Electric conductivities of 1:1 electrolytes in liquid methanol along the liquid-vapor coexistence curve up to the critical temperature. II. KBr and KI solutions

The molar conductivities Lambda of KBr and KI in dilute methanol solutions were measured along the liquid-vapor coexistence curve up to the critical temperature (240 degrees C). The concentration dependence of Lambda in each condition was analyzed by the Fuoss-Chen-Justice equation to obtain the limiting molar conductivities and the molar association constants. Using the present data together with the literature ones, the validity of the Hubbard-Onsager (HO) dielectric friction theory based on the sphere-in-continuum model was examined for the translational friction coefficients zeta of the halide ions (the Cl(-), Br(-), and I(-) ions) in methanol in the density range of 2.989rho(c)> or =rho> or =1.506rho(c), where rho(c)=0.2756 g cm(-3) is the critical density of methanol. For all the halide ions studied, the friction coefficient decreased with decreasing density at rho>2.0rho(c), while the nonviscous contribution Deltazeta/zeta increased; Deltazeta was defined as the difference between zeta and the friction coefficient estimated by the Stokes law. The density dependence of zeta and Deltazeta/zeta were well reproduced by the HO theory at rho>2.0rho(c). The HO theory also explained the ion-size dependence of Deltazeta/zeta which decreased with ion-size at rho>2.0rho(c). At rho<2.0rho(c), on the other hand, the HO theory could not explain the density and the ion-size dependences of zeta and Deltazeta/zeta. These results indicated that the application limit of the HO theory lied about rho=2.0rho(c) which is the same as the application limit observed for the alkali metal ions. The present results were also compared with the results in subcritical aqueous solutions.     

Electric conductivities of 1:1 electrolytes in liquid methanol along the liquid-vapor coexistence curve up to the critical temperature. III. Tetraalkylammonium bromides

The molar conductivities of the dilute solutions of the tetraalkylammonium bromides have been measured in methanol along the liquid-vapor coexistence curve up to about 180 degrees C. The limiting molar conductivities and the molar association constants have been obtained from the analysis of the concentration dependence of the conductivity. On the basis of the present data together with the literature ones, the validity of the Hubbard-Onsager (HO) dielectric friction theory [J. Hubbard, J. Chem. Phys. 68, 1649 (1978)] derived from the continuum model has been examined for the translational friction coefficients of the tetraalkylammonium ions in methanol in the density range of 0.8232 g cm(-3) > or =rho > or =0.5984 g cm(-3) and the temperature range of -15 degrees C < or =t < or =180 degrees C. At high densities and low temperatures, the observed friction coefficients of Me(4)N(+) and Et(4)N(+) are remarkably smaller than the prediction of the HO theory (where Me stands for methyl group and Et for ethyl group); this kind of limitation of the HO theory has not been recognized for smaller ions, and can be attributed to the loosening of the solvent structure closely related to the weak charge effect for the large ions. The negative deviation from the HO theory gradually disappears with decreasing density and increasing temperature, and the friction coefficients of Me(4)N(+) and Et(4)N(+) are explained by the HO theory reasonably well at low densities and high temperatures. For Pr(4)N(+) and Bu(4)N(+) (where Pr stands for propyl group and Bu for butyl group), the experimental friction coefficients lay in the validity range of the HO theory in all the conditions studied here; the breakdown of the continuum theory at low densities and high temperatures has not been observed in this work. The density dependences of the molar association constants of the tetraalkylammonium bromides are qualitatively explained by the Fuoss theory based on the continuum model.     

