Dipole moment derivatives with respect to the internal coordinates of benzene in the liquid and gas phases

This paper presents a comparison of the dipole moment derivatives with respect to internal coordinates in the liquid and gas phases for benzene-h(6), benzene-d(6) and benzene-d(1). The literature values of the integrated intensities of the infrared active fundamentals of the three gaseous isotopomers are used to determine the dipole moment derivatives with respect to internal coordinates, using the methods described in the previous paper for the liquid phase. As was found for the liquid phase in the previous paper, there is uncertainty surrounding the intensities of the individual CH stretching fundamentals of benzene-d(1) due to intensity sharing with active combinations. The magnitudes of the dipole moment derivatives with respect to internal coordinates in the gas phase are partial differentialmicro/ partial differentials=0.50+/-0.03DA(-1), partial differentialmicro/ partial differentialt=0.28+/-0.03, partial differentialmicro/ partial differentialbeta=0.24+/-0.01, and partial differentialmicro/ partial differentialgamma=0.65+/-0.02DA(-1), where s, t, beta and gamma are the CH stretching, and CC stretching, the HCC bending and the HCCC torsion displacements, respectively. The experimental intensities are different for the three isotopomers in the liquid and gas phases, and the calculations show that these differences are mainly due to a difference between the CH stretch dipole moment derivatives in the two phases. This difference was related qualitatively to the intermolecular interaction of the H with the pi-cloud of the nearest neighbour creating a pseudo-hydrogen bond.     

Phosgene as a derivatizing reagent prior to gas and liquid chromatography

The use of phosgene as a derivatizing agent for bifunctional compounds prior to gas and liquid chromatographic analysis is reviewed. Applications include gas chromatographic determinations of metoprolol and its metabolites in biological fluids, enantiomeric separations of beta-blocking drugs and sympathomimetic agents on a chiral stationary phase and liquid chromatographic enantiomer separations.     

二组分气体在固体上吸附的研究(Ⅵ)──不同覆盖度下的二组分气体在灯黑上的吸附

通过测定不同覆盖度下的甲苯-正己烷、苯-正己烷、丙酮-正已烷和正戊烷-正己烷4个二组分气体在灯黑上的组成吸附等温线,发现它们有着共同的规律:随着覆盖度的增加,各体系的组成吸附等温线都向上靠近它们各自的气液平衡曲线。因此,基本上可以把二组分的气相与吸附相的平衡看成二组分的气液平衡,4个体系的组成吸附等温线基本上都可以通过理想溶液的相对挥发度方程式模拟得到。     

Molecular simulation of adsorption and intrusion in nanopores

This paper reports Monte Carlo simulations of the adsorption or intrusion in cylindrical silica nanopores. All the pores are opened at both ends towards an external bulk reservoir, so that they mimic real materials for which the confined fluid is always in contact with the external phase. This realistic model allows us to discuss the nature of the filling and emptying mechanisms. The adsorption corresponds to the metastable nucleation of the liquid phase, starting from a partially filled pore (a molecular thick film adsorbed at the pore surface). On the other hand, the desorption occurs through the displacement at equilibrium of a gas/liquid hemispherical interface (concave meniscus) along the pore axis. The intrusion of the non-wetting fluid proceeds through the invasion in the pore of the liquid/gas interface (convex meniscus), while the extrusion consists of the nucleation of the gas phase within the pore. In the case of adsorption, our simulation data are used to discuss the validity of the modified Kelvin equation (which is corrected for both the film adsorbed at the pore surface and the curvature effect on the gas/liquid surface tension).     

Micromechanical cohesion force measurements to determine cyclopentane hydrate interfacial properties

Hydrate aggregation and deposition are critical factors in determining where and when hydrates may plug a deepwater flowline. We present the first direct measurement of structure II (cyclopentane) hydrate cohesive forces in the water, liquid hydrocarbon and gas bulk phases. For fully annealed hydrate particles, gas phase cohesive forces were approximately twice that obtained in a liquid hydrocarbon phase, and approximately six times that obtained in the water phase. Direct measurements show that hydrate cohesion force in a water-continuous bulk may be only the product of solid-solid cohesion. When excess water was present on the hydrate surface, gas phase cohesive forces increased by a factor of three, suggesting the importance of the liquid or quasi-liquid layer (QLL) in determining cohesive force. Hydrate-steel adhesion force measurements show that, when the steel surface is coated with hydrophobic wax, forces decrease up to 96%. As the micromechanical force technique is uniquely capable of measuring hydrate-surface forces with variable contact time, the present work contains significant implications for hydrate applications in flow assurance.     

