Reactive Extraction of Citric Acid Using Tri-n-octylamine in Nontoxic Natural Diluents: Part 1—Equilibrium Studies from Aqueous Solutions

Use of cheap, nontoxic, and selective solvents could economically provide a solution to the recovery of carboxylic acids produced by the bioroute. In this regard in the present paper, reactive extraction of citric acid was studied. Problems encompassing the recovery of the acid ([H₃A] _aq ^o ?=?0.1?C0.8) was solved by using tertiary amine (tri-n-octylamine, TOA) in natural diluents (rice bran oil, sunflower oil, soybean oil, and sesame oil). TOA was very effective in removal of acid providing distribution coefficient (D) as high as 18.51 (E%?=?95?%), 12.82 (E%?=?93?%), 15.09 (E%?=?94?%), and 16.28 (E%?=?94?%) when used with rice bran oil, sunflower oil, soybean oil, and sesame oil, respectively. Overall extraction constants and association numbers for TOA + rice bran oil, TOA + sunflower oil, TOA + soybean oil, and TOA + sesame oil were evaluated to be 35.48 (mol/l)^?1.46, 29.79 (mol/l)^?1.30, 33.79 (mol/l)^?1.51, and 37.64 (mol/l)^?1.65 and 1.46, 1.30, 1.51, and 1.65, respectively. Specific equilibrium complexation constants (K _E(n/m)) were also predicted using mathematical modeling.     

Inclusion Behavior of α-Cyclodextrin with 2-Methylnaphthalene in Aqueous Solutions

By means of absorption and fluorescence spectroscopy, 2-methylnaphthalene (2MN) was found to be incorporated into the cavity of -cyclodextrin (-CD) to form a 1 : 1 inclusion complex. The 1 : 1 inclusion complex further associated with another -CD molecule, resulting in the formation of a 2 : 1 -CD-2MN inclusion complex. The equilibrium constants for the formation of the 1 : 1 and 2 : 1 inclusion complexes were estimated to be 44.6 and 376 mol-1 dm3, respectively, on the basis of a simulation of the observed 2MN fluorescence intensities. The induced circular dichroism spectra suggested that 2MN, buried within the -CD inclusion complexes, resided in a different orientation relative to the CD symmetry axis, as compared to 2MN within a -CD inclusion complex.     

Extraction of Uranium and Thorium with TBP from Fluoride — Nitric Acid Solutions

The extraction of HNO₃, thorium and uranium were studied in the presence of hydrofluoric acid. The extraction constants of both the acids are shown to be close to one another which results in their mutual displacement from the organic phase. Contrary to uranium, the extraction of thorium is much reduced as the concentration of hydrofluoric acid increases which may be explained by a stronger complexation of Th by fluoride ion in the aqueous phase.     

Determination of Stoichiometric Dissociation Constants of Benzoic Acid in Aqueous Sodium or Potassium Chloride Solutions at 25°C

Equations were determined for the calculation of the stoichiometric (molality scale) dissociation constant K_m of benzoic acid in dilute aqueous NaCl and KCl solutions at 25°C from the thermodynamic dissociation constant K_a of this acid and from the ionic strength I_m of the solution. The salt alone determines mostly the ionic strength of the solutions considered in this study and the equations for K_m were based on the single-ion activity coefficient equations of the Hückel type. The existing literature data obtained by conductance measurements and by electromotive force (EMF) measurements on Harned cells were first used to revise the thermodynamic value of the dissociation constant of benzoic acid. A value of K_a = (6.326 ± 0.005) × 10^-5 was obtained from the most precise conductivity set [Brockman and Kilpatrick] and this value is supported within their precisions by the less precise conductivity set of Dippy and Williams and by the EMF data set measured by Jones and Parton with quinhydrone electrodes. The new data measured by potentiometric titrations in a glass electrode cell were then used for the estimation of the parameters of the Hückel equations of benzoate ions. The resulting parameters were also tested with the existing literature data measured by cells with and without a liquid junction. The Hückel parameters suggested here are close to those determined previously for anions resulting from aromatic and aliphatic carboxylic acids. By means of the calculation method based on the Hückel equations, K_m can be obtained almost within experimental error at least up to I_m of about 0.5 mol-kg_-1 for benzoic acid in NaCl and KCl solutions.     

The Influence of Temperature on the Heat Effects of Acid—Base Interaction in Aqueous Solutions of Citric Acid

The heat effects of interaction of a solution of citric acid with solutions of HNO₃ and KOH at 288.15, 298.15, and 308.15 K and ionic strength values 0.5, 1.0, and 1.5 (KNO₃) were measured calorimetrically. The heat effects of acid dissociation were calculated using the HEAT program. The standard thermodynamic characteristics of step dissociation of citric acid were determined.     

