Kinetics and thermodynamics of the attack of fluorapatite by a mixture of sulfuric and phosphoric acids at 55 °C

A calorimetric study of kinetics and thermodynamics of the attack of a synthetic fluorapatite by a mixture of sulfuric and phosphoric acids is undertaken at 55 °C. The global enthalpy of the attack equals −409.3 kJ/mol. The recorded thermograms show two peaks leading to calcium sulfate hemihydrate and dihydrate, respectively. The deconvoluted curves were analysed iteratively. A kinetic mechanism based on simultaneous reactions has been proposed for the first peak and confirmed thermochemically by comparing the enthalpies deduced from iteration and that determined from experimental and calculated routes. The second peak of the thermogram was attributed to transformation of calcium sulfate hemihydrate into gypsum according to a dissolution/precipitation scheme. These phenomena are of order one and two, respectively.     

The dissociation of phosphoric acid in NaCl and NaMgCl solutions at 25°C

The pK ₁ ^* , pK ₁ ^* and pK ₃ ^* for the dissociation of H₃PO₄ have been measured in NaCl solutions from 0.5 to 6m at 25°C. The results have been used to evaluate Pitzer interaction parameters (NaClH₂PO₄)=–0.028±0.005, (NaH₃PO₄)=–0.075±0.025, (HPO₄Cl)=0.105±0.009, (PO₄Cl)=–0.59±0.02 and (NaClHPO₄)=–0.003±0.004, (PO₄NaClH)=0.110±0.008. These parameters yield values of pK ₁ ^* , pK ₂ ^* and pK ₃ ^* in NaCl that agree with the measured values with average deviations of ±0.04, ±0.03 and ±0.05 in pK ₁ ^* . Measurements of pK ₁ ^* and pK ₂ ^* were also made in NaMgCl solutions. These results have been used to evaluate ^(O)(MgH ₂ PO ₄)=–3.55±0.07,⁽¹⁾(MgH ₂ PO ₄=–16.9±0.03, ^(O)(MgH ₂ PO ₄=–17.5±0.03 and ⁽¹⁾(MgH ₂ PO ₄)=27.4±0.8 at 25°C. The results for pK ₂ ^* in NaMg–Cl solutions were also used to calculate log K _MX ^* =3.2±0.1 for the formation of the ion pair MgHPO ₄ ^o .     

Kinetics of the liquid phase esterification of acrylic acid withn-octanol and 2-ethylhexanol catalyzed by sulfuric acid

Kinetics of the liquid phase esterification of acrylic acid withn-octanol and 2-ethylhexanol catalyzed by sulfuric acid has been studied in an isothermal semibatch reactor. The reaction appears to be second order. The kinetic parameters have been determined.     

Experimental and correlational study of phase equilibria in aqueous mixtures of phosphoric acid with aromatic hydrocarbons at various temperatures

Experimental solubility and tie-line data were obtained for (water + phosphoric acid + ethyl benzene or cumene) ternary systems at T = (298.15, 308.15 and 318.15) K and P = 101.32 kPa. The experimental tie-line values were correlated using the thermodynamic models of UNIQUAC and NRTL. The quality of the experimental results was determined through the Othmer–Tobias and Hand plots. Distribution coefficients and separation factors were evaluated over the immiscibility regions. The influence of temperature on biphasic region is found to be negligible.     

Kinetics of levulinic acid formation from carbohydrates at moderate temperatures

The kinetic curves of levulinic acid accumulation in the process of saccharide dehydration at 80-98^oC are compared. The structural features of the substrates and 5-hydroxymethylfurfural, which is the intermediate of the process, explain the observed difference in the rates of fructose and glucose conversion. Sulfuric acid can be effectively used under moderate conditions to synthesize levulinic acid with yields exceeding 35 mol % for glucose and 50% for sucrose at 98^oC.     