Electric conductivities of 1:1 electrolytes in high-temperature ethanol along the liquid-vapor coexistence curve. II. Tetraalkylammonium bromides

The molar electrolyte conductivities of dilute solutions of the tetramethyl, tetraethyl, tetra-n-propyl, and tetra-n-butylammonium bromides were measured in ethanol along the liquid-vapor coexistence curve up to 160 °C. The limiting molar electrolyte conductivities and the molar association constants were obtained from the analysis of the concentration dependence of the conductivity. The ionic friction coefficients were estimated from the electrolyte conductivities. On the basis of the present data together with the literature ones at higher densities (lower temperatures) and comparisons with the continuum dielectric friction theory, the density (temperature) dependence of the translational friction coefficients of the tetraalkylammonium ions were discussed in the range of 0.810 ≥ ρ ≥ 0.634 g cm(-3) (-5 °C ≤ t ≤ 160 °C). The dielectric friction effect was important for the tetramethylammonium ion in the whole range studied. The tetraethylammonium ion showed a relatively small friction coefficient in ambient condition indicating the structure-loosening effect around the ion, while the dielectric friction effect became more important as the density reduces and the temperature raises. For the tetra-n-butylammonium ion, the friction coefficients were determined mainly by the bulky size effect. The tetra-n-propylammonium ion showed an intermediate tendency between the tetraethylammonium and tetra-n-butylammonium ions.     

Thermophysical properties of binary mixtures of {ionic liquid 2-hydroxy ethylammonium acetate + (water,methanol, or ethanol)}

In this work, density and speed of sound data of binary mixtures of an ionic liquid consisting of {2-hydroxy ethylammonium acetate (2-HEAA) + (water, methanol, or ethanol)} have been measured throughout the entire concentration range, from the temperature of (288.15 to 323.15) K at atmospheric pressure. The excess molar volumes, variations of the isentropic compressibility, the apparent molar volume, isentropic apparent molar compressibility, and thermal expansion coefficient were calculated from the experimental data. The excess molar volumes were negative throughout the whole composition range. Compressibility data in combination with low angle X-ray scattering and NMR measurements proved that the presence of micelles formed due to ion pair interaction above a critical concentration of the ionic liquid in the mixtures. The Peng–Robinson equation of state coupled with the Wong–Sandler mixing rule and COSMO–SAC model was used to predict densities and the calculated deviations were lower than 3%, for binary mixtures in all composition range.     

Streaming current, permeability, and microelectrophoresis of polystyrene latices in methanol-ethanol mixtures

The influence of the solvent (methanol-ethanol mixtures) on the electrokinetic behavior of polystyrene latices with sulfate groups was studied (methanol content was increased by 0.2 at a constant KBr concentration of 1 mM). Viscosity, density, and dielectric constant (eta, rho, and epsilon) were determined at experimental conditions. Two latices (with different surface charge densities and sizes) were used. Electrophoresis measurements were used for dilute dispersions. Streaming current and hydrodynamic permeability were measured for porous plugs. Linear trends in the electrokinetic measurements were observed in the whole molar fraction range. The experimental data obtained from different techniques allow determining the zeta potential according to a well-established classical relationship. The results obtained were analyzed on the basis of the solvent mixture properties and the electrical interface behavior. In addition, permeability data provided valuable information to interpret effects at the solid-liquid interface of the porous plug.     

Application of the PFV EoS correlation to excess molar volumes of (1-ethyl-3-methylimidazolium ethylsulfate + alkanols) at different temperatures

The experimental densities for the binary systems of an ionic liquid and an alkanol {1-ethyl-3-methylimidazolium ethylsulfate [EMIM]⁺ [EtSO₄]^? + methanol or 1-propanol or 2-propanol} were determined at T = (298.15, 303.15, and 313.15) K. The excess molar volumes for the above systems were then calculated from the experimental density values for each temperature. The Redlich–Kister smoothing polynomial was used to fit the experimental results and the partial molar volumes were determined from the Redlich–Kister coefficients. For all the systems studied, the excess molar volume results were negative over the entire composition range for all the temperatures. The excess molar volumes were correlated with the pentic four parameter virial (PFV) equation of state (EoS) model.     

