Solutions Of Carboxylic Acids Research Articles

A single-step process to leach out rare earth elements from coal ash using organic carboxylic acids

The ever increasing applications of rare earth elements and their limited primary resources has compelled researchers worldwide to find alternate methods of efficient leaching from various secondary resources, in particular from end of life products. The present research work describes such a process to extract rare earth elements from coal ash using low molecular weight carboxylic acids. Different carboxylic acids, i.e. monocarboxylic (lactic acid), dicarboxylic (malonic acid, succinic acid, tartaric acid) and tricarboxylic acid (citric acid) were used to successfully leach out significant proportion of rare earth elements (up to 62%) from coal ash at the natural pH of the carboxylic acid solutions (pH 1.6–2.3). The carboxylic acid concentration, leaching duration, temperature, and pulp density were optimized for the leaching process. Best leaching efficiency (65% for LREE, 19% for HREE & 62% for total REE) was achieved using 5% tartaric acid solution having natural solution pH 1.8 at 90 °C with a leaching duration of 60 min. The leaching efficiency of the different carboxylic acids were in the order of tartaric acid>lactic acid>citric acid>malonic acid>succinic acid. The leaching kinetics of individual rare earth elements was found to be different from each other owing to their different complex formation ability with carboxylic acids. Appreciable selectivity was observed for leaching of rare earth elements over transition metal and main group elements. XRD and electron probe micro analyzer (EPMA) studies revealed that unlike mineral acids, carboxylic acids leached out rare earth elements without damaging the minerology of coal ash, thus providing the opportunity to utilize the treated coal ash for other applications like in cement and bricks industries. Thus, the novelty of the present work lies in efficient and selective leaching of lanthanides from coal ash using only organic acids, which are considered much milder and greener options compared to mineral acids.

Spinodal decomposition of chemically fueled polymer solutions.

Out-of-equilibrium phase transitions driven by dissipation of chemical energy are a common mechanism for morphological organization and temporal programming in biology. Inspired by this, dissipative self-assembly utilizes chemical reaction networks (CRNs) that consume high-energy molecules (chemical fuels) to generate transient structures and functionality. While a wide range of chemical fuels and building blocks are now available for chemically fueled systems, so far little attention has been paid to the phase-separation process itself. Herein, we investigate the chemically fueled spinodal decomposition of poly(norbornene dicarboxylic acid) (PNDAc) solution, which is driven by a cyclic chemical reaction network. Our analysis encompasses both the molecular level in terms of the CRN, but also the phase separation process. We investigate the morphology of formed domains, as well as the kinetics and mechanism of domain growth, and develop a kinetic/thermodynamic hybrid model to not only rationalize the dependence of the system on fuel concentration and pH, but also open pathways towards predictive design of future fueled polymer systems.

Carboxylic acid recovery from Fischer\u2013Tropsch aqueous product by fractional freezing

About half of the product from iron-based high-temperature Fischer–Tropsch synthesis is an aqueous product containing dissolved oxygenates. Volatile oxygenates can be recovered by distillation, but the bulk of the carboxylic acids remain in the water, which is called acid water. Fractional freezing was explored as a process for producing a more concentrated carboxylic acid solution from which the carboxylic acids could be recovered as petrochemical products, while concomitantly producing a cleaner wastewater. Solid–liquid equilibrium data were collected for aqueous solutions of acetic acid, propionic acid, and butyric acid. A synthetic Fischer–Tropsch acid water mixture (0.70 wt% acetic acid, 0.15 wt% propionic acid, and 0.15 wt% butyric acid) was prepared and the liquid phase concentrations of the acid species at solid–liquid equilibrium were determined. Control experiments with material balance closure on each of the carboxylic acid species were performed at selected conditions. Having more than one carboxylic acid species present in the mixture meaningfully changed the solid–liquid equilibrium versus temperature of the system. The carboxylic acids partitioned between the solid phase and the liquid phase and a practical design would require multiple duty-controlled solid–liquid equilibrium stages, with most of the separation taking place in the temperature range 0 to − 5 °C.