Analysis of complex samples by solvating gas chromatography (supercritical fluid to gas transition)

The various forms of chromatography are primarily determined by differences in the physical state of the mobile phases. The main chromatographic categories include gas chromatography (GC), liquid chromatography, and supercritical fluid chromatography. Adjusting a temperature and pressure will change the mobile phase from liquid to supercritical fluid to gas, with concomitant changes in their physical properties. In this paper, the technique transition-phase chromatography (TPC) is described. In TPC, different mobile phase conditions exist inside the column. This phase transformation within the column results in huge differences in density, solvating power, viscosity, diffusivity, and, as a consequence, in the chromatographic properties of the mobile phase. TPC experiments using capillary columns packed in our laboratory have shown that when the mobile phase is transformed from supercritical fluid to gas, high column efficiencies can be achieved. The transition from supercritical fluid to gas (also called solvating GC), a particular case of the TPC, is evaluated for the separation of complex real samples (environmental, food, and fuels).     

Kinetic study on isomerization of verbenol to isopiperitenol and citral

Thermal isomerization of verbenol in the gas and liquid phases is discussed. The effect of temperature and residence time on the reaction mixture composition was studied (at 460-600°C and a residence time t of about 10^-3 min for the gas phase conditions; at 200-350°С and t = 10-80 min for the liquid phase process). The kinetic behavior and the reaction mechanisms are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Determination of the enantiomers of 3-tert.-butylamino-1,2-propanediol by high-performance liquid chromatography coupled to evaporative light scattering detection

A method for the separation and quantitation of the enantiomers of 3-tert.-butylamino-1,2-propanediol by high-performance liquid chromatography and evaporative light scattering detection has been developed. Separation of the enantiomers was performed in normal-phase liquid chromatography on a Chiralpak AS chiral stationary phase. The influence of the gas nature, gas pressure and temperature of the drift tube of the evaporative light scattering detector on the detection sensitivity was investigated. The method was validated in terms of linearity, limit of quantitation, accuracy and precision. The enantiomeric excess of (S)-3-tert.-butylamino-1,2-propanediol, used for the industrial synthesis of (S)-timolol, was measured from 0 to 94%.     

Influence of the ionic liquid/gas surface on ionic liquid chemistry

Applications such as gas storage, gas separation, NP synthesis and supported ionic liquid phase catalysis depend upon the interaction of different species with the ionic liquid/gas surface. Consequently, these applications cannot proceed to the full extent of their potential without a profound understanding of the surface structure and properties. As a whole, this perspective contains more questions than answers, which demonstrates the current state of the field. Throughout this perspective, crucial questions are posed and a roadmap is proposed to answer these questions. A critical analysis is made of the field of ionic liquid/gas surface structure and properties, and a number of design rules are mined. The effects of ionic additives on the ionic liquid/gas surface structure are presented. A possible driving force for surface formation is discussed that has, to the best of my knowledge, not been postulated in the literature to date. This driving force suggests that for systems composed solely of ions, the rules for surface formation of dilute electrolytes do not apply. The interaction of neutral additives with the ionic liquid/gas surface is discussed. Particular attention is focussed upon H(2)O and CO(2), vital additives for many applications of ionic liquids. Correlations between ionic liquid/gas surface structure and properties, ionic liquid surfaces plus additives, and ionic liquid applications are given.     

A general gas‐assisted three‐liquid‐phase extraction method for separation and concentration of puerarin, 3′‐methoxydaidzin,puerarinxyloside, daidzin and daidzein from puerariae extract

In this work, a general and novel separation technique gas‐assisted three‐liquid‐phase extraction was established and applied in separating and concentrating isoflavonoids from the actual sample of puerariae extract by one step. For the gas‐assisted three‐liquid‐phase extraction method, optimal conditions were selected: polyethylene glycol 2000 and ethyl acetate as the flotation solvent, pH 5, (NH₄)₂SO₄ concentration 350 g/L in aqueous phase, N₂ flow rate 30 mL/min, flotation time 50 min, and flotation twice. Five isoflavonoids compounds puerarin, 3′‐methoxydaidzin, puerarinxyloside, daidzin and daidzein were separated with recoveries of 82, 84, 80, 88 and 89%, respectively. The separated products were purified by preparative high‐performance liquid chromatography, and the purity of the final products was >96%. The established general gas‐assisted three‐liquid‐phase extraction was used to separate anthraquinones from Cassiae Semen under the optimal conditions, and the recoveries were >75%. The experimental results showed that the established gas‐assisted three‐liquid‐phase extraction method is a general technique for separating active compounds from herb extract.     