质子型离子液体N,N-二甲基乙醇胺丙酸盐的密度、粘度及电导率

在283.15-333.15 K温度范围内, 测量了质子型离子液体N,N-二甲基乙醇胺丙酸盐(DMEOAP)的密度、粘度及电导率. 讨论了温度对密度、粘度和电导率等物理化学参数的影响. 通过经验和半经验方程得到了该离子液体的热膨胀系数、分子体积、标准摩尔熵及晶格能等热力学性质参数. 由电导率和密度计算出了该离子液体的摩尔电导率. 利用Vogel-Fulcher-Tamman (VFT)方程, 将测量的动力粘度和电导率对温度拟合, 得到了动力粘度和电导率随温度变化方程式.并通过Walden规则, 建立了粘度与摩尔电导率之间的联系.     

Molecular solvation in water-methanol and water-sorbitol mixtures: the roles of preferential hydration, hydrophobicity, and the equation of state

Molecular dynamics simulations of aqueous mixtures of methanol and sorbitol were performed over a wide range of binary composition, density (pressure), and temperature to study the equation of state and solvation of small apolar solutes. Experimentally, methanol is a canonical solubilizing agent for apolar solutes and a protein denaturant in mixed-aqueous solvents; sorbitol represents a canonical "salting-out" or protein-stabilizing cosolvent. The results reported here show increasing sorbitol concentration under isothermal, isobaric conditions results in monotonic increases in apolar solute excess chemical potential (mu2ex) over the range of experimentally relevant temperatures. For methanol at elevated temperatures, increasing cosolvent composition results in monotonically decreasing mu2ex. However, at lower temperatures mu2ex exhibits a maximum versus cosolvent concentration, as seen experimentally for Ar in ethanol-water solutions. Both density anomalies and hydrophobic effects--characterized by temperatures of density maxima and apolar solute solubility minima, respectively--are suppressed upon addition of either sorbitol or methanol at all temperatures and compositions simulated here. Thus, the contrasting effects of sorbitol and methanol on solute chemical potential cannot be explained by qualitative differences in their ability to enhance or suppress hydrophobic effects. Rather, we find mu2ex values across a broad range of temperatures and cosolvent composition can be quantitatively explained in terms of isobaric changes in solvent density--i.e., the equation of state--along with the corresponding packing fraction of the solvent. Analysis in terms of truncated preferential interaction parameters highlights that care must be taken in interpreting cosolvent effects on solvation in terms of local preferential hydration.     

Volumetric Properties of Difurylmethane in Methanol from 288.15 to 308.15 K

The densities of binary systems of difurylmethane (DFM) in methanol have been measured with an Anton Parr DMA 4500 vibrating-tube densimeter over the entire composition range at intervals of 5 K in the temperature range between 288.15 and 308.15 K. Excess molar volumes of the mixture, apparent molar volumes of DFM, and excess partial molar volumes of both components have been calculated to provide insight into the intermolecular interaction present in the mixtures investigated. Excess molar volumes have been fitted to a Redlich–Kister equation and they exhibited negative deviations from ideal behavior. Both the apparent molar volume of DFM and excess partial molar volumes of DFM and methanol exhibit a dependence on composition but are less sensitive to temperature.     

Electrical conductances of aqueous sodium trifluoromethanesulfonate from 0 to 450°C and pressures to 250 MPa

The electrical conductances of dilute (0.001 to 0.1 mol-kg^?1) aqueous sodium trifluoromethanesulfonate (NaCF₃SO₃) solutions have been measured from 0 to 450°C and pressures to 250 MPa. The limiting molar conductance $\Lambda _0 $ increases with increasing temperature from 0 to 300°C and decreasing density from 0.8 to 0.3 g-cm^?3. Above 300°C, $\Lambda _0 $ is nearly temperature independent, but increases linearly with decreasing density. The logarithm of the molal association constant of NaCF₃SO₃ calculated at temperatures from 372 to 450°C is represented as a function of temperature (Kelvin) and density of water (g-cm^?3) by $$\log K_m = 0.888 - 330.4/T - (12.83 - 5349/T)\log \rho _w $$ The relative strengths of NaCF₃SO₃ and NaCl are similar within the accuracy of the current measurements over the limited range of temperature and pressure that could be investigated here.     