2MgO．2B2O3．MgCl2．14H2O在60℃水中的溶解 及相转化动力学研究

用动力学方法研究了2MgO     

Vibrational spectral studies of solutions at elevated temperatures and pressures. IX. Acetic acid

Raman spectra of glacial acetic acid from 350 to 3700 cm^–1 have been measured at temperatures up to 275°C and at a pressure of 9 MPa. Raman spectra of aqueous solutions of acetic acid from 3.9 to 16 molar have been measured up to 200°C at a pressure of 7 MPa. The spectral region 800 to 1850 cm^–1 for both glacial acetic acid and its aqueous solutions have been studied in detail since this region is significantly affected by variations in temperature and concentration. An interpretation of the bands in this spectral region was made with the aid of factor analysis, difference spectroscopy, band resolution techniques and the existing extensive literature. The results suggest that the major equilibrium in glacial acetic acid is between cyclic and linear dimers; however, in aqueous solutions in the concentration range studied, mono- and di-hydrated dimers and cyclic dimers are the predominant species.     

Kinetics and thermodynamics of the blocking reaction of several aliphatic isocyanates

The oxime-blocking reaction of several aliphatic isocyanates, such as 1,6-Hexane diisocyanate (HDI), isophorone diisocyanate (IPDI), and dicyclohexylmethane-4,4′-diisocyanate (H₁₂MDI), is investigated. The reaction is carried on in various solvents that are divided into two categories: aromatic solvents and oxygen-contained solvents. In situ FT-IR is used to monitor the reaction and show the large difference of solvent and the structure of isocyanate. Kinetic studies indicate that the reaction rate appears faster in aromatic solvents although the polarity of aromatic solvents is lower. Then, thermodynamic parameters of the blocking reaction, such as activation energy (E_a), enthalpy (ΔH*) and entropy (ΔS*), are determined from the Arrhenius and Eyring equations. It is found that activation energy in aromatic solvents is higher, but the reaction rate is much faster, all of which are discussed corresponding to the reaction mechanism.     

Determination of phosphate in hydroponic nutrient solutions using flow injection potentiometry and a cobalt-wire phosphate ion-selective electrode

The direct flow injection potentiometric (FIP) analysis of phosphate in hydroponic nutrient solution has been carried out using a cobalt-wire ion-selective electrode (ISE). Synthetic hydroponic nutrient solution, commercial hydroponic nutrient solution and working hydroponic farm nutrient solution were analysed for phosphate using the FIP technique. It is shown that FIP results compare favourably to standard methods of analysis such as spectrophotometry and indirect photometric ion-pair chromatography. Reproducible FIP response curves with a slope of −(47.57±0.03) mV per decade and intercept of −(169.7±0.1) mV were obtained for four separate calibrations in the concentration range 5.0×10⁻⁴–1.0×10⁻² M H₂PO₄⁻. Anion corrections for interferences by Cl⁻, NO₃⁻ and SO₄²⁻ were applied to all samples using the selectivity coefficients determined independently using a fixed interference method. Nevertheless, it was found that anion corrections were not necessary, as the deviations fell within the bounds of experimental error for the cobalt-wire ISE technique (i.e.±2–5% R.S.D.). The proposed FIP method enables the direct determination of phosphate in hydroponic nutrient solutions.     

Kinetics and thermodynamics of the sorption of uranium and thorium ions from nitric acid solutions onto a TBP-impregnated sorbent

Summary Kinetics and equilibrium studies on the sorption of uranium and thorium ions were carried out from nitric acid solutions by tri-n-butyl phosphate (TBP) loaded supported sorbent, commercially known as Egy-Sorb, using batch technique. Analysis of the rate data in accordance with three kinetic models revealed that the particle diffusion process was the rate determining mechanism and the sorption process of the metal ions onto impregnated sorbent follows first order reversible kinetics. The values of the first order rate constants, the rate constants of intraparticle transport, and the particle diffusion coefficients for the uranium and thorium ions were determined from the graphical representation of the proposed models. Experimental isotherms of both ions were successfully fit to Langmuir and Freundlich isotherm models over the entire concentration range studied. The effect of temperature on the equilibrium distribution values has been utilized to evaluate the changes in standard thermodynamic quantities.     

