must be accurately calculated. Models representing the combined effects of the variables temperature, mass fraction and pH values of ionic liquid were adjusted and presented good fit.

Thermodynamic characterisation of aqueous alkanolamine and amine solutions for acid gas processing by transferable molecular models

The development of new alkanolamines/amines is a topic which has attracted a great deal research interest, particularly as absorbents for the removal of acid gases from industrial sources and CO2 capture applications. One of the major challenges when evaluating the techno-economic performance of selected new single amines or blends is the lack of experimental data on the thermophysical properties required for a reliable process design and simulation. In this contribution, a robust theoretical framework for the description of key thermophysical properties of aqueous solutions of single and mixed alkanolamines/amines at relevant gas separation process conditions is proposed. The approach is based on the coupling of the Free-Volume Theory and the Density Gradient Theory with a molecular-based equation of state (soft-SAFT) for the integrated modelling of phase behaviour, enthalpies, densities, viscosities and interfacial tensions. The alkanolamines and amines investigated differ in their family and structure, and included primary (monoethanolamine), secondary (diethanolamine), tertiary (methyldiethanolamine), sterically hindered (2-amino-2-methyl-1-propanol) and cyclic amines (piperazine). The study was performed in a systematic manner, starting from the development of the models for the pure amines, the description of their thermophysical properties, and the properties of the aqueous mixtures. Compared to other models described in literature, the present modelling approach preserves the effects due the chemical structure and key intermolecular interactions of the examined alkanolamines/amines through a set of molecular parameters obtained from pure substance data, whenever available, or transferred from substances of different chemical families. This enabled the development of a consistent modelling framework which can provide reliable thermodynamic property predictions of both single and blended amine solutions over a broad range of temperatures (298–373 K) and compositions (0–50 wt% amine). The proposed approach is well-suited for implementation and extension to other alkanolamines and amines, making it a valuable tool for having reliable process simulations as well as for the screening and discovery of new amine systems, which will be required for the deployment of more economical acid gas removal processes.

Thermophysical characterization of aqueous deep eutectic solvent (choline chloride/urea) solutions in full ranges of concentration at T = (293.15–323.15) K

Deep eutectic solvents (DESs) as a novel generation of green solvents have been used in several processes in academia and technology in the recent years. In this study, it was measured some thermophysical properties of aqueous solutions of the deep eutectic solvents (choline chloride/urea) in full ranges concentration of DES at T=(293.15–323.15)K. The densities, speeds of sound, refractive indices, and viscosities of the investigated systems have been measured by precise methods and those results used to calculate various thermodynamic and transport properties including the excess molar volumes (VE), the partial molar volumes (V¯m,1 and V¯m,2), the excess isobaric thermal expansions (αpE), the excess molar isentropic compressibility (κs,mE), the viscosity deviations (Δη), and the deviation of molar refraction (ΔRD). These variations of properties were discussed in terms of solute-solvent interactions occurring between the components of the solutions. Eyring theory of vicos flow is used to calculate excess activation functions (ΔG#E), ΔH#E and ΔS#E of DES solutions.

Thermophysical properties of aqueous solutions of tetraalkylphosphonium based ionic liquids at different temperatures and atmospheric pressure

Densities, speed of sound and viscosities of the aqueous solutions of three tetraalkylphosphonium based ionic liquids namely Tributylmethylphosphonium methyl sulfate (0 to ∼0.28)mol·kg−1, Triisobutylmehtylphosphonium tosylate (0 to ∼0.52)mol·kg−1 and Tetrabutylphosphonium chloride (0 to ∼0.57)mol·kg−1 have been measured at the temperatures (298.15, 303.15, 308.15 and 313.15)K and at atmospheric pressure. The apparent molar volume, limiting apparent molar volume and coefficient of thermal expansion values have been obtained from the experimental density data whereas relative viscosities and viscosity A and B coefficients have been determined from experimental viscosity data. The density values have been combined with speed of sound values to evaluate the isothermal and isentropic compressibilities. The hydration number has also been calculated from both viscosity and compressibility data. The data obtained are used to interpret the ion-ion and ion-solvent interactions in the studied systems and also we tried to explain the effect of temperature and concentration on it. The volumetric data, negative values of BV (the deviation parameter from Debye–Hückel theory) and the large positive values of viscosity B coefficient for the studied ionic liquids indicate strong solute-solute interaction with water structure making effect of ionic liquids. All these are discussed in terms of cation-cation, cation-anion interactions and probable alterations in water structural effects.

Thermophysical properties of aqueous solutions of the 1-ethyl-3-methylimidazolium tricyanomethanide ionic liquid

Thermophysical behavior of the binary system [water+1-ethyl-3-methylimidazolium tricyanomethanide ionic liquid (IL)] was thoroughly characterized through systematic measurements of (vapor+liquid) equilibria (water activity aw), mixing enthalpy, density, viscosity, and refractive index. The measurements were performed in the entire composition range and/or specifically in the highly dilute IL region, at T=298.15K or as a function of temperature in the range from (288.15 to 318.15)K. Effective experimental methods minimizing IL sample consumption, using flow arrangements, instrument couplings and high degree of automation were preferably employed. In particular, the aw determination based on the chilled-mirror dew point technique and implemented by an AquaLab 4TE instrument was identified as a generally superior approach to study VLE of (water+IL) systems. Excess thermodynamic properties (Gibbs free energy, enthalpy, heat capacity, and volume) and property deviations from the linear mixing rule (viscosity, refractive index) were evaluated, Padé approximants being used to correlate adequately their complex composition dependences. The extensive aw data were processed by a two-step procedure fitting first the temperature dependence at each isopleth and subsequently the composition dependence at each isotherm. Good estimates could be thus obtained for derivative thermal properties (enthalpy, heat capacity). Alternatively, the water activity and excess enthalpy data were correlated simultaneously by a NRTL-type model, providing their compact, thermodynamically consistent and adequate representation. Despite small absolute values of excess Gibbs free energy (GE), the system is revealed to be highly nonideal, the small GE resulting from close compensation of its large enthalpy and entropy contributions. Large endothermic effects and an enhanced increase of entropy upon mixing found for this system indicate relative weakness of interactions between unlike molecules and a massive structure breakage in the solution. Positive values of excess volume and negative values of viscosity and refractive index deviations found in the major part of the composition range corroborate this general energetic and structural pattern, although the situation appears to be more complicated in the highly dilute IL region, where these properties congruently exhibit a sign inversion.