Biodegradation of filled styrene-acrylic coatings in a laboratory kinetic plant

Styrene-acrylic polymer coatings rank among the most popular materials of the construction industry that protect structures from corrosion. Biocorrosion is considered to be one of quite dangerous and less studied types of destruction. There is a State standard method of testing materials for biostability in which a qualitative assessment of the resistance of coatings to biodegradation is carried out, but still it doesn’t provide the full picture of the destruction degree of the material caused by the biodegradation. Besides, the test duration is 28 days. The most informative and convenient is the kinetic method of research. It includes the applying of the facility involving exposure of coating samples in a solution of carboxylic acids (model medium) which significantly reduces the test period and also eliminates the work with microorganisms. The studies were carried out on styrene-acrylic filled free films. The changes in material was evaluated by quantitative and qualitative indicators: the change in the mass of the initial and exposed samples of free films, their geometric parameters, as well as a visual assessment (using a microscope) of the surface state of the coatings before and after exposure, including the use of the CIELab method. It was found that the level of the determined characteristics of styrene-acrylic free films when exposed in a model medium is reduced by 10-15%.

Freezing of Aqueous Carboxylic Acid Solutions on Ice.

We study the properties of acetic acid and propionic acid solutions at the surface of monocrystalline ice with surface-specific vibrational sum-frequency generation (VSFG) and heterodyne-detected vibrational sum-frequency generation spectroscopy (HD-VSFG). When we decrease the temperature toward the eutectic point of the acid solutions, we observe the formation of a freeze concentrated solution (FCS) of the carboxylic acids that is brought about by a freeze-induced phase separation (FIPS). The freeze concentrated solution freezes on top of the ice surface as we cool the system below the eutectic point. We find that for freeze concentrated acetic acid solutions the freezing causes a strong decrease of the VSFG signal, while for propionic acid an increase and a blue-shift are observed. This different behavior points at a distinct difference in molecular-scale behavior when cooling below the eutectic point. We find that cooling of the propionic acid solution below the eutectic point leads to the formation of hydrogen-bonded dimers with an opposite alignment of the carboxylic acid O–H groups.

Mechanism of iron ions sorption by chitosan-genipin films in acidic media

Chitosan-genipin (Ch-Ge) films have been proposed as wine preservative due to their capacity to uptake iron ions. The wine is an aqueous acidic solution of water and ethanol, whose acidity derives from tartaric acid. This acid has been shown to form negatively charged iron-tartrate complexes able to interact with the positively charged amine groups of chitosan, removing the iron ions from solutions. Nevertheless, it is possible that these films can uptake iron ions in the presence of other carboxylic acids. To understand the iron-binding capacity of Ch-Ge films, aqueous solutions of different carboxylic acids were prepared in the presence of iron ions and Ch-Ge films. It was observed that the Ch-Ge films only presented sorption capacity at pH 3.5 in the presence of α-hydroxypolycarboxylic acids, through electrostatic interactions. These results allow proposing a broad application of Ch-Ge films to beverages and other liquids containing malic, tartaric or citric acids.

Volumetric studies of solvation of carboxylic acids in aqueous, carbon tetrachloride, methanolic and methanolic-urea binary solutions at 298.15 K

Abstract Experimental measurements of density property at 298.15 K for aqueous, carbon tetrachloride, methanolic, and 3.0004 mol·kg−1 urea in methanol as solvent systems for binary solutions of carboxylic acids (propionic acid, n-butyric acid, n-valeric acid and n-caproic acid) are reported. The data of density are used to obtain apparent molar volume of acids at the finite concentrations of solute (Vϕ) which were appropriately extrapolated to infinitely dilute concentration of acid to obtain the limiting apparent molar volumes (Vϕ0). The calculations of volume changes due to dimerization equilibria (in carbon tetrachloride and aqueous solutions) are made and used to study the volume changes due to dimerization of acid molecules. The results of Vϕ in methanol-urea solvent system are explained on the basis of channel-like structure-formation for the species (urea and acid molecules) in solution phase. The negative volume changes observed in case of aqueous solutions are explained on the basis of hydrophobic hydration while the same in carbon tetrachloride solutions occurring with positive volume changes are interpreted in terms of hydrogen-bonded dimer formation equilibria. The Vϕ variation with acid concentrations has been explained on the basis of solute-solvent interactions foe studied acids in methanol while in aqueous solutions, the same has been attributed to ionization (limiting concentration range), hydrogen bonding and hydrophobic interactions.

On the effect of the nature of counterions on the self-assembly of polyoxyethylene alkyl ether carboxylic acids.