An NMR Study of the Equilibration of d‐Glucaric Acid with Lactone Forms in Aqueous Acid Solutions

The aqueous solution equilibration of d‐glucaric acid with its lactone forms was studied by NMR with and without acid catalysis. The kinetics of the approach to equilibrium were simulated, and approximate equilibrium and rate constants were obtained.     

Thermodynamic Studies of Amino Acid–Denaturant Interactions in Aqueous Solutions at 298.15 K

As proteins and other biomolecules consisting of amino acid residues require external additives for their dissolution and recrystallization, it is important to have information about how such additives interact with amino acids. Therefore we have studied the interactions of simple model amino acids with the additives urea and guanidine hydrochloride in aqueous solutions at 298.15 K, using vapor pressure osmometry. During the measurements, the concentration of urea was fixed as ∼2 mol⋅kg⁻¹ and that of guanidine hydrochloride was fixed as ∼1 mol⋅kg⁻¹ whereas the concentrations of amino acids were varied. The experimental water activity data were processed to get the individual activity coefficients of all the three components in the ternary mixture. Further, the activity coefficients were used to get the excess Gibbs energies of solutions and Gibbs energies for transfer of either amino acids from water to aqueous denaturant solutions or denaturant from water to aqueous amino acid solutions. An application of the McMillan-Mayer theory of solutions through virial expansion of transfer Gibbs energies was made to get pair and triplet interaction parameter whose sign and magnitude yielded information about amino acid–denaturant interactions, relative to their interactions with water. The pair interaction parameters have been further used to obtain salting constants and in turn the thermodynamic equilibrium constant values for the amino acid–denaturant mixing process in aqueous solutions at 298.15 K. The results have been explained in terms of hydrophobic hydration, hydrophobic interactions and amino acid–denaturant binding.     

Raman-Spectroscopic Measurements of the First Dissociation Constant of Aqueous Phosphoric Acid Solution from 5 to 301 °C

Dilute aqueous phosphoric acid solutions have been studied by Raman spectroscopy at room temperature and over a broad temperature range from 5 to 301?°C. R-normalized spectra (Bose?CEinstein correction) have been constructed and used for quantitative analysis. The vibrational modes of H₃PO₄(aq) (pseudo C_3v symmetry) have been assigned. The band with the highest intensity, the symmetric stretch ?? _s{P(OH)₃}(?? ₁(a ₁)) is strongly polarized while ?? ₄(e), the antisymmetric stretch ?? _asP(OH)₃) is depolarized. The stretching mode of the phosphoryl group (?CP=O), ?? ₂(a₁) occurs at 1178?cm^?1 and is polarized. In the range between 300 and 600?cm^?1, the deformation modes are observed. The deformation mode, ??{PO?CH}, involving the O?CH group has been detected at 1250?cm^?1 as a very weak and broad mode. In addition to the modes of phosphoric acid, modes of the dissociation product $\mathrm{H}_{2}\mathrm{PO}_{4}^{ -}(\mathrm{aq})$ have been observed. The mode at 1077?cm^?1 has been assigned to ?? _s{PO₂}, and the mode at 877?cm^?1 to ?? _s{P(OH)₂} which is overlapped by ?? _s{P(OH)₃} of H₃PO₄(aq). The modes of $\mathrm{H}_{2}\mathrm{PO}_{4}^{ -} \mathrm{(aq)}$ have been measured in dilute solution and were assigned and presented as well. H₃PO₄ is hydrated in aqueous solution, which can be verified with Raman spectroscopy by following the modes ?? ₂(a₁) and ?? ₁(a₁) as a function of temperature. These modes show a strong temperature dependency. The mode ?? ₁(a₁) broadens and shifts to lower wavenumbers. The mode ?? ₂(a₁) on the other hand, shifts to higher wavenumbers and broadens considerably with increases in temperature. At 301?°C the phosphoric acid is almost molecular in nature. In very dilute H₃PO₄ solutions at room temperature, however, the dissociation product, $\mathrm{H}_{2}\mathrm{PO}_{4}^{ -} \mathrm{(aq)}$ is the dominant species. In these dilute H₃PO₄(aq) solutions no spectroscopic features could be detected for a hydrogen bonded dimeric species of the formula $\mathrm{H}_{5}\mathrm{P}_{2}\mathrm{O}_{8}^{ -}$ (or the neutral dimeric acid H₆P₂O₈). Pyrophosphate formation, although favored at high temperatures, could not be detected in dilute solution even at 301?°C due to the high water activity. In highly concentrated solutions, however, pyrophosphate formation is observable and in hydrate melts the formation of pyrophosphate is already noticeable at room temperature. Quantitative Raman measurements have been carried out to follow the dissociation of H₃PO₄(aq) over a very broad temperature range. In the temperature interval from 5.0 to 301.0?°C the pK ₁ values for H₃PO₄(aq) have been determined and thermodynamic data have been derived.     