INTRAPARTICLE DIFFUSION EFFECTS IN FISCHER-TROPSCH SYNTHESIS 1. MODELING OF DIFFUSION AND REACTION

The FTS/WGS over precipitated Fe/Cu/K catalyst could be approximated as a single reaction that forms an average hydrocarbon product (CnHm) with water and carbon dioxide as its by-products. It is generally assumed that the catalyst pores are filled with liquid wax produced during the synthesis, and thus, diffusivity in wax is much less than that in gas phase. Based on the intrinsic kinetics which accounts for water inhibition, as well as reaction diffusion model and single-reaction stoichiometry, effectiveness factors were calculated by assuming different sets of stoichiometric coefficients. Reasonable calculation procedure was established for the investigated catalyst. It was found that the effectiveness factors for gas/liquid system were about half of that for gas phase, which was expected as the diffusivities.     

Phase separation of gas–liquid and liquid–liquid microflows in microchips

Phase separation of gas–liquid and liquid–liquid microflows in microchannels were examined and characterized by interfacial pressure balance. We considered the conditions of the phase separation, where the phase separation requires a single phase flow in each output of the microchannel. As the interfacial pressure, we considered the pressure difference between the two phases due to pressure loss in each phase and the Laplace pressure generated by the interfacial tension at the interface between the separated phases. When the pressure difference between the two phases is balanced by the Laplace pressure, the contact line between the two phases is static. Since the contact angle characterizing the Laplace pressure is restricted to values between the advancing and receding contact angles, the Laplace pressure has a limit. When the pressure difference between the two phases exceeds the limiting Laplace pressure, one of the phases leaks into the output channel of the other phase, and the phase separation fails. In order to experimentally verify this physical picture, microchips were used having a width of 215 μm and a depth of 34 μm for the liquid–liquid microflows, a width of 100 μm and a depth of 45 μm for the gas–liquid microflows. The experimental results of the liquid–liquid microflows agreed well with the model whilst that of the gas–liquid microflows did not agree with the model because of the compressive properties of the gas phase and evaporation of the liquid phase. The model is useful for general liquid–liquid microflows in continuous flow chemical processing.     

INTRAPARTICLE DIFFUSION EFFECTS IN FISCHER-TROPSCH SYNTHESIS Ⅰ. MODELING OF DIFFUSION AND REACTION

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SULFONATION IN A FALLING FILM REACTOR: COMPARATION OF EXPERIMENTAL RESULTS WITH MATHEMATICAL MODEL PREDICTIONS

A mathematical model is developed to simulate a falling film reactor for sulfonation/sulfation. In the model, the reaction rate is considered to be controlled by the mass transfer in the gas phase or in the liquid phase. The gas phase mass and heat transfers are calculated by empiric equations; in the liquid phase, they are calculated by solving with numerical methods the partial differential equations which describe the system. In these equations, and eddy diffusion is considered, following the Levich's theories

The model results are compared with the experimental results obtained by the authors in a pilot plant, for the dodecylbenzene sulfonation.     

What is the correct form of BET isotherm for modeling liquid phase adsorption?

In this work subtleties of application of BET isotherm for liquid phase adsorption is presented. It has been shown that direct use of the classical BET equation (which was developed for gas phase adsorption) to liquid phase adsorption leads to ambiguous and erroneous results. Some cases of misuse of BET equation for liquid phase adsorption have been revisited. By close examination of the development of the classical equation, the causes of misunderstandings were elucidated and the suitable form of the BET equation for liquid phase adsorption was developed. As case studies, the classical form of the BET equation along with the correct form of the equation for liquid phase have been applied for modeling liquid phase adsorption of methyl tert-butyl ether (MTBE) on perfluorooctyl alumina, phenol on activated carbon and pentachlorophenol on carbonized bark. It has been shown that direct application of the classical BET isotherm to liquid phase adsorption results in poor and erroneous estimation of the equation parameters. For example, in aqueous phase adsorption of MTBE on perfluorooctyl alumina, the monolayer adsorption capacity of the adsorbent was calculated as 9.7 mg/g instead of 3.3 mg/g or the saturation concentration of MTBE in water was calculated as 1212 mg/L instead of 42000 mg/L.     

