A novel experimental technique for measurement of mass transfer between liquids and gas bubbles in agitated vessels: Application to highly viscous liqu

A novel experimental transient technique for obtaining the volumetric mass transfer coefficient between an agitated liquid and a bubbling gas is propos The method uses a constant volume stirred tank in which a gas is brought into contact with a liquid. The mass transfer coefficient k_La and Henry coefficient are estimated as parameters of a dynamic model of the system from pressure evolution measurements.This method is particularly designed for gas mass transfer measurements in highly viscous fluid. Correlations between k_La, the stirring sha speed, the inlet gas velocity and the power input per unit volume are proposed.     

Gas bubbles in viscous liquids and melts

The basic set of equations and boundary conditions for viscous liquids and melts with gas has been derived. The flux of bubbles in the space of sizes, distribution of bubbles with respect to size, number of bubbles in the unit volume, and swelling of the system of viscous gas with liquid have been found. The initial and intermediate stages of the diffusion decomposition of the metastable system of viscous liquid with gas are considered.     

Rise velocities of large single two-dimensional and three-dimensional gas bubbles in liquids and in liquid fluidized beds

The rise velocities of both circular-cap gas bubbles in two-dimensional, and spherical-cap gas bubbles in three-dimensional, liquid fluidized beds are shown to be predictable by the same equations which predict the rise velocities of similar bubbles in still liquids, provided the rise velocities are expressed relative to the liquid rather than relative to the column walls.     

Rise of liquids and bubbles in angular capillary tubes

We discuss the rise of a liquid inside an angular capillary tube. It is shown that for a wetting liquid, the height of the rise is (as usually) inversely proportional to the length which characterizes the confinement. The exact laws deduced from energetic considerations are found to be in excellent agreement with the data. We then show how such tubes can be used to prevent bubbles from being trapped. The rising velocity of a bubble is finally discussed, in the particular case of a square tube.     

Improvement to the lattice-fluid prediction of gas solubilities in polymer liquids

Previously we have shown that the Lattice Fluid (LF) model can quantitatively predict, without adjustable parameters, gas solubilities for hydrocarbon and chlorinated hydrocarbon vapors in nonpolar polymers. For polar polymers, the model can also predict, with reasonable success, the solubilities of polar and aromatic vapors. However, the solubilities in polar/nonpolar combinations of gas and polymer are systematically overestimated. These are cases in which the geometric mean approximation for the interaction parameter is not expected to be valid. This paper demonstrates that with the addition of a simple empirical correlation for the interaction parameter based on Hansen's three-dimensional solubility parameters, the LF model is then able to quantitatively predict solubilities in all types of gas/polymer systems (excluding strongly self-associating systems, such as alcohols). No adjustable parameters are used; only the pure component equation-of-state and solubility parameters are required. © 1993 John Wiley & Sons, Inc.     

Excess number and charge functions in liquids

Abstract

Definitions for the excess number and charge functions are given. They are used to show how the structure of a liquid about a reference particle differs from the avarage values. Some features of the structure are ilustrated more clearly by this representation than by the radial distribution functions.     

DOSY technique applied to palladium nanoparticles in ionic liquids

Multinuclear ((1)H, (31)P, (19)F and (11)B) diffusion ordered spectroscopy (DOSY) technique has been applied to palladium nanoparticles systems dispersed in ionic liquids (ILs). Even if the nanoparticles themselves cannot be detected through NMR, observation of the solvent (methanol) and the IL ([BMI][PF(6)] or [BMI][NTf(2)]), their diffusion coefficients and their changes in the presence of nanoparticles allow us to draw significant assumptions about the organisation of palladium nanoparticles in the IL. For comparison, the corresponding molecular precursors ([PdCl(2)(cod)] or [Pd(2)(dba)(3)]) have been also studied.     

On the theory of thermocapillary motion of gas bubbles

Thermocapillary motion of gas bubbles in an individual volatile liquid and in solutions is considered. The velocity of motion is calculated within the framework of classical thermodynamics with allowance for the effect of the evaporation of liquid on the temperature field and for the dependence of saturation vapor pressure on the solution concentration. It is shown that the volatility of liquid and the addition of surfactant substantially affect the value of the velocity of thermocapillary motion.     

Generalized equations to evaluate the gas hold-up time of chromatographic systems

Summary The two approaches used for the calculation of the gas hold-up time and thus, the adjusted retention time are outlined, first for the restricted case when the carbon numbers of the three homologues used for the calculation are evenly spaced (c₃–c₂=c₂–c₁) and then, for the general case when (c₃–c₂) differs from (c₂–c₁). The basic difference in the philosophy of the two approaches is shown.     