In this contribution, we investigate the effect of the type of counterion on the properties of dilute solutions of polyoxyethylene alkyl ether carboxylic acids. Two different surfactants, presenting an oleic acid alkyl chain and on-average five and nine ethylene oxide units, and terminated by a weakly anionic carboxymethyl group were studied. The surfactants were gradually ionized with sodium hydroxide, arginine, and choline hydroxide. The solutions properties were probed by light scattering, electrophoretic mobility, density and sound velocity measurements, as well as by small-angle neutron scattering. To our initial surprise, no specific effect arising from the nature of the counterion could be determined. We ascribe this phenomenon to the fact that the presence of the ethylene oxide units markedly dilutes the surfactant head group charge density, reducing counterion condensation and subsequent counterion specific effects.

Experiment and molecular dynamics study on the mechanism for hydrophobic impregnation in cement-based materials: A case of octadecane carboxylic acid

A novel method that specimen is impregnated with octadecane carboxylic acid (OCA) solution is proposed to prevent water and ions from penetrating into concrete/mortar. Molecular dynamics is utilized to model capillary absorption in calcium silicate hydrate (C-S-H) channel to reveal related mechanism. The simplified model of decane carboxylic acid (DCA), coating on C-S-H channel and DCA mixed in solution, is used in the simulation. While the hydrophilic functional terminal of DCA chain is bridged to surface calcium in C-S-H, the other hydrophobic end diffuses free in the solution. The reduction of capillary transport rate induced by DCA is mainly due to two reasons. (1) DCA coating decreases the hydrophilicity of the channel; (2) Aqueous ions accumulate around DCA, forming huge DCA-based clusters and blocking the transport channel. This study can contribute to development of water repellent materials in durability design of cement-based materials.

(Invited) Atomic-Scale Investigations of TiO2 surfaces in Ambient and Solution Environments

Earth-abundant metal oxide nanocrystals have attracted a great deal of attention for environmental remediation and photocatalysis. These materials are attractive because they are inexpensive, they are typically very stable under reactive conditions, and their semiconducting nature enables efficient generation of long-lived photocarriers that can initiate chemical reactions. Nevertheless, an atomic-scale understanding of their reactivity in ambient and solution environments has proven elusive for two reasons. First, the complex milieu of reactants in these environments makes the discrimination of surface chemistry from adventitious contamination difficult. Second, the small size of nanocatalysts prohibits face-specific studies with most surface science techniques. In this talk, I will review our work in developing “new eyes” for nanocatalysis that address both issues. Over the past few years, researchers around the world have observed the formation of mysterious molecularly ordered structures on the surface of TiO2 photocatalysts in air and solution. These structures have been attributed to many causes, including a new ordered state of adsorbed H2O — persistent in vacuum at room temperature — in which one H2O molecule adsorbs to every other surface Ti atom. Using a combination of atomic-scale microscopy and spectroscopy, we show that these structures are due to the highly selective adsorption of atmospheric formic and acetic acids that are typically present in parts-per-billion concentrations. These surfaces effectively repel other adsorbates, such as alcohols, present in much higher concentrations. The high affinity of the surface towards carboxylic acids is attributed to their bidentate binding. The self-assembled organic acid monolayers have the unusual property of being both hydrophobic and highly water soluble, which may contribute to the self-cleaning properties of TiO2. Interestingly, these monolayers block the undercoordinated surface cation sites typically implicated in photocatalysis. In related work, we have shown that hydrothermal crystal growth techniques can produce anatase nanocrystals suitable for study at the atomic-scale with STM and other surface science techniques, as shown in the accompanying figure. Despite being synthesized in solution, the nanocrystal surfaces are very clean and passivated by a protecting monolayer. Using these crystals, we have shown that the most commonly used functionalization chemistry for oxide nanocatalysts, a carboxylic acid solution, causes the spontaneous reorganization of the nanocatalyst, leading to a five-fold increase in the number of reactive sites and revealing the atomic-scale origins of catalyst activation. Finally, we have investigated the structure of solution-deposited monolayers on TiO2 and demonstrated a rational approach to tuning intermolecular interactions and enabling long-range ordering. We show that simple electrostatic insights can be used to engineer away unfavorable intermolecular interactions, producing monolayers with exceptional long-range ordering. Quantitative measurements of the intermolecular interaction energies from molecularly resolved STM images are a factor of ~7 larger than those predicted by dispersion-corrected density functional theory (DFT). The discrepancy between experiment and simulation is not currently understood. This finding suggests a new path to the production of highly ordered monolayers and superstructures of large molecules. Figure 1