Density, Refractive Index, Apparent Specific Volume, and Electrical Conductivity of Aqueous Solutions of Poly(ethylene glycol) 1500 at Different Temperatures

Thermophysical properties of aqueous solutions of poly(ethylene glycol) 1500 g·mol–1 were measured as a function of polymer concentration w = (0.05, 0.10, 0.15, 0.20 and 0.25) and temperature T/K = (288, 293, 298, 303 and 308). Aqueous systems composed of poly(ethylene glycol) are frequently used in processes involving the separation of biological compounds. The density of the solutions varied from (1001.68 to 1042.65) kg·m–3, the refractive index ranged from (1.3377 to 1.3681), the apparent specific volume was between (0.8336 and 0.8528) g·cm–3, and the electrical conductivity varied between (66.22 and 170.29) 10–3 mS·cm–1. Polynomial models for the properties as a function of temperature and poly(ethylene glycol) 1500 g·mol–1 concentration were fitted to the experimental data. Models accounting for combined effects between variables are particularly useful in industrial applications in which physical parameters must be promptly and accurately calculated.

Thermo-physical properties of aqueous solutions of N,N-dimethylformamide

In this work, thermal properties including heat capacity, thermal conductivity and thermal diffusivity of pure and aqueous solution of N,N-dimethylformamide (DMF) at the entire range of composition were measured. All thermal properties were measured at temperatures from (303.15 to 353.15) K and at atmospheric pressure. Excess quantities of those mentioned properties were obtained and modeled by using Redlich–Kister equation. The results show that, excess molar heat capacity departs positively from rectilinear ideal solution, whereas excess thermal conductivity and thermal diffusivity deviate negatively from ideal solution at the temperature range studied in this work. The measured experimental data for all thermo-physical properties were also correlated by using the modified Setchenow equation.

SINGLE-PHASE AND TWO-PHASE SECONDARY COOLANTS: SIMULATION AND EVALUATION OF THEIR THERMOPHYSICAL PROPERTIES

This paper makes a comparative analysis of the thermophysical properties of ice slurry with conventional single-phase secondary fluids used in thermal storage cooling systems. The ice slurry is a two-phase fluid consisting of water, antifreeze and ice crystals. It is a new technology that has shown great energy potential. In addition to transporting energy as a heat transfer fluid, it has thermal storage properties due to the presence of ice, storing coolness by latent heat of fusion. The single-phase fluids analyzed are water-NaCl and water-propylene glycol solutions, which also operate as carrier fluids in ice slurry. The presence of ice changes the thermophysical properties of aqueous solutions and a number of these properties were determined: density, thermal conductivity and dynamic viscosity. Data were obtained by software simulation. The results show that the presence of 10% by weight of ice provides a significant increase in thermal conductivity and dynamic viscosity, without causing changes in density. The rheological behavior of ice slurries, associated with its high viscosity, requires higher pumping power; however, this was not significant because higher thermal conductivity allows a lower mass flow rate without the use of larger pumps. Thus, the ice slurry ensures its high potential as a secondary fluid in thermal storage cooling systems, proving to be more efficient than single-phase secondary fluids.

Properties of aqueous solutions of lithium and calcium chlorides: formulations for use in air conditioning equipment design

The dehydration of air, for air conditioning purposes, either for human comfort or for industrial processes, is done most of the times by making it contact a surface at a temperature below its dew point. In this process not only is it necessary to cool that surface continuously, but also the air is cooled beyond the temperature necessary to the process, thus requiring reheating after dehumidification. Although the equipment for this purpose is standard and mostly low-cost, the running costs are high and high grade energy is dissipated at very low efficiency. Alternative sorption-based processes require only low grade energy for regeneration of the sorbent materials, thus incurring lower running costs. On the other hand, sorption technology equipment is usually more expensive than standard mechanical refrigeration equipment, which is essentially due to their too small market share. This paper reports the development of calculation models for the thermophysical properties of aqueous solutions of the chlorides of lithium and calcium, particularly suited for use as desiccants in sorption-based air conditioning equipment. This development has been undertaken in order to create consistent methods suitable for use in the industrial design of liquid desiccant-based air conditioning equipment. We have reviewed sources of measured data from 1850 onwards, and propose calculation models for the following properties of those aqueous solutions: Solubility boundary, vapour pressure, density, surface tension, dynamic viscosity, thermal conductivity, specific thermal capacity and differential enthalpy of dilution.

An excess function method to model the thermophysical properties of one-phase secondary refrigerants

This paper describes an easy-to-use and accurate method to calculate some of the thermophysical properties of aqueous solutions which are used as secondary refrigerants. This method is based on the correction of the ideal behaviour of aqueous solutions by excess functions. This method allows to determine the following properties: freezing points, densities, heat capacities, thermal conductivities and dynamic viscosities. As an illustration, it is applied to aqueous solutions of (i) ethyl alcohol, (ii) ammonia, (iii) sodium chloride, (iv) ethylene glycol and (iii) propylene glycol.