一氧化碳、氢、甲醇和正乙烷体系的分子模拟

钟炳等将超临界流体引入固定床反应器进行催化分离一体化合成甲醇的研究,取得了良好的效果［１］．对于一氧化碳加氢合成甲醇这一体系,文献报导的相平衡实验数据十分缺乏,ＤｅＬｏｏｓ［２］和Ｚａｗｉｓｚａ［３］仅对甲醇和正己烷二元体系的相行为进行了研究．对于合...     

Reaction parameters influence on the catalytic performance of copper-silica aerogel in the methanol steam reforming

Steam reforming of methanol was carried out on the copper-silica aerogel catalyst.The effects of reaction temperature,feed rate,water to methanol molar ratio and carrier gas flowrate on the H_2 production rate and CO selectivity were investigated.M ethanol conversion was increased considerably in the range of about 240-300,after which it increased at a slightly lower rate.The used feed flowrate,steam to methanol molar ratio and carrier gas flowwere 1.2-9.0 m L/h,1.2-5.0 and 20-80 m L/min,respectively.Reducing the feed flowrate increased the H_2 production rate.It was found that an increase in the water to methanol ratio and decreasing the carrier gas flowrate slightly increases the H2production rate.Increasing the water to methanol ratio causes the lowest temperature in which CO formation was observed to rise,so that for the ratio of 5.0 no CO formation was detected in temperatures lower than 375℃.In all conditions,by approaching the complete conversion,increasing the main product concentration,increasing the temperature and contact time,and decreasing the steam to methanol ratio,the CO selectivity was increased.These results suggested that CO was formed as a secondary product through reverse water-gas shift reaction and did not participate in the methanol steam reforming reaction mechanism.     

Volume Characteristics of Lithium Salts in Alcohols

The densities of lithium chloride and nitrate in aliphatic alcohols (methanol, ethanol, 1- and 2-propanol, 1- and 2-butanol, and 1- and 2-pentanol) at 298.15 K in the salt concentration range from 0 to 3.5 mol kg^{- 1} were measured by means of vibrational densimeter. The resulting density data were used to calculate the apparent and partial molar volumes of the solvents and solutes.     

Reversed-Phase Separation of the Major Deoxyribonucleosides and Their Mononucleotides Using Tetrabutylammontum Hetaerons

Abstract

Simultaneous separation of the four major deoxyribonucleosides and their monophosphate nucleotides was achieved using tetrabutyl ammonium phosphate hetaerons with a reversed-phase (C8) packing material. Baseline resolution for all eight solutes was achieved within 48 minutes, using a 7.5% methanol mobile phase, 2.0 mM in TBA, buffered with 50 mM phosphate at pH 4.8. The effect of methanol and TBA concentrations upon the retention of neutral and anionic solutes was studied in detail. It was determined that changes in solute k' with increasing methanol could be explained by essentially independent phenomena. These are: 1) a decrease in the partition coefficient of the TBA cation with increasing organic concentration, resulting in lower surface charge densities, and 2) a decrease in the hydrophobic interactions of the solutes with the reversed-phase HPLC. The overall effect was a log-linear decrease in k' with increasing methanol concentration. An empirical equation was derived for the above model which was found to be helpful in determining the optimal separation conditions for the nucleosides and nucleotides.     