Multi-functional carboxylic acids for chitosan scaffold

In general, CS scaffold is prepared by lyophilizing CS hydrogel which traditionally can be prepared by dissolving CS in acetic acid and crosslinking with dialdehyde. However, this method expresses unpleasant odor and toxicity leading to obstruct the practical applications. Here, the aqueous solution of multi-functional carboxylic acids is considered as the alternative and ordorless solvents to provide dual functions, i.e. (i) protonation of CS for the dissolution, and (ii) providing the preferable structure to give crosslink networks under amide bond through the conjugation reaction. The present work demonstrates the potential use of multi-functional carboxylic acids for preparation of CS scaffold and shows the tunable physicochemical and mechanical properties. The work also extends to the basic studies on biological properties to propose as the potential material for dental tissue engineering.

Effect of organic acid concentration in lubricant on tribological characteristics of friction couple

Introduction.The possibility of using monocarboxylic acids as a lubricant composition additive, and the effect of their concentration in lubricant on the evolution of the friction factor of a brass-steel couple, as well as the morphology of the film surface under friction is considered. The work objective is to study the effect of the concentration of carboxylic acids in the lubricant composition on the evolution of the friction factor of copper – steel alloy.Materials and Methods.Tribological studies of a brass-steel friction couple in aqueous solutions of monocarboxylic acids with the concentrations of 0.025; 0.05; 0.1; 0.2; 0.5 mol/l are carried out. Using scanning electron microscopy, we have studied the morphology of the servovite film surface that is formed on a steel disk after frictional interaction of a brasssteel couple in aqueous solutions of acids with the concentration of 0.1 mol/l.Research Results.Tribological characteristics of the brasssteel tribocoupling in aqueous solutions of carboxylic acids of various concentrations are studied. The optimum acid concentration in the lubricant composition is specified. Herewith, a selective transfer and a wearless friction regime are implemented under friction of the brass 59–steel 40X couple. A decrease in the friction ratio to 0.009 and 0.007 is found out under friction in aqueous solutions of valeric and caproic acids, respectively. The formation of an anti-friction film on the steel surface is identified through the scanning electron microscopy. It is established that the film formed in an aqueous solution of caproic acid has a denser structure in comparison with the film formed under friction in aqueous solutions of butyric and caproic acids.Discussion and Conclusions.Thus, the tribological studies of a brass-steel friction couple in aqueous acid solutions show that the optimum molar acid concentration in the lubricant composition is 0.1 mol/l. At this acid concentration, the values of the friction factor characteristic of the wearless mode are attained.

Effect of the Composition of the Lubricating Medium on the Structure of Surface Layers Formed by the Friction of a Servovite Film

The tribological characteristics of a brass–steel friction pair in aqueous solutions of saturated carboxylic acids are studied. With an increase in the length of the carbon radical in the acid molecule used as the organic component of the lubricant composition upon the friction of brass on steel, the coefficient of friction decreases and wear reduces. A servovite film is found to form on tribocoupled surfaces during frictional interaction. In the series of monobasic carboxylic acids R–COOH (R = CnH2n + 1, n = 0–5) used as a lubricating medium, from formic acid to caproic acid, the roughness of the film surface decreases and its continuity increases. The servovite film is formed by copper nanoclusters of predominantly ellipsoidal shape up to 40 nm in height, tightly packed and directed along the slip of the counterbody.