Uptake of gas-phase nitrous acid by pH-controlled aqueous solution studied by a wetted wall flow tube

Uptake kinetics of gas phase nitrous acid (HONO) by a pH-controlled aqueous solution was investigated by using a wetted wall flow tube. The gas phase concentration of HONO after exposure to the aqueous solution was measured selectively by the chemical ionization mass spectrometer in a high sensitive manner. The uptake rate of the gaseous HONO was found to depend on the pH of the solution. For the uptake by neutral and alkaline solutions, the gas phase concentration was observed to decay exponentially, suggesting that the uptake was fully limited by the gas phase diffusion. On the other hand, the uptake by the acidic solution was found to be determined by both the gas phase diffusion and the liquid phase processes such as physical absorption and reversible acid dissociation reaction. The decay was analyzed by the rate equations using the time dependent uptake coefficient involving the saturation of the liquid surface. While the uptake processes by the solution at pH = 2-3 were well described by those calculated using the physical and chemical parameters reported for the bulk, the uptake rates by the solution at 4 < pH < 7 deviate from the calculated ones. The present result can suggest that the pH at the liquid surface is lower than that in the bulk liquid, which is responsible for the additional resistance of mass transfer from the gas to the liquid phase.     

Overtone spectroscopy of isobutane at cryogenic temperatures

The spectra of the fundamental and overtones of the C---H stretches of (CH₃)₃CH have been measured in liquid argon solutions at 90 K and for the pure liquid sample at 135 K. Absorptions in the visible were obtained with a low temperature cell and a resonant continuous wave laser technique with acoustic detection. Absorptions in the IR and near-IR were observed with a Fourier transform spectrophotometer. Comparison is made between the absorption bands in gas phase, liquid argon solution, and liquid phase isobutane. The spectra of isobutane in solution show improved resolution of the vibrational bands with respect to the room temperature gas phase bands and the pure liquid bands at 135 K. To interpret the experimental results, overtone transitions are described in terms of the local mode model. A harmonically coupled anharmonic oscillator (HCAO) model was used to determine the overtone energy levels and assign the absorption bands to vibrational transitions. Ab initio molecular orbital calculations of geometries and vibrational frequencies were also performed.     

Evaporation of the liquid stationary phase in gas chromatography

Summary The theory of the evaporation of the liquid stationary phase is elaborated and experimentally verified. On the basis of this theory the role played by the losses in the amount of liquid phase present is quantitatively determined. General techniques are examined which minimize the losses; these techniques are based on saturating the incoming carrier gas with liquid phase vapours and raising the pressure of the carrier gas in the column, e.g. by connecting a capillary to the column outlet in order to offer resistance to the gas flow. The application of these techniques ensures stable performance of the gas chromatographic columns using a volatile liquid phase.     

Shifting Chemical Equilibria in Flow—Efficient Decarbonylation Driven by Annular Flow Regimes

To efficiently drive chemical reactions, it is often necessary to influence an equilibrium by removing one or more components from the reaction space. Such manipulation is straightforward in open systems, for example, by distillation of a volatile product from the reaction mixture. Herein we describe a unique high‐temperature/high‐pressure gas/liquid continuous‐flow process for the rhodium‐catalyzed decarbonylation of aldehydes. The carbon monoxide released during the reaction is carried with a stream of an inert gas through the center of the tubing, whereas the liquid feed travels as an annular film along the wall of the channel. As a consequence, carbon monoxide is effectively vaporized from the liquid phase into the gas phase and stripped from the reaction mixture, thus driving the equilibrium to the product and preventing poisoning of the catalyst. This approach enables the catalytic decarbonylation of a variety of aldehydes with unprecedented efficiency with a standard coil‐based flow device.     

A novel method to study particle–air/liquid surface interactions

A novel method to study the dynamics of hydrophilic solid particle interactions with the gas/aqueous surface has been developed; the gas/liquid surface oscillation was monitored using light reflection microscopy. Two modes of gas/liquid surface oscillation are observed: a high mode of oscillation during the first 0.1 s and a low mode of oscillation during the last 0.4 s. It has been shown that the two modes of oscillation are related with the two-stage process of particle–gas/liquid interactions; during the first stage, the particle and gas/liquid surface interact via a long-range hydrodynamic interaction. The liquid film between the particle and the gas/liquid surface decreases its thickness. During the second stage, the particle is adhered (via liquid film) to the air/aqueous surface, and the air/aqueous surface oscillates with the particle. Effects of particle size and surface tension on the frequency of oscillation of the gas/liquid surface were also studied. Two theoretical models are used to predict the high frequency and low frequency of the air/aqueous surface oscillation.