Site-site memory equation approach in study of density/pressure dependence of translational diffusion coefficient and rotational relaxation time of polar molecular solutions: acetonitrile in water, methanol in water, and methanol in acetonitrile

We present results of the theoretical study and numerical calculation of the dynamics of molecular liquids based on the combination of the memory equation formalism and the reference interaction site model (RISM). Memory equations for the site-site intermediate scattering functions are studied in the mode-coupling approximation for the first-order memory kernels, while equilibrium properties such as site-site static structure factors are deduced from RISM. The results include the temperature-density (pressure) dependence of translational diffusion coefficients D and orientational relaxation times tau for acetonitrile in water, methanol in water, and methanol in acetonitrile--all in the limit of infinite dilution. Calculations are performed over the range of temperatures and densities employing the extended simple point charge model for water and optimized site-site potentials for acetonitrile and methanol. The theory is able to reproduce qualitatively all main features of temperature and density dependences of D and tau observed in real and computer experiments. In particular, anomalous behavior, i.e, the increase in mobility with density, is observed for D and tau of methanol in water, while acetonitrile in water and methanol in acetonitrile do not show deviations from the ordinary behavior. The variety exhibited by the different solute-solvent systems in the density dependence of the mobility is interpreted in terms of the two competing origins of friction, which interplay with each other as density increases: the collisional and dielectric frictions which, respectively, increase and decrease with increasing density.     

Refractive Index and Density Measurements for Selected Binary Protic‐Protic,Aprotic‐Aprotic,and Aprotic‐Protic Systems at Temperatures from 298.15 K to 308.15 K

The refractive indices (n) and the densities (ρ) of: (1) protic‐protic solvent mixtures (methanol‐ethanol, methanol‐porpanol, methanol‐butanol and ethanol‐water), (2) aprotic‐aprotic solvent mixtures (acetonitrile‐dimethylformamide, acetonitrile‐dimethylsulphoxide, and acetonitrile‐1,4‐dioxane) and (3) aprotic‐protic solvent mixtures (dimethylformamide, acetonitrile with water and some aliphatic alcohols) were measured experimentally at different temperatures (25, 30 and 35 °C). From the values of the measured refractive indices and densities, the excess refractive indices (n^E), molar refractions (R), atomic polarization (P_A), molar volumes (V), solvated radii (r) and polarizabilities (α) of the mixed solvents were calculated. The results show that the solvent‐solvent interaction reaches maximum value at a definite mole fraction (x) of each solvent depending on its nature. Also, the excess refractive indices, densities and atomic polarizations are found to decrease as the temperature increases. On the other hand, the molar volumes, solvated radii, molar refractions and polarizabilities are found to increase as the temperature increases.     

Temperature dependence of the HO2 + ClO reaction. 2. Reaction kinetics using the discharge-flow resonance-fluorescence technique

The total rate coefficient, k3, for the reaction HO2 + ClO --> products has been determined over the temperature range of 220-336 K at a total pressure of approximately 1.5 Torr of helium using the discharge-flow resonance-fluorescence technique. Pseudo-first-order conditions were used with both ClO and HO2 as excess reagents using four different combinations of precursor molecules. HO2 molecules were formed by using either the termolecular association of H atoms in an excess of O2 or via the reaction of F atoms with an excess of H(2)O(2). ClO molecules were formed by using the reaction of Cl atoms with an excess of O3 or via the reaction of Cl atoms with Cl(2)O. Neither HO2 nor ClO were directly observed during the course of the experiments, but these species were converted to OH or Cl radicals, respectively, via reaction with NO prior to their observation. OH fluorescence was observed at 308 nm, whereas Cl fluorescence was observed at approximately 138 nm. Numerical simulations show that under the experimental conditions used secondary reactions did not interfere with the measurements; however, some HO2 was lost on conversion to OH for experiments in excess HO2. These results were corrected to compensate for the simulated loss. At 296 K, the rate coefficient was determined to be (6.4 +/- 1.6) x 10(-12) cm3 molecule(-1) s(-1). The temperature dependence expressed in Arrhenius form is (1.75 +/- 0.52) x 10-12 exp[(368 +/- 78)/T] cm3 molecule(-1) s(-1). The Arrhenius expression is derived from a fit weighted by the reciprocal of the measurement errors of the individual data points. The uncertainties are cited at the level of two standard deviations and contain contributions from statistical errors from the data analysis in addition to estimates of the systematic experimental errors and possible errors from the applied model correction.     