Molecular ions of ionic liquids in the gas phase

Ionic liquids form neutral ion pairs (CA) upon evaporation. The softness of the gas-phase ionization of field ionization has been used to generate "molecular ions," CA(+*), of ionic liquids, most probably by neutralization of the anion. In detail, 1-ethyl-3-methylimidazolium-thiocyanate, [C(6)H(11)N(2)](+) [SCN](-), 1-butyl-3-methylimidazolium-tricyanomethide, [C(8)H(15)N(2)](+) [C(4)N(3)](-), N-butyl-3-methylpyridinium-dicyanamide, [C(10)H(16)N](+) [C(2)N(3)](-), and 1-butyl-1-methylpyrrolidinium-bis[(trifluormethyl)sulfonyl]amide, [C(9)H(20)N](+) [C(2)F(6)NO(4)S(2)](-) were used. The assignment as CA(+*) ions, which has been confirmed by accurate mass measurements and misassignments due to thermal decomposition of the ionic liquids, has been ruled out by field desorption and electrospray ionization mass spectrometry of the residues.     

The nature of ionic liquids in the gas phase

Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) experiments showed that when aprotic ionic liquids vaporize under pressure and temperature conditions similar to those of a reduced-pressure distillation, the gas phase is composed of discrete anion-cation pairs. The evolution of the mass spectrometric signals recorded during fractional distillations of binary ionic liquid mixtures allowed us to monitor the changes of the gas-phase composition and the relative volatility of the components. In addition, we have studied a protic ionic liquid, and demonstrated that it exists as separated neutral molecules in the gas phase.     

The origin of the surface charge on particles suspended in organic liquids

Donor-acceptor interactions between a solid surface and an organic liquid lead to the creation of surface charge and counterions in the liquid. In simple systems, the energy levels of the solid and the liquid determine the direction of electron transfer and the sign of the surface charge. Our experimental results show that the surface charge and counterions can be formed either by a direct electron transfer as in the case of the metal-organic liquid or by an ion transfer due to the heterolysis of the donor-acceptor complex formed at the surface. The latter case includes many inorganic solid materials. Inorganic oxides bearing hydroxyl groups acquire their charge by a proton transfer mechanism. The proton affinity of the liquid was found to correlate with the sign of the surface charge on various inorganic solids. This result was consistent for both aprotic donor and amphoteric liquids. The various mechanisms leading to the formation of the surface charge in organic liquids are reviewed and a systematic approach to the phenomenon is provided.     

Electrification of gas bubbles as an analytical tool

When a gas passes through a liquid, a charge is produced and this is carried on in the droplets formed when the bubble bursts at the surface of the liquid. A theory to account for the relationship between the bubble charge and concentration of electrolyte, viz. q proportional, variant C(-1 2 ), is derived and applied to a number of uni-univalent and multivalent electrolytes. The general agreement between theory and experiment and the reasonable reproducibility of the technique show that it could have analytical application. Such use is exemplified in laboratory simulations of flowing systems for continuous analysis and in bubble-charge indication of titration end-points.     

New stationary phase polarity parameters considering the electric intermolecular interactions in gas chromatographic column

Summary The possibility of evaluation of the parameters representing the dispersive solute-solvent interactions is presented. B_N and B_s values can be used to describe the liquid phase polarity and to predict the retention indices of alcohols when the model polyxyethylene glycol dialkyl ethers and their sulphur analogs are used as stationary phases. The possibility of the first ionization potentials estimation is also presented.     

Conformation of alkanes in the gas phase and pure liquids

Monte Carlo (MC) statistical mechanics simulations have been carried out for the homologous alkane series of n-butane through n-dodecane in the gas phase and for the pure liquids at 298 K and 1 atm using the OPLS-AA force field. The study addresses potential cumulative deviations of computed properties and potential conformational differences between the gas phase and pure liquids, for example, from self-solvation in the gas phase. The average errors in comparison with experimental data for the computed densities and heats of vaporization are modest at 0.7% and 6.9%, respectively. Also, the invariant gas and liquid-phase results for average end-to-end distances and percentages of trans conformations for each nonterminal C-C bond assert that the conformer populations are not altered upon transfer from the gas phase to the pure liquid for the n-alkanes in this size range. Average end-to-end distances were also computed from the results of conformational searches and corroborated the MC findings. Quantitatively, the OPLS-AA result for the trans population of the C3-C4 bond in n-undecane is in close agreement with the findings from (13)C NMR experiments. Finally, previous work on determining the shortest n-alkane that does not have an all-trans global energy minimum has been extended. The smallest n-alkane with a hairpin geometry that is lower in energy than the all-trans conformer occurs for C(22)H(46) with OPLS-AA, though with a correction for GG sequences, the true turning point is likely in the C(16)-C(18) range.     

Decoupling charge transport from the structural dynamics in room temperature ionic liquids

Light scattering and dielectric spectroscopy measurements were performed on the room temperature ionic liquid (RTIL) [C4mim][NTf2] in a broad temperature and frequency range. Ionic conductivity was used to estimate self-diffusion of ions, while light scattering was used to study structural relaxation. We demonstrate that the ionic diffusion decouples from the structural relaxation process as the temperature of the sample decreases toward T(g). The strength of the decoupling appears to be significantly lower than that expected for a supercooled liquid of similar fragility. The structural relaxation process in the RTIL follows well the high-temperature mode coupling theory (MCT) scenario. Using the MCT analysis we estimated the dynamic crossover temperature in [C4mim][NTf2] to be T(c) ~ 225 ± 5 K. However, our analysis reveals no sign of the dynamic crossover in the ionic diffusion process.