Carboxylic acids accelerate acidic environment-mediated nanoceria dissolution

Ligands that accelerate nanoceria dissolution may greatly affect its fate and effects. This project assessed the carboxylic acid contribution to nanoceria dissolution in aqueous, acidic environments. Nanoceria has commercial and potential therapeutic and energy storage applications. It biotransforms in vivo. Citric acid stabilizes nanoceria during synthesis and in aqueous dispersions. In this study, citrate-stabilized nanoceria dispersions (∼4 nm average primary particle size) were loaded into dialysis cassettes whose membranes passed cerium salts but not nanoceria particles. The cassettes were immersed in iso-osmotic baths containing carboxylic acids at pH 4.5 and 37 °C, or other select agents. Cerium atom material balances were conducted for the cassette and bath by sampling of each chamber and cerium quantitation by ICP-MS. Samples were collected from the cassette for high-resolution transmission electron microscopy observation of nanoceria size. In carboxylic acid solutions, nanoceria dissolution increased bath cerium concentration to >96% of the cerium introduced as nanoceria into the cassette and decreased nanoceria primary particle size in the cassette. In solutions of citric, malic, and lactic acids and the ammonium ion ∼15 nm, ceria agglomerates persisted. In solutions of other carboxylic acids, some select nanoceria agglomerates grew to ∼1 micron. In carboxylic acid solutions, dissolution half-lives were 800–4000 h; in water and horseradish peroxidase they were ≥55,000 h. Extending these findings to in vivo and environmental systems, one expects acidic environments containing carboxylic acids to degrade nanoceria by dissolution; two examples would be phagolysosomes and in the plant rhizosphere.

Surface-controlled dissolution rates: a case study of nanoceria in carboxylic acid solutions.

Nanoparticle dissolution in local milieu can affect their ecotoxicity and therapeutic applications. For example, carboxylic acid release from plant roots can solubilize nanoceria in the rhizosphere, affecting cerium uptake in plants. Nanoparticle dispersions were dialyzed against ten carboxylic acid solutions for up to 30 weeks; the membrane passed cerium-ligand complexes but not nanoceria. Dispersion and solution samples were analyzed for cerium by inductively coupled plasma mass spectrometry (ICP-MS). Particle size and shape distributions were measured by transmission electron microscopy (TEM). Nanoceria dissolved in all carboxylic acid solutions, leading to cascades of progressively smaller nanoparticles and producing soluble products. The dissolution rate was proportional to nanoparticle surface area. Values of the apparent dissolution rate coefficients varied with the ligand. Both nanoceria size and shape distributions were altered by the dissolution process. Density functional theory (DFT) estimates for some possible Ce(IV) products showed that their dissolution was thermodynamically favored. However, dissolution rate coefficients did not generally correlate with energy of formation values. The surface-controlled dissolution model provides a quantitative measure for nanoparticle dissolution rates: further studies of dissolution cascades should lead to improved understanding of mechanisms and processes at nanoparticle surfaces.

Electrochemical, Surface-Analytical, and Computational DFT Study of Alkaline Etched Aluminum Modified by Carboxylic Acids for Corrosion Protection and Hydrophobicity

Carboxylic acids were investigated as a means to fabricate a superhydrophobic and corrosion resistant aluminum surface. Alkaline etching produced a hierarchically rough, superhydrophilic and hydroxylated Al surface which could then be modified by immersion in ethanol solution of carboxylic acids of different alkyl chain lengths, from hexanoic to octadecanoic. Acids with chain length longer than seven carbon atoms acted as corrosion inhibitors, but only those with long chains (e.g., octadecanoic acid) acted as a corrosion barrier and made the surface superhydrophobic with water contact angles over 150 degrees. The morphology, topography and chemical composition of unmodified Al and etched Al modified by carboxylic acids were studied using surface analytical tools (scanning electron microscopy with chemical analysis, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry). Modelling based on density functional theory was performed to help explain experimental observations and to provide a rationale of why only carboxylic acids with long enough chains were effective in reducing the rate of corrosion. The reason was attributed to their ability to form more stable and protective organic films. Aluminum surface prepared under appropriate conditions was superhydrophobic, corrosion resistant and durable and showed self-cleaning and delayed ice-melting properties.

Nanotribology of Aqueous Solutions of Monobasic Carboxylic Acids in a Copper Alloy‒Steel Tribological Assembly

The tribological properties of the “copper alloy–carboxylic acid‒steel” system are studied. It is found that the wear-free mode accompanied by an increase in the pH of lubricant solutions, a decrease in the electrical conductivity, and a variation in the friction-surface charge is implemented in the “copper alloy–valeric acid–steel” and “copper alloy–caproic acid–steel” tribosystems. With the help of quantum-chemical calculations via the UB3LYP/Lanl2DZ method, it is demonstrated that the total charge of a metal cluster, the local distribution of electron and spin densities at copper atoms, and the structure of hydrocarbon radicals of carboxylic acids affect the physicochemical properties of the system during the formation of servovite films.