Reaction of HO with glycolaldehyde, HOCH2CHO: rate coefficients (240-362 K) and mechanism

Absolute rate coefficients for the title reaction, HO+HOCH2CHO-->products (R1), were measured over the temperature range 240-362 K using the technique of pulsed laser photolytic generation of the HO radical coupled to detection by pulsed laser induced fluorescence. Within experimental error, the rate coefficient, k1, is independent of temperature over the range covered and is given by k1(240-362 K)=(8.0+/-0.8)x10(-12) cm3 molecule-1 s-1. The effects of the hydroxy substituent and hydrogen bonding on the rate coefficient are discussed based on theoretical calculations. The present results, which extend the database on the title reaction to a range of temperatures, indicate that R1 is the dominant loss process for HOCH2CHO throughout the troposphere. As part of this work, the absorption cross-section of HOCH2CHO at 184.9 nm was determined to be (3.85+/-0.2)x10(-18) cm2 molecule-1, and the quantum yield of HO formation from the photolysis of HOCH2CHO at 248 nm was found to be (7.0+/-1.5)x10(-2).     

Ion association of dilute aqueous sodium hydroxide solutions to 600°C and 300 MPa by conductance measurements

The limiting molar conductances Λ₀ and ion association constants of dilute aqueous NaOH solutions (<0.01 mol-kg^?1) were determined by electrical conductance measurements at temperatures from 100 to 600°C and pressures up to 300 MPa. The limiting molar conductances of NaOH_(aq) were found to increase with increasing temperature up to 300°C and with decreasing water density ρ_w. At temperatures ≥400°C, and densities between 0.6 to 0.8 g-cm^?3, Λ₀ is nearly temperature-independent but increases linearly with decreasing density, and then decreases at densities <0.6 g-cm^?3. This phenomenon is largely due to the breakdown of the hydrogen-bonded, structure of water. The molal association constants K _Am for NaOH( _aq ) increase with increasing temperature and decreasing density. The logarithm of the molal association constant can be represented as a function of temperature (Kelvin) and the logarithm of the density of water by $$\begin{gathered} log K_{Am} = 2.477 - 951.53/T - (9.307 \hfill \\ - 3482.8/T)log \rho _{w } (25 - 600^\circ C) \hfill \\ \end{gathered} $$ which includes selected data taken from the literature, or by $$\begin{gathered} log K_{Am} = 1.648 - 370.31/T - (13.215 \hfill \\ - 6300.5/T)log \rho _{w } (400 - 600^\circ C) \hfill \\ \end{gathered} $$ which is based solely on results from the present study over this temperature range (and to 300 MPa) where the measurements are most precise.     

Effect of the temperature on the physical properties of pure 1-propyl 3-methylimidazolium bis(trifluoromethylsulfonyl)imide and characterization of its binary mixtures with alcohols

In this paper, physical properties of a high purity sample of the ionic liquid 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [PMim][NTf₂], and its binary mixtures with methanol, ethanol, 1-propanol, and 2-propanol were measured at atmospheric pressure. The temperature dependence of density, refractive index and speed of sound (293.15 to 343.15) K and dynamic viscosity (298.15 to 343.15) K were studied at atmospheric pressure by conventional techniques for the pure ionic liquid. For its mixtures with alcohols, density, speed of sound, and refractive index were measured at T = 298.15 K over the whole composition range. The thermal expansion coefficient of the [PMim][NTf₂] was calculated from the experimental results using an empirical equation, and values of the excess molar volume, excess refractive index, and excess molar isentropic compressibility for the binary systems at the above mentioned temperature, were calculated and fitted to the Redlich–Kister equation. The heat capacity of the pure ionic liquid at T = 298.15 K was determined using DSC.