Re-evaluation of Activity Coefficients in Dilute Aqueous Hydrobromic and Hydriodic Acid Solutions at Temperatures from 0 to 60 °C

Simple two-parameter Hückel equations can be used for the calculation of the activity coefficients in aqueous hydrobromic and hydriodic acid solutions at temperatures from 0 to 60 °C and from 0 to 50 °C, respectively, at least up to a molality of 0.5 mol·kg^?1. The data measured by Macaskill and Bates (J. Solution Chem. 12:607–619, 1983) at 25 °C and those measured by Hetzer et al. (J. Phys. Chem. 68:1929–1933, 1964) at various temperatures on galvanic cells without a liquid junction were used in the parameter estimations for the hydrogen bromide (HBr) and hydrogen iodide (HI) solutions, respectively. The latter data consist of sets from 0 to 50 °C at intervals of 5 °C. The parameter values for HBr solutions were also tested using the numerous galvanic cell points from the other three data sets existing in the literature for hydrobromic acid solutions and covering wide range of temperatures from 0 to 60 °C. It was observed in the parameter estimations and tests that all of the estimated parameters are independent of the temperature. The recommended parameter values were additionally tested using the isopiestic data of Macaskill and Bates (see the citation above) and those of Harned and Robinson (Trans. Faraday Soc. 37:302–307, 1941) for dilute HBr and HI solutions at 25 °C, respectively. In more concentrated solutions up to a HBr molality of 4.5 mol·kg^?1 and up to a HI molality of 3.0 mol·kg^?1, an extended Hückel equation was used, which contains an additional quadratic term with respect to the molality. The parameters for the extended Hückel equations were determined from these isopiestic data and tested using these data and the existing galvanic cell data. The activity and osmotic coefficients calculated from the resulting equations are recommended in the present study for the more concentrated solutions. The recommended values are compared to the activity values reported in several previous tabulations.     

Solubility, Acid–Base and Complexation Properties of Calix[4]resorcinarene in Aqueous Solutions of Nonionic Surfactants

Solubility and acid–base properties of calix[4]resorcinarene (H₈L) in aqueous solutions of nonionic surfactants Triton X-100, Triton X-405, and Brij-35, as well as isopropanol were studied by pH-potentiometry. The dependence of the amount of a nonionic surfactant necessary to dissolve H₈L on the length of ethylene oxide chain was found. The dissociation constants of macrocycle for the first four steps are low sensitive to the medium nature (micellar or water–alcohol solutions). Complexation ability of the [H_{8 – n} L] ^n– anions with respect to tetramethyl- and tetraethylammonium, N-methylpyridinium, and [Co(En)₂(C₂O₄)]⁺ cations was studied by pH-potentiometry. A noticeable increase in the selectivity of guest–host binding was found on going from aqueous or water–alcohol to micellar solutions.     

Solvent Effects on Complexation of Molybdenum（Ⅵ） with Nitrilotriacetic Acid in Different Aqueous Solutions of Propanol

By using spectrophotometric and potentiometric techniques the formation constants of the species formed in the systems H^＋＋ Mo（Ⅵ）＋nitrilotriacetic acid and H^＋ ＋ nitrilotriacetic acid have been determined in aqueous solutions of propanol at 25 ℃ and constant ionic strength 0.1 molodm^-3 sodium perchlorate. The composition of the complex was determined by the continuous variation method. It was shown that molybdenum（Ⅵ） forms a mononuclear 1 ： 1 complex with nitrilotriacetic acid of the type MoO3L^-3 at -lg[H^＋] =5.8. The formation constants in various media were analyzed in terms of Kamlet and Taft＇s parameters. Linear relationships were observed when lg Ks was plotted versusp. Finally, the results were discussed in terms of the effect of solvent on complexation.     

Conductivity Studies of Dilute Aqueous Solutions of Oxalic Acid and Neutral Oxalates of Sodium, Potassium, Cesium, and Ammonium from 5 to 35°C

Conductivity measurements of oxalic acid and neutral oxalates (disodium oxalate, dipotassium oxalate, dicesium, and diammonium oxalate) were performed on dilute aqueous solutions, c < 3 × 10^–3 mol-dm^–3, from 5 to 35°C. These data and those available from the literature were analyzed in terms of dissociation steps of oxalic acid, the Onsager conductivity equation for neutral oxalates, the Quint–Viallard conductivity equation for the acid, and the Debye–Hückel equation for activity coefficients, to give the limiting equivalent conductances of bioxalate anion ;(HC₂O₄ ^–) and oxalate anion (1/2C₂O₄ ^2–) and the corresponding dissociation constants K ₁ and K ₂.     