Viscosities and thermodynamics of viscous flow of some binary mixtures at different temperatures

Viscosities of three non-electrolyte binary mixtures have been determined at different temperatures over the complete concentration range. Excess molar viscosities and excess molar energies of activation for viscous flow for n-butylamine + dichloromethane, n-butylamine + chloroform and n-butylamine + carbon tetrachloride systems at 20°C, 25°C, 30°C and 35°C were calculated. Thermodynamic effect parameters of activation were also calculated. The predictive abilities of some equations for viscosities of mixtures were examined.Presented at the XV Jornadas sobre Investigación en Ciencias de la Ingeneriía Química y Química Aplicada, Neuquén, 1989, R. Argentina.     

Effect of dipotassium hydrogen phosphate on thermodynamic properties of glycine and l-alanine in aqueous solutions at different temperatures

Densities, ρ, speed of sound, u for glycine, l-alanine have been measured in aqueous solutions of dipotassium hydrogen phosphate (DKHP) ranging from 0.2, 0.4, 0.6 and 0.8 mol·kg⁻¹ at temperatures T = (288.15, 298.15, 308.15 and 318.15) K. The different parameters such as apparent molar volume, limiting apparent molar volume, transfer volume, partial molar expansibility have been derived from density data. Experimental speeds of sound data were used to estimate apparent molar adiabatic compressibility, limiting apparent molar adiabatic compressibility, transfer parameter and hydration number. These parameters have been discussed in the light of ion-ion and ion-solvent interactions.     

Viscosity of aqueous calcium chloride solutions at high temperatures and high pressures

Viscosity of six (0.10, 0.33, 0.65, 0.97, 1.40, and 2.00) mol kg⁻¹ binary aqueous CaCl₂ solutions has been measured with a capillary-flow technique. Measurements were made at pressures up to 60 MPa. The range of temperature was from 293 to 575 K. The total uncertainty of viscosity, pressure, temperature, and composition measurements was estimated to be less than 1.6%, 0.05%, 15 mK, and 0.014%, respectively. The effect of temperature, pressure, and concentration on viscosity of binary aqueous CaCl₂ solutions was studied. The measured values of viscosity of CaCl₂(aq) were compared with data, predictions, and correlations reported in the literature. The temperature and pressure coefficients of viscosity of CaCl₂(aq) were studied as a function of concentration and temperature. The viscosity data have been interpreted in terms of the extended Jones–Dole equation for the relative viscosity (η/η₀) to accurate calculate the values of viscosity A- and B-coefficients as a function of temperature. The derived values of the viscosity B-coefficients were compared with the values calculated from the ionic B-coefficient data. The physical meaning parameters V and E in the absolute rate theory of viscosity and hydrodynamic molar volume (effective rigid molar volume of salt) V_k were calculated using present experimental viscosity data. TTG model has been used to compare predicted values of the viscosity of CaCl₂(aq) solutions with experimental values at high pressures.     

Conductivity,apparent molar volume and isentropic compressibility of 12-tungstosilicic acid and potassium 12-tungstosilicate in aqueous solutions at different temperatures

12-Tungstosilicic acid and potassium 12-tungstosilicate were synthesized and conductivities, densities and ultrasound velocities of their aqueous solutions were studied in the 283.15–303.15 K temperature range at 5 K intervals. Apparent molar volume and apparent molar isentropic compressibility of 12-tungstosilicic acid and potassium 12-tungstosilicate and isentropic compressibility of the studied aqueous solutions have been determined from the experimental density and sound velocity data.     