Establishing the patterns in the formation of oxide films on the alloy Ti6Al4V in carbonic acid solutions

This paper reports results of studying the features of the formation of thin interference-colored oxide films on the alloy Ti6Al4V alloy in solutions of carboxylic acids. It has been established that a change in voltage on the cell corresponding to the molding dependence of the alloy depends on the anodic current density. At current densities <0.5 A∙dm –2 , a continuous oxide film is not formed at the alloy surface and the assigned voltage value is not reached. An increase in current density to values higher than 0.5 A∙dm –2 predetermines a linear change in voltage over time with followed by reaching the assigned magnitude U. The maximum film thickness for these conditions is defined by the voltage magnitude and does not depend on the electrolysis mode. Color of the oxide film is defined by the specified value for the molding voltage and does not depend on current density, nature and concentration of carboxylic acid. A match between the molding dependences of oxidation obtained in different electrolytes suggests that the formation of oxide proceeds in line with the same mechanism. The obtained data are explained by the fact that the formation of oxide under the galvanic static mode takes place under conditions of the presence of a constant potential gradient in the oxide film. An increase in the voltage magnitude applied to the cell predetermines a proportional increase in the maximum oxide thickness, since it leads to an increase in the amount of electricity passed through the cell and a corresponding increase in the mass of the oxidized metal. Results of the study into determining the effect of the nature of carboxylic acid on the formation process of an oxide film on the alloy Ti6Al4V using the method of electrochemical oxidation have demonstrated that the nature of the electrolyte does not affect the characteristics of its formation. The obtained data allow us to suggest that the choice of an electrolyte for the development of a technology for electrochemical oxidation of titanium implants should be based on the results of studying the functional properties of the obtained coatings

MECHANICAL PROPERTIES OF SERVOVITE FILMS FORMED IN DURING FRICTION AQUEOUS SOLUTIONS OF CARBOXYLIC ACIDS

Introduction. The effect of the organic component nature in the systematic series of monocarboxylic acids on the tribological characteristics of the brass-steel friction pair in aqueous solutions is described. Dependence of the mechanical-and-physical properties of the antifriction films formed during friction on the nature of the lubricating composition is investigated. The work objectives are to study the applicability of carboxylic acids as an antifriction lubricant component; to assess their effect on the mechanical properties of the servovite film formed under the brass – steel friction.Materials and Methods. Tribological studies of the brass-steel friction pair on the AE-5 end-type friction machine are carried out. Roughness parameters of the servovite film were determined through the optical profilometry. The microgeometry and the object structure at the nanoscale were considered using atomic force microscopy. The mechanical characteristics of the antifriction film were investigated using the instrument nanoindentation.Research Results. Tribological characteristics of the brass-steel tribocoupling and mechanical-and-physical properties of the servovite film formed during friction in the “brass – aqueous solution of carboxylic acid – steel” system were studied. It is established that the friction factor reduces when increasing the hydrocarbon radical length. The dimensional effects are found in the mechanical and tribological properties of the servovite film formed on the surface of the friction interaction in the carboxylic acids.Discussion and Conclusions. The study results show that the friction interaction on the wearing surface in the aqueous solutions of carboxylic acids forms a nanostructured servovite film which drops the friction factor. Its mechanical, physical and tribological parameters depend on the composition of the model lubricating medium. It is determined that the local mechanical-and-physical properties depend on the method of producing the servovite layer, the load and the size of the deformation zone. The results obtained can be used in the development of lubricants.

Differential scanning calorimetry determination of phase diagrams and water activities of aqueous carboxylic acid solutions

We have investigated the solid-liquid equilibria phase diagrams and water activities of the several carboxylic acid/water binary systems using differential scanning calorimetry (DSC) method. These mixtures were formed by water and low molecular weight carboxylic acids (formic acid, acetic acid, propionic acid and butyric acid). Water activities of the investigated solutions were obtained from the freezing point depression data in the range of the ice melting envelope. The experimental results indicated that all the aqueous carboxylic acid systems present a eutectic point in their respective phase diagrams. The activity coefficients of two components in the liquid phase were used to adjust the parameters of the Wilson and NRTL models. For all of the investigated systems, the best correlations of the solid–liquid equilibrium data have been determined by using the NRTL model. Finally, the phase behaviors of the systems were compared to the ideal state and the influence of the chemical structure of the carboxylic acids on the magnitude of the deviation from the ideal state was discussed.