Determination of the Glass Electrode Parameters by Means of Potentiometric Titration of Acetic Acid in Aqueous Sodium or Potassium Chloride Solutions at 25°C

Single-ion activity coefficient equations are presented for the calculation of stoichiometric (molality scale) dissociation constants K _m for acetic acid in aqueous NaCl or KCl solutions at 25°C. These equations are of the Pitzer or Hückel type and apply to the case where the inert electrolyte alone determines the ionic strength of the acetic acid solution considered. K _m for a certain ionic strength can be calculated from the thermodynamic dissociation constant K _a by means of the equations for ionic activity coefficients. The data used in the estimation of the parameters for the activity coefficient equations were taken from the literature. In these data were included results of measurements on galvanic cells without a liquid junction (i.e., on cells of the Harned type). Despite the theoretical difficulties associated with the single-ion activity coefficients, K _m can be calculated for acetic acid in NaCl or KCl solutions by the Pitzer or Hückel method (the two methods give practically identical K _m values) almost within experimental error at least up to ionic strengths of about 1 mol-kg^–1. Potentiometric acetic acid titrations with base solutions (NaOH or KOH) were performed in a glass electrode cell at constant ionic strengths adjusted by NaCl or KCl. These titrations were analyzed by equation E = E _o + k(RT/F) ln[m(H⁺)], where m(H⁺) is the molality of protons, and E is the electromotive force measured. m(H⁺) was calculated for each titration point from the volume of the base solution added by using the stoichiometric dissociation constant K _m obtained by the Pitzer or Hückel method. During each base titration at a constant ionic strength, E _o and k in this equation were observed to be constants and were determined by linear regression analysis. The use of this equation in the analysis of potentiometric glass electrode data represents an improvement when compared to the common methods in use for two reasons. No activity coefficients are needed and problems associated with liquid junction potentials have been eliminated.     

Solubilities, Densities and Refractive Indices of Rubidium Chloride or Cesium Chloride in Ethanol Aqueous Solutions at Different Temperatures

The data of solubilities, densities and refractive indices of rubidium chloride or cesium chloride in the system CEHsOH-H2O were measured by using a simple accurate analytical method at different temperatures, with mass fractions of ethanol in the range of 0 to 1.0. In all cases, the presence of ethanol significantly reduced the solubility of rubidium chloride and cesium chloride in aqueous solution. The solubilities of the saturated solutions were fitted via polynomial equations as a function of the mass fraction of ethanol. The CsC1-C2H5OH-H2O ternary system appeared in two liquid phases： alcoholic phase and water phase, when the mass fractions of ethanol were in the range of 10.37% to 49.59% at 35 ℃. Density and refractive index were also determined for the same ternary systems with varied unsaturated salt concentrations. Values for both experiment and theory were correlated with the salt concentrations and proportions of alcohol in the solutions. The equations proposed could also account for the saturated solutions.     

Chemistry of Solvent Extraction of Nd(NO3)3 and Pr(NO3)3 from Nitrate Solutions with TOMAN–TBP Mixtures in Toluene

Doklady Chemistry - The isomolar series method was used to identify the regions of synergistic extraction of praseodymium and neodymium from low-acid nitrate solutions containing ammonium nitrate...     

Liquid–Liquid Extraction of Sulfuric Acid from Aqueous Sulfate Waste Solution using Alamine 336/Kerosene/TBP Solvent

Generally the metallurgical industries generate huge amounts of harmful environmental wastes, which may be solids, liquids, or gases in their nature. The present study aims to recovery sulfuric acid (227 g/l) from wastes generated during hydrometallurgical digestion of titanium ores with sulfuric acid for TiO₂ production. For this purpose Alamine 336/kerosene solvent was used. Various extraction parameters as Alamine 336 concentration, shaking time, type of diluent, and O/A phase ratio were studied and optimized. Under the optimum conditions, Mc-Cabe Thiele diagram results indicated that, after four extraction stages the acid concentration in aqueous phase was reduced from the initial value of 227 g/l to about 17 g/l. Stripping of the loaded sulfuric acid from the organic phase was done with warm water (60°C). Stripping parameters as water temperature, stripping time, and A/O phase ratio were studied. Under the stripping the loaded acid concentration in organic phase was reduced from 210 to 6 g/l which matched theoretically by McCabe Thiele diagram.     

Color Indicator System for Acid–Base Titration in Aqueous Micellar Solutions of the Cationic Surfactant Tridecylpyridinium Bromide

Acid–base properties of sulfophthalein indicators were studied in aqueous micellar solutions of the cationic surfactant tridecylpyridinium bromide (TDPB). A multiple linear regression was proposed for predicting protolytic properties of the reagents of this series in micellar TDPB solutions. Conditions were found for the titrimetric determination of long-chain aliphatic carboxylic acids with the use of Xylenol Blue for detecting the titration end point.