Absence of phosphate hydrolysis in the nucleotide substitution reaction on cis-[Co(H2O)2(cyclen)] at physiological pH: Importance of hydrogen-bonding and conjugate base-catalysis

The use of classical Werner-type cis-[Co(Cl)₂(tetraamine)]⁺ (tetraamine = cyclen or tren) complexes for their complexation study of biologically relevant ligands has been pursued. These chlorocomplexes are found to be in the chloroaqua/chlorohydroxo forms under the physiological conditions used, their chloride substitution reactivity being dominated by conjugate base pathways, specially when tetraamine = cyclen. Further studies with nucleotides indicate that the substitution processes on cis-[Co(H₂O)₂(tetraamine)]³⁺, up to neutral pH, correspond to a simple reaction producing final stable phosphato bound mononucleotide complexes. These complexes are found to be an equilibrium mixture between monodentate O-phosphato and chelate O-phosphato-N-nucleotide forms. No evidence has been found for hydrolytic cleavage of the phosphato-nucleoside bond, as found in other systems with activated phosphates or higher pH values. A full kinetic profile of the process is proposed for the systems in the 2–7 pH range which is the same for chloride, nucleoside and nucleotide substitutions. The results are indicative of an important degree of outer-sphere hydrogen bonding between the cobaltocomplex and the entering biologically relevant ligands, as expected for these processes.     

Kinetics of the esterification of benzoic acid with n-octyl alcohol or isooctyl (2-ethylhexyl) alcohol using sulfuric acid catalyst

The esterificaion of benzoic acid has been studied in an experimental, isothermal, semi-batch reactor using sulfuric acid catalyst. The reaction appears to be the first order with respect to benzoic acid and does not depend on the concentration of octyl alcohol. The kinetic parameters are given. This revised version was published online in August 2006 with corrections to the Cover Date.     

Solubility and physic-chemical properties of NaH2PO4 in phosphoric acid,sodium chloride and their mixture solutions at T = (298.15 and 313.15) K

In this study, solubility and physic-chemical properties of sodium dihydrogen phosphate in sodium chloride, phosphoric acid and their mixture solutions at T = (298.15 and 313.15) K have been investigated by using isothermal dissolution method. In the three systems, the solubility of NaH₂PO₄ always increases with the temperature increasing and decreases with molar concentration of phosphoric acid (sodium chloride) increasing because of the same ion effect. Solubility data of sodium dihydrogen phosphate in the mixed solution of sodium chloride and phosphoric acid is basically required for designing and optimizing the solvent extraction process in the industrial production.     

Effect of sodium phosphate salts on the thermodynamic properties of aqueous solutions of poly(ethylene oxide) 6000 at different temperatures

Precise density, sound velocity, water activity, and phase diagram measurements have been carried out on polyethylene oxide (PEO) in aqueous solutions of sodium di-hydrogen phosphate, di-sodium hydrogen phosphate, and tri-sodium phosphate over a range of temperatures at atmospheric pressure. The experimental density and sound velocity data are used to calculate the apparent specific volume and isentropic compressibility as a function of temperature and concentration. It was found that both of the apparent specific volume and isentropic compressibility of PEO in aqueous solutions increase by increasing temperature and charge on the anion of electrolytes. The results show that the slope of constant water activity lines increased with increasing the temperature and charge on the anion of electrolytes and the vapour pressure depression for an aqueous (PEO + sodium phosphate) system is more than the sum of those for the corresponding binary solutions. Furthermore, the effect of temperature and type of anion of salt on the salting-out effect of polyethylene oxide by sodium phosphate salts has been studied.     

Solubility and phase behavior of nickel oxide in aqueous sodium phosphate solutions at elevated temperatures

A platinum-lined, flowing autoclave facility was used to investigate the solubility/phase behavior of nickel oxide (NiO) in aqueous sodium phosphate solutions between 290 and 560 K. A layer of hydrous nickel oxide was concluded to exist on the nickel oxide surface below 468 K; only at higher temperatures did the anhydrous nickel oxide phase control the nickel ion solubility behavior. The measured solubility behavior was examined via a nickel(II) ion hydrolysis/complexing model and thermodynamic functions for the hydrolysis/complexing reaction equilibria were obtained from a least-squares analysis of the data. The existence of two new nickel ion complexes are reported for the first time: Ni(OH)₂(HPO₄)⁼ and Ni(OH)₃(H₂PO₄)⁼. The positive entropy change associated with the formation of Ni(OH)₃(H₂PO₄)⁼ leads to its dominance in alkaline phosphate solutions at elevated temperatures.